KR20230048275A - Entrpy decoding method and apparatus for transform skip information - Google Patents

Abstract

The present invention provides a video decoding method which increases encoding efficiency. According to the present invention, the video decoding method comprises: a step of, if the size of a current coding unit can include a transform block allowing a transform skip, parsing a representative flag representing first information indicating the transform skip status of a transform block divided from the coding unit into information on the coding unit; a step of determining the parsing status of the first information based on the representative flag; a step of inferring the first information based on the representative flag if the first information does not need to be parsed, and parsing the first information if the first information needs to be parsed; and a step of performing or skipping a transform on the transform block in accordance with the first information.

Description

Method and apparatus for entropy decoding of transformation skipping information based on prediction mode

The present invention relates to video encoding and decoding processing, and more particularly, to a method and apparatus for entropy decoding of transform skip information based on a prediction mode.

Recently, as broadcasting services with high definition (HD) resolution are expanded not only domestically but also globally, many users are getting used to high-resolution and high-definition images, and many organizations are accelerating the development of next-generation video equipment. In addition, as interest in UHD (Ultra High Definition) having a resolution four times higher than that of HDTV increases along with HDTV, a compression technology for a higher resolution and higher quality image is required.

For image compression, an inter prediction technique for predicting pixel values included in the current picture from temporally previous and/or subsequent pictures, and pixel values included in the current picture using pixel information in the current picture. An intra (inter-screen) prediction technique for predicting , an entropy coding technique for assigning a short code to a symbol with a high frequency of occurrence and a long code to a symbol with a low frequency of occurrence may be used.

In the case of intra prediction among prediction techniques used for prediction of an image, it is a technique of compressing an image by removing spatial similarity within a current frame or current picture. During such intra prediction, a prediction value for the current prediction block is generated by referring to neighboring pixel values adjacent to the current block, and information about the predicted value is signaled.

In the case of inter prediction among prediction techniques used for prediction of an image, it is a technique of compressing an image by removing temporal similarities between different frames. In inter-prediction, an area having a pixel value similar to that of the current block is searched for in another frame and used as a predicted value for the current prediction block.

A prediction value determined through search, that is, motion estimation, is expressed as a motion vector (MV), and this motion vector is expressed as a motion vector predictor (MVp) and a motion vector difference value (MVd). can

In the case of currently applied intra prediction, since a prediction block is generated using a block adjacent to the current block, there is a restriction that pixels in a region spatially separated from the current block cannot be referred to. Also, in the case of inter prediction, even if a region in the current picture has a pixel value similar to that of the current block, it cannot be used as a prediction value.

The present invention determines a context used in context-based entropy coding such as CABAC by referring to a prediction mode of a coding unit (CU) during entropy encoding/decoding of transform skip information of compressed signals during video compression, , to provide a method and apparatus for increasing coding efficiency through this.

In the present invention, when a similar pattern repeatedly occurs in a screen and a residual signal containing a large amount of high frequency is frequently generated, there is a possibility that the transform skip mode is commonly applied or not applied to transform blocks within a predetermined unit. In this case, a video encoding/decoding method capable of increasing encoding efficiency by signaling a flag representing whether or not transformation is omitted and an apparatus using the same are provided.

According to an embodiment of the present invention, an entropy decoding method of a conversion skip flag indicating whether conversion is skipped includes deriving context information about a bin constituting a codeword of the conversion skip flag; and deriving a value of the transform skip flag by performing arithmetic decoding on the bin based on the context information, wherein in the context information derivation step, the context information is derived based on a prediction mode of a coding unit. information can be derived.

Deriving the context information for the bin may include determining a context index for the transform skip flag, and the context index may be determined based on whether a prediction mode of the coding unit is an intra block copy mode. .

The context index may be determined according to whether the current slice is an I slice, a P slice, or a B slice.

The context index may be determined according to whether the current block is a luma block or a chroma block.

