CN118355658A - Video coding method and apparatus with intra prediction derived based on reference sample lines - Google Patents

Abstract

The present disclosure relates to a video coding method and apparatus using intra prediction derived based on a reference sample line. The disclosed embodiments of video encoding methods and apparatuses, in which a reference sample line of a current block is derived using various derivation schemes, and intra prediction of the current block is performed using the derived reference sample line.

Description

Video decoding method and device using intra-frame prediction derived based on reference sample lines

Technical Field

The present disclosure relates to a video coding method and apparatus using intra-frame prediction derived based on reference sample lines.

Background technique

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Since video data has a large amount of data compared to audio or still image data, without a process for compression, the video data requires a large amount of hardware resources (including memory) to store or transmit the video data.

Thus, encoders are generally used to compress and store or transmit video data. Decoders receive compressed video data, decompress the received compressed video data, and play the decompressed video data. Video compression technologies include H.264/AVC, High Efficiency Video Coding (HEVC), and Versatile Video Coding (VVC), which have improved decoding efficiency of about 30% or more compared to HEVC.

However, as image size, resolution and frame rate gradually increase, the amount of data to be encoded also increases. Thus, a new compression technology is needed that provides higher decoding efficiency and improved image enhancement effect than existing compression technologies.

VVC (versatile video coding) technology, when used to predict a current block (also called a "prediction unit" or PU) according to an intra-frame prediction mode, generates a prediction block for the current block according to modes such as MIP (matrix-based intra-frame prediction), DC (direct current), Planar, Angular, etc. If MIP is the prediction mode, the prediction block is generated without dividing the current block into sub-blocks according to intra-frame sub-partitioning (ISP). Unless MIP is the prediction mode, the prediction block can be generated with or without dividing the current block into sub-blocks. Regardless of the involvement of the ISP, the prediction mode can be parsed for the current block. The same prediction mode as the current block can be used for the sub-blocks within the current block to generate a prediction block for each sub-block.

In order to generate these prediction blocks, reference sample lines may be derived. In addition, the reference sample lines may be filtered, and then the filtered reference sample lines may be used to generate prediction blocks according to each prediction mode. The reference sample lines derived may be pixel lines adjacent to the left side of the current block and pixel lines adjacent to the top of the current block. When the multi-reference line (MRL) mode is used, the reference pixel lines selected may be an upper pixel line and a left pixel line among three pixel lines adjacent to the left and top of the current block. As the amount of data increases, further advanced methods using reference sample lines are needed to improve video decoding efficiency and enhance video quality.

Summary of the invention

【technical problem】

The present disclosure attempts to provide a video decoding method and apparatus for improving video decoding efficiency and enhancing video quality by deriving a reference sample line of a current block using various derivation schemes. The video decoding method and apparatus perform intra-frame prediction of a current block by using the derived reference sample line.

【Technical solutions】

At least one aspect of the present disclosure provides a method performed by a video decoding device for intra-frame prediction of a current block. The method includes decoding an intra-frame prediction mode of a current block and a derivation mode index of the current block from a bitstream. Here, the derivation mode index indicates a reference sample line derivation mode that is one of a fixed position reference sample line mode, a variable position reference sample line mode, and a reference sample line list reference mode. The method also includes determining a reference sample line derivation mode according to the derivation mode index. The method also includes deriving a reference sample line of the current block according to the reference sample line derivation mode. Here, the reference sample line includes a left reference sample line and an upper reference sample line. The method also includes generating a prediction block of the current block according to the intra-frame prediction mode by using reference samples in the reference sample line.

Another aspect of the present disclosure provides a method performed by a video encoding device for intra-frame prediction of a current block. The method includes determining an intra-frame prediction mode of the current block and determining a derivation mode index of the current block. Here, the derivation mode index indicates a reference sample line derivation mode that is one of a fixed position reference sample line mode, a variable position reference sample line mode, and a reference sample line list reference mode. The method also includes determining a reference sample line derivation mode according to the derivation mode index. The method also includes deriving a reference sample line of the current block according to the reference sample line derivation mode. Here, the reference sample line includes a left reference sample line and an upper reference sample line. The method also includes generating a prediction block of the current block according to the intra-frame prediction mode by using reference samples in the reference sample line.

Another aspect of the present disclosure provides a computer-readable recording medium that stores a bitstream generated by a video encoding method. The video encoding method includes determining an intra-frame prediction mode of a current block and determining a derivation mode index of the current block. Here, the derivation mode index indicates a reference sample line derivation mode that is one of a fixed position reference sample line mode, a variable position reference sample line mode, and a reference sample line list reference mode. The video encoding method also includes determining a reference sample line derivation mode according to the derivation mode index. The video encoding method also includes deriving a reference sample line of the current block according to the reference sample line derivation mode. Here, the reference sample line includes a left reference sample line and an upper reference sample line. The video encoding method also includes generating a prediction block of the current block according to the intra-frame prediction mode by using a reference sample in the reference sample line.

【Beneficial Effects】

As described above, the present disclosure provides a video decoding method and apparatus for deriving a reference sample line of a current block by using various derivation schemes. The video decoding method and apparatus perform intra-frame prediction of the current block by using the derived reference sample line. Therefore, the video decoding method and apparatus improve video decoding efficiency and improve video quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a video encoding device that may implement the techniques of this disclosure.

FIG. 2 illustrates a method for partitioning a block using a quadtree plus binary tree ternary tree (QTBTTT) structure.

3a and 3b illustrate a plurality of intra prediction modes including a wide-angle intra prediction mode.

FIG. 4 shows a block diagram of the current block.

5 is a block diagram of a video decoding device that may implement the techniques of this disclosure.

FIG. 6 is a block diagram of a detailed intra predictor in accordance with at least one embodiment of the present disclosure.

FIG. 7 is a diagram illustrating a first condition for using a variable position reference sample line mode or a reference sample line list reference mode according to at least one embodiment of the present disclosure.

8a to 8d are diagrams illustrating derivation of reference sample lines in a variable position reference sample line mode, in accordance with at least one embodiment of the present disclosure.

FIG. 9 is a diagram illustrating subdivided reference sample lines within an upper reference sample line, in accordance with at least one embodiment of the present disclosure.

FIG. 10 is a flowchart of a video encoding method according to at least one embodiment of the present disclosure.

FIG. 11 is a flowchart of a video decoding method according to at least one embodiment of the present disclosure.

Detailed ways

Hereinafter, some embodiments of the present disclosure are described in detail with reference to the accompanying drawings. In the following description, the same reference numerals represent the same elements, although the elements are shown in different drawings. In addition, in the following description of some embodiments, for the purpose of clarity and brevity, detailed descriptions of related known components and functions may be omitted when it is considered that the subject matter of the present disclosure is obscure.

FIG1 is a block diagram of a video encoding device that can implement the technology of the present disclosure. In the following, with reference to the illustration of FIG1 , a video encoding device and components of the device are described.

The encoding device may include a picture splitter 110, a predictor 120, a subtractor 130, a transformer 140, a quantizer 145, a rearrangement unit 150, an entropy encoder 155, an inverse quantizer 160, an inverse transformer 165, an adder 170, a loop filter unit 180 and a memory 190.

Each component of the encoding device can be implemented as hardware or software or as a combination of hardware and software. In addition, the function of each component can be implemented as software, and a microprocessor can also be implemented to execute the function of the software corresponding to each component.

A video is composed of one or more sequences including multiple pictures. Each picture is split into multiple regions, and encoding is performed on each region. For example, a picture is split into one or more tiles or/and slices. Here, one or more slices can be defined as a tile group. Each tile or/and slice is split into one or more coding tree units (CTUs). In addition, each CTU is split into one or more coding units (CUs) through a tree structure. The information applied to each coding unit (CU) is encoded as the syntax of the CU, and the information commonly applied to the CU included in a CTU is encoded as the syntax of the CTU. In addition, the information commonly applied to all blocks in a slice is encoded as the syntax of the slice header, and the information applied to all blocks constituting one or more pictures is encoded into a picture parameter set (PPS) or a picture header. In addition, the information commonly referenced by multiple pictures is encoded into a sequence parameter set (SPS). In addition, the information commonly referenced by one or more SPSs is encoded into a video parameter set (VPS). Further, the information commonly applied to a slice or slice group can also be encoded as the syntax of a slice or tile group header. The syntax included in an SPS, a PPS, a slice header, a slice, or a slice group header may be referred to as a high-level syntax.

