Method and device for video coding using extrapolation filter in intra prediction

Abstract

The present embodiment discloses a method and device for video coding using an extrapolation filter. In the present embodiment, an image decoding device determines a reference sample region and a filter shape. The reference sample region includes reconstructed reference samples of a current block and is used to derive filter coefficients used for extrapolation intra prediction, and the filter shape includes an output pixel region and an input pixel region. The image decoding device obtains a prediction order of samples in the current block. The image decoding device derives filter coefficients applied to the input pixel region according to the reference sample region and the filter shape. The image decoding device generates a prediction block of the current block by recursively applying the derived filter coefficients to prediction samples and the reconstructed reference samples of the current block on the basis of the prediction order.

Description

Method and device for video coding using an extrapolation filter in intra prediction

[0001] The present disclosure relates to a video coding method and device using an extrapolation filter in intra prediction.

[0002] The content described below merely provides background information related to the present invention and does not constitute prior art.

[0003] Since video data has a large amount of data compared to voice data or still image data, it requires a lot of hardware resources, including memory, to store or transmit it without processing for compression.

[0004] Therefore, when storing or transmitting video data, the encoder compresses the video data and stores or transmits it, and the decoder receives the compressed video data, decompresses it, and plays it back. These video compression technologies include H.264 / AVC, HEVC (High Efficiency Video Coding), and VVC (Versatile Video Coding), which improves encoding efficiency by about 30% compared to HEVC.

[0005] However, as the size, resolution, and frame rate of images are gradually increasing, and the amount of data that needs to be encoded is also increasing, a new compression technology that has better encoding efficiency and better image quality improvement than existing compression technologies is required.

[0006] In the next-generation technology, the Enhanced Compression Model (ECM), the Extrapolated Intra Prediction (EIP) mode performs intra prediction using an extrapolation filter based on previously restored reference samples in the surroundings. The EIP mode uses restored reference samples and prediction samples as input, and performs extrapolation filtering in a diagonal order from the upper right to the lower left, as shown in the example of Fig. 9. At this time, the area of ​​the reference samples and the shape of the extrapolation filter are determined by explicit signaling.

[0007] As previously mentioned, in extrapolation intra prediction, the EIP mode performs extrapolation filtering in a preset order. Therefore, to improve video encoding efficiency and image quality, a method for efficiently utilizing extrapolation to perform intra prediction is needed.

[0008] The present disclosure aims to provide a video coding method and apparatus for generating EIP output samples using various generation orders and fusing EIP blocks using multiple intra prediction methods.

[0009] According to an embodiment of the present disclosure, a method for restoring a current block, performed by an image decoding device, is provided, comprising: determining a reference sample area and a filter shape, wherein the reference sample area includes restoration reference samples of the current block and is used to derive filter coefficients used for extrapolation intra prediction, and the filter shape includes an output pixel area and an input pixel area; obtaining a prediction order of samples in the current block; deriving filter coefficients applied to the input pixel area according to the reference sample area and the filter shape; and recursively applying the derived filter coefficients to restoration reference samples and prediction samples of the current block based on the prediction order, thereby generating a first prediction block of the current block.

[0010] According to another embodiment of the present disclosure, a method for encoding a current block, performed by an image encoding device, is provided, comprising: obtaining a reference sample area and a filter shape, wherein the reference sample area includes reconstructed reference samples of the current block and is used to derive filter coefficients used for extrapolated intra prediction, and the filter shape includes an output pixel area and an input pixel area; obtaining a prediction order of samples in the current block; deriving filter coefficients applied to the input pixel area according to the reference sample area and the filter shape; and recursively applying the derived filter coefficients to reconstructed reference samples and prediction samples of the current block based on the prediction order, thereby generating a first prediction block of the current block.

[0011] According to another embodiment of the present disclosure, a method for providing video data to a video decoding device is provided, comprising: encoding the video data into a bitstream; and transmitting the bitstream to the video decoding device, wherein the encoding the video data comprises: obtaining a reference sample area and a filter shape, wherein the reference sample area includes restoration reference samples of a current block and is used to derive filter coefficients used for extrapolation intra prediction, and the filter shape includes an output pixel area and an input pixel area; obtaining a prediction order of samples in the current block; deriving filter coefficients applied to the input pixel area according to the reference sample area and the filter shape; and applying the derived filter coefficients to restoration reference samples and prediction samples of the current block based on the prediction order, thereby generating a first prediction block of the current block.

[0012] As described above, according to the present embodiment, by providing a video coding method and device that generates EIP output samples using various generation orders and fuses EIP blocks using multiple intra prediction methods, it is possible to improve video encoding efficiency and enhance video quality.

[0013] In addition, according to the present embodiment, by providing a video coding method and device using an extrapolation filter in intra prediction, it is possible to reduce the burden on the network based on bit rate reduction in various contents such as UHD (Ultra High Definition) video, game broadcasting, 360-degree video streaming, VR / AR (Virtual Reality / Augmented Reality) video, online lectures, etc., and to reduce energy consumption for a video playback capable device.

[0014] FIG. 1 is an exemplary block diagram of an image encoding device capable of implementing the techniques of the present disclosure.

[0015] Figure 2 is a drawing for explaining a method of dividing a block using the QTBTTT (QuadTree plus BinaryTree TernaryTree) structure.

[0016] FIGS. 3A and 3B are diagrams illustrating multiple intra prediction modes, including wide-angle intra prediction modes.

[0017] Figure 4 is an example diagram of the surrounding blocks of the current block.

[0018] FIG. 5 is an exemplary block diagram of an image decoding device capable of implementing the techniques of the present disclosure.

[0019] Figure 6 is an example diagram showing a search area used in IntraTMP (Intra Template Matching Prediction) technology.

[0020] Figure 7 is an example diagram showing a method for deriving one or more intra prediction modes in TIMD (Template-based intra mode derivation) technology.

[0021] Figures 8a and 8b are exemplary diagrams showing the type of EIP (Extrapolated intra prediction) filter and the derivation of EIP coefficients.

[0022] Figure 9 is an example diagram showing the generation order of EIP-based prediction samples.

[0023] FIG. 10A and FIG. 10B are exemplary diagrams illustrating the generation of non-proximity EIP output samples according to one embodiment of the present disclosure.

[0024] FIG. 11 is a flowchart illustrating a method of encoding a current block performed by an image encoding device according to one embodiment of the present disclosure.

[0025] FIG. 12 is a flowchart illustrating a method for restoring a current block performed by an image decoding device according to one embodiment of the present disclosure.

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to exemplary drawings. When designating components in each drawing, it should be noted that, where possible, identical components are given the same reference numerals, even if they appear in different drawings. Furthermore, in describing the present embodiments, detailed descriptions of related known structures or functions will be omitted if they are deemed to obscure the gist of the present embodiments.

[0027] FIG. 1 is an exemplary block diagram of an image encoding device capable of implementing the techniques of the present disclosure. Hereinafter, the image encoding device and its subcomponents will be described with reference to the illustration in FIG. 1.

[0028] The video encoding device may be configured to include a picture segmentation unit (110), a prediction unit (120), a subtractor (130), a transformation unit (140), a quantization unit (145), a reordering unit (150), an entropy encoding unit (155), an inverse quantization unit (160), an inverse transformation unit (165), an adder (170), a loop filter unit (180), and a memory (190).

[0029] Each component of the video encoding device may be implemented in hardware, software, or a combination of hardware and software. Furthermore, the functions of each component may be implemented in software, with a microprocessor executing the software functions corresponding to each component.

[0030] A single image (video) is composed of one or more sequences containing multiple pictures. Each picture is divided into multiple regions, and encoding is performed for each region. For example, a single picture is divided into one or more tiles and / or slices. Here, one or more tiles can be defined as a tile group. Each tile or slice is divided into one or more Coding Tree Units (CTUs). Each CTU is then divided into one or more Coding Units (CUs) by a tree structure. Information applied to each CU is encoded as the syntax of the CU, and information commonly applied to CUs included in a CTU is encoded as the syntax of the CTU. In addition, information commonly applied to all blocks within a single slice is encoded as the syntax of the slice header, and information applied to all blocks constituting one or more pictures is encoded in the Picture Parameter Set (PPS) or the picture header. Furthermore, information commonly referenced by multiple pictures is encoded in a Sequence Parameter Set (SPS). And, information commonly referenced by one or more SPS is encoded in a Video Parameter Set (VPS). In addition, information commonly applied to one tile or tile group may be encoded as syntax of a tile or tile group header. Syntaxes included in an SPS, PPS, slice header, tile or tile group header may be referred to as high level syntax.

[0031] The picture segmentation unit (110) determines the size of the CTU. Information about the size of the CTU (CTU size) is encoded as the syntax of SPS or PPS and transmitted to the image decoding device.

[0032] The picture segmentation unit (110) divides each picture constituting an image into a plurality of CTUs having a predetermined size, and then recursively divides the CTUs using a tree structure. A leaf node in the tree structure becomes a CU, which is a basic unit of encoding.

[0033] The tree structure may be a QuadTree (QT) in which an upper node (or parent node) is divided into four lower nodes (or child nodes) of the same size, a BinaryTree (BT) in which an upper node is divided into two lower nodes, or a TernaryTree (TT) in which an upper node is divided into three lower nodes in a 1:2:1 ratio, or a structure that mixes two or more of the QT structures, BT structures, and TT structures. For example, a QTBT (QuadTree plus BinaryTree) structure may be used, or a QTBTTT (QuadTree plus BinaryTree TernaryTree) structure may be used. Here, BTTT may be combined and referred to as a MTT (Multiple-Type Tree).

[0034] Figure 2 is a drawing for explaining a method of dividing a block using the QTBTTT structure.

