Video encoding / decoding method and apparatus, and recording medium storing bitstream

Abstract

The video decoding / encoding method and apparatus according to the present disclosure can construct reference samples for linear model intra prediction based on reconstructed neighboring samples of a current block, derive linear model parameters based on the reference samples, generate predicted samples of the current block based on the linear model parameters, and decode / encode the current block based on the predicted samples of the current block.

Description

[Technical field]

[0001] The present invention relates to a video encoding / decoding method and apparatus, and a recording medium storing a bitstream. [Background technology]

[0002] 2. Description of the Related Art Recently, the demand for high-resolution, high-quality images such as high definition (HD) images and ultra high definition (UHD) images has been increasing in various application fields, and therefore, highly efficient image compression techniques have been discussed.

[0003] There are various video compression technologies, such as inter-prediction technology that predicts pixel values ​​contained in a current picture from pictures before or after the current picture, intra-prediction technology that predicts pixel values ​​contained in the current picture using pixel information within the current picture, and entropy coding technology that assigns short codes to values ​​that occur frequently and long codes to values ​​that occur less frequently. Using these video compression technologies, video data can be effectively compressed and transmitted or stored. Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a method and apparatus for deriving a linear model based on neighboring reconstructed samples and performing intra prediction using the induced linear model.

[0005] The present disclosure seeks to provide a reference sample construction method and apparatus for linear model induction.

[0006] The present disclosure seeks to provide a method and apparatus for designing diverse linear models to improve prediction accuracy.

[0007] The present disclosure seeks to provide an effective signaling method and apparatus for linear model intra prediction. [Means for solving the problem]

[0008] The video decoding method and apparatus according to the present disclosure can construct reference samples for linear model intra prediction based on reconstructed neighboring samples of a current block, derive linear model parameters based on the reference samples, and generate predicted samples of the current block based on the linear model parameters.

[0009] In the image decoding method and apparatus according to the present disclosure, the reference sample may include at least one of a reference sample included in a left sample line adjacent to the current block, a reference sample included in an upper sample line adjacent to the current block, or an upper left reference sample adjacent to the current block.

[0010] In the image decoding method and apparatus according to the present disclosure, when the current block is N×N, the reference samples may include (N+1) reference samples consecutively adjacent to the left side of the upper-left reference sample in the left sample line and (N+1) reference samples consecutively adjacent to the bottom end of the upper-left reference sample in the upper sample line.

[0011] The video decoding method and apparatus according to the present disclosure may check whether reconstructed neighboring samples of the current block are available.

[0012] In the video decoding method and apparatus according to the present disclosure, the linear model parameters may include at least one of a horizontal component parameter or a vertical component parameter.

[0013] The video decoding method and apparatus according to the present disclosure may set the horizontal component parameter or the vertical component parameter to 0 among the linear model parameters derived based on the reference sample.

[0014] The video decoding method and apparatus according to the present disclosure may generate a first predicted sample using the linear model parameters derived based on the reference sample, generate a second predicted sample using linear model parameters in which the horizontal component parameter or the vertical component parameter is set to 0, and generate a final predicted sample by weighted summing the first predicted sample and the second predicted sample.

[0015] The video decoding method and apparatus according to the present disclosure can derive linear model parameters of a first linear model using only the left reference samples of the current block, and can derive linear model parameters of a second linear model using only the upper reference samples of the current block.

[0016] In the video decoding method and apparatus according to the present disclosure, the predicted sample of the current block may be generated based on a weighted sum of a third predicted sample generated using linear model parameters of the first linear model and a fourth predicted sample generated using linear model parameters of the second linear model.

[0017] The image decoding method and apparatus according to the present disclosure may obtain a reference line index indicating one of multiple reference sample lines of the current block.

[0018] In the image decoding method and apparatus according to the present disclosure, the reference sample may be constructed using reference samples included in a reference sample line indicated by the reference line index.

[0019] The video encoding method and apparatus according to the present disclosure may construct reference samples for linear model intra prediction based on reconstructed neighboring samples of a current block, derive linear model parameters based on the reference samples, and generate predicted samples of the current block based on the linear model parameters.

[0020] In the image encoding method and apparatus according to the present disclosure, the reference sample may include at least one of a reference sample included in a left sample line adjacent to the current block, a reference sample included in an upper sample line adjacent to the current block, or an upper left reference sample adjacent to the current block.

[0021] In the image encoding method and apparatus according to the present disclosure, when the current block is N×N, the reference samples may include (N+1) reference samples consecutively adjacent to the left side of the upper-left reference sample in the left sample line and (N+1) reference samples consecutively adjacent to the bottom end of the upper-left reference sample in the upper sample line.

[0022] The video encoding method and apparatus according to the present disclosure may check whether reconstructed neighboring samples of the current block are available.

[0023] In the video encoding method and apparatus according to the present disclosure, the linear model parameters may include at least one of a horizontal component parameter or a vertical component parameter.

[0024] The video encoding method and apparatus according to the present disclosure may set the horizontal component parameter or the vertical component parameter to 0 among the linear model parameters derived based on the reference sample.

[0025] The video encoding method and apparatus according to the present disclosure may generate a first predicted sample using the linear model parameters derived based on the reference sample, generate a second predicted sample using linear model parameters in which the horizontal component parameter or the vertical component parameter is set to 0, and generate a final predicted sample by weighted summing the first predicted sample and the second predicted sample.

[0026] The video encoding method and apparatus according to the present disclosure may derive linear model parameters of a first linear model using only the left reference samples of the current block, and derive linear model parameters of a second linear model using only the upper reference samples of the current block.

[0027] In the video encoding method and apparatus according to the present disclosure, the predicted sample of the current block may be generated based on a weighted sum of a third predicted sample generated using linear model parameters of the first linear model and a fourth predicted sample generated using linear model parameters of the second linear model.

[0028] The image encoding method and apparatus according to the present disclosure may obtain a reference line index indicating one of multiple reference sample lines of the current block.

[0029] In the video encoding method and apparatus according to the present disclosure, the reference sample may be constructed using a reference sample included in a reference sample line indicated by the reference line index.

[0030] A computer-readable digital storage medium is provided that stores encoded video / image information that causes a decoding apparatus according to the present disclosure to perform a video decoding method.

[0031] A computer-readable digital storage medium is provided having video / image information generated by the video encoding method according to the present disclosure stored thereon.

[0032] A method and apparatus are provided for transmitting video / image information generated by the video encoding method according to the present disclosure. Effect of the Invention

[0033] The present disclosure derives a linear model based on surrounding reconstructed samples and performs intra prediction using the induced linear model, thereby enabling more diverse prediction methods to be taken into consideration for prediction, thereby improving prediction accuracy and compression performance.

[0034] The present disclosure can improve prediction accuracy and compression performance by effectively constructing reference samples for linear model induction.

[0035] The present disclosure can improve prediction accuracy by providing a method and apparatus for designing a variety of linear models.

[0036] The present disclosure can increase compression efficiency by effectively signaling information about linear model intra prediction. [Brief description of the drawings]

[0037] [Figure 1] 1 illustrates a video / image coding system in accordance with the present disclosure.

[0038] [Diagram 2] 1 shows a schematic block diagram of an encoding device to which an embodiment of the present disclosure can be applied, in which encoding of a video / image signal is performed.

[0039] [Diagram 3] 1 shows a schematic block diagram of a decoding device to which an embodiment of the present disclosure can be applied, in which decoding of a video / image signal is performed.

[0040] [Figure 4] 1 illustrates an inter prediction method performed by a decoding apparatus 300 according to an embodiment of the present disclosure.

[0041] [Diagram 5] 1 is a diagram illustrating a linear model intra prediction method using multiple reference lines according to an embodiment of the present disclosure.

[0042] [Figure 6] 1 illustrates a schematic configuration of an intra prediction unit 331 that performs an intra prediction method according to the present disclosure.

[0043] [Figure 7] 2 illustrates an inter prediction method performed by an encoding apparatus 200 according to an embodiment of the present disclosure.

[0044] [Figure 8] 1 illustrates a schematic configuration of an intra prediction unit 222 that performs an inter prediction method according to the present disclosure.

[0045] [Figure 9] 1 illustrates an example of a content streaming system to which embodiments of the present disclosure may be applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] The present disclosure can be modified in various ways and can have various embodiments, and a specific embodiment will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present disclosure to a specific embodiment, and it should be understood that the present disclosure includes all modifications, equivalents, and alternatives included in the spirit and technical scope of the present disclosure. In describing each drawing, similar reference numerals are used for similar components.

[0047] Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only to distinguish one component from another. For example, a first component may be named a second component, and similarly, a second component may be named a first component, without departing from the scope of the present disclosure. The term and / or includes a combination of multiple associated listed items or any item of multiple associated listed items.

[0048] When a component is said to be "coupled" or "connected" to another component, it should be understood that it may be directly coupled or connected to the other component, but that there may be other components in between. Conversely, when a component is said to be "directly coupled" or "directly connected" to another component, it should be understood that there are no other components in between.

[0049] The terms used in this application are merely used to describe certain embodiments and are not intended to limit the present disclosure. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as "include" or "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood not to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0050] The present disclosure relates to video / image coding. For example, the methods / embodiments disclosed herein may be applied to methods disclosed in the versatile video coding (VVC) standard. Also, the methods / embodiments disclosed herein may be applied to methods disclosed in the essential video coding (EVC) standard, the AOMedia Video 1 (AV1) standard, the 2nd generation of audio video coding (AVS2) standard, or next generation video / image coding standards (ex. H.267 or H.268, etc.).

[0051] This specification presents various embodiments related to video / image coding, which embodiments may be performed in combination with each other, unless otherwise stated.

