Method for coding intra-prediction mode by using history-based MPM candidates, and device using same

Abstract

Disclosed are a method for coding an intra-prediction mode by using history-based MPM candidates, and a device using same. A video encoder and a video decoder may: derive an HMPM list for the current block by using intra-prediction modes of blocks decoded prior to the current block; and insert at least one intra-prediction mode from the HMPM list into an MPM list in configuring the MPM list for the current block. Prior to constructing the MPM list, the HMPM list can be re-sorted according to a template-based cost of the current block.

Description

Coding method for intra prediction mode using history-based MPM candidates and device using the same

[0001] The present disclosure relates to encoding and decoding of video data, and more particularly, to a technique for constructing a most probable mode (MPM) list for intra prediction and determining an intra prediction mode from the MPM list.

[0002] The content described below merely provides background information related to the present embodiment 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] The present disclosure proposes a method that enables adding intra prediction modes of blocks that are not neighboring the current block as blocks encoded and decoded before the current block to the MPM list when constructing the MPM list for the current block.

[0007] One aspect of the present disclosure provides a method for decoding video data. The method comprises the steps of constructing an HMPM list for a current block using intra prediction modes of blocks decoded prior to the current block, constructing an MPM list for the current block, and decoding an intra prediction mode of the current block using the MPM list. Here, the step of constructing the MPM list includes the step of inserting at least one intra prediction mode from the HMPM list into the MPM list.

[0008] In some embodiments, the HMPM list is derived based on a FIFO table, and the FIFO table is configured to add the intra prediction mode of the intra-coded block to the last entry of the FIFO table whenever an intra-coded block is encountered.

[0009] In some embodiments, constructing an HMPM list for the current block comprises adding a plurality of intra prediction modes in the FIFO table to the HMPM list, generating prediction samples for the template based on reference samples of a template of the current block and using the individual intra prediction modes for each intra prediction mode in the HMPM list, determining a cost for the individual intra prediction mode based on differences between the prediction samples for the template and reconstructed samples for the template, and sorting the plurality of intra prediction modes in the HMPM list in ascending order according to their respective costs. Among the plurality of intra prediction modes in the HMPM list, a mode having a smaller cost may be inserted into the HMPM list first.

[0010] Another aspect of the present disclosure provides a method for encoding video data. The method comprises the steps of constructing an HMPM list for a current block using intra prediction modes of blocks encoded prior to the current block, constructing an MPM list for the current block, and decoding the intra prediction mode of the current block using the MPM list. Here, the step of constructing the MPM list includes the step of inserting at least one intra prediction mode from the HMPM list into the MPM list.

[0011] Another aspect of the present disclosure discloses a method for providing video data to a video decoding device. The method includes the steps of encoding the video data into a bitstream and transmitting the bitstream to the video decoding device. The step of encoding the video data into the bitstream includes the steps of constructing an HMPM list for the current block using intra prediction modes of blocks encoded before the current block, constructing an MPM list for the current block, and decoding the intra prediction mode of the current block using the MPM list. Here, the step of constructing the MPM list includes the step of inserting at least one intra prediction mode from the HMPM list into the MPM list.

[0012] According to embodiments of the present disclosure, the MPM list for a current block includes at least one intra prediction mode from a history-based MPM (HMPM) list, which enables efficient coding of intra prediction modes even for the current block that has correlations with non-adjacent blocks rather than adjacent blocks.

[0013] FIG. 1 is an exemplary block diagram of an image encoding device capable of implementing the techniques of the present disclosure.

[0014] Figure 2 is a drawing for explaining a method of dividing a block using the QTBTTT (QuadTree plus BinaryTree TernaryTree) structure.

[0015] FIGS. 3A and 3B are diagrams illustrating multiple intra prediction modes, including wide-angle intra prediction modes.

[0016] Figure 4 is a conceptual diagram illustrating the surrounding blocks of the current block.

[0017] FIG. 5 is an exemplary block diagram of an image decoding device capable of implementing the techniques of the present disclosure.

[0018] Figure 6 is a conceptual diagram illustrating neighboring blocks used to construct an MPM list in VVC.

[0019] Figure 7 is a conceptual diagram illustrating the inefficient aspects of VVC's MPM list construction method.

[0020] Figure 8 is a conceptual diagram illustrating neighboring blocks used to construct an MPM list in ECM.

[0021] Figure 9 illustrates four shapes of templates that can be used for HMPM list reordering.

[0022] Figure 10 is a conceptual diagram illustrating a method for calculating the sum of absolute difference (SAD) cost based on the difference between the prediction and reconstruction of a template for HMPM list reordering.

