Video encoding / decoding method and device, and recording medium storing bitstream

Abstract

An image encoding / decoding method and device according to the present disclosure may generate a candidate list for the current block, derive motion information about the current block on the basis of the candidate list, and perform inter prediction on the current block on the basis of the motion information about the current block. Here, the motion information about the current block may be stored in at least one of an HMVP list for a coding tree unit row to which the current block belongs or a CHMVP list for a coding tree unit column to which the current block belongs.

Description

Video encoding / decoding method and device and recording medium storing bitstream

[0001] The present invention relates to a video signal processing method and device.

[0002] The market demand for high-resolution video is growing, necessitating technologies capable of efficiently compressing high-resolution images. To address this market need, the ISO / IEC's Moving Picture Expert Group (MPEG) and the ITU-T's Video Coding Expert Group (VCEG) jointly formed the Joint Collaborative Team on Video Coding (JCT-VC). They completed development of the HEVC (High Efficiency Video Coding) video compression standard in January 2013 and have been actively conducting research and development on next-generation compression standards.

[0003] Video compression largely consists of intra-prediction, inter-prediction, transform, quantization, entropy coding, and in-loop filtering. Among these, inter-prediction refers to a technology that generates a prediction block for the current block based on adjacent frames that have been encoded / decoded. The encoder encodes the inter-prediction mode used for inter-prediction, and the decoder decodes the encoded inter-prediction mode to perform inter-prediction.

[0004] The present disclosure seeks to provide a method and apparatus for performing inter prediction.

[0005] The present disclosure provides a method and device for generating a candidate list for inter prediction.

[0006] The present disclosure provides a method and device for storing / managing movement information for history-based merge candidates.

[0007] The video decoding method and device according to the present disclosure can generate a candidate list for a current block, derive motion information of the current block based on the candidate list, and perform inter prediction on the current block based on the motion information of the current block. Here, the motion information of the current block can be stored in at least one of an HMVP list for a coding tree unit row (CTU row) to which the current block belongs or a CHMVP list for a coding tree unit column (CTU column) to which the current block belongs.

[0008] In the video decoding method and device according to the present disclosure, the CHMVP list can be generated when starting decoding of the first CTU row in the current picture.

[0009] In the video decoding method and device according to the present disclosure, when the current block belongs to the first CTU column, the motion information of the current block can be stored in the CHMVP list.

[0010] In the video decoding method and device according to the present disclosure, the HMVP list can be initialized in units of CTU rows.

[0011] In the video decoding method and device according to the present disclosure, motion information belonging to the CHMVP list can be stored in the HMVP list.

[0012] In the video decoding method and device according to the present disclosure, the CHMVP list can be generated independently for each CTU column in the current picture.

[0013] In the video decoding method and device according to the present disclosure, the HMVP candidate derived from the HMVP list and the CHMVP candidate derived from the CHMVP list can be added to the candidate list as independent merge candidates.

[0014] In the image decoding method and device according to the present disclosure, the candidate list can be generated by selectively using either the HMVP list or the CHMVP list.

[0015] The video encoding method and device according to the present disclosure can generate a candidate list for a current block, derive motion information of the current block based on the candidate list, and perform inter prediction on the current block based on the motion information of the current block. Here, the motion information of the current block can be stored in at least one of an HMVP list for a coding tree unit row (CTU row) to which the current block belongs or a CHMVP list for a coding tree unit column (CTU column) to which the current block belongs.

[0016] A computer-readable recording medium according to the present disclosure can store a bitstream encoded by the image encoding method.

[0017] By using the candidate list according to the present disclosure, the accuracy of inter prediction can be improved.

[0018] According to the present disclosure, video encoding efficiency can be improved by enabling history-based merge candidates to be used even when the HMVP list is initialized.

[0019] FIG. 1 is a block diagram showing an image encoding device according to the present disclosure.

[0020] FIG. 2 is a block diagram showing an image decoding device according to the present disclosure.

[0021] FIG. 3 illustrates an inter prediction method performed in a decoder / encoder as an embodiment according to the present disclosure.

[0022] The video decoding method and device according to the present disclosure can generate a candidate list for a current block, derive motion information of the current block based on the candidate list, and perform inter prediction on the current block based on the motion information of the current block. Here, the motion information of the current block can be stored in at least one of an HMVP list for a coding tree unit row (CTU row) to which the current block belongs or a CHMVP list for a coding tree unit column (CTU column) to which the current block belongs.

