CN118140476A

CN118140476A - Method and apparatus for video encoding and decoding using geometric intra prediction modes

Info

Publication number: CN118140476A
Application number: CN202280070919.0A
Authority: CN
Inventors: 安镕照; 李钟石; 许镇; 朴胜煜
Original assignee: Hyundai Motor Co; Kia Corp; DigitalInsights Inc
Current assignee: Hyundai Motor Co; Kia Corp; DigitalInsights Inc
Priority date: 2021-10-25
Filing date: 2022-09-05
Publication date: 2024-06-04

Abstract

A video encoding and decoding method and apparatus using geometric intra prediction modes are disclosed, and a video encoding and decoding method and apparatus are provided in an embodiment of the present invention, which generates two intra predictors by using two different intra prediction modes, and then generates a final intra predictor by weighted summing the two intra predictors by using weights of pixel units based on geometric block partitioning.

Description

Method and apparatus for video encoding and decoding using geometric intra prediction modes

Technical Field

The present invention relates to a video encoding and decoding method and apparatus using geometric intra prediction modes.

Background

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

Since video data has a large amount of data compared to audio data or still image data, the video data requires a large amount of hardware resources (which includes a memory) to store or transmit uncompressed video data.

Accordingly, encoders are typically used to compress and store or transmit video data. The decoder receives compressed video data, decompresses the received compressed video data, and plays the decompressed video data. Video compression techniques include h.264/AVC, high Efficiency Video Coding (HEVC), and Versatile Video Coding (VVC) which increases the Coding efficiency of HEVC by about 30% or more.

However, as the image size, resolution, and frame rate gradually increase, the amount of data to be encoded also increases. Accordingly, new compression techniques that provide higher codec efficiency and improved image enhancement effects than existing compression techniques are needed.

Intra prediction techniques when performing prediction on a current block generate a prediction signal using spatially adjacent neighboring pixels of the current block in the same image. In the conventional video encoding/decoding method and apparatus, in order to improve the codec performance of the intra prediction technique, an increased number of intra prediction modes are used or filtering is applied to spatially adjacent neighboring pixels for intra prediction. These intra prediction techniques have relatively low performance of generating a prediction signal compared to inter prediction techniques due to the constraint of utilizing limited pixels in the same image as the current block when generating the prediction signal.

In order to provide predictive performance of intra prediction, multiple line buffers may be utilized in addition to spatially adjacent pixels. For example, multi-reference line (MRL) intra-prediction techniques select pixels of one or more lines located at a particular distance to perform intra-prediction. Matrix WEIGHTED INTRA Prediction (MIP) techniques also exist that generate an intra-Prediction signal by using a product operation between neighboring pixels and a predefined Matrix. Accordingly, in order to increase video coding efficiency and enhance video quality, further improvement of the intra prediction method is required.

Disclosure of Invention

Technical problem

The present invention has been made in an effort to provide a video encoding and decoding method and apparatus that generates two intra prediction factors by using two different intra prediction modes when a geometric intra prediction mode is applied. Video encoding and decoding methods and apparatus use pixel-level weights based on geometric block partitions to weight sum two intra predictors to generate a final intra predictor.

Technical proposal

At least one aspect of the present disclosure provides a method performed by a video decoding device for intra-predicting a current block. The method includes decoding a geometric intra prediction flag from a bitstream, the geometric intra prediction flag indicating whether a geometric intra prediction mode is used for a current block, and checking the geometric intra prediction flag. If the geometric intra-prediction flag is true, the method further includes decoding the geometric partition information index, the first intra-prediction mode index, and the second intra-prediction mode index from the bitstream. The method further includes generating a list including prediction modes for intra prediction of the current block. The method further includes selecting a first intra-prediction mode from a list of prediction modes by using the first intra-prediction mode index, and generating a first intra-predictor for the current block by using pixels spatially adjacent to the current block based on the first intra-prediction mode. The method further includes selecting a second intra-prediction mode from the list of prediction modes by using the second intra-prediction mode index, and generating a second intra-predictor for the current block by using pixels spatially adjacent to the current block based on the second intra-prediction mode. The method further includes obtaining weights by indexing with the geometric partition information, the weights including a first weight for the first intra-predictor and a second weight for the second intra-predictor, and generating a final intra-predictor for the current block by weighted summing the first intra-predictor and the second intra-predictor with the weights.

Another aspect of the present invention provides a method performed by a video encoding device for intra-predicting a current block. The method includes determining a geometric intra prediction flag indicating whether a geometric intra prediction mode is used for a current block, and checking the geometric intra prediction flag. If the geometric intra prediction flag is true, the method further includes determining a geometric partition information index and generating a list including intra prediction modes for intra prediction of the current block. The method further includes determining a first intra-prediction mode, and for the first intra-prediction mode, determining a first intra-prediction mode index from a list of intra-prediction modes. The method further includes generating a first intra-prediction factor for the current block by utilizing pixels spatially adjacent to the current block based on the first intra-prediction mode. The method further includes determining a second intra-prediction mode, and for the second intra-prediction mode, determining a second intra-prediction mode index from the list of intra-prediction modes. The method further includes generating a second intra-prediction factor for the current block by utilizing pixels spatially adjacent to the current block based on the second intra-prediction mode. The method further includes obtaining weights by indexing with the geometric partition information, the weights including a first weight for the first intra-predictor and a second weight for the second intra-predictor, and generating a final intra-predictor for the current block by weighted summing the first intra-predictor and the second intra-predictor with the weights.

Still another aspect of the present invention provides a computer-readable recording medium storing a bitstream generated by a video encoding method. The video encoding method includes determining a geometric intra prediction flag indicating whether a geometric intra prediction mode is used for a current block, and checking the geometric intra prediction flag. If the geometric intra prediction flag is true, the video encoding method further includes determining a geometric partition information index and generating a list including intra prediction modes for intra prediction of the current block. The video encoding method further includes determining a first intra-prediction mode, and for the first intra-prediction mode, determining a first intra-prediction mode index from a list of intra-prediction modes. The video encoding method further includes generating a first intra predictor of the current block by using pixels spatially adjacent to the current block based on the first intra prediction mode. The video encoding method further includes determining a second intra-prediction mode, and for the second intra-prediction mode, determining a second intra-prediction mode index from the list of intra-prediction modes. The video encoding method further includes generating a second intra predictor for the current block by using pixels spatially adjacent to the current block based on the second intra prediction mode. The video encoding method further includes obtaining weights by indexing with the geometric partition information, the weights including a first weight for the first intra-predictor and a second weight for the second intra-predictor, and generating a final intra-predictor for the current block by weighted summing the first intra-predictor and the second intra-predictor with the weights.

