KR102358152B1 - Method for image encoding/decoding and apparatus thereof - Google Patents

Abstract

An image decoding method and an apparatus for decoding an image according to embodiments receive a bitstream for a video signal, and perform decoding based on signaling information included in the bitstream. A spirituality encoding method and encoding apparatus according to embodiments encodes a video signal and transmits a bitstream including the encoded video signal and signaling information.

Description

Image encoding/decoding method and apparatus

The present invention relates to image processing, and more particularly, to an intra prediction method for predicting a chroma pixel using a luma pixel, and an apparatus using the same.

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

For image compression, an inter prediction technique that predicts a pixel value included in a current picture from a preceding picture and/or a subsequent picture, and intra prediction that predicts a pixel value using pixel information in a picture technology, an entropy encoding technique in which a short code is assigned to a symbol having a high frequency of occurrence and a long code is assigned to a symbol having a low frequency of occurrence, or the like may be used.

An object of the present invention is to provide an intra chroma prediction method for predicting a chroma pixel using a luma pixel and an apparatus using the same.

Another object of the present invention is to provide an intra chroma prediction method for predicting a relationship between a luma component and a chroma component without using pixel values of neighboring blocks and an apparatus using the same.

In order to solve the above problem, an image decoding method according to embodiments includes receiving a bitstream for a video signal in which each frame is encoded by a plurality of coding unit blocks. A decoding unit block corresponding to a coding unit block according to embodiments includes at least one lower decoding block, and the lower decoding block is a block obtained by dividing the decoding unit block. The bitstream for the at least one lower decoding block includes a residual block and signaling information for decoding the at least one lower decoding block. An image decoding method according to embodiments includes generating a prediction block by performing prediction according to a prediction mode of at least one lower decoding block, and generating a reconstructed block based on the prediction block and the residual block. include The prediction mode according to the embodiments indicates at least one of an intra prediction mode and an inter prediction mode.

The decoding apparatus according to the embodiments may receive a bitstream for a video signal in which each frame is encoded by a plurality of coding unit blocks. A decoding unit block corresponding to a coding unit block according to embodiments includes at least one lower decoding block, and the lower decoding block is a block obtained by dividing the decoding unit block. The bitstream for the at least one lower decoding block includes a residual block and signaling information for decoding the at least one lower decoding block. A decoding apparatus according to embodiments includes a predictor and a subtractor. A predictor according to embodiments generates a prediction block by performing prediction according to a prediction mode of at least one lower decoding block. The prediction mode indicates at least one of an intra prediction mode and an inter prediction mode. An adder according to embodiments generates a reconstructed block based on a prediction block and a residual block.

An image encoding method according to embodiments may include determining a parameter defining a relationship between a luma component and a chroma component of an encoding object block, generating a prediction block of the encoding object block based on the determined parameter, and encoding object generating a residual block by differentiating the prediction block from the block; and transmitting a bitstream including the coded residual block and signaling information including parameters.

The encoding apparatus according to the embodiments may include a predictor that determines a parameter defining a relationship between a luma component and a chroma component of an encoding object block, and generates a prediction block of the encoding object block based on the determined parameter, in the encoding object block and a differential for generating a residual block by differentiating the prediction block, and a transmitter for transmitting a bitstream including signaling information including an coded residual block and parameters.

Hardware complexity and operating power consumption of the image encoding apparatus and/or the decoding apparatus may be reduced.

Intra chroma prediction can be performed without access to external memory.

1 is a block diagram illustrating an example of the structure of an image encoder.
2 is a block diagram illustrating an example of the structure of an image decoder.
3 shows an example in which one unit is divided into a plurality of sub-units.
4 illustrates an example of down-sampling a luma component in order to derive a linear relationship between the luma component and the chroma component in a general intra chroma prediction method.
5 illustrates an example of down-sampling a luma component in order to derive a linear relationship between the luma component and the chroma component in the intra chroma prediction method according to an embodiment of the present invention.
6 illustrates an example of intra prediction performed by an image decoder.
7 illustrates an image encoding method according to an embodiment of the present invention.
8 shows an image decoding method according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. However, in describing the embodiment of the present invention, if it is determined that a detailed description of a known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

When a component is described as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but another component may exist in the middle. In addition, when it is stated that a specific component is "included" in the present invention, it does not exclude components other than the corresponding component, but additional components may be included in the scope of the embodiment or technical spirit of the present invention. it means.

