KR20220054771A - 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, and reconstructs residual samples of the residual block by performing inverse transformation on the residual coefficient.

Description

Quantization parameter-based residual block encoding/decoding method and apparatus

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

The demand for high-resolution, high-quality images is increasing in various application fields. As the image data becomes higher resolution and higher quality, the amount of data relatively increases compared to the existing image data. The storage cost will increase. High-efficiency image compression techniques can be used to solve these problems that occur as image data becomes high-resolution and high-quality.

An object of the present invention is to improve the encoding/decoding efficiency of a residual block.

An object of the present invention is 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 transform 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 predicted value and a quantization parameter difference value.

In the video encoding/decoding method and apparatus according to the present invention, the predictive value of the quantization parameter may be derived based on quantization parameters of one or more 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 a size of a block allowing signaling of the quantization parameter difference value.

A 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 variable sizes/shapes based on at least one of a quad tree, a binary tree, and a triple tree.

According to the present invention, it is possible to improve the encoding/decoding efficiency of a residual block 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 of a tree structure.

1 is a schematic block diagram of an encoding apparatus according to an embodiment of the present invention.
2 is a schematic block diagram of a decoding apparatus according to an embodiment of the present invention.
3 illustrates a block division type 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 reconstructing a residual sample according to an embodiment to which the present invention is applied.
6 illustrates a method of deriving a quantization parameter predicted value (QPpred) according to an embodiment to which the present invention is applied.
7 is a diagram illustrating a method of deriving a quantization parameter predicted value for a chrominance component of a block T as an embodiment to which the present invention is applied.
FIG. 8 illustrates a quantization parameter derivation method based on a signaling unit of a quantization parameter difference value deltaQP according to an embodiment to which the present invention is applied.
9 illustrates an inverse transformation process of residual coefficients as an embodiment to which the present invention is applied.

Since the present invention can have various changes and can have various embodiments, specific embodiments are 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 it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements.

Terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component. and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being “connected” or “connected” to another component, it is understood that the other component may be directly connected or connected to the other component, but other components may exist in between. it should be On the other hand, when it is mentioned that a certain element is "directly connected" or "directly connected" to another element, it should be understood that no other element is present in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

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

1 is a schematic block diagram of an encoding apparatus 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 of the components shown in FIG. 1 is independently illustrated to represent different characteristic functions in the image encoding apparatus, which may mean that each component is made of separate hardware. However, each component is included in a list 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 without departing from the essence of the present invention.

In addition, some of the components are not essential components for performing essential functions in the present invention, but may be optional components for merely improving performance. The present invention can be implemented by including only essential components to implement the essence of the present invention, except for 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 the 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 quadtree, a binary tree, and a triple tree. The quad tree divides the upper block into lower blocks whose width and height are half that of the upper block. Binary tree is a method of dividing the upper block into lower blocks whose either width or height is half that of the upper block. In a binary tree, a block may have a non-square shape as well as a square shape through the binary tree-based division in which the upper block is half the height.

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

The prediction units 120 and 125 may include an inter prediction unit 120 performing inter prediction and an intra prediction unit 125 performing intra prediction. Whether to use inter prediction or to perform intra prediction for a prediction unit may be determined, and specific information (eg, intra prediction mode, motion vector, reference picture, etc.) according to each prediction method may be determined. In this case, a processing unit in which prediction is performed and a processing unit in which a prediction method and specific content 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 . Also, prediction mode information, motion vector information, etc. used for prediction may be encoded by the entropy encoder 165 together with the residual value and transmitted to the decoding apparatus. When a specific encoding mode is used, the original block may be encoded and transmitted to the decoder without generating the prediction block through the predictors 120 and 125 .

The inter prediction unit 120 may predict a prediction unit based on information on at least one of a picture before or after the current picture, and in some cases, prediction based on information of a partial region in the current picture that has been encoded Units can also be predicted. The inter prediction unit 120 may include a reference picture interpolator, a motion prediction unit, and a motion compensator.

