KR102138197B1 - Transform skip signaling method and apparatus for video coding - Google Patents

Abstract

In the method of decoding an image according to the present invention, when the size of the current coding unit may include a transform block capable of omitting transform, a representative representing first information indicating whether to skip transform of a transform block split from the coding unit Parsing a flag into information for the coding unit; determining whether to parse the first information based on the representative flag; and, if parsing of the first information is not required, based on the representative flag. Inferring first information, and parsing the first information when parsing of the first information is required, and performing or omitting conversion of the transform block according to the first information.

Description

Method and apparatus for indicating whether to omit conversion for image compression{TRANSFORM SKIP SIGNALING METHOD AND APPARATUS FOR VIDEO CODING}

The present invention relates to a video encoding and decoding process, and more particularly, to a video encoding/decoding method and apparatus for indicating whether or not to skip conversion.

Recently, as broadcast services having high definition (HD) resolution have been expanded not only in Korea but also globally, many users are accustomed to high-resolution and high-definition video, and accordingly, many organizations are accelerating the development of next-generation video devices. In addition, with the increasing interest in UHD (Ultra High Definition), which has a resolution of 4 times higher than that of HDTV, there is a need for a compression technology for higher resolution and higher quality images.

For image compression, an inter prediction technique that predicts a pixel value included in a current picture from temporally previous and/or subsequent pictures, and a pixel value included in the current picture using pixel information in the current picture An intra prediction technique for predicting, an entropy encoding technique for assigning a short code to a symbol with a high frequency of appearance and a long code to a symbol with a low frequency of frequency may be used.

On the other hand, when encoding or decoding an image, specifically, when encoding or decoding an image signal or a residual signal for an image, a transform omission mode that omits a conversion process may be applied. Currently, the transform omission mode may be applied to a transform block (TB) having a size of 4x4 having a non-zero coefficient (ie, a coded block flag (CBF) of 1). In addition, flag (transform_skip_flag) information indicating whether a transform omission mode is applied is signaled for each transform block.

The present invention provides an image encoding/decoding method and an apparatus using the same, which reduces the amount of bits for signaling conversion omission and increases the image encoding efficiency.

In the present invention, since a similar pattern occurs repeatedly within a screen, and when a residual signal containing a large amount of high frequency frequently occurs, there is a possibility that transform blocks in a predetermined unit may or may not have a transform skip mode in common. In this case, an image encoding/decoding method and an apparatus using the same are provided, which can increase encoding efficiency by signaling a flag representing whether or not to skip these transformations.

In the decoding method of an image according to an embodiment of the present invention, when the size of the current coding unit may include a transform block capable of omitting transform, first information indicating whether to skip transform of the transform block split from the coding unit Parsing a representative flag representing the information with respect to the coding unit, determining whether to parse the first information based on the representative flag, and when the first information is not required to be parsed, the representative flag Inferring the first information based on the first step, and parsing the first information when parsing the first information is necessary, and performing or omitting conversion of the transform block according to the first information. do.

The representative flag may represent that transform omission is not applied to the transform block.

If the representative flag is 1, the first information is inferred that conversion omission is not applied to the transform block, and if the representative flag is 0, the first information is determined through parsing and the transform block according to the determined first information You can decide whether or not to apply the conversion omission. In another simpler implementation, if the representative flag is 0, it may be determined that conversion omission is applied to the conversion block of the first information without parsing the first information.

The encoding method of an image according to another embodiment of the present invention includes determining whether transformation omission is applied to a transformation block divided from a coding unit to be coded, and first information indicating whether to omit transformation to the transformation block. Coding a representative representative flag, signaling the representative flag with information about the coding unit, and coding the first information when coding of the first information is required based on the representative flag do.

The representative flag may represent that transform omission is not applied to the transform block.

If transform omission is not applied to a transform block divided from the coding unit, the representative flag is coded as 1, and when transform omission is applied to a transform block split from the coding unit, the representative flag can be coded as 0. . In this case, first information indicating a case where transformation omission is applied and a case where transformation omission is applied for each transformation block may be additionally coded.

According to an embodiment of the present invention, there is provided an image encoding/decoding method and an apparatus using the same, which reduces a bit amount for signaling conversion omission and increases image encoding efficiency.

According to the present invention, when a similar pattern repeatedly occurs in a screen, and when a residual signal containing a large amount of high frequencies frequently occurs, there is a possibility that transform blocks in a predetermined unit are commonly or not applied to the transform omission mode. Therefore, in this case, an image encoding/decoding method and an apparatus using the same are provided, which can increase encoding efficiency by signaling a flag representing whether or not to skip these transformations.

Specifically, the effect of the present invention can be prominent in the encoding and decoding of artificial images 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 an image decoding apparatus to which the present invention is applied.
3 is a diagram for describing a transform block in a coding unit represented by a representative flag according to an embodiment of the present invention.
4 is a diagram for describing a transform block in a coding unit represented by a representative flag according to another embodiment of the present invention.
5 is a flowchart illustrating an image decoding method using a representative flag representing whether to omit conversion according to an embodiment of the present invention.
6 is a flowchart illustrating an image decoding method using a representative flag representing whether or not to skip conversion according to another embodiment of the present invention.
7 is a flowchart illustrating a process of inferring division information indicating whether a conversion unit is divided by referring to a representative flag according to an embodiment of the present invention.
8 is a diagram for explaining IBC prediction according to an embodiment of the present invention.
9 is a flowchart illustrating an image encoding method using a representative flag representing whether or not to skip conversion 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, when it is determined that detailed descriptions of related well-known configurations or functions may obscure the subject matter of the present specification, detailed descriptions thereof will be omitted.

When a component is said to be "connected" to or "connected" to another component, it is understood that other components may be directly connected to, or connected to, other components. It should be. In addition, in the present invention, description of “including” a specific configuration does not exclude a configuration other than the corresponding configuration, and means that an additional configuration may be included in the scope of the present invention or the technical spirit of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from other components. For example, the first component may be referred to as a second component without departing from the scope of the present invention, and similarly, the second component may be referred to as a first component.

