KR102525555B1 - A method and an apparatus for encoding/decoding a residual block based on quantization parameter - Google Patents

Abstract

An encoding/decoding apparatus according to the present invention derives a residual coefficient of a residual block from a bitstream, calculates a quantization parameter for the residual block, performs inverse quantization on the residual coefficient using the quantization parameter, and performs inverse quantization on the residual coefficient. Residual samples of the residual block may be reconstructed by performing inverse transformation on the residual coefficients.

Description

Residual block encoding/decoding method and apparatus based on quantization parameter

The present invention relates to a method and apparatus for encoding/decoding a video signal.

Demand for high-resolution, high-quality images is increasing in various application fields. As image data becomes higher resolution and higher quality, the amount of data increases relatively compared to existing image data. Therefore, when image data is transmitted using a medium such as an existing wired/wireless broadband line or stored using an existing storage medium, transmission cost and Storage costs increase. High-efficiency video compression technologies can be used to solve these problems that occur as video data becomes high-resolution and high-quality.

The present invention seeks to improve encoding/decoding efficiency of a residual block.

The present invention seeks to improve encoding/decoding efficiency through adaptive block division.

A video encoding/decoding method and apparatus according to the present invention derives a residual coefficient of a residual block from a bitstream, calculates a quantization parameter for the residual block, and uses the calculated quantization parameter for the residual coefficient. A residual sample of the residual block may be reconstructed by performing inverse quantization and performing inverse transformation on the inverse quantized residual coefficient.

In the video encoding/decoding method and apparatus according to the present invention, the quantization parameter may be derived based on at least one of a quantization parameter prediction value and a quantization parameter difference value.

In the video encoding/decoding method and apparatus according to the present invention, the predicted value of the quantization parameter may be derived based on one or more quantization parameters of neighboring blocks.

In the video encoding/decoding method and apparatus according to the present invention, the neighboring block may be a block spatially and/or temporally adjacent to the residual block.

In the video encoding/decoding method and apparatus according to the present invention, the quantization parameter difference value may be determined based on the size of a block for which signaling of the quantization parameter difference value is permitted.

The video encoding/decoding method and apparatus according to the present invention may correct the derived quantization parameter based on a predetermined quantization parameter offset.

In the video encoding/decoding method and apparatus according to the present invention, the residual block may be divided into a variable size/shape based on at least one of a quad tree, a binary tree, and a triple tree.

According to the present invention, encoding/decoding efficiency of a residual block may be improved based on at least one of a predetermined quantization parameter prediction value, a quantization parameter difference value, and a quantization parameter offset.

In addition, according to the present invention, encoding/decoding efficiency can be improved through block division in a tree structure.

1 is a schematic block diagram of an encoding device according to an embodiment of the present invention.
2 is a schematic block diagram of a decoding device according to an embodiment of the present invention.
3 illustrates block partition types as an embodiment to which the present invention is applied.
4 illustrates a block partitioning method based on a tree structure as an embodiment to which the present invention is applied.
5 illustrates a method of restoring a residual sample as an embodiment to which the present invention is applied.
6 illustrates a method of deriving a quantization parameter prediction value QPpred as an embodiment to which the present invention is applied.
FIG. 7 illustrates a method of deriving a predicted value of a quantization parameter for a color difference component of a block T as an embodiment to which the present invention is applied.
8 illustrates a quantization parameter derivation method based on a signaling unit of a quantization parameter difference value (deltaQP) as an embodiment to which the present invention is applied.
9 illustrates an inverse transform process of residual coefficients as an embodiment to which the present invention is applied.

Since the present invention can make various changes and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals have been used for like elements throughout the description of each figure.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. The terms and/or include any combination of a plurality of related recited items or any of a plurality of related recited items.

It is understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may exist in the middle. It should be. On the other hand, when an element is referred to as “directly connected” or “directly connected” to another element, it should be understood that no other element exists in the middle.

Terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail. Hereinafter, the same reference numerals are used for the same components in the drawings, and redundant descriptions of the same components are omitted.

1 is a schematic block diagram of an encoding device according to an embodiment of the present invention.

Referring to FIG. 1 , the encoding apparatus 100 includes a picture division unit 110, prediction units 120 and 125, a transform unit 130, a quantization unit 135, a rearrangement unit 160, and an entropy encoding unit 165. ), an inverse quantization unit 140, an inverse transform unit 145, a filter unit 150, and a memory 155.

Each component shown in FIG. 1 is shown independently to represent different characteristic functions in the video encoding device, which may mean that each component is made of separate hardware. However, each component is listed and included as each component for convenience of description, and at least two components of each component are combined to form one component, or one component is divided into a plurality of components to perform a function, Integrated embodiments and separate embodiments of each of these components are also included in the scope of the present invention unless departing from the essence of the present invention.

In addition, some of the components may be optional components for improving performance rather than essential components that perform essential functions in the present invention. The present invention can be implemented by including only components essential to implement the essence of the present invention, excluding components used for performance improvement, and a structure including only essential components excluding optional components used for performance improvement. Also included in the scope of the present invention.

The picture divider 110 may divide an input picture into at least one block. In this case, a block may mean a coding unit (CU), a prediction unit (PU), or a transformation unit (TU). The division may be performed based on at least one of a quad tree, a binary tree, and a triple tree. A quad tree is a method in which a parent block is divided into four sub-blocks whose width and height are half of the parent block. The binary tree is a method in which an upper block is divided into lower blocks whose width or height is half of the upper block. In a binary tree, a block may have a non-square shape as well as a square shape through the above-described binary tree-based partitioning in which the height of an upper block is half.

Hereinafter, in an embodiment of the present invention, a coding unit may be used as a unit for performing encoding or a unit for performing decoding.

The prediction units 120 and 125 may include the inter prediction unit 120 performing inter prediction and the intra prediction unit 125 performing intra prediction. It is possible to determine whether to use inter prediction or intra prediction for a prediction unit, and determine specific information (eg, intra prediction mode, motion vector, reference picture, etc.) according to each prediction method. In this case, a processing unit in which prediction is performed and a processing unit in which a prediction method and specific details are determined may be different. For example, a prediction method and a prediction mode may be determined in a prediction unit, and prediction may be performed in a transformation unit. A residual value (residual block) between the generated prediction block and the original block may be input to the transform unit 130 . In addition, prediction mode information and motion vector information used for prediction may be encoded in the entropy encoding unit 165 together with residual values and transmitted to a decoding device. When a specific encoding mode is used, it is also possible to encode an original block as it is and transmit it to a decoder without generating a prediction block through the prediction units 120 and 125 .

