KR20220040451A - A method of decoding a video signal and an apparatus having the same - Google Patents

Abstract

The present invention relates to a method for decoding a video signal and a device thereof. According to an embodiment of the present invention, with respect to a method for decoding a video signal and a device thereof, the method for scanning a transform block including a plurality of transform coefficient groups comprises: a step of obtaining transform domain information indicating at least one transform domain included in a transform block; a step of scanning a plurality of transform coefficient groups included in a first transform domain based on the transform domain information; and a step of scanning a plurality of transform coefficient groups included in a second transform region in the transform block.

Description

Video signal decoding method and device thereof

The present invention relates to a method and apparatus for decoding a video signal, and more particularly, to a method and apparatus for decoding a video signal for scanning a transform coefficient group for each of a plurality of transform regions.

Recently, the demand for high-resolution and high-quality images such as HD (High Definition) images and UHD (Ultra High Definition) images is increasing in various application fields. Since the amount of data increases relative to the existing image data as the image data becomes high-resolution and high-quality, when transmitting image data using a medium such as an existing wired/wireless broadband line or storing it using an existing storage medium, the transmission Costs and storage costs will increase. High-efficiency image compression techniques can be used to solve these problems that occur as image data becomes high-resolution and high-quality.

In video compression techniques, various effective methods are employed to improve the compression ratio by more than two times compared to the conventional compression techniques. As an inter prediction technique, a method using a motion vector predictor, a method using a merge mode, and a skip mode are used. These are all techniques for efficiently performing inter-screen prediction.

In addition, in existing video codecs, one picture is divided and split into macroblocks, which are 16x16 block units. However, in recent HEVC, a coding unit (CU) is used as a coding basic unit. The coding unit may be divided up to the maximum and minimum sizes specified by the parameter values stored in the sequence parameter set. A basic unit for prediction encoding is defined as a prediction unit (PU), and the one coding unit is divided into a plurality of the prediction units and predicted. In addition, the encoding and decoding order of each coding unit uses a raster scan method.

As described above, in HEVC, by using coding units of various sizes, it is possible to perform encoding in consideration of spatial resolution and block characteristics of an image effectively. In general, when the resolution of an image is small or pixel values vary greatly locally, it may be effective to perform intra- and inter-screen prediction using small-sized coding units. As described above, when a coding unit having a small size is used, the amount of header bits required for encoding increases, but prediction is relatively precise, so that a quantization error and an amount of bits required for encoding a transform coefficient are reduced.

Conversely, in a region where the spatial resolution of an image is large or a change in pixel values is small, using a large coding unit may increase encoding efficiency. In this case, even when using a large coding unit, the prediction error tends not to increase significantly compared to the case of prediction using a small coding unit. Therefore, when these blocks are encoded, the amount of transmission bits is saved using a large coding unit. can be efficient. However, there is a disadvantage in that it is difficult to efficiently code various images having high resolution even using various conventional coding units.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a video signal decoding method and apparatus for improving coding efficiency of intra prediction using transform blocks having various shapes.

Another object to be solved by the present invention is to provide a method and an apparatus for decoding a video signal capable of increasing coding efficiency by first coding a transform coefficient group in a low frequency domain rather than a high frequency domain.

In a method for decoding a video signal according to an embodiment of the present invention for solving the above problems, in a method of scanning a transform block including a plurality of transform coefficient groups, at least one transform region included in the transform block is provided. obtaining information on the transformation region representing the; scanning a plurality of transform coefficient groups included in a first transform domain based on the transform domain information; and scanning a plurality of transform coefficient groups included in a second transform region in the transform block.

In the plurality of transform coefficient groups, a transform coefficient group of a low frequency domain may be scanned before a transform coefficient group of a high frequency domain.

In an embodiment, the transform domain information may be received from an encoder or obtained from at least one of a sequence parameter set (SPS) and a slice header. Also, the transform domain information may be obtained by a predetermined method in the decoder.

Prior to obtaining the transform domain information, the method may further include determining whether the transform block is a non-square block. The determining may be performed based on a horizontal length and a vertical length of the transform block.

According to an aspect of the present invention, there is provided an apparatus for decoding a video signal, comprising: a transform domain information obtaining unit configured to obtain transform domain information indicating at least one transform domain included in a transform block; and a transform coefficient group scan unit configured to sequentially scan a plurality of transform coefficient groups included in the transform region for each of the at least one transform region based on the transform region information.

According to an embodiment of the present invention, when the transform block is a non-square block, the transform block is divided into at least one transform domain including a part of a plurality of transform coefficient groups, and the transform coefficient groups included in the transform domain are sequentially scanned. Accordingly, it is an object of the present invention to provide a video signal decoding method and apparatus for improving the coding efficiency of intra prediction.

In addition, according to another embodiment of the present invention, by dividing a transform block into at least one transform region and sequentially scanning transform coefficient groups included in the divided transform region, the transform coefficient group of the low frequency region is selected before the high frequency region. An object of the present invention is to provide a method and apparatus for decoding a video signal capable of increasing coding efficiency by coding.

1 is a schematic block diagram of a video encoding apparatus according to an embodiment of the present invention.
2 is a block diagram schematically illustrating a video decoding apparatus according to an embodiment of the present invention.
3 is for explaining the structure of a conventional transform block.
4 is a diagram for describing a transform coefficient group constituting a conventional 16x16 transform block.
5 is a diagram for describing a transform coefficient group and a transform scan method of the transform coefficient group according to a general method.
6A to 6D are for describing a transform coefficient group according to a general method and types of scanning methods for the transform coefficient group.
7A and 7B are for explaining an example in which a general scan method is applied to a transform block according to an embodiment of the present invention.
FIG. 8 is for explaining an example in which a general scan method is applied to transform coefficients of a 16x8 transform block.
9 is a flowchart illustrating a method of scanning a transform coefficient group according to an embodiment of the present invention.
10 illustrates an apparatus for scanning a transform coefficient group according to an embodiment of the present invention.
11A and 11B are for explaining a method of scanning a transform coefficient group for a non-square transform block according to an embodiment of the present invention.
12A to 13D are examples for explaining various methods of scanning a transform coefficient group for a non-square transform block according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Examples of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, and the scope of the present invention is as follows It is not limited to an Example. Rather, these examples are provided so that this disclosure will be more thorough and complete, and will fully convey the spirit of the invention to those skilled in the art.