The picture splitter 110 determines the size of a coding tree unit (CTU). Information on the size of the CTU (CTU size) is encoded as a syntax of an SPS or a PPS and transmitted to a video decoding device.

The picture splitter 110 splits each picture constituting a video into a plurality of coding tree units (CTUs) having a predetermined size, and then recursively splits the CTUs by using a tree structure. A leaf node in the tree structure becomes a coding unit (CU), which is a basic unit of encoding.

The tree structure can be a quadtree (QT), in which a higher node (or parent node) is divided into four lower nodes (or child nodes) of the same size. The tree structure can also be a binary tree (BT), in which a higher node is divided into two lower nodes. The tree structure can also be a ternary tree (TT), in which a higher node is split into three lower nodes at a ratio of 1:2:1. The tree structure can also be a structure in which two or more of the QT structure, BT structure, and TT structure are mixed. For example, a quadtree plus binary tree (QTBT) structure can be used or a quadtree plus binary tree ternary tree (QTBTTT) structure can be used. Here, a binary tree ternary tree (BTTT) is added to the tree structure to be referred to as a multi-type tree (MTT).

FIG. 2 is a diagram for describing a method of splitting a block by using a QTBTTT structure.

As shown in Figure 2, the CTU can first be divided into a QT structure. The quadtree splitting can be recursive until the size of the split block reaches the minimum block size (MinQTSize) of the leaf node allowed in QT. The first flag (QT_split_flag) indicating whether each node of the QT structure is split into four nodes of the lower layer is encoded by the entropy encoder 155 and is notified to the video decoding device by a signal. When the leaf node of QT is not larger than the maximum block size (MaxBTSize) of the root node allowed in BT, the leaf node can be further split into at least one of the BT structure and the TT structure. There may be multiple splitting directions in the BT structure and/or the TT structure. For example, there may be two directions, namely, the direction in which the block of the corresponding node is split horizontally and the direction in which the block of the corresponding node is split vertically. As shown in Figure 2, when the MTT splitting starts, a second flag (mtt_split_flag) indicating whether the node is split, as well as a flag indicating the splitting direction (vertical or horizontal) and/or a flag indicating the splitting type (binary or trifurcated) if the node is split, is encoded by the entropy encoder 155 and notified to the video decoding device by a signal.

Alternatively, before encoding the first flag (QT_split_flag) indicating whether each node is split into four nodes of the lower layer, a CU split flag (split_cu_flag) indicating whether the node is split may also be encoded. When the value of the CU split flag (split_cu_flag) indicates that each node is not split, the block of the corresponding node becomes a leaf node in the split tree structure and becomes a CU as a basic unit of encoding. When the value of the CU split flag (split_cu_flag) indicates that each node is split, the video encoding device first starts encoding the first flag through the above scheme.

When QTBT is used as another embodiment of a tree structure, there may be two types, namely, a type in which the block of the corresponding node is horizontally split into two blocks of the same size (i.e., symmetrical horizontal splitting) and a type in which the block of the corresponding node is vertically split into two blocks of the same size (i.e., symmetrical vertical splitting). A split flag (split_flag) indicating whether each node of the BT structure is split into blocks of the lower layer and split type information indicating the split type are encoded by the entropy encoder 155 and transmitted to the video decoding device. At the same time, there may be another type in which the block of the corresponding node is split into two blocks that are asymmetric to each other. The asymmetric form may include a form in which the block of the corresponding node is split into two rectangular blocks with a size ratio of 1:3, or may also include a form in which the block of the corresponding node is split in a diagonal direction.

A CU may have different sizes depending on the QTBT or QTBTTT split from a CTU. Hereinafter, a block corresponding to a CU to be encoded or decoded (i.e., a leaf node of a QTBTTT) is referred to as a "current block". Due to the adoption of QTBTTT splitting, the shape of the current block may be a rectangular shape in addition to a square shape.

The predictor 120 predicts the current block to generate a predicted block. The predictor 120 includes an intra predictor 122 and an inter predictor 124.

In general, each of the current blocks in a picture may be predictively coded. Typically, the prediction of the current block may be performed using intra-prediction techniques (using data from the picture including the current block) or inter-prediction techniques (using data from a picture coded before the picture including the current block). Inter-prediction includes both unidirectional prediction and bidirectional prediction.

The intra-frame predictor 122 predicts the pixels in the current block by using the pixels (reference pixels) located on the neighboring blocks of the current block in the current picture including the current block. According to the prediction direction, there are multiple intra-frame prediction modes. For example, as shown in FIG. 3a, the multiple intra-frame prediction modes may include 2 non-directional modes including a plane mode and a DC mode, and may include 65 directional modes. The neighboring pixels and the arithmetic equations to be used are defined differently according to each prediction mode.

In order to perform effective directional prediction for the current block having a rectangular shape, a directional mode (#67 to #80, intra prediction mode #-1 to #-14) as shown by the dotted arrows in FIG. 3b can be used in addition. The directional mode may be referred to as a "wide-angle intra prediction mode". In FIG. 3b, the arrow indicates the corresponding reference sample used for prediction and does not indicate the prediction direction. The prediction direction is opposite to the direction shown by the arrow. When the current block has a rectangular shape, the wide-angle intra prediction mode is a mode in which prediction is performed in the opposite direction to the specific directional mode without additional bit transmission. In this case, in the wide-angle intra prediction mode, some wide-angle intra prediction modes that can be used for the current block can be determined by the ratio of the width and height of the current block having a rectangular shape. For example, when the current block has a rectangular shape with a height less than the width, a wide-angle intra prediction mode (intra prediction mode #67 to #80) with an angle less than 45 degrees is available. When the current block has a rectangular shape with a width greater than the height, a wide-angle intra prediction mode with an angle greater than -135 degrees can be used.

The intra-frame predictor 122 may determine an intra-frame prediction to be used for encoding the current block. In some embodiments, the intra-frame predictor 122 may encode the current block by using a plurality of intra-frame prediction modes, and may further select an appropriate intra-frame prediction mode to be used from a test mode. For example, the intra-frame predictor 122 may calculate a rate-distortion value by using a rate-distortion analysis for a plurality of tested intra-frame prediction modes, and may further select an intra-frame prediction mode having the best rate-distortion characteristics in the test mode.

The intra-frame predictor 122 selects an intra-frame prediction mode among a plurality of intra-frame prediction modes and predicts the current block by using adjacent pixels (reference pixels) and an arithmetic equation determined according to the selected intra-frame prediction mode. Information about the selected intra-frame prediction mode is encoded by the entropy encoder 155 and transmitted to the video decoding device.

The inter-frame predictor 124 generates a prediction block for the current block by using a motion compensation process. The inter-frame predictor 124 searches for a block most similar to the current block in a reference picture that is encoded and decoded earlier than the current picture, and generates a prediction block for the current block by using the searched block. In addition, a motion vector (MV) is generated, which corresponds to the displacement between the current block in the current picture and the prediction block in the reference picture. Generally, motion estimation is performed on the luminance component, and the motion vector calculated based on the luminance component is used for both the luminance component and the chrominance component. Motion information including information about the reference picture and information about the motion vector for predicting the current block is encoded by the entropy encoder 155 and transmitted to the video decoding device.

The inter-frame predictor 124 may also perform interpolation on a reference picture or a reference block in order to increase the accuracy of the prediction. In other words, the subsamples between two consecutive integer samples are interpolated by applying the filter coefficients to a plurality of consecutive integer samples including two integer samples. When the process of searching for the block most similar to the current block is performed for the interpolated reference picture, the decimal unit precision may be used instead of the integer sample unit precision for the motion vector representation. The precision or resolution of the motion vector may be set differently for each target region to be encoded (e.g., units such as slices, slices, CTUs, CUs, etc.). When such an adaptive motion vector resolution (AMVR) is applied, information about the motion vector resolution to be applied to each target region should be signaled for each target region. For example, when the target region is a CU, information about the motion vector resolution applied to each CU is signaled. The information about the motion vector resolution may be information representing the precision of the motion vector difference to be described below.

