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

Abstract

An encoding device is provided that can further improve compression efficiency and reduce processing load. [Solution] The encoding device (100) determines whether a mode for selecting a transform base according to the size of the block to be encoded is enabled, and if the mode is enabled, selects a first transform base from among multiple candidate transform bases as a horizontal transform base when the horizontal size of the block to be encoded is larger than a threshold size, and selects a second transform base, which is a fixed transform base, as a horizontal transform base when the horizontal size of the block to be encoded is smaller than the threshold size, and generates first transform coefficients by performing a first transform on the residual of the block to be encoded using the selected horizontal transform base, and generates second transform coefficients by performing a second transform on the first transform coefficients, and generates a bitstream including information indicating whether the mode is enabled.

Description

[Technical Field]

[0001] The present disclosure relates to an encoding device, a decoding device, an encoding method, a decoding method, and a transmission method. [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)) [Non-patent document 2] Jianle Chen et al., Algorithm Description of Joint Exploration Test Model 5 (JEM 5), Joint Video Exploration Team (JVET) of ITU-T SG 16 WP 3and ISO / IEC JTC 1 / SC 29 / WG 11 5th Meeting: Geneva, CH, Document: JVET-E1001, January 2017 Summary of the Invention [Problem to be solved by the invention]

[0004] In such encoding and decoding techniques, there is a demand for further improvement in compression efficiency and reduction in processing load.

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

[0006] An encoding device according to one embodiment of the present disclosure is an encoding device having a circuit and a memory, wherein the circuit uses the memory to determine whether a mode for selecting a transform base according to the size of a block to be encoded is enabled, and if the mode is enabled, when the horizontal size of the block to be encoded is larger than a threshold size, selects a first transform base from among multiple candidate transform bases as a horizontal transform base, and when the horizontal size of the block to be encoded is smaller than the threshold size, selects a second transform base, which is a fixed transform base, as a horizontal transform base, uses the selected horizontal transform base to perform a first transform on the residual of the block to be encoded to generate first transform coefficients, and performs a second transform on the first transform coefficients to generate second transform coefficients, and generates a bitstream including information indicating whether the mode is enabled.

[0007] A decoding device according to one embodiment of the present disclosure is a decoding device having a circuit and a memory, wherein the circuit uses the memory to generate transform coefficients by performing a second inverse transform on coefficients of a block to be decoded, and determines whether a mode for selecting a transform base according to the size of the block to be decoded is enabled. If the mode is enabled, when the horizontal size of the block to be decoded is larger than a threshold size, a first inverse transform base is selected from multiple candidate inverse transform bases as a horizontal inverse transform base, and when the horizontal size of the block to be decoded is smaller than the threshold size, a second inverse transform base, which is a fixed inverse transform base, is selected as a horizontal inverse transform base, and a prediction residual is generated by performing a first inverse transform on the transform coefficients of the block to be decoded using the selected horizontal inverse transform base.

[0008] 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]

[0009] The present disclosure can provide an encoding device, a decoding device, an encoding method, a decoding method, or a transmission method that can further improve compression efficiency and reduce processing load. [Brief explanation of the drawings]

[0010] [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 11A] FIG. 11A is a block diagram showing an internal configuration of a conversion unit of a coding device according to the first aspect of the first embodiment. [Figure 11B] FIG. 11B is a block diagram showing an internal configuration of an inverse transform unit of a coding device according to the first aspect of Embodiment 1. As shown in FIG. [Figure 12A] FIG. 12A is a flowchart showing the processing of a transform unit and a quantization unit of the encoding device according to the first aspect of the first embodiment. [Figure 12B] FIG. 12B is a flowchart showing a modification of the processing performed by the transform unit and the quantization unit of the encoding device according to the first aspect of the first embodiment. [Figure 13A] FIG. 13A is a flowchart showing the processing of a transform unit and a quantization unit of the encoding device according to the second aspect of the first embodiment. [Figure 13B]FIG. 13B is a flowchart showing the process of the entropy coding unit of the coding device according to the second aspect of the first embodiment. [Figure 14] FIG. 14 is a diagram showing a specific example of syntax in the second aspect of the first embodiment. [Figure 15] FIG. 15 is a table showing specific examples of the transformation bases used in the second example of the first embodiment and whether or not the signal is coded. [Figure 16] FIG. 16 is a flowchart showing the processing of the transform unit and the quantization unit of the encoding device according to the third aspect of the first embodiment. [Figure 17A] FIG. 17A is a flowchart showing the processing of a transform unit and a quantization unit of the encoding device according to the fourth aspect of the first embodiment. [Figure 17B] FIG. 17B is a flowchart showing the process of the entropy coding unit of the coding device according to the fourth aspect of the first embodiment. [Figure 18] FIG. 18 is a diagram showing a specific example of syntax in the fourth aspect of the first embodiment. [Figure 19] FIG. 19 is a table showing specific examples of the transformation bases and whether or not the signals are coded, which are used in the fourth example of the first embodiment. [Figure 20] FIG. 20 is a block diagram showing an internal configuration of an inverse transform unit of a decoding device according to the fifth aspect of the first embodiment. [Figure 21] FIG. 21 is a flowchart showing the processing of the inverse quantization unit and the inverse transform unit of the decoding device according to the fifth aspect of the first embodiment. [Figure 22A] FIG. 22A is a flowchart showing the process of the entropy decoding unit of the decoding device according to the sixth aspect of the first embodiment. [Figure 22B] FIG. 22B is a flowchart showing the processing of the inverse quantization unit and the inverse transform unit of the decoding device according to the sixth aspect of Embodiment 1. [Figure 23] FIG. 23 is a flowchart showing the processing of the inverse quantization unit and the inverse transform unit of the decoding device according to the seventh aspect of the first embodiment. [Figure 24A]FIG. 24A is a flowchart showing processing by the entropy decoding unit of the decoding device according to the eighth aspect of the first embodiment. [Figure 24B] FIG. 24B is a flowchart showing the processing of the inverse quantization unit and the inverse transform unit of the decoding device according to the eighth aspect of Embodiment 1. [Figure 25] FIG. 25 is a diagram showing the overall configuration of a content supply system that realizes a content distribution service. [Figure 26] FIG. 26 is a diagram showing an example of a coding structure for scalable coding. [Figure 27] FIG. 27 is a diagram showing an example of a coding structure for scalable coding. [Figure 28] FIG. 28 is a diagram showing an example of a display screen of a web page. [Figure 29] FIG. 29 is a diagram showing an example of a display screen of a web page. [Figure 30] FIG. 30 is a diagram illustrating an example of a smartphone. [Figure 31] FIG. 31 is a block diagram showing an example of the configuration of a smartphone. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0012] 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.

[0013] (Embodiment 1) First, an overview of embodiment 1 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, embodiment 1 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 embodiment 1.

[0014] 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.

[0015] (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 may be replaced with the processes described in each aspect of the present disclosure. (7) Some of the processes included in the method performed by the encoding device or decoding device of the first embodiment may be performed in combination with the processes described in each aspect of the present disclosure. 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.

[0016] [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.

[0017] 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.

[0018] 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.

[0019] Each component included in the encoding device 100 will be described below.

[0020] [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.

[0021] 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.

[0022] 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).

[0023] 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.

[0024] The top right 64x64 block is divided horizontally into two rectangular 64x32 blocks 14 and 15 (binary tree block division).

[0025] 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.

[0026] The bottom right 64x64 block 23 is not split.

[0027] 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.

[0028] 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.

[0029] [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.

[0030] 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.

[0031] [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.

[0032] 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).

[0033] 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.

[0034] 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).

[0035] 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).

[0036] 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.

[0037] 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.

[0038] 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).

[0039] [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.

[0040] 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).

[0041] 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.

[0042] [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.

[0043] [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.

[0044] [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.

[0045] 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.

[0046] [Addition section] 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.

[0047] [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.

[0048] [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).

[0049] 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.

[0050] 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).

[0051] The gradient direction value D is derived, for example, by comparing gradients in multiple directions (e.g., horizontal, vertical, and two diagonal directions), and the gradient activity value A is derived, for example, by adding gradients in multiple directions and quantizing the sum.

[0052] Based on the result of such classification, a filter for the sub-block is determined from among a plurality of filters.

[0053] 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).

[0054] 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).

[0055] 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).

[0056] [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.

[0057] [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.

[0058] 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.

[0059] 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).

[0060] 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.

[0061] 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.

[0062] 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).

[0063] [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.

[0064] 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.

[0065] 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).

[0066] 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).

[0067] 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.

[0068] First, a predicted image (Pred) is obtained by normal motion compensation using a motion vector (MV) assigned to the block to be coded.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] The target block to be processed may be a prediction block unit or a sub-block unit obtained by further dividing the prediction block.

[0075] 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 by applying 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. Meanwhile, a decoding device decodes obmc_flag described in a stream, and switches whether to apply OBMC processing depending on the value, and performs decoding.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] The same processing may be performed when processing is performed in sub-block units.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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).

[0089] 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.

[0090] FIG. 8 is a diagram for explaining a model assuming uniform linear motion. In FIG. 8, (v x ,v y) denotes a velocity vector, and τ0 and τ1 denote the temporal distance between the current picture (Cur Pic) and two reference pictures (Ref0 and Ref1), respectively. (MVx0,MVy0) denotes a motion vector corresponding to reference picture Ref0, and (MVx1,MVy1) denotes a motion vector corresponding to reference picture Ref1.

