Encoding device, encoding method, decoding device, decoding method, and transmission method

Abstract

To provide an encoding device capable of reducing a processing load while suppressing a decrease in compression efficiency.SOLUTION: The encoding apparatus 100 performs a transform process on a residual signal of a current block when it is determined that intra prediction is used for the current block, and quantizes a transform coefficient generated by the transform process, the transform process including (i) generating a first transform coefficient by performing a first transform on a residual signal of the current block using a first transform basis when an intra prediction mode of the current block is different from a predetermined mode and the first transform basis is the same as a predetermined transform basis, the processing includes: generating a second transform coefficient by performing a second transform on the first transform coefficient using a second transform basis; and generating a first transform coefficient by performing a first transform on the residual signal of the current block using the first transform basis when the intra-prediction mode of the current block is different from a predetermined mode and the first transform basis is different from the predetermined transform basis.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] This disclosure relates to block-based image / video encoding and decoding. [Background technology]

[0002] A video coding standard called HEVC (High-Efficiency Video Coding) has been standardized by the Joint Collaborative Team on Video Coding (JCT-VC). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] H.265(ISO / IEC 23008-2 HEVC(High Efficiency Video Coding)) Summary of the Invention [Problem to be solved by the invention]

[0004] In such encoding and decoding techniques, there is a demand for reducing the processing load while preventing a decrease in compression efficiency.

[0005] Therefore, the present disclosure provides an encoding device, a decoding device, an encoding method, a decoding method, or a transmission method that can reduce the processing load while suppressing a decrease in compression efficiency. [Means for solving the problem]

[0006] An encoding device according to one embodiment of the present disclosure is an encoding device that encodes a current block in a picture, and is equipped with a circuit and a memory. The circuit uses the memory to determine whether to use intra-prediction for the current block, and if it is determined that intra-prediction is to be used for the current block, performs a transform process and quantizes the transform coefficients generated by the transform process. The transform process includes the following steps: (i) when the intra-prediction mode of the current block is different from a predetermined mode and a first transform base is the same as a predetermined transform base, generate first transform coefficients by performing a first transform on a residual signal of the current block using the first transform base, and generate second transform coefficients by performing a second transform on the first transform coefficients using a second transform base; and (ii) when the intra-prediction mode of the current block is different from the predetermined mode and the first transform base is different from the predetermined transform base, generate first transform coefficients by performing a first transform on the residual signal of the current block using the first transform base.

[0007] These general or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium. [Effects of the Invention]

[0008] The present disclosure can provide an encoding device, a decoding device, an encoding method, a decoding method, or a transmission method that can reduce the processing load while suppressing a decrease in compression efficiency. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing a functional configuration of a coding device according to the first embodiment. [Figure 2] FIG. 2 is a diagram showing an example of block division according to the first embodiment. [Figure 3]FIG. 3 is a table showing the transformation basis functions corresponding to each transformation type. [Figure 4A] FIG. 4A is a diagram showing an example of the shape of a filter used in ALF. [Figure 4B] FIG. 4B is a diagram showing another example of the shape of the filter used in ALF. [Figure 4C] FIG. 4C is a diagram showing another example of the shape of the filter used in ALF. [Figure 5A] FIG. 5A is a diagram showing 67 intra prediction modes in intra prediction. [Figure 5B] FIG. 5B is a flowchart for explaining an outline of the predicted image correction process using the OBMC process. [Figure 5C] FIG. 5C is a conceptual diagram for explaining an outline of the predicted image correction process using the OBMC process. [Figure 5D] FIG. 5D is a diagram showing an example of FRUC. [Figure 6] FIG. 6 is a diagram for explaining pattern matching (bilateral matching) between two blocks along a motion trajectory. [Figure 7] FIG. 7 is a diagram for explaining pattern matching (template matching) between a template in a current picture and a block in a reference picture. [Figure 8] FIG. 8 is a diagram for explaining a model assuming uniform linear motion. [Figure 9A] FIG. 9A is a diagram for explaining derivation of a motion vector for each sub-block based on motion vectors of a plurality of adjacent blocks. [Figure 9B] FIG. 9B is a diagram for explaining an outline of the motion vector derivation process in the merge mode. [Figure 9C] FIG. 9C is a conceptual diagram for explaining an outline of the DMVR process. [Figure 9D] FIG. 9D is a diagram for explaining an outline of a predicted image generation method using luminance correction processing by LIC processing. [Figure 10]FIG. 10 is a block diagram showing a functional configuration of a decoding device according to the first embodiment. [Figure 11] FIG. 11 is a flowchart showing the transform and quantization process in the coding device according to the second embodiment. [Figure 12] FIG. 12 is a flowchart showing the inverse quantization and inverse transform processing in the decoding device according to the second embodiment. [Figure 13] FIG. 13 is a flowchart showing the transform and quantization process in the coding device according to the third embodiment. [Figure 14] FIG. 14 is a flowchart showing the inverse quantization and inverse transform processing in the decoding device according to the third embodiment. [Figure 15] FIG. 15 is a flowchart showing the transform and quantization process in the coding device according to the fourth embodiment. [Figure 16] FIG. 16 is a flowchart showing the inverse quantization and inverse transform processing in the decoding device according to the fourth embodiment. [Figure 17] FIG. 17 is a flowchart showing the encoding process in the encoding device according to the fifth embodiment. [Figure 18] FIG. 18 is a diagram showing a specific example of syntax according to the fifth embodiment. [Figure 19] FIG. 19 is a flowchart showing the decoding process in the decoding device according to the fifth embodiment. [Figure 20] FIG. 20 is a flowchart showing the encoding process in the encoding device according to the sixth embodiment. [Figure 21] FIG. 21 is a flowchart showing the decoding process in the decoding device according to the sixth embodiment. [Figure 22] FIG. 22 is a diagram showing the overall configuration of a content supply system that realizes a content distribution service. [Figure 23] FIG. 23 is a diagram showing an example of a coding structure for scalable coding. [Figure 24] FIG. 24 is a diagram showing an example of a coding structure for scalable coding. [Figure 25] FIG. 25 is a diagram showing an example of a display screen of a web page. [Figure 26] FIG. 26 is a diagram showing an example of a display screen of a web page. [Figure 27] FIG. 27 is a diagram illustrating an example of a smartphone. [Figure 28] FIG. 28 is a block diagram showing an example of the configuration of a smartphone. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Findings that formed the basis of this disclosure) The Joint Video Exploration Team (JVET)'s (Joint Video Exploration Team) JEM (Joint Exploration Test Model) software proposes a two-stage frequency transform for blocks to which intra prediction is applied. In this two-stage frequency transform, the Explicit Multiple Core Transform (EMT) is used as the primary transform, and the Non-separable Secondary Transform (NSST) is used as the secondary transform. EMT adaptively selects multiple transform bases to convert from the spatial domain to the frequency domain.

[0011] In terms of the amount of processing required, there is room for improvement in this two-stage frequency conversion.

[0012] Hereinafter, embodiments based on such knowledge will be specifically described with reference to the drawings.

[0013] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection configurations, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the scope of the claims. Furthermore, among the components in the following embodiments, components that are not described in the independent claims that represent the highest concepts are described as optional components.

[0014] (Embodiment 1) First, an overview of the first embodiment will be described as an example of an encoding device and a decoding device to which the processes and / or configurations described in each aspect of the present disclosure can be applied. However, the first embodiment is merely an example of an encoding device and a decoding device to which the processes and / or configurations described in each aspect of the present disclosure can be applied, and the processes and / or configurations described in each aspect of the present disclosure can also be implemented in encoding devices and decoding devices different from the first embodiment.

[0015] When applying the processing and / or configurations described in each aspect of the present disclosure to the first embodiment, for example, any of the following may be performed.

[0016] (1) For the encoding device or decoding device of the first embodiment, among the multiple components constituting the encoding device or decoding device, components corresponding to the components described in each aspect of the present disclosure are replaced with the components described in each aspect of the present disclosure. (2) Any modification, such as addition, replacement, or deletion, of the functions or processes performed by some of the components constituting the encoding device or decoding device of the first embodiment may be made to the encoding device or decoding device, and then components corresponding to the components described in each aspect of the present disclosure may be replaced with the components described in each aspect of the present disclosure. (3) The method implemented by the encoding device or decoding device of the first embodiment may be modified by adding a process and / or replacing or deleting some of the processes included in the method, and then replacing the process described in each aspect of the present disclosure with the process described in each aspect of the present disclosure. (4) Some of the components constituting the encoding device or decoding device of the first embodiment may be implemented in combination with components described in each aspect of the present disclosure, components having some of the functions of the components described in each aspect of the present disclosure, or components performing some of the processing performed by the components described in each aspect of the present disclosure. (5) A component having some of the functions of some of the components constituting the encoding device or decoding device of the first embodiment, or a component that performs some of the processing performed by some of the components constituting the encoding device or decoding device of the first embodiment, is implemented in combination with a component described in each aspect of the present disclosure, a component having some of the functions of the components described in each aspect of the present disclosure, or a component that performs some of the processing performed by the components described in each aspect of the present disclosure. (6) In the method implemented by the encoding device or decoding device of the first embodiment, among the multiple processes included in the method, processes corresponding to the processes described in each aspect of the present disclosure are replaced with the processes described in each aspect of the present disclosure. (7) Some of the processes included in the method implemented by the encoding device or decoding device of the first embodiment may be implemented in combination with the processes described in each aspect of the present disclosure.

[0017] It should be noted that the manner of implementing the processes and / or configurations described in each aspect of the present disclosure is not limited to the above examples. For example, they may be implemented in a device used for a purpose different from the video / image encoding device or video / image decoding device disclosed in Embodiment 1, or the processes and / or configurations described in each aspect may be implemented independently. Furthermore, the processes and / or configurations described in different aspects may be implemented in combination.

[0018] [Outline of the encoding device] First, an overview of a coding device according to Embodiment 1 will be described. Fig. 1 is a block diagram showing a functional configuration of a coding device 100 according to Embodiment 1. The coding device 100 is a video / image coding device that codes a video / image on a block-by-block basis.

[0019] As shown in FIG. 1, the encoding device 100 is a device that encodes an image on a block-by-block basis, and includes a division unit 102, a subtraction unit 104, a transformation unit 106, a quantization unit 108, an entropy encoding unit 110, an inverse quantization unit 112, an inverse transformation unit 114, an addition unit 116, a block memory 118, a loop filter unit 120, a frame memory 122, an intra prediction unit 124, an inter prediction unit 126, and a prediction control unit 128.

[0020] The encoding device 100 is realized by, for example, a general-purpose processor and memory. In this case, when a software program stored in the memory is executed by the processor, the processor functions as the division unit 102, the subtraction unit 104, the transformation unit 106, the quantization unit 108, the entropy coding unit 110, the inverse quantization unit 112, the inverse transformation unit 114, the addition unit 116, the loop filter unit 120, the intra prediction unit 124, the inter prediction unit 126, and the prediction control unit 128. Alternatively, the encoding device 100 may be realized as one or more dedicated electronic circuits corresponding to the division unit 102, the subtraction unit 104, the transformation unit 106, the quantization unit 108, the entropy coding unit 110, the inverse quantization unit 112, the inverse transformation unit 114, the addition unit 116, the loop filter unit 120, the intra prediction unit 124, the inter prediction unit 126, and the prediction control unit 128.

[0021] Each component included in the encoding device 100 will be described below.

[0022] [Divided part] The division unit 102 divides each picture included in the input video into a plurality of blocks and outputs each block to the subtraction unit 104. For example, the division unit 102 first divides a picture into blocks of a fixed size (e.g., 128x128). These fixed-size blocks are sometimes called coding tree units (CTUs). The division unit 102 then divides each of the fixed-size blocks into blocks of a variable size (e.g., 64x64 or less) based on recursive quadtree and / or binary tree block division. These variable-size blocks are sometimes called coding units (CUs), prediction units (PUs), or transform units (TUs). Note that in this embodiment, there is no need to distinguish between CUs, PUs, and TUs, and some or all of the blocks in a picture may serve as the processing units of CUs, PUs, and TUs.

[0023] Fig. 2 is a diagram showing an example of block division according to embodiment 1. In Fig. 2, solid lines represent block boundaries based on quadtree block division, and dashed lines represent block boundaries based on binary tree block division.

[0024] Here, the block 10 is a square block of 128x128 pixels (128x128 block). This 128x128 block 10 is first divided into four square 64x64 blocks (quadtree block division).

[0025] The top-left 64x64 block is further divided vertically into two rectangular 32x64 blocks, and the left 32x64 block is further divided vertically into two rectangular 16x64 blocks (binary tree block division). As a result, the top-left 64x64 block is divided into two 16x64 blocks 11 and 12 and a 32x64 block 13.

[0026] The top right 64x64 block is divided horizontally into two rectangular 64x32 blocks 14 and 15 (binary tree block division).

[0027] The lower-left 64x64 block is divided into four square 32x32 blocks (quadtree block decomposition). Of the four 32x32 blocks, the upper-left and lower-right blocks are further divided. The upper-left 32x32 block is divided vertically into two rectangular 16x32 blocks, and the right 16x32 block is further divided horizontally into two 16x16 blocks (binary tree block decomposition). The lower-right 32x32 block is divided horizontally into two 32x16 blocks (binary tree block decomposition). As a result, the lower-left 64x64 block is divided into 16x32 block 16, two 16x16 blocks 17 and 18, two 32x32 blocks 19 and 20, and two 32x16 blocks 21 and 22.

[0028] The bottom right 64x64 block 23 is not split.

