OA18316A - Palette mode coding for video coding. - Google Patents

Abstract

Receiving a plurality of syntax elements that are indicative of a palette that was used to encode a block of video data, the plurality of syntax elements including a first syntax element that indicates a number of palette values for the palette that are explicitly signaled in the encoded video bitstream, wherein the first syntax element is encoded using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, decoding the plurality of syntax elements, including decoding the first syntax element using the one or more Golomb codes, reconstructing the palette based on the decoded plurality of syntax elements, and decoding the block of video data using the reconstructed palette.

Description

[0001] This application claims the benefit of U.S. Provisional Application No. 62/109,568 filed January 29,2015, the entire contents of which are incorporated by reference herein.

TECHNICAL FIELD [0002] This disclosure relates to video encoding and decodîng.

BACKGROUND [0003] Digital video capabilities can be incorporated into a wide range of devices, including digital télévisions, digital direct broadcast Systems, wireless broadcast Systems, persona! digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital caméras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radio téléphonés, so-callcd “smart phones,” video teleconferencing devices, video streaming devices, and the like. Digital video devices implement video compression techniques, such as those described in the standards defined by MPEG-2, MPEG-4,1TU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), the High Efficiency

Video Coding (HEVC) standard presently under development, and extensions of such standards. The video devices may transmit, receive, encode, décodé, and/or store digital video information more effîciently by implementing such video compression techniques.

[0004] Video compression techniques perform spatial (intra-picture) prédiction and/or temporal (inter-picture) prédiction to reduce or remove redundancy inhérent in video scquences. For block-based video coding, a video slice (e.g., a video frame or a portion of a video frame) may be partitioned into video blocks. Video blocks in an intra-codcd (I) slice of a picture are encoded using spatial prédiction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or

B) slice of a picture may use spatial prédiction with respect to reference samples in neighboring blocks in the same picture or temporal prédiction with respect to reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames.

[0005] Spatial or temporal prédiction results in a prédictive block for a block to be coded. Residual data rcpresents pixel différences between the original block to be coded and the prédictive block. An inter-coded block is cncoded according to a motion vector that points to a block of référencé samples forming the prédictive block, and the 5 residual data indicates the différence between the coded block and the prédictive block.

An intra-coded block is encoded according to an intra-coding mode and the residual data. For further compression, the residual data may be transfonned from the pixel domain to a transform domain, resulting in residual coefficients, which then may be quantized. The quantized coefficients, înitially arranged in a two-dimensional array, 10 may be scanned in order to produce a one-dimensional vector of coefficients, and entropy coding may be applied to achieve even more compression.

SUMMARY [0006] This disclosure relates to video encoding and decoding techniques. In particular, 15 this disclosure dcscribes techniques for encoding and decoding video data with a palette-based coding mode. In a palette-based coding mode, pixel values for a block of video data may be coded relative to a palette of color values associated with the block of video data. The palette of color values may be determïned by a video encoder and may contain the color values that arc most common for a particular block. The video encoder may assign an index into the palette of color values to each pixel in the block of video data, and signal such an index to a video décoder in an encoded video bitstream. The video décoder may then use the index into the palette to détermine what color value to use for a particular pixel in the block.

[0007] In addition to signaling indices in the palette, a video encoder may also transmit 25 the palette itself in the encoded video bitstream. Techniques for transmitting the palette may include explicitly signaling the palette values, as well as predicting the palette entries for a current block from palette entries from one or more previously coded blocks. This disclosure dcscribes techniques for coding palettes, including techniques for coding syntax éléments related to palette coding and/or palette prédiction.

[0008] In one example of the disclosure, a method of decoding video data comprises receiving a block of video data in an encoded video bitstream, the block of video data having been encoded using a palette-based coding mode, receiving a pluralîty of syntax éléments that are indicative of a palette that was used to encode the block of video data,

the plurality of syntax éléments including a first syntax élément that indicates a number of a palette values for the palette that arc explicitly signaled in the encoded video bitstream, wherein the first syntax element is encoded using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, decoding the plurality of syntax éléments, including decoding the first syntax element using the one or more Golomb codes, reconstruct in g the palette based on the decoded plurality of syntax éléments, and decoding the block of video data using the reconstructcd palette.

[0009] In another example of the disclosure, a method of encoding video data comprises 10 encoding a block of video data using a palette-based coding mode and a palette, generating a plurality of syntax éléments that are indicative of the palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of a palette values for the palette that arc explicitly signaled in the encoded video bitstream, encoding the first syntax element 15 using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, and including the plurality of syntax éléments in an encoded video bitstream.

[0010] In another example of the disclosure, an apparatus configured to décodé video data comprises a memory configured to store an encoded video bitstream, and a video 20 décoder configured to receive a block of video data in the encoded video bitstream, the block of video data having been encoded using a palette-based coding mode, receive a plurality of syntax éléments that are indicative of a palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the 25 encoded video bitstream, wherein the first syntax element is encoded using the one or more Golomb codes such that the length of the encoded first syntax element is less titan or equal to a predetermined maximum number of bits, décodé the plurality of syntax éléments, including decoding the first syntax element using one or more Golomb codes, reconstruct the palette based on the decoded plurality of syntax éléments, and décodé 30 the block of video data using the reconstructed palette.

[0011] In another example of the disclosure, an apparatus configured to encode video data comprises a memory configured to store a block of video data, and a video encoder configured to encode the block of video data using a palette-based coding mode and a palette, generate a plurality of syntax éléments that arc indicative of the palette that was

used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of a palette values for the palette that arc explicitly signaled in the encoded video bitstream, encode the first syntax element using one or more Golomb codes such that the length of the encoded first syntax element is

Iess than or equal to a predetermined maximum number of bits, and include the plurality of syntax éléments in an encoded video bitstream.

[0012] In another example of the dïsclosure, an apparatus confîgured to décode video data comprises means for rcceiving a block of video data in an encoded video bitstream, the block of video data having been encoded using a palette-bascd coding mode, means 10 for receiving a plurality of syntax éléments that are indicative of a palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of a palette values for the palette that arc explicitly signaled in the encoded video bitstream, wherein the first syntax element is encoded using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, means for decoding the plurality of syntax éléments, including dccoding the first syntax élément using the one or more Golomb codes, means for reconstructing the palette based on the decoded plurality of syntax éléments, and means for decoding the block of video data using the reconstructed palette.

[0013] In another example of the disclosure, an apparatus confîgured to encode video data comprises means for encoding a block of video data using a palette-based coding mode and a palette, means for generating a plurality of syntax éléments that arc indicative of the palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, means for encoding the first syntax element using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, and means for including the plurality of syntax éléments in an encoded video bitstream.

[0014] In another example, this disclosure describes a computer-readable storage medium storing instructions that, when executed, cause one or more processors of a device confîgured to décodé video data to receive a block of video data in an encoded video bitstream, the block of video data having been encoded using a palette-bascd coding mode, receive a plurality of syntax éléments that are indicative of a palette that

was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, wherein the first syntax element is encoded using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, décodé the plurality of syntax cléments, including decoding the first syntax element using the one or more Golomb codes, reconstruct the palette based on the decoded plurality of syntax éléments, and décodé the block of video data using the reconstructed palette.

[0015] In another example, this disclosure describes a computer-readable storage medium storing instructions that, when executed, cause one or more processors of a device configured to encode video data to encode a block of video data using a palettebased coding mode and a palette, generate a plurality of syntax éléments that are indicative of the palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, encode the first syntax element using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, and include the plurality of syntax éléments in an encoded video bitstream.

[0016] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages wîll be apparent from the description and drawings, and from the daims.

BRIEF DESCRIPTION OF DRAWINGS [0017] FIG. 1 is a block diagram illustrating an example video coding System that may utilize the techniques described in this disclosure.

[0018] FIG. 2 îs a block diagram illustrating an example video encoder that may implement the techniques described in this disclosure.

[0019] FIG. 3 is a block diagram illustrating an example video décoder that may implement the techniques described in this disclosure.

[0020] FIG. 4 is a block diagram illustrating an example palette-based encoding unit of the video encoder of FIG. 2.

[0021] FIG. 5 is a conceptual diagram illustrating an example palette prédiction technique according to the techniques of the disclosure.

[0022] FIG. 6 is a conccptual dîagram illustrating an example binary prédiction vector encoding technique according to the techniques of the disclosure.

[0023] FIG. 7 is a block diagram illustrating an example palette-based decoding unit of the video encoder of FIG. 3.

[0024] FIG. 8 is a flowchart illustrating an example video encoding method according to the techniques of the disclosure.

[0025] FIG. 9 is a flowchart illustrating an example video decoding method according to the techniques of the disclosure.

DETAILED DESCRIPTION [0026] This disclosure is related to the field of video coding, and more particularly to predicting or coding a block of video data in palette-based coding mode. In traditional video coding, images are assumed to be continuous-tone and spatially smooth. Based on these assumptions, various tools hâve been developcd, such as block-bascd transform, fïltering, etc., and such tools hâve shown good performance for naturel content videos. In applications like remote desktop, collaborative work and wireless display, however, computer generated screen content (e.g., such as text or computer graphies) may be the dominant content to be comprcssed. This type of content tends to hâve discrete-tone, and features sharp Unes and high-contrast object boundaries. The assumption of continuous-tone and smoothness may no longer apply for screen content, and thus traditional video coding techniques may not be efficient to compress video data including screen content.

[0027] This disclosure describes palette-based coding, which may be particularly suitablc for the coding of screen content. For example, assuming that a particular area of video data has a relatively small number of colors, a video coder (e.g., a video encoder or video décoder) may form a so-called “palette” to represent the video data of the particular area. The palette may be expressed as a table of colors or pixel values representing the video data of the particular area (e.g., a given block). For example, the palette may include the most dominant pixel values in the given block. In some cases, the most dominant pixel values may include the one or more pixel values that occur most frequently within the block. Addîtionally, in some cases, a video coder may apply a threshold value to détermine whether a pixel value is to be included as one of the most dominant pixel values in the block. According to various aspects of palette-based coding, the video coder may code index values indicative of one or more of the pixels

values of the current block, instead of coding actual pixel values or their rcsiduals for a current block of video data. In the context of palette-bascd coding, the index values indicate respective entries in the palette that are used to represent individual pixel values of the current block.

[0028] For example, the video encoder may encode a block of video data by determining the palette for the block (e.g., coding the palette explicitly, predicting the palette, or a combination thercof), locating an entry in the palette to represent one or more of the pixel values, and encoding the block with index values that indicate the entry in the palette used to represent the pixel values of the block. In some examples, the video encoder may signal the palette and/or the index values in an encoded bitstream. In tum, the video décoder may obtain, from an encoded bitstream, a palette for a block, as well as index values for the individual pixels of the block. The video décoder may relate the index values of the pixels to entries of the palette to reconstruct the various pixel values of the block.

[0029] In accordance with various examples discussed below, this disclosurc dcscribcs techniques for improving the coding efficiency when coding blocks of video data with a palette-based coding mode. Examples of this disclosure include techniques for coding video data using a palette-based coding mode, and techniques for coding syntax éléments related to the palette-based coding mode. In some examplcs, the techniques of this disclosure relate to coding syntax éléments used by a video décoder to détermine and/or reconstruct a palette for a block of video data.

[0030] In some examples, the palette-based coding techniques of this disclosure may be configured for use with one or more video coding standards. Some examplc video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or

ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) and Multiview Video Coding (MVC) extensions. In another example, the palette-based coding techniques may be configured for use with the Hîgh Efficiency Video Coding (HEVC). HEVC is a new video coding standard dcvelopcd by the Joint Collaboration

Team on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).

[0031] Recently, the design of HEVC has been finalizcd by the Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG). The latest HEVC spécification,

referred to as HEVC Version 1 or HEVC1 hereinafler, is descrîbed in “ITU-T H.265 (VI),’’ which as of March 24,2015 is available from httr>://www.itu.int/ITUT/recommendations/rec.asnx?rec=l 1885&lang=en . Document ITU-T H.265, SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS, Infrastructure of Audiovisual

Services—Coding of Moving Video, “High Efficiency Video Coding,” April 2013 also describcs the HEVC standard. A rccent spécification of Range extensions, referred to as RExt hereinafter, is dcscribed in “ITU-T H.265 (V2),” which as of March 24,2015 is available from httn://www,îtu.int/ITUT/recommendations/rec.asnx?rcc=12296&lang=en.

[0032] To provide more efficient coding of screen generated content, the JCT-VC is developing an extension to the HEVC standard, referred to as the HEVC Screen Content Coding (SCC) standard. A recent working draft of the HEVC SCC standard, referred to as “HEVC SCC Draft 2” or “WD2,” is descrîbed in document JCTVC-S1005, R. Joshi and J. Xu, “HEVC screen content coding draft text 2,” Joint Collaborative Team on

Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11,19¹¹¹ Meeting: Strasbourg, FR, 17-24 October 2014, [0033] FIG. 1 is a block diagram illustrating an example video coding system 10 that may utilize the techniques of this disclosure for palctte-based video coding. As used herein, the tcrm “video coder” refers generically to both video encoders and video decoders. In this disclosure, the terms “video coding” or “coding may refer generically to video encoding or video decoding. Video encoder 20 and video décoder 30 of video coding system 10 represent examples of devices that may be configured to perform techniques for palette-based video coding in accordance with various examples descrîbed in this disclosure. For example, video encoder 20 and video décoder 30 may be configured to selectively code various blocks of video data, such as CUs or PUs in HEVC coding, using either palette-based coding or non-palette based coding. Nonpalette based coding modes may refer to various inter-predictive temporal coding modes or intra-predictive spatial coding modes, such as the various coding modes specified by the HEVC standard. However, it should be understood that the techniques of this disclosure may be used with any video coding techniques and/or standards that use a palette-based coding mode.

[0034] As shown in FIG. 1, video coding system 10 includes a source device 12 and a destination device 14. Source device 12 generates encoded video data. Accordingly, source device 12 may be referred to as a video encoding device or a video encoding

apparatus. Destination device 14 may décode the encoded video data generated by source device 12. Accordingly, destination device 14 may be referred to as a video decoding device or a video decoding apparatus. Source device 12 and destination device 14 may be examples of video coding devices or video coding apparatuses.

[0035] Source device 12 and destination device 14 may comprise a wide range of devices, including desktop computers, mobile computing devices, notebook (e.g., laptop) computers, tablet computers, set-top boxes, téléphoné handsets such as so-called “smart phones, télévisions, caméras, display devices, digital media players, video gaming consoles, in-car computers, or the like.

[0036] Destination device 14 may receive encoded video data from source device 12 via a channel 16. Channel 16 may comprise one or more media or devices capable of moving the encoded video data from source device 12 to destination device 14. In one example, channel 16 may comprise one or more communication media that enable source device 12 to transmit encoded video data directly to destination device 14 in real15 time. In this example, source device 12 may modulate the encoded video data according to a communication standard, such as a wireless communication protocol, and may transmit the modulated video data to destination device 14. The one or more communication media may include wireless and/or wired communication media, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The one or more communication media may form part of a packet-based network, such as a local area network, a wide-area network, or a global network (e.g., the Internet). The one or more communication media may include routers, switches, base stations, or other equipment that facilitate communication from source device 12 to destination device 14. [0037] In another example, channel 16 may include a storage medium that stores encoded video data generated by source device 12. In this example, destination device 14 may access the storage medium via disk access or card access. The storage medium may include a variety of locally-accessed data storage media such as Blu-ray dises, DVDs, CD-ROMs, flash memory, or other suitable digital storage media for storing encoded video data.

[0038] In a further example, channel 16 may include a file server or another intermediate storage device that stores encoded video data generated by source device 12. In this example, destination device 14 may access encoded video data stored at the file server or other intermediate storage device via streaming or download. The file server may be a type of server capable of storing encoded video data and transmittîng

the encoded video data to destination device 14. Example file servers include web servers (e.g., for a website), file transfer protocol (FTP) servers, network attached storage (NAS) devices, and local disk drives.

[0039] Destination device 14 may access the encoded video data through a standard data connection, such as an Internet connection. Example types of data connections may include wireless channels (e.g., Wi-Fi connections), wired connections (e.g., DSL, cable modem, etc.), or combinations of both that are suitable for accessing encoded video data stored on a file server. The transmission of encoded video data from the file server may be a streaming transmission, a download transmission, or a combination of 10 both.

[0040] The techniques of this disclosure for palette-based video coding are not limited to wireless applications or settings. The techniques may be appiied to video coding in support of a variety of multimedia applications, such as over-the-air télévision broadeasts, cable télévision transmissions, satellite télévision transmissions, streaming 15 video transmissions, e.g., via the Internet, encoding of video data for storage on a data storage medium, decoding of video data stored on a data storage medium, or other applications. In some examplcs, video coding system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadeastîng, and/or video telephony.

[0041] Video coding system 10 illustrated in FIG. 1 is merely one example. The techniques of this disclosure may apply to video coding use cases (e.g., video encoding or video decoding) that do not necessarily include any data communication between the encoding and decoding devices. In other examples, data is retrieved from a local memory, streamed over a network, or the like. A video encoding device may encode and store data to memory, and/or a video decoding device may retrieve and décodé data from memory. In many examples, the encoding and decoding is performed by devices that do not communicate with one another, but simply encode data to memory and/or retrieve and décodé data from memory.

[0042] In the example of FIG. 1, source device 12 includes a video source 18, a video encoder 20, and an output interface 22. In some examples, output interface 22 may include a modulator/demodulator (modem) and/or a transmitter. Video source 18 may include a video capture device, e.g., a video caméra, a video archive containing prcviously-captured video data, a video feed interface to receive video data from a video

content provider, and/or a computer graphies System for gencratîng video data, or a combination of such sources of video data.

[0043] Video encoder 20 may encode video data from video source 18. In some examples, source device 12 directly transmits the encoded video data to destination device 14 via output interface 22. In other examples, the encoded video data may also be stored onto a storage medium or a file server for later access by destination device 14 for decoding and/or playback.

