KR20120100839A - Entropy encoding/decoding method - Google Patents

Abstract

PURPOSE: An entropy encoding/decoding method is provided to increase the compression efficiency of an image and to efficiency of entropy encoding. CONSTITUTION: An encoding unit scans a coefficient of a residual signal in a low frequency component order. The entropy encoding unit arranges the scanned coefficient(S510). The entropy encoding unit performs Last_coeff encoding of the aligned coefficients(S520). The entropy encoding unit performs explicit run/level mode encoding(S550). The encoding unit performs implicit level mode encoding(S560). [Reference numerals] (AA) Yes; (BB) No; (S510) Scanning; (S520) Encoding Last_coeff; (S530) Determining the number of explicit; (S540) The number of encoding<the number of explicit; (S550) Explicit run/level mode encoding; (S560) Implicit level mode encoding

Description

Entropy Encoding / Decoding Method {ENTROPY ENCODING / DECODING METHOD}

The present invention relates to entropy encoding / decoding in a video encoding / decoding apparatus.

Recently, as the broadcasting system supporting HD (High Definition) resolution has been expanded not only in Korea but also in the world, many users are getting used to high resolution and high quality images, and many organizations are accelerating the development of the next generation video equipment. . In addition, as interest in Ultra High Definition (UHD), which supports four times the resolution of HDTV, is increased along with HDTV, a compression technology for higher resolution and higher quality images is required.

For image compression, an inter prediction technique for predicting pixel values included in the current picture from preceding and / or following pictures, and intra prediction for predicting pixel values using pixel information within the picture. A technique and / or an entropy encoding technique may be used in which a short code is assigned to a symbol with a high frequency of appearance and a long code is assigned to a symbol with a low frequency of appearance.

The present invention provides a method and apparatus for increasing compression efficiency by explicitly describing an entropy encoding method of an encoding target block in entropy encoding / decoding.

The present invention provides a method and apparatus for reducing bit overhead that may occur when explicitly describing an entropy encoding method of an encoding target block in entropy encoding / decoding.

According to an embodiment of the present invention, an entropy encoding method in an image encoding apparatus is provided. The entropy encoding method includes scanning coefficients of a differential signal from high frequency components to low frequency components and arranging them in a one-dimensional array, encoding the one-dimensional array in a run mode, and generating a first coded one-dimensional array. Determining a specified number of bits indicating an entropy encoding mode of a coded one-dimensional array, comparing a current number of times with a specified number of times, and encoding a first coded one-dimensional array in an encoding mode indicated by the bits It includes.

According to the present invention, the efficiency of entropy coding can be improved.

According to the present invention can increase the compression efficiency of the image.

1 is a block diagram illustrating an example of a structure of a video encoding apparatus.
2 is a block diagram illustrating an example of a structure of an image decoding apparatus.
3 is a flowchart illustrating an entropy decoding method according to an embodiment of the present invention.
4 illustrates an example of a large gesture coding unit (LCU) level.
5 is a flowchart illustrating an explicit entropy encoding method according to an embodiment of the present invention.
6 is a flowchart illustrating an explicit entropy encoding method according to another embodiment of the present invention.
7 is a flowchart illustrating a method of determining a number of times according to an embodiment of the present invention.
8 is a flowchart illustrating a method of determining a number of times using context information of neighboring blocks according to an embodiment of the present invention.
9 is a flowchart illustrating a method of loading a neighboring block specification number according to an embodiment of the present invention.
10 is a flowchart illustrating a method of determining a specified number of times using only encoding parameters of a current coding block according to an embodiment of the present invention.
11 is a flowchart illustrating an explicit run / level mode encoding method according to an embodiment of the present invention.

In an image encoding / decoding apparatus, values of syntax elements are compressed according to statistical characteristics of each syntax element in order to increase the efficiency of entropy encoding / decoding. For example, since a differential signal has a high probability of having a value of 0 in a high frequency component, values of the high frequency component are encoded in a run mode, and values of the low frequency component are encoded in a level mode. .

In the present invention, the entropy coding method for the differential signal of the entropy coding block is specified in the bitstream in consideration of the statistical characteristics of the entropy coding block. According to this method, since the difference signal of the current coding block can be efficiently encoded according to the characteristic, the coding efficiency can be improved.