The inter-prediction unit 120 may predict a prediction unit based on information on at least one picture among pictures before or after the current picture, and in some cases, prediction based on information on a partially coded region within the current picture. Units can also be predicted. The inter prediction unit 120 may include a reference picture interpolation unit, a motion prediction unit, and a motion compensation unit.

The reference picture interpolator may receive reference picture information from the memory 155 and generate pixel information of an integer pixel or less in the reference picture. In the case of luminance pixels, a DCT-based 8-tap interpolation filter with different filter coefficients may be used to generate pixel information of an integer pixel or less in units of 1/4 pixels. In the case of a color difference signal, a DCT-based 4-tap interpolation filter with different filter coefficients may be used to generate pixel information of an integer pixel or less in units of 1/8 pixels.

The motion predictor may perform motion prediction based on the reference picture interpolated by the reference picture interpolator. As a method for calculating the motion vector, various methods such as Full search-based Block Matching Algorithm (FBMA), Three Step Search (TSS), and New Three-Step Search Algorithm (NTS) may be used. The motion vector may have a motion vector value in units of 1/2 or 1/4 pixels based on interpolated pixels. The motion prediction unit may predict the current prediction unit by using a different motion prediction method. Various methods such as a skip method, a merge method, and an advanced motion vector prediction (AMVP) method may be used as motion prediction methods.

The intra prediction unit 125 may generate a prediction unit based on reference pixel information around the current block, which is pixel information in the current picture. If a block adjacent to the current prediction unit is a block on which inter prediction is performed, and the reference pixel is a pixel on which inter prediction is performed, the reference pixel of the block on which intra prediction is performed surrounding the reference pixel included in the block on which inter prediction is performed information can be used instead. That is, when a reference pixel is unavailable, information on the unavailable reference pixel may be replaced with at least one reference pixel among available reference pixels.

In intra prediction, a prediction mode may include a directional prediction mode in which reference pixel information is used according to a prediction direction and a non-directional prediction mode in which directional information is not used during prediction. A mode for predicting luminance information and a mode for predicting chrominance information may be different, and intra prediction mode information or predicted luminance signal information used to predict luminance information may be used to predict chrominance information.

In the intra prediction method, a prediction block may be generated after applying an adaptive intra smoothing (AIS) filter to a reference pixel according to a prediction mode. The type of AIS filter applied to the reference pixel may be different. In order to perform the intra prediction method, the intra prediction mode of the current prediction unit may be predicted from the intra prediction modes of prediction units existing around the current prediction unit. When predicting the prediction mode of the current prediction unit using the mode information predicted from the neighboring prediction unit, if the intra-prediction mode of the current prediction unit and the neighboring prediction unit are identical, the current prediction unit and the neighboring prediction unit use predetermined flag information It is possible to transmit information that the prediction modes of are the same, and if the prediction modes of the current prediction unit and the neighboring prediction unit are different, entropy encoding may be performed to encode the prediction mode information of the current block.

In addition, a residual block may be generated that includes residual information that is a difference between a prediction unit performed prediction based on the prediction unit generated by the prediction units 120 and 125 and an original block of the prediction unit. The generated residual block may be input to the transform unit 130 .

The transform unit 130 may transform a residual block including residual data using a transform type such as DCT or DST. In this case, a transform method may be determined based on an intra prediction mode of a prediction unit used to generate the residual block.

The quantization unit 135 may quantize the values converted to the frequency domain by the transform unit 130 . A quantization coefficient may change according to a block or an importance of an image. The value calculated by the quantization unit 135 may be provided to the inverse quantization unit 140 and the rearrangement unit 160 .

The rearrangement unit 160 may rearrange the coefficient values for the quantized residual values.

The reordering unit 160 may change a 2D block-type coefficient into a 1-D vector form through a coefficient scanning method. For example, the reordering unit 160 may scan from DC coefficients to high-frequency coefficients using a predetermined scan type and change them into a one-dimensional vector form.

The entropy encoding unit 165 may perform entropy encoding based on the values calculated by the reordering unit 160 . Entropy encoding may use various encoding methods such as, for example, exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC).

The entropy encoding unit 165 receives residual value coefficient information and block type information of a coding unit from the reordering unit 160 and the prediction units 120 and 125, prediction mode information, division unit information, prediction unit information and transmission unit information, motion Various information such as vector information, reference frame information, block interpolation information, and filtering information can be encoded.

The entropy encoding unit 165 may entropy-encode the coefficient value of the coding unit input from the reordering unit 160 .

The inverse quantization unit 140 and the inverse transform unit 145 inversely quantize the values quantized by the quantization unit 135 and inverse transform the values transformed by the transform unit 130 . The residual generated by the inverse quantization unit 140 and the inverse transform unit 145 is combined with the prediction unit predicted through the motion estimation unit, the motion compensation unit, and the intra prediction unit included in the prediction units 120 and 125 and restored. You can create a Reconstructed Block.

The filter unit 150 may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter can remove block distortion caused by a boundary between blocks in a reconstructed picture. In order to determine whether to perform deblocking, it may be determined whether to apply the deblocking filter to the current block based on pixels included in several columns or rows included in the block. When a deblocking filter is applied to a block, a strong filter or a weak filter may be applied according to the required deblocking filtering strength. In addition, in applying the deblocking filter, when vertical filtering and horizontal filtering are performed, horizontal filtering and vertical filtering may be processed in parallel.

The offset correction unit may correct an offset of the deblocked image from the original image in units of pixels. In order to perform offset correction for a specific picture, pixels included in the image are divided into a certain number of areas, then the area to be offset is determined and the offset is applied to the area, or the offset is performed considering the edge information of each pixel method can be used.

Adaptive Loop Filtering (ALF) may be performed based on a value obtained by comparing the filtered reconstructed image with the original image. After dividing the pixels included in the image into predetermined groups, filtering may be performed differentially for each group by determining one filter to be applied to the corresponding group. Information related to whether or not to apply ALF may be transmitted for each coding unit (CU) of a luminance signal, and the shape and filter coefficients of an ALF filter to be applied may vary according to each block. In addition, the ALF filter of the same form (fixed form) may be applied regardless of the characteristics of the block to be applied.

The memory 155 may store a reconstructed block or picture calculated through the filter unit 150, and the stored reconstructed block or picture may be provided to the predictors 120 and 125 when inter prediction is performed.

