Image encoding / decoding method and apparatus for performing PDPC, and method for transmitting bitstream

Abstract

Provided are an image encoding / decoding method and apparatus for performing PDPC, and a method for transmitting a bitstream.SOLUTION: An image decoding method includes generating a prediction block by performing intra prediction on a current block, determining whether to apply PDPC to the prediction block, and generating a final prediction block of the current block by applying the PDPC to the prediction block based on the determination. The step of determining whether to apply the PDPC to the prediction block includes determining whether a size of the current block satisfies a predetermined condition, determining to apply the PDPC to the prediction block based on that the size of the current block satisfies the predetermined condition, and when the size of the current block does not satisfy the predetermined condition, skipping the determination on the color component of the current block and determining not to apply the PDPC to the prediction block.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present disclosure relates to an image encoding / decoding method and apparatus, and more particularly to an image encoding / decoding method and apparatus that perform position-dependent intra prediction (PDPC), and a method for transmitting a bitstream generated by the image encoding method / apparatus of the present disclosure. [Background technology]

[0002] Recently, demand for high-resolution, high-quality images, such as HD (High Definition) images and UHD (Ultra High Definition) images, has been increasing in various fields. As image data becomes higher in resolution and quality, the amount of information or bits to be transmitted increases relatively compared to conventional image data. The increase in the amount of information or bits to be transmitted results in an increase in transmission costs and storage costs.

[0003] This requires highly efficient image compression techniques for effectively transmitting, storing, and reproducing high-resolution, high-quality image information. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0005] Another object of the present disclosure is to provide an image encoding / decoding method and apparatus that improves encoding / decoding efficiency by making the PDPC application requirements for chrominance blocks and luminance blocks the same.

[0006] Another object of the present disclosure is to provide a method for transmitting a bitstream generated by the image encoding method or apparatus according to the present disclosure.

[0007] Another object of the present disclosure is to provide a recording medium storing a bitstream generated by the image encoding method or apparatus according to the present disclosure.

[0008] Another object of the present disclosure is to provide a recording medium storing a bitstream that is received by an image decoding device according to the present disclosure, decoded, and used to restore an image.

[0009] The technical problems to be solved by the present disclosure are not limited to the above-mentioned technical problems, and other technical problems not mentioned above will be clearly understood by a person having ordinary skill in the technical field to which the present disclosure pertains from the following description. [Means for solving the problem]

[0010] An image decoding method performed by an image decoding device according to one aspect of the present disclosure may include the steps of: performing intra prediction on a current block to generate a predicted block; determining whether to apply PDPC to the predicted block; and generating a final predicted block of the current block by applying PDPC to the predicted block based on the determination. The step of determining whether to apply PDPC to the predicted block may include determining whether a size of the current block satisfies a predetermined condition, and determining to apply PDPC to the predicted block based on whether the size of the current block satisfies the predetermined condition; and skipping a determination on a color component of the current block and determining not to apply PDPC to the predicted block based on whether the size of the current block does not satisfy the predetermined condition.

[0011] In the image decoding method according to the present disclosure, the predetermined condition may be that the size of the current block is equal to or greater than a predetermined threshold.

[0012] In the image decoding method according to the present disclosure, if the width of the current block is equal to or greater than the predetermined threshold and the height of the current block is equal to or greater than the predetermined threshold, the predetermined condition can be satisfied.

[0013] In the image decoding method according to the present disclosure, the predetermined threshold value may be four.

[0014] In the image decoding method according to the present disclosure, the step of determining whether to apply PDPC to the prediction block may further include determining a reference sample line used in intra prediction of the current block.

[0015] In the image decoding method according to the present disclosure, it is possible to determine that PDPC is applied to the predicted block based on whether the reference sample line is a predetermined reference sample line, and if the reference sample line is not a predetermined reference sample line, it is possible to skip the determination on the color component of the current block and determine that PDPC is not applied to the predicted block.

[0016] In the image decoding method according to the present disclosure, the predetermined reference sample line may be a first reference sample line adjacent to the current block.

[0017] In the image decoding method according to the present disclosure, the step of determining whether to apply PDPC to the prediction block may further include determining whether BDPCM is applied to the current block and determining the intra prediction mode of the current block.

[0018] An image decoding apparatus according to another aspect of the present disclosure may include a memory and at least one processor. The at least one processor may perform intra prediction on a current block to generate a predicted block, determine whether to apply PDPC to the predicted block, and apply PDPC to the predicted block based on the determination to generate a final predicted block for the current block. The determination of whether to apply PDPC to the predicted block may include determining whether a size of the current block satisfies a predetermined condition, and may determine to apply PDPC to the predicted block based on whether the size of the current block satisfies the predetermined condition. If the size of the current block does not satisfy the predetermined condition, the image decoding apparatus may skip a determination on a color component of the current block and determine not to apply PDPC to the predicted block.

[0019] An image encoding method performed by an image encoding device according to another aspect of the present disclosure may include the steps of performing intra prediction on a current block to generate a predicted block, determining whether to apply PDPC to the predicted block, and generating a final predicted block for the current block by applying PDPC to the predicted block based on the determination. The step of determining whether to apply PDPC to the predicted block may include determining whether a size of the current block satisfies a predetermined condition, and determining to apply PDPC to the predicted block based on whether the size of the current block satisfies the predetermined condition, and may skip a determination on a color component of the current block and determine not to apply PDPC to the predicted block if the size of the current block does not satisfy the predetermined condition.

[0020] In the image encoding method according to the present disclosure, the predetermined condition may be that the size of the current block is equal to or greater than a predetermined threshold.

[0021] In the image coding method according to the present disclosure, the predetermined condition can be satisfied if the width of the current block is equal to or greater than the predetermined threshold and the height of the current block is equal to or greater than the predetermined threshold.

[0022] In the image coding method according to the present disclosure, the predetermined threshold may be four.

[0023] In the image encoding method according to the present disclosure, the step of determining whether to apply PDPC to the predicted block may further include determining a reference sample line used in intra prediction of the current block.

[0024] In the image encoding method according to the present disclosure, it is possible to determine that PDPC is applied to the predicted block based on whether the reference sample line is a predetermined reference sample line, and if the reference sample line is not a predetermined reference sample line, it is possible to skip the determination on the color components of the current block and determine not to apply PDPC to the predicted block.

[0025] In the image encoding method according to the present disclosure, the predetermined reference sample line may be a first reference sample line adjacent to the current block.

[0026] In the image encoding method according to the present disclosure, the step of determining whether to apply PDPC to the predicted block may further include determining whether BDPCM is applied to the current block and determining an intra prediction mode of the current block.

[0027] A transmission method according to another aspect of the present disclosure can transmit a bitstream generated by the image encoding device or image encoding method of the present disclosure.

[0028] A computer-readable recording medium according to another aspect of the present disclosure can store a bitstream generated by the image encoding method or image encoding device of the present disclosure.

[0029] The features described above in this brief summary of the present disclosure are merely exemplary embodiments of the detailed description of the present disclosure that follows and are not intended to limit the scope of the present disclosure. [Effects of the Invention]

[0030] According to the present disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0031] In addition, according to the present disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided by simplifying the decision on whether to apply PDPC by using a unified PDPC application condition for the luma component and the chroma component in intra prediction encoding / decoding.

[0032] The present disclosure also provides a method for transmitting a bitstream generated by the image encoding method or apparatus according to the present disclosure.

[0033] Furthermore, according to the present disclosure, a recording medium storing a bitstream generated by the image encoding method or apparatus according to the present disclosure can be provided.

[0034] Furthermore, according to the present disclosure, it is possible to provide a recording medium that stores a bitstream that is received by the image decoding device according to the present disclosure, decoded, and used to restore an image.

[0035] The effects obtained by the present disclosure are not limited to the effects described above, and other effects not described above will be clearly understood by those having ordinary skill in the art to which the present disclosure pertains from the following description. [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 illustrates a video coding system according to the present disclosure. [Figure 2]1 is a diagram schematically illustrating an image encoding device to which an embodiment of the present disclosure can be applied. [Figure 3] FIG. 1 is a diagram schematically illustrating an image decoding device to which an embodiment of the present disclosure can be applied. [Figure 4] FIG. 1 is a diagram illustrating a division structure of an image according to an embodiment of the present disclosure. [Figure 5] FIG. 10 is a diagram showing block division types according to a multi-type tree structure. [Figure 6] FIG. 1 illustrates a signaling mechanism for block partition information in a quadtree with nested multi-type tree structure according to the present disclosure. [Figure 7] FIG. 10 illustrates an embodiment in which a CTU is divided into multiple CUs. [Figure 8] 1 illustrates an intra-prediction based video / image coding method. [Figure 9] FIG. 1 is a diagram illustrating an intra-prediction unit in an encoding device. [Figure 10] FIG. 1 illustrates an intra-prediction based video / image decoding method. [Figure 11] FIG. 10 is a diagram illustrating an intra prediction unit in a decoding device. [Figure 12] FIG. 10 is a diagram illustrating directional intra prediction modes among intra prediction modes. [Figure 13a] FIG. 1 is a diagram showing reference samples defined by PDPC. [Figure 13b] FIG. 1 is a diagram showing reference samples defined by PDPC. [Figure 13c] FIG. 1 is a diagram showing reference samples defined by PDPC. [Figure 13d] FIG. 1 is a diagram showing reference samples defined by PDPC. [Figure 14] FIG. 10 is a diagram for explaining a reference sample line that can be used in the MRL method. [Figure 15] 10 is a diagram showing the syntax structure of a coding unit signaling the multiple reference line index. [Figure 16]FIG. 10 is a diagram illustrating PDPC application conditions according to an embodiment of the present disclosure. [Figure 17] FIG. 10 is a diagram illustrating PDPC application conditions according to another embodiment of the present disclosure. [Figure 18] FIG. 10 is a diagram illustrating a PDPC application condition according to another embodiment of the present disclosure. [Figure 19] 1 is a flowchart illustrating a method for generating a prediction block according to an embodiment of the present disclosure. [Figure 20] FIG. 1 illustrates a content streaming system to which an embodiment of the present disclosure can be applied. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present disclosure will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily implement the present disclosure. However, the present disclosure may be embodied in various different forms and is not limited to the embodiments described herein.

[0038] In describing the embodiments of the present disclosure, if it is determined that a detailed description of a known configuration or function may obscure the gist of the present disclosure, the detailed description thereof will be omitted. In addition, in the drawings, parts that are not related to the description of the present disclosure will be omitted, and similar parts will be designated by similar reference numerals.