[0091] At this time, the velocity vector (v x ,v y ), (MVx0,MVy0) and (MVx1,MVy1) are respectively (v x τ0,v y τ0) and (-v x τ1,-v y τ1), and the following optical flow equation (1) holds:

[0092]

number

[0093] 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.

[0094] 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.

[0095] Here, a mode in which a motion vector is derived for each sub-block based on the motion vectors of a plurality of neighboring blocks will be described. This mode is sometimes called an affine motion compensation prediction mode.

[0096] FIG. 9A is a diagram for explaining 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, the motion vector v0 of the upper left corner control point of the current block is derived based on the motion vectors of the adjacent blocks, and the motion vector v1 of 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 vector (v x ,v y ) is derived.

[0097]

number

[0098] Here, x and y respectively indicate the horizontal and vertical positions of the sub-block, and w indicates a predetermined weighting coefficient.

[0099] 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).

[0100] [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.

[0101] 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.

[0102] 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 located spatially 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 position of the block to be coded in a 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.

[0103] 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.

[0104] Furthermore, the variable length coding unit encodes the stream by describing merge_idx, which is a signal indicating which predicted MV has been selected.

[0105] 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.

[0106] 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.

[0107] Here, an example of determining the MV using the DMVR process will be described.

[0108] FIG. 9C is a conceptual diagram for explaining an outline of the DMVR process.

[0109] 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.

[0110] Next, the template is used to search the surrounding areas of the candidate MVs of 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 value between each pixel value of the template and each pixel value of the search area, the MV value, etc.

[0111] The outline of the processing described here is basically the same for the encoding device and the decoding device.

[0112] 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.

[0113] Here, a mode for generating a predicted image using LIC processing will be described.

[0114] FIG. 9D is a diagram for explaining an outline of a predicted image generation method using luminance correction processing by LIC processing.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] The shape of the peripheral reference region in FIG. 9D is an example, and other shapes may be used.

[0119] 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.

[0120] As a method for determining whether to apply LIC processing, for example, there is a method using 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. Meanwhile, a decoding device decodes lic_flag described in the stream, and switches whether to apply LIC processing depending on the value, and performs decoding.

[0121] As another method of determining whether to apply LIC processing, for example, there is also a method of determining whether LIC processing has been applied to surrounding blocks.As a specific example, when the block to be coded is in merge mode, determine whether the surrounding coded blocks selected when deriving MV in merge mode processing have been coded using LIC processing, and then switch whether to apply LIC processing according to the result and perform coding.In addition, in this example, the process in decoding is also exactly the same.

[0122] [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.

[0123] 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.

[0124] 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.

[0125] Each component included in the decoding device 200 will be described below.

[0126] [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.

[0127] [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.

[0128] [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 .

[0129] 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.

[0130] 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.

[0131] [Addition section] 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.

[0132] [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.

[0133] [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.

[0134] 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.

[0135] [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.

[0136] [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.

[0137] 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.

[0138] 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.

[0139] [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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] [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.

[0144] (First aspect of first embodiment) Next, the first aspect of the first embodiment will be specifically described with reference to the drawings.

[0145] [Internal structure of the conversion unit of the encoding device] First, the internal configuration of the transform unit 106 of the encoding device 100 according to this aspect will be described with reference to Fig. 11A. Fig. 11A is a block diagram showing the internal configuration of the transform unit 106 of the encoding device 100 according to the first aspect of the first embodiment.

[0146] As shown in FIG. 11A, the conversion unit 106 according to this embodiment includes a conversion mode determination unit 1061, a size determination unit 1062, a first conversion base selection unit 1063, a first conversion unit 1064, a second conversion implementation determination unit 1065, a second conversion base selection unit 1066, and a second conversion unit 1067.

[0147] The transform mode determination unit 1061 determines whether or not the adaptive transform base selection mode is valid for the block to be coded. The adaptive transform base selection mode is a mode in which a transform base is adaptively selected from one or more first transform base candidates. The determination of whether or not the adaptive transform base selection mode is valid is performed based on, for example, identification information of the first transform base or the adaptive transform base selection mode.

[0148] The size determination unit 1062 determines whether the horizontal size of the block to be coded exceeds a first horizontal threshold size. The size determination unit 1062 also determines whether the vertical size of the block to be coded exceeds a first vertical threshold size. The first horizontal threshold size may be the same as or different from the first vertical threshold size. The first horizontal threshold size and the first vertical threshold size may be predefined, for example, by a standard. Alternatively, for example, the first horizontal threshold size and the first vertical threshold size may be determined based on an image and coded into a bitstream.

[0149] The first transformation basis selection unit 1063 selects a first transformation basis. In the present disclosure, selecting a basis includes selecting at least one basis from a plurality of basis candidates, as well as determining or setting at least one basis without a plurality of basis candidates.

[0150] When the adaptive transformation base selection mode is not enabled, the first transformation base selection unit 1063 selects one basic transformation base as the first transformation base in the horizontal and vertical directions. When the adaptive transformation base selection mode is enabled, the first transformation base selection unit 1063 selects the first transformation base in the horizontal and vertical directions according to the horizontal and vertical sizes of the current block to be coded, as shown in the following (1) to (4).

[0151] (1) When the horizontal size of the block to be coded is larger than a first horizontal threshold size, the first transformation base selection unit 1063 adaptively selects a first transformation base in the horizontal direction from one or more candidate transformation bases.

[0152] (2) If the horizontal size of the block to be coded is equal to or smaller than the first horizontal threshold size, the first transformation base selection unit 1063 selects a fixed transformation base in the horizontal direction as the first transformation base in the horizontal direction.

[0153] (3) If the vertical size of the block to be coded is larger than the first vertical threshold size, the first transformation base selection unit 1063 adaptively selects a first transformation base in the vertical direction from one or more candidate transformation bases.

[0154] (4) If the vertical size of the block to be coded is equal to or smaller than the first vertical threshold size, the first transformation base selection unit 1063 selects a fixed transformation base in the vertical direction as the first transformation base in the vertical direction.

[0155] The horizontally fixed transformation base may be the same as or different from the vertically fixed transformation base, and may be, for example, the type 7 discrete sine transform (DST-VII) transformation base.

[0156] The first transform unit 1064 generates first transform coefficients by performing a first transform on the residual of the current block to be coded using the first transform base selected by the first transform base selection unit 1063. Specifically, the first transform unit 1064 performs a first transform in the horizontal direction using the first transform base in the horizontal direction, and a first transform in the vertical direction using the first transform base in the vertical direction.

[0157] The second transform execution determination unit 1065 determines whether to execute a second transform for further transforming the first transform coefficients, based on whether the adaptive transform basis selection mode is enabled for the block to be coded. Specifically, the second transform execution determination unit 1065 executes the second transform when the adaptive transform basis selection mode is not enabled, and determines not to execute the second transform when the adaptive transform basis selection mode is enabled.

[0158] The second transformation basis selection unit 1066 selects the second transformation basis when it is determined that the second transformation is to be performed. That is, the second transformation basis selection unit 1066 selects the second transformation basis when the adaptive transformation basis selection mode is not enabled. Conversely, when the adaptive transformation basis selection mode is enabled, the second transformation basis selection unit 1066 does not select the second transformation basis. That is, the second transformation basis selection unit 1066 skips the selection of the second transformation basis when the adaptive transformation basis selection mode is enabled.

[0159] When it is determined that the second transform is to be performed, the second transform unit 1067 transforms the first transform coefficients using the second transform base selected by the second transform base selection unit 1066. That is, when the adaptive transform base selection mode is not enabled, the second transform unit 1067 generates the second transform coefficients by performing the second transform on the first transform coefficients using the second transform base. Conversely, when the adaptive transform base selection mode is enabled, the second transform unit 1067 does not perform the second transform on the first transform coefficients. That is, when the adaptive transform base selection mode is enabled, the second transform unit 1067 skips the second transform.

[0160] [Internal configuration of the inverse transform unit of the encoding device] Next, the internal configuration of the inverse transform unit 114 of the coding device 100 according to this aspect will be described with reference to Fig. 11B. Fig. 11B is a block diagram showing the internal configuration of the inverse transform unit 114 of the coding device 100 according to the first aspect of Embodiment 1.

[0161] As shown in FIG. 11B, the inverse transformation unit 114 according to this embodiment includes a second inverse transformation basis selection unit 1141, a second inverse transformation unit 1142, a first inverse transformation basis selection unit 1143, and a first inverse transformation unit 1144.

[0162] When the adaptive transformation base selection mode is not enabled for the block to be coded, the second inverse transformation base selection unit 1141 selects the inverse transformation base of the second transformation base selected by the second transformation base selection unit 1066 as the second inverse transformation base.

[0163] When the adaptive transform basis selection mode is not enabled for the current block to be coded, the second inverse transform unit 1142 generates second inverse transform coefficients by performing a second inverse transform on the inverse quantized coefficients using the second inverse transform basis selected by the second inverse transform basis selection unit 1141. The inverse quantized coefficients refer to coefficients that have been inverse quantized by the inverse quantization unit 112.