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

The motion prediction unit 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 of 1/2 or 1/4 pixel unit based on the interpolated pixel. The motion prediction unit may predict the current prediction unit by using a different motion prediction method. As the motion prediction method, various methods such as a skip method, a merge method, and an AMVP (Advanced Motion Vector Prediction) method may be used.

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. When the neighboring block of the current prediction unit is a block on which inter prediction is performed, and thus the reference pixel is a pixel on which inter prediction is performed, the reference pixel included in the block on which the inter prediction is performed is a reference pixel of the block on which the intra prediction is performed. information can be used instead. That is, when the reference pixel is not available, the unavailable reference pixel information may be replaced with at least one reference pixel among the available reference pixels.

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

The intra prediction method may generate a prediction block 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 mode of the prediction unit existing around the current prediction unit. When the prediction mode of the current prediction unit is predicted using mode information predicted from the neighboring prediction unit, if the intra prediction mode of the current prediction unit and the neighboring prediction unit is the same, the current prediction unit and the neighboring prediction unit are used using predetermined flag information It is possible to transmit information indicating that the prediction modes of , and if the prediction modes of the current prediction unit and the neighboring prediction units are different from each other, entropy encoding may be performed to encode the prediction mode information of the current block.

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

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

The quantization unit 135 may quantize values transformed in the frequency domain by the transform unit 130 . The quantization coefficient may vary according to blocks or the 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 on the quantized residual values.

The rearrangement unit 160 may change the two-dimensional block form coefficient into a one-dimensional vector form through a coefficient scanning method. For example, the reordering unit 160 may scan from DC coefficients to coefficients in a high frequency region using a predetermined scan type, and may change it 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 . For entropy encoding, various encoding methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be used.

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

The entropy encoder 165 may entropy-encode the coefficient values of the coding units input from the reordering unit 160 .

The inverse quantizer 140 and the inverse transform unit 145 inversely quantize the values quantized by the quantizer 135 and inversely transform the values transformed by the transform unit 130 . The residual values generated by the inverse quantizer 140 and the inverse transform unit 145 are combined with the prediction units predicted through the motion estimation unit, the motion compensator, 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 correcting unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion caused by the boundary between blocks in the 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 can be applied according to the required deblocking filtering strength. In addition, in applying the deblocking filter, horizontal filtering and vertical filtering may be concurrently processed when vertical filtering and horizontal filtering are performed.

The offset correcting unit may correct an offset from the original image in units of pixels with respect to the image on which the deblocking has been performed. In order to perform offset correction on a specific picture, a method of dividing pixels included in an image into a certain number of regions, determining the region to be offset and applying the offset to the region, or taking edge information of each pixel into account can be used to apply

Adaptive loop filtering (ALF) may be performed based on a value obtained by comparing the filtered reconstructed image and the original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the corresponding group is determined, and filtering can be performed differentially for each group. As for information related to whether to apply ALF, the luminance signal may be transmitted for each coding unit (CU), and the shape and filter coefficients of the ALF filter to be applied may vary according to each block. In addition, the ALF filter of the same type (fixed type) may be applied regardless of the characteristics of the block to be applied.

The memory 155 may store the 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 apparatus according to an embodiment of the present invention.

Referring to FIG. 2 , the decoding apparatus 200 includes an entropy decoding unit 210 , a reordering 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 of the constituent units shown in FIG. 2 is independently illustrated to represent different characteristic functions in the decoding apparatus, which may mean that each constituent unit is made of separate hardware. However, each component is listed as each component for convenience of description, and at least two components of each component are combined to form one component, or one component can be divided into a plurality of components to perform a function, such as Integrated embodiments and separate embodiments of each component are also included in the scope of the present invention without departing 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 apparatus.