In addition, the components shown in the embodiments of the present invention are shown independently to indicate different characteristic functions, and do not mean that each component is composed of separate hardware or a single software component. That is, for convenience of description, each component is listed and included as each component, and at least two components of each component are combined to form one component, or one component is divided into a plurality of components to perform a function. The integrated and separated embodiments of the components are also included in the scope of the present invention without departing from the essence of the present invention.

Also, some of the components are not essential components for performing essential functions in the present invention, but may be optional components for improving performance. The present invention can be implemented by including only components necessary for realizing the essence of the present invention, except components used for performance improvement, and structures 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 transformation 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 intra prediction, and inter prediction means inter prediction. In the intra mode, the switch (not shown) is switched to intra, and in the inter mode, the switch is switched to inter. After generating the prediction block for the input block of the input image, the image encoding apparatus 100 may encode the 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 performing inter prediction, and a motion compensation unit, and an IBC prediction unit performing intra block copy (IBC) prediction as detailed components. have. In addition, the video encoding apparatus 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 intra mode, the intra prediction unit may generate a prediction block by performing spatial prediction using pixel values of an already coded block around the current block.

In the case of the inter mode, the motion prediction 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 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 subtractor 125 may generate a residual block by the difference between the input block and the generated prediction block. The transform unit 130 may transform a residual block to output a transform coefficient. For some residual blocks, the transform unit 130 may be configured to omit the transform, and in this case, the output of the transform unit 130 is also called a transform coefficient for convenience. In addition, the quantization unit 140 may quantize the input transform coefficient according to a quantization parameter to output a quantized coefficient.

The entropy encoding unit 150 entropy-encodes a symbol according to a probability distribution based on values calculated by the quantization unit 140 or encoding parameter values calculated in an encoding process, and performs a bitstream. Can print The entropy encoding method is a method of receiving a symbol having various values and expressing it as a column of a binary number that can be decoded while removing statistical redundancy.

Here, the symbol means a syntax element to be encoded/decoded, a coding parameter, a value of a residual signal, and the like. The encoding parameter is a parameter necessary for encoding and decoding, and may include information that is encoded in an encoding device and transmitted to a decoding device, such as syntax elements, as well as information that can be inferred in the encoding or decoding process, and encode or decode an image. It means the information you need to do. Coding parameters include, for example, intra/inter prediction mode, motion/motion vector, reference image index, coding block pattern, residual signal presence, transform coefficient, quantized transform coefficient, quantization parameter, block size, block segmentation information It may include values or statistics. In addition, the residual signal may mean a 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. Alternatively, 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 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, so that the symbol is represented, so that the size of a bit string for symbols to be coded is Can be reduced. Therefore, compression performance of image encoding may be improved through entropy encoding.

For entropy encoding, encoding methods such as exponential golomb, 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 (VLC) table, and the entropy encoding unit 150 may store the variable length encoding. (VLC) entropy encoding may be performed using a table. Also, the entropy encoding unit 150 derives a binarization method of a target symbol and a probability model of a target symbol/bin, and then performs entropy coding using the derived binarization method or probability model. You may.

The quantized coefficients can be inversely quantized by the inverse quantization unit 160 and inversely transformed by the inverse transformation unit 170. For some blocks, the inverse transform unit 170 may be configured to omit the inverse transform, and in this case, the output of the inverse transform unit 170 is called an inverse transform 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 restoration block passes through the filter unit 180, and the filter unit 180 applies at least one of a deblocking filter, SAO (Sample Adaptive Offset), and ALF (Adaptive Loop Filter) to the restoration block or restoration picture. can do. The 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 an image 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 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 adding a reconstructed residual block and a predicted block after obtaining a residual block reconstructed from the received bitstream and generating a predictive block.

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

The quantized coefficients are inversely quantized by the inverse quantization unit 220 and inversely transformed by the inverse transformation unit 230. As a result of the 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 configured to be omitted for some blocks.

The prediction unit 240 is a detailed component of an intra prediction unit performing intra prediction, a motion prediction unit performing inter prediction, and a motion compensation unit, and an IBC prediction unit performing intra block copy (IBC) prediction. It can contain as.

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

The reconstructed residual block and the predicted block are added through the adder 255, and the added block is passed 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 reconstructed picture. The filter unit 260 outputs a reconstructed image, that is, a reconstructed image. The reconstructed image may 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 apparatus 200 The components directly related to the decoding of the image, 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, and the like are separated from other components Can be expressed as a decoding unit or a decoding unit.

In addition, 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. The parsing unit may also be implemented as one component of the decoding unit.

Meanwhile, among the existing video coding methods, a transform skip is applied to a block that contains many high-frequency components.

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

Alternatively, the value for 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 omission signaled in a picture parameter set can be applied. A flag (transform_skip_flag) indicating whether or not to omit the transform may be individually signaled for all transform blocks having a CBF of 1 or less.

In the case of such a transform omitting signaling method, a flag (transform_skip_flag) information indicating whether or not to omit transform is individually signaled for all transform blocks capable of omitting a transform having a CBF of 1 may cause a problem of an increase in bit amount.

Accordingly, the present invention may be one or a plurality of units included in a predetermined unit (according to one embodiment, a coding unit (CU), and another embodiment may be a prediction unit (PU)). For the purpose of reducing the amount of bits for signaling the conversion omission, and ultimately increasing the video encoding efficiency, by setting information indicating representative of whether the conversion units are omitted or not and signaling it to the decoding apparatus do.

In particular, in the case of an image in which a similar pattern repeatedly occurs in a screen or a residual signal frequently containing a large amount of high frequency is frequently generated, transformation blocks belonging to a predetermined unit are all likely to be omitted or transformed. In this case, instead of signaling a flag indicating whether to skip conversion for each individual conversion block, encoding efficiency can be increased by signaling a flag representing whether to skip conversion in a predetermined unit.

For example, in the case of an artificial image created by a computer, a repetitive similar pattern is generated or a tendency to include a high frequency is strong, so that the effect can be increased when applying the present invention.

In the description of the present invention, for convenience, a specific unit is specifically described using the term of a coding unit, but the predetermined unit of the present invention is not necessarily limited to a coding unit. Meanwhile, a coding unit and a coding block (CB) used in the present specification are as follows.