[0035] As illustrated in FIG. 2, a CTU may first be split into a QT structure. The quadtree splitting may be repeated until the size of the splitting block reaches the minimum block size (MinQTSize) of the leaf node allowed in the QT. A 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 encoding unit (155) and signaled to the image decoding device. If the leaf node of the QT is not larger than the maximum block size (MaxBTSize) of the root node allowed in the BT, it may be further split into one or more of the BT structure or 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 in which the block of the corresponding node is split horizontally and two directions in which the block is split vertically. As illustrated in FIG. 2, when MTT splitting begins, a second flag (mtt_split_flag) indicating whether nodes have been split, and if splitting has occurred, a flag indicating the splitting direction (vertical or horizontal) and / or a flag indicating the splitting type (Binary or Ternary) are encoded by the entropy encoding unit (155) and signaled to the image decoding device.

[0036] Alternatively, before encoding the first flag (QT_split_flag) indicating whether each node is split into four nodes of a lower layer, a CU split flag (split_cu_flag) indicating whether the node is split may be encoded. If the CU split flag (split_cu_flag) value indicates that the node is not split, the block of the corresponding node becomes a leaf node in the split tree structure and becomes a CU (coding unit), which is a basic unit of encoding. If the CU split flag (split_cu_flag) value indicates that the node is split, the video encoding device starts encoding from the first flag in the above-described manner.

[0037] As another example of a tree structure, when QTBT is used, there may be two types: a type that horizontally splits the block of the corresponding node into two blocks of the same size (i.e., symmetric horizontal splitting) and a type that vertically splits it (i.e., symmetric vertical splitting). A split flag (split_flag) indicating whether each node of the BT structure is split into blocks of a lower layer and split type information indicating the type of split are encoded by the entropy encoding unit (155) and transmitted to the image decoding device. Meanwhile, there may additionally be a type that splits the block of the corresponding node into two blocks of an asymmetrical shape. The asymmetric shape may include a shape that splits the block of the corresponding node into two rectangular blocks with a size ratio of 1:3, or a shape that splits the block of the corresponding node in a diagonal direction.

[0038] A CU can have various sizes depending on the QTBT or QTBTTT partitioning from the CTU. Hereinafter, the block corresponding to the CU to be encoded or decoded (i.e., the leaf node of the QTBTTT) is referred to as the "current block." Depending on the QTBTTT partitioning employed, the current block may be rectangular as well as square.

[0039] The prediction unit (120) predicts the current block and generates a prediction block. The prediction unit (120) includes an intra prediction unit (122) and an inter prediction unit (124).

[0040] In general, each current block within a picture can be predictively coded. Prediction of the current block can typically be performed using either intra-prediction (using data from the picture containing the current block) or inter-prediction (using data from a picture coded before the picture containing the current block). Inter-prediction encompasses both unidirectional and bidirectional prediction.

[0041] The intra prediction unit (122) predicts pixels within the current block using pixels (reference pixels) located around the current block within the current picture including the current block. There are multiple intra prediction modes depending on the prediction direction. For example, as shown in Fig. 3a, the multiple intra prediction modes may include two non-directional modes including the Planar mode and the DC mode, and 65 directional modes. The surrounding pixels to be used and the calculation formula are defined differently depending on each prediction mode.

[0042] For efficient directional prediction for a rectangular current block, directional modes (intra prediction modes 67 to 80 and -1 to -14) indicated by dotted arrows in Fig. 3b may be additionally used. These may be referred to as "wide-angle intra-prediction modes." In Fig. 3b, the arrows point to corresponding reference samples used for prediction, and do not indicate the prediction direction. The prediction direction is opposite to the direction indicated by the arrows. Wide-angle intra-prediction modes are modes that perform prediction in the opposite direction of a specific directional mode without additional bit transmission when the current block is rectangular. At this time, among the wide-angle intra-prediction modes, some wide-angle intra-prediction modes available for the current block may be determined based on the ratio of the width and height of the rectangular current block. For example, wide-angle intra prediction modes (intra prediction modes 67 to 80) having an angle less than 45 degrees are available when the current block is a rectangular shape whose height is smaller than its width, and wide-angle intra prediction modes (intra prediction modes -1 to -14) having an angle greater than -135 degrees are available when the current block is a rectangular shape whose width is larger than its height.

[0043] The intra prediction unit (122) can determine an intra prediction mode to be used to encode the current block. In some examples, the intra prediction unit (122) can encode the current block using multiple intra prediction modes and select an appropriate intra prediction mode to be used from the tested modes. For example, the intra prediction unit (122) can calculate bit-rate distortion values ​​using rate-distortion analysis for multiple tested intra prediction modes and select an intra prediction mode with the best bit-rate distortion characteristics among the tested modes.

[0044] The intra prediction unit (122) selects one intra prediction mode from among multiple intra prediction modes and predicts the current block using surrounding pixels (reference pixels) and an operation formula determined according to the selected intra prediction mode. Information about the selected intra prediction mode is encoded by the entropy encoding unit (155) and transmitted to the image decoding device.

[0045] The inter prediction unit (124) generates a prediction block for the current block using a motion compensation process. The inter prediction unit (124) searches for a block most similar to the current block within reference pictures that were encoded and decoded before the current picture, and generates a prediction block for the current block using the searched block. Then, a motion vector (MV) corresponding to the displacement between the current block within the current picture and the prediction block within the reference picture is generated. Generally, motion estimation is performed on the luma component, and the motion vector calculated based on the luma component is used for both the luma component and the chroma component. The motion information including information on the reference picture used to predict the current block and information on the motion vector is encoded by the entropy encoding unit (155) and transmitted to the image decoding device.

[0046] The inter prediction unit (124) may perform interpolation on a reference picture or a reference block to improve prediction accuracy. That is, subsamples between two consecutive integer samples are interpolated by applying filter coefficients to a plurality of consecutive integer samples including the two integer samples. When a process of searching for a block most similar to the current block is performed on the interpolated reference picture, the motion vector can be expressed up to a precision in decimal units rather than a precision in integer sample units. The precision or resolution of the motion vector can be set differently for each target region to be encoded, such as a slice, tile, CTU, CU, etc. When such adaptive motion vector resolution (AMVR) is applied, information on the motion vector resolution to be applied to each target region must be signaled for each target region. For example, when the target region is a CU, information on the motion vector resolution applied to each CU is signaled. Information on the motion vector resolution may be information indicating the precision of a differential motion vector, which will be described later.

[0047] Meanwhile, the inter prediction unit (124) can perform inter prediction using bi-prediction. In the case of bi-prediction, two reference pictures and two motion vectors indicating the block position most similar to the current block within each reference picture are used. The inter prediction unit (124) selects a first reference picture and a second reference picture from reference picture list 0 (RefPicList0) and reference picture list 1 (RefPicList1), respectively, and searches for a block similar to the current block within each reference picture to generate a first reference block and a second reference block. Then, the first reference block and the second reference block are averaged or weighted averaged to generate a prediction block for the current block. Then, motion information including information on two reference pictures used to predict the current block and information on two motion vectors is transmitted to the entropy encoding unit (155). Here, reference picture list 0 may be composed of pictures that are before the current picture in display order among the restored pictures, and reference picture list 1 may be composed of pictures that are after the current picture in display order among the restored pictures. However, this is not necessarily limited to this, and restored pictures that are after the current picture in display order may be additionally included in reference picture list 0, and conversely, restored pictures that are before the current picture may be additionally included in reference picture list 1.

[0048] Various methods can be used to minimize the number of bits required to encode motion information.

[0049] For example, if the reference picture and motion vector of the current block are identical to those of a neighboring block, the motion information of the current block can be transmitted to the image decoding device by encoding information that can identify the neighboring block. This method is called 'merge mode'.

[0050] In merge mode, the inter prediction unit (124) selects a predetermined number of merge candidate blocks (hereinafter referred to as 'merge candidates') from the surrounding blocks of the current block.

[0051] As the surrounding blocks for deriving merge candidates, all or part 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 within the current picture may be used, as illustrated in FIG. 4. In addition, a block located within a reference picture (which may or may not be the same as the reference picture used to predict the current block) other than the current picture in which the current block is located may be used as a merge candidate. For example, a block co-located with the current block within the reference picture or blocks adjacent to the block at 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 0 vector is added to the merge candidates.

[0052] The inter prediction unit (124) uses these surrounding blocks to construct a merge list containing a predetermined number of merge candidates. Among the merge candidates included in the merge list, the merge candidate to be used as motion information of the current block is selected and merge index information for identifying the selected candidate is generated. The generated merge index information is encoded by the entropy encoding unit (155) and transmitted to the video decoding device.

[0053] Merge Skip mode is a special case of merge mode. After quantization, when all transform coefficients for entropy encoding are close to zero, only neighboring block selection information is transmitted without transmitting residual signals. By utilizing merge skip mode, relatively high encoding efficiency can be achieved for low-motion images, still images, and screen content images.

[0054] Hereinafter, merge mode and merge skip mode are collectively referred to as merge / skip mode.

[0055] Another method for encoding motion information is Advanced Motion Vector Prediction (AMVP) mode.

[0056] In AMVP mode, the inter prediction unit (124) derives predicted motion vector candidates for the motion vector of the current block using neighboring blocks of the current block. As neighboring blocks used to derive predicted motion vector 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 as shown in FIG. 4 may be used. In addition, a block located in a reference picture (which may or may not be the same as the reference picture used to predict the current block) other than the current picture in which the current block is located may be used as the neighboring block used to derive predicted motion vector candidates. For example, a block co-located with the current block in the reference picture or blocks adjacent to the block in the co-located block may be used. If the number of motion vector candidates is less than a preset number by the method described above, a 0 vector is added to the motion vector candidates.

[0057] The inter prediction unit (124) derives predicted motion vector candidates using the motion vectors of these surrounding blocks, and determines a predicted motion vector for the motion vector of the current block using the predicted motion vector candidates. Then, the predicted motion vector is subtracted from the motion vector of the current block to produce a differential motion vector.

