WO2020003262A1 - Mode de bi-prédiction symétrique de codage vidéo - Google Patents

Mode de bi-prédiction symétrique de codage vidéo Download PDF

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WO2020003262A1
WO2020003262A1 PCT/IB2019/055550 IB2019055550W WO2020003262A1 WO 2020003262 A1 WO2020003262 A1 WO 2020003262A1 IB 2019055550 W IB2019055550 W IB 2019055550W WO 2020003262 A1 WO2020003262 A1 WO 2020003262A1
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motion vector
video
frame
reference picture
motion
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Hsiao Chiang Chuang
Li Zhang
Yue Wang
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Beijing ByteDance Network Technology Co Ltd
ByteDance Inc
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ByteDance Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/46—Embedding additional information in the video signal during the compression process
    • H04N19/463—Embedding additional information in the video signal during the compression process by compressing encoding parameters before transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/513—Processing of motion vectors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
    • H04N19/172—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a picture, frame or field
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
    • H04N19/176—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/513—Processing of motion vectors
    • H04N19/517—Processing of motion vectors by encoding
    • H04N19/52—Processing of motion vectors by encoding by predictive encoding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/577—Motion compensation with bidirectional frame interpolation, i.e. using B-pictures
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/103—Selection of coding mode or of prediction mode
    • H04N19/105—Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/136—Incoming video signal characteristics or properties
    • H04N19/137—Motion inside a coding unit, e.g. average field, frame or block difference
    • H04N19/139—Analysis of motion vectors, e.g. their magnitude, direction, variance or reliability

Definitions

  • This document is related to image and video coding technologies.
  • Digital video accounts for the largest bandwidth use on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, it is expected that the bandwidth demand for digital video usage will continue to grow.
  • the disclosed techniques may be used by visual media decoder or encoder embodiments in which coding efficiency is improved using symmetricity of motion vectors to reduce bits used for signaling motion information.
  • a video bitstream processing method includes generating, in response to a mirror mode flag in the video bitstream, a second motion vector difference information based on a symmetry mle and a first motion vector difference information.
  • the method further includes reconstmcting a video block in a current picture using the first motion vector difference information and the second motion vector difference, wherein the reconstruction is performed using bi-predictive prediction.
  • another method of video bitstream processing includes receiving, for a first reference picture list associated with a video block, motion vector difference information for a first set of motion vectors.
  • the method further includes deriving, from the motion vector difference information for the first set of motion vectors, using a multi-hypothesis symmetry mle, motion vector difference information associated with a second set of motion vectors for a second reference picture list associated with the video block, wherein the multi-hypothesis symmetry mle specifies that the second motion vector difference value is (0,0), and a corresponding motion vector predictor is set to a mirrored motion vector value derived from the first motion vector difference information, and performing, using a result of the deriving, a conversion between the video block and a bitstream representation of the video block.
  • another method of video bitstream processing includes receiving, for a video block, a first motion vector difference information associated with a first reference picture list.
  • the method further includes receiving, for the video block, a second motion vector difference information associated with a second reference picture list, and deriving, from the first motion vector difference information and the second motion vector difference information, using a multi-hypothesis symmetry rule, a third motion vector difference information associated with the first reference picture list and a fourth motion vector difference information associated with the second reference picture list, wherein the multi-hypothesis symmetry mle specifies that the second motion vector difference value is (0,0), and a corresponding motion vector predictor is set to a mirrored motion vector value derived from the first motion vector difference information.
  • another method of video bitstream processing includes receiving a future frame of video relative to a reference frame of video, receiving a motion vector related to the future frame of video and a past frame of video, applying a predetermined relationship between the future frame of video and the past frame of video, and reconstmcting the past frame of video based on the future frame of video, the motion vector, and the predetermined relationship between the past frame of video and the future frame of video.
  • the above-described method may be implemented by a video decoder apparatus that comprises a processor.
  • the above-described method may be implemented by a video encoder apparatus comprising a processor for decoding encoded video during video encoding process.
  • these methods may be embodied in the form of processor- executable instructions and stored on a computer-readable program medium.
  • FIG. 1 shows an example of a derivation process for merge candidates list constmction.
  • FIG. 2 shows example positions of spatial merge candidates.
  • FIG. 3 is an illustration of motion vector scaling for spatial motion vector candidate.
  • FIG. 4 shows an example derivation process for motion vector prediction candidates.
  • FIG. 5 shows example of candidate pairs considered for redundancy check of spatial merge candidates.
  • FIG. 6 shows example positions for the second PU of Nx2N and 2NxN partitions.
  • FIG. 7 is an example of motion vector scaling for temporal merge candidates.
  • FIG. 8 shows an example of candidate positions for temporal merge candidates labeled as CO and Cl .
