KR20240078641A - Method and apparatus for encoding/decoding a video signal - Google Patents

Abstract

A video encoding/decoding method and device are disclosed. An image decoding method according to an embodiment of the present disclosure includes encoding intra hybrid mode information of a current coding block and generating a prediction sample of at least one prediction block in the current coding block based on the intra hybrid mode information. and generating a prediction sample of at least one prediction block in the current coding block when the current coding block is in an intra hybrid mode, dividing the current coding block into a first prediction block and a second prediction block. Splitting, generating a prediction sample of the first prediction block using an intra-prediction mode of the first prediction block derived from neighboring blocks of the first prediction block, and intra-prediction of the second prediction block It may include determining an intra-prediction mode of the second prediction block based on mode information or DIMD mode information, and generating a prediction sample of the second prediction block using the determined intra-prediction mode.

Description

Video signal encoding/decoding method and device {METHOD AND APPARATUS FOR ENCODING/DECODING A VIDEO SIGNAL}

The present invention relates to a method and device for encoding/decoding video signals, and more specifically, to a method and device for encoding/decoding video signals to which an intra hybrid mode is applied.

Recently, demand for multimedia data such as video is rapidly increasing on the Internet. However, the speed at which channel bandwidth develops is difficult to keep up with the rapidly increasing amount of multimedia data. Accordingly, the international standardization organization ITU-T's VCEG (Video Coding Expert Group) and ISO/IEC's MPEG (Moving Picture Expert Group) announced version 1 of HEVC (High Efficiency Video Coding), a video compression standard, in February 2014. It was enacted.

HEVC defines technologies such as intra-screen prediction (or intra-prediction), inter-screen prediction (or inter-prediction), transformation, quantization, entropy coding, and in-loop filter.

In HEVC, the current video compression standard, only Planar mode, DC mode, and Angular mode can be performed as intra-screen prediction modes, so there is a problem that prediction accuracy is low.

The present invention is intended to solve the above-mentioned problems, and its main purpose is to provide a method for determining an intra-prediction mode by considering the positional characteristics of prediction blocks within a coding block during intra-prediction.

The technical problems to be achieved by this disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the description below. You will be able to.

An image decoding method according to an aspect of the present disclosure includes decoding intra hybrid mode information of a current coding block and generating a prediction sample of at least one prediction block in the current coding block based on the intra hybrid mode information. Includes, when the current coding block is an intra hybrid mode, generating a prediction sample of at least one prediction block in the current coding block includes dividing the current coding block into a first prediction block and a second prediction block. generating a prediction sample of the first prediction block using an intra-prediction mode of the first prediction block derived from a neighboring block of the first prediction block, and an intra-prediction mode of the second prediction block. Decoding information or DIMD (Decoder-side Intra Mode Derivation) mode information to determine an intra-prediction mode of the second prediction block, and generating a prediction sample of the second prediction block using the determined intra-prediction mode. May include steps.

In the image decoding method, the DIMD mode derives final intra prediction based on an intra prediction mode derived from a neighboring block of the coding block, and uses the derived intra prediction mode as prediction information of the prediction block within the coding block. You can.

In the image decoding method, the step of generating a prediction sample of the first prediction block includes applying an intra-prediction mode of a neighboring block determined according to a preset priority among neighboring blocks of the first prediction block to the first prediction block. A prediction sample of the first prediction block can be generated by inducing the intra-screen prediction mode of the block.

In the image decoding method, the step of generating a prediction sample of the first prediction block includes deriving the intra-prediction mode of the neighboring block determined based on neighboring block index information to the intra-prediction mode of the first prediction block. A prediction sample of the prediction block of the first prediction block may be generated.

In the video decoding method, the step of splitting the current coding block into a first prediction block and a second prediction block may involve corner splitting the current coding block.

In the image decoding method, when the first prediction block and the second prediction block are corner divided within the current coding block, diagonal filtering may be applied to pixels adjacent to a corner boundary of the first prediction block. .

An image encoding method according to an aspect of the present invention includes encoding intra-hybrid mode information of a current coding block and generating a prediction sample of at least one prediction block in the current coding block based on the intra-hybrid mode information. Includes, when the current coding block is an intra hybrid mode, generating a prediction sample of at least one prediction block in the current coding block includes dividing the current coding block into a first prediction block and a second prediction block. generating a prediction sample of the first prediction block using an intra-prediction mode of the first prediction block derived from a neighboring block of the first prediction block, and an intra-prediction mode of the second prediction block. Or, determining an intra-prediction mode of the second prediction block based on DIMD (Decoder-side Intra Mode Derivation) mode information and generating a prediction sample of the second prediction block using the determined intra-prediction mode. may include.

In the image encoding method, the step of generating a prediction sample of the first prediction block includes changing the intra-prediction mode of a neighboring block determined according to a preset priority among neighboring blocks of the first prediction block to the first prediction block. A prediction sample of the first prediction block can be generated by inducing the intra-screen prediction mode of the block.

In the video encoding method, the step of generating a prediction sample of the first prediction block includes deriving the intra-prediction mode of the neighboring block determined based on neighboring block index information to the intra-prediction mode of the first prediction block. A prediction sample of the prediction block of the first prediction block may be generated.

In the video encoding method, the step of dividing the current coding block into a first prediction block and a second prediction block may result in corner splitting the current coding block.

In the image encoding method, when the first prediction block and the second prediction block are edge-sliced within the current coding block, diagonal filtering may be applied to pixels adjacent to a corner boundary of the first prediction block. .

A recording medium according to an aspect of the present invention includes the steps of encoding intra hybrid mode information of a current coding block and generating a prediction sample of at least one prediction block in the current coding block based on the intra hybrid mode information. Wherein, when the current coding block is in an intra hybrid mode, generating a prediction sample of at least one prediction block in the current coding block includes dividing the current coding block into a first prediction block and a second prediction block. A step of generating a prediction sample of the first prediction block using an intra-prediction mode of the first prediction block derived from a neighboring block of the first prediction block, and an intra-prediction mode of the second prediction block, or Determining an intra-prediction mode of the second prediction block based on Decoder-side Intra Mode Derivation (DIMD) mode information and generating a prediction sample of the second prediction block using the determined intra-prediction mode. A bitstream generated by a video encoding method including:

The present invention can improve prediction accuracy by determining the intra-screen prediction mode by considering the positional characteristics of the prediction block within the coding block.

