KR20220066242A - Method and apparatus for image encoding/decoding - Google Patents

Abstract

Disclosed are a method and device for encoding/decoding an image. The method for decoding an image comprises the steps of: deriving a scale factor for the current block according to whether the current block is a transform skip block; and scaling the current block based on the scale factor. The scale factor for the current block is derived based on a position of the transform coefficient in the current block. The transform skip block is a block to which transform is not applied to the current block. The transform skip block is specified based on information indicating whether to apply inverse transform to the current block.

Description

Image encoding/decoding method and apparatus

The present invention relates to encoding/decoding of an image, and more particularly, to a method and apparatus for scaling a transform coefficient.

Recently, a broadcasting service having a high definition (HD) resolution (1280x1024 or 1920x1080) is expanding not only in Korea but also worldwide. Accordingly, many users are accustomed to high-resolution and high-definition images, and many institutions are spurring the development of next-generation imaging devices to keep pace with it. Also, along with HDTV, as interest in Ultra High Definition (UHD), which has a resolution four times higher than that of HDTV, increases, video standardization organizations recognize the need for compression technology for higher resolution and high-definition images. In addition, there is an urgent need for a new standard that can obtain many benefits in terms of frequency band or storage while maintaining the same image quality through higher compression efficiency than H.264/AVC currently used in HDTVs, mobile phones, and Blu-ray players.

Currently, MPEG (Moving Picture Experts Group) and VCEG (Video Coding Experts Group) are jointly standardizing HEVC (High Efficiency Video Coding), which is a next-generation video codec. It aims to encode with compression efficiency. This can provide not only HD and UHD images, but also 3D broadcasting and high-definition images at lower frequencies than the present in mobile communication networks.

The present invention provides an image encoding/decoding method and apparatus capable of improving encoding/decoding efficiency.

The present invention provides a method and apparatus for scaling a transform coefficient (or a residual signal) capable of improving encoding/decoding efficiency.

The present invention provides a quantization/inverse quantization method and apparatus for a transform skip block capable of improving encoding/decoding efficiency.

According to one aspect of the present invention, an image decoding method is provided. The image decoding method includes deriving a scale factor for the current block according to whether the current block is a transform skip block, and performing scaling on the current block based on the scale factor.

The scale factor for the current block is derived based on a position of a transform coefficient in the current block, and the transform skip block is a block to which a transform is not applied to the current block, and an inverse transform is applied to the current block. It is specified based on information indicating whether or not to do so.

In the step of deriving the scale factor for the current block, when the current block is a transform skip block, a basic scale factor may be derived regardless of a position of a transform coefficient in the current block.

The basic scale factor may have a predetermined scale factor value, and the predetermined scale factor value may be 16.

The basic scale factor may have a different scale factor value depending on whether the current block uses a quantization matrix.

The basic scale factor may have a different scale factor value depending on whether the current block is a luminance block or a chrominance block.

A flag indicating whether a transform skip algorithm is used for the picture including the current block may be signaled through a picture parameter set (PPS).

The basic scale factor may include scale factor information for a luminance signal and a chrominance signal.

In the step of deriving the scale factor for the current block, when the current block is a transform skip block or the current block does not use a quantization matrix, a basic scale factor is derived regardless of the position of the transform coefficient in the current block can do.

In the step of deriving the scale factor for the current block, if the current block is not a transform skip block, the scale factor for the current block is derived using a quantization matrix based on the position of the transform coefficient in the current block. can

According to another aspect of the present invention, an image decoding apparatus is provided. The image decoding apparatus includes an inverse quantizer that derives a scale factor for the current block according to whether the current block is a transform skip block, and performs scaling on the current block based on the scale factor.

The scale factor for the current block is derived based on a position of a transform coefficient in the current block, and the transform skip block is a block to which a transform is not applied to the current block, and a transform is applied to the current block. It may be specified based on information indicating whether or not to do so.

According to another aspect of the present invention, an image encoding method is provided. The image encoding method includes deriving a scale factor for the current block according to whether the current block is a transform skip block, and performing scaling on the current block based on the scale factor.

The scale factor for the current block is derived based on a position of a transform coefficient in the current block, and the transform skip block is a block to which a transform is not applied to the current block, and a transform is applied to the current block. It may be specified based on information indicating whether or not to do so.

In the step of deriving the scale factor for the current block, when the current block is a transform skip block, a basic scale factor may be derived regardless of a position of a transform coefficient in the current block.

The basic scale factor may have a predetermined scale factor value, and the predetermined scale factor value may be 16.

The basic scale factor may have a different scale factor value depending on whether the current block uses a quantization matrix.

The basic scale factor may have a different scale factor value depending on whether the current block is a luminance block or a chrominance block.

A flag indicating whether a transform skip algorithm is used for the picture including the current block may be signaled through a picture parameter set (PPS).

The basic scale factor may include scale factor information for a luminance signal and a chrominance signal.

In the step of deriving the scale factor for the current block, when the current block is a transform skip block or the current block does not use a quantization matrix, a basic scale factor is derived regardless of the position of the transform coefficient in the current block can do.

In the step of deriving the scale factor for the current block, if the current block is not a transform skip block, the scale factor for the current block is derived using a quantization matrix based on the position of the transform coefficient in the current block. can

According to another aspect of the present invention, an image encoding apparatus is provided. The image encoding apparatus includes a quantizer that derives a scale factor for the current block according to whether the current block is a transform skip block, and performs scaling on the current block based on the scale factor.

The scale factor for the current block is derived based on a position of a transform coefficient in the current block, and the transform skip block is a block to which a transform is not applied to the current block, and a transform is applied to the current block. It may be specified based on information indicating whether or not to do so.

Since the block to which the transform skip algorithm is applied does not perform the transform/inverse transform process, it has different transform coefficient characteristics from the block to which the existing transform/inverse transform process is performed. That is, when the scaling method applied to the block on which the existing transform/inverse transform process is performed is applied to the transform skip block as it is, the encoding/decoding efficiency can be reduced. Accordingly, encoding and decoding efficiency can be increased by applying the same scale factor to the transform skip block regardless of the position of the transform coefficient in the block.

1 is a block diagram illustrating a configuration of an image encoding apparatus to which the present invention is applied according to an embodiment.
2 is a block diagram illustrating a configuration of an image decoding apparatus to which the present invention is applied according to an embodiment.
3 is a diagram schematically illustrating a split structure of an image when an image is encoded.
4 is a diagram illustrating a form of a prediction unit (PU) that a coding unit (CU) may include.
5 is a diagram illustrating a form of a transform unit (TU) that a coding unit (CU) may include.
6 is a flowchart illustrating a scaling method for a residual signal (or a transform coefficient) according to an embodiment of the present invention.
7 is a flowchart illustrating a scaling method for a residual signal (or transform coefficient) according to another embodiment of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described concretely with reference to drawings. In describing the embodiments of the present specification, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present specification, the corresponding description may be omitted.

