WO2019199149A1 - Intra-prediction mode-based image processing method and device therefor - Google Patents

Intra-prediction mode-based image processing method and device therefor Download PDF

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Publication number
WO2019199149A1
WO2019199149A1 PCT/KR2019/004521 KR2019004521W WO2019199149A1 WO 2019199149 A1 WO2019199149 A1 WO 2019199149A1 KR 2019004521 W KR2019004521 W KR 2019004521W WO 2019199149 A1 WO2019199149 A1 WO 2019199149A1
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prediction
reference sample
current block
sample
intra prediction
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PCT/KR2019/004521
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French (fr)
Korean (ko)
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허진
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엘지전자 주식회사
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Priority to KR20180061028 priority
Application filed by 엘지전자 주식회사 filed Critical 엘지전자 주식회사
Publication of WO2019199149A1 publication Critical patent/WO2019199149A1/en

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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/103Selection of coding mode or of prediction mode
    • H04N19/105Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/132Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/17Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
    • H04N19/176Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/593Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving spatial prediction techniques

Abstract

A video signal processing method and a device therefor are disclosed. In particular, the method may comprise the steps of: parsing an LIP flag indicating whether or not linear interpolation intra-prediction (LIP) is applicable to a current block; if LIP is applicable to the current block, deriving a first reference sample by means of at least one among left, upper, and upper-left reference samples of the current block on the basis of an intra-prediction mode of the current block; parsing a directional index indicating information about an LIP direction, on the basis of a first prediction direction indicating the prediction direction of the intra-prediction mode; deriving a second reference sample by means of at least one among right, lower, and lower-right reference samples of the current block, on the basis of the LIP direction determined by the directional index; and generating a prediction sample of the current block by performing weighted summation on the first reference sample and the second reference sample.

Description

Intra prediction mode based image processing method and apparatus therefor

The present invention relates to a still image or moving image processing method, and more particularly, to a method for encoding / decoding a still image or moving image 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 for storing in a form suitable for a storage medium. Media such as an image, an image, an audio, and the like may be a target of compression encoding. In particular, a technique of performing compression encoding on an image is called video image compression.

Next-generation video content will be characterized by high spatial resolution, high frame rate and high dimensionality of scene representation. Processing such content would result in a tremendous increase in terms of memory storage, memory access rate, and processing power.

Accordingly, there is a need to design coding tools for more efficiently processing next generation video content.

An object of the present invention is to propose a linear interpolation intra prediction method for generating a weighted prediction sample based on a distance between a prediction sample and a reference sample.

An object of the present invention is to propose a method for generating an intra prediction block in consideration of more directionality in order to increase the accuracy of prediction in applying linear interpolation intra prediction.

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

According to an aspect of the present invention, in a method of processing an image based on an intra prediction mode, parsing an LIP flag indicating whether Linear Interpolation Intra Prediction (LIP) is applied to a current block Doing; When LIP is applied to the current block, deriving a first reference sample using at least one of a left, an upper, and an upper left reference sample of the current block based on an intra prediction mode of the current block; Parsing a directional index indicating information about a LIP direction based on a first prediction direction indicating a prediction direction of the intra prediction mode; Deriving a second reference sample using at least one of the right, lower, and lower right reference samples of the current block based on the LIP direction determined by the directional index; And weighting the first reference sample and the second reference sample to generate a prediction sample of the current block.

Preferably, the LIP direction is a first prediction direction, a second prediction direction indicating a prediction direction of the prediction mode by adding 1 to the intra prediction mode, and a third direction indicating a prediction direction of the prediction mode by subtracting 1 from the intra prediction mode. It may include a prediction direction.

Preferably, a bit shorter than an index indicating the second prediction direction or the third prediction direction may be allocated to the index indicating the first prediction direction.

Preferably, generating a lower right reference sample adjacent to the lower right side of the current block; And generating at least one of a right reference sample and a lower reference sample using the right bottom reference sample.

According to another aspect of the present invention, in an apparatus for processing an image based on an intra prediction mode, a LIP flag indicating whether Linear Interpolation Intra Prediction (LIP) is applied to a current block is used. A LIP flag parsing unit for parsing; When LIP is applied to the current block, a first reference sample derivation unit for deriving a first reference sample using at least one of a left, an upper, and an upper left reference sample of the current block based on an intra prediction mode of the current block ; A directional index parser for parsing a directional index representing information about a LIP direction based on a first prediction direction indicating a prediction direction of the intra prediction mode; A second reference sample deriving unit for deriving a second reference sample using at least one of the right, lower and right lower reference samples of the current block based on the LIP direction determined by the directional index; And a prediction sample generator that weights the first reference sample and the second reference sample to generate a prediction sample of the current block.

Preferably, the LIP direction is a first prediction direction, a second prediction direction indicating a prediction direction of the prediction mode by adding 1 to the intra prediction mode, and a third direction indicating a prediction direction of the prediction mode by subtracting 1 from the intra prediction mode. It may include a prediction direction.

Preferably, a bit shorter than an index indicating the second prediction direction or the third prediction direction may be allocated to the index indicating the first prediction direction.

Preferably, the second reference sample derivation unit may generate a lower right reference sample adjacent to the lower right side of the current block, and generate at least one of a right reference sample or a lower reference sample by using the lower right reference sample.

According to an embodiment of the present invention, the accuracy of prediction may be improved by linearly interpolating a plurality of reference samples based on the intra prediction mode.

An object of the present invention, in generating linear interpolation prediction samples, can increase the accuracy of prediction and improve the compression performance by considering more directionality.

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, included as part of the detailed description in order to provide a thorough understanding of the present invention, provide embodiments of the present invention and together with the description, describe the technical features of the present invention.

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

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

3 is a diagram illustrating an example of a multi-type tree structure as an embodiment to which the present invention can be applied.

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

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

FIG. 6 is a diagram illustrating a method of limiting ternary-tree splitting as an embodiment to which the present invention may be applied.

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

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

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

12 and 13 illustrate a prediction direction of an intra prediction mode according to an embodiment to which the present invention may be applied.

14 and 15 are diagrams for explaining a linear interpolation prediction method according to an embodiment to which the present invention is applied.

FIG. 16 is a diagram for describing a method of generating a lower right reference sample in a linear interpolation prediction method according to an embodiment to which the present invention may be applied.

FIG. 17 is a diagram for describing a method of generating right reference samples and bottom reference samples according to an embodiment to which the present invention is applied.

18 is a diagram illustrating a method of determining an optimal prediction mode in intra prediction coding according to an embodiment to which the present invention is applied.

FIG. 19 is a diagram illustrating a method of performing linear interpolation intra prediction in consideration of an adjacent prediction direction as an embodiment to which the present invention is applied.

20 and 21 are flowcharts illustrating a linear interpolation intra prediction method using adjacent directionality according to an embodiment of the present invention.

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

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

24 is a diagram illustrating a method of performing linear interpolation intra prediction using multi-reference lines as an embodiment to which the present invention is applied.

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

26 is a diagram illustrating the structure of a content streaming system according to an embodiment to which the present invention is applied.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates that the present invention may be practiced without these specific details.

In some instances, well-known structures and devices may be omitted or shown in block diagram form centering on the core functions of the structures and devices in order to avoid obscuring the concepts of the present invention.

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

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

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

The processing unit may be interpreted to include a unit for the luma component and a unit for the 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).

In addition, 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 be a coding tree block (CTB), a coding block (CB), a prediction block (PU), or a transform block (TB) for a luma component. May correspond to. Or, 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 luma component and a unit for a chroma component.

