WO2020141880A1

WO2020141880A1 - Image decoding method and device using deblocking filtering in image coding system

Info

Publication number: WO2020141880A1
Application number: PCT/KR2020/000017
Authority: WO
Inventors: 장형문
Original assignee: 엘지전자 주식회사
Priority date: 2019-01-02
Filing date: 2020-01-02
Publication date: 2020-07-09

Abstract

An image decoding method carried out by a decoding device, according to the present document, comprises the steps of: receiving a bitstream including image information; generating a restored picture on the basis of the image information; deriving, as a boundary subjected to deblocking filtering, a boundary of a coding sub-block of a coding block in the restored picture corresponding to an NxN grid; and deriving a modified restored picture by carrying out deblocking filtering on the boundary subjected to deblocking filtering.

Description

Image decoding method and apparatus using deblocking filtering in image coding system

This document relates to image coding technology, and more particularly, to an image decoding method and apparatus using deblocking filtering in an image coding system.

Recently, demands for high-resolution and high-quality images such as high definition (HD) images and ultra high definition (UHD) images are increasing in various fields. As the image data becomes high-resolution and high-quality, the amount of information or bits transmitted relative to the existing image data increases, so the image data is transmitted using a medium such as a conventional wired/wireless broadband line or the image data is stored using an existing storage medium. When storing, the transmission cost and storage cost are increased.

Accordingly, a high-efficiency image compression technique is required to effectively transmit, store, and reproduce high-resolution, high-quality image information.

The technical task of this document is to provide a method and apparatus for improving the visual quality of an image.

Another technical task of the present document is to provide an image decoding method and apparatus for deriving a boundary of a coding sub-block as a boundary for deblocking filtering based on an NxN grid, and performing deblocking filtering for the derived boundary for deblocking filtering. .

According to an embodiment of the present document, an image decoding method performed by a decoding apparatus is provided. The method includes receiving a bitstream including image information, generating a reconstructed picture based on the image information, and dividing a boundary of a coding subblock of a coding block in the reconstructed picture corresponding to an NxN grid. And deriving the modified reconstructed picture by performing deblocking filtering on the deblocking filtering target boundary and deriving it as a blocking filtering target boundary.

According to another embodiment of the present document, a decoding apparatus for performing image decoding is provided. The decoding apparatus includes an entropy decoding unit that receives a bitstream including image information, a prediction unit that generates a reconstructed picture based on the image information, and a coding sub of a coding block in the reconstructed picture corresponding to an NxN grid. It characterized in that it comprises a filter for deriving the boundary of the block as a deblocking filtering target boundary, and performing deblocking filtering on the deblocking filtering target boundary to derive a corrected reconstructed picture.

According to another embodiment of the present document, a video encoding method performed by an encoding device is provided. The method includes predicting a coding sub-block of a coding block to generate a reconstructed picture, deriving a boundary of the coding sub-block corresponding to an NxN grid as a deblocking filtering target boundary, and the deblocking And performing deblocking filtering on a boundary to be filtered to derive a corrected reconstructed picture and encoding image information including prediction-related information of the coding block.

According to another embodiment of the present document, a video encoding apparatus is provided. A prediction unit that generates a reconstructed picture by performing prediction on a coding subblock of the encoding coding block, derives a boundary of the coding subblock corresponding to an NxN grid as a deblocking filtering target boundary, and filters the deblocking It characterized in that it comprises a filter unit for deriving a modified reconstructed picture by performing deblocking filtering on a target boundary and an entropy encoding unit for encoding image information including prediction-related information of the coding block.

According to this document, overall visual/video visual quality can be improved.

According to this document, it is possible to perform deblocking filtering to effectively remove blocking artifacts of a subblock boundary due to prediction performed on a subblock basis, thereby improving subjective/objective visual quality.

1 schematically shows an example of a video/image coding system to which embodiments of the present document can be applied.

2 is a diagram schematically illustrating a configuration of a video/video encoding apparatus to which embodiments of the present document can be applied.

3 is a diagram schematically illustrating a configuration of a video/video decoding apparatus to which embodiments of the present document can be applied.

4 exemplarily shows an embodiment of a method for performing deblocking filtering.

5 shows an example of deriving a block boundary on which deblocking filtering is performed based on an 8x8 grid.

6 exemplarily shows a movement expressed through the affine movement model.

7 exemplarily shows the affine motion model in which motion vectors for three control points are used.

8 exemplarily shows the affine motion model in which motion vectors for two control points are used.

9 exemplarily shows a method of deriving a motion vector in units of sub-blocks based on the affine motion model.

10 schematically shows a video encoding method by an encoding device according to the present document.

11 schematically shows an encoding apparatus that performs a video encoding method according to the present document.

12 schematically shows an image decoding method by a decoding apparatus according to the present document.

13 schematically shows a decoding apparatus performing an image decoding method according to the present document.

14 exemplarily shows a structure diagram of a content streaming system to which embodiments of the present document are applied.

Since this document may have various changes and may have various embodiments, specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the embodiments of this document to specific embodiments. Terms used in this specification are only used to describe specific embodiments, and are not intended to limit the technical spirit of the present document. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms "include" or "have" are intended to indicate that a feature, number, step, operation, component, part, or combination thereof described on the specification exists, or that one or more other features or It should be understood that numbers, steps, operations, components, parts, or combinations thereof do not preclude the presence or addition possibilities of those.

On the other hand, each configuration in the drawings described in this document is independently shown for convenience of description of different characteristic functions, and does not mean that each configuration is implemented with separate hardware or separate software. For example, two or more components of each component may be combined to form a single component, or one component may be divided into a plurality of components. Embodiments in which each component is integrated and/or separated are also included in the scope of this document as long as they do not depart from the nature of this document.

Hereinafter, exemplary embodiments of the present document will be described in detail with reference to the accompanying drawings. Hereinafter, the same reference numerals are used for the same components in the drawings, and duplicate descriptions for the same components may be omitted.

Referring to FIG. 1, a video/image coding system may include a first device (source device) and a second device (receiving device). The source device may transmit the encoded video/image information or data to a receiving device through a digital storage medium or network in the form of a file or streaming.

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

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

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

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

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

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

This document is about video/video coding. For example, the methods/embodiments disclosed in this document include a versatile video coding (VVC) standard, an essential video coding (EVC) standard, an AOMedia Video 1 (AV1) standard, a 2nd generation of audio video coding standard (AVS2), or next-generation video/ It can be applied to the method disclosed in the video coding standard (ex. H.267 or H.268, etc.).

In this document, various embodiments of video/image coding are proposed, and the above embodiments may be performed in combination with each other unless otherwise specified.

In this document, video may mean a set of images over time. A picture generally refers to a unit representing one image in a specific time period, and a slice/tile is a unit constituting a part of a picture in coding. The slice/tile may include one or more coding tree units (CTUs). One picture may be composed of one or more slices/tiles. One picture may be composed of one or more tile groups. One tile group may include one or more tiles. The brick may represent a rectangular region of CTU rows within a tile in a picture. Tiles can be partitioned into multiple bricks, and each brick can be composed of one or more CTU rows in the tile (A tile may be partitioned into multiple bricks, each of which consisting of one or more CTU rows within the tile ). A tile that is not partitioned into multiple bricks may be also referred to as a brick. A brick scan can indicate a specific sequential ordering of CTUs partitioning a picture, the CTUs can be aligned with a CTU raster scan within a brick, and the bricks in a tile can be aligned sequentially with a raster scan of the bricks of the tile. A, and tiles in a picture can be sequentially aligned with a raster scan of the tiles of the picture (A brick scan is a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in a brick , bricks within a tile are ordered consecutively in a raster scan of the bricks of the tile, and tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture). A tile is a rectangular region of CTUs within a particular tile column and a particular tile row in a picture. The tile column is a rectangular area of CTUs, the rectangular area has a height equal to the height of the picture, and the width can be specified by syntax elements in a picture parameter set (The tile column is a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements in the picture parameter set). The tile row is a rectangular region of CTUs, the rectangular region has a width specified by syntax elements in a picture parameter set, and the height can be the same as the height of the picture (The tile row is a rectangular region of CTUs having a height specified by syntax elements in the picture parameter set and a width equal to the width of the picture). A tile scan can indicate a specific sequential ordering of CTUs partitioning a picture, the CTUs can be successively aligned with a CTU raster scan in a tile, and the tiles in a picture can be successively aligned with a raster scan of the tiles of the picture. A tile scan is a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in a tile whereas tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture). A slice may include an integer number of bricks of a picture, and the integer number of bricks may be included in one NAL unit (A slice includes an integer number of bricks of a picture that may be exclusively contained in a single NAL unit). A slice may consist of either a number of complete tiles or only a consecutive sequence of complete bricks of one tile ). Tile groups and slices are used interchangeably in this document. For example, the tile group/tile group header in this document may be referred to as a slice/slice header.

A pixel or a pel may mean a minimum unit constituting one picture (or image). Also, as a term corresponding to a pixel,'sample' may be used. The sample may generally represent a pixel or a pixel value, may represent only a pixel/pixel value of a luma component, or may represent only a pixel/pixel value of a chroma component.