Meanwhile, the inter-frame predictor 124 may perform inter-frame prediction by using bidirectional prediction. In the case of bidirectional prediction, two reference pictures and two motion vectors representing the block position most similar to the current block in each reference picture are used. The inter-frame predictor 124 selects a first reference picture and a second reference picture from a reference picture list 0 (RefPicList0) and a reference picture list 1 (RefPicList1), respectively. The inter-frame predictor 124 also searches for a block most similar to the current block in the corresponding reference picture to generate a first reference block and a second reference block. In addition, a prediction block of the current block is generated by averaging or weighted averaging the first reference block and the second reference block. In addition, motion information including information about two reference pictures used to predict the current block and information about two motion vectors is transmitted to the entropy encoder 155. Here, the reference picture list 0 may be composed of pictures that are before the current picture in the display order in the pre-reconstructed picture, and the reference picture list 1 may be composed of pictures that are after the current picture in the display order in the pre-reconstructed picture. However, although not particularly limited thereto, a pre-reconstructed picture after the current picture in the display order may be additionally included in the reference picture list 0. Conversely, a pre-reconstructed picture before the current picture may also be additionally included in the reference picture list 1.

In order to minimize the number of bits consumed for encoding motion information, various methods may be used.

For example, when the reference picture and motion vector of the current block are the same as those of the adjacent block, information capable of identifying the adjacent block is encoded to transmit the motion information of the current block to the video decoding device. This method is called merge mode.

In the merge mode, the inter predictor 124 selects a predetermined number of merge candidate blocks (hereinafter, referred to as “merge candidates”) from neighboring blocks of the current block.

As shown in FIG. 4 , all or some of the left block A0, the lower left block A1, the upper block B0, the upper right block B1, and the upper left block B2 adjacent to the current block in the current picture may be used as neighboring blocks for deriving merge candidates. Further, blocks located in a reference picture (which may be the same as or different from the reference picture used to predict the current block) other than the current block within the current picture where the current block is located may also be used as merge candidates. For example, a block co-located with the current block within the reference picture or a block adjacent to the co-located block may be additionally used as a merge candidate. If the number of merge candidates selected by the method described above is less than a preset number, a zero vector is added to the merge candidate.

The inter-frame predictor 124 configures a merge list including a predetermined number of merge candidates by using adjacent blocks. A merge candidate to be used as motion information of the current block is selected from the merge candidates included in the merge list, and merge index information for identifying the selected candidate is generated. The generated merge index information is encoded by the entropy encoder 155 and transmitted to the video decoding device.

Merge skip mode is a special case of merge mode. After quantization, when all transform coefficients for entropy coding are close to zero, only the neighbor block selection information is transmitted without the residual signal. By using merge skip mode, relatively high coding efficiency can be achieved for images with slight motion, still images, screen content images, etc.

Hereinafter, the merge mode and the merge skip mode are collectively referred to as the merge/skip mode.

Another method for encoding motion information is the Advanced Motion Vector Prediction (AMVP) mode.

In the AMVP mode, the inter-frame predictor 124 derives a motion vector predictor candidate for a motion vector of the current block by using the neighboring blocks of the current block. As the neighboring blocks for deriving the motion vector predictor candidates, all or some of the left block A0, the lower left block A1, the upper block B0, the upper right block B1, and the upper left block B2 adjacent to the current block in the current picture shown in FIG. 4 can be used. In addition, a block located in a reference picture (which may be the same as or different from the reference picture used to predict the current block) other than the current block located in the current picture can also be used as a neighboring block for deriving the motion vector predictor candidate. For example, a block co-located with the current block in the reference picture or a block adjacent to the co-located block can be used. If the number of motion vector predictor candidates selected by the above method is less than the preset number, a zero vector is added to the motion vector predictor candidate.

The inter predictor 124 derives a motion vector predictor candidate by using the motion vector of the neighboring block, and determines a motion vector predictor for the motion vector of the current block by using the motion vector predictor candidate. In addition, a motion vector difference is calculated by subtracting the motion vector predictor from the motion vector of the current block.

The motion vector predictor can be obtained by applying a predefined function (e.g., center value and average value calculation, etc.) to the motion vector predictor candidate. In this case, the video decoding device also knows the predefined function. In addition, since the neighboring blocks used to derive the motion vector predictor candidate are blocks for which encoding and decoding have been completed, the video decoding device may also already know the motion vectors of the neighboring blocks. Therefore, the video encoding device does not need to encode the information for identifying the motion vector predictor candidate. Thus, in this case, information about the motion vector difference and information about the reference picture used to predict the current block are encoded.

Meanwhile, the motion vector predictor may also be determined by selecting any one of the motion vector predictor candidates. In this case, information for identifying the selected motion vector predictor candidate is additionally encoded jointly with information about the motion vector difference and information about the reference picture used to predict the current block.

The subtractor 130 generates a residual block by subtracting a prediction block generated by the intra predictor 122 or the inter predictor 124 from the current block.

The transformer 140 converts the residual signal in the residual block having the pixel value in the spatial domain into a transform coefficient in the frequency domain. The transformer 140 may transform the residual signal in the residual block by using the total size of the residual block as a transform unit, or may also split the residual block into a plurality of sub-blocks, and may perform the transform by using the sub-block as a transform unit. Optionally, the residual block is divided into two sub-blocks, namely a transform region and a non-transform region, so as to transform the residual signal using only the transform region sub-block as a transform unit. Here, the transform region sub-block may be one of two rectangular blocks having a size ratio of 1:1 based on the horizontal axis (or vertical axis). In this case, the flag (cu_sbt_flag) indicates that only the sub-block is transformed, and the directional (vertical/horizontal) information (cu_sbt_horizontal_flag) and/or the position information (cu_sbt_pos_flag) are encoded by the entropy encoder 155 and signaled to the video to the decoding device. In addition, the size of the transform region sub-block may have a size ratio of 1:3 based on the horizontal axis (or vertical axis). In this case, a flag (cu_sbt_quad_flag) for dividing the corresponding split is additionally encoded by the entropy encoder 155 and signaled to the video decoding apparatus.

Meanwhile, the transformer 140 may perform transformation on the residual block separately in the horizontal direction and the vertical direction. For the transformation, different types of transformation functions or transformation matrices may be used. For example, a pair of transformation functions for horizontal transformation and vertical transformation may be defined as a multiple transform set (MTS). The transformer 140 may select a pair of transformation functions having the highest transformation efficiency in the MTS, and may transform the residual block in each of the horizontal and vertical directions. Information (mts_idx) of the transformation function pair in the MTS is encoded by the entropy encoder 155 and notified to the video decoding device with a signal.

The quantizer 145 quantizes the transform coefficients output from the transformer 140 using the quantization parameter and outputs the quantized transform coefficients to the entropy encoder 155. The quantizer 145 can also immediately quantize the relevant residual block without transforming any block or frame. The quantizer 145 can also apply different quantization coefficients (scaling values) according to the position of the transform coefficient in the transform block. The quantization matrix applied to the quantized transform coefficients arranged in 2 dimensions can be encoded and notified to the video decoding device with a signal.

The rearrangement unit 150 may perform rearrangement of coefficient values for the quantized residual block.

The rearrangement unit 150 may change the 2D coefficient array into a 1D coefficient sequence by using coefficient scanning. For example, the rearrangement unit 150 may output an ID coefficient sequence by scanning the DC coefficient into a high frequency domain coefficient using a zigzag scan or a diagonal scan. Depending on the size of the transform unit and the intra prediction mode, a vertical scan that scans the 2D coefficient array in the column direction and a horizontal scan that scans the 2D block type coefficients in the row direction may also be used instead of the zigzag scan. In other words, depending on the size of the transform unit and the intra prediction mode, the scanning method to be used may be determined among zigzag scanning, diagonal scanning, vertical scanning, and horizontal scanning.