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

In the following specification, a pixel, a pixel, and the like are referred to collectively as samples. In addition, using a sample may mean using a pixel value or a pixel value.

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

Referring to FIG. 1, the encoding apparatus 100 may include an image splitter 110, a subtractor 115, a transformer 120, a quantizer 130, an inverse quantizer 140, an inverse transformer 150, The adder 155, the filter 160, the memory 170, the inter predictor 180, the intra predictor 185, and the entropy encoder 190 may be configured. The inter predictor 180 and the intra predictor 185 may be collectively referred to as a predictor. In other words, the predictor may include an inter predictor 180 and an intra predictor 185. The transform unit 120, the quantization unit 130, the inverse quantization unit 140, and the inverse transform unit 150 may be included in the residual processing unit. The residual processing unit may further include a subtracting unit 115. As an example, the image divider 110, the subtractor 115, the transformer 120, the quantizer 130, the inverse quantizer 140, the inverse transformer 150, and the adder 155 may be described. 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 (eg, an encoder or a processor). In addition, the memory 170 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium.

The image divider 110 may divide the input image (or picture or 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, the quad tree structure may be applied first and the binary tree structure may be applied later. Alternatively, the binary tree structure may be applied first. The coding procedure according to the present invention may be performed based on the final coding unit that is no longer split. In this case, the maximum coding unit may be used as the final coding unit immediately based on coding efficiency according to the image characteristic, or if necessary, the coding unit is recursively divided into coding units of lower depths and optimized. A coding unit of size may be used as the final coding unit. Here, the coding procedure may include a procedure of prediction, transform, 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 aforementioned 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 block or area in some cases. In a general case, an M × N block may represent a set of samples or transform coefficients composed of M columns and N rows. A sample may generally represent a pixel or a value of a pixel, and may only represent pixel / pixel values of the luma component, or only pixel / pixel values of the chroma component. A sample may be used as a term corresponding to one picture (or image) for a pixel or a pel.

The encoding apparatus 100 subtracts the prediction signal (predicted block, 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 may be generated (residual signal, residual block, residual sample array), and the generated residual signal is transmitted to the converter 120. In this case, as shown, a unit that subtracts a prediction signal (prediction block, prediction sample array) from an input image signal (original block, original sample array) in the encoder 100 may be called a subtraction unit 115. The prediction unit may perform a 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 on a current block or CU basis. As described later in the description of each prediction mode, the prediction unit may generate various information related to prediction, such as prediction mode information, and transmit the generated information to the entropy encoding unit 190. The information about the prediction may be encoded in the entropy encoding unit 190 and output in the form of a bitstream.

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

The inter predictor 180 may derive the predicted block with respect to the current block based on the reference block (reference sample array) specified by the motion vector on the reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, subblocks, or samples based on the correlation of the motion information between the neighboring block and the 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 as a collocated reference block, a collocated CU (colCU), and the like, and a reference picture including the temporal neighboring block is called a collocated picture (colPic). It may be. For example, the inter prediction unit 180 constructs a motion information candidate list based on neighboring blocks and provides information indicating which candidates are used to derive a motion vector and / or a reference picture index of the current block. Can be generated. Inter prediction may be performed based on various prediction modes. For example, in case of a skip mode and a merge mode, the inter prediction unit 180 may use motion information of a neighboring block as motion information of a current block. In the skip mode, unlike the merge mode, the residual signal may not be transmitted. In the motion vector prediction (MVP) mode, the motion vector of the neighboring block is used as a motion vector predictor and the motion vector difference is signaled by signaling a motion vector difference. Can be directed.

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

The transformer 120 may apply transform techniques to the residual signal to generate transform coefficients. For example, the transformation technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-loeve transform (KLT), a graph-based transform (GBT), or a conditionally non-linear transform (CNT). It may include. Here, GBT means a conversion obtained from this graph when the relationship information between pixels is represented by a graph. CNT refers to a transform that is generated based on and generates a prediction signal using all previously reconstructed pixels. In addition, the conversion process may be applied to pixel blocks having the same size as the square, or may be applied to blocks of variable size rather than square.

The quantization unit 130 quantizes the transform coefficients and transmits them to the entropy encoding unit 190. The entropy encoding unit 190 encodes the quantized signal (information about the quantized transform coefficients) and outputs the bitstream. have. The information about the quantized transform coefficients may be referred to as residual information. The quantization unit 130 may rearrange block quantized transform coefficients into a one-dimensional vector form based on a coefficient scan order, and quantize the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. Information about transform coefficients may be generated. The entropy encoding unit 190 may perform various encoding methods such as, for example, exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), and the like. The entropy encoding unit 190 may encode information necessary for video / image reconstruction other than quantized transform coefficients (for example, values of syntax elements) together or separately. Encoded information (eg, encoded video / image information) may be transmitted or stored in units of NALs (network abstraction layer) in the form of a bitstream. The bitstream may be transmitted over a network or may be stored in a digital storage medium. 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, and the like. The signal output from the entropy encoding unit 190 may include a transmitting unit (not shown) for transmitting and / or a storing unit (not shown) for storing as an internal / external element of the encoding apparatus 100, 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 quantized transform coefficients may be reconstructed in the residual signal by applying inverse quantization and inverse transform through inverse quantization unit 140 and inverse transform unit 150 in a 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 a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) is added. Can be generated. 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 the reconstructed block. The adder 155 may be called a restoration unit or a restoration block generation unit. The generated reconstruction signal may be used for intra prediction of a next processing target block in a current picture, and may be used for inter prediction of a next picture through filtering as described below.

The filtering unit 160 may improve subjective / objective image quality by applying filtering to the reconstruction signal. 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 is stored in the memory 170, specifically, the DPB of the memory 170. Can be stored in The various filtering methods may include, for example, deblocking filtering, a sample adaptive offset, an adaptive loop filter, a bilateral filter, and the like. As described below in the description of each filtering method, the filtering unit 160 may generate various information about the filtering and transmit the generated information to the entropy encoding unit 190. The filtering information may be encoded in 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 the reference picture in the inter predictor 180. When the inter prediction is applied through the encoding apparatus, the encoding apparatus may avoid prediction mismatch between the encoding apparatus 100 and the decoding apparatus, and may improve encoding efficiency.

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

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

Referring to FIG. 2, the decoding apparatus 200 includes an entropy decoding unit 210, an inverse quantizer 220, an inverse transform unit 230, an adder 235, a filter 240, a memory 250, and an inter The prediction unit 260 and the intra prediction unit 265 may be configured. The inter predictor 260 and the intra predictor 265 may be collectively called a predictor. That is, the predictor may include an inter predictor 180 and an intra predictor 185. The inverse quantization unit 220 and the inverse transform unit 230 may be collectively called a residual processing unit. That is, the residual processing unit may include an inverse quantization unit 220 and an inverse transformation unit 230. The entropy decoder 210, the inverse quantizer 220, the inverse transformer 230, the adder 235, the filter 240, the inter predictor 260, and the intra predictor 265 are described in the embodiment. Can be configured by one hardware component (eg, decoder or processor). In addition, 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 reconstruct an image corresponding to a process in which 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 a coding unit, for example, which may be split along a quad tree structure and / or a binary tree structure from a coding tree unit or a maximum coding unit. The reconstructed video signal decoded and output through the decoding apparatus 200 may be reproduced through the reproducing apparatus.