[0039] In this disclosure, when a component is referred to as being "coupled," "coupled," or "connected" to another component, this includes not only a direct connection, but also an indirect connection where another component exists between them. Furthermore, when a component is referred to as "including" or "having" another component, this does not mean that the other component is excluded, but that the component can further include the other component, unless otherwise specified.

[0040] In this disclosure, terms such as "first" and "second" are used only to distinguish one component from another component, and do not limit the order or importance of the components unless otherwise specified. Therefore, within the scope of this disclosure, a first component in one embodiment may be called a second component in another embodiment, and similarly, a second component in one embodiment may be called a first component in another embodiment.

[0041] In this disclosure, components that are distinguished from one another are used to clearly describe the characteristics of each component and do not necessarily mean that the components are separate. In other words, multiple components may be integrated into a single hardware or software unit, or a single component may be distributed into multiple hardware or software units. Therefore, even if not otherwise specified, such integrated or distributed embodiments are also included within the scope of this disclosure.

[0042] In this disclosure, the components described in various embodiments are not necessarily essential components, and some may be optional components. Therefore, an embodiment consisting of a subset of the components described in one embodiment is also within the scope of this disclosure. Furthermore, an embodiment including other components in addition to the components described in various embodiments is also within the scope of this disclosure.

[0043] The present disclosure relates to image encoding and decoding, and terms used in this disclosure may have their ordinary meaning in the technical field to which the present disclosure belongs unless they are newly defined in this disclosure.

[0044] In this disclosure, a "picture" generally refers to a unit representing any one image in a specific time period, and a slice / tile is a coding unit constituting a part of a picture, and one picture may be composed of one or more slices / tiles. Furthermore, a slice / tile may include one or more coding tree units (CTUs).

[0045] In this disclosure, "pixel" or "pel" may refer to the smallest unit constituting one picture (or image). Also, "sample" may be used as a term corresponding to pixel. A sample may generally indicate a pixel or a pixel value, may indicate only a pixel / pixel value of a luma component, or may indicate only a pixel / pixel value of a chroma component.

[0046] In this disclosure, the term "unit" refers 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 that region. The term "unit" may be used interchangeably with terms such as "sample array," "block," or "area," depending on the situation. In general, an M×N block may include a set (or array) of samples or transform coefficients consisting of M columns and N rows.

[0047] In the present disclosure, a "current block" may refer to any one of a "current coding block," a "current coding unit," a "block to be coded," a "block to be decoded," or a "block to be processed." When prediction is performed, a "current block" may refer to a "current predicted block" or a "block to be predicted." When transformation (inverse transformation) / quantization (inverse quantization) is performed, a "current block" may refer to a "current transformed block" or a "block to be transformed." When filtering is performed, a "current block" may refer to a "block to be filtered."

[0048] In this disclosure, "current block" may mean "luma block of the current block" unless explicitly stated as a chroma block. "Chroma block of the current block" may be expressed explicitly as "chroma block" or "current chroma block" including the explicit statement of a chroma block.

[0049] In the present disclosure, " / " and "," can be interpreted as "and / or." For example, "A / B" and "A, B" can be interpreted as "A and / or B." Also, "A / B / C" and "A, B, C" can mean "at least one of A, B, and / or C."

[0050] In this disclosure, "or" can be interpreted as "and / or." For example, "A or B" can mean 1) only "A," 2) only "B," or 3) "A and B." Alternatively, in this disclosure, "or" can mean "additionally or alternatively."

[0051] Video Coding System Overview

[0052] FIG. 1 is a diagram illustrating a video coding system according to this disclosure.

[0053] A video coding system according to one embodiment may include an encoding device 10 and a decoding device 20. The encoding device 10 may transmit encoded video and / or image information or data to the decoding device 20 in a file or streaming format via a digital storage medium or a network.

[0054] An encoding device 10 according to an embodiment may include a video source generation unit 11, an encoding unit 12, and a transmission unit 13. A decoding device 20 according to an embodiment may include a reception unit 21, a decoding unit 22, and a rendering unit 23. The encoding unit 12 may be referred to as a video / image encoding unit, and the decoding unit 22 may be referred to as a video / image decoding unit. The transmission unit 13 may be included in the encoding unit 12. The reception unit 21 may be included in the decoding unit 22. The rendering unit 23 may include a display unit, which may be configured as a separate device or an external component.

[0055] The video source generation unit 11 can acquire video / images through a video / image capture, synthesis, or generation process. The video source generation unit 11 can include a video / image capture device and / or a video / image generation device. The video / image capture device can include, for example, one or more cameras, a video / image archive containing previously captured video / images, etc. The video / image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate video / images. For example, a virtual video / image can be generated via a computer, etc. In this case, the video / image capture process can be replaced with a process in which related data is generated.

[0056] The encoder 12 may encode the input video / image. The encoder 12 may perform a series of steps such as prediction, transformation, and quantization for compression and coding efficiency. The encoder 12 may output the encoded data (encoded video / image information) in a bitstream format.

[0057] The transmitter 13 may transmit the encoded video / image information or data output in a bitstream format to the receiver 21 of the decoding device 20 in a file or streaming format via a digital storage medium or a network. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray®, HDD, and SSD. The transmitter 13 may include elements for generating a media file in a predetermined file format and elements for transmitting via a broadcasting / communication network. The receiver 21 may extract / receive the bitstream from the storage medium or network and transmit it to the decoder 22.

[0058] The decoding unit 22 can decode the video / image by performing a series of steps such as inverse quantization, inverse transformation, and prediction corresponding to the operations of the encoding unit 12.

[0059] The rendering unit 23 can render the decoded video / images, and the rendered video / images can be displayed via the display unit.

[0060] Overview of the image encoding device

[0061] FIG. 2 is a diagram schematically illustrating an image encoding device to which an embodiment of the present disclosure can be applied.

[0062] 2, the image encoding device 100 may include an image division unit 110, a subtraction unit 115, a transform unit 120, a quantization unit 130, an inverse quantization unit 140, an inverse transform unit 150, an addition unit 155, a filtering unit 160, a memory 170, an inter prediction unit 180, an intra prediction unit 185, and an entropy encoding unit 190. The inter prediction unit 180 and the intra prediction unit 185 may be collectively referred to as a "prediction unit." The transform unit 120, the quantization unit 130, the inverse quantization unit 140, and the inverse transform unit 150 may be included in a residual processing unit. The residual processing unit may further include a subtraction unit 115.

[0063] Depending on the embodiment, all or at least some of the components constituting the image encoding device 100 may be realized by a single hardware component (e.g., an encoder or a processor). Also, the memory 170 may include a decoded picture buffer (DPB) and may be realized by a digital storage medium.

[0064] The image division unit 110 may divide an input image (or picture, frame) input to the image encoding device 100 into one or more processing units. As an example, the processing units may be called coding units (CUs). The coding units may be obtained by recursively dividing a coding tree unit (CTU) or a largest coding unit (LCU) using a QT / BT / TT (quad-tree / binary-tree / ternary-tree) structure. For example, one coding unit may be divided into multiple coding units at deeper depths based on a quad-tree structure, a binary-tree structure, and / or a ternary-tree structure. To divide the coding units, the quad-tree structure may be applied first, and then the binary-tree structure and / or the ternary-tree structure may be applied later. The coding procedure according to the present disclosure may be performed based on the final coding unit that is not further divided. The maximum coding unit may be used as the final coding unit, or a lower-depth coding unit obtained by dividing the maximum coding unit may be used as the final coding unit. Here, the coding procedure may include procedures such as prediction, transformation, and / or reconstruction, which will be described later. As another example, a processing unit of the coding procedure may be a prediction unit (PU) or a transform unit (TU). The prediction unit and the transform unit may be divided or partitioned from the final coding unit, respectively. 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.

[0065] The prediction unit (inter prediction unit 180 or intra prediction unit 185) may perform prediction on a current block (current block) to generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied to the current block or CU. The prediction unit may generate various information related to prediction of the current block and transmit it to the entropy coding unit 190. The prediction information may be coded by the entropy coding unit 190 and output in a bitstream format.

[0066] The intra prediction unit 185 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located far away from the current block according to the intra prediction mode and / or intra prediction technique. The intra prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The non-directional modes may include, for example, DC mode and Planar mode. The directional modes may include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the degree of precision of the prediction direction. However, this is merely an example, and more or less directional prediction modes may be used depending on the settings. The intra prediction unit 185 may also determine the prediction mode to be applied to the current block using the prediction modes applied to neighboring blocks.

[0067] The inter prediction unit 180 may derive a predicted block for a current block based on a reference block (reference sample array) identified by a motion vector on a reference picture. To reduce the amount of motion information transmitted in inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation between the motion information of neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include information on the inter prediction direction (e.g., L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks 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. The reference picture including the temporal neighboring block may be called a collocated picture (colPic). For example, the inter predictor 180 may construct a motion information candidate list based on neighboring blocks and generate information indicating which candidate is used to derive a motion vector and / or a reference picture index for the current block. Inter prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter predictor 180 may use motion information of neighboring blocks as motion information for the current block. In the case of skip mode, unlike in merge mode, a residual signal may not be transmitted.In the case of a motion vector prediction (MVP) mode, the motion vector of a neighboring block is used as a motion vector predictor, and the motion vector of the current block can be signaled by encoding a motion vector difference and an indicator for the motion vector predictor. The motion vector difference may mean the difference between the motion vector of the current block and the motion vector predictor.

[0068] The predictor may generate a prediction signal based on various prediction methods and / or prediction techniques, which will be described later. For example, the predictor may apply intra prediction or inter prediction to predict the current block, or may simultaneously apply intra prediction and inter prediction. A prediction method that simultaneously applies intra prediction and inter prediction to predict the current block may be referred to as combined inter and intra prediction (CIIP). The predictor may also perform intra block copy (IBC) to predict the current block. Intra block copy can be used for content image / video coding, such as screen content coding (SCC), for games. IBC is a method of predicting a current block using an already reconstructed reference block in a current picture that is located a predetermined distance away from the current block. When IBC is applied, the position of the reference block in the current picture may be coded as a vector (block vector) corresponding to the predetermined distance. IBC is essentially performed within the current picture, but may be similar to inter prediction in that a reference block is derived within the current picture. That is, the IBC may use at least one of the inter prediction techniques described in this disclosure.

[0069] The prediction signal generated by the prediction unit may be used to generate a restored signal or a residual signal. The subtraction unit 115 may subtract the prediction signal (predicted block, predicted sample array) output from the prediction unit from the input image signal (original block, original sample array) to generate a residual signal (residual signal, residual block, residual sample array). The generated residual signal may be transmitted to the conversion unit 120.