However, in all cases, when the entropy encoding mode is specified, the additional bits may be increased, thereby lowering the encoding efficiency. In order to solve this problem, the present invention adaptively determines the number of times of syntax for selecting a run mode and a level mode using an encoding parameter. In the determination of the number of specified times, not only encoding parameters of the current coding block but also context information of neighboring blocks or offsets input by a user may be used.

That is, the present invention provides a method and apparatus for increasing compression efficiency by explicitly describing a suitable entropy encoding method in consideration of the characteristics of a differential signal in entropy encoding / decoding.

Further, the present invention provides a method and apparatus for reducing bit overhead that may occur when explicitly describing an entropy encoding method of an encoding target block in entropy encoding / decoding.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail with reference to drawings. However, in describing the embodiments of the present invention, when it is determined that the detailed description of the known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

When a component is described as being "connected" or "connected" to another component, it may be directly connected to or connected to another component, but another component may be present in between. . In addition, when the present invention is described as "includes" a specific component, rather than excluding components other than the component, it is understood that additional components may be included in the scope of the embodiments or technical spirit of the present invention. it means.

Terms such as "first" and "second" may be used to describe various components, but the components are not limited by the terms. In other words, the terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and likewise, the second component may be referred to as the first component.

In addition, the components shown in the embodiments of the present invention are shown independently to indicate that they perform different characteristic functions, and do not mean that each component may not be implemented in one hardware or software. That is, each component is divided for convenience of description, and a plurality of components may be combined to operate as one component, or one component may be divided into and operate as a plurality of components, which does not depart from the essence of the present invention. Unless included in the scope of the present invention.

In addition, some components may be optional components for improving performance rather than essential components for performing essential functions of the present invention. The present invention may be implemented in a structure including only essential components except for optional components, and a structure including only essential components is also included in the scope of the present invention.

1 is a block diagram illustrating an example of a structure of a video encoding apparatus.

Referring to FIG. 1, the image encoding apparatus 100 may include a motion predictor 111, a motion compensator 112, an intra predictor 120, a switch 115, a subtractor 125, a transformer 130, A quantization unit 140, an entropy encoding unit 150, an inverse quantization unit 160, an inverse transform unit 170, an adder 175, a filter unit 180, and a reference picture buffer 190 are included.

The image encoding apparatus 100 encodes an input image in an intra prediction mode or an inter prediction mode to output a bitstream. Intra prediction means intra prediction and inter prediction means inter prediction. The image encoding apparatus 100 transitions between the intra prediction mode and the inter prediction mode through the switching of the switch 115. The image encoding apparatus 100 generates a prediction block for an input block of an input image and then encodes a residual between the input block and the prediction block.

In the intra prediction mode, the intra predictor 120 generates a prediction block by performing spatial prediction using pixel values of blocks already encoded around the current block.

In the inter prediction mode, the motion predictor 111 finds a motion vector that finds the best match with the input block in the reference picture stored in the reference picture buffer 190 during the motion prediction process. The motion compensation unit 112 generates a prediction block by performing motion compensation using the motion vector. Here, the motion vector is a two-dimensional vector used for inter prediction, and represents an offset between the target block of the current encoding / decoding and the reference block.

The subtractor 125 generates a residual block based on the difference between the input block and the prediction block, and the transformer 130 transforms the difference block and outputs a transform coefficient. The quantization unit 140 quantizes the transform coefficients and outputs quantized coefficients.

The entropy encoding method is a method of receiving a symbol having various values, removing statistical redundancy, and expressing it in a decodable column. The entropy encoder 150 outputs a bitstream by entropy encoding a symbol according to a probability distribution based on a value output from the quantizer 140 or an encoding parameter calculated in an encoding process.

Here, the symbol means a syntax element, a coding parameter, and a residual signal, which are encoding / decoding targets. The encoding parameter is a parameter necessary for encoding and decoding, and may include information that may be inferred in the encoding or decoding process, as well as information encoded in the encoding apparatus and delivered to the decoding apparatus. For example, the coding parameter may include an intra / inter prediction mode, a motion vector, a reference picture index, a coding block pattern, presence or absence of a differential signal, transform coefficients, quantized coefficients, quantization parameters, block size, block partitioning information, and the like. . The difference signal may mean a difference between the original signal and the prediction signal, and may mean a signal in which the difference between the original signal and the prediction signal is transformed or a signal in which the difference between the original signal and the prediction signal is transformed and quantized. Accordingly, the difference signal may be referred to as a difference block in block units.

