KR20180096194A - Apparatus for coding and decoding a transform coefficient, and coding device and decoding device for the same - Google Patents

Abstract

The present invention relates to a coding device and a decoding device for a transform coefficient at high speed. According to the present invention, the coding device for a transform coefficient can code at least one of a syntax element for coded sub-block flag (CSBF) information and a syntax element for a position of the last important coefficient with a preset value based on a size and/or a shape of a transform block while coding at least one among the syntax element for the position of the last important coefficient representing a transform coefficient other than zero which is present at the final scan order in the transform block, a syntax element for whether the transform coefficient other than zero in a sub-block is at least one of the transform blocks (which is called CSBF information), and a syntax element for whether a value of each transform coefficient in the sub-block is zero or not.

Description

TECHNICAL FIELD [0001] The present invention relates to a transform coefficient encoding and decoding apparatus, and a coding apparatus and a decoding apparatus having the same.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present disclosure relates to an image encoding and decoding method and apparatus, and more particularly to an apparatus for encoding and decoding a transform coefficient.

Recently, the demand for high resolution and high quality images such as high definition (HD) image and ultra high definition (UHD) image is increasing in various applications. As the image data has high resolution and high quality, the amount of data increases relative to the existing image data. Therefore, when the image data is transmitted using a medium such as a wired / wireless broadband line or stored using an existing storage medium, The storage cost is increased. High-efficiency image compression techniques can be used to solve these problems caused by high-resolution and high-quality image data.

An inter picture prediction technique for predicting a pixel value included in a current picture from a previous or a subsequent picture of a current picture using an image compression technique, an intra picture prediction technique for predicting a pixel value included in a current picture using pixel information in the current picture, There are various techniques such as an entropy encoding technique in which a short code is assigned to a value having a high appearance frequency and a long code is assigned to a value having a low appearance frequency. Image data can be effectively compressed and transmitted or stored using such an image compression technique.

On the other hand, demand for high resolution images is increasing, and demand for stereoscopic image contents as a new image service is also increasing. Video compression techniques are being discussed to effectively provide high resolution and ultra-high resolution stereoscopic content.

It is an object of the present disclosure to provide a method for reducing the complexity of encoding even in the presence of a large number of transform coefficients to be encoded.

It is another object of the present disclosure to encode a combination of at least one of syntax elements to be encoded in the regular mode in the transform coefficient encoding in the rate-distortion optimization process in the bypass mode.

Another object of the present disclosure is to encode the position of the last significant coefficient among the transform coefficients to be coded and the transform coefficient included in the important map of the subblock in the bypass mode.

A transform coefficient encoding apparatus according to an aspect of the present disclosure includes a syntax element for a location of a last significant coefficient indicating a non-zero transform coefficient existing at the end of a scan order in a transform block, a sub-block of the transform block, A syntax element for at least one non-zero transform coefficient (CSBF information), and a syntax element for determining whether the value of each transform coefficient in the subblock is 0 or not. , At least one of the syntax element and the CSBF information for the position of the last significant coefficient is encoded into a preset value based on the size of the conversion block and / or the shape of the conversion block .

The present disclosure has the effect of reducing the complexity of the encoder even in the presence of a large number of transform coefficients to be coded.

The present disclosure can provide encoding in bypass mode for at least one or more combinations of syntax elements encoded in regular mode in the transform coefficient encoding in the rate-distortion optimization process. Therefore, the present disclosure has the effect of reducing the complexity of the encoder even in the presence of a large number of transform coefficients to be encoded, such as a high bit rate application field.

1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present disclosure.
2 is a block diagram illustrating a configuration of an entropy encoding unit included in an image encoding apparatus according to an embodiment of the present disclosure.
Figures 3A and 3B are diagrams illustrating the location of the last significant coefficient set in accordance with one embodiment of the present disclosure.
Figures 4A and 4B are diagrams illustrating the location of the last significant coefficient set in accordance with one embodiment of the present disclosure.
Figures 5A-5C are diagrams illustrating CSBF information set in accordance with one embodiment of the present disclosure.
6A-6C are diagrams illustrating CSBF information set in accordance with one embodiment of the present disclosure.
7 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present disclosure.
8 is a flowchart showing a procedure of a transform coefficient encoding method according to an embodiment of the present disclosure.
9 is a flowchart showing a procedure of a transform coefficient decoding method according to an embodiment of the present disclosure.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, which will be easily understood by those skilled in the art. However, the present disclosure may be embodied in many different forms and is not limited to the embodiments described herein.

In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear. Parts not related to the description of the present disclosure in the drawings are omitted, and like parts are denoted by similar reference numerals.

In the present disclosure, when an element is referred to as being "connected", "coupled", or "connected" to another element, it is understood that not only a direct connection relationship but also an indirect connection relationship May also be included. Also, when an element is referred to as " comprising "or" having "another element, it is meant to include not only excluding another element but also another element .

In the present disclosure, the terms first, second, etc. are used only for the purpose of distinguishing one element from another, and do not limit the order or importance of elements, etc. unless specifically stated otherwise. Thus, within the scope of this disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly a second component in one embodiment may be referred to as a first component .

In the present disclosure, the components that are distinguished from each other are intended to clearly illustrate each feature and do not necessarily mean that components are separate. That is, a plurality of components may be integrated into one hardware or software unit, or a single component may be distributed into a plurality of hardware or software units. Thus, unless otherwise noted, such integrated or distributed embodiments are also included within the scope of this disclosure.

In the present disclosure, the components described in the various embodiments are not necessarily essential components, and some may be optional components. Thus, embodiments consisting of a subset of the components described in one embodiment are also included within the scope of the present disclosure. Also, embodiments that include other elements in addition to the elements described in the various embodiments are also included in the scope of the present disclosure.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, the same reference numerals will be used for the same constituent elements in the drawings, and redundant explanations for the same constituent elements will be omitted.

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

1, the image encoding apparatus 100 includes a picture division unit 110, prediction units 120 and 125, a transform unit 130, a quantization unit 135, a reordering unit 160, an entropy encoding unit An inverse quantization unit 140, an inverse transform unit 145, a filter unit 150, and a memory 155. [

Each of the components shown in FIG. 1 is shown independently to represent different characteristic functions in the image encoding apparatus, and does not mean that each component is composed of separate hardware or one software configuration unit. That is, each constituent unit is included in each constituent unit for convenience of explanation, and at least two constituent units of the constituent units may be combined to form one constituent unit, or one constituent unit may be divided into a plurality of constituent units to perform a function. The integrated and separate embodiments of the components are also included in the scope of the present disclosure without departing from the spirit of the present disclosure.

In addition, some of the elements are not essential components to perform essential functions in the present disclosure, but may be optional components only to improve performance. This disclosure can be implemented only with components that are essential to implementing the essentials of the present disclosure, except for those components used for performance enhancement, and only those components that include only the essential components, Are also included in the scope of the present disclosure.

The picture division unit 110 may divide the input picture into at least one processing unit. At this time, the processing unit may be a prediction unit (PU), a transform unit (TU), or a coding unit (CU). The picture division unit 110 divides one picture into a plurality of coding units, a prediction unit, and a combination of conversion units, and generates a coding unit, a prediction unit, and a conversion unit combination So that the picture can be encoded.

For example, one picture may be divided into a plurality of coding units. In order to divide a coding unit in a picture, a recursive tree structure such as a quad tree structure can be used. In a coding or decoding scheme in which one picture or a largest coding unit is used as a root and divided into other coding units A unit can be divided with as many child nodes as the number of divided coding units. Under certain constraints, an encoding unit that is no longer segmented becomes a leaf node. That is, when it is assumed that only one square division is possible for one coding unit, one coding unit can be divided into a maximum of four different coding units.