In addition, in the drawings, the thickness or size of each unit is exaggerated for convenience and clarity of description, and the same reference numerals in the drawings refer to the same elements. As used herein, the term “and/or” includes any one and all combinations of one or more of those listed items.

The terminology used herein is used to describe specific embodiments, not to limit the present invention. As used herein, the singular form may include the plural form unless the context clearly dictates otherwise. Also, as used herein, “comprise” and/or “comprising” refers to the specified presence of the recited shapes, numbers, steps, actions, members, elements, and/or groups thereof. and does not exclude the presence or addition of one or more other shapes, numbers, movements, members, elements and/or groups.

Although the terms first, second, etc. are used herein to describe various components, members, parts, regions, and/or parts, these components, members, parts, regions, and/or parts are used herein to refer to these terms. It is obvious that it should not be limited by These terms are used only to distinguish one component, member, part, region or portion from another region or portion. Accordingly, a first component, member, component, region or portion discussed below may refer to a second component, member, component, region or portion without departing from the teachings of the present invention. Also, and/or terms include combinations of a plurality of related recited items or any of a plurality of related recited items.

When a component is referred to as being “connected” or “connected” to another component, it is not only directly connected or connected to the other component, but also between the component and the other component. It should be understood including the case where other components exist in However, when a component is referred to as being “directly connected” or “directly connected” to another component, there is no other component in the middle and the component and the other component are directly connected or connected to each other. should be understood as being

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings schematically illustrating ideal embodiments of the present invention. In the drawings, for example, the size and shape of the members may be exaggerated for convenience and clarity of description, and in actual implementation, variations of the illustrated shape may be expected. Accordingly, embodiments of the present invention should not be construed as limited to the specific shapes of the regions shown herein.

1 is a block diagram schematically illustrating an image encoding apparatus according to an embodiment of the present invention.

Referring to FIG. 1 , the image encoding apparatus 100 includes an image division unit 105 , an inter prediction unit 110 , an intra prediction unit 115 , a transform unit 120 , a quantization unit 125 , and a rearrangement unit. 130 , an entropy encoding unit 135 , an inverse quantization unit 140 , an inverse transform unit 145 , a filter unit 150 , and a memory 155 .

Each component shown in FIG. 1 is independently illustrated to represent different characteristic functions in the image encoding apparatus, and does not mean that each component is composed of separate hardware or one software component. That is, each component is listed as each component for convenience of description, and at least two components of each component are combined to form one component, or one component is divided into a plurality of components to provide a function. can be done An embodiment in which each of these components is integrated or a separate embodiment may be included in the scope of the present invention without departing from the essential aspect of the present invention.

The image dividing unit 105 may divide the input image into at least one processing unit. The processing unit may be a prediction block (hereinafter referred to as "PU"), a transform block (hereinafter referred to as "TU"), or a coding block (Coding Unit, hereinafter referred to as "CU") ) may be However, in the present specification, for convenience of explanation, a prediction block may be expressed as a prediction unit, a transform block may be expressed as a transformation unit, and a coding or decoding block may be expressed as a coding unit or a decoding unit.

In an embodiment, the image segmentation unit 105 divides one image into a combination of a plurality of coding blocks, prediction blocks, and transform blocks, and divides one image into one image based on a predetermined criterion (eg, a cost function). An image may be encoded by selecting a combination of a coding block, a prediction block, and a transform block.

For example, one image may be divided into a plurality of coding blocks. In an embodiment, one picture may divide the coding block using a recursive tree structure such as a quad tree structure or a binary tree structure, and one picture or a largest coding block (largest coding block) unit) as a root, a coding block divided into other coding blocks may be divided having as many child nodes as the number of divided coding blocks. A coding block that is no longer divided through this process may become a leaf node. For example, if it is assumed that only square division is possible with respect to one coding block, one coding block may be divided into, for example, four coding blocks. However, in the present invention, the coding block, the prediction block, and/or the transform block are not limited to symmetric partitioning when partitioning, and an asymmetric partition is also possible, and not only four partitions but also two partitions are possible. However, the number of divisions is merely exemplary and the present invention is not limited thereto.

The prediction block may also be partitioned in the form of at least one square or non-square having the same size within one coding block, and any of the prediction blocks divided within one coding block. One prediction block may be divided to have a shape and size different from that of the other prediction block. In one embodiment, the coding block and the prediction block may be the same. That is, the prediction may be performed based on the divided coding block without distinguishing the coding block and the prediction block.

The prediction unit may include an inter prediction unit 110 performing inter prediction and an intra prediction unit 115 performing intra prediction. In order to increase coding efficiency, an image is predicted by using a specific region inside an image that has already been encoded and decoded, instead of encoding the image signal as it is, and a residual value between the original image and the predicted image is encoded. Also, prediction mode information, motion vector information, etc. used for prediction may be encoded in the entropy encoder 135 together with a residual value and transmitted to the decoder. When a specific encoding mode is used, it is also possible to encode the original block as it is and transmit it to the decoder without generating the prediction block through the inter prediction unit 110 and the intra prediction unit 115 .

In an embodiment, the inter prediction unit 110 and the intra prediction unit 115 determine whether to perform inter prediction or intra prediction on the prediction block, and determine the inter prediction mode and the motion vector. , and specific information according to each of the prediction methods such as a reference image may be determined. In this case, a processing unit in which prediction is performed, a prediction method, and a detailed processing unit may be different. For example, although a prediction mode and a prediction method are determined according to a prediction block, prediction may be performed according to a transform block.

The inter prediction unit 110 and the intra prediction unit 115 may generate a prediction block composed of predicted samples by performing prediction on the processing unit of the image divided by the image division unit 105 . The image processing unit in the inter prediction unit 110 and the intra prediction unit 115 may be a coding block unit, a transform block unit, or a prediction block unit.