In this specification, when it is mentioned that a component is connected to or connected to another component, it may mean that it is directly connected or connected to the other component, and another component is present in the middle. could mean that In addition, the content described as including a specific configuration in the present specification does not exclude configurations other than the corresponding configuration, it means that an additional configuration may be included in the practice of the present invention or the scope of the technical spirit of the present invention.

Terms such as first, second, etc. may be used to describe various components, but the components are not limited by the terms. The terms are used for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first configuration may be named as a second configuration, and similarly, a second configuration may also be called a first configuration.

In addition, the components shown in the embodiment of the present invention are shown independently to represent different characteristic functions, and it does not mean that each component is formed of separate hardware or a single software component. That is, each component is listed as each component for convenience of description, and at least two components among each component may form one component, or one component may be divided into a plurality of components to perform a function. 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.

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.

First, for convenience of description and understanding of the present invention, terms used herein will be briefly described.

* A unit means a unit of video encoding and decoding. In other words, when encoding/decoding an image, the encoding or decoding unit refers to the divided unit when encoding or decoding an image by dividing one image into subdivided units. Block, Macro Block (MB), Coding Unit (CU), Prediction Unit (PU), Transform Unit (TU), Coding Block (CB), It may be referred to as a prediction block (PB), a transform block (TB), or the like. One unit may be divided into smaller sub-units.

A block is an MxN array of samples, and M and N have positive integer values. A block may refer to an array in a two-dimensional form.

A transform unit (TU) is a basic unit when encoding/decoding a residual signal such as transform, inverse transform, quantization, inverse quantization, and transform coefficient encoding/decoding is performed, and one transform unit is divided Thus, it can be divided into a plurality of small conversion units. In this case, if the residual signal exists in the form of a block, it may be referred to as a residual block.

A quantization matrix refers to a matrix used in a quantization or inverse quantization process to improve subjective or objective image quality of an image. The quantization matrix is also called a scaling list.

The quantization matrix may be divided into a default matrix, a non-default matrix, and a flat matrix. The basic matrix may mean a predetermined quantization matrix predefined in the encoder and the decoder. The non-basic matrix may mean a quantization matrix transmitted/received by a user that is not predefined in the encoder and the decoder. A planar matrix may mean a matrix in which all elements in the matrix have the same value.

Scaling refers to a process of multiplying a transform coefficient level by a factor, and a transform coefficient is generated as a result. Scaling is also called dequantization.

A transform coefficient refers to a coefficient value generated after transformation is performed. In the present specification, a quantized transform coefficient level obtained by applying quantization to a transform coefficient is also commonly referred to as a transform coefficient.

A quantization parameter refers to a value used when scaling a transform coefficient level in quantization and inverse quantization. In this case, the quantization parameter may be a value mapped to a quantization step size.

A parameter set corresponds to header information in a structure in a bitstream, and collectively refers to a sequence parameter set, a picture parameter set, an adaptation parameter set, and the like. have

1 is a block diagram illustrating a configuration of an image encoding apparatus to which the present invention is applied according to an embodiment.

Referring to FIG. 1 , the image encoding apparatus 100 includes a motion prediction unit 111 , a motion compensation unit 112 , an intra prediction unit 120 , a switch 115 , a subtractor 125 , a transform unit 130 , It includes a quantizer 140 , an entropy encoder 150 , an inverse quantizer 160 , an inverse transform unit 170 , an adder 175 , a filter unit 180 , and a reference image buffer 190 .

The image encoding apparatus 100 may encode an input image in an intra mode or an inter mode and output a bitstream. In the intra mode, the switch 115 may be switched to the intra mode, and in the inter mode, the switch 115 may be switched to the inter mode. Intra prediction refers to intra prediction, and inter prediction refers to inter prediction. The image encoding apparatus 100 may generate a prediction block for an input block of an input image, and then encode a residual between the input block and the prediction block. In this case, the input image may mean an original picture.

In the intra mode, the intra prediction unit 120 may generate a prediction block by performing spatial prediction using pixel values of an already encoded/decoded block around the current block.

In the inter mode, the motion prediction unit 111 may obtain a motion vector by finding a region that best matches the input block in the reference image stored in the reference picture buffer 190 during the motion prediction process. The motion compensator 112 may generate a prediction block by performing motion compensation using a motion vector. Here, the motion vector is a two-dimensional vector used for inter prediction, and may indicate an offset between a current encoding/decoding target image and a reference image.

The subtractor 125 may generate a residual block by the difference between the input block and the generated prediction block.

The transform unit 130 may perform transform on the residual block to output a transform coefficient. In addition, the quantization unit 140 may quantize the input transform coefficient according to a quantization parameter (or quantization parameter) to output a quantized coefficient.

The entropy encoding unit 150 may output a bit stream by performing entropy encoding based on the values calculated by the quantization unit 140 or encoding parameter values calculated during the encoding process. When entropy encoding is applied, a small number of bits are allocated to a symbol having a high probability of occurrence and a large number of bits are allocated to a symbol having a low probability of occurrence to express the symbol, so that bits for symbols to be encoded The size of the column may be reduced. Accordingly, compression performance of image encoding may be improved through entropy encoding. The entropy encoder 150 may use an encoding method such as Exponential-Golomb, Context-Adaptive Variable Length Coding (CAVLC), or Context-Adaptive Binary Arithmetic Coding (CABAC) for entropy encoding.

Since the image encoding apparatus 100 according to the embodiment of FIG. 1 performs inter prediction encoding, that is, inter prediction encoding, the currently encoded image needs to be decoded and stored to be used as a reference image. Accordingly, the quantized coefficients are inverse quantized by the inverse quantization unit 160 and inversely transformed by the inverse transformation unit 170 . The inverse-quantized and inverse-transformed coefficients are added to the prediction block through an adder 175 to generate a reconstructed block.

The reconstructed block passes through the filter unit 180, and the filter unit 180 applies at least one of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF) to the reconstructed block or the reconstructed picture. can do. The filter unit 180 may be referred to as an adaptive in-loop filter. The deblocking filter can remove block distortion caused at the boundary between blocks. The SAO may add an appropriate offset value to a pixel value to compensate for a coding error. The ALF may perform filtering based on a value obtained by comparing the reconstructed image and the original image. The reconstructed block that has passed through the filter unit 180 may be stored in the reference picture buffer 190 .

2 is a block diagram illustrating a configuration of an image decoding apparatus to which the present invention is applied according to an embodiment.

Referring to FIG. 2 , the image decoding apparatus 200 includes an entropy decoding unit 210 , an inverse quantization unit 220 , an inverse transform unit 230 , an intra prediction unit 240 , a motion compensator 250 , and an adder 255 . ), a filter unit 260 and a reference picture buffer 270 .