Hereinafter, in the embodiment of the present invention, a coding unit may be used as a unit for performing coding, or may be used as a unit for performing decoding.

The prediction unit may be one divided into at least one square or rectangular shape having the same size in one coding unit, and one of the prediction units in one coding unit may be divided into another prediction Or may have a shape and / or size different from the unit.

If a prediction unit performing intra prediction on the basis of an encoding unit is not the minimum encoding unit at the time of generation, intraprediction can be performed without dividing the prediction unit into a plurality of prediction units NxN.

The prediction units 120 and 125 may include an inter prediction unit 120 for performing inter prediction and an intra prediction unit 125 for performing intra prediction. It is possible to determine whether to use inter prediction or intra prediction for a prediction unit and to determine concrete information (e.g., intra prediction mode, motion vector, reference picture, etc.) according to each prediction method. At this time, the processing unit in which the prediction is performed may be different from the processing unit in which the prediction method and the concrete contents are determined. For example, the method of prediction, the prediction mode and the like are determined as a prediction unit, and the execution of the prediction may be performed in a conversion unit. The residual value (residual block) between the generated prediction block and the original block can be input to the conversion unit 130. [ In addition, the prediction mode information, motion vector information, and the like used for prediction can be encoded by the entropy encoding unit 165 together with the residual value and transmitted to the decoder. When a particular encoding mode is used, it is also possible to directly encode the original block and transmit it to the decoding unit without generating a prediction block through the prediction units 120 and 125.

The inter-prediction unit 120 may predict a prediction unit based on information of at least one of a previous picture or a following picture of the current picture, and may predict a prediction unit based on information of a partially- Unit may be predicted. The inter prediction unit 120 may include a reference picture interpolation unit, a motion prediction unit, and a motion compensation unit.

In the reference picture interpolating unit, reference picture information is supplied from the memory 155 and pixel information of an integer pixel or less can be generated in the reference picture. In the case of a luminance pixel, a DCT-based Interpolation Filter (DCT) based on a different filter coefficient may be used to generate pixel information of less than an integer number of pixels in quarter-pixel units. In the case of a color difference signal, a DCT-based 4-tap interpolation filter may be used that generates a pixel information of an integer number of pixels or less in units of 1/8 pixel.

The motion prediction unit may perform motion prediction based on the reference picture interpolated by the reference picture interpolating unit. Various methods such as Full Search-based Block Matching Algorithm (FBMA), Three Step Search (TSS), and New Three-Step Search Algorithm (NTS) can be used as methods for calculating motion vectors. The motion vector may have a motion vector value of 1/2 or 1/4 pixel unit based on the interpolated pixel. The motion prediction unit can predict the current prediction unit by making the motion prediction method different. Various methods such as a skip method, a merge method, an AMVP (Advanced Motion Vector Prediction) method, and an Intra Block Copy method can be used as the motion prediction method.

The intraprediction unit 125 may set a prediction unit based on reference pixel information around the current block, which is pixel information in the current picture, and perform intra prediction on the set prediction unit to generate a prediction block. In the case where the neighboring block of the current prediction unit is the block in which the inter prediction is performed so that the reference pixel is the pixel performing the inter prediction, the reference pixel included in the block in which the inter prediction is performed is referred to as the reference pixel Information. That is, when the reference pixel is not available, the reference pixel information that is not available may be replaced by at least one reference pixel among the available reference pixels.

In intra prediction, the prediction mode may have a directional prediction mode in which reference pixel information is used according to a prediction direction, and a non-directional mode in which direction information is not used in prediction. The mode for predicting the luminance information may be different from the mode for predicting the chrominance information and the intra prediction mode information or predicted luminance signal information used for predicting the luminance information may be utilized to predict the chrominance information.

When intraprediction is performed, when the size of the prediction unit is the same as the size of the conversion unit, intra prediction is performed on the prediction unit based on pixels existing on the left side of the prediction unit, pixels existing on the upper left side, Can be performed. However, when intra prediction is performed, when the size of the prediction unit differs from the size of the conversion unit, intraprediction can be performed using the reference pixel based on the conversion unit. It is also possible to use intra prediction using N x N divisions for only the minimum coding units.

The intra prediction method can generate a prediction block after applying an adaptive intra-smoothing filter (AISF) to a reference pixel according to a prediction mode. The type of adaptive intra smoothing filter applied to the reference pixel may be different. In order to perform the intra prediction method, the intra prediction mode of the current prediction unit can be predicted from the intra prediction mode of the prediction unit existing around the current prediction unit. In the case where the prediction mode of the current prediction unit is predicted using the mode information predicted from the peripheral prediction unit, if the intra prediction mode of the current prediction unit is the same as the intra prediction mode of the current prediction unit, The prediction mode information of the current block can be encoded by performing entropy encoding if the prediction mode of the current prediction unit is different from the prediction mode of the neighbor prediction unit.

In addition, a residual block including a prediction unit that has been predicted based on the prediction unit generated by the prediction units 120 and 125 and a residual value that is a difference value from the original block of the prediction unit may be generated. The generated residual block may be input to the transform unit 130. [

The transforming unit 130 transforms the residual block including the residual information of the prediction unit generated through the original block and the predictors 120 and 125 into a DCT (Discrete Cosine Transform), a DST (Discrete Sine Transform), a KLT Karhunen-Loeve Transform). The decision to apply the DCT, DST, or KLT to transform the residual block may be based on the intra prediction mode information of the prediction unit used to generate the residual block.

The quantization unit 135 may quantize the values converted into the frequency domain by the conversion unit 130. [ The quantization factor may vary depending on the block or the importance of the image. The values calculated by the quantization unit 135 may be provided to the inverse quantization unit 140 and the reorder unit 160.

The reordering unit 160 can reorder the coefficient values with respect to the quantized residual values.

The reordering unit 160 may change the two-dimensional block type coefficient to a one-dimensional vector form through a coefficient scanning method. For example, the rearranging unit 160 may scan a coefficient by using a Zig-Zag scan method and change it into a one-dimensional vector form. Instead of the jig-jag scan, a vertical scan may be used to scan two-dimensional block type coefficients in a column direction, and a horizontal scan to scan a two-dimensional block type coefficient in a row direction depending on the size of the conversion unit and the intra prediction mode. That is, it is possible to determine whether any scanning method among the jig-jag scan, the vertical direction scan and the horizontal direction scan is used according to the size of the conversion unit and the intra prediction mode.

The entropy encoding unit 165 may perform entropy encoding based on the values calculated by the reordering unit 160. For entropy encoding, various encoding methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be used.

The entropy encoding unit 165 receives the residual value count information of the encoding unit, the block type information, the prediction mode information, the division unit information, the prediction unit information and the transmission unit information, and the motion information of the motion unit from the reordering unit 160 and the prediction units 120 and 125 Vector information, reference frame information, interpolation information of a block, filtering information, and the like.

The entropy encoding unit 165 can entropy-encode the coefficient value of the encoding unit input by the reordering unit 160. [

The entropy encoding unit 165 may encode the syntax element for the position of the last significant coefficient in the transform block. The last significant coefficient may mean the last non-zero transform coefficient in the scan block in the scan block. At this time, the scan order may be a forward scan order.

Syntax elements that encode the syntax elements for the position of the last significant coefficient may be illustrated in Table 1. Here, the syntax element may mean a syntax element.

In particular, the entropy encoding unit 165 sets the syntax element for the position of the last significant coefficient in the transform block based on at least one of the block size and the block type, and according to the set syntax element, Syntax elements can be encoded. Here, the size of the block may be set to at least one of the size of the conversion unit and the size of the conversion block, and the block shape may be set to at least one of the shape of the conversion unit and the shape of the conversion block.