The inter prediction unit 110 may predict a prediction block based on information on at least one image of a previous image or a subsequent image of the current image, and in some cases, prediction based on information of a partial region where coding is completed in the current image Blocks can be predicted. The inter prediction unit 110 may include a reference image interpolator, a motion prediction unit, and a motion compensator.

In an embodiment, the information of the one or more images used for prediction by the inter prediction unit 110 may be information of images that have already been encoded and decoded, or information of images that have been transformed and stored in an arbitrary method. there is. For example, the image transformed by the arbitrary method and stored may be an image obtained by enlarging or reducing an image that has been encoded and decoded, or an image in which the brightness of all pixel values in the image is changed or a color format is changed. may be

The reference image interpolator may receive reference image information from the memory 155 and generate pixel information of integer pixels or less from the reference image. In the case of a luminance pixel, pixel information of less than an integer may be generated in units of 1/4 pixels using a DCT-based 8-tap interpolation filter with different filter coefficients. In the case of a color difference signal, pixel information of less than an integer may be generated in units of 1/8 pixel by using a DCT-based interpolation filter that has different filter coefficients. However, the type of filter and the unit for generating pixel information less than or equal to an integer are not limited thereto, and a unit for generating pixel information less than or equal to an integer may be determined by using various interpolation filters.

The motion predictor may perform motion prediction based on the reference image interpolated by the reference image interpolator. Various methods may be used to calculate the motion vector. The motion vector may have a motion vector value in integer pixel units or in 1/2 or 1/4 pixel units based on interpolated pixels. In an embodiment, the motion prediction unit may predict the prediction unit of the current block by using a different motion prediction method. Various methods may be used as the motion prediction method, including a merge method, an advanced motion vector prediction (AMVP) method, and a skip method. As described above, information including the index of the reference image selected by the inter prediction unit 110, the predicted motion vector (MVP), and the residual signal may be entropy-coded and transmitted to the decoder.

Unlike inter prediction, the intra prediction unit 115 may generate a prediction block based on reference pixel information around the current block, which is pixel information in the current image. When the neighboring blocks of the prediction block are blocks on which inter prediction is performed, that is, when the reference pixel is a pixel on which inter prediction is performed, the reference pixel included in the block on which inter prediction is performed is predicted as the neighboring blocks. It can also be used by replacing it with reference pixel information of a block that has performed .

Also, the intra prediction unit 115 may use the most probable intra prediction mode (MPM) obtained from neighboring blocks to encode the intra prediction mode. According to various embodiments of the present invention, the most probable intra prediction mode list (MPM List) composed of the most probable intra prediction modes may be configured in various ways.

Even when the intra prediction unit 115 performs intra prediction, a processing unit in which prediction is performed and a processing unit in which a prediction method and specific content are determined may be different from each other. For example, a prediction mode may be determined as a prediction unit (PU) and prediction may be performed in the prediction unit, or the prediction mode may be determined as a prediction unit, but prediction may be performed in a transform unit (TU). In an embodiment, a prediction mode may be determined in units of coding blocks (CUs), and prediction may be performed in units of coding blocks because the units of coding blocks and prediction units are the same.

The prediction mode of intra prediction may include 65 directional prediction modes and at least two non-directional modes. The non-directional mode may include a DC prediction mode and a planar mode. The number of the 67 inter prediction modes is only an example, and the present invention is not limited thereto. In order to make predictions in various ways, intra prediction may be performed in more directional or non-directional modes.

In an embodiment, intra prediction may generate a prediction block after applying a filter to a reference pixel. In this case, whether to apply the filter to the reference pixel may be determined according to the intra prediction mode and/or size of the current block.

A prediction unit (PU) may be determined in various sizes and shapes from a coding unit (CU) that is no longer split. For example, in the case of inter prediction, the prediction unit may have a size such as 2N x 2N, 2N x N, N x 2N, or N x N. In the case of intra prediction, the prediction unit may have a size such as 2N x 2N or N x N (where N is an integer), but intra prediction can be performed not only with such a forward size but also with a non-forward size shape. In this case, the N x N prediction unit may be set to be applied only in a specific case. In addition to the above-mentioned size of the prediction unit, an intra prediction unit having a size such as N x mN, mN x N, 2N x mN, or mN x 2N (m is a fraction or an integer) may be further defined and used.

A residual value (a residual block or a residual signal) between the prediction block generated by the intra prediction unit 115 and the original block may be input to the transform unit 120 . Also, prediction mode information, interpolation filter information, etc. used for prediction may be encoded by the entropy encoder 135 together with a residual value and transmitted to a decoder.

The transform unit 120 converts an original block as a transform unit and a residual block including residual value information of a prediction unit generated through the prediction units 110 and 115 to DCT (Discrete Cosine Transform), DST (Discrete Sine Transform) , can be transformed using a transformation method such as Karhunen Loeve Transform (KLT). Whether to apply DCT, DST, or KLT to transform the residual block may be determined based on intra prediction mode information of a prediction unit used to generate the residual block.

The transform block in the transform unit 120 may be a TU, and the transform block may include a block having a square shape and/or a block having a non-square shape, and the transform blocks are square. It may have a quad tree structure, a non-square quad tree structure, or a binary tree structure. In an embodiment, the size of the transformation unit may be determined within a range of a predetermined maximum and minimum size. In addition, one transform block may be further divided into sub-transform blocks, and the sub-transform blocks may include a square-shaped block and/or a non-square-shaped block, The transform blocks may have a square quad tree structure, a non-square quad tree structure, or a binary tree structure. Transform blocks having various sizes, shapes, and structures as described above may be used for encoding in consideration of the regional characteristics of the residual signal effectively.

The quantization unit 125 may quantize the residual values transformed by the transform unit 120 to generate a quantization coefficient. In an embodiment, the transformed residual values may be values transformed in the frequency domain. The quantization coefficient may be changed according to the transform unit or the importance of the image, and the value calculated by the quantization unit 125 may be provided to the inverse quantization unit 140 and the rearrangement unit 130 .