The entropy encoder 155 generates a bitstream by encoding the sequence of ID-quantized transform coefficients output from the rearrangement unit 150 using various encoding schemes including context-based adaptive binary arithmetic coding (CABAC), exponential Golomb, and the like.

In addition, the entropy encoder 155 encodes information related to block splitting (such as CTU size, CTU splitting mark, QT splitting mark, MTT splitting type, MTT splitting direction, etc.) to allow the video decoding device to split the block, etc. to the video encoding device. In addition, the entropy encoder 155 encodes information about the prediction type indicating whether the current block is encoded by intra-frame prediction or inter-frame prediction. The entropy encoder 155 encodes intra-frame prediction information (i.e., information about intra-frame prediction mode) or inter-frame prediction information (in the case of merge mode, merge index, and in the case of AMVP mode, information about reference picture index and motion vector difference) according to the prediction type. In addition, the entropy encoder 155 encodes information related to quantization (i.e., information about quantization parameters and information about quantization matrices).

The inverse quantizer 160 dequantizes the quantized transform coefficient output from the quantizer 145 to generate a transform coefficient. The inverse transformer 165 transforms the transform coefficient output from the inverse quantizer 160 from the frequency domain to the spatial domain to reconstruct a residual block.

The adder 170 reconstructs the current block by adding the reconstructed residual block and the prediction block generated by the predictor 120. When intra-prediction is performed on a next sequential block, pixels in the reconstructed current block may be used as reference pixels.

The loop filter unit 180 performs filtering on the reconstructed pixels to reduce block artifacts, ringing artifacts, blur artifacts, etc. that occur due to block-based prediction and transform/quantization. The loop filter unit 180 as a loop filter may include all or some of the deblocking filter 182, the sample adaptive offset (SAO) filter 184, and the adaptive loop filter (ALF) 186.

The deblocking filter 182 filters the boundaries between the reconstructed blocks to remove the block effect caused by block unit encoding/decoding, and the SAO filter 184 and the ALF 186 perform additional filtering for the deblocked filtered video. The SAO filter 184 and the ALF 186 are filters for compensating the difference between the reconstructed pixels and the original pixels, which occurs due to lossy decoding. The SAO filter 184 applies an offset as a CTU unit to enhance subjective image quality and coding efficiency. On the other hand, the ALF 186 performs block unit filtering and applies different filters to compensate for distortion by dividing the boundaries of the corresponding blocks and the degree of the change amount. Information about the filter coefficient to be used for the ALF can be encoded and notified to the video decoding device with a signal.

The reconstructed blocks filtered by the deblocking filter 182, the SAO filter 184, and the ALF 186 are stored in the memory 190. When all blocks in one picture are reconstructed, the reconstructed picture can be used as a reference picture for inter-frame prediction of blocks in a picture to be encoded later.

FIG5 is a functional block diagram of a video decoding device that can implement the technology of the present disclosure. In the following, with reference to FIG5 , a video decoding device and components of the device are described.

The video decoding device may include an entropy decoder 510 , a rearrangement unit 515 , an inverse quantizer 520 , an inverse transformer 530 , a predictor 540 , an adder 550 , a loop filter unit 560 , and a memory 570 .

Similar to the video encoding device of Figure 1, each component of the video decoding device can be implemented as hardware or software or as a combination of hardware and software. In addition, the function of each component can be implemented as software, and a microprocessor can also be implemented to execute the function of the software corresponding to each component.

The entropy decoder 510 extracts information related to block splitting by decoding a bitstream generated by a video encoding apparatus to determine a current block to be decoded, and extracts prediction information required to reconstruct the current block and information about a residual signal.

The entropy decoder 510 determines the size of the CTU by extracting information about the CTU size from a sequence parameter set (SPS) or a picture parameter set (PPS), and splits the picture into CTUs of the determined size. In addition, the CTU is determined to be the highest level of the tree structure, that is, the root node, and the split information of the CTU can be extracted to split the CTU using the tree structure.

For example, when a CTU is split using a QTBTTT structure, a first flag (QT_split_flag) associated with the splitting of the QT is first extracted to split each node into four nodes at the lower layer. In addition, with respect to a node corresponding to a leaf node of the QT, a second flag (mtt_split_flag) associated with the splitting of the MTT, a splitting direction (vertical/horizontal) and/or a splitting type (binary/trifurcated) are extracted to split the corresponding leaf node into an MTT structure. As a result, each node below the leaf node of the QT is recursively split into a BT or TT structure.

As another embodiment, when a CTU is split by using a QTBTTT structure, a CU split flag (split_cu_flag) indicating whether the CU is split is extracted. When the corresponding block is split, a first flag (QT_split_flag) may also be extracted. During the splitting process, 0 or more recursive MTT splits may occur after 0 or more recursive QT splits with respect to each node. For example, for a CTU, MTT splitting may occur immediately, or conversely, only multiple QT splits may occur.

As another embodiment, when the CTU is split using the QTBT structure, the first flag (QT_split_flag) related to the splitting of the QT is extracted to split each node into four nodes of the lower layer. In addition, the split flag (split_flag) indicating whether the node corresponding to the leaf node of the QT is further split into BTs and the split direction information are extracted.

Meanwhile, when the entropy decoder 510 determines the current block to be decoded by splitting using the tree structure, the entropy decoder 510 extracts information about a prediction type indicating whether the current block is intra-predicted or inter-predicted. When the prediction type information indicates intra-prediction, the entropy decoder 510 extracts syntax elements of intra-prediction information (intra-prediction mode) for the current block. When the prediction type information indicates inter-prediction, the entropy decoder 510 extracts information representing syntax elements for inter-prediction information (i.e., motion vectors and reference pictures to which motion vectors refer).

Also, the entropy decoder 510 extracts quantization-related information and extracts information on a quantized transform coefficient of the current block as information on a residual signal.

The rearrangement unit 515 may change the sequence of 1D quantized transform coefficients entropy-decoded by the entropy decoder 510 into a 2D coefficient array (ie, block) again in the reverse order of the coefficient scanning order performed by the video encoding device.

The inverse quantizer 520 dequantizes the quantized transform coefficients and dequantizes the quantized transform coefficients by using quantization parameters. The inverse quantizer 520 may also apply different quantization coefficients (scaling values) to the quantized transform coefficients arranged in 2D. The inverse quantizer 520 may perform inverse quantization by applying a matrix (scaling value) of quantization coefficients from a video encoding device to a 2D array of quantized transform coefficients.

The inverse transformer 530 generates a residual block for the current block by reconstructing a residual signal by inversely transforming the dequantized transform coefficients from the frequency domain into the spatial domain.

In addition, when the inverse transformer 530 inversely transforms a partial region (sub-block) of the transform block, the inverse transformer 530 extracts a flag (cu_sbt_flag) that only the sub-block of the transform block is transformed, direction (vertical/horizontal) information (cu_sbt_horizontal_flag) of the sub-block, and/or position information (cu_sbt_pos_flag) of the sub-block. The inverse transformer 530 also inversely transforms the transform coefficient of the corresponding sub-block from the frequency domain to the spatial domain to reconstruct the residual signal and fills the region that is not inversely transformed with a value of "0" as the residual signal to generate a final residual block for the current block.

In addition, when MTS is applied, the inverse transformer 530 determines a transform index or a transform matrix applied in each of the horizontal and vertical directions by using MTS information (mts_idx) signaled from the video encoding device. The inverse transformer 530 also performs inverse transform on the transform coefficients in the transform block in the horizontal and vertical directions by using the determined transform function.

The predictor 540 may include an intra predictor 542 and an inter predictor 544. The intra predictor 542 is activated when the prediction type of the current block is intra prediction, and the inter predictor 544 is activated when the prediction type of the current block is inter prediction.

The intra predictor 542 determines an intra prediction mode of a current block among a plurality of intra prediction modes according to a syntax element of the intra prediction mode extracted from the entropy decoder 510. The intra predictor 542 also predicts the current block by using neighboring reference pixels of the current block according to the intra prediction mode.

The inter predictor 544 determines a motion vector of a current block and a reference picture to which the motion vector refers by using a syntax element for the inter prediction mode extracted from the entropy decoder 510 .

