KR20240013885A - Entrpy decoding method and apparatus for transform skip information - Google Patents

Abstract

The video decoding method according to the present invention includes a representative representing first information indicating whether or not to skip transform of a transform block divided from the coding unit when the size of the current coding unit may include a transform block in which transform can be omitted. Parsing a flag into information about the coding unit, determining whether to parse the first information based on the representative flag, and, if parsing the first information is not necessary, based on the representative flag It includes inferring first information, parsing the first information if parsing of the first information is necessary, and performing or omitting transformation on the transform block according to the first information.

Description

Entropy decoding method and device for transformation skip information based on prediction mode {ENTRPY DECODING METHOD AND APPARATUS FOR TRANSFORM SKIP INFORMATION}

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

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

For video compression, inter prediction technology predicts the pixel value included in the current picture from the temporally previous and/or subsequent picture, and uses pixel information in the current picture to predict the pixel value included in the current picture. Intra (inter-screen) prediction technology that predicts, entropy coding technology that assigns short codes to symbols with a high frequency of appearance and long codes to symbols with a low frequency of appearance, etc. can be used.

Among the prediction techniques used to predict images, intra prediction is a technique that compresses images by removing spatial similarities within the current frame or current picture. During such intra prediction, a prediction value for the current expected block is generated by referring to surrounding pixel values adjacent to the current block, and information about this is signaled.

Among the prediction techniques used to predict images, inter prediction is a technique that compresses images by removing temporal similarities between different frames. During inter prediction, an area with similar pixel values to the current block is searched for in another frame and used as a prediction value for the current prediction block.

The predicted value determined through search, or 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). You can.

In the case of intra prediction currently being applied, since a prediction block is generated using a block adjacent to the current block, there is a limitation in that pixels in an area spatially distant from the current block cannot be referenced. Additionally, in the case of inter prediction, even if there is a region in the current picture with similar pixel values to the current block, it has a limitation in 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 the coding unit (CU) when entropy coding/decoding the transformation skip information of compressed signals when compressing video. , thereby providing a method and device for increasing coding efficiency.

According to the present invention, when similar patterns occur repeatedly within a screen and residual signals containing a large amount of high frequencies are 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, an image encoding/decoding method that can increase encoding efficiency by signaling a flag representing whether to skip conversion and a device using the same are provided.

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

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

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

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

The step of deriving context information for the bin involves 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 the 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 the transform_skip_flag according to the prediction mode of the coding unit and allowing reference to the prediction mode of the coding unit in the entropy coding process. By reducing the amount, video coding 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 considering the high probability of transform omission occurring to improve the encoding/decoding efficiency of the image. can be increased.

Specifically, this effect of the present invention can be noticeable in encoding and decoding of artificial images created by computers.

Figure 1 is a block diagram showing the configuration of a video encoding device according to an embodiment to which the invention is applied.
Figure 2 is a block diagram showing the configuration of a video decoding device according to an embodiment to which the present invention is applied.
Figure 3 is a diagram for explaining IBC prediction according to an embodiment of the present invention.
Figure 4 is a flowchart showing an entropy decoding method of a transform skip flag according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the 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 will be omitted.

Additionally, the components appearing in the embodiments of the present invention are shown independently to show different characteristic functions, and this does not mean that each component is comprised of separate hardware or a single software component. That is, each component is listed and included as a separate component for convenience of explanation, and at least two of each component can be combined to form one component, or one component can be divided into a plurality of components to perform a function, and each of these components can perform a function. Integrated embodiments and separate embodiments of the constituent parts are also included in the scope of the present invention as long as they do not deviate from the essence of the present invention.

Additionally, some components may not be essential components that perform essential functions in the present invention, but may simply be optional components to improve performance. The present invention can be implemented by including only essential components for implementing the essence of the present invention excluding components used only to improve performance, and a structure including only essential components excluding optional components used only to improve performance. is also included in the scope of rights of the present invention.