[0052] In this specification, video may mean a set of a series of images over time. A picture generally means a unit that indicates one image in a specific time period, and a slice / tile is a unit that constitutes a part of a picture in coding. A slice / tile may include one or more coding tree units (CTUs). A picture may be composed of one or more slices / tiles. A tile is a rectangular area composed of multiple CTUs in a specific tile column and a specific tile row of a picture. A tile column is a rectangular area of ​​CTUs with a height equal to the height of the picture and a width specified by a syntax requirement of a picture parameter set. A tile row is a rectangular area of ​​CTUs with a height specified by a picture parameter set and a width equal to the width of the picture. While CTUs are consecutively arranged in a tile by CTU raster scanning, tiles in a picture may be consecutively arranged by tile raster scanning. A slice may include an integer number of complete tiles or an integer number of consecutive complete CTU rows in tiles of a picture that may be exclusively included in a single NAL unit. Meanwhile, a picture may be divided into two or more sub-pictures. A subpicture can be a rectangular region of one or more slices within a picture.

[0053] A pixel or pel may refer to the smallest unit that constitutes a picture (or image). A term corresponding to a pixel may be "sample." A sample may generally refer to a pixel or a pixel value, and may refer to only a pixel / pixel value of a luminance (luma) component or only a pixel / pixel value of a chrominance (chroma) component.

[0054] A unit may refer to a basic unit of image processing. A unit may include at least one of a specific region of a picture and information related to the region. A unit may include one luma block and two chroma (ex. cb, cr) blocks. A unit may be used interchangeably with terms such as block or area depending on the case. In general, an MxN block may include a set (or array) of samples or transform coefficients consisting of M columns and N rows.

[0055] As used herein, "A or B" may mean "only A," "only B," or "all of A and B." In other words, as used herein, "A or B" may be interpreted as "A and / or B." For example, as used herein, "A, B or C" may mean "only A," "only B," "only C," or "any combination of A, B and C."

[0056] As used herein, a slash ( / ) or a comma may mean "and / or." For example, "A / B" may mean "A and / or B." Accordingly, "A / B" may mean "only A," "only B," or "both A and B." For example, "A, B, C" may mean "A, B, or C."

[0057] In this specification, "at least one of A and B" may mean "only A," "only B," or "all of A and B." In addition, in this specification, the expressions "at least one of A or B" and "at least one of A and / or B" may be interpreted as the same as "at least one of A and B."

[0058] Additionally, in this specification, "at least one of A, B and C" can mean "only A," "only B," "only C," or "any combination of A, B and C." Additionally, "at least one of A, B or C" and "at least one of A, B and / or C" can mean "at least one of A, B and C."

[0059] In addition, parentheses used in this specification may mean "for example." Specifically, when "prediction (intra prediction)" is displayed, "intra prediction" may be proposed as an example of "prediction." In other words, "prediction" in this specification is not limited to "intra prediction," and "intra prediction" may be proposed as an example of "prediction." In addition, when "prediction (i.e., intra prediction)" is displayed, "intra prediction" may be proposed as an example of "prediction."

[0060] Technical features individually described in one drawing in this specification may be embodied individually or simultaneously.

[0061] FIG. 1 illustrates a video / image coding system according to this disclosure.

[0062] Referring to FIG. 1, a video / image coding system may include a first device (a source device) and a second device (a receiving device).

[0063] A source device may transmit encoded video / image information or data to a receiving device in the form of a file or streaming through a digital storage medium or a network. The source device may include a video source, an encoding device, and a transmitting unit. The receiving device may include a receiving unit, 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 unit, which may be a separate device or an external component.

[0064] A video source may acquire video / images through a video / image capture, synthesis, or generation process, etc. A video source may include a video / image capture device and / or a video / image generation device. A video / image capture device may include one or more cameras, a video / image archive containing previously captured video / images, etc. A video / image generation device may include a computer, tablet, smartphone, etc., and may (electronically) generate video / images. For example, a virtual video / image may be generated through a computer, etc., in which case the video / image capture process may be substituted as the process by which related data is generated.

[0065] An encoding device can encode input video / images. The encoding device can perform a series of procedures such as prediction, transformation, quantization, etc. for compression and coding efficiency. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0066] The transmitting unit can transmit the encoded video / image information or data output in the form of a bitstream to a receiving unit of a receiving device through a digital storage medium or a network in the form of a file or streaming. The digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitting unit can include elements for generating a media file through a predetermined file format and can include elements for transmission through a broadcasting / communication network. The receiving unit can receive / extract the bitstream and transmit it to a decoding device.

[0067] The decoding device can decode the video / image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoding device.

[0068] The renderer can render the decoded video / image. The rendered video / image can be displayed through a display unit.

[0069] FIG. 2 shows a schematic block diagram of an encoding device to which the embodiments of the present disclosure can be applied, in which encoding of a video / image signal is performed.

[0070] Referring to FIG. 2, the encoding apparatus 200 may include an image partitioner (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 predictor 221 and an intra predictor 222. The residual processor 230 may include a transformer (232), a quantizer (233), a dequantizer (234), and an inverse transformer (235). The residual processor 230 may further include a subtractor (231). The adder 250 may be referred to as a reconstructor or a reconstructed block generator. The image division unit 210, the prediction unit 220, the residual processing unit 230, the entropy encoding unit 240, the addition unit 250, and the filtering unit 260 may be configured by one or more hardware components (e.g., an encoding device chipset or a processor) according to an embodiment. In addition, the memory 270 may include a decoded picture buffer (DPB) and may be configured by a digital storage medium. The hardware components may further include the memory 270 as an internal / external component.

[0071] The image division unit 210 may divide an input image (or picture, frame) input to the encoding device 200 into one or more processing units. As an example, the processing units may be called coding units (CUs). In this case, the coding units may be recursively divided from a coding tree unit (CTU) or a largest coding unit (LCU) according to a quad-tree binary-tree ternary-tree (QTBTTT) structure.

[0072] For example, one coding unit may be divided into a plurality of coding units having a deeper depth based on a quad tree structure, a binary tree structure, and / or a ternary structure. In this case, for example, the quad tree structure may be applied first, and the binary tree structure and / or the ternary structure may be applied later. Or, the binary tree structure may be applied before the quad tree structure. The coding procedure according to the present specification may be performed based on the final coding unit that is not further divided. In this case, based on coding efficiency according to image characteristics, the largest coding unit may be immediately used as the final coding unit, or the coding unit may be recursively divided into coding units of lower depth as necessary, and the coding unit having the optimal size may be used as the final coding unit. Here, the coding procedure may include procedures such as prediction, transformation, and restoration, which will be described later.

[0073] As another example, the processing unit may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may be divided or partitioned from the final coding unit. The prediction unit may be a unit of sample prediction, and the transform unit may be a unit for deriving transform coefficients and / or a unit for deriving a residual signal from the transform coefficients.

[0074] Unit may be used interchangeably with terms such as block or area. In the general case, an MxN block may refer to a set of samples or transform coefficients consisting of M columns and N rows. A sample may generally refer to a pixel or pixel value, and may refer to only a pixel / pixel value of a luma component or only a pixel / pixel value of a chroma component. A sample may be used as a term corresponding to a pixel or pel in one picture (or image).

[0075] The encoding apparatus 200 may generate a residual signal (residual block, residual sample array) by subtracting a prediction signal (prediction block, prediction sample array) output from the inter prediction unit 221 or the intra prediction unit 222 from an input video signal (original block, original sample array), and the generated residual signal is transmitted to the conversion unit 232. In this case, a unit in the encoding apparatus 200 that subtracts the prediction signal (prediction block, prediction sample array) from the input video signal (original block, original sample array) may be referred to as a subtraction unit 231.

[0076] The prediction unit 220 may perform prediction on a block to be processed (hereinafter, referred to as a current block) and generate a predicted block including prediction samples for the current block. The prediction unit 220 may determine whether intra prediction or inter prediction is applied in units of the current block or CU. The prediction unit 220 may generate various information related to prediction, such as prediction mode information, as described below in the description of each prediction mode, and transmit the information to the entropy encoding unit 240. The prediction information may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

[0077] The intra prediction unit 222 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located a certain distance away from the current block depending on the prediction mode. In intra prediction, the prediction mode may include one or more non-directional modes and a plurality of directional modes. The non-directional mode may include at least one of a DC mode or a planar mode. The directional mode may include 33 directional modes or 65 directional modes depending on the fineness of the prediction direction. However, this is merely an example, and more or less directional modes may be used depending on the settings. The intra prediction unit 222 may determine the prediction mode applied to the current block using the prediction modes applied to the neighboring blocks.

[0078] The inter prediction unit 221 may derive a prediction block for a current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted from the inter prediction mode, the motion information may be predicted in units of a block, a sub-block, or a sample based on the correlation of motion information between a neighboring block and a current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction direction information (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter prediction, the neighboring block may include a spatial neighboring block present in the current picture and a temporal neighboring block present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be called a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block may be called a collocated picture (colPic). For example, the inter prediction unit 221 may generate information indicating which candidate is used to derive a motion vector and / or a reference picture index of the current block by forming a motion information candidate list based on neighboring blocks. Inter prediction may be performed based on various prediction modes, and for example, in the case of a skip mode and a merge mode, the inter prediction unit 221 may use motion information of neighboring blocks as motion information of the current block. In the case of the skip mode, unlike the merge mode, a residual signal may not be transmitted.In the case of motion vector prediction (MVP) mode, the motion vector of the surrounding block can be used as a motion vector predictor, and the motion vector of the current block can be indicated by signaling the motion vector difference.

