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

Abstract

To provide an encoding device capable of achieving further improvement in compression efficiency and reduction in processing load.SOLUTION: The encoding device (100) determines whether or not a mode for selecting a transform basis in accordance with a size of a block to be encoded is valid, and when the mode is valid, selects a first transform basis as a transform basis in a horizontal direction from among a plurality of candidates for the transform basis when a horizontal size of the block to be encoded is larger than a threshold size. When the horizontal size of the encoding target block is smaller than the threshold size, a second transform basis that is a fixed transform basis is selected as a transform basis in the horizontal direction, a first transform is performed on a residual of the encoding target block using the selected transform basis in the horizontal direction to generate a first transform coefficient, a second transform is performed on the first transform coefficient to generate a second transform coefficient, and a bitstream including information indicating whether or not a mode is valid is generated.SELECTED DRAWING: FIG. 12A

Description

[Technical Field]

[0001] This disclosure relates to an encoding device, a decoding device, an encoding method, a decoding method, and a transmission method. [Background technology]

[0002] The video coding standard known as HEVC (High-Efficiency Video Coding) has been standardized by JCT-VC (Joint Collaborative Team on Video Coding). [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 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Such encoding and decoding technologies require further improvements in compression efficiency and reductions in processing load.

[0005] Therefore, this disclosure provides an encoding device, a decoding device, an encoding method, a decoding method, or a transmission method that can achieve further improvements in compression efficiency and reductions in processing load. [Means for solving the problem]

[0006] An encoding device according to one aspect of the present disclosure is an encoding device comprising a circuit and a memory, wherein the circuit uses the memory to determine whether a mode for selecting a transformation basis 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 greater than a threshold size, it selects a first transformation basis from among a plurality of candidate transformation basis as the horizontal transformation basis, when the horizontal size of the block to be encoded is less than the threshold size, it selects a second transformation basis which is a fixed transformation basis as the horizontal transformation basis, generates a first transformation coefficient by performing a first transformation on the residual of the block to be encoded using the selected horizontal transformation basis, generates a second transformation coefficient by performing a second transformation on the first transformation coefficient, and generates a bitstream including information indicating whether the mode is enabled or not.

[0007] A decoding device according to one aspect of the present disclosure is a decoding device comprising a circuit and a memory, wherein the circuit generates conversion coefficients by performing a second inverse transformation on the coefficients of the block to be decoded using the memory, determines whether a mode for selecting a conversion basis according to the size of the block to be decoded is enabled, and if the mode is enabled, selects a first inverse transformation basis from among a plurality of candidate inverse transformation basis bases as the horizontal inverse transformation basis when the horizontal size of the block to be decoded is greater than a threshold size, selects a second inverse transformation basis which is a fixed inverse transformation basis as the horizontal inverse transformation basis when the horizontal size of the block to be decoded is less than the threshold size, and generates a predicted residual by performing a first inverse transformation on the conversion coefficients of the block to be decoded using the selected horizontal inverse transformation basis.

[0008] These general or specific embodiments may be implemented as a system, method, integrated circuit, computer program, or recording medium such as a computer-readable CD-ROM, or as any combination of a system, method, integrated circuit, computer program, and recording medium. [Effects of the Invention]

[0009] This disclosure can provide an encoding device, a decoding device, an encoding method, a decoding method, or a transmission method that can achieve further improvements in compression efficiency and reductions in processing load. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a block diagram showing the functional configuration of the encoding device according to Embodiment 1. [Figure 2] Figure 2 shows an example of block division in Embodiment 1. [Figure 3] Figure 3 is a table showing the transformation basis functions corresponding to each transformation type. [Figure 4A] Figure 4A shows an example of the filter shape used in ALF. [Figure 4B] Figure 4B shows another example of the filter shape used in ALF. [Figure 4C] Figure 4C shows another example of the filter shape used in ALF. [Figure 5A] Figure 5A shows the 67 intra-prediction modes in intra-prediction. [Figure 5B] Figure 5B is a flowchart illustrating the overview of the predictive image correction process using OBMC processing. [Figure 5C] Figure 5C is a conceptual diagram illustrating the overview of the predictive image correction process using OBMC processing. [Figure 5D] Figure 5D shows 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 in subblock units based on motion vectors of a plurality of adjacent blocks. [Figure 9B] FIG. 9B is a diagram for explaining an outline of motion vector derivation processing in merge mode. [Figure 9C] FIG. 9C is a conceptual diagram for explaining an outline of DMVR processing. [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 the decoding device according to Embodiment 1. [Figure 11A] FIG. 11A is a block diagram showing an internal configuration of a transforming unit of the encoding device according to the first aspect of Embodiment 1. [Figure 11B] FIG. 11B is a block diagram showing an internal configuration of an inverse transforming unit of the encoding device according to the first aspect of Embodiment 1. [Figure 12A] FIG. 12A is a flowchart showing processing of a transforming unit and a quantizing unit of the encoding device according to the first aspect of Embodiment 1. [Figure 12B] FIG. 12B is a flowchart showing a modified example of processing of the transforming unit and the quantizing unit of the encoding device according to the first aspect of Embodiment 1. [Figure 13A] FIG. 13A is a flowchart showing processing of a transforming unit and a quantizing unit of the encoding device according to the second aspect of Embodiment 1. [Figure 13B]Figure 13B is a flowchart showing the processing of the entropy coding unit of the coding device according to the second aspect of Embodiment 1. [Figure 14] Figure 14 shows a specific example of the syntax in the second aspect of Embodiment 1. [Figure 15] Figure 15 is a table showing specific examples of the transformation basis used in the second embodiment of Embodiment 1, with and without signal coding. [Figure 16] Figure 16 is a flowchart showing the processing of the conversion unit and quantization unit of the encoding device according to the third aspect of Embodiment 1. [Figure 17A] Figure 17A is a flowchart showing the processing of the conversion unit and quantization unit of the encoding device according to the fourth aspect of Embodiment 1. [Figure 17B] Figure 17B is a flowchart showing the processing of the entropy coding unit of the coding device according to the fourth aspect of Embodiment 1. [Figure 18] Figure 18 shows a specific example of the syntax in the fourth aspect of Embodiment 1. [Figure 19] Figure 19 is a table showing specific examples of the transformation basis used in the fourth embodiment of Embodiment 1, with and without signal coding. [Figure 20] Figure 20 is a block diagram showing the internal configuration of the inverse transformer section of the decoding device according to the fifth aspect of Embodiment 1. [Figure 21] Figure 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 Embodiment 1. [Figure 22A] Figure 22A is a flowchart showing the processing of the entropy decoding section of the decoding device according to the sixth aspect of Embodiment 1. [Figure 22B] Figure 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] Figure 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 Embodiment 1. [Figure 24A]Figure 24A is a flowchart showing the processing of the entropy decoding section of the decoding device according to the eighth aspect of Embodiment 1. [Figure 24B] Figure 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] Figure 25 is an overall diagram of the content supply system that enables the content distribution service. [Figure 26] Figure 26 shows an example of an encoding structure during scalable encoding. [Figure 27] Figure 27 shows an example of an encoding structure during scalable encoding. [Figure 28] Figure 28 shows an example of how a web page is displayed. [Figure 29] Figure 29 shows an example of how a web page is displayed. [Figure 30] Figure 30 shows an example of a smartphone. [Figure 31] Figure 31 is a block diagram showing an example of a smartphone configuration. [Modes for carrying out the invention]

[0011] The embodiments will be described in detail below with reference to the drawings.

[0012] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement and connection configurations of components, steps, and the order of steps shown in the following embodiments are examples only and are not intended to limit the scope of the claims. Furthermore, among the components in the following embodiments, those not described in the independent claim representing the highest-level concept will be described as optional components.

[0013] (Embodiment 1) First, an overview of Embodiment 1 will be given as an example of an encoding and decoding device to which the processes and / or configurations described in each aspect of this disclosure, described later, can be applied. However, Embodiment 1 is merely an example of an encoding and decoding device to which the processes and / or configurations described in each aspect of this disclosure can be applied, and the processes and / or configurations described in each aspect of this disclosure can also be implemented in encoding and decoding devices different from Embodiment 1.

[0014] When applying the processes and / or configurations described in each aspect of this disclosure to Embodiment 1, for example, one of the following may be performed:

[0015] (1) With respect to the encoding or decoding device of Embodiment 1, replace the component corresponding to the component described in each aspect of the disclosure with the component described in each aspect of the disclosure, among the plurality of components constituting the encoding or decoding device. (2) With respect to the encoding or decoding device of Embodiment 1, any modifications such as adding, replacing, or deleting functions or processes performed by some of the multiple components constituting the encoding or decoding device are made, and then the components corresponding to the components described in each aspect of the Disclosure are replaced with the components described in each aspect of the Disclosure. (3) Adding processing to and / or replacing, deleting, or otherwise modifying some of the processing included in the method performed by the encoding or decoding device of Embodiment 1, and then replacing the processing corresponding to the processing described in each aspect of the Disclosure with the processing described in each aspect of the Disclosure. (4) Combining some of the multiple components constituting the encoding or decoding device of Embodiment 1 with a component described in each aspect of the Disclosure, a component that provides some of the functions of the components described in each aspect of the Disclosure, or a component that performs some of the processing performed by the components described in each aspect of the Disclosure. (5) A component that has some of the functions of some of the components that constitute the encoding or decoding device of Embodiment 1, or a component that performs some of the processing performed by some of the components that constitute the encoding or decoding device of Embodiment 1, in combination with a component described in each aspect of this disclosure, a component that has some of the functions of the components described in each aspect of this disclosure, or a component that performs some of the processing performed by the components described in each aspect of this disclosure. (6) With respect to the method performed by the encoding or decoding device of Embodiment 1, replace with the process corresponding to the process described in each aspect of the Disclosure among the plurality of processes included in the method with the process described in each aspect of the Disclosure. (7) Performing some of the processes included in the method performed by the encoding or decoding device of Embodiment 1 in combination with the processes described in each aspect of the present disclosure. The methods of implementing the processes and / or configurations described in each aspect of this disclosure are not limited to the examples above. For example, they may be implemented in a device used for a purpose other than the video / image encoding device or video / image decoding device disclosed in Embodiment 1, or the processes and / or configurations described in each embodiment may be implemented individually. Furthermore, the processes and / or configurations described in different embodiments may be implemented in combination.

[0016] [Overview of the coding device] First, an overview of the encoding device according to Embodiment 1 will be described. Figure 1 is a block diagram showing the functional configuration of the encoding device 100 according to Embodiment 1. The encoding device 100 is a video / image encoding device that encodes video / images in block units.

[0017] As shown in Figure 1, the encoding device 100 is a device that encodes an image in block units and comprises 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 can be implemented, for example, by a general-purpose processor and memory. In this case, when a software program stored in memory is executed by the processor, the processor functions as a splitting unit 102, a subtraction unit 104, a conversion unit 106, a quantization unit 108, an entropy encoding unit 110, an inverse quantization unit 112, an inverse conversion unit 114, an addition unit 116, a loop filter unit 120, an intra prediction unit 124, an inter prediction unit 126, and a prediction control unit 128. Alternatively, the encoding device 100 may be implemented as one or more dedicated electronic circuits corresponding to the splitting unit 102, a subtraction unit 104, a conversion unit 106, a quantization unit 108, an entropy encoding unit 110, an inverse quantization unit 112, an inverse conversion unit 114, an addition unit 116, a loop filter unit 120, an intra prediction unit 124, an inter prediction unit 126, and a prediction control unit 128.

[0019] The following describes each component included in the encoding device 100.

[0020] [Divided part] The splitting unit 102 divides each picture contained in the input video into multiple blocks and outputs each block to the subtraction unit 104. For example, the splitting unit 102 first divides the picture into blocks of a fixed size (e.g., 128x128). These fixed-size blocks are sometimes called coding tree units (CTUs). Then, based on recursive quadtree and / or binary tree block partitioning, the splitting unit 102 divides each of the fixed-size blocks into blocks of a variable size (e.g., 64x64 or less). These variable-size blocks are sometimes called coding units (CUs), prediction units (PUs), or transformation units (TUs). In this embodiment, CUs, PUs, and TUs do not need to be distinguished, and some or all of the blocks in the picture may become processing units for CUs, PUs, and TUs.

[0021] Figure 2 shows an example of block partitioning in Embodiment 1. In Figure 2, solid lines represent block boundaries due to quadtree block partitioning, and dashed lines represent block boundaries due to binary tree block partitioning.

[0022] Here, block 10 is a 128x128 pixel square block (128x128 block). This 128x128 block 10 is first divided into four 64x64 square blocks (quadtree block partitioning).

[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 partitioning). As a result, the top-left 64x64 block is divided into two 16x64 blocks 11 and 12 and a 32x64 block 13.

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

[0025] The bottom-left 64x64 block is divided into four square 32x32 blocks (quadrutree block division). Of the four 32x32 blocks, the top-left and bottom-right blocks are further divided. The top-left 32x32 block is vertically divided into two rectangular 16x32 blocks, and the rightmost 16x32 block is further horizontally divided into two 16x16 blocks (binary tree block division). The bottom-right 32x32 block is horizontally divided into two 32x16 blocks (binary tree block division). As a result, the bottom-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 64x64 block 23 in the bottom right will not be divided.

[0027] As described above, in Figure 2, block 10 is divided into 13 variable-sized blocks 11-23 based on recursive quad-tree and binary tree block partitioning. Such partitioning is sometimes called QTBT (quad-tree plus binary tree) partitioning.

