KR102544554B1 - Method and Apparatus for Expressing Position of Non-zero Coefficients - Google Patents

Abstract

The present disclosure is concerned with efficiently representing the location of non-zero coefficients within a coefficient block. According to one aspect of the present disclosure, in encoding a coefficient block divisible into a plurality of sub-blocks, for a coefficient block, a block determined as an effective block is divided into small blocks of equal size until a single effective coefficient is reached. While dividing recursively, it signals whether or not it is a valid block for each generated block. According to another aspect of the present disclosure, in encoding a coefficient block divisible into a plurality of sub-blocks, a method of efficiently expressing the position of non-zero coefficients in a coefficient block based on the position of the last valid sub-block is provided. .

Description

Method and Apparatus for Expressing Position of Non-zero Coefficients

The present invention relates to video encoding or decoding, and more particularly to representing the location of non-zero coefficients.

The contents described in this part merely provide background information on the present embodiment and do not constitute prior art.

Image compression techniques include spatial prediction and/or temporal prediction to reduce or remove redundancy inherent within video sequences. In block-based video coding, a video frame or slice may be partitioned into blocks. Each block can be further partitioned. Blocks within an intra-coded (I) frame or slice are encoded using spatial prediction with respect to reference samples within neighboring blocks within the same frame or slice. Blocks within an inter-coded (P or B) frame or slice may use spatial prediction with respect to reference samples within neighboring blocks within the same frame or slice or temporal prediction with respect to reference samples within other reference frames. Spatial or temporal prediction results in a predictive block for the block to be encoded. Residual data represents pixel differences between the original block to be encoded and the prediction block.

An inter-coded block is encoded according to a motion vector pointing to a block of reference samples forming a prediction block and residual data representing a difference between the coded block and the prediction block. An intra-coded block is encoded according to an intra-coding mode and residual data. For further compression, the residual data may be transformed from the pixel domain to the transform domain to generate residual transform coefficients, which may then be quantized. Quantized transform coefficients arranged in a two-dimensional array may be scanned in a specific order to generate a one-dimensional vector of transform coefficients for entropy coding.

The main object of the present invention is to efficiently represent the positions of non-zero coefficients in a coefficient block having an array of coefficients divisible into a plurality of (sub)blocks.

According to one aspect of the present invention, an image encoding method is provided, which includes encoding a distribution of significant coefficients that are non-zero coefficients in a coefficient block. The video encoding method may include encoding a significant flag indicating whether a current coefficient block is a valid block having at least one non-zero coefficient; When the valid flag indicates that the current coefficient block is a valid block, for the current coefficient block, sub-blocks determined as valid blocks are selected in n (n is 2 or more determining whether each of the n sub-blocks is a valid block while recursively dividing the sub-blocks into equal-sized sub-blocks of a natural number); skipping encoding of valid flags related to the n sub-blocks if the sizes of the n sub-blocks are greater than or equal to a preset threshold; and encoding valid flags related to the n sub-blocks if the sizes of the n sub-blocks are smaller than a preset threshold.

According to another aspect of the present invention, an image decoding method including determining a distribution of significant coefficients that are non-zero coefficients in a coefficient block is provided. The video decoding method may include parsing a significant flag indicating whether a current coefficient block is a valid block having at least one non-zero coefficient, from a bit stream; When the valid flag indicates that the current coefficient block is a valid block, for the current coefficient block, sub-blocks determined as valid blocks are selected in n (n is 2 or more natural number) of equally sized sub-blocks, and determining whether each of the n sub-blocks is a valid block. In the step of determining whether each of the n sub-blocks is a valid block, if the size of the n sub-blocks is greater than or equal to a preset threshold, parsing of valid flags related to the n sub-blocks is skipped. doing; and parsing valid flags related to the n sub-blocks when the sizes of the n sub-blocks are smaller than a preset threshold.

According to another aspect of the present invention, an image decoding apparatus comprising determining a distribution of significant coefficients that are non-zero coefficients in a coefficient block, comprising: a memory; and one or more processors, the one or more processors configured to perform a method comprising the following steps. The method includes parsing a significant flag from the bit stream indicating whether a current coefficient block is a valid block having at least one non-zero coefficient; When the valid flag indicates that the current coefficient block is a valid block, for the current coefficient block, sub-blocks determined as valid blocks are divided into n equally sized sub-blocks until a single effective coefficient is reached. and performing the step of determining whether each of the n sub-blocks is a valid block while recursively dividing into blocks. In the step of determining whether each of the n sub-blocks is a valid block, if the size of the n sub-blocks is greater than or equal to a preset threshold, parsing of valid flags related to the n sub-blocks is skipped. doing; and parsing valid flags related to the n sub-blocks when the sizes of the n sub-blocks are smaller than a preset threshold.

According to another aspect of the present invention, a method of encoding a coefficient block having an array of coefficients divisible into coefficients of a plurality of sub-blocks is provided. The coding method of the coefficient block may include determining a last valid subblock, wherein the last valid subblock is a last subblock in a subblock scan order having at least one non-zero coefficient; encoding information indicating the location of the determined last valid subblock; Each subblock indicating whether each of the subblocks preceding the last valid subblock in the subblock scan order, except for the upper left subblock of the coefficient block, is a valid subblock having at least one non-zero coefficient. Encoding syntax elements for sub-blocks; and encoding the coefficients of the last valid subblock, the coefficients of the upper left subblock, and the coefficients of the subblocks indicating that the syntax element is a valid subblock having at least one non-zero coefficient.

According to another aspect of the present invention, a method of decoding a coefficient block having an array of coefficients divisible into coefficients of a plurality of sub-blocks is provided. The method of decoding the coefficient block may include decoding information indicating a position of a last valid subblock, wherein the last valid subblock is the last subblock having at least one non-zero coefficient in the subblock scan order; Each subblock indicating whether each of the subblocks preceding the last valid subblock in the subblock scan order, except for the upper left subblock of the coefficient block, is a valid subblock having at least one non-zero coefficient. decoding syntax elements for sub-blocks; and decoding coefficients of the last valid subblock, coefficients of the upper left subblock, and coefficients of subblocks indicating that the syntax element is a valid subblock having at least one non-zero coefficient.

According to another aspect of the present invention, an apparatus for decoding a coefficient block having an array of coefficients divisible into coefficients of a plurality of sub-blocks is provided. The device includes a memory; and one or more processors, the one or more processors configured to perform a method comprising the following steps. The method includes decoding information indicating a location of a last valid sub-block, wherein the last valid sub-block is a last sub-block in the sub-block scan order having at least one non-zero coefficient; Each subblock indicating whether each of the subblocks preceding the last valid subblock in the subblock scan order, except for the upper left subblock of the coefficient block, is a valid subblock having at least one non-zero coefficient. decoding syntax elements for sub-blocks; and decoding coefficients of the last valid subblock, coefficients of the upper left subblock, and coefficients of subblocks indicating that the syntax element is a valid subblock having at least one non-zero coefficient.