The unit may represent a basic unit of image processing. The unit may include at least one of a specific region of a picture and information related to the region. One unit may include one luma block and two chroma (ex. cb, cr) blocks. The unit may be used interchangeably with terms such as a block or area in some cases. In the general case, the MxN block may include samples (or sample arrays) of M columns and N rows or a set (or array) of transform coefficients.

In this document, "/" and "," are interpreted as "and/or". For example, “A/B” is interpreted as “A and/or B”, and “A, B” is interpreted as “A and/or B”. Additionally, “A/B/C” means “at least one of A, B and/or C”. Also, “A, B, and C” means “at least one of A, B, and/or C”. (In this document, the term "/" and "," should be interpreted to indicate "and/or." For instance, the expression "A/B" may mean "A and/or B." Further, "A, B" may mean "A and/or B." Further, "A/B/C" may mean "at least one of A, B, and/or C." Also, "A/B/C" may mean " at least one of A, B, and/or C.")

Additionally, "or" in this document is interpreted as "and/or." For example, "A or B" may mean 1) only "A", 2) only "B", or 3) "A and B". In other words, “or” in this document may mean “additionally or alternatively”. (Further, in the document, the term "or" should be interpreted to indicate "and/or." For instance, the expression "A or B" may comprise 1) only A, 2) only B, and/or 3) both A and B. In other words, the term "or" in this document should be interpreted to indicate "additionally or alternatively.")

2 is a diagram schematically illustrating a configuration of a video/video encoding apparatus to which embodiments of the present document can be applied. Hereinafter, the video encoding device may include a video encoding device.

Referring to FIG. 2, the encoding apparatus 200 includes an image partitioner 210, a predictor 220, a residual processor 230, and an entropy encoder 240. It may be configured to include an adder (250), a filtering unit (filter, 260) and a memory (memory, 270). The prediction unit 220 may include an inter prediction unit 221 and an intra prediction unit 222. The residual processing unit 230 may include a transform unit 232, a quantizer 233, a dequantizer 234, and an inverse transformer 235. The residual processing unit 230 may further include a subtractor 231. The adder 250 may be referred to as a reconstructor or a recontructged block generator. The above-described image segmentation unit 210, prediction unit 220, residual processing unit 230, entropy encoding unit 240, adding unit 250, and filtering unit 260 may include one or more hardware components ( For example, it may be configured by an encoder chipset or processor). In addition, the memory 270 may include a decoded picture buffer (DPB), or may be configured by a digital storage medium. The hardware component may further include a memory 270 as an internal/external component.

The image division unit 210 may divide an input image (or picture, frame) input to the encoding apparatus 200 into one or more processing units. For example, the processing unit may be called a coding unit (CU). In this case, the coding unit is recursively divided according to a quad-tree binary-tree ternary-tree (QTBTTT) structure from a coding tree unit (CTU) or a largest coding unit (LCU). Can. For example, one coding unit may be divided into a plurality of coding units of a deeper depth based on a quad tree structure, a binary tree structure, and/or a ternary structure. In this case, for example, a quad tree structure may be applied first, and a binary tree structure and/or a ternary structure may be applied later. Alternatively, a binary tree structure may be applied first. The coding procedure according to this document may be performed based on the final coding unit that is no longer split. In this case, the maximum coding unit may be directly used as the final coding unit based on coding efficiency according to image characteristics, or the coding unit may be recursively divided into coding units having a lower depth than optimal if necessary. The coding unit of the size of can be used as the final coding unit. Here, the coding procedure may include procedures such as prediction, transformation, and reconstruction, which will be described later. As another example, the processing unit may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may be partitioned or partitioned from the above-described final coding unit, respectively. The prediction unit may be a unit of sample prediction, and the transformation unit may be a unit for deriving a transform coefficient and/or a unit for deriving a residual signal from the transform coefficient.

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

The encoding device 200 subtracts a prediction signal (a predicted block, a prediction sample array) output from the inter prediction unit 221 or the intra prediction unit 222 from the input image signal (original block, original sample array). A signal (residual signal, residual block, residual sample array) may be generated, and the generated residual signal is transmitted to the conversion unit 232. In this case, as illustrated, a unit that subtracts a prediction signal (a prediction block, a prediction sample array) from an input image signal (original block, original sample array) in the encoder 200 may be referred to as a subtraction unit 231. The prediction unit may perform prediction on a block to be processed (hereinafter, referred to as a current block) and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied in units of the current block or CU. As described later in the description of each prediction mode, the prediction unit may generate various information about prediction, such as prediction mode information, and transmit it to the entropy encoding unit 240. The prediction information may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

The intra prediction unit 222 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located apart depending on a prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The non-directional mode may include, for example, a DC mode and a planar mode (Planar mode). The directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the degree of detail of the prediction direction. However, this is an example, and more or less directional prediction modes may be used depending on the setting. The intra prediction unit 222 may determine a prediction mode applied to the current block by using a prediction mode applied to neighboring blocks.

The inter prediction unit 221 may derive the predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture. At this time, to reduce the amount of motion information transmitted in the inter prediction mode, motion information may be predicted in units of blocks, subblocks, or samples based on the correlation of motion information between a neighboring block and a current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring block may include a spatial neighboring block present in the current picture and a temporal neighboring block present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to by a name such as a collocated reference block or a colCU, and a reference picture including the temporal neighboring block may be called a collocated picture (colPic). It might be. For example, the inter prediction unit 221 constructs a motion information candidate list based on neighboring blocks, and provides information indicating which candidate is used to derive the motion vector and/or reference picture index of the current block. Can be created. Inter prediction may be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the inter prediction unit 221 may use motion information of neighboring blocks as motion information of the current block. In the skip mode, unlike the merge mode, the residual signal may not be transmitted. In the motion vector prediction (MVP) mode, the motion vector of the current block is obtained by using the motion vector of the neighboring block as a motion vector predictor and signaling a motion vector difference. I can order.

The prediction unit 220 may generate a prediction signal based on various prediction methods described below. For example, the prediction unit may apply intra prediction or inter prediction as well as intra prediction and inter prediction at the same time for prediction for one block. This can be called combined inter and intra prediction (CIIP). Also, the prediction unit may be based on an intra block copy (IBC) prediction mode or a palette mode for prediction of a block. The IBC prediction mode or palette mode may be used for content video/video coding such as a game, such as screen content coding (SCC). IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction in that a reference block is derived in the current picture. That is, the IBC can use at least one of the inter prediction techniques described in this document. The palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, a sample value in a picture may be signaled based on information on the palette table and palette index.

The prediction signal generated through the prediction unit (including the inter prediction unit 221 and/or the intra prediction unit 222) may be used to generate a reconstructed signal or may be used to generate a residual signal. The transform unit 232 may generate transform coefficients by applying a transform technique to the residual signal. For example, at least one of a DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), KLT (Karhunen-Loeve Transform), GBT (Graph-Based Transform), or CNT (Conditionally Non-linear Transform) It can contain. Here, GBT means a transformation obtained from this graph when it is said that the relationship information between pixels is graphically represented. CNT means a transform obtained by generating a prediction signal using all previously reconstructed pixels and based on it. Also, the transform process may be applied to pixel blocks having the same size of a square, or may be applied to blocks of variable sizes other than squares.

The quantization unit 233 quantizes the transform coefficients and transmits them to the entropy encoding unit 240, and the entropy encoding unit 240 encodes a quantized signal (information about quantized transform coefficients) and outputs it as a bitstream. have. Information about the quantized transform coefficients may be called residual information. The quantization unit 233 may rearrange block-type quantized transform coefficients into a one-dimensional vector form based on a coefficient scan order, and quantize the quantized transform coefficients based on the one-dimensional vector form. Information regarding transform coefficients may be generated. The entropy encoding unit 240 may perform various encoding methods, such as exponential Golomb (CAVLC), context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). The entropy encoding unit 240 may encode information necessary for video/image reconstruction (eg, a value of syntax elements, etc.) together with the quantized transform coefficients together or separately. The encoded information (ex. encoded video/video information) may be transmitted or stored in units of network abstraction layer (NAL) units in the form of a bitstream. The video/video information may further include information regarding various parameter sets such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video/video information may further include general constraint information. In this document, information and/or syntax elements transmitted/signaled from an encoding device to a decoding device may be included in video/video information. The video/video information may be encoded through the above-described encoding procedure and included in the bitstream. The bitstream can be transmitted over a network or stored on a digital storage medium. Here, the network may include a broadcasting network and/or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD. The signal output from the entropy encoding unit 240 may be configured as an internal/external element of the encoding device 200 by a transmitting unit (not shown) and/or a storing unit (not shown) for storing, or the transmitting unit It may be included in the entropy encoding unit 240.

