KR20210031669A - Method for image encoding/decoding and apparatus thereof - Google Patents

Abstract

According to embodiments of the present invention, an image encoding/decoding device receives a bitstream for a video signal and performs decoding based on signaling information included in the bitstream. According to embodiments of the present invention, the image encoding/decoding device encodes the video signal and transmits the bitstream including the encoded video signal and signaling information. The present invention can reduce hardware complexity and operating power consumption.

Description

Video encoding/decoding method and apparatus {METHOD FOR IMAGE ENCODING/DECODING AND APPARATUS THEREOF}

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.

With the recent expansion of broadcasting systems supporting HD (High Definition) resolution not only in Korea but also globally, many users are becoming accustomed to high-definition and high-definition images, and accordingly, many organizations are accelerating the development of next-generation video devices. . In addition, as interest in UHD (Ultra High Definition) that supports 4 times or more resolutions of HDTV in addition to HDTV is increasing, a compression technology for higher resolution and high-definition images is required.

For image compression, an inter prediction technology that predicts a pixel value included in a current picture from a preceding picture and/or a picture that follows, and an intra prediction that predicts a pixel value using pixel information in a picture. A technique, an entropy encoding technique in which a short code is assigned to a symbol with a high frequency of appearance and a long code is assigned to a symbol with a low frequency of occurrence, 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-described problem, an image decoding method according to embodiments includes receiving a bitstream for a video signal in which each frame is encoded with 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 in which a decoding unit block is divided. The bitstream for at least one lower decoding block includes signaling information for decoding a residual block and 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 difference block. Includes. The prediction mode according to embodiments represents at least one of an intra prediction mode and an inter prediction mode.

The decoding apparatus according to embodiments may receive a bitstream for a video signal in which each frame is encoded with 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 in which a decoding unit block is divided. The bitstream for at least one lower decoding block includes signaling information for decoding a residual block and at least one lower decoding block. The decoding apparatus according to the 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 represents 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 difference block.

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

An encoding apparatus according to embodiments may determine a parameter defining a relationship between a luma component and a chroma component of an encoding object block, and generate a prediction block of an encoding object block based on the determined parameter, in the encoding object block. And a transmission unit for transmitting a bitstream including signaling information including a difference block and an encoded difference block and a parameter to generate a residual block by differentiating the prediction blocks.

It is possible to reduce hardware complexity and operation power consumption of an image encoding apparatus and/or a decoding apparatus.

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

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

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

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

Terms such as "first" and "second" may be used to describe various components, but the components are not limited by the terms. That is, the terms are used only for the purpose of distinguishing one component from another component. Accordingly, the first component may be referred to as the second component, and similarly, the second component may be referred to as the first component.

In addition, components shown in the embodiments of the present invention are shown independently to indicate that they perform different characteristic functions, but 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 a single component, or one component may be divided into a plurality of components to operate, which does not depart from the essence of the present invention. Unless 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 for performing the essential functions of the present invention. The present invention may be implemented in a structure including only essential elements excluding optional elements, and a structure including only essential elements is also included in the scope of the present invention.

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

The image 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 an entropy. An encoding unit 150, an inverse quantization unit 160, an inverse transform unit 170, an adder 175, a filter unit 180, and a reference picture buffer 190 are included.

The image encoder 100 encodes an input image in an intra prediction mode or an inter prediction mode and outputs a bitstream. Intra prediction means intra prediction, and inter prediction means inter prediction. The video encoder 100 transitions between the intra prediction mode and the inter prediction mode through switching of 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 case of the intra prediction mode, the intra prediction unit 120 generates a prediction block by performing spatial prediction using pixel values of a block that has already been coded around a block to be coded.