The image decoding apparatus 200 may receive a bitstream output from the encoder, perform decoding in an intra mode or an inter mode, and output a reconstructed image, that is, a reconstructed image. In the case of the intra mode, the switch may be switched to the intra mode, and in the case of the inter mode, the switch may be switched to the inter mode.

The image decoding apparatus 200 obtains a reconstructed residual block from the received bitstream, generates a prediction block, and then adds the reconstructed residual block and the prediction block to generate a reconstructed block, that is, a reconstructed block. .

The entropy decoding unit 210 may entropy-decode the input bitstream according to a probability distribution to generate symbols including symbols in the form of quantized coefficients.

When the entropy decoding method is applied, a small number of bits are allocated to a symbol having a high occurrence probability and a large number of bits are allocated to a symbol having a low occurrence probability to represent the symbol, so that the size of the bit stream for each symbol is can be reduced.

The quantized coefficient is inverse quantized by the inverse quantization unit 220 and inversely transformed by the inverse transformation unit 230 , and as a result of inverse quantization/inverse transformation of the quantized coefficient, a reconstructed residual block may be generated.

In the intra mode, the intra prediction unit 240 may generate a prediction block by performing spatial prediction using pixel values of an already decoded block around the current block. In the inter mode, the motion compensator 250 may generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference picture buffer 270 .

The residual block and the prediction block may be added through the adder 255 , and the added block may pass through the filter unit 260 . The filter unit 260 may apply at least one of a deblocking filter, SAO, and ALF to a reconstructed block or a reconstructed picture. The filter unit 260 may output a reconstructed image, that is, a reconstructed image. The reconstructed image may be stored in the reference picture buffer 270 and used for inter prediction.

3 is a diagram schematically illustrating a split structure of an image when an image is encoded.

In High Efficiency Video Coding (HEVC), encoding is performed using a coding unit (CU) to efficiently segment an image.

Referring to FIG. 3 , in HEVC, an image 300 is sequentially partitioned in units of Largest Coding Units (LCUs) (hereinafter referred to as LCUs), and then a division structure is determined in units of LCUs. The division structure means a distribution of coding units (hereinafter, referred to as CUs) for efficiently encoding an image in the LCU 310 , and this distribution divides one CU by half of its horizontal and vertical sizes. It may be determined according to whether to split into CUs. A divided CU may be recursively divided into four CUs whose horizontal size and vertical size are reduced by half with respect to the divided CU in the same manner.

In this case, the division of the CU may be recursively divided up to a predefined depth. Depth information is information indicating the size of a CU, and is stored for each CU. For example, the depth of the LCU may be 0, and the depth of the Smallest Coding Unit (SCU) may be a predefined maximum depth. Here, the LCU is a coding unit having the largest coding unit size as described above, and the Smallest Coding Unit (SCU) is a coding unit having the smallest coding unit size.

The depth of the CU increases by 1 whenever division is performed from the LCU 310 to half of the horizontal and vertical sizes. For each depth, a CU that does not perform division has a size of 2Nx2N, and a CU that performs division is divided into four CUs having a size of NxN from a CU of 2Nx2N size. The size of N is halved for each increase in depth by 1.

Referring to FIG. 3 , the size of an LCU having a minimum depth of 0 may be 64x64 pixels, and a size of an SCU having a maximum depth of 3 may be 8x8 pixels. In this case, a CU (LCU) of 64x64 pixels may be expressed as depth 0, a CU of 32x32 pixels as depth 1, a CU of 16x16 pixels as depth 2, and a CU (SCU) of 8x8 pixels as depth 3 may be expressed.

In addition, information on whether to split a specific CU may be expressed through 1-bit partition information for each CU. This partition information may be included in all CUs except for the SCU. For example, when a CU is not divided, 0 may be stored in the partition information, and 1 may be stored in the partition information when a CU is divided.

On the other hand, the CU divided from the LCU is composed of a prediction unit (PU or Prediction Block; PB), which is a basic unit for prediction, and a transform unit (Transform Unit; TU or Transform Block; TB), which is a basic unit for transformation. can

4 is a diagram illustrating a form of a prediction unit (PU) that a coding unit (CU) may include.

A CU that is no longer split among CUs split from an LCU is split into one or more prediction units, and this action itself is also referred to as a partition (or partition). A prediction unit (hereinafter, referred to as PU) is a basic unit for performing prediction and is encoded in any one of a skip mode, an inter mode, and an intra mode, and is partitioned into various forms according to each mode. can

Referring to FIG. 4 , in the case of the skip mode, the 2Nx2N mode 410 having the same size as the CU may be supported without a partition within the CU.

In the case of inter mode, there are 8 partitioned types within a CU, for example, 2Nx2N mode 410, 2NxN mode 415, Nx2N mode 420, NxN mode 425, 2NxnU mode 430, 2NxnD mode 435 ), nLx2N mode 440 , and nRx2N mode 445 may be supported.

In the case of the intra mode, the 2Nx2N mode 410 and the NxN mode 425 may be supported within the CU.

5 is a diagram illustrating a form of a transform unit (TU) that a coding unit (CU) may include.

A transform unit (hereinafter, referred to as a TU) is a basic unit used for spatial transform and quantization/inverse quantization (scaling) processes within a CU. A TU may have a square or rectangular shape. A CU that is no longer split among CUs split from an LCU may be split into one or more TUs.

In this case, the partition structure of the TU may be a quad-tree structure. For example, as shown in FIG. 5 , one CU 510 may be divided one or more times according to a quadtree structure and configured as TUs of various sizes.

Meanwhile, in HEVC, like H.264/AVC, intra prediction (hereinafter, intra prediction) encoding may be performed. In this case, the intra prediction mode (or prediction directionality) of the current block may be derived and encoded from the neighboring blocks located in the vicinity of the current block.

As described above, a prediction image for a signal obtained by performing prediction based on the intra prediction mode may have a difference value from the original image. A difference image having a difference value between the predicted image and the original image may be entropy-encoded through frequency domain transformation and quantization. In this case, in order to increase the encoding efficiency of the frequency domain transform, integer transform, integer discrete cosine transform (DCT), integer discrete sine transform (DST), or intra prediction mode-dependent DCT/DST, etc. are block It can be applied selectively and adaptively according to the size.

In addition, in order to increase encoding efficiency in screen contents such as a document image or a presentation image of PowerPoint, a transform skip algorithm may be applied.

When the transform skip algorithm is applied, the encoder directly quantizes a difference image (residual block) having a difference value between the original image and the predicted image without a frequency transformation process and entropy-encoding the residual block. In addition, the decoder generates a reconstructed residual block by entropy-decoding the residual block and performing inverse quantization (scaling). Accordingly, the block to which the transform skip algorithm is applied skips the frequency transform/inverse transform process.