The quantized transform coefficients output from the quantization unit 233 may be used to generate a prediction signal. For example, a residual signal (residual block or residual samples) may be restored by applying inverse quantization and inverse transformation through the inverse quantization unit 234 and the inverse transformation unit 235 to the quantized transform coefficients. The adder 250 adds the reconstructed residual signal to the predicted signal output from the inter predictor 221 or the intra predictor 222, so that the reconstructed signal (restored picture, reconstructed block, reconstructed sample array) 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 a reconstructed block. The adder 250 may be called a restoration unit or a restoration block generation unit. The generated reconstructed signal may be used for intra prediction of a next processing target block in a current picture, or may be used for inter prediction of a next picture through filtering as described below.

Meanwhile, LMCS (luma mapping with chroma scaling) may be applied during picture encoding and/or reconstruction.

The filtering unit 260 may improve subjective/objective image quality by applying filtering to the reconstructed signal. For example, the filtering unit 260 may generate a modified restoration picture by applying various filtering methods to the restoration picture, and the modified restoration picture may be a DPB of the memory 270, specifically, the memory 270. Can be stored in. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like. The filtering unit 260 may generate various pieces of information regarding filtering as described later in the description of each filtering method, and transmit them to the entropy encoding unit 240. The filtering information may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

The modified reconstructed picture transmitted to the memory 270 may be used as a reference picture in the inter prediction unit 221. When the inter prediction is applied through the encoding apparatus, prediction mismatches in the encoding apparatus 200 and the decoding apparatus 300 can be avoided, and encoding efficiency can be improved.

The memory 270 DPB may store the modified reconstructed picture for use as a reference picture in the inter prediction unit 221. The memory 270 may store motion information of a block from which motion information in a current picture is derived (or encoded) and/or motion information of blocks in a picture that has already been reconstructed. The stored motion information may be transmitted to the inter prediction unit 221 to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory 270 may store reconstructed samples of blocks reconstructed in the current picture, and may transmit the reconstructed samples to the intra prediction unit 222.

Referring to FIG. 3, the decoding apparatus 300 includes an entropy decoder (310), a residual processor (320), a prediction unit (predictor, 330), an adder (340), and a filtering unit (filter, 350) and memory (memory, 360). The prediction unit 330 may include an inter prediction unit 331 and an intra prediction unit 332. The residual processing unit 320 may include a deequantizer (321) and an inverse transformer (321). The entropy decoding unit 310, the residual processing unit 320, the prediction unit 330, the adding unit 340, and the filtering unit 350 described above may include one hardware component (eg, a decoder chipset or processor) according to an embodiment. ). Also, the memory 360 may include a decoded picture buffer (DPB), or may be configured by a digital storage medium. The hardware component may further include a memory 360 as an internal/external component.

When a bitstream including video/image information is input, the decoding apparatus 300 may restore an image corresponding to a process in which the video/image information is processed in the encoding apparatus of FIG. 2. For example, the decoding apparatus 300 may derive units/blocks based on block partitioning related information obtained from the bitstream. The decoding apparatus 300 may perform decoding using a processing unit applied in the encoding apparatus. Accordingly, the processing unit of decoding may be, for example, a coding unit, and the coding unit may be divided along a quad tree structure, a binary tree structure and/or a ternary tree structure from a coding tree unit or a largest coding unit. One or more transform units can be derived from the coding unit. Then, the decoded video signal decoded and output through the decoding device 300 may be reproduced through the reproduction device.

The decoding apparatus 300 may receive the signal output from the encoding apparatus of FIG. 2 in the form of a bitstream, and the received signal may be decoded through the entropy decoding unit 310. For example, the entropy decoding unit 310 may parse the bitstream to derive information (eg, video/image information) necessary for image reconstruction (or picture reconstruction). The video/video information may further include information regarding various parameter sets such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video/video information may further include general constraint information. The decoding apparatus may decode a picture further based on the information on the parameter set and/or the general restriction information. Signaling/receiving information and/or syntax elements described later in this document may be decoded through the decoding procedure and obtained from the bitstream. For example, the entropy decoding unit 310 decodes information in a bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and quantizes a value of a syntax element required for image reconstruction and a transform coefficient for residual. Can output In more detail, the CABAC entropy decoding method receives bins corresponding to each syntax element in a bitstream, and decodes syntax element information to be decoded and decoding information of neighboring and decoding target blocks or symbol/bin information decoded in the previous step. The context model is determined by using, and the probability of occurrence of the bin is predicted according to the determined context model, and arithmetic decoding of the bin is performed to generate a symbol corresponding to the value of each syntax element. have. At this time, the CABAC entropy decoding method may update the context model using the decoded symbol/bin information for the next symbol/bin context model after determining the context model. Among the information decoded by the entropy decoding unit 310, prediction information is provided to a prediction unit (inter prediction unit 332 and intra prediction unit 331), and the entropy decoding unit 310 performs entropy decoding. The dual value, that is, quantized transform coefficients and related parameter information may be input to the residual processing unit 320. The residual processor 320 may derive a residual signal (residual block, residual samples, residual sample array). Also, information related to filtering among information decoded by the entropy decoding unit 310 may be provided to the filtering unit 350. Meanwhile, a receiving unit (not shown) receiving a signal output from the encoding device may be further configured as an internal/external element of the decoding device 300, or the receiving unit may be a component of the entropy decoding unit 310. Meanwhile, the decoding device according to this document may be called a video/picture/picture decoding device, and the decoding device may be classified into an information decoder (video/picture/picture information decoder) and a sample decoder (video/picture/picture sample decoder). It might be. The information decoder may include the entropy decoding unit 310, and the sample decoder may include the inverse quantization unit 321, an inverse transformation unit 322, an addition unit 340, a filtering unit 350, and a memory 360 ), at least one of an inter prediction unit 332 and an intra prediction unit 331.

The inverse quantization unit 321 may inverse quantize the quantized transform coefficients to output transform coefficients. The inverse quantization unit 321 may rearrange the quantized transform coefficients in a two-dimensional block form. In this case, the reordering may be performed based on the coefficient scan order performed by the encoding device. The inverse quantization unit 321 may perform inverse quantization on the quantized transform coefficients by using a quantization parameter (for example, quantization step size information), and obtain transform coefficients.

The inverse transform unit 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

The prediction unit may perform prediction on the current block and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction is applied to the current block or inter prediction is applied based on the information on the prediction output from the entropy decoding unit 310, and may determine a specific intra/inter prediction mode.

The prediction unit 320 may generate a prediction signal based on various prediction methods described below. For example, the prediction unit may apply intra prediction or inter prediction as well as intra prediction and inter prediction at the same time for prediction for one block. This can be called combined inter and intra prediction (CIIP). Also, the prediction unit may be based on an intra block copy (IBC) prediction mode or a palette mode for prediction of a block. The IBC prediction mode or palette mode may be used for content video/video coding such as a game, such as screen content coding (SCC). IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction in that a reference block is derived in the current picture. That is, the IBC can use at least one of the inter prediction techniques described in this document. The palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, information on the palette table and palette index may be signaled by being included in the video/image information.

The intra prediction unit 331 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located apart depending on a prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The intra prediction unit 331 may determine a prediction mode applied to the current block using a prediction mode applied to neighboring blocks.

The inter prediction unit 332 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. At this time, to reduce the amount of motion information transmitted in the inter prediction mode, motion information may be predicted in units of blocks, subblocks, or samples based on the correlation of motion information between a neighboring block and a current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring block may include a spatial neighboring block present in the current picture and a temporal neighboring block present in the reference picture. For example, the inter prediction unit 332 may construct a motion information candidate list based on neighboring blocks, and derive a motion vector and/or reference picture index of the current block based on the received candidate selection information. Inter-prediction may be performed based on various prediction modes, and information on the prediction may include information indicating a mode of inter-prediction for the current block.

The adder 340 reconstructs the obtained residual signal by adding it to the predicted signal (predicted block, predicted sample array) output from the predictor (including the inter predictor 332 and/or the intra predictor 331) A signal (restored picture, reconstructed block, reconstructed sample array) 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 a reconstructed block.

The adding unit 340 may be called a restoration unit or a restoration block generation unit. The generated reconstructed signal may be used for intra prediction of a next processing target block in a current picture, may be output through filtering as described below, or may be used for inter prediction of a next picture.

Meanwhile, LMCS (luma mapping with chroma scaling) may be applied in a picture decoding process.

The filtering unit 350 may apply subjective/objective filtering to improve subjective/objective image quality. For example, the filtering unit 350 may generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and the modified reconstructed picture may be a DPB of the memory 360, specifically, the memory 360 Can be transferred to. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.

The (corrected) reconstructed picture stored in the DPB of the memory 360 may be used as a reference picture in the inter prediction unit 332. The memory 360 may store motion information of a block from which motion information in a current picture is derived (or decoded) and/or motion information of blocks in a picture that has already been reconstructed. The stored motion information may be transmitted to the inter prediction unit 260 to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory 360 may store reconstructed samples of blocks reconstructed in the current picture, and may transmit the reconstructed samples to the intra prediction unit 331.