[0044] In the cxample of FIG. 1, destination device 14 includes an input interface 28, a video décoder 30, and a display device 32. In some examples, input interface 28 includes a receiver and/or a modem. Input interface 28 may receive encoded video data over channel 16. Dîsplay device 32 may be integrated with or may be extemal to destination device 14. In general, display device 32 displays decoded video data. Display device 32 may comprise a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0045] This disclosure may generally refer to video encoder 20 “signaling” or “transmitting” certain information to another device, such as video décoder 30. The term “signaling” or “transmitting” may generally refer to the communication of syntax éléments and/or other data used to décodé the compressed video data. Such communication may occur in real- or near-real-time. Altemately, such communication may occur over a span of time, such as might occur when storing syntax éléments to a computer-readable storage medium in an encoded bitstream at the time of encoding, which then may be retrieved by a decoding device at any time after being stored to this medium. Thus, while video décoder 30 may be referred to as “receiving” certain information, the receiving of information docs not neccssarily occur in real- or nearreal-time and may be retrieved from a medium at some time after storage. [0046] Video encoder 20 and video décoder 30 each may be implemented as any of a variety of suitable circuitry, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gâte arrays (FPGAs), discrète logic, hardware, or any combinations thereof. If the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Any of the foregoing (including hardware, software, a

combination of hardware and software, etc.) may bc considered to be one or more processors. Each of video encoder 20 and video décoder 30 may bc includcd in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device.

[0047] In some examples, video encoder 20 and video décoder 30 operate accordîng to a video compression standard, such as HEVC standard mentioned above. In addition to the base HEVC standard, there are ongoing efforts to produce scalable video coding, multivîew video coding, and 3D coding extensions for HEVC. In addition, palettcbascd coding modes, e.g., as described in this disclosure, may be provided for extension of the HEVC standard. In some examples, the techniques described in this disclosure for palette-based coding may be applied to encoders and decoders confîgured to operation according to other video coding standards. Accordingly, application of a palette-based coding mode for coding of coding units (CUs) or prédiction units (PUs) in an HEVC codée is described for purposes of example.

[0048] In HEVC and other video coding standards, a video sequence typically includes a séries of pictures. Pictures may also be referred to as “frames.” A picture may include three sample array.s, denoted Su Scb and Sc_r. Sl is a two-dimensional array (e.g., a block) of luma samples. Scn is a two-dimensional array of Cb chrominance samples. Scr is a two-dimensional array of Cr chrominance samples. Chrominance samples may also be referred to herein as “chroma” samples. In other instances, a picture may be monochrome and may only include an array of luma samples. [0049] To generate an encoded représentation of a picture, in HEVC, video encoder 20 may generate a set of coding tree units (CTUs). Each of the CTUs may be a coding tree block of luma samples, two corresponding coding tree blocks of chroma samples, and syntax structures used to code the samples of the coding tree blocks. A coding tree block may be an NxN block of samples. A CTU may also be referred to as a “tree block or a “largest coding unit” (LCU). The CTUs of HEVC may be broadly analogous to the macroblocks of other standards, such as H.264/AVC. However, a CTU is not necessarily limited to a partîcular size and may include one or more coding units (CUs). A slice may include an integer number of CTUs ordered consecutivcly in the raster scan. A coded slice may comprise a slice header and slice data. The slice header of a slice may be a syntax structure that includes syntax éléments that provide information about the slice. The slice data may include coded CTUs of the slice.

[0050] This disclosure may use the term “video unit” or “video block or “block” to refer to one or more sample blocks and syntax structures used to code samples of the one or more blocks of samples. Example types of video units or blocks may include CTUs, CUs, PUs, transform units (TUs), macroblocks, macroblock partitions, and so on. In some contexts, discussion of PUs may be interchanged with discussion of macroblocks or macroblock partitions.

[0051] To generate a coded CTU, video encoder 20 may rccursively perform quad-tree partîtioning on the coding tree blocks of a CTU to divide the coding tree blocks into coding blocks, hencc the name “coding tree units.” A coding block is an NxN block of 10 samples. A CU may be a coding block of luma samples and two corresponding coding blocks of chroma samples of a picture that has a luma sample array, a Cb sample array and a Cr sample array, and syntax structures used to code the samples of the coding blocks. Video encoder 20 may partition a coding block of a CU into one or more prédiction blocks. A prédiction block may be a rectangular (e.g., square or non-squarc) 15 block of samples on which the same prédiction is applied. A prédiction unit (PU) of a

CU may be a prédiction block of luma samples, two corresponding prédiction blocks of chroma samples of a picture, and syntax structures used to predict the prédiction block samples. Video encoder 20 may generate prédictive luma, Cb and Cr blocks for luma, Cb and Cr prédiction blocks of each PU of the CU.

[0052] Video encoder 20 may use intra prédiction or inter prédiction to generate the prédictive blocks for a PU. If video encoder 20 uses intra prédiction to generate the prédictive blocks of a PU, video encoder 20 may generate the prédictive blocks of the PU based on decoded samples of the picture associated with the PU.

[0053] If video encoder 20 uses inter prédiction to generate the prédictive blocks of a 25 PU, video encoder 20 may generate the prédictive blocks of the PU based on decoded samples of one or more pictures other than the picture associated with the PU. Video encoder 20 may use uni-prediction or bi-prediction to generate the prédictive blocks of a PU. When video encoder 20 uses uni-prediction to generate the prédictive blocks for a PU, the PU may hâve a single motion vector (MV). When video encoder 20 uses bi30 prédiction to generate the prédictive blocks for a PU, the PU may hâve two MVs.

[0054] After video encoder 20 generates prédictive blocks (e.g., prédictive luma, Cb and Cr blocks) for one or more PUs of a CU, video encoder 20 may generate residual blocks for the CU. Each sample in a residual block of the CU may indicatc a différence between a sample in a prédictive block of a PU of the CU and a corresponding sample

in a coding block of the CU. For example, video encoder 20 may generate a luma residual block for the CU. Each sample in the CU’s luma residual block indicates a différence between a luma sample in one of the CU’s prédictive luma blocks and a corresponding sample in the CU’s original luma coding block. In addition, video encoder 20 may generate a Cb residual block for the CU. Each sample in the CU’s Cb residual block may indicate a différence between a Cb sample in one of the CU’s prédictive Cb blocks and a corresponding sample in the CU’s original Cb coding block. Video encoder 20 may also generate a Cr residual block for the CU. Each sample in the CU’s Cr residual block may indicate a différence between a Cr sample in one of the

CU’s prédictive Cr blocks and a corresponding sample in the CU’s original Cr coding block.

[0055] Furthermore, video encoder 20 may use quad-trec partitioning to décomposé the residual blocks (e.g., luma, Cb and Cr residual blocks) of a CU into one or more transform blocks (e.g., luma, Cb and Cr transform blocks). A transform block may be a rectangular block of samples on which the same transform is applicd. A transform unit (TU) of a CU may be a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax structures used to transform the transform block samples. Thus, each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block. The luma transform block associated with tire TU may be a sub-block of the CU’s luma residual block. The Cb transform block may be a sub-block of the CU’s Cb residual block. The Cr transform block may be a sub-block of the CU’s Cr residual block.

[0056] Video encoder 20 may apply one or more transforms to a transform block to generate a coefficient block for a TU. A coefficient block may be a two-dimensional array of transform coefficients. A transform coefficient may be a scalar quantity. For example, video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU. Video encoder 20 may apply one or more transforms to a Cb transform block of a TU to generate a Cb coefficient block for the TU. Video encoder 20 may apply one or more transforms to a Cr transform block of a TU to generate a Cr coefficient block for the TU.

[0057] After generating a coefficient block (e.g., a luma coefficient block, a Cb coefficient block or a Cr coefficient block), video encoder 20 may quantize the coefficient block. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression. After video encoder 20 quantizes a coefficient block, video encoder 20 may entropy encoding syntax éléments indicating the quantized transform coefficients. For example, video encoder 20 may perform Context-Adaptîve Binary Arithmetic Coding (CABAC) on the syntax éléments indicating the quantized transform coefficients. Video encoder 20 may output the cntropy-encoded syntax éléments in a bitstream. The bitstream may also include syntax éléments that are not entropy encoded.

[0058] Video encoder 20 may output a bitstream that includes the entropy-encoded syntax éléments. The bitstream may include a sequence of bits that forms a représentation of coded pictures and associated data. The bitstream may comprise a sequence of network abstraction layer (NAL) units. Each of the NAL units includes a NAL unit header and encapsulâtes a raw byle sequence payload (RBSP). The NAL unit header may include a syntax élément that indicates a NAL unit type code. The NAL unit type code specified by the NAL unit header of a NAL unit indicates the type of the NAL unit. A RBSP may be a syntax structure containing an integer number of bytes that is encapsulated within a NAL unit. In some instances, an RBSP includes zéro bits. [0059] Different types of NAL units may encapsulate different types of RBSPs. For example, a first type of NAL unit may encapsulate an RBSP for a picture parameter set (PPS), a second type of NAL unit may encapsulate an RBSP for a coded slice, a third type of NAL unit may encapsulate an RBSP for supplémentai enhancement information (SEI), and so on. NAL units that encapsulate RBSPs for video coding data (as opposed to RBSPs for parameter sets and SEI messages) may be referred to as video coding layer (VCL) NAL units.

[0060] Video décoder 30 may receive a bitstream generated by video encoder 20. In addition, video décoder 30 may obtain syntax éléments from the bitstream. For example, video décoder 30 may parse the bitstream to décodé syntax cléments from the bitstream. Video décoder 30 may reconstruct the pictures of the video data based at least in part on the syntax éléments obtained (e.g., decoded) from the bitstream. The process to reconstruct the video data may be generally reciprocal to the process performed by video encoder 20. For instance, video décoder 30 may use MVs of PUs to détermine inter-prcdictive sample blocks (e.g., inter-predictive blocks) for the PUs of a current CU. In addition, video décoder 30 may inverse quantize transform coefficient blocks associated with TUs of the current CU. Video décoder 30 may perform inverse transforms on the transform coefficient blocks to reconstruct transform blocks

associated with the TUs of the current CU. Video décoder 30 may reconstruct the coding blocks of the current CU by adding the samples of the prédictive sample blocks for PUs of the current CU to corresponding samples of the transform blocks of the TUs of the current CU. By reconstructing the coding blocks for each CU of a picture, video décoder 30 may reconstruct the picture.

[0061] In some examples, video encoder 20 and video décoder 30 may be configured to perform palette-based coding. For example, in palette based coding, rather than performtng the intra-predictive or inter-predictive coding techniques described above, video encoder 20 and video décoder 30 may code a so-called palette as a table of colors or pixel values representing the video data of a partïcular area (e.g., a given block). In this way, rather than coding actual pixel values or their residuals for a current block of video data, the video coder may code index values for one or more of the pixel values of the current block, wherc the index values indicate entries in the palette that are used to represent the pixel values of the current block (e.g., the index may map to a set of Y, Cr, and Cb values or to a set of R, G, and B values).

[0062] For example, video encoder 20 may encode a block of video data by determining a palette for the block, Iocating an entry in the palette having a value représentative of the value of one or more individual pixels of the block, and encoding the block with index values that indicate the entry in the palette used to represent the one or more individual pixel values of the block. Additionally, video encoder 20 may signal the index values in an encoded bitstream. In tum, a video decoding device (e.g., video décoder 30) may obtain, from the encoded bitstream, the palette for a block, as well as index values used for determining the various individual pixels of the block using the palette. Video décoder 30 may match the index values of the individual pixels to entries of the palette to reconstruct the pixel values of the block. In instances where a pixel value of an individual pixel is not close enough to any of the pixel values represented by the corresponding palette for the block, video décoder 30 may identify such an individual pixel as an escape pixel, for the purposes of palette-based coding. The pixel value of an escape pixel may be encoded explicitly rather than by way of a palette index.

[0063] In another example, video encoder 20 may encode a block of video data according to the following operations. Video encoder 20 may détermine prédiction residual values for individual pixels of the block, détermine a palette for the block, and locate an entry (e.g., index value) in the palette having a value représentative of the

value of onc or more of the prédiction residual values of the individual pixels.

Additionally, video encoder 20 may encode the block with index values that indicatc the entry in the palette used to represent the corresponding prédiction residual value for each individual pixel of the block. Video décoder 30 may obtain, from an encoded 5 bitstream signaled by source device 12, a palette for a block, as well as index values for the prédiction residual values corresponding to the individual pixels of the block. As described, the index values may correspond to entries in the palette associated with the current block. In tum, video décoder 30 may relate the index values of the prédiction residual values to entries of the palette to rcconstruct the prédiction residual values of 10 the block. The prédiction residual values may be added to the prédiction values (for example, obtained using intra or inter prédiction) to rcconstruct the pixel values of the block.

[0064] As described in more detail below, the basic idea of palelte-based coding is that, for a given block of video data to be coded, video encoder 20 may dérivé a palette that 15 includes the most dominant pixel values in the current block. For instance, the palette may refer to a number of pixel values which are determined or assumed to be dominant and/or représentative for the current CU. Video encoder 20 may first transmit the size and the éléments of the palette to video décoder 30. Additionally, video encoder 20 may encode the pixel values in the given block according to a certain scannîng order.

For each pixel includcd in the given block, video encoder 20 may signal the index value that maps the pixel value to a corresponding entry in the palette. If the pixel value is not close enough to the value of any of the palette entries (e.g., close enough in value compared some predetermined threshold), then such a pixel is defined as an “escape pixel. In accordance with palette-based coding, video encoder 20 may encode and signal an index value that is reserved for an escape pixel, i.e., to indicate that it is an escape pixel and not a pixel for which there is an entry in the palette. In some examples, video encoder 20 may also encode and signal the pixel value or a residual value (or quantized versions thereof) for an escape pixel included in the given block. [0065] Upon receiving the encoded video bitstream signaled by video encoder 20, video 30 décoder 30 may first détermine the palette based on the information received from video encoder 20. Video décoder 30 may then map the received index values associated with the pixel locations in the given block to entries of the palette to rcconstruct the pixel values of the given block. In some instances, video décoder 30 may déterminé that a pixel of a palette-coded block is an escape pixel, such as by determining that the pixel is

I8

palette-coded with an index value reserved for escapc pixels. In instances where video décoder 30 identifies an escape pixel in a palette-coded block, video décoder 30 may receive the pixel value or a residual value (or quantized versions thereof) for an escape pixel included în the given block. Video décoder 30 may reconstruct the palette-coded 5 block by mapping the individual pixel values to the corresponding palette entries, and by using the pixel value or residual value (or quantized versions thereof) to reconstruct any escape pixels included in the palette-coded block.

[0066] Video encoder 20 and/or video décoder 30 may be configured to operate according to the techniques described in this disclosure, as will be described în more 10 detail below. In general, video encoder 20 and/or video décoder 30 may be configured to encode and décodé video data using one or more palette coding modes, wherein the palette coding modes do not include a palette sharing mode. Techniques of this disclosure include a video coding device, such as video encoder 20, being configured to détermine a first bin of a first syntax element that indicates a number of entries in a current palette that are explicitly signaled. Video encoder 20 may be further configured to encode a bitstream. The bitstream may include the first syntax clément. The bitstream also may not include a second syntax element that indicates a palette sharing mode. In some examples, determining the first bin of the first syntax element comprises determining the first bin of the first syntax element using a context-adaptive binary arithmetic coding. In other examples, determining the first bin of the first syntax element comprises determining the first bin of the first syntax element using one or more contexts. In some examples of using one or more contexts, the one or more contexts may be based on at least one of a predicted number of palate coding entries or a block size.

[0067] Further, this disclosure describes video encoder 20 being configured to détermine that a cunent pixel is a first pixel in a line in a scanning order. Video encoder 20 may further déterminé that a neighboring pixel situated above the current pixel is available. In response to determining that the current pixel is the first pixel in the line in the scanning order and determining that the neighboring pixel situated above the current pixel is available, video encoder 20 may be further configured to bypass encoding a first syntax element in a bitstream, wherein the first syntax element indicates a run type and encode a rcmainder of the bitstream.

[0068] Further, techniques of this disclosure include video encoder 20 being configured to détermine a first syntax element that indicates a maximum allowed palette size and

has a minimum value of zéro. Video encoder 20 may also be configured to encode a bitstream that includes the first syntax element. In some examples, the bitstream further includcs a second syntax element that indicates a maximum predictor palette size and has a minimum value of zéro. In some examples, the first syntax element has a maximum value of 4096 and the second syntax element has a maximum value of 8192. In other examples, the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 4095. In other examples, the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 8191. In still other examples, the first syntax element has a maximum value that is equal to a number of pixels in a largest coding unit and the second syntax element has a maximum value that is equal to a positive constant, such as 2, multiplied by the maximum value of the first syntax element. In other examples, the bitstream includes another syntax element that indicates a number of entries in a current palette that are explicitly signaled. In some examples of this, this syntax element is represented by one of a Golomb Rice code, an Exponential Golomb code, a Truncated Rice code, or a Unary code. In other examples of this, this syntax element is represented by one of a truncated Golomb Rice code, a truncated Exponential Golomb code, a truncated Truncated Rice code, a truncated Unary code, or a code that is also used to code a third syntax element included in the encoded bitstream that indicates whether a palette index is copied from a palette index in a row above a current pixel or is explicitly coded in the encoded bitstream. In some examples, this syntax element is represented by a Truncated Rice mode. In some examples, the syntax element that indicates a number of entries in a current palette that are explicitly signaled has a maximum value that is equal to the number of pixels in a current block of the video data.

[0069] Further, this disclosure describes a video coding device, such as video décoder 30, beîng configured to receive an encoded bitstream. The encoded bitstream docs not include a first syntax element that indicates a palette sharing mode. Further, the encoded bitstream includes a second syntax element that indicates a number of entries in a current palette that are explicitly signaled. Video décoder 30 may be further configured to décodé a first bin of the second syntax element. In some examples, decoding the first bin of the second syntax element comprises decoding the first bin of the second syntax element using a context-adaptive bînary arithmetic coding element. In other examples, decoding the first bin of the second syntax element comprises

decodîng the first bin of the second syntax element using one or more contexts. In some examples of using one or more contexts, the one or more contexts may bc based on at least one of a predîcted number of palate coding entrîcs or a block size.

