KR20220116109A - Entrpy decoding method and apparatus for transform skip information - Google Patents

Abstract

According to a decoding method of an image comprises: a step of parsing a representative flag, which represents first information commanding whether to skip transformation of a transformation block divided from a coding unit, with information on the coding unit when a size of the current coding unit can include the transformation block capable of skipping transformation; a step of determining whether the information is parsed based on the representative flag; a step of inferring the first information based on the representative flag when parsing of the first information is not necessary and parsing the first information when parsing of the first information is necessary; and a step of performing or skipping transformation of the transformation block according to the first information. The present invention can increase efficiency of video encoding.

Description

Method and apparatus for entropy decoding of transform skip 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 expanding not only domestically but also worldwide, many users are getting used to high-resolution and high-definition images, and accordingly, many institutions are spurring the development of next-generation imaging devices. 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 higher resolution and high-definition images is required.

For image compression, inter (in-screen) prediction technology that predicts pixel values included in the current picture from temporally previous and/or later pictures, 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 allocating a short code to a symbol with a high frequency of occurrence and a long code for assigning a long code to a symbol with a low frequency of occurrence, etc. may be used.

Among prediction techniques used for image prediction, intra prediction is a technique for compressing an image by removing spatial similarity within the current frame or current picture. In such intra prediction, a prediction value for the current prediction block is generated with reference to pixel values adjacent to the current block, and information on the prediction value is signaled.

Among prediction techniques used for image prediction, inter prediction is a technique for compressing an image by removing temporal similarity between different frames. In inter prediction, a region having a pixel value similar to that of the current block is searched for and found in another frame, and this is used as a prediction value for the current prediction block.

The predicted 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 (MVd). can

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

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

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

An entropy decoding method of a transform skip flag indicating whether to skip transform according to an embodiment of the present invention includes the steps of deriving context information on bins constituting a codeword of the transform skip flag; and deriving the 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 is based on a prediction mode of a coding unit. information can be derived.

The deriving context information for the bin may include determining a context index for the transform skip flag, wherein 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.

The deriving the context information for the bin may include performing initialization by setting 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 a coding unit.

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

According to one aspect of the present invention, when a specific prediction mode is used in an image in which transform omission frequently occurs, context-based entropy coding is performed in consideration of a high probability of occurrence of transform omission to improve image encoding/decoding efficiency. can be increased.

Specifically, the effect of the present invention can be prominently shown in encoding and decoding of artificial images created by a computer.

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 for explaining IBC prediction according to an embodiment of the present invention.
4 is a flowchart illustrating a method for entropy decoding of a transform 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, 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 composed 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 of each component are combined to form one component, or one component can be divided into a plurality of components to perform a function, and each Integrated embodiments and separate embodiments of the components are also included in the scope of the present invention without departing from the essence of the present invention.

In addition, some of the components are not essential components for performing essential functions in the present invention, but may be optional components for merely improving performance. The present invention can be implemented by including only essential components to implement the essence of the present invention except for components used for improving performance, and only having a structure including essential components excluding optional components used for improving performance Also included in the scope of the present invention.

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 predictor 110 , a subtractor 125 , a transform unit 130 , a quantizer 140 , an entropy encoder 150 , and 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 perform encoding on an input image in an intra mode or an inter mode and output a bit stream. Intra prediction refers to intra prediction, and inter prediction refers to inter prediction. In the intra mode, a switch (not shown) is switched to intra, and in the inter mode, the switch is switched to inter. The image encoding apparatus 100 may generate a prediction block for an input block of an input image, and then 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. have. Also, the image encoding apparatus may include a switch (not shown), and the switch may be switched between the inter prediction unit, the intra prediction unit, and the IBC prediction unit.

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

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

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. For some residual blocks, the transform unit 130 may be configured to omit transform, and even in this case, the output of the transform unit 130 is referred to as a transform coefficient for convenience. In addition, the quantization unit 140 may quantize the input transform coefficient according to the quantization parameter to output a quantized coefficient.

The entropy encoding unit 150 entropy-encodes a symbol according to a probability distribution based on the values calculated by the quantization unit 140 or an encoding parameter value calculated during 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, removing statistical redundancy, and expressing them as a decodable binary number sequence.

Here, the symbol means a syntax element to be encoded/decoded, a coding parameter, and a value of a residual signal. The encoding parameter is a parameter necessary for encoding and decoding, and may include information that can be inferred during the encoding or decoding process as well as information encoded by the encoding device and transmitted to the decoding device, such as syntax elements, for encoding or decoding an image. information needed to do so.

Coding parameters include, for example, intra/inter prediction modes, motion/motion vectors, reference image indexes, coding block patterns, presence or absence of residual signals, transform coefficients, quantized transform coefficients, quantization parameters, block size, and block partition information. It may include values or statistics such as In addition, the residual signal may mean a difference between the original signal and the predicted signal, and a signal in which the difference between the original signal and the predicted signal is transformed or a signal in which the difference between the original signal and the predicted signal is transformed and quantized. , or a signal in which the difference signal between the original signal and the prediction signal or the difference signal between the original signal and the prediction signal is a quantized signal. The residual signal may be referred to as a residual block in block units.