[0029] 2, block 10 is divided into 13 variable-sized blocks 11 to 23 based on recursive quad-tree and binary tree block division. This type of division is sometimes called QTBT (quad-tree plus binary tree) division.

[0030] In Fig. 2, one block is divided into four or two blocks (quadtree or binary tree block division), but the division is not limited to this. For example, one block may be divided into three blocks (ternary tree block division). Division including such ternary tree block division is sometimes called MBT (multi type tree) division.

[0031] [Subtraction section] The subtraction unit 104 subtracts a prediction signal (prediction sample) from an original signal (original sample) for each block divided by the division unit 102. That is, the subtraction unit 104 calculates a prediction error (also referred to as a residual) of a block to be coded (hereinafter referred to as a current block). Then, the subtraction unit 104 outputs the calculated prediction error to the conversion unit 106.

[0032] The original signal is an input signal to the encoding device 100, and is a signal representing an image of each picture constituting a moving image (for example, a luminance (luma) signal and two color difference (chroma) signals). Hereinafter, the signal representing an image may also be referred to as a sample.

[0033] [Conversion section] The transform unit 106 transforms the spatial domain prediction errors into frequency domain transform coefficients and outputs the transform coefficients to the quantization unit 108. Specifically, the transform unit 106 performs, for example, a predetermined discrete cosine transform (DCT) or discrete sine transform (DST) on the spatial domain prediction errors.

[0034] The transform unit 106 may adaptively select a transform type from among a plurality of transform types and transform the prediction errors into transform coefficients using a transform basis function corresponding to the selected transform type. Such a transform is sometimes called an explicit multiple core transform (EMT) or an adaptive multiple transform (AMT).

[0035] The multiple transform types include, for example, DCT-II, DCT-V, DCT-VIII, DST-I, and DST-VII. Fig. 3 is a table showing transform basis functions corresponding to each transform type. In Fig. 3, N represents the number of input pixels. Selection of a transform type from among these multiple transform types may depend, for example, on the type of prediction (intra prediction or inter prediction) or the intra prediction mode.

[0036] Information indicating whether EMT or AMT is applied (e.g., referred to as an AMT flag) and information indicating the selected transformation type are signaled at the CU level. Note that signaling of this information does not need to be limited to the CU level, and may be at other levels (e.g., sequence level, picture level, slice level, tile level, or CTU level).

[0037] Furthermore, the transform unit 106 may retransform the transform coefficients (transform results). Such retransformation may be referred to as an adaptive secondary transform (AST) or a non-separable secondary transform (NSST). For example, the transform unit 106 performs retransformation for each sub-block (e.g., 4x4 sub-block) included in a block of transform coefficients corresponding to intra-prediction errors. Information indicating whether or not to apply NSST and information regarding the transform matrix used for NSST are signaled at the CU level. Note that signaling of this information does not need to be limited to the CU level, and may be at other levels (e.g., the sequence level, picture level, slice level, tile level, or CTU level).

[0038] Here, a separable transformation is a method in which the transformation is performed multiple times by separating the input into directions equal to the number of dimensions, and a non-separable transformation is a method in which, when the input is multidimensional, two or more dimensions are treated as one dimension and the transformation is performed all at once.

[0039] For example, one example of a non-separable transformation is when the input is a 4x4 block, it is treated as a single array with 16 elements, and the transformation process is performed on that array using a 16x16 transformation matrix.

[0040] Similarly, a non-separable transformation is one that treats a 4x4 input block as a single array with 16 elements and then performs multiple Givens rotations on that array (Hypercube Givens Transform).

[0041] [Quantization section] The quantization unit 108 quantizes the transform coefficients output from the transform unit 106. Specifically, the quantization unit 108 scans the transform coefficients of the current block in a predetermined scanning order and quantizes the transform coefficients based on quantization parameters (QP) corresponding to the scanned transform coefficients. The quantization unit 108 then outputs the quantized transform coefficients of the current block (hereinafter referred to as quantized coefficients) to the entropy coding unit 110 and the inverse quantization unit 112.

[0042] The predetermined order is an order for quantizing / dequantizing the transform coefficients. For example, the predetermined scanning order is defined as an ascending order (low frequency to high frequency) or a descending order (high frequency to low frequency).

[0043] The quantization parameter is a parameter that defines the quantization step (quantization width). For example, as the value of the quantization parameter increases, the quantization step also increases. In other words, as the value of the quantization parameter increases, the quantization error also increases.

[0044] [Entropy coding section] The entropy coding unit 110 generates a coded signal (coded bit stream) by variable-length coding the quantized coefficients input from the quantization unit 108. Specifically, the entropy coding unit 110, for example, binarizes the quantized coefficients and arithmetically codes the binary signal.

[0045] [Dequantization section] The inverse quantization unit 112 inverse quantizes the quantized coefficients input from the quantization unit 108. Specifically, the inverse quantization unit 112 inverse quantizes the quantized coefficients of the current block in a predetermined scanning order. The inverse quantization unit 112 then outputs the inverse quantized transform coefficients of the current block to the inverse transform unit 114.

[0046] [Inverse conversion section] The inverse transform unit 114 restores the prediction error by inverse transforming the transform coefficients that are input from the inverse quantization unit 112. Specifically, the inverse transform unit 114 restores the prediction error of the current block by performing an inverse transform on the transform coefficients that corresponds to the transform performed by the transform unit 106. Then, the inverse transform unit 114 outputs the restored prediction error to the adder unit 116.

[0047] Note that the restored prediction error does not match the prediction error calculated by the subtraction unit 104 because information has been lost due to quantization. In other words, the restored prediction error includes a quantization error.

[0048] [Adder] The adder 116 reconstructs the current block by adding the prediction error input from the inverse transformer 114 and the prediction sample input from the prediction control unit 128. The adder 116 then outputs the reconstructed block to the block memory 118 and the loop filter unit 120. The reconstructed block is sometimes called a local decoded block.

[0049] [Block Memory] The block memory 118 is a storage unit for storing blocks that are referenced in intra prediction and are in a picture to be coded (hereinafter referred to as a current picture). Specifically, the block memory 118 stores the reconstructed blocks output from the adder 116.

[0050] [Loop filter section] The loop filter unit 120 applies a loop filter to the block reconstructed by the adder 116 and outputs the filtered reconstructed block to the frame memory 122. The loop filter is a filter (in-loop filter) used in the encoding loop, and includes, for example, a deblocking filter (DF), a sample adaptive offset (SAO), and an adaptive loop filter (ALF).

[0051] ALF applies a least squares error filter to remove coding artifacts, for example, for each 2x2 sub-block in the current block, one filter selected from multiple filters based on local gradient direction and activity.

[0052] Specifically, first, sub-blocks (e.g., 2x2 sub-blocks) are classified into a plurality of classes (e.g., 15 or 25 classes). The sub-blocks are classified based on the gradient direction and activity. For example, a classification value C (e.g., C=5D+A) is calculated using a gradient direction value D (e.g., 0 to 2 or 0 to 4) and a gradient activity value A (e.g., 0 to 4). Then, based on the classification value C, the sub-blocks are classified into a plurality of classes (e.g., 15 or 25 classes).

[0053] The gradient direction value D is derived by, for example, comparing gradients in multiple directions (e.g., horizontal, vertical, and two diagonal directions), and the gradient activity value A is derived by, for example, adding gradients in multiple directions and quantizing the sum.

[0054] Based on the result of such classification, a filter for the sub-block is determined from among a plurality of filters.

[0055] The filter shape used in ALF is, for example, a circularly symmetric shape. FIGS. 4A to 4C are diagrams showing several examples of filter shapes used in ALF. FIG. 4A shows a 5x5 diamond-shaped filter, FIG. 4B shows a 7x7 diamond-shaped filter, and FIG. 4C shows a 9x9 diamond-shaped filter. Information indicating the filter shape is signaled at the picture level. Note that signaling of the information indicating the filter shape does not need to be limited to the picture level, and may be at other levels (e.g., sequence level, slice level, tile level, CTU level, or CU level).

[0056] Whether ALF is turned on or off is determined, for example, at the picture level or the CU level. For example, whether ALF is applied to luminance is determined at the CU level, and whether ALF is applied to chrominance is determined at the picture level. Information indicating whether ALF is turned on or off is signaled at the picture level or the CU level. Note that signaling of information indicating whether ALF is turned on or off does not need to be limited to the picture level or the CU level, and may be at another level (for example, the sequence level, the slice level, the tile level, or the CTU level).

[0057] The coefficient sets of multiple selectable filters (e.g., up to 15 or 25 filters) are signaled at the picture level. Note that the signaling of the coefficient sets does not need to be limited to the picture level, but may also be at other levels (e.g., sequence level, slice level, tile level, CTU level, CU level, or sub-block level).

[0058] [Frame memory] The frame memory 122 is a storage unit for storing reference pictures used in inter prediction, and is sometimes called a frame buffer. Specifically, the frame memory 122 stores the reconstructed blocks filtered by the loop filter unit 120.

[0059] [Intra prediction section] The intra prediction unit 124 generates a prediction signal (intra prediction signal) by performing intra prediction (also referred to as intra-picture prediction) of the current block with reference to blocks in the current picture stored in the block memory 118. Specifically, the intra prediction unit 124 generates the intra prediction signal by performing intra prediction with reference to samples (e.g., luminance values, chrominance values) of blocks adjacent to the current block, and outputs the intra prediction signal to the prediction control unit 128.

[0060] For example, the intra prediction unit 124 performs intra prediction using one of a plurality of predefined intra prediction modes. The plurality of intra prediction modes includes one or more non-directional prediction modes and a plurality of directional prediction modes.

[0061] The one or more non-directional prediction modes include, for example, a planar prediction mode and a DC prediction mode defined in the H.265 / High-Efficiency Video Coding (HEVC) standard (Non-Patent Document 1).

[0062] The multiple directional prediction modes include, for example, the 33 prediction modes defined in the H.265 / HEVC standard. Note that the multiple directional prediction modes may also include 32 prediction modes in addition to the 33 directions (65 directional prediction modes in total). Fig. 5A is a diagram showing 67 intra prediction modes (2 non-directional prediction modes and 65 directional prediction modes) in intra prediction. Solid arrows represent the 33 directions defined in the H.265 / HEVC standard, and dashed arrows represent the additional 32 directions.

[0063] Note that a luminance block may be referenced in intra prediction of a chrominance block. That is, the chrominance component of the current block may be predicted based on the luminance component of the current block. This type of intra prediction is sometimes called CCLM (cross-component linear model) prediction. An intra prediction mode of a chrominance block that references such a luminance block (e.g., called a CCLM mode) may be added as one of the intra prediction modes for the chrominance block.

[0064] The intra prediction unit 124 may correct pixel values ​​after intra prediction based on gradients of reference pixels in the horizontal / vertical directions. Intra prediction involving such correction is sometimes called PDPC (position dependent intra prediction combination). Information indicating whether PDPC is applied (e.g., called a PDPC flag) is signaled, for example, at the CU level. Note that signaling of this information does not need to be limited to the CU level, and may be at other levels (e.g., sequence level, picture level, slice level, tile level, or CTU level).

[0065] [Inter prediction section] The inter prediction unit 126 generates a prediction signal (inter prediction signal) by performing inter prediction (also referred to as inter prediction) on the current block with reference to a reference picture stored in the frame memory 122 that is different from the current picture. The inter prediction is performed in units of the current block or sub-blocks (e.g., 4x4 blocks) within the current block. For example, the inter prediction unit 126 performs motion estimation on the current block or sub-block within the reference picture. The inter prediction unit 126 then generates an inter prediction signal for the current block or sub-block by performing motion compensation using motion information (e.g., a motion vector) obtained by the motion estimation. The inter prediction unit 126 then outputs the generated inter prediction signal to the prediction control unit 128.

[0066] The motion information used for motion compensation is signaled. For the signaling of the motion vector, a motion vector predictor may be used, i.e., the difference between the motion vector and the motion vector predictor may be signaled.

[0067] Note that an inter-prediction signal may be generated using not only the motion information of the current block obtained by motion estimation, but also the motion information of adjacent blocks. Specifically, an inter-prediction signal may be generated for each sub-block in the current block by weighting and adding a prediction signal based on the motion information obtained by motion estimation and a prediction signal based on the motion information of adjacent blocks. Such inter-prediction (motion compensation) may be called OBMC (overlapped block motion compensation).

[0068] In such an OBMC mode, information indicating the size of a sub-block for OBMC (e.g., called an OBMC block size) is signaled at the sequence level. Also, information indicating whether the OBMC mode is applied (e.g., called an OBMC flag) is signaled at the CU level. Note that the signaling level of this information is not limited to the sequence level and the CU level, and may be other levels (e.g., the picture level, slice level, tile level, CTU level, or sub-block level).

[0069] The OBMC mode will now be described in more detail. Figures 5B and 5C are a flowchart and a conceptual diagram for explaining an outline of the predictive image correction process using the OBMC process.

[0070] First, a predicted image (Pred) is obtained by normal motion compensation using a motion vector (MV) assigned to the block to be coded.

[0071] Next, the motion vector (MV_L) of the coded left adjacent block is applied to the block to be coded to obtain a predicted image (Pred_L), and the predicted image is weighted and superimposed with Pred_L to perform the first correction of the predicted image.

[0072] Similarly, the motion vector (MV_U) of the already coded upper adjacent block is applied to the block to be coded to obtain a predicted image (Pred_U), and the predicted image that has been corrected the first time is weighted and overlaid with Pred_U to perform a second correction of the predicted image, which is then used as the final predicted image.

