JP7122838B2 - Encoding device, decoding device and program - Google Patents

Description

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

In a moving image (video) coding method represented by H.265/HEVC (High Efficiency Video Coding), after dividing the entire screen into large blocks (coding tree units: Coding Tree Units/CTUs), they are further divided into In order to control the encoding mode in detail, it is configured to be divided into encoding target blocks (encoding units: Coding Units/CUs).

In HEVC, for each encoding target block, prediction is performed while switching between two types of prediction, inter prediction using temporal correlation between frames and intra prediction using spatial correlation within a frame, and a residual signal is obtained. is generated, and then orthogonal transform processing, loop filter processing, and entropy coding processing are performed, and the obtained stream is output.

In addition, in HEVC, the block division shape is not independently controlled by the luminance signal (Luma) and the color difference signals (Chroma: Cb and Cr) that constitute the color image. In order to make the block division shape more flexible, it is possible to independently control the division shape of the luminance signal block and the division shape of the color difference signal block in the intra frame.

In intra prediction in HEVC, a target block is predicted by planar prediction, DC prediction, directional prediction, or the like, using decoded pixels adjacent to the upper side or left side of the target block as reference pixels.

"Algorithm Description of Joint Exploration Test Model 5 (JEM5) (JVET-E1001-v2)", Joint Video Exploration Team (JVET) of ITU-T SG16 WP3 and ISO/GSC1W/IEC J2TC9

However, in the existing HEVC, reference pixels used for intra prediction cannot be used as reference pixels if they are outside the image edge or slice boundary, or have not been coded. As shown, those reference pixel values (e.g., reference pixels in region R1 in FIG. 7) are copied such that neighboring available reference pixel values (e.g., reference pixels in region R2 in FIG. 7) are copied. It is configured.

As described above, there is a problem that the prediction efficiency is lowered when the reference pixels used for intra prediction cannot be used and the reference pixels are configured by copies of other neighboring pixels.

In particular, in Non-Patent Document 1, since it is possible to independently control the division shape of the luminance signal block and the division shape of the color difference signal block, pixels adjacent to the color difference signal block cannot be used as reference pixels. However, there are cases where the luminance signal pixels at positions corresponding to the reference pixels of the color difference signal block have been decoded and can be referenced, and the color difference signal pixels and the luminance signal that exist at positions corresponding to each other Although there is a correlation with the pixels of , Non-Patent Document 1 does not consider this point.

Specifically, in Non-Patent Document 1, as shown in FIG. 8B, a pixel P1 included in a block C3 adjacent to a color-difference signal block C2 has not been decoded and cannot be used as a reference pixel. However, as shown in FIG. 8A, even in the case where the pixel P2 of the luminance signal at the position corresponding to the position of the pixel P1 has been decoded and can be referred to, adjacent available reference pixels (for example, the reference pixels in the region R2 in FIG. 7) are copied, there is also the problem that the prediction efficiency decreases.

Therefore, the present invention has been made to solve the above-described problems, and makes it possible to prevent deterioration of prediction efficiency to a minimum even when reference pixels for color difference signals cannot be used. An object is to provide an encoding device, a decoding device, and a program.

A first feature of the present invention is an encoding apparatus configured to divide an original image in units of frames constituting a moving image into separate blocks for luminance signals and color difference signals and encode them. and determining whether or not to correct the reference pixels of the encoding target block of the chrominance signal according to an intra prediction mode applied to the encoding target block of the chrominance signal. a decoded chrominance signal adjacent to an encoding target block of the chrominance signal, and a decoded luminance signal at a position corresponding to the decoded chrominance signal, to derive a prediction parameter. and a correction unit configured to correct the reference pixel using the prediction parameter and the decoded luminance signal at a position corresponding to the reference pixel. is the gist.

