KR20220140677A - Method and Apparatus for Expressing Position of Non-zero Coefficients - Google Patents

Abstract

The present disclosure relates to a method for efficiently expressing positions of non-zero coefficients in a coefficient block. In accordance with one aspect of the present disclosure, in regard to the encoding of a coefficient block dividable into a plurality of sub blocks, the method includes a step of recursively dividing a block determined as an effective block into small blocks of a uniform size until reaching a single effective coefficient, with respect to the coefficient block, while signaling whether each of the generated blocks is an effective block. In accordance another aspect of the present disclosure, in regard to the encoding of a coefficient block dividable into a plurality of sub blocks, provided is a method for efficiently expressing positions of non-zero coefficients in a coefficient block based on a position of a last effective sub block.

Description

Method and Apparatus for Expressing Position of Non-zero Coefficients

The present invention relates to image encoding or decoding, and more particularly, to representing positions of non-zero coefficients.

The content described in this section merely provides background information for the present embodiment and does not constitute the prior art.

Image compression techniques reduce or remove redundancy inherent in video sequences, including spatial prediction and/or temporal prediction. 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 in 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 produces a predictive block for the block to be encoded as a result. Residual data represents pixel differences between an original block to be encoded and a prediction block.

An inter-coded block is encoded according to a motion vector pointing to a block of reference samples forming a predictive block, and residual data representing the difference between the coded block and the predictive block. The intra-coded block is encoded according to the intra-coding mode and residual data. For further compression, the residual data may be transformed from the pixel domain to the transform domain, generating residual transform coefficients, which may then be quantized. The quantized transform coefficients arranged in a two-dimensional array may be scanned in a particular 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 position of non-zero coefficients in a coefficient block having an array of coefficients that is divisible into a plurality of (sub) blocks.

According to an aspect of the present invention, there is provided an image encoding method including encoding a distribution of significant coefficients, which are non-zero coefficients, in a coefficient block. The video encoding method includes: 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, there are n (n is 2 or more) sub-blocks determined as valid blocks, until a single significant coefficient is reached. determining whether each of the n sub-blocks is a valid block while recursively dividing the sub-blocks into sub-blocks of equal size; skipping encoding of valid flags related to the n sub-blocks when the sizes of the n sub-blocks are greater than or equal to a preset threshold; and encoding a valid flag related to the n sub-blocks when the size of the n sub-blocks is smaller than a preset threshold.

According to another aspect of the present invention, there is provided an image decoding method including determining a distribution of significant coefficients that are non-zero coefficients in a coefficient block. The image decoding method may include parsing, from a bit stream, 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, there are n (n is 2 or more) sub-blocks determined as valid blocks, until a single significant coefficient is reached. and determining whether each of the n sub-blocks is a valid block while recursively dividing the n sub-blocks into sub-blocks of equal size. Here, 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 the valid flags related to the n sub-blocks is skipped. to do; and parsing valid flags related to the n sub-blocks when the size of the n sub-blocks is smaller than a preset threshold.

According to another aspect of the present invention, there is provided 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, wherein the one or more processors are configured to perform a method comprising the following steps. The method includes parsing, from a bit stream, a significant flag indicating whether a current block of coefficients is a valid block with 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, a sub-block determined as a valid block is replaced with n equal-sized sub-blocks until a single significant coefficient is reached. and determining whether each of the n sub-blocks is a valid block while recursively dividing the block into blocks. Here, 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 the valid flags related to the n sub-blocks is skipped. to do; and parsing valid flags related to the n sub-blocks when the size of the n sub-blocks is smaller than a preset threshold.

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

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

According to another aspect of the present invention, there is provided an apparatus for decoding a coefficient block having an array of coefficients that is divisible into coefficients of a plurality of sub-blocks. The device includes a memory; and one or more processors, wherein the one or more processors are 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 sub-block indicating whether each sub-block except the upper-left sub-block of the coefficient block among the sub-blocks preceding the last valid sub-block in the sub-block scan order is a valid sub-block having at least one non-zero coefficient decoding a syntax element for a sub-block; and decoding coefficients of the last valid sub-block, coefficients of the upper-left sub-block, and coefficients of sub-blocks indicating that the syntax element is a valid sub-block having at least one non-zero coefficient.

