JP7320573B2 - Image decoding device, image decoding method and program - Google Patents

Description

The present invention relates to an image decoding device, an image decoding method and a program.

Conventionally, there is known a technique of realizing non-linear filtering by clipping an input signal to an "ALF (Adaptive Loop Filter)" with a threshold value (see Non-Patent Document 1, for example).

Here, the threshold is defined by a formula, and the final value is derived according to the set value of the internal bit depth and the like. Such thresholds are defined respectively for the luminance signal and the color difference signal.

Versatile Video Coding (Draft 5), JVET-N1001

However, in the above-described conventional technology, the magnitude relationship between the threshold value of the luminance signal and the threshold value of the color difference signal is reversed depending on the internal bit depth. As a result, even for the same input signal, there is a problem that the characteristics of the decoded image may change depending on the setting of the internal bit depth, which may affect the subjective image quality.

Accordingly, the present invention has been made in view of the above problems, and provides an image decoding device, an image decoding method, and a program capable of preventing a situation in which the characteristics of a decoded image change and affect the subjective image quality. intended to provide

A first feature of the present invention is an image decoding device, comprising a filter unit configured to receive a pre-filtering decoded signal and output a post-filtering decoded signal, the filter unit comprising: clipping the pre-filtering decoded signal such that the absolute value of the difference between the pixel value and the pixel value of the pre-filtering decoded signal is equal to or less than a predefined threshold; and pixel values of the pre-filtering decoded signal to generate the post-filtering decoded signal, and even if the internal bit depth changes, the threshold value for the luminance signal and The gist is that it is defined so that the magnitude relationship with the threshold value for the color difference signal is preserved.

A second feature of the present invention is an image decoding method having a step of inputting a pre-filtering decoded signal and outputting a post-filtering decoded signal, wherein in the step, a reference pixel value and the pre-filtering decoded signal Clipping processing is performed on the pre-filtered decoded signal so that the absolute value of the difference between the pixel value of so that even if the internal bit depth changes, the magnitude relationship between the threshold for the luminance signal and the threshold for the color difference signal is preserved. The gist is that it is defined in

A third feature of the present invention is a program for use in an image decoding device, which causes a computer to execute a step of inputting a pre-filtering decoded signal and outputting a post-filtering decoded signal; Clipping processing is performed on the pre-filtering decoded signal so that an absolute value of a difference value between the pixel value of the pre-filtering decoded signal and the pixel value of the pre-filtering decoded signal is equal to or less than a predetermined threshold value, and after the clipping processing is performed, The filtered decoded signal is generated by a linearly weighted sum of the pixel values of the unfiltered decoded signal and the threshold for the luminance signal and the threshold for the chrominance signal even if the internal bit depth changes. The gist is that it is defined so that the magnitude relationship between is preserved.

Advantageous Effects of Invention According to the present invention, it is possible to provide an image decoding device, an image decoding method, and a program that can prevent a situation in which the characteristics of a decoded image change and affect the subjective image quality.

It is a figure showing an example of composition of image processing system 10 concerning one embodiment. 1 is a diagram showing an example of functional blocks of an image encoding device 100 according to an embodiment; FIG. 4 is a diagram showing an example of functional blocks of an in-loop filtering unit 150 of the image encoding device 100 according to one embodiment; FIG. FIG. 4 is a diagram for explaining an example of the function of a filter section 150B of an in-loop filtering section 150 of the image encoding device 100 according to one embodiment; FIG. 4 is a diagram for explaining an example of the function of a filter section 150B of an in-loop filtering section 150 of the image encoding device 100 according to one embodiment; FIG. 4 is a diagram for explaining an example of the function of a filter section 150B of an in-loop filtering section 150 of the image encoding device 100 according to one embodiment; FIG. 4 is a diagram for explaining an example of the function of a filter section 150B of an in-loop filtering section 150 of the image encoding device 100 according to one embodiment; 2 is a diagram showing an example of functional blocks of an image decoding device 200 according to one embodiment; FIG. 4 is a diagram showing an example of functional blocks of an in-loop filtering unit 250 of the image decoding device 200 according to one embodiment; FIG. 4 is a flowchart showing an example of a processing procedure of an in-loop filtering unit 250 of the image decoding device 200 according to one embodiment;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that constituent elements in the following embodiments can be appropriately replaced with existing constituent elements and the like, and various variations including combinations with other existing constituent elements are possible. Therefore, the following description of the embodiments is not intended to limit the scope of the invention described in the claims.