  • FIG. 9 shows an example of combined bi-predictive merge candidates.
  • FIG. 10 shows an example of a bilateral matching process.
  • FIG. 1 1 shows an example of a template matching process.
  • FIG. 12 illustrates an example of unilateral motion estimation (ME) in frame rate up- conversion (FRUC).
  • ME unilateral motion estimation
  • FRUC frame rate up- conversion
  • FIG. 13 illustrates an example of a bilateral template matching process.
  • FIG. 14 illustrates an example of alternative temporal motion vector prediction (ATMVP) method.
  • ATMVP alternative temporal motion vector prediction
  • FIG. 15 shows an example identifying source block and source picture.
  • FIG. 16 is an example of one coding unit (CU) with four sub-blocks (A-D) and its neighboring sub-blocks (a-d).
  • FIG. 17 shows a block diagram example of a video encoding apparatus.
  • FIG. 18 is a block diagram of an example of a video processing apparatus.
  • FIG. 19 is a flowchart for an example of a video bitstream processing method.
  • FIG. 20 is a flowchart for another example of a video bitstream processing method.
  • Section headings are used in the present document to facilitate ease of understanding and do not limit the embodiments disclosed in a section to only that section. As such, embodiments from one section can be combined with embodiments from other sections. Furthermore, while certain embodiments are described with reference specific video codecs, the disclosed techniques are applicable to other video coding technologies also. Furthermore, while some embodiments describe video coding steps in detail, it will be understood that corresponding steps decoding that undo the coding will be implemented by a decoder. Furthermore, the term video processing encompasses video coding or compression, video decoding or decompression and video transcoding in which video pixels are represented from one compressed format into another compressed format or at a different compressed bitrate.
  • the present document provides various techniques that can be used by a decoder of video bitstreams to improve the quality of decompressed or decoded digital video. Furthermore, a video encoder may also implement these techniques during the process of encoding in order to reconstruct decoded frames used for further encoding.
  • the inter PU-level signaling can be divided into three different modes.
  • Table 1 and Table 2 show the related syntax elements for inter PU signaling in HEVC.
  • the first mode is the skip mode, where only a single merge index needs to be signalled (merge_idx).
  • the second mode is the merge mode, where only the merge flag (merge_flag) and the merge index (merge_idx) are signalled.
  • the third mode is the AMVP mode, where a direction index (inter_pred_idc), a reference index (ref_idx_lO/ref_idx_ll), mvp index (mvp_lO_flag/mvp_ll_flag), and the MVD (mvd_coding) are signaled.
  • a direction index inter_pred_idc
  • a reference index ref_idx_lO/ref_idx_ll
  • mvp index mvp_lO_flag/mvp_ll_flag
  • MVD MVD
  • Motion vector prediction exploits spatio-temporal correlation of motion vector with neighboring PUs, which is used for explicit transmission of motion parameters. It constmcts a motion vector candidate list by firstly checking availability of left, above temporally neighboring PU positions, removing redundant candidates and adding zero vector to make the candidate list to be constant length. Then, the encoder can select the best predictor from the candidate list and transmit the corresponding index indicating the chosen candidate. Similarly, with merge index signaling, the index of the best motion vector candidate is encoded using truncated unary. The maximum value to be encoded in this case is 2. In the following sections, details about derivation process of motion vector prediction candidate are provided.
  • FIG. 1 summarizes derivation process for motion vector prediction candidate.
  • motion vector candidate two types are considered: spatial motion vector candidate and temporal motion vector candidate.
  • spatial motion vector candidate derivation two motion vector candidates are eventually derived based on motion vectors of each PU located in five different positions as depicted in Figure 2.
  • one motion vector candidate is selected from two candidates, which are derived based on two different co-located positions. After the first list of spatio-temporal candidates is made, duplicated motion vector candidates in the list are removed. If the number of potential candidates is larger than two, motion vector candidates whose reference picture index within the associated reference picture list is larger than 1 are removed from the list. If the number of spatio-temporal motion vector candidates is smaller than two, additional zero motion vector candidates is added to the list.
  • Spatial motion vector candidates [0041] In the derivation of spatial motion vector candidates, a maximum of two candidates are considered among five potential candidates, which are derived from PUs located in positions as depicted in FIG. 2, those positions being the same as those of motion merge.
  • the order of derivation for the left side of the current PU is defined as A0, Al, scaled A0, and scaled Al .
  • the order of derivation for the above side of the current PU is defined as B0, Bl, B2, scaled B0, scaled Bl, and scaled B2.
  • the non-spatial-scaling cases are checked first followed by the spatial scaling.
  • Spatial scaling is considered when the POC is different between the reference picture of the neighboring PU and that of the current PU regardless of reference picture list. If all PUs of left candidates is not available or are intra coded, scaling for the above motion vector can help parallel derivation of left and above MV candidates. Otherwise, spatial scaling is not allowed for the above motion vector.
