Image encoding / decoding apparatus and image data transmitting apparatus

Abstract

The present application relates to an image encoding / decoding apparatus and an image data transmitting apparatus. An image decoding method according to the present application includes the steps of deriving a history-based motion vector prediction (HMVP) buffer of a current block; deriving motion information of the current block based on HMVP candidates included in the HMVP buffer; generating predicted samples of the current block based on the motion information; and generating restored samples based on the predicted samples, wherein the HMVP buffer is initialized when a first CTU in a CTU row in which a current CTU including the current block is located is processed.

Description

[0001] This application is a divisional application of the original invention patent application No. 201980053553.4 (International Application No.: PCT / KR2019 / 010312, Application Date: August 13, 2019, Invention Title: Inter-frame Prediction Method and Apparatus Based on Historical Motion Vectors). Technical Field

[0002] This disclosure relates to image coding techniques, and more specifically, to an inter-frame prediction method and apparatus based on historical motion vectors. Background Technology

[0003] Recently, there has been a growing demand for high-resolution, high-quality images / videos, such as 4K or 8K Ultra High Definition (UHD) images / videos, across various fields. As image / video resolution or quality increases, relatively more information or bits are transmitted compared to traditional image / video data. Therefore, if image / video data is transmitted via media such as existing wired / wireless broadband lines or stored in traditional storage media, the costs of transmission and storage can easily increase.

[0004] In addition, there is growing interest and demand for virtual reality (VR) and artificial reality (AR) content, as well as immersive media such as holograms; and the broadcasting of images / videos that exhibit characteristics different from actual images / videos (e.g., game images / videos) is also increasing.

[0005] Therefore, highly efficient image / video compression technology is needed to effectively compress and send, store, or play high-resolution, high-quality images / videos that exhibit the various characteristics described above. Summary of the Invention

[0006] Technical issues

[0007] The purpose of this disclosure is to provide a method and apparatus for increasing image coding efficiency.

[0008] Another objective of this disclosure is to provide an efficient inter-frame prediction method and apparatus.

[0009] Another objective of this disclosure is to provide a method and apparatus for deriving history-based motion vectors.

[0010] Another objective of this disclosure is to provide a method and apparatus for efficiently deriving history-based motion vector prediction (HMVP) candidates.

[0011] Another object of this disclosure is to provide a method and apparatus for efficiently initializing an HMVP buffer.

[0012] Technical solution

[0013] Embodiments of this disclosure provide an image decoding method performed by a decoding device. The method includes the following steps: deriving a history-based motion vector prediction (HMVP) buffer for the current block; deriving motion information for the current block based on HMVP candidates included in the HMVP buffer; generating prediction samples for the current block based on the motion information; and generating reconstructed samples based on the prediction samples, wherein the HMVP buffer is initialized when processing the first sequential CTU in the CTU row containing the current CTU, and the current block is included in the current CTU.

[0014] Another embodiment of this disclosure provides a decoding device configured to perform image decoding. The decoding device includes: a predictor configured to derive a history-based motion vector prediction (HMVP) buffer for the current block, derive motion information of the current block based on HMVP candidates included in the HMVP buffer, and generate a prediction sample for the current block based on the motion information; and an adder configured to generate a reconstructed sample based on the prediction sample, and initialize the HMVP buffer when processing a first sequential CTU in the CTU row containing the current CTU, and the current block is included in the current CTU.

[0015] Another embodiment of this disclosure provides an image encoding method performed by an encoding device. The method includes the following steps: deriving a history-based motion vector prediction (HMVP) buffer for the current block; deriving motion information for the current block based on HMVP candidates included in the HMVP buffer; generating prediction samples for the current block based on the motion information; deriving residual samples based on the prediction samples; and encoding image information including information about the residual samples, wherein the HMVP buffer is initialized when processing a first sequential CTU in the CTU row containing the current CTU, and the current block is included in the current CTU.

[0016] Another embodiment of this disclosure provides an encoding apparatus configured to perform image encoding. The encoding apparatus includes: a predictor configured to derive a history-based motion vector prediction (HMVP) buffer for the current block, derive motion information of the current block based on HMVP candidates included in the HMVP buffer, and generate prediction samples for the current block based on the motion information; a residual processor configured to derive residual samples based on the prediction samples; and an entropy encoder configured to encode image information including information about the residual samples, and initialize the HMVP buffer when processing a first sequential CTU in the CTU row containing the current CTU, and the current block is included in the current CTU.

[0017] Another embodiment of this disclosure provides a digital storage medium storing image data including encoded image information generated according to an image encoding method performed by an encoding device.

[0018] Another embodiment of this disclosure provides a digital storage medium storing image data including encoded image information that causes an image decoding method to be performed by a decoding device.

[0019] Beneficial effects

[0020] According to embodiments of this disclosure, overall image / video compression efficiency can be increased.

[0021] According to embodiments of this disclosure, the amount of data that needs to be sent for residual processing can be reduced through efficient inter-frame prediction.

[0022] According to the embodiments of this disclosure, HMVP buffers can be managed efficiently.

[0023] According to embodiments of this disclosure, parallel processing can be supported through efficient HMVP buffer management.

[0024] According to embodiments of this disclosure, motion vectors for inter-frame prediction can be derived efficiently. Attached Figure Description

[0025] Figure 1 This is a diagram schematically illustrating an example of a video / image coding system to which this disclosure can be applied.

[0026] Figure 2 This is a diagram schematically illustrating the configuration of a video / image encoding device to which this disclosure can be applied.

[0027] Figure 3 This is a diagram illustrating the configuration of a video / image decoding device to which this disclosure can be applied.

[0028] Figure 4 This is a diagram illustrating an example of a video / image coding method based on inter-frame prediction.

[0029] Figure 5 This is a diagram illustrating an example of a video / image decoding method based on inter-frame prediction.

[0030] Figure 6 This is a diagram illustrating the inter-frame prediction process as an example.

[0031] Figure 7 This is an exemplary diagram illustrating spatial neighbor blocks used to derive motion information candidates in either the conventional merging or AMVP modes.

[0032] Figure 8This is a diagram that schematically illustrates an example of the decoding process based on HMVP candidates.

[0033] Figure 9 This is an example diagram illustrating the updating of the HMVP table according to the FIFO rule. Figure 10 This is an example diagram illustrating the updating of the HMVP table according to the finite FIFO rule.

[0034] Figure 11 This is an example diagram illustrating wavefront parallel processing (WPP), one of the parallel processing techniques.

[0035] Figure 12 This is an illustrative diagram that illustrates the problems when considering parallel processing applications using a general HMVP approach.

[0036] Figure 13 This is a diagram illustrating an exemplary method for initializing a history management buffer (HMVP buffer) according to an embodiment of this disclosure.

[0037] Figure 14 This is a diagram illustrating an HMVP buffer management method according to an embodiment of the present disclosure.

[0038] Figure 15 This is an illustrative diagram showing an HMVP buffer management method according to another embodiment of this disclosure.

[0039] Figure 16 This is an illustrative diagram showing an HMVP buffer management method according to another embodiment of this disclosure.

[0040] Figure 17 This is a diagram illustrating an HMVP buffer management method.

[0041] Figure 18 and Figure 19 This is a diagram schematically illustrating an example of a video / image coding method and related components that include an inter-frame prediction method according to embodiments of the present disclosure.

[0042] Figure 20 and Figure 21 This is a diagram schematically illustrating an example of an image decoding method and related components that include an inter-frame prediction method according to an embodiment of the present disclosure.

[0043] Figure 22 This is a diagram illustrating examples of content streaming systems that can be applied to the disclosures included in this document. Detailed Implementation

[0044] Because this disclosure is subject to various modifications and embodiments, specific embodiments will be shown and described in detail in the accompanying drawings. However, this is not intended to limit the disclosure to the specific embodiments. The terminology used in this specification is for describing specific embodiments only and is not intended to limit the technical spirit of the disclosure. Singular expressions include plural expressions unless the context clearly indicates otherwise. It should be understood that the terms "comprising," "having," etc., in this specification are intended to indicate the presence of the features, quantities, steps, operations, components, parts, or combinations thereof described in this specification, without precluding the possibility of the presence or addition of one or more other features, quantities, steps, operations, components, parts, or combinations thereof.

[0045] Furthermore, for ease of explanation of the different features and functions, the various configurations in the accompanying drawings described in this disclosure are shown independently, and this does not imply that each configuration is implemented by separate hardware or separate software. For example, two or more configurations may be combined to form one configuration, or one configuration may be divided into multiple configurations. Implementations in which the various configurations are integrated and / or separated are also included within the scope of this disclosure without departing from its subject matter.

[0046] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Hereinafter, the same reference numerals will be used for the same components in the drawings, and redundant descriptions of the same components may be omitted.

[0047] Figure 1 Examples of video / image coding systems to which this disclosure can be applied are shown.

[0048] Reference Figure 1 A video / image encoding system may include a first device (source device) and a second device (receiving device). The source device may transmit encoded video / image information or data to the receiving device in the form of a file or stream via a digital storage medium or network.

[0049] The source device may include a video source, an encoding device, and a transmitter. The receiving device may include a receiver, a decoding device, and a renderer. The encoding device may be referred to as a video / image encoding device, and the decoding device may be referred to as a video / image decoding device. The transmitter may be included in the encoding device. The receiver may be included in the decoding device. The renderer may include a display, and the display may be configured as a separate device or an external component.

[0050] Video sources can acquire video / images through processes that capture, synthesize, or generate video / images. Video sources may include video / image capture devices and / or video / image generation devices. For example, a video / image capture device may include one or more cameras, a video / image archive containing previously captured video / images, etc. For example, a video / image generation device may include a computer, tablet computer, and smartphone, and may generate video / images (electronically). For example, virtual video / images may be generated via a computer, etc. In this case, the video / image capture process may be replaced by a process that generates related data.

