JP7315509B2 - 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.

Non-Patent Document 1 defines that one of the application conditions for BDPCM (Block-wise Differential Pulse-Code Modulation) is to determine whether the size of a coded block is equal to or less than the maximum size of the transform skip mode.

Versatile Video Coding (Draft 8), JVET-Q2001

However, in Non-Patent Document 1, the inventors of the present application have found a problem that the maximum size of the transform skip mode is determined independently of the maximum size of the transform block, so that the maximum size of the transform skip mode used to determine the BDPCM application condition and the transform block size for which the actual transform skip processing is performed may not match.

Therefore, the present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an image decoding device, an image decoding method, and a program that can realize determination of BDPCM application conditions in consideration of the transform block size in which the transform skip process is actually performed by using both the maximum size of the transform skip mode and the maximum size of the transform block as the conditions for applying the BDPCM.

A first feature of the present invention is an image decoding device comprising an intra-prediction mode decoding unit configured to use both the maximum size of a transform skip mode and the maximum size of a transform block as a predetermined condition for determining whether or not BDPCM can be applied to a coded block.

A second aspect of the present invention is summarized in comprising the step of using both the transform skip mode maximum size and the transform block maximum size as predetermined conditions for determining whether BDPCM is applicable to a coded block.

A third feature of the present invention is a program for use in an image decoding device, the gist of which is to cause a computer to execute a step of using both the maximum size of a transform skip mode and the maximum size of a transform block as predetermined conditions for determining whether or not BDPCM can be applied to an encoded block.

According to the present invention, by using both the maximum size of the transform skip mode and the maximum size of the transform block as the conditions for applying BDPCM, it is possible to provide an image decoding device, an image decoding method, and a program that can determine the conditions for applying BDPCM in consideration of the transform block size in which transform skip processing is actually performed.

It is a figure showing an example of composition of image processing system 10 concerning 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 intra prediction unit 242 of the image decoding device 200 according to one embodiment; FIG. FIG. 11 is a flowchart showing an example of a flow of decoding processing in an intra prediction mode of a luminance signal by an intra prediction mode decoding unit 242B of an intra prediction unit 242 of the image decoding device 200 according to one embodiment; FIG. 10 is a flowchart showing an example of a flow of decoding processing in an intra prediction mode of a color difference signal by an intra prediction mode decoding unit 242B of an intra prediction unit 242 of the image decoding device 200 according to an embodiment; FIG. 10 is a diagram showing how a luminance CU and a chrominance CU are each divided into four TUs when MaxTbSizeY=32; 1 is a diagram showing an example of functional blocks of an image encoding device 100 according to an embodiment; FIG. 3 is a diagram showing an example of functional blocks of an intra prediction unit 112 of the image encoding device 100 according to one embodiment; FIG. FIG. 11 is a flowchart showing an example of a flow of decoding processing in an intra prediction mode of a luminance signal by an intra prediction mode decoding unit 242B of an intra prediction unit 242 of the image decoding device 200 according to one embodiment; FIG. 10 is a flowchart showing an example of a flow of decoding processing in an intra prediction mode of a color difference signal by an intra prediction mode decoding unit 242B of an intra prediction unit 242 of the image decoding device 200 according to an embodiment; FIG. 11 is a table showing an example of the correspondence between the maximum size of a transform block, MaxTsSize, and BDPCM applicability; FIG. 3 is a table showing an example of correspondence between color formats, maximum sizes of conversion blocks, and MaxTsSize;

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 the 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 8. 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 line. 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 decoding device 200)
The image decoding device 200 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 decoding device 200 according to this embodiment.

As shown in FIG. 2, 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, 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, decoding is decoding of entropy-encoded data that assigns codes of different lengths based on the probability of occurrence of coefficient level values.

The decoding unit 210 may be configured to obtain the control data by decoding the encoded data.

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 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.

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, and outputs the pre-filtering decoded signal to the intra prediction unit 242 and the in-loop filtering unit 250.