In the quantization/inverse quantization process, a scale factor may be applied differently according to the location of a transform coefficient in a block to improve subjective image quality. On the other hand, when performing quantization/inverse quantization, there is a method in which the scale factor is equally applied regardless of the position of the transform coefficient in the block. Whether this method is applied may be signaled through a sequence parameter set (SPS) or a picture parameter set (PPS) of the bitstream.

As an embodiment of the above process, a scaling process for transform coefficients may be performed as follows.

Scaling process of transform coefficients

The input here is as follows.

- Width of the current transformation block Width; nW

- Height of the current transformation block Height; nH

- an array of transform coefficients with element c _ij ; (nWxnH) array d

- indices for the luminance signal and chrominance signal of the current block; cidx

If cIdx is ‘0’, it means a luminance signal, and if cIdx is ‘1’ or cIdx is ‘2’, it means a color difference signal. Also, if cIdx is ‘1’, it means Cb in the color difference signal, and if cIdx is ‘2’, it means Cr in the color difference signal.

- quantization parameters; qP

The output here is:

- array for scaled transform coefficients; (nWxnH) array d _ij

The variable log2TrSize is derived through log2TrSize = ( Log2( nW ) + Log2( nH ) ) >> 1. Variable shift is derived differently according to cIdx. If cIx is equal to '0' (if luminance signal), it is derived from shift = BitDepth _Y + log2TrSize - 5, otherwise (color difference signal), it is derived from shift = BitDepth _C + log2TrSize - 5 . Here, BitDepth _Y and BitDepth _C mean the number of bits (eg, 8 bits) of a sample for the current image.

The array levelScale[ ] for the scaling variables is as shown in Equation 1 below.

[Equation 1]

The scaled transform coefficient is calculated through the following process.

First, a scale factor m _ij is derived through the following process.

- If scaling_list_enable_flag is '0', m _ij is derived as shown in Equation 2 below.

[Equation 2]

- Otherwise, m _ij is derived as in Equation 3 below.

[Equation 3]

Here, SizeID is derived from Table 1 below according to the size of the transform block, and RefMatrixID and trafoType are derived from Equations 4 and 5, respectively. In addition, in Equation 4, scaling_list_pred_matrix_id_delta is signaled through a sequence parameter set (SPS) or a picture parameter set (PPS) of a bitstream.

[Equation 4]

[Equation 5]

Table 1 is an example showing the SizeID value according to the size of the transform block.

[Table 1]

Next, the scaled transform coefficient d _ij is derived from the following Equation (6).

[Equation 6]

Meanwhile, as described above, a block to which the transform skip algorithm is applied (hereinafter referred to as a transform skip block) does not perform a frequency transform process. Accordingly, the block on which the conventional frequency transform process has been performed and the transform skip block may have different transform coefficient characteristics. That is, when the scaling method applied to the block on which the conventional frequency transform process is performed is applied to the transform skip block as it is, the encoding efficiency can be reduced.

Accordingly, the present invention provides a method of performing scaling in consideration of a case of a transform skip block.

When quantization matrices (basic matrix and non-basic matrix) are used to improve subjective image quality in the encoder and decoder, a scale factor derived from the quantization matrix according to the position of a transform coefficient in a block ) may be applied differently. This method utilizes the characteristic that the energy of the residual block is compressed to the upper left position (low frequency region) of the block during block transformation, and is generally applied to the high frequency region less sensitive to the human eye than the low frequency region sensitive to the human eye. Quantization is performed with a larger quantization step size. Through this method, it is possible to improve subjective image quality in a region sensitive to the human eye during image encoding.

However, when the transform skip is applied, the residual block is not compressed toward the low frequency domain within the block because the frequency domain transform/inverse transform is not performed. In this case, when the quantization/inverse quantization method used in the conventional frequency domain is applied, there is a disadvantage in that the distortion in the image or block becomes severe. Therefore, when a quantization matrix is used in an image, a scaling (quantization/inverse quantization) method capable of minimizing distortion in the image or block is required for a block (transform skip block) that does not perform frequency domain transformation/inverse transformation. For example, there is a method of not applying a quantization matrix to a transform skip block. In this method, the basic scale factor can be equally applied regardless of the position of the transform coefficient in the block.

[Embodiment 1] Method and apparatus for equally applying a scale factor to a transform skip block regardless of a position of a transform coefficient in the block

6 is a flowchart illustrating a scaling method for a residual signal (or a transform coefficient) according to an embodiment of the present invention.

The method of FIG. 6 may be performed by the above-described encoding apparatus of FIG. 1 or the above-described decoding apparatus of FIG. 2 . More specifically, it may be performed in the quantization unit or inverse quantization unit of FIG. 1 or 2 . In the embodiment of FIG. 6 , it is described that the method of FIG. 6 is performed in the encoding apparatus for convenience of description, but this method may be equally applied to the decoding apparatus.

Referring to FIG. 6 , a scale factor m _ij applied when scaling (quantization or inverse quantization) of a residual signal (or transform coefficient) of a current block may be derived according to whether the current block is a transform skip block.

The encoding apparatus determines whether the current block is a transform skip block (S600).

In this case, whether the current block is a transform skip block may be determined based on information indicating whether the current block is a transform skip block. For example, information indicating whether it is a transform skip block may be a flag (transSkipFlag). This flag transSkipFlag value may be derived by entropy-decoding information on the transform skip block in the bitstream. If the current block is a transform skip block, the transSkipFlag value may be 1, otherwise the transSkipFlag value may be 0.

If the current block is a transform skip block (eg, when the transSkipFlag value is 1), the encoding apparatus derives the scale factor m _ij regardless of the position of the residual signal (or transform coefficient) in the current block (S610) .

In this case, as shown in FIG. 6 , the scale factor m _ij may be set to a predetermined basic scale factor value T. For example, the predetermined basic scale factor value T may be 16.

Otherwise, when the current block is not a transform skip block (eg, when the transSkipFlag value is 0), the encoding apparatus derives a scale factor m _ij based on the position of the residual signal (or transform coefficient) in the current block ( S620).

In this case, the scale factor m _ij may be set differently according to the position of the residual signal (or transform coefficient) in the current block using the quantization matrix, and may be derived as shown in Equation 7 below as shown in FIG. 6 . have.

[Equation 7]

Here, ScalingFactor is an array storing the scale factor. SizeID may be a value for indicating the size of the current block (transform block or quantization matrix), and as shown in Table 1 above, the SizeID value may be derived according to the size of the current block (transform block). RefMatrixID and trafoType may be derived from Equations 8 and 9, respectively. nW means the width of the current block.

[Equation 8]

Here, the MatrixID value may mean a type of a quantization matrix according to a prediction mode and a color component, and for example, a MatrixID value may be derived as shown in Table 2 below. scaling_list_pred_matrix_id_delta is signaled through SPS (Sequence Parameter Set) or PPS (Picture Parameter Set) of the bitstream.