[0070] The transform unit 120 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a Karhunen-Loeve transform (KLT), a graph-based transform (GBT), or a conditionally non-linear transform (CNT). Here, the GBT refers to a transform obtained from a graph representing inter-pixel relationship information. The CNT refers to a transform obtained based on a predicted signal generated using all previously reconstructed pixels. The transform process may be applied to pixel blocks having the same square size or to non-square blocks of variable size.

[0071] The quantization unit 130 may quantize the transform coefficients and transmit the quantized transform coefficients to the entropy coding unit 190. The entropy coding unit 190 may encode the quantized signal (information about the quantized transform coefficients) and output the encoded signal in a bitstream format. The information about the quantized transform coefficients may be referred to as residual information. The quantization unit 130 may rearrange the quantized transform coefficients in a block format into a one-dimensional vector format 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 format.

[0072] The entropy coding unit 190 may perform various coding methods, such as exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). The entropy coding unit 190 may also code information necessary for video / image restoration (e.g., values ​​of syntax elements) together with or separately from the quantized transform coefficients. The coded information (e.g., coded video / image information) may be transmitted or stored in a bitstream format in 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 also include general constraint information. The signaling information, transmitted information and / or syntax elements mentioned in this disclosure may be encoded through the above-described encoding procedure and included in the bitstream.

[0073] The bitstream may be transmitted via 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) that transmits and / or a storing unit (not shown) that stores the signal output from the entropy encoding unit 190 may be provided as an internal / external element of the image encoding device 100, or the transmitting unit may be provided as a component of the entropy encoding unit 190.

[0074] The quantized transform coefficients output from the quantization unit 130 can be used to generate a residual signal. For example, the residual signal (residual block or residual sample) can be reconstructed by applying inverse quantization and inverse transform to the quantized transform coefficients via the inverse quantization unit 140 and the inverse transform unit 150.

[0075] The adder 155 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 180 or the intra prediction unit 185. When there is no residual for the current block to be processed, such as when a skip mode is applied, the predicted block may be used as the reconstructed block. The adder 155 may be referred to as a reconstruction unit or a reconstructed block generation unit. The generated reconstructed signal may be used for intra prediction of the next current block to be processed in the current picture, and may also be used for inter prediction of the next picture after filtering, as will be described later.

[0076] The filtering unit 160 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 160 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture and store the modified reconstructed picture in the memory 170, specifically, in the DPB of the memory 170. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, an adaptive loop filter, a bilateral filter, etc. The filtering unit 160 may generate various information related to filtering and transmit it to the entropy coding unit 190, as will be described later in connection with each filtering method. The filtering information may be coded by the entropy coding unit 190 and output in a bitstream format.

[0077] The modified reconstructed picture transmitted to the memory 170 can be used as a reference picture in the inter prediction unit 180. When inter prediction is applied through this, the image encoding device 100 can avoid a prediction mismatch between the image encoding device 100 and the image decoding device, and can also improve encoding efficiency.

[0078] The DPB in the memory 170 may store modified reconstructed pictures for use as reference pictures in the inter predictor 180. The memory 170 may store motion information of blocks from which motion information in the current picture is derived (or coded) and / or motion information of already reconstructed intra-picture blocks. The stored motion information may be transmitted to the inter predictor 180 to be used as motion information of spatially surrounding blocks or temporally surrounding blocks. The memory 170 may store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra predictor 185.

[0079] Overview of the image decoding device

[0080] FIG. 3 is a diagram schematically illustrating an image decoding device to which an embodiment of the present disclosure can be applied.

[0081] 3, the image decoding apparatus 200 may include an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an adder 235, a filtering unit 240, a memory 250, an inter prediction unit 260, and an intra prediction unit 265. The inter prediction unit 260 and the intra prediction unit 265 may be collectively referred to as a "prediction unit." The inverse quantization unit 220 and the inverse transform unit 230 may be included in a residual processing unit.

[0082] Depending on the embodiment, all or at least some of the components constituting the image decoding device 200 may be realized by a single hardware component (e.g., a decoder or a processor). Also, the memory 170 may include a DPB and may be realized by a digital storage medium.

[0083] The image decoding device 200, which receives a bitstream including video / image information, can reconstruct an image by performing a process corresponding to the process performed by the image encoding device 100 of FIG. 2. For example, the image decoding device 200 can perform decoding using a processing unit applied in the image encoding device. Therefore, the decoding processing unit can be, for example, a coding unit. The coding unit can be obtained by dividing a coding tree unit or a maximum coding unit. The reconstructed image signal decoded and output by the image decoding device 200 can be reproduced by a reproduction device (not shown).

[0084] The image decoding apparatus 200 may receive a signal output from the image encoding apparatus of FIG. 2 in a bitstream format. The received signal may be decoded via an entropy decoding unit 210. For example, the entropy decoding unit 210 may parse the bitstream to derive information (e.g., video / image information) necessary for image reconstruction (or picture reconstruction). 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 also include general constraint information. The image decoding apparatus may further use the information on the parameter sets and / or the general constraint information to decode an image. The signaling information, received information, and / or syntax elements referred to in the present disclosure may be obtained from the bitstream by being decoded via the decoding procedure. For example, the entropy decoding unit 210 may decode information in a bitstream based on a coding method such as Exponential-Golomb coding, CAVLC, or CABAC, and output values ​​of syntax elements required for image restoration and quantized values ​​of transform coefficients related to residuals. More specifically, the CABAC entropy decoding method receives bins corresponding to each syntax element from the bitstream, determines a context model using information on the syntax element to be decoded and decoded information on neighboring blocks and the block to be decoded, or information on symbols / bins decoded in a previous step, predicts the occurrence probability of the bins based on the determined context model, and performs arithmetic decoding of the bins to generate symbols corresponding to the values ​​of each syntax element. After determining the context model, the CABAC entropy decoding method may update the context model using information on the decoded symbol / bin for the context model of the next symbol / bin.Among the information decoded by the entropy decoding unit 210, information related to prediction is provided to the prediction units (inter prediction unit 260 and intra prediction unit 265), and residual values ​​entropy decoded by the entropy decoding unit 210, i.e., quantized transform coefficients and related parameter information, may be input to the inverse quantization unit 220. Also, among the information decoded by the entropy decoding unit 210, information related to filtering may be provided to the filtering unit 240. Meanwhile, a receiving unit (not shown) for receiving a signal output from the image encoding device may be further provided as an internal / external element of the image decoding device 200, or the receiving unit may be provided as a component of the entropy decoding unit 210.

[0085] Meanwhile, the image decoding apparatus according to the present disclosure may be referred to as a video / image / picture decoding apparatus. The image decoding apparatus may include an information decoder (video / image / picture information decoder) and / or a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoding unit 210, and the sample decoder may include at least one of an inverse quantization unit 220, an inverse transform unit 230, an adder 235, a filtering unit 240, a memory 250, an inter prediction unit 260, and an intra prediction unit 265.

[0086] The inverse quantization unit 220 may inverse quantize the quantized transform coefficients and output the transform coefficients. The inverse quantization unit 220 may rearrange the quantized transform coefficients in a two-dimensional block format. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The inverse quantization unit 220 may perform inverse quantization on the quantized transform coefficients using a quantization parameter (e.g., quantization step size information) to obtain transform coefficients.

[0087] The inverse transform unit 230 can inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0088] The prediction unit may perform prediction on a current block and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied to the current block based on information about the prediction output from the entropy decoding unit 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0089] The prediction unit can generate a prediction signal based on various prediction methods (techniques) described below, as described in the description of the prediction unit of the image encoding device 100.

[0090] The intra predictor 265 may predict the current block by referring to samples in the current picture. The description of the intra predictor 185 may also be applied to the intra predictor 265.

[0091] The inter prediction unit 260 may derive a predicted block for a current block based on a reference block (reference sample array) identified by a motion vector on a reference picture. To reduce the amount of motion information transmitted in inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on correlations between motion information of neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include information on an inter prediction direction (e.g., L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter prediction unit 260 may construct a motion information candidate list based on the neighboring blocks and derive a motion vector and / or a reference picture index for the current block based on received candidate selection information. Inter prediction may be performed based on various prediction modes (techniques), and the prediction information may include information indicating the inter prediction mode (technique) for the current block.

[0092] The adder 235 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to a prediction signal (predicted block, predicted sample array) output from a prediction unit (including the inter prediction unit 260 and / or the intra prediction unit 265). When there is no residual for the current block, such as when a skip mode is applied, the predicted block may be used as the reconstructed block. The description of the adder 155 also applies to the adder 235. The adder 235 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, and may also be used for inter prediction of the next picture after undergoing filtering, as described below.

[0093] The filtering unit 240 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 240 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 250, specifically, in a DPB of the memory 250. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, an adaptive loop filter, a bilateral filter, etc.

[0094] The (modified) reconstructed picture stored in the DPB of the memory 250 can be used as a reference picture in the inter predictor 260. The memory 250 can 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 an already reconstructed picture. The stored motion information can be transmitted to the inter predictor 260 to be used as motion information of a spatially surrounding block or a temporally surrounding block. The memory 250 can store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra predictor 265.

[0095] In this specification, the embodiments described for the filtering unit 160, inter prediction unit 180 and intra prediction unit 185 of the image encoding device 100 can also be applied in a similar or corresponding manner to the filtering unit 240, inter prediction unit 260 and intra prediction unit 265 of the image decoding device 200, respectively.

[0096] Image Segmentation Overview

[0097] The video / image coding method according to the present disclosure may be performed based on the following image partition structure. Specifically, procedures such as prediction, residual processing (e.g., (inverse) transform, (inverse) quantization), syntax element coding, and filtering, which will be described later, may be performed based on CTUs and CUs (and / or TUs and PUs) derived based on the image partition structure. An image may be divided into blocks, and the block partition procedure may be performed by the image partitioning unit 110 of the encoding device described above. Partition-related information may be coded by the entropy coding unit 190 and transmitted to the decoding device in the form of a bitstream. The entropy decoding unit 210 of the decoding device may derive a block partition structure of the current picture based on the partition-related information obtained from the bitstream, and perform a series of procedures for image decoding (e.g., prediction, residual processing, block / picture reconstruction, in-loop filtering, etc.) based on the block partition structure.

[0098] A picture can be divided into a sequence of coding tree units (CTUs). FIG. 4 shows an example of dividing a picture into CTUs. A CTU can correspond to a coding tree block (CTB). Alternatively, a CTU can include a coding tree block of luma samples and two coding tree blocks of corresponding chroma samples. For example, for a picture containing three sample arrays, a CTU can include an N×N block of luma samples and two corresponding blocks of chroma samples.