1 is an exemplary block diagram of an image encoding apparatus that can implement techniques of the present disclosure.
2 is an exemplary diagram of a neighboring block of a current block.
3 is an exemplary block diagram of an image decoding apparatus capable of implementing the techniques of the present 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 order of sub-blocks and coefficients for a diagonal scan scheme.
6 is a diagram showing an example of a 32×32 coefficient block.
FIG. 7 is a diagram illustrating sub-blocks preceding the last valid sub-block in the scan order in the 32×32 coefficient block of FIG. 6 .
FIG. 8 is a diagram illustrating sub-blocks following the last valid sub-block in the 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 illustrating blocks generated by hierarchically dividing a valid block until a single significant coefficient is reached for the 32×32 block illustrated in FIG. 6 .
12 is a tree constructed by scanning blocks generated from the coefficient block 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 64×64 coefficient block.
15 is a flowchart illustrating a processing process for a large coefficient block by an image decoding apparatus.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that in adding identification codes to the components of each drawing, the same components are given the same reference numerals as much as possible even though they are indicated 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 thereof will be omitted.

Techniques of this disclosure generally relate to efficiently representing the location of non-zero coefficients (ie, significant coefficients) relative to a coefficient block that is an array of quantized coefficients that are the result of transform and quantization.

1 is an exemplary block diagram of an image encoding apparatus that can implement techniques of the present disclosure.

The image encoding apparatus includes a block divider 110 , a predictor 120 , a subtractor 130 , a transform unit 140 , a quantizer 145 , an encoder 150 , an inverse quantizer 160 , and an inverse transform unit ( 165 ), an adder 170 , a filter unit 180 , and a memory 190 . In the image encoding apparatus, each component may be implemented as a hardware chip, or may be implemented as software and a microprocessor may be implemented to execute a function of software 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 child nodes (or child nodes) of the same size, or a QT structure and a parent node divided into two child nodes A QTBT (QuadTree plus BinaryTree) structure mixed with a binary tree (BinaryTree, BT) structure may be used. That is, QTBT can be used to divide a CTU into multiple CUs.

In a QTBT (QuadTree plus BinaryTree) structure, a CTU may first be divided into a QT structure. The quadtree splitting may be repeated until the size of a splitting block reaches the minimum block size of a leaf node (MinQTSize) allowed in QT. If the leaf node of the quadtree is not larger than the maximum block size (MaxBTSize) of the root node allowed in the BT, it may be further partitioned into the 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 blocks of the same size (ie, symmetric horizontal splitting) and a vertical splitting type (ie, symmetric vertical splitting). In addition, a type for dividing a block of a corresponding node into two blocks having an asymmetric shape may further 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 may include a form in which the block of the corresponding node is divided in a diagonal direction.

The division information generated by the block dividing unit 110 dividing the CTU according to the QTBT structure is encoded by the coding unit 150 and transmitted to the image 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 generates a prediction block by predicting the current block. The prediction unit 120 includes an intra prediction unit 122 and an inter prediction unit 124 .

In general, each of the current blocks in a picture may be predictively coded. Prediction of the current block is performed using either 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). This can be done in general. Inter prediction includes both uni-prediction and bi-prediction.

For each inter-predicted block, a set of motion information may be available. One set of motion information may include motion information for forward and backward prediction directions. Here, the forward and backward prediction directions are two prediction directions of a bi-directional prediction mode, and the terms “forward” and “reverse” do not necessarily have a geometric meaning. Instead, they generally correspond to whether the reference picture will be displayed before (“reverse”) or after (“forward”) the current picture. In some examples, “forward” and “reverse” 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. The 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, which is 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, which is 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 in the reference picture encoded and decoded before the current picture, and generates a prediction block for the current block by using the searched block. Then, a motion vector corresponding to the 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 for a 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 about a reference picture and information about a motion vector used to predict the current block is encoded by the encoder 150 and transmitted to the image 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 may be transmitted to the decoding apparatus by encoding information for 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.

As the neighboring blocks for inducing the merge candidate, as shown in FIG. 2 , the left block (L), the upper block (A), the upper right block (AR), and the lower left block (BL) adjacent to the current block in the current picture. ), 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 the reference picture used to predict the current block) other than the current picture in which the current block is located may be used as a merge candidate. For example, a block co-located with the current block in the reference picture or blocks adjacent to the co-located block may be further used as merge candidates.

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

Another method for encoding motion information is to encode a differential motion vector.