In the present specification, the embodiments described in the filtering unit 260, the inter prediction unit 221, and the intra prediction unit 222 of the encoding device 200 are respectively the filtering unit 350 and the inter prediction of the decoding device 300. The unit 332 and the intra prediction unit 331 may be applied to the same or corresponding.

Meanwhile, for example, as described above, the encoding device/decoding device may generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture in order to improve subjective/objective image quality. The modified reconstructed picture may be stored in the memory of the encoding device/decoding device, specifically, the DPB of the memory 270. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.

Specifically, the deblocking filtering may be performed as described below.

As described above, the encoding device/decoding device may reconstruct a picture in block units. When such block-based image reconstruction is performed, block distortion may occur at a boundary between blocks in a reconstructed picture. Therefore, the encoding device and the decoding device may use a deblocking filter to remove block distortion occurring in a boundary between blocks in the reconstructed picture.

Accordingly, the encoding device/decoding device may derive a boundary between blocks in which deblocking filtering in a reconstructed picture is performed. Meanwhile, a boundary on which deblocking filtering is performed may be referred to as an edge. In addition, the boundary on which the deblocking filtering is performed may include two types, and the two types may be a vertical boundary and a horizontal boundary. The vertical boundary may be referred to as a vertical edge, and the horizontal boundary may be referred to as a horizontal edge. The encoding device/decoding device may perform deblocking filtering on a vertical edge and deblocking filtering on a horizontal edge.

When performing deblocking filtering for one direction (that is, deblocking filtering for a vertical boundary or deblocking filtering for a horizontal boundary), referring to FIG. 4, the encoding device/decoding device may derive a transform block boundary. (S400). The encoding device/decoding device may derive a coding subblock boundary (S410).

The encoding device/decoding device may derive a block boundary on which deblocking filtering is performed based on an NxN size grid.

For example, the encoding device/decoding device may derive a block boundary on which the deblocking filtering is performed based on whether a boundary of a block (transformation block or coding sub-block) corresponds to the NxN size grid. In other words, for example, the encoding device/decoding device determines a block boundary on which the deblocking filtering is performed based on whether a boundary of a block (transformation block or coding subblock) is a block boundary located on the NxN size grid. Can be derived. The encoding device/decoding device may derive a block boundary where the deblocking filtering is performed on a boundary of a block corresponding to the NxN size grid. Here, the NxN size grid may mean a boundary derived by dividing a reconstructed picture into an NxN size square.

5 shows an example of deriving a block boundary on which deblocking filtering is performed based on an 8x8 grid. For example, as shown in FIG. 5, deblocking filtering target boundaries may be derived.

The dotted line shown in FIG. 5 may represent an 8x8 grid, the solid line may indicate the boundary of blocks in the reconstructed picture, and the thick solid line may represent a block boundary derived from which deblocking filtering is performed. For example, when an 8x8 grid is used, the encoding device/decoding device may derive a block boundary where the deblocking filtering is performed on the boundary of a block corresponding to the 8x8 grid as illustrated in FIG. 5.

Referring back to FIG. 4, the encoding device/decoding device may determine a boundary strength (bS) for a boundary for which deblocking filtering is performed (S420). The bS may also be referred to as boundary filtering strength.

The encoding device/decoding device may determine the bS based on blocks adjacent to a boundary where the deblocking filtering is performed. For example, it may be assumed that a bS value is obtained for a boundary (block edge) between block P and block Q. In this case, the encoding device/decoding device determines the bS value for the boundary based on the location of the block P and the block Q and/or information on whether the block P and the block Q are coded in intra mode. Can.

As an example, the bS may be determined as shown in the following table.

Here, p may denote a sample of a block P adjacent to the deblocking filtering target boundary, and q may denote a sample of a block Q adjacent to the deblocking filtering target boundary.

Further, for example, p0 may represent a sample of a block adjacent to the left or upper side of the deblocking filtering target boundary, and q0 may represent a sample of a block adjacent to the right or lower side of the deblocking filtering target boundary. have. For example, when the direction of the target boundary is a vertical direction (that is, when the target boundary is a vertical boundary), p0 may represent a sample of a block adjacent to the left side of the deblocking filtering target boundary, and q0 is the A sample of a block adjacent to the right side of the boundary to be deblocked can be represented. Alternatively, as an example, when the direction of the target boundary is horizontal (ie, when the target boundary is a horizontal boundary), p0 may represent a sample of a block adjacent to an upper side of the deblocking filtering target boundary, and q0 is A sample of a block adjacent to a lower boundary of the deblocking filtering target boundary may be represented.

Referring back to FIG. 4, the encoding device/decoding device may perform deblocking filtering based on the bS.

For example, the encoding device/decoding device may determine whether a filtering process for all block boundaries in the reconstructed picture has been performed (S430), and if no filtering process for all block boundaries has been performed, the encoding device/decoding device It may be determined whether the position of the boundary of the sub-block corresponds to an NxN size grid (eg, 8x8 grid) (S440). For example, it may be determined whether the remainder derived by dividing the x component and the y component of the boundary position of the sub-block by N is 0. If the remainder derived by dividing the x component and the y component of the boundary location of the subblock by N is 0, the location of the boundary of the subblock may correspond to an NxN size grid.

When the position of the boundary of the sub-block corresponds to an NxN size grid, the encoding device/decoding device may perform deblocking filtering for the boundary based on bS for the boundary (S450).

Meanwhile, a filter applied to a boundary between blocks may be determined based on the determined bS value. The filter can be divided into a strong filter (strong filter) and a weak filter (weak filter). The encoding device/decoding device can improve encoding efficiency by filtering with a different filter on a boundary of a location at which a block distortion is likely to occur and a boundary at a location at which a block distortion is likely to occur in the reconstructed picture.

The encoding device/decoding device may perform deblocking filtering on a boundary between blocks using the determined filter (for example, a strong filter or a weak filter).

When all of the deblocking filtering processes for the boundaries derived from performing the deblocking filtering are performed, the deblocking filtering process may be terminated.

Meanwhile, this document proposes a method of performing deblocking filtering on sub-block boundaries aligned to an NxN size grid. When prediction is performed by being divided into sub-block units, blocking artifacts may occur at a sub-block boundary, which is a prediction boundary, and thus, visual quality (by performing de-blocking filtering on a sub-block boundary aligned to an NxN size grid) visual quality).

In one embodiment of the present document, a method of performing deblocking filtering on sub-block boundaries of luma components arranged in an 8x8 size grid is proposed. That is, as an embodiment, a method of performing the deblocking filtering on a boundary of a block corresponding to an 8x8 size grid may be proposed. In other words, as an embodiment, a method of performing the deblocking filtering on a boundary of a block located on an 8x8 size grid may be proposed.

For example, the coding sub-block boundary derivation process according to this embodiment may be derived as shown in the following table.

Referring to Table 2 above, a coding sub-block boundary in which deblocking filtering is performed in a coding block in the reconstructed picture may be derived. For example, the input of the process of deriving the coding sub-block boundary where the deblocking filtering is performed is (xCb, yCb) indicating the upper left sample position of the current coding block, and the width of the current coding block. NCbW indicating, nCbH indicating the height of the current coding block, edgeFlag indicating whether to perform deblocking filtering on a sample of the current coding block, vertical boundary or horizontal boundary, or a type of boundary in which deblocking filtering is performed is vertical It may be an edgeType indicating whether it is a boundary or a horizontal boundary, and an output of a process of deriving a coding sub-block boundary where the deblocking filtering is performed is an edgeFlag indicating whether to perform deblocking filtering on a sample of the current coding block. It may be a modified value.

Referring to Table 2, the encoding device/decoding device can derive the number of coding sub-blocks numSbX of the current coding block in the horizontal direction and the number of coding sub-blocks numSbY of the current coding block in the vertical direction as follows. .

-When the prediction mode of the current coding block is an intra prediction mode, numSbX and numSbY are 1

-Otherwise, the numSbX is set as the number of coding sub-blocks in the horizontal direction of the current coding block, and the numSbY is set as the number of coding sub-blocks in the vertical direction of the current coding block.

For example, affine inter prediction in which the current coding block derives motion information in units of sub-blocks and performs prediction in units of sub-blocks may be applied. That is, affine inter prediction using an affine motion model for deriving a motion vector for coding sub-blocks of the current coding block may be performed. Here, a detailed description of the affine inter prediction will be described later.

After the numSbX and the numSbY are derived, when the edgeType is a vertical boundary, the encoding device/decoding device may set edgeFlags[ i * nCbW / numSbX ][ k] to 1. Here, i = 1.., numSbX-1, k = 0..nCbH-1. That is, the encoding device/decoding device may set edgeFlag for vertical borders of coding sub-blocks in the current coding block to 1. In other words, the encoding device/decoding device may derive vertical boundary boundaries of coding sub-blocks in the current coding block as a boundary where deblocking filtering is performed.