[0023] Figure 11 is a conceptual diagram illustrating how the HMPM list is sorted in ascending order according to template-based SAD cost.

[0024] Figure 12 is a conceptual diagram illustrating a method of adding an intra prediction mode within an HMPM list to an MPM list.

[0025] FIG. 13 is a flowchart illustrating a method of coding (encoding or decoding) video data according to one embodiment of the present disclosure.

[0026] Hereinafter, some embodiments of the present disclosure 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 the 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 the 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] Now, improved coding techniques that can be performed by the aforementioned video encoder (e.g., the video encoding device illustrated in FIG. 1) or video decoder (e.g., the video decoding device illustrated in FIG. 5) are disclosed. The techniques of the present disclosure are particularly related to constructing a most probable mode (MPM) list for intra prediction and determining an intra prediction mode from the MPM list.

[0096] A video encoder and a video decoder can construct or generate an MPM list for each block (e.g., PU) to be coded with intra prediction.

[0097] VVC has 67 intra prediction modes, and the length of the MPM list is 6. The MPM list includes a Planar mode as the first entry, and may further include five intra modes derived based on the intra prediction modes of the left neighboring block and the upper neighboring block. Referring to Fig. 6, the MPM list may include at most two neighboring intra modes, including the intra mode of the left neighboring block including a sample position L located to the left of the lower-left sample of the current block, and the intra mode of the upper neighboring block including a sample position A located above the upper-right sample. In addition, the MPM list may include derived intra modes obtained by adding or subtracting offsets (e.g., 1 or 2) to the neighboring intra modes. In addition, default modes, which are statistically frequently used predefined modes, may be used to fill the MPM list.

[0098] The process of VVC using the intra prediction modes of two neighboring PUs to construct the MPM list can lead to inefficient coding of the intra prediction modes, as shown in the following example.

[0099] Fig. 7 is a conceptual diagram illustrating an inefficient aspect of the MPM list construction method of VVC. In the example of Fig. 7, according to the MPM list construction method of VVC, the MPM list of the current block includes the Planar mode (0), neighboring intra modes (18, 34), and derived intra modes (17, 19, 33). That is, the MPM list is composed of {Planar, 18, 34, 17, 19, 33}. In the example of Fig. 7, even though there are many blocks encoded with intra mode 50 around the current block, the MPM list of the current block does not include intra mode 50 according to the MPM list construction method of VVC. Therefore, if the current block is encoded with intra mode 50, which does not exist in the MPM list, the encoder has no choice but to consume many bits to signal the intra mode of the current block.

[0100] In the Enhanced Compression Model (ECM), the length of the MPM list has been increased to 22. The first six modes of the MPM list are referred to as the Primary MPM list (PMPM list), and the next 16 modes of the MPM list are referred to as the Secondary MPM list (SMPM list). The first entry of the MPM list is the Planar mode. Following the Planar mode, the MPM list may include intra modes of the left, top, bottom-left, top-right, and top-left neighboring blocks, including positions L, A, BL, AR, and AL, as illustrated in FIG. 8. Subsequently, modes derived by adding or subtracting offsets to some of the modes of the neighboring blocks (e.g., the first two modes) may be included.

[0101] Although this can be somewhat mitigated by more neighboring intra modes and modes derived from them, the way ECM constructs its MPM list can also lead to inefficient coding of intra prediction modes for the current block that has correlations with non-adjacent blocks rather than adjacent blocks.

[0102] According to one aspect of the present disclosure, a video encoder and a video decoder can derive an HMPM list for a current block of video data using intra prediction modes of blocks already encoded / decoded before the current block, and use the HMPM list to construct an MPM list for the current block. The blocks already encoded / decoded before the current block can include blocks adjacent to the current block and blocks not adjacent to the current block. An intra prediction mode in the HMPM list can be referred to as an 'HMPM candidate'. The video encoder and the video decoder can add at least one HMPM candidate in the HMPM list to the MPM list.

[0103] The HMPM list can be constructed based on the intra prediction modes of blocks that have already been encoded / decoded before the current block. The items of the HMPM list can be composed of intra prediction modes stored as integer values. The length of the HMPM list can have a predefined value (e.g., 6, 16, 21, etc.). That is, the HMPM list can include a fixed number of entries. In some embodiments, the length of the HMPM list can also be set by a higher-level syntax, such as a picture header or a slice header.

[0104] The HMPM list can be implemented as a FIFO table or derived based on a FIFO table. For example, the HMPM list for the current block can be obtained by directly using the FIFO table entries or by performing a reordering process on the FIFO table entries described below. The length of the FIFO table can be equal to the length of the HMPM list.