Advantageous effects

As described above, the present invention provides a video encoding and decoding method and apparatus that generates two intra prediction factors by using two different intra prediction modes when a geometric intra prediction mode is applied. Video coding methods and apparatus use pixel-level weights based on geometric block partitions to generate a final intra-predictor from two intra-predictors. Accordingly, the video encoding and decoding method and apparatus improve video encoding efficiency and enhance video quality.

Furthermore, the present invention provides a video encoding and decoding method and apparatus for generating a final intra predictor from two different intra predictors by using pixel level weights. When the geometric intra prediction mode is applied, the video encoding and decoding method and apparatus can utilize the effect of arbitrary block partitions generated by the mixing process of analog geometric block partitions.

Drawings

Fig. 1 is a block diagram of a video encoding device in which the techniques of the present invention may be implemented.

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

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

Fig. 4 shows neighboring blocks of the current block.

Fig. 5 is a block diagram of a video decoding apparatus in which the techniques of the present invention may be implemented.

Fig. 6 is a block diagram illustrating an intra prediction factor generating device according to at least one embodiment of the present invention.

Fig. 7 is a schematic diagram illustrating an application of a geometric intra prediction mode according to at least one embodiment of the present invention.

Fig. 8 is a schematic diagram illustrating a mixing process of two predictors according to at least one embodiment of the present invention.

Fig. 9a and 9b are schematic diagrams depicting straight lines of aliquoting blocks in accordance with at least one embodiment of the present invention.

Fig. 10 is a flowchart of an intra prediction method performed by a video encoding device according to at least one embodiment of the present disclosure.

Fig. 11 is a flowchart of an intra prediction method performed by a video decoding apparatus according to at least one embodiment of the present invention.

Detailed Description

Hereinafter, some embodiments of the present invention will be described in detail with reference to the accompanying illustrative drawings. In the following description, like reference numerals denote like elements, although the elements are shown in different drawings. Furthermore, in the following description of some embodiments, detailed descriptions of related known components and functions may be omitted for clarity and conciseness when it may be considered that the subject matter of the present invention is obscured.

Fig. 1 is a block diagram of a video encoding device in which the techniques of the present invention may be implemented. Hereinafter, a video encoding apparatus and components of the apparatus are described with reference to the diagram of fig. 1.

The encoding apparatus may include: an image divider 110, a predictor 120, a subtractor 130, a transformer 140, a quantizer 145, a reordering unit 150, an entropy encoder 155, an inverse quantizer 160, an inverse transformer 165, an adder 170, a loop filtering unit 180, and a memory 190.

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

A video is made up of one or more sequences comprising a plurality of images. Each image is divided into a plurality of regions, and encoding is performed on each region. For example, an image is segmented into one or more tiles (tiles) or/and slices (slices). Here, one or more tiles may be defined as a tile set. Each tile or/and slice is partitioned into one or more Coding Tree Units (CTUs). In addition, each CTU is partitioned into one or more Coding Units (CUs) by a tree structure. Information applied to each Coding Unit (CU) is encoded as a syntax of the CU, and information commonly applied to the CUs included in one CTU is encoded as a syntax of the CTU. In addition, information commonly applied to all blocks in one slice is encoded as a syntax of a slice header, and information applied to all blocks constituting one or more images is encoded as an image parameter set (Picture PARAMETER SET, PPS) or an image header. In addition, information commonly referred to by a plurality of images is encoded as a Sequence parameter set (Sequence PARAMETER SET, SPS). In addition, information commonly referenced by one or more SPS is encoded as a Video parameter set (Video PARAMETER SET, VPS). Furthermore, information commonly applied to one tile or group of tiles may also be encoded as syntax of the tile or group of tiles header. The syntax included in the SPS, PPS, slice header, tile, or tile set header may be referred to as a high level syntax.

The image divider 110 determines the size of a Coding Tree Unit (CTU). Information about the size of the CTU (CTU size) is encoded as a syntax of the SPS or PPS and transmitted to the video decoding apparatus.

The image divider 110 divides each image constituting a video into a plurality of Coding Tree Units (CTUs) having a predetermined size, and then recursively divides the CTUs by using a tree structure. Leaf nodes in the tree structure become Coding Units (CUs), which are the basic units of coding.

The tree structure may be a quadtree (quadtree, QT) in which a higher node (or parent node) is partitioned into four lower nodes (or child nodes) of the same size. The tree structure may also be a binary tree (binarytree, BT) in which a higher node is split into two lower nodes. The tree structure may also be a trigeminal tree (ternarytree, TT) in which the higher node is split into three lower nodes at a ratio of 1:2:1. The tree structure may also be a structure in which two or more of a QT structure, a BT structure, and a TT structure are mixed. For example, a quad-plus-binary tree (quadtree plus binarytree, QTBT) structure may be used, or a quad-plus-binary tree (quadtree plus binarytree ternarytree, QTBTTT) structure may be used. Here, a Binary Tree Trigeminal Tree (BTTT) is added to the tree structure to be called a multiple-type tree (MTT).

Fig. 2 is a schematic diagram for describing a method of dividing a block by using QTBTTT structures.

As shown in fig. 2, the CTU may be first partitioned into QT structures. Quadtree partitioning may be recursive until the size of the partitioned block reaches the minimum block size of leaf nodes allowed in QT (MinQTSize). A first flag (qt_split_flag) indicating whether each node of the QT structure is partitioned into four lower-layer nodes is encoded by the entropy encoder 155 and signaled to the video decoding apparatus. When the leaf node of QT is not greater than the maximum block size (MaxBTSize) of the root node allowed in BT, the leaf node may be further partitioned into at least one of BT structure or TT structure. There may be multiple directions of segmentation in the BT structure and/or the TT structure. For example, there may be two directions, i.e., a direction of dividing the block of the corresponding node horizontally and a direction of dividing the block of the corresponding node vertically. As shown in fig. 2, when the MTT division starts, a second flag (MTT _split_flag) indicating whether a node is divided, and a flag additionally indicating a division direction (vertical or horizontal) and/or a flag indicating a division type (binary or trigeminal) in case that a node is divided are encoded by the entropy encoder 155 and signaled to the video decoding apparatus.

Alternatively, a CU partition flag (split_cu_flag) indicating whether a node is partitioned may be further encoded before encoding a first flag (qt_split_flag) indicating whether each node is partitioned into four nodes of a lower layer. When the value of the CU partition flag (split_cu_flag) indicates that each node is not partitioned, the block of the corresponding node becomes a leaf node in the partition tree structure and becomes a CU, which is a basic unit of encoding. When the value of the CU partition flag (split_cu_flag) indicates that each node is partitioned, the video encoding apparatus first starts encoding the first flag in the above scheme.