[0023] In the video decoding method and device according to the present disclosure, the CHMVP list can be generated when starting decoding of the first CTU row in the current picture.

[0024] In the video decoding method and device according to the present disclosure, when the current block belongs to the first CTU column, the motion information of the current block can be stored in the CHMVP list.

[0025] In the video decoding method and device according to the present disclosure, the HMVP list can be initialized in units of CTU rows.

[0026] In the video decoding method and device according to the present disclosure, motion information belonging to the CHMVP list can be stored in the HMVP list.

[0027] In the video decoding method and device according to the present disclosure, the CHMVP list can be generated independently for each CTU column in the current picture.

[0028] In the video decoding method and device according to the present disclosure, the HMVP candidate derived from the HMVP list and the CHMVP candidate derived from the CHMVP list can be added to the candidate list as independent merge candidates.

[0029] In the image decoding method and device according to the present disclosure, the candidate list can be generated by selectively using either the HMVP list or the CHMVP list.

[0030] The video encoding method and device according to the present disclosure can generate a candidate list for a current block, derive motion information of the current block based on the candidate list, and perform inter prediction on the current block based on the motion information of the current block. Here, the motion information of the current block can be stored in at least one of an HMVP list for a coding tree unit row (CTU row) to which the current block belongs or a CHMVP list for a coding tree unit column (CTU column) to which the current block belongs.

[0031] A computer-readable recording medium according to the present disclosure can store a bitstream encoded by the image encoding method.

[0032] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings attached to this specification so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. In addition, in the drawings, parts irrelevant to the description have been omitted to clearly explain the present invention, and similar parts have been designated with similar reference numerals throughout the specification.

[0033] Throughout this specification, when a part is said to be 'connected' to another part, this includes not only cases where they are directly connected, but also cases where they are electrically connected with another element in between.

[0034] Additionally, whenever a part throughout this specification is said to "include" a component, this does not mean that other components are excluded, but rather that other components may be included, unless specifically stated otherwise.

[0035] Additionally, while terms such as "first," "second," etc. may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another.

[0036] Additionally, in the embodiments of the devices and methods described herein, some components of the devices or some steps of the methods may be omitted. Furthermore, the order of some components of the devices or some steps of the methods may be changed. Furthermore, other components or other steps may be inserted into some components of the devices or some steps of the methods.

[0037] Additionally, some components or some steps of the first embodiment of the present invention may be added to the second embodiment of the present invention, or some components or some steps of the second embodiment may be replaced.

[0038] In addition, the components shown in the embodiments of the present invention are independently depicted to represent different characteristic functions, and this does not mean that each component is composed of separate hardware or a single software component. That is, each component is described by listing each component for convenience of explanation, and at least two components among each component may be combined to form a single component, or a single component may be divided into multiple components to perform a function. Such integrated and separate embodiments of each component are also included in the scope of the present invention as long as they do not deviate from the essence of the present invention.

[0039] In this specification, a block can be variously expressed as a unit, an area, a unit, a partition, etc., and a sample can be variously expressed as a pixel, a pel, a pixel, etc.

[0040] Hereinafter, embodiments of the present invention will be described in more detail with reference to the attached drawings. In describing the present invention, duplicate descriptions of identical components will be omitted.

[0041] FIG. 1 is a block diagram showing an image encoding device according to the present disclosure.

[0042] Referring to FIG. 1, a video encoding device (100) may include a picture segmentation unit (110), a prediction unit (120, 125), a transformation unit (130), a quantization unit (135), a reordering unit (160), an entropy encoding unit (165), an inverse quantization unit (140), an inverse transformation unit (145), a filter unit (150), and a memory (155).

[0043] The picture segmentation unit (110) can segment the input picture into at least one processing unit. At this time, the processing unit may be a prediction unit (PU), a transform unit (TU), or a coding unit (CU). Hereinafter, in the embodiments of the present disclosure, the coding unit may be used to mean a unit that performs encoding or a unit that performs decoding.

[0044] A prediction unit may be divided into at least one square or rectangular shape of the same size within a single coding unit, or may be divided such that one prediction unit among the divided prediction units within a single coding unit has a different shape and / or size from another prediction unit. When a prediction unit that performs intra prediction based on a coding unit is generated and is not the minimum coding unit, intra prediction can be performed without being divided into a plurality of NxN prediction units.