[0070] Further, techniques of this disclosure include video décoder 30 being confîgured to receive an encoded bitstream. The encoded bitstream may include a first syntax element that indicates a run type. Video décoder 30 may further be confîgured to détermine that a current pixel is a first pixel in a line in a scanning order. Video décoder 30 may further détermine that a neighboring pixel situated above the current pixel is available. In response to determining that a current pixel is a first pixel in a line in a scanning order and determining that a neighboring pixel situated above the current pixel is available, video décoder 30 may bypass decodîng the first syntax element.

[0071] Further, techniques of this disclosure include video décoder 30 being confîgured to receive an encoded bitstream that includes a first syntax element that indicates a maximum allowed palette size and has a minimum value of zéro. Video décoder 30 may be further confîgured to décodé the encoded bitstream. In some examples, the encoded bitstream further includes a second syntax element that indicates a maximum predictor palette size and has a minimum value of zéro. In some examples, the first syntax element has a maximum value of 4096 and the second syntax element has a maximum value of 8192. In other examples, the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 4095. In other examples, the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 8191. In still other examples, the first syntax element has a maximum value that is equal to a number of pixels in a largest coding unit and the second syntax element has a maximum value that is equal to a positive constant, such as

2, multiplied by the maximum value of the first syntax element. In other examples, the encoded bitstream includes another syntax element that indicates a number of entries in a current palette that are explicitly signaled. In some examplcs,, the syntax element that indicates a number of entries in a current palette that are explicitly signaled is represented by one of a Golomb Rice code, an Exponential Golomb code, a Truncated

Rice code, or a Unary code. In other examples, the syntax element that indicates a number of entries in a current palette that are explicitly signaled is represented by one of a truncated Golomb Rice code, a truncated Exponential Golomb code, a truncated Truncated Rice code, a truncated Unary code, or the same code that is used to code a syntax element that indicates whether a palette index is copied from a palette index in a

row above a current pixel or is explicitly coded in the encoded bitstream. In some examples, the syntax element that indicates a number of entries in a current palette that are explicitly signaled îs represented by a Truncated Rice mode. In some examples, the syntax element that indicates a number of entries in a current palette that are explicitly signaled has a maximum value that is equal to the number of pixels in a current block of the video data.

[0072] In another example of the disclosure, video dccoder 30 may be configured to receive a block of video data in an encoded video bitstream, tlie block of video data having bcen encoded using a palettc-based coding mode, receive a plurality of syntax 10 éléments that are indicative of a palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, décodé the plurality of syntax éléments, including decoding the first syntax element using one or more Golomb codes, rcconstruct the palette based on the decoded 15 plurality of syntax éléments, and décodé the block of video data using the reconstructed palette.

[0073] In another example of the disclosure, video encoder 20 may be configured to encode a block of video data using a palette-based coding mode and a palette, generate a plurality of syntax éléments that are indicative of the palette that was used to encode the 20 block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, encode the first syntax element using one or more Golomb codes, and include the plurality of syntax éléments in an encoded video bitstream.

[0074] FIG. 2 is a block diagram illustrating an example video encoder 20 that may 25 implement various techniques of this disclosure. FIG. 2 is provided for purposes of explanation and should not be considered limiting of the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video encoder 20 in the context of HEVC coding. However, the techniques of this disclosure may be applicable to other coding standards or methods.

[0075] In the example of FIG. 2, video encoder 20 includes a video data memory 98, a prédiction processing unit 100, a residual génération unit 102, a transform processing unit 104, a quantization unit 106, an inverse quantization unit 108, an inverse transform processing unît 110, a reconstruction unit 112, a filter unit 114, a dccoded picture buffer 116, and an entropy encoding unit 118. Prédiction processing unit 100 includes an

inter-prediction processing unit 120 and an intra-prediction processing unit 126. Interprediction processing unit 120 includes a motion estimation unit and a motion compensation unit (not shown). Video encoder 20 also includes a palette-based encoding unit 122 confîgured to perform various aspects of the palette-based coding 5 techniques described in this disclosure. In other examples, video encoder 20 may include more, fewer, or different structural components.

[0076] Video data memory 98 may store video data to be encoded by the components of video encoder 20, The video data stored in video data memory 98 may be obtained, for example, from video source 18 of FIG. 1. Decoded picture buffer 116 may be a reference picture memory that stores reference video data for use in encoding video data by video encoder 20, e.g., in intra- or inter-coding modes. Video data memory 98 and decoded picture buffer 116 may be formed by any of a variety of memory de vices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), résistive RAM (RRAM), or other types of memory devices. Video data memory 98 and decoded picture buffer 116 may be provided by the same memory device or separate memory devices. In various examples, video data memory 98 may be on-chip with other components of video encoder 20, or off-chip relative to those components.

[0077] Video encoder 20 may reçoive video data. Video encoder 20 may encode each 20 CTU in a slice of a picture of the video data. Each of the CTUs may be associated with equally-sîzed luma coding tree blocks (CTBs) and corresponding CTBs of the picture. As part of encoding a CTU, prédiction processing unit 100 may perform quad-tree partitioning to divide the CTBs of the CTU into progressively-smaller blocks. The smaller block may be coding blocks of CUs. For example, prédiction processing unit 25 100 may partition a CTB associated with a CTU into four cqually-sized sub-blocks, partition one or more of the sub-blocks into four equally-sized sub-sub-blocks, and so on.

[0078] Video encoder 20 may encode CUs of a CTU to generate encoded représentations of the CUs (e.g., coded CUs). As part of encoding a CU, prédiction 30 processing unit 100 may partition the coding blocks associated with the CU among one or more PUs of the CU. Thus, each PU may be associated with a luma prédiction block and corresponding chroma prédiction blocks. Video encoder 20 and video décoder 30 may support PUs having various sizes. As indicated above, the size of a CU may refer to the size of the luma coding block of the CU and the size of a PU may refer to the size

of a luma prédiction block of the PU. Assuming that the size of a particular CU is 2Nx2N, video encoder 20 and video décoder 30 may support PU sizes of 2Nx2N or NxN for intra prédiction, and symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, NxN, or similar for inter prédiction. Video encoder 20 and video décoder 30 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter prédiction.

[0079] Inter-prediction processing unit 120 may generate prédictive data for a PU by performing inter prédiction on each PU of a CU. The prédictive data for the PU may include one or more prédictive sample blocks of the PU and motion information for the

PU. Inter-prediction processing unit 120 may perform different operations for a PU of a CU depending on whether the PU is in an I slice, a P slice, or a B slice. In an I slice, ail PUs are intra predicted. Hence, if the PU is in an 1 slice, inter-prediction processing unit 120 does not perform inter prédiction on the PU. Thus, for blocks encoded in I-mode, the prédictive block is formed using spatial prédiction from previously-encoded neighboring blocks within the same frame.

[0080] If a PU is in a P slice, the motion estimation unit of inter-prediction processing unit 120 may search the référence pictures in a list of reference pictures (e.g., “RefPicListO”) for a reference région for the PU. The reference région for the PU may be a région, within a reference picture, that contains sample blocks that most closely correspond to the sample blocks of the PU. Tire motion estimation unit may generate a reference index that indicates a position in RefPicListO of the reference picture containing the reference région for the PU. In addition, the motion estimation unit may generate an MV that indicates a spatial displacement between a coding block of the PU and a reference location associated with the reference région. For instance, the MV may be a two-dimensional vector that provides an offset from the coordinatcs in the current decoded picture to coordînates in a reference picture. The motion estimation unit may output the reference index and the motion vector (MV) as the motion information of the PU. The motion compensation unit of inter-prediction processing unit 120 may generate the prédictive sample blocks of the PU based on actual or interpolated samples at the reference location indicated by the MV of the PU.

[0081] If a PU is in a B slice, the motion estimation unit may perform uni-prediction or bi-prediction for the PU. To perform uni-prediction for the PU, the motion estimation unit may search the référence pictures of RefPicListO or a second reference picture list (“RefPicListl) for a reference région for the PU. The motion estimation unit may output, as the motion information of the PU, a référencé index that indicates a position in RefPicListO or RefPicListl of the référencé picture that contains the référence région, an MV that indicates a spatial displacement between a sample block of the PU and a référencé location associated with the référencé région, and one or more prédiction direction indicators that indicate whether the référencé picture is in RefPicListO or RefPicListl. The motion compensation unit of inter-prediction processing unit 120 may generate the prédictive sample blocks of the PU based at least in part on actual (i.e., integer précision) or interpolated (i.e., fractional précision) samples at the référencé région indicated by the motion vector of the PU.

[0082] To perform bi-directional inter prédiction for a PU, the motion estimation unit may search the référencé pictures in RefPicListO for a référencé région for the PU and may also search the référencé pictures in RefPicListl for another référencé région for the PU. The motion estimation unit may generate référencé picture indexes that indicate positions in RefPicListO and RefPicListl of the référencé pictures that contain the référencé régions. In addition, the motion estimation unit may generate MVs that indicate spatial displacements between the référencé location associated with the référencé régions and a sample block of the PU. The motion information of the PU may include the référencé indexes and the MVs of the PU. The motion compensation unit may generate the prédictive sample blocks of the PU based at least in part on actual or interpolated samples at the référencé région indicated by the motion vector of the PU.

[0083] In accordance with various examples of this disclosure, video encoder 20 may be configured to perform palette-based coding. With respect to the HEVC framework, as an example, the palette-based coding techniques may be configured to be used as a CU mode. In other cxamples, the palette-based coding techniques may be configured to be used as a PU mode in the framework of HEVC. Accordingly, ail of the disclosed processes described hercin (throughout this disclosure) in the context of a CU mode may, addîtionally or altematively, apply to a PU mode. Howcver, these HEVC-based examples should not be considered a restriction or limitation of the palette-based coding techniques described herein, as such techniques may be applied to work îndependently or as part of other existing or yet to be developed systems/standards. In these cases, the unit for palette coding can be square blocks, rectangular blocks or even régions of nonrectangular shape.

[0084] Palette-based encoding unit 122, for example, may perform palette-based coding when a palette-based encoding mode is selected, e.g., for a CU or PU. For example.

palette-based encoding unit 122 may be configured to generate a palette having cntries indicating pixel values, select pixel values in a palette to rcprcsent pixel values of at least some positions of a block of video data, and signal information associating at least some of the positions of the block of video data with entries in the palette corresponding, respcctively, to the selected pixel values. Although various fonctions are descrîbed as being performed by palette-based encoding unit 122, some or ali of such fonctions may be performed by other processing units, or a combination of different processing units.

[0085] Palette-based encoding unit 122 may be configured to generate any of the various syntax éléments descrîbed herein related to palette-based coding. Accordingly, video encoder 20 may be configured to encode blocks of video data using palette-based code modes as descrîbed in this disclosure. Video encoder 20 may selectively encode a block of video data using a palette coding mode, or encode a block of video data using a different mode, e.g., such an HEVC inter-predictive or intra-predictive coding mode. The block of video data may be, for example, a CU or PU generated according to an HEVC coding process. A video encoder 20 may encode some blocks with interpredictive temporal prédiction or intra-predictive spatial coding modes and décodé other blocks with the palette-based coding mode.

[0086] Intra-prediction processing unit 126 may générale prédictive data for a PU by performing intra prédiction on the PU. The prédictive data for the PU may include prédictive sample blocks for the PU and various syntax cléments. Intra-prediction processing unit 126 may perform intra prédiction on PUs in I slices, P slices, and B slices.

[0087] To perform intra prédiction on a PU, intra-prediction processing unit 126 may use multiple intra prédiction modes to generate multiple sets of prédictive data for the PU. When using some intra prédiction modes to generate a set of prédictive data for the PU, intra-prediction processing unit 126 may extend values of samples from sample blocks of neighboring PUs across the prédictive blocks of the PU in directions associated with the intra prédiction modes. The neighboring PUs may be above, above and to the right, above and to the left, or to the left of the PU, assuming a left-to-right, top-to-bottom encoding order for PUs, CUs, and CTUs. Intra-prediction processing unit 126 may use any of a number of different intra prédiction modes, e.g., 33 directional intra prédiction modes. In some examples, the number of intra prédiction modes may dépend on the size of the région associated with the PU.

[0088] Prédiction processing unit 100 may select the prédictive data for PUs of a CU from among the prédictive data generated by inter-prediction processing unit 120 for the PUs or the prédictive data generated by întra-prediction processing unit 126 for the PUs. In some examples, prédiction processing unit 100 selects the prédictive data for the PUs 5 of the CU based on ratc/distortion metrics of the sets of prédictive data. The prédictive sample blocks of the selected prédictive data may be referred to herein as the selected prédictive sample blocks.

[0089] Residual génération unit 102 may generate, based on the coding blocks (e.g., luma, Cb and Cr coding blocks) of a CU and the selected prédictive sample blocks (e.g., 10 prédictive luma, Cb and Cr blocks) of the PUs of the CU, residual blocks (e.g., luma, Cb and Cr residual blocks) of the CU. For instance, residual génération unit 102 may generate the residual blocks of the CU such that each sample in the residual blocks has a value equal to a différence between a sample in a coding block of the CU and a corresponding sample in a corresponding selected prédictive sample block of a PU of 15 the CU.

[0090] Transform processing unit 104 may perform quad-tree partitioning to partition the residual blocks associated with a CU into transform blocks associated with TUs of the CU. Thus, in some examples, a TU may be associated with a luma transform block and two chroma transform blocks. The sizes and positions of the luma and chroma transform blocks of TUs of a CU may or may not be based on the sizes and positions of prédiction blocks of the PUs of the CU. A quad-tree structure known as a “residual quad-tree” (RQT) may include nodes associated with each of the régions. The TUs of a CU may correspond to leaf nodes of the RQT.

[0091] Transform processing unit 104 may generate transform coefficient blocks for each TU of a CU by applying one or more transforms to the transform blocks of the TU.

Transform processing unit 104 may apply various transforms to a transform block associated with a TU. For example, transform processing unit 104 may apply a discrète cosine transform (DCT), a directional transform, or a conceptually similar transform to a transform block. In some examples, transform processing unit 104 docs not apply transforms to a transform block. In such examples, the transform block may be treated as a transform coefficient block.

[0092] Quantization unit 106 may quantize the transform coefficients in a coefficient block. The quantization process may reduce the bit depth associated with some or ail of the transform coefficients. For example, an n-bit transform coefficient may be rounded

down to an /n-bit transform coefficient during quantizatîon, where n is greater than m. Quantizatîon unit 106 may quantize a coefficient block associated with a TU of a CU based on a quantizatîon parameter (QP) value associated with the CU. Video encoder 20 may adjust the degrec of quantizatîon applied to the coefficient blocks associated 5 with a CU by adjusting the QP value associated with the CU. Quantizatîon may introduce loss of information, thus quantized transform coefficients may hâve lower précision than the original ones.

[0093] Inverse quantizatîon unit 108 and inverse transform processing unit 110 may apply inverse quantizatîon and inverse transforms to a coefficient block, respectïvely, to 10 reconstruct a residual block from the coefficient block. Reconstruction unit 112 may add the reconstructed residual block to corresponding samples from one or more prédictive sample blocks generated by prédiction processing unit 100 to produce a reconstructed transform block associated with a TU. By reconstructing transform blocks for each TU of a CU in this way, video encoder 20 may reconstruct the coding 15 blocks of the CU.

[0094] Filter unit 114 may perform one or more deblockîng operations to reduce blocking artifacts in the coding blocks associated with a CU. Decodcd picture buffer 116 may store the reconstructed coding blocks after filter unit 114 performs the one or more deblockîng operations on the reconstructed coding blocks. Inter-prediction processing unit 120 may use a reference picture that contains the reconstructed coding blocks to perform inter prédiction on PUs of other pictures. In addition, intra-prediction processing unit 126 may use reconstructed coding blocks in decodcd picture buffer 116 to perform intra prédiction on other PUs in the same picture as the CU.

[0095] Entropy encoding unit 118 may receive data from other functional components 25 of video encoder 20. For example, entropy encoding unit 118 may receive coefficient blocks from quantizatîon unit 106 and may receive syntax éléments from prédiction processing unit 100. Entropy encoding unit 118 may perform one or more entropy encoding operations on the data to generatc entropy-encoded data. For example, entropy encoding unit 118 may perform a CAB AC operation, a context-adaptive variable length coding (CAVLC) operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmctic coding (SBAC) operation, a Probabilîty Interval Partitioning Entropy (PIPE) coding operation, an ExponentialGolomb encoding operation, or another type of entropy encoding operation on the data. Video encoder 20 may output a bitstream that includes entropy-encodcd data generated

by entropy encoding unit 118. For instance, the bitstream may include data that represents a RQT for a CU.

[0096] In some examples, residual coding is not performed with palette coding. Accordingly, video encoder 20 may not perform transformation or quantization when coding using a palette coding mode. In addition, video encoder 20 may entropy encode data generated using a palette coding mode separately from residual data.

[0097] According to one or more of the techniques of this dîsclosure, video encoder 20, and specifically palette-based encoding unit 122, may perform palette-based video coding of predicted video blocks. As described above, a palette generated by video encoder 20 may be explicitly encoded and sent to video décoder 30, predicted from previous palette entrics, predicted from previous pixel values, or a combination thereof. [0098] In accordance with one or more techniques of this dîsclosure, palette-based encoding unit 122 may apply techniques of this dîsclosure to perform sample value to index conversion to encode video data using one or more palette coding modes, wherein the palette coding modes do not include a palette sharing mode. Techniques of this dîsclosure include palette-based encoding unit 122 of video encoder 20, being configured to détermine a first bin of a first syntax element that indicates a number of entries in a current palette that are explicitly signalcd. Palette-based encoding unit 122 of video encoder 20 may be further configured to encode a bitstream. The bitstream may include the first syntax element. The bitstream also may not include a second syntax element that indicates a palette sharing mode. In some examples, determining the first bin of the first syntax element comprises determining the first bin of the first syntax element using a context-adaptive binary arithmetic coding. In other examples, determining the first bin of the first syntax element comprises determining the first bin of the first syntax element using one or more contexts. In some examples of using one or more contexts, the one or more contexts may be based on at least one of a predicted number of palette coding entries or a block size.

