KR20230083247A - Method and apparatus for vedeo decoding and encoding by adjusting the number of multiple transformation selection candidates in multiple transform selection - Google Patents

Abstract

A video encoding/decoding method and apparatus are provided. A video decoding method according to the present disclosure selects one multi-transform from among a plurality of multi-transform selection candidate sets based on at least one of the number of non-zero coefficients in a current block and the position of the last non-zero coefficient in the current block. Determining a selection candidate set, selecting one inverse transform method based on the one multi-transform selection candidate set, and performing the one inverse transform method on coefficients of the current block to obtain the current block A step of generating a residual block may be included, and at least one candidate in the set of the plurality of multiple transform selection candidates may correspond to a non-DCT (Discrete Cosine Transform) 2 transform method.

Description

Video encoding/decoding method and apparatus for adjusting the number of multiple transform selection candidates in multiple transform selection

The present invention relates to a method and apparatus for adjusting the number of multiple transform selection candidates in multiple transform selection, and more specifically, to multiple transforms using the position of the last non-zero coefficient and the number of non-zero coefficients in a current block. A method and apparatus for adjusting the number of selection candidates.

The contents described below merely provide background information related to the present embodiment and do not constitute prior art.

Since video data has a large amount of data compared to audio data or still image data, it requires a lot of hardware resources including memory to store or transmit itself without processing for compression.

Therefore, when video data is stored or transmitted, an encoder is used to compress and store or transmit the video data, and a decoder receives, decompresses, and reproduces the compressed video data. Examples of such video compression technologies include H.264/AVC, High Efficiency Video Coding (HEVC), and Versatile Video Coding (VVC), which has improved coding efficiency by about 30% or more compared to HEVC.

However, since the size, resolution, and frame rate of video are gradually increasing, and the amount of data to be encoded accordingly increases, a new compression technology with higher encoding efficiency and higher picture quality improvement effect than existing compression technologies is required.

The multiple transform selection (MTS) method uses four multiple transform selection candidates other than DCT (Discrete Cosine Transform) 2 regardless of the characteristics of the residual signal of the current block. When the energy of the residual signal in the block to be encoded is small or the number of non-zero coefficients is small, using four multiple change selection candidates may cause a waste of bits in transmitting or parsing the transform information of the corresponding block. When the energy of the residual signal in the encoding target block is large or the number of non-zero coefficients is large, using four multiple transform selection candidates may reduce the number of transform candidates, resulting in a decrease in encoding efficiency. Accordingly, it is necessary to variably adjust the number of multiple transformation selection candidates.

An object of the present disclosure is to provide a method and apparatus for variably adjusting the number of multiple transform candidates according to the position of the last non-zero coefficient in a current block.

In addition, an object of the present disclosure is to provide a method and apparatus for variably adjusting the number of multiple transform candidates according to the number of non-zero coefficients in a current block.

In addition, an object of the present disclosure is to provide a method and apparatus for variably adjusting the number of multiple transform candidates according to the position of the last non-zero coefficient in the current block and the number of non-zero coefficients in the current block.

In addition, an object of the present disclosure is to provide a method and apparatus for improving video encoding/decoding efficiency.

In addition, an object of the present disclosure is to provide a recording medium storing a bitstream generated by a video encoding/decoding method or apparatus of the present disclosure.

In addition, an object of the present disclosure is to provide a method and apparatus for transmitting a bitstream generated by the video encoding/decoding method or apparatus of the present disclosure.

According to the present disclosure, a video decoding method selects one multi-transform from among a plurality of multi-transform selection candidate sets based on at least one of the number of non-zero coefficients in a current block and the position of the last non-zero coefficient in the current block. Determining a set of transform selection candidates, selecting one inverse transform method based on the one multi-transform selection candidate set, and performing the one inverse transform method on coefficients of the current block to obtain the current block Generating a residual block of , and one or more candidates in the set of the plurality of multiple transform selection candidates may correspond to a non-DCT (Discrete Cosine Transform) 2 transform method.

According to the present disclosure, a video encoding method selects one multi-transform from among a plurality of multi-transform selection candidate sets based on at least one of the number of non-zero coefficients in a current block and the position of the last non-zero coefficient in the current block. Determining a set of transform selection candidates, selecting a transform method based on the one multi-transform selection candidate set, performing the one transform method on a residual block of the current block to obtain the current block obtaining coefficients of and encoding the coefficients of the current block, and at least one candidate in the set of multiple transform selection candidates may correspond to a non-DCT2 transform method.

Also, according to the present disclosure, a method of transmitting a bitstream generated by a video encoding method or apparatus according to the present disclosure may be provided.

Also, according to the present disclosure, a recording medium storing a bitstream generated by a video encoding method or apparatus according to the present disclosure may be provided.

In addition, according to the present disclosure, a recording medium storing a bitstream used for image restoration after being received and decoded by the video decoding apparatus according to the present disclosure may be provided.

According to the present disclosure, a method and apparatus for variably adjusting the number of multiple transform candidates according to a position of a last non-zero coefficient in a current block may be provided.

Also, according to the present disclosure, a method and apparatus for variably adjusting the number of multiple transform candidates according to the number of non-zero coefficients in a current block may be provided.

Also, according to the present disclosure, a method and apparatus for variably adjusting the number of multiple transform candidates according to the position of the last non-zero coefficient in the current block and the number of non-zero coefficients in the current block may be provided.

Also, according to the present disclosure, a method and apparatus for improving video encoding/decoding efficiency may be provided.

Effects obtainable in the present disclosure are not limited to the effects mentioned above, and other effects not mentioned may be clearly understood by those skilled in the art from the description below. will be.

1 is an exemplary block diagram of an image encoding apparatus capable of implementing the techniques of this disclosure.
2 is a diagram for explaining a method of dividing a block using a QTBTTT structure.
3A and 3B are diagrams illustrating a plurality of intra prediction modes including wide-angle intra prediction modes.
4 is an exemplary diagram of neighboring blocks of a current block.
5 is an exemplary block diagram of a video decoding apparatus capable of implementing the techniques of this disclosure.
6 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates according to a position of a last non-zero coefficient in a current block according to an embodiment of the present disclosure.
7 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates according to a position of a last non-zero coefficient in a current block according to another embodiment of the present disclosure.
8 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates according to a position of a last non-zero coefficient in a current block according to another embodiment of the present disclosure.
9 is a diagram for explaining a syntax structure for deriving mts_idx according to an embodiment of the present disclosure.
10 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates according to the number of non-zero coefficients in a current block that does not use the size of the current block, according to an embodiment of the present disclosure.
11 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates according to the number of non-zero coefficients in a current block using the size of the current block, according to an embodiment of the present disclosure.
12 is a diagram for variably adjusting the number of multiple transform selection candidates according to the number of non-zero coefficients and the position of the last non-zero coefficient in a current block that does not use the size of the current block according to an embodiment of the present disclosure. It is a drawing for explaining the method.
FIG. 13 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates under the exceptional condition of FIG. 12 according to an embodiment of the present disclosure.
14 variably adjusts the number of multiple transform selection candidates according to the number of non-zero coefficients and the position of the last non-zero coefficient in the current block that does not use the size of the current block according to another embodiment of the present disclosure. It is a drawing to explain how to do it.
15 illustrates a method for variably adjusting the number of multiple transform selection candidates according to the number of non-zero coefficients and the location of the last non-zero coefficient in the current block using the size of the current block, according to an embodiment of the present disclosure. It is a drawing for explanation.
FIG. 16 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates under the exceptional condition of FIG. 15 according to an embodiment of the present disclosure.
17 is a method for variably adjusting the number of multiple transform selection candidates according to the number of non-zero coefficients and the position of the last non-zero coefficient in the current block using the size of the current block according to another embodiment of the present disclosure. It is a drawing for explaining.
18 is a diagram for explaining a video decoding method according to an embodiment of the present disclosure.
19 is a diagram for explaining a video encoding method according to an embodiment of the present disclosure.

DETAILED DESCRIPTION Some embodiments of the present disclosure are described in detail below with reference to exemplary drawings. In adding reference numerals to components of each drawing, it should be noted that the same components have the same numerals as much as possible even if they are displayed on different drawings. In addition, in describing the present embodiments, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present embodiments, the detailed description will be omitted. In the present disclosure, image and video may be used interchangeably.

1 is an exemplary block diagram of an image encoding apparatus capable of implementing the techniques of this disclosure. Hereinafter, with reference to the illustration of FIG. 1, an image encoding device and sub-components of the device will be described.

The image encoding apparatus includes a picture division unit 110, a prediction unit 120, a subtractor 130, a transform unit 140, a quantization unit 145, a rearrangement unit 150, an entropy encoding unit 155, and an inverse quantization unit. 160, an inverse transform unit 165, an adder 170, a loop filter unit 180, and a memory 190.

Each component of the image encoding device may be implemented as hardware or software, or as a combination of hardware and software. Also, the function of each component may be implemented as software, and the microprocessor may be implemented to execute the software function corresponding to each component.

One image (video) is composed of one or more sequences including a plurality of pictures. Each picture is divided into a plurality of areas and encoding is performed for each area. For example, one picture is divided into one or more tiles or/and slices. Here, one or more tiles may be defined as a tile group. Each tile or/slice is divided into one or more Coding Tree Units (CTUs). And each CTU is divided into one or more CUs (Coding Units) by a tree structure. Information applied to each CU is coded as a CU syntax, and information commonly applied to CUs included in one CTU is coded as a CTU syntax. In addition, information commonly applied to all blocks in one slice is coded as syntax of a slice header, and information applied to all blocks constituting one or more pictures is a picture parameter set (PPS) or picture coded in the header. Furthermore, information commonly referred to by a plurality of pictures is coded into a Sequence Parameter Set (SPS). Also, information commonly referred to by one or more SPSs is coded into a video parameter set (VPS). Also, information commonly applied to one tile or tile group may be encoded as syntax of a tile or tile group header. Syntax included in the SPS, PPS, slice header, tile or tile group header may be referred to as high level syntax.