[0028] In Figure 2, one block was divided into four or two blocks (quadrutree or binary tree block partitioning), but the partitioning is not limited to these. For example, one block may be divided into three blocks (ternary tree block partitioning). Partitioning that includes such ternary tree block partitioning is sometimes called MBT (multi-type tree) partitioning.

[0029] [Subtraction Unit] The subtraction unit 104 subtracts the predicted signal (predicted sample) from the original signal (original sample) in block units divided by the division unit 102. In other words, the subtraction unit 104 calculates the prediction error (also called the residual) of the block to be encoded (hereinafter referred to as the current block). The subtraction unit 104 then outputs the calculated prediction error to the conversion unit 106.

[0030] The source signal is the input signal to the encoding device 100, and is a signal representing the image of each picture that makes up the moving image (for example, a luminance (luma) signal and two chroma (chroma) signals). In the following, the signal representing the image may also be called a sample.

[0031] [Conversion section] The conversion unit 106 converts the prediction error in the spatial domain into conversion coefficients in the frequency domain and outputs the conversion coefficients to the quantization unit 108. Specifically, the conversion unit 106 performs a predetermined discrete cosine transform (DCT) or discrete sine transform (DST) on the prediction error in the spatial domain, for example.

[0032] The transformation unit 106 may also adaptively select a transformation type from among several transformation types and use a transformation basis function corresponding to the selected transformation type to convert the prediction error into transformation coefficients. Such a transformation is sometimes called an EMT (explicit multiple core transform) or an AMT (adaptive multiple transform).

[0033] Multiple transformation types include, for example, DCT-II, DCT-V, DCT-VIII, DST-I, and DST-VII. Figure 3 is a table showing the transformation basis functions corresponding to each transformation type. In Figure 3, N represents the number of input pixels. The selection of a transformation type from among these multiple transformation types may depend, for example, on the type of prediction (intra-prediction and inter-prediction) or on the intra-prediction mode.

[0034] Information indicating whether or not to apply such EMT or AMT (e.g., called an AMT flag) and information indicating the selected conversion type are signaled at the CU level. However, the signaling of this information is not 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 transformation unit 106 may retransform the transformation coefficients (transformation results). Such retransformation is sometimes called AST (adaptive secondary transform) or NSST (non-separable secondary transform). For example, the transformation unit 106 performs retransformation for each subblock (e.g., 4x4 subblock) contained in the block of transformation coefficients corresponding to the intra-prediction error. Information indicating whether or not to apply NSST and information regarding the transformation matrix used for NSST are signaled at the CU level. Note that the signaling of this information is not limited to the CU level, but may be at other levels (e.g., sequence level, picture level, slice level, tile level, or CTU level).

[0036] Here, a separable transformation is a method in which the input is separated into directions equal to the number of dimensions and transformed multiple times, while a non-separable transformation is a method in which, when the input is multidimensional, two or more dimensions are treated as one dimension and transformed together.

[0037] For example, one example of a non-separable transformation is to treat a 4x4 block as a single array with 16 elements and then perform a transformation on that array using a 16x16 transformation matrix.

[0038] Similarly, the Hypercube Givens Transform, which treats a 4x4 input block as a single array with 16 elements and then performs multiple Givens rotations on that array, is another example of a non-separable transformation.

[0039] [Quantization section] The quantization unit 108 quantizes the conversion coefficients output from the conversion unit 106. Specifically, the quantization unit 108 scans the conversion coefficients of the current block in a predetermined scanning order and quantizes the conversion coefficients based on the quantization parameter (QP) corresponding to the scanned conversion coefficients. The quantization unit 108 then outputs the quantized conversion coefficients of the current block (hereinafter referred to as quantization coefficients) to the entropy coding unit 110 and the inverse quantization unit 112.

[0040] The predetermined order is the order for quantization / inverse quantization of the transformation coefficients. For example, the predetermined scanning order is defined as ascending frequency (from low frequency to high frequency) or descending frequency (from high frequency to low frequency).

[0041] Quantization parameters are parameters that define the quantization step (quantization width). For example, if the value of the quantization parameter increases, the quantization step also increases. In other words, if the value of the quantization parameter increases, the quantization error increases.

[0042] [Entropy coding unit] The entropy coding unit 110 generates an encoded signal (encoded bitstream) by variable-length encoding the quantization coefficients, which are input from the quantization unit 108. Specifically, the entropy coding unit 110, for example, binarizes the quantization coefficients and arithmetically encodes the binary signal.

[0043] [Dequantization section] The inverse quantization unit 112 inversely quantizes the quantization coefficients, which are input from the quantization unit 108. Specifically, the inverse quantization unit 112 inversely quantizes the quantization coefficients of the current block in a predetermined scanning order. Then, the inverse quantization unit 112 outputs the inversely quantized conversion coefficients of the current block to the inverse conversion unit 114.

[0044] [Inverse Transformation Section] The inverse transform unit 114 restores the prediction error by inversely transforming the transformation coefficients, which 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 transformation coefficients that corresponds to the transformation by the transformation unit 106. The inverse transform unit 114 then outputs the restored prediction error to the summation unit 116.

[0045] Furthermore, the recovered prediction error does not match the prediction error calculated by the subtraction unit 104 because information is lost due to quantization. In other words, the recovered prediction error includes quantization errors.

[0046] [Addition section] The adder 116 reconstructs the current block by adding the prediction error, which is the input from the inverse transformer 114, and the prediction sample, which is the 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 the local decoded block.

[0047] [Block memory] The block memory 118 is a storage unit for storing blocks within the picture to be encoded (hereinafter referred to as the current picture) that are referenced in intra prediction. 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 unit 116 and outputs the filtered reconstructed block to the frame memory 122. A loop filter is a filter used within the encoding loop (in-loop filter), and includes, for example, a deblocking filter (DF), sample adaptive offset (SAO), and adaptive loop filter (ALF).

[0049] In ALF, a least-squares error filter is applied to remove coding distortion. For example, for each 2x2 subblock within the current block, one filter selected from several filters is applied based on the direction and activity of the local gradient.

[0050] Specifically, first, subblocks (e.g., 2x2 subblocks) are classified into multiple classes (e.g., 15 or 25 classes). The classification of subblocks is based on the direction and activity of the gradient. For example, a classification value C (e.g., C = 5D + A) is calculated using the gradient direction value D (e.g., 0-2 or 0-4) and the gradient activity value A (e.g., 0-4). Then, based on the classification value C, the subblocks are classified into multiple 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). The gradient activation value A is derived, for example, by adding the gradients in multiple directions and quantizing the sum.

[0052] Based on the results of this classification, a filter for the subblock is determined from among multiple filters.

[0053] For example, a circularly symmetric shape is used as the filter shape in ALF. Figures 4A to 4C show several examples of filter shapes used in ALF. Figure 4A shows a 5x5 diamond-shaped filter, Figure 4B shows a 7x7 diamond-shaped filter, and Figure 4C shows a 9x9 diamond-shaped filter. Information indicating the filter shape is signaled at the picture level. However, the signaling of information indicating the filter shape is not 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] The on / off status of ALF is determined, for example, at the picture level or CU level. For instance, the decision to apply ALF to luminance is made at the CU level, and the decision to apply ALF to color difference is made at the picture level. Information indicating whether ALF is on or off is signaled at the picture level or CU level. However, the signaling of information indicating whether ALF is on or off is not limited to the picture level or CU level, but may be at other levels (e.g., sequence level, slice level, tile level, or CTU level).

[0055] The coefficient sets of multiple selectable filters (e.g., up to 15 or 25 filters) are signaled at the picture level. However, the signaling of the coefficient sets is not limited to the picture level; it may be at other levels (e.g., sequence level, slice level, tile level, CTU level, CU level, or subblock level).

[0056] [Frame memory] The frame memory 122 is a storage unit for storing reference pictures used in interpretation, 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 Unit] The intra-prediction unit 124 generates a prediction signal (intra-prediction signal) by performing intra-prediction (also called in-screen prediction) of the current block by referring to the block in the current picture stored in the block memory 118. Specifically, the intra-prediction unit 124 generates an intra-prediction signal by performing intra-prediction by referring to samples (e.g., luminance values, color difference 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 predetermined set of intra-prediction modes. The set of intra-prediction modes includes one or more non-directional prediction modes and multiple directional prediction modes.

[0059] One or more non-directional prediction modes include, for example, the Planar prediction mode and DC prediction mode as defined in the H.265 / HEVC (High-Efficiency Video Coding) standard (Non-Patent Document 1).

[0060] Multiple directional prediction modes include, for example, the 33 directional prediction modes defined in the H.265 / HEVC standard. Note that multiple directional prediction modes may also include 32 additional directional prediction modes (a total of 65 directional prediction modes). Figure 5A shows 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] Furthermore, in the intra-prediction of a color difference block, a luminance block may be referenced. That is, the color difference component of the current block may be predicted based on the luminance component of the current block. Such intra-prediction is sometimes called CCLM (cross-component linear model) prediction. Such an intra-prediction mode for a color difference block that references a luminance block (e.g., called the CCLM mode) may be added as one of the intra-prediction modes for a color difference block.

[0062] The intra-prediction unit 124 may correct the pixel values ​​after intra-prediction based on the gradient of the horizontal / vertical reference pixels. Intra-prediction with such correction is sometimes called PDPC (position dependent intra-prediction combination). Information indicating whether or not PDPC is applied (for example, called a PDPC flag) is signaled at, for example, the CU level. Note that the signaling of this information is not limited to the CU level, but may be at other levels (for example, sequence level, picture level, slice level, tile level, or CTU level).

[0063] [International Prediction Department] The inter-prediction unit 126 generates a prediction signal (inter-prediction signal) by performing inter-prediction (also called inter-screen prediction) of the current block by referring to a reference picture stored in the frame memory 122 that is different from the current picture. Inter-prediction is performed in units of the current block or sub-blocks within the current block (e.g., 4x4 blocks). For example, the inter-prediction unit 126 performs motion estimation within the reference picture for the current block or sub-block. Then, the inter-prediction unit 126 generates an inter-prediction signal for the current block or sub-block by performing motion compensation using motion information (e.g., motion vectors) obtained from the motion estimation. Finally, the inter-prediction unit 126 outputs the generated inter-prediction signal to the prediction control unit 128.

[0064] The motion information used for motion compensation is converted into a signal. A motion vector predictor may be used to convert the motion vector into a signal. In other words, the difference between the motion vector and the predicted motion vector may be converted into a signal.

[0065] Furthermore, an inter-prediction signal may be generated using not only the motion information of the current block obtained through motion search, but also the motion information of adjacent blocks. Specifically, an inter-prediction signal may be generated for each sub-block within the current block by weighted addition of a prediction signal based on motion information obtained through motion search and a prediction signal based on the motion information of adjacent blocks. Such inter-prediction (motion compensation) is sometimes called OBMC (overlapped block motion compensation).

[0066] In this OBMC mode, information indicating the size of the subblock for OBMC (e.g., called the OBMC block size) is signaled at the sequence level. Information indicating whether or not to apply OBMC mode (e.g., called the OBMC flag) is signaled at the CU level. Note that the signaling levels for this information are not limited to the sequence and CU levels; other levels (e.g., picture level, slice level, tile level, CTU level, or subblock level) may also be used.

[0067] Let's explain the OBMC mode in more detail. Figures 5B and 5C are flowcharts and conceptual diagrams illustrating the overview of the predictive image correction process using OBMC processing.

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

[0069] Next, the motion vector (MV_L) of the encoded left adjacent block is applied to the block to be encoded to obtain a predicted image (Pred_L), and the first correction of the predicted image is performed by superimposing the predicted image and Pred_L with weights.

[0070] Similarly, the motion vector (MV_U) of the encoded upper adjacent block is applied to the block to be encoded to obtain a predicted image (Pred_U). The predicted image is then corrected a second time by weighting the first corrected predicted image and Pred_U, and this is used as the final predicted image.

[0071] While this explanation describes a two-stage correction method using the left adjacent block and the upper adjacent block, it is also possible to use the right adjacent block and the lower adjacent block to perform corrections more than two times.

[0072] Furthermore, the area to be superimposed does not have to be the entire pixel area of ​​the block, but rather only a portion of the area near the block boundary.

[0073] Although this explanation describes the predictive image correction process using a single reference picture, the process is similar when correcting predictive images from multiple reference pictures. After obtaining corrected predictive images from each reference picture, the resulting predictive images are superimposed to create the final predictive image.

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

[0075] One method for determining whether or not to apply OBMC processing is to use an obmc_flag signal, which indicates whether or not to apply OBMC processing. Specifically, in an encoding device, it is determined whether or not the block to be encoded belongs to a region with complex motion. If it belongs to a region with complex motion, the obmc_flag is set to a value of 1 and OBMC processing is applied to perform encoding. If it does not belong to a region with complex motion, the obmc_flag is set to a value of 0 and encoding is performed without applying OBMC processing. On the other hand, in a decoding device, the obmc_flag written in the stream is decoded, and the device switches whether or not to apply OBMC processing depending on its value and performs decoding.

[0076] Furthermore, motion information may be derived by the decoder without being converted into a signal. For example, the merge mode specified in the H.265 / HEVC standard may be used. Alternatively, motion information may be derived by performing a motion search on the decoder side. In this case, the motion search is performed without using the pixel values ​​of the current block.