The reordering unit 215 may reorder the bitstream entropy decoded by the entropy decoding unit 210 . Coefficients expressed in the form of a one-dimensional vector may be restored and rearranged as coefficients in the form of a two-dimensional block. The reordering unit 215 may receive information related to coefficient scanning performed by the encoding apparatus, and may perform rearrangement by performing a reverse scanning method based on the scanning order performed by the encoding apparatus.

The inverse quantization unit 220 may perform inverse quantization based on the quantization parameter and the reordered coefficient values of the blocks.

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

The prediction units 230 and 235 may generate a prediction block based on the prediction block generation related information 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 determiner, an inter prediction unit, and an intra prediction unit. The prediction unit determining unit receives various information such as prediction unit information input from the entropy decoder 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 whether the prediction unit performs inter prediction or intra prediction may be determined. The inter prediction unit 230 uses information necessary for inter prediction of the current prediction unit provided from the encoding apparatus, and based on information included in at least one of a picture 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 on a pre-restored partial region in the current picture including the current prediction unit.

In order to perform inter prediction, based on a coding unit, whether a method of predicting motion of a prediction unit included in a corresponding coding unit is one of a skip mode, a merge mode, and an AMVP mode can be judged

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 on which intra prediction is performed, intra prediction may be performed based on intra prediction mode information of the prediction unit provided by the encoding apparatus. The intra prediction unit 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 the reference pixel 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 the reference pixel of the current block by using the prediction mode and AIS filter information of the prediction unit provided by the encoding apparatus. When the prediction mode of the current block is a mode in which AIS filtering is not performed, the AIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction unit in which intra prediction is performed 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 of a pixel unit having an integer value or less. When the prediction mode of the current prediction unit is a prediction mode that generates a prediction block without interpolating the reference pixel, the reference pixel 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 correcting unit, and an ALF.

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

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

ALF may be applied to a coding unit based on information on whether ALF is applied, ALF coefficient information, etc. provided from the encoder. Such ALF information may be provided by being included in a specific parameter set.

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

3 illustrates a block division type 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 and a horizontal line. The vertical line and the horizontal line 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, and the like, and will be described in detail below with reference to FIG. 3 .

Figure 3 (a) shows a 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 QTs, the first block may be divided into four second blocks having a size of NxN. QT may be limited to be applied only to square blocks, but it is also possible to apply to non-square blocks.

FIG. 3(b) shows the division of a horizontal binary tree (hereinafter referred to as Horizontal BT). Horizontal BT is a division type in which a first block is divided into two second blocks by one horizontal line. The dichotomy may be performed symmetrically or asymmetrically. For example, when a first block of 2Nx2N is divided into Horizontal BT, 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.

FIG. 3( c ) illustrates partitioning of a vertical binary tree (hereinafter, referred to as Vertical BT). Vertical BT is a division type in which a first block is divided into two second blocks by one vertical line. The dichotomy may be performed symmetrically or asymmetrically. For example, when a first block of 2Nx2N is divided into vertical BT, 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 ) is a diagram illustrating a horizontal triple tree (hereinafter referred to as Horizontal TT) partitioning. Horizontal TT is a division type in which a first block is divided into three second blocks by two horizontal lines. For example, when the first block of 2Nx2N is divided by Horizontal TT, 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 greater than or less than a.

FIG. 3(e) illustrates a 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 the first block of 2Nx2N is divided by vertical TT, 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 greater than or less than a. Alternatively, a and b may be the same, and c may be greater than or less than a. Alternatively, b and c may be the same, and a may be greater than or less than b.

The above-described division may be performed based on division information signaled from the encoding apparatus. The division information may include at least one of division type information, division direction information, and division ratio information.

The partition type information may specify any one of partition types pre-defined in the encoding/decoding apparatus. The pre-defined splitting 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, which may be encoded in the form of a flag or an index. The division direction information may indicate whether the division is divided in a horizontal direction or a vertical direction in the case of BT or TT. The division ratio information may indicate a ratio of a width and/or a height of the second block in the case of BT or TT.