[0099] Overview of CTU division

[0100] As described above, a coding unit can be obtained by recursively dividing a coding tree unit (CTU) or a largest coding unit (LCU) according to a QT / BT / TT (quad-tree / binary-tree / ternary-tree) structure. For example, a CTU can be first divided into a quad-tree structure. Then, the leaf nodes of the quad-tree structure can be further divided according to a multi-type tree structure.

[0101] Quadtree division refers to dividing the current CU (or CTU) into four equal parts. By quadtree division, the current CU can be divided into four CUs with the same width and height. If the current CU is not further divided into a quadtree structure, the current CU corresponds to a leaf node of the quadtree structure. A CU corresponding to a leaf node of the quadtree structure is not further divided and can be used as the final coding unit described above. Alternatively, a CU corresponding to a leaf node of the quadtree structure can be further divided into four parts according to a multi-type tree structure.

[0102] 5 is a diagram showing the types of division of blocks using a multi-type tree structure. Division using a multi-type tree structure can include two divisions using a binary tree structure and two divisions using a ternary tree structure.

[0103] The two divisions based on the binary tree structure can include vertical binary splitting (SPLIT_BT_VER) and horizontal binary splitting (SPLIT_BT_HOR). Vertical binary splitting (SPLIT_BT_VER) refers to a division that divides the current CU into two equal parts vertically. As shown in FIG. 4, vertical binary splitting can generate two CUs each having the same height as the current CU and half the width of the current CU. Horizontal binary splitting (SPLIT_BT_HOR) refers to a division that divides the current CU into two equal parts horizontally. As shown in FIG. 5, horizontal binary splitting can generate two CUs each having a height half the height of the current CU and a width equal to the width of the current CU.

[0104] The two divisions based on the ternary tree structure include vertical ternary splitting (SPLIT_TT_VER) and horizontal ternary splitting (SPLIT_TT_HOR). Vertical ternary splitting (SPLIT_TT_VER) divides the current CU vertically at a ratio of 1:2:1. As shown in FIG. 5, vertical ternary splitting can generate two CUs each having the same height as the current CU and a width equal to one-quarter of the current CU's width, and a CU each having the same height as the current CU and a width equal to half the current CU's width. Horizontal ternary splitting (SPLIT_TT_HOR) divides the current CU horizontally at a ratio of 1:2:1. As shown in FIG. 4, horizontal ternary splitting can generate two CUs each having a height equal to one-quarter of the current CU's height and a width equal to the current CU's width.

[0105] FIG. 6 is a diagram illustrating an exemplary signaling mechanism for block partition information in a quadtree with nested multi-type tree structure according to the present disclosure.

[0106] Here, the CTU is treated as the root node of the quadtree, and the CTU is first split into a quadtree structure. Information (e.g., qt_split_flag) indicating whether quadtree splitting is performed on the current CU (CTU or quadtree node (QT_node)) is signaled. For example, if qt_split_flag is a first value (e.g., '1'), the current CU can be split into a quadtree. On the other hand, if qt_split_flag is a second value (e.g., '0'), the current CU is not split into a quadtree but becomes a quadtree leaf node (QT_leaf_node). Each quadtree leaf node can then be further split into a multitype tree structure. That is, the quadtree leaf node can become a multitype tree node (MTT_node). A first flag (e.g., mtt_split_cu_flag) is signaled to indicate whether the current node is further split into a multitype tree structure. If the node is to be further split (e.g., the first flag is 1), a second flag (e.g., mtt_split_cu_vertical_flag) is signaled to indicate the splitting direction. For example, if the second flag is 1, the splitting direction may be vertical, and if the second flag is 0, the splitting direction may be horizontal. Then, a third flag (e.g., mtt_split_cu_binary_flag) is signaled to indicate whether the splitting type is a binary split type or a ternary split type. For example, if the third flag is 1, the splitting type may be a binary split type, and if the third flag is 0, the splitting type may be a ternary split type. Nodes of a multitype tree obtained by binary splitting or ternary splitting can be further partitioned into a multitype tree structure. However, nodes of a multitype tree cannot be partitioned into a quadtree structure.If the first flag is 0, the corresponding node of the multitype tree is not further divided and becomes a leaf node (MTT_leaf_node) of the multitype tree. The CU corresponding to the leaf node of the multitype tree can be used as the final coding unit described above.

[0107] Based on the above mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag, the multi-type tree splitting mode (MttSplitMode) of the CU can be derived as shown in Table 1. In the following description, the multi-type tree splitting mode may be abbreviated as multi-tree split type or split type.

[0108] [Table 1]

[0109] 7 shows an example in which a CTU is divided into multiple CUs by applying a multi-type tree after applying a quadtree. In FIG. 7, a bold block edge 710 indicates the quadtree division, and the remaining edges 720 indicate the multi-type tree division. A CU may correspond to a coding block CB. In one embodiment, a CU may include a coding block of luma samples and two coding blocks of chroma samples corresponding to the luma samples.

[0110] The size of the chroma components (samples) CB or TB may be derived based on the size of the luma components (samples) CB or TB according to the component ratio according to the color format of the picture / image (chroma format, for example, 4:4:4, 4:2:2, 4:2:0, etc.). If the color format is 4:4:4, the size of the chroma components CB / TB may be set to be the same as the size of the luma components CB / TB. If the color format is 4:2:2, the width of the chroma components CB / TB may be set to half the width of the luma components CB / TB, and the height of the chroma components CB / TB may be set to the height of the luma components CB / TB. If the color format is 4:2:0, the width of the chroma components CB / TB may be set to half the width of the luma components CB / TB, and the height of the chroma components CB / TB may be set to half the height of the luma components CB / TB.

[0111] In one embodiment, when the size of the CTU is 128 based on the luma sample unit, the size of the CU can be from 128 x 128, which is the same size as the CTU, to 4 x 4. In one embodiment, in the case of a 4:2:0 color format (or chroma format), the chroma CB size can be from 64 x 64 to 2 x 2.

[0112] In one embodiment, the CU size and the TU size may be the same, or multiple TUs may exist within a CU region. The TU size generally refers to the luma component (sample) TB (Transform Block) size.

[0113] The TU size may be derived based on a preset maximum allowable TB size (maxTbSize). For example, if the CU size is larger than the maxTbSize, multiple TUs (TBs) having the maxTbSize may be derived from the CU, and transform / inverse transform may be performed in units of the TUs (TBs). For example, the maximum allowable luma TB size may be 64x64, and the maximum allowable chroma TB size may be 32x32. If the width or height of a CB divided by the tree structure is larger than the maximum transform width or height, the CB may be automatically (or implicitly) divided until the horizontal and vertical TB size constraints are satisfied.

[0114] Also, for example, when intra prediction is applied, the intra prediction mode / type may be derived in units of the CU (or CB), and the procedure for deriving neighboring reference samples and generating predicted samples may be performed in units of TU (or TB). In this case, one or more TUs (or TBs) may exist within one CU (or CB) region, and in this case, the multiple TUs (or TBs) may share the same intra prediction mode / type.

[0115] Meanwhile, for a quadtree coding tree scheme with a multitype tree, the following parameters can be signaled from the encoding device to the decoding device as SPS syntax elements. For example, at least one of CTUsize, a parameter indicating the size of the root node of a quadtree, MinQTSize, a parameter indicating the minimum allowable size of a leaf node of a quadtree, MaxBTSize, a parameter indicating the maximum allowable size of a root node of a binary tree, MaxTTSize, a parameter indicating the maximum allowable size of a root node of a ternary tree, MaxMttDepth, a parameter indicating the maximum allowed hierarchy depth of a multitype tree split from a leaf node of a quadtree, MinBtSize, a parameter indicating the minimum allowable leaf node size of a binary tree, and MinTtSize, a parameter indicating the minimum allowable leaf node size of a ternary tree, can be signaled.

[0116] In one embodiment using a 4:2:0 chroma format, the CTU size can be set to a 128x128 luma block and two 64x64 chroma blocks corresponding to the luma block. In this case, MinQTSize can be set to 16x16, MaxBtSize can be set to 128x128, MaxTtSize can be set to 64x64, MinBtSize and MinTtSize can be set to 4x4, and MaxMttDepth can be set to 4. Quadtree division can be applied to the CTU to generate quadtree leaf nodes. The quadtree leaf nodes can be called leaf QT nodes. The quadtree leaf nodes can range in size from 16x16 (e.g., the MinQTSize) to 128x128 (e.g., the CTU size). If the leaf QT node is 128x128, it can no longer be further divided into a binary tree or ternary tree. This is because even if the division is performed in this case, the MaxBtSize and MaxTtSize (e.g., 64x64) will be exceeded. In other cases, the leaf QT node can be further divided into multitype trees. Thus, the leaf QT node is the root node for the multitype tree, and the leaf QT node can have a multitype tree depth (mttDepth) value of 0. If the multitype tree depth reaches MaxMttDepth (e.g., 4), no further divisions can be considered. If the width of the multitype tree node is equal to MinBtSize and equal to or less than 2xMinTtSize, no further horizontal divisions can be considered. If the height of the multitype tree node is equal to MinBtSize and equal to or less than 2xMinTtSize, no further vertical divisions can be considered. If division is not considered in this way, the encoding device can omit signaling of division information. In such cases, the decoding device can guide the division information to a predetermined value.

[0117] Meanwhile, one CTU may include a coding block of luma samples (hereinafter referred to as a "luma block") and two coding blocks of corresponding chroma samples (hereinafter referred to as "chroma blocks"). The above-mentioned coding tree scheme may be applied equally to the luma blocks and chroma blocks of the current CU, or may be applied separately. Specifically, the luma blocks and chroma blocks in one CTU may be divided into the same block tree structure, which is referred to as a single tree (SINGLE_TREE). Alternatively, the luma blocks and chroma blocks in one CTU may be divided into separate block tree structures, which is referred to as a dual tree (DUAL_TREE). In other words, when a CTU is divided into a dual tree, a block tree structure for the luma blocks and a block tree structure for the chroma blocks may exist separately. In this case, the block tree structure for the luma block may be referred to as a dual tree luma (DUAL_TREE_LUMA), and the block tree structure for the chroma block may be referred to as a dual tree chroma (DUAL_TREE_CHROMA). For P and B slices / tile groups, the luma block and the chroma block in one CTU may be restricted to have the same coding tree structure. However, for I slices / tile groups, the luma block and the chroma block may have separate block tree structures. If a separate block tree structure is applied, the luma coding tree block (CTB) may be divided into CUs based on a specific coding tree structure, and the chroma CTB may be divided into chroma CUs based on another coding tree structure. In other words, this may mean that a CU in an I slice / tile group to which a separate block tree structure is applied may be composed of a coding block of a luma component or a coding block of two chroma components, and a CU in a P or B slice / tile group may be composed of blocks of three color components (a luma component and two chroma components).