[0073] Although a two-stage correction method using the left adjacent block and the upper adjacent block has been described here, it is also possible to configure a method in which correction is performed more than two times using the right adjacent block or the lower adjacent block.

[0074] The area to be superimposed does not have to be the pixel area of ​​the entire block, but may be only a part of the area near the block boundary.

[0075] Although the process of correcting a predicted image from one reference picture has been described here, the process is similar when correcting a predicted image from multiple reference pictures. After obtaining corrected predicted images from each reference picture, the obtained predicted images are further superimposed to form the final predicted image.

[0076] The target block to be processed may be a prediction block unit or a sub-block unit obtained by further dividing the prediction block.

[0077] As a method for determining whether to apply OBMC processing, for example, there is a method using obmc_flag, which is a signal indicating whether to apply OBMC processing. As a specific example, an encoding device determines whether a block to be encoded belongs to an area with complex motion, and if it belongs to an area with complex motion, sets the value of obmc_flag to 1 and performs encoding using OBMC processing, and if it does not belong to an area with complex motion, sets the value of obmc_flag to 0 and performs encoding without applying OBMC processing. On the other hand, a decoding device decodes obmc_flag described in a stream, and switches whether to apply OBMC processing depending on the value, and performs decoding.

[0078] Alternatively, the motion information may be derived on the decoding device side without being signaled. For example, a merge mode defined in the H.265 / HEVC standard may be used. Alternatively, the motion information may be derived by performing motion estimation on the decoding device side. In this case, the motion estimation is performed without using pixel values ​​of the current block.

[0079] Here, a mode in which motion estimation is performed on the decoding device side will be described. This mode in which motion estimation is performed on the decoding device side is sometimes called a pattern matched motion vector derivation (PMMVD) mode or a frame rate up-conversion (FRUC) mode.

[0080] An example of the FRUC process is shown in Figure 5D. First, a list of multiple candidates (which may be the same as the merge list) each having a predicted motion vector is generated by referring to the motion vectors of coded blocks spatially or temporally adjacent to the current block. Next, a best candidate MV is selected from the multiple candidate MVs registered in the candidate list. For example, an evaluation value of each candidate included in the candidate list is calculated, and one candidate is selected based on the evaluation value.

[0081] Then, a motion vector for the current block is derived based on the motion vector of the selected candidate. Specifically, for example, the motion vector of the selected candidate (best candidate MV) is derived as the motion vector for the current block as is. Also, for example, the motion vector for the current block may be derived by performing pattern matching in a peripheral area of ​​a position in a reference picture corresponding to the motion vector of the selected candidate. That is, a search is performed in a similar manner in a peripheral area of ​​the best candidate MV, and if an MV with a better evaluation value is found, the best candidate MV may be updated to the MV and used as the final MV for the current block. Note that a configuration may be adopted in which this process is not performed.

[0082] The same processing may be performed when processing is performed in sub-block units.

[0083] The evaluation value is calculated by finding the difference between the reconstructed image and a predetermined area by pattern matching between the area in the reference picture corresponding to the motion vector. The evaluation value may be calculated using other information in addition to the difference.

[0084] As the pattern matching, first pattern matching or second pattern matching is used. The first pattern matching and second pattern matching are sometimes called bilateral matching and template matching, respectively.

[0085] In the first pattern matching, pattern matching is performed between two blocks in two different reference pictures that are along the motion trajectory of the current block. Therefore, in the first pattern matching, an area in another reference picture that is along the motion trajectory of the current block is used as a predetermined area for calculating the evaluation value of the candidate.

[0086] FIG. 6 is a diagram illustrating an example of pattern matching (bilateral matching) between two blocks along a motion trajectory. As shown in FIG. 6, in the first pattern matching, two motion vectors (MV0, MV1) are derived by searching for the most closely matched pair of two blocks along the motion trajectory of a current block (Cur block) in two different reference pictures (Ref0, Ref1). Specifically, for the current block, a difference is derived between a reconstructed image at a specified position in a first coded reference picture (Ref0) specified by a candidate MV and a reconstructed image at a specified position in a second coded reference picture (Ref1) specified by a symmetric MV obtained by scaling the candidate MV by the display time interval, and an evaluation value is calculated using the obtained difference value. The candidate MV with the best evaluation value among multiple candidate MVs may be selected as the final MV.

[0087] Under the assumption of continuous motion trajectories, motion vectors (MV0, MV1) pointing to two reference blocks are proportional to the temporal distances (TD0, TD1) between a current picture (CurPic) and two reference pictures (Ref0, Ref1). For example, if the current picture is located between two reference pictures temporally and the temporal distances from the current picture to the two reference pictures are equal, the first pattern matching derives bidirectional motion vectors that are mirror-symmetric.

[0088] In the second pattern matching, pattern matching is performed between a template in the current picture (a block adjacent to the current block in the current picture (e.g., an upper and / or left adjacent block)) and a block in the reference picture. Therefore, in the second pattern matching, the block adjacent to the current block in the current picture is used as a predetermined area for calculating the evaluation value of the candidate.

[0089] 7 is a diagram illustrating an example of pattern matching (template matching) between a template in a current picture and a block in a reference picture. As shown in FIG. 7, in the second pattern matching, a motion vector of a current block is derived by searching a reference picture (Ref0) for a block that best matches a block adjacent to a current block (Cur block) in the current picture (Cur Pic). Specifically, a difference is derived between a reconstructed image of both or either of the coded areas adjacent to the left and / or above the current block and a reconstructed image at the same position in the coded reference picture (Ref0) specified by a candidate MV, an evaluation value is calculated using the obtained difference value, and the candidate MV with the best evaluation value among the multiple candidate MVs is selected as the best candidate MV.

[0090] Information indicating whether such a FRUC mode is applied (e.g., called an FRUC flag) is signaled at the CU level. Furthermore, when the FRUC mode is applied (e.g., when the FRUC flag is true), information indicating a pattern matching method (first pattern matching or second pattern matching) (e.g., called an FRUC mode flag) is signaled at the CU level. Note that signaling of this information does not need to be limited to the CU level, and may be at other levels (e.g., the sequence level, the picture level, the slice level, the tile level, the CTU level, or the sub-block level).

[0091] Here, we will explain a mode that derives a motion vector based on a model that assumes uniform linear motion. This mode is based on BIO (bi-directional optical This is sometimes called flow mode.

[0092] Fig. 8 is a diagram illustrating a model assuming uniform linear motion. In Fig. 8, (vx, vy) indicate a velocity vector, and τ0 and τ1 indicate the temporal distances between the current picture (Cur Pic) and two reference pictures (Ref0, Ref1), respectively. (MVx0, MVy0) indicate the motion vector corresponding to reference picture Ref0, and (MVx1, MVy1) indicate the motion vector corresponding to reference picture Ref1.

[0093] In this case, under the assumption of uniform linear motion of the velocity vector (vx, vy), (MVx0, MVy0) and (MVx1, MVy1) are expressed as (vxτ0, vyτ0) and (-vxτ1, -vyτ1), respectively, and the following optical flow equation (1) holds.

[0094]

number

[0095] Here, I(k) denotes the luminance value of reference image k (k=0,1) after motion compensation. This optical flow equation indicates that the sum of (i) the time derivative of the luminance value, (ii) the product of the horizontal velocity and the horizontal component of the spatial gradient of the reference image, and (iii) the product of the vertical velocity and the vertical component of the spatial gradient of the reference image is equal to zero. Based on a combination of this optical flow equation and Hermite interpolation, block-wise motion vectors obtained from a merge list or the like are corrected pixel by pixel.

[0096] Note that the decoding device may derive motion vectors using a method other than that based on a model assuming constant-velocity linear motion. For example, a motion vector may be derived for each sub-block based on the motion vectors of multiple adjacent blocks.

[0097] Here, a mode in which a motion vector is derived for each sub-block based on the motion vectors of multiple neighboring blocks will be described. This mode is sometimes called an affine motion compensation prediction mode.

[0098] 9A is a diagram illustrating the derivation of motion vectors for each sub-block based on the motion vectors of multiple adjacent blocks. In FIG. 9A, the current block includes 16 4x4 sub-blocks. Here, a motion vector v0 for the upper left corner control point of the current block is derived based on the motion vectors of the adjacent blocks, and a motion vector v1 for the upper right corner control point of the current block is derived based on the motion vectors of the adjacent sub-blocks. Then, using the two motion vectors v0 and v1, the motion vectors (vx, vy) of each sub-block within the current block are derived according to the following equation (2):

[0099]

number

[0100] Here, x and y respectively indicate the horizontal and vertical positions of the sub-block, and w indicates a predetermined weighting coefficient.

[0101] Such an affine motion compensation prediction mode may include several modes in which the methods of deriving the motion vectors of the upper-left and upper-right corner control points are different. Information indicating such an affine motion compensation prediction mode (e.g., called an affine flag) is signaled at the CU level. Note that the signaling of the information indicating this affine motion compensation prediction mode does not need to be limited to the CU level, and may be at other levels (e.g., the sequence level, the picture level, the slice level, the tile level, the CTU level, or the sub-block level).

[0102] [Predictive control unit] The prediction control unit 128 selects either the intra-prediction signal or the inter-prediction signal, and outputs the selected signal to the subtraction unit 104 and the addition unit 116 as a prediction signal.

[0103] Here, an example of deriving a motion vector for a picture to be coded in merge mode will be described. Fig. 9B is a diagram for explaining an overview of the motion vector derivation process in merge mode.

[0104] First, a prediction MV list is generated in which prediction MV candidates are registered. The prediction MV candidates include spatially adjacent prediction MVs, which are MVs held by multiple coded blocks spatially located around the block to be coded, temporally adjacent prediction MVs, which are MVs held by blocks in the vicinity of the block to be coded projected onto the coded reference picture, joint prediction MVs, which are MVs generated by combining the MV values ​​of the spatially adjacent prediction MVs and the temporally adjacent prediction MVs, and zero prediction MVs, which are MVs with a value of zero.

[0105] Next, one prediction MV is selected from the plurality of prediction MVs registered in the prediction MV list, and is determined as the MV for the block to be coded.

[0106] Furthermore, the variable length coding unit encodes the stream by describing merge_idx, which is a signal indicating which predicted MV has been selected.

[0107] Note that the predicted MVs registered in the predicted MV list described in Figure 9B are just an example, and the number may be different from the number shown in the figure, the configuration may not include some of the types of predicted MVs shown in the figure, or the configuration may include predicted MVs other than the types of predicted MVs shown in the figure.

[0108] The final MV may be determined by performing the DMVR process, which will be described later, using the MV of the block to be coded derived in the merge mode.

[0109] Here, an example of determining the MV using the DMVR process will be described.

[0110] FIG. 9C is a conceptual diagram for explaining an outline of the DMVR process.

[0111] First, the optimal MVP set for the block to be processed is set as a candidate MV, and reference pixels are obtained from the first reference picture, which is a processed picture in the L0 direction, and the second reference picture, which is a processed picture in the L1 direction, according to the candidate MV, and a template is generated by averaging each reference pixel.

[0112] Next, the template is used to search the surrounding areas of the candidate MVs in the first and second reference pictures, and the MV with the smallest cost is determined as the final MV. The cost value is calculated using the difference between each pixel value of the template and each pixel value of the search area, the MV value, etc.

[0113] The outline of the processing described here is basically the same for the encoding device and the decoding device.

[0114] Note that other processing may be used instead of the processing described here, as long as it is processing that can search the vicinity of the candidate MV and derive the final MV.

[0115] Here, a mode for generating a predicted image using LIC processing will be described.

[0116] FIG. 9D is a diagram for explaining an outline of a predicted image generation method using luminance correction processing by LIC processing.

[0117] First, an MV for obtaining a reference image corresponding to a block to be coded is derived from a reference picture that is a coded picture.

[0118] Next, for the block to be coded, the luminance pixel values ​​of the coded surrounding reference areas adjacent to the left and above and the luminance pixel values ​​at the equivalent positions in the reference picture specified by the MV are used to extract information indicating how the luminance values ​​have changed between the reference picture and the picture to be coded, and a luminance correction parameter is calculated.

[0119] A predicted image for the block to be coded is generated by performing luminance correction processing on a reference image in a reference picture specified by the MV using the luminance correction parameters.

[0120] The shape of the peripheral reference region in FIG. 9D is an example, and other shapes may be used.

[0121] Although the process of generating a predicted image from one reference picture has been described here, the process is similar when generating a predicted image from multiple reference pictures, and a luminance correction process is performed in a similar manner on the reference images obtained from each reference picture before generating a predicted image.

[0122] One method for determining whether to apply LIC processing is to use lic_flag, which is a signal indicating whether to apply LIC processing. As a specific example, an encoding device determines whether the encoding target block belongs to an area where a luminance change occurs, and if it belongs to an area where a luminance change occurs, sets the value of lic_flag to 1 and performs encoding by applying LIC processing, and if it does not belong to an area where a luminance change occurs, sets the value of lic_flag to 0 and performs encoding without applying LIC processing. On the other hand, a decoding device decodes lic_flag described in the stream, and switches whether to apply LIC processing depending on the value, and performs decoding.

[0123] As another method for determining whether to apply LIC processing, for example, there is also a method for determining whether LIC processing has been applied to surrounding blocks.As a specific example, when the block to be coded is in merge mode, it is determined whether the surrounding coded blocks selected when deriving MV in merge mode processing have been coded using LIC processing, and depending on the result, whether to apply LIC processing is switched and coded.In addition, in this example, the process in decoding is exactly the same.