A second feature of the present invention is a decoding device configured to be able to divide an original image in units of frames that constitute a moving image into separate blocks for luminance signals and color-difference signals and decode them. a determination unit configured to determine whether or not to perform correction on reference pixels of the decoding target block of the chrominance signal according to an intra prediction mode applied to the decoding target block of the chrominance signal; A derivation unit configured to derive a prediction parameter using a decoded color difference signal adjacent to a decoding target block of the color difference signal and a decoded luminance signal at a position corresponding to the decoded color difference signal. and a correction unit configured to correct the reference pixel using the prediction parameter and the decoded luminance signal at the position corresponding to the reference pixel.

A gist of a third aspect of the present invention is a program for causing a computer to function as the encoding device according to the first aspect.

A gist of a fourth aspect of the present invention is a program for causing a computer to function as the decoding device according to the second aspect.

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to provide an encoding device, a decoding device, and a program that can prevent deterioration of prediction efficiency to a minimum even when reference pixels for color difference signals cannot be used. .

FIG. 1 is a diagram showing an example of functional blocks of an encoding device 1 according to the first embodiment. FIG. 2 is a diagram showing an example of the division shape of blocks of luminance signals and color difference signals determined by the division shape determination unit 12 of the encoding device 1 according to the first embodiment. FIG. 3 is a diagram showing an example of functional blocks of the prediction unit 13a of the encoding device 1 according to the first embodiment. FIG. 4 is a diagram for explaining an example of a reference pixel correction method by the prediction unit 13a of the encoding device 1 according to the first embodiment. FIG. 5 is a diagram for explaining an example of a reference pixel correction method by the prediction unit 13a of the encoding device 1 according to the first embodiment. FIG. 6 is a diagram showing an example of functional blocks of the decoding device 3 according to the first embodiment. FIG. 7 is a diagram for explaining the conventional technology. FIG. 8 is a diagram for explaining the conventional technology.

(First embodiment)
An encoding device 1 and a decoding device 3 according to the first embodiment of the present invention will be described below with reference to FIGS. 1 to 6. FIG.

Here, the encoding device 1 and the decoding device 3 according to this embodiment are configured to support intra prediction in a video encoding method such as HEVC. Note that the encoding device 1 and the decoding device 3 according to the present embodiment are configured to be compatible with any video encoding method as long as it is a video encoding method that performs intra prediction.

The encoding device 1 according to the present embodiment is configured to be capable of encoding a frame-by-frame original image that constitutes a moving image by dividing it into separate blocks for luminance signals and color-difference signals. In this embodiment, a case where a CU is used as an encoding target block will be described below, but the present embodiment can also be applied to a case where another block such as a TU (Transform Unit) is used as an encoding target block.

As shown in FIG. 1, the encoding device 1 according to the present embodiment includes a prediction mode determination unit 11, a division shape determination unit 12, a decoded image generation unit 13, a memory 14, and an entropy encoding unit 15. equipped.

The prediction mode determination unit 11 is configured to determine the optimum prediction mode to be applied to the encoding target CU (encoding target block).

The division shape determination unit 12 is configured to determine the division shape of the luminance signal (that is, the division shape of the CU of the luminance signal) and the division shape of the color difference signal (that is, the division shape of the CU of the color difference signal).

Here, the division shape determination unit 12 is configured to determine the division shape of the luminance signal and the division shape of the color difference signal by applying binary tree division, quadtree division, or the like for each CTU.

Note that the partition shape determination unit 12 is configured to first apply hierarchical quadtree partitioning to CUs of luminance signals and color difference signals to be encoded, and then apply hierarchical binary tree partitioning. may have been FIG. 2(a) shows an example of the division shape of the luminance signal, and FIG. 2(b) shows an example of the division shape of the color difference signal.

The decoded image generation unit 13 is configured to generate a local decoded image (decoded image for each CU) based on the division shape of the luminance signal and the division shape of the color difference signal determined by the division shape determination unit 12 .

As shown in FIG. 1, the decoded image generation unit 13 includes a prediction unit 13a, a residual signal generation unit 13b, a transformation/quantization unit 13c, an inverse quantization/inverse transformation unit 13d, and a local decoded image generation unit. 13e.