(First embodiment)
An image processing system 10 according to a first embodiment of the present invention will be described below with reference to FIGS. 1 to 10. FIG. FIG. 1 is a diagram showing an image processing system 10 according to an embodiment according to this embodiment.

As shown in FIG. 1 , the image processing system 10 has an image encoding device 100 and an image decoding device 200 .

The image encoding device 100 is configured to generate encoded data by encoding an input image signal. The image decoding device 200 is configured to generate an output image signal by decoding encoded data.

Here, such encoded data may be transmitted from the image encoding device 100 to the image decoding device 200 via a transmission path. Also, the encoded data may be stored in a storage medium and then provided from the image encoding device 100 to the image decoding device 200 .

(Image encoding device 100)
The image coding apparatus 100 according to this embodiment will be described below with reference to FIG. FIG. 2 is a diagram showing an example of functional blocks of the image encoding device 100 according to this embodiment.

As shown in FIG. 2, the image coding apparatus 100 includes an inter prediction unit 111, an intra prediction unit 112, a subtractor 121, an adder 122, a transform/quantization unit 131, an inverse transform/inverse quantization It has a section 132 , an encoding section 140 , an in-loop filtering section 150 and a frame buffer 160 .

The inter prediction unit 111 is configured to generate a prediction signal by inter prediction (inter-frame prediction).

Specifically, the inter prediction unit 111 identifies a reference block included in the reference frame by comparing a frame to be encoded (hereinafter referred to as a target frame) and a reference frame stored in the frame buffer 160, and identifies a reference block included in the reference frame. It is configured to determine a motion vector for the reference block.

Also, the inter prediction unit 111 is configured to generate, for each prediction block, a prediction signal included in the prediction block based on the reference block and motion vector. The inter prediction section 111 is configured to output the prediction signal to the subtractor 121 and the adder 122 . Here, the reference frame is a frame different from the target frame.

The intra prediction unit 112 is configured to generate a prediction signal by intra prediction (intra-frame prediction).

Specifically, the intra prediction unit 112 is configured to identify a reference block included in the target frame and generate a prediction signal for each prediction block based on the identified reference block. Also, the intra prediction unit 112 is configured to output the prediction signal to the subtractor 121 and the adder 122 .

Here, the reference block is a block that is referred to for a prediction target block (hereinafter referred to as target block). For example, the reference block is a block adjacent to the target block.

The subtractor 121 is configured to subtract the prediction signal from the input image signal and output the prediction residual signal to the transform/quantization section 131 . Here, the subtractor 121 is configured to generate a prediction residual signal that is a difference between a prediction signal generated by intra prediction or inter prediction and an input image signal.

The adder 122 adds the prediction signal to the prediction residual signal output from the inverse transform/inverse quantization unit 132 to generate a pre-filtering decoded signal. It is configured to output to the loop filter processing unit 150 .

Here, the unfiltered decoded signal constitutes a reference block used in intra prediction section 112 .

The transform/quantization unit 131 is configured to perform transform processing on the prediction residual signal and to obtain coefficient level values. Further, the transform/quantization unit 131 may be configured to quantize the coefficient level values.

Here, transform processing is processing for transforming a prediction residual signal into a frequency component signal. In such transformation processing, a basis pattern (transformation matrix) corresponding to discrete cosine transform (DCT) may be used, and a basis pattern (transformation matrix) corresponding to discrete sine transform (DST) may be used. may be used.