The reordering unit 130 may rearrange the quantization coefficients provided from the quantization unit 125 . The reordering unit 130 may improve encoding efficiency in the entropy encoding unit 135 by rearranging the quantization coefficients. The reordering unit 130 may rearrange the quantized coefficients in the form of a two-dimensional block into a form of a one-dimensional vector through a coefficient scanning method. As for the coefficient scanning method, it may be determined which scanning method is used according to the size of the transform unit and the intra prediction mode. The coefficient scanning method may include a zig-zag scan, a vertical scan for scanning two-dimensional block-shaped coefficients in a column direction, and a horizontal scan for scanning two-dimensional block-shaped coefficients in a row direction. In an embodiment, the reordering unit 130 may increase the entropy encoding efficiency of the entropy encoding unit 135 by changing the order of coefficient scanning based on probabilistic statistics of coefficients transmitted from the quantization unit.

The entropy encoding unit 135 may perform entropy encoding on the quantization coefficients rearranged by the reordering unit 130 . For entropy encoding, various encoding methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Content-Adaptive Binary Arithmetic Coding (CABAC) may be used.

The entropy encoding unit 135 includes quantization coefficient information and block type information, prediction mode information, division unit information, prediction unit information and transmission unit information of the coding unit received from the reordering unit 130 and the prediction units 110 and 115, Various information such as motion vector information, reference image information, block interpolation information, and filtering information may be encoded. Also, according to an embodiment, the entropy encoder 135 may apply a certain change to a transmitted parameter set or syntax, if necessary.

The inverse quantization unit 140 inverse quantizes the values quantized by the quantization unit 125 , and the inverse transform unit 145 inversely transforms the values inverse quantized in the inverse quantization unit 140 . The residual values generated by the inverse quantizer 140 and the inverse transform unit 145 may be combined with the prediction blocks predicted by the predictors 110 and 115 to generate a reconstructed block. The image composed of the generated reconstructed blocks may be a motion compensated image or an MC image (Motion Compensated Picture).

The motion compensation image may be input to the filter unit 150 . The filter unit 150 may include a deblocking filter unit, an offset correction unit (Sample Adaptive Offset, SAO), and an adaptive loop filter unit (ALF). In summary, the motion compensation image is deblocking After the deblocking filter is applied in the filter unit to reduce or remove blocking artifacts, it may be input to the offset correcting unit to correct the offset. The image output from the offset correcting unit may be input to the adaptive loop filter unit and pass through an adaptive loop filter (ALF) filter, and the image passing through the filter may be transmitted to the memory 155 .

In detail with respect to the filter unit 150 , the deblocking filter unit may remove distortion within a block generated at a boundary between blocks in a reconstructed image. In order to determine whether to perform deblocking, it may be determined whether to apply the deblocking filter to the current block based on pixels included in several columns or rows included in the block. When a deblocking filter is applied to a block, a strong filter or a weak filter may be applied according to the required deblocking filtering strength. In addition, in applying the deblocking filter, horizontal filtering and vertical filtering may be concurrently processed when vertical filtering and horizontal filtering are performed.

The offset correcting unit may correct an offset with respect to the residual block to which the deblocking filter is applied in units of pixels from the original image. In order to correct the offset for a specific image, a method of dividing pixels included in an image into a certain number of regions, determining an region to be offset, and applying the offset to the region (Band Offset) or the edge of each pixel It may be applied in the form of a method of applying an offset in consideration of information (Edge Offset). However, in an embodiment, the filter unit 150 may not apply filtering to the reconstructed block used for inter prediction.

The adaptive loop filter (ALF) may be performed only when high efficiency is applied based on a value obtained by comparing the filtered reconstructed image and the original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the corresponding group may be determined and filtering may be performed differentially for each group. As for information related to whether to apply the ALF, the luminance signal may be transmitted for each coding unit (CU), and the shape and filter coefficients of the ALF filter to be applied may vary according to each block. Also, the ALF filter of the same type (fixed type) may be applied regardless of the characteristics of the application block.

The memory 155 may store the restored block or image calculated through the filter unit 150 . The reconstructed block or image stored in the memory 155 may be provided to the inter prediction unit 110 or the intra prediction unit 115 that performs inter prediction. The pixel values of the reconstructed blocks used in the intra prediction unit 115 may be data to which the deblocking filter unit, the offset corrector, and the adaptive loop filter unit are not applied.

2 is a block diagram schematically illustrating an image decoding apparatus according to an embodiment of the present invention. Referring to FIG. 2 , the image decoding apparatus 200 includes an entropy decoding unit 210 , a reordering unit 215 , an inverse quantization unit 220 , an inverse transform unit 225 , an inter prediction unit 230 , and an intra prediction unit. It includes a unit 235 , a filter unit 240 , and a memory 245 .

When an image bitstream is input from the image encoding apparatus, the input bitstream may be decoded by a reverse process of a procedure of processing image information in the encoding apparatus. For example, when variable length coding (VLC, hereinafter referred to as "VLC") such as CAVLC is used to perform entropy encoding in the image encoding apparatus, the entropy decoding unit 210 also performs the entropy encoding in the encoding apparatus. Entropy decoding can be performed by implementing the same VLC table as the used VLC table. In addition, when CABAC is used to perform entropy encoding in the encoding apparatus, the entropy decoding unit 210 may perform entropy decoding using CABAC in response thereto.

The entropy decoding unit 210 provides information for generating a prediction block among the decoded information to the inter prediction unit 230 and the intra prediction unit 235, and the entropy decoding unit performs entropy decoding on the residual value. may be input to the rearrangement unit 215 .

The reordering unit 215 may rearrange the entropy-decoded bitstream by the entropy decoding unit 210 based on a method in which the image encoder rearranges the bitstream. The reordering unit 215 may receive information related to coefficient scanning performed by the encoding apparatus, and may perform rearrangement through a method of scanning inversely based on the scanning order performed by the encoding apparatus.

The inverse quantizer 220 may perform inverse quantization based on the quantization parameter provided by the encoding apparatus and the reordered coefficient values of the blocks. The inverse transform unit 225 may perform inverse DCT, inverse DST, or inverse KLT on DCT, DST, or KLT performed by the transform unit of the encoding apparatus on the quantization result performed by the image encoding apparatus. Inverse transform may be performed based on a transmission unit or an image division unit determined by the encoding apparatus. The transform unit of the encoding apparatus may selectively perform DCT, DST, or KLT according to information such as a prediction method, a size of a current block, and a prediction direction, and the inverse transform unit 225 of the decoding apparatus performs the inverse transformation in the transform unit of the encoding apparatus. An inverse transformation method may be determined based on the performed transformation information to perform the inverse transformation.