In the inter prediction mode, the motion prediction unit 111 finds a reference block that best matches an input block in a reference picture stored in the reference picture buffer 190 and obtains a motion vector. The motion compensation unit 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 a difference between the input block and the prediction block, and the transform unit 130 transforms the difference 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 string for a symbol to be encoded by expressing a symbol that is frequently generated with a small number of bits. Therefore, it is expected to improve the compression performance of an image through entropy encoding. The entropy encoding unit 150 may use an encoding method such as exponential golomb and Context-Adaptive Binary Arithmetic Coding (CABAC) 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 coefficients, and the inverse transform unit 170 outputs a reconstructed difference block by inverse transforming the inverse quantized coefficient. The adder 175 generates a reconstructed block by adding the reconstructed difference block to the prediction block.

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

2 is a block diagram illustrating an example of a 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 compensation unit 250, an adder 255, and a filter unit 260. ) And a reference picture buffer 270.

The image decoder 200 outputs a reconstructed image by decoding the bitstream in an intra prediction mode or an inter prediction mode. The video decoder 200 transitions between an intra prediction mode and an inter prediction mode through switching of a switch. The image decoder 200 obtains a difference block from the bitstream, generates a prediction block for the reconstructed block, and then adds the difference 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 decoder 210 generates a symbol including quantized coefficients from a bitstream in which frequently generated symbols are represented 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 difference block.

In the case of the intra prediction mode, the intra prediction unit 240 generates a prediction block by performing spatial prediction using pixel values of a block that has already been decoded around a block to be decoded.

In the case of the inter prediction mode, the motion compensation unit 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 difference block, and the filter unit 260 outputs a reconstructed image by performing at least one of deblocking filtering, SAO compensation, and ALF to the block that has been subjected to the adder.

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

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 uppermost node may have a depth of level 0 and may indicate the first unit that is not divided.

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

A level 3 leaf node may represent a unit in which the first unit is divided three times. For example, in 320 of FIG. 3, the unit d corresponding to the node d is a unit divided three times from the first 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. In addition, 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 generally 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 indicated by Y, and the chroma signal may be indicated 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 can be set to be smaller than the number of pixels of the luma component. For example, in the 4:2:0 video format, the number of horizontal/vertical pixels of an arbitrary chroma block may be 1/2 of the number of horizontal/vertical pixels of the number of pixels of a corresponding luma block. For example, in a 4:2:2 video format, the number of horizontal pixels of an arbitrary 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 luma signals and chroma signals using these characteristics, a frequency band used for image processing can 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 can be encoded using the prediction mode of the corresponding luma block, and the decoder uses the prediction mode of the luma block. The prediction mode can be derived.

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

Here, P _U/V represents a predicted value for a chroma component in a block to be predicted. In general, the parameters α _U/V and β _U/V of Equation 1 are derived using the luma component pixel value and the chroma component pixel value of an already reconstructed neighboring block. R _Y ′ denotes a pixel value of a sample generated by down-sampling pixels of the luma component that have already been reconstructed in the prediction target block by the number of pixels of the chroma component. R _Y 'can be represented by the following equation (2).

Here, R _Y represents a pixel value of a luma component that has already been reconstructed in the prediction target block.

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

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

The coding method adopted as a standard is integrated into one software for fair verification and easy coding tool development, and the software is called a HEVC test model (HM). HM contains various algorithms related to 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 referred to as an intra chroma prediction mode or an Intra_FromLuma mode. According to the LM mode, when a boundary of a current block is a boundary of a Largest Coding Unit (LCU), intra chroma prediction is performed using pixel values of luma samples of a block 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 shows an example of downsampling a luma component to derive a linear relationship between a luma component and a 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' represents a sample obtained by down-sampling the surrounding luma block, and Rec _C represents a sample of the surrounding chroma block.

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

Here, I denotes the number of samples of the luma block and 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, and R Y} '(i) is the surrounding luma block (i.e. Rec _L ') used for parameter calculation. Means the pixel value of.

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

Meanwhile, in a general intra-chroma prediction method, as described above, a linear relationship between a luma component and a chroma component is predicted by using an already reconstructed surrounding luma block and a surrounding chroma block as a reference sample. The process can be carried out. Therefore, 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 reconstructed neighboring blocks must be read from the memory. Therefore, when the boundary of the current block coincides with the boundary of the LCU, the internal memory for storing the pixel values of the reconstructed neighboring blocks must be allocated, and power and processing time are consumed to access the external memory and read the pixel values each time. 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 in order to predict a linear relationship between the luma component and the chroma component. In particular, if the boundary of the current block coincides with the boundary of the LCU, 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 variable is transmitted to the decoder. I can. By not using samples outside the boundary of the LCU, it is possible to eliminate the complexity of reading pixel values of neighboring samples stored in an external memory when implementing hardware, and to save power consumption.