When entropy encoding is performed, a small number of bits are allocated to a symbol having a high probability of occurrence, and a large number of bits are allocated to a symbol having a low probability of occurrence. Therefore, the size of the bit string of the encoding target symbols is reduced, thereby increasing the compression performance of the video encoding.

For entropy coding, coding methods such as exponential golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC) may be used.

For example, the entropy encoder 150 may store a table for performing entropy encoding, such as a variable length coding (VLC) table, and perform entropy encoding using the stored table.

In addition, the entropy encoder 150 derives a binarization method of the target symbol and / or a probability model of the target symbol / bin, and then uses the derived binarization method and / or the probability model. Entropy encoding may be performed.

Here, binarization means expressing a symbol value as a binary sequence (bin sequence / string), and bin means each binary value when the symbol is represented as a binary column through binarization. , Meaning 0 or 1. The probabilistic model means a predicted probability of a symbol / bin to be encoded / decoded derived from a context information / context model. In this case, the context information / context model means information for determining a probability of a symbol / bin to be encoded / decoded.

More specifically, in CABAC, a symbol is binarized and converted into a bin, and a context model is determined based on encoding information of a neighboring block and a current encoding block or information of an already encoded symbol / bin. A probability of occurrence of a bin is predicted according to the determined context model, and an arithmetic encoding of the bin is performed to generate a bitstream. In this case, after the context model is determined, the context model may be updated using information on the encoded symbol / bin to determine the context model of the next symbol / bin.

Meanwhile, the coded picture needs to be decoded and stored again to be used as a reference picture for performing inter prediction encoding. Accordingly, the inverse quantization unit 160 inverse quantizes the quantized coefficients, and the inverse transform unit 170 inverse transforms the inverse quantized coefficients to output the reconstructed difference block. The adder 175 adds the reconstructed difference block to the prediction block to generate a reconstruction block.

The filter unit 180 may also be referred to as an adaptive in-loop filter, and may include at least one of deblocking filtering, sample adaptive offset (SAO) compensation, and adaptive loop filtering (ALF). Apply. Deblocking filtering means removing block distortion at an inter-block boundary, and SAO compensation means adding an appropriate offset to pixel values to compensate for coding errors. Also, ALF means filtering based on a value obtained by comparing a reconstructed image with an original image.

The reference picture buffer 190 stores the reconstructed block that has passed through the filter unit 180.

2 is a block diagram illustrating an example of a structure of an image decoding apparatus.

2, the image decoding apparatus 200 may include an entropy decoder 210, an inverse quantizer 220, an inverse transformer 230, an intra predictor 240, a motion compensator 250, and an adder 255. ), A filter unit 260 and a reference picture buffer 270.

The image decoding apparatus 200 outputs a reconstructed image by decoding the bitstream in an intra prediction mode or an inter prediction mode. The image decoding apparatus 200 transitions between the intra prediction mode and the inter prediction mode by switching a switch. The image decoding apparatus 200 obtains a difference block from a bitstream, generates a prediction block, and then adds the difference block and the prediction block to generate a reconstruction block.

The entropy decoder 210 entropy decodes the bitstream according to a probability distribution to generate quantized coefficients. The entropy decoding process is symmetrical with the entropy encoding process described above.

For example, the entropy decoding unit obtains a bin corresponding to each syntax element from the bitstream, and uses the decoded syntax element, the decoded information of the neighboring block and the decoded block, or the information of the symbol / bin already decoded. Can be determined. According to the determined context model, the entropy decoding unit predicts a probability of occurrence of a bin and performs arithmetic decoding of the bin. As a result, a symbol corresponding to each syntax element is generated. In this case, after the context model is determined, the context model may be updated using information of the decoded symbol / bin to determine the context model of the next symbol / bin.

The inverse quantizer 220 inversely quantizes the quantized coefficients, and the inverse transformer 230 inversely transforms the inverse quantized coefficients to generate a difference block.

In the intra prediction mode, the intra predictor 240 generates a predictive block by performing spatial prediction using pixel values of blocks already decoded around the current block.

In the inter prediction mode, the motion compensation unit 250 generates a prediction block by performing motion compensation using a motion picture and a reference picture stored in the reference picture buffer 270.

The adder 255 adds the prediction block to the difference block, and the filter unit 260 outputs the reconstructed image by applying at least one of deblocking filtering, SAO compensation, and ALF to the block that has passed through the adder.

The reconstructed image may be stored in the reference picture buffer 270 to be used for motion compensation.