[0099] Further, techniques of this dîsclosure include palette-based encoding unît 122 of video encoder 20 being configured to détermine that a current pixel is a first pixel in a line in a scanning order. Palette-based encoding unit 122 of video encoder 20 may further détermine that a neighboring pixel situated above the current pixel is available.

In response to determining that the current pixel is the first pixel in the line in the scanning order and determining that the neighboring pixel situated above the current pixel is available, palette-based encoding unit 122 of video encoder 20 may be further

configured to bypass encoding a first syntax element in a bitstream, wherein the first syntax element indicates a run type, and encode a rcmainder of the bitstream.

[0100] Further, techniques of this disclosure include palette-based encoding unit 122 of video encoder 20 being configured to détermine a first syntax element that indicates a maximum allowed palette size and has a minimum value of zéro. Palette-based encoding unit 122 of video encoder 20 may also be configured to encode a bitstream that includes the first syntax element. In some examples, the bitstream further includes a second syntax element that indicates a maximum prcdictor palette size and has a minimum value of zéro. In some examples, the first syntax element has a maximum value of 4096 and the second syntax element has a maximum value of 8192. In other examples, the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 4095. In other examples, the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 8191. In still other examples, the first syntax element has a maximum value that is equal to a number of pixels in a largest coding unit and the second syntax élément has a maximum value that is equal to a positive constant, such as 2, multiplied by the maximum value of the first syntax element. In other examples, the bitstream includes another syntax element that indicates a number of entries in a current palette that arc explicitly signaled. In some examples of this, this syntax element is represented by one of a Golomb Rîce code, an Exponential Golomb code, a Truncated Rice code, or a Unary code. In other examples of this, this syntax element is represented by one of a truncated Golomb Rice code, a truncated Exponential Golomb code, a truncated Truncated Rice code, a truncated Unary code, or a code that is also used to code a third syntax element included in the encoded bitstream that indicates whether a palette index is copied from a palette index in a row above a current pixel or is explicitly coded in the encoded bitstream. In some examples, this syntax element is represented by a Truncated Rico mode. In some examples, the syntax element that indicates a number of entries in a current palette that are explicitly signaled has a maximum value that is equal to the number of pixels in a current block of the video data.

[0101] FIG. 3 is a block diagram illustrating an example video décoder 30 that is configured to implement the techniques of this disclosure. Video décoder 30 may operate in a reciprocal manner to that of video encoder 20 described with reference to FIG. 2. FIG. 3 is provided for purposes of explanation and is not limiting on the techniques as broadly exemplified and described in this disclosure. For purposes of

explanation, this disclosure describes video décoder 30 in the context of HEVC coding. However, the techniques of this disclosure may be applicable to other coding standards or methods whcre palette mode coding is used.

[0102] In the example of FIG. 3, video décoder 30 includes a video data memory 148, an entropy decoding unit 150, a prédiction processïng unit 152, an inverse quantization unit 154, an inverse transform processïng unit 156, a reconstruction unit 158, a fîltcr unit 160, and a decoded picture buffer 162. Prédiction processïng unit 152 includes a motion compensation unit 164 and an intra-prediction processïng unit 166. Video décoder 30 also includes a palette-based decoding unit 165 configured to perform various aspects of the palette-based coding techniques described in this disclosure. In other examples, video décoder 30 may include more, fewer, or different structural components.

[0103] Video data memory 148 may store video data, such as an encoded video bitstream, to be decoded by the components of video décoder 30. The video data stored 15 in video data memory 148 may be obtained, for example, from channel 16, e.g., from a local video source, such as a caméra, via wired or wireless network communication of video data, or by accessing physicaï data storage media. Video data memory 148 may form a coded picture buffer (CPB) that stores encoded video data from an encoded video bitstream. Decoded picture buffer 162 may be a reference picture memory that 20 stores reference video data for use in decoding video data by video décoder 30, e.g., in intra- or inter-coding modes. Video data memory 148 and decoded picture buffer 162 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), résistive RAM (RRAM), or other types of memory devices. Video data memory 148 and decoded picture buffer 162 may be provided by the same memory device or separate memory devices. In various examples, video data memory 148 may be οπ-chip with other components of video décoder 30, or off-chip relative to those components.

[0104] Video data memory 148, e.g., a CPB, may receive and store encoded video data 30 (e.g., NAL units) of a bitstream. Entropy decoding unit 150 may receive encoded video data (e.g., NAL units) from video data memory 148 and may parse the NAL units to décodé syntax éléments. Entropy decoding unit 150 may entropy décodé entropyencoded syntax éléments in the NAL units. Prédiction processïng unit 152, inverse quantization unit 154, inverse transform processïng unit 156, reconstruction unit 158,

and filter unit 160 may generate decoded video data based on the syntax cléments obtaincd (e.g., cxtracted) from the bitstream.

[0105] The NAL units of the bitstream may include coded slice NAL units. As part of decoding the bitstream, entropy decoding unit 150 may extract and entropy décodé syntax éléments from the coded slice NAL units. Each of the coded slices may include a slice header and slice data. The slice header may contain syntax éléments pertaining to a slice. The syntax éléments in the slice header may include a syntax element that identifies a PPS associated with a picture that contains the slice.

[0106] In addition to decoding syntax éléments from the bitstream, video décoder 30 may perform a reconstruction operation on a non-partitioned CU. To perform the reconstruction operation on a non-partitioned CU, video décoder 30 may perform a reconstruction operation on each TU of the CU. By performing the reconstruction operation for each TU of the CU, video décoder 30 may reconstruct residual blocks of the CU.

[0107] As part of performing a reconstruction operation on a TU of a CU, inverse quantization unit 154 may inverse quantize, e.g., de-quantize, coefficient blocks associated with the TU. Inverse quantization unit 154 may use a QP value associated with the CU of the TU to détermine a degree of quantization and, likewise, a degree of inverse quantization for inverse quantization unit 154 to apply. That is, the compression ratio, e.g., the ratio of the number of bits used to represent original sequence and the compressed one, may be controlled by adjusting the value of the QP used when quantizing transform coefficients. The compression ratio may also dépend on the method of entropy coding employed.

[0108] After inverse quantization unit 154 inverse quantizes a coefficient block, inverse 25 transform processing unit 156 may apply one or more inverse transforms to the coefficient block in order to generate a residual block associated with the TU. For example, inverse transform processing unit 156 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the coefficient block.

[0109] If a PU is encoded using intra prédiction, intra-prediction processing unit 166 may perform intra prédiction to generate prédictive blocks for the PU. Intra-prediction processing unit 166 may use an intra-prediction mode to generate the prédictive luma, Cb and Cr blocks for the PU based on the prédiction blocks of spatially-neighboring

PUs. Intra-prcdictîon processing unît 166 may détermine the intra prédiction mode for the PU based on one or more syntax éléments decoded from the bitstream. [0110] Prédiction processing unit 152 may construct a first reference picture list (RefPicListO) and a second reference picture list (RefPicListl) based on syntax éléments extracted from the bitstream. Furthermore, if a PU is encoded using inter prédiction, entropy decodîng unit 150 may extract motion information for the PU. Motion compensation unit 164 may détermine, based on the motion information of the PU, one or more reference régions for the PU. Motion compensation unit 164 may generate, based on samples blocks at the one or more reference blocks for the PU, prédictive blocks (e.g., prédictive luma, Cb and Cr blocks) for the PU.

[0111] Reconstruction unit 158 may use the transform blocks (e.g., luma, Cb and Cr transform blocks) associated with TUs of a CU and the prédictive blocks (e.g., luma, Cb and Cr blocks) of the PUs of the CU, e.g., either intra-prediction data or inter-prediction data, as applicable, to reconstruct the coding blocks (e.g., luma, Cb and Cr coding blocks) of the CU. For example, reconstruction unit 158 may add samples of the transform blocks (e.g., luma, Cb and Cr transform blocks) to corresponding samples of the prédictive blocks (e.g., prédictive luma, Cb and Cr blocks) to reconstruct the coding blocks (e.g., luma, Cb and Cr coding blocks) of the CU.

[0112] Filtcr unit 160 may perform a deblocking operation to rcduce blocking artifacts associated with the coding blocks (e.g., luma, Cb and Cr coding blocks) of the CU. Video décoder 30 may store the coding blocks (e.g., luma, Cb and Cr coding blocks) of the CU in decoded picture buffer 162. Decoded picture buffer 162 may provide reference pictures for subséquent motion compensation, intra prédiction, and présentation on a display device, such as display device 32 of FIG. 1. For instance, video décoder 30 may perform, based on the blocks (e.g., luma, Cb and Cr blocks) in decoded picture buffer 162, intra prédiction or inter prédiction operations on PUs of other CUs. In this way, video décoder 30 may extract, from the bitstream, transform coefficient levels of a significant coefficient block, inverse quantize the transform coefficient levels, apply a transform to the transform coefficient levels to generate a transform block, generate, based at least in part on the transform block, a coding block, and output the coding block for display.

[0113] In accordance with various examples of this disclosure, video décoder 30 may be confîgured to perform palette-based coding. Palette-based decodîng unit 165, for example, may perform palette-based decodîng when a palette-based decodîng mode is selected, e.g., for a CU or PU. For example, palettc-based decoding unit 165 may be configured to generate a palette having entries indicating pixel values. Furthermore, in this example, palette-based decoding unit 165 may receive information assocîating at least some positions of a block of video data with entries in the palette. In this example, palette-based decoding unit 165 may select pixel values in the palette based on the information. Additionally, in this example, palette-based decoding unit 165 may reconstruct pixel values of the block based on the selected pixel values. Although various fonctions are described as being performed by palette-based decoding unit 165, some or ail of such fonctions may be performed by other processing units, or a combination of different processing units.

[0114] In accordance with one or more techniques of this disclosure, palette-based decoding unit 165 may receive palette coding mode information, and perform the above operations when the palette coding mode information indicates that the palette coding mode applies to the block. When the palette coding mode information indicates that the palette coding mode docs not apply to the block, or when other mode information indicates the use of a different mode, palette-based decoding unit 165 décodes the block of video data using a non-palette based coding mode, e.g., such an HEVC interpredictive or intra-predictive coding mode, when the palette coding mode information indicates that the palette coding mode does not apply to the block. The block of video data may be, for example, a CU or PU generated according to an HEVC coding process. A video décoder 30 may décodé some blocks with inter-predictive temporal prédiction or intra-predictive spatial coding modes and décodé other blocks with the palette-based coding mode. The palette-based coding mode may comprise one of a plurality of different palette-based coding modes, or there may be a single palette-based coding mode.

[0115] According to one or more of the techniques of this disclosure, video décoder 30, and specifically palette-based decoding unit 165, may perform palette-based video decoding of palette-coded video blocks. As described above, a palette decoded by video décoder 30 may be explicitly encoded and signaled by video encoder 20, reconstructed by video décoder 30 with respect to a received palette-coded block, predicted from previous palette entries, predicted from previous pixel values, or a combination thereof. [0116] Palette-based decoding unit 165 may apply techniques of this disclosure to perform sample value to index conversion décodé video data using one or more palette coding modes, wherein the palette coding modes do not include a palette sharing mode.

Further, techniques of this disclosure include palette-bascd decoding unit 165 of video décoder 30 being configured to receive an encoded bitstream. In this example, the encoded bitstream does not include a first syntax element that indicates a palette sharing mode. Further, the encoded bitstream includes a second syntax element that indicates a number of entries in a current palette that are explicitly signaled. Palette-based decoding unit 165 of video décoder 30 may be further configured to décode a first bin of the second syntax element. In some examples, decoding the first bin of the second syntax element comprises decoding the first bin of the second syntax element using a context-adaptive binary arithmetic coding (CABAC) unit. In other examples, decoding the first bin of the second syntax element comprises decoding the first bin of the second syntax element using one or more contexts. In some examples of using one or more contexts, the one or more contexts may be based on at least one of a predicted number of palate coding entries or a block size.

[0117] Further, techniques of this disclosure include palette-based decoding unit 165 of video décoder 30 being configured to receive an encoded bitstream. The encoded bitstream may include a first syntax element that indicates a run type. Palette-based decoding unit 165 of video décoder 30 may further be configured to détermine that a current pixel is a first pixel in a line in a scanning order. Palette-based decoding unit 165 of video décoder 30 may further détermine that a neighboring pixel situated above the current pixel is available. In response to determining that a current pixel is a first pixel in a line in a scanning order and determining that a neighboring pixel situated above the current pixel is available, palette-based decoding unit 165 of video décoder 30 may bypass decoding the first syntax element.

[0118] Further, techniques of this disclosure include palette-based decoding unit 165 of video décoder 30 being configured to receive an encoded bitstream that includes a first syntax element that indicates a maximum allowed palette size and has a minimum value of zéro. Palette-based decoding unit 165 of video décoder 30 may be further configured to décode the encoded bitstream. In some examples, the encoded bitstream further includes a second syntax element that indicates a maximum predictor palette size and has a minimum value of zéro. In some examples, the first syntax element has a maximum value of 4096 and the second syntax element has a maximum value of 8192. In other examples, the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 4095. In other cxamples, the first syntax element has a maximum value of 4095 and the second syntax element has a

maximum value of 8191. In still other cxamples, the first syntax element has a maximum value that is equal to a number of pixels in a largcst coding unit and the second syntax element has a maximum value that is equal to a positive constant, such as 2, multiplied by the maximum value of the first syntax element. In other examplcs, the encoded bitstream includes another syntax element, e.g., a third syntax element that indicates a number of entries in a current palette that are explicitly signaled. In some examples of this disclosure, the syntax element that indicates a number of entries in a current palette that are explicitly signaled is represented by one of a Golomb Rice code, an Exponential Golomb code, a Truncated Rico code, or a Unary code. In other examples of this disclosure, the syntax element that indicates a number of entries in a current palette that are explicitly signaled is represented by one of a truncated Golomb Rice code, a truncated Exponential Golomb code, a truncated Truncated Rice code, a truncated Unary code, or a code that is also used to code a third syntax element included in the encoded bitstream that indicates whether a palette index is copied from a palette index in a row above a current pixel or is explicitly coded in the encoded bitstream. In some examples, the syntax element that indicates a number of entries in a current palette that arc explicitly signaled is represented by a Truncated Rice mode. In some examples, the syntax element that indicates a number of entries in a current palette that are explicitly signaled has a maximum value that is equal to the number of pixels in a current block of the video data.

[0119] It is to be recognized that depending on the example, certain acts or events of any of the techniques descrîbed herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not ail descrîbed acts or events are ncccssary for the practice of the techniques). Moreover, in certain cxamples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially. In addition, while certain aspects of this disclosure are descrîbed as being performed by a single module or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or modules associated with a video coder.

[0120] Certain aspects of this disclosure hâve been descrîbed with respect to the developing HEVC standard for purposes of illustration. However, the techniques descrîbed in this disclosure may be useful for other video coding processes, including other standard or proprietary video coding processes not yet developed.

[0121] The techniques described above may be performcd by video encoder 20 (FIGS.

and 2) and/or video décoder 30 (FIGS, 1 and 3), both of which may be generally referred to as a video coder. Likewise, video coding may refer to video encoding or video decoding, as applicable.

[0122] In some examples, the palette-based coding techniques may be configured for use in one or more coding modes of the HEVC standard or the HEVC SCC standard. In other examples, the palette-based coding techniques can be used indepcndently or as part of other existing or future Systems or standards. In some examples, the techniques for palette-based coding of video data may be used with one or more other coding techniques, such as techniques for inter-predictive coding or intra-predictive coding of video data. For example, as described in greater detail below, an encoder or décoder, or combined encoder-decoder (codée), may be configured to perform inter- and intrapredictive coding, as well as palette-based coding.

[0123] With respect to the HEVC framework, as an example, the palette-based coding 15 techniques may be configured to be used as a coding unit (CU) mode. In other examples, the palette-based coding techniques may be configured to be used as a prédiction unit (PU) mode in the framework of HEVC. Accordingly, ail of the following disclosed processcs described in the context of a CU mode may, addîtionally or altemativeïy, apply to PU. However, these HEVC-based examples should not be considered a restriction or limitation of the palette-based coding techniques described herein, as such techniques may be applied to work independently or as part of other existing or yet to be developcd systems/standards. In these cases, the unit for palette coding can be square blocks, rectangular blocks or even régions of non-rectangular shape.

[0124] The basic idea of palette-based coding is that, for each CU, a palette is derived which comprises (and may consist of) the most dominant pixel values in the current CU. The size and the éléments of the palette arc first transmitted from a video encoder to a video décoder. The size and/or the éléments of the palette can be directly coded or predictively coded using the size and/or the éléments of the palette in the neighboring

CUs (e.g. above and/or left coded CU). After that, the pixel values in the CU are encoded based on the palette according to a certain scanning order. For each pixel location in the CU, a flag, e.g., palette_flag, >s first transmitted to indicate whether the pixel value is included in the palette. In some examplcs, such a flag is callcd a copy_above_palette_indices_flag. For thosc pixel values that map to an entry in the

palette, the palette index associated with that entry is signaled for the given pixel location in the CU. For those pixel values that do not exist in the palette, a spécial index may be assigned to the pixel and the actual pixel value (in some cases, a quantized pixel value) is transmitted for the given pixel location in the CU. These pixels arc referred to as escape pixels. An escape pixel can be coded using any existing entropy coding method such as fixed length coding, unary coding, etc.