The present invention can improve compression efficiency by determining the intra-screen prediction mode by considering the positional characteristics of the prediction block within the coding block.

The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the description below. will be.

Figure 1 is a block diagram showing a video encoding device according to an embodiment of the present invention.
Figure 2 is a diagram for explaining an intra-screen prediction mode according to an embodiment of the present invention.
Figure 3 is a flowchart showing a method of encoding the optimal prediction mode of the current prediction block among inter-screen prediction modes.
Figure 4 is a diagram for explaining an embodiment of a method for setting an MPM candidate in intra-prediction mode.
Figure 5 is a block diagram showing an image decoding device according to an embodiment of the present invention.
Figure 6 is a flowchart showing a method of decoding the intra-prediction mode of the current prediction block.
FIG. 7 is a diagram illustrating a first method for splitting a current coding block.
FIGS. 8 and 9 are diagrams for explaining a second method for splitting a current coding block.
10 (FIGS. 10A, 10B, 10C) and 11 (FIGS. 11A, 11B, 11C) show referenceable neighboring blocks when the prediction information of prediction blocks within a coding block is referred to in the prediction information of neighboring blocks. This is an illustrative drawing.
FIG. 12 is a diagram for explaining a method of encoding prediction information of a current encoding block.
FIG. 13 is a flowchart illustrating a method of encoding intra hybrid mode information in a video encoding device.
FIG. 14 is a flowchart illustrating a method of determining prediction information of the first prediction block within an intra-hybrid mode coding block in a video encoding device.
Figure 15 is a diagram for explaining a method of decoding prediction information of a current coding block.
Figure 16 is a diagram for explaining a boundary filtering method.
Figure 17 is a flowchart for explaining an image decoding method according to an embodiment of the present invention.
Figure 18 is a flowchart for explaining an image decoding method according to an embodiment of the present invention.
Figure 19 is a flowchart for explaining an image encoding method according to an embodiment of the present invention.
Figure 20 is a diagram to explain a method of deriving an intra prediction mode according to DIMD mode.

Since the present invention can make various changes and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention. While describing each drawing, similar reference numerals are used for similar components.

Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, a first component may be named a second component without departing from the scope of the present invention, and similarly, the second component may also be named a first component. The term and/or includes any of a plurality of related stated items or a combination of a plurality of related stated items.

When a component is said to be "connected" or "connected" to another component, it is understood that it may be directly connected or connected to the other component, but that other components may exist in between. It should be. On the other hand, when it is mentioned that a component is “directly connected” or “directly connected” to another component, it should be understood that there are no other components in between.

The terms used in this application are only used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the attached drawings. Hereinafter, the same reference numerals will be used for the same components in the drawings, and duplicate descriptions of the same components will be omitted.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the attached drawings. Hereinafter, the same reference numerals will be used for the same components in the drawings, and duplicate descriptions of the same components will be omitted.

Figure 1 is a block diagram showing the configuration of an image encoding device 100 according to an embodiment of the present invention.

The image encoding device 100 is a device that encodes an image and includes a block division unit 101, a prediction unit 102, a transform unit 103, a quantization unit 104, an entropy encoding unit 105, and an inverse quantization unit 106. ), an inverse transform unit 107, an adder 108, an in-loop filter unit 109, a memory unit 110, and a subtractor 111.

The block division unit 101 may perform division from the block to be encoded of the maximum size (hereinafter referred to as the maximum coding block) to the block to be encoded of the minimum size (hereinafter referred to as the minimum coding block). The partitioning may be performed based on at least one of quad-tree partitioning (hereinafter referred to as Quad-Tree (QT) partitioning) or dual-tree partitioning (hereinafter referred to as Dual-Tree (DT) partitioning). QT division is a method of dividing a parent block into four child blocks whose width and height are half that of the parent block. DT splitting is a method of dividing a parent block into two child blocks whose width or height is half that of the parent block. Here, DT division may be called binary tree division.

The block division unit 101 may divide the input image into at least one block. At this time, the input image may have various shapes and sizes, such as pictures, slices, tiles, and segments. A block may refer to a coding unit (CU), prediction unit (PU), or transformation unit (TU).

Hereinafter, in the embodiments of the present invention, the coding unit may be used to mean a unit that performs encoding, or may be used to mean a unit that performs decoding. And, a coding unit may mean a coding block.

The prediction unit 102 may include an inter-screen prediction unit that performs inter-screen prediction and an intra-screen prediction unit that performs intra-screen prediction. The prediction unit 102 may generate a prediction block using surrounding pixels of the block to be currently predicted (hereinafter referred to as prediction block) in the current original block or a previously decoded reference picture. Here, the prediction block may be generated from at least one prediction block within a coding block. When there is one prediction block in a coding block, the prediction block may have the same form as the coding block. Meanwhile, generating a prediction block in the prediction unit 102 may have the same meaning as generating a prediction sample of the prediction block.

Prediction technology for video signals largely consists of intra-screen prediction and inter-screen prediction. Intra-screen prediction is a method of generating a prediction block using surrounding pixels of the current block, and inter-screen prediction is a method that has already been encoded and decoded before. This is a method of generating a prediction block by finding the block most similar to the current block in the finished reference picture. Here, prediction between screens may be called inter prediction, and prediction within a screen may be called intra prediction.

The prediction unit 102 may determine the optimal prediction mode of the prediction block by using various techniques such as rate-distortion optimization (RDO) on the residual block obtained by subtracting the prediction block from the current original block. The RDO cost calculation formula is as shown in Equation 1 below.

Here, D is deterioration due to quantization, R is the rate of the compressed stream, J is the RD cost, Φ is the encoding mode, and λ is the Lagrangian multiplier, a scale correction coefficient to match the unit between the amount of error and the amount of bits. It can be. In order to be selected as the optimal encoding mode in the encoding process, the J when the mode is applied, that is, the RD-cost value, must be smaller than when other modes are applied. The bit rate and error are considered simultaneously in the equation for calculating the RD-cost value. It can be calculated by:

The residual value (residual block) between the generated prediction block and the original block may be input to the conversion unit 103. Additionally, prediction mode information, motion vector information, etc. used for prediction may be encoded in the entropy encoder 105 together with the residual value and transmitted to the decoder. When using a specific encoding mode, it is possible to encode the original block as is and transmit it to the decoder without generating a prediction block through the prediction unit 102.