In the deriving of the context information for the bin, initialization is performed to set a probability value corresponding to the context index as an initial value, and the initial value may be set based on a prediction mode of the coding unit.

According to an embodiment of the present invention, a bit for signaling transform skipping by defining the context of a transform skip flag (transform_skip_flag) according to the prediction mode of a coding unit and enabling reference to the prediction mode of the coding unit in an entropy coding process. amount is reduced, and the video encoding efficiency is increased.

According to an aspect of the present invention, when a specific prediction mode is used in an image in which transform skipping occurs frequently, encoding/decoding efficiency of an image is improved by performing context-based entropy coding in consideration of the fact that the probability of skipping transform is high. can be increased

Specifically, the effect of the present invention can be conspicuously manifested in encoding and decoding of an artificial image created by a computer.

1 is a block diagram showing a configuration according to an embodiment of an image encoding apparatus to which the present invention is applied.
2 is a block diagram showing a configuration according to an embodiment of a video decoding apparatus to which the present invention is applied.
3 is a diagram for explaining IBC prediction according to an embodiment of the present invention.
4 is a flowchart illustrating an entropy decoding method of a conversion skip flag according to an 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 detailed description thereof will be omitted.

In addition, components appearing in the embodiments of the present invention are shown independently to represent different characteristic functions, and do not mean that each component is made of separate hardware or a single software component unit. That is, each component is listed and included as each component for convenience of explanation, and at least two components of each component can be combined to form a single component, or one component can be divided into a plurality of components to perform a function, and each of these components can be divided into a plurality of components. Integrated embodiments and separated embodiments of components are also included in the scope of the present invention as long as they do not depart from the essence of the present invention.

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

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

Referring to FIG. 1 , the image encoding apparatus 100 includes a prediction unit 110, a subtractor 125, a transform unit 130, a quantization unit 140, an entropy encoding unit 150, and an inverse quantization unit 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 bit stream. Intra prediction means prediction within a picture, and inter prediction means prediction between pictures. In the intra mode, the switch (not shown) is converted to intra, and in the case of the inter mode, the switch is converted to inter. After generating a prediction block for an input block of an input image, the image encoding apparatus 100 may encode a difference between the input block and the prediction block.

The prediction unit may include an intra prediction unit performing intra prediction, a motion prediction unit and motion compensation unit performing inter prediction, and an IBC prediction unit performing intra block copy (IBC) prediction as detailed components. there is. Also, the video encoding apparatus may include a switch (not shown), and the switch may switch between an inter prediction unit, an intra prediction unit, and an IBC prediction unit.

In the case of the intra mode, the intra prediction unit may generate a prediction block by performing spatial prediction using pixel values of previously encoded blocks adjacent to the current block.

In the case of the inter mode, the motion estimation unit may obtain a motion vector by finding a region that best matches the input block in the reference image stored in the reference image buffer 190 during the motion prediction process. The motion compensation unit may generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference image buffer 190 .

The IBC predictor may determine a region similar to the current block by performing motion prediction, that is, search within the current picture, and obtain a prediction value and a block vector for the current block. Prediction by the IBC prediction unit is described in detail below.

The subtractor 125 may generate a residual block by a difference between the input block and the generated prediction block. The transform unit 130 may output a transform coefficient by performing transform on the residual block. For some residual blocks, the transform unit 130 may be configured to omit the transform. Even in this case, the output of the transform unit 130 is referred to as a transform coefficient for convenience. The quantization unit 140 may quantize the input transform coefficient according to a quantization parameter and output a quantized coefficient.

The entropy encoding unit 150 entropy-encodes symbols according to a probability distribution based on the values calculated by the quantization unit 140 or the encoding parameter values calculated in the encoding process to generate a bit stream. can be printed out. The entropy encoding method is a method of receiving symbols having various values and expressing them as a sequence of decodable binary numbers while removing statistical redundancy.