[0105] The FIFO table can be maintained during the encoding and decoding processes. The video encoder and video decoder can add the intra prediction mode of the block to the end of the FIFO table each time they encode / decode a block based on intra prediction.

[0106] Once a FIFO table is fully populated, adding a new entry to the FIFO table can always result in removing an entry from the FIFO table. When adding a new entry, the new entry can be added to the end of the FIFO table. If there is no existing entry with the same value in the FIFO table before the new entry is added, the first entry in the FIFO table can be removed. If there is an existing entry with the same value in the FIFO table before the new entry is added, the existing entry can be removed from the FIFO table.

[0107] In some embodiments, if there is an existing entry with the same value in the FIFO table before a new entry is added, the new entry may not be added to the FIFO table, or an entry with a value that is equal to the new entry plus a predefined offset (e.g., -1) may be added to the FIFO table.

[0108] The FIFO table may be initialized on a per-picture, per-slice, per-tile, per-CTU row, or per-CTU basis. For example, when a new slice is discovered, the FIFO table may be emptied. Alternatively, when a new slice is discovered, the FIFO table may be filled with predefined directional modes. Accordingly, the HMPM list of the current block may be constructed based on the intra prediction modes of already encoded / decoded blocks within a specific range, where the specific range (which may also be referred to as a search region) may be the current picture, the current slice, the current tile, the current CTU row, or the current CTU.

[0109] The intra prediction mode of a block already encoded / decoded before the current block may be a directional mode or a non-directional mode (DC mode, Planar mode). Since the first entry of the MPM list is always fixed to the Planar mode, the HMPM list used to construct the MPM list does not need to include the Planar mode. Therefore, even if a block already encoded / decoded in the Planar mode is encountered before the current block, the FIFO table may not be changed (i.e., the Planar mode may not be added to the last entry of the FIFO table). In some embodiments, whenever a block encoded / decoded only in the directional mode is encountered before the current block, that directional mode may be added to the last entry of the FIFO table.

[0110] The video encoder and the video decoder may insert the entries of the most recently updated FIFO table into the HMPM list in the same order to construct or derive the HMPM list for the current block. In this case, the video encoder and the video decoder may insert one or more HMPM candidates into the MPM list starting from the last entry of the HMPM list (i.e., the intra prediction mode that was most recently added to the FIFO table). In a variant, the video encoder and the video decoder may insert the entries of the most recently updated FIFO table into the HMPM list in the opposite order. In this case, the video encoder and the video decoder may insert one or more HMPM candidates into the MPM list starting from the first entry of the HMPM list (i.e., the intra prediction mode that was most recently added to the FIFO table).

[0111] In some embodiments, the intra prediction modes in the FIFO table may undergo a reordering process to generate or derive an HMPM list for the current block. For example, a video encoder and a video decoder may generate an initial HMPM list that includes the intra prediction modes in the recently updated FIFO table, and perform a reordering process on the initial HMPM list to generate a final HMPM list to be used in constructing the MPM list for the current block. For the reordering, each intra prediction mode in the initial HMPM list may be tested against a template of the current block. The intra prediction modes in the initial HMPM list may be reordered based on the difference between the prediction and reconstruction of the template.

[0112] Figure 9 illustrates four template shapes that can be used for HMPM list reordering. Figure 9 (a) illustrates an L-shaped template that includes an above part, an above-left part, and a left part. Figure 9 (b) illustrates a template that includes only the above part. Figure 9 (c) illustrates a template that includes only the left part. Figure 9 (d) illustrates a template that includes the above part and the left part, but not the above-left part. The above part and the left part together form a template.

[0113] Here, the upper part is a set of reconstructed upper samples of size W×T1 neighboring the current block of size W×H, and the left part is a set of reconstructed left samples of size T2×H neighboring the current block. The upper-left part is a set of reconstructed upper-left samples of size T2×T1 neighboring the current block. The parameters T1 and T2, which specify the size of the template, can be predefined values ​​(e.g., 1, 2, 4, etc.) or signaled at a higher level, such as a picture header or a slice header.

[0114] Figure 10 is a conceptual diagram illustrating a method for calculating the sum of absolute difference (SAD) cost based on the difference between the template prediction and reconstruction for HMPM list reordering. Figure 11 is a conceptual diagram illustrating a method for sorting the HMPM list in ascending order based on the template-based SAD cost.

[0115] A video encoder and a video decoder can derive prediction samples for a template from reference samples of the template using each intra prediction mode in the HMPM list, and compute a SAD cost for each intra prediction mode based on differences between the prediction samples of the template and the reconstructed samples of the template. The video encoder and the video decoder can reorder the individual intra prediction modes in the HMPM list in ascending order according to their respective SAD costs. In addition to SAD, other cost functions such as SATD (sum of absolute transformed difference) and MR-SAD (mean removed sum of absolute difference) can be used.