[0058] The predicted motion vector can be obtained by applying a predefined function (e.g., median, mean, etc.) to the predicted motion vector candidates. In this case, the image decoding device also knows the predefined function. In addition, since the surrounding blocks used to derive the predicted motion vector candidates are blocks that have already been encoded and decoded, the image decoding device also already knows the motion vectors of the surrounding blocks. Therefore, the image encoding device does not need to encode information to identify the predicted motion vector candidates. Therefore, in this case, information about the differential motion vector and information about the reference picture used to predict the current block are encoded.

[0059] Alternatively, the predicted motion vector can be determined by selecting one of the predicted motion vector candidates. In this case, information for identifying the selected predicted motion vector candidate is additionally encoded, along with information about the differential motion vector and the reference picture used to predict the current block.

[0060] The subtractor (130) subtracts the prediction block generated by the intra prediction unit (122) or inter prediction unit (124) from the current block to generate a residual block.

[0061] The transformation unit (140) transforms residual signals within a residual block having pixel values ​​in a spatial domain into transform coefficients in a frequency domain. The transformation unit (140) may transform the residual signals within the residual block using the entire size of the residual block as a transformation unit, or may divide the residual block into a plurality of sub-blocks and use the sub-blocks as transformation units to perform the transformation. Alternatively, the residual signals may be transformed using only the transformation domain sub-block as a transformation unit by dividing the sub-blocks into two sub-blocks, that is, a transformation domain and a non-transform domain. Here, the transformation domain sub-block may be one of two rectangular blocks having a size ratio of 1:1 with respect to the horizontal axis (or vertical axis). In this case, a flag (cu_sbt_flag) indicating that only a sub-block has been converted, directionality (vertical / horizontal) information (cu_sbt_horizontal_flag), and / or position information (cu_sbt_pos_flag) are encoded by the entropy encoding unit (155) and signaled to the image decoding device. In addition, the size of the conversion area sub-block may have a size ratio of 1:3 with respect to the horizontal axis (or vertical axis), and in this case, a flag (cu_sbt_quad_flag) distinguishing the corresponding division is additionally encoded by the entropy encoding unit (155) and signaled to the image decoding device.

[0062] Meanwhile, the transformation unit (140) can individually perform transformations on the residual block in the horizontal and vertical directions. For the transformation, various types of transformation functions or transformation matrices can be used. For example, a pair of transformation functions for horizontal transformation and vertical transformation can be defined as a Multiple Transform Set (MTS). The transformation unit (140) can select one transformation function pair with the best transformation efficiency among the MTS and transform the residual block in the horizontal and vertical directions, respectively. Information (mts_idx) on the transformation function pair selected among the MTS is encoded by the entropy encoding unit (155) and signaled to the image decoding device.

[0063] The quantization unit (145) quantizes the transform coefficients output from the transform unit (140) using quantization parameters and outputs the quantized transform coefficients to the entropy encoding unit (155). The quantization unit (145) may directly quantize a related residual block without transformation for a certain block or frame. The quantization unit (145) may also apply different quantization coefficients (scaling values) according to the positions of the transform coefficients within the transform block. The quantization matrix applied to the quantized transform coefficients arranged in two dimensions may be encoded and signaled to an image decoding device.

[0064] The rearrangement unit (150) can perform rearrangement of coefficient values ​​for quantized residual values.

[0065] The reordering unit (150) can change a two-dimensional coefficient array into a one-dimensional coefficient sequence by using coefficient scanning. For example, the reordering unit (150) can output a one-dimensional coefficient sequence by scanning from the DC coefficient to the coefficients of the high-frequency region by using a zig-zag scan or a diagonal scan. Depending on the size of the transformation unit and the intra prediction mode, a vertical scan that scans the two-dimensional coefficient array in the column direction or a horizontal scan that scans the two-dimensional block-shaped coefficients in the row direction may be used instead of the zig-zag scan. That is, depending on the size of the transformation unit and the intra prediction mode, the scanning method to be used may be determined among the zig-zag scan, the diagonal scan, the vertical scan, and the horizontal scan.

[0066] The entropy encoding unit (155) generates a bitstream by encoding a sequence of one-dimensional quantized transform coefficients output from the rearrangement unit (150) using various encoding methods such as CABAC (Context-based Adaptive Binary Arithmetic Code) and Exponential Golomb.

[0067] In addition, the entropy encoding unit (155) encodes information related to block division, such as CTU size, CU division flag, QT division flag, MTT division type, and MTT division direction, so that the image decoding device can divide the block in the same manner as the image encoding device. In addition, the entropy encoding unit (155) encodes information about a prediction type indicating whether the current block is encoded by intra prediction or inter prediction, and encodes intra prediction information (i.e., information about an intra prediction mode) or inter prediction information (information about an encoding mode of motion information (merge mode or AMVP mode), a merge index in the case of a merge mode, and a reference picture index and a differential motion vector in the case of an AMVP mode) according to the prediction type. In addition, the entropy encoding unit (155) encodes information related to quantization, that is, information about a quantization parameter and information about a quantization matrix.

[0068] The inverse quantization unit (160) inversely quantizes the quantized transform coefficients output from the quantization unit (145) to generate transform coefficients. The inverse transform unit (165) transforms the transform coefficients output from the inverse quantization unit (160) from the frequency domain to the spatial domain to restore the residual block.

[0069] An adder (170) adds the restored residual block and the predicted block generated by the prediction unit (120) to restore the current block. The pixels within the restored current block are used as reference pixels when intra-predicting the next block.

[0070] The loop filter unit (180) performs filtering on restored pixels to reduce blocking artifacts, ringing artifacts, blurring artifacts, etc. that occur due to block-based prediction and transformation / quantization. The loop filter unit (180) may include all or part of a deblocking filter (182), a sample adaptive offset (SAO) filter (184), and an adaptive loop filter (ALF, 186) as an in-loop filter.

[0071] The deblocking filter (182) filters the boundaries between restored blocks to remove blocking artifacts caused by block-based encoding / decoding, and the SAO filter (184) and the ALF (186) perform additional filtering on the deblocking-filtered image. The SAO filter (184) and the ALF (186) are filters used to compensate for the differences between restored pixels and original pixels caused by lossy coding. The SAO filter (184) improves not only subjective image quality but also encoding efficiency by applying an offset in units of CTUs. In contrast, the ALF (186) performs block-based filtering, and compensates for distortion by applying different filters by distinguishing the edges and degrees of variation of the corresponding block. Information on filter coefficients to be used in the ALF can be encoded and signaled to an image decoding device.

[0072] The restored blocks filtered through the deblocking filter (182), SAO filter (184), and ALF (186) are stored in the memory (190). When all blocks within a picture are restored, the restored picture can be used as a reference picture for inter-predicting blocks within a picture to be encoded later.

[0073] The video encoding device can store the bitstream of encoded video data on a non-transitory storage medium or transmit it to the video decoding device using a communication network.

[0074] FIG. 5 is an exemplary block diagram of an image decoding device capable of implementing the techniques of the present disclosure. Hereinafter, the image decoding device and its subcomponents will be described with reference to FIG. 5.

[0075] The video decoding device may be configured to include an entropy decoding unit (510), a rearrangement unit (515), an inverse quantization unit (520), an inverse transformation unit (530), a prediction unit (540), an adder (550), a loop filter unit (560), and a memory (570).

[0076] Similar to the video encoding device of FIG. 1, each component of the video decoding device may be implemented in hardware, software, or a combination of hardware and software. Furthermore, the functions of each component may be implemented in software, with a microprocessor executing the software functions corresponding to each component.

[0077] The entropy decoding unit (510) decodes the bitstream generated by the image encoding device to extract information related to block division, thereby determining the current block to be decoded, and extracts prediction information, information on residual signals, etc. required to restore the current block.

[0078] The entropy decoding unit (510) extracts information about the CTU size from the Sequence Parameter Set (SPS) or the Picture Parameter Set (PPS), determines the size of the CTU, and divides the picture into CTUs of the determined size. Then, the CTU is determined as the top layer of the tree structure, i.e., the root node, and the CTU is divided using the tree structure by extracting division information about the CTU.

[0079] For example, when splitting a CTU using the QTBTTT structure, first, the first flag (QT_split_flag) related to the splitting of QT is extracted, and each node is split into four nodes of the lower layer. Then, for the nodes corresponding to the leaf nodes of QT, the second flag (mtt_split_flag) related to the splitting of MTT and the split direction (vertical / horizontal) and / or split type (binary / ternary) information are extracted, and the corresponding leaf nodes are split into the MTT structure. Accordingly, each node below the leaf nodes of QT are split recursively into the BT or TT structure.

[0080] As another example, when splitting a CTU using the QTBTTT structure, the CU split flag (split_cu_flag) indicating whether the CU is split is first extracted, and if the block is split, the first flag (QT_split_flag) may be extracted. During the splitting process, each node may undergo zero or more repeated QT splits followed by zero or more repeated MTT splits. For example, a CTU may undergo an MTT split right away, or conversely, may undergo only multiple QT splits.

[0081] As another example, when splitting a CTU using the QTBT structure, the first flag (QT_split_flag) related to the splitting of QT is extracted, and each node is split into four nodes of the lower layer. Furthermore, for nodes corresponding to leaf nodes of QT, a split flag (split_flag) indicating whether to further split into BTs and splitting direction information are extracted.

[0082] Meanwhile, when the entropy decoding unit (510) determines the current block to be decoded by using the division of the tree structure, it extracts information on the prediction type indicating whether the current block is intra-predicted or inter-predicted. If the prediction type information indicates intra-prediction, the entropy decoding unit (510) extracts syntax elements for intra-prediction information (intra-prediction mode) of the current block. If the prediction type information indicates inter-prediction, the entropy decoding unit (510) extracts syntax elements for inter-prediction information, i.e., information indicating a motion vector and a reference picture referenced by the motion vector.

[0083] Additionally, the entropy decoding unit (510) extracts information about the quantized transform coefficients of the current block as information related to quantization and information about residual signals.