The coding unit is composed of one coding block or a plurality of coding blocks and syntax element information used by them. In the case of a color image, since there are generally three components, one coding unit has one coding block for each component, and a total of three coding blocks (for example, an image having three components, but not independently encoded for each component) Or not, or one coding block (for example, in the case of a monochrome image, or even in the case of a color image independently encoded for each component).

In addition, a transformation block (TB) to which transformation is applied or transformation omission is applied, and a transformation unit (TU) that is a unit of division are as follows.

A transform unit (TU) according to the present invention is a unit that can be split from a coding unit. One coding unit may be divided into one or a plurality of transform units for transform coding. Specifically, how to split is indicated by quadtree information using a coding unit as a root. This is called splitting (split information or split_transform_flag information). The transform unit is composed of one transform block or a plurality of transform blocks and syntax element information used by them. The transform unit may have a collective concept of transform blocks constituting each color component (eg, Y, Cb, Cr), and the number of transform blocks of one transform unit depends on the color format. can be different

The transform block corresponds to a basic unit that performs transform and quantization.

For a color image with three components, if the color format is 4:2:0 or 4:4:4, one transform unit has three transform blocks (one is the transform block for the luma component, the rest Two are transform blocks for chroma components). On the other hand, in the case of a 4:2:2 color format, there are five transform blocks (one is a transform block for luma components and the other four are transform blocks for chroma components), and each component is a monochrome image or a color image. When not encoded independently, it may have one transform block.

Meanwhile, when the color format is 4:4:4, all of the transform blocks belonging to one transform unit may have the same size.

When the color format is 4:2:0, the size of the luma transform block is the same as the size of the transform unit, but the size of the chroma transform block may be smaller than the transform unit. That is, even if the transform block belongs to the same transform unit, the size of the transform block may be changed according to luma and chroma. However, when the 8x8 coding unit is divided into quadtrees once, and the transform unit has a size of 4x4, both the luma and chroma transform blocks may have the same size of 4x4. This is because a conversion block that is too small (for example, less than 4x4) has little utility over increasing complexity in real applications.

Hereinafter, the present invention provides a method for signaling a representative flag (for example, transform_skip_all_zeros_in_cu_flag), which is information representatively representing whether or not to skip conversion of transform blocks included in a coding unit, and decoding the same.

At this time, depending on whether or not to consider the transform depth (TU depth) of transform blocks included in the coding unit, the transform blocks in the coding unit represented by the representative flag can be divided into two types as follows.

In the first case, the representative flag may only represent transform blocks of the maximum transform depth (MaxTrafoDepth) that the current coding unit can reach. In other words, it is a case where the representative flag represents a transform block of the smallest size that can be split in the current coding unit.

Here, in the expression maximum conversion depth, depth may mean the following. When the depth is 0, it may mean that the current coding unit is no longer split for conversion. In addition, when the depth is 1, it may mean that the coding unit is divided into one step into a quad tree for transformation. At this time, if the specific transform block constituting the transform unit after division becomes smaller than the minimum transform block size predetermined by the encoding apparatus, the corresponding transform block may not be further split. Also, each time the depth increases by 1, it can be further divided into quad trees under the condition that it does not become smaller than the minimum transform block size. In addition, in the description of the present invention, since the depth means that the coding unit is divided for transformation, it is used in the same sense as the term transformation depth (trafoDepth) when there is no special description.

In the second case, the representative flag can represent all transform blocks (with a size that can be omitted) in the current coding unit.

3 is a diagram for describing a transform block in a coding unit represented by a representative flag according to an embodiment of the present invention.

The embodiment of FIG. 3 shows a case where a representative flag represents transform blocks having a maximum transform depth in a current coding unit.

For example, assuming that the transform omission is applied to a transform block having a size of 4x4 to 16x16, in case of a coding unit having a size of 16x16, a representative flag may be signaled on behalf of the transform block included in the 4x4 transform unit divided into the maximum depth. Can. In FIG. 3, blocks shown in gray represent a transformation unit including a transformation block represented by a representative flag.

That is, the encoding device may determine a representative flag value for transform blocks divided into the maximum depth in the coding unit, and signal the value to the decoding device. Then, the decoding apparatus may receive and parse the representative flag value, and determine whether to apply transform omission to transform blocks of the maximum depth in the current coding unit based on the parsed representative flag value.

4 is a diagram for describing a transform block in a coding unit represented by a representative flag according to another embodiment of the present invention.

The embodiment of FIG. 4 shows a case in which the representative flag represents all transform blocks of a size capable of omitting transform in the current coding unit.

For example, a 16x16 coding unit may be divided into 16x16, 8x8, and 4x4 transform units. Assuming that the transform omission is applied to a transform block ranging from 4x4 to 16x16, transform omission can be applied to all transform units having sizes of 16x16, 8x8, and 4x4. The blocks shown in gray in FIG. 4 represent a transform unit including a transform block to which a representative flag is applied.

That is, the encoding apparatus may determine representative flag values for all transform blocks having a size capable of omitting transformation in the coding unit, and signal the value to the decoding apparatus. Then, the decoding apparatus may receive and parse the representative flag value, and determine whether to apply the transform omission to all transform blocks having a size that can be transformed in the current coding unit based on the parsed representative flag value.

5 is a flowchart illustrating an image decoding method using a representative flag representing whether to omit conversion according to an embodiment of the present invention. The method of FIG. 5 may be performed by the image decoding apparatus of FIG. 2 described above.

Referring to FIG. 5, a representative flag (eg, transform_skip_all_zeros_in_cu_flag) representing whether to omit transform for a transform block to which transform omission is applied according to the present embodiment and a transformation process of an image performed accordingly will be described as follows.

The decoding apparatus determines whether the representative flag parsing condition is satisfied in order to determine whether to parse the representative flag for the current coding unit (CU) (S510).

In the process of encoding and decoding an image, a size of a transform block to which transform omission can be applied is determined in advance and then signaled. For example, the size of a transform block to which transform omission can be applied is limited to 4X4, or a size of a maximum transform block to which transform omission can be applied can be determined. If the size of the transform block in the current coding unit does not correspond to the size to which the transform omission can be applied, since the transform omission itself does not occur by default, the parsing of the representative flag indicating whether to omit the transform itself is unnecessary. .