[0051] Encoding devices can encode input video / images. For compression and encoding efficiency, encoding devices can perform a series of processes such as prediction, transformation, and quantization. The encoded data (encoded video / image information) can be output as a bitstream.

[0052] The transmitter can send encoded image / image information or data, output as a bitstream, to a receiver of a receiving device in the form of a file or stream via a digital storage medium or network. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter may include elements for generating media files according to a predetermined file format and may include elements for transmission over a broadcast / communication network. The receiver can receive / extract the bitstream and send the received bitstream to a decoding device.

[0053] Decoding devices can decode video / images by performing a series of processes such as dequantization, inverse transform, and prediction, which correspond to the operations of encoding devices.

[0054] The renderer can render decoded video / images. The rendered video / images can be displayed on a monitor.

[0055] This document relates to video / image coding. For example, the methods / implementations disclosed in this document can be applied to methods disclosed in the Universal Video Coding (VVC) standard, the EVC (Essential Video Coding) standard, the AOMedia Video 1 (AV1) standard, the second-generation Audio Video Coding Standard (AVS2), or next-generation video / image coding standards (e.g., H.267 or H.268).

[0056] This document presents various implementations of video / image coding, and unless otherwise stated, these implementations can be combined with each other.

[0057] In this document, video can refer to a series of images over time. A frame typically refers to a unit representing an image within a specific time range, and a slice / tile refers to a unit that constitutes a frame in terms of coding. A slice / tile may include one or more coding tree units (CTUs). A frame may consist of one or more slices / tiles. A frame may consist of one or more tile groups. A tile group may include one or more tiles. A tile can represent a rectangular area of ​​a CTU row within a tile in a frame. A tile can be divided into multiple tiles, each tile consisting of one or more CTU rows within the tile. A tile that is not divided into multiple tiles may also be referred to as a tile. Tile scanning is a specific ordering of CTUs that divide a frame, wherein CTUs are ordered consecutively in a CTU raster scan within a tile, tiles are ordered consecutively within a tile in a tile raster scan, and tiles in a frame are ordered consecutively in a tile raster scan of a frame. A tile is a rectangular area of ​​CTUs within a specific tile column and a specific tile row in a frame. A tile column is a rectangular region of CTUs whose height is equal to the height of the frame and whose width is specified by a syntax element in the frame parameter set. A tile row is a rectangular region of CTUs whose height is specified by a syntax element in the frame parameter set and whose width is equal to the width of the frame. A tile scan is a specified ordering of CTUs that divide the frame, wherein CTUs are ordered consecutively in a tile CTU raster scan, and tiles in the frame are ordered consecutively in a frame tile raster scan. A slice comprises an integer number of tiles in the frame that can be exclusively contained in a single NAL unit. A slice can consist of a consecutive sequence of multiple complete tiles or a single complete tile. In this document, tile groups and slices are used interchangeably. For example, in this document, a tile group / tile group header may also be referred to as a slice / slice header.

[0058] A pixel or image unit can refer to the smallest unit that makes up a picture (or image). Additionally, the term "sample" can be used as the counterpart to a pixel. A sample can typically represent a pixel or pixel value, and can represent only the pixel / pixel value of the luminance component or only the pixel / pixel value of the chrominance component.

[0059] A unit can represent a basic unit of image processing. A unit may include a specific region of the image and at least one of the information associated with that region. A unit may include a luminance block and two chrominance (e.g., cb, cr) blocks. In some cases, the term "unit" may be used interchangeably with terms such as "block" or "region". In general, an M×N block may include a set (or array) of samples (or sample arrays) or transform coefficients in M ​​columns and N rows.

[0060] In this document, the terms “ / ” and “,” should be interpreted as indicating “and / or”. For example, the expression “A / B” can mean “A and / or B”. Furthermore, “A, B” can mean “A and / or B”. Additionally, “A / B / C” can mean “at least one of A, B, and / or C”. Also, “A / B / C” can mean “at least one of A, B, and / or C”.

[0061] Furthermore, in this document, the term "or" should be interpreted as indicating "and / or". For example, expressing "A or B" can include 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 as indicating "additionally or alternatively".

[0062] Figure 2 The diagram illustrates the structure of a video / image encoding apparatus to which this disclosure can be applied. In the following, a video encoding apparatus may include an image encoding apparatus.

[0063] Reference Figure 2 The encoding device 200 includes an image segmenter 210, a predictor 220, a residual processor 230, an entropy encoder 240, an adder 250, a filter 260, and a memory 270. The predictor 220 may include an inter-frame predictor 221 and an intra-frame predictor 222. The residual processor 230 may include a transform 232, a quantizer 233, a dequantizer 234, and an inverse transform 235. The residual processor 230 may also include a subtractor 231. The adder 250 may be referred to as a reconstructor or a reconstruction block generator. According to embodiments, the image segmenter 210, predictor 220, residual processor 230, entropy encoder 240, adder 250, and filter 260 may be configured by at least one hardware component (e.g., an encoder chipset or processor). Additionally, the memory 270 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium. The hardware component may also include the memory 270 as an internal / external component.

[0064] Image segmenter 210 can segment an input image (or picture or frame) input to encoding device 200 into one or more processors. For example, a processor may be referred to as a coding unit (CU). In this case, the coding unit may be recursively segmented from coding tree unit (CTU) or maximum coding unit (LCU) according to a quadtree-binary-trinary tree (QTBTTT) structure. For example, a coding unit may be segmented into multiple deeper coding units based on a quadtree structure, a binary tree structure, and / or a ternary structure. In this case, for example, a quadtree structure may be applied first, followed by a binary tree structure and / or a ternary structure. Alternatively, a binary tree structure may be applied first. The encoding process according to this document may be performed based on the final coding unit that is no longer segmented. In this case, based on the image characteristics and encoding efficiency, the maximum coding unit may be used as the final coding unit, or if necessary, the coding unit may be recursively segmented into deeper coding units, and the coding unit with the optimal size may be used as the final coding unit. Here, the encoding process may include prediction, transformation, and reconstruction processes (described later). As another example, the processor may also include a predictor (PU) or a transform unit (TU). In this case, the predictor and transform unit may be split or separated from the final encoding unit described above. The predictor may be a unit for sample prediction, and the transform unit may be a unit for deriving transform coefficients and / or a unit for deriving residual signals from transform coefficients.

[0065] In some cases, a unit can be used interchangeably with terms such as a block or region. Generally, an M×N block can represent a set of samples or transform coefficients consisting of M columns and N rows. Samples can typically represent pixels or pixel values, and may represent pixel / pixel values ​​of only the luminance component or only the chrominance component. A sample can be used as a term corresponding to a frame (or image) of pixels or picometers.

[0066] In the encoding device 200, a residual signal (residual block, residual sample array) is generated by subtracting the prediction signal (prediction block, prediction sample array) output from the inter-frame predictor 221 or the intra-frame predictor 222 from the input image signal (original block, original sample array), and the generated residual signal is sent to the converter 232. In this case, as shown, the unit in the encoder 200 that subtracts the prediction signal (prediction block, prediction sample array) from the input image signal (original block, original sample array) may be called the subtractor 231. The predictor can perform prediction on the block to be processed (hereinafter referred to as the current block) and generate a prediction block including the prediction samples of the current block. The predictor can determine whether to apply intra-frame prediction or inter-frame prediction based on the current block or CU. As described later in the description of the various prediction modes, the predictor can generate various information related to the prediction (e.g., prediction mode information) and send the generated information to the entropy encoder 240. The information about the prediction can be encoded in the entropy encoder 240 and output in the form of a bitstream.

[0067] Intra-predictor 222 can refer to samples in the current frame to predict the current block. Depending on the prediction mode, the referenced samples may be located near or separated from the current block. In intra-prediction, the prediction mode may include multiple non-directional modes and multiple directional modes. For example, non-directional modes may include DC mode and planar mode. For example, depending on the level of detail in the prediction direction, the directional modes may include 33 or 65 directional prediction modes. However, this is just an example, and more or fewer directional prediction modes may be used depending on the settings. Intra-predictor 222 can use the prediction modes applied to neighboring blocks to determine the prediction mode applied to the current block.

[0068] Inter-frame predictor 221 can deduce the prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference frame. Here, to reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted on a block, sub-block, or sample basis based on the correlation between motion information between neighboring blocks and the current block. Motion information may include motion vectors and reference frame indices. Motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, neighboring blocks may include spatially neighboring blocks existing in the current frame and temporally neighboring blocks existing in the reference frame. The reference frame including the reference block and the reference frame including the temporally neighboring block may be the same or different. The temporally neighboring block may be referred to as a juxtaposed reference block, a juxtaposed CU (colCU), etc., and the reference frame including the temporally neighboring block may be referred to as a juxtaposed frame (colPic). For example, inter-frame predictor 221 can configure a motion information candidate list based on neighboring blocks and generate information indicating which candidate is used to deduce the motion vector and / or reference frame index of the current block. Inter-frame prediction can be performed based on various prediction modes. For example, in skip mode and merge mode, the inter-frame predictor 221 can use motion information from neighboring blocks as motion information for the current block. In skip mode, unlike merge mode, residual signals may not be sent. In motion vector prediction (MVP) mode, motion vectors from neighboring blocks can be used as motion vector predictors, and the motion vector of the current block can be indicated by signaling the motion vector difference.