[0084] The rearrangement unit (515) can change the sequence of one-dimensional quantized transform coefficients entropy-decoded in the entropy decoding unit (510) back into a two-dimensional coefficient array (i.e., block) in the reverse order of the coefficient scanning performed by the image encoding device.

[0085] The inverse quantization unit (520) inversely quantizes the quantized transform coefficients and inversely quantizes the quantized transform coefficients using the quantization parameters. The inverse quantization unit (520) may also apply different quantization coefficients (scaling values) to the quantized transform coefficients arranged in two dimensions. The inverse quantization unit (520) may perform inverse quantization by applying a matrix of quantized coefficients (scaling values) from an image encoding device to a two-dimensional array of quantized transform coefficients.

[0086] The inverse transform unit (530) inversely transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain to restore residual signals, thereby generating a residual block for the current block.

[0087] In addition, when the inverse transform unit (530) inversely transforms only a portion of a transform block (sub-block), it extracts a flag (cu_sbt_flag) indicating that only a sub-block of the transform block has been transformed, directionality (vertical / horizontal) information (cu_sbt_horizontal_flag) of the sub-block, and / or position information (cu_sbt_pos_flag) of the sub-block, and inversely transforms the transform coefficients of the corresponding sub-block from the frequency domain to the spatial domain to restore residual signals, and fills “0” values ​​with residual signals for areas that have not been inversely transformed, thereby generating a final residual block for the current block.

[0088] In addition, when MTS is applied, the inverse transform unit (530) determines a transform function or a transform matrix to be applied in the horizontal and vertical directions using MTS information (mts_idx) signaled from the image encoding device, and performs inverse transform on the transform coefficients within the transform block in the horizontal and vertical directions using the determined transform function.

[0089] The prediction unit (540) may include an intra prediction unit (542) and an inter prediction unit (544). The intra prediction unit (542) is activated when the prediction type of the current block is intra prediction, and the inter prediction unit (544) is activated when the prediction type of the current block is inter prediction.

[0090] The intra prediction unit (542) determines the intra prediction mode of the current block among a plurality of intra prediction modes from the syntax elements for the intra prediction mode extracted from the entropy decoding unit (510), and predicts the current block using reference pixels around the current block according to the intra prediction mode.

[0091] The inter prediction unit (544) uses the syntax elements for the inter prediction mode extracted from the entropy decoding unit (510) to determine the motion vector of the current block and the reference picture referenced by the motion vector, and predicts the current block using the motion vector and the reference picture.

[0092] An adder (550) adds the residual block output from the inverse transform unit (530) and the predicted block output from the inter prediction unit (544) or the intra prediction unit (542) to restore the current block. The pixels within the restored current block are used as reference pixels when intra-predicting a block to be decoded later.

[0093] The loop filter unit (560) may include a deblocking filter (562), an SAO filter (564), and an ALF (566) as in-loop filters. The deblocking filter (562) deblocks the boundaries between restored blocks to remove blocking artifacts caused by block-by-block decoding. The SAO filter (564) and the ALF (566) perform additional filtering on restored blocks after deblocking filtering to compensate for differences between restored pixels and original pixels caused by lossy coding. The filter coefficients of the ALF are determined using information about filter coefficients decoded from the non-stream.

[0094] The restored blocks filtered through the deblocking filter (562), SAO filter (564), and ALF (566) are stored in the memory (570). When all blocks within a picture are restored, the restored picture is used as a reference picture for inter-predicting blocks within a picture to be encoded later.

[0095] The present embodiment relates to encoding and decoding of images (videos) as described above. More specifically, the present invention provides a video coding method and device that generates EIP output samples using various generation orders and fuses EIP blocks using multiple intra prediction methods.

[0096] The following embodiments may be performed by an intra prediction unit (122) within a video encoding apparatus. In addition, the following embodiments may be performed by an intra prediction unit (542) within a video decoding apparatus.

[0097] The video encoding device can generate signaling information related to the present embodiment in terms of rate distortion optimization in encoding the current block. The video encoding device can encode the signaling information using the entropy encoding unit (155) and then transmit it to the video decoding device. The video decoding device can decode the signaling information related to the decoding of the current block from the bitstream using the entropy decoding unit (510).

[0098] In the following description, the term "target block" may be used interchangeably with the current block or coding unit (CU). Alternatively, the term "target block" may also refer to a portion of a coding unit.

[0099] Also, a value of a flag being true indicates that the flag is set to 1. Also, a value of a flag being false indicates that the flag is set to 0.

[0100] The decoder side includes all or part of the inverse quantization unit (160), the inverse transform unit (165), the prediction unit (120), the adder (170), the loop filter unit (180), and the memory (190) in the video encoding device illustrated in FIG. 1. Alternatively, the decoder side includes all or part of the inverse quantization unit (520), the inverse transform unit (530), the prediction unit (540), the adder (550), the loop filter unit (560), and the memory (570) in the video decoding device illustrated in FIG. 5. With respect to a series of decoding processes, the decoder side of the video encoding device and the decoder side of the video decoding device perform the same operation. The video encoding device determines information related to the operation of the decoder side and signals the determined information to the video decoding device. The video decoding device can decode the signaled information and operate the decoder side based on the decoded information.

[0101] I-1. VVC's intra prediction technology

[0102] In intra prediction of VVC, the angular prediction direction is subdivided into 65, as shown in the example of Fig. 3a. Depending on the prediction angle of the intra prediction mode, prediction modes (predModeIntra) from 2 to 66 can be used. By introducing Wide-Angle Intra Prediction (WAIP), prediction modes of -14 to -1 and 67 to 80, which are directional modes with larger angles, can be used depending on the aspect ratio of the block. In intra prediction, a prediction block can be generated based on 67 Intra Prediction Modes (IPMs). The 67 IPMs refer to 67 intra prediction modes that can be signaled according to the aspect ratio of the block among prediction modes -14 to 80, including non-directional prediction modes such as Planar and DC modes.

[0103] In addition, VVC's intra prediction technology can generate intra prediction blocks using technologies such as MRLP (Multiple Reference Line intra Prediction), CCLM (Cross-Component Linear Model), PDPC (Position Dependent intra Prediction Combination), ISP (Intra Sub-Partitions), and MIP (Matrix-based Intra Prediction).

[0104] I-2. IBC (Intra Block Copy)

[0105] IBC performs intra prediction of the current block by copying a reference block within the same frame using a block vector to generate a prediction block of the current block.

[0106] A video encoding device performs block matching to derive an optimal block vector. Here, the block vector represents the displacement from the current block to the reference block. In order to increase encoding efficiency, the video encoding device may not transmit the block vector as is, but may divide it into a block vector predictor (BVP) and a block vector difference (BVD), encode the BVP and BVD, and then transmit them to the video decoding device.

[0107] In terms of utilizing block vectors, IBC features inter prediction. Therefore, IBC can be divided into IBC Merge / Skip mode and IBC AMVP mode.

[0108] In IBC merge / skip mode, a video encoding device constructs an IBC merge list. In order to optimize encoding efficiency, the video encoding device can select a block vector from among the candidates included in the IBC merge list and use the selected candidate as a block vector predictor (BVP). The video encoding device determines a merge index indicating the selected block vector. However, the video encoding device does not generate a BVD. The video encoding device encodes the merge index and transmits it to the video decoding device. The IBC merge list can be constructed by the video encoding device and the video decoding device in the same manner. The video decoding device can decode the merge index and then generate a block vector from the IBC merge list using the merge index.

[0109] The video encoding device uses the same block vector transmission method as the IBC merge mode in the case of the IBC skip mode, but does not transmit a residual block corresponding to the difference between the current block and the predicted block.

[0110] In IBC AMVP mode, in order to optimize encoding efficiency, the video encoding device determines a block vector and constructs an IBC AMVP list. The video encoding device determines a candidate index that designates one of the candidate block vectors included in the IBC AMVP list as a BVP. The video encoding device calculates the BVD, which is the difference between the BVP and the block vector. Thereafter, the video encoding device encodes the candidate index and BVD and transmits them to the video decoding device.

[0111] The video decoding device decodes the candidate index and BVD. The video decoding device can obtain the BVP indicated by the candidate index from the IBC AMVP list, and then restore the block vector by adding the BVP and BVD.

[0112] I-3. Template Matching Prediction

[0113] Template matching prediction (TMP) searches for a prediction block that minimizes the differences between templates in a predefined restoration region, i.e., a search region, within the current frame. The template of the current block (hereinafter, "current template") consists of upper and left neighboring samples. The difference between the template of the current block and the template of the predicted block found in the search region is defined as a cost function. Template matching prediction determines the prediction block with the minimum cost as the prediction block of the current block. The Sum of Absolute Differences (SAD) is used as the cost function.

[0114] IntraTMP (Intra Template Matching Prediction) technology in ECM (Enhanced Compression Model), the next-generation technology of VVC, sets an L-shaped / left / upper template around the current block, searches for the template most similar to the current template in the restoration area of ​​the current frame, and then uses a block adjacent to the searched template and having the same size as the current block as the prediction block of the current block. IntraTMP technology searches for similar templates based on a cost function, and uses SAD (Sum of Absolute Differences) as the cost function. The video encoding device transmits whether to use IntraTMP mode, and the video decoding device can perform the same template matching task when applying IntraTMP mode.

[0115] Figure 6 is an example diagram showing a search area used in IntraTMP technology.

[0116] To save memory, the current CTU (coding tree unit) where the current block is located, the upper left CTU, the upper CTU, and the left CTU can be limited to the possible search areas. In Fig. 6, the search areas are represented by R1 to R4. In addition, among the possible search areas, an area generated according to the product of the width and height (w, h) of the current block and a preset constant a can be adaptively set as the search range. For example, by setting a = 5, the search ranges SearchRange_w and SearchRange_h can be determined as in Equation 1.

[0117]

[0118] In mathematical expression 1, BlkW and BlkH represent the width and height of the current block.