The inverse transform/inverse quantization unit 132 is configured to perform inverse transform processing on the coefficient level values output from the transform/quantization unit 131 . Here, the inverse transform/inverse quantization unit 132 may be configured to perform inverse quantization of the coefficient level values prior to the inverse transform processing.

Here, the inverse transform processing and inverse quantization are performed in the reverse order of the transform processing and quantization performed by the transform/quantization unit 131 .

The encoding unit 140 is configured to encode the coefficient level values output from the transform/quantization unit 131 and output encoded data.

Here, for example, the coding is entropy coding that assigns codes of different lengths based on the probability of occurrence of coefficient level values.

In addition to the coefficient level values, the encoding unit 140 is also configured to encode control data used in the decoding process.

Here, the control data may include size data such as a coding block (CU: Coding Unit) size, a prediction block (PU: Prediction Unit) size, a transform block (TU: Transform Unit) size, and the like.

The in-loop filtering section 150 is configured to perform filtering on the unfiltered decoded signal output from the adder 122 and output the filtered decoded signal to the frame buffer 160 .

Also, the in-loop filtering unit 150 may be configured to receive the input image signal and the decoded signal before filtering, determine parameters related to filtering, and output the parameters to the encoding unit 140 . The encoding unit 140 may be configured to encode such parameters and transmit them to the image decoding device 200 as additional information.

Here, for example, the filter processing is adaptive loop filter processing that reduces encoding distortion of a decoded image.

The frame buffer 160 is configured to accumulate reference frames used by the inter prediction section 111 .

Here, the filtered decoded signal constitutes a reference frame used in inter prediction section 111 .

(In-loop filtering unit 150)
The in-loop filtering unit 150 according to this embodiment will be described below. FIG. 3 is a diagram showing the in-loop filtering unit 150 according to this embodiment.

As shown in FIG. 3, the in-loop filtering unit 150 has a class determining unit 150A, a filtering unit 150B, and a parameter determining unit 150C.

The in-loop filtering unit 150 can select either application or non-application of adaptive loop filtering for each coding tree block (CTU: Coding Tree Unit). Also, when adaptive loop filtering is applied, in-loop filtering section 150 can select which filter set to use from among a plurality of filter sets.

Each filter set includes up to 25 types (classes) of luminance signal filters and one class of color difference signal filters.

Parameters including information related to application or non-application of adaptive loop filtering, information related to filter sets to be used in adaptive loop filtering, etc. are encoded for each CTU as additional information as described later, and are used for image decoding. It is transmitted to the device 200 . Note that such parameters are determined by the parameter determination unit 150C as described later.

Here, for example, when the input signal is in the "YCbCr4:2:0 format", the CTU, for example, has a luminance (Y) signal of 128×128 pixel size and a color difference signal (Cb, Cr) of 64×64 pixel size. You may define it as each block divided into each size.

For pixels of luminance signals and color difference signals belonging to CTUs determined not to apply adaptive loop filtering, determination processing by the class determination unit 150A and filtering by the filter unit 150B, which will be described later, can be omitted.

Class determination section 150A receives the unfiltered decoded signal as input, and outputs class determination information indicating which type (class) of filters (adaptive loop filters) is to be used from a plurality of types of predetermined filters (adaptive loop filters). is configured as

Here, the class determining section 150A is configured to divide the unfiltered decoded signal into small blocks and determine the class to be used for each block. For example, the class determination unit 150A can determine which class of 25 types of filters should be used for each 4×4 pixel block.

Here, as a class determination method, any determination method may be used as long as it is a method that can make a determination using only information obtained on both the image encoding device 100 side and the image decoding device 200 side as input. can be done.

For example, in Non-Patent Document 1, the above class determination is performed using the gradient of the pixel values of the pre-filtering decoded signal. By using only the information obtained on both the image encoding device 100 side and the image decoding device 200 side, the image decoding device 200 side can make the same class determination as the image encoding device 100 side. This eliminates the need to transmit information from the image encoding device 100 side to the image decoding device 200 side.

Filter section 150B is configured to receive the pre-filtering decoded signal and output the post-filtering decoded signal.