In addition, after the numSbX and the numSbY are derived, when the edgeType is a horizontal boundary, the encoding device/decoding device may set edgeFlags[ k ][ j * 8, nCbH / numSbY] to 1. Alternatively, after the numSbX and the numSbY are derived, when the edgeType is a horizontal boundary, the encoding device/decoding device may set edgeFlags[ k ][ j * nCbH / numSbY] to 1. Here, j = 1.. numSbY-1, k = 0..nCbW-1 may be. That is, the encoding device/decoding device may set edgeFlag for horizontal borders of coding sub-blocks in the current coding block to 1. In other words, the encoding device/decoding device may derive horizontal boundary boundaries of coding sub-blocks in the current coding block as a boundary where deblocking filtering is performed.

Meanwhile, for example, a process of determining whether a vertically coded sub-block boundary according to the present embodiment is a boundary on an 8x8 grid and performing deblocking filtering may be derived as shown in the following table.

Referring to Table 3 above, the variable xN may be set to a larger value of 0 and (( nCbW / 4)-1), and the variable yN may be set to a larger value of 0 and (( nCbH / 4)-1). Can.

Also, referring to Table 3 above, the following process is performed for xD _k with k<<2 when k = 0..xN and with yD _m with m<<2 when m = 0..yN. Can be.

For example, if the remainder (i.e., xD _k %8) derived by dividing xD _k by 8 is 0, and bS for a sample of (xD _k, yD _m ) coordinates is greater than 0, coding in the vertical direction Deblocking filtering on sub-block boundaries may be performed. When the remainder derived by dividing xD _k by 8 is 0, it may be a case where a block boundary adjacent to a sample of (xD _k _, yD _m ) coordinates is a boundary on an 8x8 grid. When the remainder (i.e., xD _k %8) derived by dividing xD _k by 8 is 0, and bS for a sample of (xD _k _, yD _m ) coordinates is greater than 0, of the coding subblock boundary in the vertical direction Variables dE, dEp, dEq, and t _C for deblocking filtering may be derived, and deblocking filtering on the coding sub-block boundary in the vertical direction may be performed based on the variables.

In addition, for example, a process of determining whether a horizontal coding sub-block boundary according to the present embodiment is a boundary on an 8x8 grid and performing deblocking filtering may be derived as shown in the following table.

Referring to Table 4 above, the variable yN may be set to a larger value among 0 and (( nCbH / 4)-1), and the variable xN may be set to a larger value among 0 and (( nCbW / 4)-1). Can.

Further, the above-mentioned reference to a table 4 m = 0..yN one when m is 2 << yD _m and k = 0..xN one when k << 2 is subject to the following processes performed on the _k xD have.

For example, the coding in the horizontal direction when the remainder (ie, yD _m %8) derived by dividing yD _m by 8 is 0, and bS for a sample of (xD _k, yD _m ) coordinates is greater than 0 Deblocking filtering on sub-block boundaries may be performed. When the remainder derived by dividing yD _m by 8 is 0, it may be a case where a block boundary adjacent to a sample of (xD _k _, yD _m ) coordinates is a boundary on an 8x8 grid. If the remainder (ie, yD _m %8) derived by dividing yD _m by 8 is 0, and bS for a sample of (xD _k _, yD _m ) coordinates is greater than 0, the horizontal coding subblock boundary Variables dE, dEp, dEq, and t _C for deblocking filtering may be derived, and deblocking filtering on the coding sub-block boundary in the horizontal direction may be performed based on the variables.

Meanwhile, the above-described affine inter prediction may be performed as follows.

Specifically, an affine motion model that efficiently derives motion vectors for sub-blocks of a current block and increases inter prediction accuracy despite variations such as rotation, zoom-in, or zoom-out of an image has been proposed. That is, an affine motion model for deriving a motion vector for sub-blocks of a current block has been proposed. Here, the current block may be a coding block, and the sub-blocks of the current block may be coding sub-blocks of the coding block.

For example, the affine inter prediction using the affine motion model can efficiently express four movements, that is, four transformations as described later, as described later.

6 exemplarily shows a movement expressed through the affine movement model. Referring to FIG. 6, movements that can be expressed through the affine movement model may include translation movements, scale movements, rotate movements, and shear movements. That is, as well as the translational motion in which the image (part of) is flatly moved according to the passage of time shown in FIG. 6, as well as the scale movement in which the image (part of) is scaled according to the passage of time, according to the passage of time The rotational motion in which the image (part of) is rotated, and the shear motion in which the image (part of) is transformed in an equilibrium quadrilateral over time can be efficiently expressed through the affine inter prediction.

The encoding device/decoding device may predict the distortion form of the image based on motion vectors at control points (CPs) of the current block through the affine inter prediction, thereby increasing prediction accuracy. It is possible to improve the compression performance of the image. In addition, a motion vector for at least one control point of the current block may be derived by using a motion vector of a neighboring block of the current block, thereby reducing the burden of data amount for additional information and improving inter prediction efficiency. It can be improved significantly.

As an example of the affine inter prediction, motion information at three control points, that is, three reference points may be required.

When the top-left sample position in the current block 700 is referred to as (0,0), (0,0), (w, 0), (0, as shown in FIG. 7 above) h) Sample positions can be set with the control points. Hereinafter, the control point of the (0,0) sample position is CP0, the control point of the (w, 0) sample position is CP1, and the control point of the (0,h) sample position is CP2.

Equations for the affine motion model may be derived using the above-described respective control points and motion vectors for the corresponding control points. The equation for the affine motion model can be expressed as follows.

Here, w represents the width of the current block 700, h represents the height of the current block 700, and v _0x , v _0y are the x components of the motion vector of CP0, y Component, v _1x and v _1y denote the x component and y component of the CP1 motion vector, respectively, and v _2x and v _2y denote the x component and y component of the CP2 motion vector, respectively. In addition, x represents the x component of the position of the target sample in the current block 700, y represents the y component of the position of the target sample in the current block 700, and v _x is the current block 700 ) X component of the motion vector of the target sample, v _y represents the y component of the motion vector of the target sample in the current block 700.

Since the motion vector of the CP0, the motion vector of the CP1, and the motion vector of the CP2 are known, a motion vector according to the sample position in the current block may be derived based on Equation (1). That is, according to the affine motion model, motion vectors v0 (v _0x , v _0y ) at the control points based on a distance ratio between the coordinates (x, y) of the target sample and three control points, Since v1(v _1x , v _1y ), v2(v _2x , v _2y ) is scaled, a motion vector of the target sample according to the target sample position may be derived. That is, according to the affine motion model, motion vectors of each sample in the current block may be derived based on motion vectors of the control points. Meanwhile, a set of motion vectors of samples in the current block derived according to the affine motion model may be represented as an affine motion vector field (MVF).

Meanwhile, the six parameters for Equation 1 may be represented by a, b, c, d, e, f as in the following equation, and the equation for the affine motion model represented by the six parameters is Can be equal to

The affine motion model or the affine inter prediction using the six parameters may be represented as a six-parameter affine motion model or AF6.

Further, as an example of the affine inter prediction, motion information at two control points, that is, two reference points may be required.

8 exemplarily shows the affine motion model in which motion vectors for two control points are used. The affine movement model using two control points can express three movements including translational movement, scale movement, and rotational movement. The affine motion model representing the three motions may also be referred to as a simplicity affine motion model or a simplified affine motion model.

When the top-left sample position in the current block 800 is (0,0), (0,0), (w, 0) sample positions as shown in FIG. Control points can be set. Hereinafter, the control point of the (0,0) sample position is CP0, and the control point of the (w, 0) sample position is CP1.

Here, w denotes the width of the current block 800, v _0x and v _0y denote the x component and y component of the CP0 motion vector, respectively, and v _1x and v _1y denote the CP1 motion vector, respectively. It represents x component and y component. In addition, x represents the x component of the position of the target sample in the current block 800, y represents the y component of the position of the target sample in the current block 800, and v _x is the current block 800 ) X component of the motion vector of the target sample, v _y represents the y component of the motion vector of the target sample in the current block 800.

Meanwhile, the four parameters for Equation 3 may be represented by a, b, c, d as in the following equation, and the equation for the affine motion model represented by the four parameters may be as follows. .

Here, w denotes the width of the current block 800, v _0x and v _0y denote the x component and y component of the CP0 motion vector, respectively, and v _1x and v _1y denote the CP1 motion vector, respectively. It represents x component and y component. In addition, x represents the x component of the position of the target sample in the current block 800, y represents the y component of the position of the target sample in the current block 800, and v _x is the current block 800 ) X component of the motion vector of the target sample, v _y represents the y component of the motion vector of the target sample in the current block 800. The affine motion model using the two control points can be represented by four parameters a, b, c, and d as in Equation 4, and the affine motion model using the four parameters Alternatively, the affine inter prediction may be represented by a 4-parameter affine motion model or AF4. That is, according to the affine motion model, motion vectors of each sample in the current block may be derived based on motion vectors of the control points. Meanwhile, a set of motion vectors of samples in the current block derived according to the affine motion model may be represented as an affine motion vector field (MVF).

On the other hand, as described above, through the affine motion model, a motion vector in units of samples may be derived, and through this, accuracy of inter prediction may be significantly improved. However, in this case, the complexity in the process of motion compensation may be greatly increased.