2 is a schematic block diagram of a decoding device according to an embodiment of the present invention.

Referring to FIG. 2 , the decoding apparatus 200 includes an entropy decoding unit 210, a rearrangement unit 215, an inverse quantization unit 220, an inverse transform unit 225, prediction units 230 and 235, and a filter unit 240. ), a memory 245 may be included.

Each component shown in FIG. 2 is independently shown to represent different characteristic functions in the decoding apparatus, which may mean that each component is made of separate hardware. However, each component is listed and included as each component for convenience of explanation, and at least two components of each component may be combined to form one component, or one component may be divided into a plurality of components to perform functions, such Integrated embodiments and separate embodiments of each component are included in the scope of the present invention as long as they do not depart from the essence of the present invention.

The entropy decoding unit 210 may perform entropy decoding on the input bitstream. For example, for entropy decoding, various methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC) may be applied.

The entropy decoding unit 210 may decode information related to intra prediction and inter prediction performed by the encoding device.

The rearrangement unit 215 may perform rearrangement on the entropy-decoded bitstream in the entropy decoding unit 210 . Coefficients expressed in the form of one-dimensional vectors may be reconstructed into coefficients in the form of two-dimensional blocks and rearranged. The rearrangement unit 215 may perform rearrangement by receiving information related to coefficient scanning performed by the encoding device and performing reverse scanning based on the scanning order performed by the corresponding encoding device.

The inverse quantization unit 220 may perform inverse quantization based on the quantization parameter and the rearranged coefficient value of the block.

The inverse transform unit 225 may perform inverse transform on the inverse quantized transform coefficient using a predetermined transform method. In this case, the conversion method may be determined based on information about a prediction method (inter/intra prediction), block size/shape, intra prediction mode, and the like.

The prediction units 230 and 235 may generate a prediction block based on information related to prediction block generation provided from the entropy decoding unit 210 and previously decoded block or picture information provided from the memory 245 .

The prediction units 230 and 235 may include a prediction unit determining unit, an inter prediction unit, and an intra prediction unit. The prediction unit determination unit receives various information such as prediction unit information input from the entropy decoding unit 210, prediction mode information of the intra prediction method, and motion prediction related information of the inter prediction method, and selects a prediction unit from the current coding unit (CU). and it is possible to determine whether the prediction unit performs inter prediction or intra prediction. The inter-prediction unit 230 uses information necessary for inter-prediction of the current prediction unit provided from the encoding device, and based on information included in at least one picture among pictures before or after the current picture including the current prediction unit. Inter prediction may be performed on the current prediction unit. Alternatively, inter prediction may be performed based on information of a pre-reconstructed partial region in the current picture including the current prediction unit.

Whether or not the motion prediction method of the prediction unit included in the coding unit is skip mode, merge mode, or AMVP mode based on the coding unit to perform inter prediction. can judge

The intra prediction unit 235 may generate a prediction block based on pixel information in the current picture. When the prediction unit is a prediction unit that has undergone intra prediction, intra prediction may be performed based on intra prediction mode information of the prediction unit provided by the encoding device. The intra predictor 235 may include an Adaptive Intra Smoothing (AIS) filter, a reference pixel interpolator, and a DC filter. The AIS filter is a part that performs filtering on reference pixels of the current block, and can be applied by determining whether to apply the filter according to the prediction mode of the current prediction unit. AIS filtering may be performed on reference pixels of the current block by using the prediction mode and AIS filter information of the prediction unit provided by the encoding device. When the prediction mode of the current block is a mode in which AIS filtering is not performed, AIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on a pixel value obtained by interpolating the reference pixel, the reference pixel interpolator may interpolate the reference pixel to generate a reference pixel in pixel units having an integer value or less. When the prediction mode of the current prediction unit is a prediction mode for generating a prediction block without interpolating reference pixels, the reference pixels may not be interpolated. The DC filter may generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

The reconstructed block or picture may be provided to the filter unit 240 . The filter unit 240 may include a deblocking filter, an offset correction unit, and an ALF.

Information on whether a deblocking filter is applied to a corresponding block or picture and, when a deblocking filter is applied, information on whether a strong filter or a weak filter is applied may be provided from the encoding device. The deblocking filter of the decoding device may receive information related to the deblocking filter provided by the encoding device, and the decoding device may perform deblocking filtering on the corresponding block.

The offset correction unit may perform offset correction on the reconstructed image based on the type and offset value information of the offset correction applied to the image during encoding.

ALF may be applied to a coding unit based on ALF application information and ALF coefficient information provided from an encoder. Such ALF information may be included in a specific parameter set and provided.

The memory 245 may store a reconstructed picture or block so that it can be used as a reference picture or reference block, and may also provide the reconstructed picture to an output unit.

3 illustrates block partition types as an embodiment to which the present invention is applied.

One block (hereinafter referred to as a first block) may be divided into a plurality of sub-blocks (hereinafter referred to as a second block) by at least one of a vertical line or a horizontal line. The number of vertical and horizontal lines may be one, two or more. Here, the first block may be a coding block (CU), which is a basic unit of image encoding/decoding, a prediction block (PU), which is a basic unit of prediction encoding/decoding, or a transform block (TU), which is a basic unit of transform encoding/decoding. there is. The first block may be a square block or a non-square block.

The division of the first block may be performed based on a quad tree, a binary tree, a triple tree, or the like, and will be described in detail with reference to FIG. 3 below.

Figure 3(a) shows quad tree partitioning (QT). QT is a division type in which a first block is divided into four second blocks. For example, when a first block of 2Nx2N is divided into QT, the first block may be divided into four second blocks having a size of NxN. QT can be restricted to apply only to square blocks, but it can also be applied to non-square blocks.

3(b) illustrates horizontal binary tree (hereinafter referred to as Horizontal BT) partitioning. Horizontal BT is a division type in which a first block is divided into two second blocks by one horizontal line. The bipartitioning may be performed symmetrically or asymmetrically. For example, when a 2Nx2N first block is divided into Horizontal BTs, the first block may be divided into two second blocks having a height ratio of (a:b). Here, a and b may have the same value, and a may be larger or smaller than b.

3(c) illustrates vertical binary tree (hereinafter referred to as Vertical BT) partitioning. Vertical BT is a division type in which a first block is divided into two second blocks by one vertical line. The bipartitioning may be performed symmetrically or asymmetrically. For example, when a 2Nx2N first block is divided into vertical BTs, the first block may be divided into two second blocks having a width ratio of (a:b). Here, a and b may have the same value, and a may be larger or smaller than b.