Terms such as “first” and “second” may be used to describe various elements, but the elements are not limited by the terms. That is, the above terms are used only for the purpose of distinguishing one component from another component. Accordingly, a first component may be termed a second component, and likewise the second component may also be termed a first component.

In addition, the components shown in the embodiment of the present invention are shown independently to indicate that they perform different characteristic functions, and it does not mean that each component cannot be implemented as one piece of hardware or software. That is, each component is divided for convenience of description, and a plurality of components may be combined to operate as one component, or one component may be divided into a plurality of components to operate, which does not deviate from the essence of the present invention. Unless otherwise specified, it is included within the scope of the present invention.

In addition, some components may be optional components for improving performance rather than essential components performing the essential function of the present invention. The present invention may be implemented with a structure including only essential components except for optional components, and a structure including only essential components is also included in the scope of the present invention.

1 is a block diagram illustrating an example of the structure of an image encoder.

The video encoder 100 includes a motion prediction unit 111 , a motion compensation unit 112 , an intra prediction unit 120 , a switch 115 , a subtractor 125 , a transform unit 130 , a quantization unit 140 , and entropy. It includes an encoder 150 , an inverse quantizer 160 , an inverse transform unit 170 , an adder 175 , a filter unit 180 , and a reference picture buffer 190 .

The image encoder 100 encodes an input image in an intra prediction mode or an inter prediction mode and outputs a bitstream. Intra prediction refers to intra prediction, and inter prediction refers to inter prediction. The video encoder 100 transitions between the intra prediction mode and the inter prediction mode by switching the switch 115 . The image encoder 100 generates a prediction block for an input block of an input image, and then encodes a residual between the input block and the prediction block.

In the intra prediction mode, the intra prediction unit 120 generates a prediction block by performing spatial prediction using pixel values of an already encoded block around the encoding object block.

In the inter prediction mode, the motion prediction unit 111 finds a reference block that best matches the input block in the reference picture stored in the reference picture buffer 190 to obtain a motion vector. The motion compensator 112 performs motion compensation using the motion vector and generates a prediction block. Here, the motion vector is a two-dimensional vector used for inter prediction, and represents an offset between a current encoding/decoding target block and a reference block.

The subtractor 125 generates a residual block based on the difference between the input block and the prediction block, and the transform unit 130 transforms the residual block to output a transform coefficient. The quantization unit 140 quantizes the transform coefficient and outputs a quantized coefficient.

The entropy encoding unit 150 outputs a bitstream by performing entropy encoding based on information obtained in the encoding/quantization process. Entropy encoding reduces the size of a bit stream of a symbol to be encoded by expressing frequently occurring symbols with a small number of bits. Therefore, it is expected that the compression performance of the image can be improved through entropy encoding. The entropy encoder 150 may use an encoding method such as exponential golomb or CABAC (Context-Adaptive Binary Arithmetic Coding) for entropy encoding.

Meanwhile, the coded picture needs to be decoded and stored again in order to be used as a reference picture for performing inter prediction. Accordingly, the inverse quantization unit 160 inverse quantizes the quantized coefficient, and the inverse transformation unit 170 inverse transforms the inverse quantized coefficient to output a reconstructed residual block. The adder 175 generates a reconstructed block by adding the reconstructed residual block to the prediction block.

The filter unit 180 is also referred to as an adaptive in-loop filter, and includes at least one of deblocking filtering, sample adaptive offset (SAO) compensation, and adaptive loop filtering (ALF) on the reconstructed block. carry out Deblocking filtering means removing block distortion caused at the boundary between blocks, and SAO compensation means adding an appropriate offset to a pixel value to compensate for a coding error. In addition, ALF means performing filtering based on a comparison value between the reconstructed image and the original image.

2 is a block diagram illustrating an example of the structure of an image decoder.

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

The image decoder 200 decodes the bitstream in the intra prediction mode or the inter prediction mode to output a reconstructed image. The image decoder 200 transitions between the intra prediction mode and the inter prediction mode by switching the switch. The image decoder 200 obtains a residual block from a bitstream, generates a prediction block for the reconstructed block, and then adds the residual block and the prediction block to generate a reconstructed block.

The entropy decoding unit 210 performs entropy decoding based on a probability distribution. The entropy decoding process is the opposite of the entropy encoding process described above. That is, the entropy decoding unit 210 generates a symbol including a quantized coefficient from a bitstream in which frequently generated symbols are expressed by a small number of bits.