Accordingly, it is possible to limit the motion vector of the sub-block in the current block to be derived instead of the motion vector of the sample unit.

9 exemplarily shows a method of deriving a motion vector in units of sub-blocks based on the affine motion model. 9 exemplarily shows a case in which the size of the current block is 16×16 and motion vectors are derived in units of 4×4 sub-blocks. The sub-block may be set to various sizes, for example, when the sub-block is set to an n×n size (n is a positive integer, ex, n is 4), the current block based on the affine motion model Motion vectors may be derived in units of n×n sub-blocks, and various methods for deriving motion vectors representing each sub-block may be applied.

For example, referring to FIG. 9, a motion vector of each sub-block may be derived using a center or lower right-side sample position of each sub-block as representative coordinates. Here, the center lower right position may represent a sample position located at the lower right of the four samples located at the center of the sub-block. For example, when n is odd, one sample may be located at the center of the sub-block, and in this case, a center sample position may be used to derive a motion vector of the sub-block. However, when n is even, four samples may be located adjacent to the center of the sub-block, and in this case, the lower right sample position may be used to derive the motion vector. For example, referring to FIG. 9, representative coordinates of each sub-block may be derived from (2, 2), (6, 2), (10, 2),..., (14, 14), and encoding The apparatus/decoding apparatus may derive a motion vector of each sub-block by substituting each of the representative coordinates of the sub-blocks into Equation 1 or 3 described above. Motion vectors of sub-blocks in the current block derived through the affine motion model may be represented as affine MVF.

Meanwhile, as an example, the size of a sub-block in the current block may be derived based on the following equation.

Here, M represents the width of the sub-block, and N represents the height of the sub-block. In addition, v _0x, v _0y denotes an x component, y component of CPMV0 of the current block, respectively, v _0x, v _0y are each the current represents the CPMV1 x component, y component of the block, w is in the current block The width represents h, the height of the current block, and MvPre represents motion vector fraction accuracy. For example, the motion vector fractional accuracy may be set to 1/16.

Meanwhile, in the affine inter prediction, there may be an affine merge mode (AF_MERGE) and an affine inter mode (AF_INTER). Here, the affine inter mode may be referred to as affine MVP vector (affine motion vector prediction mode, AF_MVP).

The affine merge mode is similar to the existing merge mode in that the MVD for the motion vectors of the control points is not transmitted. That is, the affine merge mode is similar to a conventional skip/merge mode without coding for a motion vector difference (MVD) for each of two or three control points from neighboring blocks of the current block. An encoding/decoding method for performing prediction by deriving CPMV may be represented.

For example, when the AF_MRG mode is applied to the current block, MVs (ie, CPMV0 and CPMV1) for CP0 and CP1 may be derived from a neighboring block to which an affine mode is applied among neighboring blocks of the current block. That is, CPMV0 and CPMV1 of the neighboring block to which the affine mode is applied may be derived as merge candidates, and the merge candidate may be derived as CPMV0 and CPMV1 for the current block. When the affine merge mode is applied, the encoding device/decoding device may construct an affine merge candidate list based on the neighboring blocks, and the encoding device may encode neighboring blocks coded in the affine mode for deriving the CPMV of the current block. The index for can be signaled to the decoding device. The index for the neighboring block may indicate a neighboring block to be referred to in order to derive the CPMV of the current block from the list of affine merge candidates. The affine merge candidate list may be referred to as a subblock merge candidate list.

In addition, the affine inter mode derives a motion vector predictor (MVP) for the motion vectors of the control points, and a motion vector of the control points based on the received motion vector difference (MVD) and the MVP, An inter-prediction that performs prediction based on the affine MVF may be represented by deriving the affine MVF of the current block based on the motion vectors of the control points. Here, the motion vector of the control point is CPMV (Control Point Motion Vector), the MVP of the control point is CPMVP (Control Point Motion Vector Predictor), and the MVD of the control point is CPMVD (Control Point Motion Vector Difference). . Specifically, for example, the encoding device may derive a control point point motion vector predictor (CPMVP) and a control point point motion vector (CPMVP) for CP0 and CP1 (or CP0, CP1 and CP2), respectively, and the CPMVP Information and/or CPMVD, which is a difference between the CPMVP and CPMV, may be transmitted or stored. Here, when the affine inter mode is applied to the current block, the encoding device/decoding device may construct an affine MVP candidate list based on neighboring blocks of the current block, and the affine MVP candidate is a CPMVP pair ) May be referred to as a candidate, and the list of affine MVP candidates may be referred to as a CPMVP candidate list.

In addition, each affine MVP candidate may mean a combination of CP0 and CPMVP of CP1 in a four-parameter affine motion model, and CP0 in a six-parameter affine motion model. , CP1 and CP2 may mean a combination of CPMVP.

10 schematically shows a video encoding method by an encoding device according to the present document. The method disclosed in FIG. 10 may be performed by the encoding device disclosed in FIG. 2. Specifically, for example, S1500 to S1560 of FIG. 15 may be performed by the prediction unit of the encoding device, and S1570 may be performed by the entropy encoding unit of the encoding device. Further, although not shown, the process of deriving the residual sample for the current block based on the original sample and the prediction sample for the current block may be performed by the subtraction unit of the encoding device, and the current block The process of deriving reconstructed samples for the current block based on residual samples and prediction samples for the current block may be performed by an adder of the encoding apparatus, and the residual for the current block based on the residual sample The process of generating information may be performed by the conversion unit of the encoding device, and the process of encoding the residual information may be performed by the entropy encoding unit of the encoding device.

The encoding apparatus performs prediction on a coding sub-block of the coding block to generate a reconstructed picture (S1000).

The encoding apparatus may determine whether to perform inter prediction or intra prediction on a coding block, and may determine a specific inter prediction mode or a specific intra prediction mode based on RD cost. According to the determined mode, the encoding device may derive a prediction sample for the coding block. For example, the encoding apparatus may derive a prediction sample by performing affine inter prediction on the coding block.

As an example, the encoding apparatus may construct an affine merge candidate list for the coding block based on neighboring blocks of the coding block, and affine for the coding block among the affine merge candidates of the affine merge candidate list A merge candidate may be selected, and motion information of a coding sub-block of the coding block may be derived based on the affine merge candidate. Alternatively, as an example, the encoding apparatus may configure an affine MVP candidate list for the coding block based on neighboring blocks of the coding block, and the coding block for the coding block among affine MVP candidates in the affine MVP candidate list An affine MVP candidate may be selected, and control point motion vector predictors (CPMVPs) of control points (CPs) of the coding block may be derived based on the affine MVP candidates, and the coding block may include Control point motion vector difference (CPMVD) of CPs can be derived, and control point motion vector (CPMV) of the CPs can be derived based on the CPMVPs and the CPMVDs, and based on the CPMVs Motion information of a coding sub-block of the coding block may be derived.

Thereafter, the encoding device may derive a prediction sample of the coding subblock based on motion information of the coding subblock, and generate the reconstructed picture based on the prediction sample.

For example, the encoding apparatus may derive the residual sample through subtraction of the original sample and the prediction sample for the coding sub-block of the coding block, and a reconstructed sample based on the residual sample and the prediction sample You can create The encoding device may generate a reconstructed block or reconstructed picture based on the reconstructed sample.

Meanwhile, the encoding device may generate and encode prediction related information for the coding block. Also, the encoding apparatus may generate and encode an affine merge candidate index indicating the selected affine merge candidate. The prediction-related information may include the affine merge candidate index. In addition, the encoding apparatus may generate and encode an affine MVP candidate index indicating the selected affine MVP candidate. The prediction-related information may include the affine MVP candidate index.

The encoding device derives a boundary of the coding sub-block corresponding to an NxN grid as a boundary for deblocking filtering (S1010). The encoding apparatus may derive a deblocking filtering target boundary in a reconstructed picture based on an NxN grid. The NxN grid may be represented as an NxN size grid.

For example, the encoding apparatus may derive a boundary of a coding subblock of a coding block in the reconstructed picture as a boundary to be deblocked based on an NxN grid. The encoding apparatus may determine whether the boundary of the coding sub-block corresponds to the NxN grid, and when the boundary corresponds to the NxN grid, the boundary may be derived as a deblocking filtering target boundary. That is, the encoding device may derive the deblocking filtering target boundary based on whether the boundary of the coding sub-block is a boundary located on the NxN grid. Whether the boundary corresponds to the NxN grid may be determined as whether the remainder derived by dividing the x component or the y component of the location of the boundary by N is 0. For example, when the boundary is a vertical boundary, if the remainder derived by dividing the x component of the location of the boundary by N is 0, the boundary may correspond to the NxN grid, and the x component of the location of the boundary is N If the remainder derived by dividing is not 0, the boundary may not correspond to the NxN grid. Further, for example, when the boundary is a horizontal boundary, if the remainder derived by dividing the y component of the location of the boundary by N is 0, the boundary may correspond to the NxN grid, and the y component of the location of the boundary may be determined. If the remainder derived by dividing by N is not 0, the boundary may not correspond to the NxN grid. Here, the NxN grid may indicate a boundary derived by dividing the reconstructed picture into an NxN-sized square. Further, for example, the N may be 4 or 8. Also, for example, a boundary of the coding sub-block that does not correspond to the NxN grid may be excluded from the boundary for deblocking filtering.