3(d) illustrates horizontal triple tree (hereinafter referred to as Horizontal TT) splitting. Horizontal TT is a division type in which a first block is divided into three second blocks by two horizontal lines. For example, when a 2Nx2N first block is divided into Horizontal TTs, the first block may be divided into three second blocks having a height ratio of (a:b:c). Here, a, b, and c may have the same value. Alternatively, a and c may be the same, and b may be larger or smaller than a.

3(e) illustrates vertical triple tree (hereinafter, referred to as Vertical TT) partitioning. Vertical TT is a division type in which a first block is divided into three second blocks by two vertical lines. For example, when a 2Nx2N first block is divided into vertical TTs, the first block may be divided into three second blocks having a width ratio of (a:b:c). Here, a, b, and c may have the same value or different values. Alternatively, a and c may be the same, and b may be larger or smaller than a. Alternatively, a and b may be the same, and c may be larger or smaller than a. Alternatively, b and c are the same, and a may be larger or smaller than b.

The aforementioned division may be performed based on division information signaled from an encoding device. The splitting information may include at least one of splitting type information, splitting direction information, and splitting ratio information.

The partition type information may specify one of partition types pre-defined in the encoding/decoding device. The pre-defined split type may include at least one of QT, Horizontal BT, Vertical BT, Horizontal TT, Vertical TT, and no split mode. Alternatively, the partition type information may mean information on whether QT, BT, or TT is applied, and may be coded in the form of a flag or index. In the case of BT or TT, the division direction information may indicate whether division is performed in a horizontal direction or a vertical direction. In the case of BT or TT, the division ratio information may indicate the ratio of the width and/or height of the second block.

4 illustrates a block partitioning method based on a tree structure as an embodiment to which the present invention is applied.

It is assumed that the block 400 shown in FIG. 4 is a square block (hereinafter, referred to as a first block) having a size of 8Nx8N and a division depth of k. When the division information of the first block indicates QT division, the first block may be divided into four sub-blocks (hereinafter, referred to as second blocks). The second block may have a size of 4Nx4N and a split depth of (k+1).

The four second blocks may be further divided based on any one of QT, BT, TT or non-split mode. For example, when the division information of the second block indicates a binary tree (Horizontal BT) in the horizontal direction, the second block is divided into two sub-blocks (hereinafter referred to as the third block 410 of FIG. 4). block) can be divided into two parts. In this case, the third block may have a size of 4Nx2N and a split depth of (k+2).

The third block may also be partitioned again based on any one of QT, BT, TT or non-division mode. For example, when the partition information of the third block indicates a vertical binary tree (Vertical BT), the third block is divided into two sub-blocks 411 and 412 as shown in FIG. It can be. In this case, the sub-blocks 411 and 412 may have a size of 2Nx2N and have a split depth of (k+3). Alternatively, when the division information of the third block indicates a horizontal binary tree (Horizontal BT), the third block may be divided into two sub-blocks 413 and 414 as shown in FIG. there is. In this case, the sub-blocks 413 and 414 may have a size of 4NxN and a split depth of (k+3).

The division may be performed independently or in parallel with neighboring blocks, or may be performed sequentially according to a predetermined priority.

Partition information of the current block to be split may be dependently determined based on at least one of partition information of an upper block of the current block and partition information of neighboring blocks. For example, when the second block is divided into Horizontal BTs and the upper third block is divided into Vertical BTs, the lower third block does not need to be divided into Vertical BTs. This is because when the third block at the bottom is divided into Vertical BT, the same result as when the second block is divided into QT is obtained. Accordingly, encoding of division information (particularly, division direction information) of the lower third block may be omitted, and the decoding apparatus may set the lower third block to be horizontally divided.

The upper block may mean a block having a split depth smaller than the split depth of the current block. For example, when the division depth of the current block is (k+2), the division depth of the upper block may be (k+1). The neighboring block may be a block adjacent to the top or left side of the current block. The neighboring block may be a block having the same split depth as the current block.

The above division may be repeatedly performed up to the minimum unit of encoding/decoding. When the block is divided into minimum units, division information for the corresponding block is no longer signaled from the encoding device. The information on the minimum unit may include at least one of the size or shape of the minimum unit. The size of the minimum unit may be expressed as the width and height of the block, the minimum or maximum value of the width and height, the sum of the width and height, the number of pixels, the division depth, and the like. Information on the minimum unit may be signaled in at least one of a video sequence, picture, slice, or block unit. Alternatively, the information on the minimum unit may be a value pre-promised to the encoding/decoding device. Information on the minimum unit may be signaled for each CU, PU, and TU. Information on one minimum unit may be equally applied to CUs, PUs, and TUs.

5 illustrates a method of restoring a residual sample as an embodiment to which the present invention is applied.

Referring to FIG. 5 , a residual coefficient of a residual block may be derived from a bitstream (S500).

The derivation may be performed by decoding at least one of information about whether a non-zero residual coefficient exists, an absolute value (abs), or a sign of the encoded residual coefficient.

The derivation may further include setting a residual coefficient of a high-frequency region in the residual block to 0. The high-frequency region may be defined as a region excluding at least one of n columns from the left side of the residual block or m rows from the top side of the residual block. The n and m may be pre-promised values in the encoding/decoding apparatus, or may be variably determined according to the size/shape of the residual block. For example, when the residual block is 64x32, a region excluding 32 columns from the left side of the residual block (here, n = 32 and m = 0) may be defined as a high frequency region. When the residual block is 32x64, an area excluding 32 rows (here, n=0, m=32) from the top of the residual block may be defined as a high frequency area. Alternatively, n and m may be derived based on information encoded to specify a high frequency region.

Also, the process of setting the residual coefficient to 0 may be selectively performed in consideration of at least one of the size or shape of the residual block. For example, the above process may be applied only when the size of the residual block is greater than or equal to a predetermined threshold value. The size of the residual block may be expressed as at least one of a width or a height of the residual block. The threshold value may mean a minimum size allowed to set the residual coefficient to 0. The threshold value may be a pre-promised value in the encoding/decoding device, or may be encoded and signaled in the encoding device. The threshold may be 32, 64, 128, 256 or more.