[0124] [Overview of the decoding device] Next, an overview will be given of a decoding device capable of decoding the coded signal (coded bitstream) output from the above coding device 100. Fig. 10 is a block diagram showing the functional configuration of a decoding device 200 according to Embodiment 1. The decoding device 200 is a video / image decoding device that decodes video / images on a block-by-block basis.

[0125] As shown in FIG. 10, the decoding device 200 includes an entropy decoding unit 202, an inverse quantization unit 204, an inverse transform unit 206, an addition unit 208, a block memory 210, a loop filter unit 212, a frame memory 214, an intra prediction unit 216, an inter prediction unit 218, and a prediction control unit 220.

[0126] The decoding device 200 is realized by, for example, a general-purpose processor and memory. In this case, when a software program stored in the memory is executed by the processor, the processor functions as the entropy decoding unit 202, the inverse quantization unit 204, the inverse transform unit 206, the addition unit 208, the loop filter unit 212, the intra prediction unit 216, the inter prediction unit 218, and the prediction control unit 220. Alternatively, the decoding device 200 may be realized as one or more dedicated electronic circuits corresponding to the entropy decoding unit 202, the inverse quantization unit 204, the inverse transform unit 206, the addition unit 208, the loop filter unit 212, the intra prediction unit 216, the inter prediction unit 218, and the prediction control unit 220.

[0127] Each component included in the decoding device 200 will be described below.

[0128] [Entropy Decoding] The entropy decoding unit 202 entropy-decodes the coded bitstream. Specifically, the entropy decoding unit 202 arithmetically decodes the coded bitstream into a binary signal. The entropy decoding unit 202 then debinarizes the binary signal. As a result, the entropy decoding unit 202 outputs quantized coefficients to the inverse quantization unit 204 on a block-by-block basis.

[0129] [Dequantization section] The inverse quantization unit 204 inverse quantizes the quantized coefficients of a block to be decoded (hereinafter referred to as a current block) that is input from the entropy decoding unit 202. Specifically, the inverse quantization unit 204 inverse quantizes each quantized coefficient of the current block based on a quantization parameter corresponding to the quantized coefficient. The inverse quantization unit 204 then outputs the inverse quantized coefficients (i.e., transform coefficients) of the current block to the inverse transform unit 206.

[0130] [Inverse conversion section] The inverse transform unit 206 restores the prediction error by inverse transforming the transform coefficients input from the inverse quantization unit 204 .

[0131] For example, if the information interpreted from the encoded bitstream indicates that EMT or AMT is to be applied (e.g., the AMT flag is true), the inverse transform unit 206 inverse transforms the transform coefficients of the current block based on the interpreted information indicating the transform type.

[0132] Also, for example, if the information decoded from the coded bitstream indicates that NSST is to be applied, then inverse transform unit 206 applies an inverse re-transform to the transform coefficients.

[0133] [Adder] The adder 208 reconstructs the current block by adding the prediction error input from the inverse transformer 206 and the prediction sample input from the prediction control unit 220. The adder 208 then outputs the reconstructed block to the block memory 210 and the loop filter unit 212.

[0134] [Block Memory] The block memory 210 is a storage unit for storing blocks that are referenced in intra prediction and are in a picture to be decoded (hereinafter referred to as a current picture). Specifically, the block memory 210 stores the reconstructed blocks output from the adder 208.

[0135] [Loop filter section] The loop filter unit 212 applies a loop filter to the block reconstructed by the adder unit 208, and outputs the filtered reconstructed block to a frame memory 214, a display device, or the like.

[0136] If the information indicating ALF on / off read from the encoded bitstream indicates that ALF is on, one filter is selected from multiple filters based on the local gradient direction and activity, and the selected filter is applied to the reconstructed block.

[0137] [Frame memory] The frame memory 214 is a storage unit for storing reference pictures used in inter prediction, and is sometimes called a frame buffer. Specifically, the frame memory 214 stores the reconstructed blocks filtered by the loop filter unit 212.

[0138] [Intra prediction section] The intra prediction unit 216 generates a prediction signal (intra prediction signal) by performing intra prediction based on the intra prediction mode interpreted from the encoded bitstream, by referring to blocks in the current picture stored in the block memory 210. Specifically, the intra prediction unit 216 generates the intra prediction signal by performing intra prediction by referring to samples (e.g., luminance values, chrominance values) of blocks adjacent to the current block, and outputs the intra prediction signal to the prediction control unit 220.

[0139] Note that when an intra prediction mode that references a luminance block in intra prediction of a chrominance block is selected, the intra prediction unit 216 may predict the chrominance component of the current block based on the luminance component of the current block.

[0140] Furthermore, when information interpreted from the coded bitstream indicates the application of PDPC, the intra prediction unit 216 corrects pixel values ​​after intra prediction based on the gradients of reference pixels in the horizontal and vertical directions.

[0141] [Inter prediction section] The inter prediction unit 218 predicts the current block by referring to a reference picture stored in the frame memory 214. The prediction is performed in units of the current block or sub-blocks (e.g., 4x4 blocks) within the current block. For example, the inter prediction unit 218 generates an inter prediction signal for the current block or sub-block by performing motion compensation using motion information (e.g., motion vectors) interpreted from the coded bitstream, and outputs the inter prediction signal to the prediction control unit 220.

[0142] In addition, if the information interpreted from the encoded bitstream indicates that the OBMC mode is to be applied, the inter prediction unit 218 generates an inter prediction signal using not only the motion information of the current block obtained by motion search, but also the motion information of adjacent blocks.

[0143] Furthermore, if the information interpreted from the coded bitstream indicates that the FRUC mode is to be applied, the inter prediction unit 218 derives motion information by performing motion search according to the pattern matching method (bilateral matching or template matching) interpreted from the coded bitstream. Then, the inter prediction unit 218 performs motion compensation using the derived motion information.

[0144] Furthermore, when the BIO mode is applied, the inter prediction unit 218 derives a motion vector based on a model assuming constant-velocity linear motion. Furthermore, when information interpreted from the coded bitstream indicates that the affine motion compensation prediction mode is to be applied, the inter prediction unit 218 derives a motion vector for each sub-block based on the motion vectors of multiple adjacent blocks.

[0145] [Predictive control unit] The prediction control unit 220 selects either the intra-prediction signal or the inter-prediction signal, and outputs the selected signal to the addition unit 208 as a prediction signal.

[0146] (Embodiment 2) Next, a second embodiment will be described. In this embodiment, transform and inverse transform will be described in detail. Note that the configurations of the encoding device and the decoding device according to this embodiment are substantially the same as those of the first embodiment, and therefore illustrations and descriptions thereof will be omitted.

[0147] [Processing of the transform and quantization units of the encoding device] First, the processing of transform unit 106 and quantization unit 108 of coding device 100 according to the second embodiment will be described in detail with reference to Fig. 11. Fig. 11 is a flowchart showing the transform and quantization processing in coding device 100 according to the second embodiment.

[0148] First, the transform unit 106 selects a first transform basis for a block to be coded from one or more first transform basis candidates (S101). For example, the transform unit 106 may fixedly select a DCT-II transform basis as the first transform basis for the block to be coded. Alternatively, for example, the transform unit 106 may select the first transform basis using an adaptive basis selection mode.

[0149] The adaptive basis selection mode is a mode in which a transformation basis is adaptively selected from a plurality of predetermined transformation basis candidates based on a cost based on the difference between an original image and a reconstructed image and / or the amount of code. This adaptive basis selection mode is also called EMT mode or AMT mode. As the plurality of transformation basis candidates, for example, the plurality of transformation bases shown in FIG. 6 can be used. Note that the plurality of transformation basis candidates are not limited to the plurality of transformation bases shown in FIG. 6. For example, the plurality of transformation basis candidates may include a transformation base equivalent to performing no transformation.

[0150] By encoding identification information in the bitstream that indicates whether the adaptive basis selection mode or the fixed basis mode using a fixed transform basis (e.g., a type II DCT basis) is enabled, the adaptive basis selection mode and the fixed basis mode can be selectively used. This identification information corresponds to identification information indicating whether the adaptive basis selection mode is enabled. In this case, the identification information may be used to determine whether the first transform basis matches a predetermined transform basis. For example, EMT has identification information (emt_cu_flag) that indicates whether the adaptive basis selection mode or the fixed basis mode is enabled in units such as CU, so that the identification information can be used to determine whether the first transform basis matches a predetermined transform basis.

[0151] Then, the transform unit 106 generates first transform coefficients by performing a first transform on the residual of the block to be coded using the first transform base selected in step S102 (S102). The first transform corresponds to a linear transform.

[0152] The transform unit 106 determines whether the first transform base selected in step S101 matches a predetermined transform base (S103). For example, the transform unit 106 determines whether the first transform base matches any of a plurality of predetermined transform bases. Alternatively, for example, the transform unit 106 may determine whether the first transform base matches one predetermined transform base.

[0153] The predetermined transform base may be, for example, a transform base of a type II DCT (i.e., DCT-II) and / or a transform base similar thereto. Such a predetermined transform base may be predefined by a standard or the like. Alternatively, for example, the predetermined transform base may be determined based on coding parameters or the like.

[0154] If the first transform base matches the predetermined transform base (YES in S103), the transform unit 106 selects a second transform base for the block to be coded from one or more candidate second transform bases (S104). The transform unit 106 generates second transform coefficients by performing a second transform on the first transform coefficients using the selected second transform base (S105). The second transform corresponds to a secondary transform. The quantization unit 108 quantizes the generated second transform coefficients (S106), thereby completing the transform and quantization process.

[0155] The second transformation may be a secondary transformation called NSST, or may be a transformation that selectively uses one of multiple second transformation base candidates. In this case, the selected second transformation base may be fixed. That is, a predetermined fixed transformation base may be selected as the second transformation base. Alternatively, a transformation base equivalent to not performing the second transformation may be used as the second transformation base.

[0156] The NSST may also be a frequency space transform after the DCT or DST. For example, the NSST may be a Karhunen Loveve Transform (KLT) for transform coefficients of the DCT or DST obtained offline, or a Hypercube-Givens Transform (HyGT) that represents a basis equivalent to the KLT and is expressed by a combination of rotational transforms.

[0157] On the other hand, if the first transform base is different from the predetermined transform base (NO in S103), the transform unit 106 skips the second transform base selection step (S104) and the second transform step (S105). That is, the transform unit 106 does not perform the second transform. In this case, the first transform coefficients generated in step S207 are quantized (S106), and the transform and quantization process ends.

[0158] When the second transform step is skipped in this way, information indicating that the second transform will not be performed may be notified to the decoding device. Alternatively, when the second transform step is skipped, the second transform may be performed using a second transform base that is equivalent to not performing the transform, and information indicating the second transform base may be notified to the decoding device.

[0159] The inverse quantization unit 112 and the inverse transform unit 114 of the encoding device 100 perform processes that are the inverse of the processes performed by the transform unit 106 and the quantization unit 108, thereby reconstructing the current block to be encoded.

[0160] [Processing of the inverse quantization unit and inverse transform unit of the decoding device] Next, the processing of the inverse quantization unit 204 and the inverse transform unit 206 of the decoding device 200 according to the second embodiment will be specifically described with reference to Fig. 12. Fig. 12 is a flowchart showing the inverse quantization and inverse transform processing in the decoding device 200 according to the second embodiment.

[0161] First, the inverse quantization unit 204 inversely quantizes the quantized coefficients of the block to be decoded (S601). The inverse transform unit 206 determines whether or not a first inverse transform base for the block to be decoded matches a predetermined inverse transform base (S602). As the predetermined inverse transform base, an inverse transform base corresponding to the predetermined transform base used in the encoding device 100 is used.

[0162] If the first inverse transform base matches the predetermined inverse transform base (YES in S602), the inverse transform unit 206 selects a second inverse transform base for the block to be decoded (S603). Selecting an inverse transform base (the first inverse transform base or the second inverse transform base) in the decoding device 200 means determining the inverse transform base based on predetermined information. For example, a base selection signal can be used as the predetermined information. Alternatively, an intra prediction mode, a block size, or the like can be used as the predetermined information.

[0163] The inverse transform unit 206 generates second inverse transform coefficients by performing a second inverse transform on the inverse quantized coefficients of the block to be decoded using the selected second inverse transform base (S604). Furthermore, the inverse transform unit 206 selects a first inverse transform base (S605). The inverse transform unit 206 performs a first inverse transform on the second inverse transform coefficients generated in step S605 using the selected first inverse transform base (S606), thereby completing the inverse quantization and inverse transform process.

[0164] On the other hand, if the first inverse transform base is different from the predetermined inverse transform base (NO in S602), the inverse transform unit 206 skips the step of selecting a second inverse transform base (S603) and the step of performing a second inverse transform (S604). That is, the inverse transform unit 206 selects the first inverse transform base (S605) without performing a second inverse transform. The inverse transform unit 206 performs a first inverse transform on the coefficients inversely quantized in step S501 using the selected first inverse transform base (S606), and then ends the inverse quantization and inverse transform process.

[0165] [Effects, etc.] The inventors have found that conventional coding requires a huge amount of processing to search for an optimal combination of transform bases and transform parameters (e.g., filter coefficients) for both the first transform and the second transform. In contrast, the coding device 100 and the decoding device 200 according to this embodiment can skip the second transform depending on the first transform base. As a result, it is possible to reduce the processing required to search for an optimal combination of transform bases and transform parameters for both the first transform and the second transform, thereby realizing a reduction in processing load while suppressing a decrease in compression efficiency.