[0079] The prediction unit 220 may generate a prediction signal based on various prediction methods described below. For example, the prediction unit may apply intra prediction or inter prediction for prediction of one block, and may simultaneously apply intra prediction and inter prediction. This may be called a combined inter and intra prediction (CIIP) mode. The prediction unit may also be based on an intra block copy (IBC) prediction mode or a palette mode for prediction of a block. The IBC prediction mode or palette mode may be used for content image / video coding such as games, such as screen content coding (SCC). IBC basically performs prediction within a current picture, but may be performed similarly to inter prediction in that a reference block is derived within the current picture. That is, IBC may use at least one of the inter prediction techniques described herein. The palette mode may be seen as an example of intra coding or intra prediction. When the palette mode is applied, a sample value within a picture may be signaled based on information on a palette table and a palette index. The prediction signal generated by the prediction unit 220 may be used to generate a reconstruction signal or a residual signal.

[0080] The transform unit 232 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), KLT (Karhunen-Loeve Transform), GBT (Graph-Based Transform), or CNT (Conditionally Non-linear Transform). Here, GBT refers to a transform obtained from a graph when the relationship information between pixels is expressed as a graph. CNT refers to a transform obtained based on a predicted signal generated using all previously restored pixels. In addition, the transform process may be applied to pixel blocks having the same size as a regular square, or may be applied to blocks of variable size other than a regular square.

[0081] The quantization unit 233 quantizes the transform coefficients and transmits the quantized transform coefficients to the entropy encoding unit 240, and the entropy encoding unit 240 may encode the quantized signal (information about the quantized transform coefficients) and output it as a bitstream. The information about the quantized transform coefficients may be called residual information. The quantization unit 233 may rearrange the quantized transform coefficients in a block form into a one-dimensional vector form based on a coefficient scan order, and may generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0082] The entropy encoding unit 240 can perform various encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), etc. The entropy encoding unit 240 can also encode information required for video / image restoration (e.g., values ​​of syntax elements, etc.) together with or separately from the quantized transform coefficients.

[0083] The encoded information (e.g., encoded video / image information) may be transmitted or stored in the form of a bitstream in units of network abstraction layer (NAL) units. The video / image information may further include information on various parameter sets, such as an adaptation parameter set APS, a picture parameter set PPS, a sequence parameter set SPS, or a video parameter set VPS. The video / image information may further include general constraint information. In this specification, information and / or syntax elements transmitted / signaled from an encoding device to a decoding device may be included in the video / image information. The video / image information may be encoded through the above-mentioned encoding procedure and included in the bitstream. The bitstream may be transmitted through a network or stored in a digital storage medium. Here, the network may include a broadcasting network and / or a communication network, and the digital storage medium may include various storage media, such as a USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitting unit (not shown) for transmitting the signal output from the entropy encoding unit 240 and / or a storage unit (not shown) for storing the signal may be configured as an internal / external element of the encoding apparatus 200, or the transmitting unit may be included in the entropy encoding unit 240.

[0084] The quantized transform coefficients output from the quantizer 233 may be used to generate a prediction signal. For example, a residual signal (residual block or residual sample) may be restored by applying inverse quantization and inverse transform to the quantized transform coefficients through the inverse quantizer 234 and the inverse transformer 235. The adder 250 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the reconstructed residual signal to the prediction signal output from the inter prediction unit 221 or the intra prediction unit 222. When there is no residual for the current block, such as when a skip mode is applied, the predicted block may be used as a reconstructed block. The adder 250 may be referred to as a reconstruction unit or a reconstructed block generator. The generated reconstructed signal may be used for intra prediction of the next current block in the current picture, or may be used for inter prediction of the next picture after filtering as described below. Meanwhile, LMCS (luma mapping with chroma scaling) may be applied during picture encoding and / or reconstruction.

[0085] The filtering unit 260 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 260 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and may store the modified reconstructed picture in the memory 270, specifically, in the DPB of the memory 270. The various filtering methods may include deblocking filtering, sample adaptive offset, an adaptive loop filter, a bilateral filter, etc. The filtering unit 260 may generate various information related to filtering and transmit it to the entropy encoding unit 240. The information related to filtering may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

[0086] The modified reconstructed picture transmitted to the memory 270 may be used as a reference picture in the inter prediction unit 221. In this way, when inter prediction is applied, the encoding apparatus can avoid prediction mismatch between the encoding apparatus 200 and the decoding apparatus, and can also improve encoding efficiency.

[0087] The DPB of the memory 270 may store the modified reconstructed picture for use as a reference picture in the inter prediction unit 221. The memory 270 may store motion information of a block from which motion information in the current picture is derived (or encoded) and / or motion information of an already reconstructed block in the picture. The stored motion information may be transmitted to the inter prediction unit 221 to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory 270 may store reconstructed samples of blocks reconstructed in the current picture and transmit them to the intra prediction unit 222.

[0088] FIG. 3 shows a schematic block diagram of a decoding device to which an embodiment of the present disclosure can be applied, in which decoding of a video / image signal is performed.

[0089] 3, the decoding device 300 may include an entropy decoding unit (entropy decoder, 310), a residual processor (residual processor, 320), a predictor (predictor, 330), an adder (adder, 340), a filter (filter, 350), and a memory (memory, 360). The predictor 330 may include an inter predictor 332 and an intra predictor 331. The residual processor 320 may include a dequantizer (dequantizer, 321) and an inverse transformer (inverse transformer, 321).

[0090] The entropy decoding unit 310, the residual processing unit 320, the prediction unit 330, the addition unit 340, and the filtering unit 350 may be configured as one hardware component (e.g., a decoding device chipset or processor) according to an embodiment. Also, the memory 360 may include a decoded picture buffer (DPB) and may be configured as a digital storage medium. The hardware components may further include the memory 360 as an internal / external component.

[0091] When a bitstream including video / image information is input, the decoding apparatus 300 can restore an image corresponding to the process in which the video / image information is processed by the encoding apparatus of FIG. 2. For example, the decoding apparatus 300 can derive a unit / block based on block division related information acquired from the bitstream. The decoding apparatus 300 can perform decoding using a processing unit applied in the encoding apparatus. Thus, the processing unit for decoding can be a coding unit, and the coding unit can be divided from a coding tree unit or a maximal coding unit according to a quad tree structure, a binary tree structure, and / or a ternary tree structure. One or more transform units can be derived from the coding unit. And, the restored image signal decoded and output by the decoding apparatus 300 can be reproduced through a playback device.

[0092] The decoding apparatus 300 may receive a signal output from the encoding apparatus of FIG. 2 in the form of a bitstream, and the received signal may be decoded through the entropy decoding unit 310. For example, the entropy decoding unit 310 may parse the bitstream to derive information (ex. video / image information) required for image restoration (or picture restoration). The video / image information may further include information on various parameter sets, such as an adaptation parameter set APS, a picture parameter set PPS, a sequence parameter set SPS, or a video parameter set VPS. The video / image information may further include general constraint information. The decoding apparatus may decode a picture based on information on the parameter set and / or the general constraint information. Signaling / received information and / or syntax elements described later in this specification may be obtained from the bitstream by being decoded through the decoding procedure. For example, the entropy decoding unit 310 may decode information in a bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output the value of a syntax element required for image restoration and the quantized value of a transform coefficient related to a residual. More specifically, the CABAC entropy decoding method receives a bin corresponding to each syntactic element in the bitstream, determines a context model using the syntax element information to be decoded and the decoding information of the neighboring and decoding target blocks or the symbol / bin information decoded in the previous step, predicts the occurrence probability of the bin according to the determined context model, and performs arithmetic decoding of the bin to generate a symbol corresponding to the value of each syntactic element. At this time, the CABAC entropy decoding method may update the context model using the decoded symbol / bin information for the context model of the next symbol / bin after determining the context model.Among the information decoded by the entropy decoding unit 310, information related to prediction is provided to a prediction unit (inter prediction unit 332 and intra prediction unit 331), and residual values ​​entropy-decoded by the entropy decoding unit 310, i.e., quantized transform coefficients and related parameter information, may be input to the residual processing unit 320. The residual processing unit 320 may generate a residual signal (residual block, residual sample, residual sample array). Also, among the information decoded by the entropy decoding unit 310, information related to filtering may be provided to the filtering unit 350. Meanwhile, a receiving unit (not shown) for receiving a signal output from an encoding apparatus may be further configured as an internal / external element of the decoding apparatus 300, or the receiving unit may be a component of the entropy decoding unit 310.

[0093] Meanwhile, the decoding device according to the present specification may be called a video / image / picture decoding device, and the decoding device may be divided into an information decoding device (video / image / picture information decoding device) and a sample decoding device (video / image / picture sample decoding device). The information decoding device may include the entropy decoding unit 310, and the sample decoding device may include at least one of the inverse quantization unit 321, the inverse transform unit 322, the addition unit 340, the filtering unit 350, the memory 360, the inter prediction unit 332, and the intra prediction unit 331.

[0094] The inverse quantization unit 321 can inverse quantize the quantized transform coefficients and output transform coefficients. The inverse quantization unit 321 can rearrange the quantized transform coefficients in a two-dimensional block form. In this case, the rearrangement can be performed based on the coefficient scan order performed in the encoding device. The inverse quantization unit 321 can perform inverse quantization on the quantized transform coefficients using a quantization parameter (e.g., quantization step size information) and obtain transform coefficients.

[0095] The inverse transform unit 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0096] The prediction unit 320 may perform prediction on a current block and generate a predicted block including prediction samples for the current block. The prediction unit 320 may determine whether intra prediction or inter prediction is applied to the current block based on information related to the prediction output from the entropy decoding unit 310, and may determine a specific intra / inter prediction mode.