  • Step 1 Initial candidates derivation
  • Step 2 Additional candidates insertion
  • Figure 6 depicts the second PU for the case of Nx2N and 2NxN, respectively.
  • candidate at position Al is not considered for list constmction.
  • position Bl is not considered when the current PU is partitioned as 2NxN.
  • the scaled motion vector for temporal merge candidate is obtained as illustrated by the dotted line in Figure 7, which is scaled from the motion vector of the co-located PU using the POC distances, tb and td, where tb is defined to be the POC difference between the reference picture of the current picture and the current picture and td is defined to be the POC difference between the reference picture of the co-located picture and the co-located picture.
  • the reference picture index of temporal merge candidate is set equal to zero.
  • a practical realization of the scaling process is described in the HEVC specification. For a B-slice, two motion vectors, one is for reference picture list 0 and the other is for reference picture list 1 , are obtained and combined to make the bi-predictive merge candidate.
  • the position for the temporal candidate is selected between candidates CO and Cl, as depicted in Figure 8. If PU at position CO is not available, is intra coded, or is outside of the current coding tree unit (CTU), position Cl is used. Otherwise, position CO is used in the derivation of the temporal merge candidate.
  • CTU current coding tree unit
  • Additional candidate insertion Besides spatio-temporal merge candidates, there are two additional types of merge candidates: combined bi-predictive merge candidate and zero merge candidate.
  • Combined bi- predictive merge candidates are generated by utilizing spatio-temporal merge candidates.
  • Combined bi-predictive merge candidate is used for B-Slice only.
  • the combined bi-predictive candidates are generated by combining the first reference picture list motion parameters of an initial candidate with the second reference picture list motion parameters of another. If these two tuples provide different motion hypotheses, they will form a new bi-predictive candidate.
  • Figure 9 depicts the case when two candidates in the original list (on the left), which have mvLO and refldxLO or mvLl and refldxLl , are used to create a combined bi-predictive merge candidate added to the final list (on the right). There are numerous rules regarding the combinations which are considered to generate these additional merge candidates.
  • Zero motion candidates are inserted to fill the remaining entries in the merge candidates list and therefore hit the MaxNumMergeCand capacity. These candidates have zero spatial displacement and a reference picture index which starts from zero and increases every time a new zero motion candidate is added to the list. The number of reference frames used by these candidates is one and two for uni- and bi-directional prediction, respectively. Finally, no redundancy check is performed on these candidates.
  • Pattern matched motion vector derivation (PMMVD) mode is a special merge mode based on Frame-Rate Up Conversion (FRUC) techniques. With this mode, motion information of a block is not signaled but derived at decoder side.
  • FRUC Frame-Rate Up Conversion
  • a FRUC flag is signaled for a CU when its merge flag is tme.
  • the FRUC flag is false, a merge index is signaled and the regular merge mode is used.
  • the FRUC flag is tme, an additional FRUC mode flag is signaled to indicate which method (bilateral matching or template matching) is to be used to derive motion information for the block.
  • FRUC merge mode for a CU is based on RD cost selection as done for normal merge candidate. That is the two matching modes (bilateral matching and template matching) are both checked for a CU by using RD cost selection. The one leading to the minimal cost is further compared to other CU modes. If a FRUC matching mode is the most efficient one, FRUC flag is set to tme for the CU and the related matching mode is used. [0069] Motion derivation process in FRUC merge mode has two steps. A CU-level motion search is first performed, then followed by a Sub-CU level motion refinement. At CU level, an initial motion vector is derived for the whole CU based on bilateral matching or template matching.
  • a list of MV candidates is generated and the candidate which leads to the minimum matching cost is selected as the starting point for further CU level refinement. Then a local search based on bilateral matching or template matching around the starting point is performed and the MV results in the minimum matching cost is taken as the MV for the whole CU. Subsequently, the motion information is further refined at sub-CU level with the derived CU motion vectors as the starting points.
  • the following derivation process is performed for a WxH CU motion information derivation.
  • MV for the whole WxH CU is derived.
  • the CU is further split into MxM sub-CUs.
  • the value of M is calculated as in (1), D is a predefined splitting depth which is set to 3 by default in the JEM.
  • the MV for each sub-CU is derived. (Equation 1)
  • the bilateral matching is used to derive motion information of the current CU by finding the closest match between two blocks along the motion trajectory of the current CU in two different reference pictures.
  • the motion vectors MV0 and MV1 pointing to the two reference blocks shall be proportional to the temporal distances, i.e., TD0 and TD1 , between the current picture and the two reference pictures.
  • the bilateral matching becomes mirror based bi-directional MV.