1 is an exemplary block diagram of an image encoding apparatus capable of implementing the techniques of this disclosure.
2 is an exemplary diagram of neighboring blocks of a current block.
3 is an exemplary block diagram of a video decoding apparatus capable of implementing the techniques of this disclosure.
4 is a diagram illustrating exemplary scan schemes used for encoding quantized coefficients of a square coefficient block.
5 is a diagram illustrating a more detailed scan sequence of subblocks and coefficients for a diagonal scan method.
6 is a diagram showing an example of a 32×32 coefficient block.
FIG. 7 is a diagram showing subblocks preceding the last valid subblock in the scan order in the 32×32 coefficient block of FIG. 6 .
FIG. 8 is a diagram showing subblocks following the last effective subblock in scan order in the 32×32 coefficient block of FIG. 6 .
9 is a flowchart illustrating a method of encoding a coefficient block by an image encoding apparatus according to an embodiment of the present invention.
10 is a flowchart illustrating a method of encoding a coefficient block by an image decoding apparatus according to an embodiment of the present invention.
FIG. 11 is a diagram showing blocks generated by hierarchically dividing an effective block until a single effective coefficient is reached for the 32×32 block illustrated in FIG. 6 .
12 is a tree formed by scanning blocks generated from the coefficient blocks of FIG. 11 in a diagonal manner.
13 is a diagram illustrating a tree of a simple structure composed of three layers.
14 is a diagram illustrating a 64x64 coefficient block.
15 is a flowchart illustrating a process of processing a large coefficient block by an image decoding apparatus.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary drawings. It should be noted that in adding identification codes to components of each drawing, the same components have the same symbols as much as possible even if they are displayed on different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description will be omitted.

The techniques of this disclosure generally relate to efficiently representing the location of non-zero coefficients (ie, significant coefficients) with respect to a coefficient block, which is an array of quantized coefficients that result from transform and quantization.

1 is an exemplary block diagram of an image encoding apparatus capable of implementing the techniques of this disclosure.

The image encoding apparatus includes a block division unit 110, a prediction unit 120, a subtractor 130, a transform unit 140, a quantization unit 145, an encoding unit 150, an inverse quantization unit 160, an inverse transform unit ( 165), an adder 170, a filter unit 180, and a memory 190. Each component of the image encoding apparatus may be implemented as a hardware chip or may be implemented as software and a microprocessor may execute software functions corresponding to each component.

The block divider 110 divides each picture constituting an image into a plurality of Coding Tree Units (CTUs), and then recursively divides the CTUs using a tree structure. A leaf node in the tree structure becomes a coding unit (CU), which is a basic unit of encoding. As a tree structure, a QuadTree (QT) in which a parent node (or parent node) is divided into four subnodes (or child nodes) of the same size, or a QT structure and a parent node are divided into two subnodes A QTBT (QuadTree plus BinaryTree) structure using a binary tree (BinaryTree, BT) structure may be used. That is, QTBT can be used to divide a CTU into multiple CUs.

In the QTBT (QuadTree plus BinaryTree) structure, the CTU may first be divided into the QT structure. Quadtree splitting can be repeated until the size of the splitting block reaches the minimum block size (MinQTSize) of leaf nodes allowed by QT. If the leaf node of the quad tree is not larger than the maximum block size (MaxBTSize) of the root node allowed in BT, it can be further partitioned into a BT structure. In BT, a plurality of partition types may exist. For example, in some examples, there may be two types of horizontally splitting a block of a corresponding node into two equal-sized blocks (ie, symmetric horizontal splitting) and a vertical splitting type (ie, symmetric vertical splitting). In addition, a type in which a block of a corresponding node is divided into two blocks having an asymmetric shape may additionally exist. The asymmetric form may include a form in which the block of the corresponding node is divided into two rectangular blocks having a size ratio of 1:3, or a form in which the block of the corresponding node is divided in a diagonal direction.

Split information generated by the block division unit 110 by dividing the CTU by the QTBT structure is encoded by the encoder 150 and transmitted to the video decoding apparatus.

Hereinafter, a block corresponding to a CU to be encoded or decoded (ie, a leaf node of QTBT) is referred to as a 'current block'.

The prediction unit 120 predicts a current block and generates a prediction block. The prediction unit 120 includes an intra prediction unit 122 and an inter prediction unit 124 .

In general, each current block in a picture can be coded predictively. Prediction of the current block is performed using intra-prediction techniques (using data from the picture containing the current block) or inter-prediction techniques (using data from pictures previously coded for the picture containing the current block). can be done normally. Inter prediction includes both uni-prediction and bi-prediction.

For each inter predicted block, a set of motion information may be available. A set of motion information may include motion information for forward and backward prediction directions. Here, forward and backward prediction directions are two prediction directions of a bi-directional prediction mode, and the terms "forward direction" and "backward direction" do not necessarily have geometric meanings. Instead, they generally correspond to whether the reference picture is to be presented before (“backwards”) or after (“forward”) the current picture. In some examples, the “forward” and “backward” prediction directions may correspond to reference picture list 0 (RefPicList0) and reference picture list 1 (RefPicList1) of the current picture.

For each prediction direction, the motion information includes a reference index and a motion vector. A reference index can be used to identify a reference picture in the current reference picture list (RefPicList0 or RefPicList1). A motion vector has horizontal (x) and vertical (y) components. In general, the horizontal component represents the horizontal displacement in the reference picture relative to the position of the current block in the current picture, necessary to locate the x-coordinate of the reference block. The vertical component represents a vertical displacement in the reference picture relative to the position of the current block, required to locate the y-coordinate of the reference block.

The inter-prediction unit 124 searches for a block most similar to the current block within the encoded and decoded reference picture prior to the current picture, and generates a prediction block for the current block using the searched block. Then, a motion vector corresponding to displacement between the current block in the current picture and the prediction block in the reference picture is generated. In general, motion estimation is performed on the luma component, and a motion vector calculated based on the luma component is used for both the luma component and the chroma component. Motion information including information on reference pictures and motion vectors used to predict the current block is encoded by the encoder 150 and transmitted to the video decoding apparatus.

Various methods may be used to minimize the amount of bits required to encode motion information.

For example, when the reference picture and motion vector of the current block are the same as the reference picture and motion vector of the neighboring block, the motion information of the current block can be transmitted to the decoding apparatus by encoding information capable of identifying the neighboring block. This method is called 'merge mode'.

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

Neighboring blocks for deriving a merge candidate include a left block (L) adjacent to the current block in the current picture, an upper block (A), an upper right block (AR), and a lower left block (BL), as shown in FIG. ), all or part of the upper left block AL may be used. Also, a block located in a reference picture (which may be the same as or different from a reference picture used to predict the current block) other than the current picture in which the current block is located may be used as a merge candidate. For example, a block co-located with the current block in the reference picture or blocks adjacent to the co-located block may be additionally used as a merge candidate.