[0069] Predictor 220 can generate a prediction signal based on various prediction methods described below. For example, the predictor can apply not only intra-frame prediction or inter-frame prediction to predict a block, but also both intra-frame prediction and inter-frame prediction simultaneously. This can be referred to as combined intra-frame and inter-frame prediction (CIIP). Alternatively, the predictor can predict blocks based on an intra-block copy (IBC) prediction mode or a palette mode. The IBC prediction mode or palette mode can be used for content image / video coding such as screen content coding (SCC) in games, etc. IBC essentially performs prediction in the current frame, but can be performed similarly to inter-frame prediction, such that a reference block is derived in the current frame. That is, IBC can use at least one inter-frame prediction technique described in this document. The palette mode can be considered as an example of intra-frame coding or intra-frame prediction. When the palette mode is applied, the sample values ​​in the frame can be signaled based on information about the palette table and palette index.

[0070] The predicted signal generated by the predictor (including inter-frame predictor 221 and / or intra-frame predictor 222) can be used to generate a reconstructed signal or a residual signal. Transformer 232 can generate transform coefficients by applying transform techniques to the residual signal. For example, the transform technique may include at least one of Discrete Cosine Transform (DCT), Discrete Sine Transform (DST), Karhunen–Loève Transform (KLT), Graphical Based Transform (GBT), or Conditional Nonlinear Transform (CNT). Here, GBT refers to a transform obtained from a graphic when the relationship information between pixels is represented graphically. CNT refers to a transform generated based on the predicted signal generated using all previously reconstructed pixels. Furthermore, the transform processing can be applied to square pixel blocks of the same size or to blocks of variable size other than square.

[0071] Quantizer 233 quantizes the transform coefficients and sends them to entropy encoder 240, which encodes the quantized signal (information about the quantized transform coefficients) and outputs a bitstream. This information about the quantized transform coefficients can be referred to as residual information. Quantizer 233 can rearrange the block-type quantized transform coefficients into a one-dimensional vector based on the coefficient scan order, and generate information about the quantized transform coefficients based on this one-dimensional vector. Entropy encoder 240 can perform various encoding methods such as exponential Golomb, context-adaptive variable-length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). Entropy encoder 240 can encode information required for video / image reconstruction other than the quantized transform coefficients (e.g., values ​​of syntax elements, etc.) together or separately. The encoded information (e.g., encoded video / image information) can be sent or stored in NAL (Network Abstraction Layer) units as a bitstream. The video / image information may also include information about various parameter sets, such as Adaptive Parameter Set (APS), Picture Parameter Set (PPS), Sequence Parameter Set (SPS), or Video Parameter Set (VPS). Additionally, the video / image information may include general constraint information. In this document, information and / or syntactic elements transmitted from the encoding device / notified by signal to the decoding device may be included in the video / picture information. The video / image information may be encoded by the above-described encoding process and included in the bitstream. The bitstream may be transmitted via a network or stored in a digital storage medium. The network may include broadcast networks and / or communication networks, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that transmits the signal output from the entropy encoder 240 and / or a storage unit (not shown) that stores the signal may be included as an internal / external element of the encoding device 200, and alternatively, the transmitter may be included in the entropy encoder 240.

[0072] The quantized transform coefficients output from quantizer 233 can be used to generate a prediction signal. For example, the residual signal (residual block or residual sample) can be reconstructed by applying dequantization and inverse transform to the quantized transform coefficients via dequantizer 234 and inverse transformer 235. Adder 250 adds the reconstructed residual signal to the prediction signal output from inter-frame predictor 221 or intra-frame predictor 222 to generate a reconstructed signal (reconstructed frame, reconstructed block, reconstructed sample array). If the block to be processed has no residual (e.g., in the case of applying skip mode), the prediction block can be used as a reconstructed block. Adder 250 may be referred to as a reconstructor or reconstructed block generator. As described below, the generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current frame and can be filtered for inter-frame prediction of the next frame.

[0073] In addition, luminance mapping with chroma scaling (LMCS) can be applied during screen encoding and / or reconstruction.

[0074] Filter 260 can improve subjective / objective image quality by applying filtering to the reconstructed signal. For example, filter 260 can generate a modified reconstructed image by applying various filtering methods to the reconstructed image and store the modified reconstructed image in memory 270 (specifically, the DPB of memory 270). Various filtering methods may include deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc. Filter 260 can generate various filtering-related information and send the generated information to entropy encoder 240, as described later in the description of each filtering method. The filtering-related information can be encoded by entropy encoder 240 and output as a bitstream.

[0075] The modified reconstructed frame sent to memory 270 can be used as a reference frame in inter-frame predictor 221. When inter-frame prediction is applied by the encoding device, prediction mismatch between the encoding device 200 and the decoding device can be avoided and encoding efficiency can be improved.

[0076] The DPB of memory 270 can store reconstructed frames modified for use as reference frames in inter-frame predictor 221. Memory 270 can store motion information of blocks in the current frame that derive (or encode) motion information and / or motion information of already reconstructed blocks in the frame. The stored motion information can be sent to inter-frame predictor 221 and used as motion information for spatially or temporally neighboring blocks. Memory 270 can store reconstructed samples of reconstructed blocks in the current frame and can transmit the reconstructed samples to intra-frame predictor 222.

[0077] Figure 3 The structure of a video / image decoding device to which this disclosure can be applied is shown.

[0078] Reference Figure 3 The decoding device 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an intra-frame predictor 331 and an inter-frame predictor 332. The residual processor 320 may include a dequantizer 321 and an inverse transformer 322. According to embodiments, the entropy decoder 310, residual processor 320, predictor 330, adder 340, and filter 350 may be configured by hardware components (e.g., a decoder chipset or processor). Additionally, the memory 360 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium. The hardware components may also include the memory 360 as an internal / external component.

[0079] When the input includes a bitstream containing video / image information, the decoding device 300 can reconstruct and... Figure 2 The encoding device processes video / image information corresponding to the image. For example, the decoding device 300 can deduce units / blocks based on block segmentation information obtained from the bitstream. The decoding device 300 can use a processor applied in the encoding device to perform decoding. Therefore, for example, the processor for decoding can be an encoding unit, and the encoding unit can be segmented from encoding tree units or maximum encoding units according to a quadtree structure, binary tree structure, and / or ternary tree structure. One or more transform units can be derived from the encoding units. The reconstructed image signal decoded and output by the decoding device 300 can be reproduced by a reproduction device.

[0080] Decoding device 300 can receive from Figure 2The encoding device outputs a signal in the form of a bitstream, and the received signal can be decoded by the entropy decoder 310. For example, the entropy decoder 310 can parse the bitstream to derive information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets, such as adaptive parameter sets (APS), picture parameter sets (PPS), sequence parameter sets (SPS), or video parameter sets (VPS). In addition, the video / image information may also include general constraint information. The decoding device can also decode the picture based on the information about the parameter sets and / or general constraint information. The information and / or syntax elements notified / received by signals, as described later in this document, can be decoded and obtained from the bitstream through the decoding process. For example, the entropy decoder 310 decodes the information in the bitstream based on encoding methods such as exponential Golomb coding, CAVLC, or CABAC, and outputs the quantized values ​​of the syntax elements and transform coefficients of the residuals required for image reconstruction. More specifically, the CABAC entropy decoding method receives bins corresponding to each syntactic element in the bitstream, determines a context model using information about the target syntactic element, decoding information about the target block, or information about symbols / bins decoded in a previous stage, and performs arithmetic decoding on the bins by predicting the probability of bin occurrence based on the determined context model, generating symbols corresponding to the values ​​of each syntactic element. In this case, the CABAC entropy decoding method can update the context model after determining the context model by using the information of the decoded symbols / bins for the context model of the next symbol / bin. Information related to prediction from the information decoded by the entropy decoder 310 can be provided to the predictors (inter-frame predictor 332 and intra-frame predictor 331), and the residual values ​​(i.e., quantized transform coefficients and related parameter information) from the entropy decoder 310 can be input to the residual processor 320. The residual processor 320 can derive residual signals (residual blocks, residual samples, residual sample arrays). Additionally, information about filtering from the information decoded by the entropy decoder 310 can be provided to the filter 350. Furthermore, a receiver (not shown) for receiving signals output from the encoding device may be configured as an internal / external element of the decoding device 300, or the receiver may be a component of the entropy decoder 310. Additionally, the decoding device according to this document may be referred to as a video / image / picture decoding device, and the decoding device may be classified as an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include the entropy decoder 310, and the sample decoder may include at least one of a dequantizer 321, an inverse transformer 322, an adder 340, a filter 350, a memory 360, an inter-frame predictor 332, and an intra-frame predictor 331.

[0081] Dequantizer 321 can dequantize the quantized transform coefficients and output the transform coefficients. Dequantizer 321 can rearrange the quantized transform coefficients in a two-dimensional block format. In this case, the rearrangement can be performed based on the coefficient scan order performed in the encoding device. Dequantizer 321 can use quantization parameters (e.g., quantization step size information) to perform dequantization on the quantized transform coefficients and obtain the transform coefficients.

[0082] The inverse transformer 322 performs inverse transformation on the transformation coefficients to obtain the residual signal (residual block, residual sample array).

[0083] The predictor can perform prediction on the current block and generate a prediction block that includes prediction samples of the current block. The predictor can determine whether to apply intra-frame prediction or inter-frame prediction to the current block based on information about the prediction output from the entropy decoder 310, and can determine a specific intra-frame / inter-frame prediction mode.