[0166] As described above, the encoding device 100 and the decoding device 200 according to this embodiment can skip the second transform when the first transform base is different from the predetermined transform base. The first transform coefficients generated by the first transform are affected by the first transform. Therefore, the effect of improving the compression ratio obtained by performing the second transform on the first transform coefficients often depends on the first transform base. Therefore, by skipping the second transform when the first transform base is different from the predetermined transform base that is highly effective in improving the compression ratio, it is possible to reduce the processing load while suppressing a decrease in compression efficiency.

[0167] In particular, with the Type II DCT, the concentration of low frequencies is often high, so the effect of the second transform is likely to be high. Therefore, by using the Type II DCT base as the predetermined transform base, the second transform is performed when the effect of improving compression efficiency by the second transform is large, and the second transform is skipped when this effect is not large, which is expected to realize a reduction in processing load while further suppressing a decrease in compression efficiency.

[0168] The above processing can be applied to both luminance signals and color difference signals, and if the input signal is in RGB format, it may be applied to each of the R, G, and B signals. Furthermore, the bases selectable in the first transform or the second transform may be different for luminance signals and color difference signals. For example, luminance signals have a wider frequency band than color difference signals. Therefore, in the transform of luminance signals, more bases may be selectable than for color differences.

[0169] The predetermined transformation base is not limited to one transformation base. In other words, the predetermined transformation base may be a plurality of transformation bases. In this case, it is sufficient to determine whether the first transformation base matches any of the plurality of predetermined transformation bases.

[0170] This aspect may be implemented in combination with at least a part of other aspects of the present disclosure. Also, some of the processes, some of the device configurations, and some of the syntax described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0171] (Embodiment 3) Next, a third embodiment will be described. This embodiment differs from the second embodiment in that the conversion process differs depending on whether intra prediction is used for the block to be coded / decoded. This embodiment will be described below with reference to the drawings, focusing on the differences from the second embodiment. In the following figures, steps that are substantially the same as those in the second embodiment will be given the same reference numerals, and duplicated descriptions will be omitted or simplified.

[0172] [Processing of the transform and quantization units of the encoding device] First, the processing of transform unit 106 and quantization unit 108 of coding device 100 according to the third embodiment will be described in detail with reference to Fig. 13. Fig. 13 is a flowchart showing the transform and quantization processing in coding device 100 according to the third embodiment.

[0173] First, the conversion unit 106 determines whether to use intra prediction or inter prediction for a current block to be coded (S201). For example, the conversion unit 106 determines whether to use intra prediction or inter prediction based on a cost based on the difference between an original image and a reconstructed image obtained by locally decoding a compressed image and / or the amount of coding. Alternatively, for example, the conversion unit 106 may determine whether to use intra prediction or inter prediction based on information (e.g., picture type) other than the cost based on the difference and / or the amount of coding.

[0174] Here, when it is determined that inter prediction is used for the current block to be coded (inter in S201), the transform unit 106 selects a first transform base for the current block to be coded from one or more first transform base candidates (S202). For example, the transform unit 106 fixedly selects a DCT-II transform base as the first transform base for the current block to be coded. Alternatively, for example, the transform unit 106 may select the first transform base from a plurality of first transform base candidates.

[0175] Then, the transform unit 106 performs a first transform on the residual of the block to be coded using the first transform base selected in step S202, thereby generating first transform coefficients (S203). The quantization unit 108 quantizes the generated first transform coefficients (S204), thereby completing the transform and quantization process.

[0176] On the other hand, if it is determined that intra prediction is to be used for the current block to be coded (intra in S201), the transform unit 106 executes steps S101 to S105 in the same manner as in Embodiment 2. Then, the quantization unit 108 quantizes the first transform coefficient generated in step S102 or the second transform coefficient generated in step S105 (S204), and the transform and quantization process ends.

[0177] [Processing of the inverse quantization unit and inverse transform unit of the decoding device] Next, the processing of the inverse quantization unit 204 and the inverse transform unit 206 of the decoding device 200 according to the third embodiment will be specifically described with reference to Fig. 14. Fig. 14 is a flowchart showing the inverse quantization and inverse transform processing in the decoding device 200 according to the third embodiment.

[0178] First, the inverse quantization unit 204 inversely quantizes the quantized coefficients of the block to be decoded (S601). The inverse transform unit 206 determines whether to use intra prediction or inter prediction for the block to be decoded (S701). For example, the inverse transform unit 206 determines whether to use intra prediction or inter prediction based on information acquired from a bitstream.

[0179] When it is determined that inter prediction is used for the block to be decoded (inter in S701), the inverse transform unit 206 selects a first inverse transform basis for the block to be decoded (S702). The inverse transform unit 206 performs a first inverse transform on the inverse quantized coefficients of the block to be decoded using the first inverse transform basis selected in step S503 (S703), and ends the inverse quantization and inverse transform process.

[0180] On the other hand, if it is determined that intra prediction is to be used for the block to be decoded (intra in S701), the inverse transform unit 206 executes steps S602 to S606, as in the second embodiment, and ends the inverse quantization and inverse transform process.

[0181] [Effects, etc.] According to the encoding device 100 and the decoding device 200 of this embodiment, it is possible to skip the second transform depending on the intra / inter prediction and the first transform base. As a result, it is possible to reduce the processing for searching for an optimal combination of the transform base and the transform parameters for both the first transform and the second transform, and it is possible to realize a reduction in the processing load while suppressing a decrease in compression efficiency.

[0182] This aspect may be implemented in combination with at least a part of other aspects of the present disclosure. Also, some of the processes, some of the device configurations, and some of the syntax described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0183] (Fourth embodiment) Next, a fourth embodiment will be described. This embodiment differs from the second and third embodiments in that the conversion process differs depending on the intra-prediction mode of the block to be coded / decoded. The following describes the fourth embodiment with reference to the drawings, focusing on the differences from the second and third embodiments. In the following drawings, steps that are substantially the same as those in the second or third embodiment are denoted by the same reference numerals, and duplicated descriptions are omitted or simplified.

[0184] [Processing of the transform and quantization units of the encoding device] First, the processing of transform unit 106 and quantization unit 108 of coding device 100 according to the fourth embodiment will be specifically described with reference to Fig. 15. Fig. 15 is a flowchart showing the transform and quantization processing in coding device 100 according to the fourth embodiment.

[0185] The transform unit 106 determines whether to use intra prediction or inter prediction for the current block to be coded (S201), as in Embodiment 2. If it is determined that inter prediction is to be used for the current block to be coded (inter in S201), the transform unit 106 executes steps S202 and S203, as in Embodiment 2. Furthermore, the quantization unit 108 quantizes the first transform coefficient generated in step S203 (S302).

[0186] On the other hand, when it is determined that intra prediction is to be used for the current block to be coded (intra in S201), the conversion unit 106 executes steps S101 and S102, as in the first embodiment. Then, the conversion unit 106 determines whether the intra prediction mode of the current block to be coded is a predetermined mode (S106). For example, the conversion unit 106 determines whether the intra prediction mode is a predetermined mode based on a cost based on the difference between the original image and the reconstructed image and / or the code amount. Note that the determination of whether the intra prediction mode is a predetermined mode may be performed based on information other than the cost.

[0187] The predetermined mode may be defined in advance by, for example, a standard specification, etc. Alternatively, for example, the predetermined mode may be determined based on encoding parameters, etc. For example, a diagonal directional prediction mode may be used as the predetermined mode.

[0188] The directional prediction mode is an intra prediction mode that uses a specific direction for predicting a block to be coded. In the directional prediction mode, pixel values ​​are predicted by extending the values ​​of reference pixels in a specific direction. Note that the pixel value is a value of each pixel that constitutes a picture, such as a luminance value or a chrominance value. For example, the directional prediction mode is an intra prediction mode excluding the DC prediction mode and the planar prediction mode.

[0189] The diagonal directional prediction mode is a directional prediction mode having a direction inclined with respect to the horizontal and vertical directions. For example, the diagonal directional prediction mode may be three directional prediction modes identified by 2 (lower left), 34 (upper left), and 66 (upper right) among 65 directional prediction modes identified by numbers 2 to 66 from lower left to upper right (see FIG. 5A). Furthermore, for example, the diagonal directional prediction mode may be seven directional prediction modes identified by numbers 2 to 3 (lower left), 33 to 35 (upper left), and 65 to 66 (upper right) among the 65 directional prediction modes.

[0190] If the intra prediction mode is not the predetermined mode (NO in S301), the transform unit 106 determines whether the first transform base selected in step S101 matches the predetermined transform base (S103).

[0191] If the intra prediction mode is a predetermined mode (YES in S301), or if the first transform base matches the predetermined transform base (YES in S103), the transform unit 106 selects a second transform base for the current block from one or more second transform base candidates (S104). The transform unit 106 generates second transform coefficients by performing a second transform on the first transform coefficients using the selected second transform base (S105). The quantization unit 108 quantizes the generated second transform coefficients (S302), and the transform and quantization process ends.

[0192] If the intra prediction mode is different from the predetermined mode (NO in S301) and the first transform base is different from the predetermined transform base (NO in S103), the transform unit 106 skips the second transform base selection step (S104) and the second transform step (S105). That is, the transform unit 106 does not perform the second transform. In this case, the first transform coefficient generated in step S102 is quantized (S302), and the transform and quantization process ends.

[0193] [Processing of the inverse quantization unit and inverse transform unit of the decoding device] Next, the processing of the inverse quantization unit 204 and the inverse transform unit 206 of the decoding device 200 according to the fourth embodiment will be specifically described with reference to Fig. 16. Fig. 16 is a flowchart showing the inverse quantization and inverse transform processing in the decoding device 200 according to the fourth embodiment.

[0194] First, the inverse quantization unit 204 inversely quantizes the quantized coefficients of the block to be decoded (S601). The inverse transform unit 206 determines whether intra prediction or inter prediction is to be used for the block to be decoded (S701).

[0195] When it is determined that inter prediction is to be used for the block to be decoded (inter in S701), the inverse transform unit 206 executes steps S702 and S703, as in the third embodiment, and ends the inverse quantization and inverse transform process.

[0196] On the other hand, when it is determined that intra prediction is to be used for the block to be decoded (intra at S701), the inverse transform unit 206 determines whether the intra prediction mode of the block to be decoded is a predetermined mode (S801). The predetermined mode used by the decoding device 200 is the same as the predetermined mode used by the encoding device 100.

[0197] If the intra prediction mode is not a predetermined mode (NO in S801), the inverse transform unit 206 determines whether or not the first inverse transform base for the current block matches a predetermined inverse transform base (S602).

[0198] If the intra prediction mode is a predetermined mode (YES in S801), or if the first inverse transform base matches the predetermined inverse transform base (YES in S602), steps S603 to S606 are executed, as in embodiment 2, and the inverse quantization and inverse transform processing is terminated.

[0199] On the other hand, if the intra prediction mode is different from the predetermined mode (NO in S801) and the first inverse transform base is different from the predetermined inverse transform base (NO in S602), the inverse transform unit 206 skips the second inverse transform base selection step (S603) and the second inverse transform step (S604). That is, the inverse transform unit 206 selects the first inverse transform base without performing the second inverse transform (S605). The inverse transform unit 206 performs the first inverse transform on the coefficients inversely quantized in step S501 using the selected first inverse transform base (S606), and ends the inverse quantization and inverse transform process.

[0200] [Effects, etc.] As described above, the encoding device 100 and the decoding device 200 according to this embodiment can skip the second transform depending on the intra prediction mode and the first transform base. As a result, it is possible to reduce the processing for searching for an optimal combination of transform bases and transform parameters for both the first transform and the second transform, and it is possible to reduce the processing load while suppressing a decrease in compression efficiency.

[0201] In particular, if a diagonal directional prediction mode is used as the predetermined mode, the second transform can be performed when the diagonal directional prediction mode is used for the encoding / decoding target block, and the second transform can be skipped in other cases. This makes it possible to reduce the processing load while suppressing a decrease in compression efficiency.

[0202] Generally, the first transform performs DCT or DST that can be separated in the vertical and horizontal directions. In this case, the first transform does not utilize diagonal correlation. Therefore, when a diagonal directional prediction mode with high diagonal correlation is used, it is difficult to sufficiently aggregate coefficients using only the first transform. Therefore, when a diagonal directional prediction mode is used for intra prediction, the second transform is performed using a second transform base that utilizes diagonal correlation, thereby making it possible to further aggregate coefficients and improve compression efficiency.

[0203] Note that the order of steps in the flowcharts of Figures 15 and 16 is not limited to the order described in Figures 15 and 16. For example, in Figure 15, the step of determining whether or not the intra prediction mode is a predetermined mode (S801) and the step of determining whether or not the first transformation base matches the predetermined transformation base (S602) may be performed in the reverse order or simultaneously.

[0204] This aspect may be implemented in combination with at least a part of other aspects of the present disclosure. Also, some of the processes, some of the device configurations, and some of the syntax described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0205] (Embodiment 5) Next, a fifth embodiment will be described. In this embodiment, encoding / decoding of information related to transform / inverse transform will be described. The following describes this embodiment with reference to the drawings, focusing on differences from the second to fourth embodiments. Note that in this embodiment, the transform and quantization processes, and the inverse quantization and inverse transform processes are substantially the same as those in the fourth embodiment, and therefore their description will be omitted.

[0206] [Entropy coding process of the coding device] The encoding process of information related to transformation in the entropy encoding unit 110 of the encoding device 100 according to the fifth embodiment will be specifically described with reference to Fig. 17. Fig. 17 is a flowchart showing the encoding process in the encoding device 100 according to the fifth embodiment.