The decoding apparatus 200 may receive a 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, quantized values of syntax elements required for image reconstruction, and transform coefficients for residuals. Can be output. More specifically, the CABAC entropy decoding method receives a bin corresponding to each syntax element in a bitstream, and decodes syntax element information and decoding information of neighboring and decoding target blocks or information of symbols / bins decoded in a previous step. The context model may be determined using the context model, the probability of occurrence of a bin may be predicted according to the determined context model, and arithmetic decoding of the bin may be performed to generate a symbol corresponding to the value of each syntax element. have. In this case, the CABAC entropy decoding method may update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bean after determining the context model. The information related to the prediction among the information decoded by the entropy decoding unit 2110 is provided to the prediction unit (the inter prediction unit 260 and the intra prediction unit 265), and the entropy decoding performed by the entropy decoding unit 210 is performed. Dual values, that is, quantized transform coefficients and related parameter information, may be input to the inverse quantizer 220. In addition, information on filtering among information decoded by the entropy decoding unit 210 may be provided to the filtering unit 240. Meanwhile, a receiver (not shown) that receives a signal output from the encoding apparatus may be further configured as an internal / external element of the decoding apparatus 200, or the receiver may be a component of the entropy decoding unit 210.

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

The inverse transformer 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 or inter prediction is applied to the current block based on the information about the prediction output from the entropy decoding unit 210, and may determine a specific intra / inter prediction mode.

The intra predictor 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 according to the prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The intra predictor 265 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

The inter prediction unit 260 may derive the predicted block for the current block based on the reference block (reference sample array) specified by the motion vector on the reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, subblocks, or samples based on the correlation of the motion information between the neighboring block and the 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 a 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 the information about the prediction may include information indicating a mode of inter prediction for the current block.

The adder 235 adds the obtained residual signal to the predictive signal (predicted block, predictive sample array) output from the inter predictor 260 or the intra predictor 265 to restore the reconstructed signal (reconstructed picture, reconstructed block). , Restore 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 the reconstructed block.

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

The filtering unit 240 may improve subjective / objective image quality by applying filtering to the reconstruction 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 stored in the memory 250, specifically, the DPB of the memory 250. Can be sent to. The various filtering methods may include, for example, deblocking filtering, a sample adaptive offset, an adaptive loop filter, a bilateral filter, and the like.

The (modified) reconstructed picture stored in the DPB of the memory 250 may be used as the reference picture in the inter predictor 260. The memory 250 may store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the blocks in the picture that are already reconstructed. The stored motion information may be transmitted to the inter predictor 260 to use the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 170 may store reconstructed samples of reconstructed blocks in the current picture, and transfer the reconstructed samples to the intra predictor 265.

In the present specification, the embodiments described by 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 also apply to the unit 260 and the intra predictor 265.

Block Partitioning

The video / image coding method according to this document may be performed based on various detailed techniques, and each detailed technique will be described as follows. Techniques described below include prediction, residual processing ((inverse) transformation, (inverse) quantization, etc.), syntax element coding, filtering, partitioning / division, etc. in the video / image encoding / decoding procedures described above and / or described below. It will be apparent to those skilled in the art that they may be involved in related procedures.

The block partitioning procedure according to this document may be performed by the image splitter 110 of the encoding apparatus described above, and the partitioning related information may be processed (encoded) by the entropy encoding unit 190 and transmitted to the decoding apparatus 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 (eg, prediction and residual) for image decoding. 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 that includes three sample arrays, the CTU may include an N × N block of luma samples and two corresponding blocks of chroma samples.

The maximum allowable size of the CTU for coding and prediction may be different from the maximum allowable size of the CTU for transform. 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 the present document, the CTU may be divided based on a multitype tree structure partition 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 partition structure, and the QTBTTT may include a quadtree, binary tree, and ternary tree based partition structure. Alternatively, the QTBT structure may include a quadtree, binary tree and ternary tree based partitioning structure. In a coding tree structure, a CU may have a square or rectangular shape. The CTU may first be divided into quadtree structures. After that, the leaf nodes of the quadtree structure may be further divided by the multitype tree structure.

3 is a diagram illustrating an example of a multi-type tree structure as an embodiment to which the present invention can be applied.

In one embodiment of the present invention, the multitype tree structure may include four partition types as shown in FIG. The four types of split include vertical binary splitting (SPLIT_BT_VER), horizontal binary splitting (SPLIT_BT_HOR), vertical ternary splitting (SPLIT_TT_VER), and horizontal ternary splitting (SPLIT_TT_HOR). ) May be included. Leaf nodes of the multitype tree structure may be called CUs. These CUs can be used for prediction and transform procedures. In general, CU, PU, and TU may have the same block size in this document. 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.

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

Here, the CTU is treated as the root of the quadtree, and is partitioned for the first time into a quadtree structure. Each quadtree leaf node may then be further partitioned into a multitype tree structure. In the multitype tree structure, a first flag (ex. Mtt_split_cu_flag) is signaled to indicate whether the node is additionally partitioned. If the node is additionally partitioned, a second flag (ex. Mtt_split_cu_verticla_flag) may be signaled to indicate the splitting direction. Thereafter, 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.

Figure PCTKR2019004521-appb-img-000001

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

Here, bold block edges represent quadtree partitioning and the remaining edges represent multitype tree partitioning. Quadtree partitions involving 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 CTU, or may be cut by 4 × 4 in luma sample units. For example, in the 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.

For example, in this document, the maximum allowable luma TB size may be 64x64 and the maximum allowable chroma TB size may be 32x32. If the width or height of the CB divided according to the tree structure is larger than the maximum transform width or height, the CB may be automatically (or implicitly) split until the TB size limit in the horizontal and vertical directions is 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 involving 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 can be set to 16x16, MaxBtSize to 128x128, MaxTtSzie to 64x64, MinBtSize and MinTtSize (for both width and height) to 4x4, and MaxMttDepth to 4. Quarttree partitioning may be applied to the CTU to generate quadtree leaf nodes. The quadtree leaf node may be called a leaf QT node. Quadtree leaf nodes may have a 128x128 size (i.e. the CTU size) from a 16x16 size (i.e. the MinOTSize). If the leaf QT node is 128x128, it may not be additionally divided into a binary tree / a ternary tree. This is because in this case, even if split, it exceeds MaxBtsize and MaxTtszie (i.e. 64x64). In other cases, leaf QT nodes may be further partitioned into a multitype tree. Therefore, the leaf QT node is the root node for the multitype tree, and the leaf QT node may have a multitype tree depth (mttDepth) 0 value. If the multitype tree depth reaches MaxMttdepth (ex. 4), further splitting may not be considered further. If the width of the multitype tree node is equal to MinBtSize and less than or equal to 2xMinTtSize, then no further horizontal split may be considered. If the height of the multitype tree node is equal to MinBtSize and less than or equal to 2xMinTtSize, no further vertical split may be considered.

FIG. 6 is a diagram illustrating a method of limiting ternary-tree splitting as an embodiment to which the present invention may be applied.

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

In this document, the coding tree scheme may support that the luma and chroma blocks have separate block tree structures. For P and B slices, luma and chroma CTBs in one CTU may be limited 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 an individual block tree mode is applied, the luma CTB may be split into CUs based on a particular coding tree structure, and the chroma CTB may be split into chroma CUs based on another coding tree structure. This may mean that a CU in an I slice may consist of a coding block of a luma component or coding blocks of two chroma components, and a CU of a P or B slice may 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 involving a multitype tree has been described, but a structure in which a CU is divided is not limited thereto. For example, the BT structure and the TT structure may be interpreted as a concept included in a multiple partitioning tree (MPT) structure, and the CU may be interpreted to be divided through the QT structure and the MPT structure. In one example where a CU is split through a QT structure and an MPT structure, a syntax element (eg, MPT_split_type) that contains information about how many blocks the leaf node of the QT structure is divided into and the leaf node of the QT structure are vertical The partition structure may be determined by signaling a syntax element (eg, MPT_split_mode) including information about which direction is divided into and horizontally.