[Equation 9]

Here, nW means the width of the current block, and nH means the height of the current block.

Table 2 shows MatrixID values according to prediction modes and color components.

[Table 2]

7 is a flowchart illustrating a scaling method for a residual signal (or transform coefficient) according to another embodiment of the present invention.

The method of FIG. 7 may be performed by the above-described encoding apparatus of FIG. 1 or the above-described decoding apparatus of FIG. 2 . More specifically, it may be performed in the quantization unit or inverse quantization unit of FIG. 1 or 2 . In the embodiment of FIG. 7 , it is described that the method of FIG. 7 is performed in the encoding apparatus for convenience of description, but this method may be equally applied to the decoding apparatus.

Referring to FIG. 7 , the scale factor (m _ij ) applied when scaling (quantization or inverse quantization) of the residual signal (or transform coefficient) of the current block depends on whether the current block is a transform skip block and whether a quantization matrix is used. can be induced accordingly.

The encoding apparatus determines whether the current block uses a quantization matrix and whether it is a transform skip block (S700).

In this case, whether the current block uses the quantization matrix may be determined through information indicating whether the quantization matrix is used. For example, information indicating whether a quantization matrix is used may be a flag (scaling_list_enable_flag). The value of this flag scaling_list_enable_flag may be derived by entropy-decoding information on the use of a quantization matrix in a bitstream. If the current block uses a quantization matrix, the value of scaling_list_enable_flag is 1, otherwise, the value of scaling_list_enable_flag is 0.

Also, whether the current block is a transform skip block may be determined through information indicating whether the current block is a transform skip block. For example, information indicating whether it is a transform skip block may be a flag (transSkipFlag). This flag transSkipFlag value may be derived by entropy-decoding information on the transform skip block in the bitstream. If the current block is a transform skip block, the transSkipFlag value may be 1, otherwise the transSkipFlag value may be 0.

If the current block is a transform skip block or does not use a quantization matrix (eg, transSkipFlag == 1 or scaling_list_enable_flag == 0), the encoding device performs the scale factor regardless of the position of the residual signal (or transform coefficient) in the current block. (m _ij ) is derived (S710).

In this case, as shown in FIG. 7 , the scale factor m _ij may be set to a predetermined basic scale factor value T. For example, the predetermined basic scale factor value T may be 16.

Otherwise (when the current block is not a transform skip block and a quantization matrix is used), the encoding apparatus derives a scale factor m _ij based on the position of the residual signal (or transform coefficient) in the current block ( S720 ).

In this case, the scale factor m _ij may be set differently according to the position of the residual signal (or transform coefficient) in the current block using the quantization matrix, and may be derived as shown in the equation shown in step S720 of FIG. 7 . Since the scale factor m _ij derived through the equation shown in step S720 is the same as described in FIG. 6 (step S620 ), a description thereof will be omitted.

As described above with reference to FIGS. 6 and 7 , when the current block (the current block to be encoded or decoded) is a transform skip block, regardless of the position of the coefficients (or signals) in the current block, the current block (transform skip block) A scale factor having a predetermined value (T) was applied to . In this case, the scale factor value according to the embodiment of the present invention may be set differently according to various encoding parameters applied to the corresponding block.

For example, a scale factor value to be applied to a corresponding block may be set as follows according to a value of a parameter (eg, scaling_list_enable_flag) indicating whether a quantization matrix is used.

- When using a quantization matrix (eg, scaling_list_enable_flag == 1), the default scale factor value is set to 'T1' (m _ij = T1)

- When the quantization matrix is not used (eg, scaling_list_enable_flag == 0), the default scale factor value is set to 'T2' (m _ij = T2)

Here, the T1 and/or T2 values may be determined and signaled by the encoder, or a predetermined value may be used. When signaled through a bitstream, the decoder may parse the bitstream to obtain T1 and/or T2 values.

As another example, the scale factor value to be applied to the corresponding block may be set as follows according to the value of information (eg, color component index cIdx) capable of inducing color characteristics of the signal of the corresponding block. The color component index cIdx represents a luminance signal (Y signal) or a color difference signal (Cb signal or Cr signal) according to its value.

- Example 1: Set the basic scale factor to ‘Ty’ or ‘Tc’ depending on whether the signal of the corresponding block is a brightness signal (luminance signal) or not. For example, if it is a brightness signal, the default scale factor value is set to ‘Ty’, and if it is not a brightness signal (color difference signal), the default scale factor value is set to ‘Tc’.

- Example 2: Set the default scale factor value for each color component of the block. For example, in the case of a luminance signal (Y signal), the default scale factor value is set to 'Ty', when the chrominance signal is a Cb signal, the default scale factor value is set to 'Tcb', and when the color difference signal is a Cr signal, the default scale Set the factor value to 'Tcr'.

Here, the Ty, Tc, Tcb, and/or Tcr values may be determined and signaled by the encoder, or a predetermined value may be used. When signaled through a bitstream, the decoder may parse the bitstream to obtain Ty, Tc, Tcb, and/or Tcr values.

The above-described methods for determining the basic scale factor according to the encoding parameter according to the embodiment of the present invention may be applied independently or in combination, but with respect to the same transform skip block, a coefficient (or The same scale factor value should always be applied regardless of the position of the signal).

The scaling process for transform coefficients reflecting the above-described embodiments of the present invention may be performed as follows.

Scaling process of transform coefficients

The input here is as follows.

- Width of the current transformation block Width; nW

- Height of the current transformation block Height; nH

- an array of transform coefficients with element c _ij ; (nWxnH) array d

- Information on whether transform skip is applied to the current transform block

- indices for the luminance signal and chrominance signal of the current block; cidx

If cIdx is ‘0’, it means a luminance signal, and if cIdx is ‘1’ or cIdx is ‘2’, it means a color difference signal. Also, if cIdx is ‘1’, it means Cb in the color difference signal, and if cIdx is ‘2’, it means Cr in the color difference signal.

- quantization parameters; qP

The output here is:

- array for scaled transform coefficients; (nWxnH) array d _ij

The variable log2TrSize is derived through log2TrSize = ( Log2( nW ) + Log2( nH ) ) >> 1. Variable shift is derived differently according to cIdx. If cIx is equal to '0' (if luminance signal), it is derived from shift = BitDepth _Y + log2TrSize - 5, otherwise (color difference signal), it is derived from shift = BitDepth _C + log2TrSize - 5 . Here, BitDepth _Y and BitDepth _C mean the number of bits (eg, 8 bits) of a sample for the current image.

The array levelScale[] of the scaling variables is as shown in Equation 10 below.

[Equation 10]

The scaled transform coefficient is calculated through the following process.

First, a scale factor m _ij is derived through the following process.