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

Like 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. In addition, Rec _L' denotes a sample obtained by down-sampling the surrounding luma block, and Rec _C denotes a sample of the surrounding 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 such as Equation 1. In the present invention, a parameter defining a linear relationship between a luma component and a chroma component is derived from the current luma block and the current chroma block. For example, parameters can be derived by Equations 5 and 6.

Here, I denotes the number of samples of the luma block and 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 a relationship between the luma component and the chroma component. That is, in the intra-chroma prediction method according to the present invention, the current luma block and pixel values of 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 in the parameter calculation are down-sampled by the number of pixels of the chroma component of the samples in the current luma block. Downsampling for luma samples can be performed in various patterns. For example, downsampling may be performed in a pattern as shown in FIG. 5. In the above example, the pixel value of the down-sampled luma sample can be expressed as Equation 2 above. In addition, the number of samples used to obtain the parameter may be determined by an image encoder and transmitted to an image decoder, or may be predetermined by a certain rule or the like. For example, as shown in FIG. 5, when it is predetermined to calculate a parameter using samples adjacent to the upper boundary and the left boundary and luma samples corresponding thereto in the current chroma block, a sample used to obtain the parameter The number becomes 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 image encoder may calculate a parameter defining a linear relationship between a luma component and a 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 coding 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 boundary of the LCU. 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 can be defined as a nonlinear relationship. In this case, the relationship between the luma component and the chroma component may be expressed as a function of a second order or higher, not a linear function as shown in Equation 1, and parameters of the function may be derived from the current luma block and the current chroma block.

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

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

The image decoder receives the bitstream from the image encoder and obtains a difference block for the decoding target block (S610). The bitstream may include information on an encoding mode of a block to be decoded.

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

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

The video decoder generates a reconstructed block by adding a difference 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 not an essential step, but an optional step. Therefore, the step S710 may be omitted.

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

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

The video encoder determines a parameter defining a relationship between the luma component and the chroma component of the encoding target block (S720). As described above, the relationship between the luma component and the chroma component of the encoding target block can be expressed as a linear relationship as shown in Equation 1. In addition, parameters defining the relationship between the luma component and the chroma component of the encoding target 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 video encoder generates a prediction block for the encoding target block based on the parameter (S730). That is, the chroma component can be predicted from the already reconstructed luma component by using the relationship between the luma component and the chroma component of the encoding target block.

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

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

The image decoder obtains a difference block for a chroma component of the decoding target block and a parameter for decoding the decoding target block (S810). The difference block may be obtained by decoding a bitstream transmitted from an image encoder. A parameter for performing decoding may include information on an encoding mode of a decoding object block. In addition, 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 video decoder determines whether the boundary of the current block, that is, the decoding object block coincides with the LCU boundary (S820). As in step 710 of FIG. 7, step S820 is an optional step that is not an essential step, and the image decoder may determine whether the condition for performing intra-chroma prediction according to the present invention is satisfied through step S820.

For example, if the boundary of the decoding target block coincides with the LCU boundary, a parameter defining the relationship between the luma component and the chroma component of the decoding target block will be included in the parameter for decoding the decoding target block transmitted from the video encoder. I can.

For example, if the boundary of the decoding target block does not coincide with the LCU boundary, a parameter defining the relationship between the luma component and the chroma component of the decoding target block is included in the parameter for decoding the decoding target block transmitted from the video encoder. May not be included.