[0119] The template search area in IntraTMP mode can be defined in advance according to an agreement between the video encoding device and the video decoding device.

[0120] IntraTMP technology may include sub-modes such as a mode using a single template (TMP single), a technology that fuses multiple templates (TMP fusion), a sub-pixel precision mode, and a linear filter model mode.

[0121] In single-template mode, the template search process involves two steps. In the first step, a search is performed at 3-pixel intervals, and block vectors (BVs) designating 30 candidate templates (i.e., templates of candidate reference blocks) are included in a candidate list. In the second step, an additional search is performed at 1-pixel intervals in a surrounding 3×3 region for the 30 BVs in the candidate list, resulting in a final selection of 19 BVs. Thereafter, an optimal reference block is selected in terms of rate-distortion optimization, and a candidate list index indicating the finally selected BV is signaled from the video encoding device to the video decoding device.

[0122] TMP fusion combines multiple reference templates and reference blocks using weights.

[0123] Sub-pixel precision mode searches for similar templates based on precisions of 1 / 2-Pel, 1 / 4-Pel, and 3 / 4-Pel.

[0124] The linear filter model mode utilizes a 6-tap filter to filter predicted blocks. The 6-tap filter is a cross-shaped 5-tap filter with an added bias. The filter coefficients can be calculated based on the relationship between the current template and the reference template. The current block is predicted using the reference block to which the generated filter is applied.

[0125] I-4. DIMD (Decoder-side intra mode derivation) technology

[0126] The DIMD method sets reconstructed pixels adjacent to the current block as a template, and performs gradient analysis on the set template to derive directional intra prediction modes. The DIMD method extracts orientation and magnitude information by analyzing vertical and horizontal gradients within the template. The DIMD method can calculate the horizontal gradient Gx and the vertical gradient Gy, respectively, by applying a horizontal Sobel filter and a vertical Sobel filter to the pixel position at the center of the template. The angle (orientation) at the corresponding pixel position is calculated through atan(Gy / Gx), and the sum of the absolute values ​​of Gx and Gy can be calculated as the magnitude of the angle (orientation). The size of the template may be equal to or larger than the size of the Sobel filter. The template may include adjacent samples at the lower left and upper right of the current block.

[0127] The angle and magnitude calculated for each pixel position in the center of the template region are used to generate a Histogram of Gradient (HoG), which is constructed by accumulating the angle along the x-axis and the magnitude along the y-axis. The DIMD method can derive or determine corresponding intra prediction modes and corresponding weights by mapping a plurality of angles (e.g., up to 5) with relatively high accumulated magnitude values ​​on the HoG to directional modes. The intra prediction modes determined by the DIMD method may be referred to as DIMD modes and can be subsequently utilized to generate a most probable mode (MPM).

[0128] To form the final predicted block, the predictors of the intra prediction modes determined by DIMD can be weighted and combined with non-directional predictors (based on planar or block vectors).

[0129] I-5. TIMD (Template-based intra mode derivation) technology

[0130] TIMD technology performs template prediction by applying the intra prediction mode of the MPM list to the template region surrounding the current block. TIMD technology calculates the Sum of Absolute Transformed Differences (SATD) cost between the predicted value in the template region and the reconstructed template value. Based on the estimated cost, TIMD technology selects the mode with the lowest cost (costMode1) (hereinafter, the first mode) and the mode with the second lowest cost (costMode2) (hereinafter, the second mode). The undirected mode with the lower SATD cost (costMode3) among DC or Planar is selected as the third mode. Undirected modes can also be used if the following conditions are met.

[0131] - If the third non-directional mode is different from the first and second modes.

[0132] - If costMode3 < 1.5×costMode1

[0133] When both of the above conditions are true, the predicted blocks according to the three intra prediction modes are combined using weights as shown in Equation 2.

[0134]

[0135] If either of the two conditions described above is false, the first and second modes are used. The TIMD technique determines whether to combine the weights of the two TIMD modes according to Equation 3.

[0136]

[0137] If Equation 3 is satisfied, prediction blocks according to the two modes are weighted and combined. Conversely, if Equation 3 is not satisfied, the prediction mode with the lower cost is used. When two modes are combined, a greater weight is assigned to the mode with the lower SATD cost according to Equation 4.

[0138]

[0139] Figure 7 is an example diagram showing a method for deriving one or more intra prediction modes in TIMD technology.

[0140] The size of the template area can be determined based on the size of the current block, as shown in Fig. 7. If the width (W) or height (H) of the current block is greater than 8, the template size L1 or L2 is set to 4. If the width or height of the current block is 8 or less, L1 or L2 is set to 2.

[0141] I-6. Extended multiple reference line (EMRL) technology

[0142] In VVC, lines 0, 1, and 2 are used as reference lines for intra prediction. In contrast, in ECM, lines 0, 1, 3, 5, 7, and 12 can be used as extended reference lines.

[0143] I-7. EIP (Extrapolated intra prediction) technology

[0144] In ECM, EIP technology is utilized in the intra prediction process. The image decoding device derives EIP filter coefficients (hereinafter, used interchangeably with EIP coefficients) using three types of filters as shown in Fig. 8a and a reference sample area around the current block as shown in Fig. 8b, and predicts the current block using the derived EIP filter. In Fig. 8a, the EIP filter includes an input pixel area corresponding to the input (hereinafter, used interchangeably with the input area) and an output pixel area corresponding to the output (hereinafter, used interchangeably with the output area). The output area corresponds to one pixel. To generate an output sample, the EIP coefficients are applied to samples of the input pixel area. In Fig. 8b, fWhidth and fHeight represent the height and width of the EIP filter, respectively, and leftSize and aboveSize define the reference sample area used for the EIP.

[0145] The EIP technique includes 1) a process of deriving EIP coefficients, 2) a process of recursively generating prediction samples within the current block, and 3) a process of analyzing the gradient of the predicted block to derive the mode of the predicted block, and using the derived mode to select a kernel such as MTS (Multiple Transform Set) or LFNST (Low-frequency Non-separable Transform).

[0146] The video decoding device derives the EIP coefficients as follows.

[0147] For a filter selected from the three types in Fig. 8a, the EIP coefficients can be calculated by moving pixels one by one in the reference sample area. Using an auto-correlation matrix and a cross-correlation vector to predict output samples in the EIP output area, the EIP coefficients (c) can be calculated as in Equation 5.

[0148]

[0149] Autocorrelation matrix, A, based on the samples (A) of the input region shown in Fig. 8a T A can be calculated, and the cross-correlation vector, A, based on the input samples and the restored samples (p) of the output region T p can be calculated.

[0150] The video decoding device can select a filter type based on syntax transmitted from the video encoding device.

[0151] The video decoding device can generate a prediction sample of the current block as follows. The video decoding device predicts a sample at the (x, y) location using 15 filter taps as in Equation 6.

[0152]

[0153] In Equation 6, pred(x,y) is the predicted value at the (x, y) location within the current block, and c i are EIP coefficients. t(x-offsetXi, y-offsetYi) represents a reconstructed sample or a predicted sample. In Fig. 8a, offsetXi and offsetYi have values ​​greater than or equal to 0. As another example, for some EIP coefficients, offsetXi and offsetYi can be set to values ​​less than 0. The prediction process uses a recursive structure that uses the values ​​output by EIP as input again.

[0154] Figure 9 is an example diagram showing the generation order of EIP-based prediction samples.

[0155] The video decoding device generates prediction samples of EIP in diagonal order from the upper right to the lower left, as shown in Fig. 9.

[0156] If the current block is coded in EIP mode, the video encoding device can signal an EIP Merge Flag, which indicates whether information inherited from a block previously coded in EIP mode can be used. If the EIP Merge Flag is true, the video decoding device can inherit filter shapes and filter coefficients from a block previously coded in EIP mode. On the other hand, if the EIP Merge Flag is false, the video decoding device parses an index indicating the type of the filter and the type of the reference sample area, and derives the EIP coefficients based on the parsed index. Table 1 shows the syntax related to the EIP mode.

[0157]

[0158] After generating prediction samples of the current block using the EIP filter, the image decoding device applies the DIMD process to the prediction samples to derive the prediction mode of the current block. The image decoding device calculates horizontal gradients and vertical gradients for each prediction sample and constructs a histogram between the gradient angles and magnitudes. Then, a transform set of LFNST, NSPT (Non-separable primary transform), or MTS can be determined based on the directional mode corresponding to the largest histogram frequency. That is, LFNST, NSPT, and MTS can utilize the directional mode selected based on the DIMD process when determining the transform kernel of the primary transform or secondary transform.

[0159] The following embodiments are described with a focus on a video decoding device, but can be implemented in the same or similar manner in a video encoding device. Alternatively, the following embodiments are described with a focus on the decoder side of a video decoding device, but can also be implemented in the same or similar manner in the decoder side of a video encoding device.

[0160] II. Embodiments according to the present disclosure

[0161] With respect to generation of prediction blocks according to EIP, embodiments according to the present disclosure include 1) generation of EIP output samples according to various generation orders, and 2) fusion of multiple prediction blocks including EIP blocks.

[0162] As an example, a video decoding device may determine the generation order of EIP prediction samples in a vertical or horizontal direction, rather than the conventional diagonal direction. In this case, the information for determining the vertical, horizontal, and conventional diagonal directions may be signaled or derived based on decoded compressed information on the decoder side. Alternatively, in addition to generating output samples starting from adjacent samples in the reference region, the video decoding device may also generate output samples in an order based on regions further away from the reference region.

[0163] As another example, when generating a prediction block according to EIP, in addition to generating blocks along one direction, the video decoding device can generate two or more blocks along different directions. Thereafter, the video decoding device can mix the two blocks to generate the final prediction block. The EIP sample generation process is a recursive structure that reuses previously output samples as input. Therefore, if the sample generation order changes, the configuration of the prediction block also changes, and thus the video decoding device can generate the final prediction block by mixing blocks generated along different directions.