[0045] The prediction unit (120, 125) may include an inter prediction unit (120) that performs inter prediction or inter prediction, and an intra prediction unit (125) that performs intra prediction or intra prediction. It may determine whether to use inter prediction or intra prediction for a prediction unit, and determine specific information (e.g., intra prediction mode, motion vector, reference picture, etc.) according to each prediction method. A residual value (residual block) between the generated prediction block and the original block may be input to the transformation unit (130). In addition, prediction mode information, motion vector information, etc. used for prediction may be encoded together with the residual value by the entropy encoding unit (165) and transmitted to the decoder.

[0046] The inter prediction unit (120) may predict a prediction unit based on information of at least one picture among the previous or subsequent pictures of the current picture, and in some cases, may predict a prediction unit based on information of a portion of an encoded region within the current picture. The inter prediction unit (120) may include a reference picture interpolation unit, a motion prediction unit, and a motion compensation unit.

[0047] The reference picture interpolation unit can receive reference picture information from the memory (155) and generate pixel information less than an integer pixel from the reference picture. In the case of luminance pixels, a DCT-based 8-tap interpolation filter with different filter coefficients can be used to generate pixel information less than an integer pixel in units of 1 / 4 pixels. In the case of a chrominance signal, a DCT-based 4-tap interpolation filter with different filter coefficients can be used to generate pixel information less than an integer pixel in units of 1 / 8 pixels.

[0048] The motion prediction unit can perform motion prediction based on a reference picture interpolated by the reference picture interpolation unit. Various methods such as FBMA (Full search-based Block Matching Algorithm), TSS (Three Step Search), and NTS (New Three-Step Search Algorithm) can be used to derive a motion vector. The motion vector can have a motion vector value in units of 1 / 2 or 1 / 4 pixels based on the interpolated pixel. The motion prediction unit can predict the current prediction unit by using different motion prediction methods. Various methods such as Skip Mode, Merge Mode, AMVP Mode, Affine Mode, and Affine Merge Mode can be used as motion prediction methods.

[0049] The intra prediction unit (125) can generate a prediction unit based on reference pixel information surrounding the current block, which is pixel information within the current picture. If the surrounding block of the current prediction unit is a block on which inter prediction has been performed and the reference pixel is a pixel on which inter prediction has been performed, the reference pixel included in the block on which inter prediction has been performed can be replaced and used with reference pixel information of the surrounding block on which intra prediction has been performed. That is, if the reference pixel is not available, the unavailable reference pixel information can be replaced and used with at least one reference pixel among the available reference pixels.

[0050] Additionally, a residual block containing residual value information, which is the difference between the prediction unit that performed the prediction based on the prediction unit generated in the prediction unit (120, 125) and the original block of the prediction unit, can be generated. The generated residual block can be input to the transformation unit (130).

[0051] In the transformation unit (130), the residual block including the residual value information of the prediction unit generated through the original block and the prediction unit (120, 125) can be transformed using a transformation method such as DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), or KLT. Whether to apply DCT, DST, or KLT to transform the residual block can be determined based on the intra prediction mode information of the prediction unit used to generate the residual block.

[0052] The quantization unit (135) can quantize values ​​converted to the frequency domain by the transformation unit (130). The quantization coefficients may vary depending on the block or the importance of the image. The values ​​produced by the quantization unit (135) can be provided to the dequantization unit (140) and the reordering unit (160).

[0053] The rearrangement unit (160) can perform rearrangement of coefficient values ​​for quantized residual values.

[0054] The rearrangement unit (160) can change a two-dimensional block-shaped coefficient into a one-dimensional vector form through a coefficient scanning method. For example, the rearrangement unit (160) can change the two-dimensional block-shaped coefficient into a one-dimensional vector form by scanning from the DC coefficient to the coefficient of the high-frequency region using a zig-zag scan method. Depending on the size of the transformation unit and the intra prediction mode, a vertical scan that scans the two-dimensional block-shaped coefficient in the column direction or a horizontal scan that scans the two-dimensional block-shaped coefficient 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, it is possible to determine which scan method among the zig-zag scan, the vertical scan, and the horizontal scan is to be used.

[0055] The entropy encoding unit (165) can perform entropy encoding based on the values ​​produced by the rearrangement unit (160). Entropy encoding can use various encoding methods such as, for example, Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC). In this regard, the entropy encoding unit (165) can encode residual value coefficient information of the encoding unit from the rearrangement unit (160) and the prediction units (120, 125). In addition, according to the present disclosure, it is possible to signal and transmit information indicating that motion information is derived and used on the decoder side and information on a technique used to derive motion information.