The inter prediction unit 124 constructs a merge list including a predetermined number of merge candidates using these neighboring blocks. Among the merge candidates included in the merge list, a merge candidate to be used as motion information of the current block is selected, and merge index information for identifying the selected candidate is generated. The generated merge index information is encoded by the encoder 150 and transmitted to the decoding device.

Another method of encoding motion information is encoding differential motion vectors.

In this method, the inter prediction unit 124 derives predicted motion vector candidates for the motion vector of the current block by using neighboring blocks of the current block. Neighboring blocks used to derive predictive motion vector candidates include a left block (L), an upper block (A), an upper right block (AR), and a lower left block adjacent to the current block in the current picture shown in FIG. 5 ( BL), and all or part of the upper left block (AL) may be used. In addition, a block located in a reference picture (which may be the same as or different from the reference picture used to predict the current block) other than the current picture in which the current block is located will be used as a neighboring block used to derive motion vector candidates. may be For example, a block co-located with the current block in the reference picture or blocks adjacent to the co-located block may be used.

The inter-prediction unit 124 derives predicted motion vector candidates using the motion vectors of the neighboring blocks, and determines a predicted motion vector for the motion vector of the current block using the predicted motion vector candidates. Then, a differential motion vector is calculated by subtracting the predicted motion vector from the motion vector of the current block.

The predicted motion vector may be obtained by applying a predefined function (eg, median value, average value operation, etc.) to predicted motion vector candidates. In this case, the video decoding apparatus also knows the predefined function. In addition, since a neighboring block used to derive a predicted motion vector candidate is a block that has already been encoded and decoded, the video decoding apparatus also knows the motion vector of the neighboring block. Therefore, the video encoding apparatus does not need to encode information for identifying a predictive motion vector candidate. Therefore, in this case, information on differential motion vectors and information on reference pictures used to predict the current block are encoded.

Meanwhile, the predicted motion vector may be determined by selecting one of the predicted motion vector candidates. In this case, along with information on differential motion vectors and information on reference pictures used to predict the current block, information for identifying the selected predictive motion vector candidate is additionally encoded.

The intra predictor 122 predicts pixels in the current block using pixels (reference pixels) located around the current block in the current picture including the current block. A plurality of intra prediction modes exist according to prediction directions, and neighboring pixels to be used and operation expressions are defined differently according to each prediction mode. In particular, the intra prediction unit 122 may determine an intra prediction mode to be used for encoding the current block. In some examples, the intra prediction unit 122 may encode the current block using several intra prediction modes and select an appropriate intra prediction mode to use from the tested modes. For example, the intra prediction unit 122 calculates rate-distortion values using rate-distortion analysis for several tested intra-prediction modes, and selects a rate-distortion having the best rate-distortion characteristics among the tested modes. Intra prediction mode can also be selected.

The intra predictor 122 selects one intra prediction mode from among a plurality of intra prediction modes, and predicts a current block using neighboring pixels (reference pixels) determined according to the selected intra prediction mode and an arithmetic expression. Information on the selected intra prediction mode is encoded by the encoder 150 and transmitted to the video decoding apparatus.

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

The transform unit 140 transforms the residual signal in the residual block having pixel values in the spatial domain into transform coefficients in the frequency domain. The transform unit 140 may transform the residual signals in the residual block by using the size of the current block as a transform unit, or divide the residual block into a plurality of smaller subblocks and transform the residual signals into subblock size transform units. can also be converted. There may be various methods of dividing a residual block into smaller subblocks. For example, it may be divided into subblocks having the same predefined size, or a QT (quadtree) method partitioning using a residual block as a root node may be used.

The quantization unit 145 quantizes transform coefficients output from the transform unit 140 and outputs the quantized transform coefficients to the encoder 150 .

The encoder 150 encodes the quantized transform coefficients using a coding scheme such as CABAC to generate a bitstream. This encoding is typically performed on the quantized transform coefficients using one of a plurality of available scan patterns.

One aspect of the techniques of this disclosure relates to efficiently representing the location of non-zero coefficients (ie, significant coefficients) with respect to a coefficient block, which is generally an array of quantized coefficients that result from transform and quantization. As such, certain techniques of the present disclosure may be performed by the encoder 150 . That is, for example, the encoder 150 may perform the techniques of the present disclosure described with respect to FIGS. 6 to 15 below. In other examples, one or more other units of the encoding device may additionally be involved in performing the techniques of this disclosure.

In addition, the encoder 150 encodes information such as CTU size, MinQTSize, MaxBTSize, MaxBTDepth, MinBTSize, QT splitting flag, BT splitting flag, and splitting type related to block splitting so that the video decoding apparatus can perform the same operation as the video encoding apparatus. Blocks can be split.

The encoder 150 encodes prediction type information indicating whether the current block is coded by intra prediction or inter prediction, and encodes intra prediction information or inter prediction information according to the prediction type.

When the current block is intra predicted, a syntax element for an intra prediction mode is encoded as intra prediction information. When the current block is inter-predicted, the encoder 150 encodes syntax elements for inter-prediction information. Syntax elements for inter prediction information include the following.

(1) Mode information indicating whether the motion information of the current block is coded in a merge mode or a differential motion vector encoding mode.

(2) Syntax elements for motion information

When motion information is encoded by merge mode, the encoder 150 uses merge index information indicating which of merge candidates is selected as a candidate for extracting motion information of the current block as a syntax element for the motion information. Encode.

On the other hand, when motion information is coded using a differential motion vector encoding mode, information on differential motion vectors and information on reference pictures are encoded as syntax elements for motion information. If the predicted motion vector is determined by selecting one of a plurality of predicted motion vector candidates, the syntax element for the motion information further includes predictive motion vector identification information for identifying the selected candidate. include

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

The adder 170 restores the current block by adding the restored residual block and the predicted block generated by the predictor 120. Pixels in the reconstructed current block are used as reference pixels when intra-predicting the next block.

The filter unit 180 performs deblocking filtering on boundaries between reconstructed blocks in order to remove blocking artifacts generated due to block-by-block encoding/decoding and stores them in the memory 190. When all blocks in one picture are reconstructed, the reconstructed picture is used as a reference picture for inter-prediction of blocks in the picture to be encoded later.

Hereinafter, a video decoding apparatus will be described.

3 is an exemplary block diagram of a video decoding apparatus capable of implementing the techniques of this disclosure.

The image decoding apparatus includes a decoding unit 310, an inverse quantization unit 320, an inverse transform unit 330, a prediction unit 340, an adder 350, a filter unit 360, and a memory 370. Like the video encoding apparatus of FIG. 2 , each component of the video decoding apparatus may be implemented as a hardware chip or implemented as software and a microprocessor may execute software functions corresponding to each component.