[0164] Below, a method for determining the generation order of EIP prediction samples is described.

[0165] The generation order of the existing EIP prediction block is diagonally from the upper right to the lower left, as shown in Fig. 9. At this time, the output sample can be reused as an EIP input sample, as in Equation 6, and used to generate the next adjacent prediction sample. In addition to generating samples along the existing direction (diagonally from the upper right to the lower left), the image decoding device can also use the following method.

[0166] As an example, a video decoding device generates samples starting from the upper left of a block in a vertical direction. According to Equation 6, all samples in adjacent reference regions are used as 15 inputs for generating the sample located at the upper leftmost position within the prediction block. The video decoding device outputs all prediction samples located in the leftmost column while moving vertically from the upper leftmost sample one sample at a time. The video decoding device can output a sample located one position to the right of the upper left and proceed with prediction up to the sample located at the lower right in the same manner.

[0167] As another example, the video decoding device generates samples horizontally starting from the upper left of the block. According to Equation 6, all samples in the adjacent reference region are used as 15 inputs for generating the sample located at the upper leftmost position within the prediction block. The video decoding device outputs all prediction samples located in the uppermost row while moving the sample horizontally one by one starting from the upper leftmost sample. The video decoding device can output a sample located one position downward from the upper left and proceed with prediction up to the sample located at the lower right in the same manner.

[0168] As another example, the video decoding device generates samples in a diagonal direction starting from the upper left of the block. Instead of the conventional direction from the upper right to the lower left, the video decoding device uses a diagonal direction from the lower left to the upper right. According to Equation 6, all samples in the adjacent reference region are used as 15 inputs for generating the sample located at the upper leftmost position in the prediction block. Instead of outputting prediction samples in a diagonal direction by moving samples one by one to the right from the upper leftmost sample, the video decoding device outputs prediction samples in the opposite diagonal direction by moving samples one by one downward from the upper leftmost sample. The video decoding device can proceed with prediction up to the sample located at the lower right in the same manner.

[0169] The video encoding device can determine an optimal order in relation to generation of EIP prediction blocks and signal the determined order to the video decoding device.

[0170] Meanwhile, using the compression information available on the decoder side, the video decoding device can derive the generation order of EIP prediction blocks as follows.

[0171] For example, the generation order can be predicted based on the filter shape or reference region shape used in the EIP. If the EIP technology uses a horizontally elongated filter shape as shown in FIG. 8A, the image decoding device can generate samples in the horizontal direction. On the other hand, if the EIP technology uses a vertically elongated filter shape, the image decoding device can generate samples in the vertical direction. In other cases, samples can be generated in the diagonal direction.

[0172] As another example, an EIP merge list may be utilized. When using information inherited from a block previously encoded in EIP mode, the video decoding device may generate an EIP merge list. The video decoding device may determine the generation order of EIP prediction samples based on the filter type or reference region type included in the EIP merge list.

[0173] As another example, a prediction mode within the MPM list or a mode derived from DIMD may be utilized. If a horizontal intra prediction mode is used in an adjacent region, the video decoding device may determine the generation order of EIP prediction samples in the horizontal direction. If a vertical intra prediction mode is used in an adjacent region, the video decoding device may determine the generation order of EIP prediction samples in the vertical direction.

[0174] As another example, the TIMD method can be utilized. Prediction templates are calculated based on horizontal and vertical prediction modes within the template area of ​​the current block, and SATD values ​​are generated between the prediction templates and the restoration template. Then, the image decoding device can utilize the prediction mode with the minimum SATD value. In other words, the image decoding device can determine the generation order of EIP prediction samples based on the direction (i.e., horizontal or vertical) of the prediction mode with the minimum SATD value.

[0175] When deriving the EIP coefficient, the cost function can be defined as the Mean Square Error (MSE) between the predicted value based on the EIP coefficient and the reconstructed output value. Both the predicted value and the reconstructed output value are generated in the output domain. The image decoding device determines the EIP coefficient using the aforementioned autocorrelation matrix and cross-correlation vector so that the cost function is minimized. In addition, ridge regression can be utilized by additionally considering the identity matrix (I) in addition to the MSE in the cost function to be robust to noise. When deriving the EIP coefficient, the identity matrix can be utilized in the form of λI (λ is a preset value), so that the EIP coefficient (c) can be normalized as in Equation 7.

[0176]

[0177] At this time, all EIP coefficients can be derived using ridge regression. Alternatively, some of the EIP coefficients may not be normalized. For example, if the ith coefficient is not normalized, the element corresponding to (ith row, ith column) of the identity matrix λI may be set to 0.

[0178] As another example, coefficients can be derived differently depending on the generation order of prediction samples. For example, when outputting prediction samples in both horizontal and vertical directions, the image decoding device can derive EIP coefficients using a cost function that minimizes MSE, rather than using ridge regression.

[0179] Below, the fusion of multiple prediction blocks including an EIP block is described.

[0180] As an example, a video decoding device may have a previously diagonally predicted EIP block (B E ) in one block (B) A) can be mixed, i.e., weighted, to generate the final prediction block (B). The final prediction block can be calculated as in Equation 8.

[0181]

[0182] In Equation 8, the weight w is a value between 0 and 1.

[0183] As an example, B A is, B E This is an EIP block constructed based on the vertical, horizontal, or opposite diagonal directions described above, using the original EIP filter used in the calculation. The EIP sample generation process is a recursive structure that reuses the previously output samples as input. Therefore, since the configuration of the prediction block also changes when the sample generation order is changed, the image decoding device can generate the final prediction block by mixing blocks generated according to different directions.

[0184] As another example, B A is B E The predicted EIP block may be based on an EIP filter (hereinafter, referred to as a second EIP filter) different from the original EIP filter (hereinafter, referred to as a first EIP filter) used in the calculation. The second EIP filter may be of the same type as the original filter, but may include different EIP coefficients.

[0185] Meanwhile, with respect to the second EIP filter of the same type, the EIP coefficients may be calculated based on reference samples different from the reference samples used to calculate the original filter. The two EIP filters (i.e., the first EIP filter and the second EIP filter) may have different output pixel areas in the reference sample area. For example, the output pixel areas generated by the two EIP filters may be distinguished based on a sample value at a specific location in an input pixel area corresponding to the output pixel area. Correlations may be generated for calculating the coefficients of the two EIP filters, respectively, based on the distinguished output pixel areas and the corresponding input pixel areas. When the two EIP filters are generated based on the distinction in the output pixel areas, a single prediction block may be generated instead of a weighted sum. For example, the prediction sample of the current block may be recursively generated by having one of the two EIP filters generate an output pixel value based on a sample value at a specific location in the input pixel area.

[0186] As another example, the second EIP filter may be of a different type than the original filter. For example, if the original filter is of a square type, the second EIP filter may be of a rectangular type. Alternatively, the second EIP filter may include a different number of filter coefficients than those indicated in Equation 6. When multiple EIP filters including different numbers of filter coefficients are used, the video encoding device may signal an index indicating each EIP filter to the video decoding device.

[0187] As another example, B A It may be a prediction block generated according to a prediction method other than EIP technology.

[0188] As another example, when generating prediction samples in the vertical direction, the leftmost EIP output sample (E(x, y)) in the prediction block and the leftmost reference sample R(x-1, y) are used to obtain the final prediction sample E in the prediction block as in Equation 9. f(x, y) can be calculated.

[0189]

[0190] In Equation 9, the weight w is a value between 0 and 1.

[0191] As another example, when generating prediction samples in the horizontal direction, the topmost EIP output sample (E(x, y)) in the prediction block and the top reference sample R(x, y-1) are used to generate the topmost final prediction sample E in the prediction block as in Equation 10. f (x, y) can be calculated.

[0192]

[0193] In Equation 10, the weight w is a value between 0 and 1.

[0194] As another example, when generating prediction samples in the diagonal direction,

[0195] 1) The upper leftmost EIP output sample (E(x, y)) in the prediction block,

[0196] 2) One of the reference sample R(x-1, y-1) in the upper left, the reference sample R(x-1, y) on the left, and the reference sample R(x, y-1) on the top (or a combination of these)

[0197] The final prediction sample E in the upper left corner of the prediction block is weighted and added. f (x, y) can be calculated.

[0198] Alternatively, when generating prediction samples diagonally,

[0199] 1) The leftmost EIP output sample (E(x, y)) in the prediction block and

[0200] 2) One of the reference samples R(x-1, y-1) in the upper left and the reference samples R(x-1, y) on the left (or a combination of them)

[0201] The final prediction sample E on the leftmost side of the prediction block is weighted and added. f (x, y) can be calculated.

[0202] Alternatively, when generating prediction samples diagonally,

[0203] 1) The topmost EIP output sample (E(x, y)) in the prediction block and

[0204] 2) One of the reference samples R(x-1, y-1) in the upper left and the reference samples R(x, y-1) above (or a combination of them)

[0205] The final prediction sample E at the top of the prediction block is weighted and added together. f (x, y) can be calculated.

[0206] A video encoding device can determine a flag indicating the fusion of a plurality of prediction blocks including an EIP block, and then signal the determined flag to a video decoding device. The video decoding device can decode the aforementioned flag and perform fusion of a plurality of prediction blocks including an EIP block based on the decoded flag.

[0207] Below, we describe a method for using distant reference samples or generating non-contiguous EIP output samples. Hereinafter, "distant" may be used interchangeably with "non-contiguous" or "non-contiguous."

[0208] As shown in FIG. 9, rather than outputting samples in the order of proximity to the reference area, the video decoding device can construct an EIP block by first generating samples that are further away from the reference area. For example, in FIG. 10a, the video decoding device first predicts samples located at the bottom of the block using an EIP filter that uses the upper reference samples. After generating the lower predicted samples, the video decoding device can construct the final EIP block by interpolating intermediate samples based on the reference samples of the upper reconstructed block and the lower EIP samples, as in the planar mode of VVC.