When QTBT is used as another example of the tree structure, there may be two types, i.e., a type of horizontally dividing a block of a corresponding node into two blocks having the same size (i.e., symmetrical horizontal division) and a type of vertically dividing a block of a corresponding node into two blocks having the same size (i.e., symmetrical vertical division). A partition flag (split_flag) indicating whether each node of the BT structure is partitioned into lower-layer blocks and partition type information indicating a partition type are encoded by the entropy encoder 155 and transmitted to the video decoding apparatus. On the other hand, there may additionally be a type in which a block of a corresponding node is divided into two blocks asymmetric to each other. The asymmetric form may include a form in which a block of a corresponding node is divided into two rectangular blocks having a size ratio of 1:3, or may also include a form in which a block of a corresponding node is divided in a diagonal direction.

The CUs may have various sizes according to QTBT or QTBTTT divided from the CTU. Hereinafter, a block corresponding to a CU to be encoded or decoded (i.e., a leaf node of QTBTTT) is referred to as a "current block". When QTBTTT partitions are used, the shape of the current block may be rectangular in shape in addition to square in shape.

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

In general, each of the current blocks in the image may be predictively encoded. In general, prediction of a current block may be performed by using an intra prediction technique using data from an image including the current block or an inter prediction technique using data from an image encoded before the image including the current block. Inter prediction includes both unidirectional prediction and bi-directional prediction.

The intra predictor 122 predicts pixels in the current block by using pixels (reference pixels) located adjacent to the current block in the current image including the current block. Depending on the prediction direction, there are multiple intra prediction modes. For example, as shown in fig. 3a, the plurality of intra prediction modes may include two non-directional modes including a Planar (Planar) mode and a DC mode, and may include 65 directional modes. The neighboring pixels and algorithm equations to be used are defined differently according to each prediction mode.

For efficient direction prediction of a current block having a rectangular shape, direction modes (# 67 to # 80) indicated by dotted arrows in fig. 3b, intra prediction modes # -1 to # -14) may be additionally used. The direction mode may be referred to as a "wide-angle intra prediction mode (WIDE ANGLE INTRA-prediction modes)". In fig. 3b, the arrows indicate the respective reference samples for prediction, rather than representing the prediction direction. The prediction direction is opposite to the direction indicated by the arrow. When the current block has a rectangular shape, the wide-angle intra prediction mode is a mode in which prediction is performed in a direction opposite to a specific direction mode without additional bit transmission. In this case, in the wide-angle intra prediction mode, some of the wide-angle intra prediction modes available for the current block may be determined by a ratio of a width to a height of the current block having a rectangular shape. For example, when the current block has a rectangular shape having a height smaller than a width, wide-angle intra prediction modes (intra prediction modes #67 to # 80) having angles smaller than 45 degrees are available. When the current block has a rectangular shape with a width greater than a height, a wide-angle intra prediction mode having an angle greater than-135 degrees is available.

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

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

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

The inter predictor 124 may also perform interpolation of reference pictures or reference blocks to increase the accuracy of prediction. In other words, the sub-samples are interpolated between two consecutive integer samples by applying the filter coefficients to a plurality of consecutive integer samples comprising the two integer samples. When the process of searching for a block most similar to the current block is performed on the interpolated reference image, the decimal-unit precision may be represented for the motion vector instead of the integer-sample-unit precision. The precision or resolution of the motion vector may be set differently for each target region to be encoded, e.g., a unit such as a slice, tile, CTU, CU, etc. When such an adaptive motion vector resolution (adaptive motion vector resolution, AMVR) is applied, information on the motion vector resolution to be applied to each target area should be signaled for each target area. For example, when the target area is a CU, information about the resolution of a motion vector applied to each CU is signaled. The information on the resolution of the motion vector may be information representing the accuracy of a motion vector difference to be described below.

On the other hand, the inter predictor 124 may perform inter prediction by using bi-directional prediction. In the case of bi-prediction, two reference pictures and two motion vectors representing block positions most similar to the current block in each reference picture are used. The inter predictor 124 selects a first reference picture and a second reference picture from the reference picture list0 (RefPicList 0) and the reference picture list1 (RefPicList 1), respectively. The inter predictor 124 also searches for a block most similar to the current block in the corresponding reference picture to generate a first reference block and a second reference block. Further, a prediction block of the current block is generated by averaging or weighted-averaging the first reference block and the second reference block. Further, motion information including information on two reference pictures for predicting the current block and including information on two motion vectors is transmitted to the entropy encoder 155. Here, the reference image list0 may be constituted by an image preceding the current image in display order among the pre-reconstructed images, and the reference image list1 may be constituted by an image following the current image in display order among the pre-reconstructed images. However, although not particularly limited thereto, a pre-reconstructed image following the current image in the display order may be additionally included in the reference image list 0. Conversely, a pre-reconstructed image preceding the current image may be additionally included in the reference image list 1.

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

For example, when a reference image and a motion vector of a current block are identical to those of a neighboring block, information capable of identifying the neighboring block is encoded to transmit motion information of the current block to a video decoding apparatus. This method is called merge mode (merge mode).

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

As the neighboring blocks used to derive the merge 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 image may be used, as shown in fig. 4. In addition, in addition to the current picture in which the current block is located, a block located within a reference picture (which may be the same as or different from the reference picture used to predict the current block) may also be used as a merging candidate. For example, a co-located block (co-located block) of a current block within a reference picture or a block adjacent to the co-located block may additionally be used as a merging candidate. If the number of merging candidates selected by the above method is less than a preset number, a zero vector is added to the merging candidates.

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

The merge skip mode is a special case of the merge mode. After quantization, when all transform coefficients used for entropy coding are near zero, only neighboring block selection information is transmitted without transmitting a residual signal. By using the merge skip mode, relatively high encoding efficiency can be achieved for images with slight motion, still images, screen content images, and the like.

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

Another method for encoding motion information is advanced motion vector prediction (advanced motion vector prediction, AMVP) mode.

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

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

Motion vector prediction may be obtained by applying a predefined function (e.g., median and average calculations, etc.) to the motion vector prediction candidates. In this case, the video decoding device is also aware of the predefined function. Further, since the neighboring block used to derive the motion vector prediction candidates is a block for which encoding and decoding have been completed, the video decoding apparatus may also already know the motion vector of the neighboring block. Therefore, the video encoding device does not need to encode information for identifying motion vector prediction candidates. Accordingly, in this case, information on a motion vector difference and information on a reference image for predicting a current block are encoded.

