WO2020050697A1

WO2020050697A1 - Intra-prediction mode-based image processing method and device therefor

Info

Publication number: WO2020050697A1
Application number: PCT/KR2019/011588
Authority: WO
Inventors: 이령; 김승환; 허진
Original assignee: 엘지전자 주식회사
Priority date: 2018-09-06
Filing date: 2019-09-06
Publication date: 2020-03-12

Abstract

Disclosed according to the present invention are a method of decoding a video signal and a device therefor. Specifically, a method of decoding an image on the basis of an intra-prediction mode may comprise the steps of: acquiring a most probable mode (MPM) flag indicating whether the MPM is applied to the current block, wherein the MPM represents a mode in which an intra-prediction mode for the current block is derived from an intra-predicted block around the current block; when the MPM is applied to the current block, forming an MPM list on the basis of intra-prediction modes for neighboring blocks lying to the left of and above the current block; acquiring an MPM index indicating a particular intra-prediction mode in the MPM list; and generating a prediction block for the current block by using an intra-prediction mode specified by the MPM index.

Description

Intra prediction mode based image processing method and apparatus therefor

The present invention relates to a method for processing a still image or a video, and more particularly, to a method for encoding / decoding a still image or a video based on an intra prediction mode and an apparatus supporting the same.

Compression coding refers to a series of signal processing techniques for transmitting digitized information through a communication line or storing it in a form suitable for a storage medium. Media such as video, image, and audio may be the subject of compression encoding, and a technique for performing compression encoding on an image is referred to as video image compression.

Next-generation video content will have the characteristics of high spatial resolution, high frame rate and high dimensionality of scene representation. In order to process such content, a huge increase in terms of memory storage, memory access rate and processing power will be produced.

Therefore, it is necessary to design a coding tool for processing next-generation video content more efficiently.

In general, the more various modes of intra-consideration are considered from various neighboring locations, the better coding efficiency can be achieved. For this reason, recently, as more MPM candidates are considered than HEVC, a method of constructing an MPM list using more neighboring blocks has been discussed. However, in the case of searching for a block around a large number of locations, there is a problem that the complexity is significantly increased.

Accordingly, an object of the present invention is to propose a method for generating an MPM list that can improve such problems and increase diversity of MPM candidates.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems that are not mentioned will be clearly understood by those skilled in the art from the following description. Will be able to.

According to an aspect of the present invention, in a method of decoding an image based on an intra prediction mode, obtaining an MPM flag indicating whether a Most Probable Mode (MPM) is applied to a current block, wherein the MPM is Indicates a mode in which the intra prediction mode of the current block is derived from the intra predicted block around the current block; When MPM is applied to the current block, constructing an MPM list based on intra prediction modes of left and upper neighboring blocks of the current block; Obtaining an MPM index indicating a specific intra prediction mode in the MPM list; And generating a prediction block of the current block using an intra prediction mode specified by the MPM index, wherein the left neighboring block is a block including pixels adjacent in the horizontal direction of the lower left sample in the current block. Is set, and the upper neighboring block may be set as a block including pixels adjacent in a vertical direction of a right uppermost sample in the current block.

Preferably, the constructing the MPM list may include: checking whether intra prediction modes of the left and upper neighboring blocks are the same; Checking whether the intra prediction mode of the upper neighboring block is less than 2 when the intra prediction mode of the left and upper neighboring blocks are the same; If the intra prediction mode of the upper neighboring block is less than 2, generating a first MPM list; And when the intra prediction mode of the upper neighboring block is not less than 2, generating a second MPM list.

Preferably, the first MPM list includes a planar mode, a DC mode, a vertical mode, a horizontal mode, a horizontal diagonal mode and a vertical diagonal mode, and the second MPM list includes a planar mode, a DC mode, and the upper neighbor The intra prediction mode of the block and the two intra prediction modes closest to the intra prediction mode of the upper neighboring block may be included.

Preferably, the step of constructing the MPM list is that the left or upper neighboring block is not available, is not a block coded in intra prediction mode, or is not located in a current coding tree unit (CTU). If not, the method may further include setting the intra prediction mode of the left or upper neighboring block to a planar mode.

Preferably, the MPM list includes 6 MPM candidates, and among indexes indicating the 6 MPM candidates, index 0 is binarized to 00, index 1 is binarized to 01, and index 2 is It can be binarized to 100, index 3 is binarized to 101, index 4 is binarized to 110, and index 5 can be binarized to 111.

Another aspect of the present invention, in an apparatus for decoding an image based on an intra prediction mode, an MPM flag acquiring unit that acquires an MPM flag indicating whether a Most Probable Mode (MPM) is applied to a current block, Here, the MPM indicates a mode in which the intra prediction mode of the current block is derived from the intra predicted block around the current block; An MPM list construction unit configured to configure an MPM list based on intra prediction modes of left and upper neighboring blocks of the current block when MPM is applied to the current block; An MPM index obtaining unit for obtaining an MPM index indicating a specific intra prediction mode in the MPM list; And a prediction block generator configured to generate a prediction block of the current block using an intra prediction mode specified by the MPM index, wherein the left neighboring block includes pixels adjacent in the horizontal direction of the lower left sample in the current block. The upper neighboring block may be set as a block including pixels adjacent in the vertical direction of the upper right sample in the current block.

According to an embodiment of the present invention, according to an embodiment of the present invention, by using the intra prediction mode of the left and upper neighboring blocks at different positions from the conventional image compression technique, more various MPM lists can be constructed.

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description. .

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as part of the detailed description to aid understanding of the present invention, provide embodiments of the present invention and describe the technical features of the present invention together with the detailed description.

1 is an embodiment to which the present invention is applied, and shows a schematic block diagram of an encoding device in which encoding of a video / image signal is performed.

2 is an embodiment to which the present invention is applied, and shows a schematic block diagram of a decoding apparatus in which decoding of a video / image signal is performed.

3 is an embodiment to which the present invention can be applied, and is a view showing an example of a multi-type tree structure.

4 is an embodiment to which the present invention can be applied, and is a diagram illustrating a signaling mechanism of partition partitioning information of a quadtree with nested multi-type tree structure.

5 is an embodiment to which the present invention can be applied, and is a diagram illustrating a method of dividing a CTU into multiple CUs based on a quadtree and nested multi-type tree structure.

6 is an embodiment to which the present invention can be applied, and is a diagram illustrating a method for limiting ternary-tree partitioning.

7 is an embodiment to which the present invention can be applied, and is a diagram illustrating redundant splitting patterns that may occur in binary tree splitting and ternary tree splitting.

8 and 9 are diagrams illustrating an intra prediction-based video / video encoding method according to an embodiment of the present invention and an intra prediction unit in an encoding device according to an embodiment of the present invention.

10 and 11 are diagrams illustrating an intra prediction-based video / image decoding method according to an embodiment of the present invention and an intra prediction unit in a decoding apparatus according to an embodiment of the present invention.

12 and 13 are views illustrating a prediction direction of an intra prediction mode according to an embodiment to which the present invention can be applied.

14 shows an example of a neighboring block used as an MPM candidate according to an embodiment to which the present invention can be applied.

15 is a diagram illustrating an example of a component that generates an MPM list according to an embodiment of the present invention.

16 is a flowchart illustrating a method of generating an intra prediction block according to an embodiment to which the present invention is applied.

17 is a diagram illustrating an intra prediction apparatus according to an embodiment to which the present invention is applied.

18 shows a video coding system to which the present invention is applied.

19 is an embodiment to which the present invention is applied, and shows a structure diagram of a content streaming system.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION The detailed description set forth below, in conjunction with the accompanying drawings, is intended to describe exemplary embodiments of the invention, and is not intended to represent the only embodiments in which the invention may be practiced. The following detailed description includes specific details to provide a thorough understanding of the present invention. However, one skilled in the art knows that the present invention can be practiced without these specific details.

In some cases, in order to avoid obscuring the concept of the present invention, well-known structures and devices may be omitted, or block diagrams centered on the core functions of each structure and device may be illustrated.

In addition, the terminology used in the present invention has been selected as a general terminology that is currently widely used as much as possible, but in a specific case, the term will be described using the term arbitrarily selected by the applicant. In such a case, since the meaning is clearly described in the detailed description of the relevant part, it should not be interpreted simply by the name of the term used in the description of the present invention and the meaning of the term should be understood and interpreted. .

Certain terms used in the following description are provided to help understanding of the present invention, and the use of these specific terms may be changed to other forms without departing from the technical spirit of the present invention. For example, in the case of signals, data, samples, pictures, frames, blocks, etc., each coding process may be appropriately replaced and interpreted.

Hereinafter, the term 'processing unit' in the present specification means a unit in which encoding / decoding processing processes such as prediction, transformation, and / or quantization are performed. Hereinafter, for convenience of description, the processing unit may be referred to as a 'processing block' or a 'block'.

The processing unit may be interpreted to include a unit for a luminance component and a unit for a chroma component. For example, the processing unit may correspond to a coding tree unit (CTU), a coding unit (CU), a prediction unit (PU), or a transform unit (TU).