  • template matching is used to derive motion information of the current CU by finding the closest match between a template (top and/or left neighboring blocks of the current CU) in the current picture and a block (same size to the template) in a reference picture.
  • the template matching is also applied to AM VP mode.
  • AMVP mode In JEM, there are two AMVP candidates.
  • a new candidate is derived. If the newly derived candidate by template matching is different to the first existing AMVP candidate, it is inserted at the very beginning of the AMVP candidate list and then the list size is set to two (meaning remove the second existing AMVP candidate).
  • AMVP mode only CU level search is applied.
  • the MV candidate set at CU level consists of:
  • each valid MV of a merge candidate is used as an input to generate a MV pair with the assumption of bilateral matching.
  • one valid MV of a merge candidate is (MVa, refa) at reference list A.
  • the reference picture refb of its paired bilateral MV is found in the other reference list B so that refa and refb are temporally at different sides of the current picture. If such a refb is not available in reference list B, refb is determined as a reference which is different from refa and its temporal distance to the current picture is the minimal one in list B.
  • MVb is derived by scaling MVa based on the temporal distance between the current picture and refa, refb.
  • MVs from the interpolated MV field are also added to the CU level candidate list. More specifically, the interpolated MVs at the position (0, 0), (W/2, 0), (0, FI/2) and (W/2, FI/2) of the current CU are added.
  • the MV candidate set at sub-CU level consists of:
  • the scaled MVs from reference pictures are derived as follows. All the reference pictures in both lists are traversed. The MVs at a collocated position of the sub-CU in a reference picture are scaled to the reference of the starting CU-level MV.
  • ATMVP and STMVP candidates are limited to the four first ones.
  • interpolated motion field is generated for the whole picture based on unilateral ME. Then the motion field may be used later as CU level or sub-CU level MV candidates.
  • the motion field of each reference pictures in both reference lists is traversed at 4x4 block level.
  • the motion of the reference block is scaled to the current picture according to the temporal distance TD0 and TD1 (the same way as that of MV scaling of TMVP in HEVC) and the scaled motion is assigned to the block in the current frame. If no scaled MV is assigned to a 4x4 block, the block’s motion is marked as unavailable in the interpolated motion field.
  • the matching cost is the absolute sum difference (SAD) of bilateral matching or template matching.
  • SAD absolute sum difference
  • the matching cost C of bilateral matching at sub-CU level search is calculated as follows: (Equation 2) where w is a weighting factor which is empirically set to 4, MV and MV S indicate the current MV and the starting MV, respectively. SAD is still used as the matching cost of template matching at sub-CU level search.
  • MV is derived by using luma samples only. The derived motion will be used for both luma and chroma for MC inter prediction. After MV is decided, final MC is performed using 8-taps interpolation filter for luma and 4-taps interpolation filter for chroma.
  • MV refinement is a pattern based MV search with the criterion of bilateral matching cost or template matching cost.
  • two search patterns are supported - an unrestricted center- biased diamond search (UCBDS) and an adaptive cross search for MV refinement at the CU level and sub-CU level, respectively.
  • UMBDS center- biased diamond search
  • the MV is directly searched at quarter luma sample MV accuracy, and this is followed by one-eighth luma sample MV refinement.
  • the search range of MV refinement for the CU and sub-CU step are set equal to 8 luma samples.
  • the encoder can choose among uni-prediction from listO, uni-prediction from listl or bi -prediction for a CU. The selection is based on a template matching cost as follows:
  • costO is the SAD of listO template matching
  • costl is the SAD of list 1 template matching
  • costBi is the SAD of bi -prediction template matching.
  • the value of factor is equal to 1.25, which means that the selection process is biased toward bi-prediction.
  • the inter prediction direction selection is only applied to the CU-level template matching process.
  • bi-prediction operation for the prediction of one block region, two prediction blocks, formed using a motion vector (MV) of listO and a MV of list 1, respectively, are combined to form a single prediction signal.
  • MV motion vector
  • MV of listO motion vector of listO
  • MV of list 1 motion vector of list 1
  • DMVR decoder-side motion vector refinement
  • the two motion vectors of the bi-prediction are further refined by a bilateral template matching process.
  • the bilateral template matching applied in the decoder to perform a distortion-based search between a bilateral template and the reconstruction samples in the reference pictures to obtain a refined MV without transmission of additional motion information.
  • a bilateral template is generated as the weighted combination (i.e. average) of the two prediction blocks, from the initial MV0 of listO and MV1 of listl, respectively, as shown in Figure 10.
  • the template matching operation consists of calculating cost measures between the generated template and the sample region (around the initial prediction block) in the reference picture. For each of the two reference pictures, the MV that yields the minimum template cost is considered as the updated MV of that list to replace the original one.