On the other hand, motion vector prediction may also be determined by selecting a scheme of any one of the motion vector prediction candidates. In this case, the information for identifying the selected motion vector prediction candidates is additionally encoded together with the information about the motion vector difference and the information about the reference picture for predicting the current block.

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

The transformer 140 transforms a residual signal in a residual block having pixel values of a spatial domain into transform coefficients of a frequency domain. The transformer 140 may transform a residual signal in a residual block by using the entire size of the residual block as a transform unit, or may divide the residual block into a plurality of sub-blocks, and may perform the transform by using the sub-blocks as transform units. Alternatively, the residual block is divided into two sub-blocks, i.e., a transform region and a non-transform region, to transform the residual signal by using only the transform region sub-block as a transform unit. Here, the transform region sub-block may be one of two rectangular blocks having a size ratio of 1:1 based on a horizontal axis (or a vertical axis). In this case, a flag (cu_sbt_flag) indicating that only the sub-block is transformed, and direction (vertical/horizontal) information (cu_sbt_horizontal_flag) and/or position information (cu_sbt_pos_flag) are encoded by the entropy encoder 155 and signaled to the video decoding apparatus. In addition, the size of the transform region sub-block may have a size ratio of 1:3 based on the horizontal axis (or vertical axis). In this case, a flag (cu_sbt_quad_flag) dividing the corresponding division is additionally encoded by the entropy encoder 155 and signaled to the video decoding device.

On the other hand, the transformer 140 may perform transformation of the residual block separately in the horizontal direction and the vertical direction. For this transformation, various types of transformation functions or transformation matrices may be used. For example, the pair-wise transformation function for horizontal and vertical transformations may be defined as a transformation set (multiple transform set, MTS). The transformer 140 may select one transform function pair having the highest transform efficiency among the MTSs, and may transform the residual block in each of the horizontal and vertical directions. Information (mts_idx) about the transform function pairs in the MTS is encoded by the entropy encoder 155 and signaled to the video decoding means.

The quantizer 145 quantizes the transform coefficient output from the transformer 140 using a quantization parameter, and outputs the quantized transform coefficient to the entropy encoder 155. The quantizer 145 may also immediately quantize the relevant residual block without transforming any block or frame. The quantizer 145 may also apply different quantization coefficients (scaling values) according to the positions of the transform coefficients in the transform block. A quantization matrix applied to quantized transform coefficients arranged in two dimensions may be encoded and signaled to a video decoding apparatus.

The reordering unit 150 may perform the rearrangement of the coefficient values on the quantized residual values.

The rearrangement unit 150 may change the 2D coefficient array to a 1D coefficient sequence by using coefficient scanning. For example, the rearrangement unit 150 may scan the DC coefficients to the coefficients of the high frequency region using zigzag scanning (zig-zag scan) or diagonal scanning (diagonal scan) to output a 1D coefficient sequence. Instead of the zig-zag scan, a vertical scan that scans the 2D coefficient array in the column direction and a horizontal scan that scans the 2D block type coefficients in the row direction may also be utilized, depending on the size of the transform unit and the intra prediction mode. In other words, the scanning method to be used may be determined in zigzag scanning, diagonal scanning, vertical scanning, and horizontal scanning according to the size of the transform unit and the intra prediction mode.

The entropy encoder 155 encodes the sequence of the 1D quantized transform coefficients output from the rearrangement unit 150 by using various encoding schemes including Context-based adaptive binary arithmetic coding (Context-based Adaptive Binary Arithmetic Code, CABAC), exponential golomb (Exponential Golomb), and the like to generate a bitstream.

Further, the entropy encoder 155 encodes information related to block division (e.g., CTU size, CTU division flag, QT division flag, MTT division type, MTT division direction, etc.) so that the video decoding apparatus can divide blocks equally to the video encoding apparatus. Further, the entropy encoder 155 encodes information on a prediction type indicating whether the current block is encoded by intra prediction or inter prediction. The entropy encoder 155 encodes intra prediction information (i.e., information about an intra prediction mode) or inter prediction information (a merge index in the case of a merge mode, and information about a reference picture index and a motion vector difference in the case of an AMVP mode) according to a prediction type. Further, the entropy encoder 155 encodes information related to quantization (i.e., information about quantization parameters and information about quantization matrices).

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

The adder 170 adds the reconstructed residual block and the prediction block generated by the predictor 120 to reconstruct the current block. Upon intra prediction of the next block, pixels in the reconstructed current block are used as reference pixels.

The loop filtering unit 180 performs filtering on the reconstructed pixels to reduce block artifacts (blocking artifacts), ringing artifacts (RINGING ARTIFACTS), blurring artifacts (blurring artifacts), and the like, which occur due to block-based prediction and transform/quantization. The loop filtering unit 180 as an in-loop filter may include all or some of a deblocking filter 182, a Sample Adaptive Offset (SAO) filter 184, and an adaptive loop filter (adaptive loop filter, ALF) 186.

Deblocking filter 182 filters boundaries between reconstructed blocks to remove block artifacts (blocking artifacts) that occur due to block unit encoding/decoding, and SAO filter 184 and ALF 186 additionally filter the deblock filtered video. The SAO filter 184 and ALF 186 are filters for compensating for differences between reconstructed pixels and original pixels that occur due to lossy encoding (lossy coding). The SAO filter 184 applies an offset as a CTU unit to enhance subjective image quality and coding efficiency. On the other hand, the ALF 186 performs block unit filtering, and applies different filters to compensate for distortion by dividing boundaries of respective blocks and the degree of variation. Information about filter coefficients to be used for ALF may be encoded and signaled to the video decoding apparatus.

The reconstructed blocks filtered by the deblocking filter 182, the SAO filter 184, and the ALF 186 are stored in a memory 190. When all blocks in one image are reconstructed, the reconstructed image may be used as a reference image for inter prediction of blocks within a subsequently to be encoded image.

Fig. 5 is a functional block diagram of a video decoding apparatus in which the techniques of the present invention may be implemented. Hereinafter, with reference to fig. 5, a video decoding apparatus and components of the apparatus are described.

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

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

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

The entropy decoder 510 determines the size of CTUs by extracting information about the CTU size from a Sequence Parameter Set (SPS) or a Picture Parameter Set (PPS), and partitions a picture into CTUs having the determined size. Further, the CTU is determined as the highest layer (i.e., root node) of the tree structure, and the partition information of the CTU is extracted to partition the CTU by using the tree structure.