- If scaling_list_enable_flag is '0' or if the current transform block is a transform skip block, m _ij is derived as shown in Equation 11 below.

[Equation 11]

- Otherwise, m _ij is derived as in Equation 12 below.

[Equation 12]

Here, SizeID is derived from Table 1 according to the size of the block, and RefMatrixID and trafoType are derived from Equations 13 and 14 below, respectively. Also, in Equation 13, scaling_list_pred_matrix_id_delta is signaled through a sequence parameter set (SPS) of the bitstream.

[Equation 13]

[Equation 14]

Next, the scaled transform coefficient d _ij is derived from the following Equation (15).

[Equation 15]

Meanwhile, the transform coefficient scaled through the scaling process as described above performs an inverse transform process. At this time, the current transform block to which the transform skip is applied does not perform the inverse transform process, but only performs the following 'shift' operation process.

1. If the cIdx of the current block is '0' (for a luminance signal), shift = 13 - BitDepth _Y , otherwise (for a chrominance signal) shift = 13 - BitDepth _C.

2. The array r _ij (i=0..(nW)-1, j=0..(nH)-1) for the residual block is set as follows.

If shift is greater than '0', then r _ij = ( d _ij + (1 << ( shift - 1) ) ) >> shift, otherwise r _ij = ( d _ij << ( -shift ).

Here, d _ij is an array of scaled transform coefficients, and r _ij is an array of residual blocks obtained by inverse transforming the scaled transform coefficients.

As an embodiment reflecting the above-described inverse transformation process of the scaled transform coefficients, a transformation process for scaled transform coefficients may be performed as follows.

Transformation Process for Scaled Transform Coefficients

The input here is as follows.

- Width of the current transformation block Width; nW

- Height of the current transformation block Height; nH

- an array of scaled transform coefficients with element d _ij ; (nWxnH) array d

- Information on whether transformation skip is applied to the current block

- indices for the luminance signal and chrominance signal of the current block; cidx

If cIdx is ‘0’, it means a luminance signal, and if cIdx is ‘1’ or cIdx is ‘2’, it means a color difference signal. Also, if cIdx is ‘1’, it means Cb in the color difference signal, and if cIdx is ‘2’, it means Cr in the color difference signal.

The output here is:

- an arrangement for a residual block obtained by inverse transforming the scaled transform coefficients; (nWxnH) array r

If the encoding mode (PredMode) for the current block is the intra prediction mode (Intra), the Log2(nW*nH) value is equal to '4' and the cIdx value is '0', the intra prediction direction mode (intra) of the luminance signal According to the prediction mode), the variables horizTrType and vertTrType are obtained through Table 3 below. If not, the variables horizTrType and vertTrType are set to '0'.

Table 3 shows an example of horizTrType and vertTrType values according to the intra prediction mode.

[Table 3]

The residual signal for the current block is obtained in the following order.

First, if transform skip is applied to the current block, the following is applied.

1. If cIdx is '0' then shift = 13 - BitDepth _Y , otherwise shift = 13 - BitDepth _C.

2. The array r _ij (i=0..(nW)-1, j=0..(nH)-1) for the residual block is set as follows.

- if shift is greater than '0', r _ij = ( d _ij + (1 << ( shift - 1) ) ) >> shift, otherwise r _ij = ( d _ij << ( -shift ) .

If the transform skip for the current block is not applied, the following is applied.

1. The inverse transform process is performed on the scaled transform coefficients using the variables horizTrType and vertTrType. First, it receives the size of the current block (nW, nH), the scaled transform coefficient array (nWxnH array d), and the variable horizTrType, performs one-dimensional inverse transformation in the horizontal direction, and outputs an array (nWxnH array e).

2. Next, an array (nWxnH array e) is input and an array (nWxnH array g) is derived as in Equation 16 below.

[Equation 16]

3. Next, the size of the current block (nW, nH), the array (nWxnH array g), and the variable vertTrType are received and one-dimensional inverse transformation is performed in the vertical direction.

4. Next, according to cIdx, an array (nWxnH) array r for the remaining blocks is set as in Equation 17 below.

[Equation 17]

Here, shift has a value of shift = 20 - BitDepth _Y when cIdx is '0', and shift = 20 - BitDepth _C otherwise. BitDepth means the number of bits (eg, 8 bits) of a sample for the current image.

A reconstructed residual block may be generated by performing the above-described scaling process for transform coefficients and a transform process for the scaled transform coefficients. In addition, a reconstructed block may be generated by adding a prediction block generated through intra prediction or inter prediction to the reconstructed residual block. In this case, the reconstruction block may be a block to which a loop filter is applied or a block to which a loop filter is not applied.

Hereinafter, the present invention provides a method of signaling a basic scale factor derived according to whether a transform skip block is present.

According to an embodiment of the present invention, a basic scale factor derived according to whether a transform skip block or not may be signaled through a sequence parameter set (SPS).

Table 4 shows an example of SPS syntax for signaling basic scale factor information according to an embodiment of the present invention.

[Table 4]

Referring to Table 4, transform_skip_enabled_flag indicates whether to use the transform skip algorithm for the current sequence.

If the transform skip algorithm is used, flat_scale_factor_y_minus16, flat_scale_factor_cb_minus16, and flat_scale_factor_cr_minus16 are signaled. Here, these values may be encoded (se(v)) in a form having a positive or negative sign. Alternatively, these values may be encoded (ue(v)) in a form having 0 and a positive sign.

flat_scale_factor_y_minus16 means a scale factor for the luminance signal. For example, if the flat_scale_factor_y_minus16 value is '0', the scale factor for the luminance signal has a value of '16' by adding '16' to the '0'.

flat_scale_factor_cb_minus16 means a scale factor for the color difference signal Cb, and flat_scale_factor_cr_minus16 means a scale factor for the color difference signal Cr.

In this regard, the scale factor for the luminance signal or the chrominance signal may be derived as shown in Equations 18 to 20 below.

Here, the basic scale factor FlatScalingFactor[cIdx] stores scale factors for the luminance signal and the chrominance signal. For example, if the color component index cIdx is 0, it may indicate a luminance (Y) signal, if it is 1, it may indicate a Cb chrominance signal, and if it is 2, it may indicate a Cr chrominance signal. In addition, the FlatScalingFactor[cIdx] value may have an arbitrary range of values, and for example, in the case of an 8-bit signal, it may have a value of '-15' to '255-16'.

A basic scale factor for the luminance signal may be derived as in Equation (18).

[Equation 18]

A basic scale factor for the Cb color difference signal may be derived as in Equation (19).

[Equation 19]

A basic scale factor for the Cr chrominance signal may be derived as in Equation (20).

[Equation 20]

By reflecting the above-described method of signaling a basic scale factor derived according to whether a transform skip block is a transform skip block according to an embodiment of the present invention, a scaling process for transform coefficients may be performed as follows.