The image decoder generates a prediction block for the chroma component of the decoding target block based on the parameter (S830). For example, since the relationship between the luma component and the chroma component of the decoding target block can be expressed as a linear relationship as shown in Equation 1, the luma component that has already been restored using the relationship between the luma component and the chroma component of the encoding target block The chroma component can be predicted from. In other words. The image decoder predicts the chroma component of the decoding target block based on parameters that define the relationship between the luma component and the chroma component of the decoding target block (e.g., α _U/V and β _{U/V in Equation 1).} You can do it.

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

On the other hand, the above-described embodiments have been described through a flow chart expressed as a series of steps or blocks, but the present invention is not limited to the order of the above-described steps, and some steps may occur in a different order or simultaneously with other steps. have. In addition, those of ordinary skill in the art to which the present invention pertains will appreciate 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. In order to represent the various aspects, it is not possible to describe all possible combinations, but those of ordinary skill in the art will recognize that other combinations are possible. Accordingly, the present invention will be said to include all other replacements, modifications and changes falling within the scope of the following claims.

Claims (12)

Receiving a bitstream for a video signal in which each frame is encoded with 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 is the decoding A unit block is a divided block, and the bitstream for the at least one lower decoding block includes a differential block and signaling information for decoding the at least one lower decoding block;
A step of generating a prediction block by performing prediction according to a prediction mode of the at least one sub-decoding block, wherein the prediction mode is one of an intra prediction mode and an inter prediction mode. Represents at least any one; And
And generating a reconstructed block based on the prediction block and the difference block. The method of claim 1, wherein the intra prediction mode includes information indicating whether a chroma component of the current lower decoding block is decoded in an intra prediction mode based on luma samples and chroma samples of a current lower decoding block. The method of claim 2, wherein the signaling information includes a parameter defining a relationship between the chroma samples and the luma samples. The method of claim 1, wherein the intra prediction mode includes information indicating whether a chroma component of the current lower decoding block is decoded in an intra prediction mode based on reference luma samples and reference chroma samples of an adjacent block of a current lower decoding block. Video decoding method. A decoding apparatus for receiving a bitstream for a video signal in which each frame is encoded with a plurality of coding unit blocks, wherein a decoding unit block corresponding to a coding unit block includes at least one sub-division/decoding block, and the sub-decoding block comprises: The decoding unit block is a divided block, and the bitstream for the at least one lower decoding block includes a differential block and signaling information for decoding the at least one lower decoding block,
The decoding device,
Predictor; And
An adder is included, and the predictor generates a prediction block by performing prediction according to a prediction mode of the at least one sub-decoding block, and the prediction mode is an intra prediction mode and an inter prediction mode. A decoding apparatus representing at least one of (inter prediction mode), wherein the adder generates a reconstructed block based on the prediction block and the difference block. The decoding apparatus of claim 5, wherein the intra prediction mode includes information indicating whether a chroma component of the current lower decoding block is decoded in an intra prediction mode based on luma samples and chroma samples of a current lower decoding block. The decoding apparatus of claim 6, wherein the signaling information includes a parameter defining a relationship between the chroma samples and the luma samples. The method of claim 5, wherein the intra prediction mode includes information indicating whether a chroma component of the current lower decoding block is decoded in an intra prediction mode based on reference luma samples and reference chroma samples of an adjacent block of the current lower decoding block. Decryption device. Determining a parameter defining a relationship between a luma component and a chroma component of a block to be encoded;
Generating a prediction block of the encoding object block based on the determined parameter;
Generating a residual block by differentiating the prediction block from the encoding target block; And
An image encoding method comprising the step of transmitting a bitstream including an encoded difference block and signaling information including the parameter. The image encoding method of claim 9, wherein the parameter is calculated based on a pixel value of a luma component of the encoding target block and a pixel value of the chroma component. A predictor for determining a parameter defining a relationship between a luma component and a chroma component of the encoding object block, and generating a prediction block of the encoding object block based on the determined parameter;
A difference branch configured to generate a residual block by differentiating the prediction block from the encoding target block; And
An encoding apparatus comprising a transmission unit for transmitting a bitstream including an encoded difference block and signaling information including the parameter. The encoding apparatus of claim 11, wherein the parameter is calculated based on a pixel value of a luma component of the encoding object block and a pixel value of the chroma component.

Images