  • nine MV candidates are searched for each list. The nine MV candidates include the original MV and 8 surrounding MVs with one luma sample offset to the original MV in either the horizontal or vertical direction, or both.
  • the two new MVs i.e., MV0' and MV1' as shown in Figure 10, are used for generating the final bi-prediction results.
  • a sum of absolute differences (SAD) is used as the cost measure.
  • DMVR is applied for the merge mode of bi-prediction with one MV from a reference picture in the past and another from a reference picture in the future, without the transmission of additional syntax elements.
  • JEM when LIC, affine motion, FRUC, or sub-CU merge candidate is enabled for a CU, DMVR is not applied.
  • MVDs motion vector differences
  • LAMVR locally adaptive motion vector resolution
  • MVD can be coded in units of quarter luma samples, integer luma samples or four luma samples.
  • the MVD resolution is controlled at the coding unit (CU) level, and MVD resolution flags are conditionally signaled for each CU that has at least one non-zero MVD components.
  • a first flag is signaled to indicate whether quarter luma sample MV precision is used in the CU.
  • the first flag (equal to 1) indicates that quarter luma sample MV precision is not used, another flag is signaled to indicate whether integer luma sample MV precision or four luma sample MV precision is used.
  • the quarter luma sample MV resolution is used for the CU.
  • the MVPs in the AMVP candidate list for the CU are rounded to the corresponding precision.
  • CU-level RD checks are used to determine which MVD resolution is to be used for a CU. That is, the CU-level RD check is performed three times for each MVD resolution.
  • the following encoding schemes are applied in the JEM.
  • the motion information of the current CU (integer luma sample accuracy) is stored.
  • the stored motion information (after rounding) is used as the starting point for further small range motion vector refinement during the RD check for the same CU with integer luma sample and 4 luma sample MVD resolution so that the time-consuming motion estimation process is not duplicated three times.
  • RD check of a CU with 4 luma sample MVD resolution is conditionally invoked.
  • RD cost integer luma sample MVD resolution is much larger than that of quarter luma sample MVD resolution
  • the RD check of 4 luma sample MVD resolution for the CU is skipped.
  • each CU can have at most one set of motion parameters for each prediction direction.
  • Two sub-CU level motion vector prediction methods are considered in the encoder by splitting a large CU into sub-CUs and deriving motion information for all the sub-CUs of the large CU.
  • Alternative temporal motion vector prediction (ATMVP) method allows each CU to fetch multiple sets of motion information from multiple blocks smaller than the current CU in the collocated reference picture.
  • STMVP spatial-temporal motion vector prediction
  • the motion vectors temporal motion vector prediction (TMVP) is modified by fetching multiple sets of motion information (including motion vectors and reference indices) from blocks smaller than the current CU.
  • the sub-CUs are square NxN blocks (N is set to 4 by default).
  • Figure 13 illustrates an example of a bilateral template matching process.
  • a bilateral template is generated from prediction blocks.
  • bilateral template matching is used to find the best matched blocks.
  • ATMVP predicts the motion vectors of the sub-CUs within a CU in two steps.
  • the first step is to identify the corresponding block in a reference picture with a so-called temporal vector.
  • the reference picture is called the motion source picture.
  • the second step is to split the current CU into sub-CUs and obtain the motion vectors as well as the reference indices of each sub-CU from the block corresponding to each sub-CU, as shown in Figure 14.
  • a reference picture and the corresponding block is determined by the motion information of the spatial neighboring blocks of the current CU.
  • the first merge candidate in the merge candidate list of the current CU is used.
  • the first available motion vector as well as its associated reference index are set to be the temporal vector and the index to the motion source picture.
  • the corresponding block may be more accurately identified, compared with TMVP, wherein the corresponding block (sometimes called collocated block) is always in a bottom-right or center position relative to the current CU.
  • the associated MV and reference picture are utilized to identify the source block and source picture.
  • a corresponding block of the sub-CU is identified by the temporal vector in the motion source picture, by adding to the coordinate of the current CU the temporal vector.
  • the motion information of its corresponding block (the smallest motion grid that covers the center sample) is used to derive the motion information for the sub-CU.
  • the motion information of a corresponding NxN block is identified, it is converted to the motion vectors and reference indices of the current sub-CU, in the same way as TMVP of HEVC, wherein motion scaling and other procedures apply.
  • the decoder checks whether the low- delay condition (i.e.
  • motion vector MVx the motion vector corresponding to reference picture list X
  • motion vector MVy the motion vector MVy
  • the motion derivation for sub-CU A starts by identifying its two spatial neighbors.
  • the first neighbor is the NxN block above sub-CU A (block c). If this block c is not available or is intra coded the other NxN blocks above sub-CU A are checked (from left to right, starting at block c).
  • the second neighbor is a block to the left of the sub-CU A (block b). If block b is not available or is intra coded other blocks to the left of sub-CU A are checked (from top to bottom, staring at block b).