[0164] The first inverse transformation basis selection unit 1143 selects an inverse transformation basis of the first transformation basis selected by the first transformation basis selection unit 1063 as the first inverse transformation basis.

[0165] When the adaptive transform basis selection mode is not enabled for the current block to be coded, the first inverse transform unit 1144 performs a first inverse transform on the second inverse transform coefficients using the first inverse transform basis to reconstruct the residual of the current block to be coded. On the other hand, when the adaptive transform basis selection mode is enabled for the current block to be coded, the first inverse transform unit 1144 performs a first inverse transform on the inverse quantization coefficients using the first inverse transform basis to reconstruct the residual of the current block to be coded.

[0166] [Processing of the transform and quantization units of the encoding device] Next, the processing of the transform unit 106 configured as above will be described together with the processing of the quantization unit 108 with reference to Fig. 12A. Fig. 12A is a flowchart showing the processing of the transform unit 106 and the quantization unit 108 of the coding device 100 according to the first aspect of the first embodiment.

[0167] The transform mode determination unit 1061 determines whether or not the adaptive transform basis selection mode is enabled for the block to be coded (S101).

[0168] If the adaptive transformation basis selection mode is not enabled (NO in S101), the first transformation basis selection unit 1063 selects one basic transformation basis as the first transformation basis in the horizontal and vertical directions (S102).

[0169] If the adaptive transformation basis selection mode is enabled (YES in S101), the size determination unit 1062 determines whether the horizontal transformation size exceeds a certain range (S103). That is, the size determination unit 1062 determines whether the horizontal size of the block to be coded is larger than a first horizontal threshold size.

[0170] If the horizontal transformation size exceeds a certain range (YES in S103), the first transformation base selection unit 1063 selects a horizontal transformation base from the multiple adaptive transformation bases as a first horizontal transformation base (S104).

[0171] If the transformation size in the horizontal direction is within a certain range (NO in S103), the first transformation base selection unit 1063 selects a fixed transformation base as the first transformation base in the horizontal direction (S105).

[0172] Next, the size determination unit 1062 determines whether the vertical transformation size exceeds a certain range (S106). That is, the size determination unit 1062 determines whether the vertical size of the current block to be coded is larger than a first vertical threshold size.

[0173] If the vertical transformation size exceeds a certain range (YES in S106), the first transformation base selection unit 1063 selects a vertical transformation base from the multiple adaptive transformation bases as a first vertical transformation base (S107).

[0174] If the transformation size in the vertical direction is within a certain range (NO in S106), the first transformation base selection unit 1063 selects a fixed transformation base as the first transformation base in the vertical direction (S108).

[0175] The order of selection of the horizontal and vertical transformation bases may be the horizontal and vertical order, or the reverse order. Also, the horizontal and vertical transformation bases may be selected simultaneously.

[0176] The first transform unit 1064 performs a first transform on the prediction residual using the first transform base selected in step S102, S107, or step S108, to generate first transform coefficients (S109).

[0177] Next, the second transform execution determination unit 1065 determines whether to execute the second transform on the first transform coefficients (S110). Here, the second transform execution determination unit 1065 determines whether to execute the second transform based on whether the adaptive transform basis selection mode is enabled for the block to be coded.

[0178] If the adaptive transform basis selection mode is enabled (YES in S110), neither the selection of the second transform basis nor the second transform is performed, and the quantization unit 108 generates quantized coefficients by quantizing the first transform coefficients (S113). That is, steps S111 and S112 in Fig. 12A are skipped.

[0179] If the adaptive transform base selection mode is not enabled (NO in S110), the second transform base selection unit 1066 selects a second transform base from one or more second transform base candidates (S111). Then, the second transform unit 1067 performs a second transform on the first transform coefficients using the selected second transform base to generate second transform coefficients (S112). Thereafter, the quantization unit 108 quantizes the second transform coefficients to generate quantized coefficients (S113).

[0180] A predetermined transformation base can be used as the basic transformation base. In this case, whether the adaptive transformation base selection mode is enabled may be determined based on whether the first transformation bases in the horizontal and vertical directions are the predetermined transformation bases. The predetermined transformation bases may be one transformation base or two or more transformation bases.

[0181] Furthermore, when the second conversion is not performed (skipped), the second conversion may not be performed, or a conversion equivalent to not performing the conversion may be performed as the second conversion. In the former case, information indicating that the second conversion is not performed may be coded in the bitstream. In the latter case, information indicating a conversion equivalent to not performing the conversion may be coded in the bitstream. The same applies to the process of skipping each conversion below.

[0182] Note that the steps and the order of steps shown in Fig. 12A are merely examples and are not limited to these. For example, as shown in Fig. 12B, the adaptive transformation basis selection mode decision (S101) and the second transformation execution decision (S110) in Fig. 12A may be integrated. Fig. 12B is a flowchart showing a modified example of the processing of the transform unit 106 and the quantization unit 108 of the encoding device 100 according to the first aspect of Embodiment 1. The flowchart in Fig. 12B is substantially the same as the flowchart in Fig. 12A.

[0183] 12B, the step of determining whether to perform the second transform (S110) is omitted, and the first transform (S109) is divided into two (S109A, S109B). In this case, the transform unit 106 of the encoding device 100 does not need to include the second transform execution determination unit 1065.

[0184] The selection of the second inverse transformation base and the second inverse transformation in the inverse transformation unit 114, as well as the selection of the first inverse transformation base and the first inverse transformation, may be performed in accordance with the transformation of the transformation unit 106 in Figure 12A, and therefore explanation and illustration thereof will be omitted.

[0185] The first transform may be a frequency transform capable of adaptively selecting a transform base, such as EMT described in Non-Patent Document 2, or a frequency transform that switches transform bases under certain conditions, or may be any other general transform. For example, a fixed transform base may be set instead of selecting the first transform base. Alternatively, a first transform base equivalent to not performing the first transform may be used. In addition, the first transform may be capable of selecting one of two modes using identification information indicating whether the adaptive transform base selection mode or the fixed transform base mode using a fixed basic transform base (e.g., the transform base of a type-2 discrete cosine transform (DCT-II)) is active. In this case, the identification information may also be used to determine whether the adaptive transform base selection mode or the fixed transform base mode is active for the block to be coded. For example, in the EMT described in non-patent document 2, there is identification information (emt_cu_flag) that indicates whether the adaptive transformation basis selection mode is enabled in units such as CU (Coding Unit), and this identification information can be used to determine whether the adaptive transformation basis selection mode is enabled for the block to be coded.

[0186] The second transform may be a secondary transform process such as NSST described in Non-Patent Document 2, a transform that switches transform bases under certain conditions, or any other general transform. For example, a fixed transform base may be set instead of selecting the second transform base. Alternatively, a second transform base equivalent to not performing the second transform may be used. The NSST may be a frequency space transform after the DCT or DST, such as the KLT (Karhunen Loveve Transform) for transform coefficients of the DCT or DST obtained offline, or the HyGT (Hypercube-Givens Transform), which expresses a basis equivalent to the KLT and is expressed by a combination of rotational transforms.

[0187] This process can be applied to both luminance 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 or second transform may be different for luminance and color difference signals. For example, since the frequency band of a luminance signal is wider than that of a color difference signal, in order to perform optimal transform, a larger number of bases may be used as selectable candidates in the first or second transform of the luminance signal than for the color difference signal. Furthermore, this process can be applied to both intra-processing and inter-processing.

[0188] [Effects, etc.] In the first transform (primary transform) and second transform (secondary transform) described in Non-Patent Document 2, optimal transform bases or transform coefficients (filters) are selected, achieving optimal overall coding efficiency. Therefore, in order to find an optimal combination of candidate transform bases and transform coefficients (filters) used in the first transform and the second transform, it is necessary to perform multiple trials of the first transform and the second transform. That is, in the transform method described in Non-Patent Document 2, it is necessary to calculate evaluation values ​​for all combinations of candidate transform bases for the first transform and candidate transform bases for the second transform, and select the combination that minimizes the evaluation value. Therefore, the present inventors have discovered a problem with the transform method described in Non-Patent Document 2: the amount of processing required becomes enormous.

[0189] Therefore, the encoding device 100 according to this embodiment does not always perform both the first transform and the second transform, but skips the second transform based on whether the adaptive transform basis selection mode is enabled. This allows the encoding device 100 to reduce the number of combinations of candidate transform bases for the first transform and candidate transform bases for the second transform, thereby reducing the amount of processing.

[0190] Furthermore, according to the encoding device 100 of this aspect, it is possible to limit candidates for the first transform base based on conditions of horizontal and vertical transform sizes. This makes it possible to reduce the amount of processing required to search for the best first transform base through trials. It is also possible to reduce the amount of processing required to search for the best second transform base through trials based on conditions such as the base selected as the first transform base. Furthermore, it is possible to reduce the amount of processing required to search for combinations of the first transform and the second transform.

[0191] As an example, the DCT-II transform basis can be used as the basic transform basis. DCT-II is likely to be adopted when the residual shape is flat or random. For example, if DCT-II is used as the first transform basis, there is a tendency for the concentration of low frequencies to increase, which may increase the effectiveness of the second transform. On the other hand, transform bases other than DCT-II tend to leave high-frequency components, which may reduce the effectiveness of the second transform.

[0192] As an example, the DST-VII transformation bases can be used as fixed transformation bases when the transformation size is within a certain range. DST-VII tends to be selected with a very high probability, especially in intra-processing, when the residual shape is slanted and small in size.