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 illustrated 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 partition information of the first block indicates QT partitioning, the first block may be divided into four sub-blocks (hereinafter, referred to as a second block). The second block may have a size of 4Nx4N and may have a division depth of (k+1).

The four second blocks may be divided again based on any one of QT, BT, TT, or non-split mode. For example, when the partition 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 ) as in the second block 410 of FIG. 4 . It can be divided into blocks). In this case, the third block may have a size of 4Nx2N and may have a division depth of (k+2).

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

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

The upper block may mean a block having a division depth smaller than a division 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 division depth as the current block.

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

5 illustrates a method of reconstructing a residual sample according to 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 on the presence or absence of a non-zero residual coefficient and an absolute value (abs) or 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 or m rows from the top of the residual block. The n and m may be predetermined values to 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 (here, n=32, m=0) from the left side of the residual block may be defined as a high frequency region. When the residual block is 32x64, a region excluding 32 rows (here, n=0, m=32) from the upper end of the residual block may be defined as a high-frequency region. Alternatively, n and m may be derived based on encoded information 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 and 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. The size of the residual block may be expressed by at least one of a width and 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 value pre-promised to the encoding/decoding apparatus, or may be encoded and signaled by the encoding apparatus. 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 derived from the decoding apparatus based on the size/shape of the residual block, or may be encoded and signaled by the encoding apparatus. However, the above process may be limited to be performed only when the residual block is not encoded 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 predicted value (QPpred) and a quantization parameter difference value (deltaQP). In other words, the quantization parameter may be set as the quantization parameter predicted value QPpred, or may be derived by adding the quantization parameter difference deltaQP to the quantization parameter predicted value QPpred.

As an example, merge mode, skip mode, non-transform mode, PCM mode, when non-zero coefficients do not exist (ie, coded block flag=0), etc. Similarly, when inverse quantization is unnecessary for a corresponding block, the quantization parameter differential value deltaQP may not be encoded. In this case, the quantization parameter predicted value QPpred may be set as the quantization parameter.

A method of deriving the quantization parameter predicted 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 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 apparatus, or may be encoded and signaled by the encoding apparatus. The quantization parameter offset (QPoffset) may be signaled at at least one level of a video sequence, a picture, a slice, a tile, or a block. A unit in which the quantization parameter offset is signaled may be larger than a unit in which a quantization parameter difference value is signaled. The value and number of the quantization parameter offset (QPoffset) may be adaptively determined according to block size/form, number of divisions, prediction mode, intra prediction mode, component type (e.g., luminance, chrominance), 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 at least one of a picture level, a slice level, and a block level. The quantization parameter offset may be defined for each of the intra mode and the inter mode, or may be defined for each of the luminance component and the chrominance component. Alternatively, a separate offset for the LM mode among the intra prediction modes may be defined. Here, the LM mode may mean a mode in which the chrominance block is predicted using prediction/reconstruction samples of the 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 value pre-promised to the encoding/decoding apparatus, or may be encoded and signaled by the encoding apparatus. 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 values may be defined as different values, 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 result 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 apparatus (method A). In this case, the quantization weight may be one and 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 apparatus (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, and a prediction mode. Alternatively, the encoding apparatus may determine the quantization weight for each position of the residual coefficient and encode the quantization weight. The decoding apparatus may decode the encoded information on the quantization weight to derive the quantization weight (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 partition type, a prediction mode, a component type, a transform type, and predetermined flag information. The flag information may include a flag regarding whether to apply a quantization weight or not, a flag regarding whether to skip transform, and the like.

In the aforementioned 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 with reference 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 transform candidate set may include n transform 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 transform candidate sets may be defined. The m may be 1, 2, 3 or more. The number and/or type of transform types belonging to any one of the m transform candidate sets (hereinafter, referred to as a first transform candidate set) may be different from the other one (hereinafter, referred to as a second transform candidate set). For example, the first transform candidate set may include p transform types, and the second transform candidate set may include q transform 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 included in the first transform candidate set may be different from a transform type included in the second transform candidate set.