The prediction units 230 and 235 may generate prediction blocks based on information related to generation of prediction blocks provided from the entropy decoding unit 210 and previously decoded blocks and/or image information provided from the memory 245 . The reconstructed block may be generated using the prediction block generated by the prediction units 230 and 235 and the residual block provided by the inverse transform unit 225 . The specific prediction method performed by the prediction units 230 and 235 may be the same as the prediction method performed by the prediction units 110 and 115 of the encoding apparatus.

The prediction units 230 and 235 may include a prediction unit determiner (not shown), an inter prediction unit 230 , and an intra prediction unit 235 . The prediction unit determining unit receives various information such as prediction unit information input from the entropy decoder 210, prediction mode information of the intra prediction method, and motion prediction related information of the inter prediction method, and receives a prediction block in the current coding block. , and it can be determined whether the prediction block performs inter prediction or intra prediction.

The inter prediction unit 230 uses information necessary for inter prediction of the current prediction block provided from the image encoder, based on information included in at least one of a previous image or a subsequent image of the current image including the current prediction block. can perform inter prediction for the current prediction block.

Specifically, in inter prediction, a prediction block for the current block may be generated by selecting a reference image for the current block and selecting a reference block for the current block. In this case, in order to use the information of the reference image, information on neighboring blocks of the current image may be used. For example, a prediction block for the current block may be generated based on information on the neighboring block by using a skip mode, a merge mode, and a method such as AMVP (Advanced Motion Vector Prediction).

In the AMVP mode, a prediction motion vector list may be configured by selecting a motion information candidate using temporal and spatial neighboring blocks of the current block. In addition, the motion vector of the current block may be decoded using index information and differential motion vector (MVD) on the motion information candidate selected as the prediction motion vector of the current block received from the encoding apparatus.

Also, in the merge mode, motion information candidates may be obtained as merge candidates by using temporal and spatial neighboring blocks of the current block. Among them, the motion vector of the current block may be obtained by using index information on the motion information candidate of the current block received from the encoding apparatus. The motion vector candidates may be obtained as spatial motion vector candidates from a spatial neighboring block of the current block or may be obtained as temporal motion vector candidates from a corresponding block included in the reference image of the current block.

The prediction block may be generated in units of samples equal to or less than an integer, such as 1/2 pixel sample unit and 1/4 pixel sample unit. In this case, the motion vector may also be expressed in units of integer pixels or less. For example, the luminance pixel may be expressed in units of 1/4 pixels and the chrominance pixels may be expressed in units of 1/8 pixels.

Motion information including a motion vector and a reference picture index required for inter prediction of the current block may be derived by checking a skip flag, a merge flag, etc. received from the encoding apparatus and corresponding thereto.

The intra prediction unit 235 may generate a prediction block based on pixel information in the current image. When the prediction unit is a prediction unit on which intra prediction is performed, intra prediction may be performed based on intra prediction mode information of the prediction unit provided by the image encoder. When the neighboring blocks of the prediction unit are blocks on which inter prediction is performed, that is, when the reference pixel is a pixel on which inter prediction is performed, a reference pixel included in the block on which inter prediction is performed is predicted as the neighboring blocks. It can also be used by replacing it with reference pixel information of a block that has performed .

Also, the intra prediction unit 235 may use the most probable intra prediction mode (MPM) obtained from neighboring blocks to encode the intra prediction mode. In an embodiment, the most probable intra prediction mode may use an intra prediction mode of a spatial neighboring block of the current block.

In an embodiment, a processing unit in which prediction is performed by the intra prediction unit 235 and a processing unit in which a prediction method and specific content are determined may be different from each other. For example, a prediction mode may be determined in a prediction unit and prediction may be performed in a prediction unit, or a prediction mode may be determined in a prediction unit and intra prediction may be performed in a transformation unit.

In this case, the prediction block PU may be determined in various sizes and shapes from the coding block CU that is no longer split. For example, in the case of intra prediction, the prediction block may have a size such as 2N x 2N or N x N (N is an integer). , 2N x mN or mN x 2N (m is a fraction or an integer) can also perform intra prediction. In this case, the N x N prediction unit may be set to be applied only in a specific case.

In addition, the transform block (TU) may also be determined in various sizes and shapes. For example, the transform block may have a size such as 2N x 2N or N x N (N is an integer), but not only such a forward size but also a non-forward size shape of N x mN, mN x N, 2N x mN, or In-picture prediction can also be performed with mN x 2N (m is a fraction or an integer). In this case, the N x N prediction unit may be set to be applied only in a specific case. In one embodiment, the transform block is a square structure, a non-square structure, a square quad tree structure, a non-square quad tree structure, or a binary tree ( It may be one of blocks having a binary tree) structure. In an embodiment, the size of the transform block may be determined within a range of a predetermined maximum and minimum size. In addition, one transform block may be divided into sub-transform blocks. In this case, the sub-transform blocks also have a square structure, a non-square structure, a square quad tree structure, and a non-transform block. It may be divided into a non-square quad tree structure or a binary tree structure.

The intra prediction unit 235 may include an Adaptive Intra Smoothing (AIS) filter unit, a reference pixel interpolator unit, and a DC filter unit. The AIS filter unit is a part that performs filtering on the reference pixel of the current block, and may determine whether to apply the filter according to the prediction mode of the current prediction unit and apply the filter. AIS filtering may be performed on the reference pixel of the current block by using the prediction mode and AIS filter information of the prediction unit provided by the image encoder. When the prediction mode of the current block is a mode in which AIS filtering is not performed, the AIS filter unit may not be applied to the current block.

When the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on a sample value obtained by interpolating the reference pixel, the reference pixel interpolator interpolates the reference pixel to generate a reference pixel of a pixel unit having an integer value or less. there is. 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. When the prediction mode of the current block is the DC mode, the DC filter unit may generate the prediction block through filtering.