The inverse quantization unit 220 inverse quantizes the quantized coefficient, and the inverse transform unit 230 inversely transforms the inverse quantized coefficient to generate a differential block.

In the intra prediction mode, the intra prediction unit 240 generates a prediction block by performing spatial prediction using pixel values of an already decoded block around the decoding object block.

In the inter prediction mode, the motion compensator 250 generates a prediction block by performing motion compensation using a motion vector and a reference picture stored in the reference picture buffer 270 .

The adder 255 adds the prediction block to the residual block, and the filter unit 260 outputs a reconstructed image by performing at least one of deblocking filtering, SAO compensation, and ALF on the block that has been subjected to the adder.

Hereinafter, a unit means a unit of image encoding and decoding. In the encoding/decoding process, an image is divided into predetermined sizes and encoded/decoded. Accordingly, the unit may be divided into a coding unit (CU), a prediction unit (PU), a transform unit (TU), and the like according to an encoding/decoding process. Also, a unit may be referred to as a block. One unit may be further divided into smaller sub-units.

3 shows an example in which one unit is divided into a plurality of sub-units.

One unit may be hierarchically divided with depth information based on a tree structure. Each divided sub-unit may have depth information. Since the depth information indicates the number and/or degree of division of the unit, it may include information on the size of the sub-unit.

Referring to 310 of FIG. 3 , the highest node may be referred to as a root node and may have the smallest depth value. In this case, the highest node may have a depth of level 0 and may represent an undivided first unit.

A lower node having a depth of level 1 may indicate a unit in which the initial unit is divided once, and a lower node having a depth of level 2 may indicate a unit in which the initial unit is divided twice. For example, unit a corresponding to node a in 320 of FIG. 3 is a unit divided once from the initial unit, and may have a depth of level 1.

A leaf node of level 3 may indicate a unit in which the initial unit is divided three times. For example, in 320 of FIG. 3 , a unit d corresponding to node d is a unit divided three times in the initial unit, and may have a depth of level 3. Accordingly, the leaf node of level 3, which is the lowest node, may have the deepest depth.

Hereinafter, the encoding/decoding target block may be referred to as a current block in some cases. Also, when intra prediction is performed on an encoding/decoding object block, the encoding/decoding object block may be referred to as a prediction object block.

Meanwhile, the image signal may include three color signals representing three primary color components of light. The three color signals may be represented by R (Red), G (Green), and B (Blue), respectively. The R, G, and B signals may be converted into one luma signal and two chroma signals equivalent to the R, G and B signals. Here, the luma signal is a component representing the brightness of the screen, and the chroma signal is a component representing the color of the screen. The luma signal may be denoted by Y, and the chroma signal may be denoted by C. Hereinafter, a block including a luma component is referred to as a luma block, and a block including a chroma component is referred to as a chroma block.

Since the human eye is sensitive to the luma signal and insensitive to the chroma signal, the number of pixels of the chroma component in one image or block may be set to be smaller than the number of pixels of the luma component. For example, in a 4:2:0 image format, the number of horizontal/vertical pixels of any chroma block may be 1/2 of the number of horizontal/vertical pixels of the corresponding luma block. For example, in a 4:2:2 image format, the number of horizontal pixels of any chroma block may be 1/2 of the number of horizontal pixels of a corresponding luma block (the number of vertical pixels is the same). When the R, G, and B signals are converted into a luma signal and a chroma signal using these characteristics, a frequency band used for image processing may be reduced.

Intra prediction is performed according to the intra prediction mode of the current block. Since the chroma component in the image has a high correlation with the corresponding luma component, the prediction mode of the chroma block may be encoded using the prediction mode of the corresponding luma block, and the decoder uses the prediction mode of the luma block to generate the chroma block. A prediction mode can be derived.

The correlation between the luma component and the chroma component may be expressed as a linear relationship using parameters. Equation 1 is an example showing the correlation between the luma component and the chroma component.

Here, P _U/V represents a prediction value for a chroma component in a prediction object block. In general, the parameters α _U/V and β _U/V of Equation 1 are derived using the luma component pixel values and the chroma component pixel values of the already reconstructed neighboring blocks. R _Y ' denotes a pixel value of a sample generated by down-sampling the pixels of the luma component already reconstructed in the prediction object block by the number of pixels of the chroma component. R _Y ' may be represented by Equation 2 below.

Here, R _Y denotes a pixel value of an already reconstructed luma component in the prediction object block.