[0097] The prediction unit 320 may generate a prediction signal based on various prediction methods described below. For example, the prediction unit 320 may apply intra prediction or inter prediction for prediction of one block, and may simultaneously apply intra prediction and inter prediction. This may be called a combined inter and intra prediction (CIIP) mode. In addition, the prediction unit may be based on an intra block copy (IBC) prediction mode or a palette mode for prediction of a block. The IBC prediction mode or palette mode may be used for content image / movie coding such as games, such as screen content coding (SCC). IBC basically performs prediction within a current picture, but may be performed similarly to inter prediction in that a reference block is derived within the current picture. That is, IBC may use at least one of the inter prediction techniques described herein. The palette mode may be seen as an example of intra coding or intra prediction. When the palette mode is applied, information regarding a palette table and a palette index may be included in the video / image information and signaled.

[0098] The intra prediction unit 331 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located a certain distance away from the current block depending on the prediction mode. In intra prediction, the prediction mode may include one or more non-directional modes and a plurality of directional modes. The intra prediction unit 331 may determine the prediction mode applied to the current block by using the prediction modes applied to the neighboring blocks.

[0099] The inter prediction unit 332 may derive a prediction block for a current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted from an inter prediction mode, the motion information may be predicted in units of a block, a sub-block, or a sample based on correlation of motion information between a neighboring block and a current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction direction information (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter prediction, the neighboring block may include a spatial neighboring block present in the current picture and a temporal neighboring block present in the reference picture. For example, the inter prediction unit 332 may form a motion information candidate list based on the neighboring block, and may derive a motion vector and / or a reference picture index for the current block based on the received candidate selection information. Inter prediction may be performed based on various prediction modes, and the prediction information may include information indicating an inter prediction mode for the current block.

[0100] The adder 340 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the acquired residual signal to a prediction signal (prediction block, prediction sample array) output from a prediction unit (including the inter prediction unit 332 and / or the intra prediction unit 331). When there is no residual for a current block, such as when a skip mode is applied, the prediction block may be used as a reconstructed block.

[0101] The adder 340 may be referred to as a reconstruction unit or a reconstruction block generator. The generated reconstruction signal may be used for intra prediction of the next block to be processed in the current picture, may be output after filtering as described below, or may be used for inter prediction of the next picture. Meanwhile, LMCS (luma mapping with chroma scaling) may be applied during the picture decoding process.

[0102] The filtering unit 350 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 350 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and may transmit the modified reconstructed picture to the memory 360, specifically, to the DPB of the memory 360. The various filtering methods may include deblocking filtering, sample adaptive offset, an adaptive loop filter, a bilateral filter, etc.

[0103] The (modified) reconstructed picture stored in the DPB of the memory 360 may be used as a reference picture in the inter prediction unit 332. The memory 360 may store motion information of a block from which motion information in the current picture is derived (or decoded) and / or motion information of a block in the picture that has already been reconstructed. The stored motion information may be transmitted to the inter prediction unit 332 to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory 360 may store reconstructed samples of blocks reconstructed in the current picture and transmit them to the intra prediction unit 331.

[0104] In this specification, the embodiments described for the filtering unit 260, the inter prediction unit 221, and the intra prediction unit 222 of the encoding apparatus 200 may also be applied identically or correspondingly to the filtering unit 350, the inter prediction unit 332, and the intra prediction unit 331 of the decoding apparatus 300, respectively.

[0105] FIG. 4 illustrates an inter-prediction method performed by a decoding apparatus 300 according to an embodiment of the present disclosure.

[0106] In the embodiment of the present disclosure, a method is proposed in which a linear model is derived based on reconstructed samples around a current block, and intra prediction is performed using the induced linear model. In describing the embodiment of the present disclosure, the intra prediction method using a linear model is referred to as linear model prediction, but it goes without saying that the name is not limited to this. In the present disclosure, linear model prediction may be referred to as linear model intra prediction, linear prediction, linear intra prediction, model prediction, model intra prediction, linear model-based prediction, linear model-based intra prediction, position-based linear prediction, position-based linear model prediction, position-based linear model intra prediction, etc.

[0107] 4, the decoding apparatus may construct reference samples for linear model intra prediction based on reconstructed neighboring samples of the current block (S400), and derive linear model parameters (or variables) based on the constructed reference samples (S410). In other words, the decoding apparatus may construct reference samples for linear model intra prediction based on reconstructed neighboring samples of the current block, and derive (or determine) a linear model based on the constructed reference samples. A linear model used for linear model intra prediction may be induced by the linear model parameters induced in step S410. Various embodiments of the linear model-based intra prediction method will be described in detail below.

[0108] According to an embodiment of the present disclosure, a linear model may be derived based on reconstruction samples around a current block. Specifically, linear model parameters may be derived using values ​​and / or coordinate information (or position information) of the surrounding reconstruction samples, and a linear model may be determined by the induced linear model parameters. In the present disclosure, a linear model may be referred to as a linear equation. Assuming that the current block is N×N, a predicted sample at a (x, y) position may be generated (or calculated or derived) using the following mathematical formula 1. In other words, a linear model such as the following mathematical formula 1 may be defined, and a predicted sample at a (x, y) position may be generated using the linear model such as the mathematical formula 1.

[0109]

number

[0110] In the mathematical formula 1, a, b, and c indicate linear model parameters (or variables). In the present disclosure, c is a constant and may be referred to as a linear model parameter or an offset. A linear model may be determined by the linear model parameters. Also, a and b may be referred to as a horizontal direction (horizontal component) parameter and a vertical direction (vertical component) parameter, respectively. Since a linear model is determined by the linear model parameters, the linear model parameters may be a linear model and may be abbreviated as a linear model. To derive the parameters a, b, and c in the mathematical formula 1, values ​​and coordinate information (or position information) of already restored samples around the current block may be used.

[0111] Specifically, a formula for minimizing an error between a predicted sample and a restored sample by using a formula expressing a correlation between a restored pixel value and the pixel coordinate may be derived through the following Equation 2. As described above, in this disclosure, the term "sample" may be used as a term corresponding to a pixel.

[0112]

number

[0113] In Equation 2, L means the number of neighboring restored samples. As an example, L may be 4N+1, or may be defined as various multiple numbers as in the following embodiment. At this time, as in Equation 1, Pred=ax+by+c, and the minimum value of the squared error is 0, so that the following Equation 3 can be derived by performing partial differentiation with respect to a, b, and c for Equation 2.

[0114]

number

[0115] If we rearrange mathematical equation 3 using matrices for a, b, and c, it can be expressed as the following mathematical equation 4.

[0116]

number

[0117] matrix A= When JPEG2025511385000006.jpg17169 is used, according to the Cremo formula The solution to JPEG2025511385000007.jpg12169 can be shown as the following mathematical equation 5.

[0118]

number

[0119] In mathematical formula 5, B0= JPEG2025511385000009.jpg17169, B1= JPEG2025511385000010.jpg17169, B2= JPEG2025511385000011.jpg15155. Matrix A can be calculated using only the coordinate information, and matrices B0, B1, and B2 can be calculated using one coordinate information and the reconstructed sample values ​​of the neighboring blocks.

[0120] As an example, assume that 1) the current block is a 4x4 block, 2) the value of the upper left reference sample adjacent to the upper left sample (or corner) of the current block is 533, 3) the reference sample values ​​included in the upper reference sample line adjacent to the right side of the upper left reference sample are {514, 487, 456, 470, 535, 533, 527, 525} from the left, and 4) the reference sample values ​​included in the left reference sample line adjacent to the bottom end of the upper left reference sample are {540, 528, 504, 489, 489, 489, 489, 489} from the top. In this case, the linear model parameters a, b, and c can be derived as shown in the following Equation 6.

[0121]

number

[0122] Thereafter, a linear model according to Equation 1 may be determined based on the calculated parameter values ​​a, b, and c. As an example, the values ​​of the linear model parameters calculated based on the reconstructed reference sample according to the embodiment of the present disclosure may be approximated values ​​through methods such as scaling, shifting, fixed-point arithmetic, and integer arithmetic. A predicted sample may be calculated according to the position of a sample in a current block based on the induced linear model. As an example, a predicted sample (or predicted block) of a 4×4 current block may be determined as shown in Table 1 below.

[0123] [Table 1]

[0124] Referring to Table 1, a predicted sample of the current sample may be calculated based on the induced linear model and the position of the current sample in the current block. In other words, a predicted sample may be calculated on a sample-by-sample (i.e., pixel-by-pixel) basis based on the induced linear model and the sample position.

[0125] In the above embodiment, it is assumed that when the current block is N×N, 4N+1 reference samples (i.e., 1 upper left reference sample, 2N reference samples in the upper sample line, and 2N reference samples in the left sample line) are used to derive a linear model (i.e., linear model parameters). In the following embodiment, a method of deriving a linear model using various numbers or positions of reference samples will be described without being limited thereto.

[0126] According to an embodiment of the present invention, a linear model may be determined using a predefined specific number of reference samples and / or reference samples at specific positions. In other words, according to an embodiment of the present invention, the number and / or positions of reference samples used to derive linear model parameters may be predefined. The linear model according to the above-mentioned Equation 1 may change linear model parameter values ​​depending on which sample is used among the neighboring reference samples of the current block.

[0127] As an example, when the current block is N×N, the linear model parameters can be derived using one upper left reference sample, N reference samples of the upper sample line, and N reference samples of the left sample line, totaling 2N+1 reference samples. For example, the N reference samples of the upper sample line can indicate N reference samples adjacent to the right of the upper left reference sample adjacent to the current block. Also, the N reference samples of the left sample line can indicate N reference samples adjacent to the lower end of the upper left reference sample adjacent to the current block.