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

Referring to FIG. 1, the image encoding device 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 device 100 may perform encoding on an input image in intra mode or inter mode and output a bit stream. Intra prediction refers to prediction within a screen, and inter prediction refers to prediction between screens. In the case of intra mode, the switch (not shown) is converted to intra, and in the case of inter mode, the switch is converted to inter. The image encoding apparatus 100 may generate a prediction block for an input block of an input image and then encode the difference between the input block and the prediction block.

The prediction unit may include detailed components of an intra prediction unit that performs intra prediction, a motion prediction unit and motion compensation unit that performs inter prediction, and an IBC prediction unit that performs intra block copy (IBC) prediction. there is. Additionally, the video encoding device may include a switch (not shown), and the switch may be switched between an inter prediction unit, an intra prediction unit, and an IBC prediction unit.

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

In the case of inter mode, the motion prediction unit can obtain a motion vector by finding an area 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 prediction unit can perform motion prediction, that is, search, within the current picture to determine an area similar to the current block and obtain a prediction value and block vector for the current block. Predictions by the IBC prediction unit are 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 remaining block and output a transform coefficient. The transform unit 130 may be configured to omit transformation for some remaining blocks. In this case, the output of the transform unit 130 is also called a transform coefficient for convenience. Additionally, the quantization unit 140 may quantize the input transform coefficient according to the quantization parameter and output a quantized coefficient.

The entropy encoding unit 150 entropy encodes symbols according to a probability distribution based on values calculated by the quantization unit 140 or encoding parameter values calculated during the encoding process to produce a bit stream. Can be printed. The entropy encoding method is a method of receiving symbols with various values as input and expressing them as a string of decodable binary numbers while removing statistical redundancy.

Here, the symbol means a syntax element to be encoded/decoded, a coding parameter, a residual signal value, etc. Encoding parameters are parameters necessary for encoding and decoding, and may include information that is encoded in the encoding device and transmitted to the decoding device, such as syntax elements, as well as information that can be inferred during the encoding or decoding process and may include information that can be inferred during the encoding or decoding process. This refers to the information needed when doing this.

Encoding parameters include, for example, intra/inter prediction mode, translation/motion vector, reference image index, coding block pattern, presence or absence of residual signal, transform coefficient, quantized transform coefficient, quantization parameter, block size, block division information. It may include values or statistics such as: In addition, the residual signal can refer to the difference between the original signal and the predicted signal, and can also be 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 the difference signal between the original signal and the prediction signal or the difference signal between the original signal and the prediction signal may mean a signal in a quantized form. The residual signal can be referred to as a residual block in block units.

When entropy coding 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 the symbols, thereby reducing the size of the bit string for the symbols to be encoded. can be reduced. Therefore, the compression performance of video encoding can be improved through entropy coding.

For entropy coding, coding methods such as exponential gollomb, CAVLC (Context-Adaptive Variable Length Coding), and CABAC (Context-Adaptive Binary Arithmetic Coding) may be used. For example, the entropy encoding unit 150 may store a table for performing entropy encoding, such as a Variable Length Coding/Code (VLC) table, 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 transformation, 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 restored block may be generated.

The restored block passes through the filter unit 180, and the filter unit 180 applies at least one of a deblocking filter, Sample Adaptive Offset (SAO), and Adaptive Loop Filter (ALF) to the restored block or restored picture. can do. The restored block that has passed through the filter unit 180 may be stored in the reference image buffer 190.

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

Referring to FIG. 2, the image decoding device 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 video decoding device 200 may receive a bitstream output from an encoding device, perform decoding in intra mode, inter mode, or IBC mode, and output a reconstructed image, that is, a restored image.

The image decoding apparatus 200 may obtain a reconstructed residual block from an input bitstream, generate a prediction block, and then add 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. The entropy decoding method is a method that receives a string of binary numbers and generates each symbol. The entropy decoding method is similar to the entropy encoding method described above.

The quantized coefficient is inversely quantized in the inverse quantization unit 220 and inversely transformed in the inverse transformation unit 230. As a result of the inverse quantization/inverse transformation of the quantized coefficient, a restored residual block may be generated. The inverse transform unit 230 may be configured to omit the inverse transform for some blocks. Additionally, the inverse quantization unit 220 may also be configured to be omitted for some blocks.