The intra-screen prediction unit may generate a prediction block based on reference pixel information around the current block, which is pixel information in the current picture. If the coding mode of the neighboring block of the current block to which intra-screen prediction is to be performed is inter-screen prediction, the reference pixel included in the neighboring block to which inter-screen prediction has been applied will be replaced with a reference pixel in another neighboring block to which intra-screen prediction has been applied. You can. That is, when the reference pixel is not available, the unavailable reference pixel information can be used by replacing at least one reference pixel among the available reference pixels.

In intra-screen prediction, the prediction mode can include a directional prediction mode that uses reference pixel information according to the prediction direction and a non-directional mode that does not use directional information when performing prediction. The mode for predicting luminance information and the mode for predicting chrominance information may be different, and the prediction mode information or predicted luminance signal information within the screen used to predict luminance information may be used to predict chrominance information. .

Meanwhile, in intra-screen prediction, there may be a total of (N+2) prediction modes, including N Planar mode, DC mode, and N Angular prediction modes.

201 in FIG. 2 shows a method of generating a prediction block in DC mode.

Referring to 201 in FIG. 2, after applying the average value of reference pixels a to s to all prediction pixels in areas R1 to R4, R1 is two adjacent reference pixels (a, j), and areas R2 and R3 are adjacent reference pixels. The final prediction block is generated through FIR filtering with one block (b~h, k~q).

202 in FIG. 2 shows a method of generating a prediction block in Planar mode.

Referring to 202 in FIG. 2, Planar mode generates the final prediction block using a linear interpolation method between the reference pixel located at the top/left and the reference pixel copied to the bottom/right for each prediction pixel position.

203 in FIG. 2 shows the prediction directions of N Angular prediction modes.

Referring to 203 in FIG. 2, the Angular prediction mode generates the final prediction block by applying the values of adjacent reference pixels in each prediction direction to the prediction block.

Figure 3 is a flowchart showing a method of encoding the optimal prediction mode of the current prediction block.

Referring to FIG. 3, in step S301, a Most Probable Mode (MPM) candidate can be set. Here, the method of setting the MPM candidate will be described later with reference to FIG. 4.

And, in step S302, information indicating whether to encode the optimal intra-prediction mode can be encoded using MPM.

And, in step S303, it is possible to determine whether MPM operation information exists. If the information is true, index information indicating which MPM candidate the optimal intra-screen prediction mode is identical to can be encoded in step S304. Conversely, if the information is false, information indicating which prediction mode is optimal among the remaining intra-prediction modes excluding the intra-prediction mode that is an MPM candidate can be encoded in step S305.

Figure 4 is a diagram for explaining an embodiment of a method for setting an MPM candidate.

In Figure 4, L represents the intra-prediction mode information of the neighboring block located to the left of the current prediction block, and A represents the intra-prediction mode information of the neighboring block located at the top.

Referring to Figure 4, three MPM candidates can be finally determined according to each specified condition.

Meanwhile, the number of MPM candidates can be determined as P (P>0, P is an integer), and methods for determining candidates can also vary.

Returning to the description of the prediction unit 102 of FIG. 1, the inter-screen prediction unit included in the prediction unit 102 may generate a prediction block based on information on at least one picture among the previous picture or the next picture of the current picture. And, in some cases, a prediction block can be generated based on information on a part of the encoded area in the current picture. The inter-screen prediction unit may include a reference picture interpolation unit, a motion prediction unit, and a motion compensation unit.

Meanwhile, in inter-screen prediction, there may be prediction modes of AMVP mode, Merge mode, and Skip mode.

Meanwhile, the prediction unit 102 can encode coding mode information indicating the prediction method of the encoded block. As described above, a coding block may be divided into at least one prediction block, and one prediction method may be applied to a prediction block divided from one coding block. However, the prediction mode of each prediction block may be different.

For example, when the current coding block is encoded by intra-prediction, the first prediction block in the current coding block may generate prediction samples based on DC mode and the second prediction block may generate prediction samples based on Planar mode.

That is, coding mode information can be encoded in units of coding blocks, and prediction mode information can be encoded in units of prediction blocks.

Returning to the description of FIG. 1, the transform unit 103 may generate a transform block by transforming the residual block, which is the difference between the original block and the prediction block. Here, the transform block may be the smallest unit used for transform and quantization processes.

The transform unit 103 can convert the residual signal into the frequency domain and generate a transform block with transform coefficients. Here, various transformation techniques such as Discrete Cosine Transform (DCT)-based transformation, Discrete Sine Transform (DST), and Karhunen Loeve Transform (KLT) can be used to transform the residual signal into the frequency domain. And using this, the residual signal can be converted to the frequency domain and a conversion coefficient can be generated. To use a transformation technique, matrix calculation is performed using a basis vector. Depending on which prediction mode the prediction block is encoded in, various combinations of transformation techniques can be used during matrix calculation. For example, during intra-screen prediction, depending on the prediction mode, discrete cosine transformation may be used in the horizontal direction and discrete sine transformation may be used in the vertical direction.

Meanwhile, the transformation method may be determined based on the intra prediction mode of the prediction block used to generate the residual block. For example, depending on the intra prediction mode, DCT may be used in the horizontal direction and DST may be used in the vertical direction.

The transform block is divided in the coding block unit using the QT (Quad Tree) method or the BT (Binary Tree) method, the optimal transform block division type is determined, and the transform block division information can be transmitted to the video decoding device. This conversion block division method can be referred to as a CU-unit RT (Residual Tree) structure. This means that transformation may or may not be performed on a prediction block basis, and the transformation block can be determined by ignoring the boundary of the prediction block.

In addition, the transform block is divided in the prediction block unit using the QT method or the BT split method to determine the transform block division type, and the transform block division information can be transmitted to the video decoding device in each transform block unit. This transform block division method can be referred to as a PU unit RT structure. This means that the transform block cannot be generated in a split form beyond the prediction block boundary, and the transform block cannot be determined beyond the boundary of the prediction block.

In the above-described CU unit RT structure, transformation may be performed by determining the entire coding block as a transform block without transmitting transform block partition information. The same method can be applied to the PU unit RT structure.