[0128] As in the above embodiment, when the reference sample values ​​included in the upper reference sample line adjacent to the right side of the upper left reference sample are {514, 487, 456, 470} from the left, and the reference sample values ​​included in the left reference sample line adjacent to the lower side of the upper left reference sample are {540, 528, 504, 489} from the top, the linear model parameters a, b, and c can be calculated as -21.3228, -10.3905, and 505.8571, respectively. The predicted block can be generated as shown in Table 2 below using the induced linear model.

[0129] [Table 2]

[0130] Also, as an example, when the current block is N×N, the linear model parameters can be derived using N reference samples of the top sample line and N reference samples of the left sample line, totaling 2N reference samples. For example, the N reference samples of the top sample line may be N reference samples adjacent to the right of the top-left reference sample adjacent to the current block. Also, the N reference samples of the left sample line may be N reference samples adjacent to the bottom of the top-left reference sample adjacent to the current block.

[0131] As in the above embodiment, when the reference sample values ​​included in the upper reference sample line adjacent to the right side of the upper left reference sample are {514, 487, 456, 470} from the left, and the reference sample values ​​included in the left reference sample line adjacent to the lower side of the upper left reference sample are {540, 528, 504, 489} from the top, the linear model parameters a, b, and c may be induced to be −22.4667, −11.5333, and 507, respectively. Using the induced linear model, a prediction block may be generated as shown in Table 3 below.

[0132] [Table 3]

[0133] In addition, as an embodiment, when the current block is N×N, the linear model parameters can be derived using N+1 reference samples of the upper sample line, N+1 reference samples of the left sample line, and a total of 2N+2 reference samples. At this time, the N+1 reference samples of the upper sample line may be N+1 reference samples adjacent to the right of the upper left reference sample adjacent to the current block. Also, the N+1 reference samples of the left sample line may be N+1 reference samples adjacent to the lower end of the upper left reference sample adjacent to the current block. In this embodiment, the reference samples used to derive the linear model parameters may be the same as the surrounding reference samples used in the planar prediction mode of VVC.

[0134] As in the above embodiment, when the reference sample values ​​included in the upper reference sample line adjacent to the right side of the upper left reference sample are {514, 487, 456, 470, 535} from the left, and the reference sample values ​​included in the left reference sample line adjacent to the lower side of the upper left reference sample are {540, 528, 504, 489, 489} from the top, the linear model parameters a, b, and c can be induced to 8.08446, -6.30264, and 509.3226, respectively. Using the induced linear model, a prediction block can be generated as shown in Table 4 below.

[0135] [Table 4]

[0136] Also, as an embodiment, only even-numbered or odd-numbered pixels among the reference samples, not consecutive pixels, may be used to derive the linear model parameters. In other words, only even-numbered or odd-numbered pixels from the left side among the reference samples included in the upper reference sample line may be used to derive the linear model parameters, and only even-numbered or odd-numbered pixels from the top side among the reference samples included in the left reference sample line may be used to derive the linear model parameters.

[0137] In addition, as an embodiment, the number of pixels used to derive the linear model parameters to be referenced may be variably determined according to the size of the block. For example, in the case of a block smaller than or equal to a predefined size, a linear model may be determined using A number of reference samples, and in the case of a block larger than the predefined size, a linear model may be determined using B number of reference samples. A and B may each be a specific number according to any one of the above-mentioned embodiments. For example, in a block having a pixel number of 16×16 or less, the above-mentioned 4N+1 reference samples may be used to determine a linear model, and in the case of a block having a pixel number of more than 16×16, 2N reference samples may be used to determine a linear model. The predefined size may be a maximum size or a minimum size for linear model prediction. In addition, the number of reference samples according to the size of the block may be defined in various combinations.

[0138] According to an embodiment of the present invention, a linear model can be derived based on available reference pixels among reconstructed pixels around the current block. In other words, the present embodiment proposes a method of performing linear model prediction using only pixels having valid values ​​among the surrounding pixels of the current block.

[0139] In general video compression technologies, if there is no restored reference sample for a surrounding block, available samples around the reference sample are copied and used, or an intermediate value based on the bit depth is used. VVC checks whether surrounding pixels are available in 4x4 units. If there is an unavailable sample in between, it copies the adjacent pixel value. Therefore, when constructing a reference sample (or reference sample buffer), it is possible to distinguish whether the reference pixel at each position is a valid pixel or a pixel copied or extrapolated from the surrounding area, and using this information, only available pixels can be used in the linear model calculation.

[0140] In addition, the method proposed in this embodiment can be used in combination with the above-mentioned embodiment. That is, the maximum number of usable samples is defined as in the above-mentioned embodiment, and only usable samples can be used for model calculation. For example, if the maximum number of surrounding pixels is defined as 2N+2, a linear model can be determined using only usable pixels out of the 2N+2 pixels.

[0141] Also, according to an embodiment of the present invention, a method of deriving a linear model using some of the induced parameters is proposed. In other words, a linear equation is induced using reconstructed pixels around the current block and coordinate information of the pixels, but a linear model can be determined using only some of the induced linear model parameters. As an example, a horizontal linear model and a vertical linear model can be induced by a method that does not use parameters for the x coordinate or y coordinate, and a predicted block can be generated based on the horizontal linear model and vertical linear model.

[0142] Looking again at the above-mentioned mathematical formula 1, the parameter a is a parameter for the x-axis, and b is a parameter for the y-axis. In other words, the parameter a is a parameter for the horizontal direction, and the parameter b is a parameter for the vertical direction. In this embodiment, a horizontal linear model and / or a vertical linear model can be defined by forcing (or setting) the a or b parameter to 0. In describing the embodiment of the present disclosure, a linear model in which some of the induced linear model parameters are set to 0 is referred to as a horizontal / vertical linear model, but it goes without saying that the present disclosure is not limited to such a name. In this disclosure, the horizontal / vertical linear model may be referred to as a horizontal / vertical constrained model, a horizontal / vertical constrained linear model, a first / second constrained linear model, a horizontal / vertical approximate model, a horizontal / vertical approximate linear model, a first / second approximate linear model, a constrained model, a constrained linear model, an approximate model, or an approximate linear model.

[0143] That is, according to the present embodiment, after deriving the linear model parameters of Equation 1 based on the surrounding reference samples according to the above-described embodiment, the horizontal / vertical linear models can be finally determined by setting a or b to 0. The finally derived horizontal / vertical linear models can be expressed as Equation 7 below, respectively.

[0144]

number

[0145] Referring to Equation 7, HorPred has the same predicted sample value in the horizontal direction, and VerPred has the same predicted sample value in the vertical direction, so HorPred may be referred to as a horizontal linear model, and VerPred may be referred to as a vertical linear model. On the other hand, HorPred may be referred to as a vertical linear model, and VerPred may be referred to as a horizontal linear model, in that a parameter related to the horizontal change amount is set to 0 and a parameter related to the vertical change amount remains, and VerPred may be referred to as a horizontal linear model, in that a parameter related to the vertical change amount is set to 0 and a parameter related to the horizontal change amount remains. In other words, HorPred / VerPred in Equation 7 may be referred to as a horizontal / vertical linear model or a vertical / horizontal linear model, respectively, but in the following embodiment, HorPred / VerPred in Equation 7 will be described as a horizontal / vertical linear model, respectively.

[0146] For example, a prediction block may be generated using either the vertical linear model or the horizontal linear model of Equation 7. Alternatively, for example, two prediction blocks (or prediction samples) may be generated using the vertical linear model and the horizontal linear model, and the final prediction block (or prediction sample) may be generated by weighting and summing the two generated prediction blocks. The two prediction blocks generated using the respective models may be referred to as an initial prediction block or a temporary prediction block.

[0147] Alternatively, for example, a predicted sample may be generated using either a vertical linear model or a horizontal linear model, and the generated predicted block may be blended (or weighted summed) at a certain ratio with a predicted block generated by the linear model described in Equation 1 to derive a final predicted sample. For example, the final predicted block may be calculated as FinalPred=(3*HorPred+Pred) / 4, where Pred represents the predicted block generated by the linear model described in Equation 1.

[0148] Alternatively, the prediction block generated from the vertical linear model or the horizontal linear model may be blended with the prediction block generated in the planar mode at a certain ratio to be derived as a final prediction sample. For example, the final prediction block may have a form such as FinalPred=(3*HorPred+Planar) / 4, where Planar indicates the prediction block generated in the planar mode.

[0149] According to an embodiment of the present invention, a method is proposed in which a linear model is derived using only some of the reference samples, and a predicted sample is generated based on the linear model. As an example, a linear model is derived using the left reference sample and the upper reference sample, and a predicted sample is generated using each linear model, and the generated predicted samples are blended (or weighted summed) to generate a final predicted sample.

[0150] Using the value and coordinate information of the given reference sample, a model for the left reference sample and a model for the upper reference sample can be derived as shown in Equation 8 below.

[0151]

number

[0152] In mathematical formula 8, Pred Left denotes the linear model induced using the left reference sample, and Pred Abovedenotes a linear model induced using the upper reference sample. Left is a left-sided linear model, Pred Above is referred to as, but not limited to, the upper linear model. Left / Pred Above may be referred to as a left / upper reference linear model, a left / upper reference restricted model, a left / upper reference restricted linear model, or a left / upper reference restricted model. According to the sample position in the prediction block, a weighted sum type prediction sample may be generated as shown in the following Equation 9.