Hereinafter, a block composed of an already reconstructed luma component in a prediction object block is a current luma block, a block composed of an already reconstructed luma component in a neighboring block adjacent to the prediction object block is a neighboring luma block, and a chroma component in the prediction object block. The configured block is referred to as a current chroma block, and a block composed of already reconstructed chroma components in a neighboring block adjacent to the prediction object block is referred to as a neighboring chroma block.

Meanwhile, JCT-VC, an international video compression standardization organization, is in the process of standardizing HEVC (High Efficiency Video Coding), a new video compression standard. HEVC introduced various encoding methods to exceed the encoding performance of the previous video compression standard H.264/AVC.

The encoding method adopted as a standard is integrated into one software for fair verification and easy development of an encoding tool, and the software is called HM (HEVC test model). HM includes various algorithms for image encoding.

HM 4.0 supports a luma (LM) mode that uses the luma component of a neighboring block adjacent to the boundary of the current block for prediction of the chroma component. The LM mode may be called an intra chroma prediction mode or an Intra_FromLuma mode. According to the LM mode, when the boundary of the current block is the boundary of a Largest Coding Unit (LCU), intra chroma prediction is performed using pixel values of luma samples of blocks adjacent to the boundary of the current block. Since the pixel value of the luma sample of the block adjacent to the boundary of the current block is stored in the external memory, in this case, the pixel value of the restored luma sample must be read by accessing the external memory each time. For this reason, it is necessary to allocate an internal memory for storing it, and an increase in power consumption and a decrease in speed due to access to the external memory are caused.

4 illustrates an example of down-sampling a luma component in order to derive a linear relationship between the luma component and the chroma component in a general intra chroma prediction method.

Referring to FIG. 4 , the height and width of the current luma block 400 are 2N, and the height and width of the current chroma block 500 are N. Rec _L ' denotes a sample obtained by down-sampling the neighboring luma block, and Rec _C denotes a sample of the neighboring chroma block.

As described above, the correlation between the luma component and the chroma component may be expressed as a linear relationship using a parameter as in Equation 1, and in general, the parameter is derived from the surrounding luma block and the surrounding chroma block. For example, the parameter can be derived by Equations 3 and 4.

Here, I means the number of samples of the luma block and the chroma block used to obtain the parameters α _U/V and β _U/V . R _U/V (i) is the pixel value of the surrounding chroma block (i.e. Rec _C ) used for parameter calculation, R _Y '(i) is the surrounding luma block used for parameter calculation (i.e. Rec _L ') is the pixel value of

4 and Equations 3 and 4, a neighboring luma block and a neighboring chroma block are used to derive the relationship between the luma component and the chroma component. That is, in a general intra chroma prediction method, pixel values of the neighboring luma block and the neighboring chroma block are used as reference samples in order to derive a parameter defining a linear relationship between the luma component and the chroma component.

On the other hand, in the general intra chroma prediction method, as described above, the linear relationship between the luma component and the chroma component is predicted by using the already reconstructed neighboring luma block and the neighboring chroma block as reference samples. The process may be performed. Accordingly, it is not necessary to separately transmit a parameter defining a linear relationship between the luma component and the chroma component.

However, the pixel values of the restored neighboring blocks must be read from the memory. Therefore, when the boundary of the current block coincides with the boundary of the LCU, it is necessary to allocate an internal memory to store the pixel values of the restored neighboring blocks, and it consumes power and processing time to access the external memory each time to read the pixel values. Should be.

To solve this problem, in the intra chroma prediction method according to the present invention, the current luma block and the current chroma block are used as reference samples to predict the linear relationship between the luma component and the chroma component. In particular, when the boundary of the current block coincides with the LCU boundary, a parameter defining a linear relationship between the luma component and the chroma component is calculated based on the current luma block and the current chroma block, and the calculated parameter parameters are transmitted to the decoder. can By not using the samples outside the LCU boundary, it is possible to remove the complexity of reading pixel values of neighboring samples stored in an external memory when implementing hardware, and power consumption can be saved.

5 illustrates an example of performing downsampling on a luma component in order to derive a linear relationship between the luma component and the chroma component in the intra chroma prediction method according to an embodiment of the present invention.

4 , the height and width of the current luma block 400 are 2N, and the height and width of the current chroma block 500 are N. In addition, Rec _L ' denotes a sample obtained by down-sampling a neighboring luma block, and Rec _C denotes a sample of a neighboring chroma block.