In processing the encoding, the entropy encoding unit 165 processes a regular mode for processing derivation and update operations for the context model and a bypass mode for processing the encoding in accordance with predetermined rules without deriving the context model can do. Based on this, information on the position of the last significant coefficient can be encoded in the bypass mode based on at least one of the block size and the block type. Therefore, the entropy encoding unit 165 can calculate the rate with a low complexity.

The entropy encoding unit 165 may encode a syntax element corresponding to the position of the last significant coefficient and then perform encoding on a significance map. The important map may include at least one of information indicating whether a non-zero transform coefficient exists in a sub-block and information on whether or not the value of each transform coefficient in the sub-block is zero or not. At this time, the subblock may be 4x4 units.

A syntax element for information indicating whether a non-zero transform coefficient exists in a sub-block can be represented as coded_sub_block_flag, and a syntax element for information on whether or not the value of each transform coefficient in the sub-block is 0 sig_coeff_flag.

A syntax element (coded_sub_block_flag) for information indicating whether a non-zero transform coefficient exists in a sub-block and a syntax element (sig_coeff_flag) for information on whether or not the value of each transform coefficient in the sub- May be exemplified in Table 1. < tb > < TABLE >

The entropy encoding unit 165 may encode coded_sub_block_flag, which is a syntax element for information on whether any non-zero transform coefficient exists in a sub-block, based on at least one of a block size and a block type have.

The entropy encoding unit 165 sets the value (coded_sub_block_flag) as to whether any non-zero transform coefficient exists in the sub-block based on at least one of the block size and the block type, It is possible to perform the rate calculation only on the significant transform coefficients corresponding to the low frequency among the transform coefficients transformed into the transform coefficients, thereby making it possible to reduce the complexity of the encoding process.

The inverse quantization unit 140 and the inverse transformation unit 145 inverse quantize the quantized values in the quantization unit 135 and inversely transform the converted values in the conversion unit 130. [ The residual value generated by the inverse quantization unit 140 and the inverse transform unit 145 is combined with the prediction unit predicted through the motion estimation unit, the motion compensation unit and the intra prediction unit included in the prediction units 120 and 125, A block (Reconstructed Block) can be generated.

The filter unit 150 may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter can remove block distortion caused by the boundary between the blocks in the reconstructed picture. It may be determined whether to apply a deblocking filter to the current block based on pixels included in a few columns or rows included in the block to determine whether to perform deblocking. When a deblocking filter is applied to a block, a strong filter or a weak filter may be applied according to the deblocking filtering strength required. In applying the deblocking filter, horizontal filtering and vertical filtering may be performed concurrently in performing vertical filtering and horizontal filtering.

The offset correction unit may correct the offset of the deblocked image with respect to the original image in units of pixels. In order to perform offset correction for a specific picture, pixels included in an image are divided into a predetermined number of areas, and then an area to be offset is determined and an offset is applied to the area. Alternatively, Can be used.

The adaptive loop filter can be performed based on a value obtained by comparing the filtered reconstructed image with the original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the group may be determined and different filtering may be performed for each group. Information related to whether to apply the adaptive loop filter can be transmitted for each coding unit (CU), and the shape and the filter coefficient of the adaptive loop filter to be applied according to each block can be changed. In addition, an adaptive loop filter of the same type (fixed form) may be applied irrespective of the characteristics of the application target block.

The memory 155 may store the reconstructed block or picture calculated through the filter unit 150 and the reconstructed block or picture stored therein may be provided to the predictor 120 or 125 when the inter prediction is performed.

2 is a block diagram illustrating a configuration of an entropy encoding unit included in an image encoding apparatus according to an embodiment of the present disclosure.

2, the entropy encoding unit 165 includes a binarizer 21, a context modeler 22, and a binary arithmetic coder 23. The binary arithmetic coding unit 23 may include a regular coding engine 24 and a bypass coding engine 25.

The binarization unit 21 binarizes a syntax element when Syntax Elements are not binary values, and outputs a bit string composed of binary values of 0 or 1, that is, a Bin string. Bin represents each bit of a bit string composed of 0 or 1. Depending on the type of syntax element, one of the following may be used: Unary Binarization, Truncated Unary Binarization, Exponential Golomb Binarization, and Fixed Length Binarization. A binarization method can be applied.

The binarization unit 21 classifies a syntax element currently coded on the basis of a threshold value determined based on the size of a current block into a prefix and a suffix and performs a predetermined binarization Method, so that a prefix bit string and a suffix bit string can be output. For example, the binarization unit 21 sets the column position of the last significant coefficient as a prefix (last_sig_coeff_x_prefix) and a suffix (last_sig_coeff_x_suffix) based on the threshold determined based on the width of the current block, ), A predetermined first binarization method is applied to the column position prefix (last_sig_coeff_x_prefix) to output a prefix bit string at the column position, and a predetermined second binarization method is applied to the column position suffix (last_sig_coeff_x_prefix) Can be applied to output the suffix bit string for the column position.

Similarly, the binarization unit 21 classifies the row position of the last significant coefficient into a prefix (last_sig_coeff_y_prefix) and a suffix (last_sig_coeff_y_supix) based on a threshold determined based on the height of the current block A prefix bit string of an action value is applied by applying a first binarization method to a prefix (last_sig_coeff_y_prefix) of a row position, and a second binary method is applied to a suffix of a row position (last_sig_coeff_y_prefix) It is possible to output a bit stream.

The first binarization method and the second binarization method may be the same or different from each other.

Depending on the type of the syntax element, each bin Bin of the bit string can be arithmetically encoded by applying the context model in the regular coding unit 24, or arithmetic-coded by the bypass coding unit 25. [

When the position of the last significant coefficient is classified into a prefix bit string and a suffix bit string, the regular coding section 24 firstly performs arithmetic coding on bit strings classified into a prefix by sequentially applying a context model according to CABAC, The coding unit 25 may arithmetic-code the bit streams classified as the suffix in a bypass mode.

In particular, the binarization unit 21 according to the present disclosure sets the syntax element for the position of the last significant coefficient on the basis of the block size, and sets the syntax element for the position of the last significant coefficient Can be encoded. Here, the size of the block may be set to at least one of the size of the conversion unit and the size of the conversion block.

Figures 3A and 3B are diagrams illustrating the location of the last significant coefficient set in accordance with one embodiment of the present disclosure. FIG. 3A illustrates a transform block of 4 × 4 units, and FIG. 3B illustrates a transform block of 8 × 8 units.

The binarization unit 21 according to the present disclosure can set the position of the last significant coefficient to (N, M) in the 4x4 block when the current block size is 4x4 (N, M is a natural number, N? 4, 1? M? 4). In an embodiment of the present invention, the position of the significant coefficient is set to (4, 4) for a block having a size of 4 × 4 block. The binarization unit 21 according to the present disclosure is identical to (N, M), i.e., (4, 4) if the size of the current block is 4 x 4, irrespective of the region where the last significant coefficient is actually located Can be set.

The binarization unit 21 according to the present disclosure can set the position of the last significant coefficient in the 8x8 block (O, P) when the current block size is 8x8 (O, P is a natural number, 1 4, 1? P? 4). In an embodiment of the present invention, the position of the significant coefficient is set to (4, 4) for a block having a size of 8x8 block. Similarly, the binarization unit 21 according to the present disclosure can obtain the same (O, P), i.e., (4, 4), if the current block size is 8x8, irrespective of the region where the last significant coefficient is actually located. ).

The binarization unit 21 according to the present disclosure can set the position of the last significant coefficient to the (Q, R) position in the 16x16 block when the current block size is 16x16 (Q, R are natural numbers, 1 16, 1? R? 16). In an embodiment of the present invention, the position of the significant coefficient is set to (8, 8) for a block having a size of 16 × 16 blocks. Likewise, the binarization unit 21 according to the present disclosure can obtain the same (Q, R), i.e., (8, 8), if the current block size is 16x16, irrespective of the region where the last significant coefficient is actually located. ).