  • the motion information obtained from the neighboring blocks for each list is scaled to the first reference frame for a given list.
  • temporal motion vector predictor (TMVP) of sub block A is derived by following the same procedure of TMVP derivation as specified in HEVC.
  • the motion information of the collocated block at location D is fetched and scaled accordingly.
  • all available motion vectors (up to 3) are averaged separately for each reference list.
  • the averaged motion vector is assigned as the motion vector of the current sub-CU.
  • the sub-CU modes are enabled as additional merge candidates and there is no additional syntax element required to signal the modes.
  • Two additional merge candidates are added to merge candidates list of each CU to represent the ATM VP mode and STM VP mode. Up to seven merge candidates are used, if the sequence parameter set indicates that ATMVP and STMVP are enabled.
  • the encoding logic of the additional merge candidates is the same as for the merge candidates in the HM, which means, for each CU in P or B slice, two more RD checks is needed for the two additional merge candidates.
  • MVD constitutes a large portion of bitstream. Especially during bi-prediction, MVDs of both L0 and Ll need to be signaled and they introduce large overhead, especially for low-rate visual communication. Some properties about motion symmetricity can be utilized to save the rate spent on coding of motion information.
  • the property of symmetricity of motion vector can be utilized to generate the basis MV set for AMVP mode.
  • the MVD is only signaled for a single direction (list), and the MV of the other direction is set using a mirrored condition.
  • the MV may be further refined.
  • Such a mode is called sym-bi- mode.
  • the bi-prediction refers to prediction by using one reference frame from the past and the other reference frame from the future in display order.
  • VVC versatile video coding
  • JVET-Nl00l-v5 and other versions and standards includes a symmetric motion vector difference (SMVD) mode which may skip the signaling of Ll MVD.
  • SMVD symmetric motion vector difference
  • the skipped Ll MVD may be set to the mirror of the L0 MVD without scaling.
  • MVD value of L N is not sent (i.e., inherited to be (0, 0)), and the MVP value is set to the mirrored MV value from L(i -N) MV.
  • a motion refinement may be applied to L N motion vector.
  • the DMVR refinement process may be applied.
  • the FRUC refinement process may be applied to refine L N motion vector.
  • the search range of the refinement can be pre-defined or signalled through the SPS (Sequence Parameter Set), PPS (Picture Parameter Set), VPS (Video Parameter set), or slice headers.
  • the motion refinement can be applied to a specific grid.
  • the uniform sampling grid with grid distance d can be used to define the search points.
  • the grid distance d can be pre-defined, or signalled via SPS, PPS, VPS, or slice headers.
  • the use of the sampling grid can be considered as a sub-sampled search region and hence has the benefit of reducing memory bandwidth required by the search.
  • the signalling of the mirror mode can be done in either the CU level, CTU level, region level (covering multiple CUs/CTUs) or slice level.
  • a one-bit flag needs to be signalled when it is sym- bi-mode. That is, when this flag is signalled to be 1, the associated L N MVD as well as its MVP index can be skipped.
  • all sym-bi-mode will not signal the L N MVD values and their MVP indexes.
  • the signaling of a SMVD flag occurs at the CU level.
  • the slice header/picture parameter set/sequence parameter set signalling whether the refinement process should be invoked or not.
  • it may be also signaled in CU/CTU/region level.
  • the signalling can occur at CU level, region level, CTU level, or slice level.
  • a one-bit flag needs to be signaled in sym-bi-mode.
  • region level, CTU level, or slice level all belonging bi-predictive CUs will skip the MVD signalling of the specified list and use the mirrored MVP as its starting point to find the final motion vector.
  • mirrored MVP needs to be stored in the MV buffer for motion prediction (AMVP, merge) of subsequent blocks.
  • the refined motion vectors do not need to be stored in the MV buffer.
  • the MVP can be placed along with the conventional MVP indexes, and one extra bit (as a total of 2) is required to signal the three MVP indexes.
  • both MVP indices are signaled as a regular AMVP mode.
  • the mirrored MVP candidate is added in place of the second AMVP candidate. Still, only one -bit is required to signal the MVP index.
  • the mirrored MVP mode can be applied when the POC distances between the two reference frames are equal.
  • two references are derived as the closest reference frames to the current frame in both L0 and Ll.
  • the refinement process can be done using various matching schemes. Let the patches from L0 and Ll pictures be P0 and Pl, respectively. A patch is defined as the prediction samples generated by the interpolation process of a MV.
  • the refinement finds the MW (N-0 or 1) which minimizes the sum of absolute difference (SAD) between P0 and PL
  • a temporary patch is generated by the P0 and Pl and the criteria could be defined as finding the MV with the highest correlation between the prediction patch and the temporary patch.