Scaling process of transform coefficients

The input here is as follows.

- Width of the current transformation block Width; nW

- Height of the current transformation block Height; nH

- an array of transform coefficients with element c _ij ; (nWxnH) array d

- information on whether transform skip is applied to the current transform block; transSkipFlag

A transSkipFlag value of 1 indicates that transform skip is applied to the current block, and a transSkipFlag value of 0 indicates that no transform skip is applied to the current block.

- indices for the luminance signal and chrominance signal of the current block; cidx

If cIdx is ‘0’, it means a luminance signal, and if cIdx is ‘1’ or cIdx is ‘2’, it means a color difference signal. Also, if cIdx is ‘1’, it means Cb in the color difference signal, and if cIdx is ‘2’, it means Cr in the color difference signal.

- quantization parameters; qP

The output here is:

- array for scaled transform coefficients; (nWxnH) array d _ij

The variable log2TrSize is derived through log2TrSize = ( Log2( nW ) + Log2( nH ) ) >> 1. Variable shift is derived differently according to cIdx. If cIx is equal to '0' (if luminance signal), it is derived from shift = BitDepth _Y + log2TrSize - 5, otherwise (color difference signal), it is derived from shift = BitDepth _C + log2TrSize - 5 . Here, BitDepth _Y and BitDepth _C mean the number of bits (eg, 8 bits) of a sample for the current image.

The array levelScale[] of the scaling variables is expressed by Equation 21 below.

[Equation 21]

The scaled transform coefficient is calculated through the following process.

First, a scale factor m _ij is derived through the following process.

- If scaling_list_enable_flag is '0', m _ij is derived as shown in Equation 22 below.

[Equation 22]

- Otherwise (that is, if scaling_list_enable_flag is '1', m _ij is derived as in Equation 23 below.

[Equation 23]

Here, SizeID is derived from Table 1 according to the size of the block, and RefMatrixID and trafoType are derived from Equations 24 and 25 below, respectively. In Equation 24, scaling_list_pred_matrix_id_delta is signaled through a sequence parameter set (SPS) of a bitstream.

[Equation 24]

[Equation 25]

Next, the scaled transform coefficient d _ij is derived from the following equation (26).

[Equation 26]

On the other hand, the basic scale factor derived according to whether a transform skip block according to an embodiment of the present invention can be signaled through a picture parameter set (PPS) or a slice header as well as the above-described SPS. Also, it may be signaled in units of CUs or units of TUs.

The flat_scale_factor_y_minus16, flat_scale_factor_cb_minus16, and flat_scale_factor_cr_minus16 values signaled in the above-described SPS may be updated and used in the PPS (or SliceHeader, CU, TU).

Table 5 shows an example of PPS syntax for signaling basic scale factor information according to another embodiment of the present invention.

[Table 5]

Referring to Table 5, transform_skip_enabled_flag indicates whether to use the transform skip algorithm for the current picture. If the transform skip algorithm is used, the pps_flat_scaling_factor_present_flag value is signaled.

For example, if the value of pps_flat_scaling_factor_present_flag is '0', flat_scale_factor_y_minus16, flat_scale_factor_cb_minus16, and flat_scale_factor_cr_minus16 applied in the above-described SPS are used as scale factors for the transform skip block. Otherwise, if the pps_flat_scaling_factor_present_flag value is ‘1’, the values are signaled to update the flat_scale_factor_y_minus16, flat_scale_factor_cb_minus16, and flat_scale_factor_cr_minus16 values applied in the above-described SPS.

The signaled flat_scale_factor_y_minus16, flat_scale_factor_cb_minus16, and flat_scale_factor_cr_minus16 values are used as scale factors for the transform skip block of the current picture. In this case, these values can continue to be used until they are not changed again. Alternatively, these values may be applied and used only to the current picture, and the scale factor values used in the SPS may be applied to the next picture.

Here, flat_scale_factor_y_minus16, flat_scale_factor_cb_minus16, and flat_scale_factor_cr_minus16 may be encoded (se(v)) in a form having a positive or negative sign. Alternatively, these values may be encoded (ue(v)) in a form having 0 and a positive sign.

The flat_scale_factor_y_minus16, flat_scale_factor_cb_minus16, and flat_scale_factor_cr_minus16 values may have different values for each of the luminance signal and the chrominance signal and may be respectively signaled. For example, the flat_scale_factor_y_minus16 value may be used to signal a scale factor for the luminance signal, the flat_scale_factor_cb_minus16 value may be used to signal a scale factor for the Cb chrominance signal, and the flat_scale_factor_cr_minus16 value may be used to signal a scale factor for the Cr chrominance signal. Alternatively, the signal may be signaled using flat_scale_factor_y_minus16 as the scale factor for the luminance signal and flat_scale_factor_cb_cr_minus16 as the scale factor for the chrominance signal. Alternatively, one value flat_scale_factor_y_cb_cr_minus16 may be used as a scale factor for the luminance signal and the chrominance signal.

As described above, the flat_scale_factor_y_minus16, flat_scale_factor_cb_minus16, and flat_scale_factor_cr_minus16 values signaled by the SPS or PPS may be updated and used in the SliceHeader (or CU, TU).

Table 6 shows an example of a slice header syntax for signaling basic scale factor information according to another embodiment of the present invention.

[Table 6]

Referring to Table 6, transform_skip_enabled_flag indicates whether to use the transform skip algorithm for the current slice. If the transform skip algorithm is used, a flat_scaling_factor_override_flag value is signaled.

For example, if the flat_scaling_factor_override_flag value is '0', flat_scale_factor_y_minus16, flat_scale_factor_cb_minus16, and flat_scale_factor_cr_minus16 applied in the aforementioned SPS or PPS are used as scale factors for the transform skip block. Otherwise, if the flat_scaling_factor_override_flag value is '1', corresponding values are signaled to update the flat_scale_factor_y_minus16, flat_scale_factor_cb_minus16, and flat_scale_factor_cr_minus16 values applied in the aforementioned SPS or PPS.

The flat_scale_factor_y_delta, flat_scale_factor_cb_delta, and flat_scale_factor_cr_delta values are used as scale factors for the transform skip block of the current slice.

Here, flat_scale_factor_y_delta, flat_scale_factor_cb_delta, and flat_scale_factor_cr_delta values may be coded (se(v)) in a form having a positive or negative sign. Alternatively, these values may be encoded (ue(v)) in a form having 0 and a positive sign.