[0077] Here, we will explain the mode in which motion detection is performed on the decoding device side. This mode in which motion detection is performed on the decoding device side is sometimes called PMMVD (pattern matched motion vector derivation) mode or FRUC (frame rate up-conversion) mode.

[0078] An example of FRUC processing is shown in Figure 5D. First, a list of multiple candidates (which may be the same as the merge list) is generated, each having a predicted motion vector, by referencing the motion vectors of spatially or temporally adjacent encoded blocks to the current block. Next, the best candidate MV is selected from among the multiple candidate MVs registered in the candidate list. For example, an evaluation value is calculated for each candidate included in the candidate list, and one candidate is selected based on the evaluation value.

[0079] Then, based on the motion vectors of the selected candidates, a motion vector for the current block is derived. Specifically, for example, the motion vector of the selected candidate (best candidate MV) is directly derived as the motion vector for the current block. Alternatively, for example, the motion vector for the current block may be derived by performing pattern matching in the area surrounding the position in the reference picture corresponding to the motion vector of the selected candidate. That is, a similar search is performed in the area surrounding the best candidate MV, and if an MV with a better evaluation value is found, the best candidate MV may be updated to this MV and used as the final MV for the current block. It is also possible to configure the system so that this process is not performed.

[0080] The same processing method can be used when processing at the sub-block level.

[0081] The evaluation value is calculated by determining the difference value of the reconstructed image through pattern matching between a region in the reference picture corresponding to the motion vector and a predetermined region. Alternatively, the evaluation value may be calculated using information other than the difference value.

[0082] For pattern matching, either first-order pattern matching or second-order pattern matching is used. First-order pattern matching and second-order 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 aligned with the motion trajectory of the current block. Therefore, in the first pattern matching, a region in another reference picture aligned with the motion trajectory of the current block is used as a predetermined region for calculating the evaluation value of the candidate described above.

[0084] Figure 6 illustrates an example of pattern matching (bilateral matching) between two blocks along a motion trajectory. As shown in Figure 6, in the first pattern matching, two motion vectors (MV0, MV1) are derived by searching for the best-matching pair of two blocks within two different reference pictures (Ref0, Ref1) that are along the motion trajectory of the current block. Specifically, for the current block, the difference between the reconstructed image at a specified position in the first encoded reference picture (Ref0) specified by the candidate MV and the reconstructed image at a specified position in the second encoded reference picture (Ref1) specified by the symmetric MV obtained by scaling the candidate MV by the display time interval is derived, and an evaluation value is calculated using the obtained difference value. It is preferable to select the candidate MV with the best evaluation value among multiple candidate MVs as the final MV.

[0085] Under the assumption of a continuous motion trajectory, the motion vector (MV0, MV1) pointing to two reference blocks is proportional to the temporal distance (TD0, TD1) between the current picture (Cur Pic) and the two reference pictures (Ref0, Ref1). For example, if the current picture is temporally located between the two reference pictures and the temporal distances from the current picture to the two reference pictures are equal, then the first pattern matching derives a mirror-symmetric bidirectional motion vector.

[0086] In the second pattern matching, pattern matching is performed between the template in the current picture (blocks adjacent to the current block in the current picture (e.g., blocks above and / or to the left)) and the blocks in the reference picture. Therefore, in the second pattern matching, the blocks adjacent to the current block in the current picture are used as a predetermined area for calculating the evaluation value of the candidates mentioned above.

[0087] Figure 7 illustrates an example of pattern matching (template matching) between a template in the current picture and a block in the reference picture. As shown in Figure 7, in the second pattern matching, the motion vector of the current block is derived by searching in the reference picture (Ref0) for the block that best matches the block adjacent to the current block (Cur block) in the current picture (Cur Pic). Specifically, for the current block, the difference is derived between the reconstructed image of the encoded region of both or either of the left adjacent and upper adjacent regions and the reconstructed image at the equivalent position in the encoded reference picture (Ref0) specified by the candidate MV. An evaluation value is calculated using the obtained difference value, and the candidate MV with the best evaluation value among multiple candidate MVs is selected as the best candidate MV.

[0088] Information indicating whether or not to apply such a FRUC mode (e.g., called the FRUC flag) is signaled at the CU level. Furthermore, if the FRUC mode is applied (e.g., the FRUC flag is true), information indicating the pattern matching method (first pattern matching or second pattern matching) (e.g., called the FRUC mode flag) is signaled at the CU level. Note that the signaling of this information is not limited to the CU level; it may be at other levels (e.g., sequence level, picture level, slice level, tile level, CTU level, or subblock level).

[0089] Here, we will explain the mode for deriving motion vectors based on a model that assumes uniform linear motion. This mode is called BIO (bi-directional optical). This is sometimes called flow mode.

[0090] Figure 8 is a diagram illustrating a model that assumes uniform linear motion. In Figure 8, (v x ,v y) represents a velocity vector, and τ0 and τ1 respectively represent the temporal distances between the current picture (Cur Pic) and the two reference pictures (Ref0, Ref1). (MVx0, MVy0) represents the motion vector corresponding to reference picture Ref0, and (MVx1, MVy1) represents the motion vector corresponding to reference picture Ref1.

[0091] At this time, the velocity vector v x , v y ) Under the assumption of uniform linear motion, (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]

Numerical formula

[0093] Here, I (k) represents the luminance value of reference image k (k=0,1) after motion compensation. This optical flow equation indicates that the sum of (i) the temporal 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 the combination of this optical flow equation and Hermite interpolation, block-level motion vectors obtained from a merge list or the like are corrected in pixel units.

[0094] Note that motion vectors may be derived at the decoding device side by a method different from the derivation of motion vectors based on a model assuming uniform linear motion. For example, motion vectors may be derived in sub-block units based on motion vectors of a plurality of adjacent blocks.

[0095] Here, we will describe a mode in which motion vectors are derived at the sub-block level based on the motion vectors of multiple adjacent blocks. This mode is sometimes called the affine motion compensation prediction mode.

[0096] Figure 9A is a diagram illustrating the derivation of subblock-level motion vectors based on the motion vectors of multiple adjacent blocks. In Figure 9A, the current block contains 16 4x4 subblocks. 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 subblocks. Then, using the two motion vectors v0 and v1, the motion vector (v) of each subblock within the current block is derived by the following equation (2). x ,v y ) is derived.

[0097]

number

[0098] Here, x and y represent the horizontal and vertical positions of the subblock, respectively, and w represents a predetermined weighting coefficient.

[0099] Such affine motion compensation prediction modes may include several modes in which the motion vectors of the upper-left and upper-right corner control points are derived. Information indicating such affine motion compensation prediction modes (e.g., called affine flags) is signaled at the CU level. Note that the signaling of this information indicating affine motion compensation prediction modes is not limited to the CU level, but may be at other levels (e.g., sequence level, picture level, slice level, tile level, CTU level, or subblock level).

[0100] [Prediction Control Unit] The prediction control unit 128 selects either the intra-prediction signal or the inter-prediction signal and outputs the selected signal as the prediction signal to the subtraction unit 104 and the addition unit 116.

[0101] Here, we will explain an example of deriving the motion vector of a picture to be encoded using merge mode. Figure 9B is a diagram illustrating the overview of the motion vector derivation process using merge mode.

[0102] First, a list of predicted MVs is generated, containing registered candidates for predicted MVs. Candidates for predicted MVs include spatially adjacent predicted MVs, which are the MVs of multiple encoded blocks located spatially around the block to be encoded; temporally adjacent predicted MVs, which are the MVs of nearby blocks projected onto the location of the block to be encoded in the encoded reference picture; combined predicted MVs, which are generated by combining the MV values ​​of spatially adjacent predicted MVs and temporally adjacent predicted MVs; and zero predicted MVs, which are MVs with a value of zero.

[0103] Next, one predicted MV is selected from the multiple predicted MVs registered in the predicted MV list to determine it as the MV for the block to be encoded.

[0104] Furthermore, the variable-length coding unit encodes the merge_idx signal, which indicates which predicted MV was selected, by writing it to a stream.

[0105] Note that the predicted MVs registered in the predicted MV list explained in Figure 9B are just an example, and the number of predicted MVs may differ from the number shown in the figure, the configuration may not include some of the types of predicted MVs shown in the figure, or it may include predicted MVs other than those shown in the figure.

[0106] Alternatively, the final MV may be determined by performing the DMVR process described later using the MV of the target block to be encoded derived by merge mode.

[0107] Here, we will explain an example of determining the MV using DMVR processing.

[0108] Figure 9C is a conceptual diagram illustrating the overview of DMVR processing.

[0109] First, the optimal MVP set for the block to be processed is used as a candidate MV. According to the candidate MV, 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, and a template is generated by taking the average of each reference pixel.

[0110] Next, using the template, the surrounding regions of candidate MVs for the first and second reference pictures are searched, and the MV with the lowest cost is determined as the final MV. The cost value is calculated using the difference between each pixel value of the template and each pixel value of the search region, as well as the MV value, etc.

[0111] Note that the general outline of the processing described here is basically the same for both encoding and decoding devices.

[0112] Note that any process that can explore the vicinity of a candidate MV and derive the final MV may be used instead of the exact process described here.

[0113] Here, we will explain the mode for generating predictive images using LIC processing.

[0114] Figure 9D is a diagram illustrating the outline of a predictive image generation method using luminance correction processing by LIC processing.

[0115] First, we derive a Music Model (MV) to obtain the reference image corresponding to the block to be encoded from the reference picture, which is an encoded picture.

[0116] Next, for the block to be encoded, information indicating how the luminance values ​​have changed between the reference picture and the image to be encoded is extracted using the luminance pixel values ​​of the left-adjacent and top-adjacent encoded surrounding reference regions, and the luminance pixel values ​​at the equivalent positions in the reference picture specified by MV, and a luminance correction parameter is calculated.

[0117] By performing brightness correction processing on the reference image within the reference picture specified in MV using the brightness correction parameter, a predicted image for the encoding target block is generated.

[0118] Note that the shape of the surrounding reference region in Figure 9D is just one example, and other shapes may be used.

[0119] Furthermore, while this explanation describes the process of generating a predicted image from a single reference picture, the process is similar when generating predicted images from multiple reference pictures. In this case, the same brightness correction process is applied to each reference image obtained from the respective reference picture before generating the predicted image.

[0120] One method for determining whether or not to apply LIC processing is to use a signal called lic_flag, which indicates whether or not to apply LIC processing. Specifically, in an encoding device, it is determined whether or not the block to be encoded belongs to a region where brightness changes are occurring. If it belongs to a region where brightness changes are occurring, the value of lic_flag is set to 1 and LIC processing is applied and encoding is performed. If it does not belong to a region where brightness changes are occurring, the value of lic_flag is set to 0 and encoding is performed without applying LIC processing. On the other hand, in a decoding device, the lic_flag written in the stream is decoded, and the device switches whether or not to apply LIC processing according to its value and performs decoding.

[0121] Another way to determine whether to apply LIC processing is, for example, by checking whether LIC processing has been applied to surrounding blocks. A specific example is that if the block to be encoded is in merge mode, during the MV derivation in merge mode processing, it is determined whether the surrounding encoded blocks selected were encoded with LIC processing. Based on this result, the application of LIC processing is switched, and encoding is performed accordingly. In this example, the decoding process is exactly the same.

[0122] [Overview of the decryption device] Next, an overview of a decoding device capable of decoding the encoded signal (encoded bitstream) output from the above-mentioned encoding device 100 will be described. Figure 10 is a block diagram showing the functional configuration of the decoding device 200 according to Embodiment 1. The decoding device 200 is a video / image decoding device that decodes video / images in block units.

[0123] As shown in Figure 10, the decoding device 200 includes an entropy decoding unit 202, an inverse quantization unit 204, an inverse transform unit 206, an adder 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 can be implemented, for example, by a general-purpose processor and memory. In this case, when the software program stored in memory is executed by the processor, the processor functions as an entropy decoding unit 202, an inverse quantization unit 204, an inverse transformation unit 206, an addition unit 208, a loop filter unit 212, an intra prediction unit 216, an inter prediction unit 218, and a prediction control unit 220. Alternatively, the decoding device 200 may be implemented as one or more dedicated electronic circuits corresponding to the entropy decoding unit 202, the inverse quantization unit 204, the inverse transformation 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] The following describes each component included in the decoding device 200.

[0126] [Entropy Decoder] The entropy decoding unit 202 entropically decodes the encoded bitstream. Specifically, the entropy decoding unit 202 arithmetically decodes the encoded bitstream into a binary signal, for example. Then, the entropy decoding unit 202 debinarizes the binary signal. As a result, the entropy decoding unit 202 outputs the quantization coefficients in block units to the inverse quantization unit 204.

[0127] [Dequantization section] The inverse quantization unit 204 inversely quantizes the quantization coefficients of the decoded block (hereinafter referred to as the current block), which is the input from the entropy decoding unit 202. Specifically, for each quantization coefficient of the current block, the inverse quantization unit 204 inversely quantizes the quantization coefficient based on the quantization parameter corresponding to that quantization coefficient. The inverse quantization unit 204 then outputs the inversely quantized quantization coefficients (i.e., transformation coefficients) of the current block to the inverse transformation unit 206.

[0128] [Inverse Transformation Section] The inverse transform unit 206 restores the prediction error by inversely transforming the transformation coefficients, which are input from the inverse quantization unit 204.

[0129] For example, if the information decoded from the encoded bitstream indicates that EMT or AMT should be applied (e.g., the AMT flag is true), the inverse transform unit 206 inversely transforms the transformation coefficients of the current block based on the information indicating the decoded transformation type.