[0118] Although the quadtree coding tree structure with a multi-type tree has been described above, the structure in which a CU is divided is not limited to this. For example, the BT structure and the TT structure may be interpreted as concepts included in a Multiple Partitioning Tree (MPT) structure, and a CU may be interpreted as being divided by a QT structure and an MPT structure. In an example in which a CU is divided by a QT structure and an MPT structure, the division structure may be determined by signaling a syntax element (e.g., MPT_split_type) containing information on whether a leaf node of the QT structure is divided into several blocks and a syntax element (e.g., MPT_split_mode) containing information on whether the leaf node of the QT structure is divided vertically or horizontally.

[0119] In another example, CUs may be divided in a manner different from that of the QT structure, BT structure, or TT structure. That is, unlike the QT structure in which lower-depth CUs are divided into 1 / 4 the size of higher-depth CUs, the BT structure in which lower-depth CUs are divided into 1 / 2 the size of higher-depth CUs, or the TT structure in which lower-depth CUs are divided into 1 / 4 or 1 / 2 the size of higher-depth CUs, lower-depth CUs may be divided into 1 / 5, 1 / 3, 3 / 8, 3 / 5, 2 / 3, or 5 / 8 the size of higher-depth CUs, as the case may be, and the manner in which CUs are divided is not limited thereto.

[0120] As such, the quadtree coding block structure with the multi-type tree can provide a very flexible block partition structure. Meanwhile, due to the partition types supported by the multi-type tree, different partition patterns can potentially result in the same coding block structure. By limiting the occurrence of such redundant partition patterns, the encoding device and the decoding device can reduce the amount of data for partition information.

[0121] The intra prediction performed by the intra prediction unit will be described below.

[0122] Intra prediction

[0123] Intra prediction may refer to a prediction that generates prediction samples for a current block based on reference samples in a picture to which the current block belongs (hereinafter, referred to as the current picture). When intra prediction is applied to the current block, neighboring reference samples used for intra prediction of the current block may be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary and bottom-left neighboring samples of a size nW×nH of the current block, a total of 2×nH samples, samples adjacent to the top boundary and top-right neighboring samples of the current block, and one sample adjacent to the top-left neighboring sample of the current block. Alternatively, the neighboring reference samples of the current block may include multiple columns of upper neighboring samples and multiple rows of left neighboring samples. In addition, the surrounding reference samples of the current block may also include a total of nH samples adjacent to the right boundary of the current block of size nW×nH, a total of nW samples adjacent to the bottom boundary of the current block, and one sample adjacent to the bottom-right of the current block.

[0124] However, some of the surrounding reference samples of the current block may not be decoded or available. In this case, the decoder can construct surrounding reference samples to be used for prediction by substituting unavailable samples with available samples, or can construct surrounding reference samples to be used for prediction through interpolation of available samples.

[0125] The following describes an encoding method based on intra prediction and an intra prediction unit in an encoding device with reference to FIGS.

[0126] Figure 8 illustrates an intra-prediction based video / image coding method, and Figure 9 illustrates an intra-prediction unit within a coding device.

[0127] S800 may be performed by the intra prediction unit 222 of the encoding device, and S810 may be performed by the residual processing unit 230 of the encoding device. Specifically, S810 may be performed by the subtraction unit 231 of the encoding device. In S820, prediction information may be derived by the intra prediction unit 222 and encoded by the entropy coding unit 240. In S820, residual information may be derived by the residual processing unit 230 and encoded by the entropy coding unit 240. The residual information is information about the residual sample. The residual information may include information about quantized transform coefficients for the residual sample. As described above, the residual sample may be derived into transform coefficients via the transform unit 232 of the encoding device, and the transform coefficients may be derived as quantized transform coefficients via the quantization unit 233. Information about the quantized transform coefficients may be encoded by the entropy coding unit 240 through a residual coding procedure.

[0128] The encoding device performs intra prediction on a current block (S800). The encoding device may derive an intra prediction mode / type for the current block, derive neighboring reference samples for the current block, and generate predicted samples within the current block based on the intra prediction mode / type and the neighboring reference samples. Here, the steps of determining the intra prediction mode / type, deriving neighboring reference samples, and generating predicted samples may be performed simultaneously, or one step may be performed before the other steps. For example, the intra prediction unit 222 of the encoding device may include an intra prediction mode / type determination unit 222-1, a reference sample derivation unit 222-2, and a predicted sample derivation unit 222-3. The intra prediction mode / type determination unit 222-1 may determine the intra prediction mode / type for the current block, the reference sample derivation unit 222-2 may derive neighboring reference samples for the current block, and the predicted sample derivation unit 222-3 may derive predicted samples for the current block. Meanwhile, although not shown, if a filtering procedure for prediction samples (described later) is performed, the intra prediction unit 222 may further include a prediction sample filter unit (not shown). The encoding device may determine a mode / type to be applied to the current block from among a plurality of intra prediction modes / types. The encoding device may compare RD costs for the intra prediction modes / types to determine the optimal intra prediction mode / type for the current block.

[0129] The encoding device generates a residual sample for the current block based on the predicted sample (S810). The encoding device may derive the residual sample by comparing the predicted sample with the original sample of the current block based on a phase.

[0130] The encoding device may encode image information including information related to the intra prediction (prediction information) and residual information related to the residual samples (S820). The prediction information may include the intra prediction mode information and the intra prediction type information. The encoding device may output the encoded image information in a bitstream format. The output bitstream may be transmitted to a decoding device via a storage medium or a network.

[0131] The residual information may include a residual coding syntax, which will be described later. The encoding device may transform / quantize the residual samples to derive quantized transform coefficients. The residual information may include information on the quantized transform coefficients.

[0132] Meanwhile, as described above, the encoding apparatus can generate a reconstructed picture (including reconstructed samples and reconstructed blocks). To this end, the encoding apparatus can again inverse-quantize / inverse-transform the quantized transform coefficients to derive (modified) residual samples. The reason for again performing inverse-quantization / inverse-transformation on the residual samples after transforming / quantizing them is to derive residual samples identical to the residual samples derived in the decoding apparatus, as described above. The encoding apparatus can generate a reconstructed block including reconstructed samples for the current block based on the predicted samples and the (modified) residual samples. A reconstructed picture for the current picture can be generated based on the reconstructed block. As described above, an in-loop filtering procedure, etc., can further be applied to the reconstructed picture.

[0133] Hereinafter, a video / image decoding method based on intra prediction and an intra prediction unit in a decoding device will be described with reference to FIGS.

[0134] Figure 10 illustrates an intra-prediction based video / image decoding method, and Figure 11 illustrates an intra-prediction unit within a decoding device.

[0135] The decoding device can perform operations corresponding to those performed by the encoding device.

[0136] Steps S1000 to S1020 may be performed by an intra prediction unit 331 of a decoding device, and the prediction information of S1000 and the residual information of S1030 may be obtained from a bitstream by an entropy decoding unit 310 of the decoding device. The residual processing unit 320 of the decoding device may derive residual samples for a current block based on the residual information. Specifically, the inverse quantization unit 321 of the residual processing unit 320 may derive transform coefficients by performing inverse quantization on quantized transform coefficients derived based on the residual information, and the inverse transform unit 322 of the residual processing unit may derive residual samples for the current block by performing inverse transform on the transform coefficients. Step S1040 may be performed by an adder 340 or a reconstruction unit of the decoding device.

[0137] Specifically, the decoding apparatus may derive an intra-prediction mode / type for a current block based on received prediction information (intra-prediction mode / type information) (S1000), derive neighboring reference samples for the current block (S1010), and generate predicted samples within the current block based on the intra-prediction mode / type and the neighboring reference samples (S1020).

[0138] The decoding apparatus generates residual samples for the current block based on the received residual information. The decoding apparatus generates reconstructed samples for the current block based on the predicted samples and the residual samples, and may derive a reconstructed block including the reconstructed samples (S1030). A reconstructed picture for the current picture may be generated based on the reconstructed block. As described above, an in-loop filtering procedure may be further applied to the reconstructed picture.

[0139] Here, the intra prediction unit 331 of the decoding device may include an intra prediction mode / type determination unit 331-1, a reference sample derivation unit 331-3, and a prediction sample derivation unit 331-4, where the intra prediction mode / type determination unit 331-1 determines the intra prediction mode / type for the current block based on intra prediction mode / type information acquired by the entropy decoding unit 310, the reference sample derivation unit 331-2 derives neighboring reference samples for the current block, and the prediction sample derivation unit 331-3 derives prediction samples for the current block. Meanwhile, although not shown, if the above-mentioned prediction sample filtering procedure is performed, the intra prediction unit 331 may further include a prediction sample filter unit (not shown).

[0140] The intra prediction mode information may include, for example, flag information (e.g., intra_luma_mpm_flag) indicating whether a most probable mode (MPM) or a remaining mode is applied to the current block. If the MPM is applied to the current block, the prediction mode information may further include index information (e.g., intra_luma_mpm_idx) indicating one of the intra prediction mode candidates (MPM candidates). The intra prediction mode candidates (MPM candidates) may be configured from an MPM candidate list or an MPM list. If the MPM is not applied to the current block, the intra prediction mode information may further include remaining mode information (e.g., intra_luma_mpm_remainder) indicating one of the remaining intra prediction modes excluding the intra prediction mode candidates (MPM candidates). A decoding apparatus may determine the intra prediction mode of the current block based on the intra prediction mode information.

[0141] Also, the intra prediction type information may be implemented in various forms. For example, the intra prediction type information may include intra prediction type index information indicating one of the intra prediction types. For another example, the intra prediction type information may include at least one of reference sample line information (e.g., intra_luma_ref_idx) indicating whether the MRL is applied to the current block and, if so, which reference sample line is used, ISP flag information (e.g., intra_subpartitions_mode_flag) indicating whether the ISP is applied to the current block, ISP type information (e.g., intra_subpartitions_split_flag) indicating a subpartition split type when the ISP is applied, flag information indicating whether PDCP is applied, or flag information indicating whether LIP is applied. Also, the intra prediction type information may include an MIP flag indicating whether MIP is applied to the current block.