Hereinafter, a block means a unit of encoding / decoding. In the encoding / decoding process, an image is divided into a predetermined size and encoded / decoded. Therefore, a block may also be called a macro block (MB), a coding unit (CU), a prediction unit (PU), a transform unit (TU), or the like. It may be divided into smaller blocks of smaller size.

Here, the prediction unit means a basic unit of performing prediction and / or motion compensation. The prediction unit may be divided into a plurality of partitions, and each partition is called a prediction unit partition. When the prediction unit is divided into a plurality of partitions, the prediction unit partition may be a basic unit of performing prediction and / or motion compensation. Hereinafter, in an embodiment of the present invention, the prediction unit may mean a prediction unit partition.

CAVLC, which is one of entropy encoding methods, sequentially encodes the number of nonzero coefficients, the number of consecutive ones, the size and sign of nonzero coefficients, and the number of zeros between nonzero coefficients among differential signals. At this time, the encoding of each information is performed by the mapping table of the current coding block, which is selected using the encoding information of the quantized coefficients of the neighboring blocks.

In low complexity entropy coding (LCEC), one of low complexity entropy encoding methods, a non-zero quantized coefficient is compared with a fixed threshold to select whether to encode in a run mode or a level mode. The run mode is a method of encoding the number of nonzero coefficients and the number of zeros between nonzero coefficients separately, and is suitable for encoding a high frequency region in which a large number of zero coefficients are continuously distributed. On the other hand, the level mode is a method of encoding the magnitude of the coefficient as it is, and is suitable for encoding in the low frequency region where the coefficient of zero is relatively distributed. LCEC applies a run mode for some coefficients and a level mode for some coefficients according to a fixed threshold, thereby enabling high coding performance even with low complexity techniques.

Meanwhile, in entropy encoding, a code length is variably allocated in consideration of statistical characteristics of a probability of occurrence of an encoding target. LCEC also encodes coefficients in the order of high frequency components to low frequency components after discrete transform and quantization of a differential block and then sorting them by a scanning method such as zigzag scanning. That is, LCEC takes into account the statistical property that zero occurs frequently in coefficients that are relatively later when coefficients are aligned in one dimension. However, statistical characteristics may vary depending on the type of image, slice type, characteristics of the image in the block, QP (Quantization Parameter) value in the block, intra prediction mode of the block, scanning method, and the like.

For example, there may be a case where a coefficient greater than or equal to a threshold exists in the high frequency component and there is a continuous zero in front of it. In this case, when the fixed threshold value is used, even in successive zeros, all of the encoding is performed in the level mode, thereby reducing the compression efficiency. In order to solve this problem, if the statistical characteristics of the encoding target are accurately predicted, the compression efficiency can be increased, but the complexity of the encoding / decoding device is increased.

Accordingly, in order to provide an encoding / decoding apparatus having a low complexity and high compression efficiency, the present invention considers characteristics of an image and encoding parameters. That is, according to an embodiment of the present invention, in order to select the optimal mode, the entropy encoding mode used among the run mode and the level mode is explicitly described. In addition, according to another embodiment of the present invention, in order to minimize the bit overhead that may occur when specifying the entropy encoding mode to be used, the specified number of times is determined by encoding parameters, context information of neighboring blocks, and offset information input by a user. The decision is made adaptively in consideration of the

The above objects, features and methods will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art to which the present invention pertains may easily implement the technical idea of the present invention. Could be. In addition, the following description is based on an encoding method and apparatus, but a person having ordinary knowledge in the art to which the present invention belongs may easily apply the technical idea of the present invention to a decoding method and apparatus.

3 is a flowchart illustrating an entropy decoding method according to an embodiment of the present invention.

The entropy decoder selectively selects an implicit entropy decoding method that selects a run mode and a level mode based on a fixed threshold and an explicit entropy decoding method that selects a decoding mode based on bits that explicitly indicate a coding mode used. Can be used. In this case, in selecting an entropy decoding method, a defined syntax element such as mode_flag may be used.

Referring to FIG. 3, the entropy decoding unit derives mode_flag in order to select an entropy decoding method (S310). Information necessary for the selection of the entropy decoding method is signaled at the sequence, picture, group of picture (GOP), slice, and large coding unit (LCU) levels. Accordingly, the entropy decoding unit derives mode_flag of the current decoding block through parsing of syntax elements signaled at the sequence, picture, GOP, slice, and LCU levels.