[0130] For example, if the information decoded from the encoded bitstream indicates that NSST should be applied, the inverse transform unit 206 applies inverse retransformation to the transformation coefficients.

[0131] [Addition section] The adder 208 reconstructs the current block by adding the prediction error, which is the input from the inverse transformer 206, and the prediction sample, which is the 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 located within the decoded picture (hereinafter referred to as the 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 the frame memory 214 and the display device, etc.

[0134] If the information interpreted from the encoded bitstream indicating ALF on / off indicates ALF is on, one filter is selected from among several filters based on the direction and activity of the local gradient, and the selected filter is applied to the reconstruction block.

[0135] [Frame memory] The frame memory 214 is a memory unit for storing reference pictures used for interpretation, 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 Unit] The intra-prediction unit 216 generates a prediction signal (intra-prediction signal) by performing intra-prediction based on the intra-prediction mode decoded from the encoded bitstream, and by referring to the blocks in the current picture stored in the block memory 210. Specifically, the intra-prediction unit 216 generates an 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] Furthermore, if an intra-prediction mode that references a luminance block is selected in the intra-prediction of a color difference block, the intra-prediction unit 216 may predict the color difference component of the current block based on the luminance component of the current block.

[0138] Furthermore, if the information decoded from the encoded bitstream indicates the application of PDPC, the intra-prediction unit 216 corrects the pixel value after intra-prediction based on the gradient of the horizontal / vertical reference pixels.

[0139] [International Prediction Department] The inter-prediction unit 218 predicts the current block by referring to a reference picture stored in the frame memory 214. Prediction is performed in units of the current block or sub-blocks within the current block (e.g., 4x4 blocks). 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) decoded from the encoded bitstream, and outputs the inter-prediction signal to the prediction control unit 220.

[0140] Furthermore, if the information decoded from the encoded bitstream indicates that OBMC mode should be applied, the interpretation unit 218 generates an interpretation 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 decoded from the encoded bitstream indicates that FRUC mode should be applied, the interpretation unit 218 derives motion information by performing a motion search according to the pattern matching method (bilateral matching or template matching) decoded from the encoded stream. Then, the interpretation unit 218 performs motion compensation using the derived motion information.

[0142] Furthermore, when the BIO mode is applied, the inter-prediction unit 218 derives motion vectors based on a model that assumes uniform linear motion. Also, if the information decoded from the encoded bitstream indicates that the affine motion compensation prediction mode should be applied, the inter-prediction unit 218 derives motion vectors on a sub-block basis based on the motion vectors of multiple adjacent blocks.

[0143] [Prediction Control Unit] The prediction control unit 220 selects either the intra-prediction signal or the inter-prediction signal and outputs the selected signal as the prediction signal to the adder 208.

[0144] (First aspect of Embodiment 1) Next, the first aspect of Embodiment 1 will be described in detail with reference to the drawings.

[0145] [Internal configuration of the conversion section of the encoding device] First, the internal configuration of the conversion unit 106 of the encoding device 100 according to this embodiment will be explained with reference to Figure 11A. Figure 11A is a block diagram showing the internal configuration of the conversion unit 106 of the encoding device 100 according to the first embodiment of Embodiment 1.

[0146] As shown in Figure 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 conversion mode determination unit 1061 determines whether the adaptive conversion basis selection mode is enabled in the block to be encoded. The adaptive conversion basis selection mode is a mode that adaptively selects a conversion basis from one or more candidate first conversion basis. The determination of whether the adaptive conversion basis selection mode is enabled is made, for example, based on identification information of the first conversion basis or the adaptive conversion basis selection mode.

[0148] The size determination unit 1062 determines whether the horizontal size of the block to be encoded exceeds a first horizontal threshold size. The size determination unit 1062 also determines whether the vertical size of the block to be encoded 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, in a standard specification. Alternatively, the first horizontal threshold size and the first vertical threshold size may be sizes determined based on the image and may be encoded within the bitstream.

[0149] The first transformation basis selection unit 1063 selects a first transformation basis. In this disclosure, selecting a basis includes, in addition to selecting at least one basis from a plurality of basis candidates, determining or setting at least one basis without a plurality of basis candidates.

[0150] When the adaptive transformation basis selection mode is not enabled, the first transformation basis selection unit 1063 selects one basic transformation basis as the first transformation basis for the horizontal and vertical directions. When the adaptive transformation basis selection mode is enabled, the first transformation basis selection unit 1063 selects the first transformation basis for the horizontal and vertical directions based on the horizontal and vertical sizes of the block to be encoded, as shown in (1) to (4) below.

[0151] (1) If the horizontal size of the block to be encoded is greater than the first horizontal threshold size, the first transformation basis selection unit 1063 adaptively selects a first horizontal transformation basis from one or more candidate transformation basis.

[0152] (2) If the horizontal size of the block to be encoded is less than or equal to the first horizontal threshold size, the first transformation basis selection unit 1063 selects a fixed horizontal transformation basis as the first horizontal transformation basis.

[0153] (3) If the vertical size of the block to be encoded is greater than the first vertical threshold size, the first transformation basis selection unit 1063 adaptively selects a first vertical transformation basis from one or more candidate transformation basis.

[0154] (4) If the vertical size of the block to be encoded is less than or equal to the first vertical threshold size, the first transformation basis selection unit 1063 selects a fixed vertical transformation basis as the first vertical transformation basis.

[0155] The fixed horizontal transformation basis may be the same as or different from the fixed vertical transformation basis. For example, the type 7 discrete sine transform (DST-VII) transformation basis can be used as the fixed horizontal and vertical transformation basis.

[0156] The first transformation unit 1064 generates first transformation coefficients by performing a first transformation on the residual of the encoding target block using the first transformation basis selected by the first transformation basis selection unit 1063. Specifically, the first transformation unit 1064 performs a first horizontal transformation using the first horizontal transformation basis and a first vertical transformation using the first vertical transformation basis.

[0157] The second transformation execution determination unit 1065 determines whether to perform a second transformation that further transforms the first transformation coefficients, based on whether the adaptive transformation basis selection mode is enabled in the block to be encoded. Specifically, the second transformation execution determination unit 1065 determines that it will perform the second transformation if the adaptive transformation basis selection mode is not enabled, and will not perform the second transformation if the adaptive transformation 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 should be performed. In other words, 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. In other words, the second transformation basis selection unit 1066 skips selecting the second transformation basis when the adaptive transformation basis selection mode is enabled.

[0159] The second transformation unit 1067, when it determines that a second transformation should be performed, transforms the first transformation coefficients using the second transformation basis selected by the second transformation basis selection unit 1066. In other words, the second transformation unit 1067 generates the second transformation coefficients by performing a second transformation on the first transformation coefficients using 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 unit 1067 does not perform a second transformation on the first transformation coefficients. In other words, the second transformation unit 1067 skips the second transformation when the adaptive transformation basis selection mode is enabled.

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

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

[0162] The second inverse transform basis selection unit 1141 selects the inverse transform basis of the second transform basis selected by the second transform basis selection unit 1066 as the second inverse transform basis when the adaptive transform basis selection mode is not enabled for the block to be encoded.

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

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

[0165] The first inverse transform unit 1144 reconstructs the residual of the target block by performing a first inverse transform on the second inverse transform coefficients using the first inverse transform basis when the adaptive transform basis selection mode is not enabled for the target block. On the other hand, when the adaptive transform basis selection mode is enabled for the target block, it reconstructs the residual of the target block by performing a first inverse transform on the inverse quantization coefficients using the first inverse transform basis.

[0166] [Processing in the conversion and quantization sections of the encoding device] Next, the processing of the conversion unit 106 configured as described above will be explained together with the processing of the quantization unit 108 with reference to Figure 12A. Figure 12A is a flowchart showing the processing of the conversion unit 106 and the quantization unit 108 of the encoding device 100 according to the first aspect of Embodiment 1.

[0167] The conversion mode determination unit 1061 determines whether or not the adaptive conversion basis selection mode is enabled for the block to be encoded (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 for 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). In other words, the size determination unit 1062 determines whether the horizontal size of the block to be encoded is greater than the first horizontal threshold size.

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

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

[0172] Next, the size determination unit 1062 determines whether the vertical conversion size exceeds a certain range (S106). In other words, the size determination unit 1062 determines whether the vertical size of the block to be encoded is greater than the first vertical threshold size.

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

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

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

[0176] The first transformation unit 1064 performs a first transformation on the predicted residuals using the first transformation basis selected in step S102, S107, or step S108 to generate first transformation coefficients (S109).

[0177] Next, the second conversion execution determination unit 1065 determines whether or not to perform the second conversion on the first conversion coefficient (S110). Here, the second conversion execution determination unit 1065 determines whether or not to perform the second conversion based on whether or not the adaptive conversion basis selection mode is enabled in the block to be encoded.

[0178] If the adaptive transformation basis selection mode is enabled (YES in S110), neither the selection of the second transformation basis nor the second transformation is performed, and the quantization unit 108 generates quantization coefficients by performing quantization of the first transformation coefficients (S113). In other words, steps S111 and S112 in Figure 12A are skipped.

[0179] If the adaptive transformation basis selection mode is not enabled (NO in S110), the second transformation basis selection unit 1066 selects a second transformation basis from one or more candidate second transformation basis (S111). Then, the second transformation unit 1067 generates second transformation coefficients by performing a second transformation on the first transformation coefficients using the selected second transformation basis (S112). Subsequently, the quantization unit 108 generates quantized coefficients by performing quantization on the second transformation coefficients (S113).

[0180] As the basic transformation basis described above, a predetermined transformation basis can be used. In this case, whether or not the adaptive transformation basis selection mode is enabled may be determined based on whether or not the first transformation basis in the horizontal and vertical directions is the predetermined transformation basis. Furthermore, the predetermined transformation basis may be one transformation basis or two or more transformation basis sets.

[0181] Furthermore, if the second transformation is not performed (skipped), it is not necessary to perform the second transformation, or a transformation equivalent to not performing the transformation may be performed as the second transformation. In the former case, information indicating that the second transformation is not performed may be encoded in the bitstream. In the latter case, information indicating a transformation equivalent to not performing the transformation may be encoded in the bitstream. The same applies to the process of skipping each transformation thereafter.

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

[0183] In Figure 12B, the second conversion execution determination (S110) is removed, and the first conversion (S109) is split into two parts (S109A, S109B). In this case, the conversion unit 106 of the encoding device 100 does not need to include the second conversion execution determination unit 1065.

[0184] The selection of the second inverse base and the second inverse transformation in the inverse transformation unit 114, as well as the selection of the first inverse base and the first inverse transformation, can be carried out in accordance with the transformation of the transformation unit 106 in Figure 12A, so their explanation and illustration are omitted.

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

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

[0187] This process can be applied to both luminance signals and chrominance 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 selectable basis in the first or second conversion may differ between luminance signals and chrominance signals. For example, since luminance signals have a wider frequency bandwidth than chrominance signals, more types of basis can be selected as candidates in the first or second conversion of luminance signals than in chrominance signals in order to perform the optimal conversion. This process can also be applied to both intra-processing and inter-processing.

[0188] [Effects, etc.] In the first transformation (linear transformation) and second transformation (quadratic transformation) described in Non-Patent Document 2, the optimal transformation basis or transformation coefficient (filter) is selected to achieve the optimal encoding efficiency overall. Therefore, it is necessary to perform the first and second transformations many times in order to search for the optimal combination of candidate transformation basis and transformation coefficient (filter) used in the first and second transformations. In other words, in the transformation method described in Non-Patent Document 2, it is necessary to calculate evaluation values ​​for all combinations of candidate transformation basis for the first transformation and candidate transformation basis for the second transformation, and select the combination with the minimum evaluation value. As a result, the present inventors have found that the transformation method described in Non-Patent Document 2 has the problem of requiring an enormous amount of processing.

[0189] Therefore, the encoding device 100 according to this embodiment does not always perform both the first and second transformations, but skips the second transformation based on whether or not the adaptive transformation basis selection mode is enabled. As a result, the encoding device 100 can reduce the number of combinations of candidate transformation basis for the first transformation and candidate transformation basis for the second transformation, thereby reducing the processing load.

[0190] Furthermore, according to the encoding device 100 of this embodiment, the candidates for the first transformation basis can be limited based on the conditions of the horizontal and vertical transformation sizes. This makes it possible to reduce the processing load required to search for the best first transformation basis by trial and error. It also makes it possible to reduce the processing load required to search for the best second transformation basis by trial and error based on conditions such as the basis selected for the first transformation basis. Moreover, it makes it possible to reduce the processing load required for trial and error of combinations of the first and second transformations.

[0191] As an example, the DCT-II transformation basis can be used as the basic transformation basis. DCT-II is more likely to be adopted when the residual shape is flat or random. For example, using DCT-II as the first transformation basis tends to increase the concentration to low frequencies, which may enhance the effect of the second transformation. On the other hand, with transformation basis other than DCT-II, high-frequency components tend to remain, which may reduce the effect of the second transformation.

[0192] As an example, the DST-VII transformation basis can be used as a fixed transformation basis selected 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 sloped and small in size.

[0193] Furthermore, the basis for fundamental transformations is not limited to a single predetermined transformation basis; multiple predetermined transformation bases may be used.

[0194] Furthermore, whether or not to select a second transformation basis and perform the second transformation may be switched depending on the transformation size. Also, the candidates for the second transformation basis may be switched depending on the transformation size.