[0125] In other examplcs, no fiag is used to explicitly indicate whether a pixel is an “escape pixel. Instead, a fiag or other syntax element may be used to indicate a run type. The syntax element indicating the run type may indicate whether the following indices are copied from the position above the current pixel or if there is a run of signaled index values. If the derived index value of a particular pixel corresponds to an “escape index” (e.g., a predetermined index in the palette indicating the use of an escape pixel), then video décoder 30 may détermine that such a pixel is an escape pixel. [0126] To improve screcn content coding effïciency, several methods hâve been proposed that extend palette mode. For example, such methods may be found in JCTVC-S0114 (Kim, J., et al., “CE6-related: Enabling copy above mode prédiction at the boundary of CU,” Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11,19¹¹¹ Meeting: Strasbourg, FR, 17-24 October 2014); JCTVC-S0120 (Ye, J., et al., “Non-CE6: Copy previous mode,” Joint

Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11,19* Meeting: Strasbourg, FR, 17-24 October 2014); and JCTVCS0151 (Wang, W., et al., Non-CE6: 2-D Index Map Coding of Palette Mode in HEVC SCC” Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11,19^,h Meeting: Strasbourg, FR, 17-24 October 2014).

[0127] The document X. Guo and A. Saxena, “RCE4: Summary report of HEVC Range

Extension Core Experiments 4 (RCE4) on palette coding for screen content,” JCTVCP0035, San José, US, 9-17 Jan. 2014 describes two test results of palette-based modes, which were reported to achieve significant Bjontegaard Distortion-rate (BD-rate) réduction, especially for screcn contents. The two methods are briefly summarized below.

[0128] In one example method, as described, for cxample, in the document X. Guo, Y. Lu, and S. Li, “RCE4: Test 1. Major-color-based scrcen content coding,” JCTVCP0108, San José, US, 9-17 Jan. 2014, a histogram-based algorithm is used to classify the pixels. In particular, the most significant N peak values in a histogram are selected as major colors for coding. The pixel values that are close to a major color will be quantized to the major color. Other pixels that do not bclong to any major color sets are escape pixels, which are also quantized before coding. For Iossless coding, no quantization is used.

[0129] By using classification, pixels of a coding unit (CU) can be converted into color indices. After that, the major color number and values are coded. Then, the color indices are coded as follows:

• For each pixel line, a flag is signalled to indicate the coding mode. There are thrcc modes: horizontal mode, vertical mode and normal mode.

o If the mode is horizontal mode, the whole line (i.e., ail of the pixels in the entirc line) shares the same color index. In this case, the color index is transmitted.

o If the mode is vertical mode, the whole line is the same with the above line. In this case, nothing is transmitted. The current line copies the color indices of the above line.

o If the mode is normal mode, a flag is signalled for each pixel position to indicate whether it is the same with one of the left and above pixels. If not, the index îtself is transmitted.

In addition, if the pixel is escape pixel, the pixel value is transmitted.

[0130] In another example method, as described, for example, in the document L. Guo, W. Pu, M. Karczewicz, J. Sole, R. Joshi, and F. Zou, “RCE4: Results of Test 2 on Palette Mode for Screen Content Coding,” JCTVC-P0198, San José, US, 9-17 Jan. 2014, a palette-based coding mode is included as a CU mode. The encoding process of the second method may include the following:

• Transmission of the palette: an entry-wise prédiction scheme is used to encode the current palette based on the palette of the left CU (the CU neighboring the CU currently being coded to the left). After that, non-prcdictcd entries of the palette are transmitted.

• Transmission of pixel values: the pixels in the CU are encoded in a raster scan order using the following three modes:

o Run mode”: A palette index is first signaled, followed by “palette_run” (M). The following M palette indexes are the same as the signaled palette index first signaled.

o “Copy above mode”: A value “copy_run (N) is transmitted to indicate that for the following N palette indexes are the same as their above neighbors, respectively.

o “Pixel mode”: A prédiction flag is first transmitted. The flag value being 5 equal to 1 indicates prédiction residual using the reconstructed top neighboring pixel as a predictor is transmitted. If the value of this flag is 0, the pixel value is transmitted without prédiction.

[0131] The palette may make up a relatively significant portion of the bits for a palette coded block (e.g., CU). Accordingly, the video coder may predict one or more entries 10 of the palette based on one or more entries of a previously coded palette (e.g., as noted above with respect to the transmission of the palette”).

[0132] In some examples, the video coder may generate a palette predictor list when predîcting palette entries. For example, the document C. Gisquet, G. Laroche, and P. Onno, “AhGIO: Palette predictor stuffing,” JCTVC-Q0063 discloses one example process for determining palette predictors. In some examples, the video coder may use a Boolean vector to indicate whether each item in a palette predictor list is used (or not used) for predîcting one or more entries in the palette for the block currently being coded.

[0133] In some examples, ali of the items in the palette predictor list are derived from 20 the previously-coded palette (e.g., the palette coded with the previously coded block).

However, such palettes may be spatially far away from the current CU, which may make the palette corrélation relatively weak. In general, expanding the palette predictor table may be helpful (e.g., may provide more accurate predictors, which may rcsult in an efficiency gain). However, determining and using a relatively large palette predictor 25 table results in a relatively longer Boolean vector.

[0134] In one example of palette coding, video encoder 20 may generate a syntax element, such as a flag “PLT_Mode_flag,” that indicates whether or not a palette-based coding mode is used for a particular région of a video frame. For example, the PLT_Mode_flag may be generated at the slice level, the CU-level, the PU-îevel, or any 30 other level of a video frame. For example, video encoder 20 may generate the

PLT_Mode_flag at the CU level and signal the PLT_Mode_flag in an encoded video bitstream. Video décoder 30 may then parse the PLT_Modc_flag upon decoding the encoded video bitstream. In this example, a value of this PLT_Mode_flag equal to 1 spécifiés that the current CU is encoded using a palette mode. In this case, video

décoder 30 may apply lhe palette-based coding mode to décodé the CU. In some examples, a syntax element may indicate one of a plurality of different palette modes for lheCU.

[0135] A value of this PLT_Mode_flag equal to 0 spécifiés that the current CU is encoded using a mode other than palette mode. For example, any of a variety of interpredictive, intra-predictive, or other coding modes may be used. When a value of PLT_Mode_flag is 0, further information may be transmitted to signal which spécifie mode is used for encoding the respective CU, where such spécifie mode, typically, may be an HEVC coding mode (e.g., intra coding or inter coding). The use of the

PLT_Mode_flag is described for purposes of example. In other examples, however, other syntax éléments such as multi-bit codes may be used to indicate whether the palette-based coding mode is to be used for a CU (or PU in other examples) or to indicate which of a plurality of modes are to be used.

[0136] The PLT_Mode_flag or other syntax element may also be transmitted at a higher level. For example, the PLT_Mode_flag may be transmitted at slice level. In this case, a value of the flag equal to 1 implies that ail of the CUs in the slice will be encoded using palette mode (which means no mode information, e.g., for palette mode or other modes, needs to be transmitted at CU level). Similarly, this flag can be signaled at the picture parameter set (PPS), sequence parameter set (SPS) or video parameter set (VPS) level. Also, a flag can be sent at one of these levels spccifying whether the palette mode is enabled or disabled for the particular picture, slice, etc., while the PLT_Modc_flag indicates whether the palette-based coding mode is used for each CU. In this case, if a flag or other syntax element sent at the slice, PPS, SPS or VPS level indicates that palette coding mode is disabled, in some examples, there may be no need to signal the

PLT_Mode_flag for each CU. Altematively, if a flag or other syntax element sent at the slice, PPS, SPS or VPS level indicates that palette coding mode is enabled; the PLT_Mode_flag may be further signaled to indicate whether the palette-based coding mode is to be used for each CU. Again, as mentioned above, application of thèse techniques for indicating palette-based coding of a CU could additionally or altematively be used to indicate palette-based coding of a PU.

[0137] A flag, such as PLT_Mode_flag, may also or altematively be conditionally transmitted or inferred. The conditions for transmitting the PLT_Modc_flag or inferring the flag can be one or more of, as examples, the size of the CU, the frame type, the color

space, the color component, the frame size, the frame rate, the layer id in scalable video coding or the view id in multi-view coding.

[0138] Techniques for the génération and transmission of a palette will now be discussed. Video encoder 20 may be configured to generate and signal one or more syntax éléments and values that may be used by video décoder 30 to construct and/or reconstruct the palette used by video encoder 20 to encode a particular level of the video frame (e.g., a CU). In some examples, video encoder 20 may indicate or otherwise signal a palette for each CU. In other examples, video encoder 20 may indicate or otherwise signal a palette that may be shared among sevcral CUs.

[0139] The size of the palette, e.g., in terms of the number of pixel values included, can be a fixed value or can be signaled by video encoder 20 in an encoded video bitstream. Video décoder 30 may receive and décodé the indication of the palette size from the encoded video bitstream. The signaling can be separate for different components or a single size can be signaled for ail the components. The different components may be, for examplc, luma and chroma components. The signaling can use unary codes or truncated unary codes (e.g., that truncates at a maximum limit of the palette size). Exponential-Golomb or Rice-Golomb codes can also be used. In some cxamples, the signaling of the size can be done in the following way: after signaling an entry in the palette, a “stop” flag is signaled. A value of this fiag equal to 1 spécifies that the current entry is the last one in the palette; a value of this flag equal to 0 spécifiés that there are more entries in the palette. The “stop” flag may not be transmitted by the encoder if the alrcady constructed palette hits the maximum limit of the palette size. In some examples, the size of the palette can also be conditionally transmitted or inferred based on sidc information in the same way as described above for “Transmission of flag

PLT_Mode_flag.” [0140] The palette can be transmitted separateïy for each color component in the CU. For example, there may be a palette for the Y component of this CU, another palette for the U component of this CU, and yet another palette for the V component of this CU. For the Y palette, the entry may (assumedly) be a représentative Y value in this CU.

The same applies to the U and V components. It is also possible that the palette may be transmitted for ail of the color components in the CU. In this examplc, the i-th entry in the palette is a triple (Yi, Ui, Vi). In this case, the palette includcs values for each of the components.

[0141] Prédiction of a palette is an alternative approach to the “transmission of palette” described above. In some examples, palette prédiction techniques may be used in conjunction with palette signaling techniques. That is, video encoder 20 may be confîgured to signal syntax éléments that may be used by video décoder 30 to predict a 5 portion of the total number of palette entries. In addition, video encoder 20 may be confîgured to explicitly signal another portion of the palette entries.

[0142] In one example of a palette prédiction approach, for each CU, one flag “pred_palette_flag” is transmitted. A value of this flag equal to 1 spécifiés that the palette for the current CU will be predicted from past data and thus there is no need for 10 the palette to be transmitted. A value of this flag equal to 0 means that the palette of the current CU needs to be transmitted. The flag can be separate for different color components (e.g., so that 3 flags need to be transmitted for a CU in YUV video), or a single flag can be signaled for ali the color components. For examplc, a single flag may indicate whether the palettes are transmitted for ail of the components or whether the palettes for ali of the components will be predicted.

[0143] In some examples, the prédiction can be performed in the following manner. If the prédiction flag value is equal to 1, for the current CU, video encoder 20 copies the palette of one or more of the already encoded neighboring CUs. The palette of the alrcady encoded neighboring CUs may hâve been transmitted or predicted. For example, the copied neighboring CU can be the left neighboring CU. In the case that the palette of the left CU is not available (as in the case in which the left CU is not encoded using the palette mode or the current CU is at the first column of the picture), the copy of the palette can be from the CU above the current CU. The copied palette can also be a combination of the palettes of a number of neighboring CUs. For example, one or more formulas, functions, rules or the like may be applied to generate a palette based on palettes of one or a combination of a plurality of neighboring CUs. [0144] It is also possible that a candidate list may be constructed and an index is transmitted by video encoder 20 to indicate the candidate CU from which the current CU copies the palette. Video décoder 30 may construct the same candidate list and then use the index to select the palette of the corresponding CU for use with the current CU. For examplc, the candidate list may include one CU above and one CU on the left, relative to the current CU to be coded within a slice or picture. In this example, a flag or other syntax element may be signaled to indicate the candidate sélection. For example, a transmitted flag equal to 0 means the copy is from the left CU, and a

transmitted flag equa! to 1 means the copy is from the top CU. Video décoder 30 selects the palette to be copied from the corresponding ncighbor CU and copies it for use in dccoding the current CU. The prédiction can also be derived using the most frequent sample values in the causal neighbors of the current CU.

[0145] The prédiction of palettes can also be entry-wise. For each entry in the palette, video encoder 20 generates and signais a flag. A value of a flag equal to 1 for a given entry spécifiés that a predicted value (for example, the corresponding entry from a selected candidate CU like the left CU) is used as the value of this entry. A value of a flag equal to 0 spécifiés that this entry is not predicted and its value will be transmitted to video décoder 30 from video encoder 20, e.g., signaled in a bitstream encoded by video encoder 20 for later decoding by video décoder 30.

[0146] The value of *‘pred_palette_flag,” the candidate CU whose palette is used to predict the palette of the current CU or the rules for constructing the candidates, can be also conditionally transmitted or inferred based on side information in the samc way as described above for “Transmission of flag PLT_Mode_flag.” [0147] Next, video encoder 20 may generate and signal a map which indicates what respective palette entry is associated with each pixel in a CU. The i-th entry in the map is corresponding to the i-th position in the CU. A value of the i-th entry equal to 1 spécifiés that the pixel value at this i-th location in the CU is one of the values in the palette, and a palette index is further transmitted so that video décoder 30 can reconstruct the pixel value (in case there is only one entry in the palette, the transmission of palette index may be skipped). A value of the i-th entry equal to 0 spécifiés that the pixel value at the i-th position in the CU is not in the palette and thus the pixel value will be transmitted to video décoder 30 explicitly.

[0148] If the pixel value at one position in the CU is a value in the palette, it is observed that there is a high probability that the neighboring positions in the CU hâve the samc pixel value. So, after encoding a palette index (say j, which is corresponding to pixel value s) for a position, video encoder 20 may transmit a syntax element “run” to indicate the number of consecutive values of the samc pixel value s in the CU before the scan reaches a different pixel value. For example, if the immédiate next one has a value different than s, then run=0 is transmitted. If the next one is s but the one after is not s, then run = 1.

[0149] In the case where a run is not transmitted (e.g., Implicit Run Dérivation), the value of the run may be a constant, for example, 4, 8,16, etc., or the value of the run

may also be dépendent on side information. For example, the value of the run may dépend on block size, e.g., the run is equal to the widtli of the current block, or the height of the current block, or the half-width (or half-hcight) of the current block, or a fraction of the width and the height of the block, or a multiple of the heîght/widlh of the 5 block. The value of the run may also be dépendent on the QP, framc-type, color component, color format (e.g., 444,422,420) and/or color space (e.g., YUV, RGB). The value of the run may also dépend on the scan direction. In other examples, the value of the run may dépend on other types of side information. The value of the run may also be signaled using high level syntax (e.g., PPS, SPS).

[0150] In some examples, the map may not need to be transmitted. The run may only start at certain locations. For example, the run may only start at the beginning of each row, or the beginning of every N rows. The starting location may be different for different scan directions. For example, if the vertical scan is used, the run may only start at the beginning of a column or the beginning of every N columns. The start location may dépend on side information. For example, the start location may be the mid-point of each row, or each column, or 1/n, 2/n,... (η-1 )/n (i.e., fractions) of each row/column. The start location may also dépend on the QP, frame-type, color component, color format (e.g., 444,422,420) and/or color space (e.g., YUV, RGB). In other examples, the start position of the run may dépend on other types of side information. The start position can also be signaled using high level syntax (e.g., PPS, SPS, etc.).

[0151] It is also possible that the implicit start position dérivation and the implicit run dérivation are combined. For example, the run is equal to the distance between two neighboring start positions. In the case that the start point is the beginning (i.e., the first position) of every row, the length of the run is a row.

[0152] The scan direction may be vertical or horizontal. It is possible that a flag is transmitted for each CU to indicate the scan direction. Flags may be transmitted separately for each component or a single flag may be transmitted and the indicated scan direction applies to ail the color components. It is also possible that other scan directions, like 45 degree or 135 degree, are used. The scan order may be fixed or may be dépendent on side information in the same way as described above for ‘Transmission of flag PLT_Mode_flag”.

[0153] Above, it is explaincd how to transmit a palette. An alternative to the abovedescribed examples is to construct the palette on-the-fly. In this case, at the beginning

of the CU, there is no cntry in the palette, and as video encoder 20 signais new values of tire pixels for the positions in the CU, these values are includcd in the palette. That is, video encoder 20 adds pixel values to the palette as they are generated and transmitted for positions in the CU. Then, later positions in the CU that hâve the same values may refer to pixel values in the palette, e.g., with index values, instcad of having video encoder 20 transmit the pixel values. Similarly, when video décoder 30 receivcs a new pixel value (e.g., signaled by the encoder) for a position in the CU, it includes the pixel value in the palette constructed by video décoder 30. When later positions in the CU hâve pixel values that hâve been added to the palette, video décoder 30 may receive information such as, e.g., index values, that identify the corresponding pixel values in the palette for reconstruction of the pixel values in the CU.

[0154] If the maximum palette size is reached, e.g., as the palette îs constructed dynamically on-the-fly, then the encoder and décoder share the same mechanism to remove an entry of the palette. One method is to remove the oldest entry in the palette (FIFO queue). Another method is to remove the least used entry in the palette. Another is to weight both methods (time in palette and usage frequency) to décide the entry to be replaced. As one example, if a pixel value entry is removed from the palette, and the pixel value occurs again at a later position in the palette, the encoder may transmit the pixel value instead of including an entry in the palette. Additionally, or altematively, it is possible that such a pixel value could be re-entered into the palette after having been removed, e.g., as the encoder and décoder scan the positions in the CU.