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

The inter prediction unit 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 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 .

The in-loop filtering section 250 is configured to filter the unfiltered decoded signal output from the adder 230 and output the filtered decoded signal to the frame buffer 260 .

Here, the in-loop filtering process may consist of a plurality of filtering processes. For example, the filter processing is deblocking filter processing that reduces distortion occurring at the boundary of blocks (encoding blocks, prediction blocks, transform blocks, or sub-blocks obtained by dividing them), or adaptive loop filtering that switches filters based on filter coefficients, filter selection information, local properties of image patterns, etc. transmitted from the image encoding device 100.

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

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

(Intra prediction unit 242)
The intra prediction unit 242 according to this embodiment will be described below with reference to FIG. FIG. 3 is a diagram showing an example of functional blocks of the intra prediction unit 242 of the image decoding device 200 according to this embodiment.

As shown in FIG. 3, the intra prediction unit 242 has an intra prediction mode decoding unit 242B and a prediction signal generation unit 242C.

The intra prediction unit 242 is an example of a prediction unit configured to generate a prediction signal by intra prediction (intra-frame prediction).

The intra-prediction mode decoding unit 242B is configured to decode information necessary to perform intra-prediction for each block.

FIG. 4 is a flowchart showing an example of a flow of decoding processing in the intra prediction mode of the luminance signal by the intra prediction mode decoding unit 242B. An example of the flow of the intra prediction mode decoding process of the luminance signal by the intra prediction mode decoding unit 242B will be described below with reference to FIG.

In step S401, the intra-prediction mode decoding unit 242B determines whether or not the predetermined condition 1 is satisfied.

Such predetermined condition 1 may include a condition that the width of the target CU is equal to or less than the maximum size (for example, MaxTsSize in Non-Patent Document 1) when applying Transform Skip.

The predetermined condition 1 may also include a condition that the height of the target CU is equal to or less than the maximum size (for example, MaxTsSize in Non-Patent Document 1) when applying Transform Skip.

Here, the width and height of the CU may be the CU size (width/height) of the luminance signal.

A specific value of MaxTsSize may be determined by the image encoding device 100 and included in the control data decoded by the decoding unit 210 . Possible values for MaxTsSize may be 4, 8, 16, 32, for example.

Similarly, a specific value of the maximum size of the transform block (TU) of the luminance signal (for example, MaxTbSizeY in Non-Patent Document 1) may also be determined by the image encoding device 100 and included in the control data decoded by the decoding unit 210. Possible values for MaxTbSizeY may be 32 and 64.

For example, when MaxTbSizeY is set to 32, a CU with a width or height greater than 32 is divided into a plurality of TUs so that both the width and height are 32 pixels or less, and then the inverse transformation is performed. For example, as shown in FIG. 6, a luminance (Y signal) CU with a size of 64×64 pixels is divided into four TUs of 32×32 pixels.

When the above two conditions are included in the predetermined condition 1, even if MaxTsSize is set to the maximum possible value (32), the CU that satisfies the above-described predetermined condition 1 is always 32×32 pixel size or less.

On the other hand, since the minimum value of MaxTbSizeY is 32, the size of a CU that satisfies the predetermined condition 1 including the above two conditions is always MaxTbSizeY or less, so such a CU is not split into multiple TUs, and CU size=TU size.

FIG. 12 shows the relationship between the maximum size of the transform block when MaxTsSize=32 and the color format of the decoded image (4:2:0, 4:2:2 or 4:4:4) and MaxTbSizeY are changed, and the maximum size when Transform Skip is applied.

As described above, when MaxTbSizeY=32 (Nos. 4 to 6 in FIG. 12), both the maximum transform block size of the luminance signal and the maximum transform skip size of the luminance signal are 32×32 pixels.

Furthermore, the predetermined condition 1 may include a condition that BDPCM (Block DPCM) is enabled in SPS (Sequence Parameter Set) (for example, the value of sps_bdcpm_enabled_flag is greater than "0").