The reconstructed block and/or image may be provided to the filter unit 240 . The filter unit 240 may include a deblocking filter unit, an offset correction unit (Sample Adaptive Offset) and/or an adaptive loop filter unit in the reconstructed block and/or image. The deblocking filter unit may receive information indicating whether a deblocking filter is applied to a corresponding block or image from an image encoder and information indicating whether a strong filter or a weak filter is applied when the deblocking filter is applied. The deblocking filter unit may receive the deblocking filter related information provided from the image encoder, and the image decoder may perform deblocking filtering on the corresponding block.

The offset correction unit may perform offset correction on the reconstructed image based on the type of offset correction applied to the image during encoding and information on the offset value. The adaptive loop filter unit may be applied as a coding unit based on information such as information on whether or not the adaptive loop filter is applied and information on coefficients of the adaptive loop filter provided from the encoder. The information related to the adaptive loop filter may be provided in a specific parameter set.

The memory 245 may store the reconstructed image or block to be later used as a reference image or reference block, and may also provide the reconstructed image to an output unit.

Although omitted herein for convenience of description, the bitstream input to the decoding apparatus may be input to the entropy decoding unit through a parsing step. Also, the entropy decoding unit may perform a parsing process.

In the present specification, coding may be interpreted as encoding or decoding in some cases, and information includes all values, parameters, coefficients, elements, flags, and the like. can be understood as 'Screen' or 'picture' generally means a unit representing one image in a specific time period, and 'slice' and 'frame' are It is a unit constituting a part, and may be used interchangeably with image if necessary.

A 'pixel', 'pixel' or 'pel' represents the smallest unit constituting one image. Also, as a term indicating a value of a specific pixel, a 'sample' may be used. A sample may be divided into a luminance (Luma) and a chroma (Chroma) component, but in general, a term including both of them may be used. In the above, the color difference component represents a difference between predetermined colors and is generally composed of Cb and Cr.

A 'unit' refers to a basic unit of image processing or a specific position of an image, such as the above-described coding unit, prediction unit, and transformation unit, and in some cases, terms such as 'block' or 'area' and may be used interchangeably. Also, a block may be used as a term indicating a set of samples or transform coefficients composed of M columns and N rows.

3 and 4 are for explaining the structure of a transform block according to a general method and a transform coefficient group for configuring the 16x16 transform block.

Referring to FIG. 3 , one coding block CB may include a plurality of transform blocks TB0, TB1, ..., TB12. The plurality of transform blocks may include transform blocks having various shapes and/or sizes. The transform block may include a block having a square shape and a block having a non-square shape, and the transform block may include a square quad tree structure, a non-square quad tree structure, or a binary tree. It may be one of blocks having a (binary tree) structure.

Referring to FIG. 4 , the transform block 10 may include one or more transform coefficient groups CG0, CG1, ..., CG15. For example, the transform block 10 may be a block having a size of 16x16, and the size of a transform coefficient group included in the transform block may be 4x4. That is, the 16x16 transform block may include 16 4x4 transform coefficient groups, and the index of the transform coefficient group may follow the transform coefficient scan order as shown in FIG. 4 .

5 is a diagram for describing a transform coefficient group and a transform scan method of the transform coefficient group according to a general method.

Referring to FIG. 5 , in general, the scan order of the transform coefficient groups of the transform block 20 may be the same as the scan order of the transform coefficients. For example, when the transform block 20 has a size of 8x8, the size of the transform coefficient group is a block with a size of 4x4, and an up-right diagonal scan method is used for the transform block 20 . , the transform coefficient group applies the same scan method as the transform coefficients. As shown in FIG. 5 , transform coefficients 15 to 0 included in CG3, which is a transform coefficient group at the lower right of the transform block 20, are scanned by an up-right diagonal method, and then the transform coefficient group at the upper right After the transform coefficients are scanned for CG2 in the same manner, transform coefficients included in the transform coefficient group may be scanned in the same manner in the order of the transform coefficient group CG1 at the lower left and the transform coefficient group CG0 at the upper left.

6A to 6D are for describing a transform coefficient group according to a general method and various examples of a scanning method of the transform coefficient group. 6A to 6C show a scanning method of a transform coefficient group in an intra prediction mode, and FIG. 6D shows a scanning method of a transform coefficient group in an inter prediction mode.

Referring to FIGS. 6A to 6C , in the case of intra prediction, an Up-right diagonal scan (FIG. 6A) that scans from the lower right to the upper left, from the right to the left, and from the bottom to the top A horizontal scan (FIG. 6b) of scanning with , and a vertical scan (FIG. 6c) of scanning from the bottom to the top and from the right to the left may be used. Referring to FIG. 6D , in the case of inter-screen prediction, only the up-right diagonal scan method may be used.

In an embodiment, a scanning method of a transform coefficient group in intra prediction may be determined according to an intra prediction mode. For example, when the intra prediction mode indexes 6 to 14 in which the intra prediction mode is prediction in the horizontal direction, the transform coefficient group may be scanned using the vertical scan method, and the intra prediction mode is the prediction in the vertical direction. In the case of indices 22 to 30, the horizontal scan method may be used, and the up-right diagonal scan method may be used for the remaining intra prediction modes.

In video coding until recently, a forward transform block is always considered as a transform block. Therefore, a transform coefficient group and a scan method of transform coefficients in the transform coefficient group have been designed to be suitable for a forward transform block. However, when a non-square transform block is used as a transform block, coding efficiency may be reduced when an existing transform coefficient group and a scan method of a transform coefficient are applied. Accordingly, a method of scanning a transform coefficient group capable of improving coding efficiency according to an embodiment of the present invention will be described with reference to FIGS. 7A to 12B .

7A and 7B are for explaining an example in which a general scan method is applied to a transform block according to an embodiment of the present invention.

Referring to FIG. 7A , when the current transform block TB1 30a is a non-square block and has a size of 8x16, if the existing method is applied as a method of scanning a transform coefficient group and transform coefficients, one of three scan methods will be selected. can For example, the up-right scan method, the vertical scan method, and the lateral scan method are applied from the left among the illustrated examples of scanning a transform coefficient group by applying three existing scan methods to the current transform block 30a to scan the transform coefficient group.