[0153]

number

[0154] In mathematical formula 9, w x denotes the weighting applied to the forecast samples generated by the left-sided linear model, and w y denotes a weighting value applied to a predicted sample generated by the upper linear model. In one embodiment, the weighting value may be variably defined according to the sample position within the predicted block. For example, w x +w y = 1, the closer the sample position of the current predicted block is to the left reference sample, the x has a large value, and the closer the sample position of the current predicted block is to the upper reference sample, the larger w y may be set to have a large value. In other words, the weight value may be variably determined according to the distance between the left / upper reference sample and the current sample in the prediction block.

[0155] Also, for example, the shape of the block or the ratio of width to height may affect the w x And w y In this case, the value of w x And w y can be a fixed value. For example, if the current block size is 16x8, then w x And w y can be defined as 0.75 and 0.25, respectively.

[0156] Or the ratio of width to height is x And w y The value may be defined as 0. That is, if the width of a block is greater than the height, a prediction block may be constructed after calculating parameters of a linear model using only the upper reference samples, or if the height of a block is greater than the width, a prediction block may be constructed after calculating parameters of a linear model using only the left reference samples.

[0157] Furthermore, according to an embodiment of the present invention, a method for defining a linear model based on reference samples included in multiple reference lines is proposed.

[0158] FIG. 5 is a diagram illustrating a linear model intra prediction method using multiple reference lines according to an embodiment of the present disclosure.

[0159] 5, multiple reference lines including not only adjacent sample lines to the current block but also non-adjacent neighboring samples may be used to derive a linear model. The embodiment previously described in FIG. 4 uses coordinate information and pixel values, so it can be applied in substantially the same manner when multiple reference lines are used.

[0160] As an example, as shown in FIG 5, four reference sample lines around the current block may be available. That is, at least one of the four reference sample lines may be used for linear model prediction. For example, the reference sample line farthest from the current block may be used. When the upper left sample coordinate of the current block is (0, 0), a linear model may be derived using a reconstructed sample value located at (x, -4) or (-4, y).

[0161] As described above, the method proposed in this embodiment can be combined with the embodiment previously described in Fig. 4. For example, in deriving the linear model according to Equation 1, the horizontal / vertical linear model according to Equation 7, and the left / upper linear model according to Equation 8, multiple reference lines may be available in addition to the reference line adjacent to the current block.

[0162] In addition, if it is possible to obtain coordinate information and reconstructed sample values, a further extension of the multi-reference sample lines shown in FIG. 5 (i.e., linear model design and parameter derivation using reconstructed samples outside the fourth reference line) may also be applied.

[0163] 4, the decoding apparatus may generate a prediction sample of the current block based on the linear model parameters (S420). In other words, the decoding apparatus may perform intra prediction on the current block based on the induced linear model parameters (or linear model). A prediction sample may be generated on a sample-by-sample basis according to the position of the current sample in the current block based on the induced linear model.

[0164] Hereinafter, a method for signaling information related to the linear model prediction method described above will be described. The linear model prediction method described above may be the linear model prediction method previously described in the embodiment of FIG. 4 and / or FIG. 5. The MPM mode may be used to effectively transmit intra prediction mode information, and the remaining modes not included in the MPM candidates may be signaled with mode information of specific bits. In addition, prediction modes different from general directional prediction modes such as Matrix-based Intra Prediction (MIP), Template based intra mode derivation (TIMD), Decoder-side intra mode derivation (DIMD), Intra Sub-Partitions (ISP), Multi-reference line (MRL), etc. may perform prediction and reconstruction based on the flag received by the decoder by transmitting a separate flag. Alternatively, such as Position dependent intra prediction (PDPC), Mode Dependent Intra Smoothing (MDIS), etc. may be performed according to a specific condition without transmitting separate usage information.

[0165] In an embodiment of the present disclosure, a method for signaling information for the linear model prediction method previously described in the embodiment of FIG. 4 and / or FIG. 5 is described.

[0166] In one embodiment, a flag indicating whether linear model prediction is applied may be signaled. Also, as an example, flag transmission for the linear model prediction method may vary depending on the combination with other intra prediction methods. The linear model prediction method may not be applied to a specific intra prediction method among the above-mentioned intra prediction methods. For example, if the linear model prediction method is not used in ISP (Intra Sub-Partitions), a flag for the linear model prediction method may be signaled before the ISP flag. That is, when ISP information needs to be parsed as shown in Table 5 below, it is possible to determine whether or not ISP information parsing is performed according to the flag for the prediction method. That is, a flag value indicating whether or not the linear model prediction method is applied may be checked as a condition for parsing ISP information.

[0167] [Table 5]

[0168] In Table 5, pos_dep_linear_model_flag indicates a syntax element indicating whether linear model prediction is applied. If the pos_dep_linear_model_flag value is 1, it may indicate that linear model prediction is applied. If the pos_dep_linear_model_flag value is 0, it may indicate that linear model prediction is not applied. isp_flag indicates a syntax element indicating whether ISP is applied. isp_flag may be signaled only if the pos_dep_linear_model_flag value is 0.

[0169] Also, as an example, a higher priority can be applied to the ISP, i.e., whether or not to parse the information indicating whether or not the linear model prediction is applied only when the ISP is not used can be determined based on the parsed ISP information as shown in Table 6 below.

[0170] [Table 6]

[0171] As another example, a syntax element indicating whether linear model prediction is applied regardless of ISP information may be signaled / parsed. The flag transmission method for linear model prediction is not limited to the correlation with ISP, and the above-mentioned method may be applied in the same manner in combination with other prediction methods. That is, the presence or absence of parsing may be determined depending on the correlation between other prediction methods such as MIP, DIMD, TIMD, MRL, etc. and the linear model prediction method.

[0172] Also, for example, whether or not information regarding the linear model prediction method is signaled may be determined depending on the size of the block. For example, the linear model prediction flag may not be signaled for blocks having less than a certain number of pixels, or the linear model prediction flag may not be signaled for blocks having a size smaller than a certain size.

[0173] Also, for example, whether or not information regarding the linear model prediction method is signaled may be determined according to chrominance component information. For example, a linear model prediction flag may be signaled for a luminance component, and a linear model prediction flag may not be signaled for a chrominance component.

[0174] Alternatively, the application or activation of linear model prediction may be controlled through higher level syntax such as a video parameter set (VPS), sequence parameter set (SPS), picture parameter set (PPS), slice header, etc. For example, whether or not linear model prediction is used in the entire sequence may be signaled by signaling sps_pos_dep_linear_model_enabled_flag in the SPS. In addition, whether or not linear model prediction is applied at a lower level may be determined depending on whether or not linear model prediction is activated at a higher level.

[0175] Also, in one embodiment of the present disclosure, information regarding the linear model prediction method may be coded as a general intra prediction mode. The general intra prediction mode refers to an intra prediction mode defined according to a prediction directionality. In VVC, the general intra prediction mode may be configured with 67 non-directional and directional modes. According to this embodiment, a linear model prediction mode may be added to the general intra prediction modes. When 67 general intra prediction modes are defined, 68 intra prediction modes may be defined including the linear model prediction mode.

[0176] For example, the linear model prediction mode may be the second mode. That is, the linear model prediction mode may be assigned a mode number next to the non-directional prediction modes DC and planar modes. Or the linear model prediction mode may be number 67. That is, the linear model prediction mode may be assigned a mode number after the last mode number of the existing prediction modes, number 66. The linear model prediction mode may be added to the MPM candidates according to the MPM configuration method and may be coded as one of the MPM modes. Or, when not inserted into the MPM candidate list, the linear model prediction mode may be grouped with the remaining intra modes and coded.

[0177] Alternatively, information for the linear model prediction method can be combined with the MRL, i.e., the linear model prediction method can parse the MRL index, which indicates information on adjacent pixels as well as non-adjacent reference lines, and derive a linear model based on this.

[0178] Also, in one embodiment of the present disclosure, information on the linear model prediction method may be signaled with a relatively high priority. As an example, information on the linear model prediction method may be signaled using a separate flag together with the planar mode. That is, the linear model prediction mode and the planar mode may be grouped for the current block, and the use or non-use of the linear model prediction method may be signaled in preference to other intra prediction modes. As shown in Table 7 below, information indicating whether the current block is coded in the linear model prediction mode or the planar mode may be signaled first, and a flag may be additionally signaled to indicate the mode to be applied in the linear model prediction mode or the planar mode.

[0179] [Table 7]

[0180] In Table 7, plane_coding_flag indicates a syntax element indicating whether the current block is coded in linear model prediction mode or planar mode. A plane_coding_flag value of 1 may indicate that the current block is coded in linear model prediction mode or planar mode. A plane_coding_flag value of 0 may indicate that the current block is not coded in linear model prediction mode or planar mode. If the plane_coding_flag value is 1, is_planar_mode_flag may be signaled. If the plane_coding_flag value is 0, an MPM-based intra-prediction mode induction method may be performed.

[0181] The linear model prediction method may have a similar property to the planar mode, in that the amount of change in the x-axis and y-axis is determined according to the reference sample value and the coordinate of the reference sample. Therefore, after a flag is transmitted in consideration of assigning a relatively high priority to the planar mode having a relatively high selection probability, if the corresponding flag is 1, a flag indicating whether the mode is the linear model prediction mode or the planar mode may be additionally transmitted to distinguish the mode.

[0182] For example, a flag for distinguishing between a planar mode and a linear model prediction method may be coded by detouring coding with a probability of 0.5 at all times, or the flag for distinguishing between a planar mode and a linear model prediction method may be coded by context coding (using CABAC context).

[0183] Also, as described above, a linear model using the left reference sample and the upper reference sample can be derived, and intra prediction can be performed based on the linear model. In one embodiment of the present disclosure, a method for deriving a linear model using the left reference sample and / or the upper reference sample and a flag signaling method therefor are proposed.