In another example, the CU may be partitioned in a different way than 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 size of the CU of the upper depth, or the CU of the lower depth is divided into 1/2 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 is divided into 1/4 or 1/2 size of the CU of the upper depth, the CU of the lower depth is sometimes 1/5, 1/3, 3/8, 3 of the CU of the upper depth. It can be divided into / 5, 2/3 or 5/8 size, the way in which the CU is divided is not limited to this.

If a portion of a tree node block exceeds the bottom or right picture boundary, the tree node block is placed so that all samples of all coded CUs are located within the picture boundaries. May 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,

-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_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 quadtree coded block structure with the multi-type tree described above can provide a very flexible block partitioning structure. Because of the partition types supported in a multitype tree, different partition patterns can sometimes lead to potentially identical coding block structure results. By limiting the occurrence of such redundant partition patterns, the data amount of partitioning information can be reduced. It demonstrates with reference to the following drawings.

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

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

Prediction

The decoded portion of the current picture or other pictures in which the current processing unit is included may be used to reconstruct the current processing unit in which decoding is performed.

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

Inter prediction means a prediction method of deriving a current processing block based on data elements (eg, sample values or motion vectors, etc.) of pictures other than the current picture. That is, a method of predicting pixel values of the current processing block by referring to reconstructed regions in other reconstructed pictures other than the current picture.

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

Intra prediction (or intra prediction)

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

Intra prediction may indicate prediction for generating a prediction sample for a current block based on reference samples outside the current block in a picture to which the current block belongs (hereinafter, referred to as a current picture).

The present invention describes the detailed description of the intra prediction method described above with reference to FIGS. 1 and 2, and the decoder may be represented by the intra prediction-based video / image decoding method of FIG. 10 described later and the intra prediction unit in the decoding apparatus of FIG. 11. . In addition, the encoder may be represented by the intra prediction-based video / video encoding method of FIG. 8 and the intra prediction unit in the encoding apparatus of FIG. 9. In addition, the data encoded by FIGS. 8 and 9 may 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 peripheral reference samples of the current block are samples adjacent to the left boundary of the current block of size nWxnH and a total of 2xnH samples neighboring the bottom-left, and 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 a plurality of upper peripheral samples and a plurality of left peripheral samples. In addition, the peripheral reference samples of the current block are a total of nH samples adjacent to the right boundary of the current block of size nWxnH, a total of nW samples adjacent to the bottom boundary of the current block and the lower right side of the current block. It may include one sample neighboring (bottom-right).

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

When the neighbor reference samples are derived, the prediction sample can be derived based on the average or interpolation of neighboring reference samples of the current block, and (ii) the prediction among the neighbor reference samples of the current block. The prediction sample may be derived based on a reference sample present in a specific (prediction) direction with respect to the sample. In case of (i), it may be called non-directional mode or non-angle mode, and in case of (ii), it may be called directional mode or angular mode. 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 prediction sample of the current block among the neighboring reference samples may be performed. Prediction samples may be generated. The above 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 neighbor reference samples, and at least one of the existing neighbor reference samples, that is, unfiltered neighbor reference samples, derived according to the intra prediction mode. A weighted sum of a reference sample and the temporary prediction sample may be used to derive the prediction sample of the current block. The above case may be referred to as position dependent intra prediction (PDPC). Meanwhile, post-processing filtering may be performed on the predicted sample derived as needed.

In detail, 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. In addition, a post-filtering step may be performed on the predicted sample derived as needed.

A video / image encoding procedure based on intra prediction and an intra prediction unit in the encoding apparatus may roughly include, for example, the following.

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

8 and 9, S801 may be performed by the intra predictor 185 of the encoding apparatus, and S802 may be performed by the residual processor of the encoding apparatus. In detail, S802 may be performed by the subtraction unit 115 of the encoding apparatus. In S803, the prediction information may be derived by the intra prediction unit 185 and encoded by the entropy encoding unit 190. In S803, the residual information may be derived by the residual processor and 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 transform coefficients quantized through the quantization unit 130. Information about the quantized transform coefficients may be encoded by the entropy encoding unit 190 through a residual coding procedure.

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

Meanwhile, the encoding 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 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 regarding the residual samples (S803). The encoded image information may be output in the form of a bitstream. The output bitstream may be delivered to the decoding apparatus via a storage medium or a network.

Meanwhile, as described above, the encoding apparatus may generate a reconstructed picture (including the reconstructed samples and the reconstructed block) based on the reference samples and the residual samples. This is because the encoding apparatus derives the same prediction result as that performed in the decoding apparatus, and thus the coding efficiency can be increased. As described above, an in-loop filtering procedure may be further applied to the reconstructed picture.

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

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

In detail, the decoding apparatus may derive the intra prediction mode for the current block based on the received prediction mode information (S1001). The decoding apparatus may derive peripheral 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 peripheral 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) prediction samples and the residual samples, and generate a reconstructed picture based on the (S1005).

Here, the intra prediction unit 265 of the decoding apparatus may include a prediction mode determiner 266, a reference sample derivator 267, and a prediction sample derivator 268, and the prediction mode determiner 266 may be encoded. The intra prediction mode for the current block is determined based on the prediction mode information received by the prediction mode determiner 186 of the apparatus, and the reference sample derivator 266 derives the neighbor reference samples of the current block and predicts the prediction mode. The sample derivator 267 may derive the predictive samples of the current block. Although not shown, when the above-described prediction sample filtering procedure is performed, the intra prediction unit 265 may further include a prediction sample filter (not shown).

The prediction mode information may include flag information (ex. Prev_intra_luma_pred_flag) indicating whether a most probable mode (MPM) is applied to the current block or a remaining mode is applied, 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 consist of 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 remaining mode information (ex. Rem_inra_luma_pred_mode) indicating one of the intra prediction modes except for the intra prediction mode candidates (MPM candidates). It may include. The decoding apparatus may determine the 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 (ex. CABAC, CAVLC) based on truncated (rice) binary code.

Determine intra prediction mode

When intra prediction is applied, the intra prediction mode applied to the current block may be determined using the intra prediction mode of the neighboring block. 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 not included in the mpm candidates may be selected based on the remaining intra prediction mode information. The mpm index may be signaled in the form of an mpm_idx syntax element, and the remaining intra prediction mode information may be signaled in the form of a rem_intra_luma_pred_mode syntax element. For example, the remaining intra prediction mode information may index remaining intra prediction modes not included in the mpm candidates among all intra prediction modes in order of prediction mode number to indicate one of them.

12 and 13 illustrate a prediction direction of an intra prediction mode according to an embodiment to which the present invention may be applied.

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 2 to 34 intra prediction modes. 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 33 to 65 as shown in FIG. 13. 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 2 to 66 intra prediction modes. Extended Directional Intra Prediction It can be applied to blocks of all sizes and to both luma and chroma components.

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 apparatus / decoding apparatus may derive a reference sample according to the intra prediction mode of the current block among neighbor reference samples of the current block, and generate a prediction sample of the current block based on the reference sample. .

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

In the conventional image compression technology, 33 (or 65) directional prediction methods and two non-directional prediction methods, 35 (or 67) prediction methods are used through intra prediction (or intra prediction). A prediction sample is generated using a neighbor reference sample (upper reference sample or left reference sample, assuming that the case is encoded / decoded in the raster scan order). The generated prediction sample is copied according to the direction of the intra prediction mode.