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 the size of the bit string for the symbols to be encoded is increased. can be reduced. Accordingly, compression performance of image encoding may be improved through entropy encoding.

For entropy encoding, an encoding method such as exponential golomb, Context-Adaptive Variable Length Coding (CAVLC), or Context-Adaptive Binary Arithmetic Coding (CABAC) may be used. For example, the entropy encoding unit 150 may store a table for performing entropy encoding, such as a variable length coding (VLC) table, and the entropy encoding unit 150 may store the stored variable length encoding. Entropy encoding can be performed using a (VLC) table. In addition, the entropy encoder 150 derives a binarization method of a target symbol and a probability model of a target symbol/bin, and then performs entropy encoding using the derived binarization method or probability model. You may.

The quantized coefficient may be inverse quantized by the inverse quantizer 160 and inversely transformed by the inverse transform unit 170 . For some blocks, the inverse transform unit 170 may be configured to omit the inverse transform, and even in this case, the output of the inverse transform unit 170 is called an inverse transformed coefficient for convenience. The inverse-quantized and inverse-transformed coefficients may be added to the prediction block through the adder 175 and a reconstructed block may be generated.

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 reconstructed block passing through the filter unit 180 may be stored in the reference image 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, a prediction unit 240, a filter unit 260, and a reference image buffer ( 270).

The image decoding apparatus 200 may receive a bitstream output from the encoding apparatus, perform decoding in an intra mode, an inter mode, or an 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 received bitstream, generating a prediction block, and adding the reconstructed residual block and the prediction 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. The entropy decoding method is a method of generating each symbol by receiving a binary string as an input. The entropy decoding method is similar to the entropy encoding method described above.

The quantized coefficient is inverse quantized by the inverse quantization unit 220 and inverse 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. For some blocks, the inverse transform unit 230 may be configured to omit the inverse transform. Also, the inverse quantization unit 220 may be configured to be omitted for some blocks.

The prediction unit 240 includes 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. can be included as

In the intra mode, the intra prediction unit may generate a prediction block by performing spatial prediction using pixel values of an already encoded block around the current block. In the inter mode, the motion compensator 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, searching within the current picture, to obtain a prediction value and a block vector for the current block. The prediction by the IBC prediction unit is described in detail below.

The reconstructed residual block and the prediction block are added through the adder 255 , and the added block passes 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 outputs a reconstructed image, that is, a reconstructed image. The restored 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 , Components directly related to image decoding, for example, entropy decoding unit 210, inverse quantization unit 220, inverse transform unit 230, prediction unit 240, filter unit 260, etc. are distinguished from other components. Thus, it can be expressed as a decoder or a decoder.

Also, the image decoding apparatus 200 may further include a parsing unit (not shown) that parses information related to the encoded image included in the 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 may be used as a reference block of the current block, and a block vector (hereinafter, BV) similar to a motion vector used for inter prediction to indicate the location of the specific region. ) can be used.

In the case of conventional inter prediction, the reference picture is a previous picture or a later 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 coding tree unit (CTU) on the left adjacent to the current prediction block in the current picture may be selected as a reference block of the current prediction block.

When IBC prediction is performed, an area for searching 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 within the current CTU to which the current prediction block belongs or a left CTU adjacent to the current CTU.

Conversely, when performing IBC prediction, it may be possible to extend a region for searching a reference block to all regions that have been decoded before the current coding unit in the current picture.

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

BV may be derived from a BV predictor and a BV difference similar to a motion vector.

The BV predictor for the current block may be coded by the encoding device and signaled to the decoding device, and the BV of a block previously predicted in the 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.

In this case, since there is a need to reset or refresh data 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 a current coding unit.

The BV difference value represents a difference between BV and BV predictors, and may be coded in the encoding apparatus as BVdx and BVdy values and signaled to the decoding apparatus.

On the other hand, in the existing video coding method, transform skip (Transform Skip) is applied to a block containing a lot of high-frequency components to omit the transform.

For example, a value for transform_skip_enabled_flag signaled in an upper stage such as a picture parameter set is 1, and when encoding/decoding a residual signal, a coded block flag (CBF) is 1 for all 4x4 size transform blocks. A flag (transform_skip_flag) indicating whether to skip transform for (transform block, TB) 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 a transform block to which transform skip signaled in the picture parameter set can be applied. A flag (transform_skip_flag) indicating whether to skip transform can be individually signaled for all transform blocks that are less than or equal to and whose CBF is 1.