The adder 550 reconstructs the current block by adding the residual block output from the inverse transformer 530 and the prediction block output from the inter predictor 544 or the intra predictor 542. When intra prediction is performed on a block to be decoded later, pixels within the reconstructed current block are used as reference pixels.

The loop filter unit 560 as a loop filter may include a deblocking filter 562, an SAO filter 564, and an ALF 566. The deblocking filter 562 performs deblocking filtering on the boundary between the reconstructed blocks in order to remove the block effect that occurs due to the block unit decoding. The SAO filter 564 and the ALF 566 perform additional filtering on the reconstructed blocks after the deblocking filtering in order to compensate for the difference between the reconstructed pixels and the original pixels that occurs due to the lossy encoding. The filter coefficients of the ALF are determined by using information about the filter coefficients decoded from the bitstream.

The reconstructed blocks filtered by the deblocking filter 562, the SAO filter 564, and the ALF 566 are stored in the memory 570. When all blocks in one picture are reconstructed, the reconstructed picture can be used as a reference picture for inter-frame prediction of blocks in a picture to be encoded later.

In some embodiments, the present disclosure relates to encoding and decoding a video image as described above. More specifically, the present disclosure provides a video encoding method and apparatus for deriving a reference sample line of a current block by using various derivation schemes. The video encoding method and apparatus use the derived reference sample line to perform intra-frame prediction of the current block.

The following embodiments may be performed by the intra predictor 122 in the video encoding device. They may also be performed by the intra predictor 542 in the video decoding device.

In performing intra prediction on the current block, the video encoding device may generate signaling information associated with the present embodiment in terms of optimizing rate distortion. The video encoding device may use the entropy encoder 155 to encode the signaling information and transmit it to the video decoding device. The video decoding device may use the entropy decoder 510 to decode the signaling information associated with intra prediction of the current block from the bitstream.

In the following description, the term 'prediction unit' (PU), specifically, current prediction unit, may be used interchangeably with a current block or coding unit (CU) as described above, or a prediction unit may refer to some area of a coding unit.

In addition, a true value of the flag indicates a case where the flag is set to 1. In addition, a false value of the flag indicates a case where the flag is set to 0.

I. Inter-frame prediction merge mode

The following embodiments may be applied to the inter-frame predictor 124 in the video encoding apparatus.

A method for constituting a merge candidate list of motion information in a merge mode of inter prediction is described below. To support the merge mode, the inter predictor 124 in the video encoding device may select a preset number (eg, six) of merge candidates to form a merge candidate list.

The inter predictor 124 detects a spatial merging candidate. The inter predictor 124 searches for a spatial merging candidate from neighboring blocks, as shown in FIG4. Up to four spatial merging candidates may be selected.

The inter-frame predictor 124 searches for temporal merge candidates. The inter-frame predictor 124 may add a block that is co-located with the current block and in a reference picture (the same picture as used to predict the current block or a different picture) but not in the current picture where the target block is located as a temporal merge candidate. One temporal merge candidate may be selected.

The inter-frame predictor 124 searches for a history-based motion vector predictor (HMVP) candidate. The inter-frame predictor 124 may store the motion vectors of the previous n (where n is a natural number) CUs in a table and use the motion vectors as merge candidates. The size of the table is 6, and the motion vectors of the previous CUs are stored in a first-in-first-out (FIFO) scheme. This indicates that up to 6 HMVP candidates are stored in the table. The inter-frame predictor 124 may set the most recent motion vector among the HMVP candidates stored in the table as a merge candidate.

The inter predictor 124 searches for a paired average motion vector predictor (PAMVP) candidate. The inter predictor 124 may set an average of motion vectors of a first candidate and a second candidate in the merge candidate list as a merge candidate.

If the merge candidate list cannot be filled (ie, the preset number of candidates is not satisfied) after performing all the above-mentioned search procedures, the inter predictor 124 adds a zero motion vector as a merge candidate.

The aforementioned method of constructing a merge candidate list in the video encoding device may be similarly performed by the inter-frame predictor 544 in the video decoding device.

II. Derivation of reference sample lines

The following embodiments are described with the intra-frame predictor 542 of the video decoding apparatus as the center, but can also be implemented in the intra-frame predictor 122 of the video encoding apparatus.

FIG. 6 is a block diagram of a detailed intra predictor in accordance with at least one embodiment of the present disclosure.

The intra predictor 542 of the video decoding apparatus may include all or part of a subblock split-no-split information deriver 602 , a prediction mode deriver 604 , a reference sample line deriver 606 , and a prediction executor 608 .

The sub-block split-no-split information deriver 602 may derive information on whether the current block is to be split into sub-blocks. If the current block is split into sub-blocks, the reference sample line deriver 606 and the prediction executor 608 may perform their related operations by sub-block units.

The prediction mode deriver 604 may derive an intra prediction mode for the current block. Here, the prediction mode may be a matrix-based prediction mode, a directional prediction mode, a non-directional prediction mode (such as DC or plane), etc. For example, the prediction mode deriver 604 may decode the intra prediction mode from the bitstream.

On the other hand, the operations of the sub-block splitting-non-splitting information deriver 602 and the prediction mode deriver 604 may also be performed by the entropy decoder 510 .

The reference sample line deriver 606 may derive reference sample lines at required positions according to the prediction mode.

The prediction performer 608 may generate a prediction block of the current block according to the prediction mode by using the reference samples in the derived reference sample line.

For example, the reference sample line exporter 606 may decode an export mode index indicating a reference sample line export mode of the current block or sub-block. The reference sample line exporter 606 may select one of the export modes of the fixed position reference sample line mode, the variable position reference sample line mode, and the reference sample line list reference mode according to the export mode index, as shown in FIG6, and then use the selected export mode to export the reference sample line of the current block or the current sub-block. If at least one of the first condition to the third condition is satisfied, the export mode index may be encoded by the video encoding device to indicate the variable position reference sample line mode or the reference sample line list reference mode. On the other hand, if none of the first condition to the third condition is satisfied, the export mode index may be encoded by the video encoding device to indicate the fixed position reference sample line mode.

As another embodiment, the reference sample line exporter 606 may check whether at least one of the first to third conditions is satisfied, and if at least one condition is satisfied, it may use the variable position reference sample line mode or the reference sample line list reference mode. At this time, the reference sample line exporter 606 may parse a flag indicating one of the two modes. On the other hand, if none of the first to third conditions is satisfied, the reference sample line exporter 606 may use the fixed position reference sample line mode.

The first to third conditions are described below. In addition, the (x, y) coordinates of the upper left pixel of the current block are defined as (0, 0).

7, the first condition is when at least a preset number of prediction units among the reconstructed prediction units including neighboring pixels of the current block at preset positions (such as (-1, -1), (-1, 0), (0, -1), (-1, puH), and (puW, -1)) have been reconstructed by inter-frame prediction. Under the first condition, puW and puH represent the horizontal length and vertical length of the current block (i.e., the current prediction unit).

The second condition is that the motion vector encoding mode of the prediction unit reconstructed by inter prediction in the first condition is the spatial merging mode as described above.

The third condition is that motion vectors of prediction units reconstructed by inter prediction under the first condition are similar to each other.

In the reference sample line derivation mode, the fixed position reference sample line mode utilizes a conventional reference sample line derivation scheme. The reference sample line deriver 606 can be responsive to the selection of the fixed position reference sample line mode to derive pixel lines adjacent to the left and top boundaries of the current block as reference sample lines.

8a to 8d are diagrams illustrating derivation of reference sample lines in a variable position reference sample line mode, in accordance with at least one embodiment of the present disclosure.

When the variable position reference sample line mode is selected in the reference sample line derivation mode, the reference sample line deriver 606 may derive a reference sample line that is not adjacent to the current block. For example, the reference sample line deriver 606 may derive a left reference sample line and an upper reference sample line from a pixel line of N pixels away from the left boundary or the upper boundary of the current block, respectively. Optionally, the reference sample line deriver 606 may select one of a plurality of derivation methods as shown in FIGS. 8a to 8d , and derive the left reference sample line and the upper reference sample line according to the selected method. The derivation method index of the left reference sample line and the derivation method index of the upper reference sample line may be sent from the video encoding device to the video decoding device using a signal. As another embodiment, one derivation method index may be shared by the left reference sample line and the upper reference sample line.