In step S510, a transform block in which the size of the current coding unit satisfies a size condition to which the transform omission is applicable, that is, a transform block requiring parsing of a transform (skip_flag) indicating whether or not the transform block is omitted exists in the current coding unit. Includes judgment of whether it can. The flag indicating whether to omit the transform may be expressed as a transform omit flag (transform_skip_flag) or first information for convenience of description.

Meanwhile, according to an embodiment of the present invention, before parsing the representative flag, it is possible to further receive flag information indicating whether to use a function for determining whether to omit conversion using the representative flag. Flag information indicating whether or not to use a function representative of conversion omission using a representative flag may be signaled as shown in Table 1 below, and the decoding apparatus may receive it.

<Table 1>

In addition, when the transform omission function itself is not used, since the function for signaling the transform omission information itself is not required, it is necessary to link the transform_skip_enabled_flag information, which is flag information indicating whether to use the transform omission function using a representative flag. , Flag information indicating whether or not to use a function representative of conversion omission using a representative flag may be signaled as shown in Table 2 below, and the decoding apparatus receives it.

<Table 2>

In the embodiment according to Table 2, when transform_skip_enabled_flag is 0, transform_skip_group_signalling_enabled_flag is not signaled, and the decoding device infers this value to 0.

Information (transform_skip_group_signalling_enabled_flag) indicating whether to use the function of the representative flag according to an embodiment of the present invention as shown in Table 1 and Table 2 may be transmitted through a predetermined parameter set.

Specifically, it may be signaled through an extension level of a sequence parameter set or a picture parameter set, which is a higher level. For example, it may be signaled through sps_range_extensions (sequence parameter set range extensions), sps_scc_extensions (sequence parameter set screen content coding extensions), pps_range_extensions (picture parameter set range extensions) or pps_range_extensions (picture parameter set screen content coding extensions).

If transform_skip_group_signalling_enabled_flag is 1, it indicates that a function representing transform omission is used, and thus a representative flag may be signaled at a coding unit level. If transform_skip_group_signalling_enabled_flag is 0, it may indicate that a function representing transform omission is not used, or it may be used in a different meaning set in advance in the encoding device and the decoding device.

If the function for signaling the transform omission information is not used, the transform_skip_group_signalling_enabled_flag may not be signaled.

When a function representing transform omission is used (transform_skip_group_signalling_enabled_flag=1), a representative flag according to an embodiment of the present invention may be signaled as shown in Table 3 below.

<Table 3>

Referring to Table 3, when the representative flag parsing condition in step S510 is satisfied, it may be as follows.

1) transform_skip_group_signalling_enabled_flag signaled in Table 1 is 1,

2) A flag (transform_skip_enabled_flag) indicating whether transformation omission is applicable is 1,

3) The current coding unit is not losslessly coded (!cu_transquant_bypass_flag),

4) When the minimum sized transform block that can be split in the current coding unit is equal to or smaller than the maximum transformed block size to which transform omission can be applied (if ((log2CbSize-MaxTrafoDepth-(ChromaArrayType% 3 = = 0? 0: 1 ) )<= Log2MaxTransformSkipSize).

If the above 1), 2), 3) and 4) are satisfied, the decoding apparatus may determine that the representative flag (transform_skip_all_zeros_in_cu_flag) representing the first information indicating whether to omit the transform is parsed.

If at least one of 1), 2), 3), and 4) is not satisfied (for example, a transform block having a size capable of omitting transform cannot exist in the current coding unit), or a representative flag of the present invention The decoding device may not parse the representative flag because it is determined that the representative flag parsing condition is not satisfied. In this case, the decoding apparatus regards the value of the representative flag (transform_skip_all_zeros_in_cu_flag) as 0 (S511), and may perform a subsequent decoding process (S515).

When it is determined that the representative flag is parsed by satisfying the representative flag parsing condition (the condition described with reference to Table 3 above), the decoding apparatus parses the representative flag representing the first information indicating whether or not to skip conversion (S520).

If the value of the parsed representative flag is 1 (S530), the decoding device determines whether the representative flag is a transform block to which the first information is applied (ie, the first information if the first information is a transform block to be applied) To not parse), it is determined whether a condition for omitting parsing of the first information is satisfied (S540).

In the embodiment of Table 3, the first information parsing omission condition may be whether a transform block to be currently decoded is a transform unit having a maximum depth that can be split in a current coding unit.

If the transform block to be currently decoded corresponds to a transform unit having a maximum depth (MaxTrafoDepth), the decoding apparatus may infer the first information to 0 without parsing the first information about the transform block to be decoded (S550). . Here, when the first information has a value of 0, it means that transform omission is not applied to the transform block. That is, it means that the transform is performed on the transform block.

In other words, when the condition of step S540 is satisfied, the decoding apparatus determines that transformation omission has not been applied to the transform block included in the transform unit having the maximum depth divided from the coding unit, and displays the first information indicating whether or not to omit the transform. It can be determined that no parsing is necessary.

When the first information has a value of 0 (if the first information indicates that transform omission is not applied to the transform block), the decoding apparatus does not apply transform omission to the transform block, that is, performs a transform process And may perform a subsequent decoding process (S560).

If the representative flag is 0 in step S530 or the first information parsing omission condition is not satisfied in step S540, the decoding apparatus parses the first information indicating whether or not to individually transform the transform block according to the existing method (S570). ).

That is, if the representative flag is 0, it means that a series of processes for signaling the first information (transform_skip_flag) is performed according to a conventional method, which means that the first information is signaled for each transform block requiring transform_skip_flag signaling. On the other hand, in some other simple embodiments, when the representative flag is 0, the decoding apparatus omits the step S570 of parsing the first information about the transform block and infers the value of the first information to 1 (that is, the transform is omitted) Can be implemented simply.

If the representative flag (transform_skip_all_zeros_in_cu_flag) does not exist, the representative flag may be regarded as 0.

Transformation may be performed on the transform block according to the first information, or the transform may be omitted. That is, the decoding apparatus may perform a transform omission or a transform process according to whether or not a transform is omitted based on the first information, and a subsequent decoding process (S560, S580).