[0184] As shown in Table 8 below, after a flag signaling indicating whether or not linear model prediction is applied, information indicating whether to use left and upper reference samples or whether to use left or upper reference samples may be signaled.

[0185] [Table 8]

[0186] Referring to Table 8, pos_dep_linear_model_flag is a syntax element indicating whether or not linear model prediction is applied. If the pos_dep_linear_model_flag value is 1, it may indicate that linear model prediction is applied. If the pos_dep_linear_model_flag value is 0, it may indicate that linear model prediction is not applied. is_above_left_flag is a syntax element indicating whether the current block uses all upper and left reference samples for linear model induction. If the is_above_left_flag value is 1, all upper and left reference samples may be used for linear model induction. If the is_above_left_flag value is 0, it may indicate that a reference sample in one direction, either the upper or left reference sample, is used for linear model induction. If the is_above_left_flag value is 0, it may be signaled through the is_left_flag syntax element whether a reference sample is used to calculate parameters from the upper and left reference samples.

[0187] FIG. 6 illustrates a schematic configuration of an intra prediction unit 331 that performs the intra prediction method according to the present disclosure.

[0188] Referring to FIG. 6, the intra prediction unit 331 may include a reference sample construction unit 600, a linear model parameter derivation unit 610, and a predicted sample generation unit 620.

[0189] Specifically, the reference sample constructing unit 600 may construct reference samples for linear model intra prediction based on the restored surrounding samples of the current block. And, the linear model parameter inducing unit 610 may derive linear model parameters (or variables) based on the constructed reference samples. In other words, the reference sample constructing unit 600 may construct reference samples for linear model intra prediction based on the restored surrounding samples of the current block, and the linear model parameter inducing unit 610 may derive (or determine) a linear model based on the constructed reference samples. A linear model used for linear model intra prediction may be induced by the linear model parameters induced by the linear model parameter inducing unit 610. Various embodiments of the linear model-based intra prediction method have been described in detail above with reference to FIG. 4 and FIG. 5, and a duplicated description related thereto will be omitted.

[0190] As described above, the linear model parameter inducer 610 can induce a linear model based on the reconstructed samples around the current block. Specifically, the linear model parameter inducer 610 can induce linear model parameters using values ​​and / or coordinate information (or position information) of the surrounding reconstructed samples, and a linear model can be determined by the induced linear model parameters. At this time, a linear model such as the above-mentioned mathematical formula 1 can be defined, and a predicted sample at the (x, y) position can be generated using the linear model such as the mathematical formula 1.

[0191] Also, as described above, a linear model may be determined using a predefined specific number of reference samples and / or reference samples at specific positions. In other words, according to an embodiment of the present invention, the number and / or positions of reference samples used to derive linear model parameters may be predefined. The linear model according to the above-described Equation 1 may change linear model parameter values ​​depending on which sample is used among the neighboring reference samples of the current block.

[0192] Also, as described above, the linear model parameter inducer 610 can induce a linear model based on available reference pixels among the restored pixels surrounding the current block. In other words, the linear model parameter inducer 610 can induce a linear model using only pixels having valid values ​​among the surrounding pixels of the current block.

[0193] Also, as described above, the linear model parameter inducer 610 may induce a linear model using some of the induced parameters. In other words, the linear model parameter inducer 610 induces a linear equation using reconstructed pixels around the current block and coordinate information of the pixels, but may determine a linear model using only some of the induced linear model parameters. As an example, a horizontal linear model and a vertical linear model may be induced in a manner that does not use parameters for the x coordinate or y coordinate, and a predicted block may be generated based on the horizontal linear model and vertical linear model.

[0194] Also, as described above, a linear model may be derived using only some of the reference samples, and a predicted sample may be generated based on the linear model. As an example, a linear model may be derived using the left reference sample and the upper reference sample. A predicted sample may be generated using each linear model, and the generated predicted samples may be blended (or weighted summed) to generate a final predicted sample.

[0195] Also, as described above, multiple reference lines, including not only sample lines adjacent to the current block but also non-adjacent neighboring samples, may be used to derive the linear model. The embodiment previously described with reference to FIG. 4 uses coordinate information and pixel values, so it can be applied in substantially the same manner when multiple reference lines are used.

[0196] Also, as described above, the embodiments previously described in Tables 5 to 8 may be substantially applied in the same manner. That is, information related to linear model intra prediction may be signaled in the manner previously described in Tables 5 to 8. Repetitive descriptions related thereto will be omitted.

[0197] The predicted sample generator 620 may generate a predicted sample of the current block based on the linear model parameters. In other words, the predicted sample generator 620 may perform intra prediction on the current block based on the induced linear model parameters (or linear model). A predicted sample may be generated on a sample-by-sample basis according to the position of the current sample within the current block based on the induced linear model.

[0198] FIG. 7 illustrates an inter prediction method performed by an encoding apparatus 200 according to an embodiment of the present disclosure.

[0199] In one embodiment of the present disclosure, a linear model intra prediction method performed by an encoding device will be described. The encoding device can derive a linear model based on reconstructed samples around a current block and perform intra prediction using the induced linear model. The embodiments previously described in FIG. 5 and FIG. 6 for linear model intra prediction can be applied in substantially the same manner, and therefore repeated description will be omitted here.

[0200] 7, the encoding apparatus may configure reference samples for linear model intra prediction based on reconstructed neighboring samples of the current block (S700), and derive linear model parameters (or variables) based on the constructed reference samples (S710). In other words, the encoding apparatus may configure reference samples for linear model intra prediction based on reconstructed neighboring samples of the current block, and derive (or determine) a linear model based on the constructed reference samples. A linear model used for linear model intra prediction may be induced based on the linear model parameters induced in step S710.

[0201] The encoding device may derive a linear model based on reconstructed samples around the current block. Specifically, the encoding device may derive linear model parameters using values ​​and / or coordinate information (or position information) of the surrounding reconstructed samples, and a linear model may be determined based on the induced linear model parameters. In this case, a linear model such as the above-mentioned Equation 1 may be defined, and a predicted sample at the (x, y) position may be generated using the linear model such as the above-mentioned Equation 1.

[0202] Also, as described above, a linear model may be determined using a predefined number of reference samples and / or reference samples at predefined positions. In other words, the number and / or positions of reference samples used to derive linear model parameters may be predefined. The linear model according to Equation 1 may change linear model parameter values ​​depending on which sample is used among the neighboring reference samples of the current block.

[0203] Also, as described above, the encoding device can derive a linear model based on available reference pixels among the reconstructed pixels surrounding the current block, i.e., the encoding device can derive a linear model using only pixels having valid values ​​among the surrounding pixels of the current block.

[0204] Also, as described above, the encoding apparatus may induce a linear model using some of the induced parameters. In other words, the encoding apparatus may induce a linear equation using reconstructed pixels around the current block and coordinate information of the pixels, but may determine a linear model using only some of the induced linear model parameters. As an example, a horizontal linear model and a vertical linear model may be induced in a manner that does not use parameters for the x coordinate or y coordinate, and a prediction block may be generated based on the horizontal linear model and the vertical linear model.

[0205] Also, as described above, a linear model may be derived using only some of the reference samples, and a predicted sample may be generated based on the linear model. As an example, a linear model may be derived using the left reference sample and the upper reference sample. A predicted sample may be generated using each linear model, and the generated predicted samples may be blended (or weighted summed) to generate a final predicted sample.

[0206] Also, as described above, multiple reference lines, including not only sample lines adjacent to the current block but also non-adjacent neighboring samples, may be used to derive the linear model. The embodiment previously described with reference to FIG. 4 uses coordinate information and pixel values, so it can be applied in substantially the same manner when multiple reference lines are used.

[0207] Also, as mentioned above, the embodiments previously described with reference to Figures 5 to 8 may be applied in substantially the same manner, that is, information related to linear model intra prediction may be signaled in the manner previously described with reference to Figures 5 to 8.

[0208] The encoding apparatus may generate a predicted sample of the current block based on the linear model parameters (S720). In other words, the encoding apparatus may perform intra prediction for the current block based on the induced linear model parameters (or linear model). A predicted sample may be generated on a sample-by-sample basis according to the position of the current sample within the current block based on the induced linear model.

[0209] FIG. 8 illustrates a schematic configuration of the intra prediction unit 222 that performs the inter prediction method according to the present disclosure.

[0210] Referring to FIG. 8, the intra prediction unit 222 may include a reference sample construction unit 800, a linear model parameter derivation unit 810, and a predicted sample generation unit 820.

[0211] Specifically, the reference sample constructing unit 800 may construct reference samples for linear model intra prediction based on the restored surrounding samples of the current block. And, the linear model parameter inducing unit 810 may derive linear model parameters (or variables) based on the constructed reference samples. In other words, the reference sample constructing unit 800 may construct reference samples for linear model intra prediction based on the restored surrounding samples of the current block, and the linear model parameter inducing unit 810 may derive (or determine) a linear model based on the constructed reference samples. A linear model used for linear model intra prediction may be induced by the linear model parameters induced by the linear model parameter inducing unit 810. Various embodiments of the linear model-based intra prediction method have been described in detail with reference to FIG. 4 and FIG. 5, and a duplicated description related thereto will be omitted.

[0212] As described above, the linear model parameter inducer 810 can induce a linear model based on the reconstructed samples around the current block. Specifically, the linear model parameter inducer 810 can induce linear model parameters using values ​​and / or coordinate information (or position information) of the surrounding reconstructed samples, and a linear model can be determined by the induced linear model parameters. At this time, a linear model such as the above-mentioned mathematical formula 1 can be defined, and a predicted sample at the (x, y) position can be generated using the linear model such as the mathematical formula 1.