[0056] The inverse quantization unit (140) and the inverse transformation unit (145) inversely quantize the values ​​quantized in the quantization unit (135) and inversely transform the values ​​transformed in the transformation unit (130). The residual values ​​generated in the inverse quantization unit (140) and the inverse transformation unit (145) can be combined with the predicted prediction units predicted through the motion estimation unit, motion compensation unit, and intra prediction unit included in the prediction unit (120, 125) to generate a reconstructed block.

[0057] The filter unit (150) may include at least one of a deblocking filter, an offset correction unit, and an ALF (Adaptive Loop Filter). The deblocking filter may remove block distortion caused by boundaries between blocks in a restored picture. The offset correction unit may correct the offset from the original image on a pixel-by-pixel basis for the image on which deblocking has been performed. In order to perform offset correction for a specific picture, a method may be used in which the pixels included in the image are divided into a certain number of regions, the regions to be offset are determined, and the offset is applied to the regions, or the offset is applied by considering edge information of each pixel. The ALF (Adaptive Loop Filtering) may be performed based on a value obtained by comparing the filtered restored image with the original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the group is determined, and filtering may be performed differentially for each group.

[0058] The memory (155) can store a restored block or picture produced through the filter unit (150), and the stored restored block or picture can be provided to the prediction unit (120, 125) when performing inter prediction.

[0059] FIG. 2 is a block diagram showing an image decoding device according to the present disclosure.

[0060] Referring to FIG. 2, the image decoding device (200) may include an entropy decoding unit (210), a rearrangement unit (215), an inverse quantization unit (220), an inverse transformation unit (225), a prediction unit (230, 235), a filter unit (240), and a memory (245).

[0061] When a video bitstream is input to a video encoding device, the input bitstream can be decoded in the opposite procedure to that of the video encoding device.

[0062] The entropy decoding unit (210) can perform entropy decoding in a procedure opposite to that of the entropy encoding unit of the video encoder. For example, various methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) can be applied in response to the method performed in the video encoder.

[0063] The entropy decoding unit (210) can decode information related to intra prediction and inter prediction performed in the encoder.

[0064] The reordering unit (215) can perform reordering based on the method by which the bitstream entropy-decoded by the entropy decoding unit (210) is reordered by the encoding unit. The coefficients expressed in the form of a one-dimensional vector can be reordered by restoring them back to coefficients in the form of a two-dimensional block.

[0065] The inverse quantization unit (220) can perform inverse quantization based on the quantization parameters provided by the encoder and the coefficient values ​​of the rearranged block.

[0066] The inverse transform unit (225) can perform inverse transform, i.e., inverse DCT, inverse DST, and inverse KLT, on the transforms performed by the transform unit, i.e., DCT, DST, and KLT, on the quantization result performed by the image encoder. The inverse transform can be performed based on the transmission unit determined by the image encoder. In the inverse transform unit (225) of the image decoder, a transform technique (e.g., DCT, DST, KLT) can be selectively performed according to a plurality of pieces of information, such as a prediction method, the size of the current block, and the prediction direction.

[0067] The prediction unit (230, 235) can generate a prediction block based on the prediction block generation related information provided by the entropy decoding unit (210) and the previously decoded block or picture information provided by the memory (245).

[0068] As described above, when performing intra prediction or intra prediction in the same manner as the operation in the image encoder, if the size of the prediction unit and the size of the transformation unit are the same, intra prediction for the prediction unit is performed based on the pixels on the left side of the prediction unit, the pixels on the upper left side, and the pixels on the upper side. However, when performing intra prediction, if the size of the prediction unit and the size of the transformation unit are different, intra prediction can be performed using reference pixels based on the transformation unit. In addition, intra prediction using NxN division only for the minimum coding unit can be used.

[0069] The prediction unit (230, 235) may include a prediction unit determination unit, an inter prediction unit, and an intra prediction unit. The prediction unit determination unit may receive various information such as prediction unit information input from the entropy decoding unit (210), prediction mode information of an intra prediction method, and motion prediction-related information of an inter prediction method, and may distinguish a prediction unit from a current encoding unit and determine whether the prediction unit performs inter prediction or intra prediction. On the other hand, if the encoder (100) does not transmit motion prediction-related information for the inter prediction, but instead transmits information indicating that motion information is to be derived and used on the decoder side and information on a technique used to derive motion information, the prediction unit determination unit determines whether the inter prediction unit (230) performs prediction based on the information transmitted from the encoder (100).