The picture divider 110 determines the size of a coding tree unit (CTU). Information on the size of the CTU (CTU size) is encoded as SPS or PPS syntax and transmitted to the video decoding apparatus.

The picture division unit 110 divides each picture constituting an image into a plurality of Coding Tree Units (CTUs) having a predetermined size, and then iteratively divides the CTUs using a tree structure. Divide (recursively). A leaf node in the tree structure becomes a coding unit (CU), which is a basic unit of encoding.

As a tree structure, a quad tree (QT) in which a parent node (or parent node) is divided into four subnodes (or child nodes) of the same size, or a binary tree (BinaryTree) in which a parent node is divided into two subnodes , BT), or a TernaryTree (TT) in which a parent node is split into three subnodes at a ratio of 1:2:1, or a structure in which two or more of these QT structures, BT structures, and TT structures are mixed. there is. For example, a QuadTree plus BinaryTree (QTBT) structure may be used, or a QuadTree plus BinaryTree TernaryTree (QTBTTT) structure may be used. Here, BTTT may be combined to be referred to as MTT (Multiple-Type Tree).

2 is a diagram for explaining a method of dividing a block using a QTBTTT structure.

As shown in FIG. 2, the CTU may first be divided into QT structures. Quadtree splitting can be repeated until the size of the splitting block reaches the minimum block size (MinQTSize) of leaf nodes allowed by QT. A first flag (QT_split_flag) indicating whether each node of the QT structure is split into four nodes of a lower layer is encoded by the entropy encoder 155 and signaled to the video decoding device. If the leaf node of QT is not larger than the maximum block size (MaxBTSize) of the root node allowed in BT, it may be further divided into either a BT structure or a TT structure. A plurality of division directions may exist in the BT structure and/or the TT structure. For example, there may be two directions in which blocks of the corresponding node are divided horizontally and vertically. As shown in FIG. 2, when MTT splitting starts, a second flag (mtt_split_flag) indicating whether nodes are split, and if split, a flag indicating additional split direction (vertical or horizontal) and/or split type (Binary or Ternary) is encoded by the entropy encoding unit 155 and signaled to the video decoding apparatus.

Alternatively, prior to coding the first flag (QT_split_flag) indicating whether each node is split into four nodes of a lower layer, a CU split flag (split_cu_flag) indicating whether the node is split is coded. It could be. When the value of the CU split flag (split_cu_flag) indicates that it is not split, the block of the corresponding node becomes a leaf node in the split tree structure and becomes a coding unit (CU), which is a basic unit of encoding. When the value of the CU split flag (split_cu_flag) indicates splitting, the video encoding apparatus starts encoding from the first flag in the above-described manner.

As another example of a tree structure, when QTBT is used, the block of the corresponding node is divided into two blocks of the same size horizontally (i.e., symmetric horizontal splitting) and the type that splits vertically (i.e., symmetric vertical splitting). Branches may exist. A split flag (split_flag) indicating whether each node of the BT structure is split into blocks of a lower layer and split type information indicating a split type are encoded by the entropy encoder 155 and transmitted to the video decoding device. Meanwhile, a type in which a block of a corresponding node is divided into two blocks having an asymmetric shape may additionally exist. The asymmetric form may include a form in which the block of the corresponding node is divided into two rectangular blocks having a size ratio of 1:3, or a form in which the block of the corresponding node is divided in a diagonal direction may be included.

A CU can have various sizes depending on the QTBT or QTBTTT split from the CTU. Hereinafter, a block corresponding to a CU to be encoded or decoded (ie, a leaf node of QTBTTT) is referred to as a 'current block'. Depending on the adoption of the QTBTTT division, the shape of the current block may be rectangular as well as square.

The prediction unit 120 predicts a current block and generates a prediction block. The prediction unit 120 includes an intra prediction unit 122 and an inter prediction unit 124 .

In general, each current block in a picture can be coded predictively. In general, prediction of a current block uses an intra-prediction technique (using data from a picture containing the current block) or an inter-prediction technique (using data from a picture coded before the picture containing the current block). can be performed Inter prediction includes both uni-prediction and bi-prediction.

The intra predictor 122 predicts pixels in the current block using pixels (reference pixels) located around the current block in the current picture including the current block. A plurality of intra prediction modes exist according to the prediction direction. For example, as shown in FIG. 3A, the plurality of intra prediction modes may include two non-directional modes including a planar mode and a DC mode and 65 directional modes. Depending on each prediction mode, the neighboring pixels to be used and the arithmetic expression are defined differently.

For efficient directional prediction of the rectangular current block, directional modes (numbers 67 to 80 and -1 to -14 intra prediction modes) indicated by dotted arrows in FIG. 3B may be additionally used. These may be referred to as “wide angle intra-prediction modes”. In FIG. 3B , arrows indicate corresponding reference samples used for prediction and do not indicate prediction directions. The prediction direction is opposite to the direction the arrow is pointing. Wide-angle intra prediction modes are modes that perform prediction in the opposite direction of a specific directional mode without additional bit transmission when the current block is rectangular. At this time, among the wide-angle intra prediction modes, some wide-angle intra prediction modes usable for the current block may be determined by the ratio of the width and height of the rectangular current block. For example, wide-angle intra prediction modes (67 to 80 intra prediction modes) having an angle smaller than 45 degrees are usable when the current block has a rectangular shape with a height smaller than a width, and a wide angle having an angle greater than -135 degrees. Intra prediction modes (-1 to -14 intra prediction modes) are available when the current block has a rectangular shape where the width is greater than the height.

The intra prediction unit 122 may determine an intra prediction mode to be used for encoding the current block. In some examples, the intra prediction unit 122 may encode the current block using several intra prediction modes and select an appropriate intra prediction mode to be used from the tested modes. For example, the intra predictor 122 calculates rate-distortion values using rate-distortion analysis for several tested intra-prediction modes, and has the best rate-distortion characteristics among the tested modes. Intra prediction mode can also be selected.

The intra prediction unit 122 selects one intra prediction mode from among a plurality of intra prediction modes, and predicts a current block using neighboring pixels (reference pixels) determined according to the selected intra prediction mode and an arithmetic expression. Information on the selected intra prediction mode is encoded by the entropy encoder 155 and transmitted to the video decoding apparatus.

The inter prediction unit 124 generates a prediction block for a current block using a motion compensation process. The inter-prediction unit 124 searches for a block most similar to the current block in the encoded and decoded reference picture prior to the current picture, and generates a prediction block for the current block using the searched block. Then, a motion vector (MV) corresponding to displacement between the current block in the current picture and the prediction block in the reference picture is generated. In general, motion estimation is performed on a luma component, and a motion vector calculated based on the luma component is used for both the luma component and the chroma component. Motion information including reference picture information and motion vector information used to predict the current block is encoded by the entropy encoding unit 155 and transmitted to the video decoding apparatus.

The inter-prediction unit 124 may perform interpolation on a reference picture or reference block in order to increase prediction accuracy. That is, subsamples between two consecutive integer samples are interpolated by applying filter coefficients to a plurality of consecutive integer samples including the two integer samples. When a process of searching for a block most similar to the current block is performed for the interpolated reference picture, the motion vector can be expressed with precision of decimal units instead of integer sample units. The precision or resolution of the motion vector may be set differently for each unit of a target region to be encoded, for example, a slice, tile, CTU, or CU. When such adaptive motion vector resolution (AMVR) is applied, information on motion vector resolution to be applied to each target region must be signaled for each target region. For example, when the target region is a CU, information on motion vector resolution applied to each CU is signaled. Information on the motion vector resolution may be information indicating the precision of differential motion vectors, which will be described later.

Meanwhile, the inter prediction unit 124 may perform inter prediction using bi-prediction. In the case of bi-directional prediction, two reference pictures and two motion vectors representing positions of blocks most similar to the current block within each reference picture are used. The inter prediction unit 124 selects a first reference picture and a second reference picture from reference picture list 0 (RefPicList0) and reference picture list 1 (RefPicList1), respectively, and searches for a block similar to the current block within each reference picture. A first reference block and a second reference block are generated. Then, a prediction block for the current block is generated by averaging or weighted averaging the first reference block and the second reference block. Further, motion information including information on two reference pictures used to predict the current block and information on two motion vectors is delivered to the encoder 150. Here, reference picture list 0 may include pictures prior to the current picture in display order among restored pictures, and reference picture list 1 may include pictures after the current picture in display order among restored pictures. there is. However, it is not necessarily limited to this, and in order of display, ups and downs pictures subsequent to the current picture may be additionally included in reference picture list 0, and conversely, ups and downs pictures prior to the current picture may be additionally included in reference picture list 1. may also be included.

Various methods may be used to minimize the amount of bits required to encode motion information.

For example, when the reference picture and motion vector of the current block are the same as those of the neighboring block, the motion information of the current block can be delivered to the video decoding apparatus by encoding information capable of identifying the neighboring block. This method is called 'merge mode'.

In the merge mode, the inter prediction unit 124 selects a predetermined number of merge candidate blocks (hereinafter referred to as 'merge candidates') from neighboring blocks of the current block.

Neighboring blocks for deriving merge candidates include a left block (A0), a lower left block (A1), an upper block (B0), and an upper right block (B1) adjacent to the current block in the current picture, as shown in FIG. ), and all or part of the upper left block A2 may be used. Also, a block located in a reference picture (which may be the same as or different from a reference picture used to predict the current block) other than the current picture in which the current block is located may be used as a merge candidate. For example, a block co-located with the current block in the reference picture or blocks adjacent to the co-located block may be additionally used as a merge candidate. If the number of merge candidates selected by the method described above is less than the preset number, a 0 vector is added to the merge candidates.

The inter prediction unit 124 constructs a merge list including a predetermined number of merge candidates using these neighboring blocks. Among the merge candidates included in the merge list, a merge candidate to be used as motion information of the current block is selected, and merge index information for identifying the selected candidate is generated. The generated merge index information is encoded by the encoder 150 and transmitted to the video decoding apparatus.