The binarization unit 21 according to the present disclosure can set the position of the last significant coefficient to the (S, T) position within the 32x32 block when the current block size is 32x32 (S, T are natural numbers, 1 16, 1? T? 16). In an embodiment of the present invention, the position of the significant coefficient is set to (16, 16) for a block having a size of 32x32 blocks. Likewise, the binarization unit 21 according to the present disclosure is identical to (S, T), i.e., (16, 16) if the size of the current block is 32 x 32, ).

Meanwhile, the syntax element for the position of the last significant coefficient set based on the block size may be transmitted to the bypass coding unit 25. Therefore, the bypass coding unit 25 performs arithmetic coding on both the suffix bit string and the prefix bit string at the position of the last significant coefficient according to the bypass mode.

In one embodiment of the present disclosure, the binarization section 21 sets the position of the last significant coefficient to a predetermined region according to the block size, regardless of the actual position, and the bypass coding section 25 sets the last significant coefficient The arithmetic coding of the suffix bit string and the prefix bit string at the position of " 1 " is performed according to the bypass mode, but the present disclosure is not limited thereto.

It is sufficient that the present disclosure can be set to a predetermined region according to the block size irrespective of the region where the position of the last significant coefficient is actually located. Therefore, the binarization unit 21 transmits to the bypass coding unit 25 information indicating the block size, information indicating that the position of the last significant coefficient is set based on the block size, and the bypass coding unit 25 Information indicating that the position of the last significant coefficient is set based on the block size, and information indicating the block size may be arithmetic-coded according to the bypass mode.

As another example, the binarization unit 21 according to the present disclosure sets the syntax element for the position of the last significant coefficient based on the block type, and encodes the syntax element for the position of the last significant coefficient according to the set syntax element . Here, the shape of the block may be set to at least one of the shape of the conversion unit and the shape of the conversion block.

Figures 4A and 4B are diagrams illustrating the location of the last significant coefficient set in accordance with one embodiment of the present disclosure. FIG. 4A illustrates a 4x2 transform block, and FIG. 4B illustrates a 4X8 transform block.

The binarization unit 21 according to the present disclosure can set the position of the last significant coefficient to (N ', M') in the 4x2 block if the current block type is 4x2 (N ', M' Natural number, 1? N '? 4, 1? M'? 2). In an embodiment of the present invention, it is exemplified that the position of the significant coefficient is set to (2, 1) for a block having a shape of 4 × 2 blocks. The binarization unit 21 according to the present disclosure is identical to (N ', M'), i.e., (2, 1) if the current block has a size of 4 × 2, ).

The binarization unit 21 according to the present disclosure can set the position of the last significant coefficient to (O ', P') in the 4x8 block if the current block type is 4x8 (O ', P' Is a natural number, 1? O'? 4, 1? P '? 4). In an embodiment of the present invention, it is exemplified that the position of the significant coefficient is set to (2, 4) for a block having the shape of 4x8 block. Likewise, the binarization unit 21 according to the present disclosure is identical (O ', P'), that is, when the current block has a size of 4 × 8, regardless of the area where the last significant coefficient is actually located, 4).

The binarization unit 21 according to the present disclosure can set the position of the last significant coefficient to the position (Q ', R') in the 16x4 block when the current block type is 16x4 (Q ', R' Is a natural number, 1? Q '? 16, 1? R'? 4). In the embodiment of the present invention, it is exemplified that the position of the significant coefficient is set to (4, 1) for a block having the shape of 16x4 block. Likewise, the binarization unit 21 according to the present disclosure is identical to (Q ', R'), i.e., (4) if the current block has a size of 16x4, irrespective of the region where the last significant coefficient is actually located. , 1).

The binarization unit 21 according to the present disclosure can set the position of the last significant coefficient to the (S ', T') position within the 16x32 block if the current block type is 16x32 (S ', T' Is a natural number, 1? S '? 16, 1? T'? 16). In an embodiment of the present invention, it is exemplified that the position of the significant coefficient is set to (8, 8) for a block having a shape of 16x32 blocks. Likewise, the binarization unit 21 according to the present disclosure is identical (S ', T'), that is, when the shape of the current block is 16 × 32, , 8).

On the other hand, the syntax element for the position of the last significant coefficient set on the basis of the block type may be transmitted to the bypass coding unit 25. Therefore, the bypass coding unit 25 performs arithmetic coding on both the suffix bit string and the prefix bit string at the position of the last significant coefficient according to the bypass mode.

In the embodiment of the present disclosure, the binarization unit 21 sets the position of the last significant coefficient to a predetermined region according to the block shape, regardless of the actual position, and the bypass coding unit 25 sets the last significant coefficient The arithmetic coding of the suffix bit string and the prefix bit string at the position of " 1 " is performed according to the bypass mode, but the present disclosure is not limited thereto.

It is sufficient that the present disclosure can be set to a predetermined region according to the block shape irrespective of the region where the position of the last significant coefficient is actually located. Accordingly, the binarization unit 21 transmits to the bypass coding unit 25 information indicating that the position of the last significant coefficient is set based on the block type, indicating the block type, and the bypass coding unit 25 Information indicating that the position of the last significant coefficient is set based on the block type, and information indicating the block type can be arithmetically encoded according to the bypass mode.

Furthermore, in the above-described embodiment, the binarization unit 21 sets the position of the last significant coefficient as a predetermined region according to the size of the block, or sets the predetermined important region according to the block type. However, the binarization unit 21 ) Can set the position of the last significant coefficient to a predetermined region in consideration of both the size of the block and the block shape. In this case, the binarization unit 21 outputs information indicating that the position of the last significant coefficient is set by at least one of the size of the block and the block type, the information indicating the size of the block or the block type, 25, and the bypass coding unit 25 can arithmetically encode such information according to the bypass mode.

In addition, the binarization unit 21 according to the present disclosure can proceed with coding for a significance map. The important map includes information (coded_sub_block_flag) indicating whether non-zero transform coefficients exist in a sub-block (hereinafter referred to as 'CSBF information') and whether or not the value of each transform coefficient in the sub- Information (sig_coeff_flag) (hereinafter, referred to as 'CSF information').

Figures 5A-5C are diagrams illustrating CSBF information set in accordance with one embodiment of the present disclosure. Fig. 5A illustrates a transform block of 4x4 units, Fig. 5B illustrates a transform block of 8x8 units, and Fig. 5C illustrates a transform block of 16x16 units.

Referring to FIG. 5A, when the current block is a 4 × 4 subblock 51, the binarization unit 21 according to the present disclosure can set the CSBF information of the current subblock to 0. In an embodiment of the present invention, it is exemplified that CSBF information is set to 0 for a subblock having a size of 4x4 block. The binarization unit 21 according to the present disclosure can set the CSBF information to be equal to 0 when the size of the current subblock is 4x4 regardless of whether a nonzero transform coefficient exists in the subblock. At this time, when CSBF information is set to 0, it indicates that there is no non-zero transform coefficient in the subblock, and when CSBF information is set to 1, it indicates that a non-zero transform coefficient exists in the subblock .

Referring to FIG. 5B, in the case where the current block is the sub-block 52 of 8 × 8 size, the CSBF information may be set to 0 in the CSBF information of the subblock located at the end in the scanning order have. For example, if the scan order is a diagonal scan order, the binarization unit 21 may set the CSBF information of the remaining subblocks 522, 523, and 524 to 0 except for the first subblock 521 located at the upper left corner. The binary unit 21 according to the present disclosure determines whether or not a non-zero transform coefficient exists in a subblock, if the size of the current block is 8x8, the remaining subblocks All of the CSBF information of " 0 "

Referring to FIG. 5C, in the case where the current block is a 16 × 16 block 53, the binarization unit 21 according to the present disclosure sets the CSBF information to the remaining sub-blocks excluding the U sub- Can be set to zero. In this case, U may be 0 or a positive integer, and may be expressed as 3 in the example of FIG. 5C. For example, when the scan order is the diagonal scan order, the binarization unit 21 may set the CSBF information of the remaining subblocks 534, 535, 536, 537, 538, 539, 540, 541, 542, 543, 544, 545, 546 excluding the U subblocks 531, The binarization unit 21 according to the present disclosure determines whether or not the non-zero transform coefficient exists in the subblock, if the size of the current block is 16 x 16, excluding the U subblocks positioned at the end in the scan order All the CSBF information of the subblock can be set to zero.