In this method, the inter prediction unit 124 derives motion vector prediction candidates for the motion vector of the current block using neighboring blocks of the current block. As the neighboring blocks used to derive the prediction motion vector candidates, the left block (L), the upper block (A), the upper right block (AR), the lower left block ( BL), 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 is used as a neighboring block used to derive prediction 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 prediction motion vector candidates by using the motion vectors of the neighboring blocks, and determines a predicted motion vector with respect to the motion vector of the current block by using the prediction 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 prediction motion vector may be obtained by applying a predefined function (eg, a median value, an average value operation, etc.) to the prediction motion vector candidates. In this case, the image decoding apparatus also knows the predefined function. In addition, since the neighboring block used to derive the prediction motion vector candidate is a block that has already been encoded and decoded, the video decoding apparatus already knows the motion vector of the neighboring block. Therefore, the image encoding apparatus does not need to encode information for identifying the prediction motion vector candidate. Accordingly, in this case, information on a differential motion vector and information on a reference picture used to predict a current block are encoded.

Meanwhile, the prediction motion vector may be determined by selecting any one of the prediction motion vector candidates. In this case, information for identifying the selected prediction motion vector candidate is additionally encoded together with information on the differential motion vector and information on the reference picture used to predict the current block.

The intra prediction unit 122 predicts pixels in the current block by using pixels (reference pixels) located in the vicinity of the current block in the current picture including the current block. A plurality of intra prediction modes exist according to a prediction direction, and neighboring pixels to be used and an operation expression 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 has the best rate-distortion characteristics among the tested modes. An intra prediction mode may be selected.

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

The subtractor 130 generates a residual block by subtracting the prediction block generated by the intra prediction unit 122 or the inter prediction unit 124 from the current 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 using the size of the current block as a transform unit, or divide the residual block into a plurality of smaller sub-blocks and convert the residual signals in the transform unit of the sub-block size. You can also convert There may be various methods for dividing the residual block into smaller subblocks. For example, it may be divided into subblocks having the same size as a predefined size, or a quadtree (QT) method using a residual block as a root node may be used.

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

The encoder 150 generates a bitstream by encoding the quantized transform coefficients using an encoding method such as CABAC. Such 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 generally to efficiently representing the location of non-zero coefficients (ie, significant coefficients) relative to a coefficient block, which is an array of quantized coefficients that are the result of 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 reference to FIGS. 6 to 15 below. In other examples, one or more other units of the encoding apparatus may be additionally involved in performing the techniques of this disclosure.

In addition, the encoder 150 encodes information such as CTU size, MinQTSize, MaxBTSize, MaxBTDepth, MinBTSize, QT split flag, BT split flag, and split type related to block splitting so that the video decoding apparatus is identical to the video encoding apparatus. Allows the block to be partitioned.

The encoder 150 encodes information on a prediction type indicating whether the current block is encoded 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 the intra-prediction mode is encoded as intra-prediction information. When the current block is inter-predicted, the encoder 150 encodes a syntax element for inter prediction information. The syntax element for inter prediction information includes the following.

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

(2) Syntax elements for motion information

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

On the other hand, when the motion information is encoded according to the differential motion vector encoding mode, information on the differential motion vector and information on the reference picture are encoded as syntax elements for the motion information. If the prediction motion vector is determined by selecting any one candidate from among a plurality of prediction motion vector candidates, the syntax element for the motion information further includes prediction motion vector identification information for identifying the selected candidate. include

The inverse quantization unit 160 inverse quantizes the quantized transform coefficients output from the quantization unit 145 to generate transform coefficients. The inverse transform unit 165 restores the residual block by transforming the transform coefficients output from the inverse quantization unit 160 from the frequency domain to the spatial domain.

The addition unit 170 reconstructs the current block by adding the reconstructed residual block to the prediction block generated by the prediction unit 120 . Pixels in the reconstructed current block are used as reference pixels when intra-predicting the next block.

The filter unit 180 deblocks and filters the boundary between the reconstructed blocks in order to remove a blocking artifact caused by block-by-block encoding/decoding, and stores the deblocking-filtering 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 a picture to be encoded later.

Hereinafter, an image decoding apparatus will be described.

3 is an exemplary block diagram of an image decoding apparatus capable of implementing the techniques of the present 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 image encoding apparatus of FIG. 2 , each component of the image decoding apparatus may be implemented as a hardware chip, or may be implemented as software and a microprocessor may be implemented to execute a function of software corresponding to each component.

The decoder 310 decodes the bitstream received from the image encoding apparatus, extracts information related to block division, determines a current block to be decoded, and predicts information necessary for reconstructing the current block, information on the residual signal, etc. to extract

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

Meanwhile, when the decoding unit 310 determines a current block to be decoded through tree structure division, information on a prediction type indicating whether the current block is intra-predicted or inter-predicted is extracted.