Also, the processing unit may be interpreted as a unit for a luma component or a unit for a chroma component. For example, the processing unit may include a coding tree block (CTB) for a luminance component, a coding block (CB), a prediction block (PU), or a transform block (TB). ). Alternatively, it may correspond to a coding tree block (CTB), a coding block (CB), a prediction block (PU), or a transform block (TB) for a chroma component. In addition, the present invention is not limited thereto, and the processing unit may be interpreted to include a unit for a luminance component and a unit for a chroma component.

In addition, the processing unit is not necessarily limited to square blocks, and may be configured in a polygonal shape having three or more vertices.

In addition, hereinafter, a pixel or a pixel is referred to as a sample in this specification. And, using a sample may mean using a pixel value or a pixel value.

Referring to FIG. 1, the encoding apparatus 100 includes an image segmentation unit 110, a subtraction unit 115, a conversion unit 120, a quantization unit 130, an inverse quantization unit 140, and an inverse conversion unit 150, It may be configured to include an adder 155, a filtering unit 160, a memory 170, an inter prediction unit 180, an intra prediction unit 185, and an entropy encoding unit 190. The inter prediction unit 180 and the intra prediction unit 185 may be collectively referred to as a prediction unit. In other words, the prediction unit may include an inter prediction unit 180 and an intra prediction unit 185. The transform unit 120, the quantization unit 130, the inverse quantization unit 140, and the inverse transform unit 150 may be included in a residual processing unit. The residual processing unit may further include a subtraction unit 115. As an embodiment, the above-described image segmentation unit 110, subtraction unit 115, conversion unit 120, quantization unit 130, inverse quantization unit 140, inverse conversion unit 150, addition unit 155 The filtering unit 160, the inter prediction unit 180, the intra prediction unit 185, and the entropy encoding unit 190 may be configured by one hardware component (for example, an encoder or processor). Further, the memory 170 may include a decoded picture buffer (DPB), or may be configured by a digital storage medium.

The image splitter 110 may divide the input image (or picture, frame) input to the encoding apparatus 100 into one or more processing units. For example, the processing unit may be called a coding unit (CU). In this case, the coding unit may be recursively divided according to a quad-tree binary-tree (QTBT) structure from a coding tree unit (CTU) or a largest coding unit (LCU). For example, one coding unit may be divided into a plurality of coding units of a deeper depth based on a quad tree structure and / or a binary tree structure. In this case, for example, a quad tree structure may be applied first, and a binary tree structure may be applied later. Alternatively, a binary tree structure may be applied first. The coding procedure according to the present invention can be performed based on the final coding unit that is no longer split. In this case, the maximum coding unit may be directly used as a final coding unit based on coding efficiency according to image characteristics, or the coding unit may be recursively divided into coding units having a lower depth than optimal if necessary. The coding unit of the size of can be used as the final coding unit. Here, the coding procedure may include procedures such as prediction, transformation, and reconstruction, which will be described later. As another example, the processing unit may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may be partitioned or partitioned from the above-described final coding unit, respectively. The prediction unit may be a unit of sample prediction, and the transformation unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

The unit may be used interchangeably with terms such as a block or area depending on the case. In a general case, the MxN block may represent samples of M columns and N rows or a set of transform coefficients. The sample may generally represent a pixel or a pixel value, and may indicate only a pixel / pixel value of a luma component or only a pixel / pixel value of a saturation component. The sample may be used as a term for one picture (or image) corresponding to a pixel or pel.

The encoding apparatus 100 subtracts a prediction signal (a predicted block, a prediction sample array) output from the inter prediction unit 180 or the intra prediction unit 185 from the input image signal (original block, original sample array) A signal (residual signal, residual block, residual sample array) may be generated, and the generated residual signal is transmitted to the converter 120. In this case, as illustrated, a unit that subtracts a prediction signal (a prediction block, a prediction sample array) from an input image signal (original block, original sample array) in the encoder 100 may be referred to as a subtraction unit 115. The prediction unit may perform prediction on a block to be processed (hereinafter, referred to as a current block), and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied in units of a current block or CU. As described later in the description of each prediction mode, the prediction unit may generate various information regarding prediction, such as prediction mode information, and transmit it to the entropy encoding unit 190. The prediction information may be encoded by the entropy encoding unit 190 and output in the form of a bitstream.

The intra prediction unit 185 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located apart depending on a prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The non-directional mode may include, for example, a DC mode and a planar mode (Planar mode). The directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the degree of detail of the prediction direction. However, this is an example, and more or less directional prediction modes may be used depending on the setting. The intra prediction unit 185 may determine a prediction mode applied to the current block using a prediction mode applied to neighboring blocks.

The inter prediction unit 180 may derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture. At this time, to reduce the amount of motion information transmitted in the inter prediction mode, motion information may be predicted in units of blocks, subblocks, or samples based on the correlation of motion information between a neighboring block and a current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to by a name such as a collocated reference block or a colCU, and a reference picture including the temporal neighboring block may be called a collocated picture (colPic). It might be. For example, the inter prediction unit 180 constructs a motion information candidate list based on neighboring blocks, and provides information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Can be created. Inter prediction may be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the inter prediction unit 180 may use motion information of neighboring blocks as motion information of the current block. In the skip mode, unlike the merge mode, the residual signal may not be transmitted. In the case of a motion vector prediction (MVP) mode, a motion vector of a current block is obtained by using a motion vector of a neighboring block as a motion vector predictor and signaling a motion vector difference. I can order.

The prediction signal generated by the inter prediction unit 180 or the intra prediction unit 185 may be used to generate a reconstructed signal or may be used to generate a residual signal.

The transform unit 120 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transformation technique may include at least one of a DCT (Discrete Cosine Transform), a DST (Discrete Sine Transform), a KLT (Karhunen-Loeve Transform), a GBT (Graph-Based Transform), or a CNT (Conditionally Non-linear Transform). It can contain. Here, GBT refers to a transformation obtained from this graph when it is said that the relationship information between pixels is graphically represented. CNT means a transform obtained by generating a predictive signal using all previously reconstructed pixels and based on it. Further, the transform process may be applied to pixel blocks having the same size of a square, or may be applied to blocks of variable sizes other than squares.

The quantization unit 130 quantizes the transform coefficients and transmits them to the entropy encoding unit 190, and the entropy encoding unit 190 encodes a quantized signal (information about quantized transform coefficients) and outputs it as a bitstream. have. Information about the quantized transform coefficients may be called residual information. The quantization unit 130 may rearrange block-type quantized transform coefficients into a one-dimensional vector form based on a coefficient scan order, and quantize the quantized transform coefficients based on the one-dimensional vector form. Information regarding transform coefficients may be generated. The entropy encoding unit 190 may perform various encoding methods such as exponential Golomb (CAVLC), context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). The entropy encoding unit 190 may encode information necessary for video / image reconstruction (eg, values of syntax elements, etc.) together with the quantized transform coefficients together or separately. The encoded information (ex. Encoded video / video information) may be transmitted or stored in units of network abstraction layer (NAL) units in the form of a bitstream. The bitstream can be transmitted over a network or stored on a digital storage medium. Here, the network may include a broadcasting network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD. The signal output from the entropy encoding unit 190 may be configured as an internal / external element of the encoding apparatus 100 by a transmitting unit (not shown) and / or a storing unit (not shown) for storing, or the transmitting unit It may be a component of the entropy encoding unit 190.

The quantized transform coefficients output from the quantization unit 130 may be used to generate a prediction signal. For example, the residual signal may be reconstructed by applying inverse quantization and inverse transform to the quantized transform coefficients through the inverse quantization unit 140 and the inverse transform unit 150 in the loop. The adder 155 adds the reconstructed residual signal to the predicted signal output from the inter predictor 180 or the intra predictor 185, so that the reconstructed signal (restored picture, reconstructed block, reconstructed sample array) Can be created. If there is no residual for the block to be processed, such as when the skip mode is applied, the predicted block may be used as a reconstructed block. The adding unit 155 may be called a restoration unit or a restoration block generation unit. The generated reconstructed signal may be used for intra prediction of the next processing target block in the current picture, or may be used for inter prediction of the next picture through filtering as described below.

The filtering unit 160 may apply subjective filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 160 may generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and the modified reconstructed picture may be a DPB of the memory 170, specifically, the memory 170 Can be stored in. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like. The filtering unit 160 may generate various information regarding filtering as described later in the description of each filtering method and transmit it to the entropy encoding unit 190. The filtering information may be encoded by the entropy encoding unit 190 and output in the form of a bitstream.

The modified reconstructed picture transmitted to the memory 170 may be used as a reference picture in the inter prediction unit 180. When the inter prediction is applied through the encoding apparatus, prediction mismatch between the encoding apparatus 100 and the decoding apparatus can be avoided, and encoding efficiency can be improved.