As described above, the correlation between the luma component and the chroma component may be expressed as a linear relationship using a parameter as in Equation 1. In the present invention, a parameter defining a linear relationship between the luma component and the chroma component is derived from the current luma block and the current chroma block. For example, the parameter can be derived by Equations 5 and 6.

Here, I means the number of samples of the luma block and the chroma block used to obtain the parameters α _U/V and β _U/V . O _U/V (i) denotes a pixel value of the current chroma block 500 used for parameter calculation, and O _Y '(i) denotes a pixel value of the current luma block 400 used for parameter calculation.

5 and Equations 5 and 6, a current luma block and a current chroma block are used to derive the relationship between the luma component and the chroma component. That is, in the intra chroma prediction method according to the present invention, pixel values of the current luma block and the current chroma block are used as reference samples in order to derive a parameter value defining a linear relationship between the luma component and the chroma component. In this case, the luma samples used for parameter calculation are down-sampled from samples in the current luma block to the number of pixels of the chroma component. Downsampling of the luma sample may be performed in various patterns. For example, down-sampling may be performed in the pattern shown in FIG. 5 . In the above example, the pixel value of the down-sampled luma sample may be expressed by Equation 2 above. In addition, the number of samples used to obtain the parameter may be determined by the video encoder and transmitted to the video decoder, or may be predetermined by a certain rule or the like. For example, when it is predetermined to calculate a parameter using samples adjacent to the upper boundary and the left boundary and corresponding luma samples in the current chroma block as shown in FIG. 5 , the sample used to obtain the parameter The number will be 2N-1.

Meanwhile, according to the intra chroma prediction method according to the present invention, a parameter defining a linear relationship between a luma component and a chroma component may be transmitted. That is, the video encoder may calculate a parameter defining a linear relationship between the luma component and the chroma component, and transmit the calculated parameter to the decoder. When the parameter is transmitted, the parameter value used in the upper block may be reused in the lower block in order to reduce the amount of the transmitted parameter and prevent the encoding efficiency from being lowered.

In addition, the intra chroma prediction method according to the present invention can be applied only when the boundary of the current block coincides with the LCU boundary. That is, when the left and/or upper boundary of the prediction target chroma block is in contact with the LCU boundary, the pixel value of the current block may be referred to without referring to the pixel value of the neighboring block.

In addition, the relationship between the luma component and the chroma component may be defined as a non-linear relationship. In this case, the relationship between the luma component and the chroma component may be expressed as a second-order or higher-order function rather than a linear function as in Equation 1, and a parameter of the function may be derived by the current luma block and the current chroma block.

According to the present invention, since the pixel value of the current chroma block can be predicted without reading the pixel value of the neighboring luma block into the memory, the disadvantages of the general intra chroma prediction method can be overcome.

6 illustrates an example of intra prediction performed by an image decoder.

The image decoder receives the bitstream from the image encoder to obtain a residual block with respect to the decoding object block (S610). The bitstream may include information about the encoding mode of the decoding object block.

The image decoder determines the intra prediction mode of the decoding object block ( S620 ). The intra prediction mode of the decoding object block may be obtained from an image encoder or determined by a predetermined rule. Examples of the intra prediction mode include Intra_Angular, Intra_DC, Intra_Planar, and the like, and in the case of a chroma block, an LM mode may be used.

The image decoder generates a prediction block for the decoding object block based on the intra prediction mode (S630). For example, when the intra prediction mode is the LM mode, the chroma block may be predicted from the already reconstructed luma block.

The image decoder generates a reconstructed block by adding a residual block to the prediction block (S640).

7 illustrates an image encoding method according to an embodiment of the present invention.

The video encoder determines whether the boundary of the current block, that is, the encoding target block coincides with the LCU boundary (S710). The step S710 is a step of determining whether a condition for performing intra chroma prediction according to the present invention is satisfied, and is an optional step, not an essential step. Accordingly, the step S710 may be omitted.

For example, when the boundary of the encoding object block coincides with the LCU boundary, the image encoder sets a parameter defining a relationship between the luma component and the chroma component of the encoding object block to the pixel value of the luma component in the encoding object block and the It can be calculated based on the pixel value of the chroma component in the encoding object block.

For example, when the boundary of the encoding object block does not coincide with the LCU boundary, the image encoder may perform general intra chroma prediction. That is, the image encoder may calculate a parameter defining the relationship between the luma component and the chroma component of the encoding object block based on the pixel value of the luma component and the pixel value of the chroma component in a block adjacent to the encoding object block.