[0207] When inter prediction is used for the current block to be coded (inter in S401), the entropy coding unit 110 codes a first basis selection signal into the bitstream (S402). Here, the first basis selection signal is information or data indicating the first transformation basis selected in step S202 of FIG. 15.

[0208] Encoding a signal into a bitstream means placing a code representing information in the bitstream. The code is generated by, for example, context-adaptive binary arithmetic coding (CABAC). Note that the code does not necessarily have to be generated by CABAC or entropy coding. For example, the code may be the information itself (e.g., a flag of 0 or 1).

[0209] Next, the entropy coding unit 110 codes the coefficients quantized in step S302 of FIG. 15 (S403), and ends the coding process.

[0210] When intra prediction is used for the encoding target block (intra in S401), the entropy encoding unit 110 encodes an intra prediction mode signal indicating the intra prediction mode of the encoding target block into the bitstream (S404). Furthermore, the entropy encoding unit 110 encodes a first basis selection signal into the bitstream (S405). Here, the first basis selection signal is information or data indicating the first transform base selected in step S101 of FIG. 15.

[0211] Here, if the second transform has been performed (YES in S406), the entropy coding unit 110 encodes the second basis selection signal into the bitstream (S407). Here, the second basis selection signal is information or data indicating the second transform base selected in step S104. On the other hand, if the second transform has not been performed (NO in S406), the entropy coding unit 110 skips the step of encoding the second basis selection signal (S407). In other words, the entropy coding unit 110 does not encode the second basis selection signal.

[0212] Finally, the entropy coding unit 110 codes the coefficients quantized in step S302 (S408), and the coding process ends.

[0213] [Syntax] FIG. 18 shows a specific example of syntax in the fifth embodiment.

[0214] In Figure 18, a prediction mode signal (pred_mode), an intra prediction mode signal (pred_mode_dir), and an adaptive selection mode signal (emt_mode), and, if necessary, a first basis selection signal (primary_transform_type) and a second basis selection signal (secondary_transform_type), are coded in the bitstream.

[0215] The prediction mode signal (pred_mode) indicates whether intra prediction or inter prediction is used for the current block to be coded / decoded (here, the coding unit). The inverse transform unit 206 of the decoding device 200 can determine whether to use intra prediction for the current block to be coded or decoded based on this prediction mode signal.

[0216] The intra prediction mode signal (pred_mode_dir) indicates the intra prediction mode when intra prediction is used for the block to be coded / decoded. Based on this intra prediction mode signal, the inverse transform unit 206 of the decoding device 200 can determine whether the intra prediction mode of the block to be coded is a predetermined mode.

[0217] The adaptive selection mode signal (emt_mode) indicates whether an adaptive basis selection mode, which adaptively selects a transform basis from among multiple candidate transform bases, is used for the block to be coded / decoded. Here, when the adaptive selection mode signal is "ON," a transform basis is selected from among Type V DCT, Type VIII DCT, Type I DST, and Type VII DST. Conversely, when the adaptive selection mode signal is "OFF," a Type II DCT is selected. Based on this adaptive selection mode signal, the inverse transform unit 206 of the decoding device 200 can determine whether the first inverse transform basis for the block to be coded matches a predetermined inverse transform basis.

[0218] The first basis selection signal (primary_transform_type) indicates the first transform basis / inverse transform basis used for the transform / inverse transform of the current block to be coded / decoded. The first basis selection signal is coded in the bitstream when the adaptive selection mode signal is "ON". Conversely, when the adaptive selection mode signal is "OFF", the first basis selection signal is not coded. The inverse transform unit 206 of the decoding device 200 can select the first inverse transform basis based on this first basis selection signal.

[0219] The second basis selection signal (secondary_transform_type) indicates a second transform basis / inverse transform basis used for transform / inverse transform of the current block to be coded / decoded. The second basis selection signal is coded into the bitstream when the adaptive selection mode signal is "ON" and the intra prediction mode signal is "2," "34," or "66." The intra prediction mode signals "2," "34," and "66" all indicate a diagonal directional prediction mode. That is, when the first transform basis matches the type II DCT basis and the intra prediction mode is a diagonal directional prediction mode, the second basis selection signal is coded into the bitstream. Conversely, when the intra prediction mode is not a diagonal directional prediction mode, the second basis selection signal is not coded into the bitstream. The inverse transform unit 206 of the decoding device 200 can select a second inverse transform basis based on this second basis selection signal.

[0220] Although the type V DCT, type VIII DCT, type I DST, and type VII DST have been used as transform bases selectable in the adaptive basis selection mode, the present invention is not limited to these. For example, a type IV DCT may be used instead of the type V DCT. The type IV DCT can reuse part of the processing of the type II DCT, thereby reducing the processing load. Alternatively, a type IV DST may be used. The type IV DST can reuse part of the processing of the type IV DCT, thereby reducing the processing load.

[0221] [Entropy decoding process of the decoding device] Next, the processing of the entropy decoding unit 202 of the decoding device 200 according to the fifth embodiment will be specifically described with reference to Fig. 19. Fig. 19 is a flowchart showing the decoding processing in the decoding device 200 according to the fifth embodiment.

[0222] When inter prediction is used for the current block to be decoded (inter in S901), the entropy decoding unit 202 decodes a first basis selection signal from the bitstream (S902).

[0223] Decoding a signal from a bit stream means deciphering a code representing information from the bit stream and restoring the information from the deciphered code. Context-adaptive binary arithmetic decoding (CABAD), for example, is used to restore information from the code. It is not necessary to use CABAD or entropy decoding to restore information from the code. For example, if the deciphered code itself represents information (e.g., a flag of 0 or 1), it is sufficient to simply decipher the code.

[0224] Next, the entropy decoding unit 202 decodes the quantized coefficients from the bitstream (S903), and ends the decoding process.

[0225] When intra prediction is used for the block to be decoded (intra in S901), the entropy decoding unit 202 decodes an intra prediction mode signal from the bitstream (S904). Furthermore, the entropy decoding unit 202 decodes a first basis selection signal from the bitstream (S905).

[0226] Here, if the second inverse transform is to be performed (YES in S906), the entropy decoding unit 202 decodes the second basis selection signal from the bitstream (S907). On the other hand, if the second inverse transform is not to be performed (NO in S906), the entropy decoding unit 202 skips the step of decoding the second basis selection signal (S907). In other words, the entropy decoding unit 202 does not decode the second basis selection signal.

[0227] Finally, the entropy decoding unit 202 decodes the quantized coefficients from the bitstream (S908), and the decoding process ends.

[0228] [Effects, etc.] As described above, according to the encoding device 100 and the decoding device 200 according to this embodiment, the first base selection signal and the second base selection signal can be encoded in a bitstream. Then, by encoding the intra prediction mode signal and the first base selection signal before the second base selection signal, it is possible to determine whether to skip the second inverse transform before decoding the second base selection signal. Therefore, if the second inverse transform is skipped, it is also possible to skip encoding the second base selection signal, thereby improving compression efficiency.

[0229] (Sixth embodiment) Next, a sixth embodiment will be described. This embodiment differs from the fifth embodiment in that information indicating the intra prediction mode in which the second transform is performed is encoded. This embodiment will be described below with reference to the drawings, focusing on the differences from the fifth embodiment. In the following drawings, steps that are substantially the same as those in the fifth embodiment will be denoted by the same reference numerals, and duplicated descriptions will be omitted or simplified.

[0230] [Entropy coding process of the coding device] The encoding process of information related to transformation in the entropy encoding unit 110 of the encoding device 100 according to the sixth embodiment will be specifically described with reference to Fig. 20. Fig. 20 is a flowchart showing the encoding process in the encoding device 100 according to the sixth embodiment.

[0231] If inter prediction is used for the current block to be coded (inter in S401), the entropy coding unit 110 executes steps S402 and S403 in the same manner as in the fifth embodiment, and ends the coding process.

[0232] On the other hand, when intra prediction is used for the encoding target block (intra in S401), the entropy coding unit 110 encodes a second conversion target prediction mode signal into a bitstream (S501). The second conversion target prediction mode signal indicates a predetermined mode for determining whether to perform a second inverse transform. Specifically, the second conversion target prediction mode signal indicates, for example, an intra prediction mode number (e.g., 2, 34, and 66).

[0233] The coding unit of the second conversion target prediction mode signal may be a CU (Coding Unit) or a CTU (Coding Tree Unit) unit, or an SPS (Sequence Parameter Set) or PPS (Picture Parameter Set) or slice unit corresponding to the H.265 / HEVC standard.

[0234] Thereafter, the entropy encoding unit 110 executes steps S404 to S408 in the same manner as in the fifth embodiment, and ends the encoding process.

[0235] [Entropy decoding process of the decoding device] Next, the processing of the entropy decoding unit 202 of the decoding device 200 according to the sixth embodiment will be specifically described with reference to Fig. 21. Fig. 21 is a flowchart showing the decoding processing in the decoding device 200 according to the sixth embodiment.

[0236] When inter prediction is used for the block to be decoded (inter in S901), the entropy decoding unit 202 executes steps S902 and S903 in the same manner as in the fifth embodiment, and ends the decoding process.

[0237] On the other hand, when intra prediction is used for the block to be decoded (intra in S901), the entropy decoding unit 202 decodes the second conversion current prediction mode signal from the bitstream (S1001).

[0238] Thereafter, the entropy decoding unit 202 executes steps S904 to S908 in the same manner as in the fifth embodiment, and ends the decoding process.

[0239] [Effects, etc.] As described above, according to the encoding device 100 and the decoding device 200 of this embodiment, it is possible to encode, into a bitstream, a second transform target prediction mode signal indicating a predetermined mode, which is an intra prediction mode for performing a second transform / inverse transform. Therefore, it is possible to arbitrarily determine the predetermined mode on the encoding device 100 side, thereby improving compression efficiency.

[0240] The order in which each signal is coded may be determined in advance, and the various signals may be coded in an order different from the above-described coding order.

[0241] This aspect may be implemented in combination with at least a part of other aspects of the present disclosure. Also, some of the processes, some of the device configurations, and some of the syntax described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0242] (Embodiment 7) Various modifications may be made to the above second to sixth embodiments.

[0243] For example, in each of the above embodiments, the first transform base may be fixed depending on the size of the block to be coded / decoded. For example, if the block size is smaller than a certain size (e.g., 4x4 pixels, 4x8 pixels, or 8x4 pixels), the first transform base may be fixed to the transform base of Type VII DST, and coding of the first basis selection signal may be skipped.

[0244] Furthermore, for example, in each of the above embodiments, a signal indicating whether or not to enable the selection of the first transform base and the first transform, or the selection of the second transform base and the second transform, may be coded. For example, if the process of skipping the second transform is enabled, the second base selection signal may not be coded, and therefore the decoding operation differs from when skipping the second transform is disabled. The coding unit for such a signal is CU (Coding Unit). It may be in units of a coding unit (CTU) or coding tree unit (CTU), or it may be in units of a sequence parameter set (SPS), picture parameter set (PPS), or slice, which correspond to the H.265 / HEVC standard.

[0245] Also, for example, in each of the above embodiments, the selection of the first transform base and the first transform may be skipped, and the selection of the second transform base and the second transform may be skipped, based on the picture type (I, P, B), slice type (I, P, B), block size, number of non-zero coefficients, quantization parameter, and Temporal_id (layer of hierarchical coding).

[0246] When the encoding device performs the above operations, the decoding device also performs corresponding operations. For example, if information indicating whether to enable the process of skipping the first transform or the second transform is encoded, the decoding device decodes the information and determines whether the first or second transform is enabled and whether the first or second basis selection signal is encoded.

[0247] In the above-mentioned fifth and sixth embodiments, a plurality of signals (for example, an intra-prediction mode signal, an adaptive selection mode signal, a first basis selection signal, and a second basis selection signal) are coded in a bitstream, but in the above-mentioned second to fourth embodiments, these signals do not have to be coded in a bitstream. For example, these signals may be notified from the coding device 100 to the decoding device 200 separately from the bitstream.

[0248] In this embodiment, the positions of each of the multiple signals (e.g., intra prediction mode signal, adaptive selection mode signal, first basis selection signal, and second basis selection signal) in the bitstream are not particularly limited. The multiple signals are, for example, encoded into at least one of multiple headers. The multiple headers may be, for example, a video parameter set, a sequence parameter set, a picture parameter set, and a slice header. When signals exist in multiple layers (e.g., picture parameter sets and slice headers), a signal in a lower layer (e.g., slice header) overwrites a signal in a higher layer (e.g., picture parameter set).

[0249] (Embodiment 8) In the above-described embodiments and modifications, each of the functional blocks can typically be realized by an MPU, memory, etc. Furthermore, the processing by each of the functional blocks is typically realized by a program execution unit such as a processor reading and executing software (programs) recorded on a recording medium such as a ROM. The software may be distributed by downloading, etc., or may be recorded on a recording medium such as a semiconductor memory and distributed. Naturally, each functional block can also be realized by hardware (dedicated circuits).

[0250] Furthermore, the processes described in the embodiments and modifications may be realized by centralized processing using a single device (system), or may be realized by distributed processing using multiple devices. The processor that executes the program may be a single processor or multiple processors. That is, centralized processing or distributed processing may be performed.

[0251] The present invention is not limited to the above-described embodiments, and various modifications are possible, and these modifications are also included within the scope of the present invention.

[0252] Furthermore, here, we will explain application examples of the video encoding method (image encoding method) or video decoding method (image decoding method) shown in the above embodiment and each modification, and a system using the same. The system is characterized by having an image encoding device using the image encoding method, an image decoding device using the image decoding method, and an image encoding / decoding device that includes both. Other components of the system can be appropriately changed depending on the situation.