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

When the prediction type information indicates inter prediction, the decoder 310 extracts a syntax element for the inter prediction information. First, mode information indicating whether the motion information of the current block is 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 merge index information indicating whether to derive the motion vector of the current block from any of the merge candidates as a syntax element for the motion information. On the other hand, when the mode information indicates a differential motion vector encoding mode, the decoder 310 extracts information on the differential motion vector and information on the reference picture referenced by the motion vector of the current block as syntax elements for the motion vector. do. On the other hand, when the video encoding apparatus uses any one of the plurality of prediction motion vector candidates as the prediction motion vector of the current block, the prediction motion vector identification information is included in the bitstream. Accordingly, in this case, information on the differential motion vector and information on the reference picture as well as the prediction motion vector identification information are extracted as syntax elements for the motion vector.

Meanwhile, the decoder 310 extracts information on the 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) with respect to a coefficient block, which is an array of quantized coefficients that are the result of transform and quantization. Accordingly, certain techniques of the present disclosure may be performed by the decoder 310 . That is, for example, the decoder 310 may perform the techniques of the present disclosure described with reference to FIGS. 4 to 15 below. In other examples, one or more other units of the encoding apparatus may be additionally involved in performing the techniques of this disclosure.

The inverse quantization unit 320 inverse 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 to generate 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 prediction unit 342 is activated when the prediction type of the current block is intra prediction, and the inter prediction unit 344 is activated when the prediction type of the current block is intra prediction.

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

The inter prediction unit 344 determines motion information of the current block by 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 inter prediction extracted from the decoder 310 . When the mode information indicates a merge mode, the inter prediction unit 344 constructs a merge list including a predetermined number of merge candidates using neighboring blocks of the current block. The method of the inter prediction unit 344 constructing the merge list is the same as that of the inter prediction unit 124 of the image encoding apparatus. Then, one merge candidate is selected from among the merge candidates in the merge list by using the merge index information transmitted from the decoder 310 . Then, motion information of the selected merge candidate, that is, the motion vector and reference picture of the merge candidate, is 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 prediction unit 344 derives prediction motion vector candidates using motion vectors of neighboring blocks of the current block, and uses the prediction motion vector candidates to obtain the current block. A prediction motion vector is determined for the motion vector of . The method of the inter prediction unit 344 inducing prediction motion vector candidates is the same as that of the inter prediction unit 124 of the image encoding apparatus. If the video encoding apparatus uses any one of the plurality of prediction motion vector candidates as the prediction motion vector of the current block, the syntax element for the motion information includes the prediction motion vector identification information. Accordingly, in this case, the inter prediction unit 344 may select a candidate indicated by the prediction motion vector identification information from among the prediction motion vector candidates as the prediction motion vector. However, when the video encoding apparatus determines the predicted motion vector by using a function predefined for the plurality of prediction motion vector candidates, the inter prediction unit 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 prediction unit 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, the reference picture referred to by the motion vector of the current block is determined by 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 the merge mode or the differential motion vector encoding mode, the inter prediction unit 342 generates a prediction block of the current block by using the block at the position indicated by the motion vector in the reference picture. do.

The adder 350 reconstructs 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 the 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 deblocks and filters the boundary between the reconstructed blocks in order to remove a blocking artifact caused by block-by-block decoding, and stores the deblocking filter in the memory 370 . When all blocks in one picture are reconstructed, the reconstructed picture is used as a reference picture for inter prediction of blocks in a picture to be decoded later.

As described above, the techniques of the present disclosure relate to efficiently encoding and decoding positions of non-zero coefficients (ie, significant coefficients) with respect to a coefficient block that is an array of quantized coefficients that are the result of transformation and quantization. Some of the techniques disclosed can be directly applied to the residual block that has not undergone transformation.

In the H.265 (HEVC) standard, a syntax for expressing the position of a non-zero coefficient among quantized coefficients that have undergone a quantization process consists of a total of six.

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 first 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 the y component for that position, and each component is It is expressed by dividing it into a prefix (prefix) and a suffix (suffix). coded_sub_block_flag is a flag indicating whether a coefficient block is divided into a plurality of sub-blocks and each sub-block includes one or more non-zero coefficients. Here, coded_sub_block_flag is indicated by "0" if all coefficients in the corresponding sub-block are zero, and "1" if one or more non-zero coefficients exist. sig_coeff_flag is a flag indicating whether each coefficient in one sub - block is non-zero or zero. sig _ coeff _flag is indicated by "0" in the case of a zero coefficient, and indicated by "1" in the case of a non-zero coefficient.