The decoder 310 decodes the bitstream received from the video encoding device, extracts information related to block division, determines a current block to be decoded, predictive information required to reconstruct the current block, and information on a residual signal, etc. extract

The decoder 310 determines the size of the CTU by extracting information about the CTU size from a Sequence Parameter Set (SPS) or a Picture Parameter Set (PPS), and divides the picture into CTUs of the determined size. In addition, the CTU is divided using the tree structure by determining the CTU as the top layer of the tree structure, that is, the root node, and extracting division information for the CTU. For example, when splitting a CTU using a QTBT structure, first, a first flag (QT_split_flag) related to splitting of QT is extracted and each node is split into four nodes of a lower layer. Then, for a node corresponding to a leaf node of QT, a second flag (BT_split_flag) related to BT splitting and split type information are extracted to split the corresponding leaf node into a BT structure.

Meanwhile, when the decoder 310 determines a current block to be decoded through partitioning of a tree structure, it extracts information about a prediction type indicating whether the current block is intra-predicted or inter-predicted.

When the prediction type information indicates intra prediction, the decoder 310 extracts syntax elements for intra prediction information (intra prediction mode) of the current block.

When the prediction type information indicates inter prediction, the decoder 310 extracts syntax elements for the inter prediction information. First, mode information indicating whether the motion information of the current block has been encoded by which mode among a plurality of encoding modes is extracted. Here, the plurality of encoding modes include a merge mode including a skip mode and a differential motion vector encoding mode. When the mode information indicates the merge mode, the decoder 310 extracts, as a syntax element for the motion information, merge index information indicating which of merge candidates to derive the motion vector of the current block from. On the other hand, when the mode information indicates the differential motion vector encoding mode, the decoding unit 310 extracts information on the differential motion vector and information on a reference picture referred to by the motion vector of the current block as syntax elements for the motion vector. do. Meanwhile, when an image encoding apparatus uses one of a plurality of predictive motion vector candidates as a predictive motion vector of a current block, predictive motion vector identification information is included in the bitstream. Therefore, in this case, not only information on the differential motion vector and information on the reference picture, but also prediction motion vector identification information is extracted as a syntax element for the motion vector.

Meanwhile, the decoder 310 extracts information on quantized transform coefficients of the current block as information on the residual signal. Another aspect of the techniques of this disclosure relates generally to efficiently decoding the location of non-zero coefficients (ie, significant coefficients) relative to a coefficient block, which is an array of quantized coefficients that result from transform and quantization. Accordingly, certain techniques of this disclosure may be performed by decryption unit 310 . That is, for example, the decoder 310 may perform the techniques of the present disclosure described with respect to FIGS. 4 to 15 below. In other examples, one or more other units of the encoding device may additionally be involved in performing the techniques of this disclosure.

The inverse quantization unit 320 inversely quantizes the quantized transform coefficients, and the inverse transform unit 330 inversely transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain to restore residual signals, thereby generating a residual block for the current block.

The prediction unit 340 includes an intra prediction unit 342 and an inter prediction unit 344 . The intra predictor 342 is activated when intra prediction is the prediction type of the current block, and the inter predictor 344 is activated when intra prediction is the prediction type of the current block.

The intra-prediction unit 342 determines an intra-prediction mode of the current block from among a plurality of intra-prediction modes from the syntax element for the intra-prediction mode extracted from the decoder 310, and reference pixels around the current block according to the intra-prediction mode. Predict the current block using .

The inter predictor 344 determines motion information of the current block using the syntax element for the intra prediction mode extracted from the decoder 310 and predicts the current block using the determined motion information.

First, the inter prediction unit 344 checks mode information in the inter prediction extracted from the decoding unit 310. When the mode information indicates a merge mode, the inter predictor 344 constructs a merge list including a predetermined number of merge candidates using neighboring blocks of the current block. The inter predictor 344 configures the merge list in the same way as the inter predictor 124 of the video encoding apparatus. Then, one merge candidate is selected from among merge candidates in the merge list using the merge index information transmitted from the decoder 310 . Then, the motion information of the selected merge candidate, that is, the motion vector and reference picture of the merge candidate are set as the motion vector and reference picture of the current block.

On the other hand, when the mode information indicates the differential motion vector encoding mode, the inter predictor 344 derives motion vector prediction candidates using the motion vectors of neighboring blocks of the current block, and uses the motion vectors of the prediction motion vector candidates for the current block. Determines a predicted motion vector for the motion vector of . A method for the inter predictor 344 to derive predictive motion vector candidates is the same as that of the inter predictor 124 of the video encoding apparatus. If an image encoding apparatus uses one of a plurality of predictive motion vector candidates as a predictive motion vector of a current block, a syntax element for motion information includes predictive motion vector identification information. Therefore, in this case, the inter predictor 344 may select a candidate indicated by the predicted motion vector identification information among the predicted motion vector candidates as the predicted motion vector. However, when the video encoding apparatus determines the predicted motion vector by using a function predefined for a plurality of predicted motion vector candidates, the inter predictor may determine the predicted motion vector by applying the same function as that of the video encoding apparatus. When the predicted motion vector of the current block is determined, the inter predictor 344 determines the motion vector of the current block by adding the predicted motion vector and the differential motion vector transmitted from the decoder 310 . Then, a reference picture referred to by the motion vector of the current block is determined using the information on the reference picture transmitted from the decoder 310 .

When the motion vector of the current block and the reference picture are determined in merge mode or differential motion vector coding mode, the inter-prediction unit 342 generates a prediction block of the current block using the block at the position indicated by the motion vector in the reference picture. do.

The adder 350 restores the current block by adding the residual block output from the inverse transform unit and the prediction block output from the inter prediction unit or intra prediction unit. Pixels in the reconstructed current block are used as reference pixels when intra-predicting a block to be decoded later.

The filter unit 360 performs deblocking filtering on boundaries between reconstructed blocks and stores them in the memory 370 in order to remove blocking artifacts generated by block-by-block decoding. When all blocks in one picture are reconstructed, the reconstructed picture is used as a reference picture for inter-prediction of blocks in the picture to be decoded later.

As noted above, the techniques of this disclosure are concerned with efficiently encoding and decoding the location of non-zero coefficients (i.e., significant coefficients) relative to a coefficient block, which is an array of quantized coefficients that result from transform and quantization. Some of the disclosed techniques can be applied directly to a residual block that has not undergone transformation.

In the H.265 (HEVC) standard, a total of six syntaxes are used to express the position of a non-zero coefficient among quantized coefficients that have undergone a quantization process.