The memory 170 DPB may store the modified reconstructed picture for use as a reference picture in the inter prediction unit 180. The memory 170 may store motion information of a block from which motion information in a current picture is derived (or encoded) and / or motion information of blocks in a picture that has already been reconstructed. The stored motion information may be transmitted to the inter prediction unit 180 for use as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory 170 may store reconstructed samples of blocks reconstructed in the current picture, and may transmit the reconstructed samples to the intra prediction unit 185.

Referring to FIG. 2, the decoding apparatus 200 includes an entropy decoding unit 210, an inverse quantization unit 220, an inverse conversion unit 230, an addition unit 235, a filtering unit 240, a memory 250, and an inter It may be configured to include a prediction unit 260 and the intra prediction unit 265. The inter prediction unit 260 and the intra prediction unit 265 may be collectively called a prediction unit. That is, the prediction unit may include an inter prediction unit 180 and an intra prediction unit 185. The inverse quantization unit 220 and the inverse conversion unit 230 may be collectively referred to as a residual processing unit. That is, the residual processing unit may include an inverse quantization unit 220 and an inverse conversion unit 230. The entropy decoding unit 210, the inverse quantization unit 220, the inverse transform unit 230, the addition unit 235, the filtering unit 240, the inter prediction unit 260, and the intra prediction unit 265 described above are embodiments. It may be configured by one hardware component (for example, a decoder or processor). Also, the memory 170 may include a decoded picture buffer (DPB), or may be configured by a digital storage medium.

When a bitstream including video / image information is input, the decoding apparatus 200 may restore an image in response to a process in which the video / image information is processed in the encoding apparatus of FIG. 1. For example, the decoding apparatus 200 may perform decoding using a processing unit applied in the encoding apparatus. Thus, the processing unit of decoding may be, for example, a coding unit, and the coding unit may be divided along a quad tree structure and / or a binary tree structure from a coding tree unit or a largest coding unit. Then, the decoded video signal decoded and output through the decoding apparatus 200 may be reproduced through the reproduction apparatus.

The decoding apparatus 200 may receive the signal output from the encoding apparatus of FIG. 1 in the form of a bitstream, and the received signal may be decoded through the entropy decoding unit 210. For example, the entropy decoding unit 210 may parse the bitstream to derive information (eg, video / image information) necessary for image reconstruction (or picture reconstruction). For example, the entropy decoding unit 210 decodes information in a bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and quantizes a value of a syntax element required for image reconstruction and a transform coefficient for residual. Can output In more detail, the CABAC entropy decoding method receives bins corresponding to each syntax element in the bitstream, and decodes the syntax element information to be decoded and decoding information of neighboring and decoding target blocks or information of symbols / bins decoded in the previous step. The context model is determined by using, and the probability of occurrence of the bin is predicted according to the determined context model, and arithmetic decoding of the bin is performed to generate a symbol corresponding to the value of each syntax element. have. At this time, the CABAC entropy decoding method may update the context model using the decoded symbol / bin information for the next symbol / bin context model after determining the context model. Among the information decoded by the entropy decoding unit 2110, information regarding prediction is provided to the prediction unit (inter prediction unit 260 and intra prediction unit 265), and the entropy decoding unit 210 performs entropy decoding. The dual value, that is, quantized transform coefficients and related parameter information may be input to the inverse quantization unit 220. Also, information related to filtering among information decoded by the entropy decoding unit 210 may be provided to the filtering unit 240. Meanwhile, a receiving unit (not shown) receiving a signal output from the encoding device may be further configured as an internal / external element of the decoding device 200, or the receiving unit may be a component of the entropy decoding unit 210.

The inverse quantization unit 220 may inverse quantize the quantized transform coefficients to output transform coefficients. The inverse quantization unit 220 may rearrange the quantized transform coefficients in a two-dimensional block form. In this case, the reordering may be performed based on the coefficient scan order performed by the encoding device. The inverse quantization unit 220 may perform inverse quantization on the quantized transform coefficients by using a quantization parameter (for example, quantization step size information), and obtain transform coefficients.

The inverse transform unit 230 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

The prediction unit may perform prediction on the current block and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction is applied or inter prediction is applied to the current block based on information about the prediction output from the entropy decoding unit 210, and may determine a specific intra / inter prediction mode.

The intra prediction unit 265 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located apart depending on a prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The intra prediction unit 265 may determine a prediction mode applied to the current block using a prediction mode applied to neighboring blocks.

The inter prediction unit 260 may derive the predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture. At this time, to reduce the amount of motion information transmitted in the inter prediction mode, motion information may be predicted in units of blocks, subblocks, or samples based on the correlation of motion information between a neighboring block and a current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block present in the reference picture. For example, the inter prediction unit 260 may construct a motion information candidate list based on neighboring blocks, and derive a motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter prediction may be performed based on various prediction modes, and information on the prediction may include information indicating a mode of inter prediction for the current block.

The adding unit 235 adds the obtained residual signal to the prediction signal (predicted block, prediction sample array) output from the inter prediction unit 260 or the intra prediction unit 265, thereby restoring signals (restored pictures, reconstructed blocks). , A reconstructed sample array). If there is no residual for the block to be processed, such as when the skip mode is applied, the predicted block may be used as a reconstructed block.

The adding unit 235 may be called a restoration unit or a restoration block generation unit. The generated reconstructed signal may be used for intra prediction of the next processing target block in the current picture, or may be used for inter prediction of the next picture through filtering as described below.

The filtering unit 240 may improve subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filtering unit 240 may generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and the modified reconstructed picture may be a DPB of the memory 250, specifically, the memory 250 Can be transferred to. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.

The (corrected) reconstructed picture stored in the DPB of the memory 250 may be used as a reference picture in the inter prediction unit 260. The memory 250 may store motion information of a block from which motion information in a current picture is derived (or decoded) and / or motion information of blocks in a picture that has already been reconstructed. The stored motion information may be transmitted to the inter prediction unit 260 to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory 170 may store reconstructed samples of blocks reconstructed in the current picture, and may transmit the reconstructed samples to the intra prediction unit 265.

In the present specification, the embodiments described in the filtering unit 160, the inter prediction unit 180, and the intra prediction unit 185 of the encoding apparatus 100 are respectively the filtering unit 240 and the inter prediction of the decoding apparatus 200. The same may be applied to the unit 260 and the intra prediction unit 265.

Block PartitioningBlock Partitioning

The video / image coding method according to this document may be performed based on various detailed technologies, and the detailed description of each detailed technology is as follows. The techniques described below include prediction in the video / image encoding / decoding procedure described above and / or described below, residual processing ((inverse) transform, (inverse) quantization, etc.), syntax element coding, filtering, partitioning / partitioning, etc. It will be apparent to those skilled in the art that it may be involved in the relevant procedures.

The block partitioning procedure according to the present document is performed by the image segmentation unit 110 of the above-described encoding device, so that the partitioning-related information is (encoded) processed by the entropy encoding unit 190 and transmitted to the decoding device in the form of a bitstream. . The entropy decoding unit 210 of the decoding apparatus derives a block partitioning structure of the current picture based on the partitioning-related information obtained from the bitstream, and based on this, a series of procedures for decoding the image (ex. Prediction, residual Processing, block reconstruction, in-loop filtering, etc.).

Partitioning of picture into CTUs

Pictures can be divided into a sequence of coding tree units (CTUs). The CTU may correspond to a coding tree block (CTB). Alternatively, the CTU may include a coding tree block of luma samples and two coding tree blocks of corresponding chroma samples. In other words, for a picture containing three sample arrays, the CTU may include two corresponding blocks of chroma samples and an NxN block of luma samples.

The maximum allowable size of the CTU for coding and prediction may be different from the maximum allowable size of the CTU for transformation. For example, the maximum allowable size of the luma block in the CTU may be 128x128.

Partitionig of the CTUs using a tree structure

The CTU may be divided into CUs based on a quad-tree (QT) structure. The quadtree structure may be referred to as a quaternary tree structure. This is to reflect various local characteristics. Meanwhile, in this document, the CTU can be divided based on multi-type tree structure division including a binary tree (BT) and a ternary tree (TT) as well as a quad tree. Hereinafter, the QTBT structure may include a quadtree and binary tree based partitioning structure, and the QTBTTT may include a quadtree, binary tree and ternary tree based partitioning structure. Alternatively, the QTBT structure may include a quadtree, binary tree, and ternary tree based splitting structure. In the coding tree structure, the CU can have a square or rectangular shape. The CTU can be first divided into a quadtree structure. Thereafter, leaf nodes having a quadtree structure may be additionally divided by a multi-type tree structure.

In an embodiment of the present invention, the multitype tree structure may include four split types as shown in FIG. 3. The four division types are vertical binary splitting (SPLIT_BT_VER), horizontal binary splitting (SPLIT_BT_HOR), vertical ternary splitting (SPLIT_TT_VER), horizontal ternary splitting (horizontal ternary splitting, SPLIT_TT_HOR) ). Leaf nodes of the multi-type tree structure may be referred to as CUs. These CUs can be used for prediction and transformation procedures. In this document, CU, PU, and TU may have the same block size. However, when the maximum supported transform length is smaller than the width or height of the color component of the CU, the CU and the TU may have different block sizes.