The quantization unit 104 may quantize the transform block to generate a quantized transform block. That is, the quantization unit 104 can quantize the transform coefficients of the transform block generated by the transform unit 103 to generate a quantized transform block (Quantized Transform Coefficient) having quantized transform coefficients. Dead zone uniform threshold quantization (DZUTQ) or quantization weighted matrix can be used as a quantization method, but various quantization methods, such as improved quantization, can be used.

Meanwhile, in the above, the image encoding device 100 is shown and described as including both the transform unit 103 and the quantization unit 104, but the transform unit 103 and the quantization unit 104 may be optionally included. In other words, the image encoding device 100 may generate a transform block by transforming the residual block and not perform a quantization process. Not only can it perform only the quantization process without converting the residual block into a frequency coefficient, but it can even perform transformation. and quantization processes may not all be performed.

In the image encoding device 100, even if some or all of the processes of the transform unit 103 and the quantization unit 104 are not performed, the block input to the entropy encoder 105 is typically referred to as 'quantized transform.' It is called a ‘block’.

The entropy encoding unit 105 may encode the quantized transform block and output a bitstream. That is, the entropy encoding unit 105 encodes the coefficients of the quantized transform block output from the quantization unit 104 using various encoding techniques of entropy encoding, and decodes the corresponding block in an image decoding device to be described later. A bitstream containing additional information (e.g., information about prediction mode, quantization coefficient, etc.) required for processing can be generated and output.

Entropy coding can use various coding methods, such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC).

The inverse quantization unit 106 may restore the inverse quantization transform block by inversely performing the quantization technique used when quantizing the quantized transform block.

The inverse transform unit 107 restores the residual block by inversely transforming the inverse quantization transform block using the same method as the method used during transformation. Inverse transformation can be performed by reversing the transformation technique used in the transform unit 104. there is.

Meanwhile, in the above, the inverse quantization unit 106 and the inverse transformation unit 107 can perform inverse quantization and inverse transformation by using the quantization method and transformation method used in the quantization unit 104 and the transformation unit 103 inversely. Additionally, when the transform unit 103 and the quantization unit 104 perform only quantization and do not perform transformation, only inverse quantization may be performed and no inverse transformation may be performed. If neither the transformation nor the quantization are performed, the inverse quantization unit 106 and the inverse transformation unit 107 may not perform both the inverse transformation and the inverse quantization, or may not be included in the image encoding device 100 and may be omitted. .

The adder 108 can restore the current block by adding the residual signal generated by the inverse transform unit 107 and the prediction block generated through prediction.

The in-loop filter unit 109 is a process of additionally filtering the entire picture after all blocks in the current picture are restored, and may include at least one of deblocking filtering, Sample Adaptive Offset (SAO), and Adaptive Loop Filter (ALF). You can.

The deblocking filter can remove block distortion caused by boundaries between blocks in the restored picture. To determine whether to perform deblocking, it is possible to determine whether to apply a deblocking filter to the current block based on the pixels included in several columns or rows included in the block. When applying a deblocking filter to a block, a strong filter or a weak filter can be applied depending on the required deblocking filtering strength. Additionally, when applying a deblocking filter, horizontal filtering and vertical filtering can be processed in parallel when vertical filtering and horizontal filtering are performed.

SAO (Sample Adaptive Offset) refers to the process of minimizing the difference between the restored image and the original image by subtracting or adding a specific value to the restored pixel.

Adaptive Loop Filtering (ALF) can be performed based on a comparison between the filtered restored image and the original image. After dividing the pixels included in the image into predetermined groups, filtering can be performed differentially for each group by determining one filter to be applied to that group. Information related to whether to apply ALF may be transmitted for each coding unit (CU), and the shape and filter coefficients of the ALF filter to be applied may vary for each block. Additionally, an ALF filter of the same type (fixed type) may be applied regardless of the characteristics of the block to which it is applied.

The memory 110 adds the residual signal generated in the inverse transform unit 107 and the prediction block generated through prediction, then stores the restored current block that has undergone additional filtering in the in-loop filter unit 109, and then It can be used to predict blocks or the next photo.

The subtractor 111 may generate a residual block by subtracting the prediction block from the current original block.

Figure 5 is a block diagram showing an image decoding device 500 according to an embodiment of the present invention.

Referring to FIG. 5, the image decoding device 500 includes a block entropy decoding unit 501, an inverse quantization unit 502, an inverse transform unit 503, a prediction unit 504, an adder 505, and an in-loop filter. It may include a unit 506 and a memory unit 507.

When the video bitstream generated by the video encoding device 100 is input to the video decoding device 1000, the input bitstream may be decoded according to a process opposite to the process performed in the video encoding device 100. . Additionally, a 'coding block' in the video encoding device 100 may be referred to as a 'decoding block' in the video decoding device 500.

The entropy decoder 501 can interpret the bitstream received from the video encoding device 100 and obtain various information and quantized transform coefficients necessary to decode the corresponding block.

Additionally, the entropy decoding unit 501 may perform entropy decoding in a procedure opposite to that of the entropy encoding unit 105 of the video encoding device 100. For example, various methods such as Exponential Golomb, CAVLC (Context-Adaptive Variable Length Coding), and CABAC (Context-Adaptive Binary Arithmetic Coding) can be applied in response to the method performed in the image encoder. In the entropy decoding unit 501, the coefficients of the transform block are based on various types of flags indicating coefficients other than 0, coefficients whose absolute value is greater than 1 or 2, and signs of the coefficients, in units of partial blocks within the transform block. It can be decrypted. Coefficients that are not expressed only by the flag can be decoded through the sum of the coefficients expressed through the flag and the signaled coefficients.

Additionally, the entropy decoder 501 can decode information related to intra prediction and inter prediction performed in the video encoding device.

The inverse quantization unit 502 may inversely perform the quantization technique used during quantization on the quantized coefficients decoded by the entropy decoder 501 to obtain an inverse quantized block having the inverse quantized coefficients. The inverse quantization unit 502 may operate substantially the same as the inverse quantization unit 106 of FIG. 1 .

The inverse transform unit 503 can obtain a residual block having a difference signal by inversely transforming the inverse quantization transform block using the same method as the method used during transformation. The inverse transform unit 503 may operate substantially the same as the inverse transform unit 107 of FIG. 1 .