[0084] Predictor 330 can generate prediction signals based on various prediction methods. For example, the predictor can not only apply intra-frame prediction or inter-frame prediction to predict a block, but also apply both intra-frame prediction and inter-frame prediction simultaneously. This can be referred to as combined intra-frame and inter-frame prediction (CIIP). Alternatively, the predictor can predict blocks based on an intra-block copy (IBC) prediction mode or a palette mode. IBC prediction mode or palette mode can be used for content image / video coding in games, such as screen content coding (SCC). IBC essentially performs prediction in the current frame, but can be performed similarly to inter-frame prediction, such that a reference block is derived in the current frame. That is, IBC can use at least one inter-frame prediction technique described in this document. Palette mode can be considered as an example of intra-frame coding or intra-frame prediction. When applying palette mode, sample values ​​within the frame can be signaled based on information about the palette table and palette index.

[0085] Intra-predictor 331 can refer to samples in the current frame to predict the current block. Depending on the prediction mode, the referenced samples may be located near or separated from the current block. In intra-prediction, the prediction mode may include multiple non-directional modes and multiple directional modes. Intra-predictor 331 can use the prediction modes applied to neighboring blocks to determine the prediction mode applied to the current block.

[0086] Inter-frame predictor 332 can deduce the predicted block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference frame. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted on a block, sub-block, or sample basis based on the correlation between motion information between neighboring blocks and the current block. Motion information may include motion vectors and reference frame indices. Motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, neighboring blocks may include spatially neighboring blocks existing in the current frame and temporally neighboring blocks existing in the reference frame. For example, inter-frame predictor 332 can configure a motion information candidate list based on neighboring blocks and deduce the motion vector and / or reference frame index of the current block based on the received candidate selection information. Inter-frame prediction can be performed based on various prediction modes, and the information about the prediction may include information indicating the inter-frame prediction mode of the current block.

[0087] Adder 340 generates a reconstruction signal (reconstructed frame, reconstruction block, reconstruction sample array) by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the predictor (including inter-frame predictor 332 and / or intra-frame predictor 331). If the block to be processed has no residual, such as when a skip mode is applied, the prediction block can be used as a reconstruction block.

[0088] Adder 340 may be referred to as a reconstructor or reconstruction block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current frame, and can be output through filtering as described below, or it can be used for inter-frame prediction of the next frame.

[0089] In addition, Luminance Mapping with Chroma Scaling (LMCS) can be applied in the image decoding process.

[0090] Filter 350 can improve subjective / objective image quality by applying filtering to the reconstructed signal. For example, filter 350 can generate a modified reconstructed image by applying various filtering methods to the reconstructed image and store the modified reconstructed image in memory 360 (specifically, the DPB of memory 360). For example, various filtering methods may include deblocking filtering, sample adaptive shifting, adaptive loop filtering, bilateral filtering, etc.

[0091] The (modified) reconstructed frame stored in the DPB of memory 360 can be used as a reference frame in inter-frame predictor 332. Memory 360 can store motion information of blocks in the current frame that have had their motion information derived (or decoded) and / or motion information of already reconstructed blocks in the frame. The stored motion information can be sent to inter-frame predictor 221 as motion information of spatially or temporally neighboring blocks. Memory 360 can store reconstructed samples of reconstructed blocks in the current frame and transmit the reconstructed samples to intra-frame predictor 331.

[0092] In this disclosure, the embodiments described in the filter 260, inter-frame predictor 221, and intra-frame predictor 222 of the encoding device 200 can be applied in the same way as or respectively corresponding to the filter 350, inter-frame predictor 332, and intra-frame predictor 331 of the decoding device 300. This can also be applied to unit 332 and intra-frame predictor 331.

[0093] As described above, prediction is performed during video encoding to increase compression efficiency. Therefore, a prediction block can be generated that includes prediction samples of the current block (the target encoding block). Here, the prediction block includes prediction samples in the spatial domain (or pixel domain). The prediction block is derived identically in both the encoding and decoding devices, and the encoding device can use signals to inform the decoding device about information regarding the residual between the original block and the prediction block (residual information), rather than the original sample values ​​of the original block themselves, thereby increasing image encoding efficiency. The decoding device can derive a residual block including residual samples based on the residual information, generate a reconstructed block including reconstructed samples by summing the residual block and the prediction block, and generate a reconstructed image including the reconstructed block.

[0094] Residual information can be generated through transform and quantization processes. For example, an encoding device can derive a residual block between the original block and the prediction block, derive transform coefficients by performing a transform process on residual samples (residual sample arrays) included in the residual block, and derive quantized transform coefficients by performing a quantization process on the transform coefficients, thereby signaling the relevant residual information (via a bitstream) to the decoding device. Here, residual information may include information such as the values ​​of the quantized transform coefficients, position information, transform technique, transform core, and quantization parameters. The decoding device can perform a dequantization / inverse transform process based on the residual information and derive residual samples (or residual blocks). The decoding device can generate a reconstructed frame based on the prediction block and the residual block. The encoding device can also perform a dequantization / inverse transform on the quantized transform coefficients used as a reference for inter-frame prediction of subsequent frames to derive residual blocks and generate a reconstructed frame based on them.

[0095] If inter-frame prediction is applied, the predictor of the encoding / decoding device can derive prediction samples by performing inter-frame prediction on a block-by-block basis. Inter-frame prediction can be derived in a manner that depends on data elements (e.g., sample values, motion information, etc.) of frames other than the current frame. If inter-frame prediction is applied to the current block, the prediction block (prediction sample array) of the current block can be derived based on the reference block (reference sample array) specified by the motion vector on the reference frame indicated by the reference frame index. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, the motion information of the current block can be predicted on a block, sub-block, or sample-by-sample basis based on the correlation of motion information between neighboring blocks and the current block. Motion information may include motion vectors and reference frame indices. Motion information may also include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. If inter-frame prediction is applied, neighboring blocks may include spatially neighboring blocks existing in the current frame and temporally neighboring blocks existing in the reference frame. The reference frame including the reference block and the reference frame including the temporally neighboring block may be the same or different. Temporally neighboring blocks can be referred to as collated reference blocks, collated CUs (colCU), etc., and reference frames including temporally neighboring blocks can be referred to as collated frames (colPic). For example, a candidate list of motion information can be configured based on the neighboring blocks of the current block, and a signal can be used to indicate which candidate's flag or index information is selected (used) to derive the motion vector of the current block and / or the reference frame index. Inter-frame prediction can be performed based on various prediction modes, and for example, in skip mode and (normal) merge mode, the motion information of the current block can be the same as the motion information of the selected neighboring blocks. In skip mode, unlike merge mode, residual signals may not be sent. In motion vector prediction (MVP) mode, the motion vectors of the selected neighboring blocks can be used as motion vector predictors, and the motion vector difference can be signaled. In this case, the motion vector of the current block can be derived using the sum of the motion vector predictor and the motion vector difference.

[0096] The video / image coding process based on inter-frame prediction may schematically include, for example, the following.

[0097] Figure 4 An example of a video / image coding method based on inter-frame prediction is shown.

[0098] The encoding device performs inter-frame prediction on the current block (S400). The encoding device can deduce the inter-frame prediction mode and motion information of the current block, and generate prediction samples for the current block. Here, the processes of determining the inter-frame prediction mode, deduce motion information, and generate prediction samples can be performed simultaneously, or any one of these processes can be performed before the others. For example, the inter-frame predictor of the encoding device may include a prediction mode determiner, a motion information derivator, and a prediction sample derivator. The prediction mode determiner can determine the prediction mode of the current block, the motion information derivator can deduce the motion information of the current block, and the prediction sample derivator can deduce the prediction samples for the current block. For example, the inter-frame predictor of the encoding device can search for blocks similar to the current block in a specific region (search region) of a reference frame through motion estimation, and deduce the reference block with the smallest difference from the current block or a specific reference or lower. Based on this, a reference frame index indicating the reference frame where the reference block is located can be derived, and a motion vector can be derived based on the positional difference between the reference block and the current block. The encoding device can determine the mode applicable to the current block from various prediction modes. The encoding device can compare the RD costs of various prediction modes and determine the optimal prediction mode for the current block.

[0099] For example, if a skip mode or merge mode is applied to the current block, the encoding device can construct a merge candidate list, as described later, and deduce the reference block among the reference blocks indicated by the merge candidates included in the merge candidate list that has the smallest difference with the current block or is at or below a specific reference. In this case, a merge candidate associated with the deduced reference block can be selected, and merge index information indicating the selected merge candidate can be generated and signaled to the decoding device. Motion information of the current block can be deduced using the motion information of the selected merge candidate.

[0100] As another example, if (A)MVP mode is applied to the current block, the encoding device can construct an (A)MVP candidate list, as described later, and use the motion vector of the selected MVP candidate from the motion vector predictor (MVP) candidates included in the (A)MVP candidate list as the MVP of the current block. In this case, for example, indicating that the motion vector of the reference block derived through the above motion estimation can be used as the motion vector of the current block, and the MVP candidate with the motion vector having the smallest difference from the motion vector of the current block can be the selected MVP candidate. The motion vector difference (MVD) can be derived, which is the difference obtained by subtracting the MVP from the motion vector of the current block. In this case, information about the MVD can be signaled to the decoding device. Additionally, if (A)MVP mode is applied, the value of the reference screen index can be configured as reference screen index information and signaled separately to the decoding device.

[0101] The encoding device can derive residual samples based on the predicted samples (S410). The encoding device can derive residual samples by comparing the original samples of the current block with the predicted samples.

[0102] The encoding device encodes image information including prediction information and residual information (S420). The encoding device can output the encoded image information in the form of a bitstream. The prediction information may include information about prediction mode information (e.g., skip flag, merge flag, mode index, etc.) and motion information as information related to the prediction process. The information about motion information may include candidate selection information (e.g., merge index, MVP flag, or MVP index) as information used to derive motion vectors. In addition, the information about motion information may include the aforementioned information about MVD and / or reference frame index information. Furthermore, the information about motion information may include information indicating whether to apply L0 prediction, L1 prediction, or bi prediction. The residual information is information about the residual samples. The residual information may include information about the quantized transform coefficients of the residual samples.