If all of the predetermined conditions 1 are satisfied, the process proceeds to step S402, and if even one of them is not satisfied, the process proceeds to step S403.

In step S402, the intra prediction mode decoding unit 242B decodes intra_bdpcm_luma_flag.

If the value of intra_bdpcm_luma_flag is '1', it means that BDPCM is applied in the corresponding luminance CU, and if the value of intra_bdpcm_luma_flag is '0', it means that BDPCM is not applied in this luminance CU.

In step S403, the intra prediction mode decoding unit 242B determines whether the value of intra_bdpcm_luma_flag is greater than "0".

If the value of intra_bdpcm_luma_flag is greater than "0", the process proceeds to step S408; otherwise, the process proceeds to step S404.

In addition, when the above-mentioned predetermined condition 1 is not satisfied and the process of step S402 is skipped, the intra prediction mode decoding unit 242B regards the value of intra_bdpcm_luma_flag as "0".

In step S408, the intra prediction mode decoding unit 242B decodes intra_bdpcm_luma_dir_flag. intra_bdpcm_luma_dir_flag indicates whether prediction is performed from the vertical direction or from the horizontal direction when BDPCM is applied to the luminance CU.

After the process of step S408 ends, the process proceeds to step S410 and ends.

In step S404, the intra-prediction mode decoding unit 242B determines whether or not the predetermined condition 2 is satisfied.

Here, the predetermined condition 2 may include a condition that MIP (matrix-based intra prediction) can be used in the luminance CU.

If the predetermined condition 2 is satisfied, the process proceeds to step S405; otherwise, the process proceeds to step S406.

In step S405, the intra prediction mode decoding unit 242B decodes intra_mip_flag.

When the value of intra_mip_flag is '1', it means that MIP is applied to the luminance CU, and when the value of intra_mip_flag is '0', it means that MIP is not applied to the luminance CU.

In step S406, the intra prediction mode decoding unit 242B determines whether the value of intra_mip_flag is greater than "0".

If the value of intra_mip_flag is greater than "0", the process proceeds to step S409; otherwise, the process proceeds to step S407.

In addition, when the above-mentioned predetermined condition 2 is not satisfied and the process of step S405 is skipped, the intra prediction mode decoding unit 242B regards the value of intra_mip_flag as "0".

In step S409, the intra-prediction mode decoding unit 242B decodes syntax necessary for MIP processing.

After the process of step S409 ends, the process proceeds to step S410 and ends.

In step S407, the intra-prediction mode decoding unit 242B decodes syntax such as the normal intra-prediction mode and whether intra sub-division is applied.

After the process of step S407 ends, the process proceeds to step S410 and ends.

As described above, the condition that the size (width or height) of the luminance CU is equal to or smaller than MaxTsSize is included in the determination of whether or not the luminance BDPCM can be applied. As described above, regardless of the set value of MaxTbSizeY, the CU to which the luminance BDPCM can be applied is not divided into a plurality of TUs, and the CU size is always equal to the TU size.

FIG. 5 is a flow chart showing an example of a decoding process flow in intra prediction mode for color difference signals by the intra prediction mode decoding unit 242B. An example of the intra prediction mode decoding processing flow of the color difference signal by the intra prediction mode decoding unit 242B will be described below with reference to FIG.

In step S501, the intra-prediction mode decoding unit 242B determines whether or not the predetermined condition 3 is satisfied.

The predetermined condition 3 described above may include a condition that the width of the CU is less than or equal to MaxBdpcmWidthC calculated by a method described later.

Further, the predetermined condition 3 may include a condition that the height of the CU is less than or equal to MaxBdpcmHeightC calculated by a method described later.

Here, the width and height of the CU are the actual CU size (width/height) of the color difference signal according to the sampling ratio of the color difference signal. For example, in the case of YUV 4:2:0 sampling, the CU size (width/height) of the chrominance signal is half that of the luma signal.