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

In the case of intra mode, the intra prediction unit may generate a prediction block by performing spatial prediction using pixel values of already encoded blocks surrounding the current block. In the case of 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 can perform motion prediction, that is, search, within the current picture to determine an area similar to the current block and obtain a prediction value and block vector for the current block. Predictions by the IBC prediction unit are described in detail below.

The restored residual block and the prediction 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 restored block or a restored picture. The filter unit 260 outputs a reconstructed image, that is, a restored image. The restored image can be stored in the reference image buffer 270 and used for inter-screen prediction.

Among the entropy decoding unit 210, inverse quantization unit 220, inverse transform unit 230, prediction unit 240, filter unit 260, and reference image buffer 270 included in the image decoding device 200. Components directly related to image decoding, such as the entropy decoder 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 decoding unit or a decoding unit.

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

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

In the case of IBC prediction, a specific area 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 (BV) is used to indicate the location of this specific area. ) can be used.

In the case of conventional inter prediction, the reference picture is a previous picture or a subsequent picture that is 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, an area existing in the left coding tree unit (CTU) adjacent to the current prediction block in the current picture may be selected as a reference block for the current prediction block.

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

Conversely, when performing IBC prediction, it may be possible to expand the area for searching the reference block to all areas in the current picture where decoding has been completed before the current coding unit.

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

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

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

At this time, since there is a need to reset or refresh the 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 the current coding unit.

The BV difference value represents the difference between BV and BV predictor, and can be coded in the encoding device as BVdx and BVdy values and signaled to the decoding device.

Meanwhile, among existing video coding methods, Transform Skip, which omits transformation for blocks containing many high-frequency components, is applied.

For example, the value of transform_skip_enabled_flag signaled at a higher level, such as a picture parameter set, is 1, and when coding/decoding the residual signal, all 4x4-sized transform blocks with a CBF (coded block flag) of 1. A flag (transform_skip_flag) indicating whether to skip transformation can be individually signaled for (transform block, TB).

Or, the value for transform_skip_enabled_flag is 1, and the size of the current transform block is larger than the maximum block size defined by information indicating the maximum size of the transform block to which transform skipping can be applied (e.g., log2_max_transform_skip_block_size_minus2) signaled in the picture parameter set. A flag (transform_skip_flag) indicating whether to skip transformation can be individually signaled for all transform blocks that are less than or equal to and have a CBF of 1.

Meanwhile, in conventional video encoding and decoding, whether or not transform is omitted is signaled in the transform block (TB) unit as syntax element information called transform_skip_flag[ is transmitted to Here, x0, y0 represents the top left position of the transform block, and ‘cIdx’ represents the color information of the current transform block. For a luma signal, cIdx is set to 0, and for a chroma signal, cIdx can 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 example, for the transformation skip flag (transform_skip_flag), six context indexes may be defined as shown in Table 1.

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

initType is a value determined depending on the type of slice on which encoding/decoding is currently performed. For I slices, initType is set to 0, and for P slices and B slices, it can be set differently depending on the cabac_init_flag value. For example, if 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.

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

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

In CABAC, the 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 decoder generates a probability value (pState index) for each context index for the first syntax element of an independent slice segment or 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. ) perform initialization.

At this time, 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 the initial value of the transformation skip flag (transform_skip_flag) according to the context index.

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 determines 1) the current slice type and 2) whether the current transform block represents a luma component, or It can be determined depending on whether it represents a chroma component.

Meanwhile, the coding unit predicted by IBC described with reference to FIG. 3 has the characteristic that transformation omission frequently occurs. However, the relationship between IBC and transform skip mode was not considered in the context design process for entropy coding of the existing transform skip flag.

That is, in the conventional case, when entropy coding/decoding of the transform skip flag (transform_skip_flag), the context was determined with reference to only the slice type and color component, 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 can be increased by entropy encoding/decoding the transform skip flag using the determined context.

The present invention defines the context of the transform skip flag according to the prediction mode of the coding unit, reduces the amount of bits for signaling transform skip by referring to the prediction mode of the coding unit in the entropy coding process, and consequently increases video coding efficiency. Provides a method and device 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 the I slice is 0, and the initTypes of the 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 to this and in case of a mode other than IBC It can also be expanded to .