[0103] The output bitstream can be stored in (digital) storage media and transmitted to the decoding device, or it can be transmitted to the decoding device via a network.

[0104] Furthermore, as mentioned above, the encoding device can generate reconstructed frames (including reconstructed samples and reconstructed blocks) based on reference samples and residual samples. This is to derive the same prediction result derived by the decoding device from the encoding device, thus increasing encoding efficiency. Therefore, the encoding device can store the reconstructed frames (or reconstructed samples, reconstructed blocks) in memory and use them as reference frames for inter-frame prediction. As mentioned above, loop filtering processes, etc., can also be applied to the reconstructed frames.

[0105] The video / image decoding process based on inter-frame prediction may schematically include, for example, the following.

[0106] Figure 5 An example of a video / image decoding method based on inter-frame prediction is shown.

[0107] Reference Figure 5 The decoding device can perform operations corresponding to those performed by the encoding device. The decoding device can perform predictions on the current block and derive prediction samples based on the received prediction information.

[0108] Specifically, the decoding device can determine the prediction mode of the current block based on the received prediction information (S500). The decoding device can determine the inter-frame prediction mode applied to the current block based on the prediction mode information in the prediction information.

[0109] For example, the decoding device may determine whether to apply a merge mode or (A)MVP mode to the current block based on a merge flag. Alternatively, the decoding device may select one of a variety of inter-frame prediction mode candidates based on a mode index. Inter-frame prediction mode candidates may include skip mode, merge mode, and / or (A)MVP mode, or may include a variety of inter-frame prediction modes described later.

[0110] The decoding device derives motion information for the current block based on the determined inter-frame prediction mode (S510). For example, if a skip mode or a merge mode is applied to the current block, the decoding device may construct a merge candidate list, described later, and select a merge candidate from among the merge candidates included in the merge candidate list. The selection may be performed based on the selection information (merge index) described above. The motion information of the current block may be derived using the motion information of the selected merge candidate. The motion information of the selected merge candidate may be used as the motion information of the current block.

[0111] As another example, if (A)MVP mode is applied to the current block, the decoding device can construct an (A)MVP candidate list, as described later, and use the motion vector of the selected MVP candidate from the motion vector predictor (MVP) candidates included in the (A)MVP candidate list as the MVP of the current block. Selection can be performed based on the aforementioned selection information (MVP flag or MVP index). In this case, the MVD of the current block can be derived based on information about the MVD, and the motion vector of the current block can be derived based on the MVP and MVD of the current block. Additionally, the reference frame index of the current block can be derived based on reference frame index information. The frame indicated by the reference frame index in the reference frame list on the current block can be derived as the reference frame referenced by the inter-frame prediction of the current block.

[0112] Furthermore, as described later, motion information for the current block can be derived without forming a candidate list, and in this case, the motion information for the current block can be derived according to the process disclosed in the prediction mode described later. In this case, the aforementioned candidate list configuration can be omitted.

[0113] The decoding device can generate a prediction sample for the current block based on the motion information of the current block (S520). In this case, the decoding device can derive a reference frame based on the reference frame index of the current block, and derive the prediction sample for the current block using the sample of the reference block indicated by the motion vector of the current block on the reference frame. In this case, as described later, a prediction sample filtering process for all or some of the prediction samples of the current block can also be performed in some cases.

[0114] For example, the inter-frame predictor of the decoding device may include a prediction mode determiner, a motion information inferrer, and a prediction sample inferrer. The prediction mode determiner may determine the prediction mode of the current block based on the received prediction mode information, the motion information inferrer may infer the motion information of the current block (e.g., motion vectors and / or reference frame indices) based on information about the received motion information, and the prediction sample inferrer may infer the prediction samples of the current block.

[0115] The decoding device generates a residual sample for the current block based on the received residual information (S530). The decoding device can generate a reconstructed sample for the current block based on the predicted sample and the residual sample, and generate a reconstructed image based on it (S540). Thereafter, as described above, a loop filtering process can also be applied to the reconstructed image.

[0116] Figure 6 An example of the inter-frame prediction process is shown.

[0117] Reference Figure 6 As described above, the inter-frame prediction process may include: determining an inter-frame prediction mode, deriving motion information based on the determined prediction mode, and performing prediction (generating prediction samples) based on the derived motion information. The inter-frame prediction process may be performed by the encoding and decoding devices described above. The encoding apparatus in this document may include encoding devices and / or decoding devices.

[0118] Reference Figure 6 The encoding device determines the inter-frame prediction mode for the current block (S600). Various inter-frame prediction modes can be used to predict the current block in the frame. For example, modes such as merge mode, skip mode, motion vector prediction (MVP) mode, affine mode, sub-block merge mode, and various modes with MVD merge (MMVD) mode can be used. Alternatively, or as supplementary modes, decoder-side motion vector refinement (DMVR) mode, adaptive motion vector resolution (AMVR) mode, dual prediction with CU-level weights (BCW), bidirectional optical flow (BDOF), etc., can be used. The affine mode can be referred to as the affine motion prediction mode. The MVP mode can be referred to as the advanced motion vector prediction (AMVP) mode. In this document, some modes and / or motion information candidates derived from some modes can also be included as one of the motion information related candidates for another mode. For example, HMVP candidates can be added as merge candidates in merge / skip mode, or as MVP candidates in MVP mode. If HMVP candidates are used as motion information candidates in merge mode or skip mode, then HMVP candidates can be referred to as HMVP merge candidates.

[0119] Prediction mode information, indicating the inter-frame prediction mode of the current block, can be signaled from the encoding device to the decoding device. The prediction mode information can be included in the bitstream and received by the decoding device. The prediction mode information may include index information indicating one of several candidate modes. Alternatively, the prediction mode information may also indicate the inter-frame prediction mode via hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags. For example, the prediction mode information may indicate whether a skip mode is applied by signaling a skip flag, whether a merge mode is applied by signaling a merge flag if a skip mode is not applied, and whether an MVP mode is applied if a merge mode is not applied, or may further indicate the application of additional classification flags by signaling. Affine modes may be signaled as independent modes or as modes dependent on merge modes, MVP modes, etc. For example, affine modes may include affine merge modes and affine MVP modes.

[0120] The encoding device derives the motion information of the current block (S610). The motion information can be derived based on the inter-frame prediction mode.

[0121] The encoding device can use motion information of the current block to perform inter-frame prediction. The encoding device can derive optimal motion information for the current block through a motion estimation process. For example, the encoding device can derive motion information by searching for highly correlated similar reference blocks in a predetermined search range in a reference frame, using original blocks from the original frame as units of pixels. Block similarity can be derived based on the difference between phase-based sample values. For example, block similarity can be calculated based on the SAD (Self-Average Difference) between the current block (or its template) and a reference block (or its template). In this case, motion information can be derived based on the reference block with the minimum SAD within the search area. The derived motion information can be signaled to the decoding device based on the inter-frame prediction mode using various methods.

[0122] The encoding device performs inter-frame prediction based on the motion information of the current block (S620). The encoding device can derive the prediction samples of the current block based on the motion information. The current block, which includes the prediction samples, can be referred to as the prediction block.

[0123] Furthermore, based on the traditional merging or AMVP mode in inter-frame prediction, a method has been used to reduce the amount of motion information by using the motion vectors of the spatial / temporal neighboring blocks of the current block as motion information candidates. For example, the neighboring blocks used to derive the motion information candidates of the current block may include the lower-left neighboring block, the left neighboring block, the upper-right neighboring block, the upper neighboring block, and the upper-left neighboring block of the current block.

[0124] Figure 7 An example is shown of spatial neighbor blocks used to derive motion information candidates in either the conventional merging or AMVP modes.

[0125] Essentially, spatially neighboring blocks are restricted to those directly contacting the current block. This is to increase hardware implementability and because of the increased line buffers required to derive information about blocks far from the current block. However, using motion information from non-neighboring blocks to derive motion information candidates for the current block can construct various candidates, thereby improving performance. A history-based motion vector prediction (HMVP) method can be used to utilize motion information from non-neighboring blocks without increasing line buffers. In this document, HMVP may represent history-based motion vector prediction or a history-based motion vector predictor. According to this disclosure, inter-frame prediction can be performed efficiently and parallel processing can be supported by using HMVP. For example, embodiments of this disclosure propose various methods for managing history buffers for parallel processing, and parallel processing can be supported based on these methods. However, supporting parallel processing does not necessarily mean that parallel processing must be performed; depending on hardware performance or service type, the encoding apparatus may or may not perform parallel processing. For example, if the encoding apparatus has a multi-core processor, it may process some slices, tiles, and / or mosaics in parallel. Furthermore, even when the encoding device has a single-core processor or a multi-core processor, the encoding device can perform sequential processing while reducing the computational and memory burden.

[0126] The HMVP candidates according to the HMVP method described above may include motion information from previously encoded blocks. For example, if a previously encoded block is not adjacent to the current block, the motion information of the previously encoded blocks in the current frame according to the block encoding order is not considered the motion information of the current block. However, HMVP candidates can be considered as motion information candidates for the current block (e.g., merge candidates or MVP candidates), regardless of whether a previously encoded block is adjacent to the current block. In this case, multiple HMVP candidates can be stored in a buffer. For example, if a merge mode is applied to the current block, an HMVP candidate (HMVP merge candidate) can be added to the merge candidate list. In this case, an HMVP candidate can be added after the spatial merge candidates and temporal merge candidates included in the merge candidate list.