MaxBdpcmWidthC and MaxBdpcmHightC may be calculated as follows. Note that Min( ) is a function that returns the minimum value among the arguments.

MaxBdpcmWidthC=Min(maxTbWidth, MaxTsSize)
MaxBdpcmHeightC=Min(maxTbHeight, MaxTsSize)
Here, maxTbWidth and maxTbHeight are the maximum TU size (MaxTbSizeY) of the luminance signal and the maximum TU size of the color difference signal determined according to the color format (4:2:0, 4:2:2 or 4:4:4), and are specifically calculated as follows.

maxTbWidth=MaxTbSizeY/SubWidthC
maxTbHeight=MaxTbSizeY/SubHeightC
where SubWidthC is "2" for 4:2:0 and 4:2:2 formats, and "1" otherwise. SubHeightC is "2" for 4:2:0 format and "1" otherwise.

For example, if the format is 4:2:0 and the value of MaxTbSizeY is 32 (the smallest possible value), then maxTbWidth and maxTbHeight will both be 16. On the other hand, if the value of MaxTbSize is 32 (maximum possible value), MaxBdpcmWidthC and MaxBdpcmHeightC are assigned the smaller values of 16 and 32, respectively, so both are 16.

The above example corresponds to No. 4 in FIG. In this case, for example, a 32×32 pixel size chrominance CU is divided into four 16×16 pixel size TUs as shown in FIG.

That is, the intra-prediction mode decoding unit 242B is configured to use both MaxTsSize (maximum size of the transform skip mode) and MaxTbSizeY (maximum size of the transform block) as the predetermined condition 3 for determining whether or not the chroma BDPCM can be applied to the chroma CU (encoding block).

As described above, by including the condition that the width of the color difference CU is MaxBdpcmWidthC and the height of the color difference CU is MaxBdpcmHeightC or less in the predetermined condition 3, it is ensured that the CU size that satisfies the predetermined condition 3 is always maxTbWidth and maxTbHeight or less. Therefore, the CU is not divided into a plurality of TUs, and it is ensured that CU size=TU size.

Predetermined condition 3 may include a condition that BDPCM (Block-wise DPCM) is enabled in SPS (Sequence Parameter Set) (for example, the value of sps_bdpcm_chroma_enabled_flag is greater than “0”).

If all of the predetermined conditions 3 are satisfied, the process proceeds to step S502, and if even one of them is not satisfied, the process proceeds to step S503.

In step S502, the intra prediction mode decoding unit 242B decodes intra_bdpcm_chroma_flag.

If the value of intra_bdpcm_chroma_flag is '1', it means that BDPCM is applied in the chrominance CU, and if the value of intra_bdpcm_chroma_flag is '0', it means that BDPCM is not applied.

In step S503, the intra prediction mode decoding unit 242B determines whether the value of intra_bdpcm_chroma_flag is greater than "0".

If the value of intra_bdpcm_chroma_flag is greater than "0", the process proceeds to step S508; otherwise, the process proceeds to step S504.

In addition, when the process of step S502 is skipped without satisfy|filling the predetermined condition 3, the intra prediction mode decoding part 242B regards the value of intra_bdpcm_chroma_flag as "0".

In step S508, the intra prediction mode decoding unit 242B decodes intra_bdpcm_chroma_dir_flag.

intra_bdpcm_chroma_dir_flag indicates whether prediction is performed from the vertical direction or from the horizontal direction when BDPCM is applied to the chrominance CU.

After the process of step S508 ends, the process proceeds to step S510 and ends.

In step S504, the intra-prediction mode decoding unit 242B determines whether or not the predetermined condition 4 is satisfied.

Here, the predetermined condition 4 may include a condition that CCLM (color difference linear prediction) can be used in the relevant color difference CU.

If the predetermined condition 4 is satisfied, the process proceeds to step S505; otherwise, the process proceeds to step S506.