The prediction unit 504 generates a prediction block using the coding mode information decoded by the entropy decoder 501, which uses the same prediction method as the prediction method performed by the prediction unit 102 of the video encoding device 100. You can.

Figure 6 is a flowchart showing a method of decoding the intra-prediction mode of the current prediction block.

Referring to Figure 6, in step S601, an MPM candidate can be set. The method of setting the MPM candidate may be the same as the MPM candidate setting method of FIG. 3 described above in the prediction unit 102 of the video encoding device 100.

And, in step S602, information indicating whether to encode the intra-prediction mode can be decoded using MPM.

And, in step S603, it can be determined whether there is MPM operation information based on the information decrypted in step S602. If the information is true, the optimal intra-prediction mode of the current prediction block can be determined in step S604 by decoding the index information indicating which MPM candidate the intra-prediction mode is identical to. Conversely, if the information is false, in step S605, the information indicating which prediction mode is optimal among the remaining intra-prediction modes, excluding the intra-prediction mode that is the MPM candidate, is decoded to determine the intra-prediction mode of the current prediction block. You can decide.

Returning to the description of FIG. 5 , the adder 505 may generate a restored block by adding the prediction block generated in the prediction unit 504 and the residual block generated through the inverse transform unit 503.

The in-loop filter unit 506 restores all blocks in the current picture and then performs additional filtering on the entire picture, including deblocking filtering and SAO (Sample Adaptive Offset). Information on whether a deblocking filter has been applied to the corresponding block or picture can be received from the video encoding device 100, and when a deblocking filter has been applied, information on whether a strong filter or a weak filter has been applied. The in-loop filter unit 506 may operate substantially the same as the in-loop filter unit 109 of FIG. 1 .

The memory 507 adds the residual signal generated in the inverse transform unit 503 and the prediction block generated through prediction, and then stores the restored current block that has undergone additional filtering in the in-loop filter unit 506, It can be used to predict the next block or next photo, etc.

As described above, hereinafter, in the embodiments of the present invention, the term coding unit is used as a coding unit for convenience of explanation, but it may also be a unit that performs not only encoding but also decoding. Additionally, a unit or unit may be an area created by dividing one picture. Additionally, in an embodiment of the present invention, a unit may mean a block, and the current block may mean a current encoding target block or a current decoding target block.

Hereinafter, a method of dividing a coding block will be described with reference to FIGS. 7 to 9.

FIG. 7 is a diagram illustrating a first method for splitting a current coding block.

Referring to FIG. 7, the coding block may be divided into a square or rectangular shape. 701 in FIG. 7 is an example of a coding block being split vertically, and 702 is an example of a coding block being split horizontally. In each example, the coding order of the prediction blocks within the coding block may be encoded in the following order: prediction block A, followed by prediction block B, and the dotted line within the coding block indicates a coding block dividing line, which may mean a boundary line between prediction blocks. In 701 and 702 of FIG. 7, the coding block dividing line can be divided into two parts of various sizes in addition to dividing the coding block exactly into two.

Meanwhile, the first method of determining the division type of the coding block calculates the RD-Cost for each division type in all cases from 1 to 2N-1 with the value of P for each horizontal and vertical division of the coding block, and RD-Cost is The minimum division type can be determined as the optimal division type of the current coding block.

FIGS. 8 and 9 are diagrams for explaining a second method for splitting a current coding block.

The second method of determining the partition type of a coding block is to preset an available coding block partition set and determine the optimal partition form by calculating the RD-Cost of the preset partition types. At this time, information of a preset usable segmentation type may be transmitted in the upper header. Here, the upper header refers to the transport layer at the block level or higher, such as the video parameter layer, sequence parameter layer, picture parameter layer, and slide layer.

Predefined division types may include symmetric vertical division, symmetric horizontal division, asymmetric vertical division, and asymmetric horizontal division.

Referring to Figure 8, (1/4, 3/4) vertical division, (1/2, 1/2) vertical division, (3/4, 1/4) vertical division, (1/4, 3/4) ) There can be horizontal division, (1/2, 1/2) horizontal division, and (3/4, 1/4) horizontal division. where (1/4, 3/4) horizontal split, (3/4, 1/4) horizontal split, (1/4, 3/4) vertical split, and (3/4, 1/4) vertical split. is an asymmetric division form, and the (1/2, 1/2) horizontal division and (1/2, 1/2) vertical division may be symmetric division forms.

Meanwhile, there may be corner division in a predefined division form.

Referring to FIG. 9, there may be an upper left corner split (901), an upper right corner split (902), a lower left corner split (903), and a lower right corner split (904). Here, the prediction block of the divided edge portion may be 1/4 the area of the coding block.

In the upper left corner division 901, the upper left prediction block may be prediction block A (NxN), and the remaining area may be prediction block B.

In addition, in the upper right corner division 902, the upper right prediction block may be prediction block A (NxN), and the remaining area may be prediction block B.

And, in the lower left corner division 903, the lower left prediction block may be prediction block A (NxN), and the remaining area may be prediction block B.

And, in the lower right corner division 904, the lower right prediction block may be prediction block B, and the remaining area may be prediction block A (NxN). For each split type, the coding order of coding blocks may be prediction block A and prediction block B. In addition, in the corresponding partitioning method, the size of the prediction block of 1/4 area may become larger or smaller.

Additionally, in each division method, the shape may also be of various shapes, such as a rectangle rather than a square. Also, by comparing the RD-Cost for each partition type, the partition form with the minimum RD-Cost can be determined as the optimal partition form of the current coding block.

Below, the intra hybrid mode according to an embodiment of the present invention will be described.

Intra hybrid mode is one of the intra-screen prediction modes. When the coding mode of the coding block is intra-screen mode and intra-hybrid mode, the prediction information of the first prediction block (prediction block A) is determined by using the intra-screen prediction information of neighboring blocks of the coding block, and the prediction information of the second prediction block is determined by using the intra-screen prediction information of the coding block's neighboring blocks. The prediction information of the block (prediction block B) may be determined on a prediction block basis in the same manner as shown in FIG. 3, or may be determined on a prediction block basis using the DIMD mode.

Here, the DIMD mode may refer to a prediction mode in which a prediction sample of a prediction block is generated by directly deriving an uncoded intra prediction mode in the image decoding device 500 without encoding in the image encoding device 100.