  • template-based matching scheme can be used to define the refinement process.
  • the procedure of finding MW (N-0 or 1) resembles the procedure described in the above two examples.
  • the interpolation process can be skipped for some of the search points. No interpolation process is involved when searching for points where their distances to the MVP/V (N-0 or 1) exceed a threshold T. Only the integer-pixel reference samples are used as patches to derive motion vector. T can be predefined, or signalled via SPS, PPS, VPS, or slice headers.
  • the value of l can be pre-defined, signaled through SPS, PPS, VPS, or slice headers.
  • the MVDN, MVN, and MVPN defined below are two- dimensional vectors. i.
  • , where MVD/V MV7V- MVP N.
  • represents the Ll norm.
  • R round(log2(
  • R mvd_coding(MVDA , where the function mvd_coding indicates standard-compliant binarization process of the input MVD value.
  • the MVD_Ll_ZERO_FLAG is a slice-level flag which imposes a strong constraint on Ll MVD signaling by removing all the Ll MVD values.
  • the mirrored MV and refinement can be used in conjunction with such design in the following ways.
  • MVD_Ll_ZERO_FLAG when MVD_Ll_ZERO_FLAG is enabled, no MVP index is signalled, and the mirrored MVP constraint and refinement process can still be applied.
  • MVP index is still signalled (e.g., as in l.e or l.f) and the mirrored MVP constraint is not imposed. However, the MV refinement process can still be applied.
  • the mirrored MVP is added to the MVP candidate lists, followed by the MV refinement process.
  • a joint MVP list can be created to support the mirrored MVD mode. That is, the MVP list is derived jointly for L0 and Ll (given a pair of specific reference indexes), and only a single index needs to be signalled.
  • the signaling of refldx/V can be skipped and only the reference frame which is closest to the mirrored location of L( -N) reference frame is selected as its reference frame for MVP scaling.
  • both reference indices are skipped as they are chosen to be the closest reference frames to the current frame in both lists.
  • MVP candidates which are unable to create Bi-predictors should be considered invalid during the derivation process.
  • the derivation can be done by following the existing procedure of MVP derivation for L (1-N), except that when the scaling occurs, the candidate pairs which result in motion vectors lying on both reference frames of L0 and Ll in the Decoded Picture Buffer (DPB) are considered as valid candidates.
  • DPB Decoded Picture Buffer
  • Mirrored MVD mode may be expressed including: if( sym_mvd_flag[ x0 ] [ yO ] ) ⁇
  • the proposed methods may be also applied to the multi hypothesis mode.
  • MV information when there are two sets MV information for each reference picture list, MV information may be signaled for one reference picture list. However, the MVD of the sets of MV information of the other reference picture list may be derived. For each set of MV information of one reference picture list, it may be treated in the same way as the sym-bi-mode.
  • one set of MV information of the two reference picture lists may be signaled. While the other two sets of MV information of the two reference picture lists may be derived on the fly using the sym-bi-mode.
  • FIG. 18 is a block diagram l800of a video processing apparatus.
  • the apparatus 1800 may be used to implement one or more of the methods described herein.
  • the apparatus 1800 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on.
  • the apparatus 1800 may include one or more processors 1802, one or more memories 1804 and video processing hardware 1806.
  • the processor(s) 1802 may be configured to implement one or more methods described in the present document.
  • the memory (memories) 1804 may be used for storing data and code used for implementing the methods and techniques described herein.
  • the video processing hardware 1806 may be used to implement, in hardware circuitry, some techniques described in the present document.
  • FIG. 19 is a flowchart for an example method 1900 of video bitstream processing.
  • the method 1900 includes generating (1902), in response to a mirror mode flag in the video bitstream, a second motion vector difference information based on a symmetry rule and a first motion vector difference information; and reconstructing (1904) a video block using the first motion vector difference and the second motion vector difference information, wherein the reconstmction is performed bi-predictively.
  • FIG. 20 is a flowchart for an example method 2000 of video bitstream processing.
  • the method 2000 includes receiving (2002), for a first reference picture list associated with a video block, motion vector difference information for a first set of motion vectors; and deriving (2004), from the motion vector difference information for the first set of motion vectors, using a multi hypothesis symmetry rule, the motion vector difference information associated with a second set of motion vectors for a second reference picture list associated with the video block. This information may be generated using the received motion vector difference information for the first set of motion vectors.
  • a method of video bitstream processing may include a variation of the method 2000 in which the partial motion vector difference information in case of multi hypothesis is signaled in an interweaved manner.
  • Such a method includes receiving, for a video block, a first motion vector difference information associated with a first reference picture list, receiving, for the video block, a second motion vector difference information associated with a second reference picture list; deriving, from the first motion vector difference information and the second motion vector difference information, using a multi -hypothesis symmetry mle, a third motion vector difference information associated with the first reference picture list and a fourth motion vector difference information associated with the second reference picture list.