[0195] Alternatively, the system may simply switch whether to perform the second transformation based on whether the adaptive transformation basis selection mode is enabled, without switching the first transformation basis according to the transformation size. In other words, steps S103, S105, S106 and S108 in Figure 12A may be omitted. Here, whether the adaptive transformation basis selection mode is enabled may be determined based on identification information indicating the use of the mode, or based on the type of the first transformation basis.

[0196] Similarly, the configuration may be such that the switching of whether or not to perform the second transformation is not performed based on whether or not the adaptive transformation basis selection mode is enabled is not performed, and only the switching of the first transformation basis according to the transformation size is performed. In other words, step S110 may be omitted in Figure 12A.

[0197] Furthermore, the selection of the second transformation basis and the second transformation may not be skipped, regardless of whether the adaptive transformation basis selection mode is enabled or not. Alternatively, regardless of the method for selecting the first transformation basis, the selection of the second transformation basis and the second transformation may be performed when the adaptive transformation basis selection mode is not enabled, and the selection of the second transformation basis and the second transformation may be skipped when the adaptive transformation basis selection mode is enabled.

[0198] Furthermore, the specific horizontal or vertical thresholds for the transformation size (i.e., the first horizontal threshold size and the first vertical threshold size) used to select a candidate from a plurality of adaptive transformation bases or to select a fixed transformation base as the first transformation base may be 4, 8, 16, 32, or 64 pixels, etc.

[0199] [Combined with other embodiments] This embodiment may be implemented in combination with at least some of the other embodiments of this disclosure. Furthermore, some of the processes, some of the configurations of the apparatus, some of the syntax, etc., described in the flowchart of this embodiment may be implemented in combination with the other embodiments.

[0200] (Second aspect of Embodiment 1) Next, a second aspect of Embodiment 1 will be described. In this aspect, an example of encoding various signals related to the first and second transformations in the first aspect will be described. Below, this aspect will be described in detail with reference to the drawings, focusing on the differences from the first aspect.

[0201] The internal configurations of the conversion unit 106 and the inverse conversion unit 114 of the encoding device 100 in this embodiment are the same as in the first embodiment, so they are not shown in the illustration.

[0202] [Processing of the conversion, quantization, and entropy coding units of the encoding device] The processing of the conversion unit 106, quantization unit 108, and entropy coding unit 110 of the coding device 100 according to this embodiment will be described with reference to Figures 13A and 13B. Figure 13A is a flowchart showing the processing of the conversion unit 106 and quantization unit 108 of the coding device 100 according to the second embodiment of Embodiment 1. Figure 13B is a flowchart showing the processing of the entropy coding unit 110 of the coding device 100 according to the second embodiment of Embodiment 1. In Figures 13A and 13B, the same reference numerals are used for processing that is common to the first embodiment, and their explanation is omitted.

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

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

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

[0206] Next, the entropy coding unit 110 encodes the quantization 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] Furthermore, the encoding order for each signal may be predetermined, and the various signals may be encoded in a different order than that described above.

[0209] If the second transformation is not performed (skipped), a signal indicating that the second transformation is not performed may be encoded, or a signal selecting a second basis equivalent to not performing the transformation may be encoded.

[0210] [Syntax] Here, the syntax in this embodiment will be described. Figure 14 shows a specific example of the syntax in the second embodiment of Embodiment 1.

[0211] In Figure 14, for example, if the adaptive transformation basis selection mode signal (emt_cu_flag) is set (line 4), and the horizontal transformation size (horizontal_tu_size) is greater than the first horizontal threshold size (horizontal_tu_size_th) (line 5), then the first horizontal basis selection signal (emt_horizontal_tridx) is encoded (line 6). Also, if the vertical transformation size (vertical_tu_size) is greater than the first vertical threshold size (vertical_tu_size_th) (line 11), then the first vertical basis selection signal (emt_vertical_tridx) is encoded (line 12). Under all other conditions (lines 8 and 14), the encoding 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] [Specific examples of conversion basis and encoded signals] Next, specific examples of the transformation basis and encoded signal will be described. Figure 15 shows specific examples of the transformation basis and signal with and without encoding used in the second embodiment of Embodiment 1.

[0214] In Figure 15, when the adaptive transform basis selection mode is not enabled, the DCT-II transform basis is used as the first horizontal and vertical transform basis, regardless of the size of the encoded block. In other words, the DCT-II transform basis is used as the basic transform basis. Additionally, 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 encoded within the bitstream.

[0215] On the other hand, when the adaptive transformation basis selection mode is enabled, combinations of DST-VII transformation basis and other transformation basis (index0 to index3) are used as candidates for the first horizontal and vertical transformation basis, depending on the horizontal size H and vertical size V of the block to be encoded. In addition, the second transformation is not performed (OFF) regardless of the size of the block to be encoded. The second basis selection signal (secondary_tridx) is also not encoded, but the adaptive transformation basis selection mode signal (emt_cu_flag) is encoded in the bitstream. Furthermore, if the horizontal size H of the block to be encoded is greater than 4 pixels, the first horizontal basis selection signal (emt_horizontal_tridx) is encoded in the bitstream. Also, if the vertical size V of the block to be encoded is greater than 4 pixels, the first vertical basis selection signal (emt_vertical_tridx) is encoded 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 basis is used as a candidate for the first transformation basis 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 encoded.

[0217] For example, if the horizontal size H is 4 pixels or less and the vertical size V is greater than 4 pixels, only the DST-VII transformation basis is used as a candidate for the first horizontal transformation basis, and the DST-VII transformation basis and other transformation basis are used as candidates for the first vertical transformation basis. In this case, the first horizontal basis selection signal (emt_horizontal_tridx) is not encoded, but the first vertical basis selection signal (emt_vertical_tridx) is encoded.

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

[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 basis and other transformation basis are used as candidates for the first transformation basis 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 encoded.

[0220] [Effects, etc.] As described above, according to the encoding device 100 of this embodiment, information indicating the first transformation basis (first basis selection signal) can be encoded only when the adaptive transformation basis selection mode is enabled and the transformation size exceeds a certain range, potentially reducing the amount of code required for signaling the first transformation basis. Furthermore, information indicating the second transformation basis (second basis selection signal) can be encoded only when the adaptive transformation basis selection mode is not enabled, potentially reducing the amount of code required for signaling the second transformation basis. In addition, by encoding information for determining whether to skip the second transformation (such as the adaptive transformation basis selection mode signal) before the information indicating the second transformation basis, it is possible to determine at the time of decoding whether the information indicating the second transformation basis has been encoded.

[0221] Furthermore, the encoding of the second basis selection signal may always be performed regardless of the adaptive transformation basis selection mode. Also, the encoding of the first basis selection signal may always be performed if the adaptive transformation basis selection mode is in place, regardless of the transformation size. In addition, the presence or absence of encoding of the first basis selection signal may be determined independently of the horizontal size and the vertical size, or in combination.

[0222] [Combined with other embodiments] This embodiment may be implemented in combination with at least some of the other embodiments of this disclosure. Furthermore, some of the processes, some of the configurations of the apparatus, some of the syntax, etc., described in the flowchart of this embodiment may be implemented in combination with the other embodiments.

[0223] (Third aspect of Embodiment 1) Next, a third aspect of Embodiment 1 will be described. This aspect differs from the first aspect in that, when the adaptive transformation basis selection mode is not enabled, different basic transformation basis sets are used as the first transformation basis depending on the size of the block to be encoded. Below, this aspect will be described in detail with reference to the drawings, focusing on the differences from the first and second aspects.

[0224] The internal configurations of the conversion unit 106 and the inverse conversion unit 114 of the encoding device 100 in this embodiment are the same as in the first embodiment, so they are not shown in the illustration.

[0225] [Processing in the conversion and quantization sections of the encoding device] The processing of the conversion unit 106 and quantization unit 108 of the encoding device 100 according to this embodiment will be described with reference to Figure 16. Figure 16 is a flowchart showing the processing of the conversion unit 106 and quantization unit 108 of the encoding device 100 according to the third embodiment of Embodiment 1. In Figure 16, the same reference numerals are used for processing that is common to the first embodiment, and their explanation is 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 encoded is less than or equal to a second threshold size. For example, the size determination unit 1062 determines whether the size of the block to be encoded is less than or equal to a second threshold size by determining whether the product of the horizontal size and vertical size of the block to be encoded is less than or equal to a threshold.

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

[0228] For example, the DCT-II transformation basis can be used as the first basic transformation basis, and the DST-VII transformation basis can be used as the second basic transformation basis.

[0229] Note that the elementary transformation basis may be selected from among several candidate elementary transformation bases.

[0230] Furthermore, the selection of the second transformation basis and the second transformation may not be skipped, regardless of whether the adaptive transformation basis selection mode is enabled or not. Alternatively, regardless of the method for selecting the first transformation basis, the selection of the second transformation basis and the second transformation may be performed when the adaptive transformation basis selection mode is not enabled, and the selection of the second transformation basis and the second transformation may be skipped when the adaptive transformation basis selection mode is enabled.

[0231] Furthermore, when the adaptive transformation basis selection mode is not enabled, a second threshold size for selecting one of the first or second basic transformation basis can be, for example, a 4x4, 4x8, 8x4, or 8x8 pixel size. Also, the transformation size compared to the threshold may be the product of the horizontal and vertical sizes of the block to be encoded, as in this embodiment, or it may be the horizontal and vertical sizes separately.

[0232] If the adaptive transformation basis selection mode is not enabled, and the product of the horizontal size and vertical size is within a certain range, the second basic transformation basis may be selected as the first transformation basis for the horizontal and vertical directions, and the selection of the second transformation basis and the second transformation may be skipped.

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

[0234] [Combined with other embodiments] This embodiment may be implemented in combination with at least some of the other embodiments of this disclosure. Furthermore, some of the processes, some of the configurations of the apparatus, some of the syntax, etc., described in the flowchart of this embodiment may be implemented in combination with the other embodiments.

[0235] (Fourth aspect of Embodiment 1) 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 conversion and the second conversion according to the third aspect will be described. Hereinafter, this aspect will be specifically described with reference to the drawings, focusing on points that differ from the first to third aspects.

[0236] Note that illustration of the internal configuration of the conversion unit 106 and the inverse conversion unit 114 of the encoding apparatus 100 according to this aspect is omitted because it is the same as that of the first aspect.

[0237] [Processing of conversion unit, quantization unit and entropy encoding unit of encoding apparatus] Processing of the conversion unit 106, the quantization unit 108 and the entropy encoding unit 110 of the encoding apparatus 100 according to this aspect will be described with reference to FIGS. 17A and 17B. FIG. 17A is a flowchart showing processing of the conversion unit 106 and the quantization unit 108 of the encoding apparatus 100 according to the fourth aspect of the first embodiment. FIG. 17B is a flowchart showing processing of the entropy encoding unit 110 of the encoding apparatus 100 according to the fourth aspect of the first embodiment. In FIGS. 17A and 17B, processes common to any of the first to third aspects are assigned the same reference signs, and description thereof is omitted.

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

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

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

[0241] (B1) The conversion size is less than or equal to the second threshold size W1xH1 used in step S301.

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

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

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

[0245] As a specific example, if 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 both the second basic transformation basis and the fixed transformation basis are DST-VII transformation basis, then if the transformation size is 4x4 pixels or less, the entropy coding unit 110 will determine to skip coding the adaptive transformation basis selection mode signal.

[0246] Conversely, if neither of the above conditions (A) and (B) is met, the entropy coding unit 110 determines that it will not skip coding the adaptive transformation basis selection mode signal.

[0247] If it is determined that coding of the adaptive transformation basis selection mode signal should be skipped (YES in S401), the entropy coding unit 110 skips steps S201 to S206 and codes the quantization coefficients (S207). On the other hand, if it is determined that coding of the adaptive transformation basis selection mode signal should not be skipped (NO in S401), the entropy coding unit 110 performs steps S201 to S206 and then codes the quantization coefficients (S207), similar to the second embodiment.

[0248] Furthermore, the encoding order for each signal may be predetermined, and the various signals may be encoded in a different order than that described above.

[0249] [Syntax] Here, the syntax in this embodiment will be described. Figure 18 shows a specific example of the syntax in the fourth embodiment of Embodiment 1.

[0250] In Figure 18, for example, if the coding of the adaptive transformation basis selection mode signal is skipped (line 20), the coding of the adaptive transformation basis selection mode signal (emt_cu_flag) and the first basis selection signals (emt_horizontal_tridx and emt_vertical_tridx) is also skipped (line 21). Here, the coding of the adaptive transformation basis selection mode signal is skipped if the horizontal transformation size (horizontal_tu_size) is less than or equal to the first horizontal threshold size (horizontal_tu_size_th) and the vertical transformation size (vertical_tu_size) is less than or equal to the first vertical threshold size (vertical_tu_size_th). 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 needed, similar to the second embodiment (lines 7-16).

[0251] If the coding of the adaptive transform basis selection mode signal is skipped, the selection of the second transform basis and the second transform may also be skipped.

[0252] [Specific examples of conversion basis and encoded signals] Next, specific examples of the transformation basis and encoded signal will be described. Figure 19 shows specific examples of the transformation basis and the presence or absence of signal encoding used in the fourth embodiment of Embodiment 1. In Figure 19, the transformation basis and the presence or absence of encoding when both the horizontal and vertical sizes of the block to be encoded are 4 pixels or less differ from those in Figure 15. Figure 19 will be explained focusing on the differences from Figure 15.