A method of deriving the left reference sample line is described below with reference to FIGS. 8 a to 8 d .

The first derivation method of the left reference sample line defines the coordinates of the pixel that shares the common y-axis coordinate with the upper left pixel of the current block among the left neighboring samples of the processing unit containing the current block as (xL, yL). The reference sample line deriver 606 can obtain samples in the range of (xL, yL+α) to (xL, yL+puH×2-1) as the left reference sample line, as shown in FIG8a.

Here, α may be a preset integer such as −1. In addition, as described above, puW and puH represent the horizontal length and the vertical length of the current block (ie, the current prediction unit).

The processing unit may be generated by segmenting the decoding tree unit. One or more decoding units may be included in the processing unit, or one or more processing units may be included in the decoding unit. An exemplary processing unit is a virtual pipeline data unit (VPDU). A VPDU is a data unit that can be processed by a virtual pipeline. A VPDU is the largest unit that can be encoded and decoded at one time, and can be used to reduce the cost of hardware implementation when the size of a CTU increases. In the embodiment of FIG. 8a, vpduW and vpduH represent the width and height of a VDPU.

The second derivation method for the left reference sample line defines the coordinates of the pixel that shares the common y-axis coordinate with the upper left (0, 0) pixel of the current block among the left neighboring samples of the prediction unit including the (-1, 0) pixel as (xL, yL). The reference sample line deriver 606 can derive samples in the range of (xL, yL+α) to (xL, yL+puH×2-1) as the left reference sample line, as shown in FIG8b.

The third derivation method of the left reference sample line defines the coordinates of any pixel existing on the left side of the current block in the area decoded before the current block within the processing unit as (xL, yL). The reference sample line deriver 606 can obtain samples in the range of (xL, yL+α) to (xL, yL+puH×2-1) as the left reference sample line, as shown in FIG8c. In this case, the y-axis coordinate of the upper left pixel of the current block may be different from the yL coordinate of any pixel. The pixels in the derived reference sample line may all be included in the same prediction unit. Alternatively, some pixels may be included in different prediction units.

The coordinates (xL, yL) of any pixel may be sent from the video encoding device to the video decoding device using a signal. As another embodiment, the offset value between the coordinates of any pixel and the coordinates of the upper left pixel of the current block may be sent from the video encoding device to the video decoding device using a signal.

The fourth derivation method of the left reference sample line as shown in Figure 8d can make the x-axis coordinates of the pixels in the left reference sample line derived according to the first derivation method, the second derivation method or the third derivation method different. The pixels with the same x-axis coordinate and continuous y-axis coordinate included in the left reference sample line are defined as a continuous pixel group. There may be two or more continuous pixel groups. The number of continuous pixel groups may be preset, or the number of continuous pixel groups may be parsed. Optionally, when a specific directional prediction mode is applied, the number of continuous pixel groups may be parsed. The length of the continuous pixel group may be puH, puH+1, puH/2, puH/2+1, etc.

For each continuous pixel group, the coordinates and length of the starting pixel can be parsed. As another embodiment, a list including the coordinates of the starting pixel and a list including the length of the starting pixel can be established. Then, for each continuous pixel group, an index indicating the coordinates of the starting pixel and an index indicating the length of the starting pixel can be parsed.

A method of obtaining the upper reference sample line is described below with reference to FIGS. 8 a to 8 d .

The first derivation method for the upper reference sample line defines the coordinates of the pixel that shares a common x-axis coordinate with the upper left pixel of the current block among the upper neighboring samples of the processing unit including the current block as (xT, yT). The reference sample line deriver 606 can derive samples in the range of (xT+α, yT) to (xT+puW×2-1, yT) as the upper reference sample line, as shown in FIG8a.

The second derivation method for the upper reference sample line defines the coordinates of the pixel that shares the common x-axis coordinate with the upper left (0, 0) pixel of the current block among the upper neighboring samples of the prediction unit including the (0, -1) pixel as (xT, yT). The reference sample line deriver 606 can derive samples in the range of (xT+α, yT) to (xT+puW×2-1, yT) as the upper reference sample line, as shown in FIG8b.

The third derivation method for the upper reference sample line defines the coordinates of any pixel existing in the upper part of the current block in the area decoded before the current block in the processing unit as (xT, yT). The reference sample line deriver 606 can derive samples in the range of (xT+α, yT) to (xT+puW×2-1, yT) as the upper reference sample line, as shown in FIG8c. In this case, the x-axis coordinate of the upper left pixel of the current block may be different from the xT coordinate of any pixel.

The coordinates (xT, yT) of any pixel may be notified from the video encoding device to the video decoding device by a signal. As another embodiment, the offset value between the coordinates of any pixel and the coordinates of the upper left pixel of the current block may be notified from the video encoding device to the video decoding device by a signal.

The fourth derivation method of the upper reference sample line as shown in Figure 8d can make the y-axis coordinates of the pixels in the left reference sample line derived according to the first derivation method, the second derivation method or the third derivation method different. Pixels included in the upper reference sample line with the same y-axis coordinate and continuous x-axis coordinates can be referred to as a continuous pixel group. There can be two or more continuous pixel groups. The number of continuous pixel groups can be preset, or the number of continuous pixel groups can be parsed. Optionally, when a specific directional prediction mode is applied, the number of continuous pixel groups can be parsed. The length of the continuous pixel group can be puW, puW+1, puW/2, puW/2+1, etc.

For each continuous pixel group, the coordinates and length of the starting pixel can be parsed. As another embodiment, a list including the coordinates of the starting pixel and a list including the length of the starting pixel can be established. Then, for each continuous pixel group, an index indicating the coordinates of the starting pixel and an index indicating the length of the starting pixel can be parsed.

FIG. 9 is a diagram illustrating subdivided reference sample lines within an upper reference sample line, in accordance with at least one embodiment of the present disclosure.

When an upper reference sample line or a left reference sample line is derived according to the first derivation method, the second derivation method, the third derivation method, or the fourth derivation method of the upper reference sample line or the left reference sample line, the pixels in the derived reference sample line may all be included in the same prediction unit. Optionally, some pixels may be included in different prediction units. For example, in the upper reference sample line as shown in FIG. 9 , pixels in the range (xT, yT) to (xT+a-1, yT) may be included in prediction unit A, pixels in the range (xT+a, yT) to (xT+a+b-1, yT) may be included in prediction unit B, and pixels in the range (xT+a+b, yT) to (xT+a+b+c-1, yT) may be included in prediction unit C. In the following, as shown in FIG. 9 , a reference sample included in one prediction unit in a reference sample line is defined as a subdivided reference sample line.

When the upper reference sample line or the left reference sample line is derived according to the first derivation method, the second derivation method, or the third derivation method of the upper reference sample line or the left reference sample line, the reference sample line deriver 606 may perform deblocking filtering on pixels adjacent to or close to the boundary between prediction units. In the illustration of FIG9 , (xT, yT), (xT+a-1, yT), (xT+a, yT), (xT+a+b-1, yT), (xT+a+b, yT), and (xT+a+b+c-1, yT) represent pixels adjacent to the boundary in the upper reference sample line.

The reference sample line deriver 606 may determine whether to perform filtering to remove blocking artifacts at candidate pixel boundaries. Filtering may be performed on candidate pixel boundaries that satisfy one or more of the following conditions.

The first condition is that the two prediction unit quantization parameters on either side of the boundary are different.

The second condition is that the difference in pixel values between two pixels on the boundary is greater than a lower threshold and less than an upper threshold. In this case, the upper threshold may be determined based on the quantization parameters of the two pixels.

The third condition is that the pixel value difference between the start pixel and the end pixel of the subdivided reference sample line is less than or equal to the upper threshold.