The entropy decoding unit selects an entropy decoding method using the mode_flag derived through the mode_flag derivation step (S310) (S320). For example, when mode_flag is 0, the current decoding block is decoded by an implicit entropy decoding method. When mode_flag is 1, it is decoded by an explicit entropy decoding method.

When decoding the current decoding block by an implicit entropy decoding method, the entropy decoding unit determines an entropy decoding mode based on a fixed threshold value, and performs decoding in the determined decoding mode. That is, it is determined without additional information which mode is decoded in the run mode or the level mode.

When the current decoding block is decoded by the explicit entropy decoding method, the entropy decoding unit determines the entropy decoding mode based on a bit that explicitly indicates the used encoding mode, and performs decoding in the determined decoding mode. In other words, whether the current decoding block is to be decoded in the run mode or the level mode is determined using a bit that explicitly indicates the encoding mode used.

Tables 1 to 3 show examples of syntaxes used in the explicit entropy encoding / decoding method.

The image encoding / decoding apparatus according to an embodiment of the present invention may use selective_entropy_mode_flag, which is a syntax element specified at a picture parameter set (PPS) level. The selective_entropy_mode_flag indicates whether to apply the selective entropy encoding mode in picture units.

The current_slice_sem_flag specified at the slice level is specified when the selective_entropy_mode_flag is 1. current_slice_sem_flag is a syntax element used to control whether the selective entropy encoding mode is applied in units of slices. If current_slice_sem_flag is 0, no syntax is specified at the LCU level.

Mode_flag specified at the LCU level is a flag for selecting one of an implicit entropy encoding method and an explicit entropy encoding method. mode_flag is specified only when current_slce_sem_flag is 1, and no syntax for entropy encoding mode selection is specified when current_slice_sem_flag is 0.

4 illustrates an example of a large gesture coding unit (LCU) level.

Referring to FIG. 4, mode_flag is input to each LCU. When mode_flag of a specific LCU is 1 (410), an explicit entropy encoding method is used for all entropy coding blocks located in the LCU. At this time, in determining the run mode and the level mode, a bit that explicitly indicates the encoding mode is used.

On the other hand, when mode_flag of a specific LCU is 0 (420), an implicit entropy encoding method is used for all entropy coding blocks located in the LCU. That is, based on the threshold value, a run mode or a level mode is selected, and entropy encoding for coefficient values in a block is performed in the selected mode.

5 is a flowchart illustrating an explicit entropy encoding method according to an embodiment of the present invention.

Referring to FIG. 5, in the explicit entropy encoding method according to an embodiment of the present invention, a scanning step (S510), a Last_coeff encoding step (S520), an explicit number determination step (S530), an entropy encoding mode selection step (S540), An explicit run / level mode encoding step S550 and an implicit level mode encoding step S560 are included.

In order to perform entropy encoding using general characteristics of frequencies, the entropy encoder scans the coefficients of the quantized differential signal in order from high frequency components to low frequency components and arranges them in a one-dimensional array (S510).

Thereafter, the entropy encoder performs Last_coeff encoding of the aligned coefficients (S520). Last_coeff encoding means to generate a first coded one-dimensional array by performing run mode coding on the scanned one-dimensional array based on a non-zero coefficient.

On the other hand, when the run mode or the level mode is explicitly indicated, the performance of entropy encoding is improved, but the overhead due to the bits explicitly indicating the encoding mode to be used increases. In order to solve this problem, it is possible to limit the number of times of specifying the bit explicitly indicating the encoding mode to be used.

Therefore, according to the entropy encoding method according to an embodiment of the present invention, an explicit number of bits for explicitly indicating an encoding mode to be used is adaptively determined (S530). In this way, the performance of entropy encoding can be improved while minimizing the overhead caused by bits explicitly indicating the encoding mode to be used.

Meanwhile, an encoding parameter may be used to selectively determine the specified number of times. Types of coding parameters include a prediction mode of a current coding block, context information of a neighboring block, a position of a quantized coefficient of a current coding block, a QP value, a slice type, and the like. Each parameter can change the statistical properties of the quantized coefficients.

For example, if the number of counts is determined to be 3 using the encoding parameter in the step of determining the number of times (S530), the bit for explicitly indicating the encoding mode to be used is informed three times.