Table 4 below shows an example of syntax signaling the first information (transform_skip_flag) indicating whether or not to skip the transform using the representative flag (transform_skip_all_zeros_in_cu_flag) according to an embodiment of the present invention.

<Table 4>

Referring to Table 4, the representative flag (transform_skip_all_zeros_in_cu_flag) may represent a transform omission flag of transform blocks that satisfy the first information parsing omission condition (S540). As described above, when the representative flag is 1, the decoding apparatus may determine whether to parse the individual conversion omission flag by determining the first information parsing omission condition.

In the first information parsing omission, the representative flag transform_skip_all_zeros_in_cu_flag is 1, and (log2TrafoSize == Max(2, log2CbSize-MaxTrafoDepth-(ChromaArrayType% 3 == 0? 0: (cIdx?1:0)))) It may be the case that the block condition is satisfied. When the parsing omission condition is satisfied, the first information of the currently decoded transform block is not parsed, and may be set to 0, which means that transform omission is not applied (transform_skip_flag[x0][y0][cIdx] = 0).

The application of the condition of S540 is basically a block to which a transform omission function used in the existing technology can be applied (for example, a transform block having a size less than or equal to a maximum transform block size to which a transform block to be currently decoded is subjected to transform omission) is encoded. Targeting the coefficient information (that is, CBF means 1) transform block) is the same as the existing technology, and thus, redundant description is omitted here.

According to the above-described embodiment of the present invention, the representative flag may represent whether to skip conversion of a transform block belonging to a transform unit having a maximum depth that can be split from the current coding unit. This has described transform blocks in a coding unit represented by a representative flag with reference to FIG. 3.

In addition, in the present invention, a representative flag can represent all conversion units having a specific depth or a size capable of omitting conversion. This has been described with reference to FIG. 4 when a representative flag represents all conversion units having a size capable of omitting conversion. An embodiment in which the representative flag represents all conversion units having a specific depth or a size capable of omitting conversion will be described with reference to FIG. 6.

6 is a flowchart illustrating an image decoding method using a representative flag representing whether or not to skip conversion according to another embodiment of the present invention. The method of FIG. 6 may be performed by the image decoding apparatus of FIG. 2 described above.

Referring to FIG. 6, in order to determine whether to parse a representative flag for the current coding unit (CU), the decoding apparatus determines whether the representative flag parsing condition is satisfied (S610).

At this time, the representative flag according to the present embodiment may be signaled as in Table 3 above. Therefore, when the representative flag parsing condition satisfies the same condition as described with reference to Table 3, the decoding apparatus parses the representative flag (S620). Since the representative flag parsing conditions have been described with reference to Table 3, the description is omitted here.

If the representative flag parsing condition is not satisfied, the decoding apparatus does not parse the representative flag, regards the representative flag value as 0 (S611), and may perform a subsequent decoding process (S615).

If the representative flag parsed by satisfying the representative flag parsing condition is 1 (S630), the decoding apparatus does not parse the first information indicating whether or not to skip the transformation of the transform block included in the transform unit to be split from the coding unit, without parsing. It can be inferred that the first information for the 0 (S650).

On the other hand, if the parsed representative flag is 0, the decoding device parses the first information about the transform block (S670), and omits the transform according to the value of the parsed first information (if the first information is 1) or transforms it. Can be performed (when the first information is 0). On the other hand, in some other simple embodiments, when the parsed representative flag is 0, the decoding apparatus omits the step S670 of parsing the first information about the transform block and infers the value of the first information to 1 (that is, It can also be implemented briefly (to avoid the conversion).

That is, the decoding apparatus of the first information about the block of the coded unit included in the coded block is not larger than the size of the maximum transformed block to which transformation omission can be applied and the representative flag has a value of 1 It is determined that no parsing is necessary, and the first information can be inferred as 0.

According to the present exemplary embodiment, a conversion omission flag of transform blocks that satisfy a condition in which transform omission in a coding unit being decoded (encoded transform block having a block size capable of transform omission) is satisfied without representing a transform depth may be represented. have.

Table 5 below shows an example of syntax signaling the first information (transform_skip_flag) indicating whether or not to skip the transform using the representative flag (transform_skip_all_zeros_in_cu_flag) according to another embodiment of the present invention.

Table 5

Referring to Table 5, if the representative flag (transform_skip_all_zeros_in_cu_flag) is 1, the first information may be parsed and set to 0 (transform_skip_flag[x0][y0][cIdx]=0).

That is, according to the present embodiment, when the representative flag is 1, the decoding apparatus may not parse the transform omission flag individually for transform blocks in the coding unit.

If the first information is inferred as 0, the decoding apparatus may not apply transform omission to the transform block for which the transform is determined by the first information, that is, perform transformation and perform a subsequent decoding process (S660). ).

If the representative flag is 0 in step S630, the decoding apparatus parses the first information indicating whether or not to individually transform the transform block in the conventional method (S670).

That is, if the representative flag is 0, it means that a series of processes for parsing transform_skip_flag of each transform block is performed according to a conventional method. That is, the first information is parsed for each transform block for which transform_skip_flag signaling is required.

If the representative flag (transform_skip_all_zeros_in_cu_flag) does not exist, the representative flag may be regarded as 0.

Transformation may be performed on the transform block according to the first information, or the transform may be omitted. That is, the decoding apparatus may perform a transform omission or a transform process according to whether or not a transform is omitted based on the first information and a subsequent decoding process (S660, S680).

In the present invention, as described above, it is possible to represent whether or not conversion of a transform block in which a representative flag is split from a coding unit is omitted. In addition, in the embodiment of the present invention using the representative flag representing the first information of the maximum conversion depth described above with reference to FIG. 5, it is possible to determine whether or not the conversion unit is divided. This will be described with reference to FIG. 7.

7 is a flowchart illustrating a process of inferring division information indicating whether a conversion unit is divided by referring to a representative flag according to an embodiment of the present invention. The method of FIG. 7 may be performed by the image decoding apparatus of FIG. 2 described above.