Referring to FIG. 7B , when the current transform block TB2 30b is a non-square block and has a size of 16x8, if the existing method is applied as a method of scanning a transform coefficient group and transform coefficients, one of three scan methods will be selected. can For example, the up-right scan method, the vertical scan method, and the lateral scan method are applied from the left among the illustrated examples of scanning a transform coefficient group by applying the three existing scan methods to the current transform block 30b to scan the transform coefficient group.

FIG. 8 is for explaining an example in which a general scan method is applied to transform coefficients of a 16x8 transform block.

Referring to FIG. 8 , when the horizontal scan method is applied to the current transform block TB2 30b, the same scan method, which is the same scan method, may be applied to a transform coefficient and a transform coefficient group. For example, a plurality of transform coefficient groups including a plurality of transform coefficients may be scanned in units of each transform coefficient group. After scanning the transform coefficients included in the rightmost lowermost transform coefficient group among the transform blocks in a horizontal way, the transform coefficients included in the transform coefficient group located at the left of the rightmost lowermost transform coefficient group are called It can be scanned in a regental fashion. Thereafter, in the same manner, the transform coefficient group unit may also be scanned in a horizontal manner.

Through this conversion process, most of the energy of the residual signal may be gathered in the DC region of the upper left. Therefore, for the efficiency of entropy coding, it may be efficient for the transform coefficients and/or transform coefficient groups of the low frequency region to have an index indicating a scan order of a small value. However, when the scan order of the general transform coefficient group as shown in FIGS. 7A to 8 is applied to the non-square transform block, the transform coefficient group of the high frequency domain can be coded before the transform coefficient group of the low frequency domain, so coding efficiency This can fall.

Therefore, the method of scanning transform scan coefficients according to an embodiment of the present invention divides a transform block into a transform region that is an upper region including a plurality of transform scan coefficients, and scans the transform scan coefficients for each divided transform region. may include

9 and 10 are flowcharts showing a method for scanning a transform coefficient group and an apparatus according to an embodiment of the present invention.

9 and 10 , the transform unit represents a transform domain in which the transform domain information obtaining unit 40 divides a plurality of transform coefficient groups included in a transform block into at least one partition in order to scan the transform coefficient group. Area information may be obtained (S10). The transform block may have various sizes and/or shapes. In an embodiment, the transform block may be a transform block having a non-square shape.

The transform domain information may divide the transform block into at least one domain, and each transform domain may include a plurality of transform coefficient groups. Of course, the transform coefficient group includes a plurality of transform coefficients. Also, the transform domain information may be information received from an encoder. For example, the transformation domain information may be obtained from at least one of a sequence parameter set (SPS) and a slice header, and the present invention is not limited thereto, and the form and level of syntax included in the present invention is not limited thereto. No, it can be any information received from the encoder

In an embodiment, the transform domain information may be obtained by a predetermined method in the decoding apparatus. For example, the transform region information may be obtained by calculating the horizontal length and vertical length of the transform region based on the horizontal length and vertical length of the transform block to determine the size and number of transform regions. Alternatively, the transform region information may determine the size and number of transform regions by dividing the smaller of the horizontal and vertical lengths of the transform block by the block size of the transform coefficient group. The horizontal and vertical lengths, shapes, and number of transformation regions indicated by the transformation region information may follow a method determined by the decoding apparatus, and are not limited to the above-described example.

Thereafter, the transform coefficient group scan unit 50 may scan a plurality of transform coefficient groups in at least one divided transform region based on the transform region information. The transform coefficient group scan unit 50 may include a first transform region scan unit 51 and a second transform region scan unit 52 to scan transform coefficient groups of the divided transform regions. The transform region scan unit is not limited to the first transform region scan unit 51 and the second transform region scan unit 52 , and the transform block may be included in correspondence to the number of divided transform regions.

First, the first transform domain scan unit 51 may scan a plurality of transform coefficient groups included in the first transform domain among a plurality of divided transform domains based on the transform domain information (S20). Thereafter, the second transform region scan unit 52 may scan a plurality of transform coefficient groups included in the second transform region. If three or more transform domain scan units are included, it is assumed that transform coefficient groups included in the transform domain are sequentially scanned.

In an embodiment, the first transform domain scan unit 51 may include transform coefficient groups of a lower frequency domain than the second transform domain scan unit 52 . As described above, in the method of scanning transform coefficient groups of the present invention, the scan order is determined so that the transform coefficient groups of the low frequency domain are scanned before the transform coefficient groups of the high frequency domain, so that the transform coefficient group of the high frequency domain is first coded and transmitted, Since the transform coefficient groups of the low frequency region have a large scan order index, it is possible to solve the disadvantage of inhibiting coding efficiency.

Also, in an embodiment, it may be first determined whether the transform block is a non-square block before obtaining transform domain information. A transform coefficient group corresponding to a high frequency domain is scanned earlier than a transform coefficient group corresponding to a low frequency domain, thereby impairing coding efficiency, which may frequently occur when the transform block is a non-square block. Therefore, before obtaining the transform domain information, it may be first determined whether the current transform block is a non-square block.

In an embodiment, various methods may be employed to determine whether the transform block is a non-square block. For example, it may be determined whether the transform block is a non-square block by comparing the horizontal and vertical lengths of the transform block. Alternatively, information on the size and shape of the transform block is received from the encoding device or determined based on any one or more of partition information, direction information, α, β, and pixel information of the transform block specially acquired by the decoding device can be

Also, it may be determined based on transform block type information indicating the type of the transform block. The transform block type information may be received from the encoding apparatus, or may be calculated by the decoding apparatus based on at least one of partition information, direction information, pixel information, and horizontal length and vertical length information of the transform block. When the transform block is determined to be a non-square block in this way, the transform coefficient group included in the transform region may be scanned for each transform region of the transform block by the method described above with reference to FIGS. 9 and 10 .

11A and 11B are for explaining a method of scanning a transform coefficient group for a non-square transform block according to an embodiment of the present invention.