The coded_sub_block_flag syntax is signaled only for 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”, a sig_coeff_flag syntax for each of all coefficients in the corresponding sub-block is signaled.

Coding of the coefficients in 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 object block is encoded using the inter prediction method, the coefficients of the corresponding block are scanned in an up-right diagonal method, and when the encoding object block is encoded using the intra prediction method, the above three By selecting one of the branches, the coefficients of the corresponding block are scanned.

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

6 is a diagram showing an example of a 32×32 coefficient block. Here, the scanning method of the 32×32 coefficient block used the diagonal method, pixels marked in gray mean non-zero coefficients, pixels marked in black mean the last non-zero coefficient in the scan order, and other All white coefficients have a value of zero. If the coded_sub_block_flag and sig_coeff_flag syntax among the above three pieces of information indicating the position of the non-zero coefficient is 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 indicated in bold in FIG. 6 ) out of a total of 64 sub-blocks in consideration of the position of the last significant coefficient. coded_sub_block_flag is not signaled for the upper-left sub-block including the DC component. The coefficient block of FIG. 6 has 7 sub-blocks (ie, valid sub-blocks) including one or more non-zero coefficients, and thus approximately 112 bits to indicate sig _ coeff _ flag for 7 valid sub blocks. (= 7×16; less than 16 bits may be needed 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 significant number of bits is required for the encoding of the syntax expressing the position of the last significant coefficient by the x-axis component and the 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 a position of a last significant sub-block within a coefficient block to be encoded. Here, the last valid sub-block is the last sub-block in the sub-block 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 in the coefficient block of the last valid sub-block

(2) The number of sub-blocks preceding the last valid sub-block in scan order

(3) The number of sub-blocks following the last valid sub-block in scan order

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

For example, with respect to the 32×32 coefficient block illustrated in FIG. 6 , the position of the last valid sub-block is expressed in the above-described four ways, respectively, as follows.

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

(2) 31 (when the diagonal scan method is used) - Referring to FIG. 7 , the number of sub-blocks preceding the last valid sub-block in the scan order is 31.

(3) 32 (in case of using the diagonal scan method) - Referring to FIG. 8 , the number of sub-blocks following the last valid sub-block in the scan order is 32.

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

Based on the method of signaling the position of the last valid subblock as described above, a method for encoding a coefficient block by an image encoding apparatus and an overall process for 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 image encoding apparatus determines the last significant sub-block in the current coefficient block to be encoded ( S910 ). Here, the last valid sub-block is the last sub-block in the sub-block scan order having at least one non-zero coefficient.

The image encoding apparatus encodes information indicating the determined last valid sub-block position (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 location 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 another exemplary embodiment, the information indicating the position of the last valid sub-block may be information on the number of sub-blocks following the last valid sub-block in the scan order. In some other embodiments, the information indicating the location of the last valid sub-block includes information on one selected from information on the number of sub-blocks preceding the last valid sub-block in the scan order or information on the number of sub-blocks following the last valid sub-block, and which information It may include a flag value indicating whether or not it is selected.

The image encoding apparatus determines whether each sub-block except for the upper-left sub-block of the coefficient block among the sub-blocks preceding the last valid sub-block in the sub-block scan order is a valid sub-block having at least one non-zero coefficient A syntax element for each sub-block pointing to is encoded (S930). In this case, the upper-left sub-block and the last valid sub-block of the coefficient block may be set as valid sub-blocks having at least one non-zero coefficient.

The image encoding apparatus includes coefficients of the upper-left sub-block of the coefficient block, coefficients of the last valid sub-block, and coefficients of sub-blocks indicating that the syntax element is a valid sub-block having at least one non-zero coefficient; Coefficients of sub-blocks set as valid sub-blocks are encoded (S940). The encoding of these coefficients may include encoding a flag indicating whether each coefficient in the corresponding sub-blocks is non-zero or zero. The video encoding apparatus skips encoding of coefficients of sub-blocks indicating that the syntax element is not a valid sub-block having at least one non-zero coefficient. Also, the image encoding apparatus skips encoding of coefficients of subblocks following the last valid subblock in the subblock scan 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 image decoding apparatus decodes information indicating the position of the last valid subblock in the current coefficient block to be decoded from the coded bitstream (S1010).