[0127] According to the HMVP method, motion information of previously encoded blocks can be stored in the form of a table and used as motion information candidates (e.g., merge candidates) for the current block. A table (or buffer, list) including multiple HMVP candidates can be maintained during the encoding / decoding process. This table (or buffer, list) may be referred to as an HMVP table (or buffer, list). According to embodiments of this disclosure, the table (or buffer, list) can be initialized when a new slice is encountered. Alternatively, according to embodiments of this disclosure, the table (or buffer, list) can be initialized when a new CTU row is encountered. If the table is initialized, the number of HMVP candidates included in the table can be set to zero. The size of the table (or buffer, list) can be fixed to a specific value (e.g., 5, etc.). For example, if there are inter-frame encoded blocks, the associated motion information can be added as a new HMVP candidate to the last entry of the table. The (HMVP) table may be referred to as an (HMVP) buffer or an (HMVP) list.

[0128] Figure 8 An example of an HMVP candidate-based decoding process is illustrated schematically. Here, the HMVP candidate-based decoding process may include an HMVP candidate-based inter-frame prediction process.

[0129] Reference Figure 8 The decoding device loads an HMVP table including HMVP candidates and decodes blocks based on at least one HMVP candidate. Specifically, for example, the decoding device may derive motion information for the current block based on at least one HMVP candidate and derive a predicted block (including predicted samples) by performing inter-frame prediction on the current block based on the motion information. As described above, a reconstructed block may be generated based on the predicted block. The derived motion information for the current block may be updated in the table. In this case, the motion information may be added as the last entry of the table as a new HMVP candidate. If the number of HMVP candidates previously included in the table is equal to the table size, the candidate first entered into the table may be deleted, and the derived motion information may be added as the last entry of the table as a new HMVP candidate.

[0130] Figure 9 An example is shown showing HMVP table updates based on a first-in-first-out (FIFO) rule. Figure 10 An example is shown of HMVP table updates based on finite FIFO rules.

[0131] The FIFO rule can be applied to a table. For example, if the table size (S) is 16, this indicates that the table can include 16 HMVP candidates. If more than 16 HMVP candidates are generated from previously encoded blocks, the FIFO rule can be applied, and therefore the table can include at most 16 most recently encoded motion information candidates. In this case, such as Figure 9As shown, FIFO rules can be applied to eliminate the oldest HMVP candidate, and new HMVP candidates can be added.

[0132] In addition, to further improve coding efficiency, one can also... Figure 10 The example shown applies a finite FIFO rule. (Refer to...) Figure 10 When an HMVP candidate is inserted into a table, a redundancy check is first applied. This determines whether an HMVP candidate with the same motion information already exists in the table. If an HMVP candidate with the same motion information exists, it is removed from the table, and all subsequent HMVP candidates are moved one position (i.e., every index -1), before a new HMVP candidate can be inserted.

[0133] As described above, HMVP candidates can be used during the process of constructing the merge candidate list. In this case, for example, all insertable HMVP candidates from the last entry to the first entry in the table can be inserted after the spatial merge candidate and the temporal merge candidate. In this case, a pruning check can be applied to the HMVP candidates. A signal can be used to indicate the maximum number of merge candidates allowed, and the merge candidate list construction process can end if the total number of available merge candidates reaches the maximum number of merge candidates.

[0134] Similarly, HMVP candidates can also be used in the (A) MVP candidate list construction process. In this case, the motion vectors of the last k HMVP candidates in the HMVP table can be added after the TMVP candidates that constitute the MVP candidate list. In this case, for example, HMVP candidates with the same reference frame as the MVP target reference frame can be used to construct the MVP candidate list. Here, the MVP target reference frame can represent the reference frame for the inter-frame prediction of the current block to which the MVP mode has been applied. In this case, a pruning check can be applied to the HMVP candidates. For example, k can be 4. However, this is just an example, and k can have various values ​​such as 1, 2, 3, and 4.

[0135] Furthermore, if the total number of merge candidates is equal to or greater than 15, the truncated unary plus fixed-length (3-bit) binarization method can be applied to merge index coding, as shown in Table 1 below.

[0136] Table 1

[0137]

[0138] The table assumes Nmrg = 15, where Nmrg refers to the total number of merge candidates.

[0139] Furthermore, when developing solutions that utilize video codecs, parallel processing can be supported in image / video encoding to optimize implementation.

[0140] Figure 11 Wavefront parallel processing (WPP) is illustrated as an example of a parallel processing technique.

[0141] Reference Figure 11 If WPP is applied, parallel processing can be performed on a CTU line basis. In this case, when encoding (encoding / decoding) a block labeled X, there are positions and dependencies indicated by the arrows. Therefore, it is necessary to wait for the top-right CTU of the currently encoded block to be fully encoded. Furthermore, if WPP is applied, the initialization of the CABAC (context) probability table can be performed on a slice-by-slice basis, and in order to perform parallel processing including entropy encoding / decoding, the CABAC probability table should be initialized on a CTU line basis. WPP can be viewed as a technique proposed to determine efficient initialization positions.

[0142] The HMVP method described above stores motion information derived from the encoding process of each block based on the size of a predetermined buffer (HMVP table) as candidates. In this case, such as... Figure 9 As disclosed, without any additional conditions, the number of candidates can be filled as many as the number of buffers, or the candidates can be filled without redundancy by a redundancy check between newly added candidates and those existing in the buffer (HMVP table). Therefore, a variety of candidates can be configured. However, when developing solutions that apply video codecs, it is often impossible to know when to fill the buffer with HMVP candidates, making parallel processing impossible regardless of whether WPP is applied or not.

[0143] Figure 12 This example illustrates a problem when considering parallel processing applications using a general HMVP approach.

[0144] Reference Figure 12 When parallelization is performed on a per-CTU line basis, as in WPP, a dependency problem with the HMVP buffer can occur. For example, this is because the HMVP buffer for the first sequential CTU in the Nth (N>=1)th sequential CTU line can only be filled when the encoding (encoding / decoding) of the block present in the (N-1)th sequential CTU line (e.g., the block in the last CTU of the (N-1)th sequential CTU line) is complete. That is, if parallel processing is applied under the current architecture, the decoding device may not know whether the current HMVP candidate stored in the HMVP buffer matches the HMVP buffer used to decode the current (target) block. This is because there may be differences between the HMVP buffer derived from the encoding time of the current block when applying sequential processing and the HMVP buffer derived from the encoding time of the current block when applying parallel processing.

[0145] In embodiments of this disclosure, to address the aforementioned issues, when HMVP is applied, a history management buffer (HMVP buffer) is initialized to enable parallel processing.

[0146] Figure 13 An exemplary method for initializing a history management buffer (HMVP buffer) according to an embodiment of the present disclosure is shown.

[0147] Reference Figure 13 The HMVP buffer can be initialized for each first CTU in a CTU row. That is, when encoding the first sequential CTU in a CTU row, the HMVP buffer can be initialized such that the number of HMVP candidates included in the HMVP buffer is zero. By initializing the HMVP buffer for each CTU row as described above, HMVP candidates derived from the encoding process of the CTU located to the left of the current block can be used without constraint, even when parallel processing is supported. In this case, for example, if the current CU, which is the current block, is located in the first sequential CTU in the CTU row, and the current CU corresponds to the first sequential CU in the first sequential CTU, then the number of HMVP candidates included in the HMVP buffer is zero. In addition, for example, if a CU in the CTU row encoded earlier than the current CU is encoded in inter-frame mode, then HMVP candidates can be derived based on the motion information of the earlier encoded CU and included in the HMVP buffer.

[0148] Figure 14 An HMVP buffer management method according to an embodiment of the present disclosure is illustrated by way of example.

[0149] Reference Figure 14 The HMVP buffer can be initialized in slices, and even for CTUs within a slice, it can be determined whether the encoded target CTU (current CTU) is the first-order CTU in each CTU row. Figure 14For example, if (ctu_idx % Num) is zero, it is described as being identified as the first-order CTU. Here, Num refers to the number of CTUs in each CTU row. As another example, using the above tile concept, if (ctu_idx_in_brick % BrickWidth) is zero, it can be identified as the first-order CTU in the CTU row (corresponding tile). Here, ctu_idx_in_brick refers to the index of the corresponding CTU in the tile, and BrickWidth refers to the width of the tile in units of CTUs. That is, BrickWidth can refer to the number of CTU columns in the corresponding tile. If the current CTU is the first-order CTU in the CTU row, the HMVP buffer is initialized (i.e., the number of candidates in the HMVP buffer is set to zero); otherwise, the HMVP buffer is maintained. Subsequently, prediction processing is performed on each CU in the corresponding CTU (e.g., based on merge or MVP mode), and at this time, candidates stored in the HMVP buffer under merge or MVP mode can be included as motion information candidates (e.g., merge candidates or MVP candidates). The motion information of the target block (current block) derived based on the merge or MVP mode in the inter-frame prediction processing is stored (updated) in the HMVP buffer as a new HMVP candidate. In this case, the redundancy check process described above can be further performed. The above process can then be repeated for both CUs and CTUs.

[0150] As another example, when applying HMVP, the dependency on CTU units can be eliminated by initializing the HMVP buffer for each CTU. In this case, since the HMVP buffer is initialized on a CTU-by-CTU basis, the motion information of the blocks existing in the CTU is stored in the HMVP table. In this case, HMVP candidates can be derived based on the motion information of blocks (e.g., CUs) in the same CTU, and the HMVP buffer can be initialized as follows without determining whether the current CTU is the first-order CTU in each CTU row.

[0151] Figure 15 An HMVP buffer management method according to another embodiment of this disclosure is illustrated by way of example.