Here, the CTU is treated as the root of the quadtree, and is first partitioned into a quadtree structure. Each quadtree leaf node can then be further partitioned into a multitype tree structure. In the multi-type tree structure, a first flag (ex. Mtt_split_cu_flag) is signaled to indicate whether the corresponding node is additionally partitioned. If the corresponding node is additionally partitioned, a second flag (a second flag, ex. Mtt_split_cu_verticla_flag) may be signaled to indicate a splitting direction. Then, a third flag (a third flag, ex. Mtt_split_cu_binary_flag) may be signaled to indicate whether the partition type is binary partition or ternary partition. For example, based on the mtt_split_cu_vertical_flag and the mtt_split_cu_binary_flag, a multi-type tree splitting mode (MttSplitMode) of a CU may be derived as shown in Table 1 below.

Here, bold block edges represent quadtree partitioning, and the remaining edges represent multitype tree partitioning. A quadtree partition with a multitype tree can provide a content-adapted coding tree structure. The CU may correspond to a coding block (CB). Alternatively, the CU may include a coding block of luma samples and two coding blocks of corresponding chroma samples. The size of a CU may be as large as a CTU, or may be cut by 4x4 in luma sample units. For example, in the case of a 4: 2: 0 color format (or chroma format), the maximum chroma CB size may be 64x64 and the minimum chroma CB size may be 2x2.

In this document, for example, the maximum allowed luma TB size may be 64x64 and the maximum allowed chroma TB size may be 32x32. If the width or height of the CB divided according to the tree structure is greater than the maximum conversion width or height, the CB may be automatically (or implicitly) divided until the horizontal and vertical TB size limitations are satisfied.

Meanwhile, for a quadtree coding tree scheme involving a multitype tree, the following parameters may be defined and identified as SPS syntax elements.

-CTU size: the root node size of a quaternary tree

-MinQTSize: the minimum allowed quaternary tree leaf node size

-MaxBtSize: the maximum allowed binary tree root node size

-MaxTtSize: the maximum allowed ternary tree root node size

-MaxMttDepth: the maximum allowed hierarchy depth of multi-type tree splitting from a quadtree leaf

-MinBtSize: the minimum allowed binary tree leaf node size

-MinTtSize: the minimum allowed ternary tree leaf node size

As an example of a quadtree coding tree structure with a multitype tree, the CTU size may be set to 64x64 blocks of 128x128 luma samples and two corresponding chroma samples (in 4: 2: 0 chroma format). In this case, MinOTSize is set to 16x16, MaxBtSize is set to 128x128, MaxTtSzie is set to 64x64, MinBtSize and MinTtSize (for both width and height) can be set to 4x4, and MaxMttDepth can be set to 4. Quarttree partitioning can be applied to CTU to generate quadtree leaf nodes. The quadtree leaf node may be referred to as a leaf QT node. Quadtree leaf nodes may have a size of 128x128 (i.e. the CTU size) from a size of 16x16 (i.e. the MinOTSize). If the leaf QT node is 128x128, it may not be additionally divided into a binary tree / ternary tree. This is because, even in this case, it exceeds MaxBtsize and MaxTtszie (i.e. 64x64). In other cases, the leaf QT node may be further divided into a multi-type tree. Therefore, the leaf QT node is a root node for the multitype tree, and the leaf QT node may have a multitype tree depth (mttDepth) 0 value. If the multi-type tree depth reaches MaxMttdepth (ex. 4), further partitioning may not be considered. If the width of the multitype tree node is equal to MinBtSize and less than or equal to 2xMinTtSize, additional horizontal splitting may no longer be considered. If the height of the multitype tree node is equal to MinBtSize and less than or equal to 2xMinTtSize, additional vertical splitting may not be considered any more.

Referring to FIG. 6, TT partitioning may be limited in certain cases to allow for a 64x64 luma block and 32x32 chroma pipeline design in a hardware decoder. For example, if the width or height of the luma coding block is greater than a predetermined specific value (eg, 32, 64), as illustrated in FIG. 6, TT segmentation may be limited.

In this document, the coding tree scheme may support luma and chroma blocks having a separate block tree structure. For P and B slices, luma and chroma CTBs in one CTU can be restricted to have the same coding tree structure. However, for I slices, luma and chroma blocks may have a separate block tree structure from each other. If the individual block tree mode is applied, the luma CTB may be divided into CUs based on a specific coding tree structure, and the chroma CTB may be divided into chroma CUs based on another coding tree structure. This may mean that a CU in an I slice is composed of a coding block of luma components or coding blocks of two chroma components, and a CU of a P or B slice can be composed of blocks of three color components.

In the above-described “Partitionig of the CTUs using a tree structure”, a quadtree coding tree structure with a multi-type tree has been described, but the structure in which the CU is divided is not limited to this. For example, the BT structure and the TT structure may be interpreted as a concept included in a multiple partitioning tree (MPT) structure, and a CU may be divided through a QT structure and an MPT structure. In an example in which a CU is split through a QT structure and an MPT structure, a syntax element (for example, MPT_split_type) including information about how many blocks a leaf node of the QT structure is divided into, and a leaf node of the QT structure are vertical The splitting structure may be determined by signaling a syntax element (for example, MPT_split_mode) including information about which direction is divided between and horizontal.

In another example, the CU may be divided in a different way from the QT structure, BT structure or TT structure. That is, according to the QT structure, the CU of the lower depth is divided into 1/4 the size of the CU of the upper depth, or the CU of the lower depth is divided into 1/2 the size of the CU of the upper depth according to the BT structure, or according to the TT structure Unlike the CU of the lower depth, which is divided into 1/4 or 1/2 the size of the CU of the upper depth, the CU of the lower depth may be 1/5, 1/3, 3/8, 3 of the CU of the upper depth depending on the case. It may be divided into / 5, 2/3, or 5/8 size, and the method in which the CU is divided is not limited thereto.

If a portion of a tree node block exceeds the bottom or right picture boundary, the tree node block ensures that all samples of all coded CUs are located within the picture boundaries. Can be limited. In this case, for example, the following division rule may be applied.

-If a portion of a tree node block exceeds both the bottom and the right picture boundaries,

-If the block is a QT node and the size of the block is larger than the minimum QT size, the block is forced to be split with QT split mode.

-Otherwise, the block is forced to be split with SPLIT_BT_HOR mode

-Otherwise if a portion of a tree node block exceeds the bottom picture boundaries,

-If the block is a QT node, and the size of the block is larger than the minimum QT size, and the size of the block is larger than the maximum BT size, the block is forced to be split with QT split mode.

-Otherwise, if the block is a QT node, and the size of the block is larger than the minimum QT size and the size of the block is smaller than or equal to the maximum BT size, the block is forced to be split with QT split mode or SPLIT_BT_HOR mode.

-Otherwise (the block is a BTT node or the size of the block is smaller than or equal to the minimum QT size), the block is forced to be split with SPLIT_BT_HOR mode.

-Otherwise if a portion of a tree node block exceeds the right picture boundaries,

-Otherwise, if the block is a QT node, and the size of the block is larger than the minimum QT size and the size of the block is smaller than or equal to the maximum BT size, the block is forced to be split with QT split mode or SPLIT_BT_VER mode.

-Otherwise (the block is a BTT node or the size of the block is smaller than or equal to the minimum QT size), the block is forced to be split with SPLIT_BT_VER mode.

On the other hand, the above-described quadtree coding block structure accompanying the multi-type tree can provide a very flexible block partitioning structure. Due to the division types supported in the multitype tree, different division patterns can potentially result in the same coding block structure in some cases. By limiting the occurrence of such redundant partition patterns, the data amount of partitioning information can be reduced. It will be described with reference to the drawings below.

As shown in FIG. 7, two levels of consecutive binary splits in one direction have the same coding block structure as binary partitions for the center partition after ternary splitting. . In this case, the binary tree partition for the center partition of the ternary tree partition (in the given direction) may be limited. This limitation can be applied to CUs of all pictures. When such a specific partition is limited, signaling of corresponding syntax elements can be modified to reflect this limited case, thereby reducing the number of bits signaled for partitioning. For example, as in the example shown in FIG. 7, when the binary tree partition for the center partition of the CU is limited, the mtt_split_cu_binary_flag syntax element indicating whether the partition is a binary partition or a ternary partition is not signaled, and its value is It can be inferred by the decoder to zero.

예측(prediction)Prediction

In order to restore the current processing unit in which decoding is performed, a decoded portion of the current picture or other pictures including the current processing unit may be used.

Predict a picture (slice) that uses only the current picture for reconstruction, i.e., a picture (slice) that performs only intra-picture prediction, an intra picture or an I picture (slice), and up to one motion vector and a reference index to predict each unit A picture (slice) using a predictive picture or a P picture (slice), up to two motion vectors and a reference index may be referred to as a bi-predictive picture or a B picture (slice).