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

[0254] Furthermore, when the adaptive transformation basis selection mode is enabled, if both the horizontal size H and vertical size V of the block to be encoded are 4 pixels or less, the adaptive transformation basis selection mode signal (emt_cu_flag) will not be encoded.

[0255] [Effects, etc.] As described above, according to the encoding device 100 of this embodiment, if the conditions for skipping the encoding of the adaptive transformation basis selection mode signal are met, the encoding of both the adaptive transformation basis selection mode signal and the first basis selection signal can be omitted, potentially reducing the amount of encoding.

[0256] [Combined with other embodiments] This embodiment may be implemented in combination with at least some of the other embodiments of this disclosure. Furthermore, some of the processes, some of the configurations of the apparatus, some of the syntax, etc., described in the flowchart of this embodiment may be implemented in combination with the other embodiments.

[0257] (Fifth aspect of Embodiment 1) Next, a fifth aspect of Embodiment 1 will be described. In this aspect, a decoding device will be described. The decoding device in this aspect corresponds to the encoding device in the first aspect described above. In other words, the decoding device in this aspect can decode a bitstream encoded by the encoding device in the first aspect described above. This aspect will be described in detail below with reference to the drawings.

[0258] [Internal configuration of the conversion and inverse conversion sections of the decoding device] First, the internal configuration of the inverse transformer 206 of the decoding device 200 according to this embodiment will be described. Figure 20 is a block diagram showing the internal configuration of the inverse transformer 206 of the decoding device 200 according to the fifth embodiment of Embodiment 1.

[0259] As shown in FIG. 20, the inverse transform unit 206 according to this aspect comprises a second inverse transform execution determining unit 2061, a second inverse transform basis selecting unit 2062, a second inverse transform unit 2063, a transform mode determining unit 2064, a size determining unit 2065, a first inverse transform basis selecting unit 2066, and a first inverse transform unit 2067.

[0260] The second inverse transform execution determining unit 2061 determines whether to perform the second inverse transform on the inverse quantization coefficients of the decoding target block output from the inverse quantization unit 204, based on whether the adaptive transform basis selection mode is enabled for the decoding target block. Specifically, the second inverse transform execution determining unit 2061 determines that the second inverse transform is to be performed when the adaptive transform basis selection mode is not enabled, and determines that the second inverse transform is not to be performed when the adaptive transform basis selection mode is enabled.

[0261] The second inverse transform basis selecting unit 2062 selects a second inverse transform basis when it is determined that the second inverse transform is to be performed. Specifically, when the adaptive transform basis selection mode is not enabled, the second inverse transform basis selecting unit 2062 acquires the second basis selection signal 2062S that indicates the second inverse transform basis and is decoded from the bit stream by the entropy decoding unit 202. Then, the second inverse transform basis selecting unit 2062 selects the second inverse transform basis based on the second basis selection signal 2062S. Conversely, the second inverse transform basis selecting unit 2062 does not select the second inverse transform basis when the adaptive transform basis selection mode is enabled. That is, the second inverse transform basis selecting unit 2062 skips the selection of the second inverse transform basis when the adaptive transform basis selection mode is enabled.

[0262] The second inverse transform unit 2063, when it determines that a second inverse transform should be performed, uses the second inverse transform basis selected by the second inverse transform basis selection unit 2062 to perform a second inverse transform on the inverse quantization coefficients of the decoded block. In other words, the second inverse transform unit 2063 generates second inverse transform coefficients by performing a second inverse transform on the inverse quantization coefficients using the second inverse transform basis when the adaptive transform basis selection mode is not enabled. Conversely, the second inverse transform unit 2063 does not perform a second inverse transform on the inverse quantization coefficients when the adaptive transform basis selection mode is enabled. In other words, the second inverse transform unit 2063 skips the second inverse transform when the adaptive transform basis selection mode is enabled.

[0263] The conversion mode determination unit 2064 determines whether the adaptive conversion basis selection mode is enabled in the block to be decoded. The determination of whether the adaptive conversion basis selection mode is enabled is made based on the first basis selection signal 2066S or the adaptive conversion basis selection mode signal 2064S, which are decoded from the bitstream by the entropy decoding unit 202. In other words, the determination is made based on the identification information of the first inverse conversion basis or the adaptive conversion 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 determination of the horizontal and vertical sizes is performed based on the size signal 2065S decoded from the bitstream by the entropy decoding unit 202.

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

[0266] (1) If the horizontal size of the block to be decoded is greater than the first horizontal threshold size, the first inverse transform basis selection unit 2066 obtains a first basis selection signal 2066S indicating the first inverse transform basis, which has been decoded from the bitstream by the entropy decoding unit 202. Then, the first inverse transform basis selection unit 2066 selects the first horizontal inverse transform basis based on the first basis selection signal 2066S.

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

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

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

[0270] The first inverse transform unit 2067 restores the residual of the decoded block by performing a first inverse transform on the inverse quantization coefficients of the decoded block using the first inverse transform basis selected by the first inverse transform basis selection unit 2066. Specifically, the first inverse transform unit 2067 performs a first horizontal inverse transform using the first horizontal inverse transform basis, and a first vertical inverse transform using the first vertical inverse transform basis.

[0271] [Processing in the dequantization and inverse transformation sections of the decoding device] Next, the processing of the inverse transform unit 206 configured as described above will be explained together with the processing of the inverse quantization unit 204 with reference to Figure 21. Figure 21 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 fifth aspect of Embodiment 1.

[0272] The inverse quantization unit 204 generates inverse quantization coefficients by inverse quantizing the quantization coefficients of the decoded block decoded by the entropy decoding unit 202 (S501).

[0273] The second inverse transformation execution determination unit 2061 determines whether or not to perform a second inverse transformation on the inverse quantization coefficients (S502). Here, the second inverse transformation execution determination unit 2061 determines whether or not to perform a second inverse transformation based on whether or not the adaptive transformation basis selection mode is enabled in the decoding target block.

[0274] 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. In other words, steps S503 and S504 are skipped.

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

[0276] Next, the conversion mode determination unit 2064 determines whether the adaptive conversion basis selection mode is enabled in the block to be decoded (S505). For example, the conversion mode determination unit 2064 determines whether the adaptive conversion basis selection mode is enabled based on the adaptive conversion 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 for 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 greater than the first horizontal threshold size.

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

[0279] The size determination unit 2065 determines whether the vertical conversion size exceeds a certain range (S509). In other words, the size determination unit 2065 determines whether the vertical size of the block to be decoded is greater than the first vertical threshold size.

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

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

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

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

[0284] Furthermore, a decoding method corresponding to the encoding method of the first embodiment shown in Figure 12A or Figure 12B may be adopted.

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

[0286] [Combined with other embodiments] This embodiment may be implemented in combination with at least some of the other embodiments of this disclosure. Furthermore, some of the processes, some of the configurations of the apparatus, some of the syntax, etc., described in the flowchart of this embodiment may be implemented in combination with the other embodiments.

[0287] (Sixth aspect of Embodiment 1) Next, a sixth aspect of Embodiment 1 will be described. In this aspect, an example of decoding various signals related to the first and second transformations in the fifth aspect will be described. The decoding device in this aspect corresponds to the encoding device in the second aspect described above. Below, this aspect will be described in detail with reference to the drawings, focusing on the differences from the fifth aspect.

[0288] The internal configuration of the inverse transformer 206 of the decoding device 200 according to this embodiment is the same as that of the fifth embodiment, so it is not shown in the illustration.

[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 transformation unit 206 of the decoding device 200 according to this embodiment will be explained with reference to Figures 22A and 22B. In Figures 22A and 22B, processes common to the fifth embodiment are denoted by the same reference numerals and their explanation is omitted.

[0290] First, the entropy decoding unit 202 decodes the adaptive transformation basis selection mode signal from the bitstream (S601). Then, the transformation mode determination unit 2064 determines, based on the adaptive transformation basis selection mode signal, whether or not the adaptive transformation basis selection mode is enabled in the block to be decoded (S602).

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

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

[0293] Next, the entropy decoding unit 202 decodes the quantization 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] Furthermore, the decoding order may be predetermined along with the encoding method, and various signals may be decoded in a different order than the decoding order described above. Also, if the second inverse transform is not performed (skipped), the entropy decoding unit 202 may decode a signal from the bitstream indicating that the second inverse transform is not performed, or it may decode a signal from the bitstream for selecting a second inverse transform basis equivalent to not performing the transform.

[0296] Furthermore, a decoding method corresponding to the encoding method of the second embodiment shown in Figures 13A, 13B, and 14 may be adopted.

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

[0298] [Combined with other embodiments] This embodiment may be implemented in combination with at least some of the other embodiments of this disclosure. Furthermore, some of the processes, some of the configurations of the apparatus, some of the syntax, etc., described in the flowchart of this embodiment may be implemented in combination with the other embodiments.

[0299] (Seventh aspect of Embodiment 1) Next, a seventh aspect of Embodiment 1 will be described. This aspect differs from the fifth aspect in that, when the adaptive transform basis selection mode is not enabled, different fundamental transform basis sets are used as the first inverse transform basis sets depending on the size of the block to be encoded. The decoding device in this aspect corresponds to the encoding device in the third aspect. Below, this aspect will be described in detail with reference to the drawings, focusing on the differences from the fifth and sixth aspects.

[0300] The internal configuration of the inverse transformer 206 of the decoding device 200 according to this embodiment is the same as that of the fifth embodiment, so it is not shown in the illustration.

[0301] [Processing in the dequantization and inverse transformation sections of the decoding device] The processing of the conversion unit 106 and quantization unit 108 of the encoding device 100 according to this embodiment will be explained with reference to Figure 23. Figure 23 is a flowchart showing the processing of the inverse quantization unit 204 and inverse conversion unit 206 of the decoding device 200 according to the seventh embodiment of Embodiment 1. In Figure 23, processes common to the fifth embodiment are denoted by the same reference numerals and their explanation is omitted.

[0302] If the adaptive conversion basis selection mode is not enabled (NO in S505), the size determination unit 2065 determines whether the conversion 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 less than or equal to 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 less than or equal to a threshold.

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

[0304] Furthermore, a decoding method corresponding to the encoding method of the third embodiment shown in Figure 16 may be adopted.

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

[0306] [Combined with other embodiments] This embodiment may be implemented in combination with at least some of the other embodiments of this disclosure. Furthermore, some of the processes, some of the configurations of the apparatus, some of the syntax, etc., described in the flowchart of this embodiment may be implemented in combination with the other embodiments.

[0307] (Eighth aspect of Embodiment 1) Next, an eighth aspect of Embodiment 1 will be described. In this aspect, an example of decoding various signals related to the first and second transformations in the seventh aspect will be described. The decoding device in this aspect corresponds to the encoding device in the fourth aspect described above. Below, this aspect will be described in detail with reference to the drawings, focusing on the differences from the fifth to seventh aspects.

[0308] The internal configuration of the inverse transformer 206 of the decoding device 200 according to this embodiment is the same as that of the fifth embodiment, so it is not shown in the illustration.

[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 transformation unit 206 of the decoding device 200 according to this embodiment will be explained with reference to Figures 24A and 24B. In Figures 24A and 24B, processes common to any of the 5th to 7th embodiments are denoted by the same reference numerals and their explanation is omitted.

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

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

[0312] (B) Adaptive transformation basis selection mode is enabled and all of the following conditions (B1) to (B4) are met.

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

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

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

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

[0317] As a specific example, if 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 both the second basic transformation basis and the fixed transformation basis are DST-VII transformation basis, then if the transformation size is 4x4 pixels or less, the entropy decoding unit 202 will determine to skip decoding the adaptive transformation basis selection mode signal.

[0318] Conversely, if neither of the above conditions (A) and (B) is met, the entropy decoding unit 202 determines that it will not skip decoding the adaptive transformation basis selection mode signal.

[0319] If it is determined that the decoding of the adaptive transformation basis selection mode signal should 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 should not be skipped (NO in S801), the entropy decoding unit 202 executes steps S601 to S606 and then decodes the quantization coefficients (S207), similar to the sixth embodiment.

[0320] Furthermore, a decoding method corresponding to the encoding method of the fourth embodiment shown in Figures 17A, 17B, and 18 may be adopted.

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

[0322] [Combined with other embodiments] This embodiment may be implemented in combination with at least some of the other embodiments of this disclosure. Furthermore, some of the processes, some of the configurations of the apparatus, some of the syntax, etc., described in the flowchart of this embodiment may be implemented in combination with the other embodiments.

[0323] (Modified versions of each aspect of Embodiment 1) Furthermore, signals indicating whether or not to enable some or all of the processing described in any of the first to eighth aspects may be encoded and decoded. Such signals may be encoded in units of CU (Coding Unit) or CTU (Coding Tree Unit), or in units of SPS (Sequence Parameter Set), PPS (Picture Parameter Set), or slice, corresponding to the H.265 / HEVC standard.

[0324] Based on the picture type (I, P, B), slice type (I, P, B), transformation size (4x4 pixels, 8x8 pixels, or other), number of non-zero coefficients, quantization parameters, Temporal_id (layer of hierarchical coding), or any combination thereof, the selection of a first transformation basis and the first transformation may be skipped, and the selection of a second transformation basis and the second transformation may also be skipped.

[0325] When the encoding device according to the first to fourth embodiments performs the operations described above, the decoding device according to the fifth to eighth embodiments also performs the corresponding operations. For example, if the encoding device encodes information indicating whether to enable the process of skipping the first or second transformation, the decoding device decodes the information and determines whether the first or second transformation is enabled, and whether information indicating the first or second transformation is encoded.