[0116] If the intra prediction modes in the HMPM list are sorted in ascending order according to their SAD costs, the video encoder and the video decoder can insert one or more HMPM candidates into the MPM list, starting from the first entry in the HMPM list (i.e., the intra prediction mode with the minimum SAD cost).

[0117] Various methods may be considered when using at least one HMPM candidate in the HMPM list to construct an MPM list. For example, HMPM candidates in the HMPM list may be added to the MPM list until the MPM list is full. For another example, all HMPM candidates in the HMPM list may be added to the MPM list as long as they do not overlap with modes already in the MPM list. For another example, a predefined number of HMPM candidates (e.g., three or five HMPM candidates) in the HMPM list may be added to the MPM list. For another example, the number of HMPM candidates in the HMPM list to be added to the MPM list may be signaled in a high-level syntax, such as a picture header, a slice header, etc. If an HMPM candidate in the HMPM list already exists in the MPM list, an HMPM candidate in a subsequent entry in the HMPM list may be added to the MPM list.

[0118] An HMPM candidate may be added before the derived intra modes and after the neighboring intra modes in the MPM list. In some embodiments, it may be added before the default intra modes and after the derived intra modes.

[0119] Figure 12 is a conceptual diagram illustrating a method of adding an intra prediction mode within the HMPM list to the MPM list. In the example of Figure 12, the Planar mode (fixed), mode 18 (left neighbor mode), and mode 34 (upper neighbor mode) are already included in the MPM list of the current block, and modes 50, 27, and 19 in the HMPM list are subsequently added to the MPM list. Since the second entry in the HMPM list, mode 18 (with HMPM index 1), and the fourth entry, mode 34 (with HMPM index 3), already exist in the MPM list, these two modes are not added to the MPM list again.

[0120] FIG. 13 is a flowchart illustrating a method of coding (encoding or decoding) video data according to one embodiment of the present disclosure.

[0121] The video encoder and the video decoder can derive an HMPM list for the current block using intra prediction modes of blocks decoded before the current block (S1310).

[0122] The HMPM list can be derived based on a FIFO table. The FIFO table can be configured to add the intra prediction mode of the intra-coded block to the last entry of the FIFO table whenever an intra-coded block is encountered.

[0123] As part of deriving the HMPM list for the current block, the video encoder and the video decoder add a plurality of intra prediction modes in the FIFO table to the HMPM list. Then, for each intra prediction mode (HMPM candidate) in the HMPM table, a cost for each HMPM candidate can be determined based on differences between prediction samples for the template of the current block and reconstructed samples for the template of the current block. Here, the prediction samples for the template can be generated based on reference samples of the template using the individual HMPM candidate. The video encoder and the video decoder can sort the plurality of HMPM candidates in the HMPM list in ascending order according to their respective costs. Thus, after sorting, the first entry in the HMPM list may be the HMPM candidate with the minimum cost.

[0124] Among multiple HMPM candidates within the HMPM list, candidates with lower costs are preferentially inserted into the MPM list. Therefore, HMPM candidates that better match the template prediction of the current block are likely to be inserted into the MPM list first.

[0125] The size of the HMPM list can have a predefined value. Alternatively, the size of the HMPM list can be indicated at a higher level, such as the header of the picture or slice to which the current block belongs. The HMPM list can be reset on a per-picture, per-slice, per-tile, per-CTU row, or per-CTU basis.

[0126] The video encoder and video decoder can construct an MPM list for the current block (S1320).

[0127] To construct an MPM list, the video encoder and the video decoder can insert at least one HMPM candidate from the HMPM list into the MPM list. Furthermore, the video encoder and the video decoder can insert one or more spatial neighboring candidates, which are intra prediction modes derived from neighboring blocks of the current block, into the MPM list. Here, the one or more spatial neighboring candidates can be inserted before at least one HMPM candidate from the HMPM list in the MPM list.

[0128] The video encoder and video decoder may insert the Planar mode as the first entry in the MPM list. In such a case, the HMPM list may be configured not to include the Planar mode. For example, the FIFO table may be configured to add the intra prediction mode of the intra-coded block to the last entry of the FIFO table whenever the FIFO table encounters an intra-coded block as a decoded block before the current block, only if the intra prediction mode of the intra-coded block is a directional mode.