The reference sample line deriver 606 may perform filtering on the d pixels on either side of the boundary as follows. The reference sample line deriver 606 may derive a filtered value by performing a weighted sum of the values of the 2d pixels to filter any pixel P among the 2d pixels. In this case, the position of the pixel used for filtering and the weight multiplied by each pixel may be determined by the distance between the pixel P and the boundary. For example, for the pixel at the coordinate (xT+a, yT) and the pixel at the coordinate (xT+a+1, yT) shown in FIG. 9 , filtering may be performed as shown in Equations 1 and 2.

[Equation 1]

I′(xT+a,yT)＝(I(xT+a-2,yT)+2·I(xT+a-1,yT)+2·I(xT+a,yT)+2·I(xT+a+1,yT)+I(xT+a+2,yT)+4)＞＞3

[Equation 2]

I′(xT+a+1,yT)＝(I(xT+a-1,yT)+I(xT+a,yT)+I(xT+a+1,yT)+I(xT+a+2,yT)+2)＞＞2

Here, I() and I'() represent pixel values before and after filtering.

The same or similar number of pixels to the left and right (or top and bottom) of pixel p can be used in the filtering process. The closer the pixel p is to the border, the more near-border pixels can be used in the filtering process. The weights or filter coefficients can have the characteristics of a low-pass filter. A filter coefficient based on the distance between pixel p and the border can be used, and the closer the pixel is to pixel p, the larger the absolute value of the filter coefficient can be multiplied.

When the reference sample line list reference mode is selected in the reference sample line export mode, the reference sample line exporter 606 may select a reference sample line from the reference sample line list.

One reference sample line list can be used for the left reference sample line and the upper reference sample line. Optionally, there can be separate reference sample line lists for the left reference sample line and the upper reference sample line. In addition, there can be separate reference sample line lists for different reference sample line lengths.

The reference sample line exporter 606 may use the same fixed list as the reference sample line list. Alternatively, the reference sample line exporter 606 may initialize and sequentially update the reference sample line list in units such as subframes, frames, frame groups, etc. The reference sample line list may be updated as follows.

For example, the upper boundary or left boundary sample line of the reconstructed prediction unit can be added to the reference sample line list. In addition, using the variable position reference sample line mode or the reference sample line list reference mode, the upper boundary or left boundary sample line of the reconstructed prediction unit can be added to the reference sample line list.

The reference sample line deriver 606 may select a (left or top) reference sample line by parsing a list reference index indicating one of the reference sample lines included in the reference sample line list. The video decoding device may also parse a weight to multiply each pixel of the reference sample line, or may parse an offset to add to each pixel of the reference sample line.

Referring now to FIG. 10 and FIG. 11 , a video encoding method and a video decoding method using intra prediction derived based on a reference sample line are described.

FIG. 10 is a flowchart of a video encoding method according to at least one embodiment of the present disclosure.

The video encoding apparatus determines an intra prediction mode of a current block (S1000).

The video encoding apparatus determines a derivation mode index ( S1002 ).

Here, the derivation mode index indicates a reference sample line derivation mode, which is one of a fixed position reference sample line mode, a variable position reference sample line mode, and a reference sample line list reference mode.

In one embodiment, the video encoding device determines whether at least one of the first to third conditions described above is satisfied, and if satisfied, determines a derived mode index indicating a variable position reference sample line mode or a reference sample line list reference mode. On the other hand, if none of the first to third conditions is satisfied, the video encoding device determines a derived mode index indicating a fixed position reference sample line mode.

As another embodiment, when checking whether at least one of the first condition to the third condition is satisfied, and if satisfied, the video encoding device may use the variable position reference sample line mode or the reference sample line list reference mode. In terms of optimizing encoding efficiency, the video encoding device may determine a flag indicating one of the two modes. On the other hand, if any one of the first condition to the third condition is not satisfied, the video encoding device may use the fixed position reference sample line mode.

The video encoding apparatus determines a reference sample line derivation mode according to the derivation mode index ( S1004 ).

As another embodiment, the video encoding device may determine the reference sample line derivation mode based on whether the first to third conditions are satisfied and a flag indicating one of the variable position reference sample line mode and the reference sample line list reference mode.

The video encoding apparatus derives a reference sample line of the current block according to the reference sample line deriving mode (S1006). Here, the reference sample line includes a left reference sample line and an upper reference sample line.

If the reference sample line derivation mode is the fixed position reference sample line mode, the video encoding apparatus derives pixel lines respectively adjacent to the left boundary and the upper boundary of the current block as reference sample lines.

When the reference sample line derivation mode is the variable position reference sample line mode, in terms of optimizing encoding efficiency, the video encoding device determines the derivation method index of the left reference sample line and the derivation method index of the upper reference sample line. Here, the derivation method index of the left reference sample line and the derivation method index of the upper reference sample line both indicate the first derivation method, the second derivation method, the third derivation method, or the fourth derivation method as described above.

Since the method of deriving the reference sample line by the video encoding apparatus according to the first to fourth derivation methods has been described, further detailed description is omitted.

If the reference sample line derived according to the first, second, or third derivation method is included in a plurality of prediction units, the video encoding apparatus may perform filtering to remove blocking effects on pixels adjacent to a boundary between the plurality of prediction units.

If the reference sample line derivation mode is the reference sample line list reference mode, the video encoding apparatus determines a reference index indicating a reference sample line included in the reference sample line list. The video encoding apparatus derives a left reference sample line and an upper reference sample line from the reference sample line list using the reference index.

Furthermore, the video encoding device may update the reference sample line list. For example, the video encoding device may add the upper boundary sample line or the left boundary sample line of the reconstructed prediction unit to the reference sample line list.

The video encoding apparatus generates a prediction block of the current block according to the intra prediction mode by using reference samples in the reference sample line ( S1008 ).

The video encoding apparatus subtracts a prediction block from a current block to generate a residual block (S1010).

The video encoding apparatus encodes the derivation mode index, the intra prediction mode, and the residual block (S1012).

FIG. 11 is a flowchart of a video decoding method according to at least one embodiment of the present disclosure.

The video decoding apparatus decodes a residual block of a current block, an intra prediction mode of the current block, and a derived mode index from a bitstream ( S1100 ).

Here, the derivation mode index indicates a reference sample line derivation mode, which is one of a fixed position reference sample line mode, a variable position reference sample line mode, and a reference sample line list reference mode.

In one embodiment, if at least one of the first to third conditions as described above is satisfied, the derivation mode index may be encoded by the video encoding device to indicate the variable position reference sample line mode or the reference sample line list reference mode. On the other hand, if none of the first to third conditions is satisfied, the derivation mode index may be encoded by the video encoding device to indicate the fixed position reference sample line mode.

As another embodiment, when at least one of the first condition to the third condition is checked to determine whether it is satisfied, the video decoding device may use the variable position reference sample line mode or the reference sample line list reference mode. In this case, the video decoding device may parse a flag indicating one of the two modes. On the other hand, if any one of the first condition to the third condition is not satisfied, the video decoding device may use the fixed position reference sample line mode.

The video decoding apparatus determines a reference sample line derivation mode according to a derivation mode index ( S1102 ).

As another embodiment, the video decoding device may determine the reference sample line derivation mode based on whether the first to third conditions are satisfied and a flag indicating one of the variable position reference sample line mode and the reference sample line list reference mode.

The video decoding apparatus derives a reference sample line of the current block according to a reference sample line deriving mode (S1104). Here, the reference sample line includes a left reference sample line and an upper reference sample line.

If the reference sample line derivation mode is the fixed position reference sample line mode, the video decoding apparatus derives pixel lines respectively adjacent to the left boundary and the upper boundary of the current block as reference sample lines.

When the reference sample line derivation mode is the variable position reference sample line mode, the video decoding apparatus decodes a derivation method index of a left reference sample line and a derivation method index of an upper reference sample line from a bitstream. The derivation method index of the left reference sample line and the derivation method index of the upper reference sample line both indicate their first derivation method, second derivation method, third derivation method, or fourth derivation method.

Since the method of deriving the reference sample line by the video decoding apparatus according to the first to fourth derivation methods has been described, further detailed description is omitted.