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

The 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 less than or equal to the threshold, the first transform candidate set composed of p transform types is selected, otherwise, the second transform candidate set composed of q transform types is selected. can The threshold may be 32, 64, 128, 256 or more, and p may be a value greater than q.

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

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

Meanwhile, the inverse transform may be selectively performed based on a predetermined flag. Here, the flag may indicate whether the inverse transform is skipped for the residual block. For example, when the flag is 1, inverse transform may not be performed on the residual block, and when the flag is 0, inverse transform may be performed on the residual block. Accordingly, 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 the attribute 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 partition 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 a first inverse transform), an additional inverse transform (hereinafter, referred to as a 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 predicted value (QPpred) according to an embodiment to which the present invention is applied.

Referring to FIG. 6 , a quantization parameter predicted value (QPpred) for a block T may be derived based on a quantization parameter of a neighboring block. The block T is a block of size NxM, and may be square or non-square.

The neighboring block is a block 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 the 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 different picture from the block T, and may be defined as a block including a position of at least one of an upper-left corner sample, a lower-right corner sample, or a center sample of the block T.

The position of the neighboring block may be a position pre-promised to the encoding/decoding apparatus. 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, the present invention is not limited thereto, and may further include a lower left block, an upper right block, and the like. The position of the neighboring block may be variably determined based on attributes (eg, size, shape, division depth, division type, component type, etc.) of the block T or at least one of the neighboring 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 length of an adjacent boundary. This may be performed for the upper block and the left block of block T, respectively.

Alternatively, information specifying the position of the neighboring block may be encoded and signaled by the encoding apparatus. The information may be encoded in the form of a flag, an index, or the like. For example, when the information is index 0, the quantization parameter predicted value (QPpred) of the block T may be derived using the quantization parameter of the left block. When the information is index 1, the quantization parameter predicted value (QPpred) of the block T may be derived using the quantization parameter of the upper block.

The number of the neighboring blocks is n, where n may be 1, 2, 3, 4 or more natural numbers. The number may be a fixed value pre-promised in the encoding/decoding device. Alternatively, the number may be variably determined based on attributes (e.g., size, shape, division depth, division type, component type, etc.) of at least one of the block T or neighboring blocks. Alternatively, information on the maximum number of neighboring blocks used to derive the quantization parameter predicted value (QPpred) of the block T may be encoded and signaled by the encoding apparatus. 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 of a video sequence, a picture, and other fragment regions (e.g., slice, tile, Coding Tree Block row, block).

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

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

Alternatively, the quantization parameter predicted 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 there are a plurality of upper block or left block, the QP of the upper block or left block may be determined through a calculation process such as a median value, an average value, a minimum value, a maximum value, or a mode value.

When an unavailable block exists among the neighboring blocks, the predicted 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 region. The fragment area may mean a slice, a tile, a Coding Tree Block row, a block, and the like. The fragment region may mean a region encoded/decoded before the block T, or may mean a region to which a block T, which is 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 according to a rule of an encoding/decoding apparatus. For example, when the block T and the neighboring block belong to different parallel processing regions (e.g., slice, tile, etc.), the block T may not be allowed to refer to the neighboring block.

7 is a diagram illustrating a method of deriving a quantization parameter predicted value for a chrominance 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 4:2:0 color format, the chrominance block Tc may correspond to the luminance block TY. A quantization parameter predicted value of a chrominance block may be derived using a quantization parameter of a 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 quantization parameter predicted value of the chrominance block may be derived using any one quantization parameter among a plurality of luminance blocks. In this case, a luminance block corresponding to the position of the center sample or the upper left sample of the chrominance 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 through calculation of the average value, the median value, the minimum value, the maximum value, the mode value, etc. of the quantization parameters of the 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 described in detail with reference to FIG. 6 , so a detailed description thereof will be omitted.