Inter-prediction refers to a prediction method that derives a current processing block based on a data element (eg, a sample value or a motion vector) of a picture other than the current picture. That is, it means a method of predicting a pixel value of a current processing block by referring to reconstructed regions in another reconstructed picture other than the current picture.

Hereinafter, intra prediction (or intra prediction) will be described in more detail.

Intra prediction (or intra prediction)

Intra prediction refers to a prediction method that derives a current processing block from data elements (eg, sample values, etc.) of the same decoded picture (or slice). That is, it means a method of predicting the pixel value of the current processing block by referring to the reconstructed regions in the current picture.

The intra prediction may represent prediction for generating a prediction sample for the current block based on a reference sample outside the current block in a picture to which the current block belongs (hereinafter, the current picture).

The present invention describes the detailed technique of the intra prediction method described above with reference to FIGS. 1 and 2, and may be represented by the intra prediction based video / image decoding method of FIG. 10 and the intra prediction unit of the decoding apparatus of FIG. 11, which will be described later. . In addition, the encoder may be represented by the intra prediction-based video / video encoding method of FIG. 8 described later and the intra prediction unit in the encoding apparatus of FIG. 9. In addition, the data encoded by FIGS. 8 and 9 can be stored in the form of a bitstream.

When intra prediction is applied to the current block, peripheral reference samples to be used for intra prediction of the current block may be derived. The neighboring reference samples of the current block are samples adjacent to the left boundary of the current block of nWxnH size and total 2xnH samples adjacent to the bottom-left, samples adjacent to the top boundary of the current block. And a total of 2xnW samples neighboring the top-right and one sample neighboring the top-left of the current block. Alternatively, the peripheral reference samples of the current block may include multiple columns of upper peripheral samples and multiple rows of left peripheral samples. In addition, the neighboring reference samples of the current block have a total nH samples adjacent to the right boundary of the current block of size nWxnH, a total nW samples adjacent to the bottom boundary of the current block, and the lower right side of the current block. (bottom-right) may include one neighboring sample.

However, some of the neighboring reference samples of the current block may not be decoded yet or may not be available. In this case, the decoder may construct surrounding reference samples to be used for prediction by substituting unavailable samples with available samples. Alternatively, peripheral reference samples to be used for prediction may be configured through interpolation of available samples.

When the neighboring reference samples are derived, a prediction sample may be derived based on an average or interpolation of neighboring reference samples of the current block, and (ii) prediction among neighboring reference samples of the current block The prediction sample may be derived based on a reference sample present in a specific (predictive) direction with respect to the sample. In the case of (i), it may be called a non-directional mode or a non-angle mode, and in the case of (ii), a directional mode or an angular mode. In addition, the interpolation between the second neighboring sample and the first neighboring sample located in a direction opposite to the prediction direction of the intra prediction mode of the current block based on the predicted sample of the current block among the neighboring reference samples Predictive samples may be generated. The above-described case may be referred to as linear interpolation intra prediction (LIP). In addition, a temporary prediction sample of the current block is derived based on filtered peripheral reference samples, and at least one of the existing peripheral reference samples, ie, unfiltered peripheral reference samples, derived according to the intra prediction mode A prediction sample of the current block may be derived by weighting a sum of a reference sample and the temporary prediction sample. The above-described case may be called PDPC (Position dependent intra prediction). On the other hand, post-process filtering may be performed on the predicted samples derived as necessary.

Specifically, the intra prediction procedure may include an intra prediction mode determination step, a peripheral reference sample derivation step, and an intra prediction mode based prediction sample derivation step. Also, a post-filtering step may be performed on the predicted sample derived as necessary.

The video / video encoding procedure based on intra prediction and the intra prediction unit in the encoding device may schematically include, for example, the following.

8 and 9, S801 may be performed by the intra prediction unit 185 of the encoding device, and S802 may be performed by the residual processing unit of the encoding device. Specifically, S802 may be performed by the subtraction unit 115 of the encoding device. In S803, the prediction information is derived by the intra prediction unit 185 and may be encoded by the entropy encoding unit 190. In S803, the residual information is derived by the residual processing unit and may be encoded by the entropy encoding unit 190. The residual information is information about the residual samples. The residual information may include information about quantized transform coefficients for the residual samples.

As described above, the residual samples may be derived as transform coefficients through the transform unit 120 of the encoding apparatus, and the transform coefficients may be derived as quantized transform coefficients through the quantization unit 130. Information about the quantized transform coefficients may be encoded in the entropy encoding unit 190 through a residual coding procedure.

The encoding device performs intra prediction on the current block (S801). The encoding apparatus may derive an intra prediction mode for the current block, derive neighbor reference samples of the current block, and generate prediction samples in the current block based on the intra prediction mode and the neighbor reference samples. Here, the intra prediction mode determination, neighboring reference samples (procedures of generating and predicting samples may be performed simultaneously, or one procedure may be performed before another procedure. For example, the intra prediction unit of the encoding apparatus ( 185) may include a prediction mode determination unit 186, a reference sample derivation unit 187, a prediction sample derivation unit 188, and the prediction mode determination unit 186 determines an intra prediction mode for the current block The reference sample derivation unit 187 may derive neighboring reference samples of the current block, and the prediction sample derivation unit 188 may deduce motion samples of the current block. When the prediction sample filtering procedure is performed, the intra prediction unit 185 may further include a prediction sample filter unit (not shown) The encoding device may include the current block among a plurality of intra prediction modes. The encoding apparatus may compare the RD cost for the intra prediction modes and determine an optimal intra prediction mode for the current block.

Meanwhile, the encoding device may perform a prediction sample filtering procedure. Predictive sample filtering may be referred to as post filtering. Some or all of the prediction samples may be filtered by the prediction sample filtering procedure. In some cases, the prediction sample filtering procedure may be omitted.

The encoding apparatus generates residual samples for the current block based on the (filtered) prediction sample (S802). The encoding apparatus may encode image information including prediction mode information indicating the intra prediction mode and residual information about the residual samples (S803). The encoded image information may be output in the form of a bit stream. The output bitstream may be delivered to a decoding device through a storage medium or network.

Meanwhile, as described above, the encoding apparatus may generate a reconstructed picture (including reconstructed samples and reconstructed blocks) based on the reference samples and the residual samples. This is for deriving the same prediction result as that performed in the decoding device in the encoding device, because it is possible to increase coding efficiency. The above-described in-loop filtering procedure may be further applied to the reconstructed picture.

10 and 11, the decoding apparatus may perform an operation corresponding to an operation performed in the encoding apparatus. The decoding apparatus may perform prediction on the current block based on the received prediction information and derive prediction samples.

Specifically, the decoding apparatus may derive an intra prediction mode for the current block based on the received prediction mode information (S1001). The decoding apparatus may derive neighboring reference samples of the current block (S1002). The decoding apparatus generates prediction samples in the current block based on the intra prediction mode and the surrounding reference samples (S1003). In this case, the decoding apparatus may perform a prediction sample filtering procedure. Predictive sample filtering may be referred to as post filtering. Some or all of the prediction samples may be filtered by the prediction sample filtering procedure. In some cases, the prediction sample filtering procedure may be omitted.

The decoding apparatus generates residual samples for the current block based on the received residual information (S1004). The decoding apparatus may generate reconstructed samples for the current block based on the (filtered) predicted samples and the residual samples, and generate a reconstructed picture based on the reconstructed pictures (S1005).

Here, the intra prediction unit 265 of the decoding apparatus may include a prediction mode determination unit 266, a reference sample derivation unit 267, and a prediction sample derivation unit 268, and the prediction mode determination unit 266 is encoded. The intra prediction mode for the current block is determined based on the prediction mode information received from the prediction mode determination unit 186 of the device, and the reference sample derivation unit 266 derives neighboring reference samples of the current block and predicts it. The sample derivation unit 267 may derive prediction samples of the current block. Meanwhile, although not illustrated, when the above-described prediction sample filtering procedure is performed, the intra prediction unit 265 may further include a prediction sample filter unit (not shown).

The prediction mode information may include flag information (ex. Prev_intra_luma_pred_flag) indicating whether most probable mode (MPM) is applied to the current block or remaining mode, and the MPM is the current When applied to a block, the prediction mode information may further include index information (ex. Mpm_idx) indicating one of the intra prediction mode candidates (MPM candidates). The intra prediction mode candidates (MPM candidates) may be configured as an MPM candidate list or an MPM list. In addition, when the MPM is not applied to the current block, the prediction mode information further includes remodeling mode information (eg, rem_inra_luma_pred_mode) indicating one of the remaining intra prediction modes except the intra prediction mode candidates (MPM candidates). It can contain. The decoding apparatus may determine an intra prediction mode of the current block based on the prediction mode information. The prediction mode information may be encoded / decoded through a coding method described below. For example, the prediction mode information may be encoded / decoded through encoding coding (eg, CABAC, CAVLC) based on truncated (rice) binary code.