Step S710 and step S730 of FIG. 7 are similar to step S510 and step S530 of FIG. 5, so a duplicate description is omitted. That is, the representative flag according to the present embodiment represents conversion omission of a transform block belonging to a split unit having a maximum depth that can be split from the current coding unit, and whether or not to split the transform unit can be determined based on the representative flag. .

When the representative flag is parsed, the decoding apparatus may determine whether to parse the second information (split_transform_flag) indicating whether the transform unit is split based on the representative flag. As a result of determination, when the second information is not required to be parsed, the second information may be inferred based on the representative flag, and when the second information is required to be parsed, the second information may be parsed.

If the representative flag is 1, the decoding apparatus may determine whether the transform depth for the transform unit is 0 (S740).

If the transform depth for the transform unit is 0, the decoding apparatus may infer the second information to 1 without parsing the second information for the transform unit having a transform depth of 0 (S750).

That is, when the step S740 is satisfied, the decoding apparatus needs to parse the second information (split_transform_flag indicating whether to split transform depth 0 -> 1) indicating whether to split the transform unit having the same size as the size of the coding unit. It can be judged as missing.

At this time, the size of the current coding unit must satisfy the condition that can have a split transform unit. For example, if the size of the minimum transform unit is set to 8X8, and the size of the current coding unit is 8X8, it is not necessary to determine whether to split because the current coding unit cannot have a split transform unit.

Table 6 shows an example of syntax signaling the second information (split_transform_flag) indicating whether the transform unit is split using the representative flag (transform_skip_all_zeros_in_cu_flag) according to an embodiment of the present invention.

<Table 6>

Referring to Table 6, if the representative flag (transform_skip_all_zeros_in_cu_flag) is 1 and the transformation depth is 0 (trafoDepth = 0), the second information may be set to 1 without being parsed (split_transform_flag[ x0 ][ y0 ][ trafoDepth] = 1).

When the second information is inferred to be 1, the decoding apparatus may perform division on the corresponding transform unit (S760) and perform subsequent decoding (S780).

On the other hand, for a transform unit having a transform depth other than 0, parsing of the second information (split_transform_flag indicating whether to split other than transform depth 0 -> 1) is parsed as in the conventional method to determine whether to split the transform unit.

If the representative flag is 0 in step S730 or the transform depth of the transform unit is not 0 in step S740, the decoding apparatus parses the second information to determine whether to split the transform unit (S770).

When the second information is parsed, the transform block may be split (S760) or split may be omitted, and accordingly, the decoding apparatus may perform a subsequent decoding process (S780).

In summary, when the representative flag is 1, since the coding unit can be split up to the maximum transform depth, it is inferred that the split unit is split without signaling a split flag for a transform unit having a transform depth of 0.

Meanwhile, in the present invention, the above-described representative flag may be applied corresponding to the prediction mode applied to the coding unit. That is, whether the representative flag is signaled may be determined according to a specific prediction mode applied to the coding unit.

As an example, the proposed representative flag may be signaled only when the prediction mode of the coding unit is a specific predetermined prediction mode.

As another example, when the prediction mode of the coding unit is an intra mode or an intra block copy (IBC) prediction mode, the proposed representative flag may be signaled. In this case, the decoding apparatus may parse the representative flag only when the prediction mode is intra mode or IBC prediction mode. Alternatively, in the case of a prediction mode for screen content, or when a prediction mode of a coding unit is limited by signaling defining a specific mode, a representative flag may be signaled only in the prediction mode.

IBC prediction is a prediction method that can be used when the same (or similar) region or object exists in the current picture, and the decoding apparatus can generate a prediction value for the current block using the IBC mode.

8 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 the existing inter prediction, the reference picture is a previous picture or a 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 represents a vector indicating a reference block in the current picture.

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

When performing IBC prediction, a region for searching for a reference block may be limited or set as a specific region. According to an example, the reference block may be limited to being searched in a 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 for a reference block to all regions in which decoding has been completed before a current coding unit in a current picture.

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

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

At this time, since it is necessary to reset or refresh the data in the middle of image processing, the BV predictor for each CTU can 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 a difference between a BV and a BV predictor, and can be coded in an encoding device with BVdx and BVdy values and signaled to a decoding device.

For a realization example in which a representative flag is signaled based on a prediction mode of a current coding unit, a syntax in which a coding device signals to a decoding device at a coding unit level in connection with the present invention may be expressed as shown in Table 7.

Table 7

Referring to Table 7, at the coding unit level, transform_skip_group_signalling_enabled_flag, transform_skip_enabled_flag is 1, is not lossless image coding (!cu_transquant_bypass_flag), and when IBC prediction is not applied (!intra_bc_flag[x0][y0]), representative flag (transform_skip_transform_skip ) May be received. In addition, the decoding apparatus may parse the representative flag when this series of conditions is satisfied.

Of course, the condition ((log2CbSize-MaxTrafoDepth-(ChromaArrayType% 3 = = 0? 0: 1)) <= Log2MaxTransformSkipSize) that the current coding unit may contain a transform block smaller than the size of the maximum transform block to which transform omission is applied. When satisfied, the representative flag (transform_skip_all_zeros_in_cu_flag) can be received or parsed.

Table 7 can be applied to the embodiments described with reference to FIGS. 5 to 7 above. For example, for the sake of understanding, the representative flag parsing condition of S510 of FIG. 5 is transform_skip_group_signalling_enabled_flag, transform_skip_enabled_flag is 1, is not lossless image encoding (!cu_transquant_bypass_flag), and IBC prediction is not applied (!intra_bc_flag[ x0 ][ y0 ]). Meanwhile, as in the embodiment of Table 2, when transform_skip_enabled_flag is 0, transform_skip_group_signalling_enabled_flag is not signaled, and in the embodiment in which the decoding apparatus infers this value to 0, the representative flag parsing condition of S510 of FIG. 5 is transform_skip_group_signalling_enabled_flag is 1, It may include that it is not lossless image coding (!cu_transquant_bypass_flag) and IBC prediction is not applied (!intra_bc_flag[x0][y0]).

On the other hand, in the present invention, it is possible to signal whether the above-described representative flag represents the first information (transform_skip_flag) indicating whether or not to omit the transformation or whether the transformation omission is not applied. In other words, the representative flag may signal whether the transform_skip_flag value is 0 or whether the transform_skip_flag value is 1 or not.