1. last_sig_coeff_x_prefix

2. last_sig_coeff_y_prefix

3. last_sig_coeff_x_suffix

4. last_sig_coeff_y_suffix

5. coded_sub_block_flag

6. sig_coeff_flag

The previous four syntaxes relate to the position of the last significant coefficient in the scan order in the coefficient block, and separately indicate the x component and y component for that position, respectively, and each component is It is expressed by dividing it into a prefix and a suffix. coded_sub_block_flag is a flag indicating whether each sub-block includes one or more non-zero coefficients by dividing a coefficient block into a plurality of sub-blocks. Here, coded_sub_block_flag is displayed as “0” if all coefficients in the corresponding sub block are zero, and as “1” if one or more non-zero coefficients exist. sig_coeff_flag is a flag indicating whether each coefficient in one subblock is non-zero or zero. sig_coeff_flag is displayed as "0" for zero coefficients and as "1" for non-zero coefficients .

The coded_sub_block_flag syntax is signaled only in the sub-block preceding the last significant sub-block in which the last significant coefficient exists in the scan order for the coefficient block. When coded_sub_block_flag is “1”, sig _ coeff _flag syntax for each of all coefficients in the sub-block is signaled.

Coding of the coefficients within a coefficient block is typically performed using one of a plurality of available scan schemes. 4 is a diagram illustrating exemplary scan schemes used for encoding quantized coefficients of a square coefficient block. These scan methods include an up-right diagonal method, a horizontal method, and a vertical method. When the encoding target block is encoded using the inter-prediction method, the coefficients of the block are scanned in an up-right diagonal method, and when the encoding target block is encoded using the intra-prediction method, the coefficients of the block are scanned according to the intra-prediction mode. By selecting one of the types, the coefficients of the corresponding block are scanned.

The illustrated scan scheme shows the same type of scan pattern for subblocks in a coefficient block and coefficients in each subblock. For example, in the case of the horizontal scan method, the scan order of subblocks is also the horizontal method, and the scan order of coefficients in each subblock is also the horizontal method. 5 shows a more detailed scan sequence of subblocks and coefficients for the diagonal scan method. However, the order of being stored in the actual bitstream is stored in the reverse order of the scan order. That is, they are stored in the bitstream in the order from the pixel at position 255 in FIG. 5 to the pixel at position 0. In other words, once the location of the last valid (non-zero) coefficient is known, the coefficients can be decoded in the opposite direction of the scan order towards the first coefficient in the scan pattern, as described further below.

6 is a diagram showing an example of a 32×32 coefficient block. Here, the diagonal method was used for the scanning method of the 32×32 coefficient block, and pixels marked in gray represent non-zero coefficients, pixels marked in black represent the last non-zero coefficient in the scan order, and other The white coefficients all have zero values. If the coded_sub_block_flag and sig_coeff_flag syntaxes among the above three pieces of information indicating the location of non - zero coefficients are applied to the block illustrated in FIG . 6, the number of bits required to indicate these two syntaxes is as follows. coded_sub_block_flag requires 30 bits for 30 sub-blocks (sub-blocks marked in bold in FIG. 6) out of a total of 64 sub-blocks, considering the position of the last significant coefficient. Coded_sub_block_flag is not signaled for an upper-left sub-block including a DC component. The coefficient block of FIG . 6 has 7 subblocks (i.e., valid subblocks) containing one or more non-zero coefficients , so to indicate sig_coeff_flag for the 7 valid subblocks, approximately 112 bits (= 7×16; less than 16 bits may be required for the last valid subblock). As a result, the number of bits required to express the two syntaxes for the coefficient block of FIG. 6 is approximately 142 bits (= 30 + 112).

As described above, to reduce the overhead of flag bits, the last significant coefficient position is used. The problem is that since the size of the transform block currently being discussed can be as large as 64 × 64 or 128 × 128, a considerable number of bits are required for encoding the syntax expressing the position of the last significant coefficient as an x-axis component and a y-axis component. will be.

In order to provide a similar function while requiring fewer bits, the present invention proposes a method of signaling information indicating the location of a last significant sub-block within a coefficient block to be encoded. Here, the last valid subblock is the last subblock in the subblock scan order having at least one non-zero coefficient. There are a total of four methods for efficiently expressing the position of the last valid subblock proposed by the present invention.

(1) X-axis index and Y-axis index within the coefficient block of the last valid subblock

(2) The number of subblocks preceding the last valid subblock in scan order

(3) The number of subblocks following the last valid subblock in scan order

(4) Determines an advantageous method among (2) method or (3) method according to the position of the last valid subblock in the coefficient block, and signals a flag indicating the determined method and number information according to the determined method.

For example, for the 32×32 coefficient block illustrated in FIG. 6, the positions of the last effective subblocks are expressed in the four methods proposed above as follows.

(1) (3, 4) - Referring to FIG. 7 or 8, the last effective subblock in the scan order within the coefficient block is X axis index 3 and Y axis index 4 in terms of horizontal and vertical positions from the upper left subblock. have

(2) 31 (when using the diagonal scan method) - Referring to FIG. 7, the number of subblocks preceding the last effective subblock in the scan order is 31.

(3) 32 (when using the diagonal scan method) - Referring to FIG. 8, the number of subblocks following the last effective subblock in the scan order is 32.

(4) 0 31 or 1 32 - Here, the underlined “ 0 ” and “ 1 ” are flag values indicating which method (2) or (3) is used.

Based on the method of signaling the position of the last valid subblock as described above, a method of encoding a coefficient block by an image encoding apparatus and an overall process of decoding a coefficient block by an image decoding apparatus will be described with reference to FIGS. 9 and 10, respectively. .

9 is a flowchart illustrating a method of encoding a coefficient block by an image encoding apparatus according to an embodiment of the present invention.

First, the video encoding apparatus determines the last significant sub-block in the current coefficient block to be encoded (S910). Here, the last valid subblock is the last subblock in the subblock scan order having at least one non-zero coefficient.

The video encoding apparatus encodes information indicating the position of the determined last valid subblock (S920). In some embodiments, the information indicating the position of the last valid sub-block may be (1) an X-axis index and a Y-axis index value within a coefficient block of the last valid sub-block. In some other embodiments, the information indicating the position of the last valid sub-block may be information on the number of sub-blocks preceding the last valid sub-block in the scan order. In some other embodiments, the information indicating the location of the last valid subblock may be information on the number of subblocks following the last valid subblock in the scan order. In some other embodiments, the information indicating the location of the last valid sub-block is information selected from among information on the number of sub-blocks preceding the last valid sub-block in the scan order and information on the number of sub-blocks following the last valid sub-block, and which information is It may contain a flag value indicating whether it has been selected.

The image encoding apparatus determines whether each of the subblocks preceding the last valid subblock in the subblock scan order, excluding the upper left subblock of the coefficient block, is a valid subblock having at least one non-zero coefficient. Syntax elements for each sub-block pointing to are encoded (S930). In this case, the upper left subblock of the coefficient block and the last valid subblock may be set as valid subblocks having at least one non-zero coefficient.