In the case where the current block is a 32 × 32 block 504, the CSBF information of the remaining subblocks excluding V subblocks existing last in the scan order is set to 0 . At this time, V may be 0 or a positive integer, which may be 10 in the present disclosure.

The syntax elements for the CSBF information set based on the block size can be transferred to the bypass coding unit 25. [ Therefore, the bypass coding unit 25 performs arithmetic coding on all the bit strings of the CSBF information according to the bypass mode.

In an embodiment of the present disclosure, the binarization unit 21 sets the CSBF information according to the block size regardless of whether or not the non-zero conversion coefficient in the subblock exists, and the bypass coding unit 25 sets the CSBF information bit Although arithmetic coding of the columns according to the bypass mode is exemplified, the present disclosure is not limited thereto.

It is sufficient for this disclosure to be able to set the CSBF information according to the block size regardless of whether there is a non-zero conversion coefficient in the subblock. Therefore, the binarization unit 21 transmits to the bypass coding unit 25 information indicating that the non-zero transform coefficient in the subblock exists, based on the block size, and information indicating the block size, The coding unit 25 can perform arithmetic coding on information indicating that the non-zero transform coefficient in the subblock exists, based on the block size, and information indicating the block size, according to the bypass mode.

As another example, the binarization unit 21 according to the present disclosure may set the CSBF information based on the block type, and may code the CSBF information according to the set syntax element.

6A-6C are diagrams illustrating CSBF information set in accordance with one embodiment of the present disclosure. FIG. 6A illustrates a transform block of 4 × 8 units, FIG. 6B illustrates a transform block of 8 × 4 units, and FIG. 6C illustrates a transform block of 16 × 4 units.

Referring to FIG. 6A, in the case where the block is a 4x8 block 61, the binarization unit 21 according to the present disclosure determines whether or not a nonzero transform coefficient exists in the subblock, The CSBF information of the remaining subblocks 612 excluding the subblock 611 located in the subblock 611 can be set to zero.

Referring to FIG. 6B, in the case where the block is an 8x4 block 62, the binarization unit 21 according to the present disclosure determines whether or not a nonzero transform coefficient exists in the subblock, The CSBF information of the remaining subblocks 622 excluding the subblock 621 located in the subblock 622 can be set to zero.

Referring to FIG. 6C, in the case where the block is a 16x4 block 63, the binarization unit 21 according to the present disclosure determines whether or not the current sub-block is scanned The CSBF information of the remaining subblocks 633 and 634 excluding the W subblocks 631 and 632 existing at the end of the sequence can be set to zero. At this time, W may be 0 or a positive integer and may be 2 in this disclosure.

In addition, in the case where the block is a 32x16 block, the binarization unit 21 according to the present disclosure determines whether the non-zero conversion coefficient in the sub-block exists or not, The CSBF information of the remaining subblocks excluding the subblocks can be set to zero. Z may be zero or a positive integer, and may be six in this disclosure.

On the other hand, the context modeler 22 provides the regular coding unit 24 with a context model for arithmetic coding of the current syntax element. In particular, when the regular modeling unit 22 performs arithmetic coding on the bit stream of the transform coefficient in the regular coding unit 24, the context modeler 22 sends the occurrence probability of the binary value for coding each bin of the bit stream to the regular coding unit 24 Output. The context model is a probability model for a bin. It contains information about which values 0 and 1 correspond to MPS (Most Probable Symbol) and LPS (Least Probable Symbol), and MPS or LPS probabilities. The context modeler 22 updates the context model according to whether the bin value encoded in the regular coding unit 24 is 0 or 1.

The regular coding unit 24 receives the conversion coefficient bit string based on the context model provided from the context modeler 22, that is, information on MPS (Most Probable Symbol), LPS (Least Probable Symbol), and MPS or LPS probability information And arithmetic-codes each bin constituting it.

The bypass coding unit 25 according to an embodiment of the present disclosure arithmetically codes the bit string for the position of the last significant coefficient and the bit string for the CSBF information according to the bypass mode. In the bypass mode, the probability of occurrence of binary signals of 0 and 1 has a fixed value. Therefore, the entropy encoder 20 according to an embodiment of the present disclosure can efficiently process the encoding by minimizing the resource consumed in calculating the bit stream for the position of the last significant coefficient and the bit stream for the CSBF information .

Further, by fixing the syntax element for the position of the last significant coefficient and the syntax element for the CSBF information to the predetermined rule through the entropy encoder according to the embodiment of the present disclosure, the low frequency It is possible to reduce the complexity of the encoder by performing the rate calculation only on the significant transform coefficients.

7 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present disclosure.

7, the image decoder 200 includes an entropy decoding unit 210, a reordering unit 215, an inverse quantization unit 220, an inverse transform unit 225, prediction units 230 and 235, 240, and a memory 245 may be included.

When an image bitstream is input in the image encoder, the input bitstream may be decoded in a procedure opposite to that of the image encoder.

The entropy decoding unit 210 can perform entropy decoding in a procedure opposite to that in which entropy encoding is performed in the entropy encoding unit of the image encoder. For example, various methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be applied in accordance with the method performed by the image encoder.

Since the syntax element is coded by the above-described video coding apparatus 10 through the binarization and arithmetic coding processes, the entropy decoding unit 210 restores the syntax element by performing arithmetic decoding and inverse binarization on the inverse process of the coding process.

The entropy decoding unit 210 extracts, from the received bitstream, a syntax element related to the position of the last significant coefficient of the current block (e.g., an x-axis component prefix bit string and an x-axis component suffix bit string axis component prefix syntax element and an x-axis suffix syntax element corresponding to the y-axis component prefix bit string and the y-axis component suffix bit string of the last significant coefficient position, and a y-axis component prefix syntax element and a y- Syntax element).

The entropy decoding unit 210 performs arithmetic decoding by applying an arithmetic decoding method corresponding to a syntax element (x-axis component prefix syntax element and y-axis component prefix syntax element) related to the position of the last significant coefficient, i.e., a context model (E.g., an x-axis component prefix bit string and a y-axis component prefix bit string) for the position of the last significant coefficient.

In addition, the entropy decoding unit 210 may perform an arithmetic decoding corresponding to the position of the last significant coefficient (e.g., an x-axis component suffix syntax element and a y-axis component suffix syntax element) By performing arithmetic decoding, it is possible to obtain a bit string (e.g., an x-axis component suffix bit string and a y-axis component suffix bit string) for the position of the last significant coefficient.

As described above, when a bit string (e.g., an x-axis component prefix bit string and a y-axis component prefix bit string, an x-axis component suffix bit string and a y-axis component suffix bit string) , The entropy decoding unit 210 can reverse-binarize the bit stream for the position of the last significant coefficient, and combine the inverse binarized information to restore the position of the last significant coefficient.

In particular, the entropy decoding unit 210 performs arithmetic decoding according to the bypass mode by reflecting the syntax element set based on at least one of the block size and the block type, so that the CSBF information (the non-zero conversion coefficient in the sub- Information indicative of whether or not the information exists).