Here, a symbol means a syntax element to be coded/decoded, a coding parameter, a value of a residual signal, and the like. An encoding parameter is a parameter necessary for encoding and decoding, and may include information that can be inferred in the process of encoding or decoding, as well as information encoded in the encoding device and transmitted to the decoding device, such as syntax elements. It means the information you need when

Coding parameters include, for example, intra/inter prediction mode, motion/motion vector, reference image index, coded block pattern, residual signal presence, transform coefficient, quantized transform coefficient, quantization parameter, block size, and block division information. values or statistics, etc. In addition, the residual signal may mean the difference between the original signal and the prediction signal, and also a signal in which the difference between the original signal and the prediction signal is transformed or a signal in which the difference between the original signal and the prediction signal is transformed and quantized. , or a difference signal between the original signal and the prediction signal or a difference signal between the original signal and the prediction signal may mean a quantized signal. The residual signal may be referred to as a residual block in a block unit.

When entropy encoding is applied, a small number of bits are allocated to symbols with a high probability of occurrence and a large number of bits are allocated to symbols with a low probability of occurrence to represent symbols, thereby increasing the size of bit streams for symbols to be encoded. can be reduced Therefore, compression performance of image encoding can be improved through entropy encoding.

For entropy encoding, encoding methods such as exponential gollomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC) may be used. For example, a table for performing entropy encoding, such as a Variable Length Coding/Code (VLC) table, may be stored in the entropy encoding unit 150, and the entropy encoding unit 150 may store the stored variable length coding. Entropy encoding can be performed using a (VLC) table. In addition, the entropy encoding unit 150 derives a binarization method of the target symbol and a probability model of the target symbol/bin, and then performs entropy encoding using the derived binarization method or probability model. You may.

The quantized coefficient may be inversely quantized in the inverse quantization unit 160 and inversely transformed in the inverse transformation unit 170 . For some blocks, the inverse transform unit 170 may be configured to omit the inverse transform. Even in this case, the output of the inverse transform unit 170 is referred to as an inverse transformed coefficient for convenience. The inverse quantized and inverse transformed coefficients are added to the prediction block through the adder 175, and a reconstructed block may be generated.

The reconstructed block passes through a 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. A reconstructed block that has passed through the filter unit 180 may be stored in the reference image buffer 190 .

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

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, a prediction unit 240, a filter unit 260, and a reference image buffer ( 270).

The image decoding apparatus 200 may receive the bitstream output from the encoding apparatus, perform decoding in an intra mode, inter mode, or IBC mode, and output a reconstructed image, that is, a reconstructed image.

The image decoding apparatus 200 may generate a reconstructed block, that is, a reconstructed block, by obtaining a reconstructed residual block from the input bitstream, generating a prediction block, and then adding the reconstructed residual block and the prediction block.

The entropy decoding unit 210 may generate symbols including symbols in the form of quantized coefficients by entropy decoding the input bitstream according to a probability distribution. The entropy decoding method is a method of generating each symbol by receiving a sequence of binary numbers. The entropy decoding method is similar to the entropy encoding method described above.

The quantized coefficients are inversely quantized in the inverse quantization unit 220 and inversely transformed in the inverse transformation unit 230, and as a result of inverse quantization/inverse transformation of the quantized coefficients, a reconstructed residual block may be generated. For some blocks, the inverse transform unit 230 may be configured to omit the inverse transform. Also, the inverse quantization unit 220 may be omitted for some blocks.

The prediction unit 240 includes an intra prediction unit that performs intra prediction, a motion prediction unit and a motion compensation unit that performs inter prediction, and an IBC prediction unit that performs intra block copy (IBC) prediction. can be included with

In the case of the intra mode, the intra prediction unit may generate a prediction block by performing spatial prediction using pixel values of previously encoded blocks adjacent to the current block. In the case of the inter mode, the motion compensation unit may generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference image buffer 270 .

In the case of IBC prediction, the IBC prediction unit may determine a region similar to the current block by performing motion prediction, that is, search within the current picture, and obtain a prediction value and a block vector for the current block. Prediction by the IBC prediction unit is described in detail below.