The image encoding apparatus includes coefficients of the upper left subblock of the coefficient block, coefficients of the last valid subblock, coefficients of subblocks indicating that the syntax element is a valid subblock having at least one non-zero coefficient, Coefficients of subblocks set as valid subblocks are encoded (S940). The process of encoding these coefficients may include a process of encoding a flag indicating whether each coefficient in the corresponding sub-blocks is non-zero or zero. The image encoding apparatus skips coding of coefficients of subblocks indicated by the syntax element not being a valid subblock having at least one non-zero coefficient. Also, the image encoding apparatus skips encoding of coefficients of subblocks following the last effective subblock in the subblock scanning order.

10 is a flowchart illustrating a method of encoding a coefficient block by an image decoding apparatus according to an embodiment of the present invention.

The video decoding apparatus decodes information indicating the position of the last valid subblock in the current coefficient block to be decoded from the encoded bitstream (S1010).

The video decoding apparatus is configured to have at least one non-zero coefficient in each sub-block except for an upper-left sub-block of the coefficient block among sub-blocks that precede the last effective sub-block in a sub-block scan order from an encoded bitstream. A syntax element for each sub-block indicating whether it is a valid sub-block is decoded (S1020). In this case, the upper left subblock of the coefficient block and the last valid subblock may be set as valid subblocks having at least one non-zero coefficient.

The video decoding apparatus determines, from an encoded bitstream, coefficients of an upper-left subblock of the coefficient block, coefficients of the last valid subblock, and the syntax element are a valid subblock having at least one non-zero coefficient. Coefficients of the indicated subblocks and coefficients of subblocks set as valid subblocks are decoded (S1030). The process of decoding these coefficients may include a process of decoding a flag indicating whether each coefficient in the corresponding sub-blocks is non-zero or zero. The video decoding apparatus skips decoding of coefficients of subblocks indicating that the syntax element is not a valid subblock having at least one non-zero coefficient. Also, the video decoding apparatus skips decoding coefficients of subblocks following the last valid subblock in the subblock scanning order.

The method described above is a method of preferentially signaling the location of the last effective coefficient or the last valid subblock, noting that most of the locations of non-zero coefficients are concentrated in low-frequency components after transformation and are not located in high-frequency components. Hereinafter, a technique capable of efficiently expressing the location of non-zero coefficients is proposed. This technique may be more useful when the transform of the block to be encoded is skipped and thus a residual value itself is transmitted instead of high and low frequency components (or coefficients).

Hierarchical division of valid blocks

Another technique proposed by the present invention is to divide sub-blocks (effective blocks) including at least one non-zero coefficient into n (2 or more natural numbers) equal sizes for a current coefficient block until a single significant coefficient is reached. While recursively dividing into small sub-blocks (squares) of , a valid flag ( significant_flag ) is used to signal whether or not it is a valid block for each generated sub-block. The valid flag is expressed as "1" when one or more non-zero coefficients (ie, valid coefficients) exist in one sub-block, and as "0" when all coefficients are zero. If the valid flag value is “0”, the corresponding sub-block is not further divided, and the valid flag values for the blocks of the lower layer are no longer needed. Conversely, if the valid flag value is “1”, the corresponding block is divided into n (a natural number greater than or equal to 2) subblocks, and the valid flag values for subblocks of the lower layer are signaled.

If the valid flag value of a given coefficient block is “0”, the corresponding block is not further divided, and thus the valid flag values for blocks in the lower layer are no longer needed. Conversely, if the effective flag value of a given coefficient block is “1” and it is a square-shaped coefficient block, it is divided into four square blocks of the lower layer, and it is expressed whether non-zero coefficients exist for each of the four blocks. . Since the effective block is repeatedly divided until reaching a single effective coefficient, the size of the generated block includes from the size of the coefficient block to the size of 1×1 (i.e., a single coefficient). For example, if the coefficient block is 8x8, the block for which the valid flag is determined includes all sizes of 8x8, 4x4, 2x2, and 1x1.

When a valid flag value of a given coefficient block is “1” and is a rectangular coefficient block, the number of square blocks in the lower layer may vary depending on the size of the corresponding coefficient block. For example, if the coefficient block is 16x8, the square block divided into lower layers becomes two 8x8s, and if the coefficient block is 4x16, the square blocks divided into lower layers become four 4x4s. do. That is, when a given coefficient block is a rectangle with a size of MxkM or kMxM, the given coefficient block can first be divided into n=k squares (MxM). At this time, the order of k squares proceeds from left to right or from top to bottom in reverse order according to the shape of the coefficient block. For example, if the coefficient block is a horizontally long rectangle, the order of the lower k square blocks proceeds in reverse order from left to right, and if the coefficient block is a vertically long rectangle, the order of the lower k square blocks proceeds in reverse order from top to bottom. It goes on. The process after dividing the rectangular coefficient block into k squares of the lower layer is performed in the same way as the (4) square subblocks of the lower layer of the square coefficient block.

FIG. 11 is a diagram illustrating blocks generated by applying the proposed technique to the 32×32 block illustrated in FIG. 6 . According to the proposed method, valid flags for blocks indicated by thick solid lines in FIG. 11 are signaled. A hierarchical structure of each block and a valid flag value of each block are expressed in a tree format as shown in FIG. 12 . Nodes in the tree of FIG. 12 refer to blocks of various sizes. A node marked in black means that the valid flag value of the corresponding block is "1", and a node marked in white means that the valid flag value of the corresponding block is "0". means that In addition, a node marked in white is a leaf node and has no subordinate nodes. That is, if the validity flag of a given block is “0”, the corresponding block becomes a leaf node and no lower layer blocks exist. Here, a corresponding block may be referred to as a parent node, and blocks of a lower layer may be referred to as child nodes. Also, if the validity flag of a given block is “1”, the corresponding block always has 4 child nodes.

The tree of FIG. 12 was constructed by scanning the blocks generated from the coefficient blocks of FIG. 11 in a diagonal manner. In addition, the tree was constructed in consideration of the storage order of the bitstream (that is, the reverse order of the scan order; the reverse order of upper left, lower left, upper right, and lower right). The diagonal method used in FIG. 12 is an example, and the three types of scan methods mentioned above may be used according to existing conditions. If a scan method other than diagonal is used, the tree for the coefficient block in FIG. 11 is configured differently from that in FIG. 12. In addition, the tree can be configured in the z-scan (reverse order) method and stored in the order of bitstream (ie, the reverse order of the z-scan order; the reverse order of top left, top right, bottom left, bottom right) can also be used.

The valid flag for a block having the same size as the coefficient block can be regarded as performing a kind of cbf (coded block flag) function. For example, in the case of the coefficient block of FIG. 11, the valid flag for the 32×32 block performs the cbf function. Since the valid flag value of the 32×32 block for the coefficient block illustrated in FIG. 11 is “1”, valid flags for the lower four 16×16 blocks are obtained. At this time, the four 16×16 blocks are scanned in the reverse order of the upper left, lower left, upper right, and lower right blocks according to the diagonal scan method. The four valid flags become "0011". Among them, only the valid flags of the lower 8x8 blocks for the lower left and upper left 16x16 blocks corresponding to "1" need to be expressed. The valid flags for the lower 4 8x8 blocks of the lower left 16x16 block are "0100", and the valid flags for the lower 4 8x8 blocks of the upper left 16x16 block are "1111". Valid flag values of lower 4x4 blocks need only be expressed for blocks whose valid flag is “1” among 8×8 blocks. The above operation is repeated until the block size is 1×1.