In step S505, the intra prediction mode decoding unit 242B decodes cclm_mode_flag.

When the value of cclm_mode_flag is "1", it means that CCLM is applied in the relevant color difference CU, and when the value of cclm_mode_flag is "0", it means that CCLM is not applied in the relevant color difference CU.

In step S506, the intra prediction mode decoding unit 242B determines whether the value of cclm_mode_flag is greater than "0".

If the value of cclm_mode_flag is greater than "0", the process proceeds to step S509; otherwise, the process proceeds to step S507.

In addition, when the above-mentioned predetermined condition 4 is not satisfied and the process of step S505 is skipped, the intra-prediction mode decoding unit 242B regards the value of cclm_mode_flag as "0".

In step S509, the intra prediction mode decoding unit 242B decodes cclm_mode_idx.

After the process of step S509 ends, the process proceeds to step S510 and ends.

In step S507, the intra prediction mode decoding unit 242B decodes the normal intra prediction mode (intra_chroma_pred_mode).

After the process of step S507 ends, the process proceeds to step S510 and ends.

As described above, by including the condition that the width of the chrominance CU is equal to or less than the smaller value of MaxTsSize and maxTbWidth and the height of the chrominance CU is equal to or less than the smaller value of MaxTsSize and maxTbHeight in the determination of whether or not to apply the chrominance BDPCM, as described above, the chrominance BDPCM can be applied regardless of the set value of MaxTbSizeY. A CU is never split into multiple TUs, and it is guaranteed that CU size=TU size.

Furthermore, as described above, it is guaranteed that CU size=TU size for CUs to which luminance BDPCM can be applied. Therefore, with the configuration described above, it is guaranteed that CU size=TU size for CUs to which BDPCM can be applied regardless of luminance and color difference.

A specific example of the above is shown in FIG. FIG. 11 is a table summarizing the luminance TU size corresponding to the luminance (Luma) CU size, the chroma CU size, the chroma TU size, and the BDPCM applicability when the color format is 4:2:0, MaxTsSize=32 (maximum possible value), and MaxTbSizeY=32 (minimum possible value).

Note that the value of the CU size Luma is merely an example, and the variations of the CU size are not limited to those listed in the table.

For example, in Non-Patent Document 1, blocks of sizes such as 64×16 and 64×8 can also be used. In Non-Patent Document 1, the size (height and width) of the chrominance CU is equal to or smaller than MaxTsSize, as in the case of the luminance BDPCM, in determining the application of the chrominance BDPCM.

Therefore, in the cases of Nos. 4 to 6 in FIG. 11, since the width or height is greater than 32 in the luminance CU, the BDPCM cannot be applied, but in the chrominance CU. BDPCM is applicable since both width and height are 32 or less.

On the other hand, in cases Nos. 4 to 6, both the luminance CU and the chrominance CU are divided into a plurality of TUs. On the other hand, in the first embodiment, with the configuration as described above, BDPCM can be applied only when the CU size=TU size for both the luminance signal and the color difference signal (corresponding to cases Nos. 7 to 10).

This makes it possible to reduce the number of combinations relating to the prediction mode (BDPCM), CU size, and presence/absence of TU partitioning, thereby facilitating design and verification of the image decoding device 200 .

242 C of prediction signal production|generation parts shown in FIG. 3 are comprised so that a prediction signal may be produced|generated based on the prediction mode of the block to be processed decoded by the intra prediction mode decoding part 242B. Here, for example, a known method described in Non-Patent Document 1 can be used as a method for generating the prediction signal.

(Image encoding device 100)
The image coding apparatus 100 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 encoding device 100 according to this embodiment.

As shown in FIG. 7, 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 unit 132, an encoding unit 140, an in-loop filtering unit 150, and a frame buffer 160.

The inter prediction unit 111, like the inter prediction unit 241, is configured to generate a prediction signal by inter prediction (inter-frame prediction).