[0326] (Embodiment 2) In each of the above embodiments, each functional block can typically be implemented by an MPU and memory, etc. Furthermore, the processing performed by each functional block is typically implemented by a program execution unit such as a processor reading and executing software (program) recorded on a recording medium such as ROM. This software may be distributed by download, etc., or it may be recorded on a recording medium such as semiconductor memory and distributed. Of course, it is also possible to implement each functional block by hardware (dedicated circuitry).

[0327] Furthermore, the processing described in each embodiment may be implemented by centralized processing using a single device (system), or by distributed processing using multiple devices. Also, the processor executing the above program may be one or multiple. In other words, centralized processing may be performed, or distributed processing may be performed.

[0328] The embodiments of this disclosure are not limited to those described above, and various modifications are possible, which are also included within the scope of the embodiments of this disclosure.

[0329] Furthermore, here we will describe application examples of the video encoding method (image encoding 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 encoding device using the image encoding method, an image decoding device using the image decoding method, and an image encoding and decoding device that includes both. Other configurations in the system can be appropriately modified as needed.

[0330] [Usage example] Figure 25 shows the overall configuration of the content supply system ex100 that realizes the content distribution service. The communication service area is divided into desired sizes, and fixed radio stations, base stations ex106, ex107, ex108, ex109, and ex110, are installed in each cell.

[0331] In this content supply system ex100, various 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~ex110. The content supply system ex100 may also connect any combination of the above elements. Each device may be directly or indirectly connected to each other via a telephone network or short-range radio, etc., without going through the base stations ex106~ex110, which are fixed radio stations. In addition, the streaming server ex103 is connected to various devices such as a computer ex111, a game console ex112, a camera ex113, a home appliance ex114, and a smartphone ex115 via the internet ex101, etc. Furthermore, the streaming server ex103 is connected to terminals in a hotspot on an airplane ex117 via satellite ex116.

[0332] Note that instead of base stations ex106~ex110, wireless access points or hotspots may be used. Also, streaming server ex103 may be connected directly to the communication network ex104 without going through the internet ex101 or internet service provider ex102, or it may be connected directly to the airplane ex117 without going through satellite ex116.

[0333] Camera ex113 is a device capable of taking still images and videos, such as a digital camera. Smartphone ex115 is a smartphone, mobile phone, or PHS (Personal Handyphone System) that supports mobile communication systems generally known as 2G, 3G, 3.9G, 4G, and the upcoming 5G.

[0334] Home appliance ex118 refers to appliances such as refrigerators or equipment included in household fuel cell cogeneration systems.

[0335] In the content supply system ex100, live streaming becomes possible when a terminal with a shooting function is connected to the streaming server ex103 via a base station ex106 or the like. In live streaming, the terminal (computer ex111, game console ex112, camera ex113, home appliance ex114, smartphone ex115, and terminal inside an airplane ex117, etc.) performs the encoding process described in each of the above embodiments on still images or video content captured by the user using the terminal, multiplexes the video data obtained by encoding with sound data encoded from the sound corresponding to the video, and transmits the obtained data to the streaming server ex103. In other words, each terminal functions as an image encoding device according to one aspect of this disclosure.

[0336] Meanwhile, the streaming server ex103 streams the content data sent to the requesting client. The client is a computer ex111, a game console ex112, a camera ex113, a home appliance ex114, a smartphone ex115, or a terminal on an airplane ex117, etc., that is capable of decoding the encoded data. Each device that receives the distributed data decodes and plays back the received data. That is, each device functions as an image decoding device according to one aspect of this disclosure.

[0337] [Distributed Processing] Furthermore, the streaming server ex103 may consist of multiple servers or computers that distribute data processing, recording, and distribution. For example, the streaming server ex103 may be implemented using a CDN (Content Delivery Network), where content delivery is achieved through a network connecting numerous edge servers distributed worldwide. In a CDN, the physically closest edge server is dynamically assigned depending on the client. Latency can be reduced by caching and delivering content to the edge server. In addition, if an error occurs or the communication state changes due to an increase in traffic, processing can be distributed among multiple edge servers, the delivery entity can be switched to another edge server, or delivery can be continued by bypassing the failed part of the network, thus enabling high-speed and stable delivery.

[0338] Furthermore, beyond the distributed processing of the distribution itself, the encoding process of the captured data can be performed on each terminal, on the server side, or shared among them. For example, encoding generally involves two processing loops. In the first loop, the complexity or code amount of the image at the frame or scene level is detected. In the second loop, processing is performed to improve encoding efficiency while maintaining image quality. For example, if the terminal performs the first encoding process and the server that receives the content performs the second encoding process, it is possible to improve the quality and efficiency of the content while reducing the processing load on each terminal. In this case, if there is a request to receive and decode near real time, the first encoded data from the terminal can be received and played back on other terminals, enabling more flexible real-time distribution.

[0339] Another example is the camera ex113, which extracts features from an image, compresses the feature data as metadata, and sends it 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. Feature data is particularly effective in improving the accuracy and efficiency of motion vector prediction during further compression on the server. Alternatively, a simple encoding such as VLC (Variable Length Coding) may be performed on the terminal, and a more computationally intensive encoding such as CABAC (Context-Adaptive Binary Arithmetic Coding) may be performed on the server.

[0340] Another example is a scenario in a stadium, shopping mall, or factory where multiple video data sets of nearly identical scenes may exist, captured by multiple terminals. In such cases, the encoding process is distributed among the multiple terminals that captured the footage, along with other terminals and servers as needed, by assigning encoding tasks to each unit, for example, at the Group of Picture (GOP) level, picture level, or tile level (a division of a picture). This reduces latency and enables more real-time performance.

[0341] Furthermore, since multiple video data sets depict essentially the same scene, the server may manage and / or instruct the video data captured by each terminal to reference each other. Alternatively, the server may receive the encoded data from each terminal, change the reference relationships between the multiple data sets, or correct or replace the pictures themselves and re-encode them. This allows for the creation of a stream with improved quality and efficiency for each individual data set.

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

[0343] Thus, the encoding process can be performed by a terminal or one or more servers. Therefore, in the following, the terms "server" or "terminal" will be used to refer to the entity performing the processing, but 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, it has become increasingly common to integrate and utilize images or videos of different scenes, or the same scene, captured from different angles, using multiple cameras ex113 and / or smartphones ex115, which are nearly synchronized with each other. The videos captured by each device are integrated based on the relative positional relationship between the devices, or on areas where feature points contained in the videos coincide, which are acquired separately.

[0345] The server may not only encode 2D video but also encode still images automatically based on scene analysis of the video, or at a time specified by the user, and send them to the receiving terminal. Furthermore, if the server can obtain the relative positional relationship between the shooting terminals, it can generate a 3D shape of the scene based not only on 2D video but also on video of the same scene taken from different angles. The server may also separately encode 3D data generated by a point cloud, or it may select or reconstruct video to send to the receiving terminal from video taken by multiple terminals based on the results of recognizing or tracking a person or object using the 3D data.

[0346] In this way, users can enjoy scenes by arbitrarily selecting each video corresponding to each shooting terminal, or they can enjoy content in which video from an arbitrary viewpoint is extracted from 3D data reconstructed using multiple images or videos. Furthermore, just like the video, sound can also be collected from multiple different angles, and the server may multiplex and transmit sound from a specific angle or space in conjunction with the video.

[0347] In recent years, content that links 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 may create separate viewpoint images for the right and left eyes and perform encoding that allows referencing between the viewpoint images using Multi-View Coding (MVC), or it may encode them as separate streams without referencing each other. When decoding the separate streams, it is advisable to synchronize playback so that the virtual 3D space is reproduced according to the user's viewpoint.

[0348] In the case of AR images, the server superimposes virtual object information from the virtual space onto camera information from the real space, based on its three-dimensional position or the user's viewpoint movement. The decoding device may acquire or store the virtual object information and three-dimensional data, generate a two-dimensional image according to the user's viewpoint movement, and create superimposed data by smoothly stitching them together. Alternatively, the decoding device may send the user's viewpoint movement to the server in addition to requesting virtual object information, and the server may create superimposed data from the three-dimensional data held by the server according to the received viewpoint movement, encode the superimposed data, and distribute it to the decoding device. The superimposed data may 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 three-dimensional data to 0, etc., so that those parts are transparent, and encode the data. Alternatively, the server may set a predetermined RGB value to the background, like chroma keying, and generate data in which parts other than the object are the background color.

[0349] Similarly, the decryption process of the distributed data can be performed on each client terminal, on the server side, or shared between them. For example, one terminal may send a reception request to the server, and other terminals may receive the content corresponding to that request, perform the decryption process, and then transmit the decrypted signal to a device with a display. By distributing the processing and selecting appropriate content regardless of the performance of the communication-capable terminals themselves, it is possible to play back data with good image quality. Another example is that while receiving large image data on a TV or similar device, a portion of the picture, such as tiles, may be decrypted and displayed on the viewer's personal terminal. This allows for sharing the overall picture while allowing users to check their own area of ​​responsibility or areas they want to examine in more detail on their own device.

[0350] In the future, it is expected that content will be seamlessly received by switching appropriate data for the connected communication, using distribution system standards such as MPEG-DASH, in situations where multiple short-range, medium-range, or long-range wireless communications are available both indoors and outdoors. This will allow users to freely select and switch in real time between decoding devices or display devices, such as displays installed indoors or outdoors, as well as their own terminals. Furthermore, decoding can be performed while switching between the decoding terminal and the display terminal based on the user's location information. This will make it possible to display map information on the wall or part of the ground of an adjacent building with a displayable device embedded, while traveling to a destination. It will also be possible to switch the bitrate of the received data based on the ease of access to the encoded data on the network, such as when the encoded data is cached on a server that can be accessed quickly from the receiving terminal, or copied to an edge server in the content delivery service.

[0351] [Scalable encoding] Regarding content switching, we will explain using a scalable stream compressed and encoded using the video encoding method described in each of the embodiments above, as shown in Figure 26. The server may have multiple streams with the same content but different qualities as individual streams, but it may also be configured to switch content by taking advantage of the characteristics of a temporally / spatially scalable stream realized by encoding it in layers, as shown in the figure. In other words, the decoding side can freely switch between decoding low-resolution and high-resolution content by deciding which layer to decode according to internal factors such as performance and external factors such as the state of the communication bandwidth. For example, if you want to watch the rest of a video that you were watching on your smartphone ex115 while traveling, on a device such as an internet TV when you get home, that device only needs to decode the same stream to different layers, thus reducing the burden on the server.

[0352] Furthermore, in addition to the configuration described above, in which pictures are encoded for each layer and an enhancement layer exists above the base layer to achieve scalability, the enhancement layer may include metadata based on statistical information of the image, and the decoding side may generate high-quality content by super-resolution the picture in the base layer based on the metadata. Super-resolution may refer to either an improvement in the signal-to-noise ratio at the same resolution or an increase in resolution. The metadata may include information for identifying linear or nonlinear filter coefficients used in the super-resolution process, or information for identifying parameter values ​​in the filtering process, machine learning, or least-squares operation used in the super-resolution process.

[0353] Alternatively, the picture may be divided into tiles or similar structures according to the meaning of objects within the image, and the decoding side may select tiles to decode, thereby decoding only a portion of the area. Furthermore, by storing the attributes of objects (people, cars, balls, etc.) and their positions within the image (coordinate positions within the same image, etc.) as metadata, the decoding side can identify the location of a desired object based on the metadata and determine the tile containing that object. For example, as shown in Figure 27, the metadata is stored using a data storage structure different from pixel data, such as the SEI message in HEVC. This metadata indicates, for example, the position, size, or color of the main object.

[0354] Furthermore, metadata may be stored in units consisting of multiple pictures, such as streams, sequences, or random access units. This allows the decryption side to obtain information such as the time when a specific person appears in the video, and by combining this with the picture-level information, it can identify the picture in which the object exists and the object's position within that picture.

[0355] [Web page optimization] Figure 28 shows an example of a web page display screen on a computer ex111, etc. Figure 29 shows an example of a web page display screen on a smartphone ex115, etc. As shown in Figures 28 and 29, a web page may contain multiple linked images, which are links to image content, and their appearance will differ depending on the viewing device. When multiple linked images are visible on the screen, the display device (decoder) will display still images or I-pictures from each content as linked images, display 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 linked image, or until the linked image approaches the center of the screen or the entire linked image is within the screen.

[0356] When a linked image is selected by the user, the display device prioritizes decoding the base layer. If the HTML of the web page contains information indicating that the content is scalable, the display device may decode up to the enhancement layer. Furthermore, to ensure real-time performance, before selection or when bandwidth is very limited, the display device can decode and display only forward-referenced pictures (I-pictures, P-pictures, and B-pictures that only use forward references), thereby reducing the delay between the decoding time and display time of the first picture (the delay from the start of content decoding to the start of display). Alternatively, the display device may deliberately ignore the reference relationships between pictures and roughly decode all B-pictures and P-pictures using forward references, then perform normal decoding as time passes and more pictures are received.

[0357] [Autonomous driving] Furthermore, when transmitting and receiving still images or video data such as 2D or 3D map information for autonomous driving or driving assistance of a vehicle, the receiving terminal may receive metadata such as weather or construction information in addition to image data belonging to one or more layers, and decode these in association with each other. The metadata may belong to a layer, or it may simply be multiplexed with the image data.