If the reference sample line derived according to the first, second, or third derivation method is included in a plurality of prediction units, the video decoding apparatus may perform filtering to remove blocking effects on pixels adjacent to a boundary between the plurality of prediction units.

If the reference sample line derivation mode is the reference sample line list reference mode, the video decoding apparatus decodes a reference index indicating a reference sample line included in the reference sample line list from the bitstream, and the video decoding apparatus uses the reference index to derive a left reference sample line and an upper reference sample line from the reference sample line list.

Furthermore, the video decoding device may update the reference sample line list. For example, the video decoding device may add the upper boundary sample line or the left boundary sample line of the reconstructed prediction unit to the reference sample line list.

The video decoding apparatus generates a prediction block of the current block according to the intra prediction mode using the reference samples in the reference sample line ( S1106 ).

The video decoding apparatus adds the prediction block and the residual block to reconstruct the current block (S1108).

Although the steps in each flowchart are described as being performed sequentially, these steps are merely illustrative of the technical concepts of some embodiments of the present disclosure. Therefore, a person of ordinary skill in the art to which the present disclosure belongs can perform the steps by changing the order described in each figure or by performing two or more steps in parallel. Therefore, the steps in each flowchart are not limited to the time series order shown.

It should be understood that the above description presents illustrative embodiments that can be implemented in different other ways. The functions described in some embodiments can be implemented by hardware, software, firmware and/or a combination thereof. It should also be understood that the functional components described in this disclosure are marked with "... units" to strongly emphasize the possibility of their independent implementation.

At the same time, the various methods or functions described in some embodiments may be implemented as instructions stored in a non-transitory recording medium that can be read and executed by one or more processors. For example, the non-transitory recording medium may include various types of recording devices, in which data is stored in a form readable by a computer system. For example, the non-transitory recording medium may include a storage medium such as an erasable programmable read-only memory (EPROM), a flash drive, an optical drive, a magnetic hard drive, and a solid-state drive (SSD).

Although the embodiments of the present disclosure have been described for illustrative purposes, however, those of ordinary skill in the art to which the present disclosure belongs should recognize that various modifications, additions, and substitutions are possible without departing from the concept and scope of the present disclosure. Therefore, for the sake of brevity and clarity, the embodiments of the present disclosure have been described. The scope of the technical concept of the embodiments of the present disclosure is not limited by the diagrams. Therefore, those of ordinary skill in the art to which the present disclosure belongs should understand that the scope of the present disclosure should not be limited by the embodiments explicitly described above, but by the claims and their equivalents.

(reference number)

122 Intra-frame predictor

542 Intra-frame predictor

602 Sub-block Split-No Split Information Exporter

604 Prediction Model Exporter

606 Reference Sample Line Exporter

606 Prediction Executor.

Related Applications

This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0172938, filed on December 6, 2021, and Korean Patent Application No. 10-2022-0129732, filed on October 11, 2022, the entire disclosure of each of which is incorporated herein by reference.

Claims (14)

1. A method performed by a video decoding device for intra-predicting a current block, the method comprising:

Decoding an intra prediction mode of the current block and a derived mode index of the current block from a bitstream, the derived mode indicating a reference sample line derived mode that is one of a fixed position reference sample line mode, a variable position reference sample line mode, and a reference sample line list reference mode;

determining the reference sample line export pattern from the export pattern index;

deriving a reference sample line for the current block according to the reference sample line derivation mode, the reference sample line comprising a left reference sample line and an upper reference sample line; and

A prediction block of the current block is generated according to the intra prediction mode by using reference samples in the reference sample line.

2. The method of claim 1, wherein the derived mode index is encoded by a video encoding device to indicate the variable bit reference sample line mode or the reference sample line list reference mode when a first condition is satisfied,

Wherein the first condition corresponds to when at least a preset number of prediction units among the reconstructed prediction units including neighboring pixels of the current block and at preset positions have been reconstructed by inter prediction.

3. The method of claim 1, wherein deriving the reference sample line comprises:

when the reference sample line derivation mode is the fixed position reference sample line mode, pixel lines adjacent to left and upper boundaries of the current block are respectively derived as the reference sample lines.

4. The method of claim 1, further comprising:

When the reference sample line derivation mode is the variable position reference sample line mode, decoding a derivation method index of a left reference sample line and a derivation method index of an upper reference sample line from the bitstream, the derivation method index of the left reference sample line and the derivation method index of the upper reference sample line each indicating utilization of a first derivation method, a second derivation method, or a third derivation method.

5. The method of claim 4, wherein deriving the reference sample line comprises:

When the first derivation method is utilized and (xL, yL) is a coordinate of a pixel sharing a common y-axis coordinate with an upper left pixel of a current block among left neighboring samples including a processing unit of the current block, samples in a range of (xL, yl+α) to (xL, yl+ puH x 2-1) are derived as left reference sample lines,

Wherein α is a preset integer, puH is the height of the current block.

6. The method of claim 5, wherein the processing unit is generated by partitioning a Coding Tree Unit (CTU), and the processing unit comprises at least one or more coding units.

7. The method of claim 4, wherein deriving the reference sample line comprises:

when the second derivation method is utilized and (xL, yL) is the coordinates of a pixel sharing common y-axis coordinates with the upper left (0, 0) pixel of the current block among left neighboring samples of a prediction unit including (-1, 0) pixels, samples in the range of (xL, yl+α) to (xL, yl+ puH x 2-1) are derived as left reference sample lines,

Wherein α is a preset integer, puH is the height of the current block.

8. The method of claim 4, wherein deriving the reference sample line comprises:

When the third derivation method is utilized and (xL, yL) is coordinates of an arbitrary pixel existing on the left side of the current block among the region decoded before the current block in the processing unit, samples in the range of (xL, yl+α) to (xL, yl+ puH x 2-1) are derived as left reference sample lines,

Wherein α is a preset integer, puH is the height of the current block.

9. The method of claim 4, wherein deriving the reference sample line comprises:

When a reference sample line derived according to the first derivation method, the second derivation method, or the third derivation method is included in a plurality of prediction units, filtering for removing a blocking effect on pixels adjacent to a boundary between the plurality of prediction units is performed.

10. The method of claim 1, further comprising, when the reference sample line derivation mode is the reference sample line list reference mode:

Decoding a reference index indicating one of reference sample lines included in a reference sample line list from the bitstream, and

Wherein deriving the reference sample line comprises:

The left reference sample line and the upper reference sample line are derived from the list of reference sample lines by using the reference index.

11. The method of claim 10, wherein deriving the reference sample line comprises:

The reference sample line list is updated by adding an upper boundary sample line or a left boundary sample line of the reconstructed prediction unit to the reference sample line list.

12. A method performed by a video encoding device for intra-predicting a current block, the method comprising:

determining an intra prediction mode of the current block;

Determining a derived pattern index for the current block, the derived pattern index indicating a reference sample line derived pattern that is one of a fixed position reference sample line pattern, a variable position reference sample line pattern, and a reference sample line list reference pattern;

determining the reference sample line export pattern from the export pattern index;

deriving a reference sample line for the current block according to the reference sample line derivation mode, the reference sample line comprising a left reference sample line and an upper reference sample line; and

A prediction block of the current block is generated according to the intra prediction mode by using reference samples in the reference sample line.

13. The method of claim 12, wherein the derived pattern index indicates the variable position reference sample line pattern or the reference sample line list reference pattern under the satisfied first condition,

Wherein the first condition corresponds to when at least a preset number of prediction units among the reconstructed prediction units including neighboring pixels of the current block and at preset positions have been reconstructed by inter prediction.

14. A computer-readable recording medium storing a bitstream generated by a video encoding method, the video encoding method comprising:

determining an intra prediction mode of the current block;

determining a derived mode index for the current block, the derived mode index indicating a reference sample line derived mode, the reference sample line derived mode being one of a fixed position reference sample line mode, a variable position reference sample line mode, and a reference sample line list reference mode;

determining the reference sample line export pattern from the export pattern index;

deriving a reference sample line for the current block according to the reference sample line derivation mode, the reference sample line comprising a left reference sample line and an upper reference sample line; and

A prediction block of the current block is generated according to the intra prediction mode by using reference samples in the reference sample line.