The reconstructed residual block and the predicted block are added through an adder 255, and the added block passes through a 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 outputs a reconstructed image, that is, a restored image. The reconstructed image may be stored in the reference image buffer 270 and used for inter prediction.

Among the entropy decoding unit 210, the inverse quantization unit 220, the inverse transform unit 230, the prediction unit 240, the filter unit 260, and the reference image buffer 270 included in the image decoding apparatus 200, Elements directly related to image decoding, such as the entropy decoding unit 210, the inverse quantization unit 220, the inverse transform unit 230, the prediction unit 240, the filter unit 260, etc., are distinguished from other components. It can be expressed as a decoding unit or a decoding unit.

Also, the video decoding apparatus 200 may further include a parsing unit (not shown) that parses information related to an encoded video included in a bitstream. The parsing unit may include the entropy decoding unit 210 or may be included in the entropy decoding unit 210 . This parsing unit may also be implemented as one component of the decoding unit.

3 is a diagram for explaining IBC prediction according to an embodiment of the present invention.

In the case of IBC prediction, a specific region in the current picture can be used as a reference block for the current block, and similar to the motion vector used in inter prediction, a block vector (hereinafter BV) is used to indicate the position of the specific region. ) can be used.

In the case of conventional inter prediction, the reference picture is a previous or subsequent picture different from the current picture, but in the case of IBC prediction, the reference picture becomes the current picture, and the block vector indicates a vector indicating a reference block in the current picture.

As shown, according to an example of the present invention, a region existing in a left coding tree unit (CTU) adjacent to a current prediction block in a current picture may be selected as a reference block of the current prediction block.

When performing IBC prediction, an area for searching for a reference block may be limited or set to a specific area. According to an example, the reference block may be limited to being searched for in a current CTU to which the current prediction block belongs or a left CTU adjacent to the current CTU.

Conversely, when IBC prediction is performed, it may be possible to extend the region for searching the reference block to all regions in the current picture where decoding has been completed prior to the current coding unit.

The type of prediction block on which IBC prediction is performed may be 2Nx2N, 2NxN, Nx2N, or NxN.

Similar to a motion vector, BV can be derived from a BV predictor and a BV difference.

A BV predictor for the current block may be coded in an encoding device and signaled to a decoding device, and a BV of a block previously predicted in IBC mode within a specific region, for example, the current CTU, may be used as a predictor, and the current block and The BV of a block predicted in the IBC mode among adjacent blocks may also be used as a predictor.

At this time, since data needs to be reset or refreshed in the middle of image processing, the BV predictor for each CTU may be initialized to an initial value such as (-2*w, 0) or (-w, 0). Here, w may be the width of the current coding unit.

The BV difference value indicates the difference between the BV and the BV predictor, and may be coded in the encoding device using BVdx and BVdy values and signaled to the decoding device.

On the other hand, among existing image coding methods, transform skip is applied in which transform is omitted for a block containing a large number of high-frequency components.

For example, when the value of transform_skip_enabled_flag signaled at an upper stage such as a picture parameter set is 1, and a coded block flag (CBF) is 1 when encoding/decoding a residual signal, all 4x4 sized transform blocks For (transform block, TB), a flag (transform_skip_flag) indicating whether or not to skip transformation may be individually signaled.

Alternatively, the value of transform_skip_enabled_flag is 1, and the size of the current transform block is greater than the maximum block size defined by information (eg, log2_max_transform_skip_block_size_minus2) indicating the maximum size of the transform block to which transform skip signaled in the picture parameter set can be applied. A flag (transform_skip_flag) indicating whether or not to skip transform may be individually signaled for all transform blocks having a CBF of 1 or less than or equal to 1.

On the other hand, in conventional video encoding and decoding, whether to skip transform is signaled with syntax element information called transform_skip_flag[x0][y0][cIdx] in units of transform blocks (TB, transform blocks), and this signal is entropy-encoded to form a bitstream is sent to Here, x0 and y0 represent the top left position of the transform block, and 'cIdx' represents the color information of the current transform block. In the case of a luma signal, cIdx is set to 0, and in the case of a chroma signal, cIdx may have values of 1 and 2, respectively.