Intra prediction mode decision

When intra prediction is applied, an intra prediction mode applied to a current block may be determined using an intra prediction mode of neighboring blocks. For example, the decoding apparatus may select one of the most probable mode (mpm) candidates derived based on the intra prediction mode of the left block of the current block and the intra prediction mode of the upper block based on the received mpm index, or One of the remaining intra prediction modes that are not included in the mpm candidates may be selected based on the remodeling intra prediction mode information. The mpm index may be signaled in the form of an mpm_idx syntax element, and the remodeling intra prediction mode information may be signaled in the form of a rem_intra_luma_pred_mode syntax element. For example, the re-maining intra-prediction mode information may indicate one of the intra-prediction modes by indexing the remaining intra-prediction modes not included in the mpm candidates in order of prediction mode number.

Referring to FIG. 12, the intra prediction mode may include two non-directional intra prediction modes and 33 directional intra prediction modes. The non-directional intra prediction modes may include a planar intra prediction mode and a DC intra prediction mode, and the directional intra prediction modes may include intra prediction modes 2 to 34. The planner intra prediction mode may be called a planner mode, and the DC intra prediction mode may be called a DC mode.

Meanwhile, in order to capture an arbitrary edge direction presented in a natural video, the directional intra prediction mode may be extended from the existing 33 to 65, as shown in FIG. 13 to be described later. In this case, the intra prediction mode may include two non-directional intra prediction modes and 65 directional intra prediction modes. The non-directional intra prediction modes may include a planar intra prediction mode and a DC intra prediction mode, and the directional intra prediction modes may include intra prediction modes 2 to 66. The extended directional intra prediction can be applied to blocks of all sizes, and can be applied to both luma and chroma components.

Referring to FIG. 13, in one embodiment, the intra prediction mode may include 67 modes. The prediction direction according to each prediction mode index (or mode number) is as illustrated in FIG. 13.

Prediction mode indexes

0 and 1 indicate planner mode and DC mode, respectively. As illustrated in FIG. 13, the prediction mode indexes 2 to 66 indicate a prediction direction of an angle divided from an arrow in the lower left direction to an arrow in the upper right direction. Of the 65 angles,

prediction modes

2, 18, 50, and 66 indicate horizontal diagonal directions, horizontal directions, vertical directions, and vertical diagonal directions, respectively.

Alternatively, the intra prediction mode may include two non-directional intra prediction modes and 129 directional intra prediction modes. The non-directional intra prediction modes may include a planar intra prediction mode and a DC intra prediction mode, and the directional intra prediction modes may include 2 to 130 intra prediction modes.

The prediction unit of the encoding device / decoding device may derive a reference sample according to the intra prediction mode of the current block among neighboring reference samples of the current block, and generate a prediction sample of the current block based on the reference sample. .

For example, a prediction sample may be derived based on an average or interpolation of neighboring reference samples of the current block, and (ii) specific to a prediction sample among neighboring reference samples of the current block. The prediction sample may be derived based on a reference sample present in the (prediction) direction. In the case of (i), it may be called a non-directional mode or a non-angle mode, and in the case of (ii), a directional mode or an angular mode. Further, in one embodiment, multi-reference sample lines using one or more reference sample lines for intra prediction may be used for more accurate prediction.

In an embodiment of the present invention, in an environment in which the number of intra prediction modes is greater than that of the conventional image compression technique as described in FIG. 13, the most probale mode (MPM) is configured to effectively reduce the overhead signaling the intra prediction mode. Suggest how to do it. According to an embodiment of the present invention, coding efficiency can be improved in terms of reducing signaling overhead by efficiently coding the intra prediction mode. By reducing the signaling overhead, better coding efficiency can be obtained in terms of BD-rate / BD-PSNR.

On the encoder side, the best intra prediction mode is determined as an optimized prediction mode by jointly considering bit-rate and distortion. Then, the optimal (selected) predictive intra mode is coded through the bit stream, and the decoder performs intra prediction using the optimal intra prediction mode parsed from the bit stream. However, as described above, the increased number of intra prediction modes require efficient intra mode coding to minimize signaling overhead.

The MPM list (or MPM candidate list) may be constructed using intra prediction modes of neighboring intra coded blocks at both the encoder and decoder. When the optimal prediction mode selected by the encoder is one of prediction modes included in the MPM list, overhead may be minimized through MPM index signaling.

In a conventional image compression technique (for example, HEVC), three MPM lists are generated based on two neighbor intra prediction modes of positions F and G shown in FIG. 14. When at least one of the following three is satisfied, F or G may be set to DC mode, respectively.

-If F or G is not available

-F or G is not an intra coded block

-F or G is outside the current coding tree unit (CTU) to which the current block belongs

In this specification, for convenience of description, intra prediction modes of the A to G position blocks illustrated in FIG. 14 may be represented by A to G, respectively. That is, the F or G represents the intra prediction mode of the F or G position block, respectively. If F and G are determined, the three MPM lists may be constructed based on the pseudo codes of Table 2 below.

Referring to Table 2, when F and G are the same, if F is less than 2 (or

prediction mode

2, 2, and 2 prediction modes), a first MPM list is generated (or derived), and F is 2 If not smaller, a second MPM list may be generated.

And, if F and G are not the same, if F or G is not in the planner mode, a third MPM list is generated, if (F + G) is less than 2, a fourth list is generated, and otherwise, A 5 MPM list can be created.

In one embodiment, the number of MPM candidates included in the MPM list may be set differently according to the number of intra prediction modes. In general, as the number of intra prediction modes increases, the number of MPM candidates may increase. However, the present invention is not limited thereto, and for example, 35 and 67 intra modes may have various numbers of MPM candidates such as 3, 4, and 5 depending on design.

Further, in one embodiment, if neighboring inter coded blocks know their intra prediction mode, this intra prediction mode may be used to construct the MPM list.

Various intra modes need to be included in the MPM list to improve the intra mode coding efficiency and make the MPM mode more frequent. In general, the more various modes of intra-consideration are considered from various neighboring locations, the better coding efficiency can be achieved. For example, when considering the intra intra prediction mode through the adjacent positions A, B, C, D, E, F, and G shown in FIG. 14, the probability of having various MPM lists may increase. For this reason, recently, as more MPM candidates are considered than HEVC, a method of constructing an MPM list using more neighboring blocks has been discussed. However, in the case of searching for a block of a large number of locations, a problem of significantly increasing complexity may occur.

Referring to FIG. 14 again, the geometrical distance between the G block and the F block is shorter than that of the B block and the D block. Since the distance between the B block and the D block is relatively larger than the distance between the G block and the F block, the probability is different between the G and the F (i.e., the difference between the B and D intra prediction modes). , Difference between intra prediction modes of G and F) may be small. At the same time, since the distance between the B block and the D block is relatively larger than the distance between the G block and the F block, the probability of B and D being equal may be lower than the probability of G and F being equal. Therefore, more diversity can be secured in the MPM candidate configuration when B and D are used than when G and F are used as the left and upper neighboring blocks, respectively, and the result is despite considering the same number of neighboring blocks as MPM candidates. As a result, a larger number of neighboring blocks may be considered as MPM candidates.

Meanwhile, in FIG. 14, the C block or the E block has a position in a diagonal direction based on the current block to be predicted, and the probability of being outside the current CTU or the current pipe lining unit is greater than the B block and the D block. If the neighboring position is located outside the current CTU or the current pipe lining unit, the intra preliminary mode of the corresponding position may be regarded as a planner mode or a DC mode as in the embodiments described below. Therefore, in this case, the C block or the E block can bring about a low diversity in MPM candidate configuration compared to the B block and the D block.

Accordingly, in an embodiment of the present invention, the encoder / decoder proposes a method of constructing an MPM list using an intra prediction mode of neighboring blocks of B and D positions. That is, in the present embodiment, the encoder / decoder proposes a method of constructing an MPM list using a limited number of neighboring locations B and D in order to increase diversity of MPM candidates. As an embodiment, the locations of B and D can be used to construct MPM lists instead of G and F, respectively. At this time, when the coordinates of the upper left position of the current block to be predicted are (xPb, yPb), the positions of B and D are (xPb + W-1, yPb-1) and (xPb-1, yPb + H-1), respectively. It can be defined as Here, W and H represent the width and height of the current block.

According to an embodiment of the present invention, by using the intra prediction mode of the neighboring blocks of the B and D positions, more various MPM lists can be constructed.

The component of FIG. 15 may be implemented with a configuration included in a decoder (or a decoding apparatus, 200 of FIG. 2 above). For convenience of explanation, the decoder is mainly described, but the MPM list generation method according to the present embodiment can be applied to the encoder substantially the same, and the component of FIG. 15 is similarly applied to the encoder (or encoding device, 100 of FIG. 1 above). It can be implemented in an included configuration.

15, a component for generating an MPM list may include a first component 1501, a second component 1502, and a third component 1503.

The first component 1501 may check whether the left and upper peripheral blocks are available. At this time, the left and upper peripheral blocks may be the peripheral blocks of positions B and D of FIG. 14 described above.