In the image decoding apparatus, from the coded bitstream, each subblock except for the upper left subblock of the coefficient block among subblocks preceding the last valid subblock in the subblock scan order has at least one non-zero coefficient. A syntax element for each sub-block indicating whether it is a valid sub-block is decoded (S1020). In this case, the upper-left sub-block and the last valid sub-block of the coefficient block may be set as valid sub-blocks having at least one non-zero coefficient.

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

The method described above is a method of preferentially signaling the position of the last significant coefficient or the last valid sub-block, paying attention to the fact that the positions of the non-zero coefficients are mostly gathered in the low frequency component and not located in the high frequency after transformation. Hereinafter, a technique for efficiently expressing the positions of non-zero coefficients wherever they are will be proposed. This technique may be more useful when the transformation of the encoding object block is skipped and the residual value itself, not the high-frequency and low-frequency components (or coefficients), is transmitted.

Hierarchical partitioning of valid blocks

Another technique proposed by the present invention is to divide a sub-block (significant block) including at least one non-zero coefficient with respect to the current coefficient block until a single significant coefficient is reached with n (a natural number greater than or equal to 2) equal sizes. While recursively dividing into small sub-blocks (squares) of , a valid flag ( significant_flag ) is used to signal whether each generated sub-block is a valid block. The validity flag is expressed as, for example, "1" if there are one or more non-zero coefficients (ie, significant coefficients) in one sub-block, and, for example, "0" if all coefficients are zero. If the valid flag value is “0”, the corresponding sub-block is no longer divided, and valid flag values for 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) sub-blocks, and the valid flag values for the sub-blocks of the lower layer are signaled.

If the valid flag value of a given coefficient block is “0”, the corresponding block is no longer divided, and therefore the valid flag values for blocks of the lower layer are no longer needed. Conversely, if the valid 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 a non-zero coefficient exists for each of the four blocks. . A valid block is iteratively divided until a single significant coefficient is reached, and the size of the generated block includes from the size of the coefficient block to the size of 1×1 (ie, a single coefficient). For example, if the coefficient block is 8×8, the block for which the valid flag is determined includes all sizes of 8×8, 4×4, 2×2, and 1×1.

When the valid flag value of a given coefficient block is "1" and it is a rectangular coefficient block, the number of square blocks of the lower layer may vary according to the size of the coefficient block. For example, if the coefficient block is 16×8, the square block divided into the lower layer becomes two 8×8, and if the coefficient block is 4×16, the square block divided into the lower layer has four 4×4 do. That is, when a given coefficient block is a rectangle of size M×kM or kM×M, the given coefficient block may first be divided into n=k squares (M×M). At this time, the order of k squares proceeds in reverse order from left to right or top to bottom 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. If the coefficient block is a vertically long rectangle, the order of the lower k square blocks is reversed from top to bottom. proceeds After dividing the rectangular coefficient block into k squares of the lower layer, the process proceeds in the same manner as the (4) square sub-blocks of the lower layer of the square-shaped 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. The hierarchical structure of each block and the effective flag value of each block are expressed in a tree format as shown in FIG. 12 . A node in the tree of FIG. 12 means each block of different 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 becomes a leaf node, and therefore there is no sub-node. That is, if the valid flag of a given block is "0", the corresponding block becomes a leaf node, and there is no lower layer block. Here, a corresponding block may be referred to as a parent node, and blocks of a lower layer thereof may be referred to as a child node. Also, if the valid flag of a given block is "1", the block always has 4 child nodes.

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

A valid flag for a block of the same size as the coefficient block can be seen as performing a function of a kind of coded block flag (cbf). For example, in the case of the coefficient block of FIG. 11, a valid flag for a 32×32 block performs a cbf function. Since the valid flag value of the 32×32 block for the coefficient block illustrated in FIG. 11 is “1”, the valid flags for the lower four 16×16 blocks are obtained. In this case, 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 are "0011". Of these, only valid flags of the lower 8×8 blocks for the lower left and upper left 16×16 blocks corresponding to “1” need to be expressed. The valid flags for the lower four 8×8 blocks of the lower left 16×16 block are “0100”, and the valid flags for the lower four 8×8 blocks of the upper left 16×16 block are “1111”. Only for a block whose valid flag is “1” among 8×8 blocks, the valid flag values of the lower 4×4 blocks need only be expressed. The above operation is repeated until the block size is 1×1.