[0193] The fundamental transformation base is not limited to one predetermined transformation base, and a plurality of predetermined transformation bases may be used.

[0194] Furthermore, whether to select the second transformation base and perform the second transformation may be switched depending on the transformation size. Furthermore, candidates for the second transformation base may be switched depending on the transformation size.

[0195] Alternatively, the configuration may be such that whether to perform the second transform is determined based on whether the adaptive transform basis selection mode is enabled, without switching the first transform basis according to the transform size. That is, in Fig. 12A, steps S103, S105, S106, and S108 may be deleted. Here, whether the adaptive transform basis selection mode is enabled may be determined based on identification information indicating the use of the mode or the type of the first transform basis.

[0196] Similarly, the configuration may be such that only the first transformation base is switched according to the transformation size, without switching whether or not to perform the second transformation based on whether the adaptive transformation base selection mode is enabled. In other words, step S110 in FIG. 12A may be deleted.

[0197] Note that the selection of the second transformation base and the second transformation may not be skipped regardless of whether the adaptive transformation base selection mode is enabled. Also, regardless of the method of selecting the first transformation base, the selection of the second transformation base and the second transformation may be performed when the adaptive transformation base selection mode is not enabled, and the selection of the second transformation base and the second transformation may be skipped when the adaptive transformation base selection mode is enabled.

[0198] In addition, the specific horizontal or vertical transformation size threshold (i.e., the first horizontal threshold size and the first vertical threshold size) for selecting a candidate from multiple adaptive transformation bases as the first transformation base or selecting a fixed transformation base may be 4, 8, 16, 32, or 64 pixels, etc.

[0199] [Combination with other aspects] 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 device configurations, and some syntaxes described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0200] (Second aspect of first embodiment) Next, a second aspect of the first embodiment will be described. In this aspect, an example of encoding of various signals related to the first transform and the second transform in the first aspect will be described. Below, this aspect will be specifically described with reference to the drawings, focusing on the differences from the first aspect.

[0201] The internal configurations of the transform unit 106 and the inverse transform unit 114 of the encoding device 100 according to this embodiment are the same as those of the first embodiment, and therefore are not shown in the drawings.

[0202] [Processing of the transform unit, quantization unit, and entropy coding unit of the coding device] The processing of the transform unit 106, the quantization unit 108, and the entropy coding unit 110 of the coding device 100 according to this aspect will be described with reference to Figs. 13A and 13B. Fig. 13A is a flowchart showing the processing of the transform unit 106 and the quantization unit 108 of the coding device 100 according to the second aspect of Embodiment 1. Fig. 13B is a flowchart showing the processing of the entropy coding unit 110 of the coding device 100 according to the second aspect of Embodiment 1. In Figs. 13A and 13B, processing that is common to the first aspect is denoted by the same reference numerals, and description thereof will be omitted.

[0203] After quantization (S113), the entropy coding unit 110 codes an adaptive transformation basis selection mode signal (S201). The adaptive transformation basis selection mode signal is an example of identification information of an adaptive transformation basis selection mode.

[0204] If the adaptive transform basis selection mode is enabled (YES in S202), and if the horizontal transform size exceeds a certain range (YES in S203), the entropy coding unit 110 encodes the first horizontal basis selection signal (S204). On the other hand, if the horizontal transform size is within the certain range (NO in S203), the entropy coding unit 110 does not encode the first horizontal basis selection signal. Furthermore, if the vertical transform size exceeds the certain range (YES in S205), the entropy coding unit 110 encodes the first vertical basis selection signal (S206). On the other hand, if the vertical transform size is within the certain range (NO in S205), the entropy coding unit 110 does not encode the first vertical basis selection signal.

[0205] If the adaptive transformation basis selection mode is not enabled (NO in S202), the encoding of the first basis selection signal (S204, S206) is skipped.

[0206] Next, the entropy coding unit 110 codes the quantized coefficients (S207).

[0207] If the adaptive transformation basis selection mode is not enabled (NO in S208), the entropy coding unit 110 encodes the second basis selection signal (S209). On the other hand, if the adaptive transformation basis selection mode is enabled (YES in S208), the encoding of the second basis selection signal (S209) is skipped.

[0208] It should be noted that the encoding order may be determined in advance, and various signals may be encoded in a different order from the above encoding order.

[0209] When the second transform is not performed (skip), a signal indicating that the second transform is not performed may be coded, or a signal selecting a second basis equivalent to no transform may be coded.

[0210] [Syntax] The syntax in this aspect will now be described. Figure 14 shows a specific example of the syntax in the second aspect of the first embodiment.

[0211] 14, for example, when the adaptive transform basis selection mode signal (emt_cu_flag) is set (line 4), if the horizontal transform size (horizontal_tu_size) is larger than the first horizontal threshold size (horizontal_tu_size_th) (line 5), the first horizontal basis selection signal (emt_horizontal_tridx) is coded (line 6). Also, if the vertical transform size (vertical_tu_size) is larger than the first vertical threshold size (vertical_tu_size_th) (line 11), the first vertical basis selection signal (emt_vertical_tridx) is coded (line 12). Under other conditions (lines 8 and 14), coding of the first basis selection signal is skipped (lines 9 and 15).

[0212] Furthermore, if the adaptive transformation basis selection mode signal (emt_cu_flag) is not set (line 19), the second basis selection signal (secondary_tridx) is encoded (line 20). Conversely, if the adaptive transformation basis selection mode signal (emt_cu_flag) is set (line 22), the encoding of the second basis selection signal (secondary_tridx) is skipped (line 23).

[0213] [Examples of transformation bases and coded signals] Next, specific examples of transform bases and coded signals will be described. Fig. 15 shows specific examples of transform bases used in the second mode of the first embodiment and whether or not signals are coded.

[0214] In Fig. 15, when the adaptive transform basis selection mode is not enabled, the transform basis of DCT-II is used as the first transform basis in the horizontal and vertical directions regardless of the size of the coding block. That is, the transform basis of DCT-II is used as the basic transform basis. In addition, when the second transform is performed (ON), a second basis selection signal (secondary_tridx) indicating the second transform basis used in the second transform is coded in the bitstream.

[0215] On the other hand, when the adaptive transform basis selection mode is enabled, a combination (index0 to index3) of the DST-VII transform basis and other transform basis is used as candidates for the first transform basis in the horizontal and vertical directions according to the horizontal size H and vertical size V of the block to be coded. Furthermore, regardless of the size of the block to be coded, the second transform is not performed (OFF). Furthermore, the second basis selection signal (secondary_tridx) is not coded, but the adaptive transform basis selection mode signal (emt_cu_flag) is coded in the bitstream. Furthermore, if the horizontal size H of the block to be coded is greater than four pixels, the first basis selection signal in the horizontal direction (emt_horizontal_tridx) is coded in the bitstream. Furthermore, if the vertical size V of the block to be coded is greater than four pixels, the first basis selection signal in the vertical direction (emt_vertical_tridx) is coded in the bitstream.

[0216] For example, if the horizontal size H is 4 pixels or less and the vertical size V is 4 pixels or less, only the DST-VII transformation bases are used as candidates for the first transformation bases in the horizontal and vertical directions. In this case, the first basis selection signals in the horizontal and vertical directions (emt_horizontal_tridx and emt_vertical_tridx) are not coded.

[0217] Furthermore, for example, when the horizontal size H is 4 pixels or less and the vertical size V is greater than 4 pixels, only the transformation bases of DST-VII are used as candidates for the first transformation base in the horizontal direction, and the transformation bases of DST-VII and other transformation bases are used as candidates for the first transformation base in the vertical direction. In this case, the first basis selection signal in the horizontal direction (emt_horizontal_tridx) is not coded, but the first basis selection signal in the vertical direction (emt_vertical_tridx) is coded.

[0218] For example, if the horizontal size H is greater than 4 pixels and the vertical size V is equal to or less than 4 pixels, the transformation base of DST-VII and other transformation bases are used as candidates for the first transformation base in the horizontal direction, and only the transformation base of DST-VII is used as a candidate for the first transformation base in the vertical direction. In this case, the first basis selection signal in the horizontal direction (emt_horizontal_tridx) is coded, but the first basis selection signal in the vertical direction (emt_vertical_tridx) is not coded.

[0219] For example, if the horizontal size H is greater than 4 pixels and the vertical size V is greater than 4 pixels, the DST-VII transformation bases and other transformation bases are used as candidates for the first transformation bases in the horizontal and vertical directions, respectively. In this case, the first basis selection signals for the horizontal and vertical directions (emt_horizontal_tridx and emt_vertical_tridx) are coded.

[0220] [Effects, etc.] As described above, according to the encoding device 100 of this embodiment, only when the adaptive transform base selection mode is enabled and the transform size exceeds a certain range, it is possible to encode information indicating the first transform base (first base selection signal), which may reduce the amount of code required for signaling the first transform base. Also, only when the adaptive transform base selection mode is not enabled, it is possible to encode information indicating the second transform base (second base selection signal), which may reduce the amount of code required for signaling the second transform base. Also, by encoding information for determining whether to skip the second transform (such as the adaptive transform base selection mode signal) before the information indicating the second transform base, it is possible to determine during decoding whether the information indicating the second transform base has been encoded.