As described above, the predicted value of the quantization parameter of the chrominance block is derived using both the method using the quantization parameter of the corresponding luminance block (the first method) and the method using the quantization parameter of the neighboring block of the chrominance block (the second method) can be Alternatively, the quantization parameter predicted value of the chrominance 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 structure of the luminance block and the chrominance block is the same, the prediction mode of the block T, the intra prediction mode, the color format, or the size/shape. For example, when the block T is encoded in the inter mode and the partition 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, if the division structure of the chrominance block is the same as that of the luminance block, the first method may be used, otherwise the second method may be used. 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 by an encoding apparatus. The information may be signaled at at least one level of a video sequence, a picture, and other fragment regions (e.g., slice, tile, Coding Tree Block row, block).

The quantization parameter of the chrominance block may be derived to be the same as the derived quantization parameter predicted value of the chrominance block, or may be derived by adding a predetermined quantization parameter difference. In addition, 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 color difference block encoded in the LM mode, a quantization parameter predicted value may be set as a quantization parameter. In this case, the quantization parameter difference value is not signaled, or the process of adding the signaled quantization parameter difference value may be omitted. Alternatively, in the case of a color difference 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 according to an embodiment to which the present invention is applied.

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

FIG. 8(a) illustrates a case where the size of the current block is 2Mx2N and the minimum size is MxN. As shown in FIG. 8A , when the size of the current block is greater than the minimum size, the quantization parameter of the current block may 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-d belonging to the current block, respectively, and blocks a-d may have different quantization parameters.

On the other hand, when the size of the current block and the minimum size are the same, it goes without saying that it can be derived using deltaQP signaled with the QPpred.

FIG. 8(b) illustrates a case where the minimum size is MxN and the current blocks a-d are smaller than the minimum size. As shown in FIG. 8B , 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 the signaled deltaQP.

The QPpred may be derived based on at least one of the first method and the second method described above with respect to the current block. For example, QPpred may be derived for each block a-d. Alternatively, QPpred may be derived for block a, and the remaining blocks b-d may share QPpred derived from block a. Alternatively, the QPpred may be derived based on at least one of the first method or the second method with reference to an upper block of the current block. Here, the upper block is a block including the current block, and may be a block having a division depth smaller than that of the current block. For example, when the division depth of the current block is k, the division depth of the upper block may be (k-1), (k-2), or 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 apparatus may determine a unit of a block sharing the QPpred and encode information specifying the unit of the block. The decoding apparatus may specify the position, size, shape, etc. of the upper block based on the encoded information.

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

On the other hand, when a specific block is a block adjacent to a boundary of a picture, a slice, or a 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 for deltaQP may be omitted.

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

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

The second inverse transform may be applied to the entire region of the residual block or may be applied only to a partial region in the residual block. The partial region may mean a low-frequency region in the residual block. A region to which the second inverse transform is applied may be variably determined in consideration of at least one of a size/shape of a residual block and a size/shape of a 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, the second inverse transform having a transform matrix of 8×8 may be applied. When the size of the residual block is 8x8, the second inverse transform is applied to the entire area of the residual block, and when the size of the residual block is 16x16, the second inverse transform can be applied only to a partial area of the residual block. The partial region may mean an area excluding the 8x8 region located at the upper left of the residual block, the 16x8 region located at the upper end of the residual block, the 8x16 region located on the left of the residual block, or the 8x8 region located at the lower right of the residual block. .