When decoding an image, the entropy decoding unit may perform entropy decoding based on a context index (ctxIdx) defined according to the context for each syntax element. For the transform skip flag (transform_skip_flag), six context indices may be defined as shown in Table 1, for example.

Referring to Table 1, the context index of transform_skip_flag, which is a syntax element, is determined according to the initType and the color component of the current block of the current block.

initType is a value determined according to the type of slice currently being encoded/decoded. In case of I slice, initType is set to 0, and in case of P slice and B slice, it can be set differently according to cabac_init_flag value. For example, in the case of cabac_init_flag =0, initType may be set to 1 for P slices, and initType may be set to 0 for B slices.

ctxTable is, for example, a table in which an initial value (initValue) is defined according to the syntax elements transform_skip_flag and initType defined in Table 1. The probability value of transform_skip_flag in Table 1 can be initialized by referring to Table 3.

When cabac_init_flag is assumed to be 0 in Table 1, the context index is shown in Table 2.

In CABAC, a context update process is performed independently for each context index. For example, if the context index of transform_skip_flag to be currently encoded is 0, CABAC encoding is performed based on the probability index (pState index) of ctxIdx = 0, and only the probability index of ctxIdx = 0 is updated.

The entropy decoding unit is the first syntax element of an independent slice segment or a probability value (pState index) for each context index for a syntax element of a CTU that cannot refer to probability information stored in an upper right CTU among the first CTUs of a row. ) is initialized.

At this time, the initialization of the probability value may be performed based on the initial value (initValue) for each context index of the syntax element.

Table 3 shows an example of an initial value according to the context index of the transform skip flag (transform_skip_flag).

In summary, the six context indices used in CABAC for entropy coding of the transform skip flag can be set as shown in Table 2, and the context index is 1) the current slice type and 2) whether the current transform block represents a luma component or It can be determined according to whether it represents a chroma component.

On the other hand, in the coding unit predicted by IBC described with reference to FIG. 3, there is a feature that transform omission occurs frequently. However, in the context design process for entropy coding of the existing transform skip flag, the correlation between IBC and transform skip mode was not considered.

That is, in the conventional case, during entropy encoding/decoding of the transform skip flag (transform_skip_flag), the context was determined by referring only to the slice type and color components, but the distribution of occurrence of transform skip may have different characteristics depending on the prediction mode of the coding unit. there is. After determining the context in consideration of these characteristics, the compression rate may be increased by entropy encoding/decoding the transform skip flag using the determined context.

The present invention defines the context of the transform skipping flag according to the prediction mode of the coding unit, and reduces the amount of bits for signaling transform skipping by referring to the prediction mode of the coding unit in the entropy coding process, and consequently increases the video encoding efficiency. It provides a method and apparatus for doing so.

Hereinafter, in describing an embodiment of the present invention, it is assumed that the cabac_init_flag value is 0, that is, the initType of I slice is 0, and the initTypes of P slice and B slice are 1 and 2, respectively.

In addition, according to one aspect of the present invention, determining the context index by referring to whether the prediction mode of the coding unit is IBC is presented as a preferred example, but the scope of the present invention is not limited thereto, and the case of modes other than IBC can also be expanded.

Compared to conventional entropy coding, the present invention additionally defines a context index determined by referring to a prediction mode of a coding unit, and newly defines initValue of each context index when the context index is additionally defined.

According to an embodiment of the present invention, when determining a context index with reference to a prediction mode of a coding unit, it may be applied to both a luma component and a chroma component. Table 4 shows this as a table.

Referring to Table 4, when compared with Table 2, additional 6 context indexes are defined, and as a result, 12 context indexes for conversion skipping flags may be provided.

According to another embodiment of the present invention, when determining a context index with reference to a prediction mode of a coding unit, it may be applied only to a luma component. Table 5 shows this as a table.