The flat_scale_factor_y_delta, flat_scale_factor_cb_delta, and flat_scale_factor_cr_delta values may have different values for each of the luminance signal and the chrominance signal and may be respectively signaled. For example, a flat_scale_factor_y_delta value may be used to signal a scale factor for a luminance signal, a flat_scale_factor_cb_delta value to a scale factor for a Cb chrominance signal, and a flat_scale_factor_cr_delta value to signal a scale factor for a Cr chrominance signal. Alternatively, the signal may be performed using flat_scale_factor_y_delta as the scale factor for the luminance signal and flat_scale_factor_cb_cr_delta as the scale factor for the chrominance signal. Alternatively, a single value flat_scale_factor_y_cb_cr_delta may be used as a scale factor for the luminance signal and the chrominance signal.

A basic scale factor may be derived as shown in Equations 27 to 29 below by using the flat_scale_factor_y_delta, flat_scale_factor_cb_delta, and flat_scale_factor_cr_delta values signaled as described above.

Here, the basic scale factor FlatScalingFactor[cIdx] stores scale factors for the luminance signal and the chrominance signal. For example, if the color component index cIdx is 0, it may indicate a luminance (Y) signal, if it is 1, it may indicate a Cb chrominance signal, and if it is 2, it may indicate a Cr chrominance signal. In addition, the FlatScalingFactor[cIdx] value may have an arbitrary range of values, and for example, in the case of an 8-bit signal, it may have a value of '-15' to '255-16'.

A basic scale factor for the luminance signal may be derived as in Equation 27 using flat_scale_factor_y_delta.

[Equation 27]

A basic scale factor for the Cb color difference signal may be derived as in Equation 28 using flat_scale_factor_cb_delta.

[Equation 28]

A basic scale factor for the Cr chrominance signal may be derived as in Equation 29 using flat_scale_factor_cr_delta.

[Equation 29]

Meanwhile, the above-described embodiments may have different application ranges according to the block size, CU depth, or TU depth. As for the variable (eg, block size or depth information) that determines the application range in this way, the encoder and the decoder may be set to use a predetermined value, or a value determined according to a profile or level may be used, and the encoder may set the variable If the value is written in the bitstream, the decoder may obtain this value from the bitstream and use it.

When changing the application range according to the CU depth, as illustrated in Table 7, the following three methods can be applied. Method A is applied only to a depth greater than or equal to a given depth, Method B is applied only to a depth below a given depth, and Method C is applied only to a given depth.

Table 7 shows an example of a method of determining a range to which the methods of the present invention are applied according to a CU (or TU) depth. In Table 7, the ‘O’ notation means that the method is applied to the corresponding depth of the CU (or TU), and the ‘X’ notation means that the corresponding method is not applied to the corresponding depth of the CU (or TU).

[Table 7]

Referring to Table 7, when a CU (or TU) depth is 2, method A, method B, and method C may all be applied to embodiments of the present invention.

If the embodiments of the present invention are not applied to all depths of a CU (or TU), it may be indicated using an arbitrary indicator (eg, flag), and a value one larger than the maximum value of the CU depth is applied. It can also be expressed by signaling with a CU depth value indicating a range.

In addition, the method for determining the range to which the methods of the present invention are applied according to the CU (or TU) depth described above can be applied differently depending on the sizes of the luminance block and the chrominance block, and also differently applied to the luminance image and the chrominance image can do.

Table 8 is an example schematically showing a combination of methods for determining an application range according to sizes of a luminance block and a chrominance block.

[Table 8]

Referring to method “4 1” among the methods in Table 8, when the size of the luminance block is 8 (8x8, 8x4, 2x8, etc.) and the size of the chrominance block is 4 (4x4, 4x2, 2x4), the present invention Example 1 of (4-1 - Example 1) can be applied to a luminance signal and a chrominance signal, and a horizontal signal and a vertical signal.

In the above-described embodiments, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in a different order or at the same time as other steps as described above. can In addition, those of ordinary skill in the art will recognize that the steps shown in the flowchart are not exclusive, other steps may be included, or that one or more steps in the flowchart may be deleted without affecting the scope of the present invention. you will understand

The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (3)

In the video decoding method,
obtaining a first flag indicating whether transform skip application to the current picture is possible or not;
obtaining a second flag indicating whether transform skip is applied or not applied to a current block included in the current picture;
deriving a quantization parameter for the current block;
deriving a scale factor for the current block based on the value of the first flag and the value of the second flag; and
performing scaling on the transform coefficients of the current block based on the scale factor and the quantization parameter,
The scale factor for the current block is,
The first flag indicates a first value indicating that transform skip is applicable to the current picture, and the second flag indicates a second value indicating that transform skip is not applied to the current block If , it is derived based on a predefined quantization matrix and the position of the transform coefficient in the current block,
The first flag indicates the first value indicating that the transform skip is applicable to the current picture, and the second flag indicates the first value indicating that the transform skip is applied to the current block. When indicated, it is derived as a fixed constant value regardless of the position of the transform coefficient in the current block,
The first flag is signaled at a picture parameter set (PPS) level, and the second flag is signaled at a transform unit (TU) level. In the video encoding method,
determining whether it is possible to apply transform skip to the current picture;
determining whether transform skip is applied to a current block included in the current picture;
determining a quantization parameter for the current block;
encoding at least one of a first flag indicating whether transform skip for the current picture is possible and a second flag indicating whether transform skip for the current block is applied, wherein the first flag is a picture Parameter Set) level is encoded, and the second flag is encoded at a TU (Transform Unit) level;
determining a scale factor for the current block according to whether transform skip can be applied to the current picture and whether transform skip is applied to the current block;
performing quantization on the transform coefficients of the current block based on the scale factor and the quantization parameter,
The scale factor for the current block is,
When the transform skip can be applied to the current picture and the transform skip is not applied to the current block, it is determined based on a predefined quantization matrix and the positions of transform coefficients in the current block,
An image encoding method characterized in that when transform skip can be applied to the current picture and transform skip is applied to the current block, a fixed constant value is determined regardless of a position of a transform coefficient in the current block . In a method of transmitting a bitstream generated using an image encoding method,
The video encoding method comprises:
determining whether it is possible to apply transform skip to the current picture;
determining whether transform skip is applied to a current block included in the current picture;
determining a quantization parameter for the current block;
encoding at least one of a first flag indicating whether transform skip for the current picture is possible and a second flag indicating whether transform skip for the current block is applied, wherein the first flag is a picture Parameter Set) level is encoded, and the second flag is encoded at a TU (Transform Unit) level;
determining a scale factor for the current block according to whether transform skip can be applied to the current picture and whether transform skip is applied to the current block;
performing quantization on the transform coefficients of the current block based on the scale factor and the quantization parameter,
The scale factor for the current block is,
When the transform skip can be applied to the current picture and the transform skip is not applied to the current block, it is determined based on a predefined quantization matrix and the positions of transform coefficients in the current block,
Bitstream transmission, characterized in that when the transform skip can be applied to the current picture and the transform skip is applied to the current block, a fixed constant value is determined regardless of the position of the transform coefficient in the current block Way.

Images