Valid flags for blocks (32×32 to 1×1) generated as a result of applying the quadrant method to the coefficient block of FIG. 11 are shown in the table below.

block size valid flag 32×32 blocks One 16×16 blocks 0011 8×8 blocks 0100
1111 4x4 blocks 0100
0110 0001 0001 1001 2×2 blocks 0010
0001 0001 0001 1000 0001 0001 1×1 block 0100
1000 1000 0010 0001 1000 0001

Hereinafter, an example of searching the tree of FIG. 12 for the coefficient block of FIG. 11 is shown. A depth-first search or a breadth-first search may be used to search the tree of FIG. 12 . Here, the depth-first method and the breadth-first method refer to the order in which nodes of the tree are searched. That is, in the present invention, bits assigned to the corresponding node are read while searching for a node of the tree according to a predetermined method among the depth-first method and the breadth-first method, thereby forming a bit-stream. For example, referring to the tree structure illustrated in (a) of FIG. 13, (1) if a bitstream is configured in a depth-first manner, bits are read in the order of A B C D F G H I E, and (2) a bitstream in a width-first manner , the bits are read in the order of A B C D E F G H I.

Accordingly, a bitstream is formed by searching the tree of FIG. 12 proposed in the present invention by breadth-first search as follows.

1. 1

2. 0011

3. 0100 1111

4. 0100 0110 0001 0001 1001

5. 0010 0001 0001 0001 1000 0001 0001

6. 0100 1000 1000 0010 0001 1000 0001

Conversely, when the tree of FIG. 12 is searched by depth-first search to construct a bitstream, it is as follows.

1. 1

Feb. 00

3. 1 01 01 001 0100 0 00 00

4. 1 1 01 0001 1000 1 0001 1000 0

5. 1 0001 0001 0010

6. 1 0001 1 0001 000

7. 1 1 0001 1000 001 0001 0001

exception rule

On the other hand, if the breadth-first search method is applied to the tree illustrated in (b) of FIG. 13, a bitstream can be configured with “1” “0001” “1000”. At this time, the valid flag value of the highest parent node is "1", which means that at least one child node among the four child nodes of the corresponding block must have a valid flag value of "1". However, if the valid flag values of the three preceding child nodes in the scan order among the four child nodes are all “0”, the flag value of the last remaining child node must be “1”. As a result, the flag value of the fourth child node can be equally inferred as “1” by the encoding device and the decoding device, so it does not need to be signaled. If this exception rule is applied to the tree illustrated in FIG. 13(b), the bitstream is composed of “1” “000” and “1000”.

By applying these exception rules, a bitstream is configured in the breadth-first search method for the tree illustrated in FIG. 12 as follows. Here, a total of 9 “1” values that are not signaled are indicated by “-”.

1. 1

2. 0011

3. 0100 1111

4. 0100 0110 000 - 000 - 1001

5. 0010 000 - 000 - 000 - 1000 000 - 000 -

6. 0100 1000 1000 0010 000 - 1000 000 -

A bitstream is constructed by depth-first search by applying the exception rule to the tree of FIG. 12 as follows. Here, a total of 9 “1” values that are not signaled are indicated by “-”.

1. 1

Feb. 00

3. 1 01 01 001 0100 0 00 00

4. 1 1 01 000 - 1000 1 000 - 1000 0

5. 1 000 - 000 - 0010

6. 1 000 - 1 000 - 000

7. 1 1 000 - 1000 001 000 - 000 -

of high frequency coefficients zeroing

Another technique proposed in the present disclosure sets the coefficient values of a certain portion of the coefficient block corresponding to the high-frequency component to “0”, regardless of the actual value, when the size of the coefficient block (or quantized transform block) is large. is to do

For example, when the size of the coefficient block is 64×64, all coefficient values of the remaining blocks (upper right, lower left, and lower right 32×32 blocks) except for the upper left 32×32 block are forcibly set to zero. 14 illustrates a 64×64 coefficient block, and if the predetermined threshold size is 32×32, all non-zero coefficients (marked in black) located in an area except for the upper left 32×32 block are zeroed. Accordingly, valid flags for the lower left 32×32 block, the upper right 32×32 block, and the lower right 32×32 block are all set to “0”.

When a given coefficient block is a rectangle with a size of M × kM or kM × M, the given coefficient block can be divided into k M × M blocks. If the predetermined threshold size is h × h (h ≤ M), the most All coefficient values of blocks other than the upper h×h block or the leftmost h×h block may be forcibly set to zero. Conversely, if the predetermined threshold size is h×h (M < h < kM), all coefficient values of blocks other than the uppermost M×h block or the leftmost h×M block may be forcibly set to zero. For example, if the coefficient block is 16×4 and the predetermined threshold size is 8×8, all non-zero coefficients of the right two 4×4 blocks among the four 4×4 blocks are zeroed.

Expressing valid flag values for the 64×64 coefficient block illustrated in FIG. 14 through a diagonal scan method (in reverse order) and breadth-first search is as follows. Among the four 32×32 blocks, the first three blocks in the scan order are set to “000” even though non-zero coefficients actually exist, and the flag value of only the last fourth block is “1”. In addition, when the exception rule is applied, all 4 bits (“0001”) for 32×32 blocks are not signaled, and information that can be inferred is obtained. Furthermore, coefficients of zeroed blocks are not signaled.

block size valid flag 64×64 blocks One 32×32 blocks 0001 16×16 blocks 1111 8×8 block 0001 0001 1001 1111 4x4 blocks 0100 0001 0100 0100
0001 1000 0001 1001 2×2 blocks 0010 0100 0001 0010
1000 0010 0100 1000 0001 1×1 block 0100 0010 0100 0001
0010 0100 0010 0001 0001

The zeroing of these high-frequency blocks may be applied again to the four blocks corresponding to the grandchild nodes of the coefficient block when the block size of the grandchild nodes is still larger than the threshold value.

As the size of the coefficient block increases, most of the non-zero coefficients are concentrated in the low-frequency component after transformation and rarely exist in the high-frequency component, so this exception rule is particularly useful for increasing the coding efficiency of the large coefficient block. Therefore, as the transform size increases, compression performance can be further increased by the proposed zeroing technique. This zeroing technique may be combined with the technique described with reference to FIGS. 6 to 10 .

Using the techniques and rules described above, for the 32×32 coefficient block illustrated in FIG. 11, valid flag values signaled to represent the distribution of non-zero coefficients are as follows. The list of applied rules is as follows.