As an example, the DIMD mode generates a prediction sample of the prediction block by deriving the intra prediction mode of the block surrounding the coding block in the image decoding device 500, and deriving the final intra prediction mode of the prediction block based on the derived intra prediction mode. It may be a mode that does this.

Figure 20 illustrates the surrounding template area for each division type when searching for the prediction mode of prediction block B generated within the current coding block using DIMD mode to explain the prediction information search method in DIMD mode. The template area can be determined from areas that have already been restored around the current encoding block.

The template area towards the top is the AboveTemplate area, and the template area towards the left is the LeftTemplate area.

Here, the horizontal length of the AboveTemplate area is W and the vertical length is AT, the horizontal length of the LeftTemplate area is LT and the vertical length is H, and the reference pixels of the Template area can be used as many as R lines. Meanwhile, the template area can be referred to as a template block.

You can explore the intra prediction mode that generates predicted pixel values with minimal errors and restored pixel values in the template area. The intra prediction mode discovered in this way can be determined as the prediction information of the template area, and the corresponding prediction information can be used as the prediction information of the current block.

Meanwhile, if the coding block in the intra-screen mode is not the intra hybrid mode, it may be determined on a prediction block basis as shown in FIG. 3.

FIG. 10 ( FIGS. 10A , 10B , and 10C ) is a diagram illustrating a method of determining prediction information of prediction block A by using intra-screen prediction information of neighboring blocks as is. Here, the prediction information may be an intra-screen prediction mode.

Prediction block A can generate a prediction block by searching for the optimal prediction information for prediction block A among the prediction information of adjacent neighboring blocks for which encoding has been completed, and determining the searched optimal prediction information as prediction information for prediction block A. there is.

The positions of neighboring blocks of prediction block A may be located as shown in numbers 1001 to 1006 of FIG. 10 . Additionally, when there is a priority between neighboring blocks, optimal prediction information can be searched according to the priority. In this example, it is assumed that the priorities are in the order of neighboring blocks 1, 2, 3, 4, and 5.

Prediction block A of 1001 in FIG. 10A can have five neighboring blocks from neighboring blocks 1 to 5. The prediction information of neighboring blocks 1 to 5 of prediction block A can be applied to prediction block A to calculate RD-Cost, and the prediction information of the neighboring block with the minimum RD-Cost can be determined as the prediction information of prediction block A.

The description of 1002 in FIG. 10A is the same as the description of 1001 except that the location of the surrounding blocks is changed.

1003 to 1006 in FIGS. 10B and 10C indicate that the number and location of neighboring blocks may vary depending on the location of prediction block A. In each case, the RD-Cost can be calculated by applying the prediction information of neighboring blocks to prediction block A, and the prediction information with the minimum RD-Cost can be determined as the optimal prediction information of prediction block A, and the prediction information can be used to A prediction block can be created.

Meanwhile, a method of determining prediction information of prediction block B can also be used to find the optimal prediction mode among Planar, DC, and N Angular modes using reference pixels around the prediction block, and to generate a prediction block using the corresponding prediction information. Also, the optimal prediction mode can be found using DIMD mode and a prediction block can be generated using the corresponding prediction information.

However, in prediction block B, the prediction information of prediction block B can be determined by referring to the prediction information of prediction block A only in some cases. Here, some cases are explained below.

Instead of the difference between the prediction block and the original block in the image decoding device 500, in DMID mode, RD-Cost is calculated using the difference between the predicted pixel value of the template area using the restored pixel value of the template area and the reference pixels around the template area. You can search for prediction information by assuming an error for

FIG. 11 (FIGS. 11A, 11B, and 11C) is a diagram for explaining a method of determining prediction information of prediction block B.

The positions of neighboring blocks of prediction block B may be located as shown in numbers 1101 to 1106 of FIG. 11 . Additionally, when priorities exist between neighboring blocks, optimal prediction information can be searched according to the priorities. In this example, it is assumed that the priorities are in the order of neighboring blocks 1, 2, 3, 4, and 5.

Meanwhile, like 1101 to 1102 in FIG. 11A, the number of neighboring block candidates may be 3 or 4 instead of 5.

At this time, the prediction information of prediction block B may be determined by referring to the prediction information of prediction block A according to the transform block partition structure.

If the current transform block partition structure is composed of a CU unit RT structure, prediction information of prediction block B cannot be determined by reference to prediction information of prediction block A.

Meanwhile, when the current transform block division structure is composed of a PU unit RT structure, prediction block B can determine the prediction information of prediction block B by referring to the prediction information of prediction block A.

Meanwhile, prediction information of prediction block B may be determined on a prediction block basis as described above. In this case, as described in the prediction unit 102 of the video encoding device 100 of FIG. 1, the optimal intra-prediction mode is determined for each prediction block, and a prediction block is generated according to the determined intra-prediction mode or DIMD mode. You can.

FIG. 12 is a diagram for explaining a method of encoding prediction information of a current encoding block. In FIG. 12, it is assumed that the current coding block is divided into prediction block A and prediction block B, and the coding mode of the current coding block is intra-screen mode.

Referring to FIG. 12, in step S1201, intra hybrid mode information of the current coding block can be encoded. Here, intra hybrid mode information may be information indicating whether a coding block is encoded in intra hybrid mode.

By comparing the RD-Cost of the intra-hybrid mode and the intra-screen prediction mode, if the RD-Cost of the intra-hybrid mode is minimum, the intra-hybrid mode information of the current coding block can be encoded as true. Here, intra hybrid mode information may be encoded in a flag format.

FIG. 13 is a flowchart showing a method of encoding intra hybrid mode information in the video encoding apparatus 100.

Referring to FIG. 13, in step S1301, it can first be determined whether the intra-screen prediction mode operation is true or not. Here, if the operation of the intra-screen prediction mode is false, this flowchart ends, and if it is true, the flowchart can proceed to step S1302.

In step S1302, index information is assigned to 0 for the intra-screen prediction mode and 1 to the intra hybrid mode.

In the first step S1303, the initial value of N is 0, Best_Cost is infinite, and the RD-Cost of the intra-screen prediction mode, which is index information 0, can be calculated and stored in N_Cost.

In step S1304, it is determined whether N_Cost is large or small by comparing it with the current Best_Cost, and if N_Cost is small, the current N value can be stored as Best_Idx and N_Cost as Best_Cost in step S1305.