Merge skip mode is a special case of merge mode. After performing quantization, when all transform coefficients for entropy encoding are close to zero, only neighboring block selection information is transmitted without transmitting a residual signal. By using the merge skip mode, it is possible to achieve a relatively high encoding efficiency in low-motion images, still images, screen content images, and the like.

Hereinafter, merge mode and merge skip mode are collectively referred to as merge/skip mode.

Another method for encoding motion information is Advanced Motion Vector Prediction (AMVP) mode.

In the AMVP mode, the inter prediction unit 124 derives predictive motion vector candidates for the motion vector of the current block using neighboring blocks of the current block. Neighboring blocks used to derive predictive motion vector candidates include a left block A0, a lower left block A1, an upper block B0, and an upper right block adjacent to the current block in the current picture shown in FIG. B1), and all or part of the upper left block (A2) may be used. In addition, a block located in a reference picture (which may be the same as or different from the reference picture used to predict the current block) other than the current picture where the current block is located will be used as a neighboring block used to derive motion vector candidates. may be For example, a collocated block co-located with the current block within the reference picture or blocks adjacent to the collocated block may be used. If the number of motion vector candidates is smaller than the preset number according to the method described above, a 0 vector is added to the motion vector candidates.

The inter-prediction unit 124 derives predicted motion vector candidates using the motion vectors of the neighboring blocks, and determines a predicted motion vector for the motion vector of the current block using the predicted motion vector candidates. Then, a differential motion vector is calculated by subtracting the predicted motion vector from the motion vector of the current block.

The predicted motion vector may be obtained by applying a predefined function (eg, median value, average value operation, etc.) to predicted motion vector candidates. In this case, the video decoding apparatus also knows the predefined function. In addition, since a neighboring block used to derive a predicted motion vector candidate is a block that has already been encoded and decoded, the video decoding apparatus also knows the motion vector of the neighboring block. Therefore, the video encoding apparatus does not need to encode information for identifying a predictive motion vector candidate. Therefore, in this case, information on differential motion vectors and information on reference pictures used to predict the current block are encoded.

Meanwhile, the predicted motion vector may be determined by selecting one of the predicted motion vector candidates. In this case, along with information on differential motion vectors and information on reference pictures used to predict the current block, information for identifying the selected predictive motion vector candidate is additionally encoded.

The subtractor 130 subtracts the prediction block generated by the intra prediction unit 122 or the inter prediction unit 124 from the current block to generate a residual block.

The transform unit 140 transforms the residual signal in the residual block having pixel values in the spatial domain into transform coefficients in the frequency domain. The transform unit 140 may transform residual signals in the residual block by using the entire size of the residual block as a transform unit, or divide the residual block into a plurality of subblocks and use the subblocks as a transform unit to perform transformation. You may. Alternatively, the residual signals may be divided into two subblocks, a transform region and a non-transform region, and transform the residual signals using only the transform region subblock as a transform unit. Here, the transformation region subblock may be one of two rectangular blocks having a size ratio of 1:1 based on a horizontal axis (or a vertical axis). In this case, a flag (cu_sbt_flag) indicating that only subblocks have been transformed, directional (vertical/horizontal) information (cu_sbt_horizontal_flag), and/or location information (cu_sbt_pos_flag) are encoded by the entropy encoding unit 155 and signaled to the video decoding device. do. In addition, the size of the transform region subblock may have a size ratio of 1:3 based on the horizontal axis (or vertical axis), and in this case, a flag (cu_sbt_quad_flag) for distinguishing the corresponding division is additionally encoded by the entropy encoder 155 to obtain an image It is signaled to the decryption device.

Meanwhile, the transform unit 140 may individually transform the residual block in the horizontal direction and the vertical direction. For the transformation, various types of transformation functions or transformation matrices may be used. For example, a pair of transformation functions for horizontal transformation and vertical transformation may be defined as a multiple transform set (MTS). The transform unit 140 may select one transform function pair having the highest transform efficiency among the MTS and transform the residual blocks in the horizontal and vertical directions, respectively. Information (mts_idx) on a pair of transform functions selected from the MTS is encoded by the entropy encoding unit 155 and signaled to the video decoding device.

The quantization unit 145 quantizes transform coefficients output from the transform unit 140 using a quantization parameter, and outputs the quantized transform coefficients to the entropy encoding unit 155 . The quantization unit 145 may directly quantize a related residual block without transformation for a certain block or frame. The quantization unit 145 may apply different quantization coefficients (scaling values) according to positions of transform coefficients in the transform block. A quantization matrix applied to the two-dimensionally arranged quantized transform coefficients may be coded and signaled to the video decoding apparatus.

The rearrangement unit 150 may rearrange the coefficient values of the quantized residual values.

The reordering unit 150 may change a 2D coefficient array into a 1D coefficient sequence using coefficient scanning. For example, the reordering unit 150 may output a one-dimensional coefficient sequence by scanning DC coefficients to coefficients in a high frequency region using a zig-zag scan or a diagonal scan. . Depending on the size of the transformation unit and intra prediction mode, instead of zig-zag scan, vertical scan that scans a 2D coefficient array in a column direction and horizontal scan that scans 2D block-shaped coefficients in a row direction may be used. That is, a scan method to be used among zig-zag scan, diagonal scan, vertical scan, and horizontal scan may be determined according to the size of the transform unit and the intra prediction mode.

The entropy encoding unit 155 uses various encoding schemes such as CABAC (Context-based Adaptive Binary Arithmetic Code) and Exponential Golomb to convert the one-dimensional quantized transform coefficients output from the reordering unit 150 to each other. A bitstream is created by encoding the sequence.

In addition, the entropy encoding unit 155 encodes information such as CTU size, CU splitting flag, QT splitting flag, MTT splitting type, and MTT splitting direction related to block splitting so that the video decoding apparatus can divide the block in the same way as the video encoding apparatus. make it possible to divide In addition, the entropy encoding unit 155 encodes information about a prediction type indicating whether the current block is encoded by intra prediction or inter prediction, and encodes intra prediction information (ie, intra prediction) according to the prediction type. mode) or inter prediction information (motion information encoding mode (merge mode or AMVP mode), merge index in case of merge mode, reference picture index and differential motion vector information in case of AMVP mode) are encoded. Also, the entropy encoding unit 155 encodes information related to quantization, that is, information about quantization parameters and information about quantization matrices.

The inverse quantization unit 160 inversely quantizes the quantized transform coefficients output from the quantization unit 145 to generate transform coefficients. The inverse transform unit 165 transforms transform coefficients output from the inverse quantization unit 160 from a frequency domain to a spatial domain to restore a residual block.

The adder 170 restores the current block by adding the restored residual block and the predicted block generated by the predictor 120. Pixels in the reconstructed current block are used as reference pixels when intra-predicting the next block.

The loop filter unit 180 reconstructs pixels in order to reduce blocking artifacts, ringing artifacts, blurring artifacts, etc. caused by block-based prediction and transformation/quantization. perform filtering on The filter unit 180 is an in-loop filter and may include all or part of a deblocking filter 182, a sample adaptive offset (SAO) filter 184, and an adaptive loop filter (ALF) 186. .

The deblocking filter 182 filters the boundary between reconstructed blocks to remove blocking artifacts caused by block-by-block encoding/decoding, and the SAO filter 184 and alf 186 perform deblocking filtering. Additional filtering is performed on the image. The SAO filter 184 and the alf 186 are filters used to compensate for a difference between a reconstructed pixel and an original pixel caused by lossy coding. The SAO filter 184 improves not only subjective picture quality but also coding efficiency by applying an offset in units of CTUs. In contrast, the ALF 186 performs block-by-block filtering. Distortion is compensated for by applying different filters by distinguishing the edge of the corresponding block and the degree of change. Information on filter coefficients to be used for ALF may be coded and signaled to the video decoding apparatus.

The reconstruction block filtered through the deblocking filter 182, the SAO filter 184, and the ALF 186 is stored in the memory 190. When all blocks in one picture are reconstructed, the reconstructed picture can be used as a reference picture for inter-prediction of blocks in the picture to be encoded later.

5 is an exemplary block diagram of a video decoding apparatus capable of implementing the techniques of this disclosure. Hereinafter, referring to FIG. 5, a video decoding device and sub-elements of the device will be described.

The image decoding apparatus includes an entropy decoding unit 510, a rearrangement unit 515, an inverse quantization unit 520, an inverse transform unit 530, a prediction unit 540, an adder 550, a loop filter unit 560, and a memory ( 570) may be configured.

Like the image encoding device of FIG. 1 , each component of the image decoding device may be implemented as hardware or software, or a combination of hardware and software. Also, the function of each component may be implemented as software, and the microprocessor may be implemented to execute the software function corresponding to each component.

The entropy decoding unit 510 determines a current block to be decoded by extracting information related to block division by decoding the bitstream generated by the video encoding apparatus, and provides prediction information and residual signals necessary for restoring the current block. extract information, etc.

The entropy decoding unit 510 determines the size of the CTU by extracting information about the CTU size from a sequence parameter set (SPS) or a picture parameter set (PPS), and divides the picture into CTUs of the determined size. Then, the CTU is divided using the tree structure by determining the CTU as the top layer of the tree structure, that is, the root node, and extracting division information for the CTU.

For example, when a CTU is split using the QTBTTT structure, a first flag (QT_split_flag) related to splitting of QT is first extracted and each node is split into four nodes of a lower layer. In addition, for a node corresponding to a leaf node of QT, a second flag (MTT_split_flag) related to splitting of MTT and split direction (vertical / horizontal) and / or split type (binary / ternary) information are extracted and the corresponding leaf node is MTT split into structures Accordingly, each node below the leaf node of QT is recursively divided into a BT or TT structure.