For example, when dividing the CTU by using the QTBTTT structure, first a first flag (qt_split_flag) related to the division of QT is extracted to divide each node into four nodes of the lower layer. In addition, a second flag (MTT _split_flag), a split direction (vertical/horizontal), and/or a split type (binary/trigeminal) related to the split of the MTT are extracted with respect to a node corresponding to a leaf node of the QT to split the corresponding leaf node into an MTT structure. As a result, each node below the leaf node of QT is recursively partitioned into BT or TT structures.

As another example, when the CTU is divided by using the QTBTTT structure, a CU division flag (split_cu_flag) indicating whether to divide the CU is extracted. When the corresponding block is partitioned, a first flag (qt_split_flag) may also be extracted. During the segmentation process, recursive MTT segmentation of 0 or more times may occur after recursive QT segmentation of 0 or more times for each node. For example, for CTUs, MTT partitioning may occur immediately, or conversely, QT partitioning may occur only multiple times.

As another example, when the CTU is divided by using the QTBT structure, a first flag (qt_split_flag) related to the division of QT is extracted to divide each node into four nodes of a lower layer. In addition, a split flag (split_flag) indicating whether or not a node corresponding to a leaf node of QT is further split into BT and split direction information are extracted.

On the other hand, when the entropy decoder 510 determines the current block to be decoded by using the partition of the tree structure, the entropy decoder 510 extracts information on a prediction type indicating whether the current block is intra-predicted or inter-predicted. When the prediction type information indicates intra prediction, the entropy decoder 510 extracts syntax elements for intra prediction information (intra prediction mode) of the current block. When the prediction type information indicates inter prediction, the entropy decoder 510 extracts information representing syntax elements of the inter prediction information, i.e., a motion vector and a reference picture to which the motion vector refers.

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

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

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

The inverse transformer 530 reconstructs a residual signal by inversely transforming the inversely quantized transform coefficients from the frequency domain to the spatial domain to generate a residual block of the current block.

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

Further, when applying MTS, the inverse transformer 530 determines a transform index or a transform matrix to be applied in each of the horizontal direction and the vertical direction by using MTS information (mts_idx) signaled from the video encoding apparatus. The inverse transformer 530 also performs inverse transformation on the transform coefficients in the transform block in the horizontal direction and the vertical direction by using the determined transform function.

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

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

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

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

The loop filtering unit 560, which is an in-loop filter, may include a deblocking filter 562, an SAO filter 564, and an ALF 566. Deblocking filter 562 performs deblocking filtering on boundaries between reconstructed blocks to remove block artifacts that occur due to block unit decoding. The SAO filter 564 and ALF 566 perform additional filtering on the reconstructed block after deblocking filtering to compensate for differences between reconstructed pixels and original pixels that occur due to lossy encoding. The filter coefficients of the ALF are determined by using information on the filter coefficients decoded from the bitstream.

The reconstructed block filtered by the deblocking filter 562, the SAO filter 564, and the ALF 566 is stored in a memory 570. When all blocks in one image are reconstructed, the reconstructed image may be used as a reference image for inter prediction of blocks within a subsequently to be encoded image.

In some embodiments the invention relates to encoding and decoding video imagery as described above. More particularly, the present invention provides a video encoding and decoding method and apparatus for generating two intra prediction factors by using two different intra prediction modes. Video coding methods and apparatus generate a final intra predictor by weighted summing two intra predictors using pixel level weights based on geometric block partitions.

The following implementation may be performed by the intra predictor 122 in the video encoding apparatus and the intra predictor 542 in the video decoding apparatus.

When performing intra prediction of the current block, the video encoding apparatus may generate signaling information related to the present embodiment in terms of optimizing rate distortion. The video encoding apparatus may encode the signaling information by using the entropy encoder 155 and may transmit it to the video decoding apparatus. The video decoding apparatus may decode the signaling information from the bitstream by using the entropy decoder 510.

In the following description, the term "target block" may be used interchangeably with the current block or Coding Unit (CU) as described above, or "target block" may mean a partial region of the coding unit.

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

I. Intra prediction mode and most probable mode (Most Probable Mode, MPM)

As described above, intra prediction is a method of predicting a current block to be encoded by referring to samples existing in the vicinity of the current block. In a multi-function video codec (VVC) technique, intra-prediction modes have sub-divided directional modes (i.e., 2 to 66) in addition to non-directional (i.e., planar and DC) modes, as shown in fig. 3 a. Further, as added to the example in fig. 3b, the intra prediction mode of the luminance block has a direction mode (-14 to-1 and 67 to 80) according to wide-angle intra prediction (WAIP).

For intra prediction, the Most Probable Mode (MPM) technique intra-predicts a current block using intra-prediction modes of neighboring blocks. The video encoding device generates the MPM list to include intra-prediction modes derived from predefined locations spatially adjacent to the current block. The video encoding apparatus may transmit an index of the MPM list instead of an index of the prediction mode, thereby improving the encoding and decoding efficiency of the intra prediction mode.

Embodiments according to the invention

When the geometric intra prediction mode is applied, the intra prediction factor generating means (hereinafter, referred to as "prediction factor generating means") according to this embodiment generates two intra prediction factors by using two different intra prediction modes for the current block, and then performs a mixing process based on pixel-level weights to generate a final intra prediction factor. The predictor generating means includes all or part of the first intra prediction mode selector 610, the first intra prediction mode generator 620, the second intra prediction mode selector 630, the second intra prediction mode generator 640, and the final intra prediction mode generator 650.

When the geometric intra prediction mode is applied, as shown in fig. 7, the intra prediction apparatus first generates a first intra prediction factor and a second intra prediction factor by using different intra prediction modes for the current block. The intra prediction apparatus may generate the final intra prediction factor by weighted summing the first intra prediction factor and the second intra prediction factor using weights based on the geometric block partition. In the example of fig. 7, nCbw and nCbh represent the width and height, respectively, of the current block.

In the example of fig. 7, the weights represent weights for the first intra predictor. The meaning and setting of the weights are described below.

In one example, the first intra predictor may be a signal generated by using one intra prediction mode in the MPM list as described above. The second intra predictor may also be a signal generated by using one intra prediction mode of other remaining modes in the MPM list instead of the intra prediction mode used for generating the first intra predictor.

The operation of the components in the intra prediction apparatus is described below from the video decoding apparatus side. As described above, the intra prediction apparatus may also be included in the video encoding apparatus.

The first intra prediction mode selector 610 generates an MPM list for intra prediction of the current block. The first intra prediction mode selector 610 selects an intra prediction mode indicated by a corresponding index in the MPM list using index information signaled from the video encoding device.

Based on the first intra prediction mode, the first intra predictor generator 620 generates a first intra predictor of the current block by using already reconstructed pixels spatially adjacent to the current block.