The prediction unit 13a uses the prediction mode determined by the prediction mode determination unit 11 and the division shape of the luminance signal and the division shape of the color difference signal determined by the division shape determination unit 12 to generate a predicted image for each CU. is configured to

Specifically, as shown in FIG. 3, the prediction unit 13a includes a determination unit 13a1, a derivation unit 13a2, a correction unit 13a3, and a generation unit 13a4.

The determining unit 13a1 is configured to determine whether or not to correct the reference pixels of the CU to be coded of the chrominance signal according to the intra prediction mode applied to the CU to be coded of the chrominance signal.

Here, the coding apparatus 1 according to the present embodiment is configured such that each CTU performs coding processing of color difference signals after all coding processing of luminance signals is performed. That is, in the examples of FIGS. 2A and 2B, the encoding device 1 according to the present embodiment performs encoding processing in the order of Y1→Y2→Y3→Y4→Y5→Y6→C1→C2→C3. is configured to do

Therefore, specifically, the determining unit 13a1 determines the reference pixel of the encoding target CU of the color difference signal, that is, the color difference signal designated as the reference pixel by the intra prediction mode when DM prediction is applied. The pixels in the CU (for example, C3 in FIG. 2(b)) adjacent to the encoding target CU (for example, C2 in FIG. 2(b)) have not been decoded, so they cannot be used as reference pixels as they are. Even if there is no such pixel, if the pixel of the luminance signal at the position corresponding to the position of such pixel has been decoded and can be used as a reference pixel, the reference pixel of the encoding target CU of such color difference signal (i.e. , pixels in a CU adjacent to the encoding target CU of the color difference signal designated as a reference pixel by the intra prediction mode when directional prediction is applied). ing.

In general, the pixels adjacent to the upper side and the left side of the CU to be coded for the color difference signal are already decoded pixels, and thus can be used as reference pixels. Since the pixels adjacent to the side are not decoded pixels, they cannot be used as reference pixels as they are.

Therefore, the determining unit 13a1 applies DM prediction as the intra prediction mode in the encoding target CU of the color difference signal (more specifically, the intra prediction modes are 51 to 66), and the encoding of the color difference signal is performed. When a pixel in a CU adjacent to the right (or lower side) of the target CU is designated as a reference pixel, and the pixel of the luminance signal at the position corresponding to the position of such pixel has been decoded. It may be configured to determine to perform correction on the reference pixel of the encoding target CU of the color difference signal when it can be used as a reference pixel.

The deriving unit 13a2 derives a prediction parameter by using the decoded color difference signal adjacent to the encoding target CU of the color difference signal and the decoded luminance signal at the position corresponding to the decoded color difference signal. It is configured.

The correction unit 13a3 uses the prediction parameter derived by the deriving unit 13a2 and the decoded luminance signal at the position corresponding to the reference pixel of the CU to be encoded for the chrominance signal to refer to the CU to be encoded for the chrominance signal. It is configured to correct pixels.

For example, the encoding device 1 according to the present embodiment may adopt cross color component prediction (CCCP) for predicting a color difference signal from a decoded luminance signal.

によって、係数α及びオフセットβを導出するように構成されている。ここで、Ｌ（ｎ）は、復号済みの輝度信号ｒｅｃ_L（ｉ,ｊ）に隣接する復号済みの輝度信号の画素ＬＬ（ｎ）を１/２にダウンコンバートしたものであり（図４（ａ）及び図４（ｂ）参照）、Ｃ（ｎ）は、色差信号の符号化対象ＣＵに隣接する復号済みの色差信号の画素である（図４（ｃ）参照）。なお、（ｉ,ｊ）は、符号化対象ＣＵ内の座標である。 When CCCP is employed, the derivation unit 13a2 is configured to derive the coefficient α and the offset β as prediction parameters. Specifically, the derivation unit 13a2

to derive the coefficient α and the offset β. Here, L(n) is obtained by down-converting the pixel LL(n) of the decoded luminance signal adjacent to the decoded luminance signal _recL (i,j) to 1/2 (FIG. 4 ( a) and FIG. 4(b)), C(n) is a pixel of the decoded color difference signal adjacent to the encoding target CU of the color difference signal (see FIG. 4(c)). Note that (i, j) are coordinates within the encoding target CU.