[0152] Reference Figure 15 HMVP buffer initialization can be performed for each CTU without determining whether the current CTU is the first sequential CTU in each CTU row.

[0153] Furthermore, when the HMVP buffer is initialized for each CTU, only HMVP candidates derived from the motion information of the blocks present in the corresponding CTU are included in the HMVP buffer, which necessitates limiting the use of candidates derived from non-adjacent blocks. Therefore, candidates from the left CTU adjacent to the current CTU can be stored in the HMVP buffer to increase the number of available candidates.

[0154] Figure 16 An HMVP buffer management method according to another embodiment of this disclosure is illustrated by way of example.

[0155] Reference Figure 16 When there exists a current CTU (the Nth order CTU) and two CTUs to its left (i.e., the (N-1)th and (N-2)th order CTUs), the CUs existing in the current CTU can use HMVP candidates derived from the blocks in the (N-1)th order CTU. In this case, HMVP candidates derived from the blocks in the (N-2)th order CTU can be omitted and initialized or eliminated.

[0156] The HMVP buffer used to apply the methods presented in this embodiment can be controlled or managed as follows.

[0157] Figure 17 An example of an HMVP buffer management method is shown.

[0158] Reference Figure 17 When the HMVP buffer size is S (e.g., 16) (buffer indices 0 to 15), the CUs in each CTU are as follows: Figure 17 The storage shown can be represented as a block index. If the encoding of the (N-1)th sequential CTU is complete, the HMVP candidate derived from the (N-2)th sequential CTU is removed from the buffer, and motion information derived from the blocks in the current CTU is stored as an HMVP candidate in the HMVP buffer. As shown in the diagram for buffer management, CTU indicators represented by CTU indices can exist, and the encoding device can use the CTU indices to find targets to be removed from the buffer.

[0159] The size of the HMVP history management buffer (HMVP buffer) can be determined based on factors such as the performance increment of the buffer size and the computational cost of redundancy checks on candidates present in the buffer. As in the above implementation, since the buffer is initialized, the available HMVP candidates are smaller than the existing HMVP, so that even if the size of the management buffer used for the HMVP is reduced, the performance change is minimal. For example, when applying an implementation that initializes the HMVP buffer for each CTU or using HMVP candidates derived from at most the left CTU adjacent to the current CTU, the buffer size (S) can be set to 5 or 6. Alternatively, for example, when applying the above implementation that initializes the HMVP buffer for each CTU, the buffer size (S) can be set to 4 or 5, and in this case, there is almost no performance degradation. Furthermore, when determining the buffer size of the history management buffer, the application of Single Instruction Multiple Data (SIMD) can be considered. For example, if multiple (e.g., 8) data can be compared and computed at once, applying SIMD is efficient without reducing the buffer size because performance can be maintained without increasing computational complexity.

[0160] Figure 18 and Figure 19 Examples of video / image coding methods and related components that include an inter-frame prediction method according to embodiments of the present disclosure are illustrated schematically. Figure 18 The method disclosed herein can be derived from Figure 2 The encoding device disclosed herein performs the operation. Specifically, for example, Figure 18 S1800 to S1830 can be executed by the predictor 220 of the encoding device. Figure 18 S1840 in the code can be executed by the residual processor 230 of the encoding device. Figure 18 S1850 in the encoding device can be executed by the entropy encoder 240. Figure 18 The methods disclosed herein may include the embodiments described above.

[0161] Reference Figure 18 The encoding device derives the HMVP buffer for the current block (S1800). The encoding device can execute the HMVP buffer management method described above in the embodiments of this document. As an example, the HMVP buffer can be initialized in units of slices.

[0162] As another example, the HMVP buffer can be initialized at the CTU line level. The encoding device can determine whether the current CTU is the first sequential CTU in the CTU line. In this case, the HMVP buffer can be initialized in the first sequential CTU in the CTU line containing the current CTU that includes the current block. That is, the HMVP buffer can be initialized when processing the first sequential CTU in the CTU line containing the current CTU that includes the current block. If it is determined that the current CTU is the first sequential CTU in the CTU line, the HMVP buffer can include HMVP candidates derived based on motion information of blocks encoded earlier than the current block in the current CTU. If it is determined that the current CTU is not the first sequential CTU in the CTU line, the HMVP buffer can include HMVP candidates derived based on motion information of blocks encoded earlier than the current block in the current CTU and HMVP candidates derived based on motion information of blocks previously encoded in previous CTUs in the CTU line. Additionally, for example, if the current CU, which is the current block, is located in the first sequential CTU in the CTU line, and the current CU corresponds to the first sequential CU in the first sequential CTU, then the number of HMVP candidates included in the HMVP buffer is zero. Additionally, for example, if a CU encoded earlier than the current CU in a CTU row (e.g., a CU encoded earlier in the current CTU and / or a CU in a CTU encoded earlier in the current CTU row) is encoded in inter-frame mode, an HMVP candidate can be derived based on the motion information of the earlier encoded CU and included in the HMVP buffer. If a merge mode is applied to the current block, an HMVP candidate can be added to the merge candidate list of the current block if the number of available merge candidates (e.g., including spatial and temporal merge candidates) in the merge candidate list is less than a predetermined maximum number of merge candidates. In this case, the HMVP candidate can be inserted after the spatial and temporal candidates in the merge candidate list. That is, the HMVP candidate can be assigned an index value larger than the index assigned to the spatial and temporal candidates in the merge candidate list.

[0163] As another example, the HMVP buffer can be initialized in units of CTU. Alternatively, the HMVP buffer can include up to HMVP candidates derived from the left CTU of the current CTU. If the HMVP buffer is initialized, the number of HMVP candidates included in the HMVP buffer can be set to zero.

[0164] The encoding device derives motion information for the current block based on the HMVP buffer (S1810). The encoding device can derive motion information for the current block based on HMVP candidates included in the HMVP buffer. For example, if a merge mode or motion vector prediction (MVP) mode is applied to the current block, the HMVP candidates included in the HMVP buffer can be used as merge candidates or MVP candidates. For example, if a merge mode is applied to the current block, the HMVP candidates included in the HMVP buffer are included as candidates in the merge candidate list, and the HMVP candidates included in the merge candidate list can be indicated based on the merge index. The merge index can be included in the image information described later as prediction-related information. In this case, HMVP candidates can be assigned indices with lower priority than spatial merge candidates and temporal merge candidates included in the merge candidate list. That is, the index value assigned to the HMVP candidate can be a higher value than the index values ​​of the spatial merge candidates and temporal merge candidates.

[0165] The encoding device generates a prediction sample for the current block based on the derived motion information (S1820). The encoding device can derive the prediction sample by using the reference sample indicated by the motion information on the reference frame through inter-frame prediction (motion compensation) based on the motion information.

[0166] The encoding device generates residual samples based on the predicted samples (S1830). The encoding device can generate residual samples based on the original samples of the current block and the predicted samples of the current block.

[0167] The encoding device derives information about the residual samples based on the residual samples and encodes image information including the information about the residual samples (S1840). The information about the residual samples may be referred to as residual information and may include information about the quantized transform coefficients. The encoding device derives the quantized transform coefficients by performing a transform / quantization process on the residual samples.

[0168] Encoded image information can be output as a bitstream. The bitstream can be sent to a decoding device via a network or storage medium. The image information may also include prediction-related information, which may include information about various prediction modes (e.g., merge mode, MVP mode, etc.), MVD information, etc.

[0169] Figure 20 and Figure 21 Examples of image decoding methods and related components, including an inter-frame prediction method according to embodiments of the present disclosure, are illustrated schematically. Figure 20 The method disclosed herein can be derived from Figure 3 The decoding device disclosed herein performs the operation. Specifically, for example, Figure 20S2000 to S2030 can be executed by the predictor 330 of the decoding device, and S2040 can be executed by the adder 340 of the decoding device. Figure 20 The methods disclosed herein may include the embodiments described above.

[0170] Reference Figure 20 The decoding device derives the HMVP buffer for the current block (S2000). The decoding device can execute the HMVP buffer management method described above in the embodiments of this document. As an example, the HMVP buffer can be initialized in units of slices.

[0171] As another example, the HMVP buffer can be initialized on a CTU line basis. The decoding device can determine whether the current CTU is the first sequential CTU in the CTU line. In this case, the HMVP buffer can be initialized in the first sequential CTU in the CTU line containing the current CTU that includes the current block. That is, the HMVP buffer can be initialized when processing the first sequential CTU in the CTU line containing the current CTU that includes the current block. If it is determined that the current CTU is the first sequential CTU in the CTU line, the HMVP buffer can include HMVP candidates derived based on motion information of blocks decoded earlier than the current block in the current CTU. If it is determined that the current CTU is not the first sequential CTU in the CTU line, the HMVP buffer can include HMVP candidates derived based on motion information of blocks decoded earlier than the current block in the current CTU and HMVP candidates derived based on motion information of previously decoded blocks in previous CTUs in the CTU line. Additionally, for example, if the current CU, which is the current block, is located in the first sequential CTU in the CTU line, and the current CU corresponds to the first sequential CU in the first sequential CTU, the number of HMVP candidates included in the HMVP buffer is zero. Additionally, for example, if a CU encoded earlier than the current CU in a CTU row (e.g., a CU encoded earlier in the current CTU and / or a CU in a CTU encoded earlier in the current CTU row) is encoded in inter-frame mode, an HMVP candidate can be derived based on the motion information of the earlier encoded CU and included in the HMVP buffer. If a merge mode is applied to the current block, an HMVP candidate can be added to the merge candidate list of the current block if the number of available merge candidates (e.g., including spatial and temporal merge candidates) in the merge candidate list is less than a predetermined maximum number of merge candidates. In this case, the HMVP candidate can be inserted after the spatial and temporal candidates in the merge candidate list. That is, the HMVP candidate can be assigned an index value larger than the index assigned to the spatial and temporal candidates in the merge candidate list.