On the other hand, whether or not transform is omitted in conventional image encoding and decoding is signaled by syntax element information called transform_skip_flag[x0][y0][cIdx] in units of transform blocks (TB), and this signal is entropy-encoded and a bitstream is sent to Here, x0 and y0 represent the upper leftmost position of the transform block, and 'cIdx' represents color information of the current transform block. For the luma signal, cIdx may be set to 0, and for the 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 a context for each syntax element. As an example of the transform skip flag (transform_skip_flag), as shown in Table 1, six context indexes may be defined.

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

The initType is a value determined according to the type of the slice on which encoding/decoding is currently performed. In the case of an I slice, initType is set to 0, and in the case of a P slice and a B slice, it may be set differently according to a cabac_init_flag value. For example, in the case of cabac_init_flag = 0, initType may be set to 1 for the P slice, and initType may be set to 0 for the B slice.

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

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

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

The entropy decoding unit is a 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 the probability information stored in the upper right CTU among the first CTUs of a row. ) is initialized.

In this case, 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, 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 indexes are 1) the current slice type and 2) whether the current transform block represents the luma component, or It may be determined according to whether a chroma component is represented.

Meanwhile, in the coding unit predicted by IBC described with reference to FIG. 3 , there is a feature that the occurrence of transformation omission is frequent. However, in the context design process for entropy coding of the existing transform skip flag, the correlation between IBC and the transform skip mode is not considered.

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

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

* 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 the I slice is 0, and the initType of the P slice and the B slice are 1 and 2, respectively.

In addition, in accordance with an 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 in the case of a mode other than IBC can also be expanded.

Compared with the existing entropy coding, the present invention further defines a context index determined by referring to the prediction mode of the coding unit, and newly defines the initValue of an individual context index when the context index is additionally defined.

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

Referring to Table 4, compared with Table 2, additionally 6 context indices are further defined, and as a result, the number of context indices for the conversion skip flag may be 12.

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

Referring to Table 5, compared with Table 2, three additional context indexes are further defined, and as a result, the number of context indexes for the conversion skip flag may be nine.

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

Referring to Table 6, compared with Table 2, three additional context indexes are further defined, and as a result, as shown in Table 5, the number of context indexes for the conversion skip flag may be nine.

According to another embodiment of the present invention, the new context indexes added to Tables 4 to 6 do not have to be different from each other. Some context indexes may be set as existing ones, and some context indexes may be set as new ones. When the number of context indexes increases and entropy encoding/decoding becomes complicated, the complexity can be reduced.

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

According to another embodiment, the context index may be determined as shown in Table 8, and according to Table 8, the context index may be determined according to whether the prediction mode of the coding unit is IBC according to the 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, when 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 The new 6 can be set.

As shown in Tables 4 to 8, an 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. Based on Table 4, initial values corresponding to the new context index are shown in Tables 9 to 11.

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

A to g of Tables 9 to 11 may be set as optimal values promised by the encoding apparatus and the decoding apparatus, 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 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 may be signaled in a parameter set (Picture parameter set, etc.). Alternatively, it may be signaled at another higher level.

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

In Table 12, when transform_skip_context_modification_enabled_flag is 0, the context index of transform_skip_flag indicates that it 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 that

Alternatively, when transform_skip_context_modification_enabled_flag is 0, the context index of transform_skip_flag indicates that it is defined as existing 0-5, 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 0-5.

4 is a flowchart illustrating a method for entropy decoding of a transform skip flag according to an embodiment of the present invention. The entropy decoding method according to the present invention will be described with reference to FIG. 4 as follows.

First, the entropy decoder may determine a 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 the coding unit, eg, whether the prediction mode of the coding unit is an intra block copy mode.

In addition, 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 decoder may perform an initialization process of setting a probability value corresponding to the determined context index as an initial value ( S420 ).

The initial value may also be set based on the prediction mode of the coding unit.

If the context index is set to a new value other than the existing one, the initial value may be set to the same value as the existing value or set to a new value.

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

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

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

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

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

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

The computer-readable recording medium is distributed in a network-connected computer system, so that the computer-readable code 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 art to which the present invention pertains.

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 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 of the flowchart 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: transform unit

Claims (3)

an inverse transform unit for generating a residual block of the current block based on a transform skip flag indicating whether to skip transform for the current block in the current picture;
a prediction unit for deriving a block vector for the current block and generating 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 a type of a current slice. a prediction unit that determines a block vector for a current block in a current picture, and generates 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
and a transform unit for encoding the residual block based on a transform skip flag indicating whether transform for 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,
An image encoding apparatus in which an initial value for each context index for initialization of context information used for arithmetic encoding of the transform skip flag of the current block is determined differently according to a type of a current slice. A computer-readable recording medium storing a bitstream generated by a video encoding apparatus, the video encoding apparatus comprising:
a prediction unit determining a block vector for 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
and a transform unit for encoding the residual block based on a transform skip flag indicating whether transform for 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,
An initial value for each context index for initialization of context information used for arithmetic encoding of the transformation skip flag of the current block is determined differently according to a type of a current slice.

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