As another example, when a CTU is split using the QTBTTT structure, a CU split flag (split_cu_flag) indicating whether the CU is split is first extracted, and when the corresponding block is split, a first flag (QT_split_flag) is extracted. may be During the splitting process, each node may have zero or more iterative MTT splits after zero or more repetitive QT splits. For example, the CTU may immediately undergo MTT splitting, or conversely, only QT splitting may occur multiple times.

As another example, when a CTU is split using a QTBT structure, a first flag (QT_split_flag) related to QT splitting is extracted and each node is split into four nodes of a lower layer. And, for a node corresponding to a leaf node of QT, a split flag (split_flag) indicating whether to further split into BTs and split direction information are extracted.

Meanwhile, when the entropy decoding unit 510 determines a current block to be decoded by using tree structure partitioning, it extracts information about a prediction type indicating whether the current block is intra-predicted or inter-predicted. When the prediction type information indicates intra prediction, the entropy decoding unit 510 extracts syntax elements for intra prediction information (intra prediction mode) of the current block. When the prediction type information indicates inter prediction, the entropy decoding unit 510 extracts syntax elements for the inter prediction information, that is, information indicating a motion vector and a reference picture to which the motion vector refers.

In addition, the entropy decoding unit 510 extracts quantization-related information and information about quantized transform coefficients of the current block as information about the residual signal.

The reordering unit 515 converts the sequence of 1-dimensional quantized transform coefficients entropy-decoded in the entropy decoding unit 510 into a 2-dimensional coefficient array (ie, in the reverse order of the coefficient scanning performed by the image encoding apparatus). block) can be changed.

The inverse quantization unit 520 inverse quantizes the quantized transform coefficients and inverse quantizes the quantized transform coefficients using a quantization parameter. The inverse quantization unit 520 may apply different quantization coefficients (scaling values) to the two-dimensionally arranged quantized transform coefficients. The inverse quantization unit 520 may perform inverse quantization by applying a matrix of quantization coefficients (scaling values) from the image encoding device to a 2D array of quantized transformation coefficients.

The inverse transform unit 530 inversely transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain to restore residual signals, thereby generating a residual block for the current block.

In addition, when the inverse transform unit 530 inverse transforms only a partial region (subblock) of a transform block, a flag (cu_sbt_flag) indicating that only a subblock of the transform block has been transformed, and direction information (vertical/horizontal) information (cu_sbt_horizontal_flag) of the transform block ) and/or the location information (cu_sbt_pos_flag) of the subblock, and inversely transforms the transform coefficients of the corresponding subblock from the frequency domain to the spatial domain to restore the residual signals. By filling , the final residual block for the current block is created.

In addition, when the MTS is applied, the inverse transform unit 530 determines transform functions or transform matrices to be applied in the horizontal and vertical directions, respectively, using MTS information (mts_idx) signaled from the video encoding device, and uses the determined transform functions. Inverse transform is performed on the transform coefficients in the transform block in the horizontal and vertical directions.

The prediction unit 540 may include an intra prediction unit 542 and an inter prediction unit 544 . The intra prediction unit 542 is activated when the prediction type of the current block is intra prediction, and the inter prediction unit 544 is activated when the prediction type of the current block is inter prediction.

The intra prediction unit 542 determines the intra prediction mode of the current block among a plurality of intra prediction modes from the syntax element for the intra prediction mode extracted from the entropy decoding unit 510, and references the current block according to the intra prediction mode. The current block is predicted using pixels.

The inter prediction unit 544 determines the motion vector of the current block and the reference picture referred to by the motion vector by using the syntax element for the inter prediction mode extracted from the entropy decoding unit 510, and converts the motion vector and the reference picture. to predict the current block.

The adder 550 restores the current block by adding the residual block output from the inverse transform unit and the prediction block output from the inter prediction unit or intra prediction unit. Pixels in the reconstructed current block are used as reference pixels when intra-predicting a block to be decoded later.

The loop filter unit 560 may include a deblocking filter 562, an SAO filter 564, and an ALF 566 as in-loop filters. The deblocking filter 562 performs deblocking filtering on boundaries between reconstructed blocks in order to remove blocking artifacts generated by block-by-block decoding. The SAO filter 564 and the ALF 566 perform additional filtering on the reconstructed block after deblocking filtering to compensate for the difference between the reconstructed pixel and the original pixel caused by lossy coding. ALF filter coefficients are determined using information on filter coefficients decoded from the non-stream.

The reconstruction block filtered through the deblocking filter 562, the SAO filter 564, and the ALF 566 is stored in the memory 570. When all blocks in one picture are reconstructed, the reconstructed picture is used as a reference picture for inter-prediction of blocks in the picture to be encoded later.

6 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates according to a position of a last non-zero coefficient in a current block according to an embodiment of the present disclosure. In multiple transform selection (MTS), a transform pair for a multiple transform selection candidate may be determined according to a size of a transform unit and an intra prediction mode. A transform pair for each multiple transform selection candidate can be constructed using the non-Discrete Cosine Transform (DCT)2 transform kernels Discrete Sine Transform (DST)7, DCT8, DCT5, DST4, DST1, and the identity transform. there is. A set of three multiple transform selection candidates for multiple transform selection may be defined based on the position of the last non-zero coefficient in the current block according to the scanning order within the current block. A set of multiple transform selection candidates may have different numbers of candidates.

Referring to FIG. 6 , when a current block uses non-DCT2 transform, information (mts_idx) representing a transform kernel applied according to the horizontal and vertical directions of a luma transform block related to the current coding unit is greater than 0. can have a large value. When mts_idx is greater than 0, an appropriate set may be selected from among three multiple transform selection candidate sets according to the position of the last non-zero coefficient in the current block. A set of three multiple transform selection candidates may include 1, 4, and 6 candidates, respectively. Set1 may include multiple transformation candidates TO. Set2 may include multiple transformation candidates T0, T1, T2, and T3. Set3 may include multiple transformation candidates T0, T1, T2, T3, T4, and T5.

lastScanPos may indicate the position of the last non-zero coefficient in the current block. When lastScanPos exists between 1 and TH[0], a set of multiple transform selection candidates, which is Set1, can be used. When lastScanPos exists between TH[0] and TH[1], a set of multiple transformation selection candidates, which is Set2, can be used. When lastScanPos exists between TH[1] and inf, a set of multiple transformation selection candidates, which is Set3, can be used. inf may correspond to positive infinity. Here, TH[0] and TH[1] may correspond to the first threshold value and the second threshold value. TH[0] may correspond to a fixed value of 6, and TH[1] may correspond to a fixed value of 32. Accordingly, the number of multiple transform selection candidates used by the current block can be variably adjusted according to the position of the last non-zero coefficient in the current block. Encoding efficiency can be improved by variably adjusting the number of multiple transform selection candidates used by the current block.

If the current block uses one multiple transform selection candidate, mts_idx is 1 and this transform information does not need to be transmitted or parsed. When the current block uses 4 multiple transformation selection candidates, mts_idx is a value between 1 and 4, and this transformation information can be transmitted or parsed using a truncated binary code (TB code). If the current block uses 6 multiple transformation selection candidates, mts_idx is a value between 1 and 6, and this transformation information can be transmitted or parsed using a truncated binary code.

7 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates according to a position of a last non-zero coefficient in a current block according to another embodiment of the present disclosure. The set of multiple transform selection candidates may include any number of multiple transform selection candidates. The number of multiple transform selection candidates used by the current block can be variably adjusted using a set of multiple transform selection candidates including an arbitrary number of multiple transform selection candidates.

Referring to FIG. 7 , lastScanPos may indicate the position of the last non-zero coefficient in the current block. If the current block uses non-DCT2 transform, mts_idx may be greater than 0. According to the position of the last non-zero coefficient in the current block, a suitable set can be selected from among the sets of two multiple transform selection candidates. An appropriate transform may be selected from multiple transform selection candidates included in the selected set. A transformation may be performed using the selected transformation. According to lastScanPos, an appropriate set can be selected from among the sets of two multiple transform selection candidates. A set of two multiple transform selection candidates may include one and four candidates, respectively. Set1 may include multiple transformation candidates TO. Set2 may include multiple transformation candidates T0, T1, T2, and T3.

When lastScanPos exists between 1 and TH[0], a set of multiple transform selection candidates, which is Set1, can be used. When lastScanPos exists between TH[0] and inf, a set of multiple transformation selection candidates, which is Set2, can be used. TH[0] is the threshold value and any value can be used. Any of four transform kernel candidates may be used in consideration of transform kernels mapped to intra prediction mode information. If the current block uses one multiple transform selection candidate, mts_idx is 1 and this transform information does not need to be transmitted or parsed. If the current block uses 4 multiple conversion selection candidates, mts_idx is a value between 1 and 4, and this conversion information can be transmitted or parsed using truncated binary code or Fixed Length code (FL). there is.

8 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates according to a position of a last non-zero coefficient in a current block according to another embodiment of the present disclosure.

Referring to FIG. 8 , lastScanPos may indicate the position of the last non-zero coefficient in the current block. If the current block uses non-DCT2 transform, mts_idx may be greater than 0. According to the position of the last non-zero coefficient in the current block, an appropriate set can be selected from among the sets of four multiple transform selection candidates. An appropriate transform may be selected from multiple transform selection candidates included in the selected set. A transformation may be performed using the selected transformation. According to lastScanPos, an appropriate set can be selected from among the sets of four multiple transform selection candidates. A set of four multiple transform selection candidates may include 1, 2, 4 and 6 candidates, respectively. Set1 may include multiple transformation candidates TO. Set2 may include multiple transformation candidates T0 and T1. Set3 may include multiple transformation candidates T0, T1, T2, and T3. Set4 may include T0, T1, T2, T3, T4, and T5.