[0209] In addition to using EIP coefficients derived according to the conventional method, the video decoding device can newly derive EIP coefficients using the autocorrelation matrix and cross-correlation vector associated with distant samples. Samples that are not adjacent to the current block within the restored region of the current block can be determined as follows. The video decoding device can search for a block vector by applying the intraTMP technique to the template of the current block and the templates within the restored region, as shown in FIG. 10b. Alternatively, the video decoding device can search for a block vector used in an adjacent block of the current block. Non-adjacent samples can be determined based on the searched block vector. The video encoding device can signal a flag indicating whether to derive EIP coefficients based on the block vector. Based on the above-described flag, the video decoding device can determine whether to derive EIP coefficients from an adjacent reference region of the current block or from a reference region indicated by the block vector.

[0210] Below, a method for performing extrapolation intra prediction using the cities of FIGS. 11 and 12 is described.

[0211] FIG. 11 is a flowchart illustrating a method of encoding a current block performed by an image encoding device according to one embodiment of the present disclosure.

[0212] The image encoding device obtains a reference sample area and a filter shape (S1100).

[0213] An image encoding device can obtain a reference sample region and a filter shape for extrapolation intra prediction from a higher level. The reference sample region includes restored reference samples of the current block and is used to derive filter coefficients used for extrapolation intra prediction. The filter shape includes an output pixel region and an input pixel region.

[0214] The video encoding device obtains the predicted order of samples in the current block (S1102).

[0215] The video encoding device can obtain a prediction order of samples according to extrapolation intra prediction, which is an order of predicting samples in a horizontal direction starting from the upper left of the current block, an order of predicting samples in a vertical direction starting from the upper left of the current block, an order of predicting samples in a diagonal direction from the upper right to the lower left starting from the upper left of the current block, or an order of predicting samples in a diagonal direction from the lower left to the upper right starting from the upper left of the current block.

[0216] The video encoding device can obtain a prediction order of samples according to extrapolated intra prediction from a higher level.

[0217] Alternatively, the video encoding device can derive the prediction order of samples according to extrapolated intra prediction using decoder-side information as follows.

[0218] As an example, an image encoding device can derive a prediction order based on a reference sample area and a filter shape.

[0219] As another example, the video encoding device can generate a merge list for extrapolation intra prediction, and derive a prediction order based on a reference sample region and filter shape for extrapolation intra prediction included in the merge list.

[0220] As another example, the video encoding device can derive the prediction order based on the directionality of the intra prediction mode used in the adjacent area of ​​the current block.

[0221] As another example, an image encoding device generates prediction templates based on horizontal prediction modes and vertical prediction modes within a template region of a current block. The image encoding device can generate differences between the prediction templates and the restoration template, and derive a prediction order based on the direction of the prediction mode corresponding to the minimum difference.

[0222] The image encoding device derives filter coefficients applied to the input pixel area according to the reference sample area and filter type (S1104).

[0223] An image encoding device calculates an autocorrelation matrix based on samples of an input pixel area, and calculates a cross-correlation vector based on samples of the input pixel area and reconstructed samples of the output pixel area. The image encoding device can calculate filter coefficients based on the autocorrelation matrix and the cross-correlation vector. The image encoding device can normalize the filter coefficients using an identity matrix. Alternatively, based on a prediction order, the image encoding device can determine whether to normalize the filter coefficients using the identity matrix.

[0224] As another example, the video encoding device can derive filter coefficients based on a non-adjacent region that is not adjacent to the current block within the reference sample region. At this time, the non-adjacent region can be determined based on a block vector searched according to template matching or a block vector used in an adjacent block of the current block. For example, in terms of optimizing encoding efficiency, the video encoding device can determine whether to derive the EIP coefficients from an adjacent reference region of the current block or from a reference region indicated by a block vector. The video encoding device can encode a flag indicating whether to derive the EIP coefficients based on the block vector.

[0225] The image encoding device generates a first prediction block of the current block by applying the derived filter coefficients to the restoration reference samples and prediction samples of the current block based on the prediction order (S1106).

[0226] The video encoding device can recursively apply the derived filter coefficients to the reconstructed reference samples surrounding the current block and the predicted samples predicted first within the current block based on the prediction order of the samples within the current block. The video encoding device can generate a predicted block of the current block by sequentially predicting the samples within the current block.

[0227] The image encoding device encodes a reference sample area and a filter shape (S1108). The image encoding device can encode information of a reference sample area as shown in FIG. 8b.

[0228] When fusion of multiple prediction blocks including extrapolated intra-predicted blocks is indicated, the video encoding device can fuse the prediction blocks as follows.

[0229] As an example, an image encoding device generates a second prediction block of the current block by applying derived filter coefficients to the restored reference samples and prediction samples of the current block based on a prediction order different from the prediction order. The image encoding device can generate a final prediction block of the current block by weighting the first prediction block and the second prediction block.

[0230] As another example, the video encoding device may calculate second filter coefficients having different values ​​from the filter coefficients and generate a second prediction block of the current block based on the second filter coefficients. The video encoding device may generate a final prediction block of the current block by weighting the first prediction block and the second prediction block.

[0231] As another example, a video encoding device generates a second prediction block of the current block based on an intra prediction mode other than extrapolation intra prediction. The video encoding device can weight and combine the first prediction block and the second prediction block to generate a final prediction block of the current block.

[0232] As another example, the video encoding device can calculate the second filter coefficients based on reference samples different from the reference samples used to calculate the original filter coefficients (i.e., the first filter coefficients). The two EIP filters (i.e., the first EIP filter and the second EIP filter) can have different output pixel areas in the reference sample area. The video encoding device can derive the first filter coefficients based on a subset including samples of the output pixel areas of the first EIP filter. The video encoding device can derive the second filter coefficients based on a subset including samples of the output pixel areas of the second EIP filter. The video encoding device can generate a final prediction block of the current block by recursively applying the first filter coefficients and the second filter coefficients to reconstructed reference samples around the current block and prediction samples predicted first within the current block.

[0233] An image encoding device can generate a residual block by subtracting a prediction block (or a final prediction block) from a current block. The image encoding device can apply transformation / quantization to the residual block to generate transformation coefficients and encode the generated transformation coefficients.

[0234] FIG. 12 is a flowchart illustrating a method for restoring a current block performed by an image decoding device according to one embodiment of the present disclosure.

[0235] The video decoding device decodes a reference sample area and a filter shape based on a bitstream (S1200). The video decoding device can decode information in the reference sample area as shown in FIG. 8b.

[0236] The reference sample region contains the restored reference samples of the current block and is used to derive the filter coefficients used for extrapolated intra prediction. The filter shape includes the output pixel region and the input pixel region.

[0237] The video decoding device obtains the predicted order of samples in the current block (S1202).

[0238] The video decoding device can obtain a prediction order of samples according to extrapolation intra prediction, which is an order of predicting samples in a horizontal direction starting from the upper left of the current block, an order of predicting samples in a vertical direction starting from the upper left of the current block, an order of predicting samples in a diagonal direction from the upper right to the lower left starting from the upper left of the current block, or an order of predicting samples in a diagonal direction from the lower left to the upper right starting from the upper left of the current block.

[0239] The video decoding device can decode the predicted order of samples according to extrapolated intra prediction from a bitstream.

[0240] Alternatively, the video decoding device can derive the prediction order of samples according to extrapolated intra prediction using the decoder-side restoration information as follows.

[0241] As an example, the image decoding device can derive a prediction order based on a reference sample area and a filter shape.

[0242] As another example, the image decoding device can generate a merge list for extrapolated intra prediction and derive a prediction order based on a reference sample region and filter shape for extrapolated intra prediction included in the merge list.

[0243] As another example, the image decoding device can derive the prediction order based on the directionality of the intra prediction mode used in the adjacent area of ​​the current block.

[0244] As another example, an image decoding device generates prediction templates based on horizontal prediction modes and vertical prediction modes within the template region of the current block. The image decoding device can generate differences between the prediction templates and the restoration template, and derive a prediction order based on the direction of the prediction mode corresponding to the minimum difference.

[0245] The image decoding device derives filter coefficients applied to the input pixel area according to the reference sample area and filter type (S1204).

[0246] An image decoding device calculates an autocorrelation matrix based on samples of an input pixel area, and calculates a cross-correlation vector based on samples of the input pixel area and reconstructed samples of an output pixel area. The image decoding device can calculate filter coefficients based on the autocorrelation matrix and the cross-correlation vector. The image decoding device can normalize the filter coefficients using an identity matrix. Alternatively, based on a prediction order, the image decoding device can determine whether to normalize the filter coefficients using the identity matrix.

[0247] As another example, the video decoding device can derive filter coefficients based on a non-adjacent region that is not adjacent to the current block within the reference sample region. At this time, the non-adjacent region can be determined based on a block vector searched according to template matching and a block vector used in an adjacent block of the current block. The video decoding device can decode a flag indicating whether to derive EIP coefficients based on the block vector. Based on the above-described flag, the video decoding device can determine whether to derive EIP coefficients from a reference region adjacent to the current block or from a reference region indicated by the block vector.

[0248] The image decoding device generates a first prediction block of the current block by applying the derived filter coefficients to the restoration reference samples and prediction samples of the current block based on the prediction order (S1206).

[0249] The image decoding device can recursively apply the derived filter coefficients to the reconstructed reference samples surrounding the current block and the predicted samples predicted earlier within the current block based on the prediction order of the samples within the current block. The image decoding device can generate a predicted block of the current block by sequentially predicting the samples within the current block.

[0250] For example, a video decoding device may decode a flag indicating the fusion of multiple prediction blocks including a first prediction block. If the decoded flag indicates the fusion of multiple prediction blocks including an extrapolated intra-predicted block, the video decoding device may fuse the prediction blocks as follows.