Further, for example, the encoding apparatus may derive a boundary of a transform block for the coding block in the reconstructed picture as a boundary to be deblocked based on the NxN grid. The encoding apparatus may determine whether a boundary of the transform block for the coding block corresponds to the NxN grid, and when the boundary corresponds to the NxN grid, the boundary may be deduced as a deblocking filtering target boundary. That is, the encoding apparatus may derive the deblocking filtering target boundary based on whether the boundary of the transform block is a boundary located on the NxN grid. Whether the boundary corresponds to the NxN grid may be determined as whether the remainder derived by dividing the x component or the y component of the location of the boundary by N is 0. For example, when the boundary is a vertical boundary, if the remainder derived by dividing the x component of the location of the boundary by N is 0, the boundary may correspond to the NxN grid, and the x component of the location of the boundary is N If the remainder derived by dividing is not 0, the boundary may not correspond to the NxN grid. Further, for example, when the boundary is a horizontal boundary, if the remainder derived by dividing the y component of the location of the boundary by N is 0, the boundary may correspond to the NxN grid, and the y component of the location of the boundary may be determined. If the remainder derived by dividing by N is not 0, the boundary may not correspond to the NxN grid. Here, the NxN grid may indicate a boundary derived by dividing the reconstructed picture into an NxN-sized square. Further, for example, the N may be 4 or 8. Also, for example, a boundary of the transform block that does not correspond to the NxN grid may be excluded from the boundary for deblocking filtering.

The encoding apparatus performs deblocking filtering on the deblocking filtering target boundary to derive a modified reconstructed picture (S1020).

The encoding device may derive a boundary strength (bS) for the deblocking filtering target boundary, and perform deblocking filtering for the deblocking filtering target boundary based on the boundary strength to obtain a modified reconstructed picture. Can be created. The encoding device may perform deblocking filtering on the deblocking filtering target boundary to derive a reconstructed sample from which blocking artifacts are removed, and generate the corrected reconstructed picture based on the reconstructed sample. . Through this, blocking artifacts at a coding sub-block boundary caused by prediction performed in units of coding sub-blocks may be removed, and visual quality of a reconstructed picture may be improved.

Meanwhile, the boundary strength for the deblocking filtering target boundary may be determined based on blocks adjacent to the deblocking filtering target boundary. For example, it may be determined based on the positions of the blocks adjacent to the deblocking filtering target boundary and/or a prediction mode applied to the blocks. In addition, boundary strength for the deblocking filtering target boundary may be determined based on whether the blocks have intra prediction mode applied. For example, the boundary strength for the deblocking filtering target boundary may be determined as shown in Table 1 above.

As described above, the encoding apparatus may further apply an in-loop filtering procedure such as a SAO procedure to the modified reconstructed picture in order to improve subjective/objective image quality if necessary.

The encoding device encodes video information including prediction-related information of the coding block (S1030). The encoding device may encode image information including prediction related information of the coding block. That is, the encoding device may generate and encode prediction-related information of the coding block. The image information may include the prediction-related information. The prediction-related information may include information on an inter prediction mode or an intra prediction mode performed on the coding block. Also, the prediction-related information may include information about affine inter prediction performed on the coding block. For example, the prediction-related information may indicate that affine inter prediction is applied to the coding block. In addition, for example, the prediction-related information may include the affine merge candidate index. Alternatively, the prediction-related information may include the affine MVP candidate index, and may include information on CPMVD for CPs of the coding block.

Meanwhile, although not shown, the encoding apparatus may derive a residual sample for the coding sub-block based on the original sample and the prediction sample for the coding sub-block of the coding block, and based on the residual sample Residual information for the coding block may be generated, and the residual information may be encoded. The image information may include the residual information.

Meanwhile, the bitstream may be transmitted to a decoding device through a network or (digital) storage medium. Here, the network may include a broadcasting network and/or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD.

11 schematically shows an encoding apparatus that performs a video encoding method according to the present document. The method disclosed in FIG. 10 may be performed by the encoding device disclosed in FIG. 11. Specifically, for example, the prediction unit and/or the adder of the encoding device of FIG. 11 may perform S1000 of FIG. 10, and the filter unit of the encoding device of FIG. 11 may perform S1010 to S1020 of FIG. 10. , The entropy encoding unit of the encoding apparatus of FIG. 11 may perform S1030 of FIG. 10. Further, although not shown, the process of deriving the residual sample for the coding sub-block based on the original sample and the prediction sample for the coding sub-block of the coding block is performed by the subtraction unit of the encoding apparatus of FIG. 11. The process of generating residual information for the coding block based on the residual sample may be performed by the converter of the encoding apparatus of FIG. 11, and the process of encoding the residual information may be performed. It can be performed by the entropy encoding unit of the encoding device of FIG.

12 schematically shows an image decoding method by a decoding apparatus according to the present document. The method disclosed in FIG. 12 may be performed by the decoding apparatus disclosed in FIG. 3. Specifically, for example, S1200 of FIG. 12 may be performed by the entropy decoding unit of the decoding device, S1210 may be performed by the prediction unit and/or the addition unit of the decoding device, and S1220 to S1230 may be It can be performed by the filter unit of the decoding device. In addition, although not shown, a process of obtaining residual information on a coding block through a bitstream may be performed by an entropy decoding unit of the decoding apparatus, and coding sub of the coding block based on the residual information The process of deriving the residual sample for the block may be performed by the inverse transform unit of the decoding apparatus.

The decoding apparatus receives a bitstream including image information (S1200). The decoding apparatus may receive image information on a coding block through a bitstream. For example, the decoding apparatus may receive image information including prediction related information for the coding block through a bitstream. The image information may include prediction-related information for the coding block. The prediction-related information may include information on an inter prediction mode or an intra prediction mode performed on the coding block. The decoding apparatus may perform inter prediction or intra prediction on the coding block based on the prediction related information received through the bitstream, and derive prediction samples of the current block. In addition, for example, the decoding apparatus may perform affine inter prediction on the coding block based on the prediction-related information received through the bitstream, and may derive prediction samples of the coding block.

Also, for example, the decoding apparatus may receive image information including residual information for the coding block through a bitstream. The image information may include residual information for the coding block. The residual information may include transform coefficients for residual samples. The decoding apparatus may derive the residual sample (or residual sample array) for a coding sub-block of the coding block based on the residual information.

The decoding apparatus generates a reconstructed picture based on the image information (S1210). For example, the decoding apparatus may derive motion information of the coding sub-block of the coding block based on the image information. As an example, the decoding apparatus may configure an affine merge candidate list for the coding block based on neighboring blocks of the coding block, and the coding block may be configured to the coding block based on the affine merge candidate index included in the prediction related information. An affine merge candidate for can be selected, and motion information of a coding sub-block of the coding block can be derived based on the affine merge candidate. Alternatively, as an example, the decoding apparatus may configure an affine MVP candidate list for the coding block based on neighboring blocks of the coding block, and the coding may be based on the affine MVP candidate index included in the prediction related information. An affine MVP candidate for a block may be selected, and control point motion vector predictors (CPMVPs) of control points (CPs) of the coding block may be derived based on the affine MVP candidate, and the prediction Control point motion vector differences (CPMVDs) of the CPs of the coding block may be derived based on related information, and control point motion vectors (CPMVs) of the CPs based on the CPMVPs and the CPMVDs may be derived. It can be derived, and motion information of a coding sub-block of the coding block can be derived based on the CPMVs.

Thereafter, the decoding apparatus may derive a prediction sample of the coding sub-block based on motion information of the coding sub-block, and generate the reconstructed picture based on the prediction sample. For example, the decoding apparatus may derive a residual sample of the coding sub-block based on the residual information, and generate a reconstructed sample based on the residual sample and the prediction sample. The decoding apparatus may generate a reconstructed block or reconstructed picture based on the reconstructed sample.

The decoding apparatus derives a boundary of a coding subblock of a coding block in the reconstructed picture corresponding to an NxN grid as a boundary to be deblocked filtering (S1220). The decoding apparatus may derive a deblocking filtering target boundary in the reconstructed picture based on the NxN grid. The NxN grid may be represented as an NxN size grid.