[0221] Note that the second basis selection signal may always be encoded regardless of the adaptive transform basis selection mode. Also, the first basis selection signal may always be encoded in the adaptive transform basis selection mode regardless of the transform size. Whether or not to encode the first basis selection signal may be determined independently based on the horizontal size and the vertical size, or may be determined in combination.

[0222] [Combination with other aspects] 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 device configurations, and some syntaxes described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0223] (Third aspect of first embodiment) Next, a third aspect of the first embodiment will be described. This aspect differs from the first aspect in that when the adaptive transformation base selection mode is not enabled, a different basic transformation base is used as the first transformation base depending on the size of the block to be coded. Below, this aspect will be specifically described with reference to the drawings, focusing on the differences from the first and second aspects.

[0224] The internal configurations of the transform unit 106 and the inverse transform unit 114 of the encoding device 100 according to this embodiment are the same as those of the first embodiment, and therefore are not shown in the drawings.

[0225] [Processing of the transform and quantization units of the encoding device] The processing of the transform unit 106 and the quantization unit 108 of the encoding device 100 according to this aspect will be described with reference to Fig. 16. Fig. 16 is a flowchart showing the processing of the transform unit 106 and the quantization unit 108 of the encoding device 100 according to the third aspect of Embodiment 1. In Fig. 16, the processing common to the first aspect is assigned the same reference numerals and description thereof will be omitted.

[0226] If the adaptive transformation basis selection mode is not enabled (NO in S101), the size determination unit 1062 determines whether the transformation size is within a certain range (S301). That is, the size determination unit 1062 determines whether the size of the block to be coded is equal to or smaller than a second threshold size. For example, the size determination unit 1062 determines whether the product of the horizontal size and vertical size of the block to be coded is equal to or smaller than a threshold, thereby determining whether the size of the block to be coded is equal to or smaller than the second threshold size.

[0227] If the transformation size is within a certain range (YES in S301), the first transformation base selection unit 1063 selects the second basic transformation base as the first transformation base in the horizontal and vertical directions (S302). On the other hand, if the transformation size exceeds the certain range (NO in S301), the first transformation base selection unit 1063 selects the first basic transformation base as the first transformation base in the horizontal and vertical directions (S303).

[0228] As an example, the transformation bases of DCT-II can be used as the first fundamental transformation base, and the transformation bases of DST-VII can be used as the second fundamental transformation base.

[0229] The fundamental transformation base may be selected from a plurality of fundamental transformation base candidates.

[0230] Note that the selection of the second transformation base and the second transformation may not be skipped regardless of whether the adaptive transformation base selection mode is enabled. Also, regardless of the method of selecting the first transformation base, the selection of the second transformation base and the second transformation may be performed when the adaptive transformation base selection mode is not enabled, and the selection of the second transformation base and the second transformation may be skipped when the adaptive transformation base selection mode is enabled.

[0231] Furthermore, when the adaptive transformation base selection mode is not enabled, the second threshold size for selecting one of the first basic transformation base and the second basic transformation base can be, for example, 4x4, 4x8, 8x4, 8x8 pixel size, etc. Furthermore, the transformation size compared with the threshold may be the product of the horizontal size and vertical size of the block to be coded as in this embodiment, or each of the horizontal size and the vertical size may be used.

[0232] In addition, when the adaptive transformation base selection mode is not enabled, if the product of the horizontal size and vertical size is within a certain range, the second basic transformation base may be selected as the first transformation base in the horizontal and vertical directions, and the selection of the second transformation base and the second transformation may be skipped.

[0233] [Effects, etc.] As described above, according to the encoding device 100 of this aspect, when the adaptive transform base selection mode is not enabled, the first transform base can be switched between the first basic transform base and the second basic transform base according to the transform size. Therefore, the first transform can be performed using the first transform base corresponding to the transform size, and the amount of code can be reduced.

[0234] [Combination with other aspects] 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 device configurations, and some syntaxes described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0235] (Fourth aspect of the first embodiment) Next, a fourth aspect of the first embodiment will be described. In this aspect, an example of encoding of various signals related to the first transform and the second transform according to the third aspect will be described. Below, this aspect will be specifically described with reference to the drawings, focusing on the differences from the first to third aspects.

[0236] The internal configurations of the transform unit 106 and the inverse transform unit 114 of the encoding device 100 according to this embodiment are the same as those of the first embodiment, and therefore are not shown in the drawings.

[0237] [Processing of the transform unit, quantization unit, and entropy coding unit of the coding device] The processing of the transform unit 106, the quantization unit 108, and the entropy coding unit 110 of the coding device 100 according to this aspect will be described with reference to Figs. 17A and 17B. Fig. 17A is a flowchart showing the processing of the transform unit 106 and the quantization unit 108 of the coding device 100 according to the fourth aspect of Embodiment 1. Fig. 17B is a flowchart showing the processing of the entropy coding unit 110 of the coding device 100 according to the fourth aspect of Embodiment 1. In Figs. 17A and 17B, processing that is common to any of the first to third aspects is denoted by the same reference numerals, and description thereof will be omitted.

[0238] After quantization (S113), the entropy coding unit 110 determines whether to skip coding of the adaptive transformation basis selection mode signal (S401). For example, the entropy coding unit 110 determines to skip coding of the adaptive transformation basis selection mode signal when either of the following conditions (A) and (B) is satisfied, and determines not to skip coding of the adaptive transformation basis selection mode signal when any of the following conditions (A) and (B) is satisfied.

[0239] (A) The adaptive transformation basis selection mode is not enabled.

[0240] (B) The adaptive transformation basis selection mode is enabled, and all of the following conditions (B1) to (B4) are satisfied.

[0241] (B1) The transformation size is equal to or smaller than the second threshold size W1×H1 used in step S301.

[0242] (B2) The horizontal transformation size is equal to or smaller than the first horizontal threshold size W2 used in step S103.

[0243] (B3) The vertical transformation size is equal to or smaller than the first vertical threshold size H2 used in step S106.

[0244] (B4) The second fundamental transformation base and the fixed transformation bases in the horizontal and vertical directions are the same transformation base.

[0245] As a specific example, when the second threshold size W1xH1 is 4x4 pixels, the first horizontal threshold size W2 is 4 pixels, the first vertical threshold size H2 is 4 pixels, and the second basic transformation base and the fixed transformation base are both DST-VII transformation bases, if the transformation size is 4x4 pixels or less, the entropy coding unit 110 determines to skip coding of the adaptive transformation base selection mode signal.

[0246] Conversely, if neither the above conditions (A) nor (B) are satisfied, the entropy coding unit 110 determines not to skip coding of the adaptive transformation basis selection mode signal.

[0247] Here, if it is determined that the encoding of the adaptive transformation basis selection mode signal is to be skipped (YES in S401), the entropy coding unit 110 skips steps S201 to S206 and encodes the quantization coefficients (S207). On the other hand, if it is determined that the encoding of the adaptive transformation basis selection mode signal is not to be skipped (NO in S401), the entropy coding unit 110 executes steps S201 to S206 and then encodes the quantization coefficients (S207), as in the second aspect.

[0248] It should be noted that the encoding order may be determined in advance, and various signals may be encoded in a different order from the above encoding order.

[0249] [Syntax] The syntax in this aspect will now be described. Figure 18 shows a specific example of the syntax in the fourth aspect of the first embodiment.

[0250] 18, for example, when encoding of the adaptive transform basis selection mode signal is skipped (line 20), encoding of the adaptive transform basis selection mode signal (emt_cu_flag) and the first basis selection signals (emt_horizontal_tridx and emt_vertical_tridx) is skipped (line 21). Here, when the horizontal transform size (horizontal_tu_size) is equal to or less than the first horizontal threshold size (horizontal_tu_size_th) and the vertical transform size (vertical_tu_size) is equal to or less than the first vertical threshold size (vertical_tu_size_th), encoding of the adaptive transform basis selection mode signal is skipped. If the encoding of the adaptive transformation basis selection mode signal is not skipped (lines 3-4), the adaptive transformation basis selection mode signal (emt_cu_flag) is encoded (line 5), and the first basis selection signals (emt_horizontal_tridx and emt_vertical_tridx) are encoded as necessary, as in the second aspect (lines 7-16).

[0251] It should be noted that when the coding of the adaptive transform basis selection mode signal is skipped, the selection of the second transform basis and the second transform may be skipped.

[0252] [Examples of transformation bases and coded signals] Next, specific examples of transform bases and coded signals will be described. Fig. 19 shows specific examples of transform bases used in the fourth aspect of the first embodiment and whether or not to code signals. In Fig. 19, the transform bases and whether or not to code when the horizontal and vertical sizes of the block to be coded are both 4 pixels or less are different from those in Fig. 15. Fig. 19 will be described focusing on the differences from Fig. 15.

[0253] In Figure 19, when the adaptive transform basis selection mode is not enabled, if the horizontal size H and vertical size V of the block to be coded are both 4 pixels or less, the transform bases of DST-VII are used as the first transform bases in the horizontal and vertical directions, rather than the transform bases of DCT-II.

[0254] Furthermore, when the adaptive transformation basis selection mode is enabled, if the horizontal size H and vertical size V of the encoding target block are both four pixels or less, the adaptive transformation basis selection mode signal (emt_cu_flag) is not encoded.