[0155] This disclosure also considéra combining an initial palette signaling with the onthe-fly dérivation of the palette. In one example, the initial palette would be updated with the coding of the pixels. For example, upon transmitting the initial palette, video encoder 20 may add values to the initial palette or change values in the initial palette as pixel values of additional locations in the CU are scanned. Likewise, upon receiving an initial palette, video décoder 30 may add values to the initial palette or change values in the initial palette as pixel values of additional locations in the CU are scanned. Similarly, the encoder can signal whether the current CU uses transmission of the entire palette, or on-the-fly palette génération, or a combination of transmission of an initial palette with updating of the initial palette by on-the-fly dérivation. In some examples, the initial palette may be a full palette at maximum palette size, in which case values in the initial palette may be changed, or a reduced size palette, in which case values are added to the initial palette and, optionally values in the initial palette are changed.

[0156] Above, it was described how to transmit the map by identifying the pixel value. Along with that method described above, the transmission of the map can be done by signaling line copying. In one example, line copying is sîgnaled by video encoder 20 such that the pixel value for an entry is equal to the pixel value of the entry of a line above (or in column on the left if the scan is vertical). Then, the ‘run’ of entries that are copied from the line may be sîgnaled. Also, the line from which it is copied can be indicated; several lines above may be buffered for this purpose. For instance, the prcvious four rows are stored and which row is copied may be sîgnaled with a truncated unary code or other codes, and then, how many entries of that row are copied, i.e., the run, may be sîgnaled. Hence, in some examples, the pixel value for an entry may be sîgnaled to be equal to a pixel value of an entry in a row immediately above or two or more rows above the current row.

[0157] In the case where no run is sîgnaled, the value of the run may be constant/fixed or may be dépendent on side information (and derived by the décoder) using the method 15 described above.

[0158] It is also possible that the map does not nced to be transmitted. For example, the run may start only at certain positions. The start position may be fixed or may be dépendent on side information (and derived by the décoder), so the signaling of the start position may be skipped. Instead, one or more the techniques described above may be 20 applied. The implicit start position dérivation and the implicit run dérivation may also be combined using the same method as described above.

[0159] If both methods of map transmission are used, then a flag or other syntax element may indicate whether the pixel is obtained from the palette or from the previous lines, and then an index indicates the entry in the palette or the row, and finally the ‘run.’ [0160] This disclosure describes methods, devices, and techniques for simplifying palette mode coding and/or for improving palette-based coding cfficicncy. The techniques of this disclosure may be used in conjunction with one another or separately to improve coding efficiency and/or reduce codée complexity. In general, according to 30 the techniques of this disclosure, a video coding device may be configured to encode and décodé video data using one or more palette coding modes, wherein the palette coding modes do not include a palette sharing mode.

[0161] In one example palette mode, a flag, such as palette_share_flag, may be sîgnaled into the bitstream to indicate that the palette for or more blocks of video data are shared

or merged from the palette of another block of video data. The block of video data from which to obtain the shared palette may be based on predetermined rules (e.g., use the palette of the block to the left or above the current block) or may be otherwisc indicated in the encoded video bitstream. As described in R. Joshî and J. Xu, “High efficient video coding (HEVC) screen content coding: Draft 2,” JCTVC-S1005, Section 7.4.9.6,” the semantics of palette_share_flag are stated as “palette_share_fiag[xO][yO] equal to 1 spécifiés that the palette for the current coding unit is derived by copying the first PreviousPalettcSîze entries from the predictor palette. The variable PrcviousPalcttcSize is derived as specificd in subclausc 8.4.5.2.8. palette_share_flag fxO] [yO] equal to 0 spécifiés the palette for the current coding unit is specified as a combination of palette entries from previous coding units and new palette entries which are explicitly signaled.” [0162] In one example, when the value of the palette_share_ flag is equal to 1, the palette_share_ flag indicates that the current block may reusc the last coded palette from 15 the prevîously coded block. This method is also known as palette sharing. Howcvcr, new research results indicate that this flag, together with the palette sharing method it represents, is not effective in improving coding cfficiency, while also introducing additional parsing and decoding complexity.

[0163] Further, some redundancies are identified in the signaling process for a syntax element that indicates a run type, such as palette_run_type_fiag. Specifically, when the current pixel is the first pixel in a line in a scanning order, and a pixel neighboring the current pixel and above the current pixel is available, the current pixel cannot be in “copy above” mode. The term “above pixel is available” mcans the above neighbor is within the current block for horizontal scanning or the left neighbor is within the block for vertical scanning order if the “copy from outside” methods arc not enabled. When the “copy from outside” methods are enabled, the “above pixel” may akvays be available for each pixel within the block. Example “copy from outside” methods are described in Y.-C. Sun, J. Kim, T.-D. Chuang, Y.-W. Chen, S. Lîu, Y.-W. Huang, and S. Lei, “Non-CE6: Cross-CU palette colour index prédiction, JCTVC-S0079 and J.

Kim, Y.-C. Sun, S. Liu, T.-D. Chuang, Y.-W. Chen, Y.-W. Huang, and S. Lei, “CE6rclated: Enabling copy above mode prédiction at the boundary of CU, JCTVC-S0114.

[0164] If the current pixel is coded according to “copy above mode, then the current pixel’s index equals the index of the current pixel’s above neighbor. Contrarily, due to the rule that “copy above” mode cannot be immediately followed by another “copy above” mode, the above neighbor must be the end of a *copy index’ run. Thereforc, the above neighbor s copy index” run can be Icngthened by at least 1 by adding the current pixel into the “copy index” run instead of making the current pixel the first pixel of a “copy above” run. Thus it îs possible to normatîvely disable “copy above” mode, if the current pixel is the first pixel in a line in a scanning order. This results in bit savings since, for such a pixel, the run type may be inferred to be “copy index”, thus eliminating the need to signal such an index.

[0165] Further, the current binarization for syntax élément palette_num_signalled_entries is in truncated unary code. The palette_num_signalled_entries syntax element indicates the number of entries in the current palette (e.g., a palette to be used to code the current block of video data) that arc explicitly signaled. The number ofsamples that are explicitly signaled may be determined by the différence between the number of entries in the palette subtracted from the number of entries in the palette that are predicted from the palette of another block of video data (including any palette entries that indicate the use of an escape sample). In some examples, the palette_num_signalled_entries syntax element may be named the num_signalled_palette_entries syntax element.

[0166] In some examples, the codeword used to code the value of the palette_num_signalled_entries syntax element may be undesirably long, which may resuit in codewords of length greater than 32. For example, in HEVC1, ail codewords are of length 32 or less. The same situation may also occur when coding the value of the palette_predictor_run syntax element. The palette_predictor_run syntax element spécifiés the number of zéros that précédé a non-zero entry in the anay predictor_palettc_entry_reuse_flag. The predictor_palctte_entry_reuse_flag indicates whether or not a particular palette entry from one or more previously-uscd palettes is reused for the current palette. The value of palelte_predictor_run may range from 0 to the maximum palette predictor size, inclusive.

[0167] In view of these drawbacks, in one example of the disclosure, this disclosure proposes that video encoder 20 and video décoder 30 be configured to perform a palette-based coding mode without palette-sharing techniques. More specifically, video encoder 20 and video décoder 30 may be configured to perform palette-based coding without using the palctte_share_flag[ xO ][ yO ] syntax élément, as indicated below:

<w(v) __ [0168] Instead of using palette sharing techniques, video encoder 20 and video décoder may be configured to code a palette for use with one more blocks of video data using other techniques, such as palette prédiction techniques descrîbed above. In other examples, video encoder 20 and/ video décoder 30 may be configured to perform palette prédiction using the following techniques.

[0169] FIG. 4 is a block diagram showing palette-based encoding unit 122 of video encoder 20 in more detail. Palette-based encoding unit 122 may be configured to perform one or more of the example techniques of this disclosure for palette-based video coding.

[0170] As descrîbed above, palette-based encoding unit 122 may be configured to encode a block of video data (e.g., a CU or PU) with a palette-based encoding mode. In a palette-based encoding mode, a palette may include entries numbered by an index and representing color component values (for example, RGB, YUV etc.) or intensifies which may be used to indicate pixel values. Palette génération unit 203 may be configured to receive pixel values 212 for a current block of video data and generate a palette of color values for the current block of video data. Palette génération unit 203 may use any techniques for generating a palette for a current block of video data, including the histogram-based techniques discussed above. Palette génération unit 203 may be configured to generate a palette of any size. In one example, palette génération unit 203 may be configured to generate 32 palette entries, where each palette entry includes pixel values for the Y, Cr, and Cb components of a pixel. In the former example, it is assumed that each palette entry spécifiés the values for ail color components of a sample (pixel). However, the concepts descrîbed in this document are applicable to using a separate palette for each color component.

[0171] Once a palette is generated by palette génération unit 203, map unit 204 may generate a map for the current block of video data that indicates whether or not a particular pixel in the current block of video data may be represented by an entry in the palette generated by palette génération unit 203. Map unit 204 may produce a map 214 that includes syntax éléments that indicate how each pixel uses (or does not use) entries from the palette. As discussed above, in some examples, escape pixels are not signaled with a separate syntax element, but rather, may be îndicated with a predetermined reserved index in a palette. If the value for a pixel in the current block of video data is

not found in the palette, map unit 204 may indicate the use of an escapc pixel with the reservcd index in the palette and explicitly transmit a pixel value for that particular pixel. In some examples, map unit 204 may predict the explicit pixel value from one of the entries found in the palette. In some other examples, map unit 204 may quantize tire 5 pixel and transmit the quantized values.

[0172] In addition to sîgnaling syntax éléments that indicate the color values used for each of the pixels in a block, palette-based encoding unît 122 may also be configured to signal the palette that is to be used for a current block of video data. In accordance with the techniques of this disclosure, palette-based encoding unit 122 may be configured to employ palette prédiction techniques to reduce the amount of data that is signaled to indicate the values of a palette for a particular block of video data.

[0173] As one example of palette prédiction, as is described in JCTVC-Q0094, which is available as of June 20,2014 from http://phenix.intevry.fr/jct/doc_end_user/documents/17_Valencia/wg! I/JCTVC-Q0094-vl.zip, a palette may include entries that are copied from a predictor palette. A predictor palette may include palette entries from prcviously-codcd blocks that use palette mode or from other reconstructed samples. As shown in FIG. 4, palette-based encoding unit 122 may include a predictor palette buffer 210. Predictor palette buffer 210 may be configured to store a number of previously-used palette entries from prevîously-encoded blocks. As one example, predictor palette buffer 210 may be configured as a first-in, fïrst-out (FIFO) buffer of a predetermined size. Predictor palette buffer 210 may be of any size. In one example, predictor palette buffer 210 includes up to 64 previously-used palette entries.

[0174] In some examplcs, palette-based encoding unit 122 may be configured to prune 25 the entries in predictor palette buffer 210 such that ail palette entries in predictor palette buffer 210 arc unique. That is, for each new palette entry to be added to predictor palette buffer 210, palette-based encoding unit 122 may be configured to first check that there are no other identical entries already stored in predictor palette buffer 210. If there are no identical entries, the new palette entry is added to predictor palette buffer 210. If the new entry is a duplîcate of an existing entry, the new palette entry is added to predictor palette buffer 210 and the duplicated entries are removed from predictor palette buffer 210.

[0175] Palette-based encoding unit 122 may include a binary prédiction vector génération unit 206 that is configured to generate and signal a binary flag (e.g.,

5!

predictor_palette_entry_reuse_flag), for each entry in a palette for a current block of video data generated by palette génération unit 203, to indicate whether a palette entry in predictor palette buffer 210 is copied (or reused) for one of the entries in the palette for the current block of video data (e.g., indicated by flag = 1). That is, a flag with a 5 value of 1 in the binary predictor vector indicates that the corresponding entry in predictor palette buffer 210 is reused for the palette for the current block, while a flag with a value of 0 in the binary prédiction vector indicates that the corresponding entry in the predictor palette buffer 210 is not reused for the palette for the current block. Additionally, palette-based encoding unit 122 may be configured to explicitly signal to some values for the current palette that cannot be copied from entries in the predictor palette buffer 210. The number of new entries may be signaled as well. In this regard, video encoder 20 and/or video décoder 30 may be configured to signal the number of explicitly signaled palette entries using the palette_num_signalled_entries syntax element.

[0176] Whcn using a palette-based coding mode that uses palette prédiction techniques, video encoder 20 and video décoder 30 may be configured to code, among other syntax éléments, a syntax element that indicates the number of palette entries that arc explicitly signaled for a current palette to be used to code the current block of video data (e.g., palette_num_signalled_entries). This disclosure proposes techniques to improve the coding efficiency or restrict the codeword length when coding such a syntax element. [0177] In one example of the disclosure, palette-based encoding unit 122 may be configured to encode the first bin of a syntax element that indicates a number of entries in a current palette that are explicitly signaled, such as the pa!ette_num_signalled_entries syntax element, using a CABAC context. Palette-based 25 encoding unit 122 may code other bins of the palctte_num_signallcd_cntrics using other encoding techniques. In another example of the disclosure, palette-based encoding unit 122 may be configured to use more than one contcxt to code the first bin of the palette_num_signalled_entries syntax element. In one example, palette-based encoding unit 122 may be configured to détermine the contexts based on a block size of the current video block being coded and/or based on the value of other syntax éléments. [0178] In accordance with one example of the disclosure, palette-based encoding unit 122 may be configured to déterminé a first bin of a first syntax element that indicates a number of entries in a current palette that are explicitly signaled. Video encoder 20 may be further configured to encode a bitstream that includes the first syntax élément. The

bitstream also may not înclude a second syntax elcment that indicates a palette sharing mode. In some examples, palette-based encoding unit 122 may be configured to encode the first bin of the first syntax element using a context-adaptive binary arithmetic coding. In other examples, palette-based encoding unit 122 may be configured to encode the first bin of the first syntax element using one or more contexts. In some examples of using one or more contexts, the one or more contexts may be based on at least one of a predicted number of palate coding entries or a block size.

[0179] In another example of the disclosure, to avoid the codeword length of palette_num_signalled_entries to grow longer than 32 bits, it is proposed that normative 10 semantic changes are made to current palette coding techniques (e.g., R. Joshi and J.

Xu, High efficient video coding (HEVC) scrcen content coding: Draft 2, JCTVCS1005). For example, the feasible values of a syntax element that spécifiés the maximum allowed palette size, such as palette_max_size, and a syntax element tirât spécifiés the maximum predictor palette size, such as palette_max_prcdictor_size, may 15 be capped by a threshold. Such a thrcshold may be predetermined and stored in a memory (e.g., video data memory 98 in FIG. 2 or video data memory 148 in FIG. 3) that is accessible by palette-based encoding unit 122. Spccifically, for palette_max_sîze, the value may be any value from0 toTl, inclusive, whereTl is the threshold. When not présent, palette-based encoding unit 122 may be configured to infer the value of palette_max_size to be 0. Further, for palette_max_predictor_size, the value may be any value from 0 to T2, inclusive, where T2 is the threshold. When not présent, palette-based encoding unit 122 may be configured to infer the value of palette_max_predictor_size to be 0.

[0180] In one cxample, Tl is equal to 4096 and T2 is equal to 8192. In another 25 cxample, Tl is equal to 4095 and T2 is equal to 4095. In yct another example, Tl is equal to 4095 and T2 is equal to 8191.

[0181] As another example, this disclosure proposes that the value of palette_max_sizc bc equal to the number of pixels in the largest size coding unit, Such a value may be predetermined and stored in a memory accessible by palette-based encoding unit 122.

In some examples, the value of palette_max_predictor_size may be less than or equal to K * palette_max_size, where K is a positive constant. In some examples, K = 2.

[0182] In another example, palette-based encoding unit 122 (e.g., using binary vector compression unit 209 or another structural component of video encoder 20, such as entropy encoding unit 118) may be configured to code the value of the

palettc_num_signallcd_cntries syntax element using one more coding techniques from the Golomb code family (e.g. Golomb-Ricc code, Exponential Golomb code, Truncated Rice code, Unary code, etc.). In one example of the disclosure, palette-based encoding unit 122 is configured to encode the value of the palette_num_signalled_entrics syntax 5 element using an exponential Golomb code of order 0. In another example of the disclosure, palette-based encoding unit 122 is configured to encode the value of the palette_num_signalled_entries syntax element using a concaténation of a Truncated Rice (TR) code and an exponential Golomb code such as the one used in coefficient coding to code coeff_abs_level_remaining syntax element in HEVC1.

[0183] An example of a concaténation of a TR code and an exponential Golomb code for Golomb Rice parameter of 0 is shown below:

Symbol	binarization
0	0
1	10
2	110
3	1110
[4,5]	llllOx
[6.9]	lllllOxx
[10, 17]	llllllOxxx
...

Here x can take a value of 0 or 1. Similarly, the table below shows an example of a concatenated binarization used in the coding of paletteRun syntax element. This is a concaténation of a truncated Rice and truncated exponential Golomb code of order 0 for 15 maximum run value of 7.

symbol	binarization
0	0
1	10
[2,3]	llOx
[4,7]	lllxx

Here x can take a value of 0 or 1.

[0184] Using one or more Golomb codes (e.g., such as an exponential Golomb code or a concaténation of TR code and an exponential Golomb code) to code the palette_num_signalled_entries syntax element provides a benefit comparcd to previous

techniques for coding the value of the palette_num_signallcd_entries syntax element. Previous techniques for coding the value of the palette_num_signalled_entries syntax element used a unary code. Use of a unary code rcsulted in the coded length of the palette_num_signalled_entries syntax element being larger than 32 bits in some circumstances. By using one or more Golomb codes to code the palette_num_signalled_entries syntax element, the techniques of this disclosure allow palette-based encoding unit 122 to encode the value of the palette_num_signalled_entries syntax element in a matter that keeps the coded length at or below some predetermined number of bits (e.g., 32 bits).