When lastScanPos exists between 1 and TH[0], a set of multiple transform selection candidates, which is Set1, can be used. When lastScanPos exists between TH[0] and TH[1], a set of multiple transformation selection candidates, which is Set2, can be used. When lastScanPos exists between TH[1] and TH[2], a set of multiple transformation selection candidates, which is Set3, can be used. When lastScanPos exists between TH[2] and inf, a set of multiple transform selection candidates, which is Set4, can be used. Here, TH[0], TH[1], and TH[2] may correspond to a first threshold value, a second threshold value, and a third threshold value, respectively. TH[0], TH[1], and TH[2] may correspond to arbitrary values.

If the current block uses one multiple transform selection candidate, mts_idx is 1 and this transform information does not need to be transmitted or parsed. If the current block uses two multiple transform selection candidates, mts_idx is 1 or 2 and this transform information can be transmitted or parsed using a fixed length code. When the current block uses 4 multiple transformation selection candidates, mts_idx is a value between 1 and 4, and this transformation information can be transmitted or parsed using a truncated binary code or a fixed length code. If the current block uses 6 multiple transformation selection candidates, mts_idx is a value between 1 and 6, and this transformation information can be transmitted or parsed using a truncated binary code.

For example, in FIGS. 7 and 8, an arbitrary number of multi-transform selection candidate sets and an arbitrary number of threshold values may be used. The number of multiple transform selection candidates included in the set of multiple transform selection candidates may also be defined as an arbitrary number. A transform pair of multiple transform selection candidates may also be determined as an arbitrary transform combination.

9 is a diagram for explaining a syntax structure for deriving mts_idx according to an embodiment of the present disclosure. When mts_idx is transmitted or parsed, encoding efficiency of the residual signal may decrease. mts_idx can be derived using mts_idx_skip_flag.

Referring to FIG. 9 , when mts_idx_skip_flag is 1, mts_idx may not be transmitted or parsed. In this case, the value of mts_idx can be derived. If mts_idx_skip_flag is 0, mts_idx may be transmitted or parsed. When mts_idx_skip_flag is 1, a method of deriving the value of mts_idx may be as follows. The location of the last non-zero coefficient in the current block using multiple transform selection and the value of mts_idx used can be accumulated according to the size of the current block. When mts_idx_skip_flag is 1, the size of the current block and the position of the last non-zero coefficient in the current block can be checked. Among the accumulated mts_idx values, the most used mts_idx value can be derived as the mts_idx value of the current block. By using this method, bits required for transmitting or parsing mts_idx are saved, and encoding efficiency can be improved.

10 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates according to the number of non-zero coefficients in a current block that does not use the size of the current block, according to an embodiment of the present disclosure. The number of multiple transform candidates used in multiple transform selection may be variably adjusted according to the number of non-zero coefficients in the current block. The number of multiple transform candidates used in multiple transform selection can be variably adjusted according to the number of non-zero coefficients in the current block without considering the size of the current block.

Referring to FIG. 10, non-zeroCoeff may correspond to the number of non-zero coefficients in the current block. When only DC coefficients or only one arbitrary AC coefficient exist as non-zero coefficients in the current block, only DCT2 transform can be used. In this case, mts_idx equals 0 and a non-DCT2 conversion kernel need not be used. According to the number of non-zero coefficients in the current block, an appropriate set may be selected from among the sets of three multiple transform selection candidates. An appropriate transform may be selected from multiple transform selection candidates included in the selected set. A transformation may be performed using the selected transformation. According to the non-zeroCoeff, an appropriate set may be selected from among the sets of three multiple transform selection candidates. A set of three multiple transform selection candidates may include 1, 4, and 6 candidates, respectively. Set1 may include multiple transformation candidates TO. Set2 may include multiple transformation candidates T0, T1, T2, and T3. Set3 may include multiple transformation candidates T0, T1, T2, T3, T4, and T5.

When non-zeroCoeff exists between 2 and TH[0], a set of multiple transform selection candidates, which is Set1, can be used. When non-zeroCoeff exists between TH[0] and TH[1], a set of multiple transformation selection candidates, which is Set2, can be used. When non-zeroCoeff exists between TH[1] and inf, a set of multiple transform selection candidates, which is Set3, can be used. Here, TH[0] and TH[1] may correspond to the first threshold value and the second threshold value, respectively. TH[0] and TH[1] can be set to any fixed value regardless of the size of the current block. Six non-DCT2 transform kernels from T0 to T5 may correspond to arbitrary transform kernels. Any number of sets of multiple transform selection candidates and any number of threshold values may be used. The number of multiple transform selection candidates included in the set of multiple transform selection candidates may also be changed to an arbitrary number.

If the current block uses one multiple transform selection candidate, mts_idx is 1 and this transform information does not need to be transmitted or parsed. When the current block uses 4 multiple transformation selection candidates, mts_idx is a value between 1 and 4, and this transformation information can be transmitted or parsed using a truncated binary code or a fixed length code. If the current block uses 6 multiple transformation selection candidates, mts_idx is a value between 1 and 6, and this transformation information can be transmitted or parsed using a truncated binary code.

11 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates according to the number of non-zero coefficients in a current block using the size of the current block, according to an embodiment of the present disclosure. The number of multiple transform candidates used in multiple transform selection can be variably adjusted by considering both the size of the current block and the number of non-zero coefficients in the current block. Different threshold values may be used depending on the size of the current block. A set of multiple transform selection candidates may be selected using different threshold values.

Referring to FIG. 11, non-zeroCoeff may correspond to the number of non-zero coefficients in the current block. When only DC coefficients or only one arbitrary AC coefficient exist as non-zero coefficients in the current block, only DCT2 transform can be used. In this case, mts_idx equals 0 and a non-DCT2 conversion kernel need not be used. An appropriate set may be selected from among three multiple transform selection candidate sets according to different threshold values considering the number of non-zero coefficients in the current block and the size of the current block. An appropriate transform may be selected from multiple transform selection candidates included in the selected set. A transformation may be performed using the selected transformation. An appropriate set may be selected from among three multiple transform selection candidate sets according to different threshold values considering non-zeroCoeff and the size of the current block. A set of three multiple transform selection candidates may include 1, 4, and 6 candidates, respectively. Set1 may include multiple transformation candidates TO. Set2 may include multiple transformation candidates T0, T1, T2, and T3. Set3 may include multiple transformation candidates T0, T1, T2, T3, T4, and T5. Different threshold values TH _blocksize [0] and TH _blocksize [1] may be used in consideration of the size of the current block.

When non-zeroCoeff exists between 2 and TH _blocksize [0], a set of multiple transform selection candidates, which is Set1, can be used. When non-zeroCoeff exists between TH _blocksize [0] and TH _blocksize [1], a set of multiple transform selection candidates of Set2 may be used. When non-zeroCoeff exists between TH _blocksize [1] and inf, a set of multiple transform selection candidates of Set3 may be used. Here, TH _blocksize [0] and TH _blocksize [1] may respectively correspond to the first threshold value and the second threshold value defined in the corresponding block size. TH _blocksize [0] and TH _blocksize [1] can be set to arbitrary values considering the size of the current block. Six non-DCT2 transform kernels from T0 to T5 may correspond to arbitrary transform kernels. Any number of sets of multiple transform selection candidates and any number of threshold values may be used. The number of multiple transform selection candidates included in the set of multiple transform selection candidates may also be changed to an arbitrary number.

If the current block uses one multiple transform selection candidate, mts_idx is 1 and this transform information does not need to be transmitted or parsed. When the current block uses 4 multiple transformation selection candidates, mts_idx is a value between 1 and 4, and this transformation information can be transmitted or parsed using a truncated binary code or a fixed length code. If the current block uses 6 multiple transformation selection candidates, mts_idx is a value between 1 and 6, and this transformation information can be transmitted or parsed using a truncated binary code.

The syntax structure of FIG. 9 may be used in the method described in FIGS. 10 and 11 . If mts_idx_skip_flag is 1, mts_idx may not be transmitted or parsed. In this case, the value of mts_idx can be derived. If mts_idx_skip_flag is 0, mts_idx may be transmitted or parsed. When mts_idx_skip_flag is 1, a method of deriving the value of mts_idx may be as follows. The number of non-zero coefficients in the current block using multiple transform selection and the value of mts_idx used may be accumulated. When mts_idx_skip_flag is 1, the number of non-zero coefficients in the current block can be checked. Among the accumulated mts_idx values, the most used mts_idx value can be derived as the mts_idx value of the current block. By using this method, bits required for transmitting or parsing mts_idx are saved, and encoding efficiency can be improved.

12 is a diagram for variably adjusting the number of multiple transform selection candidates according to the number of non-zero coefficients and the position of the last non-zero coefficient in a current block that does not use the size of the current block according to an embodiment of the present disclosure. It is a drawing for explaining the method. The number of multi-transform selection candidates used in multi-transform selection can be variably adjusted by considering both the number of non-zero coefficients in the current block and the position of the last non-zero coefficient in the current block. The number of multiple transform candidates used in multiple transform selection can be variably adjusted according to the position of the last non-zero coefficient in the current block and the number of non-zero coefficients in the current block without considering the size of the current block.

Referring to FIG. 12, lastScanPos may correspond to the position of the last non-zero coefficient in the current block. non-zeroCoeff may correspond to the number of non-zero coefficients in the current block. When only DC coefficients or only one arbitrary AC coefficient exist as non-zero coefficients in the current block, only DCT2 transform can be used. In this case, mts_idx equals 0 and a non-DCT2 conversion kernel need not be used. According to the position of the last non-zero coefficient in the current block and the number of non-zero coefficients in the current block, an appropriate set may be selected from among three multiple transform selection candidate sets. An appropriate transform may be selected from multiple transform selection candidates included in the selected set. A transformation may be performed using the selected transformation. According to lastScanPos and non-zeroCoeff, an appropriate set can be selected from among the sets of three multiple transform selection candidates. A set of three multiple transform selection candidates may include 1, 4, and 6 candidates, respectively. Set1 may include multiple transformation candidates TO. Set2 may include multiple transformation candidates T0, T1, T2, and T3. Set3 may include multiple transformation candidates T0, T1, T2, T3, T4, and T5.