[0255] [Effects, etc.] As described above, according to the encoding device 100 of this embodiment, when the conditions for skipping the encoding of the adaptive transformation basis selection mode signal are met, all encoding of the adaptive transformation basis selection mode signal and the first basis selection signal can be omitted, which may reduce the amount of code.

[0256] [Combination with other aspects] 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 device configurations, and some syntaxes described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0257] (Fifth aspect of first embodiment) Next, a fifth aspect of the first embodiment will be described. In this aspect, a decoding device will be described. Note that the decoding device according to this aspect corresponds to the encoding device according to the first aspect. In other words, the decoding device according to this aspect can decode a bitstream encoded by the encoding device according to the first aspect. This aspect will be specifically described below with reference to the drawings.

[0258] [Internal configuration of the transform unit and inverse transform unit of the decoding device] First, a description will be given of the internal configuration of the inverse transform unit 206 of the decoding device 200 according to this aspect. Fig. 20 is a block diagram showing the internal configuration of the inverse transform unit 206 of the decoding device 200 according to the fifth aspect of the first embodiment.

[0259] As shown in FIG. 20, the inverse transformation unit 206 according to this embodiment includes a second inverse transformation execution determination unit 2061, a second inverse transformation base selection unit 2062, a second inverse transformation unit 2063, a transformation mode determination unit 2064, a size determination unit 2065, a first inverse transformation base selection unit 2066, and a first inverse transformation unit 2067.

[0260] The second inverse transform execution determination unit 2061 determines, based on whether the adaptive transform basis selection mode is enabled for the block to be decoded, whether to execute the second inverse transform on the inverse quantization coefficients of the block to be decoded output from the inverse quantization unit 204. Specifically, the second inverse transform execution determination unit 2061 executes the second inverse transform when the adaptive transform basis selection mode is not enabled, and determines not to execute the second inverse transform when the adaptive transform basis selection mode is enabled.

[0261] The second inverse transform basis selection unit 2062 selects a second inverse transform basis when it is determined that a second inverse transform is to be performed. Specifically, when the adaptive transform basis selection mode is not enabled, the second inverse transform basis selection unit 2062 acquires a second basis selection signal 2062S indicating a second inverse transform basis decoded from the bitstream by the entropy decoding unit 202. The second inverse transform basis selection unit 2062 then selects the second inverse transform basis based on the second basis selection signal 2062S. Conversely, when the adaptive transform basis selection mode is enabled, the second inverse transform basis selection unit 2062 does not select the second inverse transform basis. In other words, when the adaptive transform basis selection mode is enabled, the second inverse transform basis selection unit 2062 skips the selection of the second inverse transform basis.

[0262] When it is determined that the second inverse transform is to be performed, the second inverse transform unit 2063 performs the second inverse transform on the inverse quantization coefficients of the block to be decoded, using the second inverse transform base selected by the second inverse transform base selection unit 2062. That is, when the adaptive transform base selection mode is not enabled, the second inverse transform unit 2063 generates the second inverse transform coefficients by performing the second inverse transform on the inverse quantization coefficients using the second inverse transform base. Conversely, when the adaptive transform base selection mode is enabled, the second inverse transform unit 2063 does not perform the second inverse transform on the inverse quantization coefficients. That is, when the adaptive transform base selection mode is enabled, the second inverse transform unit 2063 skips the second inverse transform.

[0263] The transform mode determination unit 2064 determines whether the adaptive transform basis selection mode is valid for the block to be decoded. The determination of whether the adaptive transform basis selection mode is valid is made based on the first basis selection signal 2066S or the adaptive transform basis selection mode signal 2064S decoded from the bitstream by the entropy decoding unit 202. That is, the determination is made based on identification information of the first inverse transform basis or the adaptive transform basis selection mode.

[0264] The size determination unit 2065 determines whether the horizontal size of the block to be decoded exceeds a first horizontal threshold size. The size determination unit 1062 determines whether the vertical size of the block to be decoded exceeds a first vertical threshold size. The horizontal and vertical sizes are determined based on a size signal 2065S decoded from the bitstream by the entropy decoding unit 202.

[0265] The first inverse transform base selection unit 2066 selects a first inverse transform base. Specifically, when the adaptive transform base selection mode is not enabled, the first inverse transform base selection unit 2066 selects one basic transform base as the first inverse transform base for the horizontal and vertical directions. Furthermore, when the adaptive transform base selection mode is enabled, the first inverse transform base selection unit 2066 selects the first inverse transform base for the horizontal and vertical directions according to the horizontal and vertical sizes of the block to be decoded, as shown in the following (1) to (4).

[0266] (1) When the horizontal size of the block to be decoded is larger than the first horizontal threshold size, the first inverse transform base selection unit 2066 acquires a first basis selection signal 2066S indicating a first inverse transform base decoded from the bitstream by the entropy decoding unit 202. Then, the first inverse transform base selection unit 2066 selects a first inverse transform base in the horizontal direction based on the first basis selection signal 2066S.

[0267] (2) If the horizontal size of the block to be decoded is equal to or smaller than the first horizontal threshold size, the first inverse transform base selection unit 2066 selects a fixed transform base in the horizontal direction as the first inverse transform base in the horizontal direction.

[0268] (3) If the vertical size of the block to be decoded is larger than the first vertical threshold size, the first inverse transform basis selection unit 2066 acquires a first basis selection signal 2066S. Then, the first inverse transform basis selection unit 2066 selects a first inverse transform basis in the vertical direction based on the first basis selection signal 2066S.

[0269] (4) If the vertical size of the block to be decoded is equal to or smaller than the first vertical threshold size, the first inverse transform base selection unit 2066 selects a fixed transform base in the vertical direction as the first inverse transform base in the vertical direction.

[0270] The first inverse transform unit 2067 restores the residual of the block to be decoded by performing a first inverse transform on the inverse quantized coefficients of the block to be decoded using the first inverse transform base selected by the first inverse transform base selection unit 2066. Specifically, the first inverse transform unit 2067 performs a first inverse transform in the horizontal direction using the first inverse transform base in the horizontal direction, and performs a first inverse transform in the vertical direction using the first inverse transform base in the vertical direction.

[0271] [Processing of the inverse quantization unit and inverse transform unit of the decoding device] Next, processing by the inverse transform unit 206 configured as above will be described together with processing by the inverse quantization unit 204 with reference to Fig. 21. Fig. 21 is a flowchart showing processing by the inverse quantization unit 204 and the inverse transform unit 206 in the decoding device 200 according to the fifth aspect of the first embodiment.

[0272] The inverse quantization unit 204 generates inverse quantized coefficients by inverse quantizing the quantized coefficients of the block to be decoded that have been decoded by the entropy decoding unit 202 (S501).

[0273] The second inverse transform execution determination unit 2061 determines whether to execute the second inverse transform on the inverse quantized coefficients (S502). Here, the second inverse transform execution determination unit 2061 determines whether to execute the second inverse transform based on whether the adaptive transform basis selection mode is enabled for the block to be decoded.

[0274] Here, if the adaptive transformation basis selection mode is enabled (YES in S502), neither the selection of the second inverse transformation basis nor the second inverse transformation is performed, i.e., steps S503 and S504 are skipped.

[0275] On the other hand, if the adaptive transform basis selection mode is not enabled (NO in S502), the second inverse transform basis selection unit 2062 selects a second inverse transform basis based on the second basis selection signal 2062S (S503). Furthermore, the second inverse transform unit 2063 performs a second inverse transform on the inverse quantized coefficients using the selected second inverse transform basis (S504).

[0276] Next, the transform mode determination unit 2064 determines whether or not the adaptive transform basis selection mode is enabled for the block to be decoded (S505). For example, the transform mode determination unit 2064 determines whether or not the adaptive transform basis selection mode is enabled based on the adaptive transform basis selection mode signal 2064S.

[0277] If the adaptive transformation basis selection mode is not enabled (NO in S505), the first inverse transformation basis selection unit 2066 selects one basic transformation basis as the first inverse transformation basis in the horizontal and vertical directions (S512). On the other hand, if the adaptive transformation basis selection mode is enabled (YES in S505), the size determination unit 2065 determines whether the horizontal transformation size exceeds a certain range (S506). In other words, the size determination unit 2065 determines whether the horizontal size of the block to be decoded is larger than a first horizontal threshold size.

[0278] If the horizontal transformation size exceeds a certain range (YES in S506), the first inverse transformation base selection unit 2066 selects a horizontal transformation base from the multiple adaptive transformation bases as the first inverse transformation base for the horizontal direction (S507). On the other hand, if the horizontal transformation size is within a certain range (NO in S506), the first inverse transformation base selection unit 2066 selects a fixed transformation base as the first inverse transformation base for the horizontal direction (S508).

[0279] The size determination unit 2065 determines whether the vertical transformation size exceeds a certain range (S509). That is, the size determination unit 2065 determines whether the vertical size of the block to be decoded is larger than the first vertical threshold size.

[0280] If the vertical transformation size exceeds a certain range (YES in S509), the first inverse transformation base selection unit 2066 selects a transformation base from a plurality of adaptive transformation bases as the first inverse transformation base for the vertical direction (S510). If the vertical transformation size is within a certain range (NO in S509), the first inverse transformation base selection unit 2066 selects a fixed transformation base as the first inverse transformation base for the vertical direction (S511).