In addition, the entropy decoding unit 210 according to an embodiment of the present disclosure may perform arithmetic decoding according to the bypass mode by reflecting the syntax element at the position of the last significant coefficient set based on at least one of the block size and the block type , It is possible to obtain the position of the last significant coefficient in the transform block.

The entropy decoding unit 210 according to an embodiment of the present disclosure decodes at least one of the CSBF information (information indicating whether a non-zero transform coefficient exists in the subblock exists) and the position of the last significant coefficient By acquiring through arithmetic decoding according to the path mode, it is possible to efficiently perform decoding processing.

The entropy decoding unit 210 may decode information related to intra prediction and inter prediction performed in the encoder.

The reordering unit 215 can perform reordering based on a method in which the entropy decoding unit 210 rearranges the entropy-decoded bitstreams in the encoding unit. The coefficients represented by the one-dimensional vector form can be rearranged by restoring the coefficients of the two-dimensional block form again. The reordering unit 215 can perform reordering by receiving information related to the coefficient scanning performed by the encoding unit and performing a reverse scanning based on the scanning order performed by the encoding unit.

The inverse quantization unit 220 can perform inverse quantization based on the quantization parameters provided by the encoder and the coefficient values of the re-arranged blocks.

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

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

As described above, when intra prediction is performed in the same manner as in the image encoder, when the size of the prediction unit is the same as the size of the conversion unit, pixels existing on the left side of the prediction unit, pixels existing on the upper left side, However, when the size of the prediction unit differs from the size of the prediction unit in intra prediction, intraprediction is performed using a reference pixel based on the conversion unit . It is also possible to use intra prediction using N x N divisions for only the minimum coding unit.

The prediction units 230 and 235 may include a prediction unit determination unit, an inter prediction unit, and an intra prediction unit. The prediction unit determination unit receives various information such as prediction unit information input from the entropy decoding unit 210, prediction mode information of the intra prediction method, motion prediction related information of the inter prediction method, and identifies prediction units in the current coding unit. It is possible to determine whether the unit performs inter prediction or intra prediction. The inter prediction unit 230 predicts the current prediction based on the information included in at least one of the previous picture of the current picture or the following picture including the current prediction unit by using information necessary for inter prediction of the current prediction unit provided by the image encoder, Unit can be performed. Alternatively, the inter prediction may be performed on the basis of the information of the partial region previously reconstructed in the current picture including the current prediction unit.

In order to perform inter prediction, a motion prediction method of a prediction unit included in a corresponding encoding unit on the basis of an encoding unit includes a skip mode, a merge mode, an AMVP mode, and an intra block copy mode It is possible to judge whether or not it is any method.

The intra prediction unit 235 can generate a prediction block based on the pixel information in the current picture. If the prediction unit is a prediction unit that performs intra prediction, intra prediction can be performed based on intra prediction mode information of a prediction unit provided by the image encoder to generate a prediction block. The intraprediction unit 235 may include an Adaptive Intra Smoothing Filter (AISF), a reference pixel interpolator, and a DC filter. The adaptive intra-smoothing filter performs filtering on the reference pixels of the current block, and can determine whether to apply the filter according to the prediction mode of the current prediction unit. The adaptive intra-smoothing filtering can be performed on the reference pixels of the current block by using the prediction mode of the prediction unit provided in the image encoder and the adaptive intra-smoothing filter information. If the prediction mode of the current block is a mode in which adaptive intra-smoothing filtering is not performed, the adaptive intra-smoothing filter may not be applied.

The reference pixel interpolator may interpolate the reference pixel to generate a reference pixel in units of pixels less than an integer value when the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on the pixel value obtained by interpolating the reference pixel. The reference pixel may not be interpolated in the prediction mode in which the prediction mode of the current prediction unit generates a prediction block without interpolating the reference pixel. The DC filter can generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

The restored block or picture may be provided to the filter unit 240. The filter unit 240 may include a deblocking filter, an offset correction unit, and an adaptive loop filter.

When information on whether a deblocking filter is applied to a corresponding block or picture from the image encoder or a deblocking filter is applied, information on whether a strong filter or a weak filter is applied can be provided. In the deblocking filter of the video decoder, the deblocking filter related information provided by the video encoder is provided, and the video decoder can perform deblocking filtering for the corresponding block.

The offset correction unit may perform offset correction on the reconstructed image based on the type of offset correction applied to the image and the offset value information during encoding.

The adaptive loop filter can be applied to an encoding unit based on adaptive loop filter application information provided from an encoder, adaptive loop filter coefficient information, and the like. Such adaptive loop filter information may be provided in a particular set of parameters.

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

8 is a flowchart showing a procedure of a transform coefficient encoding method according to an embodiment of the present disclosure.

The transform coefficient encoding method may be performed by a transform coefficient encoder included in the image encoding apparatus, and the transform coefficient encoder may be an apparatus for processing entropy encoding.

In step S801, the transform coefficient encoding apparatus may perform a scan for rearranging the transform coefficients in an array form using at least one of a diagonal scan, a horizontal scan, and a vertical scan. have.

In step S802, the transform coefficient encoding apparatus can encode the syntax element for the position of the last significant coefficient, which is the last non-zero transform coefficient existing in the transform block. At this time, the non-zero transform coefficient existing at the end of the transform block may mean the last non-zero transform coefficient in the forward scan order case.

Specifically, the transform coefficient encoding apparatus classifies the syntax element currently encoded based on the size of the current block into a prefix and a suffix, applies a predetermined binarization method independent of each other to the prefix and the suffix, and binarizes the prefix and the suffix, And a suffix bit string. For example, the transform coefficient encoding apparatus classifies the column position of the last significant coefficient into a prefix (last_sig_coeff_x_prefix) and a suffix (last_sig_coeff_x_suffix) based on the width of the current block, A predetermined first binarization method is applied to the prefix of the column position (last_sig_coeff_x_prefix) to output a prefix bit string at the column position, and a predetermined second binarization method is applied to the suffix at the column position (last_sig_coeff_x_suffix) It is possible to output the suffix bit string for the bit stream.

The transform coefficient encoding apparatus classifies the row position of the last significant coefficient into a prefix (last_sig_coeff_y_prefix) and a suffix (last_sig_coeff_y_prefix) based on a threshold determined based on the height of the current block , A prefix bit string of an action value is output by applying a first binarization method to a prefix (last_sig_coeff_y_prefix) of a row position, and a second binary method is applied to a suffix of a row position (last_sig_coeff_y_prefix) You can output the heat.

The first binarization method and the second binarization method may be the same or different from each other.

Depending on the type of syntax element, each bin of the bitstream may be arithmetically encoded by applying a context model, or arithmetically encoded by bypass mode.

When the position of the last significant coefficient is categorized into a prefix bit string and a suffix bit string, the transformation coefficient coding device first performs arithmetic coding on the bitstreams classified into the prefix by sequentially applying the context model according to CABAC, The classified bitstreams can be arithmetically encoded in a bypass mode. Preferably, the transform coefficient encoding apparatus sets the syntax element for the position of the last significant coefficient on the basis of the block size, and encodes the syntax element for the position of the last significant coefficient according to the set syntax element . Here, the size of the block may be set to at least one of the size of the conversion unit and the size of the conversion block.

Hereinafter, with reference to FIGS. 3A and 3B, the process of encoding the syntax element for the position of the last significant coefficient based on the size of the block will be described in detail.

If the current block size is 4x4, the position of the last significant coefficient can be set to (N, M) in the 4x4 block (where N, M are natural numbers, 1? N? 4, 1? ). In an embodiment of the present invention, it is illustrated that the position of the significant coefficient is set to (4, 4) for a block having a size of 4 × 4 block. Therefore, the last significant coefficient can be set to (O, P), i.e., (4, 4), if the current block is a 4 × 4 block, irrespective of the actual positioned region.