When the number of specified times is determined, the entropy encoder selects an entropy encoding mode by comparing the current number of times with the specified number of times (S540). That is, it is determined whether to perform explicit run / level mode encoding or implicit level encoding.

If the current number of encodings is less than the specified number of times, explicit run / level mode encoding is performed (S550). That is, after reading a bit that explicitly indicates an encoding mode, entropy encoding of the first encoded one-dimensional array is performed in the run mode or the level mode according to the value.

On the other hand, if the current number of encodings is greater than the specified number, implicit level mode encoding is performed (S560).

On the other hand, the number of times of encoding is initialized in the specifying number determining step S530, and increases in the explicit run / level mode encoding step S550.

6 is a flowchart illustrating an explicit entropy encoding method according to another embodiment of the present invention.

Scanning coefficients of the quantized differential signal (S610), generally, zero is continuously generated in the high frequency component. Using this characteristic, the last_coeff encoding step (S620) encodes continuous zeros existing in the high frequency component.

However, since there is still a high probability that 0 is continuously generated even after the last_coeff encoding step S620, an implicit run mode encoding step S625 may be performed after the Last_coeff encoding step S620.

The difference signal entropy-encoded through the last_coeff encoding step S620 and the implicit run mode encoding step S625 is encoded in the explicit run / level mode according to the specified number of times determined through the specifying number determining step S630 (S650). In operation S660, the signal is encoded in an implicit level mode.

That is, when the specified number of times is determined through the specifying number determining step (S630), the entropy encoding unit selects an entropy encoding mode by comparing the present encoding number with the specifying number (S640).

If the current number of encodings is less than the specified number of times, explicit run / level mode encoding is performed (S650). That is, after reading a bit that explicitly indicates an encoding mode, entropy encoding is performed in a run mode or a level mode according to the value.

On the other hand, if the current number of encodings is greater than the specified number, implicit level mode encoding is performed (S660).

Table 4 shows an example of syntax for determining the number of times in the explicit entropy encoding method.

In the explicit entropy encoding method, the specified number of bits for explicitly indicating the encoding mode, which is recorded in the current coding block, is determined in the specifying number determining step (S530, S630). Meanwhile, when the specified number of times is determined, only encoding parameters of the current coding block may be used or context information of neighboring blocks may be used together.

Current_neighbor_flag of Table 4 is a flag indicating whether to use only encoding parameters of the current coding block or context information of neighboring blocks when determining the number of times when an explicit entropy encoding method is used in a specific LCU in the current slice. . For example, when current_neighbor_flag is 1, the number of times specified in the slice is determined using the context information of the neighboring block. When current_neightbor_flag is 0, the number of times is determined using only the encoding parameter of the current coding block.

7 is a flowchart illustrating a method of determining a number of times according to an embodiment of the present invention.

5 and 6, the specifying number determining step (S530, S630) of the specifying number determining method selection step (S710), the specifying number determining step using only encoding parameters of the current coding block (S720) and the specification using the context information of the neighboring block. The number determining step S730 may be included.

In the selection count determining method selection step S710, the selection count determining method is selected based on current_neighbor_flag. For example, when current_neighbor_flag is 0, the number of specification is determined using only coding parameters of the current coding block. When current_neighbor_flag is 1, the number of specification is determined using context information of a neighboring block.

In the operation of determining the number of times using only encoding parameters of the current coding block (S720), the number of times of determination is determined by using encoding parameters of the current coding block such as a prediction mode, an intra prediction direction, a quantization parameter, and a slice type.

In the step S730 of determining the number of specified times using context information of the neighboring block, the number of specified times is determined by considering both encoding parameters of the current coding block such as prediction mode, intra prediction direction, quantization parameter, and slice type, and context information of the neighboring block. . For example, the number of times of the current incubation block may be determined in consideration of the number of times of the neighboring block.

Meanwhile, the method of determining the number of times using only encoding parameters of the current coding block is a context-adaptive number of times determining method based on the current coding block, and the method of determining the number of times using context information of the neighboring blocks is based on the current coding block and the surrounding blocks. It may be named as an adaptive specification number determination method.

8 is a flowchart illustrating a method of determining a number of times using context information of neighboring blocks according to an embodiment of the present invention.

In the step S730 of determining the number of times of using the context information of the neighboring block of FIG. The number determining step S840 may be included.

In the step of loading the left block specification number (S810), the number of specification of the block located on the left side is loaded based on the current coding block, and in the step of loading the upper block specification (S820), the number of specifying the block located above is loaded.