Alternatively, when either the width or the height of the residual block is 4, the second inverse transform having a 4x4 transform 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 transform matrix of the second inverse transform may be 4x4, 8x8, 16x16, 32x32, or more. The shape of the transformation matrix is not limited to a square, and may be implemented in a non-square shape. However, in order to reduce the complexity of the transformation, the size of the transformation matrix allowed for the second inverse transformation may be limited to NxM or less. Each of N and M may be 4, 8, or 16, 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 with reference to FIG. 5 . Alternatively, the transform type in the second inverse transform may be a pre-promised one to the encoding/decoding apparatus. For example, as a transform type in the second inverse transform, any 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 on 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 signaled separately. When the second flag is 1, a second inverse transform is not performed, and when the flag is 0, a second inverse transform may be performed. The first flag and the second flag may be encoded and signaled independently of each other. Alternatively, any one of the first flag and the second flag may be signaled dependently on the other. For example, only when either one of the first flag and the second flag is 1, the other may be signaled. Conversely, only when either one of the first flag and the second flag is 0, the other may be signaled.

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

Meanwhile, although FIG. 9 shows that the second inverse transform is performed before the first inverse transform, the order of performing the inverse transform is not limited. That is, the second inverse transform may be performed before the first inverse transform or may be performed 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 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 the inverse quantization and the first inverse transform, or between the first inverse transform and the second inverse transform.

Example methods of the present disclosure are expressed as a series of operations for clarity of description, but this is not intended to limit the order in which the steps are performed, and if necessary, each step may be performed simultaneously or in a different order. In order to implement the method according to the present disclosure, other steps may be included in addition to the illustrated steps, steps may be excluded from some steps, and/or other steps may be included except for some steps.

Various embodiments of the present disclosure do not list all possible combinations but are intended to describe representative aspects of the present disclosure, 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 implementation by hardware, 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), general purpose It may be implemented by a processor (general processor), a controller, a microcontroller, a microprocessor, and the like.

The scope of the present disclosure includes software or machine-executable instructions (eg, operating system, application, firmware, program, etc.) that cause an operation according to the method of various embodiments to be executed on a device or computer, and such software or and non-transitory computer-readable media in which instructions and the like are stored and executable on a device or computer.

Claims (13)

decoding the residual coefficients of the current block from the bitstream;
performing inverse quantization on the residual coefficients using a quantization parameter;
performing an inverse transform on the inverse quantized residual coefficient to reconstruct a residual sample of the current block,
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. According to claim 1,
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. 3. The method of claim 2,
When the size of the current block is less than or equal to a threshold value, the transformation candidate set of the current block is determined as the first transformation candidate set among the plurality of transformation 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. 4. The method of claim 3,
The threshold value is any one of 32, 64 or 128, the video decoding method. 5. The method of claim 4,
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. 6. The method of claim 5,
The first transformation candidate set includes DCT-8 and DST-7,
The second transform candidate set includes DCT-2, DCT-8, and DST-7. According to claim 1,
The transform candidate set of the current block is determined as one of the plurality of transform candidate sets based on first information signaled from the bitstream. 8. The method of claim 7,
The number of transform types included in the first transform candidate set is the same as the number of transform types included in the second transform candidate set. 9. The method of claim 8,
any one of transform types included in the first transform candidate set is different from transform types included in the second transform candidate set;
Another one of transform types included in the first transform candidate set is the same as any one of transform types included in the second transform candidate set. 10. The method of claim 9,
The first transformation candidate set includes DCT-2 and DST-7,
The second transform candidate set includes DCT-8 and DST-7. 11. The method of claim 10,
A video decoding method, wherein a transform type for the inverse transform of the current block is determined from transform types of a transform candidate set of the current block based on the second information signaled from the bitstream. performing transformation on the residual samples of the current block to obtain residual coefficients of the current block;
performing quantization on the residual coefficients using a quantization parameter;
encoding the quantized residual coefficients of the current block;
The 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 transform of the current block. A computer-readable recording medium storing a bitstream, comprising:
The bitstream includes residual coefficients generated by encoding residual samples of the current block,
The residual sample of the current block is decoded from the bitstream by performing at least one of inverse quantization and inverse transform on the residual coefficient,
The inverse quantization is performed based on a quantization parameter,
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.

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