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

According to one embodiment of the present invention, when determining the context index with reference to the prediction mode of the coding unit, it can be applied to both the luma component and the chroma component. This can be expressed in a table as Table 4.

Referring to Table 4, compared to Table 2, an additional 6 context indexes are defined, and as a result, the number of context indexes for the conversion skip flag can 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 can be applied only to the luma component. This can be expressed in a table as Table 5.

Referring to Table 5, compared to Table 2, three additional context indexes are defined, and as a result, the context index for the conversion skip flag can be 9.

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

Referring to Table 6, compared to Table 2, three additional context indexes are defined, and as a result, as shown in Table 5, there can be 9 context indexes for the conversion skip flag.

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

According to Table 7 below, when the prediction mode of the coding unit is IBC, one context index can 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 depending on whether the prediction mode of the coding unit is IBC depending on the slice type.

Referring to Table 8, the context index is determined depending on whether the prediction mode of the coding unit is IBC only when the slice type is I slice. 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 It can be set to a new 6.

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

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 newly defines the initial value of the context index applied to the luma conversion block and chroma conversion block. The initial value of the context index applied to is newly defined.

A to g of Tables 9 to 11 can be set to the optimal values promised by the encoding device and decoding device, which can 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 of 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 the parameter set transmitted from the upper layer, for example, 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.

The SPS signaling information indicating whether to use the technology itself proposed 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, it indicates that the context index of transform_skip_flag is defined as the 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. It can indicate that something is happening.

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

Figure 4 is a flowchart showing an entropy decoding method 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 the prediction mode of the coding unit, for example, whether the prediction mode of the coding unit is intra block copy mode.

Additionally, the context index may be determined depending on whether the current slice is an I slice, a P slice, or a B slice.

Additionally, the context index may be determined depending on 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 the 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 rather than the existing value, the initial value may be set to the same value as the existing value or may be set to a new value.

The entropy decoder can update the probability based on the set context index and initial value, and through this process can derive context information about the bin constituting the codeword of the conversion 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 to derive context information and perform an initialization process of setting a probability value corresponding to the context index as an initial value.

Thereafter, the entropy decoder may perform arithmetic decoding on the bin based on context information to derive the value of the conversion skip flag (S440).

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

In the above, the transformation performed in the decoding process actually refers to an inverse transform, which is the reverse process of the transformation performed by the encoding device. However, since inverse transformation is also a type of transformation, there is no possibility of confusion regarding its actual meaning.

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

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

In the above-described embodiments, the methods are described based on flowcharts 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 simultaneously with other steps as described above. You can. Additionally, a person of ordinary skill in the art will recognize that the steps shown in the flowchart are not exclusive, and that other steps may be included, or one or more steps in 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: conversion unit

Claims (3)

an inverse transform unit that generates 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 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 that restores the current block based on the residual block and the prediction block,
The current block is a block predicted in IBC mode, and the reference block is a block in the current picture,
The initial value for each context index for initializing context information used for arithmetic decoding of the transform skip flag of the current block is determined differently depending on the type of the current slice,
The image decoding device wherein the transform skip flag is obtained from a bitstream based on a comparison between the size of the current block and a predetermined threshold. 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
A transform unit that encodes the residual block based on whether transform for the current block is omitted,
The current block is a block predicted in IBC mode, and the reference block is a block in the current picture,
Whether or not to skip the transform 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 the context information used for arithmetic coding of the transform skip flag of the current block is the value of the current slice. It is determined differently depending on the type,
The video encoding device wherein the transform skip flag is encoded into a bitstream based on a comparison between the size of the current block and a predetermined threshold. A computer-readable recording medium storing a bitstream generated by an image encoding device, the image encoding device comprising:
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
A transform unit that encodes the residual block based on whether transform for the current block is omitted,
The current block is a block predicted in IBC mode, and the reference block is a block in the current picture,
Whether or not to skip the transform 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 the context information used for arithmetic coding of the transform skip flag of the current block is the value of the current slice. It is determined differently depending on the type,
The conversion skip flag is encoded into the bitstream based on a comparison of the size of the current block with a predetermined threshold.

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