[0213] Also, as described above, a linear model may be determined using a predefined specific number of reference samples and / or reference samples at specific positions. In other words, according to an embodiment of the present invention, the number and / or positions of reference samples used to derive linear model parameters may be predefined. The linear model according to the above-described Equation 1 may change linear model parameter values ​​depending on which sample is used among the neighboring reference samples of the current block.

[0214] Also, as described above, the linear model parameter inducer 810 can induce a linear model based on available reference pixels among the restored pixels surrounding the current block. In other words, the linear model parameter inducer 810 can induce a linear model using only pixels having valid values ​​among the surrounding pixels of the current block.

[0215] Also, as described above, the linear model parameter inducer 810 may induce a linear model using some of the induced parameters. In other words, the linear model parameter inducer 810 induces a linear equation using reconstructed pixels around the current block and coordinate information of the pixels, but may determine a linear model using only some of the induced linear model parameters. As an example, a horizontal linear model and a vertical linear model may be induced in a manner that does not use parameters for the x coordinate or y coordinate, and a predicted block may be generated based on the horizontal linear model and vertical linear model.

[0216] Also, as described above, a linear model may be derived using only some of the reference samples, and a predicted sample may be generated based on the linear model. As an example, a linear model may be derived using the left reference sample and the upper reference sample. A predicted sample may be generated using each linear model, and the generated predicted samples may be blended (or weighted summed) to generate a final predicted sample.

[0217] Also, as described above, multiple reference lines, including not only sample lines adjacent to the current block but also non-adjacent neighboring samples, may be used to derive the linear model. The embodiment previously described with reference to FIG. 4 uses coordinate information and pixel values, so it can be applied in substantially the same manner when multiple reference lines are used.

[0218] Also, as described above, the embodiments previously described in Tables 5 to 8 may be substantially applied in the same manner. That is, information related to linear model intra prediction may be signaled in the manner previously described in Tables 5 to 8. Repetitive descriptions related thereto will be omitted.

[0219] The predicted sample generator 820 may generate a predicted sample of the current block based on the linear model parameters. In other words, the predicted sample generator 820 may perform intra prediction on the current block based on the induced linear model parameters (or linear model). A predicted sample may be generated on a sample-by-sample basis according to the position of the current sample within the current block based on the induced linear model.

[0220] In the above embodiments, the methods are described with reference to flowcharts as a series of steps or blocks, but the embodiments are not limited to the order of steps, and certain steps may occur in a different order or simultaneously with other steps than those described. Additionally, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive, and other steps may be included, or one or more steps of the flowcharts may be omitted, without affecting the scope of the embodiments herein.

[0221] The methods according to the embodiments of this document described above may be embodied in software form, and the encoding device and / or decoding device according to this document may be included in devices that perform image processing, such as TVs, computers, smartphones, set-top boxes, and display devices.

[0222] When the embodiments in this document are implemented in software, the methods described above may be implemented with modules (processes, functions, etc.) that perform the functions described above. The modules may be stored in a memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor in a variety of ways that are well known in the art. The processor may include an application-specific integrated circuit (ASIC), 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 document may be implemented and performed on a processor, microprocessor, controller, or chip. For example, the functional units illustrated in each drawing may be implemented and performed on a computer, processor, microprocessor, controller, or chip. In this case, information on instructions or algorithms for implementation may be stored on a digital storage medium.

[0223] In addition, the decoding device and encoding device to which the embodiment(s) of the present specification are applied may be included in a multimedia broadcasting transmitting / receiving device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video interactive device, a real-time communication device such as a video communication, a mobile streaming device, a storage medium, a video camera, a video on demand (VoD) service providing device, an OTT video (Over the top video) device, an Internet streaming service providing device, a three-dimensional (3D) video device, a virtual reality (VR) device, an argumente reality (AR) device, an image telephone video device, a transportation means terminal (e.g., a vehicle (including an autonomous vehicle) terminal, an airplane terminal, a ship terminal, etc.), and a medical video device, and may be used to process a video signal or a data signal. For example, an OTT video (Over the top video) device may include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smartphone, a tablet PC, a DVR (Digital Video Recorder), etc.

[0224] In addition, the processing method to which the embodiment(s) of the present specification is applied may be produced in the form of a program executed by a computer and may be stored in a computer-readable recording medium. Multimedia data having a data structure according to the embodiment(s) of the present specification may also be stored in a computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices and distributed storage devices in which computer-readable data is stored. The computer-readable recording medium may include, for example, a Blu-ray Disc (BD), a Universal Serial Bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. The computer-readable recording medium may also include a medium embodied in the form of a carrier wave (e.g., transmission through the Internet). In addition, a bit stream generated by the encoding method may be stored in a computer-readable recording medium or transmitted through a wired / wireless communication network.

[0225] Furthermore, the embodiment(s) of the present specification may be embodied in a computer program product by program code, the program code being executable by a computer in accordance with the embodiment(s) of the present specification. The program code may be stored on a computer readable carrier.

[0226] FIG. 9 illustrates an example of a content streaming system to which embodiments of the present disclosure may be applied.

[0227] Referring to FIG. 9, a content streaming system to which the embodiment(s) of the present specification can be applied may broadly include an encoding server, a streaming server, a web server, a media repository, a user device, and a multimedia input device.

[0228] The encoding server compresses content input from a multimedia input device such as a smartphone, camera, video camera, etc. into digital data to generate a bitstream and transmits the bitstream to the streaming server. As another example, if a multimedia input device such as a smartphone, camera, video camera, etc. directly generates a bitstream, the encoding server may be omitted.

[0229] The bitstream may be generated by an encoding method or a bitstream generating method to which the embodiment(s) of the present specification is applied, and the streaming server may temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0230] The streaming server transmits multimedia data to a user device based on a user request through a web server, and the web server acts as a medium to inform the user of available services. When a user requests a desired service from the web server, the web server transmits the request to the streaming server, and the streaming server transmits multimedia data to the user. At this time, the content streaming system may include a separate control server, and in this case, the control server controls commands / responses between devices in the content streaming system.

[0231] The streaming server may receive content from a media repository and / or an encoding server. For example, if content is received from the encoding server, the content may be received in real time. In this case, the streaming server may store the bitstream for a certain period of time to provide a smooth streaming service.

[0232] Examples of the user devices include mobile phones, smart phones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation systems, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glass, head mounted displays (HMDs)), digital TVs, desktop computers, digital signage, and the like.

[0233] Each server in the content streaming system may be operated as a distributed server, in which case data received by each server may be processed in a distributed manner.

[0234] The claims described herein may be combined in various ways. For example, the technical features of the method claims herein may be combined and embodied in an apparatus, the technical features of the apparatus claims herein may be combined and embodied in a method, the technical features of the method claims herein and the technical features of the apparatus claims herein may be combined and embodied in an apparatus, and the technical features of the method claims herein and the technical features of the apparatus claims herein may be combined and embodied in a method.

Claims

1. constructing a reference sample for linear model intra prediction based on the restored neighboring samples of the current block; deriving linear model parameters based on the reference samples; generating a predicted sample of the current block based on the linear model parameters.

2. 2. The image decoding method of claim 1, wherein the reference samples include at least one of a reference sample included in a left sample line adjacent to the current block, a reference sample included in an upper sample line adjacent to the current block, or an upper left reference sample adjacent to the current block.

3. 3. The image decoding method of claim 2, wherein, when the current block is NxN, the reference samples include (N+1) reference samples consecutively adjacent to the left of the upper-left reference sample in the left sample line and (N+1) reference samples consecutively adjacent to the bottom end of the upper-left reference sample in the upper sample line.

4. The step of constructing the reference sample comprises:

2. The method of claim 1, further comprising checking whether reconstructed neighboring samples of the current block are available.

5. The image decoding method of claim 1 , wherein the linear model parameters include at least one of a horizontal component parameter and a vertical component parameter.

6. The step of deriving linear model parameters comprises: The video decoding method of claim 5 , further comprising setting the horizontal component parameter or the vertical component parameter to zero among the linear model parameters derived based on the reference sample.

7. The step of generating the predicted samples comprises: generating a first predicted sample using the linear model parameters derived based on the reference sample; generating a second predicted sample using linear model parameters with the horizontal component parameter or the vertical component parameter set to 0; and generating a final predicted sample by weighted summing the first predicted sample and the second predicted sample.

8. The step of deriving linear model parameters comprises: deriving linear model parameters of a first linear model using only the left reference samples of the current block; 2. The method of claim 1, further comprising: deriving linear model parameters of a second linear model using only the upper reference samples of the current block.

9. 9. The image decoding method of claim 8, wherein the predicted sample of the current block is generated based on a weighted sum of a third predicted sample generated using linear model parameters of the first linear model and a fourth predicted sample generated using linear model parameters of the second linear model.

10. obtaining a reference line index indicating one of multiple reference sample lines of the current block; The image decoding method of claim 1 , wherein the reference samples are constructed using reference samples included in a reference sample line indicated by the reference line index.

11. constructing a reference sample for linear model intra prediction based on the restored neighboring samples of the current block; deriving linear model parameters based on the reference samples; generating a predicted sample of the current block based on the linear model parameters.

12. A computer-readable storage medium storing a bitstream generated by the video encoding method of claim 11.

13. constructing a reference sample for linear model intra prediction based on the restored neighboring samples of the current block; deriving linear model parameters based on the reference samples; generating a predicted sample of the current block based on the linear model parameters; generating a bitstream by encoding the current block based on the predicted samples; transmitting data including the bitstream.

Images