[0253] [Usage example] 22 is a diagram showing the overall configuration of a content supply system ex100 that provides a content distribution service. The area where communication services are provided is divided into cells of a desired size, and base stations ex106, ex107, ex108, ex109, and ex110, which are fixed wireless stations, are installed in each cell.

[0254] In this content supply system ex100, devices such as a computer ex111, a game console ex112, a camera ex113, a home appliance ex114, and a smartphone ex115 are connected to the Internet ex101 via an Internet service provider ex102 or a communication network ex104 and base stations ex106 to ex110. The content supply system ex100 may be configured to connect a combination of any of the above elements. The devices may be connected to each other directly or indirectly via a telephone network or short-range wireless communication, without using the base stations ex106 to ex110, which are fixed wireless stations. Furthermore, a streaming server ex103 is connected to devices such as the computer ex111, the game console ex112, the camera ex113, the home appliance ex114, and the smartphone ex115 via the Internet ex101, etc. Furthermore, the streaming server ex103 is connected to a terminal in a hotspot on an airplane ex117, etc., via a satellite ex116.

[0255] Note that wireless access points, hotspots, etc. may be used instead of the base stations ex106 to ex110. Furthermore, the streaming server ex103 may be directly connected to the communication network ex104 without going through the Internet ex101 or the Internet service provider ex102, or may be directly connected to an airplane ex117 without going through a satellite ex116.

[0256] The camera ex113 is a device capable of taking still images and videos, such as a digital camera. The smartphone ex115 is a smartphone, mobile phone, or PHS (Personal Handyphone System) that is compatible with mobile communication systems generally known as 2G, 3G, 3.9G, 4G, and 5G.

[0257] The home appliance ex118 is a refrigerator or an appliance included in a home fuel cell cogeneration system.

[0258] In the content supply system ex100, a terminal having a photographing function is connected to a streaming server ex103 via a base station ex106 or the like, thereby enabling live streaming and the like. In live streaming, a terminal (such as a computer ex111, a game console ex112, a camera ex113, a home appliance ex114, a smartphone ex115, or a terminal on an airplane ex117) performs the encoding process described in the above embodiment and each modification on still image or video content captured by a user using the terminal, multiplexes the video data obtained by encoding with audio data obtained by encoding audio corresponding to the video, and transmits the obtained data to the streaming server ex103. In other words, each terminal functions as an image encoding device according to one aspect of the present invention.

[0259] Meanwhile, the streaming server ex103 streams the transmitted content data to the requesting client. The client is a computer ex111, a game console ex112, a camera ex113, a home appliance ex114, a smartphone ex115, a terminal on an airplane ex117, or the like, which is capable of decoding the encoded data. Each device that receives the distributed data decodes and plays back the received data. That is, each device functions as an image decoding device according to one aspect of the present invention.

[0260] [Distributed processing] The streaming server ex103 may also be multiple servers or multiple computers that process, record, and distribute data in a distributed manner. For example, the streaming server ex103 may be implemented as a CDN (Content Delivery Network), where content distribution is achieved through a network connecting numerous edge servers distributed around the world. In a CDN, a physically nearby edge server is dynamically assigned depending on the client. Content is then cached and distributed to that edge server, thereby reducing delays. Furthermore, if an error occurs or communication conditions change due to increased traffic, processing can be distributed among multiple edge servers, the distribution entity can be switched to another edge server, or distribution can be continued by bypassing the affected network portion, thereby achieving high-speed and stable distribution.

[0261] In addition to the distributed processing of the distribution itself, the encoding of captured data can be performed on each device, on the server side, or shared among devices. For example, encoding generally involves two processing loops. The first loop detects the image complexity or code size for each frame or scene. The second loop maintains image quality while improving encoding efficiency. For example, a device can perform the first encoding process, and the server that receives the content can perform the second encoding process, thereby improving content quality and efficiency while reducing the processing load on each device. In this case, if there is a request for near-real-time reception and decoding, the data encoded by a device can be received and played back on another device, enabling more flexible real-time distribution.

[0262] As another example, the camera ex113 or the like extracts features from an image, compresses the data related to the features as metadata, and transmits the data to the server. The server performs compression according to the meaning of the image, for example, by determining the importance of an object from the features and switching the quantization precision accordingly. The feature data is particularly effective in improving the accuracy and efficiency of motion vector prediction when the server recompresses the image. Alternatively, the terminal may perform simple encoding such as VLC (variable length coding), and the server may perform encoding with a heavy processing load such as CABAC (context-adaptive binary arithmetic coding).

[0263] As another example, in a stadium, shopping mall, factory, etc., there may be multiple pieces of video data that have been shot by multiple terminals of almost the same scene. In this case, using the multiple terminals that shot the video and, as necessary, other terminals and servers that did not shoot the video, encoding processes are assigned to each of them, for example, in units of GOPs (Group of Pictures), pictures, or tiles obtained by dividing a picture, for distributed processing. This reduces delays and achieves better real-time performance.

[0264] Furthermore, since multiple pieces of video data are of nearly the same scene, the server may manage and / or instruct the video data shot by each terminal to be mutually referenced. Alternatively, the server may receive encoded data from each terminal and change the reference relationships between multiple pieces of data, or correct or replace the pictures themselves and re-encode them. This allows for the generation of streams with improved quality and efficiency for each piece of data.

[0265] The server may also perform transcoding to change the encoding format of the video data before distributing it. For example, the server may convert MPEG-based encoding to VP-based encoding, or convert H.264 to H.265.

[0266] In this way, the encoding process can be performed by a terminal or one or more servers. Therefore, although the following uses terms such as "server" or "terminal" to refer to the entity performing the process, some or all of the processing performed by the server may be performed by the terminal, and some or all of the processing performed by the terminal may be performed by the server. The same applies to the decoding process.

[0267] [3D, multi-angle] In recent years, there has been an increasing trend to integrate and use images or videos of different scenes or the same scene taken from different angles by multiple devices such as cameras ex113 and / or smartphones ex115 that are nearly synchronized with each other. The videos taken by each device are integrated based on the relative positional relationship between the devices obtained separately, or on areas where feature points included in the videos match.

[0268] The server may not only encode 2D video, but also encode still images automatically or at a time specified by the user based on scene analysis of the video and transmit them to the receiving terminal. Furthermore, if the server can acquire the relative positional relationship between the capturing terminals, it can generate a 3D shape of the scene based on not only the 2D video but also images of the same scene captured from different angles. The server may also separately encode 3D data generated by point clouds, or may select or reconstruct images to be transmitted to the receiving terminal from images captured by multiple terminals based on the results of recognizing or tracking people or objects using the 3D data.

[0269] In this way, users can enjoy scenes by selecting any video corresponding to each camera device, or can enjoy content in which video from any viewpoint is extracted from 3D data reconstructed using multiple images or videos. Furthermore, like the video, sound may also be collected from multiple different angles, and the server may multiplex and transmit sound from a specific angle or space in accordance with the video.

[0270] In recent years, content that associates the real world with a virtual world, such as Virtual Reality (VR) and Augmented Reality (AR), has also become popular. In the case of VR images, the server creates viewpoint images for the right eye and left eye, and may perform encoding that allows reference between the viewpoint images using Multi-View Coding (MVC) or the like, or may encode them as separate streams without mutual reference. When decoding the separate streams, it is preferable to play them in synchronization with each other so that a virtual three-dimensional space is reproduced according to the user's viewpoint.

[0271] In the case of AR images, the server superimposes virtual object information in virtual space onto camera information in real space based on the 3D position or the user's viewpoint movement. The decoding device may acquire or store virtual object information and 3D data, generate a 2D image according to the user's viewpoint movement, and smoothly connect the images to create superimposed data. Alternatively, the decoding device may send the user's viewpoint movement to the server in addition to a request for virtual object information, and the server may create superimposed data based on the viewpoint movement received from the 3D data stored on the server, encode the superimposed data, and distribute it to the decoding device. Note that the superimposed data may also have an α value indicating transparency in addition to RGB, and the server may set the α value of parts other than the object created from the 3D data to 0, etc., to encode the parts in a transparent state. Alternatively, the server may generate data by setting a predetermined RGB value as the background, like a chromakey, and using the background color for parts other than the object.

[0272] Similarly, the decoding of distributed data may be performed by each client terminal, by the server, or by multiple terminals. For example, one terminal may first send a reception request to the server, and then other terminals may receive and decode content according to the request, after which the decoded signal is transmitted to a device with a display. By distributing the processing and selecting appropriate content regardless of the capabilities of the communication terminals themselves, high-quality data can be reproduced. As another example, large-sized image data may be received on a TV or other device, and only a portion of the picture, such as a tile into which the picture is divided, may be decoded and displayed on the viewer's personal device. This allows the viewer to share the overall picture while checking their own area of ​​responsibility or an area of ​​interest in more detail.

[0273] In the future, it is expected that content will be seamlessly received by switching the appropriate data for the current connection using delivery system standards such as MPEG-DASH in situations where multiple short-, medium-, or long-distance wireless communications are available, both indoors and outdoors. This will allow users to freely select and switch between decoding and display devices, such as their own devices, indoors and outdoors, in real time. Decoding can also be performed by switching between decoding and display devices based on user location information. This will enable users to display map information on the wall or ground of a neighboring building with an embedded display device while traveling to their destination. It is also possible to switch the bit rate of received data based on the accessibility of the encoded data on the network, such as if the encoded data is cached on a server that can be quickly accessed from the receiving device or copied to an edge server in a content delivery service.

[0274] [Scalable Coding] Content switching will be described using a scalable stream compressed and encoded using the video encoding method described in the above-described embodiment and each of the variations, as shown in FIG. 23. The server may have multiple streams with the same content but different qualities, but may also switch content by taking advantage of the characteristics of a temporally / spatially scalable stream achieved by encoding the stream in layers, as shown in the figure. In other words, the decoder determines which layer to decode based on internal factors such as performance and external factors such as communication bandwidth, allowing the decoder to freely switch between low-resolution and high-resolution content. For example, if a user wants to continue watching a video they were watching on their smartphone ex115 while on the go on a device such as an Internet TV after returning home, the device can simply decode the same stream up to different layers, thereby reducing the burden on the server.

[0275] Furthermore, in addition to the above-described scalability configuration in which pictures are coded for each layer and an enhancement layer exists above a base layer, the enhancement layer may include meta-information based on image statistics, etc., and the decoding side may generate high-quality content by super-resolving pictures in the base layer based on the meta-information. Super-resolution may mean either improving the signal-to-noise ratio at the same resolution or increasing the resolution. The meta-information may include information for specifying linear or nonlinear filter coefficients used in the super-resolution process, or information for specifying parameter values ​​in the filter process, machine learning, or least-squares calculation used in the super-resolution process.

[0276] Alternatively, a picture may be divided into tiles or the like according to the meaning of objects in the image, and the decoding side may select tiles to decode and decode only a portion of the area. Furthermore, by storing the object's attributes (such as a person, a car, or a ball) and its position in the video (such as a coordinate position in the same image) as meta information, the decoding side can identify the position of a desired object based on the meta information and determine the tile containing the object. For example, as shown in FIG. 24, the meta information is stored using a data storage structure different from that of pixel data, such as an SEI message in HEVC. This meta information indicates, for example, the position, size, or color of the main object.

[0277] Furthermore, meta information may be stored in units consisting of multiple pictures, such as streams, sequences, or random access units, which allows the decoding side to obtain the time when a specific person appears in the video, and by combining this with information in units of pictures, it is possible to identify the picture in which the object exists and the position of the object within the picture.

[0278] [Webpage optimization] FIG. 25 is a diagram showing an example of a web page display screen on a computer ex111 or the like. FIG. 26 is a diagram showing an example of a web page display screen on a smartphone ex115 or the like. As shown in FIGS. 25 and 26, a web page may include multiple link images that are links to image content, and the appearance of the web page may differ depending on the device used to view the page. When multiple link images are visible on the screen, the display device (decoding device) may display a still image or I-picture contained in each content as a link image, display a video such as a GIF animation using multiple still images or I-pictures, or receive only the base layer and decode and display the video until the user explicitly selects a link image, or until the link image approaches the center of the screen or until the entire link image is within the screen.

[0279] When a link image is selected by a user, the display device decodes the base layer with the highest priority. If the HTML constituting the web page contains information indicating that the content is scalable, the display device may decode up to the enhancement layer. To ensure real-time performance, before a selection is made or when the communication bandwidth is very limited, the display device decodes and displays only forward-referenced pictures (I-pictures, P-pictures, and forward-reference-only B-pictures), thereby reducing the delay between the decoding time of the first picture and the display time (the delay from the start of content decoding to the start of display). Alternatively, the display device may intentionally ignore the picture reference relationships and roughly decode all B-pictures and P-pictures using forward reference, and then perform normal decoding as the number of received pictures increases over time.

[0280] [Autonomous driving] Furthermore, when transmitting and receiving still image or video data such as 2D or 3D map information for automatic driving or driving assistance of a vehicle, the receiving terminal may receive weather or construction information as meta information in addition to image data belonging to one or more layers, and may associate and decode these. Note that the meta information may belong to a layer, or may simply be multiplexed with the image data.

[0281] In this case, since a vehicle, drone, airplane, etc. including a receiving terminal moves, the receiving terminal can realize seamless reception and decoding while switching between base stations ex106 to ex110 by transmitting the location information of the receiving terminal at the time of a reception request. Also, the receiving terminal can dynamically switch how much meta information to receive or how much to update map information depending on the user's selection, user situation, or communication bandwidth status.