When non-zeroCoeff exists between 2 and TH _{non - zeroCoeff} [0] or lastScanPos exists between 1 and TH _lastScanPos [0], a set of multiple transformation selection candidates, which is Set1, can be used. If non-zeroCoeff exists between TH _{non - zeroCoeff} [0] and TH _{non - zeroCoeff} [1] and lastScanPos exists between TH _lastScanPos [0] and TH _lastScanPos [1], then Set2 is a set of multiple transformation selection candidates this can be used When non-zeroCoeff exists between TH _{non - zeroCoeff} [1] and inf or lastScanPos exists between TH _lastScanPos [1] and inf, a set of multiple transformation selection candidates, which is Set3, can be used.

Here, TH _{non - zeroCoeff} [0] and TH _{non - zeroCoeff} [1] may respectively correspond to the first threshold value and the second threshold value for the number of non-zero coefficients in the current block. TH _lastScanPos [0] and TH _lastScanPos [1] may respectively correspond to a first threshold value and a second threshold value for the position of the last non-zero coefficient in the current block. TH _{non - zeroCoeff} [0], TH _{non - zeroCoeff} [1], TH _lastScanPos [0], and TH _lastScanPos [1] can be set to any fixed value regardless of the size of the current block. Six non-DCT2 transform kernels from T0 to T5 may correspond to arbitrary transform kernels. Any number of sets of multiple transform selection candidates and any number of threshold values may be used. The number of multiple transform selection candidates included in the set of multiple transform selection candidates may also be changed to an arbitrary number.

If the current block uses one multiple transform selection candidate, mts_idx is 1 and this transform information does not need to be transmitted or parsed. When the current block uses 4 multiple transformation selection candidates, mts_idx is a value between 1 and 4, and this transformation information can be transmitted or parsed using a truncated binary code or a fixed length code. If the current block uses 6 multiple transformation selection candidates, mts_idx is a value between 1 and 6, and this transformation information can be transmitted or parsed using a truncated binary code.

FIG. 13 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates under the exceptional condition of FIG. 12 according to an embodiment of the present disclosure.

Referring to FIG. 13, in FIG. 12, if non-zeroCoeff exists between 2 and TH _{non - zeroCoeff} [0] and lastScanPos exists between TH _lastScanPos [1] and inf, it corresponds to an exceptional condition with a low probability of occurrence can do. In FIG. 12, when non-zeroCoeff exists between TH _{non - zeroCoeff} [1] and inf and lastScanPos exists between 1 and TH _lastScanPos [0], it may correspond to an exceptional condition with a low probability of occurrence. Under these exceptional conditions, a set of multiple transformation selection candidates may be selected.

In method 1, a set of multiple transform selection candidates may be selected by giving priority to the number of non-zero coefficients in the current block. When non-zeroCoeff exists between 2 and TH _{non - zeroCoeff} [0] and lastScanPos exists between TH _lastScanPos [1] and inf, a set of multiple transformation selection candidates, which is Set1, can be used. When non-zeroCoeff exists between TH _{non - zeroCoeff} [1] and inf and lastScanPos exists between 1 and TH _lastScanPos [0], a set of multiple transformation selection candidates, which is Set3, can be used.

In method 2, a set of multiple transform selection candidates can be selected by giving priority to the position of the last non-zero coefficient in the current block. When non-zeroCoeff exists between 2 and TH _{non -zeroCoeff} [0] and lastScanPos exists between TH _lastScanPos [1] and inf, a set of multiple transformation selection candidates, which is Set3, can be used. When non-zeroCoeff exists between TH _{non -zeroCoeff} [1] and inf and lastScanPos exists between 1 and TH _lastScanPos [0], a set of multiple transform selection candidates, which is Set1, can be used.

14 variably adjusts the number of multiple transform selection candidates according to the number of non-zero coefficients and the position of the last non-zero coefficient in the current block that does not use the size of the current block according to another embodiment of the present disclosure. It is a drawing to explain how to do it.

Referring to FIG. 14, lastScanPos may correspond to the position of the last non-zero coefficient in the current block. non-zeroCoeff may correspond to the number of non-zero coefficients in the current block. When only DC coefficients or only one arbitrary AC coefficient exist as non-zero coefficients in the current block, only DCT2 transform can be used. In this case, mts_idx equals 0 and a non-DCT2 conversion kernel need not be used. According to the position of the last non-zero coefficient in the current block and the number of non-zero coefficients in the current block, an appropriate set may be selected from among three multiple transform selection candidate sets. An appropriate transform may be selected from multiple transform selection candidates included in the selected set. A transformation may be performed using the selected transformation. According to lastScanPos and non-zeroCoeff, an appropriate set can be selected from among the sets of three multiple transform selection candidates. A set of three multiple transform selection candidates may include 1, 4, and 6 candidates, respectively. Set1 may include multiple transformation candidates TO. Set2 may include multiple transformation candidates T0, T1, T2, and T3. Set3 may include multiple transformation candidates T0, T1, T2, T3, T4, and T5.

When non-zeroCoeff exists between 2 and TH _{non - zeroCoeff} [0] and lastScanPos exists between 1 and TH _lastScanPos [0], a set of multiple transformation selection candidates, which is Set1, can be used. When non-zeroCoeff exists between TH _{non - zeroCoeff} [1] and inf and lastScanPos exists between TH _lastScanPos [1] and inf, a set of multiple transformation selection candidates, which is Set3, can be used. If the conditions for using Set1 and Set3 described above are not satisfied, a set of multiple transformation selection candidates, which is Set2, may be used.

Here, TH _{non - zeroCoeff} [0] and TH _{non - zeroCoeff} [1] may respectively correspond to the first threshold value and the second threshold value for the number of non-zero coefficients in the current block. TH _lastScanPos [0] and TH _lastScanPos [1] may respectively correspond to a first threshold value and a second threshold value for the position of the last non-zero coefficient in the current block. TH _{non - zeroCoeff} [0], TH _{non - zeroCoeff} [1], TH _lastScanPos [0], and TH _lastScanPos [1] can be set to any fixed value regardless of the size of the current block. Six non-DCT2 transform kernels from T0 to T5 may correspond to arbitrary transform kernels. Any number of sets of multiple transform selection candidates and any number of threshold values may be used. The number of multiple transform selection candidates included in the set of multiple transform selection candidates may also be changed to an arbitrary number.

If the current block uses one multiple transform selection candidate, mts_idx is 1 and this transform information does not need to be transmitted or parsed. When the current block uses 4 multiple transformation selection candidates, mts_idx is a value between 1 and 4, and this transformation information can be transmitted or parsed using a truncated binary code or a fixed length code. If the current block uses 6 multiple transformation selection candidates, mts_idx is a value between 1 and 6, and this transformation information can be transmitted or parsed using a truncated binary code.

15 illustrates a method for variably adjusting the number of multiple transform selection candidates according to the number of non-zero coefficients and the location of the last non-zero coefficient in the current block using the size of the current block, according to an embodiment of the present disclosure. It is a drawing for explanation. The number of multi-transform selection candidates used in multi-transform selection can be variably adjusted by considering both the number of non-zero coefficients in the current block and the position of the last non-zero coefficient in the current block. Considering the size of the current block, the number of multiple transform candidates used in multiple transform selection can be variably adjusted according to the position of the last non-zero coefficient in the current block and the number of non-zero coefficients in the current block. Based on the size of the current block, a threshold value for the number of non-zero coefficients in the current block and a threshold value for the position of the last non-zero coefficient in the current block may be set.

Referring to FIG. 15, lastScanPos may correspond to the position of the last non-zero coefficient in the current block. non-zeroCoeff may correspond to the number of non-zero coefficients in the current block. When only DC coefficients or only one arbitrary AC coefficient exist as non-zero coefficients in the current block, only DCT2 transform can be used. In this case, mts_idx equals 0 and a non-DCT2 conversion kernel need not be used. An appropriate set can be selected from three multiple transform selection candidate sets according to the location of the last non-zero coefficient in the current block, the number of non-zero coefficients in the current block, and the size of the current block. An appropriate transform may be selected from multiple transform selection candidates included in the selected set. A transformation may be performed using the selected transformation. According to lastScanPos, non-zeroCoeff, and the size of the current block, an appropriate set can be selected from among three multiple transform selection candidate sets. A set of three multiple transform selection candidates may include 1, 4, and 6 candidates, respectively. Set1 may include multiple transformation candidates TO. Set2 may include multiple transformation candidates T0, T1, T2, and T3. Set3 may include multiple transformation candidates T0, T1, T2, T3, T4, and T5.

When non-zeroCoeff exists between 2 and TH _{non - zeroCoeff _ blk} [0] or lastScanPos exists between 1 and TH _{lastScanPos_blk} [0], a set of multiple transformation selection candidates, which is Set1, can be used. If non-zeroCoeff exists between TH _{non - zeroCoeff _ blk} [0] and TH _{non - zeroCoeff _ blk} [1] and lastScanPos exists between TH _{lastScanPos _ blk} [0] and TH _{lastScanPos _ blk} [1], A set of multiple transform selection candidates, which is Set2, may be used. When non-zeroCoeff exists between TH _{non - zeroCoeff _ blk} [1] and inf or lastScanPos exists between TH _{lastScanPos _ blk} [1] and inf, a set of multiple transformation selection candidates, which is Set3, can be used.

Here, TH _{non - zeroCoeff _ blk} [0] and TH _{non - zeroCoeff _ blk} [1] may respectively correspond to a first threshold value and a second threshold value for the number of non-zero coefficients in the current block. TH _{non -zeroCoeff_blk} [0] and TH _{non - zeroCoeff _ blk} [1] can be set to different random values depending on the size of the current block. TH _{lastScanPos _ blk} [0] and TH _{lastScanPos _ blk} [1] may respectively correspond to a first threshold value and a second threshold value for the position of the last non-zero coefficient in the current block. TH _{lastScanPos_blk} [0] and TH _{lastScanPos_blk} [1] can _be set to different arbitrary values according to _the size of the current block. Six non-DCT2 transform kernels from T0 to T5 may correspond to arbitrary transform kernels. Any number of sets of multiple transform selection candidates and any number of threshold values may be used. The number of multiple transform selection candidates included in the set of multiple transform selection candidates may also be changed to an arbitrary number.