[0281] The first inverse transform unit 2067 restores the residual of the block to be decoded by performing a first inverse transform on the inverse quantization coefficients or the second inverse transform coefficients using the first inverse transform base selected as described above (S513).

[0282] The selection order of the horizontal and vertical inverse transformation bases may be the horizontal and vertical order, or the reverse order. Also, the horizontal inverse transformation bases and the vertical inverse transformation bases may be selected simultaneously.

[0283] In addition, selecting an inverse transform base in the decoding device 200 means decoding information indicating the base to be used for the inverse transform contained in the encoded bitstream and determining the inverse transform base based on the decoded information, or determining an inverse transform base that is uniquely indicated based on information such as the intra prediction mode, the size of the block to be decoded, or the base in the first inverse transform.

[0284] It should be noted that a decoding method that matches the encoding method of the first aspect shown in FIG. 12A or 12B may be adopted.

[0285] [Effects, etc.] As described above, the decoding device 200 according to this aspect can achieve the same effects as the encoding device 100 according to the first aspect.

[0286] [Combination with other aspects] 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 device configurations, and some syntaxes described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0287] (Sixth aspect of the first embodiment) Next, a sixth aspect of the first embodiment will be described. In this aspect, an example of decoding of various signals related to the first transform and the second transform in the fifth aspect will be described. Note that the decoding device according to this aspect corresponds to the encoding device according to the second aspect. Below, this aspect will be specifically described with reference to the drawings, focusing on the differences from the fifth aspect.

[0288] The internal configuration of the inverse transform unit 206 of the decoding device 200 according to this embodiment is the same as that of the fifth embodiment, and therefore is not shown in the drawings.

[0289] [Processing of the entropy decoding unit, inverse quantization unit, and inverse transform unit of the decoding device] The processing of the entropy decoding unit 202, the inverse quantization unit 204, and the inverse transform unit 206 of the decoding device 200 according to this aspect will be described with reference to Figures 22A and 22B. In Figures 22A and 22B, the processing common to the fifth aspect will be denoted by the same reference numerals, and the description thereof will be omitted.

[0290] First, the entropy decoding unit 202 decodes an adaptive transformation basis selection mode signal from the bitstream (S601). Then, the transform mode determination unit 2064 determines whether the adaptive transformation basis selection mode is enabled for the block to be decoded based on the adaptive transformation basis selection mode signal (S602).

[0291] If the adaptive transform basis selection mode is enabled (YES in S602), and if the horizontal transform size exceeds a certain range (YES in S603), the entropy decoding unit 202 decodes the first horizontal basis selection signal from the bitstream (S604). On the other hand, if the horizontal transform size is within the certain range (NO in S603), the entropy decoding unit 202 does not decode the first horizontal basis selection signal. Furthermore, if the vertical transform size exceeds the certain range (YES in S605), the entropy decoding unit 202 decodes the first vertical basis selection signal from the bitstream (S606). On the other hand, if the vertical transform size is within the certain range (NO in S605), the entropy decoding unit 202 does not decode the first vertical basis selection signal.

[0292] If the adaptive transformation basis selection mode is not enabled (NO in S602), the decoding of the first basis selection signal (S604, S606) is skipped.

[0293] Next, the entropy decoding unit 202 decodes the quantized coefficients (S607).

[0294] If the adaptive transformation basis selection mode is not enabled (NO in S608), the entropy decoding unit 202 decodes the second basis selection signal from the bitstream (S609). On the other hand, if the adaptive transformation basis selection mode is enabled (YES in S608), the decoding of the second basis selection signal (S609) is skipped.

[0295] In addition, the decoding order may be determined in advance in conjunction with the encoding method, and various signals may be decoded in a different order from the above-mentioned decoding order. Furthermore, when the second inverse transform is not performed (skip), the entropy decoding unit 202 may decode from the bit stream a signal indicating that the second inverse transform is not performed, or may decode from the bit stream a signal for selecting a second inverse transform base equivalent to no transform.

[0296] It should be noted that a decoding method that matches the encoding method of the second aspect shown in FIGS. 13A, 13B, and 14 may be adopted.

[0297] [Effects, etc.] As described above, the decoding device 200 according to this aspect can achieve the same effects as the encoding device 100 according to the second aspect.

[0298] [Combination with other aspects] 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 device configurations, and some syntaxes described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0299] (Seventh aspect of the first embodiment) Next, a seventh aspect of the first embodiment will be described. This aspect differs from the fifth aspect in that when the adaptive transformation base selection mode is not enabled, a different basic transformation base is used as the first inverse transformation base depending on the size of the block to be coded. Note that the decoding device according to this aspect corresponds to the coding device according to the third aspect. Below, this aspect will be specifically described with reference to the drawings, focusing on the differences from the fifth and sixth aspects.

[0300] The internal configuration of the inverse transform unit 206 of the decoding device 200 according to this embodiment is the same as that of the fifth embodiment, and therefore is not shown in the drawings.

[0301] [Processing of the inverse quantization unit and inverse transform unit of the decoding device] The processing of the transform unit 106 and the quantization unit 108 of the encoding device 100 according to this aspect will be described with reference to Fig. 23. Fig. 23 is a flowchart showing the processing of the inverse quantization unit 204 and the inverse transform unit 206 of the decoding device 200 according to the seventh aspect of Embodiment 1. In Fig. 23, the processing common to the fifth aspect is denoted by the same reference numerals, and the description thereof will be omitted.

[0302] If the adaptive transformation basis selection mode is not enabled (NO in S505), the size determination unit 2065 determines whether the transformation size is within a certain range (S701). That is, the size determination unit 2065 determines whether the horizontal size and vertical size of the block to be decoded are equal to or smaller than a second threshold size. Specifically, the size determination unit 2065 determines, for example, whether the product of the horizontal size and vertical size of the block to be decoded is equal to or smaller than a threshold.

[0303] If the transformation size is within a certain range (YES in S701), the first inverse transformation base selection unit 2066 selects the second basic transformation base as the first inverse transformation base in the horizontal and vertical directions (S702). On the other hand, if the transformation size exceeds the certain range (NO in S701), the first inverse transformation base selection unit 2066 selects the first basic transformation base as the first inverse transformation base in the horizontal and vertical directions (S703).

[0304] It should be noted that a decoding method that matches the encoding method of the third aspect shown in FIG. 16 may be adopted.

[0305] [Effects, etc.] As described above, the decoding device 200 according to this aspect can achieve the same effects as the encoding device 100 according to the third aspect.

[0306] [Combination with other aspects] 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 device configurations, and some syntaxes described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0307] (Eighth aspect of the first embodiment) Next, an eighth aspect of the first embodiment will be described. In this aspect, an example of decoding of various signals related to the first transform and the second transform in the seventh aspect will be described. The decoding device according to this aspect corresponds to the encoding device according to the fourth aspect. Below, this aspect will be specifically described with reference to the drawings, focusing on the differences from the fifth to seventh aspects.

[0308] The internal configuration of the inverse transform unit 206 of the decoding device 200 according to this embodiment is the same as that of the fifth embodiment, and therefore is not shown in the drawings.

[0309] [Processing of the entropy decoding unit, inverse quantization unit, and inverse transform unit of the decoding device] The processing of the entropy decoding unit 202, the inverse quantization unit 204, and the inverse transform unit 206 of the decoding device 200 according to this aspect will be described with reference to Figures 24A and 24B. In Figures 24A and 24B, the processing common to any of the fifth to seventh aspects is denoted by the same reference numerals, and description thereof will be omitted.

[0310] The entropy decoding unit 202 determines whether to skip decoding of the adaptive transformation basis selection mode signal (S801). For example, the entropy decoding unit 202 determines to skip decoding of the adaptive transformation basis selection mode signal when either of the following conditions (A) and (B) is satisfied, and determines not to skip decoding of the adaptive transformation basis selection mode signal when not satisfied:

[0311] (A) The adaptive transformation basis selection mode is not enabled.

[0312] (B) The adaptive transformation basis selection mode is enabled, and all of the following conditions (B1) to (B4) are satisfied.

[0313] (B1) The transformation size is equal to or smaller than the second threshold size W1xH1 used in step S701.

[0314] (B2) The horizontal transformation size is equal to or smaller than the first horizontal threshold size W2 used in step S506.

[0315] (B3) The vertical transformation size is equal to or smaller than the first vertical threshold size H2 used in step S509.

[0316] (B4) The second fundamental transformation base and the fixed transformation bases in the horizontal and vertical directions are the same transformation base.

[0317] As a specific example, when the second threshold size W1xH1 is 4x4 pixels, the first horizontal threshold size W2 is 4 pixels, the first vertical threshold size H2 is 4 pixels, and the second basic transformation base and the fixed transformation base are both DST-VII transformation bases, if the transformation size is 4x4 pixels or less, the entropy decoding unit 202 determines to skip decoding of the adaptive transformation base selection mode signal.

[0318] Conversely, if neither the above conditions (A) nor (B) are satisfied, the entropy decoding unit 202 determines not to skip decoding of the adaptive transformation basis selection mode signal.