Since the prediction sample values are simply copied according to the prediction direction, a problem arises that the accuracy of prediction decreases as the distance from the reference sample increases. That is, the prediction accuracy is high when the distance between the reference samples and the prediction sample used for prediction is close, but the prediction accuracy is low when the distance between the reference samples and the prediction sample used for prediction is far.

In order to reduce such prediction error, the present invention proposes a linear interpolation intra prediction method for generating a weighted prediction sample based on the distance between the prediction sample and the reference sample. In particular, the present invention proposes a method for generating the lower right reference sample more accurately than the lower right reference sample generation method in the linear interpolation prediction method which is recently discussed. First, a linear interpolation prediction method will be described with reference to the drawings below.

14 and 15 are diagrams for explaining a linear interpolation prediction method according to an embodiment to which the present invention is applied.

Referring to FIG. 14, a decoder is mainly described for convenience of description, but the linear interpolation prediction method proposed by the present invention may be performed in the same manner in the encoder.

The decoder parses (or confirms) a LIP flag indicating whether Linear Interpolation Intra Prediction (LIP) (or linear interpolation intra prediction) is applied to the current block from the bit stream received from the encoder (S1401).

In one embodiment, the decoder may induce the intra prediction mode of the current block before step S1401, and may derive the intra prediction mode of the current block after step S1401. In other words, a step of deriving an intra prediction mode may be added before or after step S1401. The deriving of the intra prediction mode may include parsing an MPM flag indicating whether Most Probable Mode (MPM) is applied to the current block, and depending on whether the MPM is applied within the MPM candidate or the remaining prediction mode candidate. Parsing an index indicating a prediction mode applied to intra prediction of the current block.

The decoder generates a lower right reference sample adjacent to the lower right side of the current block (S1402). The decoder may generate the lower right reference sample using a variety of methods. This will be described later in more detail.

The decoder generates a right reference sample array or a lower reference sample array using the reconstructed reference samples around the current block and the lower right reference sample generated in step S1402 (S1403). In the present invention, a right reference sample array may be collectively referred to as a right reference sample, a right reference sample, a right reference sample array, a right buffer, a right buffer, a right sample buffer, a right sample buffer, and the like, and the lower reference sample array is a lower reference sample. It may be collectively referred to as a bottom reference sample, a bottom reference sample array, a bottom buffer, a bottom buffer, a bottom sample buffer, a bottom sample buffer, and the like. This will be described later in more detail.

The decoder generates the first prediction sample and the second prediction sample based on the prediction direction of the intra prediction mode of the current block (S1404 and S1405). Here, the first prediction sample (which may be referred to as a first reference sample) and the second prediction sample (which may also be referred to as a second reference sample) may be reference samples positioned opposite to each other in the current block with respect to the prediction direction, or Prediction samples generated using reference samples located opposite to each other in the current block are shown. The first prediction sample represents a prediction sample generated using the first reference sample determined according to the intra prediction mode of the current block among the reference samples (left, top left, and top reference samples) of the reconstructed region, and the second prediction sample is generated. The prediction sample represents a prediction sample generated using a second reference sample determined according to the intra prediction mode of the current block among the right reference sample array or the lower reference sample array in step S1403.

The decoder interpolates (or linear interpolates) the first prediction sample and the second prediction sample generated in steps S1404 and S1405 to generate a final prediction sample (S1406). In other words, the decoder may weight the first prediction sample and the second prediction sample based on the distance between the current sample and the prediction samples (or reference samples) to generate a final prediction sample.

Referring to FIG. 15, a decoder is mainly described for convenience of description, but the linear interpolation prediction method proposed by the present invention may be performed in the encoder.

The decoder may generate the first prediction sample P based on the intra prediction mode. In detail, the decoder may derive the first prediction sample by interpolating (or linear interpolating) the A reference sample and the B reference sample determined according to the prediction direction among the upper reference samples. On the other hand, unlike in FIG. 15, inter-reference interpolation may not be performed when a reference sample determined according to a prediction direction is located at an integer pixel position.

In addition, the decoder may generate a second prediction sample P ′ based on the intra prediction mode. Specifically, the decoder determines the A 'reference sample and the B' reference sample according to the prediction direction of the intra prediction mode of the current block among the lower reference samples, and linearly interpolates the A 'reference sample and the B' reference sample to make the second prediction. Samples can be derived. On the other hand, unlike in FIG. 15, inter-reference interpolation may not be performed when a reference sample determined according to a prediction direction is located at an integer pixel position.

The decoder determines weights applied to the first prediction sample and the second prediction sample based on the distance between the current sample and the prediction sample (or the reference sample), and uses the determined weights to determine the first prediction sample and the second prediction. The sample can be weighted to produce the final predicted sample. For example, the encoder / decoder may generate a final prediction sample using Equation 1 below.

Figure PCTKR2019004521-appb-img-000002

The weight determination method (w1, w2) shown in FIG. 15 is one example, and the decoder determines the weights applied to the first prediction sample and the second prediction sample, respectively, as shown in FIG. 15. The vertical distance between the prediction sample (or reference sample) may be used, or the actual distance between the current sample and the prediction sample (or reference sample) may be used. If the actual distance is used, the distance may be calculated and weighted (or derived) based on the actual position of the second reference sample used to generate the second prediction sample.

In one embodiment, the linear interpolation prediction method may be applied to a mode directional prediction mode except a planar mode and a DC mode, which are non-directional modes.

FIG. 16 is a diagram for describing a method of generating a lower right reference sample in a linear interpolation prediction method according to an embodiment to which the present invention may be applied.

Referring to FIG. 16, the encoder / decoder uses the upper right reference sample 1601 adjacent to the upper right side of the current block and the lower right adjacent to the lower right side of the current block by using the lower left reference sample 1602 adjacent to the lower left of the current block. Reference sample 1603 may be generated. For example, the encoder / decoder may generate the lower right reference sample 1603 using Equation 2 below.

Figure PCTKR2019004521-appb-img-000003

Referring to FIG. 16 (b), the encoder / decoder is a sample located at the rightmost side of the reference samples neighboring the top right side of the current block (hereinafter, referred to as the top right reference sample) (eg, at the top left of the current block). Adjacent to the lower left side of the current block, a sample that is two times the width of the current block in the horizontal direction relative to the reference sample, i.e., [2 * n-1, -1 samples] in the n × n block; The sample located at the bottom of the reference samples (hereinafter referred to as the leftmost reference sample) (for example, a sample spaced twice the current block height in the vertical direction with respect to the upper left reference sample of the current block, that is, n [-1, 2 * n-1] samples) 905 in the × n block may be used to generate the lower right reference sample 1606. For example, the encoder / decoder may generate the lower right reference sample 1606 by using Equation 3 below.

Figure PCTKR2019004521-appb-img-000004

FIG. 17 is a diagram for describing a method of generating right reference samples and bottom reference samples according to an embodiment to which the present invention is applied.

Referring to FIG. 17, it is assumed that the size of the current block is 2 × 4. The encoder / decoder may generate a right reference sample and / or a lower reference sample by using a lower right reference sample BR adjacent to the lower right side of the current block and a reconstructed reference sample around the current block.

In detail, the encoder / decoder may generate a lower reference sample by linearly interpolating a bottom right sample BR and a reference sample BL bottom left adjacent to the current block. In other words, the encoder / decoder may generate lower reference samples by performing weighted sum on a pixel basis according to a distance ratio with respect to each of the lower right reference sample BR and the lower left reference sample BL.