Further, the correction unit 13a3 calculates the coefficient α and the offset β derived by the derivation unit 13a2, the reference pixel of the CU to be chrominance signal encoding determined to be corrected by the determination unit 13a1 (that is, the CU to be chrominance signal encoding). (not available reference pixels adjacent to ) ref _C (n) (specifically, the reference pixels ref The color difference determined to be corrected by the determination unit 13a1 based on ref _L (n) obtained by down-converting the pixel ref _LL (n) of the decoded luminance signal at the position corresponding to _C (n) to 1/2 It is configured to correct the reference pixel ref _C (n) of the signal encoding target CU (see FIGS. 5(a) to 5(c)).

Specifically, the correction unit 13a3
ref _C (n)=α·ref _L (n)+β
is configured to correct the reference pixel ref _C (n) of the encoding target CU of the color difference signal determined to be corrected by the determination unit 13a1.

In the coding apparatus 1 according to the present embodiment, intra prediction for color difference signals is tried in order of planar prediction→vertical prediction→horizontal prediction→DC prediction→CCCP→DM prediction. Here, the determination unit 13a1, the derivation unit 13a2, and the correction unit 13a3 may be configured to function only when DM prediction is applied.

The generating unit 13a4 is configured to generate a predicted image for each CU using the reference pixels ref _C (n) of the encoding target CU of the color difference signal corrected by the correcting unit 13a3.

The residual signal generation unit 13b is configured to generate a residual signal from the difference between the predicted image generated by the prediction unit 13a and the original image.

The transform/quantization unit 13c is configured to perform orthogonal transform processing and quantization processing on the residual signal generated by the residual signal generation unit 13b to generate quantized transform coefficients.

The inverse quantization/inverse transform unit 13d performs the inverse quantization process and the inverse orthogonal transform process again on the quantized transform coefficients generated by the transform/quantization unit 13c to generate a residual signal. is configured to

The local decoded image generation unit 13e is configured to generate a local decoded image by adding the predicted image generated by the prediction unit 13a to the residual signal generated by the inverse quantization/inverse transform unit 13d. there is

The memory 14 is configured to hold the local decoded image generated by the decoded image generator 13 so as to be usable as a reference image.

The entropy coding unit 15 is configured to perform entropy coding processing on the flag information including the prediction mode determined by the prediction mode determination unit 11 and the quantized transform coefficients, and output a stream.

Further, the decoding device 3 according to the present embodiment is configured so as to be able to divide the original image of each frame constituting the moving image into separate blocks for the luminance signal and the color difference signal, and decode the blocks.

As shown in FIG. 6 , the decoding device 3 according to this embodiment includes an entropy decoding section 31 , a decoded image generation section 32 and a memory 33 .

The entropy decoding unit 31 is configured to decode transform coefficients, flag information, and the like from the stream output from the encoding device 1 . Here, the transform coefficients are quantized transform coefficients obtained as encoded signals by dividing the original image in frame units by the encoding device 1 .

As shown in FIG. 6, the decoded image generation unit 32 includes a prediction unit 32a, an inverse quantization/inverse transform unit 32b, and a local decoded image generation unit 32c.

The prediction unit 32a may be configured to use the prediction mode output by the entropy decoding unit 31 to generate a predicted image. Specifically, it has the same functions as the prediction unit 13a of the encoding device 1 (that is, the determination unit 13a1, the derivation unit 13a2, and the correction unit 13a3).

Note that the determination unit 13a1, the derivation unit 13a2, and the correction unit 13a3 may be configured to function only when DM prediction is applied as the prediction mode output from the entropy decoding unit 31. FIG.

The inverse quantization/inverse transform unit 32b performs inverse quantization processing and inverse transform processing (for example, inverse orthogonal transform processing) on the quantized transform coefficients output from the entropy decoding unit 31, thereby generating a residual configured to generate a signal;

The local decoded image generator 32c is configured to generate a local decoded image by adding the predicted image generated by the predicted image generator 32a and the residual signal generated by the inverse quantization/inverse transform unit 32b. ing.