[0185] In another example, palette-based encoding unit 122 may be confîgured to code the value of the palette_num_signalled_entries syntax element using truncated version of a Golomb code family (e.g., truncated Golomb Rice code, truncated Exponential Golomb code, truncated Truncated Rice code, truncated Unary code, etc.). In another example of the disclosure, palette-based encoding unit 122 may be confîgured to code the value of the palette_num_signalled_entries syntax element using the same code used to code the paletteRun syntax element. In another example, palette-based encoding unit 122 may be confîgured to code the value of the palelte_num_signalled_entries syntax element using the method used to code coeff_abs_levcl_remaining syntax element in coefficient coding (e.g., concaténation of truncated Rice (TR) and exponential Golomb code). In accordance with this example, the TR parameter is preferred to be 0. In each of these examples, the particular truncated code is choscn such that the encoded length of the palette_num_signalled_entries syntax element is kept at or below 32 bits. [0186] In another example, it is proposed to impose a restriction on the bitstream tirât palette_num_signalled_entries is equal to the number of pixels in the block. That Îs, palette-based encoding unit 122 may be confîgured to limit the possible value of the palette_num_signalled_entrics syntax element by the number of pixels in the current!y coded block. In another example, palette-based encoding unit 122 may bc confîgured to limit the possible value of the palette_num_signalled_entries by the number of pixels in the largest possible block of a particular picture (e.g., the large block size defined by a particular video coding standard).

[0187] In another example, palette-based encoding unit 122 may be confîgured to bypass sîgnaling a syntax element that indicates a run type, such as palette_run_type_flag, if the current pixel is the first pixel in the line in scanning order and the pixel neighboring the current pixel above the current pixel is available. In one

example, palette-based encoding unît 122 may be configured to détermine that a current pixel is a first pixel in a line in a scanning order. Palette-based encoding unit 122 may further détermine that a neighboring pixel situated above the current pixel is available. In response to determining that the current pixel is the first pixel in the line in the scanning order and determining that the neighboring pixel situated above the current pixel is available, palette-based encoding unit 122 may be further configured to bypass encoding a first syntax element in a bitstream, wherein the first syntax élément indicates a run type and encode a remainder of the bitstream.

[01881 Retuming to FIG. 4 and palette prédiction techniques of this dîsclosure, in U.S.

Application No. 14/667,411, filed March 24,2015, published as US Patent Publication No. 2015/0281728, a binary tree based signaling method and end-position based signaling methods were proposed for coding of the palette binary predictor vector. In U.S. Provisional Application No. 62/002,741, filed May 23,2014, a group based signaling method was proposed. This dîsclosure proposes additional techniques for generating, encoding, and decoding the binary prédiction vector.

[0189] Some examplcs described hercin relate to methods to code the palette prédiction vector to improve coding efficicncy. For example, assume that the binary prédiction vector generated by binary prédiction vector génération unit 206 is denoted by:

b = [b₀, bi,..., bw-i], N> 0, b, c {0,1 ), 0 < i < N

In the équation above, b; c {0,1}, 0 < i < N dénotés a prédiction flag (also called a binary flag or binary prédiction flag). If N-0, b = φ (i.e., b is the empty vector), which does not need to be signaled. Therefore, in the following description, it may be assumed that N>0.

[0190] FIG. 5 shows one example of a predictor palette buffer 210 and a current palette

220. As can be seen in FIG. 5, current palette 220 reuses pixel values from predictor palette buffer 210 associated with entry indices 1,2,5, and 9. As such, a binary predictor vector produced by binary prédiction vector génération unit 206 of FIG. 4 would be b = [110010001000]. As can be seen in this example, the binary prédiction vector b includes flags with a value of 1 corresponding to the 1“, 2^nd, 5^lh, and 9^th indices in the predictor palette buffer 210. That is, the l^st, 2^nd, 5^lh, and 9^,h entries in predictor palette buffer 210 are the only entries reused for current palette 220. For entry indices 5-8 în current palette 220, palette-based encoding unît 122 may be configured to signal palette entry values in the encoded video bitstream (e.g., using explicit signaling or another prédiction technique).

[0191] In accordance with one or more techniques of this disclosure, video encoder 20 may be confîgured to encode or generally encode the binary predictor vector b in order to reduce the amount of data needed to signal a palette in the encoded video bitstream. As shown in FIG. 4, binary prédiction vector compression unît 209 may be confîgured to generate and signal encoded binary prédiction vector 215. However, it should be understood that the binary prédiction vector compression techniques of this disclosure may be implemented in other structures of video encoder 20, including entropy encoding unit 118 in FIG. 2.

[0192] In one example of the disclosure, binary prédiction vector compression unit 209 may be confîgured to encode the binary prédiction vector using a run-length based encoding techniques. For example, binary prédiction vector compression unit 209 may be confîgured to encode the binary prédiction vector by signaling the number of consecutive ‘0s’ between ‘ ls’ in the binary prédiction vector using an ExponcntîalGolomb code. As an example, again assume that b = [110010001000]. In this example, as shown in FIG. 6, the binary prédiction vector (i.e., b) can be expressed as: ‘zéro consecutive Os’-'l’-'zero consecutive Os’-'l’-'two consecutive 0s*-‘l ‘-‘three consecutive 0s’-‘l ’- and ‘four consecutive 0s*. Because it is known that b, ε (0,1}, except for the last ‘consecutive 0’ group, each ‘consecutive 0’ group must be followed by a ‘Γ. Therefore, binary prédiction vector compression unit 209 may use zero-based run-length coding techniques to represent the binary prédiction vector b as ‘zéro consecutive Q’-‘zero consecutive Q'-‘two consecutive 0’-‘three consecutive Q’-‘four consecutive 0’, which can be expressed as the run-length sequence ‘0-0-2-3-4’.

[0193] In accordance with one or more examples of this disclosure related to run-length based signaling, to code the run-length sequence, a Golomb-Rice code, ExponentialGolomb code of any order, Truncated Exponential-Golomb code, Truncated-Rice code or any other binarizations, including truncated binarizations, may be used. In one example, binary prédiction vector compression unit 209 uses a O-th order ExponentialGolomb code as the run-length coding technique.

[0194] For the truncated binarization, the maxsymbol can be the maximum possible value of the run depending on the position of ‘ Γ in the binary vector and the binary vector size, since, upon moving to the end of the binary vector, the maximum possible

run value is reduced from the vector size to 0 depending on the position within the vector. For example, the max symbol can be the binary vector length or the binary vector length minus the position of the *1’ from which the run is being counted. In, other words, it is the remaining length measured from the end of the binary vector. For the above example with the binary vector b of a particular size, e.g., 13, the run-length sequence ‘0-0-2-3-4’ can be coded with the truncated binarization Ό[ 13]-0[ 12]-2[ 11J3[8]-4[4]’, where the max symbol is provided in the brackcts.

[0195] Also, in some examples, binarization may be dépendent on the position or index of the element (0 or 1) in the binary vector. As a particular example, if the position is smaller than a certain threshold, one type of binarization is used; otherwise, another type of binarization is applied. In some examples, the binarization type can be different binarization codes, or the same code family but with different order, such as Exponcntial-Golomb code.

[0196] In one example, the threshold may be the palette length from the previous block or previous palette coded block. In another example, the threshold can be fixed to some default value or signaled per block, slice, picture or elsewhere. It is to be recognized that a corresponding technique may optionally be used to define a CABAC context to code the run values. Additionally, palette-based encoding unit 122 (Sec FIG. 2) may be confîgured to stop run-length signaling when the number of signaled *1’ cléments (i.e., the number of palette entries from predictor palette buffer 210 îndicated as being reused for the current palette 220) reaches a maximum possible number. In some examples, the maximum possible number is the maximum possible palette size.

[0197] Some examples of this disclosure relate to end position coding of the run-length sequence indicating the binary prédiction vector b. In one or more examplcs of this disclosure, binary prédiction vector compression unit 209 may be confîgured to encode the binary prédiction vector b using a reserved run-length L to code the ending position of the binary prédiction vector. In one example, L=1 is used as the reserved run-length. At video encoder 20, if the run-length is equal to or greater than L, binary prédiction vector compression unit 209 is confîgured to add 1 to the run-length. If the actual run30 length is less than L, binary prédiction vector compression unit 209 is confîgured to signal the run-length as is. Binary prédiction vector compression unit 209 may signal the end position run-length with the reserved run-length L.

[0198] Likewise, at video décoder 30, if the decoded value of a run-length is larger than L, 1 is subtracted from the actual run-length. If the decoded value or a run-length is

smaller than L, the decoded value is used as the actual run-length. If the decoded value is equal to L, the remaining positions in the binary prédiction vector b are ail 0. Hence, if the decoded value is equal to L, no more run signaling is necessary.

[0199] Using the same example as above (i.e., b = [ 110010001000]) and assuming that

Lssl, binary prédiction vector compression unit 209 is configured to signal the runlength sequence Ό-0-2-3-4’ of FIG. 6 as Ό-0-3-4-Γ. Then, applying the above rules, video décoder 30 may be configured to recover the run-length sequence as ‘Ο-Ο-2-3end’. That is, the first run-length value of 0 is decoded as 0 and the next run-length sequence of 0 is decoded as 0, as both of the 0 run-length sequences are less than the to rcserved run-length value of L=l. The next run-length sequence is 3, and as such, video décoder 30 would be configured to subtract 1 from the value of 3 to obtain 2, because the received value of 3 is greater than the reserved run-length value of L=l. Likewise, video décoder 30 would be configured to subtract 1 from the received value of 4 to obtain 3 for next run-length sequence, because the received value of 4 is greater than the 15 reserved run-length value ofL=\. Finally, the last received run-length value 1 is equal to the reserved run-length value of L=l. Accordingly, video décoder 30 may déterminé that no further values of *1’ are présent in the binary prédiction vector.

[0200] FIG. 7 is a block diagram showing an example of palette-based decoding unit 165 of video décoder 30. Palette-based decoding unit 165 may be configured to perform in a reciprocal manner to palette-based encoding unit 122 of FIG. 4. Palettebased decoding unit 165 may be configured to receive a map 312 that indicates, for each pixel in a current block, whether or not entries for a palette will be used for the pixels in the current block. In addition, map 312 may further indicate what palette entries arc to be used for a given pixel. Map unit 302 may décodé the current block of video data using the map 312 and a palette generated by palette génération unit 304 to producc decoded video data 314.

[0201] In accordance with the techniques of this disclosure, palette-based decoding unît 165 may also receive an encoded binary prédiction vector 316. As discussed above, ' binary prédiction vector 316 may be encoded using a run-length coding technique that encodes a run-length sequence indicating a run of zéro values in the binary prédiction vector. Binary prédiction vector décompression unît 306 may be configured to décodé the encoded binary prédiction vector 316 using any combination of the run-length coding techniques described above with référencé to FIGS. 4-6. Once a binary prédiction vector is rccovered by binary prédiction vector décompression unit 306,

palette génération unit 304 may generale a palette for the current block of video data based on the bînary prédiction vector and previously-used palette entries stored in predictor palette buffer 310. Palette-based decoding unit 165 may be configured to store previously-used palette entries in predictor palette buffer 310 in the same manner 5 that palette-based encoding unit 122 (see FIG. 2) stored previously-used palette entries in predictor palette buffer 210.

[0202] In one example of the disclosure, palette-based decoding unît 165 may be configured to décodé the first bin of a syntax élément that indicates a number of entries in a current palette that are explicitly signaled, such as the palette_num_signalled_entries syntax element, using a CABAC contcxt. Palette-based decoding unit 165 may décodé other bins of the palette_num_signalled_entries using other decoding techniques. In another example of the disclosure, palette-based decoding unit 165 may be configured to use more than one context to décodé the first bin of the palette_num_signalled_entries syntax element. In one example, palette-based decoding unit 165 may be configured to détermine the contexts based on a block size of the current video block being decoded and/or based on the value of other syntax éléments.

[0203] In accordance with one example of the disclosure, palette-based decoding unit 165 may be configured to déterminé a first bin of a first syntax element that indicates a 20 number of entries in a current palette that are explicitly signaled. Video décoder 30 may be further configured to décodé a bitstream that includes the first syntax element. The bitstream also may not include a second syntax element that indicates a palette sharing mode. In some examples, palette-based decoding unit 165 may be configured to décodé the first bin of the first syntax element co using a context-adaptive binary arithmctic 25 coding. In other cxamples, palette-based decoding unit 165 may be configured to décodé the first bin of the first syntax element using one or more contexts. In some examples of using one or more contexts, the one or more contexts may be based on at least one of a predicted number of palatc coding entries or a block size.

[0204] In another example of the disclosure, to avoid the codeword length of palette_num_signalled_entries to grow longer than 32 bits, it is proposed that normative semantic changes are made to current palette coding techniques. For example, the feasible values of a syntax element that spécifiés the maximum allowed palette size, such as palette_max_size, and a syntax element that spécifiés the maximum predictor palette size, such as palette_max_predictor_sîze, may be capped by a threshold. Such a

threshold may be predetermined and stored in a memory (e.g., video data memory 148 in FIG. 3) that is accessible by palette-based decoding unit 165. Spccifically, for pa!ctte_max_size, the value may be any value from 0 to Tl, inclusive, wherc Tl is the threshold. When not présent, palette-based decoding unit 165 may be configured to infer the value of palette_max_size to be 0. Further, for palette_max_predictor_size, the value may be any value from 0 to T2, inclusive, where T2 is the threshold. When not présent, palette-based decoding unit 165 may be configured to infer the value of palette_max_predictor_size to be 0.

[0205] In one cxamplc, Tl is equal to 4096 and T2 is equal to 8192. In another example, Tl is equal to 4095 and T2 is equal to 4095. In yet another example, Tl is equal to 4095 and T2 is equal to 8191.

[0206] As another example, this disclosure proposes that the value of palette_max_size be equal to the number of pixels in the largest size coding unit. Such a value may be predetermined and stored in a memory accessible by palette-based decoding unit 165.

In some examples, the value of palettc_max_prcdictor_size may be less than or equal to K * palette_max_size, where K is a positive constant. In some examples, K = 2. [0207] In another example, palette-based decoding unit 165 of FIG. 3 (e.g., using binary prédiction vector décompression unit 306 or another structural component of video décoder 30, such as entropy decoding unit 150 of FIG. 3) may be configured to décodé the value of the palette_num_signalled_entries syntax element using one more decoding techniques from the Golomb code family (e.g. Golomb-Rice code, Exponential Golomb code, Truncated Rice code, Unary code, etc.). In one example of the disclosure, palettebased decoding unit 165 is configured to décodé the value of the palette_num_signallcd_entrics syntax element using a concaténation of truncated Rice and Exponential Golomb code.

[0208] In another example, palette-based decoding unit 165 may be configured to décode the value of the palette_num_signalled_cntries syntax element using truncated version of a Golomb code family (e.g., truncated Golomb Rice code, truncated Exponential Golomb code, truncated Truncated Rico code, truncated Unary code, etc.),

In another example of the disclosure, palette-based decoding unit 165 may be configured to décodé the value of the palette_num_signalled_entries syntax element using the same code used to code the paletteRun syntax element. In another example, palette-based decoding unit 165 may be configured to décode the value of the palette_num_signalled_entries syntax element using the method of decoding

coeff_abs_level_remaining syntax element in coefficient decoding (e.g., concaténation of Truncated Rice (TR) and exponential Golomb code ). In accordance with this example, the TR parameter is prcferred to be 0.

[0209] In another example, it is proposed to impose a restriction on the bitstream that pa!ette_num_signalled_entries is equal to the number of pixels in the block. That is, palette-based decoding unit 165 may be configured to limit the possible value of the palcltc_num_signalled_entries syntax element by the number of pixels in the currently coded block. In another example, palette-based decoding unît 165 may be configured to limit the possible value of the palette_num_signalled_entries by the number of pixels in the largest possible block of a particular picture (e.g., the large block size defined by a particular video coding standard).

[0210] In another example, palette-based decoding unit 165 may be configured to infer value of a syntax element that indicates a run type, such as palette_run_type_flag, if the current pixel is the first pixel in the line in scanning order and the pixel neighboring the current pixel above the current pixel is available. In one example, palette-based decoding unît 165 may be configured to détermine that a current pixel is a first pixel in a line in a scanning order. Palette-based decoding unit 165 may further détermine that a neighboring pixel situated above the current pixel is available. In response to determining that the current pixel is the first pixel in the line in the scanning order and determining that the neighboring pixel situated above the current pixel is available, palette-based decoding unît 165 may be further configured to infer the value of the first syntax element in a bitstream, wherein the first syntax element indicates a run type and encode a remainder of the bitstream.

[0211] FIG. 8 is a flowchart illustrating an example video encoding method accordîng to the techniques of the disclosure. The techniques of FIG. 8 may be implemented by one or more hardware structures of video encoder 20, including palette-based encoding unît 122 and/or entropy encoding unit 118 (see FIG. 2).

[0212] In one example of the disclosure, video encoder 20 may be configured to encode a block of video data using a palette-based coding mode and a palette (800), and generate a plurality of syntax éléments that are indicative of the palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of palette values for the palette that are explicitly signaled in the encoded video bitstream (802). Video encoder 20 may be further configured to encode the first syntax element using one or more Golomb codes such that

the length of the encoded first syntax element îs less than or equal to a predetermined number of bits (804), and include the plurality of syntax éléments in an encoded video bitstream (806).

[0213] In one example of the disclosure, the first syntax element is a palette_num_signaïled_entries syntax element. In another example of the disclosure, the plurality of syntax éléments includes the palette values indicated as being explicitly signaled by the first syntax element.

[0214] In one example of the disclosure, the predetermined maximum number of bits is 32, and the one or more Golomb codes is an exponential Golomb code of order 0. In another example of the disclosure, the predetermined maximum number of bits is 32, and the one or more Golomb codes is a concaténation of a truncated Rico code and an exponential Golomb code.

[0215] In another example of the disclosure, a maximum value of the first syntax element is defined relative to a second syntax element that indicates a maximum size of the palette, and a third syntax element that indicates a maximum size of a palette predictor. In this example, video encoder 20 may be further configured to define the second syntax element to be a value from 0 to a first threshold, and define the third syntax element to be a value from 0 to a second threshold. In one example, the first threshold is one of 4095 or 4096 and the second threshold is one of 4095, 8191, or 8192.