The second intra prediction mode selector 630 reorders the MPM list by excluding the first intra prediction mode from the MPM list. The second intra prediction mode selector 630 selects an intra prediction mode indicated by a corresponding index in the reordered MPM list using index information signaled from the video encoding device.

Based on the second intra prediction mode, the second intra predictor generator 640 generates a second intra predictor of the current block by using already reconstructed pixels spatially adjacent to the current block.

The final intra predictor generator 650 obtains the geometric block partition information by using an index signaled by the video encoding device, for example, from a lookup table. The final intra predictor generator 650 generates weights based on the geometric block partition information. Here, the weights include a weight w1 for the first intra predictor and a weight w2 for the second intra predictor. The final intra predictor generator 650 generates a final intra predictor using the weights by performing a weighted sum of the first and second intra predictors. In this case, the aforementioned weight may be a value different from pixel to pixel according to the geometric block partition information.

Syntax related to a geometric intra prediction mode applied to a current block (i.e., an encoding unit) may be expressed as shown in table 1, which is signaled from a video encoding apparatus to a video decoding apparatus.

TABLE 1

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As shown in table 1, when not in a matrix weighted intra prediction (MIP) mode, information about the geometric intra prediction mode of the current block may be signaled. Information about the geometric intra prediction mode may be signaled by using the following syntax elements.

First, a flag sps_ gim _enable_flag may be signaled using a high level syntax to indicate whether the geometric intra prediction mode is enabled. The examples shown in table 1 utilize, but are not limited to, SPS in high level syntax for signaling. That is, the use or non-use of geometric intra prediction modes may be signaled in one or more of various high level grammars such as SPS, PPS, slice header, picture header, etc.

If the flag sps gim _ enable _ flag is true and the geometric intra prediction mode is used, the geometric intra prediction flag "intra gim _ flag" may be signaled to indicate whether the geometric intra prediction mode is enabled for the coding unit.

Then, if the value of intra_ gim _flag is true and the encoding unit uses the geometric intra prediction mode, more information about the geometric intra prediction mode can be signaled or parsed.

On the other hand, if the value of intra_ gim _flag is false and the encoding unit does not use the geometric intra prediction mode, more information about the intra prediction mode may be signaled or parsed according to the conventional method.

If the value of the geometric intra prediction flag of "intra_ gim _flag" is true, the further information signaled may include a geometric partition information index "intra_ gim _partition_idx" indicating a geometric partition form applied to the coding unit, a first intra prediction mode index "intra_ gim _idx0" indicating a first intra prediction mode, and a second intra prediction mode index "intra_ gim _idx1" indicating a second intra prediction mode.

Alternatively, more information may be signaled or parsed in an order of an index "intra_ gim _partition_idx" indicating a geometric partition form, an index "intra_ gim _idx0" indicating a first intra prediction mode, and an index "intra_ gim _idx1" indicating a second intra prediction mode (for example, an order illustrated in table 1), but the signaling or parsing order is not necessarily limited thereto. In other words, a change in the order of signaling or parsing may also be included within the scope of the present invention. For example, more information may be signaled or parsed in the order of an index indicating a first intra prediction mode, an index indicating a second intra prediction mode, and an index indicating a geometric partition form.

According to table 1, among the information on the geometric intra prediction mode, the information on the geometric partition form applied to the encoding unit is signaled or parsed by using its indication index "intra_ gim _partition_idx". Such information about the geometric partition form may include information about the bisection of the block. In this case, the halving of the block may include partitioning the block by using a predefined straight line. Information about the form of geometric partitioning is described in more detail below.

According to table 1, an index indicating the first intra prediction mode and an index indicating the second intra prediction mode may be further signaled. In one example, the first intra prediction mode and the second intra prediction mode may be two different intra prediction modes of all intra prediction modes supported by the encoding and decoding processes.

In another example, the first intra prediction mode and the second intra prediction mode may be two different intra prediction modes among intra prediction modes included in a candidate list derived from a predefined position spatially adjacent to the current block. In this case, the candidate list may be an MPM list. That is, the first intra prediction mode and the second intra prediction mode according to the present invention may be defined as prediction modes selected from a candidate list of predefined intra prediction modes.

As another example, syntax related to geometric intra prediction modes, which is signaled from a video encoding apparatus to a video decoding apparatus, may be represented as shown in table 2.

TABLE 2

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As shown in table 2, when not in the MIP mode, information on the geometric intra prediction mode may be signaled after information on the intra prediction mode is signaled according to a conventional method. Information about the geometric intra prediction mode may be signaled by using the following syntax elements.

First, a flag "sps gim _ enable _ flag" may be signaled using a high level syntax to indicate whether the geometric intra prediction mode is enabled.

If the flag "sps_ gim _enable_flag" is true and the geometric intra prediction mode is used, the geometric intra prediction flag "intra_ gim _flag" may be signaled to the coding unit, indicating whether the geometric intra prediction mode is enabled.

If the value of the geometric intra prediction flag 'intra_ gim _flag' is true, the further information signaled may include a geometric partition information index 'intra_ gim _partition_idx' indicating a geometric partition form applied to the coding unit and a second intra prediction mode index 'intra_ gim _idx1' indicating a second intra prediction mode. In this case, the first intra prediction mode index "intra_ gim _idx0" indicating the first intra prediction mode may indicate an earlier parsed intra prediction mode (e.g., "intra_luma_mpm_idx" or "intra_luma_mpm_ remainder") according to a default method.

As shown in fig. 8, after two different intra prediction modes are selected for the current block, the predictor generating means generates intra predictors corresponding to the respective intra prediction modes. The predictor generating means generates a final intra predictor by weighted summation of the two intra predictors. In performing the weighted summation, the predictor generating means may mix two intra predictors with respect to a straight line bisecting the execution of the geometric block partition for the arbitrary form of block partition. In other words, the predictor generating means may perform a mixing process of differently weighted summing each pixel in the block to generate the final intra predictor from the two intra predictors.

On the other hand, when different weighted summation is performed pixel by pixel in a block with respect to a straight line, the sum of weights applied to the co-located pixels in the two intra predictors is 1. In this case, the set containing the weights may be {0,1,2,3,4,5,6,7,8}, or the foregoing set may be {0,1/8,2/8,3/8,4/8,5/8,6/8,7/8,1} in consideration of the scaling value. For example, at the (x, y) pixel position in the current block, when the weight of the first intra predictor is 1 (1/8 when the scaling value is considered), the weight of the second intra predictor is 7 (7/8 when the scaling value is considered).

In the example of fig. 8, the weights represented as integers for the final intra predictor represent weights for the first intra predictor.