[0251] As an example, an image decoding device generates a second prediction block of the current block by applying derived filter coefficients to the restored reference samples and prediction samples of the current block based on a prediction order different from the prediction order of the extrapolated intra prediction. The image decoding device can generate a final prediction block of the current block by weighting the first prediction block and the second prediction block.

[0252] As another example, the image decoding device may calculate second filter coefficients having different values ​​from the filter coefficients and generate a second prediction block of the current block based on the second filter coefficients. The image decoding device may weight and add the first prediction block and the second prediction block to generate a final prediction block of the current block.

[0253] As another example, a video decoding device generates a second prediction block of the current block based on an intra prediction mode other than extrapolation intra prediction. The video decoding device can weight and combine the first prediction block and the second prediction block to generate a final prediction block of the current block.

[0254] As another example, the image decoding device can calculate the second filter coefficients based on reference samples different from the reference samples used to calculate the original filter coefficients (i.e., the first filter coefficients). The two EIP filters (i.e., the first EIP filter and the second EIP filter) can have different output pixel areas in the reference sample area. The image decoding device can derive the first filter coefficients based on a subset including samples of the output pixel areas of the first EIP filter. The image decoding device can derive the second filter coefficients based on a subset including samples of the output pixel areas of the second EIP filter. The image decoding device can generate a final prediction block of the current block by recursively applying the first filter coefficients and the second filter coefficients to the reconstructed reference samples around the current block and the prediction samples predicted first within the current block.

[0255] An image decoding device can decode quantized transform coefficients of a current block from a bitstream and apply inverse quantization / inverse transformation to the quantized transform coefficients to generate a residual block. The image decoding device can reconstruct the current block by adding the residual block and the prediction block (or the final prediction block).

[0256] Although the flowchart / timing diagram of this specification describes each process as being executed sequentially, this is merely an illustrative description of the technical idea of ​​one embodiment of the present disclosure. In other words, a person of ordinary skill in the art to which one embodiment of the present disclosure belongs may modify and apply various modifications and variations by changing the order described in the flowchart / timing diagram without departing from the essential characteristics of one embodiment of the present disclosure, or by executing one or more of the processes in parallel. Therefore, the flowchart / timing diagram is not limited to a chronological order.

[0257] It should be understood that the exemplary embodiments described above can be implemented in many different ways. The functions or methods described in one or more examples can be implemented in hardware, software, firmware, or any combination thereof. It should be understood that the functional components described herein are labeled as "units" to further emphasize their implementation independence.

[0258] Meanwhile, the various functions or methods described in this embodiment may also be implemented as instructions stored on a non-transitory storage medium that can be read and executed by one or more processors. Non-transitory storage media include, for example, all types of storage devices that store data in a form readable by a computer system. For example, non-transitory storage media include storage media such as erasable programmable read-only memory (EPROM), flash drives, optical drives, magnetic hard drives, and solid-state drives (SSDs).

[0259] The above description is merely an example of the technical idea of ​​the present embodiment, and those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential characteristics of the present embodiment. Therefore, the present embodiments are not intended to limit the technical idea of ​​the present embodiment, but rather to explain it, and the scope of the technical idea of ​​the present embodiment is not limited by these embodiments. The scope of protection of the present embodiment should be interpreted by the claims below, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of rights of the present embodiment.

[0260]

[0261]

[0262] CROSS-REFERENCE TO RELATED APPLICATION

[0263] This patent application claims priority to Korean patent application No. 10-2024-0053594, filed in Korea on April 22, 2024, and Korean patent application No. 10-2025-0048525, filed in Korea on April 15, 2025, the entire contents of which are incorporated herein by reference.

Claims

1. In a method for restoring a current block performed by an image decryption device, A step of determining a reference sample area and a filter shape, wherein the reference sample area includes restored reference samples of the current block and is used for deriving filter coefficients used for extrapolated intra prediction, and the filter shape includes an output pixel area and an input pixel area; A step of deriving filter coefficients applied to the input pixel area according to the reference sample area and the filter shape; and A step of generating a prediction block of the current block by sequentially predicting samples in the current block by recursively applying the derived filter coefficients to the restored reference samples around the current block and the predicted samples predicted first in the current block based on the prediction order of the samples in the current block. A method comprising:

2. In paragraph 1, Further comprising a step of obtaining the above prediction order, The step of generating the above prediction block is: A method for recursively applying the derived filter coefficients based on the acquired prediction order to the restored reference samples surrounding the current block and the predicted samples predicted first within the current block.

3. In paragraph 2, The step of obtaining the above prediction order is: A method for obtaining, as the above prediction order, an order for predicting samples in a horizontal direction starting from the upper left of the current block, an order for predicting samples in a vertical direction starting from the upper left of the current block, an order for predicting samples in a diagonal direction from the upper right to the lower left starting from the upper left of the current block, or an order for predicting samples in a diagonal direction from the lower left to the upper right starting from the upper left of the current block.

4. In paragraph 2, The step of obtaining the above prediction order is: A method for decoding the prediction order from the bitstream.

5. In paragraph 2, The step of obtaining the above prediction order is: A method for deriving the prediction order based on the above reference sample area and the above filter shape.

6. In paragraph 2, The step of obtaining the above prediction order is: A step of generating a merge list for extrapolated intra prediction; and A method for deriving the prediction order based on the reference sample area and filter shape for extrapolated intra prediction included in the above merge list.

7. In paragraph 2, The step of obtaining the above prediction order is: A step of generating prediction templates based on a horizontal prediction mode and a vertical prediction mode within a template area of ​​the current block; generating differences between the above prediction templates and the restoration templates; and A method for deriving the prediction order based on the direction of the prediction mode corresponding to the minimum difference among the above differences.

8. In paragraph 1, The step of deriving the above filter coefficients is: A step of calculating an auto-correlation matrix based on samples of the input pixel area, and calculating a cross-correlation vector based on samples of the input pixel area and restored samples of the output pixel area; and A step of calculating the filter coefficients based on the autocorrelation matrix and the cross-correlation vector. Including, but not limited to, A method for normalizing the above filter coefficients using an identity matrix.

9. In paragraph 1, The step of generating the above prediction block is: A step of generating a first prediction block of the current block by recursively applying the filter coefficients to the restored reference samples around the current block and the prediction samples predicted first within the current block based on the first prediction order; and A step of generating a second prediction block of the current block by recursively applying the filter coefficients to the restored reference samples around the current block and the prediction samples predicted first within the current block based on a second prediction order different from the first prediction order; and A step of generating a final prediction block of the current block by weighting the first prediction block and the second prediction block. A method further comprising:

10. In paragraph 1, The step of deriving the above filter coefficients is: A step of deriving first filter coefficients based on a first subset of reference samples within the above reference sample area; and A step of deriving second filter coefficients based on a second subset of reference samples within the above reference sample area. Including, The step of generating the above prediction block is: A method for recursively applying the first filter coefficients and the second filter coefficients to the restored reference samples around the current block and the predicted samples predicted first within the current block.

11. In paragraph 1, The above reference sample area is, A method in which a non-adjacent area is not adjacent to the current block.

12. In paragraph 11, The above non-adjacent area is, A method determined based on a block vector searched according to template matching or a block vector used in an adjacent block of the current block.

13. In a method for encoding a current block performed by a video encoding device, A step of obtaining a reference sample area and a filter shape, wherein the reference sample area includes restored reference samples of the current block and is used for deriving filter coefficients used for extrapolated intra prediction, and the filter shape includes an output pixel area and an input pixel area; A step of deriving filter coefficients applied to the input pixel area according to the reference sample area and the filter shape; and A step of generating a prediction block of the current block by sequentially predicting samples in the current block by recursively applying the derived filter coefficients to the restored reference samples around the current block and the predicted samples predicted first in the current block based on the prediction order of the samples in the current block. A method comprising:

14. In paragraph 13, A step of encoding information of the above reference sample area and the filter shape; and Step of obtaining the above prediction order Including more, The step of generating the above prediction block is: A method for recursively applying the derived filter coefficients based on the acquired prediction order to the restored reference samples surrounding the current block and the predicted samples predicted first within the current block.

15. In paragraph 14, The step of obtaining the above prediction order is: A method for obtaining, as the above prediction order, an order for predicting samples in a horizontal direction starting from the upper left of the current block, an order for predicting samples in a vertical direction starting from the upper left of the current block, an order for predicting samples in a diagonal direction from the upper right to the lower left starting from the upper left of the current block, or an order for predicting samples in a diagonal direction from the lower left to the upper right starting from the upper left of the current block.

16. In paragraph 13, The step of deriving the above filter coefficients is: A step of calculating an auto-correlation matrix based on samples of the input pixel area, and calculating a cross-correlation vector based on samples of the input pixel area and restored samples of the output pixel area; and A step of calculating the filter coefficients based on the autocorrelation matrix and the cross-correlation vector. Including, but not limited to, A method for normalizing the above filter coefficients using an identity matrix.

17. In paragraph 13, The step of deriving the above filter coefficients is: A step of deriving first filter coefficients using a first subset of reference samples within the above reference sample area; and A step of deriving second filter coefficients using a second subset of reference samples within the above reference sample area. Including, The step of generating the above prediction block is: A method for recursively applying the first filter coefficients and the second filter coefficients to the restored reference samples around the current block and the predicted samples predicted first within the current block.

18. In a method for providing video data to a video decoding device, A step of encoding the above video data into a bitstream; and A step of transmitting the above bitstream to the image decoding device Including, The step of encoding the above video data is: A step of obtaining a reference sample area and a filter shape, wherein the reference sample area includes restored reference samples of the current block and is used for deriving filter coefficients used for extrapolated intra prediction, and the filter shape includes an output pixel area and an input pixel area; A step of deriving filter coefficients applied to the input pixel area according to the reference sample area and the filter shape; and A step of generating a prediction block of the current block by sequentially predicting samples in the current block by applying the derived filter coefficients based on the prediction order of samples in the current block to the restored reference samples around the current block and the predicted samples predicted first in the current block. A method comprising:

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