[0070] The inter prediction unit (230) can perform inter prediction on the current prediction unit based on information included in at least one picture among the previous picture or the subsequent picture of the current picture including the current prediction unit, using information required for inter prediction of the current prediction unit provided by the image encoder. In order to perform inter prediction, it can be determined based on the encoding unit whether the motion prediction method of the prediction unit included in the corresponding encoding unit is one of Skip Mode, Merge Mode, AMVP Mode, Affine Mode, and Affine Merge Mode.

[0071] The intra prediction unit (235) can generate a prediction block based on pixel information within the current picture. If the prediction unit is a prediction unit that has performed intra prediction, intra prediction can be performed based on intra prediction mode information of the prediction unit provided by the image encoder.

[0072] The intra prediction unit (235) may include an Adaptive Intra Smoothing (AIS) filter, a reference pixel interpolation unit, and a DC filter. The AIS filter is a unit that performs filtering on the reference pixels of the current block and can determine whether to apply the filter based on the prediction mode of the current prediction unit and apply it. AIS filtering can be performed on the reference pixels of the current block using the prediction mode and AIS filter information of the prediction unit provided by the image encoder. If the prediction mode of the current block is a mode that does not perform AIS filtering, the AIS filter may not be applied.

[0073] The reference pixel interpolation unit can interpolate the reference pixel to generate a reference pixel of a pixel unit less than an integer value when the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on the pixel value interpolated from the reference pixel. When the prediction mode of the current prediction unit is a prediction mode that generates a prediction block without interpolating the reference pixel, the reference pixel may not be interpolated. The DC filter can generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

[0074] The restored block or picture may be provided to a filter unit (240). The filter unit (240) may include a deblocking filter, an offset correction unit, and an ALF.

[0075] Information about whether a deblocking filter has been applied to a corresponding block or picture can be received from a video encoding device, and if a deblocking filter has been applied, information about whether a strong or weak filter has been applied. The deblocking filter of the video decoder can receive information related to the deblocking filter provided by the video encoder, and the video decoder can perform deblocking filtering on the corresponding block.

[0076] The offset correction unit can perform offset correction on the restored image based on the type of offset correction applied to the image during encoding and information on the offset value. ALF can be applied to the encoding unit based on information on whether ALF is applied and ALF coefficient information provided from the encoder. This ALF information can be provided by being included in a specific parameter set.

[0077] The memory (245) can store a restored picture or block so that it can be used as a reference picture or reference block, and can also provide the restored picture to an output unit.

[0078] FIG. 3 illustrates an inter prediction method performed in a decoder / encoder as an embodiment according to the present disclosure.

[0079] When the inter prediction mode is applied to the current block, a prediction block of the current block can be generated using a base-base / decoded reference picture. In the inter prediction mode, a motion vector indicating a block with an optimal rate-distortion cost within the reference picture can be transmitted to the decoder. The decoder can generate a prediction block based on the transmitted motion vector and the reference picture. The reference picture can be located in at least two directions among the previous direction (L0 direction) or the subsequent direction (L1 direction) in time order with respect to the current block. Hereinafter, the execution process of the inter prediction mode will be examined.

[0080] A motion vector predictor (MVP) can be set based on the motion vectors of neighboring blocks of the current block in a reference picture. Based on the MVP, the block most similar to the current block in one or more reference pictures can be searched for to derive a motion vector difference (MVD). Information about the reference picture to which the most similar block belongs, the MVP, and the MVD can be transmitted to the decoder.

[0081] To reduce the amount of information transmitted to the decoder, the encoder may support a merge mode, which performs inter-prediction using information from neighboring blocks of the current block. Merge mode can generate a predicted block based on motion information from neighboring blocks without searching for similar blocks in a reference picture.

[0082] Specifically, a candidate list may be generated for the current block (S300). The candidate list may include multiple merge candidates. Here, the multiple merge candidates may include spatial candidates. The spatial candidates may be candidates derived based on motion information of surrounding blocks. Here, the surrounding blocks may include at least one of a left surrounding block, an upper surrounding block, a lower left surrounding block, an upper right surrounding block, or an upper left surrounding block. Up to four blocks from the aforementioned surrounding blocks may be used to derive merge candidates.