- Zeroing of high-frequency blocks: set th value to 64

- Scanning method: using the diagonal method

- Tree traversal method: use breadth first

- Application of exception rules

1. 1

2. 0011

3. 0100 1111

4. 0100 0110 000 - 000 - 1001

5. 0010 000 - 000 - 000 - 1000 000 - 000 -

6. 0100 1000 1000 0010 000 - 1000 000 -

As such, a total of 80 bits are required to express the positions of non-zero coefficients of the 32×32 coefficient block illustrated in FIG. 11 . As described above, if the coefficient block of FIG. 6, which is the same as the coefficient block of FIG. and sig _ coeff _flag ) is approximately 140 bits. If information for expressing the position of the last significant coefficient is added to 140 bits, more bits are required.

If the threshold value ( th ) is 16 and other conditions are the same as above, valid flags for the 32×32 coefficient block illustrated in FIG. 4 are as follows.

1. 1

2. ----

3. 1111

4. 0110 000 - 000 - 1001

5. 000 - 000 - 000 - 1000 000 - 000 -

6. 1000 1000 0010 000 - 1000 000 -

Here, the valid flag value for the entire coefficient block (i.e., 32×32 block) is “1”, and the 16×16 block, which is a lower node, is equal to the threshold value ( th = 16), so the first three 16× The flag value for the 16th block is set to "000", and the flag value for the fourth block is set to "1". Therefore, the valid flag "0001" for the four 16x16 blocks does not need to be signaled.

15 is a flowchart illustrating a process of processing a large coefficient block by an image decoding apparatus. Although FIG. 15 assumes the use of a breadth first search method, it should be noted that a depth first search may be used. Also, for simplicity, the aforementioned exception rule is not included in FIG. 15 and it is assumed that the coefficient block has a square shape.

The video decoding apparatus sets the size (ie, TU size) of the current coefficient block to be decoded to N. The video decoding apparatus parses a valid flag for the current coefficient block and, if the valid flag is not “0”, divides the coefficient block into 4 blocks. If the size (N/2) of the generated block is greater than or equal to the threshold value th , the video decoding apparatus sets valid flags for the four generated blocks to “0001” without parsing the valid flags. Conversely, if the size (N/2) of the generated block is less than the threshold value th , the video decoding apparatus parses valid flags for the four generated blocks.

For each of the four generated blocks, if the valid flag value of that block is not "0", that block is iteratively divided into four equally sized small blocks until a single valid count (N=1) is reached. While (recursively) partitioning, valid flags for the four blocks generated each time are parsed.

As described above, the technique described with reference to FIGS. 11 to 15 is more useful when the transform of the encoding target block is skipped to transmit the residual value itself rather than the high and low frequency components (or coefficients). can In view of this, the video encoding apparatus applies the technique described with reference to FIGS. 11 to 15 when the transform of the encoding target block is skipped, and applies FIGS. 6 to 10 to the quantized transform coefficient block on which the transform is performed It may also be configured to apply the techniques described with reference.

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

Claims (3)

A method of encoding a coefficient block having an array of coefficients divisible into coefficients of a plurality of sub-blocks, comprising:
if the size of the coefficient block is greater than or equal to a preset threshold, setting all coefficients of the remaining region except for the rectangular region including the upper-left corner of the coefficient block to zero coefficients;
determining a last significant sub-block, wherein the last significant sub-block is the last sub-block in the sub-block scan order having at least one non-zero coefficient;
encoding information indicating the location of the determined last valid subblock;
Each subblock indicating whether each of the subblocks preceding the last valid subblock in the subblock scan order, except for the upper left subblock of the coefficient block, is a valid subblock having at least one non-zero coefficient. Encoding syntax elements for sub-blocks; and
Coefficients of the upper left sub-block, coefficients preceding the last non-zero coefficient in the last valid sub-block, and sub-blocks indicating that the syntax element is a valid sub-block having at least one non-zero coefficient Encoding the Coefficients
including,
The step of encoding coefficients of subblocks indicating that the syntax element is a valid subblock having at least one non-zero coefficient indicates, for each of all coefficients in the given subblock, whether the given coefficient is a non-zero coefficient. Encoding a first flag;
Characterized in that the encoding order of the first flag for each of all coefficients in the given subblock is determined based on a diagonal scan order.
Encoding method of coefficient block. A method of decoding a coefficient block having an array of coefficients divisible into coefficients of a plurality of sub-blocks, comprising:
if the size of the coefficient block is greater than or equal to a preset threshold, setting all coefficients of the remaining region except for the rectangular region including the upper-left corner of the coefficient block to zero coefficients;
decoding information indicating a location of a last non-zero coefficient in a sub-block scan sequence;
Each subblock indicating whether each subblock excluding the upper left subblock of the coefficient block among the subblocks preceding the last valid subblock in the subblock scan order is a valid subblock having at least one non-zero coefficient decoding a syntax element for a block, wherein the last valid sub-block is the sub-block having the last non-zero coefficient; and
Coefficients of the upper left sub-block, coefficients preceding the last non-zero coefficient in the last valid sub-block, and sub-blocks indicating that the syntax element is a valid sub-block having at least one non-zero coefficient decoding the coefficients
including,
The step of decoding coefficients of subblocks indicating that the syntax element is a valid subblock having at least one non-zero coefficient indicates, for each of all coefficients in the given subblock, whether the given coefficient is a non-zero coefficient. Decrypting the first flag;
Characterized in that the decoding order of the first flag for each of all coefficients in the given subblock is determined based on a diagonal scan order.
Decoding method of coefficient block. A computer-readable non-transitory recording medium storing a bitstream containing coded data for a coefficient block having an array of coefficients divisible into coefficients of a plurality of sub-blocks, the bitstream comprising:
if the size of the coefficient block is greater than or equal to a preset threshold, setting all coefficients of the remaining region except for the rectangular region including the upper-left corner of the coefficient block to zero coefficients;
decoding information indicating a location of a last non-zero coefficient in a sub-block scan sequence;
Each subblock indicating whether each subblock excluding the upper left subblock of the coefficient block among the subblocks preceding the last valid subblock in the subblock scan order is a valid subblock having at least one non-zero coefficient decoding a syntax element for a block, wherein the last valid sub-block is the sub-block having the last non-zero coefficient; and
Coefficients of the upper left sub-block, coefficients preceding the last non-zero coefficient in the last valid sub-block, and sub-blocks indicating that the syntax element is a valid sub-block having at least one non-zero coefficient decoding the coefficients
It is configured to be decrypted by a decryption process comprising
The step of decoding coefficients of subblocks indicating that the syntax element is a valid subblock having at least one non-zero coefficient indicates, for each of all coefficients in the given subblock, whether the given coefficient is a non-zero coefficient. Decrypting the first flag;
Characterized in that the decoding order of the first flag for each of all coefficients in the given subblock is determined based on a diagonal scan order.
A computer-readable, non-transitory recording medium.

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