Specifically, the filter unit 150B receives as input the unfiltered decoded signal, the class determination information output from the class determination unit 150A, and the parameters input from the parameter determination unit 150C (parameter group for loop filtering), It is configured to perform filtering and output a filtered decoded signal.

The value of each pixel of the filtered decoded signal can be calculated, for example, by the following equation.

where I(x,y) is the pixel value of the unfiltered decoded signal at coordinates (x,y), and O(x,y) is the filtered pixel value at coordinates (x,y). is the pixel value of the post-decoded signal, (i, j) is the coordinates (reference pixel position) indicating the relative position of the reference pixel with respect to the pixel at the coordinates (x, y), and C(i, j) is , is the filter coefficient corresponding to the reference pixel position (i,j), K( ) is the clipping process described below, and k(i,j) is the threshold used in the clipping process.

K(I,k)=min(k,max(-k,I))
Here, min() is a function that returns the minimum value in its arguments, and max() is a function that returns the maximum value in its arguments. Therefore, K( ) is a process that returns -k if the input value I is less than -k, returns k if the input value I is greater than k, and returns the input value I as is otherwise.

That is, the filter unit 150B sets the absolute value of the difference between the reference pixel value I(x+i, y+j) and the pixel value I(x, y) of the decoded signal before filtering to a predetermined threshold value k(i, j) or less. The clipping process is applied to the pre-filtering decoded signal so that

Further, the filter unit 150B is configured to generate the post-filtering decoded signal by linearly weighting the sum of the value after the clipping process and the pixel value I(x, y) of the pre-filtering decoded signal. there is

The filter coefficient C is determined by the parameter determination unit 150C and transmitted to the image decoding device 200 side. In order to reduce the code amount of information related to the filter coefficients C, the number of filter coefficients C can be reduced by applying the same filter coefficients C to a plurality of pixels. FIG. 4 shows a specific example.

FIG. 4(a) shows an example of the arrangement of filter coefficients C in the luminance signal filtering process, and FIG. 4(b) shows an example of the arrangement of the filter coefficients C in the color difference signal filtering process.

As shown in FIG. 4A, for example, the luminance signal uses 12 types of filter coefficients C0 to C11. In FIG. 4(a), pixels marked with X are pixel positions (x, y) whose pixel values are corrected by such filtering. Pixels to which the same filter coefficient C is applied are arranged point-symmetrically around the pixel position (x, y).

As shown in FIG. 4B, for the color difference signal, similarly, the other filter coefficients are arranged point-symmetrically around the pixel marked with X. As shown in FIG.

For example, when the reference pixel is a pixel outside the picture, the filtering process can be realized by copying (referred to as padding) the pixel value of the pre-filtering decoded signal positioned at the picture boundary.

Here, FIG. 5 shows an example of filtering at the bottom end of a picture (picture boundary).

In FIG. 5(a), the grayed out filter coefficients C0 to C3 refer to pixels outside the picture. At this time, as inputs to the grayed-out filter coefficients C2 and C0, the same pixel value as the pixel value corresponding to the filter coefficient C6 arranged immediately above the filter coefficient C2 in FIG. 5A is used.

Similarly, as an input to the grayed out filter coefficient C3, the same pixel value as the pixel value corresponding to the filter coefficient C7 arranged immediately above the filter coefficient C3 in FIG. As an input to the filter coefficient C1, the same pixel value as the pixel value corresponding to the filter coefficient C5 arranged immediately above the filter coefficient C1 in FIG. 5A is used.

Further, in consideration of the point symmetry of the filter coefficient C described above, when a padded value is used for a part of the reference pixel, the padded value is used as an input to the filter coefficient C at the position corresponding to the reference pixel. can also

In the example of FIG. 5B, in addition to the filtering process at the bottom end of the picture described in the example of FIG.

For example, as inputs to the filter coefficients C0 and C2 in FIG. 5B, the pixel value corresponding to the filter coefficient C6 immediately below the filter coefficient C2 may be padded and used.