The memory 33 is configured to hold the local decoded image generated by the decoded image generation unit 32 so that it can be used as a reference image for intra prediction and inter prediction.

According to the encoding device 1 and the decoding device 3 according to the present embodiment, when some of the reference pixels used when performing intra prediction for the encoding target CU of the color difference signal are unavailable, the color difference signal and the luminance Since it is possible to predict reference pixels for unavailable color-difference signals in consideration of the correlation with the signals, it is possible to minimize deterioration in prediction efficiency.

(Other embodiments)
As noted above, the present invention has been described through the above-described embodiments, but the statements and drawings forming part of the disclosure in such embodiments should not be understood to limit the present invention. From such disclosure, various alternative embodiments, implementations and operational techniques will become apparent to those skilled in the art.

Moreover, although not particularly mentioned in the above-described embodiment, a program may be provided that causes a computer to execute each process performed by the above-described encoding device 1 and decoding device 3 . Also, such a program may be recorded on a computer-readable medium. Such programs can be installed on a computer using a computer readable medium. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, but may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

Alternatively, a chip configured by a memory storing a program for realizing at least part of the functions in the encoding device 1 and the decoding device 3 described above and a processor executing the program stored in the memory may be provided. good.

DESCRIPTION OF SYMBOLS 1... Encoding apparatus 11... Prediction mode determination part 12... Division shape determination part 13... Decoded image generation part 13a... Prediction part 13a1... Determination part 13a2... Derivation part 13a3... Correction part 13a4... Generation part 13b... Residual signal generation part 13c transform/quantization unit 13d inverse quantization/inverse transform unit 13e local decoded image generation unit 14 memory 15 entropy coding unit 3 decoding device 31 entropy decoding unit 32 decoded image generation unit 32a prediction Unit 32b: Inverse quantization/inverse transform unit 32c: Locally decoded image generation unit 33: Memory

Claims (6)

An encoding device configured to divide an original image in units of frames constituting a moving image into blocks separately for luminance signals and color difference signals and encode the blocks,
a determining unit configured to determine whether or not to perform correction on reference pixels of the encoding target block of the chrominance signal according to an intra prediction mode applied to the encoding target block of the chrominance signal;
A prediction parameter is derived using a decoded chrominance signal adjacent to an encoding target block of the chrominance signal and a decoded luminance signal at a position corresponding to the decoded chrominance signal. a derivation unit;
a correction unit,
The determining unit identifies, as a target pixel, a pixel that has not been decoded among the pixels designated as the reference pixel by the intra prediction mode, and determines to perform the correction on the target pixel;
The encoding device , wherein the correction unit corrects the target pixel using the prediction parameter and the decoded luminance signal at a position corresponding to the target pixel. 2. The encoding apparatus according to claim 1, wherein the decoded color difference signal is adjacent to the upper side and left side of the encoding target block of the color difference signal. A decoding device configured to be able to divide and decode an original image of each frame that constitutes a moving image into separate blocks for luminance signals and color difference signals,
a determining unit configured to determine whether or not to perform correction on reference pixels of the decoding target block of the chrominance signal according to an intra prediction mode applied to the decoding target block of the chrominance signal;
A prediction parameter is derived using a decoded color difference signal adjacent to a decoding target block of the color difference signal and a decoded luminance signal at a position corresponding to the decoded color difference signal. Department and
a correction unit,
The determining unit identifies, as a target pixel, a pixel that has not been decoded among the pixels designated as the reference pixel by the intra prediction mode, and determines to perform the correction on the target pixel;
The decoding device , wherein the correction unit corrects the target pixel using the prediction parameter and the decoded luminance signal at a position corresponding to the target pixel. 4. The decoding device according to claim 3, wherein the decoded chrominance signal is adjacent to the upper and left sides of the decoding target block of the chrominance signal. A program for causing a computer to function as the encoding device according to claim 1 or 2. A program for causing a computer to function as the decoding device according to claim 3 or 4.

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