Specifically, the inter prediction unit 111 is configured to identify a reference block included in the reference frame by comparing a frame to be encoded (hereinafter referred to as the target frame) and a reference frame stored in the frame buffer 160, and to determine a motion vector for the identified 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, like the intra prediction unit 242, 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, and outputs the pre-filtering decoded signal to the intra prediction unit 112 and the in-loop filtering 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 transform processing, a base pattern (transformation matrix) corresponding to a discrete cosine transform (DCT) may be used, or a base pattern (transformation matrix) corresponding to a discrete sine transform (DST) may be used.

Like the inverse transform/inverse quantization unit 220 , 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.

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.

Like the in-loop filtering unit 250, the in-loop filtering unit 150 is configured to perform filtering on the unfiltered decoded signal output from the adder 122 and to output the filtered decoded signal to the frame buffer 160.

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 .

(Intra prediction unit 112)
The intra prediction unit 112 according to this embodiment will be described below with reference to FIG. FIG. 8 is a diagram showing an example of functional blocks of the intra prediction unit 112 of the image encoding device 112 according to this embodiment.

As shown in FIG. 8, the intra prediction unit 112 has an intra prediction mode determination unit 112A, an intra prediction mode coding unit 112B, and a prediction signal generation unit 112C.

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

The intra-prediction mode determination unit 112A is configured to determine information to be encoded by the subsequent intra-prediction mode encoding unit 112B, such as the intra-prediction mode of the block and whether or not BDPCM is applied. Since a known method can be used for the determination method, the details are omitted.

The intra prediction mode encoding unit 112B is configured to encode the prediction mode of the target block. The processing contents are the same as those of the intra prediction mode decoding unit 242B. Specifically, for example, in the processing flowcharts of the intra-prediction mode decoding unit 242B shown in FIGS. 4 and 5, the “decoding” portion is changed to “encoding”.

112 C of prediction signal production|generation parts are comprised so that the prediction signal of the said block may be produced|generated according to the prediction mode encoded by intra prediction mode 112B. The prediction signal generation method is the same as that of the prediction signal generator 242C.

(Second embodiment)
A second embodiment of the present invention will be described below with reference to FIGS. 9 to 10. FIG. In the following description, only the differences from the first embodiment will be described, and the description of the same processing as in the first embodiment will be omitted.

FIG. 9 is a flowchart showing an example of a decoding processing flow of the intra prediction mode of the luminance signal by the intra prediction mode decoding unit 242B. 9 is the same as the processing of the first embodiment described using FIG. 4, except that step S401 in FIG. 4 is replaced with step S901.

In step S901, the intra-prediction mode decoding unit 242B determines whether or not the predetermined condition 5 is satisfied.

The predetermined condition 5 may include a condition that the width of the CU is less than or equal to MaxBdpcmSizeY calculated by a method described later.

Further, the predetermined condition 5 may include a condition that the height of the CU is equal to or less than MaxBdpcmSizeY calculated by a method described later.

MaxBdpcmSizeY may be calculated as follows.

MaxBdpcmSizeY=(MaxTbSizeY>MaxTsSize)? MazTsSize: CtbSizeY
where a? b:c is a function that returns the value of b when condition a is true and returns the value of c when condition a is false.

Therefore, for example, when MaxTbSizeY is 64 and MaxTsSize is 32, the value of MaxBdpcmSizeY is MaxTsSize (=32).

Similarly, for example, if MaxTbSizeY is 32 and MaxTsSize is 32, the value of MaxBdpcmSizeY will be CtbSizeY. CtbSizeY is the maximum size of the CU, and can take values of 32, 64, and 128 in Non-Patent Document 1, for example. In this case, that is, when MaxTbSizeY≦MaxTsSize and MaxBdpcmSizeY=CtbSizeY, the predetermined condition 5 means that the width and height of the CU are equal to or less than the maximum size of the CU, so the predetermined condition 5 is satisfied for all CUs.