The second component 1502 may acquire intra prediction modes of the left and upper neighboring blocks. The third component 1503 may generate the MPM list based on a predefined condition (or branch). An embodiment of the MPM list generation method will be described later.

In an embodiment of the present invention, the length of the MPM list (ie, the number of MPM candidates) may be extended to increase the diversity of MPMs. At this time, as described above, the neighboring blocks at positions B and D can be used for generation of the extended MPM list. For example, the length of the extended MPM list may vary depending on the number of intra prediction modes, and may be defined (or determined, set) by a number greater than 3, such as 4, 5, 6, and the like.

In one embodiment, an example of a method of constructing an MPM list will be described with reference to Table 3 below.

Referring to Table 3, the encoder / decoder can confirm whether B and D (that is, intra prediction mode of B and intra prediction mode of D) are the same.

If B and D are the same, the encoder / decoder can check whether B is smaller than 2 (that is, the prediction mode 2 of FIG. 13 described above). If B is less than 2, the encoder / decoder may generate (or derive) a first MPM list, and if B is not less than 2, it may generate a second MPM list.

If B and D are not the same, the encoder / decoder can check whether B or D is not in the planner mode. If B or D is not in the planner mode, the encoder / decoder may generate a third MPM list, and if (B + D) is less than 2, a fourth list. And, in other cases, the encoder / decoder may generate the fifth MPM list.

In addition, in one embodiment, an example of the MPM list generated according to the MPM list construction method of this embodiment is shown in Table 4 below.

Referring to Table 4, when the length of the MPM list is 3 or when the length of the MPM list is 6 as an extended MPM list, the first to fifth MPM lists may include MPM candidates as shown in Table 4.

As another example, the length of the extended MPM list may be 4, and in this case, the encoder / decoder may construct 4 MPM lists by adding 1 MPM candidate to 3 existing MPM lists.

In addition, in one embodiment of the present invention, when the intra prediction mode of the neighboring blocks at positions B and D of FIG. 14 described above cannot be used, the encoder / decoder may instead use a prediction mode that occurs statistically. At this time, considering that the probability of occurrence of the planner mode is higher than that of the DC mode, the encoder / decoder sets the planner mode to the prediction mode of B or D when the intra prediction mode of the neighboring blocks of the B and D positions cannot be used ( Or use). Specifically, when at least one of the following conditions is satisfied, the encoder / decoder may set the planner mode as the prediction mode of B or D.

-When B or D is not available

-If B or D is not an intra coded block

-B or D is outside the CTU to which the current block belongs

In addition, in one embodiment of the present invention, a method for binarizing an extended MPM list is proposed to efficiently code MPM. According to statistics, when 6 MPM is used, as an optimal mode, a specific MPM index is spread to all indexes rather than being inclined to an index having a low probability of being hit. Therefore, hereinafter, a method of performing binarization using only 2 or 3 bins for indexes for 6 MPM candidates is proposed. Examples of the binarization proposed in this embodiment are shown in Table 5 below.

Referring to Table 5, both the conventional 6 MPM and the proposed extended 6 MPM are binarized. The proposed binarization has more advantages in MPM coding than the conventional 6 MPM, since the probability of choosing the optimal mode is not biased to a particular index.

Specifically, the maximum number of bins required for the proposed binarization is three, whereas according to the conventional binarization, the maximum number of bins required for binarization is five.

For example, when 35 intra modes are used, by applying the proposed method, when 6 intra modes are displayed as MPM, the remaining modes can be coded with 5 bits. The number of remaining modes is 35-6 = 29, where Floor (log2 (35-6)) = 5. Since the maximum number of bins required for MPM is 3, which is less than 5 bits for the remaining modes, the proposed binarization may have higher coding efficiency than the conventional 6 MPM in an environment in which 35 intra modes are applied.

Each of the embodiments of the present invention described above may be implemented independently, or may be implemented by combining one or more embodiments.

Referring to FIG. 16, for convenience of description, a decoder is mainly described, but the present invention is not limited thereto, and an intra prediction block generation method according to an embodiment of the present invention may be performed in the same manner in an encoder and a decoder.

The decoder acquires an MPM flag indicating whether a Most Probable Mode (MPM) is applied to the current block (S1601). Here, the MPM indicates a mode in which the intra prediction mode of the current block is derived from the intra predicted block around the current block.

When MPM is applied to the current block, the decoder configures an MPM list based on intra prediction modes of the left and upper neighboring blocks of the current block (S1602).

The decoder acquires an MPM index indicating a specific intra prediction mode in the MPM list (S1603).

The decoder generates a prediction block of the current block using the intra prediction mode specified by the MPM index (S1604).

As described above, the left neighboring block is set as a block including pixels adjacent in the horizontal direction of the lower left sample in the current block, and the upper neighboring block includes pixels adjacent in the vertical direction of the upper right sample in the current block. It can be set as a block.

In addition, as described above, the step S1602 includes: checking whether intra prediction modes of the left and upper neighboring blocks are the same; Checking whether the intra prediction mode of the upper neighboring block is less than 2 when the intra prediction mode of the left and upper neighboring blocks are the same; If the intra prediction mode of the upper neighboring block is less than 2, generating a first MPM list; And when the intra prediction mode of the upper neighboring block is not less than 2, generating a second MPM list.

In addition, as described above, the first MPM list includes a planar mode, a DC mode, a vertical mode, a horizontal mode, a horizontal diagonal mode, and a vertical diagonal mode, and the second MPM list is a planner mode, a DC mode , The intra prediction mode of the upper neighboring block and the two intra prediction modes closest to the intra prediction mode of the upper neighboring block.

Also, as described above, in step S1602, the left or upper neighboring block is not available, is not a block coded in an intra prediction mode, or is not located in a current coding tree unit (CTU). If not, the method may further include setting the intra prediction mode of the left or upper neighboring block to a planar mode.

In addition, as described above, the MPM list includes 6 MPM candidates, and among indexes indicating the 6 MPM candidates, index 0 is binarized to 00 and index 1 is binarized to 01, Index 2 can be binarized to 100, index 3 can be binarized to 101, index 4 can be binarized to 110, and index 5 can be binarized to 111.

In FIG. 17, for convenience of description, the intra prediction unit is illustrated as one block, but the intra prediction unit may be implemented in a configuration included in the encoder and / or decoder.

Referring to FIG. 17, the intra prediction unit implements the functions, processes, and / or methods previously proposed in FIGS. 8 to 16. Specifically, the intra prediction unit may include an MPM flag acquisition unit 1701, an MPM list construction unit 1702, an MPM index acquisition unit 1703, and a prediction block generation unit 1704.

The MPM flag acquiring unit 1701 acquires an MPM flag indicating whether Most Probable Mode (MPM) is applied to the current block. Here, the MPM indicates a mode in which the intra prediction mode of the current block is derived from the intra predicted block around the current block.

When the MPM is applied to the current block, the MPM list construction unit 1702 configures the MPM list based on the intra prediction mode of the left and upper neighboring blocks of the current block.

The MPM index obtaining unit 1703 acquires an MPM index indicating a specific intra prediction mode in the MPM list.

The prediction block generator 1704 generates a prediction block of the current block using an intra prediction mode specified by the MPM index.

In addition, as described above, the MPM list construction unit 1702 checks whether the intra prediction modes of the left and upper neighboring blocks are the same, and when the intra prediction modes of the left and upper neighboring blocks are the same, the It is checked whether the intra prediction mode of the upper neighboring block is less than 2, and if the intra prediction mode of the upper neighboring block is less than 2, a first MPM list is generated, and the intra prediction mode of the upper neighboring block is If not less than 2, a second MPM list may be generated.

In addition, as described above, the MPM list construction unit 1702 is not available in the left or upper neighboring block, is not a block coded in intra prediction mode, or is currently a coding tree unit (CTU). ), The intra prediction mode of the left or upper neighboring block may be set as a planar mode.

18 shows a video coding system to which the present invention is applied.

The video coding system may include a source device and a receiving device. The source device may deliver the encoded video / video information or data to a receiving device through a digital storage medium or network in the form of a file or streaming.

The source device may include a video source, an encoding apparatus, and a transmitter. The receiving device may include a receiver, a decoding apparatus, and a renderer. The encoding device may be called a video / video encoding device, and the decoding device may be called a video / video decoding device. The transmitter can be included in the encoding device. The receiver may be included in the decoding device. The renderer may include a display unit, and the display unit may be configured as a separate device or an external component.

The video source may acquire a video / image through a capture, synthesis, or generation process of the video / image. The video source may include a video / image capture device and / or a video / image generation device. The video / image capture device may include, for example, one or more cameras, a video / image archive including previously captured video / images, and the like. The video / image generating device may include, for example, a computer, a tablet and a smart phone, and the like (electronically) to generate the video / image. For example, a virtual video / image may be generated through a computer or the like, and in this case, the video / image capture process may be replaced by a process in which related data is generated.