Valid flags for (32×32 to 1×1) blocks generated as a result of applying the quadratic 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 8x8 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 method may be used to search the tree of FIG. 12 . Here, the depth-first method and the breadth-first method refer to the order of searching for nodes in the tree. That is, in the present invention, bits allocated to a corresponding node are read while searching for a node of a tree according to a predetermined method among a depth-first method and a width-first method, and a bit-stream is formed through this. For example, if described based on the tree structure illustrated in (a) of FIG. 13 , (1) if a bitstream is configured in a depth-first method, bits are read in the order of A B C D F G H I E, and (2) a bitstream in a width-first method , bits are read in the order of A B C D E F G H I.

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

One. One

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, if a bitstream is constructed by searching the tree of FIG. 12 through depth-first search, it is as follows.

One. One

2. 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, when the breadth-first search method is applied to the tree illustrated in (b) of FIG. 13 , a bitstream may be configured with “1”, “0001” and “1000”. In this case, the valid flag value of the highest parent node is “1”, which means that at least one child node of the four child nodes of the 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, since the flag value of the fourth child node can be inferred to be "1" equally by the encoding apparatus and the decoding apparatus, there is no need to be signaled. When this exception rule is applied to the tree illustrated in FIG. 13B, the bitstream is composed of “1”, “000” and “1000”.

By applying such an exception rule, a bitstream is configured in a breadth-first search method for the tree illustrated in FIG. 12 as follows. Here, a total of nine "1" values that are not signaled are indicated by "-".

One. One

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 -

When the above exception rule is applied to the tree of FIG. 12 to configure a bitstream through depth-first search, it is as follows. Here, a total of nine "1" values that are not signaled are indicated by "-".

One. One

2. 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 by the present disclosure is to set 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 the quantized transform block) is large. will do

For example, when the size of the coefficient block is 64×64, all coefficient values of the remaining blocks (top-right, bottom-left, and bottom-right 32×32 blocks) except for the upper-left 32×32 block are forcibly zeroed. 14 exemplifies a 64×64 coefficient block, and if the preset threshold size is 32×32, all non-zero coefficients (displayed in black) located in the region except for the upper left 32×32 block are zeroed. Therefore, the valid flags for the lower-left 32x32 block, the upper-right 32x32 block, and the lower-right 32x32 block are all set to "0".

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

The valid flag values for the 64×64 coefficient block illustrated in FIG. 14 are expressed through a diagonal scan method (reverse order) and a breadth-first search 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 only the last fourth block has a flag value of “1”. In addition, if the exception rule is applied, all 4 bits (“0001”) for 32×32 blocks are inferred without signaling. Furthermore, the coefficients of zeroed blocks are not signaled.

block size valid flag 64×64 blocks One 32×32 blocks 0001 16×16 blocks 1111 8x8 blocks 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 this high-frequency block may be applied again to the four blocks corresponding to the grandchild node when the block size of the grandchild node of the coefficient block is still larger than the threshold value.

As the size of the coefficient block increases, the non-zero coefficients are mostly concentrated in the low-frequency component and hardly exist in the high-frequency component after transformation, so this exception rule is particularly useful for increasing the encoding efficiency of a large coefficient block. Accordingly, as the size of the transform increases, the 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 technique 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 applied rules are listed as follows.

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

- Scan method: Use the diagonal method

- Tree traversal method: use breadth first

- Apply exception rules

One. One

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, it takes a total of 80 bits to represent the positions of the non-zero coefficients of the 32×32 coefficient block illustrated in FIG. 11 . As described above, when the coefficient block of FIG. 6, which is the same as the coefficient block of FIG. 11, is expressed in a manner adopted in the conventional HEVC, even if four syntaxes for expressing the position of the last significant coefficient are excluded, the remaining two syntaxes ( coded_sub_block_flag) and sig _ coeff _flag ) are 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, the valid flags for the 32×32 coefficient block illustrated in FIG. 4 are as follows.

One. One

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 (that is, a 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 16×16×16 blocks in the scan order The flag value for block 16 is set to "000", and the flag value for the fourth block is set to "1". Therefore, there is no need to signal the valid flag “0001” for the four 16×16 blocks.

15 is a flowchart illustrating a processing process for a large coefficient block by an image decoding apparatus. In FIG. 15 , it is assumed that the breadth-first search method is used, but it should be noted that the depth-first search may also be used. In addition, for simplicity, the above-described exception rule is not included in FIG. 15, and it is assumed that the coefficient block has a square shape.