In Non-Patent Document 1, Transform Skip (TS) must always be applied to TUs corresponding to CUs to which BDPCM is applied. However, as described above, when MaxTbSizeY (maximum size of TU) is MaxTsSize (maximum size of TU applicable to TS) or less, TS can be applied to all TUs.

That is, the intra-prediction mode decoding unit 242B is configured to use both MaxTSize (maximum size of transform skip mode) and MaxTbSizeY (maximum size of transform block) as predetermined condition 5 for determining whether or not luma BDPCM can be applied to luma CU (encoding block).

Therefore, as described above, even if BDPCM can be applied to all CU sizes, it is possible to increase the number of CU size patterns to which BDPCM can be applied, compared to the first embodiment, while ensuring the constraint of Non-Patent Document 1 (TS is always applied to TUs corresponding to CUs to which BDPCM is applied).

Furthermore, the predetermined condition 5 may include a condition that BDPCM (Block-wise DPCM) is enabled in SPS (Sequence Parameter Set) (for example, the value of sps_bdpcm_enabled_flag is greater than "0").

If all of the predetermined conditions 5 are satisfied, the process proceeds to step S402, and if even one of them is not satisfied, the process proceeds to step S403.

As described above, when maxTbWidth and maxTbHeight are equal to or less than MaxTsSize, by enabling BDPCM to be applied to all CUs as described above, it is possible to increase the number of CU size patterns to which BDPCM can be applied, compared to the first embodiment, while ensuring the constraint of Non-Patent Document 1 (TS is always applied to TUs corresponding to CUs to which BDPCM is applied). This is expected to improve coding efficiency (see FIG. 11).

FIG. 10 is a flow chart showing an example of a decoding process flow of the intra prediction mode of the color difference signal by the intra prediction mode decoding unit 242B. 10 is the same as the processing of the first embodiment described using FIG. 5, except that step S501 of FIG. 5 is replaced with step S1001.

In step S1001, the intra-prediction mode decoding unit 242B determines whether or not the predetermined condition 6 is satisfied.

The predetermined condition 6 may include a condition that the width of the CU is less than or equal to MaxBdpcmWidthC calculated by a method described later.

Further, the predetermined condition 6 may include a condition that the height of the CU is equal to or less than MaxBdpcmHeightC calculated by a method described later.

Here, the width and height of the CU are the actual CU size (width/height) of the color difference signal according to the sampling ratio of the color difference signal. For example, in the case of YUV 4:2:0 sampling, the CU size (width/height) of the chrominance signal is half that of the luma signal.

MaxBdpcmWidthC and MaxBdpcmHeightC may be calculated as follows.

MaxBdpcmWidthC=(maxTbWidth>MaxTsSize)? MaxTsSize: CtbSizeY/SubWidthC
MaxBdpcmHeightC=(maxTbHeight>MaxTsSize)? MaxTsSize: CtbSizeY/SubHeightC
That is, the intra-prediction mode decoding unit 242B is configured to use both MaxTSize (maximum size of transform skip mode) and MaxTbSizeY (maximum size of transform block) as predetermined condition 1 for determining whether chroma BDPCM can be applied to chroma CU (encoding block).

As in the case of the luminance CU described with reference to FIG. 9, for example, when maxTbWidth is MaxTsSize or less and maxTbHeight is MaxTsSize or less, MaxBdpcmWidthC is CtbSizeY/SubWidthC (the maximum value of the width of the color difference CU), and MaxBdpcmHeightC is CtbSizeY/SubHeightC (maximum height of color difference CU). Therefore, in this case, the predetermined condition 6 is satisfied for all color difference CUs.

Also, as in the case of the luminance CU, even if BDPCM can be applied to all CU sizes, it is possible to increase the number of chrominance CU size patterns to which BDPCM can be applied, compared to the first embodiment, while ensuring the constraint of Non-Patent Document 1 (TS is always applied to TUs corresponding to CUs to which BDPCM is applied).