Similarly, for the input of the filter coefficients C1 and C3, pixel values corresponding to the filter coefficients C5 and C7 immediately below the filter coefficients C1 and C3 may be padded and used.

Although the above example describes filtering at the bottom edge of the picture, similar filtering can be applied at the top and left and right edges of the picture.

In addition to picture boundaries, if the pixel values beyond the boundaries cannot be referenced, such as the boundaries of parallel processing units for encoding called slices and tiles, and the boundaries of pipeline processing called virtual boundaries, can be similarly addressed by applying the filtering method of .

By performing the same filter processing on boundaries such as picture boundaries, tile boundaries, slice boundaries, virtual boundaries, etc., the implementation can be simplified compared to the case where each boundary is processed differently.

Also, the threshold used in the clipping process is set for each filter class and for each filter coefficient C, respectively.

For example, if there are 25 classes of luminance signal filters and 12 types of filter coefficients C for each class as described above, it is necessary to set threshold values for 25×12=300 filter coefficients at maximum. Such a threshold value is determined by a parameter determination unit 150C, which will be described later, and transmitted to the image decoding device 200 side as additional information.

Here, in order to reduce the code amount related to the information related to the threshold, instead of transmitting the threshold itself as the information related to the threshold, which of several types of predetermined thresholds is selected for each filter coefficient. It is also possible to encode only index information indicating whether to use a threshold.

Further, when four types of threshold values for the luminance signal and four types of threshold values for the color difference signals are prepared in advance, the threshold values for the luminance signal and the threshold values for the color difference signals are defined as shown in FIG. 6A, for example. can be done.

Since the variance of the luminance signal tends to be larger than the variance of the color difference signal, as shown in FIG. Clipping processing can be performed in consideration of the characteristics of each signal.

That is, as shown in FIG. 6A, even if the internal bit depth ("bitdepth" in FIG. 6) changes, the magnitude relationship between the threshold for the luminance signal and the threshold for the color difference signal (for example, is greater than or equal to the threshold for the color difference signal) is preserved.

Also, as shown in FIG. 6A, the threshold for the luminance signal and the threshold for the color difference signal are defined to be calculated by multiplying each by the same multiplying value according to the change in the internal bit depth. may According to such a configuration, even if the internal bit depth changes, the magnitude relationship between the luminance signal threshold and the color difference signal threshold can be preserved, and similar clipping processing can be performed regardless of the internal bit depth.

Here, the internal bit depth means the bit precision when calculating the pixel values of the luminance signal and the color difference signal during the encoding process and the decoding process. Such internal bit depth takes an integer value of 8 to 16 bits, for example, and is transmitted from the image encoding device 100 side to the image decoding device 200 side as additional information.

Also, as shown in FIG. 6(a), by defining the scaling factor related to the internal bit depth as a power of 2, such clipping processing can be realized only by bit shifting as shown in FIG. 6(b). The processing load on hardware and software can be reduced.

That is, the threshold for luminance signal and the threshold for color difference signal may be defined so as to be calculated by bit-shifting according to changes in the internal bit depth.

Note that the threshold value corresponding to index 0 in FIGS. 6A and 6B is the same value as the maximum value that can be represented by the corresponding internal bit depth. Therefore, by selecting such a threshold, the filter coefficient C corresponding to such a threshold is substantially equivalent to not performing clipping processing.

In order to obtain the same effect as the above example, it is not necessary to set the same value for all thresholds as described above. In a predetermined internal bit depth domain (for example, 8 to 16 bits), the magnitude relationship of the thresholds corresponding to each index is not reversed in the luminance signal and the color difference signal, and the luminance signal and the color difference signal are not reversed. As long as it is guaranteed that the magnitude relationship of the thresholds corresponding to the same index is not reversed between the signals, there is no problem even if the magnification for each threshold is set to a different value.

When there are N kinds of luminance signal thresholds and chrominance signal thresholds (N is a natural number equal to or greater than 1) each assigned an index of 0 to N-1, luminance having the same index The threshold for the signal and the threshold for the color difference signal may be defined to be calculated by multiplying the same scale factor according to the internal bit depth.