[0083] The above multiple merge candidates may further include temporal candidates. The temporal candidates may be candidates derived based on motion information of a collocated block that belongs to a different picture from the current block and has the same location as the current block. The collocated block may belong to a picture encoded immediately before the picture to which the current picture belongs. Alternatively, an index may be signaled to specify the picture to which the collocated block belongs among the reference pictures in the reference picture list.

[0084] The above multiple merge candidates may further include history-based merge candidates (hereinafter referred to as HMVP candidates). The motion information of blocks previously encoded / decoded before the current block may be stored in a buffer of a predetermined size or an HMVP list. HMVP candidates may be derived based on the motion information of blocks stored in the HMVP list. Blocks previously encoded / decoded before the current block may include one or more blocks that are not adjacent to the current block. For example, a candidate list may include up to nine HMVP candidates.

[0085] A merge candidate derived from a combination of merge candidates already added to the candidate list (hereinafter referred to as a "derived candidate") may also be added to the candidate list. For example, the motion vector of the derived candidate may be generated based on a combination (e.g., an average) of the motion vector with index 0 and the motion vector with index 1 in the candidate list.

[0086] If the candidate list is not filled through the above process, a zero vector candidate may be added to the candidate list.

[0087] The HMVP list can be initialized after the encoding of the last CTU in a CTU row is completed, taking into account spatial characteristics with respect to the current block. That is, the HMVP list can be initialized on a per-CTU row basis. However, when encoding / decoding a new CTU row begins, the HMVP list is already initialized, so HMVP candidates cannot be used in the candidate list generation process. Accordingly, the present disclosure proposes a method for storing the HMVP list to improve the accuracy of predicted blocks.

[0088] Example 1

[0089] When starting to encode / decode the first CTU column (or the 0th CTU column) in the current picture, a CHMVP (Column History based Motion Vector Predictor) list can be generated. The CHMVP list can be generated and updated during the process of encode / decode blocks belonging to the first CTU column in the current picture.

[0090] If the current block is encoded / decoded using inter prediction, the motion information of the current block can be stored in the aforementioned HMVP list and CHMVP list, respectively. If the current block belongs to the first CTU column, the motion information of the current block can be stored in the CHMVP list. The CHMVP list has a size of N and can only store motion information of the 0th CTU column. N can be an integer greater than or equal to 1. The size of the CHMVP list can mean the maximum number of blocks stored in the CHMVP list.

[0091] The CHMVP list can be managed in a FIFO (First In First Out) manner. Before storing new motion information in the CHMVP list, a duplication check can be performed between the motion information already stored in the CHMVP list and the new motion information. If there is motion information that overlaps with the new motion information in the CHMVP list, the duplicate motion information can be removed from the CHMVP list and the new motion information can be stored instead.

[0092] Alternatively, the CHMVP list can be managed in a Last In First Out (LIFO) manner. Before storing new motion information in the CHMVP list, a duplication check can be performed between the motion information already stored in the CHMVP list and the new motion information. If there is motion information that overlaps with the new motion information in the CHMVP list, the new motion information will not be stored in the CHMVP list, and the overlapped motion information can be maintained in the CHMVP list as is.

[0093] When the encoding / decoding of a new CTU row begins, the HMVP list is initialized, and the motion information of the CHMVP list can be stored in the HMVP list.

[0094] Example 2

[0095] When the current block is encoded / decoded with inter prediction, the motion information of the current block can be stored in each of the HMVP list for the CTU row to which the current block belongs and the CHMVP list for the CTU column to which the current block belongs.

[0096] A CHMVP list can be independently generated and managed for each CTU column in a picture. For example, for a single picture, as many CHMVP lists can be generated as the number of CTU columns belonging to the picture. For each CTU column, the CHMVP list can be updated during the encoding / decoding process of the blocks belonging to the CTU column. The CHMVP list has a size of N, where N can be an integer greater than or equal to 1.

[0097] The CHMVP list can be managed in a FIFO (First In First Out) manner. Before storing new motion information in the CHMVP list, a duplication check can be performed between the motion information already stored in the CHMVP list and the new motion information. If there is motion information that overlaps with the new motion information in the CHMVP list, the duplicate motion information can be removed from the CHMVP list and the new motion information can be stored instead.