If the current block uses one multiple transform selection candidate, mts_idx is 1 and this transform information does not need to be transmitted or parsed. When the current block uses 4 multiple transformation selection candidates, mts_idx is a value between 1 and 4, and this transformation information can be transmitted or parsed using a truncated binary code or a fixed length code. If the current block uses 6 multiple transformation selection candidates, mts_idx is a value between 1 and 6, and this transformation information can be transmitted or parsed using a truncated binary code.

FIG. 16 is a diagram for explaining a method of variably adjusting the number of multiple transform selection candidates under the exceptional condition of FIG. 15 according to an embodiment of the present disclosure.

Referring to FIG. 16, in FIG. 15, when non-zeroCoeff exists between 2 and TH _{non - zeroCoeff _ blk} [0] and lastScanPos exists between TH _{lastScanPos _ blk} [1] and inf, an exception with a low probability of occurrence conditions may be met. In FIG _. 15, when non-zeroCoeff exists between TH _{non -zeroCoeff_blk} [1] and inf and lastScanPos exists between 1 and TH _{lastScanPos_blk} [0], this may correspond to an exceptional condition with a low probability of _occurrence . Under these exceptional conditions, a set of multiple transformation selection candidates may be selected.

In method 1, a set of multiple transform selection candidates may be selected by giving priority to the number of non-zero coefficients in the current block. When non-zeroCoeff exists between 2 and TH _{non - zeroCoeff _ blk} [0] and lastScanPos exists between TH _{lastScanPos _ blk} [1] and inf, a set of multiple transformation selection candidates, which is Set1, can be used. When non-zeroCoeff exists between TH _{non - zeroCoeff _ blk} [1] and inf and lastScanPos exists between 1 and TH _{lastScanPos _ blk} [0], a set of multiple transformation selection candidates, which is Set3, can be used.

In method 2, a set of multiple transform selection candidates can be selected by giving priority to the position of the last non-zero coefficient in the current block. When non-zeroCoeff _exists between 2 and TH _{non -zeroCoeff_blk} [0] and lastScanPos exists between TH _{lastScanPos_blk} [1] and inf, _a set of multiple transformation selection candidates, which is Set3, can be used. When non-zeroCoeff exists between TH _{non-zeroCoeff_blk} [1] and inf and lastScanPos _exists between 1 and TH _{lastScanPos_blk} [0], a set of multiple transformation selection candidates, which is Set1 _, can be used.

17 is a method for variably adjusting the number of multiple transform selection candidates according to the number of non-zero coefficients and the position of the last non-zero coefficient in the current block using the size of the current block according to another embodiment of the present disclosure. It is a drawing for explaining.

Referring to FIG. 17, lastScanPos may correspond to the position of the last non-zero coefficient in the current block. non-zeroCoeff may correspond to the number of non-zero coefficients in the current block. When only DC coefficients or only one arbitrary AC coefficient exist as non-zero coefficients in the current block, only DCT2 transform can be used. In this case, mts_idx equals 0 and a non-DCT2 conversion kernel need not be used. An appropriate set can be selected from three multiple transform selection candidate sets according to the position of the last non-zero coefficient in the current block, the number of non-zero coefficients in the current block, and the size of the current block. An appropriate transform may be selected from multiple transform selection candidates included in the selected set. A transformation may be performed using the selected transformation. According to lastScanPos, non-zeroCoeff, and the size of the current block, an appropriate set can be selected from among three multiple transform selection candidate sets. A set of three multiple transform selection candidates may include 1, 4, and 6 candidates, respectively. Set1 may include multiple transformation candidates TO. Set2 may include multiple transformation candidates T0, T1, T2, and T3. Set3 may include multiple transformation candidates T0, T1, T2, T3, T4, and T5.

_When non-zeroCoeff exists between 2 and TH _{non - zeroCoeff_blk} [0] and lastScanPos _exists between 1 and TH _{lastScanPos_blk} [0], a set of multiple transformation selection candidates, which is Set1, can be used. When non-zeroCoeff exists between TH _{non - zeroCoeff _ blk} [1] and inf and lastScanPos exists between TH _{lastScanPos _ blk} [1] and inf, a set of multiple transformation selection candidates, which is Set3, can be used. If the conditions for using Set1 and Set3 described above are not satisfied, a set of multiple transformation selection candidates, which is Set2, may be used.

Here, TH _{non - zeroCoeff _ blk} [0] and TH _{non - zeroCoeff _ blk} [1] may respectively correspond to a first threshold value and a second threshold value for the number of non-zero coefficients in the current block. TH _{non -zeroCoeff_blk} [0] and TH _{non - zeroCoeff _ blk} [1] can be set to arbitrary values depending on the size of the current block. TH _{lastScanPos _ blk} [0] and TH _{lastScanPos _ blk} [1] may respectively correspond to a first threshold value and a second threshold value for the position of the last non-zero coefficient in the current block. TH _{lastScanPos _blk} [0] and TH _{lastScanPos _ blk} [1] can be set to arbitrary values according to the size of the current block. Six non-DCT2 transform kernels from T0 to T5 may correspond to arbitrary transform kernels. Any number of sets of multiple transform selection candidates and any number of threshold values may be used. The number of multiple transform selection candidates included in the set of multiple transform selection candidates may also be changed to an arbitrary number.

If the current block uses one multiple transform selection candidate, mts_idx is 1 and this transform information does not need to be transmitted or parsed. When the current block uses 4 multiple transformation selection candidates, mts_idx is a value between 1 and 4, and this transformation information can be transmitted or parsed using a truncated binary code or a fixed length code. If the current block uses 6 multiple transformation selection candidates, mts_idx is a value between 1 and 6, and this transformation information can be transmitted or parsed using a truncated binary code.

The syntax structure of FIG. 9 may be used in the methods described in FIGS. 12 to 17 . If mts_idx_skip_flag is 1, mts_idx may not be transmitted or parsed. In this case, the value of mts_idx can be derived. If mts_idx_skip_flag is 0, mts_idx may be transmitted or parsed. When mts_idx_skip_flag is 1, a method of deriving the value of mts_idx may be as follows. The number of non-zero coefficients in the current block using multiple transform selection, the location of the last non-zero coefficient in the current block, and the value of mts_idx used may be accumulated. When mts_idx_skip_flag is 1, the number of non-zero coefficients in the current block and the position of the last non-zero coefficient in the current block can be checked. Among the accumulated mts_idx values, the most used mts_idx value can be derived as the mts_idx value of the current block. By using this method, bits required for transmitting or parsing mts_idx are saved, and encoding efficiency can be improved.

For example, in the method of variably adjusting the number of multiple transform selection candidates used in multiple transform selection described with reference to FIGS. 10 to 17 , the set of multiple transform selection candidates is not limited to three. An arbitrary number of sets of multiple transform selection candidates may be defined and the number of threshold values corresponding thereto may be defined. The number of multiple transform selection candidates included in each set of multiple transform selection candidates may also correspond to an arbitrary number. Here, a transform pair of multiple transform selection candidates may be determined as an arbitrary transform combination.

18 is a diagram for explaining a video decoding method according to an embodiment of the present disclosure.

Referring to FIG. 18, the decoding apparatus selects one multi-transform selection candidate from among a plurality of multi-transform selection candidate sets based on at least one of the number of non-zero coefficients in the current block and the position of the last non-zero coefficient in the current block. A set of may be determined (S1810). The step of determining one multi-transform selection candidate set determines one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets by using the position of the last non-zero coefficient in the current block and one or more threshold values. steps may be included. One or more threshold values may correspond to arbitrary values.

The step of determining one multi-transform selection candidate set includes determining one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets using the number of non-zero coefficients in the current block and one or more threshold values. steps may be included. One or more threshold values may correspond to arbitrary values. The step of determining one multi-transform selection candidate set is one multi-transform selection candidate from among the plurality of multi-transform selection candidate sets using the number of non-zero coefficients in the current block, one or more threshold values, and the size of the current block. It may include determining a set of. One or more threshold values may be set to arbitrary values based on the size of the current block.

The step of determining one set of multiple transform selection candidates includes a threshold value for the position of the last non-zero coefficient in the current block, the number of non-zero coefficients in the current block, and the position of the last non-zero coefficient in one or more current blocks. and determining one multi-transform selection candidate set from among a plurality of multi-transform selection candidate sets by using a threshold value for the number of non-zero coefficients in one or more current blocks. The threshold value for the position of the last non-zero coefficient in one or more current blocks may correspond to an arbitrary value. A threshold value for the number of non-zero coefficients in one or more current blocks may correspond to an arbitrary value.

The step of determining one set of multiple transform selection candidates includes the position of the last non-zero coefficient in the current block, the number of non-zero coefficients in the current block, the size of the current block, and the last non-zero coefficient in one or more current blocks. The method may include determining one multi-transform selection candidate set from among a plurality of multi-transform selection candidate sets by using a threshold value for a position and a threshold value for the number of non-zero coefficients in one or more current blocks. . The threshold value for the location of the last non-zero coefficient in one or more current blocks may be set to an arbitrary value based on the size of the current block. A threshold value for the number of non-zero coefficients in one or more current blocks may be set to an arbitrary value based on the size of the current block.

The decoding apparatus may select one inverse transform method based on one set of multiple transform selection candidates (S1820). The decoding apparatus may generate a residual block of the current block by performing one inverse transform method on coefficients of the current block (S1830). One or more candidates in the set of multiple multiple transform selection candidates may correspond to a non-DCT2 transform method. The number of sets of multiple transform selection candidates may correspond to an arbitrary number. The number of candidates in the set of multiple transform selection candidates may correspond to an arbitrary number.