Table 8 is a syntax illustrating an example of signaling whether a representative flag according to an embodiment of the present invention represents conversion omission or that conversion omission is not applied.

Table 8

Referring to Table 8, when it is defined to use a method for signaling a transform omission using a representative flag (transform_skip_group_signalling_enabled_flag = 1), information indicating whether a representative flag represents a transform omission or representing that the transform omission is not applied ( transform_skip_group_represented_value) may be signaled.

For example, if the transform_skip_group_represented_value value is 1, the representative flag may mean representing whether the transform_skip_flag value is 1. If the transform_skip_group_represented_value value is 0, the representative flag may mean representing whether the transform_skip_flag value is 0.

Here, when the value of transform_skip_group_represented_value is 0, the representative flag may be transform_skip_all_zeros_in_cu_flag as described above. That is, transform_skip_flag may be signaled using transform_skip_all_zeros_in_cu_flag, and the embodiments described with reference to FIGS. 3 to 8 may be applied.

Hereinafter, when transform_skip_group_represented_value is signaled, a method of signaling a representative flag (transform_skip_all_in_cu_flag) and deriving information about whether to skip transform based on the representative flag (transform_skip_flag) will be described.

When the information (transform_skip_group_represented_value) indicating whether the representative flag represents transformation omission or that the transformation omission is not applied is signaled, a representative flag (transform_skip_all_in_cu_flag) according to an embodiment of the present invention is signaled as in Table 9 below Can be.

Table 9

The condition in which the representative flag (transform_skip_all_in_cu_flag) of Table 9 is signaled and parsed has been described with reference to Table 3 above, so a detailed description thereof will be omitted.

If the representative flag is to be signaled based on the prediction mode of the current coding unit, a representative flag (transform_skip_all_in_cu_flag) according to an embodiment of the present invention may be signaled as shown in Table 10 below.

Table 10

The condition in which the representative flag (transform_skip_all_in_cu_flag) of Table 10 is signaled and parsed has been described with reference to Table 73 above, so a detailed description thereof will be omitted.

When information (transform_skip_group_represented_value) indicating whether the representative flag represents transformation omission or that the transformation omission is not applied is signaled, the first information (transform_skip_flag) indicating whether to omit transformation using the representative flag (transform_skip_all_in_cu_flag) is shown in the table. 11 and Table 12 may be signaled.

Table 11

Referring to Table 11, the representative flag transform_skip_all_in_cu_flag is 1, and the transform block is included in the transform unit of the maximum depth split from the coding unit (log2TrafoSize == Max(2, log2CbSize-MaxTrafoDepth-(ChromaArrayType% 3 = = 0? 0: (cIdx?1:0)))) In the case of a block, the first information (transform_skip_flag) is not parsed and is set to a value of transform_skip_group_represented_value.

Table 12

Referring to Table 12, when the representative flag transform_skip_all_in_cu_flag is 1, the first information (transform_skip_flag) is not parsed and is set to a value of transform_skip_group_represented_value. In this case, the representative flag may be applied when representing all the conversion units having a size capable of omitting conversion.

When information (transform_skip_group_represented_value) indicating whether the representative flag represents transformation omission or representing that transformation omission is not applied is signaled, second information (split_transform_flag) indicating whether to split the transform unit using the representative flag (transform_skip_all_in_cu_flag) May be signaled as shown in Table 13.

Table 13

Referring to Table 13, if the representative flag (transform_skip_all_in_cu_flag) is 1 and the transformation depth is 0 (trafoDepth = 0), the second information (split_transform_flag) may be set to 1 without being parsed.

In the present invention, it is possible to signal whether the above-described representative flag is signaled with reference to the coding mode of the coding unit. In other words, the present invention can provide information (transform_skip_group_referring_mode_flag) indicating whether the representative flag is signaled with reference to the coding mode of the coding unit.

Table 14 is a syntax illustrating an example of signaling whether a representative flag according to an embodiment of the present invention is signaled with reference to an encoding mode of a coding unit.

Table 14

Referring to Table 14, when it is defined to use a transform omission signaling method using a representative flag (transform_skip_group_signalling_enabled_flag = 1), information indicating whether a representative flag is signaled with reference to a coding unit coding mode (transform_skip_group_referring_mode_flag) is encoded It can be signaled from the device.

For example, if the value of transform_skip_group_referring_mode_flag is 1, the representative flag is signaled only when the coding mode of the coding unit is a predefined prediction mode, and when the coding mode of the coding unit is not a predefined prediction mode, the transform using the proposed representative flag Omitted signaling is not used. That is, the representative flag is not parsed for the coding unit in which the predefined prediction mode is not used.

When the transform_skip_group_referring_mode_flag value is 0, when determining whether to represent the representative flag, the representative flag can be parsed without referring to the prediction mode of the coding unit.

When transform_skip_group_represented_value is signaled and transform_skip_group_referring_mode_flag is signaled, a representative flag (transform_skip_all_in_cu_flag) may be signaled as shown in Table 15.

Table 15

(Transform_skip_group_referring_mode_flag ?(transform_skip_group_represented_value == intra_bc_flag[　x0　][　y0　]): 1) shown in Table 15 has the following meaning.

When transform_skip_group_referring_mode_flag is 0, 1 (true) is returned in the if statement including the sentence. In other words, if the representative flag is not signaled with reference to the coding mode of the coding unit, the representative flag can be parsed regardless of the prediction mode of the coding unit.

When transform_skip_group_referring_mode_flag is 1, it is determined whether (transform_skip_group_represented_value == intra_bc_flag[　x0　][　y0　]). In other words, when the representative flag is signaled with reference to the coding mode of the coding unit, the representative flag may be parsed by determining whether the coding mode of the coding unit is a predefined prediction mode (eg, an IBC prediction mode).

At this time, if the value of transform_skip_group_represented_value is 1 (that is, when the representative flag represents transformation omitted (transform_skip_flag=1)), 1 is returned only when the coding mode of the current coding unit is the IBC prediction mode.