[0172] As another example, the HMVP buffer can be initialized in units of CTU. Alternatively, the HMVP buffer can include up to HMVP candidates derived from the left CTU of the current CTU. If the HMVP buffer is initialized, the number of HMVP candidates included in the HMVP buffer can be set to zero.

[0173] The decoding device derives motion information for the current block based on the HMVP buffer (S2010). The decoding device can derive motion information for the current block based on HMVP candidates included in the HMVP buffer. For example, if a merge mode or motion vector prediction (MVP) mode is applied to the current block, the HMVP candidates included in the HMVP buffer can be used as merge candidates or MVP candidates. For example, if a merge mode is applied to the current block, the HMVP candidates included in the HMVP buffer are included as candidates in the merge candidate list, and the HMVP candidates included in the merge candidate list can be indicated based on the merge index obtained from the bitstream. In this case, HMVP candidates can be assigned indices with lower priority than spatial merge candidates and temporal merge candidates included in the merge candidate list. That is, the index value assigned to the HMVP candidate can be a higher value than the index values ​​of the spatial merge candidates and temporal merge candidates.

[0174] The decoding device generates a prediction sample for the current block based on the derived motion information (S2020). The decoding device can derive the prediction sample by using reference samples indicated by the motion information on the reference frame through inter-frame prediction (motion compensation) based on the motion information. The current block including the prediction sample can be referred to as the prediction block.

[0175] The decoding device generates reconstructed samples based on the predicted samples (S2030). As described above, reconstructed blocks / frames can be generated based on the reconstructed samples. As described above, the decoding device can obtain residual information (including information about the quantization transform coefficients) from the bitstream, derive residual samples from the residual information, and generate reconstructed samples based on the predicted samples and the residual samples. Thereafter, as described above, loop filtering processes such as deblocking filtering, SAO, and / or ALF processes can be applied to the reconstructed frames as needed to improve subjective / objective frame quality.

[0176] In the above embodiments, the method is described based on a flowchart as a series of steps or blocks. However, this disclosure is not limited to the order of these steps, and specific steps may occur or occur simultaneously in a different order than those described above. Furthermore, those skilled in the art will understand that the steps shown in the flowchart are not exclusive and may include other steps or may be deleted from the flowchart without affecting the scope of this disclosure.

[0177] The methods described above according to this disclosure can be implemented in software, and the encoding and / or decoding devices according to this disclosure can be included in devices for performing image processing, such as TVs, computers, smartphones, set-top boxes, display devices, etc.

[0178] When the embodiments of this disclosure are implemented in software, the above methods can be implemented as modules (processes, functions, etc.) for performing the above functions. These modules can be stored in memory and executed by a processor. The memory can be located inside or outside the processor and can be connected to the processor by various well-known means. The processor may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processing devices. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. That is, the embodiments described in this disclosure can be implemented and executed on a processor, microprocessor, controller, or chip. For example, the functional units shown in the various figures can be implemented and executed on a computer, processor, microprocessor, controller, or chip. In this case, the information used for implementation (e.g., information about instructions) or algorithms can be stored in a digital storage medium.

[0179] Furthermore, the decoding and encoding devices employing this disclosure can be included in multimedia broadcasting transmitting and receiving devices, mobile communication terminals, home theater video devices, digital cinema video devices, surveillance cameras, video chat devices, real-time communication devices (e.g., video communication), mobile streaming devices, storage media, cameras, video-on-demand (VoD) service providers, over-the-top (OTT) devices, internet streaming service providers, 3D video devices, virtual reality devices, augmented reality (AR) devices, video telephony devices, transportation terminal devices (e.g., vehicle (including autonomous vehicles) terminals, aircraft terminals, ship terminals, etc.), medical video devices, etc., and can be used to process video signals or data signals. For example, over-the-top (OTT) devices may include game consoles, Blu-ray players, internet access TVs, home theater systems, smartphones, tablet PCs, digital video recorders (DVRs), etc.

[0180] Furthermore, the processing method applied to this disclosure can be generated in the form of a computer-executable program and can be stored in a computer-readable recording medium. Multimedia data having the data structure according to this disclosure can also be stored in a computer-readable recording medium. Computer-readable recording media include all types of storage devices and distributed storage devices for storing computer-readable data. For example, computer-readable recording media may include Blu-ray discs (BD), Universal Serial Bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disks, and optical data storage devices. Additionally, computer-readable recording media also include media implemented in the form of carrier waves (e.g., transmission via the Internet). Furthermore, the bitstream generated by this encoding method can be stored in a computer-readable recording medium or transmitted via wired and wireless communication networks.

[0181] Furthermore, the embodiments of this disclosure can be implemented as a computer program product using program code, and the program code can be executed on a computer using the embodiments of this disclosure. The program code can be stored on a computer-readable medium.

[0182] Figure 22 Examples of content streaming systems to which this disclosure can be applied are shown.

[0183] Reference Figure 22 The content streaming system using this disclosure may mainly include an encoding server, a streaming server, a web server, a media storage device, a user device, and a multimedia input device.

[0184] An encoding server generates a bitstream by compressing content input from a multimedia input device (e.g., a smartphone, camera, or camcorder) into digital data and then sends the generated bitstream to a streaming server. As another example, if the multimedia input device (e.g., a smartphone, camera, or camcorder) generates the bitstream directly, the encoding server can be omitted.

[0185] A bit stream can be generated by applying the encoding method or bit stream generation method disclosed herein, and the streaming server can temporarily store the bit stream while sending or receiving the bit stream.

[0186] The streaming server acts as a conduit for sending multimedia data to the user's device based on user requests via a web server, and the web server also informs the user which services are available. If a user requests a desired service from the web server, the web server forwards the request to the streaming server, and the streaming server delivers the multimedia data to the user. In this case, the content streaming system may include a separate control server, which in this scenario controls the command / response interactions between devices within the content streaming system.

[0187] A streaming server can receive content from media storage devices and / or encoding servers. For example, if content is received from an encoding server, it can be received in real time. In this case, to provide a smooth streaming service, the streaming server can store the bitstream for a predetermined period of time.

[0188] Examples of user devices may include mobile phones, smartphones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation terminals, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches or smart glasses), digital TVs, desktop computers, and digital signage.

[0189] Each individual server within the content streaming system can operate as a distributed server, and in this case, data received by each server can be processed in a distributed manner.

Claims

1. A decoding device for image decoding, the decoding device comprising: Memory; as well as At least one processor, connected to the memory, is configured to: Obtain information about the merge index from the bitstream; Derive the history-based motion vector prediction HMVP buffer for the current block; The merge candidates for configuring the merge candidate list of the current block are derived, wherein the merge candidates include spatial candidates derived based on spatial candidate blocks and temporal candidates derived based on temporal candidate blocks, wherein HMVP candidates included in the HMVP buffer are inserted as merge candidates in the merge candidate list, wherein the HMVP candidates are inserted after the temporal candidates in the merge candidate list; The motion information of the current block is derived based on the HMVP candidates in the merge candidate list; Based on the motion information, a prediction sample for the current block is generated; and Reconstructed samples are generated based on the predicted samples. Specifically, the merge index is used to indicate the HMVP candidate included in the merge candidate list. Wherein, the current block is related to the coding unit CU segmented from the coding tree unit CTU, and Specifically, the HMVP buffer is initialized at the first sequential CTU of each CTU row in the slice.

2. An encoding device for image encoding, the encoding device comprising: Memory; as well as At least one processor, connected to the memory, is configured to: Derive the history-based motion vector prediction HMVP buffer for the current block; The merge candidates for configuring the merge candidate list of the current block are derived, wherein the merge candidates include spatial candidates derived based on spatial candidate blocks and temporal candidates derived based on temporal candidate blocks, wherein HMVP candidates included in the HMVP buffer are inserted as merge candidates in the merge candidate list, wherein the HMVP candidates are inserted after the temporal candidates in the merge candidate list; The motion information of the current block is derived based on the HMVP candidates in the merge candidate list; Based on the motion information, a prediction sample for the current block is generated; The residual samples are derived based on the predicted samples; and The image information, including information about the residual samples, is encoded. The image information includes information about the merge index, which indicates the HMVP candidate included in the merge candidate list. Wherein, the current block is related to the coding unit CU segmented from the coding tree unit CTU, and Specifically, the HMVP buffer is initialized at the first sequential CTU of each CTU row in the slice.

3. An apparatus for transmitting data for an image, the apparatus comprising: At least one processor is configured to obtain a bitstream, wherein the bitstream is generated based on the following operations: deriving a history-based motion vector prediction HMVP buffer for the current block; deriving merge candidates for configuring a merge candidate list for the current block, wherein the merge candidates include spatial candidates derived based on spatial candidate blocks and temporal candidates derived based on temporal candidate blocks; wherein HMVP candidates included in the HMVP buffer are inserted as merge candidates in the merge candidate list; wherein the HMVP candidates are inserted after the temporal candidates in the merge candidate list; deriving motion information of the current block based on the HMVP candidates in the merge candidate list; generating prediction samples of the current block based on the motion information; deriving residual samples based on the prediction samples; and encoding image information including information about the residual samples; and A transmitter configured to transmit the data comprising the bit stream. The image information includes information about the merge index, which indicates the HMVP candidate included in the merge candidate list. Wherein, the current block is related to the coding unit CU segmented from the coding tree unit CTU, and Specifically, the HMVP buffer is initialized at the first sequential CTU of each CTU row in the slice.

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