19 is a diagram for explaining a video encoding method according to an embodiment of the present disclosure.

Referring to FIG. 19, the encoding apparatus selects one multi-transform selection candidate from among a plurality of multi-transform selection candidate sets based on at least one of the number of non-zero coefficients in the current block and the position of the last non-zero coefficient in the current block. A set of may be determined (S1910). The step of determining one multi-transform selection candidate set determines one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets by using the position of the last non-zero coefficient in the current block and one or more threshold values. steps may be included. One or more threshold values may correspond to arbitrary values.

The step of determining one multi-transform selection candidate set includes determining one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets using the number of non-zero coefficients in the current block and one or more threshold values. steps may be included. One or more threshold values may correspond to arbitrary values. The step of determining one multi-transform selection candidate set is one multi-transform selection candidate from among the plurality of multi-transform selection candidate sets using the number of non-zero coefficients in the current block, one or more threshold values, and the size of the current block. It may include determining a set of. One or more threshold values may be set to arbitrary values based on the size of the current block.

The step of determining one set of multiple transform selection candidates includes a threshold value for the position of the last non-zero coefficient in the current block, the number of non-zero coefficients in the current block, and the position of the last non-zero coefficient in one or more current blocks. and determining one multi-transform selection candidate set from among a plurality of multi-transform selection candidate sets by using a threshold value for the number of non-zero coefficients in one or more current blocks. The threshold value for the position of the last non-zero coefficient in one or more current blocks may correspond to an arbitrary value. A threshold value for the number of non-zero coefficients in one or more current blocks may correspond to an arbitrary value.

The step of determining one set of multiple transform selection candidates includes the position of the last non-zero coefficient in the current block, the number of non-zero coefficients in the current block, the size of the current block, and the last non-zero coefficient in one or more current blocks. The method may include determining one multi-transform selection candidate set from among a plurality of multi-transform selection candidate sets by using a threshold value for a position and a threshold value for the number of non-zero coefficients in one or more current blocks. . The threshold value for the location of the last non-zero coefficient in one or more current blocks may be set to an arbitrary value based on the size of the current block. A threshold value for the number of non-zero coefficients in one or more current blocks may be set to an arbitrary value based on the size of the current block.

The encoding device may select one transform method based on one set of multiple transform selection candidates (S1920). The encoding device may obtain coefficients of the current block by performing one transformation method on the residual block of the current block (S1930). The encoding device may encode coefficients of the current block (S1940). One or more candidates in the set of multiple multiple transform selection candidates may correspond to a non-DCT2 transform method. The number of sets of multiple transform selection candidates may correspond to an arbitrary number. The number of candidates in the set of multiple transform selection candidates may correspond to an arbitrary number.

In the flow chart/timing diagram of the present specification, it is described that each process is sequentially executed, but this is merely an example of the technical idea of one embodiment of the present disclosure. In other words, those skilled in the art to which an embodiment of the present disclosure belongs may change and execute the order described in the flowchart/timing diagram within the range that does not deviate from the essential characteristics of the embodiment of the present disclosure, or one of each process Since the above process can be applied by performing various modifications and variations in parallel, the flow chart/timing chart is not limited to a time-series sequence.

In the above description, it should be understood that the exemplary embodiments may be implemented in many different ways. Functions or methods described in one or more examples may be implemented in hardware, software, firmware, or any combination thereof. It should be understood that the functional components described in this specification have been labeled "...unit" to particularly emphasize their implementation independence.

Meanwhile, various functions or methods described in this embodiment may be implemented as instructions stored in a non-transitory recording medium that can be read and executed by one or more processors. Non-transitory recording media include, for example, all types of recording devices in which data is stored in a form readable by a computer system. For example, the non-transitory recording medium includes storage media such as an erasable programmable read only memory (EPROM), a flash drive, an optical drive, a magnetic hard drive, and a solid state drive (SSD).

The above description is merely an example of the technical idea of the present embodiment, and various modifications and variations can be made to those skilled in the art without departing from the essential characteristics of the present embodiment. Therefore, the present embodiments are not intended to limit the technical idea of the present embodiment, but to explain, and the scope of the technical idea of the present embodiment is not limited by these embodiments. The scope of protection of this embodiment should be construed according to the claims below, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of rights of this embodiment.

122: intra prediction unit
510: entropy decoding unit
542: intra prediction unit

Claims (20)

determining a multi-transform selection candidate set from among a plurality of multi-transform selection candidate sets based on at least one of the number of non-zero coefficients in the current block and the position of the last non-zero coefficient in the current block;
selecting one inverse transform method based on the set of multiple transform selection candidates; and
Generating a residual block of the current block by performing the one inverse transform method on coefficients of the current block;
At least one candidate in the set of the plurality of multiple transform selection candidates corresponds to a non-DCT (Discrete Cosine Transform) 2 inverse transform method. According to claim 1,
Determining a set of one multiple transformation selection candidates,
Determining the one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets using a position of a last non-zero coefficient in the current block and one or more threshold values;
The one or more threshold values correspond to arbitrary values. According to claim 1,
Determining a set of one multiple transformation selection candidates,
Determining the one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets using the number of non-zero coefficients in the current block and one or more threshold values;
The one or more threshold values correspond to arbitrary values. According to claim 1,
Determining a set of one multiple transformation selection candidates,
Determining the one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets using the number of non-zero coefficients in the current block, one or more threshold values, and the size of the current block How to decrypt video. According to claim 4,
The one or more threshold values are set to arbitrary values based on the size of the current block. According to claim 1,
Determining a set of one multiple transformation selection candidates,
The position of the last non-zero coefficient in the current block, the number of non-zero coefficients in the current block, a threshold value for the position of one or more of the last non-zero coefficients in the current block, and one or more non-zero coefficients in the current block. and determining the one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets by using a threshold value for the number of coefficients. According to claim 6,
a threshold value for a location of a last non-zero coefficient in the one or more current blocks corresponds to an arbitrary value;
The threshold value for the number of non-zero coefficients in the one or more current blocks corresponds to an arbitrary value. According to claim 1,
Determining a set of one multiple transformation selection candidates,
the position of the last non-zero coefficient in the current block, the number of non-zero coefficients in the current block, the size of the current block, a threshold value for the position of one or more of the last non-zero coefficients in the current block, and one or more of the and determining the one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets by using a threshold value for the number of non-zero coefficients in a current block. According to claim 8,
A threshold value for a position of a last non-zero coefficient in the one or more current blocks is set to an arbitrary value based on the size of the current block;
A threshold value for the number of non-zero coefficients in the one or more current blocks is set to an arbitrary value based on the size of the current block. According to claim 1,
The number of sets of the plurality of multiple transformation selection candidates corresponds to an arbitrary number,
The number of candidates in the set of the plurality of multiple transform selection candidates corresponds to an arbitrary number. determining a multi-transform selection candidate set from among a plurality of multi-transform selection candidate sets based on at least one of the number of non-zero coefficients in the current block and the position of the last non-zero coefficient in the current block;
selecting one transformation method based on the set of multiple transformation selection candidates;
obtaining coefficients of the current block by performing the one transform method on the residual block of the current block; and
Encoding the coefficients of the current block;
At least one candidate in the set of the plurality of multiple transform selection candidates corresponds to a non-DCT2 transform method. According to claim 11,
Determining a set of one multiple transformation selection candidates,
Determining the one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets using a position of a last non-zero coefficient in the current block and one or more threshold values;
The one or more threshold values correspond to arbitrary values. According to claim 11,
Determining a set of one multiple transformation selection candidates,
Determining the one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets using the number of non-zero coefficients in the current block and one or more threshold values;
The one or more threshold values correspond to arbitrary values. According to claim 11,
Determining a set of one multiple transformation selection candidates,
Determining the one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets using the number of non-zero coefficients in the current block, one or more threshold values, and the size of the current block Video encoding method. According to claim 14,
The one or more threshold values are set to arbitrary values based on the size of the current block. According to claim 11,
Determining a set of one multiple transformation selection candidates,
The position of the last non-zero coefficient in the current block, the number of non-zero coefficients in the current block, a threshold value for the position of one or more of the last non-zero coefficients in the current block, and one or more non-zero coefficients in the current block. Determining a set of the one multi-transform selection candidate from among the plurality of multi-transform selection candidate sets by using a threshold value for the number of coefficients;
a threshold value for a location of a last non-zero coefficient in the one or more current blocks corresponds to an arbitrary value;
A threshold value for the number of non-zero coefficients in the one or more current blocks corresponds to an arbitrary value. According to claim 11,
Determining a set of one multiple transformation selection candidates,
the position of the last non-zero coefficient in the current block, the number of non-zero coefficients in the current block, the size of the current block, a threshold value for the position of one or more of the last non-zero coefficients in the current block, and one or more of the and determining the one multi-transform selection candidate set from among the plurality of multi-transform selection candidate sets by using a threshold value for the number of non-zero coefficients in a current block. According to claim 17,
A threshold value for a position of a last non-zero coefficient in the one or more current blocks is set to an arbitrary value based on the size of the current block;
A threshold value for the number of non-zero coefficients in the one or more current blocks is set to an arbitrary value based on the size of the current block. According to claim 11,
The number of sets of the plurality of multiple transformation selection candidates corresponds to an arbitrary number,
The video encoding method of claim 1 , wherein the number of candidates in the set of multiple transform selection candidates corresponds to an arbitrary number. A computer-readable recording medium storing a bitstream generated by a video encoding method, the video encoding method comprising:
determining a multi-transform selection candidate set from among a plurality of multi-transform selection candidate sets based on at least one of the number of non-zero coefficients in the current block and the position of the last non-zero coefficient in the current block;
selecting one transformation method based on the set of multiple transformation selection candidates;
obtaining coefficients of the current block by performing the one transform method on the residual block of the current block; and
Encoding the coefficients of the current block;
At least one candidate in the set of the plurality of multiple transform selection candidates corresponds to a non-DCT2 transform method.

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