[0142] The intra prediction mode information and / or the intra prediction type information may be encoded / decoded using the coding method described herein. For example, the intra prediction mode information and / or the intra prediction type information may be encoded / decoded using entropy coding (e.g., CABAC, CAVLC) based on a truncated (rice) binary code.

[0143] Meanwhile, the intra prediction modes may include two non-directional intra prediction modes and 65 directional intra prediction modes. The non-directional intra prediction modes may include a planar mode and a DC mode, and the directional intra prediction modes may include intra prediction modes numbered 2 to 66. Examples of the directional intra prediction modes are shown in FIG. 12.

[0144] The intra prediction modes may further include a cross-component linear model (CCLM) mode for chroma samples in addition to the above-described intra prediction modes. The CCLM modes may be classified into LT_CCLM, L_CCLM, and T_CCLM depending on whether the left sample, the top sample, or both are considered for deriving the LM parameters, and may be applied only to the chroma components.

[0145] The above-mentioned intra prediction modes can be indexed, for example, as shown in Table 2 below.

[0146] [Table 2]

[0147] The prediction unit of the encoding device / decoding device can derive reference samples according to the intra prediction mode of the current block from the surrounding reference samples of the current block, and can generate predicted samples of the current block based on the reference samples.

[0148] For example, (i) a prediction sample may be derived based on an average or interpolation of neighboring reference samples of the current block, or (ii) a prediction sample may be derived based on a reference sample located in a specific (prediction) direction for the prediction sample among the neighboring reference samples of the current block. (i) may be referred to as a non-directional mode or a non-angular mode, and (ii) as a directional mode or an angular mode. Furthermore, the prediction sample may be generated by interpolating the first and second neighboring samples located in the opposite direction to the prediction direction of the intra prediction mode of the current block based on a sample to be predicted of the current block among the neighboring reference samples. The above-described case may be referred to as linear interpolation intra prediction (LIP). Alternatively, a temporary prediction sample of the current block may be derived based on filtered neighboring samples, and the prediction sample of the current block may be derived by weighted summing the temporary prediction sample and at least one reference sample derived according to the intra prediction mode from the existing neighboring reference samples, i.e., from the unfiltered neighboring reference samples. The above case may be called Position Dependent Intra Prediction (PDPC). In addition, intra prediction coding may be performed by selecting a reference sample line with the highest prediction accuracy from multiple reference sample lines surrounding the current block, deriving a prediction sample using a reference sample located in a prediction direction from the selected line, and signaling the used reference sample line to a decoding device. The above case may be called Multi-Reference Line Intra Prediction (MRL) or MRL-based intra prediction.In addition, the current block may be divided into vertical or horizontal sub-partitions, and intra prediction may be performed based on the same intra prediction mode, with neighboring reference samples derived and used for each sub-partition. That is, in this case, the intra prediction mode for the current block is uniformly applied to the sub-partitions, and neighboring reference samples are derived and used for each sub-partition, thereby improving intra prediction performance as needed. This prediction method may be called intra sub-partitions (ISP) or ISP-based intra prediction. Specific details will be described later. Furthermore, when a prediction direction based on a prediction sample points between neighboring reference samples, i.e., when the prediction direction points to a fractional sample position, the value of the prediction sample may be derived through interpolation of multiple reference samples located around the prediction direction (around the fractional sample position).

[0149] The above-mentioned intra prediction methods may be called intra prediction types, distinguished from intra prediction modes. The intra prediction types may be referred to by various terms, such as intra prediction techniques or additional intra prediction modes. For example, the intra prediction types (or additional intra prediction modes, etc.) may include at least one of the above-mentioned LIP, PDPC, MRL, and ISP. Information about the intra prediction types may be coded by a coding device, included in a bitstream, and signaled to a decoding device. The information about the intra prediction types may be implemented in various forms, such as flag information indicating whether each intra prediction type is applied or index information indicating one of various intra prediction types.

[0150] Of the above-mentioned intra prediction types, PDPC, which is relevant to the present disclosure, will be described below.

[0151] Position dependent intra prediction (PDPC)

[0152] The PDPC may represent an intra prediction method that performs filtering based on a filter for the PDPC, derives filtered reference samples, derives temporary predicted samples of the current block based on the intra prediction mode of the current block and the filtered reference samples, and derives predicted samples of the current block by weighted summing the temporary predicted samples and at least one reference sample derived according to the intra prediction mode among the existing reference samples, i.e., unfiltered reference samples. Here, the predefined filter may be one of five 7-tap filters. Alternatively, the predefined filter may be one of a 3-tap filter, a 5-tap filter, and a 7-tap filter. The 3-tap filter, the 5-tap filter, and the 7-tap filter may represent a filter having three filter coefficients, a filter having five filter coefficients, and a filter having seven filter coefficients, respectively.

[0153] For example, the prediction results of the intra-planar mode can be further modified by PDPC.

[0154] Alternatively, as an example, the PDPC may be applied to an intra-planar mode, an intra-DC mode, a horizontal intra-prediction mode, a vertical intra-prediction mode, a bottom-left intra-prediction mode (i.e., intra-prediction mode No. 2), and eight directional intra-prediction modes adjacent to the bottom-left intra-prediction mode, a top-right intra-prediction mode, and eight directional intra-prediction modes adjacent to the top-right intra-prediction mode without any separate signaling.

[0155] Specifically, when the PDPC is applied, a predicted sample of (x, y) coordinates predicted based on a linear combination of an intra prediction mode and a reference sample can be derived as shown in Equation 1 below.

[0156] [Formula 1] pred(x,y)=(wL×R(-1,y)+wT×R(x,-1)-wTL×R(-1,-1)+(64-wL-wT+wTL)×pred(x,y)+32)>>6

[0157] In Equation 1, the left term pred(x,y) represents a predicted sample value of the (x,y) coordinate, and the right term pred(x,y) represents a temporary (first-order) predicted sample of the (x,y) coordinate. R(x,-1) and R(-1,y) represent an upper reference sample and a left reference sample located above and to the left of the current sample of the (x,y) coordinate, respectively, and R(-1,-1) represents an upper-left reference sample located at the upper left corner of the current block. Furthermore, wL represents a weight applied to the left reference sample, wT represents a weight applied to the upper reference sample, and wTL represents a weight applied to the upper-left reference sample.

[0158] On the other hand, when PDPC is applied to intra-planar mode, intra-DC mode, horizontal intra-prediction mode, and vertical intra-prediction mode, an additional boundary filter such as a conventional DC mode boundary filter or vertical / horizontal mode edge filter may not be necessary.

[0159] The temporary (first) predicted sample may be generated as a result of intra prediction based on an intra prediction mode of the current block and a reference sample. When PDPC is applied to the current block, a final predicted sample of the current block may be generated, for example, according to Equation 1. When PDPC is not applied to the current block, the temporary (first) predicted sample may be used as a final predicted sample of the current block.

[0160] 13a to 13d are diagrams showing reference samples defined by PDPC.

[0161] In Figures 13a to 13d, pred(x, y) indicates a predicted sample obtained by intra prediction (the above-mentioned temporary predicted sample), and R(x, -1) and R(-1, y) indicate an upper reference sample and a left reference sample located above and to the left of the current sample at the (x, y) coordinates.

[0162] FIG. 13a shows reference samples (Rx, -1, R-1, y, R-1, -1) when the prediction mode is diagonal top-right mode. FIG. 13b shows reference samples (Rx-1, R-1, y, R-1, -1) when the prediction mode is diagonal bottom-left mode. FIG. 13c shows reference samples (Rx-1, R-1, y, R-1, -1) when the prediction mode is adjacent diagonal top-right mode. FIG. 13d shows reference samples (Rx-1, R-1, y, R-1, -1) when the prediction mode is adjacent diagonal bottom-left mode. The PDPC weights can be derived based on the prediction mode. The PDPC weights (wT, wL, wTL) can be derived as shown in Table 3 below.

[0163] [Table 3]

[0164] Position-dependent intra prediction combination (PDPC) generates a prediction sample using a reference sample according to a prediction mode, and then improves the prediction sample using neighboring reference samples. PDPC can be applied to all intra prediction modes, but can also be applied to 65 directional intra prediction modes, such as Planar, DC, 2 (bottom-right direction mode), VDIA (top-left direction mode), Hor (horizontal direction mode), Ver (vertical direction mode), and neighboring modes of 2 mode (modes 3 to 10), and neighboring modes of VDIA mode (modes 58 to 65). Furthermore, instead of being applied to all prediction samples in the block currently being coded, PDPC can be applied variably taking into account the size of the block.

[0165] MRL (Multi-reference line) intra prediction

[0166] Conventional intra prediction uses only the neighboring samples of the first reference sample line above and the first reference sample line to the left of the current block as reference samples for intra prediction. However, the MRL (Multi-reference line) method can perform intra prediction using the neighboring samples located on the reference sample line one to three samples away from the top and / or left of the current block as reference samples.

[0167] FIG. 14 is a diagram for explaining a reference sample line that can be used in the MRL method.

[0168] 14, at least one reference sample line from Reference Line 0 to Reference Line 3, in order of their neighboring positions relative to the current block, may be referenced for intra prediction of the current block. In this disclosure, Reference Line 0 may be referred to as the first reference sample line. Also, Reference Line 1 to Reference Line 3 may be referred to as the second reference sample line to the fourth reference sample line, respectively.

[0169] When MRL is applied, a multiple reference line index (eg, mrl_idx) may be signaled to indicate which reference sample line is used for intra prediction for the current block.

[0170] FIG. 15 is a diagram showing the syntax structure of a coding unit that signals the multiple reference line indexes.

[0171] 15, the multiple reference line index may be signaled in the form of intra_luma_ref_idx. If the value of the multiple reference index is greater than 0, it can be said that the MRL is applied to the current block.

[0172] 15 can be used to specify the reference sample line index IntraLumaRefLineIdx[x0][y0] used for intra prediction of the current coding unit at (x0, y0) coordinates. If intra_luma_ref_idx[x0][y0] is not present in the bitstream, the value can be inferred to be 0.

[0173] The intra_luma_ref_idx can be called the (intra) reference sample line index or mrl_idx. The intra_luma_ref_idx can also be called the intra_luma_ref_line_idx.

[0174] Table 4 below shows IntraLumaRefLineIdx[x0][y0] identified based on intra_luma_ref_idx[x0][y0].

[0175] [Table 4]

[0176] In the example shown in Figure 15, the flag indicating whether MPM is applied to the current coding unit is intra_luma_mpm_flag[x0][y0], and when this flag does not exist in the bitstream, it can be inferred that its value is 1. In other words, it can be determined that MPM is applied to the current coding unit.