Referring to Table 5, when compared with Table 2, 3 additional context indexes are defined, and as a result, 9 context indexes for conversion skipping flags can be obtained.

According to another embodiment of the present invention, when determining a context index with reference to a prediction mode of a coding unit, it may be applied only to a chroma component. If this is represented as a table, it can be shown in Table 6.

Referring to Table 6, when compared with Table 2, three additional context indexes are defined. As a result, as shown in Table 5, the number of context indexes for conversion skipping flags may be nine.

According to another embodiment of the present invention, the new context indexes added to Tables 4 to 6 need not all be different from each other. Some context indexes may be set to existing ones, and some context indexes may be set to new ones. When entropy encoding/decryption becomes complicated due to the large number of context indices, the complexity can be reduced.

According to Table 7 below, when the prediction mode of a coding unit is IBC, one context index can be determined regardless of the slice type.

According to another embodiment, a context index may be determined as shown in Table 8. According to Table 8, a context index may be determined according to whether a prediction mode of a coding unit is IBC according to a slice type.

Referring to Table 8, only when the slice type is I slice, the context index is determined according to whether the prediction mode of the coding unit is IBC. That is, if the prediction mode of the coding unit is not IBC (CU mode != IBC), the context index of the I slice is set to 0, and if the prediction mode of the coding unit is IBC (CU mode = IBC), the context index of the I slice is Can be set to the new 6.

As shown in Tables 4 to 8, the initial value (initValue) corresponding to the newly defined context indexes (6 to 11 or 6 to 8) may be defined differently from the initial values of the existing context indexes (0 to 5). Tables 9 to 11 show initial values corresponding to new context indexes based on Table 4.

Table 9 newly defines the initial value of the context index applied to the luma conversion block, Table 10 newly defines the initial value of the context index applied to the chroma conversion block, and Table 11 shows the luma conversion block and chroma conversion block. The initial value of the context index applied to is newly defined.

A to g in Tables 9 to 11 may be set to optimal values promised by the encoding device and the decoding device, which may be set to a value that minimizes the rate-distortion ratio. a to g may or may not be the same as the existing initial value 139.

Whether or not the above technique is performed, that is, whether the transform skip flag is entropy-coded with reference to the prediction mode of the coding unit, is determined by a parameter set transmitted from a higher layer, for example, a sequence parameter set (SPS), SPS_extension, picture It can be signaled in a parameter set (Picture parameter set, etc.). Or it may be signaled at another higher level.

SPS signaling information indicating whether to use the proposed technology itself according to an example of the present invention is shown in Table 12.

In Table 12, when transform_skip_context_modification_enabled_flag is 0, the context index of transform_skip_flag is defined as existing 0 to 5, and when transform_skip_context_modification_enabled_flag is 1, the context index of transform_skip_flag is set according to Tables 4 to 8, which are embodiments according to the present invention. can indicate being

Alternatively, when transform_skip_context_modification_enabled_flag is 0, the context index of transform_skip_flag indicates that it is previously defined as 0 to 5, and when transform_skip_context_modification_enabled_flag is 1, the context index of transform_skip_flag may indicate that it is newly defined instead of the existing 0 to 5.

4 is a flowchart illustrating an entropy decoding method of a conversion skip flag according to an embodiment of the present invention. Referring to FIG. 4, the entropy decoding method according to the present invention will be described as follows.

First, the entropy decoding unit may determine the context index for the transform skip flag based on the prediction mode of the coding unit (S410).

The context index may be determined based on a prediction mode of a coding unit, eg, whether the coding unit's prediction mode is an intra block copy mode.

Also, the context index may be determined according to whether the current slice is an I slice, a P slice, or a B slice.

Also, the context index may be determined according to whether the current block is a luma block or a chroma block.

When the context index is determined, the entropy decoding unit may perform an initialization process of setting a probability value corresponding to the determined context index as an initial value (S420).