Also, the encoder / decoder may generate a right reference sample by linearly interpolating a lower right reference sample BR and a reference sample (TR: top right) adjacent to the upper right side of the current block. In other words, the encoder / decoder may generate lower reference samples by performing weighted summation on a pixel basis according to a distance ratio with respect to each of the lower right reference sample BR and the upper right reference sample TR.

As described above, in the linear interpolation prediction method, the encoder / decoder performs a weighted sum of reference samples of previously encoded / decoded and reconstructed regions and reference samples of a predicted (or derived) region that has not yet been encoded / decoded. Through the prediction block can be generated. That is, the reference sample of the reconstructed area and the reference sample of the unreconstructed area are used together for linear interpolation intra prediction. Therefore, the accuracy of the prediction in the linear interpolation intra prediction method depends on the accuracy of the reference sample of the unreconstructed region. In other words, the compression efficiency of the linear interpolation intra prediction method depends on how accurately the right bottom reference sample, the right reference sample or the bottom reference sample is generated.

Accordingly, the present invention proposes a method for more accurately generating a lower right reference sample, a right reference sample, and a lower reference sample used for linear interpolation intra prediction. According to an embodiment of the present invention, by effectively generating the reference samples of the unreconstructed region, it is possible to improve the accuracy of the linear interpolation intra prediction.

In the present invention, intra prediction that is not linear interpolation intra prediction may be referred to as general intra prediction (or normal intra prediction). For example, general intra prediction is an intra prediction method used in a conventional image compression technique (eg, HEVC), and is interpolated using one reference sample (or two adjacent integer pixel reference samples) determined according to a prediction direction. Reference sample).

18 is a diagram illustrating a method of determining an optimal prediction mode in intra prediction coding according to an embodiment to which the present invention is applied.

Referring to FIG. 18, the encoder / decoder starts a process of determining an intra prediction coding mode (S1801).

The encoder / decoder first determines a candidate even mode for full RD (rate-distortion) through a rough mode decision method for the even mode (S1802). In an embodiment, the encoder / decoder may determine a cost value based on the difference between the prediction block and the original block and the bits required for coding the prediction mode information, and may determine a mode having a low cost value as a candidate even mode.

The encoder / decoder again determines how to determine the rough mode for an odd mode ± 1 to the determined even mode number (e.g., ± 1 odd mode for modes 19 and 21 when the selected even mode is 20). The candidate mode for Full RD is determined through the operation (S1803).

After determining the candidate mode through the rough mode determination, the encoder / decoder finds a similar mode around the current block using the most probable mode (MPM) method and adds it to the candidate mode (S1804).

Finally, the encoder / decoder determines the final intra prediction mode through Full RD in terms of rate-distortion optimization (RDO) (S1805).

An object of the present invention proposes a method for generating an intra prediction block in consideration of more directionality in order to increase the accuracy of prediction in applying the linear interpolation prediction described above with reference to FIGS. 14 to 18.

In other words, an object of the present invention will be described a method of generating a prediction block by performing the prediction method in the linear interpolation screen based on various prediction blocks.

FIG. 19 is a diagram illustrating a method of performing linear interpolation intra prediction in consideration of an adjacent prediction direction as an embodiment to which the present invention is applied.

Referring to FIG. 19, a decoder is mainly described for convenience of description, but the linear interpolation prediction method proposed in the present invention may be performed in the same manner in an encoder. In performing linear interpolation intra prediction in FIG. 19, the decoder may apply the method described above with reference to FIGS. 14 to 18, and description thereof will be omitted.

The decoder may generate (or derive) the first prediction sample P based on the intra prediction mode. As an embodiment, the decoder may generate first prediction samples by interpolating (or linear interpolating) reference samples of integer pixel positions determined according to a prediction direction among upper reference samples. When the reference sample determined according to the prediction direction of the intra prediction mode is located at the integer pixel position, inter-reference interpolation may not be performed. The decoder may generate a second prediction sample P ′ based on the intra prediction mode.

C is a sample position to be currently encoded, P is a sample predicted from the first reference sample (upper reference sample), and P 'represents a predicted sample from the second reference sample (lower reference sample). In the conventional linear interpolation prediction method, a P sample value generated from a first reference sample and a P ′ sample value generated from a second reference sample are obtained by performing a linear interpolation (or weighted sum) of the final predicted sample value according to a distance ratio. Create

In an embodiment of the present invention, the decoder may further consider a prediction direction adjacent to the prediction direction of the intra prediction mode of the current block, as shown in FIG. 19. In other words, the decoder may generate a second reference sample using a prediction direction adjacent to the prediction direction of the intra prediction mode (that is, ± 1 mode of the intra prediction mode number).

The encoder may select an optimal reference sample among P 'reference samples, PL' reference samples, and PR 'reference samples, and signal optimal reference sample (or optimal directional) information to the decoder.

In other words, the encoder may generate the predicted sample (or reference sample) value P 'in consideration of the directionality ② corresponding to the prediction direction of the intra prediction mode of the current block. The encoder may generate reference sample (or prediction sample) values PL 'and PR' based on prediction directions +1 and -1 from the current direction, that is, ① and ③ prediction directions. The encoder may linearly interpolate each reference sample value with the first reference sample to generate a predictive sample of the current sample. Then, the reference sample having the smallest difference from the original sample (or original block) can be selected. In this way, the encoder can generate the following three prediction samples (or prediction blocks).

1) Perform linear interpolation prediction using direction ② corresponding to the current direction (or prediction direction) (for example, using P sample and P 'sample)

2) Perform linear interpolation prediction using the ① direction corresponding to the +1 direction of the current direction (for example, using P sample and PL 'sample).

3) Perform linear interpolation prediction using direction ③ corresponding to -1 direction of current direction (for example, using P sample and PR 'sample)

The encoder may select an optimal prediction block by comparing the prediction blocks generated in terms of rate-distortion optimization (RDO).

In the present embodiment, a description will be given mainly on the case of using a total of three prediction directions of ± 1 based on the current direction, but the present invention is not limited thereto. For example, the number of prediction directions (or prediction blocks) to compare may be determined variably, and five prediction directions may be considered.

In other words, the decoder may perform linear interpolation prediction using ± N prediction directions based on the current direction. For example, the decoder may use a reference sample determined in a total of five prediction directions of ± 2 based on the current directionality for linear interpolation prediction. In other words, the decoder may perform linear interpolation prediction using ± N prediction directions based on the current direction. For example, a reference sample determined in a total of five prediction directions of ± 2 based on the current direction may be used for linear interpolation prediction.

When the number of prediction directions to compare is increased, since the encoding bits for signaling the selected information also increase, it may be determined to be an optimal number in terms of encoding efficiency. That is, if the prediction direction used to generate the secondary reference samples increases, the accuracy of the prediction can be increased because more reference samples can be considered, while directional information bit signaling may be required by considering more directions. have. In consideration of this, the number of directionalities (± N prediction directions) that may be considered may vary depending on the prediction mode (ie, prediction direction) of the current block or the size of the current block.

In one embodiment, the decoder may be set to consider more directionality than if the size of the current block is greater than or equal to a certain size. For example, the decoder uses ± 2 (i.e., 5 total) directionalities if the block size is greater than or equal to the predetermined size, and ± 1 (i.e., total) if the block size is smaller than the predetermined size. Three) can be used. If the size of the current block is greater than or equal to a certain size, more directionality can be taken into account to improve prediction accuracy and prevent further splitting, which in turn improves overall compression performance.