On the other hand, when the value of transform_skip_group_represented_value is 0 (that is, when the representative flag does not apply transform omission (transform_skip_flag=0)), 1 is returned only when the encoding mode of the current coding unit is not the IBC prediction mode.

In the above, the process of signaling transform_skip_group_referring_mode_flag and parsing a representative flag when transform_skip_group_represented_value is signaled has been described. Hereinafter, a process of signaling transform_skip_group_referring_mode_flag and parsing a representative flag when transform_skip_group_represented_value is not signaled will be described.

Table 16 is a syntax illustrating an example of signaling whether a representative flag according to an embodiment of the present invention is signaled with reference to an encoding mode of a coding unit.

Table 16

Referring to Table 16, when it is defined to use a transform omission signaling method using a representative flag (transform_skip_group_signalling_enabled_flag = 1), information (transform_skip_group_referring_mode_flag) indicating whether a representative flag is signaled by referring to a coding mode of a coding unit is encoded. It can be signaled from the device.

When transform_skip_group_referring_mode_flag is signaled, the representative flag may be signaled as shown in Table 17 and Table 18. At this time, the representative flag of Table 17 (transform_skip_all_zeros_in_cu_flag) represents the case where the representative flag does not apply transformation omission (transform_skip_flag=0). The representative flag in Table 18 (transform_skip_all_ones_in_cu_flag) represents the case where the representative flag applies transformation omission (transform_skip_flag=1).

Table 17

Referring to Table 17, the representative flag transform_skip_all_zeros_in_cu_flag may be parsed by determining whether the coding mode of the coding unit is a predefined prediction mode (eg, an IBC prediction mode) according to the transform_skip_group_referring_mode_flag value.

Table 18

Referring to Table 18, the representative flag transform_skip_all_ones_in_cu_flag may be parsed by determining whether the coding mode of the coding unit is a predetermined prediction mode (eg, an IBC prediction mode) according to the transform_skip_group_referring_mode_flag value.

9 is a flowchart illustrating an image encoding method using a representative flag representing whether or not to skip conversion according to an embodiment of the present invention. The method of FIG. 9 may be performed by the image encoding apparatus of FIG. 1 described above.

The encoding apparatus determines whether transformation omission is applied to a transform block divided from a coding unit that is a target of coding (S910).

As a result of the determination, with respect to a transform block to which transform omission is applied while satisfying a predetermined condition described with reference to FIGS. 5 and 6, a representative flag representing first information indicating whether to omit the transform is coded, and the representative flag is recalled. Signaling may be performed with information about a coding unit (S920).

The encoding apparatus is encoded at the same time as a basic condition (that is, the size of a transform block is equal to or less than a maximum transform block size to which transform omission is applied) among transform blocks corresponding to a transform unit having a maximum depth split from a coding unit. If transform omission is not used in all transform blocks that satisfy the transform coefficient must exist (that is, CBF is 1), a representative flag can be coded as 1.

Alternatively, if transform omission is not used in all transform blocks that satisfy a basic condition to which transform omission is applied, among transform units included in the transform unit split from the coding unit, the encoding apparatus may code the representative flag to 1. have.

If the representative flag is 1 (S930), the coding of the first information is omitted for a transform block that satisfies the above conditions, and the first information can be coded for a transform block that requires coding of the first information. Yes (S940).

In addition, the encoding device may determine whether to code the second information indicating whether the transform unit is split based on the representative flag.

If the representative flag is 1 and the transform depth for the transform unit is 0, it may be determined that coding of the second information is not necessary, the representative flag is 1, the transform depth for the transform unit is 0, and the size of the transform unit It may be determined that coding of the second information is not necessary when the transform omission is larger than the maximum transform block size to which the transform omission is applied. In this case, the second unit may not be coded for the transform unit having a transform depth of zero.

The encoding apparatus codes the second information indicating whether to split for a transformation unit that requires coding of the second information, that is, a division unit other than a division unit having a transformation depth of 0->1 (S950).

Steps S940 and S950 may be performed sequentially, but may be performed as independent steps, or coding of the second information may be performed first. That is, the order of steps after the representative flag is coded is not limited to that shown in the figure.

If the representative flag is 0, the first information and the second information are coded and signaled according to an existing coding method (S960).

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

The method according to the present invention described above is produced as a program for execution on a computer and can be 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 implemented in the form of a carrier wave (for example, transmission via the Internet).

The computer-readable recording medium can be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. And, 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 pertains.

In the above-described embodiments, the methods are described based on a flow chart 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. Can. In addition, those of ordinary skill in the art may recognize that the steps shown in the flowcharts are not exclusive, 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.

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

Claims (19)

In the video decoding method,
Determining whether a size of a transform block in a coding unit being decoded is smaller than or equal to a transform block size to which transform omission can be applied;
Parsing information indicating whether or not to skip conversion of the conversion block according to the determination, and performing or omitting conversion of luma conversion blocks of the conversion block; And
The step of using a block indicated by a vector in the current picture-the block is a block in the current picture-as a prediction block for the current prediction block,
A region in which the decoding is completed before the current coding unit in the current picture is used as a prediction block of the current prediction block,
The step of parsing the information indicating whether to skip the conversion of the conversion block
If the flag indicating whether the application of the transform omission is applicable is 1 and the current coding unit is not losslessly coded, and the size of the transform block is smaller than or equal to a transform block size to which the transform omission can be applied, the transform omission is performed. And parsing the information indicating whether or not the image is decoded. The method of claim 1, wherein a region existing in a coding tree unit (CTU) on the left side adjacent to the current prediction block in the current picture is used as a prediction block of the current prediction block. The method of claim 1, wherein a region existing in a left CTU adjacent to a current coding tree unit (CTU) or a current coding tree unit (CTU) to which the current prediction block belongs is used as a prediction block of the current prediction block. Decoding method of video. According to claim 1,
The vector is a vector predictor (predictor) and a vector decoding method, characterized in that derived from the difference (difference). According to claim 4,
The vector difference value represents a difference between the vector and the vector predictor, and is coded by an encoding device and signaled to a decoding device. The method of claim 1, wherein a specific region in the current picture used as the prediction block is indicated by the vector received from an encoder.
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