Also, in the above example, the case where the threshold value is multiplied by the scaling factor according to the internal bit depth has been described, but processing may be performed in which an offset value is added instead of the scaling factor.

Note that even when the internal bit depth of the luminance signal and the internal bit depth of the color difference signal are different, by defining the threshold for the luminance signal and the threshold for the color difference signal as shown in FIG. And when converted so that the dynamic ranges of the color difference signals are the same, the magnitude relationship of the thresholds used in the clipping process between the luminance signal and the color difference signal can be defined so as not to always change.

Further, in the above example, the case where the threshold is set for each class and for each filter coefficient C has been described. A method of setting them one by one is also possible. In this case, since the number of thresholds to be transmitted is reduced, the amount of code associated with the threshold index can be reduced.

In addition, as will be described later, a flag indicating whether or not clipping processing is to be performed for each class is transmitted prior to the threshold index. It is no longer necessary to define a threshold value (equivalent to no clipping processing). Therefore, in the above-described example, the number of patterns that the threshold can take can be reduced from four to three, so that a further reduction in the amount of code associated with the index of the threshold can be expected.

In the above example, the case where different values are set for the threshold value for the luminance signal and the threshold value for the color difference signal has been described, but both may be set to the same value. As a result, for example, a circuit related to clipping processing of the luminance signal and the color difference signal can be shared in hardware, and the circuit scale can be reduced.

Further, even if the threshold value for the luminance signal and the threshold value for the color difference signal are defined to be calculated by performing calculations according to the current internal bit depth based on the case where the internal bit depth is 10 bits, good.

For example, in FIG. 6A, there are four thresholds of 1024, 181, 32, and 6 when the luminance signal is 10 bits, and four thresholds of 1024, 161, 25, and 4 when the color difference signal is 10 bits. An example of obtaining the final threshold value by multiplying the value of the current internal bit depth (bitdepth in FIG. 6) by a power of 2 is shown.

Here, in FIG. 6, the threshold value for 10 bits is represented by a specific numerical value (1024, 181, etc.), but this may be defined in the form of a formula.

For example, as shown in FIG. 7, the threshold for 10-bit luminance signal is set to "2^(10(10×(4-index)/4) (here, index=0, 1, 2, 3)). , and multiplied by "2^(bitdepth-10)" to obtain a final threshold according to the current internal bit depth.

Similarly, the definition of the color difference signal shown in FIG. )”, it can be considered that the threshold corresponding to the current internal bit depth is calculated.

The parameter determination unit 150C receives the input image signal and the pre-filtering decoded signal, determines parameters related to the adaptive loop filter, and outputs them as additional information to the encoding unit 140, and outputs the determined parameters to the filter unit 150B. is configured as

Parameters determined by the parameter determination unit 150C include, for example, the following.

First, such parameters include filter sets on a per-frame basis. Here, one filter set includes a maximum of 25 classes of luminance signal filters and one class of color difference signal filters. For each class of filter, a filter coefficient value, a flag indicating whether clipping processing is to be performed, a threshold index used in clipping processing for each filter coefficient when clipping processing is performed in this class, and the like are determined.

The parameter determination unit 150C can prepare a plurality of filter sets for a certain frame and select which filter set to use for each region as described later.

Secondly, such parameters include, for example, a flag indicating whether to apply an adaptive loop filter for each CTU. Note that, when an adaptive loop filter is applied, parameter determination section 150C can set index information indicating which of the plurality of filter sets is to be used.

Note that a known method can be used as a method for determining such parameters, so details thereof will be omitted.

Although not shown in FIG. 3, the parameter determination unit 150C may use the determination result of the class determination unit 150A or the result of the filter unit 150B performed with provisional parameter settings to determine the parameters.

(Image decoding device 200)
The image decoding device 200 according to this embodiment will be described below with reference to FIG. FIG. 7 is a diagram showing an example of functional blocks of the image decoding device 200 according to this embodiment.