If the current block size is 8x8, the position of the last significant coefficient can be set to (O, P) in the 8x8 block (where O, P are natural numbers, 1 < ). In an embodiment of the present invention, it is illustrated that the position of the significant coefficient is set to (4, 4) for a block having a size of 8x8 block. Therefore, if the current block is a block of 8 × 8 size, the last significant coefficient can be set to (O, P), ie, (4, 4), regardless of the actual location.

If the current block size is 16x16, the position of the last significant coefficient can be set to the (Q, R) position within the 16x16 block (Q, R are natural numbers, 1? Q? 16, 16). In an embodiment of the present invention, it is illustrated that the position of a significant coefficient is set to (8, 8) for a block having a size of 16 × 16 blocks. Therefore, if the current block is a 16 × 16 block, the last significant coefficient can be set to (Q, R), ie, (8, 8), irrespective of the actual location.

If the current block size is 32 x 32, the position of the last significant coefficient can be set to the (S, T) position within the 32x32 block (S, T are natural numbers, 1? S? 16, 1? T? 16). In an embodiment of the present invention, the position of the significant coefficient is set to (16, 16) for a block having a size of 32x32 blocks. Similarly, the last significant coefficient can be set to (S, T), i.e., (16, 16), depending on the size of the current block (e.g., 32 x 32), irrespective of the actual located region.

In this way, the position of the last significant coefficient can be set based on the block size, and the transform coefficient encoding apparatus can perform arithmetic coding on the position of the last significant coefficient set based on the size of the current block. In particular, the transform coefficient encoding device may pass a syntax element for the position of the last significant coefficient to an arithmetic coding device in bypass mode, and both the suffix and the prefix of the syntax element for the position of the last significant coefficient . ≪ / RTI >

The transform coefficient encoding apparatus sets the position of the last significant coefficient to a predetermined region according to the block size regardless of the actual positioned region and sets the suffix bit string and the prefix bit string at the position of the last significant coefficient in the bypass mode The arithmetic coding is exemplified, but the present disclosure is not limited thereto.

It is sufficient that the present disclosure can be set to a predetermined region according to the block size irrespective of the region where the position of the last significant coefficient is actually located. Therefore, the transform coefficient encoding apparatus may perform arithmetic coding on information indicating that the position of the last significant coefficient is set based on the block size, information indicating the block size, according to the bypass mode.

As another example, the transform coefficient encoding apparatus may set the syntax element for the position of the last significant coefficient based on the block type, and may code the syntax element for the position of the last significant coefficient according to the set syntax element.

Hereinafter, referring to Figs. 4A and 4B, the operation of encoding the syntax element for the position of the last significant coefficient based on the block form is illustrated.

(N ', M') in the 4 × 2 block (N ', M' is a natural number, 1 ? N? 4, 1? M'? 2). In an embodiment of the present invention, it is exemplified that the position of the significant coefficient is set to (2, 1) for a block having a shape of 4 × 2 blocks. Accordingly, the transform coefficient encoding apparatus can obtain the same (N ', M'), i.e., (2, 1) when the shape of the current block is 4 × 2, irrespective of the region where the last significant coefficient is actually located. .

If the current block type is 4x8, the position of the last significant coefficient can be set to (O ', P') in a 4x8 block (O ', P' is a natural number, 1 & 1 ≤ P ≤ 4). In an embodiment of the present invention, the position of the significant coefficient may be set to (2, 4) for a block having the form of 4x8 block. Therefore, regardless of the area where the last significant coefficient is actually located, the transform coefficient encoding apparatus can set the same (O ', P'), i.e., (2, 4) .

If the current block type is 16 × 4, the position of the last significant coefficient can be set to the position (Q ', R') in the 16 × 4 block (Q ', R' is a natural number, 1≤Q'≤16, Lt; = 4). In an embodiment of the present invention, it is illustrated that the position of the significant coefficient is set to (4, 1) for a block having a shape of 16x4 blocks. Likewise, regardless of the region where the last significant coefficient is actually located, the transform coefficient encoding apparatus may be configured so that the positions of the last significant coefficients are all the same (Q ', R') with respect to the block of the 16x4 form of the current block, , I.e., (4, 1).

If the current block type is 16 x 32, the position of the last significant coefficient can be set to a position (S ', T') within a 16x32 block (S ', T' is a natural number, 1 S ' , 1? T '? 16). In an embodiment of the present invention, it is illustrated that the position of the significant coefficient is set to (8, 8) for a block having a shape of 16x32 blocks. In consideration of this, the transform coefficient encoding apparatus can set the position of the last significant coefficient as (S ', T'), i.e., (8, 8), for the block of the current block type of 16x32.

Thus, the syntax elements for the position of the last significant coefficient set based on the block type can be arithmetically encoded according to the bypass mode. In particular, both the suffix bit string and the prefix bit string at the position of the last significant coefficient can be arithmetically encoded according to the bypass mode.

It is sufficient that the present disclosure can be set to a predetermined region according to the block shape irrespective of the region where the position of the last significant coefficient is actually located. Therefore, the transform coefficient encoding apparatus can arithmetically encode information indicating that the position of the last significant coefficient is set based on the block type, information indicating the block type according to the bypass mode.

Furthermore, in the above-described embodiment, it is exemplified that the transform coefficient encoding apparatus sets the position of the last significant coefficient to a predetermined region according to the size of the block, or sets the predetermined significant region according to the block type. However, It is also possible to set the position of the last significant coefficient to a predetermined area in consideration of both the size of the block and the block shape. In this case, the transformation-coefficient encoding apparatus may perform an arithmetic operation according to the bypass mode, such as information indicating that the position of the last significant coefficient is set by at least one of the size of the block and the block type, information indicating the size of the block, Can be encoded.

On the other hand, in step S803, the transform coefficient encoding apparatus can proceed to encoding the significance map. The important map includes information (coded_sub_block_flag) indicating whether non-zero transform coefficients exist in a sub-block (hereinafter referred to as 'CSBF information') and whether or not the value of each transform coefficient in the sub- Information (sig_coeff_flag) (hereinafter, referred to as 'CSF information').

Referring to FIG. 5A, the transform coefficient encoding apparatus can set the CSBF information to 0 for the 4 × 4 subblock 51. The transform coefficient encoding apparatus can set the CSBF information to be equal to 0 when the size of the current subblock is 4 x 4 regardless of whether or not the non-zero transform coefficient exists in the subblock.

Referring to FIG. 5B, the transform coefficient encoding apparatus may set the CSBF information of the subblock located at the end in the scan order to 0 for the subblock 52 of size 8x8. For example, when the scan order is the diagonal scan order, the CSBF information of the remaining subblocks 522, 523, and 524 except for the first subblock 521 at the upper left can be set to zero. The CSBF information of the remaining subblocks except for the subblock located at the end in the scan order with respect to the subblock 52 of the size of 8x8 can be set to all 0 regardless of whether or not the non-zero conversion coefficient in the subblock exists .

Referring to FIG. 5C, the CSBF information of the remaining subblocks excluding the U subblocks existing at the end of the diagonal scan order with respect to the 16x16 subblock 53 can be set to zero. In this case, U may be 0 or a positive integer, and may be expressed as 3 in the example of FIG. 5C. For example, when the scan order is the diagonal scan order, the CSBF information of the remaining subblocks 534, 535, 536, 537, 538, 539, 540, 541, 542, 543, 544, 545, 546 excluding the U subblocks 531, If the size of the current subblock is 16 × 16, regardless of whether there is a non-zero transform coefficient in the subblock, the CSBF information of the remaining subblocks except for the U subblocks positioned at the end of the scan order is all set to 0 Can be set.

In addition, the 32 × 32 subblock 504 may set the CSBF information of the remaining subblocks excluding the V subblocks existing at the end of the scan order to zero. At this time, V may be 0 or a positive integer, which may be 10 in the present disclosure.