The encoding device can encode the input video / video. The encoding apparatus may perform a series of procedures such as prediction, transformation, and quantization for compression and coding efficiency. The encoded data (encoded video / video information) may be output in the form of a bitstream.

The transmitting unit may transmit the encoded video / video information or data output in the form of a bitstream to a receiving unit of a receiving device through a digital storage medium or a network in a file or streaming format. The digital storage media may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD. The transmission unit may include an element for generating a media file through a predetermined file format, and may include an element for transmission through a broadcast / communication network. The receiver may extract the bitstream and transmit it to the decoding device.

The decoding apparatus may decode a video / image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoding apparatus.

The renderer can render the decoded video / image. The rendered video / image may be displayed through the display unit.

Referring to FIG. 19, a content streaming system to which the present invention is applied may largely include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

The encoding server serves to compress a content input from multimedia input devices such as a smartphone, a camera, and a camcorder into digital data to generate a bitstream and transmit it to the streaming server. As another example, when multimedia input devices such as a smartphone, a camera, and a camcorder directly generate a bitstream, the encoding server may be omitted.

The bitstream may be generated by an encoding method or a bitstream generation method to which the present invention is applied, and the streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

The streaming server transmits multimedia data to a user device based on a user request through a web server, and the web server serves as an intermediary to inform the user of the service. When a user requests a desired service from the web server, the web server delivers it to the streaming server, and the streaming server transmits multimedia data to the user. In this case, the content streaming system may include a separate control server, in which case the control server serves to control commands / responses between devices in the content streaming system.

The streaming server may receive content from a media storage and / or encoding server. For example, when content is received from the encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.

Examples of the user device include a mobile phone, a smart phone, a laptop computer, a terminal for digital broadcasting, a personal digital assistants (PDA), a portable multimedia player (PMP), navigation, a slate PC, Tablet PC, ultrabook, wearable device (e.g., smartwatch, smart glass, head mounted display (HMD)), digital TV, desktop Computers, digital signage, and the like.

Each server in the content streaming system can be operated as a distributed server, and in this case, data received from each server can be distributed.

As described above, the embodiments described in the present invention may be implemented and implemented on a processor, microprocessor, controller, or chip. For example, the functional units illustrated in each drawing may be implemented and implemented on a computer, processor, microprocessor, controller, or chip.

In addition, the decoder and encoder to which the present invention is applied are a multimedia broadcast transmission / reception device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video communication device, a real-time communication device such as video communication, a mobile streaming device, Storage media, camcorders, video-on-demand (VoD) service providers, OTT video (Over the top video) devices, Internet streaming service providers, three-dimensional (3D) video devices, video telephony video devices, and medical video devices. And can be used to process video signals or data signals. For example, the OTT video (Over the top video) device may include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smartphone, a tablet PC, and a digital video recorder (DVR).

Further, the processing method to which the present invention is applied can be produced in the form of a computer-implemented program, and can be stored in a computer-readable recording medium. Multimedia data having a data structure according to the present invention can also be stored in a computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices and distributed storage devices in which computer-readable data is stored. The computer-readable recording medium includes, for example, Blu-ray Disc (BD), Universal Serial Bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk and optical. It may include a data storage device. In addition, the computer-readable recording medium includes media implemented in the form of a carrier wave (for example, transmission via the Internet). In addition, the bitstream generated by the encoding method may be stored in a computer-readable recording medium or transmitted through a wired or wireless communication network.

Further, an embodiment of the present invention may be implemented as a computer program product by program code, and the program code may be executed on a computer by an embodiment of the present invention. The program code can be stored on a computer readable carrier.

The embodiments described above are those in which the components and features of the present invention are combined in a predetermined form. Each component or feature should be considered optional unless stated otherwise. Each component or feature may be implemented in a form that is not combined with other components or features. It is also possible to configure an embodiment of the present invention by combining some components and / or features. The order of the operations described in the embodiments of the present invention can be changed. Some configurations or features of one embodiment may be included in other embodiments, or may be replaced with corresponding configurations or features of other embodiments. It is obvious that the claims may not be explicitly included in the claims, and the embodiments may be combined or included as new claims by amendment after filing.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. For implementation by hardware, one embodiment of the invention includes one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), FPGAs ( field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. that performs the functions or operations described above. The software code can be stored in memory and driven by a processor. The memory is located inside or outside the processor, and can exchange data with the processor by various known means.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all respects but should be considered as illustrative. The scope of the invention should be determined by rational interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

The preferred embodiments of the present invention described above have been disclosed for purposes of illustration, and those skilled in the art can improve and change various other embodiments within the technical spirit and the technical scope of the present invention disclosed in the appended claims. , Replacement or addition may be possible.

Claims

In the method of decoding an image based on the intra prediction mode,

Obtaining an MPM flag indicating whether or not MPM (Most Probable Mode) is applied to the current block, wherein the MPM is an intra prediction mode of the current block derived from an intra predicted block around the current block Indicates mode;

When MPM is applied to the current block, constructing an MPM list based on intra prediction modes of left and upper neighboring blocks of the current block;

Obtaining an MPM index indicating a specific intra prediction mode in the MPM list; And

Generating a prediction block of the current block using an intra prediction mode specified by the MPM index,

The left neighboring block is set to a block including pixels adjacent to the horizontal direction of the lower left sample in the current block,

The upper neighboring block is set as a block including pixels adjacent in a vertical direction of a right uppermost sample in the current block.
The method of claim 1,

The step of constructing the MPM list,

Checking whether intra prediction modes of the left and upper neighboring blocks are the same;

Checking whether the intra prediction mode of the upper neighboring block is less than 2 when the intra prediction mode of the left and upper neighboring blocks are the same;

If the intra prediction mode of the upper neighboring block is less than 2, generating a first MPM list; And

And if the intra prediction mode of the upper neighboring block is not less than 2, generating a second MPM list.
According to claim 2,

The first MPM list includes a planar mode, a DC mode, a vertical mode, a horizontal mode, a horizontal diagonal mode, and a vertical diagonal mode,

The second MPM list includes a planar mode, a DC mode, an intra prediction mode of the upper neighboring block, and two intra prediction modes closest to the intra prediction mode of the upper neighboring block.
The method of claim 1,

The step of constructing the MPM list,

If the left or upper neighboring block is not available, is not a block coded in intra prediction mode, or is not located in a current coding tree unit (CTU), intra prediction of the left or upper neighboring block And setting the mode to a planar mode.
The method of claim 1,

The MPM list includes 6 MPM candidates,

Among the indexes indicating each of the six MPM candidates, index 0 is binarized to 00, index 1 is binarized to 01, index 2 is binarized to 100, index 3 is binarized to 101, and 4 The method of decoding an image, wherein the index number is binarized to 110 and the index 5 is binarized to 111.
In the apparatus for decoding an image based on the intra prediction mode,

An MPM flag acquiring unit that acquires an MPM flag indicating whether Most Probable Mode (MPM) is applied to the current block, wherein the MPM is an intra predicted block in which the intra prediction mode of the current block is around the current block Represents a mode derived from;

An MPM list construction unit configured to configure an MPM list based on intra prediction modes of left and upper neighboring blocks of the current block when MPM is applied to the current block;

An MPM index obtaining unit for obtaining an MPM index indicating a specific intra prediction mode in the MPM list; And

It includes a prediction block generator for generating a prediction block of the current block using the intra prediction mode specified by the MPM index,

The left neighboring block is set to a block including pixels adjacent to the horizontal direction of the lower left sample in the current block,

And the upper neighboring block is set to a block including pixels adjacent in a vertical direction of a right uppermost sample in the current block.
The method of claim 6,

The MPM list configuration unit,

Check whether intra prediction modes of the left and upper neighboring blocks are the same,

When the intra prediction mode of the left and upper neighboring blocks is the same, it is checked whether the intra prediction mode of the upper neighboring block is less than 2,

When the intra prediction mode of the upper neighboring block is less than 2, a first MPM list is generated, and

When the intra prediction mode of the upper neighboring block is not less than 2, a second MPM list is generated.
The method of claim 7,

The first MPM list includes a planar mode, a DC mode, a vertical mode, a horizontal mode, a horizontal diagonal mode, and a vertical diagonal mode,

The second MPM list includes a planar mode, a DC mode, an intra prediction mode of the upper neighboring block, and two intra prediction modes closest to the intra prediction mode of the upper neighboring block.
The method of claim 6,

The MPM list configuration unit,

If the left or upper neighboring block is not available, is not a block coded in intra prediction mode, or is not located in a current coding tree unit (CTU), intra prediction of the left or upper neighboring block An image decoding apparatus that sets the mode to a planar mode.
The method of claim 6,

The MPM list includes 6 MPM candidates,

Among the indexes indicating each of the six MPM candidates, index 0 is binarized to 00, index 1 is binarized to 01, index 2 is binarized to 100, index 3 is binarized to 101, and 4 An image decoding apparatus in which the index number is binarized to 110 and the index 5 is binarized to 111.