As shown in FIG. 7, the image decoding device 200 includes a decoding unit 210, an inverse transform/inverse quantization unit 220, an adder 230, an inter prediction unit 241, an intra prediction unit 242, and an in-loop filtering unit. 250 and a frame buffer 260 .

The decoding unit 210 is configured to decode the encoded data generated by the image encoding device 100 and decode the coefficient level values.

Here, for example, the decoding is entropy decoding in a procedure opposite to the entropy encoding performed by the encoding unit 140 .

Further, the decoding unit 210 may be configured to acquire the control data by decoding the encoded data.

Note that, as described above, the control data may include size data such as the encoding block size, prediction block size, transform block size, and the like.

The inverse transform/inverse quantization unit 220 is configured to perform inverse transform processing on the coefficient level values output from the decoding unit 210 . Here, the inverse transform/inverse quantization unit 220 may be configured to perform inverse quantization of the coefficient level values prior to the inverse transform processing.

Here, the inverse transform processing and inverse quantization are performed in the reverse order of the transform processing and quantization performed by the transform/quantization unit 131 .

The adder 230 adds the prediction signal to the prediction residual signal output from the inverse transform/inverse quantization unit 220 to generate a pre-filtering decoded signal. It is configured to output to the filter processing unit 250 .

Here, the unfiltered decoded signal constitutes a reference block used in intra prediction section 242 .

Like the inter prediction section 111, the inter prediction section 241 is configured to generate a prediction signal by inter prediction (inter-frame prediction).

Specifically, the inter prediction unit 241 is configured to generate a prediction signal for each prediction block based on a motion vector decoded from encoded data and a reference signal included in a reference frame. The inter prediction section 241 is configured to output a prediction signal to the adder 230 .

The intra prediction unit 242, like the intra prediction unit 112, is configured to generate a prediction signal by intra prediction (intra-frame prediction).

Specifically, the intra prediction unit 242 is configured to identify a reference block included in the target frame and generate a prediction signal for each prediction block based on the identified reference block. The intra prediction section 242 is configured to output the prediction signal to the adder 230 .

Similar to in-loop filtering section 150, in-loop filtering section 250 performs filtering on the unfiltered decoded signal output from adder 230, and outputs the filtered decoded signal to frame buffer 260. is configured to

Here, for example, the filter processing is adaptive loop filter processing that reduces encoding distortion of a decoded image.

The frame buffer 260, like the frame buffer 160, is configured to accumulate reference frames used by the inter prediction section 241. FIG.

Here, the decoded signal after filtering constitutes a reference frame used in the inter prediction section 241 .

(In-loop filtering unit 250)
The in-loop filtering unit 250 according to this embodiment will be described below. FIG. 9 is a diagram showing the in-loop filtering unit 250 according to this embodiment.

As shown in FIG. 9, the in-loop filtering section 250 has a class determining section 250A and a filtering section 250B.

Class determination section 250A, like class determination section 150A, receives the unfiltered decoded signal as input, and outputs class determination information indicating which class of in-loop filter is to be used from among a plurality of types of predetermined in-loop filters. is configured to

Similar to the filter unit 150B, the filter unit 250B, based on the unfiltered decoded signal, the class determination information determined by the class determination unit 250A, and the parameters transmitted as additional information from the image coding apparatus 100 side, It is configured to perform filtering and output a filtered decoded signal.

FIG. 10 is a flowchart showing an example of the processing procedure of the in-loop filtering unit 250 of the image decoding device 200 according to this embodiment.

As shown in FIG. 10, in step S101, the in-loop filtering unit 250 receives the pre-filtering decoded signal, and selects which class of filter to use from among a plurality of types of predetermined in-loop filters. Output class determination information.

In step S102, the in-loop filtering unit 250, based on the unfiltered decoded signal, the class determination information determined by the class determination unit 250A, and the parameter transmitted as additional information from the image coding apparatus 100 side, Filter processing is performed, and a filtered decoded signal is output.