[0282] In this way, in the content supply system ex100, the client can receive, decode, and play back the encoded information sent by the user in real time.

[0283] [Distribution of personal content] Furthermore, the content supply system ex100 allows not only high-quality, long-duration content from video distribution companies, but also unicast or multicast distribution of low-quality, short-duration content from individuals. It is expected that such personal content will continue to increase in the future. To improve the quality of personal content, the server may perform editing before encoding. This can be achieved, for example, with the following configuration.

[0284] During shooting, either in real time or after accumulating the footage, the server performs recognition processing such as detecting shooting errors, scene search, semantic analysis, and object detection from the original image or encoded data. Based on the recognition results, the server manually or automatically corrects out-of-focus or camera shake, deletes less important scenes (e.g., scenes with lower brightness or out-of-focus compared to other pictures), emphasizes object edges, changes color, and performs other editing. The server then encodes the edited data based on the editing results. It is also known that viewing rates decrease if the shooting time is too long. Therefore, the server may automatically clip not only less important scenes as described above but also scenes with little movement, based on the image processing results, so that the content falls within a specific time range depending on the shooting time. Alternatively, the server may generate and encode a digest based on the results of the semantic analysis of the scene.

[0285] In some cases, personal content may contain content that infringes copyright, moral rights, or portrait rights, or may cause the scope of sharing to exceed the intended scope, resulting in inconvenience to individuals. Therefore, for example, the server may intentionally defocus images of people's faces on the periphery of the screen or the interior of a house before encoding. The server may also recognize whether the image to be encoded contains the face of a person other than a pre-registered person, and if so, perform processing such as blurring the face. Alternatively, as pre- or post-processing before encoding, the user may specify a person or background area they wish to modify in the image for copyright or other reasons, and the server may replace the specified area with another image or blur the focus. For a person, the server may track the person in the video and replace the image of the face.

[0286] Furthermore, because viewing personal content with small data volumes requires real-time performance, the decoding device first receives the base layer as a top priority, and then decodes and plays it back, depending on the bandwidth. The decoding device may also receive an enhancement layer during this time, and if the content is played back more than twice, such as when playback is looped, it may play back high-quality video, including the enhancement layer. A stream that has undergone scalable encoding in this way can provide an experience in which the video appears rough when not selected or when viewing begins, but gradually becomes smoother and the image quality improves. In addition to scalable encoding, a similar experience can also be provided by configuring a single stream consisting of a rough stream played the first time and a second stream that is encoded with reference to the first video.

[0287] [Other use cases] Furthermore, these encoding or decoding processes are generally performed by the LSIex500 possessed by each terminal. The LSIex500 may be a single chip or may be configured with multiple chips. It is also possible to incorporate video encoding or decoding software into some kind of recording medium (such as a CD-ROM, flexible disk, or hard disk) that can be read by the computer ex111, and perform the encoding or decoding process using that software. Furthermore, if the smartphone ex115 is equipped with a camera, video data captured by the camera may be transmitted. This video data is data that has been encoded by the LSIex500 possessed by the smartphone ex115.

[0288] The LSIex500 may be configured to download and activate application software. In this case, the terminal first determines whether it supports the content encoding method or has the capability to execute a specific service. If the terminal does not support the content encoding method or does not have the capability to execute a specific service, the terminal downloads the codec or application software and then acquires and plays the content.

[0289] Furthermore, at least one of the video encoding devices (image encoding devices) or video decoding devices (image decoding devices) of the above-described embodiments and modifications can be incorporated into a digital broadcasting system, not limited to the content supply system ex100 via the Internet ex101. Since multiplexed data in which video and audio are multiplexed is transmitted and received over broadcast radio waves using a satellite or the like, the content supply system ex100 is more suited to multicast than the unicast configuration of the content supply system ex100, but similar applications are possible with regard to the encoding and decoding processes.

[0290] [Hardware configuration] FIG. 27 is a diagram illustrating a smartphone ex115. FIG. 28 is a diagram illustrating an example configuration of the smartphone ex115. The smartphone ex115 includes an antenna ex450 for transmitting and receiving radio waves to and from the base station ex110, a camera unit ex465 capable of capturing video and still images, and a display unit ex458 for displaying video captured by the camera unit ex465 and decoded data of the video and other data received by the antenna ex450. The smartphone ex115 further includes an operation unit ex466 such as a touch panel, an audio output unit ex457 such as a speaker for outputting voice or sound, an audio input unit ex456 such as a microphone for inputting voice, a memory unit ex467 capable of storing encoded data or decoded data such as captured video or still images, recorded voice, received video or still images, and email, and a slot unit ex464 that serves as an interface with a SIM ex468 for identifying users and authenticating access to various data, including networks. In addition, an external memory may be used instead of the memory unit ex467.

[0291] In addition, a main control unit ex460 that comprehensively controls the display unit ex458 and operation unit ex466, etc., is connected to a power supply circuit unit ex461, an operation input control unit ex462, a video signal processing unit ex455, a camera interface unit ex463, a display control unit ex459, a modulation / demodulation unit ex452, a multiplexing / separation unit ex453, an audio signal processing unit ex454, a slot unit ex464, and a memory unit ex467 via a bus ex470.

[0292] When the power key is turned on by a user, the power supply circuit unit ex461 supplies power from the battery pack to each unit, thereby starting up the smartphone ex115 into an operational state.

[0293] The smartphone ex115 processes calls, data communications, and other communications under the control of a main control unit ex460, which includes a CPU, ROM, RAM, and the like. During calls, the audio signal collected by the audio input unit ex456 is converted into a digital audio signal by the audio signal processing unit ex454, which then undergoes spectrum spread processing by the modulation / demodulation unit ex452, digital-to-analog conversion processing and frequency conversion processing by the transmission / reception unit ex451, and then transmitted via the antenna ex450. The received data is amplified, frequency-converted, and analog-to-digital converted, then subjected to spectrum despreading processing by the modulation / demodulation unit ex452, and converted into an analog audio signal by the audio signal processing unit ex454, which then outputs the amplified data from the audio output unit ex457. During data communications mode, text, still images, or video data is sent to the main control unit ex460 via the operation input control unit ex462 by operating the operation unit ex466, etc., of the main unit, and similar transmission and reception processing is performed. When transmitting video, still images, or video and audio in the data communication mode, the video signal processing unit ex455 compresses and encodes the video signal stored in the memory unit ex467 or the video signal input from the camera unit ex465 using the video encoding method described in the above embodiment and each modification, and sends the encoded video data to the multiplexing / demultiplexing unit ex453. The audio signal processing unit ex454 encodes the audio signal collected by the audio input unit ex456 while the camera unit ex465 is capturing video, still images, etc., and sends the encoded audio data to the multiplexing / demultiplexing unit ex453. The multiplexing / demultiplexing unit ex453 multiplexes the encoded video data and encoded audio data using a predetermined method, and modulates and converts the data in the modulation / demodulation unit (modulation / demodulation circuit unit) ex452 and the transmission / reception unit ex451, before transmitting the data via the antenna ex450.

[0294] When receiving video attached to an email or chat, or video linked to a web page, etc., the multiplexed data received via the antenna ex450 is decoded by the multiplexing / separation unit ex453, which separates the multiplexed data into a video data bitstream and an audio data bitstream. The multiplexing / separation unit ex453 then supplies the encoded video data to the video signal processing unit ex455 via the synchronization bus ex470, and supplies the encoded audio data to the audio signal processing unit ex454. The video signal processing unit ex455 decodes the video signal using a video decoding method corresponding to the video encoding method described in the above embodiment and each modification, and displays the video or still image included in the linked video file on the display unit ex458 via the display control unit ex459. The audio signal processing unit ex454 decodes the audio signal, and the audio is output from the audio output unit ex457. Note that with the widespread use of real-time streaming, audio playback may be socially inappropriate depending on the user's circumstances. Therefore, a configuration that initially plays only the video data without playing the audio signal is desirable. The audio may be played in synchronization only when the user performs an operation such as clicking on the video data.

[0295] Although the smartphone ex115 has been used as an example, three types of implementation are possible for the terminal: a transmitting / receiving terminal having both an encoder and a decoder, a transmitting terminal having only an encoder, and a receiving terminal having only a decoder. Furthermore, in the digital broadcasting system, multiplexed data in which audio data and the like are multiplexed onto video data is received or transmitted, but the multiplexed data may also include text data related to the video in addition to audio data, or the video data itself may be received or transmitted instead of the multiplexed data.

[0296] While the main control unit ex460, which includes a CPU, controls the encoding and decoding processes, devices often also include a GPU. Therefore, a configuration is possible in which a memory shared by the CPU and GPU, or a memory with addresses managed for common use, is used to take advantage of the GPU's performance and process a large area at once. This shortens encoding time, ensures real-time performance, and achieves low latency. It is particularly efficient to perform motion estimation, deblocking filtering, SAO (Sample Adaptive Offset), and transformation and quantization processes at a picture level or other unit in the GPU rather than the CPU. [Industrial Applicability]

[0297] The present disclosure is applicable to, for example, television receivers, digital video recorders, car navigation systems, mobile phones, digital cameras, digital video cameras, and the like. [Explanation of symbols]

[0298] 100 Encoding device 102 Division 104 Subtraction section 106 Conversion unit 108 Quantization section 110 Entropy coding unit 112, 204 Inverse quantization section 114, 206 Inverse conversion unit 116, 208 Addition section 118, 210 block memory 120, 212 Loop filter section 122, 214 frame memory 124, 216 Intra prediction section 126, 218 Inter prediction section 128, 220 Predictive control section 200 Decryption Device 202 Entropy Decoding Unit

Claims

1. 1. An encoding device for encoding a current block in a picture, comprising: circuitry and memory; The circuit uses the memory to: determining whether to use intra prediction for the current block; performing a conversion process when it is determined that intra prediction is to be used for the current block; quantizing the transform coefficients produced by the transform process; The conversion process includes: (i) when an intra prediction mode of the current block is different from a predetermined mode and a first transform base is the same as a predetermined transform base, generating first transform coefficients by performing a first transform on a residual signal of the current block using the first transform base, and generating second transform coefficients by performing a second transform on the first transform coefficients using a second transform base; (ii) generating first transform coefficients by performing a first transform on a residual signal of the current block using the first transform base when the intra prediction mode of the current block is different from the predetermined mode and a first transform base is different from the predetermined transform base; [0033] A coding device including a processing

2. A decoding device for decoding a current block in a picture, comprising: circuitry and memory; The circuit uses the memory to: determining whether to use intra prediction for the current block; performing an inverse transform process when it is determined that intra prediction is to be used for the current block; The inverse transformation process is (i) when the intra prediction mode of the current block is different from a predetermined mode and a first inverse transform base is the same as a predetermined inverse transform base, generating second inverse transform coefficients by performing a second inverse transform on inverse quantization coefficients of the current block using a second inverse transform base, and performing a first inverse transform on the second inverse transform coefficients using the first inverse transform base; (ii) when the intra prediction mode of the current block is different from the predetermined mode and the first inverse transform base is different from the predetermined inverse transform base, performing the first inverse transform on the inverse quantized coefficients of the current block using the first inverse transform base without performing the second inverse transform; a decoding device including a decoding process.

3. 1. A method for encoding a current block in a picture, the method comprising: determining whether to use intra prediction for the current block; performing a transform process when it is determined that intra prediction is to be used for the current block; quantizing the transform coefficients produced by the transform process; The conversion process includes: (i) when an intra prediction mode of the current block is different from a predetermined mode and a first transform base is the same as a predetermined transform base, generating first transform coefficients by performing a first transform on a residual signal of the current block using the first transform base, and generating second transform coefficients by performing a second transform on the first transform coefficients using a second transform base; (ii) generating first transform coefficients by performing a first transform on a residual signal of the current block using the first transform base when the intra prediction mode of the current block is different from the predetermined mode and a first transform base is different from the predetermined transform base; The encoding method includes processing.

4. 1. A decoding method for decoding a current block in a picture, the decoding method comprising: determining whether to use intra prediction for the current block; performing an inverse transform process when it is determined that intra prediction is to be used for the current block; The inverse transformation process is (i) when the intra prediction mode of the current block is different from a predetermined mode and a first inverse transform base is the same as a predetermined inverse transform base, generating second inverse transform coefficients by performing a second inverse transform on inverse quantization coefficients of the current block using a second inverse transform base, and performing a first inverse transform on the second inverse transform coefficients using the first inverse transform base; (ii) when the intra prediction mode of the current block is different from the predetermined mode and the first inverse transform base is different from the predetermined inverse transform base, performing the first inverse transform on the inverse quantized coefficients of the current block using the first inverse transform base without performing the second inverse transform; A decoding method, including processing.

5. 1. A method for transmitting a bitstream, the method comprising: determining whether to use intra prediction for the current block; performing a transform process when it is determined that intra prediction is to be used for the current block; quantizing the transform coefficients produced by the transform process; generating a bitstream; transmitting the bitstream; The conversion process includes: (i) when an intra prediction mode of the current block is different from a predetermined mode and a first transform base is the same as a predetermined transform base, generating first transform coefficients by performing a first transform on a residual signal of the current block using the first transform base, and generating second transform coefficients by performing a second transform on the first transform coefficients using a second transform base; (ii) generating first transform coefficients by performing a first transform on a residual signal of the current block using the first transform base when the intra prediction mode of the current block is different from the predetermined mode and a first transform base is different from the predetermined transform base; Transmission methods, including processing.

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