[0319] Here, if it is determined that the decoding of the adaptive transformation basis selection mode signal is to be skipped (YES in S801), the entropy decoding unit 202 skips steps S601 to S606 and decodes the quantization coefficients (S607). On the other hand, if it is determined that the decoding of the adaptive transformation basis selection mode signal is not to be skipped (NO in S801), the entropy decoding unit 202 executes steps S601 to S606 and then decodes the quantization coefficients (S207), as in the sixth aspect.

[0320] It should be noted that a decoding method that matches the encoding method of the fourth aspect shown in FIGS. 17A, 17B, and 18 may be adopted.

[0321] [Effects, etc.] As described above, the decoding device 200 according to this aspect can achieve the same effects as the encoding device 100 according to the fourth aspect.

[0322] [Combination with other aspects] 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 device configurations, and some syntaxes described in the flowcharts of this aspect may be implemented in combination with other aspects.

[0323] (Modifications of each aspect of the first embodiment) A signal indicating whether or not to enable part or all of the processing described in any of the first to eighth aspects may be coded and decoded. Such a signal may be coded in units of CU (Coding Unit) or CTU (Coding Tree Unit), or may be coded in units of SPS (Sequence Parameter Set), PPS (Picture Parameter Set), or slice, which correspond to the H.265 / HEVC standard.

[0324] 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), transform size (4x4 pixels, 8x8 pixels, or other), the number of non-zero coefficients, the quantization parameter, Temporal_id (layer of hierarchical coding), or any combination thereof.

[0325] When the encoding devices according to the first to fourth aspects perform the above-described operations, the decoding devices according to the fifth to eighth aspects also perform corresponding operations. For example, when the encoding device encodes information indicating whether to enable the process of skipping the first transform or the second transform, the decoding device decodes the information and determines whether the first transform or the second transform is enabled and whether information indicating the first transform or the second transform has been encoded.

[0326] (Embodiment 2) In each of the above embodiments, 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. Of course, each functional block can also be realized by hardware (dedicated circuits).

[0327] Furthermore, the processing described in each embodiment 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.

[0328] The aspects of the present disclosure are not limited to the above examples, and various modifications are possible, and these modifications are also included within the scope of the aspects of the present disclosure.

[0329] Furthermore, here, we will explain application examples of the video coding method (image coding method) or video decoding method (image decoding method) shown in each of the above embodiments and a system using the same. The system is characterized by having an image coding device using the image coding method, an image decoding device using the image decoding method, and an image coding / decoding device that includes both. Other components of the system can be appropriately changed depending on the situation.

[0330] [Usage example] 25 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.

[0331] 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.

[0332] 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.

[0333] 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.

[0334] The home appliance ex118 is a refrigerator or an appliance included in a home fuel cell cogeneration system.

[0335] 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 each of the above embodiments on still images 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. That is, each terminal functions as an image encoding device according to one aspect of the present disclosure.

[0336] 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, 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 disclosure.

[0337] [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.

[0338] 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.

[0339] 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).

[0340] 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.

[0341] 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.

[0342] The server may also transcode the video data to change the encoding format before distributing it. For example, the server may convert an MPEG-based encoding format to a VP-based encoding format, or convert H.264 to H.265.

[0343] 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.

[0344] [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.

[0345] 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.

[0346] 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.

[0347] 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.

[0348] 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.

[0349] 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.

[0350] 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.

[0351] [Scalable Coding] Content switching will be described using a scalable stream, shown in FIG. 26, compressed and encoded using the video encoding method described in each of the above embodiments. The server may have multiple streams with the same content but different qualities, but may also switch content by taking advantage of the temporal / spatial scalability achieved by encoding the stream in layers, as shown. 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.

[0352] 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.

[0353] 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. 27, 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.

[0354] 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.

[0355] [Webpage optimization] FIG. 28 is a diagram showing an example of a web page display screen on a computer ex111 or the like. FIG. 29 is a diagram showing an example of a web page display screen on a smartphone ex115 or the like. As shown in FIGS. 28 and 29, 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.

[0356] 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.

[0357] [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.

[0358] 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.

[0359] 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.

[0360] [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.

[0361] 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.

[0362] 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.

[0363] 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.

[0364] [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.

[0365] 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.

[0366] Furthermore, at least one of the video encoding device (image encoding device) or video decoding device (image decoding device) of each of the above embodiments 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 content supply system ex100, which is more suited to unicast, but similar applications are possible with regard to encoding and decoding processes.

[0367] [Hardware configuration] FIG. 30 is a diagram illustrating a smartphone ex115. FIG. 31 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 images 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.

[0368] 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.

[0369] 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.

[0370] 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 compression-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 each of the above embodiments, and sends the encoded video data to the multiplexing / demultiplexing unit ex453. The audio signal processing unit ex454 also encodes the audio signal picked up 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.

[0371] 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 / demultiplexing unit ex453, which separates the multiplexed data into a video data bitstream and an audio data bitstream. The multiplexing / demultiplexing unit ex453 then demultiplexes the multiplexed data and supplies the encoded video data to the video signal processing unit ex455 and the encoded audio data to the audio signal processing unit ex454 via the synchronization bus ex470. The video signal processing unit ex455 decodes the video signal using a video decoding method corresponding to the video encoding method described in each of the above embodiments, and displays the video or still image contained 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.

[0372] 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.

[0373] 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]

[0374] 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]

[0375] 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 unit 200 Decryption Device 202 Entropy Decoding Unit 1061, 2064 Conversion mode determination section 1062, 2065 Size determination section 1063 First transformation basis selection part 1064 First conversion unit 1065 Second conversion execution determination unit 1066 Second transformation basis selection section 1067 Second conversion unit 1141, 2062 Second inverse transformation basis selection part 1142, 2063 Second inverse transform unit 1143, 2066 First inverse transformation basis selection part 1144, 2067 First inverse transform unit 2061 Second inverse transformation execution determination unit 2062S Second base selection signal 2064S Adaptive Transform Basis Selection Mode Signal 2065S size signal 2066S First base selection signal

Claims

1. 1. An encoding device comprising a circuit and a memory, The circuit uses the memory to: determining whether a mode for selecting a transformation base according to the size of the block to be coded is enabled; If the mode is enabled, When the horizontal size of the encoding target block is larger than a threshold size, a first transformation base is selected from a plurality of candidate transformation bases as a transformation base in the horizontal direction; When the horizontal size of the encoding target block is smaller than the threshold size, a second transformation base that is a fixed transformation base is selected as a transformation base in the horizontal direction; generating first transform coefficients by performing a first transform on the residual of the current block using the selected horizontal transform basis; performing a second transform on the first transform coefficients to generate second transform coefficients; generating a bitstream including information indicating whether said mode is enabled; Encoding device.

2. 1. A decoding device comprising a circuit and a memory, The circuit uses the memory to: generating transform coefficients by performing a second inverse transform on coefficients of the block to be decoded; determining whether a mode for selecting a transformation base according to the size of the block to be decoded is valid; If the mode is enabled, When the horizontal size of the block to be decoded is larger than a threshold size, a first inverse transformation base is selected from a plurality of inverse transformation base candidates as an inverse transformation base in the horizontal direction; When the horizontal size of the block to be decoded is smaller than the threshold size, a second inverse transform basis that is a fixed inverse transform basis is selected as an inverse transform basis in the horizontal direction; generating a prediction residual by performing a first inverse transform on the transform coefficients of the current block using the selected horizontal inverse transform basis; Decryption device.

3. determining whether a mode for selecting a transformation base according to the size of the block to be coded is enabled; If the mode is enabled, When the horizontal size of the encoding target block is larger than a threshold size, a first transformation base is selected from a plurality of candidate transformation bases as a transformation base in the horizontal direction; When the horizontal size of the encoding target block is smaller than the threshold size, a second transformation base that is a fixed transformation base is selected as a transformation base in the horizontal direction; generating first transform coefficients by performing a first transform on the residual of the current block using the selected horizontal transform basis; performing a second transform on the first transform coefficients to generate second transform coefficients; generating a bitstream including information indicating whether said mode is enabled; Encoding method.

4. generating transform coefficients by performing a second inverse transform on coefficients of the block to be decoded; determining whether a mode for selecting a transformation base according to the size of the block to be decoded is valid; If the mode is enabled, When the horizontal size of the block to be decoded is larger than a threshold size, a first inverse transformation base is selected from a plurality of inverse transformation base candidates as an inverse transformation base in the horizontal direction; When the horizontal size of the block to be decoded is smaller than the threshold size, a second inverse transform basis that is a fixed inverse transform basis is selected as an inverse transform basis in the horizontal direction; generating a prediction residual by performing a first inverse transform on the transform coefficients of the current block using the selected horizontal inverse transform basis; Decryption method.

5. 1. A transmission method for transmitting a bitstream, comprising: determining whether a mode for selecting a transformation base according to the size of the block to be coded is enabled; If the mode is enabled, When the horizontal size of the encoding target block is larger than a threshold size, a first transformation base is selected from a plurality of candidate transformation bases as a transformation base in the horizontal direction; When the horizontal size of the encoding target block is smaller than the threshold size, a second transformation base that is a fixed transformation base is selected as a transformation base in the horizontal direction; generating first transform coefficients by performing a first transform on the residual of the current block using the selected horizontal transform basis; performing a second transform on the first transform coefficients to generate second transform coefficients; generating a bitstream including information indicating whether the mode is enabled; transmitting the generated bitstream; Sending method.

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