[0098] Alternatively, the CHMVP list can be managed in a Last In First Out (LIFO) manner. Before storing new motion information in the CHMVP list, a duplication check can be performed between the motion information already stored in the CHMVP list and the new motion information. If there is motion information that overlaps with the new motion information in the CHMVP list, the new motion information will not be stored in the CHMVP list, and the overlapped motion information can be maintained in the CHMVP list as is.

[0099] The CHMVP list described above can be used independently or dependently on the HMVP list.

[0100] For example, in the process of generating a candidate list for merge mode, an HMVP candidate derived from the HMVP list and a CHMVP candidate derived from the CHMVP list can be added to the candidate list as independent merge candidates.

[0101] Alternatively, during the process of generating a candidate list for merge mode, either the HMVP list or the CHMVP list may be selectively utilized. Either the HMVP candidate derived from the HMVP list or the CHMVP candidate derived from the CHMVP list may be selectively added to the candidate list.

[0102] Alternatively, the movement information of the blocks stored in the CHMVP list may also be stored in the HMVP list. In this case, the CHMVP list stored in the HMVP list may be the CHMVP list for the first CTU column (or the 0th CTU column). Alternatively, the CHMVP list stored in the HMVP list may be the CHMVP list for the last CTU column.

[0103] Referring to FIG. 3, the movement information of the current block can be derived based on the candidate list (S310).

[0104] The encoder can generate a prediction block using the motion information of each merge candidate in the generated candidate list, and determine the optimal merge candidate based on the rate-distortion cost. The encoder can encode a merge index indicating the determined merge candidate and transmit it to the decoder. The decoder can generate a candidate list using the same method. The decoder can specify one of the multiple merge candidates in the candidate list based on the signaled merge index, and derive the motion information of the current block based on the motion information of the specified merge candidate.

[0105] Referring to FIG. 3, inter prediction can be performed for the current block based on the motion information of the current block (S320).

[0106] The various embodiments of the present disclosure are not intended to list all possible combinations but rather to illustrate representative aspects of the present disclosure, and the matters described in the various embodiments may be applied independently or in combinations of two or more.

[0107] Additionally, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. In the case of hardware implementation, the embodiments may be implemented by one or more ASICs (Application Specific Integrated Circuits), DSPs (Digital Signal Processors), DSPDs (Digital Signal Processing Devices), PLDs (Programmable Logic Devices), FPGAs (Field Programmable Gate Arrays), general processors, controllers, microcontrollers, microprocessors, etc.

[0108] The scope of the present disclosure includes software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that cause operations according to the methods of various embodiments to be executed on a device or a computer, and a non-transitory computer-readable medium having such software or instructions stored thereon and executable on the device or computer.

Claims

1. Step of generating a candidate list for the current block; A step of deriving movement information of the current block based on the above candidate list; and A step of performing inter prediction on the current block based on motion information of the current block, A video decoding method, wherein the motion information of the current block is stored in at least one of an HMVP list for a coding tree unit row (CTU row) to which the current block belongs or a CHMVP list for a coding tree unit column (CTU column) to which the current block belongs.

2. In paragraph 1, The above CHMVP list is a video decoding method that is generated when starting to decode the first CTU row in the current picture.

3. In paragraph 2, A video decoding method, wherein if the current block belongs to the first CTU column, the motion information of the current block is stored in the CHMVP list.

4. In paragraph 1, A method for decoding a video, wherein the above HMVP list is initialized in units of CTU rows.

5. In paragraph 4, A method for decoding an image, wherein motion information belonging to the above CHMVP list is stored in the above HMVP list.

6. In paragraph 1, A method of decoding an image, wherein the above CHMVP list is generated independently for each CTU column in the current picture.

7. In paragraph 1, A method for decoding an image, wherein an HMVP candidate derived from the above HMVP list and a CHMVP candidate derived from the above CHMVP list are added to the candidate list as independent merge candidates.

8. In paragraph 1, A method for decoding an image, wherein the candidate list is generated by selectively using either the HMVP list or the CHMVP list.

9. Step of generating a candidate list for the current block; A step of deriving movement information of the current block based on the above candidate list; and A step of performing inter prediction on the current block based on motion information of the current block, A video encoding method, wherein the motion information of the current block is stored in at least one of an HMVP list for a coding tree unit row (CTU row) to which the current block belongs or a CHMVP list for a coding tree unit column (CTU column) to which the current block belongs.

10. A computer-readable recording medium storing a bitstream generated based on the image encoding method of Article 9.

Images