  • bitstream processing may include generation of bitstream that represents the video in a compressed form.
  • bitstream processing may include using the bitstream to reconstruct video from its compressed form representation.
  • the symmetry mle and the multi-hypothesis symmetry mles may be same or different.
  • the multi-hypothesis symmetry mle may only be used when a video block (or picture) is encoded using multi-hypothesis motion prediction.
  • the symmetry mle may specify that the second motion vector prediction difference value is to be (0,0), and a corresponding motion vector predictor is set to a mirrored motion vector whose value is derived from the first motion vector difference information.
  • motion vector refinement may further be performed on the mirrored motion vector value.
  • the mirror mode may be selectively used based on an indication in the bitstream at the CU/CTU/region level.
  • motion vector refinement may also be controlled to be used (or not used) by signaling of a refinement flag.
  • the refinement flag may be used at a slice header, or picture parameter set, or sequence parameter set or region level or coding unit or coding tree unit level.
  • the use of the symmetry rule -based technique for generating mirrored motion vectors may enable skipping sending motion vector difference information in the bitstream (because this information can be generated by the decoder).
  • the skipping operation may be selectively controlled via a flag in the bitstream.
  • mirrored MVP calculations using the above-described techniques may be used at the decoder side for improved decoding of subsequent blocks, without suffering from the dependency of calculation that may occur if refined motion vectors are used for prediction of subsequent blocks.
  • the symmetry mle may only be used for generating mirrored motion vectors in the case that the two reference frames have a same distance. Otherwise, scaling of motion vectors may be performed based on relative temporal distances of the reference frames.
  • the mirrored motion vectors may be calculated using a patch-based technique and may include generating a first patch of prediction samples using the first motion vector difference from list 0 of reference frames, generating a second patch of prediction samples using the first motion vector difference from list 1 of reference frames, and determining the motion vector refinement to be a value that minimizes an error function between the first patch and the second patch.
  • Various optimization criteria e.g., rate distortion, SAD, and so on
  • rate distortion e.g., SAD, and so on
  • bi directional prediction may be signaled using only half the motion information of a conventional technique, and the other half of the motion information may be generated at the decoder using a mirror symmetry of motion of objects in a video.
  • a symmetry flag and a refinement flag may be used to signal use (or no-use) of this mode and further refinement of motion vectors.
  • Mirrored motion vectors may be calculated using symmetry mles.
  • One assumption made in symmetry rule is that an object maintains its translational motion between the time of the current block and the times of reference blocks used for bi-prediction.
  • a motion vector pointing to a reference region that is delx and dely displaced from the current block in one temporal direction may be assumed to change to a scaled version of delx and dely in another direction (scaling may also include negative scaling, which may be due to changing direction of motion vectors).
  • scaling may depend on temporal distances, and other considerations and described in the present document.
  • the disclosed and other solutions, examples, embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them.
  • the disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus.
  • the computer readable medium can be a machine -readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them.
  • data processing apparatus encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers.
  • the apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.
  • a propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus.
  • a computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.
  • a computer program does not necessarily correspond to a file in a file system.
  • a program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code).
  • a computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.
  • processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer.
  • a processor will receive instmctions and data from a read only memory or a random-access memory or both.
  • the essential elements of a computer are a processor for performing instmctions and one or more memory devices for storing instmctions and data.
  • a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks.
  • mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks.
  • a computer need not have such devices.
  • Computer readable media suitable for storing computer program instmctions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks.
  • semiconductor memory devices e.g., EPROM, EEPROM, and flash memory devices
  • magnetic disks e.g., internal hard disks or removable disks
  • magneto optical disks e.g., CD ROM and DVD-ROM disks.
  • the processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

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Abstract

L'invention concerne un procédé de traitement de train de bits vidéo consistant à générer, en réponse à un drapeau de mode miroir dans le train de bits vidéo, des secondes informations de différence de vecteurs de mouvement sur la base d'une règle de symétrie et de premières informations de différence de vecteurs de mouvement ; et à reconstruire un bloc vidéo à l'aide des premières informations de différence de vecteurs de mouvement et des secondes informations de différence de vecteurs de mouvement, la reconstruction étant effectuée de manière bi-prédictive.
PCT/IB2019/055550 2018-06-30 2019-07-01 Mode de bi-prédiction symétrique de codage vidéo Ceased WO2020003262A1 (fr)

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WO2025216561A1 (fr) * 2024-04-09 2025-10-16 엘지전자 주식회사 Procédé de codage d'informations d'image, procédé de décodage d'informations d'image, support d'enregistrement lisible par ordinateur et procédé de transmission d'informations d'image

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