The process of setting the residual coefficient to 0 may be selectively performed based on flag information. The flag information may indicate whether a residual coefficient of a high frequency region in a residual block is set to 0. The flag information may be induced in a decoding device based on the size/shape of a residual block, or may be encoded and signaled in an encoding device. However, the above process may be limited to be performed only when the residual block is not coded in the transform skip mode. Accordingly, when the residual block is encoded in the transform skip mode, the encoding apparatus may not encode information necessary for setting the residual coefficient to 0.

Referring to FIG. 5 , a quantization parameter for the residual block may be calculated (S510).

The quantization parameter may be derived using at least one of a quantization parameter prediction value (QPpred) and a quantization parameter difference value (deltaQP). In other words, the quantization parameter may be set as the quantization parameter predicted value QPred, or may be derived by adding the quantization parameter difference value deltaQP to the quantized parameter predicted value QPred.

For example, merge mode, skip mode, no-transform mode, PCM mode, when non-zero coefficients do not exist (ie, coded block flag = 0), etc. Likewise, when inverse quantization is unnecessary for a corresponding block, the quantization parameter difference value (deltaQP) may not be encoded. In this case, the quantization parameter prediction value QPpred may be set as the quantization parameter.

A method of deriving the quantization parameter prediction value QPpred will be described with reference to FIGS. 6 and 7 . Meanwhile, the quantization parameter difference value deltaQP may be signaled in a predetermined unit, and a quantization parameter derivation method based on the signaling unit of the quantization parameter difference value deltaQP will be described with reference to FIG. 8 .

The calculation of the quantization parameter may further include a process of correcting the previously derived quantization parameter based on a predetermined quantization parameter offset (QPoffset).

The quantization parameter offset (QPoffset) may be a fixed value pre-promised to the encoding/decoding device, or may be coded and signaled by the encoding device. The quantization parameter offset (QPoffset) may be signaled at a level of at least one of a video sequence, picture, slice, tile, or block unit. A unit in which the quantization parameter offset is signaled may be larger than a unit in which the quantization parameter difference value is signaled. The value and number of the quantization parameter offsets (QPoffset) may be adaptively determined according to block size/shape, number of divisions, prediction mode, intra prediction mode, component type (e.g., luminance, color difference), and the like.

The number of quantization parameter offsets may be 1, 2, 3 or more. For example, the quantization parameter offset may be defined at least one of a picture level, a slice level, or a block level. The quantization parameter offset may be defined for each of an intra mode and an inter mode, and may be defined for each of a luminance component and a chrominance component. Alternatively, a separate offset for LM mode among intra prediction modes may be defined. Here, the LM mode may mean a mode in which a chrominance block is predicted using prediction/reconstruction samples of a luminance block.

Referring to FIG. 5 , inverse quantization may be performed on the residual coefficient using the calculated quantization parameter (S520).

Specifically, the inverse quantization may be performed based on at least one of the quantization parameter and a predetermined level scale value. The level scale value may be a pre-promised value in the encoding/decoding device, or may be encoded and signaled in the encoding device. The level scale value may be composed of k integer values of a one-dimensional array. For example, the level scale value may be defined as {40, 45, 51, 57, 64, 72}. However, this does not limit the number of level scale values and integer values. That is, the level scale value may be defined as another value, and the number of level scale values may be defined as 4, 5, 7, 8 or more.

Meanwhile, a predetermined quantization weight (m) may be further applied to the resultant value of the inverse quantization, and this process will be referred to as scaling.

The quantization weight may be derived as a fixed value pre-promised to the encoding/decoding device (Method A). In this case, the quantization weight may be the same value regardless of the position of the residual coefficient in the residual block. Alternatively, the quantization weight may be derived based on table information pre-defined in the encoding/decoding device (method B). The table information may define a quantization weight according to at least one of a position of a residual coefficient, a block size, a component type, or a prediction mode. Alternatively, the encoding apparatus may determine the quantization weight for each position of the residual coefficient and encode it. The decoding apparatus may derive the quantization weights by decoding the encoded information about the quantization weights (Method C). In this case, the encoding apparatus may encode only the difference between the quantization weight of the previous position and the quantization weight of the current position. The decoding apparatus may derive the quantization weight of the current position by using the decoded quantization weight of the previous position and the encoded information.

The quantization weight of the residual block may be derived by selecting any one of methods A to C described above. The selection may be performed based on at least one of a size/shape of a residual block, a division type, a prediction mode, a component type, a transform type, or predetermined flag information. The flag information may include a flag on whether to apply a quantization weight, a flag on whether to skip transform, and the like.

In the above methods A to C, the quantization weight of the scaling list may be determined for each of the luminance block and the chrominance block. For example, a scaling list for each of the luminance block and the chrominance block may be signaled. Alternatively, the scaling list of the chrominance block may be determined by referring to the scaling list of the luminance block.

Referring to FIG. 5 , a residual sample may be reconstructed by performing an inverse transform on the inverse quantized residual coefficient (S530).

The inverse transform is performed based on a predetermined transform type, and the transform type of the residual block may be determined based on a transform candidate set. The transformation candidate set may include n transformation types. For example, the transformation candidate set may include at least one of DCT-II, DCT-V, DCT-VIII, DST-I, and DST-VII.

In the encoding/decoding apparatus, m transformation candidate sets may be defined. The m may be 1, 2, 3 or more. The number and/or type of transform types included in any one of the m transform candidate sets (hereinafter referred to as a first transform candidate set) may be different from that of the other one (hereinafter referred to as a second transform candidate set). For example, the first transformation candidate set may include p transformation types, and the second transformation candidate set may include q transformation types smaller than p. Alternatively, even when the first and second transform candidate sets include the same number of transform types, at least one transform type belonging to the first transform candidate set may be different from a transform type belonging to the second transform candidate set.

Any one of the m transformation candidate sets may be selectively used.

Selection of the transform candidate set may be performed based on the size of the residual block. For example, if the size of the residual block is smaller than or equal to the threshold, a first transformation candidate set consisting of p transformation types is selected; otherwise, a second transformation candidate set consisting of q transformation types is selected. can The threshold value may be 32, 64, 128, 256 or more, and p may be a value greater than q.

Alternatively, selection of the transformation candidate set may be performed based on information signaled from an encoding device. The information may specify any one of m transformation candidate sets. The information may be signaled at the level of at least one of picture, slice, and block.

When the selected transform candidate type includes a plurality of transform types, the encoding device may encode information specifying one of the plurality of transform types. The decoding apparatus may determine the transform type of the residual block by decoding the encoded information.