Furthermore, the predetermined condition 6 may include a condition that BDPCM (Block-wise DPCM) is enabled in SPS (Sequence Parameter Set) (for example, the value of sps_bdcpm_enabled_flag is greater than "0").

If all of the predetermined conditions 6 are satisfied, the process proceeds to step S502, and if even one of them is not satisfied, the process proceeds to step S503.

As described above, when maxTbWidth and maxTbHeight are equal to or less than MaxTsSize, by making BDPCM applicable to all color difference CUs as described above, it is possible to increase the number of CU size patterns to which BDPCM can be applied as compared to the first embodiment while ensuring the constraint of Non-Patent Document 1 (TS is always applied to TUs corresponding to CUs to which BDPCM is applied). This is expected to improve coding efficiency.

Also, 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 embodiments, 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 examples, and can be applied to an image encoding/decoding system having the functions of the image encoding device 100 and the image decoding device 200.

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

Claims (8)

An image decoding device,
An intra-prediction mode decoding unit configured to use both the maximum size of the transform skip mode and the maximum size of the transform block as a predetermined condition for determining whether BDPCM can be applied to the encoded block ,
The intra prediction mode decoding unit is configured to determine that BDPCM can be applied to the coded block when the size of the coded block is equal to or smaller than the smaller of the maximum size of the transform skip mode and the maximum size of the transform block. An image decoding device characterized by being configured to determine. The intra prediction mode decoding unit is configured to determine that BDPCM can be applied to the coding block when the width of the coding block is equal to or less than the smaller one of the maximum size of the transform skip mode and the maximum width of the transform block, and the height of the coding block is equal to or less than the smaller value of the maximum size of the transform skip mode and the maximum value of the transform block height. An image decoding device,
An intra-prediction mode decoding unit configured to use both the maximum size of the transform skip mode and the maximum size of the transform block as a predetermined condition for determining whether BDPCM can be applied to the encoded block,
The intra prediction mode decoding unit is configured to determine that BDPCM can be applied to the coded blocks of all sizes when the maximum size of the transform block is equal to or less than the maximum size of the transform skip mode. An image decoding device. The image decoding device according to claim 3 , wherein the intra-prediction mode decoding unit is configured to determine that BDPCM can be applied to the coded blocks of all sizes when the maximum value of the width of the transform block is equal to or less than the maximum size of the transform skip mode and the maximum value of the height of the transform block is equal to or less than the maximum size of the transform skip mode. using both a transform skip mode maximum size and a transform block maximum size as predetermined conditions for determining whether BDPCM is applicable to an encoded block ;
In the step, if the size of the encoded block is equal to or smaller than the smaller one of the maximum size of the transform skip mode and the maximum size of the transform block, it is determined that BDPCM can be applied to the encoded block. An image decoding method. A program for use in an image decoding device, causing a computer to execute a step of using both the maximum size of a transform skip mode and the maximum size of a transform block as predetermined conditions for determining whether or not BDPCM can be applied to an encoded block ,
In the above step, if the size of the encoded block is equal to or smaller than the smaller value of the maximum size of the transform skip mode and the maximum size of the transform block, it is determined that BDPCM can be applied to the encoded block. using both a transform skip mode maximum size and a transform block maximum size as predetermined conditions for determining whether BDPCM is applicable to an encoded block;
The image decoding method, wherein, in the step, when the maximum size of the transform block is equal to or less than the maximum size of the transform skip mode, it is determined that BDPCM is applicable to the coding blocks of all sizes. A program for use in an image decoding device, causing a computer to execute a step of using both the maximum size of a transform skip mode and the maximum size of a transform block as predetermined conditions for determining whether or not BDPCM can be applied to an encoded block,
The program, wherein in the step, when the maximum size of the transform block is equal to or less than the maximum size of the transform skip mode, it is determined that BDPCM is applicable to the coding blocks of all sizes.

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