For example, the decoding apparatus may derive a boundary of a coding subblock of a coding block in the reconstructed picture as a boundary to be deblocked based on an NxN grid. The decoding apparatus may determine whether the boundary of the coding sub-block corresponds to the NxN grid, and when the boundary corresponds to the NxN grid, the boundary may be derived as a deblocking filtering target boundary. That is, the decoding apparatus may derive the deblocking filtering target boundary based on whether the boundary of the coding sub-block is a boundary located on the NxN grid. Whether the boundary corresponds to the NxN grid may be determined as whether the remainder derived by dividing the x component or the y component of the location of the boundary by N is 0. For example, when the boundary is a vertical boundary, if the remainder derived by dividing the x component of the location of the boundary by N is 0, the boundary may correspond to the NxN grid, and the x component of the location of the boundary is N If the remainder derived by dividing is not 0, the boundary may not correspond to the NxN grid. Further, for example, when the boundary is a horizontal boundary, if the remainder derived by dividing the y component of the location of the boundary by N is 0, the boundary may correspond to the NxN grid, and the y component of the location of the boundary may be determined. If the remainder derived by dividing by N is not 0, the boundary may not correspond to the NxN grid. Here, the NxN grid may indicate a boundary derived by dividing the reconstructed picture into an NxN-sized square. Further, for example, the N may be 4 or 8. Also, for example, a boundary of the coding sub-block that does not correspond to the NxN grid may be excluded from the boundary for deblocking filtering.

Also, for example, the decoding apparatus may derive a boundary of a transform block for the coding block in the reconstructed picture as a boundary to be deblocked based on the NxN grid. The decoding apparatus may determine whether the boundary of the transform block for the coding block corresponds to the NxN grid, and when the boundary corresponds to the NxN grid, the boundary may be derived as a deblocking filtering target boundary. That is, the decoding apparatus may derive the deblocking filtering target boundary based on whether the boundary of the transform block is a boundary located on the NxN grid. Whether the boundary corresponds to the NxN grid may be determined as whether the remainder derived by dividing the x component or the y component of the location of the boundary by N is 0. For example, when the boundary is a vertical boundary, if the remainder derived by dividing the x component of the location of the boundary by N is 0, the boundary may correspond to the NxN grid, and the x component of the location of the boundary is N If the remainder derived by dividing is not 0, the boundary may not correspond to the NxN grid. Further, for example, when the boundary is a horizontal boundary, if the remainder derived by dividing the y component of the location of the boundary by N is 0, the boundary may correspond to the NxN grid, and the y component of the location of the boundary may be determined. If the remainder derived by dividing by N is not 0, the boundary may not correspond to the NxN grid. Here, the NxN grid may indicate a boundary derived by dividing the reconstructed picture into an NxN-sized square. Further, for example, the N may be 4 or 8. Also, for example, a boundary of the transform block that does not correspond to the NxN grid may be excluded from the boundary for deblocking filtering.

The decoding apparatus derives a modified reconstructed picture by performing deblocking filtering on the deblocking filtering target boundary (S1230).

The decoding device may derive a boundary strength (bS) for the deblocking filtering target boundary, and perform deblocking filtering on the deblocking filtering target boundary based on the boundary strength to obtain a corrected reconstructed picture. Can be created. The decoding device may perform deblocking filtering on the deblocking filtering target boundary to derive a reconstructed sample from which blocking artifacts are removed, and generate the corrected reconstructed picture based on the reconstructed sample. . Through this, blocking artifacts at a coding sub-block boundary caused by prediction performed in units of coding sub-blocks may be removed, and visual quality of a reconstructed picture may be improved.

As described above, the decoding apparatus may further apply an in-loop filtering procedure such as a SAO procedure to the modified reconstructed picture in order to improve subjective/objective image quality if necessary.

13 schematically shows a decoding apparatus performing an image decoding method according to the present document. The method disclosed in FIG. 12 may be performed by the decoding apparatus disclosed in FIG. 13. Specifically, for example, the entropy decoding unit of the decoding apparatus of FIG. 13 may perform S1200 of FIG. 12, the prediction unit and/or adder of the decoding apparatus of FIG. 13 may perform S1210 of FIG. 12, The filter unit of the decoding apparatus of FIG. 13 may perform S1220 to S1230 of FIG. 12. In addition, although not shown, the process of obtaining image information including residual information on a coding block through a bitstream may be performed by the entropy decoding unit of the decoding apparatus of FIG. 13, and the residual information The process of deriving the residual samples for the coding sub-block of the coding block based on it may be performed by the inverse transform unit of the decoding apparatus of FIG. 13.

According to this document described above, it is possible to improve the visual quality of the overall video/video.

In addition, according to this document, deblocking filtering that effectively removes blocking artifacts of a sub-block boundary due to prediction performed in units of sub-blocks can be performed, thereby improving subjective/objective visual quality.

In the above-described embodiment, the methods are described based on a flow chart as a series of steps or blocks, but this document is not limited to the order of the steps, and some steps may occur in a different order or simultaneously with other steps as described above. have. In addition, those skilled in the art will understand that the steps shown in the flowchart are not exclusive, other steps may be included, or one or more steps in the flowchart may be deleted without affecting the scope of this document.

The embodiments described in this document may be implemented and implemented on a processor, microprocessor, controller, or chip. For example, the functional units shown in each figure may be implemented and implemented on a computer, processor, microprocessor, controller, or chip. In this case, information for implementation (ex. information on instructions) or an algorithm may be stored in a digital storage medium.

In addition, the decoding device and the encoding device to which the embodiments of the present document are applied include a multimedia broadcast transmission/reception device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video communication device, and a real time communication device such as video communication , Mobile Streaming Device, Storage Media, Camcorder, Video On Demand (VoD) Service Provider, OTT Video (Over the top video) Device, Internet Streaming Service Provider, 3D (3D) Video Device, Video Phone Video Device, Transportation It may be included in a terminal (ex. vehicle terminal, airplane terminal, ship terminal, etc.) and a medical video device, and may be used to process a video signal or a data signal. For example, the OTT video (Over the top video) device may include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smartphone, a tablet PC, and a digital video recorder (DVR).

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

In addition, embodiments of the present document may be implemented as computer program products using program codes, and the program codes may be executed on a computer according to embodiments of the present document. The program code can be stored on a computer readable carrier.

The content streaming system to which the embodiments of the present document are applied may largely include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

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

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

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

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

Examples of the user device include a mobile phone, a smart phone, a laptop computer, a terminal for digital broadcasting, a personal digital assistants (PDA), a portable multimedia player (PMP), navigation, a slate PC, Tablet PCs, ultrabooks, wearable devices, e.g., smartwatches, smart glass, head mounted display (HMD), digital TV, desktop Computers, digital signage, and the like. Each server in the content streaming system can be operated as a distributed server, and in this case, data received from each server can be distributed.

Claims

In the video decoding method performed by the decoding device,

Receiving a bitstream including image information;

Generating a reconstructed picture based on the image information;

Deriving a boundary of a coding subblock of a coding block in the reconstructed picture corresponding to an NxN grid as a deblocking filtering target boundary; And

And performing deblocking filtering on the deblocking filtering target boundary to derive a corrected reconstructed picture.
According to claim 1,

The N is 4 or 8, characterized in that the video decoding method.
According to claim 1,

Generating the reconstructed picture,

Deriving motion information of the coding sub-block of the coding block based on the image information;

Deriving a prediction sample of the coding sub-block based on motion information of the coding sub-block; And

And generating the reconstructed picture based on the prediction sample.
According to claim 3,

The coding sub-block of the coding block, characterized in that the luma component (luma component) block.
According to claim 1,

The boundary of the coding sub-block that does not correspond to the NxN grid is excluded from the deblocking filtering target boundary.
According to claim 1,

When the boundary of the coding sub-block is a vertical boundary, if the remainder derived by dividing the x component of the position of the boundary by N is 0, the boundary corresponds to the NxN grid.
According to claim 1,

When the boundary of the coding sub-block is a horizontal boundary, if the remainder derived by dividing the y component of the position of the boundary by N is 0, the boundary corresponds to the NxN grid.
In the video encoding method performed by the encoding device,

Generating a reconstructed picture by performing prediction on a coding sub-block of the coding block;

Deriving a boundary of the coding sub-block corresponding to an NxN grid as a boundary for deblocking filtering;

Deriving a corrected reconstructed picture by performing deblocking filtering on the deblocking filtering target boundary; And

And encoding video information including prediction-related information of the coding block.
The method of claim 8,

The N is 4 or 8, characterized in that the video encoding method.
The method of claim 8,

The coding sub-block of the coding block is a luma component block.
The method of claim 8,

A method of encoding an image, wherein a boundary of the coding sub-block that does not correspond to the NxN grid is excluded from the boundary to be deblocked.
The method of claim 8,

When the boundary of the coding sub-block is a vertical boundary, if the remainder derived by dividing the x component of the position of the boundary by N is 0, the boundary corresponds to the NxN grid.
The method of claim 8,

When the boundary of the coding sub-block is a horizontal boundary, if the remainder derived by dividing the y component of the position of the boundary by N is 0, the boundary corresponds to the NxN grid.
As a computer-readable digital storage medium, a decoding device,

Generating a reconstructed picture based on the image information included in the bitstream;

Deriving a boundary of a coding subblock of a coding block in the reconstructed picture corresponding to an NxN grid as a deblocking filtering target boundary; And

And performing deblocking filtering on the deblocking filtering target boundary to derive a corrected reconstructed picture.
The method of claim 14,

The N is 4 or 8, characterized in that the digital storage medium.