According to the image encoding device 100 and the image decoding device 200 according to the present embodiment, regarding the threshold processing of the input signal of the adaptive interpolation filter, the dynamic range of the luminance signal and the color difference signal is the same regardless of the setting of the internal bit depth. , the magnitude relationship between the threshold value for the luminance signal and the threshold value for the color difference signal is unchanged, so that it is possible to prevent the characteristics of the subjective image quality from changing unintentionally.

Note that the image encoding device 100 and the image decoding device 200 described above may be implemented as a program that causes a computer to execute each function (each process).

In the above-described embodiment, the present invention is applied to the image encoding device 100 and the image decoding device 200 as examples, but the present invention is not limited to such an example, and can be applied to the image encoding device. 100 and an image encoding/decoding system having each function of the image decoding apparatus 200.

DESCRIPTION OF SYMBOLS 10... Image processing system 100... Image encoding apparatus 111, 241... Inter prediction part 112, 242... Intra prediction part 121... Subtractor 122, 230... Adder 131... Transform/quantization part 132, 220... Inverse transform/inverse Quantization unit 140 Encoding units 150, 250 In-loop filtering units 150A, 250A Class determination units 150B, 250B Filter unit 150C Parameter determination units 160, 260 Frame buffer 200 Image decoding device 210 Decoding unit

Claims (3)

An image decoding device,
a class determination unit configured to determine which class of filter to use based on the unfiltered decoded signal;
a parameter determination unit configured to determine a filter coefficient for each class;
A filter unit configured to receive the pre-filtering decoded signal as an input and output a post-filtering decoded signal,
The filter section controls the reference pixel value and the pixel value of the pre-filter decoded signal so that an absolute value of a difference value between the reference pixel value and the pixel value of the pre-filter decoded signal is equal to or less than a predetermined threshold value. and generating the post-filter decoded signal by linearly weighting the sum of the value after the clipping, the filter coefficient, and the pixel value of the pre-filter decoded signal. is configured to
The threshold is set for each class and each filter coefficient,
is defined so that the magnitude relationship between the threshold for the luminance signal and the threshold for the color difference signal is preserved even if the internal bit depth changes,
An image decoding apparatus, wherein the threshold is doubled when the internal bit depth is increased by one. An image decoding method comprising:
A step A of determining which class of filter to use with the unfiltered decoded signal as an input;
A step B of determining filter coefficients for each class;
a step C of inputting the unfiltered decoded signal and outputting a filtered decoded signal;
In step C, pixel values of the reference pixel value and the pre-filter decoded signal are adjusted so that an absolute value of a difference value between the reference pixel value and the pre-filter decoded signal is equal to or less than a predetermined threshold value. performing clipping processing on the difference value between and generating the filtered decoded signal by a linearly weighted sum of the value after the clipping processing, the filter coefficient, and the pixel value of the pre-filtered decoded signal;
The threshold is set for each class and each filter coefficient,
is defined so that the magnitude relationship between the threshold for the luminance signal and the threshold for the color difference signal is preserved even if the internal bit depth changes,
An image decoding method, wherein the threshold is defined to be doubled when the internal bit depth is increased by one. A program that causes a computer to function as an image decoding device,
a class determination unit configured to determine which class of filter to use based on the unfiltered decoded signal;
a parameter determination unit configured to determine a filter coefficient for each class;
A filter unit configured to receive the pre-filtering decoded signal as an input and output a post-filtering decoded signal,
The filter section controls the reference pixel value and the pixel value of the pre-filter decoded signal so that an absolute value of a difference value between the reference pixel value and the pixel value of the pre-filter decoded signal is equal to or less than a predetermined threshold value. and generating the post-filter decoded signal by linearly weighting the sum of the value after the clipping, the filter coefficient, and the pixel value of the pre-filter decoded signal. is configured to
The threshold is set for each class and each filter coefficient,
is defined so that the magnitude relationship between the threshold for the luminance signal and the threshold for the color difference signal is preserved even if the internal bit depth changes,
A program, wherein the threshold is defined to be doubled when the internal bit depth is increased by one.