[0177] The MRL may not be available for the blocks in the first line (row) in a CTU. For example, if the upper boundary of the current coding unit is the upper boundary of the CTU, the MRL is not available for the current coding unit. This is to prevent extended reference lines that exist outside the current CTU from being used. Also, as will be described later, if a reference sample line other than the first reference sample line is used, the PDPC for the current coding unit may not be applied.

[0178] When the intra prediction mode of the coding unit to which MRL is applied is DC mode, the second or subsequent reference sample lines can be used to derive the DC value. In this case, the DC value can be derived based on the reference samples of the second or subsequent reference sample lines instead of the reference samples of the first reference sample line.

[0179] In the present disclosure, information indicating a reference sample line used for intra prediction of a current block may be expressed as refIdx. For example, refIdx equal to 0 may indicate the first reference sample line.

[0180] The embodiments of the present disclosure relate to the above-mentioned PDPC procedure: When the PDPC procedure is applied to intra-prediction samples, filtered (modified) prediction samples can be generated.

[0181] An embodiment of the present disclosure proposes a method for performing PDPC on a chroma block under specific conditions when applying PDPC in intra prediction for a chroma component (block).

[0182] The existing PDPC determines whether to apply PDPC by applying different conditions to a luminance component block and a chrominance component block.

[0183] FIG. 16 is a diagram illustrating PDPC application conditions according to an embodiment of the present disclosure.

[0184] According to the embodiment shown in FIG. 16, if all of the following conditions are met, PDPC can be applied to an intra-predicted prediction block of a current block.

[0185] (Condition 1) Both the width and height of the current block are 4 or more, or the current block is a chrominance block, or the color components of the current block are chrominance components.

[0186] (Condition 2) Intra prediction is performed using the first reference sample line (refIdx==0) adjacent to the current block, or the current block is a chrominance block.

[0187] (Condition 3) BDPCM is not applied to the current block.

[0188] (Condition 4) The intra prediction mode (predModeIntra) of the current block satisfies any one of the following conditions:

[0189] -predModeIntra is equal to INTRA_PLANAR

[0190] -predModeIntra is equal to INTRA_DC

[0191] -predModeIntra is less than or equal to INTRA_ANGULAR18

[0192] -predModeIntra is greater than or equal to INTRA_ANGULAR50 and less than INTRA_LT_CCLM

[0193] Condition 1 relates to the size of the current block. If the current block is a chrominance block, Condition 1 is met regardless of the size of the current block. Also, if the current block is a luma block, Condition 1 is met if the current block has a size of 4x4 or greater. In the present disclosure, the color component of the current block may be represented as cIdx. For example, if cIdx is 0, the current block is a luma component block, and if cIdx is not 0, the current block is a chrominance component block.

[0194] The condition 2 relates to the reference sample line used for intra prediction. If the current block is a chrominance block, the condition 2 is satisfied regardless of the reference sample line. Also, if the current block is a luminance block, the condition 2 is satisfied when intra prediction is performed using the first reference sample line adjacent to the current block.

[0195] Condition 3 relates to whether BDPCM is applied to the current block. Condition 3 can be determined based on the BdpcmFlag of the current block. For example, if the BdpcmFlag of the current block is 0, it can indicate that BDPCM is not applied to the current block. The BdpcmFlag of the current block can be determined based on a value signaled from the bitstream. If the current block is a luma (luma component) block, the value of BdpcmFlag can be derived based on the signaled intra_bdpcm_luma_flag. If the current block is a chrominance (chroma component) block, the value of BdpcmFlag can be derived based on the signaled intra_bdpcm_chroma_flag.

[0196] Condition 4 relates to the intra prediction mode of the current block. Specifically, if the intra prediction mode of the current block is one of 1) PLANAR mode, 2) DC mode, 3) a directional mode equal to or less than 18, or 4) a directional mode equal to or greater than 50 and less than LT_CCLM, PDPC can be applied to the current block.

[0197] Table 5 is a table summarizing condition 1 of the PDPC application conditions according to the embodiment shown in FIG. 16 according to the color components of the current block.

[0198] [Table 5]

[0199] As shown in Table 5, if the current block is a luminance block, Condition 1 is satisfied when both the width and height of the current block are equal to or greater than a predetermined threshold value 4. In this case, the predetermined threshold value 4 can be replaced with MIN_TB_SIZEY. MIN_TB_SIZEY can represent the minimum transform block (TB) size for the luma component, and its value can be predetermined or signaled from the encoding device to the decoding device. In the embodiment shown in FIG. 16, for example, MIN_TB_SIZEY can be 4.

[0200] However, if the current block is a chrominance block, the condition 1 in FIG. 16 is always satisfied. That is, the condition regarding the size of the current block is not applied. In this way, the condition regarding the size of the current block is applied only to the luminance block of the current block, and is not applied to the chrominance block. In conclusion, the condition regarding the size of the current block among the PDPC application conditions can be applied differently depending on the color components of the current block.

[0201] More specifically, when the current block is a chrominance block and its size is 2×2, 2×4, 4×2, or 2×N, intra prediction is not performed on the current chrominance block, and therefore, PDPC is not performed when the current block is a chrominance block of the above sizes.

[0202] On the other hand, if the current block is an Nx2 chrominance block, intra prediction may be performed, and therefore PDPC may also be performed. Thus, when the current block is an Nx2 block, PDPC is not performed in the intra prediction of the luma block, whereas PDPC may be performed in the intra prediction of the chrominance block.

[0203] FIG. 17 is a diagram illustrating PDPC application conditions according to another embodiment of the present disclosure.

[0204] According to the embodiment shown in Fig. 17, the block size condition among the PDPC application conditions can be equally applied to luma blocks and chrominance blocks. Specifically, according to the embodiment shown in Fig. 17, a method can be provided in which PDPC is not performed when the size of the current chrominance block is N × 2.

[0205] Furthermore, according to the present disclosure, by unifying the PDPC application conditions for the luma block and the chroma block, it is possible to perform simplified and unified intra prediction regardless of the color component of the current block.

[0206] According to the embodiment shown in FIG. 17, if all of the following conditions are satisfied, PDPC can be applied to an intra-predicted prediction block of a current block.

[0207] (Condition 1-1) Both the width and height of the current block are 4 or more.

[0208] (Condition 2) Intra prediction is performed using the first reference sample line (refIdx==0) adjacent to the current block, or the current block is a chrominance block.

[0209] (Condition 3) BDPCM is not applied to the current block.

[0210] (Condition 4) The intra prediction mode (predModeIntra) of the current block satisfies any one of the following conditions:

[0211] -predModeIntra is equal to INTRA_PLANAR

[0212] -predModeIntra is equal to INTRA_DC

[0213] -predModeIntra is less than or equal to INTRA_ANGULAR18

[0214] -predModeIntra is greater than or equal to INTRA_ANGULAR50 and less than INTRA_LT_CCLM

[0215] Condition 1-1 relates to the size of the current block. According to the embodiment shown in FIG. 17, condition 1 is met if the current block has a size of 4×4 or greater, regardless of the color components of the current block. That is, condition 1-1 is met if both the width and height of the current block are greater than or equal to a predetermined threshold (e.g., 4). If the width or height of the current block is smaller than a predetermined threshold, it can be determined that condition 1-1 is not met, regardless of the color components of the current block. Therefore, according to the embodiment shown in FIG. 17, in order to determine whether condition 1-1 is met, it is possible to skip determining whether the color components of the current block are luminance components or chrominance components.

[0216] Conditions 2 to 4 are the same as those explained with reference to FIG. 16, so a duplicate explanation will be omitted.

[0217] According to the embodiment shown in FIG. 17, among the PDPC application conditions, condition 1-1 regarding the size of the current block is commonly applied to the luminance block and the chrominance block, thereby solving the problem of applying PDPC to the N×2 chrominance block.

[0218] The embodiment shown in Figure 17 has a technical feature in that the condition 1-1 regarding the size of the current block is commonly applied to the luminance component block and the chrominance component block. Therefore, in addition to the condition 1-1, all or part of the conditions 2 to 4 may be modified differently from the embodiment shown in Figure 17. Such modified PDPC application conditions are also modifications of the embodiment shown in Figure 17 and may be included in the scope of the invention according to the present disclosure.

[0219] FIG. 18 is a diagram illustrating PDPC application conditions according to another embodiment of the present disclosure.

[0220] According to the embodiment shown in Figure 18, among the PDPC application conditions, the condition regarding the block size and the condition regarding the reference sample line can be equally applied to the luma block and the chroma block. Specifically, according to the embodiment shown in Figure 18, a method for not performing PDPC when the size of the current chroma block is Nx2 can be provided. Also, a method for not performing PDPC when the reference sample line used for intra prediction is not the first reference sample line can be provided.

[0221] Furthermore, according to the present disclosure, by unifying the PDPC application conditions for the luma block and the chroma block, it is possible to perform simplified and unified intra prediction regardless of the color component of the current block.

[0222] According to the embodiment shown in FIG. 18, if all of the following conditions are met, PDPC can be applied to an intra-predicted prediction block of a current block.

[0223] (Condition 1-1) Both the width and height of the current block are 4 or more.

[0224] (Condition 2-1) Intra prediction is performed using the first reference sample line (refIdx==0) adjacent to the current block.

[0225] (Condition 3) BDPCM is not applied to the current block.

[0226] (Condition 4) The intra prediction mode (predModeIntra) of the current block satisfies any one of the following conditions:

[0227] -predModeIntra is equal to INTRA_PLANAR

[0228] -predModeIntra is equal to INTRA_DC

[0229] -predModeIntra is less than or equal to INTRA_ANGULAR18

[0230] -predModeIntra is greater than or equal to INTRA_ANGULAR50 and less than INTRA_LT_CCLM

[0231] Condition 1-1 is the same as that explained with reference to FIG. 17, so a duplicate explanation will be omitted.

[0232] Condition 2-1 relates to the reference sample line used in intra prediction. According to the embodiment shown in FIG. 18, condition 2-1 is satisfied when intra prediction is performed using the first reference sample line adjacent to the current block, regardless of the color component of the current block. That is, condition 2-1 is satisfied when the first reference sample line is used for intra prediction of the current block. If the first reference sample line is not used for intra prediction of the current block, it can be determined that condition 2-1 is not satisfied, regardless of the color component of the current block. Therefore, according to the embodiment shown in FIG. 18, it is possible to skip determining whether the color component of the current block is a luma component or a chroma component in order to determine whether condition 2-1 is satisfied.