Further, the bisecting line indicates a boundary of a size change between the weight of the first intra-prediction factor and the weight of the first intra-prediction factor. For example, in the example of fig. 8, the weight of the first intra predictor may be greater than or equal to the weight of the second intra predictor for pixels included in the region a with respect to the straight line. Further, for pixels included in the region B with respect to the baseline, the weight of the second intra-prediction factor may be greater than or equal to the weight of the first intra-prediction factor.

Hereinafter, the predictor using a larger weight in each region is referred to as a main predictor. These main predictors can be determined by considering reference samples for intra prediction. For region a shown in fig. 8, the first intra predictor may be set to the main predictor because it is closer to the left reference sample than the top reference sample.

For blocks encoded/decoded according to the geometric intra prediction mode, the geometric partition form is based on straight lines representing the bisections of the blocks. The information about such a straight line may include an index "distanceIdx" indicating a distance from the center of the block to the relevant straight line, and an index "angleIdx" indicating an angle of a line segment orthogonal to the relevant straight line. An index indicating the angle of a line segment orthogonal to the relevant straight line may be set as shown in fig. 9 a. Furthermore, 64 geometric block partition forms based on these angles and distances may be provided as shown in fig. 9 b.

The 64 geometric partition forms may be signaled by using an "intra gim _partition_idx" syntax, which is an index indicating the geometric partition form, as shown in table 3.

TABLE 3

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The index "distanceIdx" derived from the example of fig. 9b is a value excluding the size of the current block. Accordingly, the actual distance between the pixel in the current block and the straight line can be calculated by using the size information of the current block, the index "angleIdx" indicating the angle, and the index "distanceIdx" indicating the distance. Here, the actual distance is a value expressed in pixel units.

Further, the actual distance may be used to calculate a weight for each pixel in the current block. For example, for a pixel in the current block, the greater the actual distance between the pixel and the straight line, the greater the weight of the main predictor as described above, and the less the weight of the remaining other predictors. For pixels lying on a straight line, the two predictors may have the same weight. In this case, the sum of the weights of the two predictors for the pixel remains 1.

Referring now to fig. 10 and 11, an intra prediction method using a geometric intra prediction mode will be described.

The video encoding apparatus determines a geometric intra prediction flag (S1000). Here, the geometric intra prediction flag "intra_ gim _flag" indicates whether or not a geometric intra prediction mode is used for the current block. As described above, the video encoding apparatus can determine the use of geometric intra prediction flags in terms of optimizing rate distortion.

The video encoding device encodes the geometric intra prediction flag (S1002).

The video encoding device checks a geometric intra prediction flag (S1004).

If the geometric intra prediction flag is true (yes at S1004), the video encoding apparatus performs the following steps.

The video encoding device determines a geometric partition information index (S1006). Here, the geometric partition information index "intra_ gim _partition_idx" indicates a geometric partition form applied to the current block. In other words, the geometric partition information index indexes information about a straight line that bisects the current block.

The video encoding apparatus generates a list including intra prediction modes for intra prediction of the current block (S1008). Here, the list may be an MPM list. Alternatively, the list may be a list including all intra prediction modes.

The video encoding apparatus determines a first intra prediction mode in optimizing a codec rate (S1010).

The video encoding device determines a first intra prediction mode index from a list for the first intra prediction mode (S1012). The first intra prediction mode index "intra_ gim _idx0" indexes the first intra prediction mode. For example, if the MPM list does not include the first intra prediction mode, the first intra prediction mode index may be determined from the list including all intra prediction modes.

Based on the first intra prediction mode, the video encoding apparatus generates a first intra predictor of the current block by using pixels spatially adjacent to the current block (S1014).

The video encoding device reorders the list by excluding the first intra prediction mode from the list (S1016).

The video encoding device determines a second intra prediction factor in optimizing the codec rate (S1018).

The video encoding device determines a second intra prediction mode index from the reordered list for the second intra prediction mode (S1020). The second intra prediction mode index "intra_ gim _idx1" indexes the second intra prediction mode. For example, if the reordered MPM list does not include the second intra prediction mode, the second intra prediction mode index may be determined from the list including all intra prediction modes.

Based on the second intra prediction mode, the video encoding apparatus generates a second intra predictor of the current block by using pixels spatially adjacent to the current block (S1022).

The video encoding apparatus obtains weights by using the geometric partition information index (S1024). Here, the weights include a first weight for the first intra predictor and a second weight for the second intra predictor.

The information on the straight line indexed according to the geometric partition information may include an index "distanceIdx" indicating a distance from the center of the block to the relevant straight line, and an index "angleIdx" indicating an angle of a line segment orthogonal to the relevant straight line. The actual distance between the pixel in the current block and the straight line can be calculated using the size information of the current block, the index "angleIdx" representing the angle, and the index "distanceIdx" indicating the distance. Based on these actual distances, weights may be calculated for pixels in the current block.

The video encoding apparatus generates a final intra predictor of the current block by weighted summing the first intra predictor and the second intra predictor using the weights (S1026).

The video encoding device encodes the geometric partition information index, the first intra prediction mode index, and the second intra prediction mode index (S1028).

If the geometric intra prediction flag is false (NO at S1004), geometric intra prediction is omitted for the current block. In this case, the video encoding apparatus may perform intra prediction of the current block by using another intra prediction mode.

The video decoding apparatus decodes the geometric intra prediction flag from the bitstream (S1100). Here, the geometric intra prediction flag "intra_ gim _flag" indicates whether or not a geometric intra prediction mode is to be used for the current block. As described above, the use of geometric intra prediction flags may be determined by the video encoding device in terms of optimizing rate distortion.

The video decoding apparatus checks a geometric intra prediction flag (S1102).

If the geometric intra prediction flag is true (yes at S1102), the video decoding apparatus performs the following steps.

The video decoding apparatus decodes the geometric partition information index, the first intra prediction mode index, and the second intra prediction mode index from the bitstream (S1104). Here, the geometric partition information index "intra_ gim _partition_idx" indicates a geometric partition form applied to the current block. That is, the geometric partition information index indexes information on a straight line that bisects the current block. The first intra prediction mode index "intra_ gim _idx0" indexes the first intra prediction mode. In addition, the second intra prediction mode index "intra_ gim _idx1" indexes the second intra prediction mode.

The video decoding apparatus generates a list including prediction modes for intra prediction of the current block (S1106). Here, the list may be an MPM list. Alternatively, the list may be a list including all intra prediction modes.

The video decoding apparatus selects a first intra prediction mode from the list by using the first intra prediction mode index (S1108). For example, if the first intra prediction mode index does not indicate an intra prediction mode in the MPM list, the first intra prediction mode may be selected from a list including all intra prediction modes.