[0129] A video encoder can encode an intra prediction mode of a current block using an MPM list, and a video decoder can decode an intra prediction mode of a current block using an MPM list (S1330). The video encoder and the video decoder can predict the current block using an intra prediction mode selected from the MPM list or an intra prediction mode selected from a non-MPM list. The video encoder and the video decoder can update the FIFO table by adding the intra prediction mode of the current block to the FIFO table.

[0130] 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.

[0131] 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.

[0132] 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).

[0133] 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.

[0134] CROSS-REFERENCE TO RELATED APPLICATION

[0135] This patent application claims priority to Korean Patent Application No. 10-2024-0050290, filed April 15, 2024, and Korean Patent Application No. 10-2025-0040869, filed March 31, 2025, the entire contents of which are incorporated herein by reference.

Claims

1. A method for decrypting video data, A step of constructing a history-based MPM (HMPM) list for the current block using intra prediction modes of blocks decrypted before the current block; A step of constructing an MPM list for the current block; and A step of decoding the intra prediction mode of the current block using the above MPM list. A method comprising: a step of constructing the MPM list, wherein the step of constructing the MPM list comprises a step of inserting at least one intra prediction mode from the HMPM list into the MPM list.

2. In paragraph 1, The steps for constructing the above MPM list are: A method comprising the step of inserting one or more spatial neighbor candidates, which are intra prediction modes derived from neighboring blocks of the current block, into the MPM list, wherein the one or more spatial neighbor candidates are inserted into the MPM list before at least one intra prediction mode from the HMPM list.

3. In paragraph 1, The method characterized in that the HMPM list is derived based on a FIFO table, and the FIFO table is configured to add the intra prediction mode of the intra-coded block to the last entry of the FIFO table whenever an intra-coded block is encountered.

4. In paragraph 3, The steps for constructing the HMPM list for the current block above are: A step of adding multiple intra prediction modes in the FIFO table to the HMPM list. For each intra prediction mode in the HMPM list, generating prediction samples for the template based on reference samples of the template of the current block and using the individual intra prediction modes, and determining a cost for the individual intra prediction mode based on differences between the prediction samples for the template and reconstructed samples for the template; and A step of sorting the multiple intra prediction modes in the above HMPM list in ascending order according to their respective costs. A method comprising:

5. In paragraph 4, A method characterized in that among the multiple intra prediction modes in the HMPM list, the one with the smaller cost is inserted first into the MPM list.

6. In paragraph 3, A method characterized in that the size of the above HMPM list is indicated in the header of the picture to which the current block belongs or the header of the slice.

7. In paragraph 3, A method characterized in that the size of the above HMPM list has a predefined value.

8. In paragraph 3, A method, characterized in that the above HMPM list is reset in units of pictures, slices, tiles, CTU rows or CTUs.

9. In paragraph 3, A method characterized in that the first entry of the above MPM list is in Planar mode, and the FIFO table is configured not to include the Planar mode.

10. In paragraph 3, The above FIFO table is, A method characterized in that, whenever an intra-coded block is encountered as a decoded block prior to the current block, the intra-prediction mode of the intra-coded block is added to the last entry of the FIFO table only when the intra-prediction mode of the intra-coded block is a directional mode.

11. A method for encoding video data, A step of deriving an HMPM list for the current block by using intra prediction modes of blocks encoded before the current block; A step of constructing an MPM list for the current block; and A step of encoding the intra prediction mode of the current block using the above MPM list. A method comprising: a step of constructing the MPM list, wherein the step of constructing the MPM list comprises a step of inserting at least one intra prediction mode from the HMPM list into the MPM list.

12. In paragraph 11, The method characterized in that the HMPM list is derived based on a FIFO table, and the FIFO table is configured to add the intra prediction mode of the intra-coded block to the last entry of the FIFO table whenever an intra-coded block is encountered.

13. In paragraph 12, The step of deriving the HMPM list for the current block above is: For each intra prediction mode among the plurality of intra prediction modes in the FIFO table, generating prediction samples for the template based on reference samples of the template of the current block and using the individual intra prediction modes, and determining a cost for the individual intra prediction mode based on differences between the prediction samples for the template and reconstructed samples for the template; and A step of adding the plurality of intra prediction modes to the HMPM list in ascending order according to the respective costs of the plurality of intra prediction modes. A method comprising:

14. 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 bitstream to the video decoding device Including, The step of encoding the above video data into a bitstream is: A step of deriving an HMPM list for the current block by using intra prediction modes of blocks encoded before the current block; A step of constructing an MPM list for the current block; and A step of encoding the intra prediction mode of the current block using the above MPM list. A method comprising: a step of constructing the MPM list, wherein the step of constructing the MPM list comprises a step of inserting at least one intra prediction mode from the HMPM list into the MPM list.

Images