In step S1306, it is compared whether the current N is 1 or not. If the current N is not 1, add 1 to the current N in step S1307, return to step S1303 and repeat the above process, and if the current N is 1, determine the current Best_Idx as the intra hybrid mode information of the current coding block in step S1308. And the process of Figure 13 ends.

The intra hybrid mode information generated through this process is encoded as the intra hybrid mode information of the current coding block in step S1301. Additionally, information on whether the intra hybrid mode is operating may be additionally transmitted in the upper header, and whether the intra hybrid mode is operating may be controlled at the transmitted upper header layer.

Returning to the description of FIG. 12 , in step S1202, it may be determined whether the current coding block is in the intra hybrid mode based on the intra hybrid information of the current coding block.

If the current coding block is in intra hybrid mode, the process proceeds to step S1203 and the division information of the current coding block can be encoded.

At this time, when the coding block is divided into two parts as shown in the example diagrams of FIG. 7, the P information may be encoded after encoding the information about whether it is horizontally or vertically divided, and the P information may be encoded as shown in the example diagram of FIG. 8 As explained, index information indicating which partition type is optimal among the preset partition sets can be encoded. In addition, when the coding block is divided into 1/4 and 3/4 as shown in the examples of FIG. 9, index information about which direction the 1/4 prediction block is located in among the four directions is encoded to determine the current coding block. You can also decide on the type of division.

In step S1204, the prediction information of prediction block A can be encoded. Among the prediction information of neighboring blocks, the index information of the neighboring block that has the most optimal prediction information for prediction block A can be encoded.

FIG. 14 is a flowchart illustrating a method of encoding prediction information of the first prediction block in an intra-hybrid mode coding block in a video encoding device.

Referring to FIG. 14, in step S1401, a prediction block is generated by applying the on-screen prediction information of available neighboring blocks to prediction block A, and then RD-Cost is calculated for each prediction information.

In step S1402, among the applied prediction information, prediction information with the minimum RD-Cost is determined, and in step S1403, index information of neighboring blocks with the corresponding prediction information can be stored.

Meanwhile, prediction information of a high-priority neighboring block among available neighboring blocks according to the priorities of the neighboring blocks may be used as is, without going through the process of FIG. 14.

In step S1205, the prediction information of prediction block B is encoded. The prediction information of prediction block B can be encoded using the intra prediction coding method of FIG. 3 described above or by transmitting DIMD mode information (or flag information) indicating the DIMD mode.

In step S1206, since the current coding block is not in intra hybrid mode, in this case, coding can be performed on a prediction block basis using the intra prediction coding method of FIG. 3 described above.

Figure 15 is a diagram for explaining a method of decoding prediction information of a current decoding block. In FIG. 15, it is assumed that the current decoding block is divided into prediction block A and prediction block B, and the coding mode of the current encoding block is intra-screen mode. Here, the current decoding block may mean the current encoding block.

Referring to FIG. 15, in step S1501, the intra hybrid mode information of the current decoding block can be decoded.

Step S1502 may determine whether the current decoding block is in intra hybrid mode based on the decrypted intra hybrid mode information.

If the current decoding block is in intra hybrid mode, the process proceeds to step S1503 and the division information of the current encoding block can be encoded.

Step S1503 may decode the partition information of the current decoding block encoded in step S1203 of FIG. 12 described above. Here, the current decrypted block can be divided using the decrypted division information. A detailed description of this will be omitted as it has been described above with reference to FIGS. 7 to 9.

Step S1504 may decode the prediction information of prediction block A encoded in step S1204 of FIG. 12 described above. Specifically, in step S1504, the prediction information of the prediction block A can be derived from the prediction information of the neighboring block selected based on the index information of the neighboring block. In addition, among the available neighboring blocks according to the priority of the preset neighboring block, the prediction information of the neighboring block with high priority can be derived as the prediction information of prediction block A.

Step S1505 may decode the prediction information of prediction block B encoded in step S1205 of FIG. 12 described above.

Meanwhile, in step S1506, since the current decoding block is not in intra hybrid mode, in this case, decoding can be done in units of prediction blocks using the intra prediction decoding method of FIG. 6 described above.

Figure 16 is a diagram for explaining a boundary filtering method according to an embodiment of the present invention.

Prediction blocks A and B generated within the current encoding block may experience blocking in the border area. Therefore, a smoothing filtering process is necessary to smooth the boundary area.

Referring to FIG. 16, after the prediction modes of prediction block A and prediction block B in the current coding block are determined and two prediction blocks are generated, filtering may be performed at the boundary of the two prediction blocks.

1601 and 1602 in FIG. 16 show pixels to be filtered at the boundary between prediction blocks when the prediction block within the coding block is divided into two. Pixels aligned with the prediction block boundary are filtered, the filter tab is indicated as 4, and the filter coefficients are indicated as W1 to W4. W1 to W4 are random real numbers, and W1+W2+W3+W4 is always 1. Equation 2 shows the filtering formula in 1601 and 1602.

1603 to 1606 of FIG. 16 show pixels to be filtered at the boundary between prediction blocks when the prediction block is edge-divided within the coding block. In this case, diagonal filtering may be applied to the pixels (e1, e2, e4, e5) at the corner boundary of the prediction block. Here, a pixel in which d1 and b1 are expressed simultaneously means that b1 and d1 point to the same pixel.

Equation 3 shows the filtering equations in numbers 1603 to 1606 of FIG. 16.

Referring to Equation 3, it can be seen that diagonal filtering is applied to the pixels (e1, e2, e4, e5) at the corner boundary.

Figure 17 is a flowchart for explaining an image decoding method according to an embodiment of the present invention.

Referring to FIG. 17, the video decoding device can decode intra hybrid mode information of the current coding block (S1701).

And, the image decoding apparatus may generate a prediction sample of at least one prediction block in the current coding block based on the intra hybrid mode information (S1702). A detailed description of step S1702 will be described with reference to FIG. 18.

Figure 18 is a flowchart for explaining an image decoding method according to an embodiment of the present invention.

Referring to FIG. 18, when the current coding block is in the intra hybrid mode (S1801 - Yes), the video decoding device may divide the current coding block into a first prediction block and a second prediction block (S1802).