Also, in one embodiment, the decoder uses ± 2 (i.e., 5 total) directionalities when the size of the current block is greater than or equal to 16x16 block size, and the block size is smaller than 16x16 size (e.g., For example, 8x8, 4x4) can use ± 1 (i.e. total 3) directionalities. The size of the predetermined block described above may be changed by way of example. For example, it may be set to a block size of 64x64, 32x32, 8x8, not 16x16. Alternatively, the decoder may set another size to a predetermined block size.

In addition, in one embodiment, the decoder may also consider ± 1, ± 2, ± 3 directionality when the block size varies. For example, ± 1 for 4x4, ± 2 for 8x8 to 16x16, and ± 3 for 32x32 to 64x64. Even in this case, the directionality according to the size of the block may be variously considered.

The decoder may first parse a LIP flag indicating whether LIP is applied to the current block. If the LIP is applied to the current block, the decoder may additionally parse the bits and identify information on which direction to perform linear interpolation prediction. In the previous example, a total of three prediction blocks were generated, and various information methods can be used to parse the information on the direction. As an example, when the frequency of occurrence is high, a small number of bits may be allocated. On the contrary, when the frequency of occurrence is low, many bits may be allocated to efficiently use the bit.

In general, the direction corresponding to the current prediction direction is likely to be selected. Therefore, in one embodiment, the encoder / decoder may allocate fewer bits to the directionality (that is, the prediction direction) corresponding to the current prediction direction rather than the adjacent directionality, as shown in Table 2 below.

Figure PCTKR2019004521-appb-img-000005

The encoder / decoder obtains weights applied to the first prediction sample (or first reference sample) and the second prediction sample (or second reference sample) based on the distance between the current sample and the prediction sample (or reference sample), respectively. The final prediction sample may be generated by weighting the first prediction sample and the second prediction sample using the determined weight.

20 and 21 are flowcharts illustrating a linear interpolation intra prediction method using adjacent directionality according to an embodiment of the present invention.

Referring to FIGS. 20 and 21, a decoder is mainly described for convenience of description, but the linear interpolation prediction method proposed in the present invention may be performed in the encoder as well.

FIG. 20 illustrates a method of applying the linear interpolation prediction proposed by the present invention in a structure of parsing an LIP flag indicating whether to apply the LIP before the MPM flag indicating whether to apply the MPM, and FIG. 21 illustrates an MPM flag before the LIP flag. A method of applying linear interpolation prediction proposed by the present invention in a parsing structure will be described.

Specifically, referring to FIG. 20, the decoder parses the LIP flag to determine whether LIP is applied to the current block.

If LIP is applied to the current block, the decoder indicates directional information (or prediction direction information, directional syntax, prediction direction syntax) indicating whether to use the adjacent prediction direction of the intra prediction mode of the current block to generate a prediction sample. Parse) The decoder parses an MPM index indicating an intra prediction mode applied to the current block among MPM candidates. The decoder performs linear interpolation intra prediction based on the parsed prediction mode.

If the LIP is not applied to the current block, the decoder parses an MPM flag indicating whether the MPM is applied. If the MPM is applied, the MPM index is parsed. If the MPM is not applied, the MPM index is parsed indicating the intra prediction mode applied to the current block among intra prediction modes except the MPM. The decoder performs general intra prediction using the determined intra prediction mode.

Referring to FIG. 21, the decoder parses an MPM flag to determine whether MPM is applied to a current block.

If the MPM is applied to the current block, the decoder parses the LIP flag to determine whether the LIP is applied to the current block. If no LIP is applied to the current block, the decoder parses the MPM index and the decoder performs general intra prediction based on the parsed prediction mode. If LIP is applied to the current block, the decoder indicates directional information (or prediction direction information, directional syntax, prediction direction syntax) indicating whether to use the adjacent prediction direction of the intra prediction mode of the current block to generate a prediction sample. Parse) The decoder parses an MPM index indicating an intra prediction mode applied to the current block among MPM candidates. The decoder performs linear interpolation intra prediction based on the parsed prediction mode.

If the MPM is not applied to the current block, the decoder parses an MPM index indicating an intra prediction mode applied to the current block among intra prediction modes except for the MPM. The decoder performs general intra prediction using the determined intra prediction mode.

Embodiments of the present invention described above may be implemented independently, or one or more embodiments may be implemented in combination.

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

Referring to FIG. 22, a decoder is mainly described for convenience of description, but the present invention is not limited thereto, and the method of generating an intra prediction block according to the embodiment of the present invention may be performed in the same manner in the encoder and the decoder.

The decoder parses a LIP flag indicating whether Linear Interpolation Intra Prediction (LIP) is applied to the current block (S2201).

When the LIP is applied to the current block, the decoder derives a first reference sample using at least one of a left, an upper, and an upper left reference sample of the current block based on the intra prediction mode of the current block (S2202). .

The decoder parses a directional index indicating information on the LIP direction based on the first prediction direction indicating the prediction direction of the intra prediction mode (S2203).

The decoder derives the second reference sample by using at least one of the right, lower, and lower right reference samples of the current block based on the LIP direction determined by the directional index (S2204).

The decoder weights (or linearly interpolates) the first reference sample and the second reference sample to generate a prediction sample of the current block (S2205).

As described above, the LIP direction represents the first prediction direction, a second prediction direction indicating a prediction direction of the prediction mode plus 1 to the intra prediction mode, and a prediction direction of the prediction mode minus 1 to the intra prediction mode. It may include a third prediction direction.

In addition, as described above, a bit shorter than an index indicating the second prediction direction or the third prediction direction may be allocated to the index indicating the first prediction direction.

In addition, as described above, the decoder may generate a lower right reference sample adjacent to the lower right side of the current block, and generate at least one of a right reference sample or a lower reference sample by using the lower right reference sample.

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

In FIG. 23, for convenience of description, the intra predictor is illustrated as one block, but the intra predictor may be implemented in a configuration included in the encoder and / or the decoder.

Referring to FIG. 23, the intra predictor implements the functions, processes, and / or methods proposed in FIGS. 8 to 22. In detail, the intra predictor may include a LIP flag parser 2301, a first reference sample derivator 2302, a directional index parser 2303, a second reference sample derivator 2304, and a predictive sample generator 2305. Can be.

The LIP flag parser 2301 parses a LIP flag indicating whether Linear Interpolation Intra Prediction (LIP) is applied to the current block.

When LIP is applied to the current block, the first reference sample deriving unit 2302 uses the first reference sample based on at least one of a left, an upper, and an upper left reference sample of the current block based on an intra prediction mode of the current block. Induce a sample.

The directional index parser 2303 parses a directional index representing information on the LIP direction based on the first prediction direction indicating the prediction direction of the intra prediction mode.

The second reference sample derivator 2304 derives the second reference sample by using at least one of the right, lower, and lower right reference samples of the current block based on the LIP direction determined by the directional index.

The prediction sample generator 2305 weights the first reference sample and the second reference sample to generate a prediction sample of the current block.

As described above, the LIP direction represents the first prediction direction, a second prediction direction indicating a prediction direction of the prediction mode plus 1 to the intra prediction mode, and a prediction direction of the prediction mode minus 1 to the intra prediction mode. It may include a third prediction direction.

In addition, as described above, a bit shorter than an index indicating the second prediction direction or the third prediction direction may be allocated to the index indicating the first prediction direction.

In addition, as described above, the second reference sample inducing unit 2304 generates a lower right reference sample adjacent to the lower right side of the current block and uses at least one of a right reference sample or a lower reference sample by using the lower right reference sample. Can be generated.

24 is a diagram illustrating a method of performing linear interpolation intra prediction using multi-reference lines as an embodiment to which the present invention is applied.