Meanwhile, the inverse transform may be selectively performed based on a predetermined flag. Here, the flag may indicate whether inverse transform is skipped for the residual block. For example, when the flag is 1, inverse transformation may not be performed on the residual block, and when the flag is 0, inverse transformation may be performed on the residual block. Therefore, the transform type of the residual block can be derived only when the flag is 0. Alternatively, the inverse transform may be selectively performed based on attributes of the residual block. The decoding apparatus may determine whether the inverse transform is skipped based on the attribute of the residual block. The attribute may mean a size/shape of a residual block, a division type, a prediction mode, a component type, and other encoding parameters related to residual coefficients.

In addition to the inverse transform (hereinafter referred to as first inverse transform), an additional inverse transform (hereinafter referred to as second inverse transform) may be further performed, which will be described with reference to FIG. 9 .

6 illustrates a method of deriving a quantization parameter prediction value QPpred as an embodiment to which the present invention is applied.

Referring to FIG. 6 , a predicted quantization parameter QPred for block T may be derived based on quantization parameters of neighboring blocks. The block T is an NxM block and may have a square or non-square shape.

The neighboring block is a block that is spatially/temporally adjacent to the block T, and may mean a block pre-decoded before the block T. For example, the neighboring block may include at least one of a left block, an upper block, an upper left block, an upper right block, or a lower left block of block T. Alternatively, the neighboring block may further include a collocated block temporally corresponding to the block T. The collocated block is a block belonging to a picture different from the block T, and may be defined as a block including a location of at least one of a top left corner sample, a bottom right corner sample, or a center sample of the block T.

The location of the neighboring block may be a pre-promised location in the encoding/decoding device. For example, the pre-promised position may be a left block and an upper block, or may be a left block, an upper block, and an upper left block. However, it is not limited thereto, and may further include a lower left block and an upper right block. The location of the neighboring block may be variably determined based on the block T or at least one property (e.g., size, shape, segmentation depth, segmentation type, component type, etc.) of the adjacent blocks. For example, the neighboring block may be determined as a block having the largest area among blocks adjacent to the block T, or may be determined as a block having the longest boundary length adjacent to each other. This may be performed for the upper block and the left block of block T, respectively.

Alternatively, information specifying the location of the neighboring block may be encoded in an encoding device and signaled. The information may be encoded in the form of a flag or index. For example, when the information is index 0, the quantization parameter prediction value QPred of block T may be derived using the quantization parameter of the left block. When the information is index 1, the quantization parameter prediction value QPred of block T can be derived using the quantization parameter of the upper block.

The number of neighboring blocks is n, where n may be a natural number of 1, 2, 3, 4 or more. The number may be a fixed value pre-promised in the encoding/decoding apparatus. Alternatively, the number may be variably determined based on at least one attribute (e.g., size, shape, split depth, split type, component type, etc.) of block T or neighboring blocks. Alternatively, information on the maximum number of neighboring blocks used to derive the quantization parameter prediction value (QPpred) of the block T may be coded in an encoding device and signaled. That is, the block T may use neighboring blocks within the number range according to the maximum number information. The maximum number information may be signaled at at least one level among video sequences, pictures, and other fragment areas (e.g., slices, tiles, coding tree block rows, blocks).

As described above, the quantization parameter prediction value QPpred of the block T may be derived using one or more neighboring blocks.

When a plurality of neighboring blocks are used, the predicted quantization parameter QPpred of the block T may be derived through an operation process such as a median value, an average value, a minimum value, a maximum value, or a mode value of quantization parameters of the plurality of neighboring blocks.

Alternatively, the quantization parameter prediction value QPpred of the block T may be derived by subtracting the QP of the upper left block from the sum of the QP of the upper block and the QP of the left block. In this case, when the upper block or the left block is plural, the QP of the upper block or the left block may be determined through an operation process such as a median value, an average value, a minimum value, a maximum value, or a mode value.

If there is an unavailable block among the neighboring blocks, the prediction value of the quantization parameter of the block T may be derived using only the available neighboring blocks. Alternatively, when the neighboring block is unavailable, the quantization parameter of the neighboring block may be derived based on a quantization parameter defined in a predetermined fragment area. The fragment area may mean a slice, a tile, a Coding Tree Block row, a block, and the like. The fragment area may refer to an area encoded/decoded prior to block T, or may refer to an area to which block T, a current encoding/decoding target, belongs. The unavailability may mean a case in which the neighboring block does not physically exist or a case in which reference is impossible due to rules of an encoding/decoding device. For example, if block T and neighboring blocks belong to different parallel processing regions (eg, slices, tiles, etc.), block T may not be allowed to refer to the neighboring blocks.

FIG. 7 illustrates a method of deriving a predicted value of a quantization parameter for a color difference component of a block T as an embodiment to which the present invention is applied.

Hereinafter, the luminance component and the chrominance component of the block T will be referred to as a luminance block and a chrominance block, respectively.

In the case of the 4:2:0 color format, the chrominance block Tc may correspond to the luminance block TY. The predicted value of the quantization parameter of the chrominance block may be derived using the quantization parameter of the corresponding luminance block.

However, as shown in FIG. 7 , the division structure between the luminance block and the chrominance block may be different. In this case, there may be a plurality of luminance blocks corresponding to the color difference blocks. The predicted value of the quantization parameter of the chrominance block may be derived using a quantization parameter of any one of a plurality of luminance blocks. In this case, a luminance block corresponding to the position of the center sample or the position of the upper left sample of the color difference block may be used. A luminance block having the largest overlapping area with the chrominance block may be used. Alternatively, the predicted value of the quantization parameter of the chrominance block may be derived by calculating an average value, a median value, a minimum value, a maximum value, and a mode of quantization parameters of a plurality of luminance blocks.

The predicted value of the quantization parameter of the chrominance block may be derived using the quantization parameter of the neighboring block, which has been reviewed in detail in FIG. 6 , and detailed description thereof will be omitted herein.

As described above, the predicted value of the quantization parameter of the chrominance block is derived using both a method using the quantization parameters of the corresponding luminance block (first method) and a method using quantization parameters of neighboring blocks of the chrominance block (second method). It can be. Alternatively, the predicted value of the quantization parameter of the color difference block may be derived by selecting either the first method or the second method.

The selection may be performed in consideration of whether the division structures of the luminance block and the chrominance block are the same, the prediction mode of the block T, intra prediction mode, color format or size/shape, and the like. For example, when block T is encoded in the inter mode and the division structure of the chrominance block is the same as that of the luminance block, the quantization parameter of the chrominance block may be predicted using the first method. Alternatively, the first method may be used when the division structure of the chrominance block is the same as the division structure of the luminance block, and the second method may be used otherwise. Alternatively, when the intra prediction mode of the block T is the LM mode, the quantization parameter of the chrominance block may be predicted using the first method.