The image decoding apparatus sets the size (ie, TU size) of the current coefficient block to be decoded to N. The image decoding apparatus parses a valid flag for the current coefficient block, and if the corresponding valid flag is not "0", the coefficient block is divided into four blocks. When the size (N/2) of the generated block is equal to or greater than the threshold value th , the image 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 image decoding apparatus parses valid flags for the four generated blocks.

For each of the four generated blocks, if the valid flag value of the corresponding block is not “0”, the corresponding block is repeatedly divided into four equally sized small blocks until a single significant coefficient (N=1) is reached. While (recursively) partitioning, valid flags for four blocks generated each time the partition is parsed are parsed.

As described above, the technique described with reference to FIGS. 11 to 15 is more useful when the transformation of the encoding object block is skipped and the residual value itself, not the high and low frequency components (or coefficients), is transmitted. can Taking this into consideration, the image encoding apparatus applies the technique described with reference to FIGS. 11 to 15 when the transformation of the encoding object block is skipped, and FIGS. 6 to 10 for the quantized transform coefficient block on which the transformation is performed. It may be configured to apply the techniques described with reference.

The above description is merely illustrative of the technical idea of this embodiment, and various modifications and variations will be possible without departing from the essential characteristics of the present embodiment by those of ordinary skill in the art to which this embodiment belongs. Accordingly, the present embodiments are intended to explain rather than limit the technical spirit of the present embodiment, and the scope of the technical spirit of the present embodiment is not limited by these embodiments. The protection scope of this embodiment should be interpreted by the claims below, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present embodiment.

Claims (3)

A method of encoding a coefficient block having an array of coefficients divisible into coefficients of a plurality of sub-blocks, the method comprising:
when the size of the coefficient block is greater than or equal to a preset threshold, setting all coefficients in the remaining area except for the rectangular area including the upper-left position of the coefficient block as zero coefficients;
determining a last significant sub-block, wherein the last significant sub-block is a last sub-block in a sub-block scan order having at least one non-zero coefficient;
encoding information indicating a position of a last non-zero coefficient in the sub-block scan order;
Each sub-block indicating whether each sub-block except the upper-left sub-block of the coefficient block among the sub-blocks preceding the last valid sub-block in the sub-block scan order is a valid sub-block having at least one non-zero coefficient encoding a syntax element for a sub-block; 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 encoding of the coefficients of the sub-blocks indicating that the syntax element is a valid sub-block having at least one non-zero coefficient may include, for each of all coefficients in the given sub-block, indicating whether the given coefficient is a non-zero coefficient. characterized in that it comprises the step of encoding the first flag,
Coding 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, the method comprising:
when the size of the coefficient block is greater than or equal to a preset threshold, setting all coefficients in the remaining area except for the rectangular area including the upper-left position of the coefficient block as zero coefficients;
decoding information indicating a position of a last non-zero coefficient in a sub-block scan order;
Each sub-block indicating whether each sub-block except the upper-left sub-block of the coefficient block among the sub-blocks preceding the last valid sub-block in the sub-block scan order is a valid sub-block having at least one non-zero coefficient decoding a syntax element for a block, wherein the last valid sub-block is the last sub-block with a 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 decoding of coefficients of sub-blocks indicating that the syntax element is a valid sub-block having at least one non-zero coefficient may include, for each of all coefficients in the given sub-block, indicating whether the given coefficient is a non-zero coefficient. characterized in that it comprises the step of decoding the first flag,
Decoding method of coefficient block. A computer-readable non-transitory recording medium storing a bitstream including coded data for a coefficient block having an array of coefficients divisible into coefficients of a plurality of sub-blocks, the bitstream comprising:
when the size of the coefficient block is greater than or equal to a preset threshold, setting all coefficients in the remaining area except for the rectangular area including the upper-left position of the coefficient block as zero coefficients;
decoding information indicating a position of a last non-zero coefficient in a sub-block scan order;
Each sub-block indicating whether each sub-block except the upper-left sub-block of the coefficient block among the sub-blocks preceding the last valid sub-block in the sub-block scan order is a valid sub-block having at least one non-zero coefficient decoding a syntax element for a block, wherein the last valid sub-block is the last sub-block with a 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
is configured to be decrypted by a decryption process comprising
The decoding of coefficients of sub-blocks indicating that the syntax element is a valid sub-block having at least one non-zero coefficient may include, for each of all coefficients in the given sub-block, indicating whether the given coefficient is a non-zero coefficient. characterized in that it comprises the step of decoding the first flag,
A computer-readable non-transitory recording medium.

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