[0358] In this case, since the vehicle, drone, or airplane containing the receiving terminal is in motion, the receiving terminal can transmit its location information when a reception request is made, enabling seamless reception and decoding while switching between base stations ex106 to ex110. Furthermore, the receiving terminal can dynamically switch how much metadata is received or how much map information is updated, depending on the user's selection, the user's situation, or the state of the communication bandwidth.

[0359] As described above, the content supply system ex100 allows the client to receive, decode, and play back encoded information transmitted by the user in real time.

[0360] [Distribution of personal content] Furthermore, the ex100 content delivery system allows for unicast or multicast distribution of not only high-definition, long-duration content from video distribution companies, but also low-definition, short-duration content from individuals. It is also expected that the amount of such individual content will continue to increase. To improve the quality of individual content, the server may perform editing before encoding. This can be achieved, for example, with the following configuration.

[0361] During shooting, or after shooting, the server performs recognition processing such as detecting shooting errors, searching for scenes, analyzing semantics, and detecting objects from the original images or encoded data in real time. Based on the recognition results, the server manually or automatically edits the images, correcting out-of-focus or shaky images, deleting less important scenes such as those with lower brightness or out of focus compared to other pictures, emphasizing object edges, and changing color tones. The server then encodes the edited data based on the editing results. It is also known that viewership decreases if the shooting time is too long, so the server may automatically clip scenes with little movement, as well as less important scenes, based on the image processing results, to ensure that the content falls within a specific time range according to the shooting time. Alternatively, the server may generate and encode a digest based on the results of the semantic analysis of the scenes.

[0362] Furthermore, personal content may contain elements that infringe on copyright, moral rights, or portrait rights, and the scope of sharing may exceed the intended scope, which can be inconvenient for the individual. Therefore, for example, the server may intentionally change the image to one that is out of focus, such as the faces of people at the edges of the screen or the interior of a house, before encoding. The server may also recognize whether the face of a person other than those previously registered is visible in the image to be encoded, and if so, it may apply a mosaic effect to the face. Alternatively, as a pre- or post-processing step before encoding, the user can specify a person or background area that they want to process from a copyright perspective, and the server can replace the specified area with a different image or blur the focus. In the case of a person, the server can track the person in a video and replace the image of their face.

[0363] Furthermore, because viewing personal content with small data volumes requires real-time processing, depending on the bandwidth, the decoder prioritizes receiving, decoding, and playing the base layer first. During this time, the decoder can receive the enhancement layer, and if playback is looped or if the content is played more than once, it may play the high-quality video including the enhancement layer. With a stream that uses this scalable encoding, it is possible to provide an experience where the video is rough when unselected or at the beginning of viewing, but gradually the stream becomes smarter and the image quality improves. In addition to scalable encoding, a similar experience can be provided even if the rough stream played the first time and the second stream encoded by referencing the first video are configured as a single stream.

[0364] [Other usage examples] Furthermore, these encoding or decoding processes are generally performed by the LSIex500 present in each terminal. The LSIex500 may be a single chip or a multi-chip configuration. Alternatively, video encoding or decoding software may be embedded in some recording medium (such as a CD-ROM, flexible disk, or hard disk) that can be read by a computer ex111, and the encoding or decoding process may be performed using that software. In addition, if the smartphone ex115 has a camera, video data acquired by that camera may be transmitted. In this case, the video data is data encoded by the LSIex500 present in the smartphone ex115.

[0365] The LSIex500 may also be configured to be activated by downloading application software. In this case, the terminal first determines whether it supports the content encoding method or whether it has the capability to perform the specific service. If the terminal does not support the content encoding method or does not have the capability to perform the specific service, the terminal downloads the codec or application software, and then acquires and plays the content.

[0366] Furthermore, not only the content supply system ex100 via the Internet ex101, but also digital broadcasting systems can incorporate at least one of the video encoding device (image encoding device) or video decoding device (image decoding device) of each of the above embodiments. While the content supply system ex100 has a configuration that is more suited to multicast than unicast, as it transmits and receives multiplexed data with video and sound multiplexed onto broadcast radio waves using satellites, etc., the encoding and decoding processes are similar and can be applied in the same way.

[0367] [Hardware configuration] Figure 30 shows the smartphone ex115. Figure 31 shows an example of the configuration of the smartphone ex115. The smartphone ex115 includes an antenna ex450 for transmitting and receiving radio waves with the base station ex110, a camera unit ex465 capable of taking video and still images, and a display unit ex458 that displays video captured by the camera unit ex465 and data decoded from video 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 captured video or still images, recorded audio, received video or still images, encoded data such as emails, or decoded data, and a slot unit ex464, which is an interface unit with SIM ex468 for identifying the user and authenticating access to various data, including the network. External memory may be used instead of the memory unit ex467.

[0368] Furthermore, the main control unit ex460, which comprehensively controls the display unit ex458 and the operation unit ex466, is connected via the bus ex470 to the power supply circuit unit ex461, the operation input control unit ex462, the video signal processing unit ex455, the camera interface unit ex463, the display control unit ex459, the modulation / demodulation unit ex452, the multiplexing / decompression unit ex453, the audio signal processing unit ex454, the slot unit ex464, and the memory unit ex467.

[0369] The power supply circuit unit ex461, when the power key is turned on by the user, supplies power from the battery pack to each component, thereby starting up the smartphone ex115 and making it operational.

[0370] The smartphone ex115 performs tasks such as phone calls and data communication based on the control of the main control unit ex460, which has a CPU, ROM, RAM, etc. During a call, the audio signal picked up by the audio input unit ex456 is converted into a digital audio signal by the audio signal processing unit ex454, which is then subjected to spread spectrum processing by the modulation / demodulation unit ex452, and after digital-to-analog conversion and frequency conversion processing by the transmission / reception unit ex451, it is transmitted via the antenna ex450. Similarly, received data is amplified, subjected to frequency conversion and analog-to-digital conversion processing, despread spectrum processing by the modulation / demodulation unit ex452, converted into an analog audio signal by the audio signal processing unit ex454, and then output from the audio output unit ex457. In data communication mode, text, still images, or video data are sent to the main control unit ex460 via the operation input control unit ex462 by the operation unit ex466 of the main unit, and transmission and reception processing is performed in the same manner. When transmitting video, still images, or video and audio in data communication mode, the video signal processing unit ex455 compresses and encodes the video signal stored in the memory unit ex467 or the video signal input from the camera unit ex465 using the video encoding method shown in each of the above embodiments, and sends the encoded video data to the multiplexing / decoding unit ex453. The audio signal processing unit ex454 encodes the audio signal picked up by the audio input unit ex456 while the camera unit ex465 is capturing video or still images, and sends the encoded audio data to the multiplexing / decoding unit ex453. The multiplexing / decoding unit ex453 multiplexes the encoded video data and encoded audio data in a predetermined manner, performs modulation and conversion processing in the modulation / demodulation unit (modulation / demodulation circuit unit) ex452 and the transmission / reception unit ex451, and transmits the data via the antenna ex450.

[0371] When receiving video attached to an email or chat, or video linked to a webpage, etc., the multiplexing / decomposition unit ex453 separates the multiplexed data received via antenna ex450 to decode it, dividing the multiplexed data into a video data bitstream and an audio data bitstream. It then 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 shown in each embodiment above, and displays the video or still image contained in the linked video file from the display unit ex458 via the display control unit ex459. The audio signal processing unit ex454 decodes the audio signal, and audio is output from the audio output unit ex457. However, since real-time streaming is widespread, there may be situations where audio playback is socially inappropriate depending on the user's circumstances. Therefore, as an initial setting, it is preferable to have a configuration that plays only video data and does not play audio signals. Audio may be synchronized and played only when the user performs an action, such as clicking on video data.

[0372] Furthermore, although the smartphone ex115 was used as an example here, there are three possible implementation formats for terminals: a transceiver-type terminal that has both an encoder and a decoder, a transmitting terminal that has only an encoder, and a receiving terminal that has only a decoder. In addition, although it was explained that multiplexed data, in which audio data etc. is multiplexed onto video data, is received or transmitted in a digital broadcasting system, 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 multiplexed data.

[0373] Although it was explained that the main control unit ex460, including the CPU, controls the encoding or decoding process, terminals often also have a GPU. Therefore, a configuration that leverages the GPU's performance to process a wide area at once using memory shared by the CPU and GPU, or memory whose addresses are managed so that it can be used in common, is also possible. This can shorten the encoding time, ensure real-time performance, and achieve low latency. In particular, it is efficient to perform motion detection, deblocking filters, SAO (Sample Adaptive Offset), and transformation / quantization processes at once on the GPU, rather than on the CPU, in units such as pictures. [Industrial applicability]

[0374] This disclosure can be used, for example, in television receivers, digital video recorders, car navigation systems, mobile phones, digital cameras, or digital video cameras. [Explanation of Symbols]

[0375] 100 Encoding device 102 Division 104 Subtraction Unit 106 Conversion Unit 108 Quantization section 110 Entropy coding unit 112, 204 Inverse quantization section 114, 206 Inverse Transform Section 116, 208 Addition section 118, 210 block memory 120, 212 Loop filter section 122,214 frame memory 124, 216 Intra Prediction Unit 126, 218 Interpretation Unit 128, 220 Prediction Control Unit 200 Decoders 202 Entropy Decoder 1061, 2064 Conversion mode determination unit 1062, 2065 Size determination section 1063 First transformation basis selection unit 1064 First conversion section 1065 Second conversion execution determination unit 1066 Second transformation basis selection unit 1067 Second conversion section 1141, 2062 Second inverse transform basis selection unit 1142, 2063 Second inverse transform section 1143, 2066 First inverse transform basis selection unit 1144, 2067 First inverse transform section 2061 Second inverse transformation execution determination unit 2062S Second base selection signal 2064S Adaptive conversion basis selection mode signal 2065S size signal 2066S First basis selection signal

Claims

1. An encoding device comprising a circuit and a memory, The circuit uses the memory, Determine whether the mode for selecting a transformation basis according to the size of the block to be encoded is enabled. If the above mode is enabled, When the horizontal size of the block to be encoded is greater than the threshold size, a first transformation basis is selected from among the candidates of multiple transformation basis sets as the horizontal transformation basis. When the horizontal size of the block to be encoded is smaller than the threshold size, a second transformation basis, which is a fixed transformation basis, is selected as the horizontal transformation basis. Using the selected horizontal transformation basis, a first transformation is performed on the residual of the block to be encoded to generate a first transformation coefficient. A second conversion coefficient is generated by performing a second conversion on the first conversion coefficient. A bitstream is generated that includes information indicating whether the aforementioned mode is enabled or not. Encoding device.

2. A decoding device comprising a circuit and memory, The circuit uses the memory, The transformation coefficients are generated by performing a second inverse transformation on the coefficients of the block to be decoded. Determine whether the mode for selecting a transformation basis according to the size of the block to be decoded is enabled, If the above mode is enabled, When the horizontal size of the block to be decoded is greater than the threshold size, a first inverse transform basis is selected from among several candidate inverse transform basis sets as the horizontal inverse transform basis. When the horizontal size of the block to be decoded is smaller than the threshold size, a second inverse transform basis, which is a fixed inverse transform basis, is selected as the horizontal inverse transform basis. Using the selected horizontal inverse transform basis, a first inverse transform is applied to the transformation coefficients of the block to be decoded to generate the predicted residual. Decoding device.

3. Determine whether the mode for selecting a transformation basis according to the size of the block to be encoded is enabled. If the above mode is enabled, When the horizontal size of the block to be encoded is greater than the threshold size, a first transformation basis is selected from among the candidates of multiple transformation basis sets as the horizontal transformation basis. When the horizontal size of the block to be encoded is smaller than the threshold size, a second transformation basis, which is a fixed transformation basis, is selected as the horizontal transformation basis. Using the selected horizontal transformation basis, a first transformation is performed on the residual of the block to be encoded to generate a first transformation coefficient. A second conversion coefficient is generated by performing a second conversion on the first conversion coefficient. A bitstream is generated that includes information indicating whether the aforementioned mode is enabled or not. Encoding method.

4. The transformation coefficients are generated by performing a second inverse transformation on the coefficients of the block to be decoded. Determine whether the mode for selecting a transformation basis according to the size of the block to be decoded is enabled, If the above mode is enabled, When the horizontal size of the block to be decoded is greater than the threshold size, a first inverse transform basis is selected from among several candidate inverse transform basis sets as the horizontal inverse transform basis. When the horizontal size of the block to be decoded is smaller than the threshold size, a second inverse transform basis, which is a fixed inverse transform basis, is selected as the horizontal inverse transform basis. Using the selected horizontal inverse transform basis, a first inverse transform is applied to the transformation coefficients of the block to be decoded to generate the predicted residual. Decryption method.

5. A transmission method for transmitting a bitstream, Determine whether the mode for selecting a transformation basis according to the size of the block to be encoded is enabled. If the above mode is enabled, When the horizontal size of the block to be encoded is greater than the threshold size, a first transformation basis is selected from among the candidates of multiple transformation basis sets as the horizontal transformation basis. When the horizontal size of the block to be encoded is smaller than the threshold size, a second transformation basis, which is a fixed transformation basis, is selected as the horizontal transformation basis. A first transformation coefficient is generated by performing a first transformation on the residual of the encoding target block using the selected horizontal transformation basis. A second conversion coefficient is generated by performing a second conversion on the first conversion coefficient. A bitstream is generated that includes information indicating whether the aforementioned mode is enabled or not. The generated bitstream is transmitted. Sending method.

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