Alternatively, the selection may be performed based on information specifying either the first method or the second method. The information may be encoded and signaled in an encoding device. The information may be signaled at at least one level among video sequences, pictures, and other fragment areas (e.g., slices, tiles, Coding Tree Block rows, blocks).

The quantization parameter of the chrominance block may be derived identically to the quantization parameter predicted value of the derived chrominance block, or may be derived by adding a predetermined quantization parameter difference value. Also, the derived quantization parameter may be corrected using a predetermined quantization parameter offset, as shown in FIG. 5 .

For example, in the case of a chrominance block encoded in the LM mode, a predicted value of a quantization parameter may be set as a quantization parameter. In this case, the quantization parameter difference value may not be signaled or the process of adding the signaled quantization parameter difference value may be omitted. Alternatively, in the case of a chrominance block encoded in the LM mode, the quantization parameter may be corrected using one, two or more quantization parameter offsets.

8 illustrates a quantization parameter derivation method based on a signaling unit of a quantization parameter difference value (deltaQP) as an embodiment to which the present invention is applied.

The encoding device may determine a block unit for encoding deltaQP and encode information indicating the size of the block. Here, the size may be expressed as at least one of the width or height of the block, the product of the width and the height, the sum of the width and the height, and the minimum/maximum value of the width and height. The decoding apparatus may decode the signaled information and know the minimum size of a block in which deltaQP signaling is allowed. The information may be signaled at a level of at least one of a video sequence, picture, slice, or tile. Alternatively, the minimum size may be derived from the minimum size of a transform block or may be defined as a fixed size pre-promised to the encoding/decoding device. For example, the minimum size may be defined as 4x4, 8x4, 4x8, 8x8, and the like. Information indicating the size of the block may be signaled for a luminance component and a chrominance component, respectively. Alternatively, the minimum size of the chrominance block may be derived based on the minimum size of the luminance block. For example, in the case of a 4:2:0 color format, the minimum size of the chrominance block may be determined to be half of the minimum size of the luminance block. In the case of the inter mode, the division structure of the chrominance block may be different from that of the luminance block, and the minimum size of the chrominance block may be determined to be half of the luminance block.

Referring to FIG. 8 , the quantization parameter of the current block may be derived based on a comparison result between the size of the current block and the minimum size. Here, the current block may mean a block that is no longer divided by a block division type such as QT, BT, or TT.

8(a) shows a case where the size of the current block is 2Mx2N and the minimum size is MxN. As shown in FIG. 8(a), when the size of the current block is greater than the minimum size, the quantization parameter of the current block can be derived using QPpred and the signaled deltaQP.

The QPpred may be derived based on at least one of the first method and the second method described above. The deltaQP may be signaled in block a, and the remaining blocks b, c, and d may share the deltaQP signaled in block a. In this case, the current block has one quantization parameter. Alternatively, the deltaQP may be signaled for each block a-d having a minimum size. In this case, quantization parameters may be derived for blocks a through d belonging to the current block, and blocks a through d may have different quantization parameters.

Meanwhile, when the size of the current block and the minimum size are the same, it can be derived using the QPpred and the signaled deltaQP.

8(b) shows a case where the minimum size is MxN and the current blocks (a-d) are smaller than the minimum size. As shown in FIG. 8(b), when the size of the current block is smaller than the minimum size, the quantization parameter of the current block may be derived using QPpred and a signaled deltaQP.

The QPpred may be derived based on the current block, based on at least one of the first method and the second method described above. For example, QPpred may be derived for each block a-d. Alternatively, QPpred is derived for block a, and the remaining blocks b-d may share QPpred derived from block a. Alternatively, the QPred may be derived based on at least one of the above-described first method or second method based on an upper block of the current block. Here, the upper block may be a block including the current block and having a split depth smaller than that of the current block. For example, when the split depth of the current block is k, the split depth of the upper block may be (k-1), (k-2), and the like. The upper block may be defined in units of blocks sharing the QPpred. The upper block may be set to the same size (MxN) as the minimum size. Alternatively, the encoding device may determine a block unit sharing the QPpred and encode information specifying the block unit. The decoding apparatus may specify the location, size, shape, etc. of the upper block based on the encoded information.

The deltaQP may be signaled from an upper block of the current block. Here, the upper block is a block including the current block and may mean a block having a split depth smaller than that of the current block. That is, when the split depth of the current block is k, the split depth of the upper block may be (k-1), (k-2), and the like. Here, it is assumed that the upper block is MxN shown in FIG. 8(b). Accordingly, the same quantization parameter may be derived for blocks a through d, and different quantization parameters may be derived for each block a through d. Alternatively, as shown in FIG. 8(b), when the size of the current block is smaller than the minimum size, the quantization parameter of the current block may be derived using QPpred. At this time, decoding for deltaQP may be omitted. As described above, the QPpred may be derived based on at least one of the first method and the second method based on the current block or the upper block, and a detailed description thereof will be omitted. Similarly, one same quantization parameter may be derived for blocks a-d belonging to an MxN block, and different quantization parameters may be derived for each block a-d.

Meanwhile, when a specific block is a block adjacent to a boundary of a picture, slice, or tile, the corresponding block may not satisfy the minimum size. In this case, the quantization parameter of the corresponding block is derived using only Qppred, and decoding of deltaQP can be omitted.

9 illustrates an inverse transform process of residual coefficients as an embodiment to which the present invention is applied.

Referring to FIG. 9 , a residual sample of a residual block may be reconstructed by performing at least one of a first inverse transform and a second inverse transform on a residual coefficient.

The second inverse transform may be applied to the entire region of the residual block or only to a partial region within the residual block. The partial region may refer to a low-frequency region within the residual block. The region to which the second inverse transform is applied may be variably determined in consideration of at least one of the size/shape of the residual block and the size/shape of the transform matrix of the second inverse transform.

For example, when either the width or the height of the residual block is equal to or greater than 8, a second inverse transform having an 8x8 transformation matrix may be applied. When the size of the residual block is 8x8, the second inverse transform is applied to the entire region of the residual block, and when the size of the residual block is 16x16, the second inverse transform may be applied only to a partial region of the residual block. The partial region may refer to an 8x8 region located at the upper left of the residual block, a 16x8 region located at the upper end of the residual block, an 8x16 region located to the left of the residual block, or an region excluding the 8x8 region located at the lower right corner of the residual block. .