An initial value may also be set based on a prediction mode of a coding unit.

If the context index is set to a new, non-existent value, the initial value may be set to the same value as the previous one or to a new value.

The entropy decoding unit may update the probability based on the set context index and the initial value, and through this process may derive context information about bins constituting the codeword of the conversion skip flag (S430).

Step S430 may be a step including steps S410 and step S420. In other words, the entropy decoder may perform an initialization setting process of determining a context index to derive context information and setting a probability value corresponding to the context index as an initial value.

Thereafter, the entropy decoding unit may derive the value of the transform skip flag by performing arithmetic decoding on the bin based on the context information (S440).

As described above, an aspect of the present invention further defines a context index determined by referring to a prediction mode of a coding unit compared to conventional entropy coding, and sets the initValue of an individual context index when the context index is additionally defined. provides a new definition.

Transformation performed in the decoding process above actually means inverse transform, which is the inverse process of the transform performed by the encoding device, but inverse transform is also a type of transform, so there will be no confusion in its actual meaning.

The method according to the present invention described above may be produced as a program to be executed on a computer and stored in a computer-readable recording medium. Examples of the computer-readable recording medium include ROM, RAM, CD-ROM, and magnetic tape. , floppy disks, optical data storage devices, and the like, and also includes those implemented in the form of carrier waves (for example, transmission through the Internet).

The computer-readable recording medium is distributed to computer systems connected through a network, so that computer-readable codes can be stored and executed in a distributed manner. In addition, functional programs, codes, and code segments for implementing the method can be easily inferred by programmers in the technical field to which the present invention belongs.

In the foregoing 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 steps, and some steps may occur in a different order or concurrently with other steps as described above. can In addition, those skilled in the art will understand that the steps shown in the flow chart are not exclusive, that other steps may be included, or that one or more steps of the flow chart may be deleted without affecting the scope of the present invention. You will understand.

111: motion prediction unit 112: motion compensation unit
120: intra prediction unit 130: conversion unit

Claims (3)

an inverse transform unit generating a residual block of the current block based on a transform skip flag indicating whether to skip transform of the current block in the current picture;
a prediction unit that derives a block vector for the current block and generates a prediction block of the current block based on a reference block indicated by the block vector; and
An adder for reconstructing the current block based on the residual block and the prediction block;
The current block is a block predicted in IBC mode, the reference block is a block in the current picture,
An initial value for each context index for initialization of context information used for arithmetic decoding of the transform skip flag of the current block is determined differently according to the type of the current slice,
The conversion skipping flag is obtained from a bitstream based on information indicating whether conversion skipping is allowed. a prediction unit determining a block vector of a current block in a current picture and generating a prediction block of the current block based on a reference block indicated by the block vector;
a subtractor for generating a residual block of the current block based on the prediction block; and
A transform unit encoding the residual block based on whether the transform of the current block is omitted;
The current block is a block predicted in IBC mode, the reference block is a block in the current picture,
Whether or not to skip transforms for the current block is encoded using the transform skip flag of the current block, and the initial value for each context index for initializing context information used for arithmetic encoding of the transform skip flag of the current block is It is determined differently depending on the type,
The conversion skipping flag is encoded into a bitstream based on information indicating whether conversion skipping is allowed or not. A computer-readable recording medium storing a bitstream generated by an image encoding device, the image encoding device comprising:
a prediction unit determining a block vector of a current block in a current picture and generating a prediction block of the current block based on a reference block indicated by the block vector;
a subtractor for generating a residual block of the current block based on the prediction block; and
A transform unit encoding the residual block based on whether the transform of the current block is omitted;
The current block is a block predicted in IBC mode, the reference block is a block in the current picture,
Whether or not to skip transforms for the current block is encoded using the transform skip flag of the current block, and the initial value for each context index for initializing context information used for arithmetic encoding of the transform skip flag of the current block is It is determined differently depending on the type,
The conversion skipping flag is encoded into the bitstream based on information indicating whether conversion skipping is allowed.

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