Referring to FIG. 24, the method described with reference to FIGS. 14 to 23 may be equally applied to a multi-reference line (or a multi-reference sample line). For example, the method proposed in the present invention can be applied even when using two or more reference lines as shown in FIG. 24. In FIG. 24, it is assumed that two reference lines are used, but the present invention is not limited thereto and may be applied to a multi-reference line intra prediction method using three or more reference lines.

When the method proposed in the intra prediction using the multi-reference line is applied, more reference samples are added to the linear interpolation prediction as additional direction is considered in generating the second reference sample (that is, P ′ of FIG. 19 described above). Can be used to effectively increase the accuracy of the prediction.

On the other hand, even when not using multiple reference lines (i.e., when referring to an existing single reference line), according to an embodiment of the present invention, two adjacent reference samples are used by considering additional directionality in linear interpolation prediction. A differential reference sample (that is, P ′ of FIG. 19 described above) can be generated, and the same effect as that of extending the single reference line according to the direction can be obtained.

According to an embodiment of the present invention, by increasing the accuracy of prediction, block division for intra prediction can be minimized, thereby maximizing compression performance.

It demonstrates concretely by an example. As described above, in intra prediction, the prediction error tends to increase as the distance between the prediction sample and the reference sample increases. In the case of the prediction direction as shown in FIG. 19, the prediction error may be higher than that of the prediction sample that is relatively far from the upper reference sample line. The influence of the sample value is large. Thus, by generating a second reference sample (i.e., P 'of FIG. 19 described above) in consideration of more directionality, the accuracy of the prediction may be relatively lower and the weight of the region with higher weight for the lower reference sample may be reduced. The accuracy can be effectively increased.

According to an embodiment of the present invention, although signaling bits may increase according to more directional considerations, further block division for intra prediction may be prevented by further increasing the accuracy of linear interpolation prediction. In general, much more (about 7 to 8 bits or more) of header information may be required for signaling prediction mode information in intra prediction, and as a result, overall compression performance may be improved by minimizing block partitioning.

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

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

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 / image encoding device, and the decoding device may be called a video / image decoding device. The transmitter may 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 the video / image through a process of capturing, synthesizing, or generating the video / image. The video source may comprise 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, video / image archives including previously captured video / images, and the like. Video / image generation devices may include, for example, computers, tablets and smartphones, and may (electronically) generate video / images. For example, a virtual video / image may be generated through a computer or the like. In this case, the video / image capturing process may be replaced by a process of generating related data.

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

The transmitter may transmit the encoded video / video information or data output in the form of a bitstream to the receiver of the receiving device through a digital storage medium or a network in the form of a file or streaming. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. 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 the extracted bitstream to the decoding apparatus.

The decoding apparatus may decode the 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 may render the decoded video / image. The rendered video / image may be displayed through the display unit.

26 is a diagram illustrating the structure of a content streaming system according to an embodiment to which the present invention is applied.

Referring to FIG. 26, 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 compresses content input from multimedia input devices such as a smart phone, a camera, a camcorder, etc. into digital data to generate a bitstream and transmit the bitstream to the streaming server. As another example, when multimedia input devices such as smart phones, cameras, camcorders, etc. 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 the multimedia data to the user device based on the user's request through the web server, and the web server serves as a medium for informing the user of what service. When a user requests a desired service from the web server, the web server delivers it to a 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 this case, the control server plays a role of controlling a command / response between devices in the content streaming system.

The streaming server may receive content from a media store and / or an encoding server. For example, when the 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 digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), navigation, a slate PC, Tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, glass glasses, head mounted displays), digital TVs, desktops Computer, digital signage, and the like.

Each server in the content streaming system may be operated as a distributed server, in which case data received from each server may be distributed.

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

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

In addition, the processing method to which the present invention is applied can be produced in the form of a program executed by a computer, and 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 may be, for example, a Blu-ray disc (BD), a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical disc. It may include a data storage device. The computer-readable recording medium also includes media embodied in the form of a carrier wave (eg, transmission over 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.

In addition, an embodiment of the present invention may be implemented as a computer program product by program code, which may be performed on a computer by an embodiment of the present invention. The program code may be stored on a carrier readable by a computer.

The embodiments described above are 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 embodied in a form that is not combined with other components or features. It is also possible to combine some of the components and / or features to form an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is obvious that the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship in the claims or as new claims by post-application correction.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of a hardware implementation, an embodiment of the present invention may include 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 may be stored in memory and driven by the processor. The memory may be located inside or outside the processor, and may 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 aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

As mentioned above, preferred embodiments of the present invention are disclosed for the purpose of illustration, and those skilled in the art can improve and change various other embodiments within the spirit and technical scope of the present invention disclosed in the appended claims below. , Replacement or addition would be possible.

Claims (8)

  1. A method of processing an image based on an intra prediction mode,
    Parsing a LIP flag indicating whether Linear Interpolation Intra Prediction (LIP) is applied to the current block;
    When LIP is applied to the current block, deriving a first reference sample using at least one of a left, an upper, and an upper left reference sample of the current block based on an intra prediction mode of the current block;
    Parsing a directional index indicating information about a LIP direction based on a first prediction direction indicating a prediction direction of the intra prediction mode;
    Deriving a second reference sample using at least one of the right, lower, and lower right reference samples of the current block based on the LIP direction determined by the directional index; And
    And generating a predictive sample of the current block by weighting the first reference sample and the second reference sample.
  2. The method of claim 1,
    The LIP direction is a first prediction direction, a second prediction direction indicating a prediction direction of the prediction mode plus 1 to the intra prediction mode, and a third prediction direction indicating a prediction direction of the prediction mode minus 1 to the intra prediction mode. Image processing method comprising.
  3. The method of claim 2,
    And a bit shorter than an index indicating the second prediction direction or the third prediction direction is allocated to the index indicating the first prediction direction.
  4. The method of claim 1,
    Generating a lower right reference sample adjacent to the lower right side of the current block; And
    And generating at least one of a right reference sample and a lower reference sample using the lower right reference sample.
  5. An apparatus for processing an image based on an intra prediction mode,
    A LIP flag parsing unit configured to parse a LIP flag indicating whether Linear Interpolation Intra Prediction (LIP) is applied to a current block;
    When LIP is applied to the current block, a first reference sample derivation unit for deriving a first reference sample using at least one of a left, an upper, and an upper left reference sample of the current block based on an intra prediction mode of the current block ;
    A directional index parser for parsing a directional index representing information about a LIP direction based on a first prediction direction indicating a prediction direction of the intra prediction mode;
    A second reference sample deriving unit for deriving a second reference sample using at least one of the right, lower and right lower reference samples of the current block based on the LIP direction determined by the directional index; And
    And a prediction sample generator configured to weight the first reference sample and the second reference sample to generate a prediction sample of the current block.
  6. The method of claim 5,
    The LIP direction is a first prediction direction, a second prediction direction indicating a prediction direction of the prediction mode plus 1 to the intra prediction mode, and a third prediction direction indicating a prediction direction of the prediction mode minus 1 to the intra prediction mode. Image processing apparatus comprising.
  7. The method of claim 6,
    And a bit shorter than an index indicating the second prediction direction or the third prediction direction is allocated to the index indicating the first prediction direction.
  8. The method of claim 5,
    The second reference sample inducing unit generates a lower right reference sample adjacent to the lower right side of the current block,
    And an at least one of a right reference sample and a lower reference sample using the lower right reference sample.
PCT/KR2019/004521 2018-04-14 2019-04-15 Intra-prediction mode-based image processing method and device therefor WO2019199149A1 (en)

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