Alternatively, when any one of the width or height of the residual block is 4, a second inverse transform having a 4x4 transformation matrix may be applied. When the size of the residual block is 4x8 or 8x4, the second inverse transform may be applied only to a partial region of the residual block (e.g., a 4x4 region located at the upper left of the residual block), and the second inverse transform may be applied to two 4x4 regions belonging to the residual block. A second inverse transform may be applied, respectively.

The size of the transformation matrix of the second inverse transform may be 4x4, 8x8, 16x16, 32x32 or larger. The shape of the transformation matrix is not limited to a square shape, and may be implemented in a non-square shape. However, in order to reduce the complexity of transformation, the size of the transformation matrix allowed for the second inverse transformation may be limited to NxM or less. N and M may be 4, 8 or 16, respectively, and N and M may be the same as or different from each other.

In the second inverse transform process, the transform type of the residual block may be determined through the transform type derivation method described in FIG. 5 . Alternatively, the transform type in the second inverse transform may be pre-promised to the encoding/decoding device. For example, as a transform type in the second inverse transform, one of the above-described five transform types may be fixedly used.

The second inverse transform may be selectively performed based on a flag (hereinafter, referred to as a first flag) indicating whether the first inverse transform is skipped in the residual block. That is, when the first inverse transform is skipped for the residual block according to the first flag, the second inverse transform may also be skipped.

Alternatively, a flag indicating whether the second inverse transform is skipped (hereinafter, referred to as a second flag) may be separately signaled. When the second flag is 1, the second inverse transform is not performed, and when the flag is 0, the second inverse transform may be performed. The first flag and the second flag may be independently encoded and signaled. Alternatively, one of the first flag and the second flag may be signaled dependently on the other flag. For example, only when one of the first flag and the second flag is 1, the other flag may be signaled. Conversely, only when one of the first flag and the second flag is 0, the other flag may be signaled.

The second inverse transform may not be applied when the number of non-zero residual coefficients belonging to the residual block is less than n. Here, n may be a value pre-promised to the encoding/decoding device. For example, n may be 1, 2, 3, or a natural number equal to or less than 8. Alternatively, n may be variably determined based on the size of the residual block.

Meanwhile, FIG. 9 shows that the second inverse transform is performed before the first inverse transform, but this does not limit the order of performing the inverse transform. That is, the second inverse transform may be performed before the first inverse transform or after the first inverse transform. When the second inverse transform is performed before the first inverse transform, the scaling described in FIG. 5 may be performed between inverse quantization and the second inverse transform, or may be performed between the first inverse transform and the second inverse transform. Conversely, when the second inverse transform is performed after the first inverse transform, the scaling described in FIG. 5 may be performed between inverse quantization and the first inverse transform, or may be performed between the first inverse transform and the second inverse transform.

Exemplary methods of this disclosure are presented as a series of operations for clarity of explanation, but this is not intended to limit the order in which steps are performed, and each step may be performed concurrently or in a different order, if desired. In order to implement the method according to the present disclosure, other steps may be included in addition to the exemplified steps, other steps may be included except for some steps, or additional other steps may be included except for some steps.

Various embodiments of the present disclosure are intended to explain representative aspects of the present disclosure, rather than listing all possible combinations, and matters described in various embodiments may be applied independently or in combination of two or more.

In addition, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. For hardware implementation, one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), It may be implemented by a processor (general processor), controller, microcontroller, microprocessor, or the like.

The scope of the present disclosure is software or machine-executable instructions (eg, operating systems, applications, firmware, programs, etc.) that cause operations according to methods of various embodiments to be executed on a device or computer, and such software or It includes a non-transitory computer-readable medium in which instructions and the like are stored and executable on a device or computer.

Claims (13)

decoding a residual coefficient of a current block from a bitstream;
performing inverse quantization on the residual coefficient using a quantization parameter;
Reconstructing a residual sample of the current block by performing an inverse transform on the inverse quantized residual coefficient;
The inverse transform is performed based on a transform candidate set of the current block,
The transform candidate set of the current block is one transform candidate set determined from among a plurality of transform candidate sets including a first transform candidate set and a second transform candidate set,
Each of the plurality of transform candidate sets includes at least one transform type usable for inverse transform of the current block,
The transform candidate set of the current block is determined as one of the plurality of transform candidate sets based on the size of the current block;
The number of transform types included in the first transform candidate set is different from the number of transform types included in the second transform candidate set. delete According to claim 1,
When the size of the current block is smaller than or equal to the threshold, a transform candidate set of the current block is determined as the first transform candidate set among the plurality of transform candidate sets;
When the size of the current block is greater than the threshold, the transform candidate set of the current block is determined as the second transform candidate set among the plurality of transform candidate sets. According to claim 3,
The threshold value is any one of 32, 64 or 128, video decoding method. delete According to claim 1,
The first conversion candidate set includes DCT-8 and DST-7,
The second transform candidate set includes DCT-2, DCT-8, and DST-7. delete delete delete delete delete obtaining residual coefficients of the current block by performing transformation on residual samples of the current block;
performing quantization on the residual coefficient using a quantization parameter;
Encoding the quantized residual coefficient of the current block,
The transformation is performed based on a transformation candidate set of the current block,
The transform candidate set of the current block is one transform candidate set determined from among a plurality of transform candidate sets including a first transform candidate set and a second transform candidate set,
Each of the plurality of transform candidate sets includes at least one transform type usable for transforming the current block,
The transform candidate set of the current block is determined as one of the plurality of transform candidate sets based on the size of the current block;
The number of transform types included in the first transform candidate set is different from the number of transform types included in the second transform candidate set. A computer-readable recording medium storing a bitstream generated by an encoding method,
The encoding method,
obtaining residual coefficients of the current block by performing transformation on residual samples of the current block;
performing quantization on the residual coefficient using a quantization parameter;
Encoding the quantized residual coefficient of the current block,
The transformation is performed based on a transformation candidate set of the current block,
The transform candidate set of the current block is one transform candidate set determined from among a plurality of transform candidate sets including a first transform candidate set and a second transform candidate set,
Each of the plurality of transform candidate sets includes at least one transform type usable for transforming the current block,
The transform candidate set of the current block is determined as one of the plurality of transform candidate sets based on the size of the current block;
The number of transformation types included in the first transformation candidate set is different from the number of transformation types included in the second transformation candidate set.

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