Referring to FIG. 11A , the non-square transform blocks 60a and 60b of the present invention may have a horizontal length A and a vertical length B. Referring to FIG. The non-square transform blocks 60a and 60b having an AxB size include a plurality of transform coefficient groups and may be divided into transform block regions having an αxβ size. The α and β represent the number of transform coefficient groups included in the transform block. That is, the αxβ region may indicate a region in which α transform coefficient groups exist in the horizontal direction and β transform coefficient groups exist in the vertical direction. In an embodiment, the transformation domain information may include information on α and β. Also, the transformation region information may include information indicating horizontal and vertical sizes of the transformation region. For example, when the non-square transform block 60a has a size of 8x16, αxβ indicating the structure of the transform region may be 2x2, and the size of the transform region dividing the transform block 60a may be 8x8.

Such transform domain information may be calculated as an upper parameter or in a previous decoding process, and may simply be calculated from the number obtained by dividing the smaller of the horizontal and vertical lengths of the non-square transform block by the size of the transform coefficient block. However, the method of obtaining transform domain information in the present invention is not limited thereto.

Referring to FIG. 11B , the transform blocks 60a and 60b divided into a plurality of transform regions may scan the transform coefficient group by applying a scan method determined from a higher parameter or higher process to each transform region. For example, when the transform block 60b having a size of 16x8 is divided into a transform region having a size of 8x8 (αxβ = 2x2), and the transform region and the transform coefficient group are scanned by the up-right scan method, the CG Region A transform coefficient group in 1 may be first scanned by the up-right scan method, and then, a transform coefficient group in CG Region 2 may be scanned by the up-right scan method.

12A to 13D are for explaining various methods of scanning a transform coefficient group for a non-square transform block according to an embodiment of the present invention.

12A to 12D , when the transform block 70 is divided into a transform region having a small side length of the transform block, a transform coefficient group may be scanned in various ways. 12A , when the transform block 70 has a size of 16x32, each of the transform regions CG Region 0 and CG Region 1 (71, 72) may have a size of 16x16. Here, α and β indicating the size of the transformation region in the horizontal and vertical directions may be α=β=4.

In an embodiment, the transform block 70 may sequentially scan the transform coefficient groups included in each transform domain for each transform domain. For example, as shown in FIG. 12B , when the transform block 70 is scanned by the up-right scan method, the 32nd transform coefficient group CG 31 included in the lower second transform region CG Region 1 . The seventeenth transform coefficient group CG 16 is sequentially scanned from can be In addition, the case in which the transform block is divided into two transform regions and the vertical scan method and the horizontal scan method are applied to the transform block are the same as those shown in FIGS. 12C and 12D .

13A to 13D , when the transform block 80 is divided into a transform region having a small side length of the transform block 80, a transform coefficient group may be scanned in various ways. 13A , when the transform block 80 has a size of 32x16, each of the transform regions CG Region 0 and CG Region 1 (81, 82) may have a size of 16x16. Here, α and β indicating the number of transform regions in the horizontal and vertical directions may be α=β=4.

In an embodiment, the transform block 80 may sequentially scan transform coefficient groups included in each transform domain for each transform domain. For example, as shown in FIG. 13B , when the transform block 80 is scanned by the up-right scan method, the second transform coefficient group CG 31 included in the right second transform region 82 is The 17 transform coefficient groups CG 16 are sequentially scanned according to the upwrite method, and then the first transform coefficient group CG 0 is generated from the 16th transform coefficient group CG 15 included in the first transform region CG Region 0 . can be scanned sequentially. Also, as shown in FIG. 13C , when the transform block 80 is scanned by the vertical scan method, the seventeenth transform coefficient group is selected from the 32nd transform coefficient group CG 31 included in the right second transform region 82 . (CG 16) may be sequentially scanned according to the vertical method, and then the first transform coefficient group CG 0 may be sequentially scanned from the 16th transform coefficient group CG 15 included in the first transformation region CG Region 0. there is. A case in which the transform block is divided into two transform regions and the lateral scan method is applied to the transform block is the same as that shown in FIG. 13D .

As described above, according to the method of dividing a transform block into at least one transform domain including a plurality of transform coefficient groups and scanning for each transform domain, the transform coefficient group of the low frequency domain is scanned before the transform coefficient group of the high frequency domain. Therefore, coding efficiency can be improved.

It is common in the art to which the present invention pertains that the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and that various substitutions, modifications and changes are possible within the scope without departing from the technical spirit of the present invention. It will be clear to those who have knowledge.

Claims (10)

Receiving a bitstream including transform region information included in a transform block and indicating transform regions in which the transform block is divided into at least two or more horizontal or vertical directions;
dividing the transform block into the at least two transform domains using the transform domain information;
obtaining a scan method of each of the divided transform regions from the transform region information; and
scanning a plurality of transform coefficient groups included in the divided first transform region and the second transform region according to the scanning method;
The transform coefficient group includes a plurality of transform coefficients. The method of claim 1,
The transform domain information is obtained from at least one of a sequence parameter set (SPS) and a slice header. The method of claim 1,
The video signal decoding method, characterized in that the transform domain information is received from an encoder. The method of claim 1,
The method of decoding a video signal, characterized in that it further comprises determining the type of the transform block. 5. The method of claim 4,
The determining of the type of the transform block is performed based on a horizontal length and a vertical length of the transform block. Receives a bitstream including transform region information included in a transform block and indicating transform regions in which the transform block is divided into at least two horizontal or vertical directions, and generating the transform block by using the transform region information a transform region dividing unit dividing the at least two transform regions; and
A transform coefficient scan for obtaining a scan method of each of the divided transform regions from the transform region information, and scanning a plurality of transform coefficient groups included in the divided first transform region and the second transform region according to the scan method includes wealth,
The transform coefficient group includes a plurality of transform coefficients. 7. The method of claim 6,
The transform domain information is obtained from at least one of a sequence parameter set (SPS) and a slice header. 7. The method of claim 6,
The video signal decoding apparatus, characterized in that the transform domain information is received from an encoder. 7. The method of claim 6,
The video signal decoding apparatus, wherein the bitstream further includes information on the type of the transform block. 10. The method of claim 9,
Information on the type of the transform block is based on the horizontal length and vertical length of the transform block,
and the transform domain divider determines the type of the transform block based on information on the type of the transform block.

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