[0233] Conditions 3 and 4 are the same as those explained with reference to FIG. 16, so a duplicate explanation will be omitted.

[0234] 18, the problem of applying PDPC to an N×2 chrominance block can be solved by applying condition 1-1, which is one of the PDPC application conditions and relates to the size of the current block, to both the luminance block and the chrominance block. Also, the problem of applying PDPC to an N×2 chrominance block can be solved by applying condition 2-1, which is one of the PDPC application conditions and relates to the reference sample line used in intra prediction of the current block, to both the luminance block and the chrominance block.

[0235] The embodiment shown in Figure 18 has a technical feature in that the condition 1-1 regarding the size of the current block and the condition 2-1 regarding the reference sample line used in intra prediction are commonly applied to the luma component block and the chroma component block. Therefore, in addition to the conditions 1-1 and 2-1, all or part of the conditions 3 and 4 may be modified differently from the embodiment shown in Figure 18. Such modified PDPC application conditions are also a modification of the embodiment shown in Figure 18 and may be included in the scope of the invention according to the present disclosure.

[0236] FIG. 19 is a flowchart illustrating a method for generating a prediction block according to an embodiment of the present disclosure.

[0237] 19 illustrates steps of performing intra prediction to generate a predicted block, which may be performed in an image encoding device and / or an image decoding device to generate a predicted block. For example, the steps of FIG. 19 may be performed in step S800 of FIG. 8, which is performed in an image encoding device. Also, the steps of FIG. 19 may be performed in step S1020 of FIG. 10, which is performed in an image decoding device.

[0238] When intra prediction is performed on a current block, a predicted block of the current block may be generated based on neighboring reference samples of the current block and an intra prediction mode (S1910). The predicted block generated in step S1910 may be modified depending on whether PDPC is applied, and may therefore be referred to as a temporary predicted block, a primary predicted block, etc. Furthermore, the predicted block generated as a result of applying PDPC may simply be referred to as a predicted block, a final predicted block, etc.

[0239] Thereafter, it is determined whether to apply PDPC to the temporary prediction block or the primary prediction block (S1920). Step S1920 may be performed by checking whether the PDPC application condition is satisfied. The PDPC application condition according to the present disclosure is the same as that described with reference to FIGS. 17 and 18. However, the PDPC application condition according to the present disclosure is not limited to the examples of FIGS. 17 and 18, and various modified examples of the PDPC application condition may be included in the scope of protection of the present disclosure, as described above.

[0240] If it is determined in step S1920 that the PDPC application conditions are not met, PDPC is not performed, and the temporary predicted block (primary predicted block) generated in step S1910 can be used as the final predicted block of the current block.

[0241] If the PDPC application condition is met as a result of the determination in step S1920, PDPC can be performed (S1930). In this case, PDPC can be performed on the temporary prediction block (primary prediction block) generated in step S1910 to generate a final prediction block of the current block.

[0242] The PDPC in step S1930 can be performed, for example, by the PDPC method described above.

[0243] The final predicted block of the current block generated according to the method of FIG. 19 can be used to generate a residual block of the current block (S810) or to reconstruct the current block together with the residual block of the current block (S1040).

[0244] According to the embodiments of the present disclosure, the PDPC application condition is set independently of the color components of the current block, so that the determination of the color components of the current block can be skipped, thereby simplifying the process of determining whether or not to apply the PDPC. Also, according to the embodiments of the present disclosure, a simplified and unified determination of whether or not to apply the PDPC can be made.

[0245] Although the exemplary method of the present disclosure is expressed as a series of operations for clarity of explanation, this is not intended to limit the order in which the steps are performed, and the steps may be performed simultaneously or in a different order if necessary. To achieve the method according to the present disclosure, the steps illustrated may include other steps, or some steps may be omitted and the remaining steps may be included, or some steps may be omitted and additional other steps may be included.

[0246] In the present disclosure, an image encoding device or an image decoding device that performs a predetermined operation (step) can perform the operation (step) to check the execution conditions or situation of the operation (step). For example, if it is described that a predetermined operation is performed when a predetermined condition is satisfied, the image encoding device or the image decoding device can perform the predetermined operation after performing an operation to check whether the predetermined condition is satisfied.

[0247] The various embodiments of the present disclosure are not intended to enumerate all possible combinations, but are intended to describe representative aspects of the present disclosure, and the matters described in the various embodiments may be applied independently or in combination of two or more.

[0248] Additionally, various embodiments of the present disclosure may be implemented using hardware, firmware, software, or a combination thereof, etc. In the case of a hardware implementation, the implementation may be using one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), general processors, controllers, microcontrollers, microprocessors, etc.

[0249] In addition, an image decoding apparatus and an image encoding apparatus to which an embodiment of the present disclosure is applied may be included in a multimedia broadcast transmitting / receiving apparatus, a mobile communication terminal, a home cinema video apparatus, a digital cinema video apparatus, a surveillance camera, a video conversation apparatus, a real-time communication apparatus such as video communication, a mobile streaming apparatus, a storage medium, a camcorder, a video on demand (VoD) service providing apparatus, an over-the-top (OTT) video apparatus, an internet streaming service providing apparatus, a three-dimensional (3D) video apparatus, an image telephone video apparatus, a medical video apparatus, etc., and may be used to process a video signal or a data signal. For example, an over-the-top (OTT) video apparatus may include a game console, a Blu-ray player, an internet-connected TV, a home theater system, a smartphone, a tablet PC, a digital video recorder (DVR), etc.

[0250] FIG. 20 is a diagram illustrating a content streaming system to which an embodiment of the present disclosure can be applied.

[0251] As shown in FIG. 20, a content streaming system to which an embodiment of the present disclosure is applied can broadly include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0252] The encoding server compresses content input from a multimedia input device such as a smartphone, camera, or camcorder 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, or video camera directly generates a bitstream, the encoding server can be omitted.

[0253] The bitstream can be generated by an image encoding method and / or image encoding device to which an embodiment of the present disclosure is applied, and the streaming server can temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0254] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server serves as an intermediary for informing 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, which then transmits the multimedia data to the user. In this case, the content streaming system may include a separate control server, which may control commands and responses between devices in the content streaming system.

[0255] The streaming server may receive content from a media storage and / or an encoding server. For example, when receiving content 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.

[0256] Examples of the user device include a mobile phone, a smartphone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation system, a slate PC, a tablet PC, an ultrabook, a wearable device such as a smartwatch, smart glass, a head mounted display (HMD), a digital TV, a desktop computer, and digital signage.

[0257] Each server in the content streaming system can be operated as a distributed server, in which case data received from each server can be processed in a distributed manner.

[0258] The scope of the present disclosure includes software or machine-executable commands (e.g., operating systems, applications, firmware, programs, etc.) that cause operations according to the methods of various embodiments to be performed on a device or computer, and non-transitory computer-readable medium on which such software or commands can be stored and executed on a device or computer. [Industrial Applicability]

[0259] Embodiments according to the present disclosure can be used to encode / decode images.

Claims

1. An image decoding method performed by an image decoding device, comprising: performing intra prediction on the current block to generate a predicted block; determining whether PDPC is applied to the prediction block; generating a final predicted block of the current block by applying PDPC to the predicted block based on the determination; The step of determining whether to apply PDPC to the prediction block includes: determining whether the size of the current block satisfies a predetermined condition; determining that PDPC is to be applied to the predicted block based on whether the size of the current block satisfies the predetermined condition; If the size of the current block does not satisfy the predetermined condition, a determination on a color component of the current block is skipped, and PDPC is determined not to be applied to the prediction block.

2. The image decoding method according to claim 1 , wherein the predetermined condition is that the size of the current block is equal to or greater than a predetermined threshold.

3. If the width of the current block is equal to or greater than the predetermined threshold and the height of the current block is equal to or greater than the predetermined threshold, the predetermined condition is met.

3. The image decoding method according to claim 2.

4. The image decoding method according to claim 3 , wherein the predetermined threshold is four.

5. The step of determining whether to apply PDPC to the prediction block includes: The image decoding method of claim 1 , further comprising determining a reference sample line used in intra prediction of the current block.

6. determining that PDPC is applied to the prediction block based on the reference sample line being a predetermined reference sample line; The image decoding method of claim 5, wherein if the reference sample line is not a predetermined reference sample line, a determination on a color component of the current block is skipped and it is determined that PDPC is not applied to the predicted block.

7. The image decoding method of claim 6 , wherein the predetermined reference sample line is a first reference sample line adjacent to the current block.

8. The step of determining whether to apply PDPC to the prediction block includes: The image decoding method of claim 1 , further comprising determining whether BDPCM is applied to the current block and determining an intra prediction mode of the current block.

9. An image decoding device including a memory and at least one processor, The at least one processor: A predicted block is generated by performing intra prediction on the current block; determining whether to apply PDPC to the predicted block; By applying PDPC to the prediction block based on the determination, generating a final predicted block of the current block; The determination of whether to apply PDPC to the prediction block is determining whether the size of the current block satisfies a predetermined condition; determining that PDPC is to be applied to the predicted block based on whether the size of the current block satisfies the predetermined condition; If the size of the current block does not satisfy the predetermined condition, the image decoding apparatus skips a determination on a color component of the current block and determines not to apply PDPC to the prediction block.

10. An image coding method performed by an image coding device, comprising: performing intra prediction on the current block to generate a predicted block; determining whether PDPC is applied to the prediction block; generating a final predicted block of the current block by applying PDPC to the predicted block based on the determination; The step of determining whether to apply PDPC to the prediction block includes: determining whether the size of the current block satisfies a predetermined condition; determining that PDPC is to be applied to the predicted block based on whether the size of the current block satisfies the predetermined condition; If the size of the current block does not satisfy the predetermined condition, a determination on a color component of the current block is skipped, and PDPC is not applied to the predicted block.

11. The image encoding method according to claim 10 , wherein the predetermined condition is that the size of the current block is equal to or greater than a predetermined threshold.

12. The image encoding method according to claim 10 , wherein the predetermined condition is satisfied when the width of the current block is equal to or greater than the predetermined threshold and the height of the current block is equal to or greater than the predetermined threshold.

13. The step of determining whether to apply PDPC to the prediction block includes: The image encoding method of claim 10 , further comprising determining a reference sample line used in intra prediction of the current block.

14. determining that PDPC is applied to the prediction block based on the reference sample line being a predetermined reference sample line; The image encoding method of claim 13, wherein if the reference sample line is not a predetermined reference sample line, a determination on a color component of the current block is skipped and it is determined that PDPC is not applied to the predicted block.

15. A method for transmitting a bitstream generated by the image coding method according to claim 10.

Images