Based on the first intra prediction mode, the video decoding apparatus generates a first intra predictor of the current block by using pixels spatially adjacent to the current block (S1110).

The video decoding apparatus reorders the list by excluding the first intra prediction mode from the list (S1112).

The video decoding apparatus selects a second intra prediction factor from the reordered list by using a second intra prediction mode index (S1114). For example, if the second intra prediction mode index does not indicate an intra prediction mode in the reordered MPM list, the second intra prediction mode may be selected from a list including all intra prediction modes.

Based on the second intra prediction mode, the video decoding apparatus generates a second intra predictor of the current block by using pixels spatially adjacent to the current block (S1116).

The video decoding apparatus obtains weights by using the geometric partition information index (S1118). Here, the weights include a first weight for the first intra predictor and a second weight for the second intra predictor.

The information on the straight line indexed according to the geometric partition information may include an index "distanceIdx" indicating a distance from the center of the block to the relevant straight line, and an index "angleIdx" indicating an angle of a line segment orthogonal to the relevant straight line. The actual distance between the pixel in the current block and the straight line can be calculated using the size information of the current block, the index "angleIdx" indicating the angle, and the index "distanceIdx" indicating the distance. Based on these actual distances, weights may be calculated for pixels in the current block.

With the weights, the video decoding apparatus may weight sum the first and second intra predictors to generate a final intra predictor of the current block (S1120).

If the geometric intra prediction flag is false (NO at S1102), geometric intra prediction is omitted for the current block. In this case, the video decoding apparatus may utilize another intra prediction mode to perform intra prediction of the current block.

Although steps in the respective flowcharts are described as sequentially performed, these steps merely exemplify the technical ideas of some embodiments of the present invention. Accordingly, one of ordinary skill in the art to which the invention pertains may perform the steps by changing the order depicted in the various figures or by performing two or more steps in parallel. Accordingly, the steps in the various flowcharts are not limited to the order in which they occur as shown.

It should be understood that the foregoing description presents illustrative embodiments that may be implemented in various other ways. The functions described in some embodiments may be implemented by hardware, software, firmware, and/or combinations thereof. It should also be understood that the functional components described in this invention are labeled "… … units" to highlight the possibility of their independent implementation.

On the other hand, the various methods or functions described in some embodiments may be implemented as instructions stored in a non-volatile recording medium, which may be read and executed by one or more processors. The nonvolatile recording medium may include various types of recording devices that store data in a form readable by a computer system, for example. For example, the nonvolatile recording medium may include a storage medium such as an erasable programmable read-only memory (EPROM), a flash memory drive, an optical disk drive, a magnetic hard disk drive, a Solid State Drive (SSD), and the like.

Although exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art to which the present invention pertains will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention. Accordingly, embodiments of the present invention have been described for brevity and clarity. The scope of the technical idea of the embodiment of the invention is not limited by the illustration. Accordingly, it will be understood by those of ordinary skill in the art that the scope of the present invention should not be limited by the embodiments explicitly described above, but by the claims and their equivalents.

(Reference numerals)

122: Intra-frame predictor

542: Intra-frame predictor

610: First intra prediction mode selector

620: First intra predictor generator

630: Second intra prediction mode selector

640: Second intra predictor generator

650: Final intra predictor generator

Cross Reference to Related Applications

The present application claims priority and benefit from korean patent application No.10-2021-0143104, filed on 25 th 10 th 2021, and korean patent application No. 10-2022-011277, filed on 9 th 2022, each of which is incorporated herein by reference in its entirety.

Claims

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

decoding a geometric intra prediction flag from a bitstream, the geometric intra prediction flag indicating whether a geometric intra prediction mode is used for a current block; and

The geometric intra-prediction flags are checked for,

Wherein if the geometric intra prediction flag is true, the method further comprises:

Decoding the geometric partition information index, the first intra-prediction mode index, and the second intra-prediction mode index from the bitstream;

generating a list including prediction modes for intra prediction of the current block;

Selecting a first intra prediction mode from a list of prediction modes by using a first intra prediction mode index;

Generating a first intra predictor of the current block by using pixels spatially adjacent to the current block based on the first intra prediction mode;

selecting a second intra prediction mode from the list of prediction modes by using the second intra prediction mode index;

generating a second intra predictor of the current block by using pixels spatially adjacent to the current block based on the second intra prediction mode;

obtaining weights by indexing with geometric partition information, the weights including a first weight for a first intra predictor and a second weight for a second intra predictor; and

The first and second intra predictors are weighted summed by a weight to generate a final intra predictor for the current block.

2. The method of claim 1, further comprising:

The list of prediction modes is reordered by excluding the first intra prediction mode from the list of prediction modes.

3. The method of claim 1, wherein obtaining weights comprises:

By using the geometric partition information index, an index of an angle and an index of a distance with respect to a straight line bisecting the current block, an index of an angle representing an angle of a line segment orthogonal to the straight line, and an index of a distance representing a distance from the straight line are obtained.

4. A method according to claim 3, wherein obtaining weights comprises:

the actual distance between the pixels in the current block and the straight line is calculated by using the size of the current block, the index of the angle, and the index of the distance.

5. The method of claim 4, wherein obtaining weights comprises:

a first weight and a second weight for pixels in the current block are calculated based on the actual distance,

Wherein, for each pixel in the current block, the sum of the weight of the first intra predictor and the weight of the second intra predictor is 1.

6. A method according to claim 3, wherein obtaining weights comprises:

a predictor is determined based on a reference sample for intra prediction, which uses a greater weight in each region of the current block equally divided along a straight line.

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

determining a geometric intra prediction flag indicating whether a geometric intra prediction mode is used for the current block; and

The geometric intra-prediction flags are checked for,

determining a geometric partition information index;

generating a list including intra prediction modes for intra prediction of the current block;

determining a first intra prediction mode;

for a first intra-prediction mode, determining a first intra-prediction mode index from a list of intra-prediction modes;

Determining a second intra prediction mode;

for a second intra-prediction mode, determining a second intra-prediction mode index from a list of intra-prediction modes;

8. The method of claim 7, further comprising:

The list of intra-prediction modes is reordered by excluding the first intra-prediction mode from the list of intra-prediction modes.

9. The method of claim 7, further comprising:

The geometric intra prediction flag is encoded.

10. The method of claim 9, further comprising, if the geometric intra prediction flag is true:

the geometric partition information index, the first intra prediction mode index, and the second intra prediction mode index are encoded.

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

The geometric intra-prediction flags are checked for,

Wherein if the geometric intra prediction flag is true, the video encoding method further comprises:

determining a geometric partition information index;

determining a first intra prediction mode;

Determining a second intra prediction mode;