In this manner, all the syntax elements for the CSBF information set based on the block size can be arithmetic-coded according to the bypass mode.

It is sufficient for this disclosure to be able to set the CSBF information according to the block size regardless of whether there is a non-zero conversion coefficient in the subblock. Therefore, information indicating that a non-zero transform coefficient in the subblock exists is set based on the block size, and information indicating the block size can be arithmetically encoded according to the bypass mode.

As another example, the CSBF information is set based on the block type, and the CSBF information can be encoded according to the set syntax elements.

6A-6C are diagrams illustrating CSBF information set in accordance with one embodiment of the present disclosure. FIG. 6A illustrates a transform block of 4 × 8 units, FIG. 6B illustrates a transform block of 8 × 4 units, and FIG. 6C illustrates a transform block of 16 × 4 units.

Referring to FIG. 6A, for a 4 × 8 subblock 61, regardless of whether a non-zero transform coefficient exists in the subblock, the remaining part excluding the subblock 611 located at the top of the current subblock, The CSBF information of block 612 can be set to zero.

Referring to FIG. 6B, in the case of the 8 × 4 subblock 62, the CSBF information of the remaining subblocks 622 excluding the subblock 621 located at the left of the current subblock may be set to zero.

6C, the CSBF information of the remaining subblocks 633 and 634 excluding the W subblocks 631 and 632 existing at the end of the current subblock scan sequence is set to 0 Can be set. At this time, W may be 0 or a positive integer and may be 2 in this disclosure.

In addition, in the case of a 32 × 16 subblock, the CSBF information of the remaining subblocks excluding Z subblocks existing at the end of the current subblock scan order can be set to zero. Z may be zero or a positive integer, and may be six in this disclosure.

Further, by fixing the syntax element for the position of the last significant coefficient and the syntax element for the CSBF information to the predetermined rule through the entropy encoder according to the embodiment of the present disclosure, the low frequency It is possible to reduce the complexity of the encoder by performing the rate calculation only on the significant transform coefficients.

In step S803, the transform coefficient encoding apparatus can encode CSF (sig_coeff_flag) information on a subblock other than the subblock in the region for which the CSBF information is forcibly set to 0. The CSF information can be coded in regular mode, and the context model can be derived using the CSF information of the position in the transform block or the transform coefficient of the surroundings.

According to one embodiment, the transform coefficient encoding apparatus may encode the CSF information in a bypass mode instead of the regular mode in calculating the rate-distortion optimization in-process rate.

At this time, in step S803, the conversion-coefficient encoding apparatus can calculate by coding in at least one of the syntax elements in the bypass mode at the rate-distortion optimization.

9 is a flowchart showing a procedure of a transform coefficient decoding method according to an embodiment of the present disclosure.

The transform coefficient decoding method may be performed by a transform coefficient decoding apparatus, and the transform coefficient decoding apparatus may include an entropy decoding unit included in the image decoder.

First, in step S901, the transform coefficient decoding apparatus performs arithmetic decoding and inverse binarization of the syntax element in an inverse process of the transform coefficient encoding process to restore the position of the last significant coefficient.

Specifically, the conversion coefficient decoding apparatus receives, from the received bitstream, a syntax element associated with the position of the last significant coefficient of the current block (e.g., corresponding to each of the x-axis component prefix bit string and the x-axis component suffix bit string of the last significant coefficient position Axis component prefix syntax element and the x-axis suffix syntax element corresponding to the y-axis component prefix bit string and the y-axis component suffix bit string of the last significant coefficient position and the y-axis component prefix syntax element and the y- Fix syntax element).

The transformation coefficient decoding apparatus then performs arithmetic decoding according to an arithmetic decoding method corresponding to a syntax element (e.g., an x-axis component suffix syntax element and a y-axis component suffix syntax element) related to the position of the last significant coefficient (E.g., the x-axis component suffix bit string and the y-axis component suffix bit string) for the position of the last significant coefficient can be obtained. In particular, the transform coefficient decoding apparatus may obtain the syntax element of the position of the last significant coefficient set based on at least one of the block size and the block shape.

As described above, when a bit string (e.g., an x-axis component prefix bit string and a y-axis component prefix bit string, an x-axis component suffix bit string and a y-axis component suffix bit string) , The transform coefficient decoding apparatus can reverse-binarize the bit stream for the position of the last significant coefficient, and combine the inverse binarized information to restore the position of the last significant coefficient. In step S902, the transform coefficient decoding apparatus performs arithmetic decoding according to the bypass mode, and sets CSBF information (based on at least one of the block size and the block type) indicating whether there is a non-zero transform coefficient in the subblock Information) can be identified. In addition, the transformation coefficient decoding apparatus performs arithmetic decoding by applying an arithmetic decoding method corresponding to a syntax element for CSBF information, i.e., a context model, to thereby generate CSBF information (i.e., indicating whether a non- Bit string) can be obtained.

The conversion coefficient decoding apparatus can confirm the syntax element for the CSF (sig_coeff_flag) information. In addition, the transformation coefficient decoding apparatus performs arithmetic decoding by applying an arithmetic decoding method corresponding to a syntax element for the CSF information, i.e., a context model, so that the CSF information (i.e., whether or not the value of each transform coefficient in the sub- A bit stream indicating the bit stream) can be obtained.

According to one embodiment of the present disclosure, in processing the decoding, the position of the last significant coefficient and the CSBF information (information indicating whether a non-zero transform coefficient exists in the subblock) and the position of the last significant coefficient are obtained through arithmetic decoding according to the bypass mode Thus, the decoding process can be performed efficiently.

The transform coefficient decoding apparatus can perform transform coefficient reordering based on a method of rearranging the entropy-decoded bit stream in the encoding unit (S903). The coefficients represented by the one-dimensional vector form can be rearranged by restoring the coefficients of the two-dimensional block form again. The transform coefficient decoding apparatus can perform reordering by receiving information related to the coefficient scanning performed by the encoding unit and performing reverse scanning based on the scanning order performed by the encoding unit.

The apparatus described above may be implemented as a hardware component, a software component, and / or a combination of hardware components and software components. For example, the apparatus and components described in the embodiments may be implemented within a computer system, such as, for example, a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable array (FPA) A programmable logic unit (PLU), a microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. The processing device may also access, store, manipulate, process, and generate data in response to execution of the software. For ease of understanding, the processing apparatus may be described as being used singly, but those skilled in the art will recognize that the processing apparatus may have a plurality of processing elements and / As shown in FIG. For example, the processing unit may comprise a plurality of processors or one processor and one controller. Other processing configurations are also possible, such as a parallel processor.

The software may include a computer program, code, instructions, or a combination of one or more of the foregoing, and may be configured to configure the processing device to operate as desired or to process it collectively or collectively Device can be commanded. The software and / or data may be in the form of any type of machine, component, physical device, virtual equipment, computer storage media, or device , Or may be permanently or temporarily embodied in a transmitted signal wave. The software may be distributed over a networked computer system and stored or executed in a distributed manner. The software and data may be stored on one or more computer readable recording media.

The method according to an embodiment may be implemented in the form of a program command that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions to be recorded on the medium may be those specially designed and configured for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced. Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (1)

An apparatus for encoding a transform coefficient of an image,
A syntax element for a position of a last significant coefficient indicating a non-zero transform coefficient existing at the end of a scan order in a transform block, and a non-zero transform coefficient in a sub-block of the transform block, a syntax element for a sub block flag (hereinafter, referred to as 'CSBF information'), and a syntax element for determining whether the value of each transform coefficient in the subblock is 0 or not,
At least one of the syntax element and the CSBF information for the position of the last significant coefficient is encoded into a preset value based on the size of the conversion block and /
Wherein the transform coefficient encoding apparatus comprises:

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