[0216] In another example of the disclosure, a maximum value of the first syntax element is defined relative to a second syntax element that indicates a maximum size of the palette, and a third syntax element that indicates a maximum size of a palette predictor. In this cxample, video encoder 20 may be further configured to define the second syntax element to be less than or equal to a number of pixels in a largest possible block in the encoded video bitstream, and define the third syntax element to be less than or equal to K ♦ a value of the second syntax element, where K is a positive constant. In one example, K is 2.

[0217] In another example of the disclosure, video encoder 20 may bc further configured to signal a syntax element indicating a palette run type in the case that a current pixel is not a first pixel in a scanning order, and not signal the syntax element indicating a palette run type in the case that the current pixel is the first pixel in the scanning order and the previous pixel/sample is available.

[0218] FIG. 9 is a flowehart illustrating an example video decoding method according to the techniques of the disclosure. The techniques of FIG. 9 may be implemented by

one or more hardware structures of video décoder 30, including palette-based decoding unit 165 and/or entropy decoding unît 150 (see FIG. 3).

[0219] In one example of the disclosure, video décoder 30 may be configured to receive a block of video data in an encoded video bitstream, the block of video data having been encoded using a palette-based coding mode (900), and receive a plurality of syntax éléments that are indicative of a palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of palette values for the palette that are explicitly signaled in the encoded video bitstream, wherein the first syntax element is encoded using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits (902). Video décoder 30 may be further configured to décodé the plurality of syntax éléments, including decoding the first syntax element using the one or more Golomb codes (904), reconstruct the palette based on the decoded plurality of syntax éléments (906), and décodé the block of video data using the reconstructed palette (908). Video décoder 30 may be further configured to display the decoded block of video data.

[0220] In one examplc of the disclosure, the first syntax element is a palettc_num_signalled_entries syntax element. In another example of the disclosure, the plurality of syntax cléments includes the palette values indicated as being explicitly signaled by the first syntax element.

[0221] In one example of the disclosure, the predetermined maximum number of bits is 32, and the one or more Golomb codes is an exponential Golomb code of order 0. In another example of the disclosure, the predetermined maximum number of bits is 32, and the one or more Golomb codes is a concaténation of a truncated Rico code and an exponential Golomb code.

[0222] In another example of the disclosure, a maximum value of the first syntax element is defined relative to a second syntax element that indicates a maximum size of the palette, and a third syntax element that indicates a maximum size of a palette predictor. In this example, video décoder 30 may be further configured to define the second syntax element to be a value from 0 to a first threshold, and define the third syntax element to be a value from 0 to a second threshold. In one example, the first threshold is one of 4095 or 4096 and the second threshold is one of 4095,8191, or 8192. [0223] In another example of the disclosure, a maximum value of the first syntax element is defined relative to a second syntax element that indicates a maximum size of

the palette, and a third syntax élément that indicates a maximum size of a palette predictor. In this examplc, video décoder 30 may be further configured to define the second syntax element to be less than or equal to a number of pixels in a largest possible block in the encoded video bitstream, and define the third syntax element to be less than 5 or equal to K * a value of the second syntax element, where K is a positive constant. In one example, K is 2.

[0224] In another example of the disclosure, video décoder 30 may be further configured to receive a syntax element indicating a palette run type in the case that a current pixel is not a first pixel in a scanning order, and infer the syntax element indicating a palette run type in the case that the current pixel is the first pixel in the scanning order.

[0225] While particular combinations of various aspects of the techniques are described above, these combinations are provided merely to illustrate examples of the techniques described in this disclosure. Accordingly, the techniques of this disclosure should not be limited to these example combinations and may encompass any conccivablc combination of the various aspects of the techniques described in this disclosure.

[0226] In one or more examples, the fonctions described may be împlemented in hardware, software, firmware, or any combination thereof. If împlemented in software, the fonctions may be stored on or transmitted over, as one or more instructions or code, 20 a computer-readable medium and executed by a hardware-based processing unit.

Computer-rcadable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitâtes transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computcr25 readable media generally may correspond to ( 1 ) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more procès sors to retrieve instructions, code and/or data structures for implémentation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

[0227] By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnctic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures

and that can be accessed by a computer. A!so, any connection is properly termed a computer-readable medium. For example, if instructions arc transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are includcd in the définition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signais, or other transient media, but are instead directed to non-transient, tangible storage media. Disk and dise, 10 as used herein, includes compact dise (CD), laser dise, optical dise, digital versatile dise (DVD), floppy disk and Blu-ray dise, where disks usually reproduce data magnctically, while dises reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0228] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application spécifie integrated circuits (ASICs), field programmable gâte arrays (FPGAs), or other équivalent integrated or discrète logic circuitry. Accordingly, the term “proccssor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implémentation of the techniques described herein. In addition, in some aspects, the functionalîty described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codée. Also, the techniques could be fully implemented in one or more circuits or logic éléments.

[0229] The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Radier, as described above, various units may be combined in a codée hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction widi suitable software and/or firmware. [0230] Various examples of the disclosure hâve been described. Any combination of the described Systems, operations, or functions is contemplated. These and other examplcs are within the scope of the following daims.

Claims (42)

1. A method of decoding video data, the method comprising:

receiving a block of video data in an encoded video bitstream, the block of video

5 data having been encoded using a palette-based coding mode without palette sharing; receiving a plurality of syntax éléments that arc indicative of a palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of palette values for the palette that are explicitly signaled in the encoded video bitstream, wherein the first syntax element is defined

10 relative to one or more of a second syntax element that indicates a maximum size of the palette or a third syntax element that indicates a maximum size of a palette prcdictor, wherein the second syntax element has a value from 0 to a first threshold and the third syntax element to be a value from 0 to a second threshold, and encoded using one or more Golomb codes such that the length of the encoded first syntax element is less than

15 or equal to a predetermined maximum number of bits;

decoding the plurality of syntax éléments, including decoding the first syntax element using the one or more Golomb codes;

rcconstructing the palette based on the decoded plurality of syntax cléments; and decoding the block of video data using the rcconstructed palette.

2. The method of claim 1, wherein the first syntax element is a num_signalled_palette_entries syntax element.

3. The method of claim 1, wherein the predetermined maximum number of bits is

25 32, and wherein the one or more Golomb codes is an exponential Golomb code of order

0.

4. The method of claim 1, wherein the predetermined maximum number of bits is 32, and wherein the one or more Golomb codes is a concaténation of a truncated Rice

30 code and an exponential Golomb code.

5. The method of claim 1, wherein the plurality of syntax cléments includes the palette values îndicatcd as being explicitly signaled by the first syntax élément.

6. The method of claim 1, wherein the first threshold is one of 4095 or 4096 and the second threshold is one of 4095,8191, or 8192.

7. The method of claim 1, wherein a maximum value of the first syntax élément is defined relative to the second syntax element, of the plurality of syntax éléments, that indicates a maximum size of the palette, and the third syntax element, of the plurality of syntax éléments, that indicates a maximum size of a palette predictor, the method

10 further comprising:

defining the second syntax element to be less than or equal to a number of pixels in a largest possible block of the video data in the encoded video bitstream; and defining the third syntax element to be less than or equal to K * a value of the second syntax element, where K is a positive constant and * indicates a multiplication

15 operation.

8. The method of claim 7, wherein K is 2.

9. The method of claim 1, further comprising:

20 displaying the decoded block of video data.

10. The method of claim 1, further comprising:

receiving a syntax element indicating a palette run type in the case that a current pixel of the block of video data is not a first pixel in a scanning order of the block of 25 video data; and inferrîng the syntax element as indicating a palette run type in the case that the current pixel is the first pixel in the scanning order.

11. An apparatus confîgured to décodé video data, the apparatus comprising:

30 a memory confîgured to store an encoded video bitstream; and a video décoder confîgured to:

receive a block of video data in the encoded video bitstream, the block of video data having been encoded using a palette-based coding mode without palette sharîng;

rcceive a pluralîty of syntax éléments that arc indicative of a palette that was used to encode the block of video data, the pluralîty of syntax éléments including a first syntax élément that indicates a number of palette values for the palette that are explicitly signaled in the encoded video bitstream, wherein the first syntax element is defined relative to one or more of a second syntax element that indicates a maximum size of the palette or a third syntax element that indicates a maximum size of a palette predictor, wherein the second syntax element has a value from 0 to a first threshold and the third syntax element to bc a value from 0 to a second threshold, and encoded using one or more Golomb codes such tirât the lcngth of the encoded first syntax élément îs less than or equal to a predetermined maximum number of bits;

décodé the pluralîty of syntax éléments, including decoding the first syntax element using the one or more Golomb codes;

reconstruct the palette based on the decoded pluralîty of syntax éléments; and décodé the block of video data using the reconstructed palette.

12. The apparatus of claim 11, wherein the first syntax élément is a num_signalled_palette_entries syntax element.

13. The apparatus of claim 11, wherein the predetermined maximum number of bits is 32, and wherein the one or more Golomb codes is an exponential Golomb code of order 0.

14. The apparatus of claim 11, wherein the predetermined maximum number of bits îs 32, and wherein the onc or more Golomb codes is a concaténation of a truncated Rice code and an exponential Golomb code.

15. The apparatus of claim 11, wherein the pluralîty of syntax cléments includes the palette values indicated as being explicitly signaled by the first syntax element.

16. The apparatus of claim 11, wherein the first threshold is one of 4095 or 4096 and the second threshold is one of 4095,8191, or 8192.

17. The apparatus of claim 11, wherein a maximum value of the first syntax élément is defined relative to the second syntax element, of the pluralîty of syntax cléments, that indicates a maximum size of the palette, and the thîrd syntax élément, of the plurality of syntax cléments, that indicates a maximum size of a palette prcdictor, and wherein the video décoder is further confîgured to:

define the second syntax element to be less than or equal to a number of pixels 5 în a largest possible block of the video data in the encoded video bitstream; and define the third syntax element to be less than or equal to K * a value of the second syntax element, where K is a positive constant and * indicates a multiplication operation.

10

18. The apparatus of claim 17, wherein K is 2.

19. The apparatus of claim 11, further comprising:

a display confîgured to display the decoded block of video data.

15 20. The apparatus of claim 11, wherein the video décoder is further confîgured to:

receive a syntax element indicating a palette run type in the case that a current pixel of the block of video data is not a first pixel in a scanning order of the block of video data; and infer the syntax element as indicating a palette run type in the case that the

20 current pixel is the first pixel in the scanning order.

21. An apparatus confîgured to décodé video data, the apparatus comprising: means for receiving a block of video data in an encoded video bitstream, the block of video data havîng been encoded using a palette-based coding mode without 25 palette sharing;

means for receiving a plurality of syntax éléments that are indicative of a palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of palette values for the palette that are explicitly signaled in the encoded video bitstream, wherein the first syntax

30 element is defined relative to one or more of a second syntax élément that indicates a maximum size of the palette or a third syntax element that indicates a maximum size of a palette prcdictor, wherein the second syntax element has a value from 0 to a first threshold and the third syntax element to be a value from 0 to a second threshold, and encoded using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits;

mcans for decoding the plurality of syntax éléments, including decoding the first syntax element using the one or more Golomb codes;

5 mcans for reconstructing the palette based on the dccoded plurality of syntax éléments; and means for decoding the block of video data using the reconstructed palette.

22. A computer-readable storage medium storing instructions that, when exccuted,

10 causes one or more processors of a device configured to décodé video data to:

receive a block of video data in an encoded video bitstream, the block of video data having been encoded using a palette-based coding mode without palette sharing;

receive a plurality of syntax éléments that are indicative of a palette that was used to encode the block of video data, the plurality of syntax éléments including a first 15 syntax element that indicates a number of palette values for the palette that are explicitly signaled in the encoded video bitstream, wherein the first syntax element is defined relative to one or more of a second syntax element that indicates a maximum size of the palette or a third syntax element that indicates a maximum size of a palette predictor, wherein the second syntax élément has a value from 0 to a first threshold and the third 20 syntax element to be a value from 0 to a second threshold, encoded using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits décodé the plurality of syntax éléments, including decoding the first syntax element using the one or more Golomb codes;

25 reconstruct the palette based on the decoded plurality of syntax éléments; and décodé the block of video data using the reconstructed palette.

23. A method of encoding video data, the method comprising:

encoding a block of video data using a palette and a palette-based coding mode 30 without palette sharing;

generating a plurality of syntax éléments that are indicative of the palette that was used to encode the block of video data, the plurality of syntax cléments including a first syntax element that indicates a number of palette values for the palette that arc explicitly signaled in an encoded video bitstream;

encoding the first syntax element that is defined relative to one or more of a second syntax element that indicates a maximum size of the palette or a third syntax element that indicates a maximum size of a palette predictor, wherein the second syntax element has a value from 0 to a first threshold and the third syntax element to be a value 5 from 0 to a second threshold, using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits; and including the plurality of syntax éléments in the encoded video bitstream.

10

24. The method of claim 23, wherein the first syntax élément is a num_signalled_palelte_entries syntax element.

25. The method of claim 23, wherein the predetermined maximum number of bits is

32, and wherein the one or more Golomb codes is an exponential Golomb code of order 15 0.

26. The method of claim 23, wherein the predetermined maximum number of bits is 32, and wherein the one or more Golomb codes is a concaténation of a truncatcd Rice code and an exponential Golomb code.

27. The method of claim 23, wherein the plurality of syntax éléments includcs the palette values indicatcd as being explicitly signaled by the first syntax element.

28. The method of claim 23, wherein the first threshold is one of 4095 or 4096 and 25 the second threshold is one of 4095, 8191, or 8192.

29. The method of claim 23, wherein a maximum value of the first syntax élément is defined relative to the second syntax element, of the plurality of syntax éléments, that indicates a maximum size of the palette, and the third syntax element, of the plurality of

30 syntax éléments, that indicates a maximum size of a palette predictor, the method further comprising:

defining the second syntax element to be less than or equal to a number of pixels in a largest possible block of the video data in the encoded video bitstream; and defining the third syntax element to be less than or equal to K * a value of the second syntax element, where K is a positive constant and * indicates a multiplication operation.

5 30. The method of claim 29, wherein K is 2.

31. The method of claim 23, further comprising:

signaling a syntax element indicating a palette run type in the case that a current pixel is not a first pixel in a scanning order, and

10 not signaling the syntax element indicating a palette run type in the case that the current pixel of the block of video data is the first pixel in the scanning order of the block of video data.

32. An apparatus confîgured to encode video data, the apparatus comprising:

15 a memory confîgured to store a block of video data; and a video encoder confîgured to:

encode the block of video data usîng a palette and a palette-bascd coding mode without palette sharing;

gcncrate a plurality of syntax éléments that arc indicative of the palette that was

20 used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of palette values for the palette that arc explicitly signaled in an encoded video bitstream;

encode the first syntax element that is defined relative to one or more of a second syntax element that indicates a maximum size of the palette or a third syntax

25 élément that indicates a maximum size of a palette prcdictor, wherein the second syntax element has a value from 0 to a first threshold and the third syntax element to be a value from 0 to a second threshold, using one or more Golomb codes such that the length of the encoded first syntax élément is less than or equal to a predetermined maximum number of bits; and

30 include the plurality of syntax éléments in the encoded video bitstream.

33. The apparatus of claim 32, wherein the first syntax élément is a num_signalled_palette_entries syntax element. .

34. The apparatus of claim 32, wherein the predetermined maximum number of bits is 32, and wherein the one or more Golomb codes is an exponential Golomb code of order 0.

5

35. The apparatus of claim 32, wherein the predetermined maximum number of bits is 32, and wherein the one or more Golomb codes is a concaténation of a truncated Rico code and an exponential Golomb code.

36. The apparatus of claim 32, wherein the plurality of syntax éléments includes the

10 palette values indicated as being explicitly signaled by the first syntax element.

37. The apparatus of claim 32, wherein the first threshold is one of 4095 or 4096 and the second threshold is one of 4095,8191, or 8192.

15

38. The apparatus of claim 32, wherein a maximum value of the first syntax élément is defmed relative to the second syntax element, of the plurality of syntax cléments, that indicates a maximum size of the palette, and the third syntax element, of the plurality of syntax éléments, that indicates a maximum size of a palette predictor, and wherein the video encoder is further configured to:

20 define the second syntax element to be less than or equal to a number of pixels in a largest possible block of the video data in the encoded video bitstream; and define the third syntax element to be less than or equal to K * a value of the second syntax element, where K is a positive constant and * indicates a multiplication operation.

39. The apparatus of claim 38, wherein K is 2.

40. The apparatus of claim 32, wherein the video encoder is further configured to: signal a syntax element indicating a palette run type in the case that a current

30 pixel is not a first pixel in a scanning order; and not signal the syntax element indicating a palette run type in the case that the current pixel of the block of video data is the first pixel in the scanning order of the block of video data.

41. An apparatus configured to encode video data, the apparatus comprising: mcans for encoding a block of video data using a palette and a palette-based coding mode without palette sharing;

means for generating a plurality of syntax éléments that are indicative of the

5 palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of palette values for the palette that are explicitly sîgnaled in an encodcd video bitstream;

means for encoding the first syntax element that is defined relative to one or more of a second syntax élément that indicates a maximum size of the palette, or a third

10 syntax element that indicates a maximum size of a palette prcdictor, wherein the second syntax element has a value from 0 to a first threshold and the third syntax element to be a value from 0 to a second threshold, using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits; and

15 means for including the plurality of syntax éléments in the encoded video bitstream.

42. A computer-readable storage medium storing instructions that, when cxecuted, causes one or more processors of a device configured to encode video data to:

20 encode a block of video data using a palette and a palette-based coding mode without palette sharing;

generate a plurality of syntax éléments that are indicative of the palette that was used to encode the block of video data, the plurality of syntax éléments including a first syntax element that indicates a number of palette values for the palette that arc explicitly 25 sîgnaled in an encoded video bitstream;

encode the first syntax element that is defincd relative to one or more of a second syntax element that indicates a maximum size of the palette or a third syntax element that indicates a maximum size of a palette prcdictor and, wherein the second syntax element has a value from 0 to a first threshold and the third syntax element to be 30 a value from 0 to a second threshold using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits; and include the plurality of syntax éléments in the encoded video bitstream.