Here, the first prediction block and the second prediction block may be in the form of corner-splitting the current coding block as shown in FIG. 9.

In this case, as described in FIG. 16, diagonal filtering may be applied to pixels adjacent to the corner boundary of the first prediction block.

And, the image decoding apparatus may generate a prediction sample of the first prediction block using the intra-prediction mode of the first prediction block derived from the neighboring blocks of the first prediction block (S1803).

Meanwhile, the image decoding apparatus may induce the intra-prediction mode of a neighboring block determined according to a preset priority among the neighboring blocks of the first prediction block to the intra-prediction mode of the first prediction block.

Alternatively, the image decoding device may induce the intra-prediction mode of the neighboring block determined based on neighboring block index information to the intra-prediction mode of the first prediction block. Here, the neighboring block index information may be information signaled from the video encoding device.

Then, the video decoding device decodes the intra-prediction mode information or DIMD mode information of the second prediction block to determine the intra-prediction mode of the second prediction block, and predicts the second prediction block using the determined intra-prediction mode. A sample can be created (S1804).

Meanwhile, if the current coding block is not in the intra hybrid mode (S1801 - No), the video decoding device may generate a prediction sample of at least one prediction block in the current coding block through intra-prediction (S1805). That is, as described in FIG. 6, prediction samples can be generated in units of prediction blocks by inducing an intra-screen prediction mode.

Figure 19 is a flowchart for explaining an image encoding method according to an embodiment of the present invention.

Referring to FIG. 19, the video encoding device can encode intra hybrid mode information of the current coding block (S1901).

And, the image encoding device may generate a prediction sample of at least one prediction block in the current coding block based on the intra hybrid mode information (S1902).

Meanwhile, to describe step S1902 in detail, when the current coding block is in intra hybrid mode, the video encoding device divides the current coding block into a first prediction block and a second prediction block, and derives the information from the neighboring blocks of the first prediction block. A prediction sample of the first prediction block can be generated using the intra-prediction mode of the first prediction block. Then, the video encoding device determines the intra-prediction mode of the second prediction block based on the intra-prediction mode information or DIMD mode information of the second prediction block, and predicts the second prediction block using the determined intra-prediction mode. Samples can be created.

Meanwhile, the bitstream generated by the video encoding method of FIG. 19 can be recorded in a storage medium.

Exemplary methods of the present disclosure are expressed as a series of operations for clarity of explanation, but this is not intended to limit the order in which the steps are performed, and each step may be performed simultaneously or in a different order, if necessary. In order to implement the method according to the present disclosure, other steps may be included in addition to the exemplified steps, some steps may be excluded and the remaining steps may be included, or some steps may be excluded and additional other steps may be included.

The various embodiments of the present disclosure do not list all possible combinations but are intended to explain representative aspects of the present disclosure, and matters described in the various embodiments may be applied independently or in combination of two or more.

Additionally, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. For hardware implementation, one or more ASICs (Application Specific Integrated Circuits), DSPs (Digital Signal Processors), DSPDs (Digital Signal Processing Devices), PLDs (Programmable Logic Devices), FPGAs (Field Programmable Gate Arrays), general purpose It can be implemented by a processor (general processor), controller, microcontroller, microprocessor, etc.

The scope of the present disclosure is software or machine-executable instructions (e.g., operating system, application, firmware, program, etc.) that cause operations according to the methods of various embodiments to be executed on a device or computer, and such software or It includes non-transitory computer-readable medium in which instructions, etc. are stored and can be executed on a device or computer.

Claims (5)

In the video decoding method,
Splitting the current encoding block into a plurality of sub-blocks; Here, the plurality of sub-blocks include a first sub-block and a second sub-block,
Generating a prediction sample of the first sub-block using an intra-prediction mode derived from a neighboring block as a prediction mode of the first sub-block, wherein the neighboring block is a top neighboring block adjacent to the current coding block. It includes a neighboring block located at the bottom of the rightmost neighboring block and left neighboring blocks adjacent to the current encoding block; and
Generating a prediction sample of the second sub-block using the intra-prediction mode used to generate the prediction sample of the first sub-block,
The first sub-block includes the top-left pixel in the current block,
The second sub-block includes a lower-right pixel in the current block,
The size of the second sub-block is 1/4 the size of the current block,
The intra-screen prediction mode is determined as one of a plurality of modes determined by an index signaled from a bitstream. According to paragraph 1,
A video decoding method wherein the division type of the division is determined based on information about the division type signaled from the bitstream. According to paragraph 2,
A video decoding method in which whether to split the current coding block is determined based on mode information signaled from the bitstream. In the video encoding method,
Splitting the current encoding block into a plurality of sub-blocks; Here, the plurality of sub-blocks include a first sub-block and a second sub-block,
Generating a prediction sample of the first sub-block using an intra-prediction mode derived from a neighboring block as a prediction mode of the first sub-block, wherein the neighboring block is a top neighboring block adjacent to the current coding block. Includes a neighboring block located at the bottom of the rightmost neighboring block and left neighboring blocks adjacent to the current encoding block; and
Generating a prediction sample of the second sub-block using the intra-prediction mode used to generate the prediction sample of the first sub-block,
The first sub-block includes the upper-left pixel in the current block,
The second sub-block includes a lower-right pixel in the current block,
The size of the second sub-block is 1/4 the size of the current block,
An index indicating the intra-prediction mode among a plurality of modes is encoded in a bitstream, and an image encoding method. A computer-readable recording medium storing a bitstream generated by an image encoding method,
The video encoding method includes dividing a current encoding block into a plurality of sub-blocks; Here, the plurality of sub-blocks include a first sub-block and a second sub-block,
Generating a prediction sample of the first sub-block using an intra-prediction mode derived from a neighboring block as a prediction mode of the first sub-block, wherein the neighboring block is a top neighboring block adjacent to the current coding block. Includes a neighboring block located at the bottom of the rightmost neighboring block and left neighboring blocks adjacent to the current encoding block; and
Generating a prediction sample of the second sub-block using the intra-prediction mode used to generate the prediction sample of the first sub-block,
The first sub-block includes the upper-left pixel in the current block,
The second sub-block includes a lower-right pixel in the current block,
The size of the second sub-block is 1/4 the size of the current block,
An index indicating the intra-screen prediction mode among a plurality of modes is encoded in the bitstream, and a computer-readable recording medium.