The video encoder determines a parameter defining the relationship between the luma component and the chroma component of the encoding object block (S720). As described above, the relationship between the luma component and the chroma component of the encoding object block may be expressed as a linear relationship as shown in Equation (1). Also, parameters defining the relationship between the luma component and the chroma component of the encoding object block (eg, α _U/V and β _U/V in Equation 1) may be expressed as Equations 5 and 6. That is, as described above, the parameter may be calculated based on the pixel value of the luma component in the encoding object block and the pixel value of the chroma component in the encoding object block.

The image encoder generates a prediction block for the encoding object block based on the parameter (S730). That is, the chroma component may be predicted from the already reconstructed luma component by using the relationship between the luma component and the chroma component of the encoding object block.

The video encoder generates a residual block by differentiating the prediction block from the encoding target block (S740), and encodes the residual block and transmits the encoded residual block to the video decoder (S750). That is, as described above, the residual block is transmitted in the form of a bitstream through a transformation process, a quantization process, an entropy encoding process, and the like. In this case, parameters for decoding the encoding object block (eg, the above-described parameters) may be transmitted together with the encoded residual block.

8 shows an image decoding method according to an embodiment of the present invention.

The image decoder obtains a residual block with respect to the chroma component of the decoding object block and a parameter for decoding the decoding object block (S810). The residual block may be obtained by decoding a bitstream transmitted from an image encoder. A parameter for performing decoding may include information about an encoding mode of a decoding object block. Also, when the chroma component of the decoding object block is encoded in the LM mode, the parameter may include a parameter defining a relationship between the luma component and the chroma component of the decoding object block.

The image decoder determines whether the boundary of the current block, that is, the decoding object block, coincides with the LCU boundary ( S820 ). Like step 710 in FIG. 7 , step S820 is an optional step, not an essential step, and the video decoder may determine whether a condition for performing intra chroma prediction according to the present invention is satisfied through step S820.

For example, when the boundary of the decoding object block coincides with the LCU boundary, a parameter defining the relationship between the luma component and the chroma component of the decoding object block is included in the parameter for decoding the decoding object block transmitted from the image encoder. can

For example, when the boundary of the decoding object block does not coincide with the LCU boundary, a parameter defining the relationship between the luma component and the chroma component of the decoding object block is a parameter for decoding the decoding object block transmitted from the image encoder. may not be included.

The image decoder generates a prediction block for the chroma component of the decoding object block based on the parameter (S830). For example, since the relationship between the luma component and the chroma component of the decoding object block can be expressed as a linear relationship as in Equation 1, the luma component already reconstructed using the relationship between the luma component and the chroma component of the encoding object block It is possible to predict the chroma component from In other words. The image decoder predicts the chroma component of the decoding object block based on parameters (eg, α _U/V and β _U/V in Equation 1) defining the relationship between the luma component and the chroma component of the decoding object block. can be done

The image decoder generates a reconstructed block by adding a residual block to the prediction block (S840).

On the other hand, although the above-described embodiments are described through a flowchart expressed as a series of steps or blocks, the present invention is not limited to the order of the above-described steps, and some steps may occur in a different order or at the same time as other steps. have. In addition, those of ordinary skill in the art to which the present invention pertains will understand that the steps shown in the flowchart are not exclusive, and other steps may be included or some steps may be deleted.

In addition, the above-described embodiments include examples of various aspects. It is not possible to describe every possible combination in order to represent various aspects, but one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the present invention cover all other substitutions, modifications and variations falling within the scope of the following claims.

Claims (12)

Receiving a bitstream for a video signal in which each frame is encoded by a plurality of coding unit blocks, wherein a decoding unit block corresponding to a coding unit block includes at least one lower decoding block, and the lower decoding block includes the decoding a unit block is a divided block, and a bitstream for the at least one lower decoding block includes a residual block and signaling information for decoding the at least one lower decoding block;
generating a prediction block by performing prediction according to a prediction mode of the at least one lower decoding block, wherein the prediction mode is selected from among an intra prediction mode and an inter prediction mode represents at least one; and
generating a reconstructed block based on the prediction block and the residual block;
The intra prediction mode includes information indicating whether a chroma component of the current lower decoding block is decoded in the intra prediction mode based on luma samples and chroma samples of the current lower decoding block. delete delete delete delete delete delete delete delete delete delete delete

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