In the step of loading the current coded block specification number (S830), the number of specified times of the current coded block is determined using the coding parameter of the current coded block, and the determined number of times is loaded. The current coded block specifying number loading step S830 includes a specifying number determining step S720 using only the number of times determined in the specifying number determining step S720 using only encoding parameters of the current encoding block of FIG. 7 or using only encoding parameters S720. can do.

In the final specifying count determining step (S840), the final specifying count to be applied to the current encoding block is determined based on at least one or more of the specifying number of the left block, the upper block, and the current encoding block. For example, the final specification number may be determined by calculating the median value, the minimum value, the maximum value, etc. by combining at least one of the specified number of times of the left block, the upper block, and the current coding block.

9 is a flowchart illustrating a method of loading a neighboring block specification number according to an embodiment of the present invention.

The left block specifying count loading step S810 and the upper block specifying count loading step S820 of FIG. 8 are examples of the neighbor block specifying count loading step. In the case of using the explicit entropy encoding method, in the neighbor block specification count loading step, the explicit count considering the encoding parameter of the current encoding block may be loaded instead of simply loading the explicit count of the corresponding block.

Referring to FIG. 9, in the method of loading neighbor blocks according to an embodiment of the present invention, the target block prediction mode determination step (S910), the target block quantization parameter determination step (S920), and the target block output count step (S930) are described. ).

In the target block prediction mode determination step (S910), it is determined whether the prediction mode of the target block, that is, the prediction mode of the corresponding neighboring block and the prediction mode of the current coding block match. If the prediction modes of the two blocks coincide, the target block quantization parameter determination step S920 is performed.

In the target block quantization parameter determination step (S920), a difference between a quantization parameter (QP) value of the current coding block and a quantization parameter value of the target block is compared with a predetermined determination reference value. The specified number of target blocks may be used only when the difference between the quantization parameter values of the two blocks is smaller than the determination reference value.

In the target block specification count output step (S930), the target block prediction mode determination step (S910) and the target block quantization parameter determination step (S920) output the specification number of the target block determined to be similar to the current coding block.

Meanwhile, the number of times of specifying the target block determined to be not similar to the current coding block is not used through the target block prediction mode determination step S910 and the target block quantization parameter determination step S920.

For example, let the current coding block be C, and the left and upper blocks of the current coding block are L and U, respectively.

If it is determined that block L is similar to block C, the number of specified blocks L output through the step of loading the left block specified number S810 is used to determine the number of specified blocks C, but otherwise, the specified block L is specified. The number of times is not used to determine the specified number of blocks C. Similarly, only when the block U is determined to be similar to the block C, the specified number of blocks U is used.

10 is a flowchart illustrating a method of determining a specified number of times using only encoding parameters of a current coding block according to an embodiment of the present invention.

Referring to FIG. 10, in the method of determining the number of times using only encoding parameters of the current coding block, the method of determining the number of candidates is determined in step S1010, the offset loading step in S1020, and the step of determining the number of times in final step S1030. ).

In the step of determining the candidate specification number (S1010), the candidate value of the specification number of times is determined based on coding parameters of the current coding block such as a quantization parameter, a prediction mode, an intra prediction direction, and a slice type.

In the offset loading step S1020, the offset syntax information of the specified number of times signaled in the picture parameter set or the slice header is loaded.

In the final specification count determining step (S1030), the candidate value of the specification count is readjusted based on the offset obtained through the offset loading step (S1020) to determine the readjusted specification count as the final specification count.

Tables 5 and 6 show examples of syntaxes used to load the specified number of offset syntax information.

In the explicit entropy encoding method according to an embodiment of the present invention, an offset may be used in units of slices in order to consider characteristics of an image when determining the number of times of explicitly indicating a coding mode to be used. The use of this offset is activated on a picture basis by the iter_offset_control_present_flag of the picture parameter set. For example, when iter_offset_control_present_flag is 0, pictures referring to the picture parameter set in the picture unit do not use an offset. On the other hand, when iter_offset_control_present_flag is 1, an offset is signaled through inter_offset in each slice unit.

In addition, in the explicit entropy encoding method according to an embodiment of the present invention, the specified number of times of the current coding block is determined using the coding parameter, the prediction mode, and the offset of the current coding block. For example, the index value is calculated by adding the inter_offset value parsed in slice units to the encoding parameter value of the current block, and the specified number of times is specified in a predetermined table based on the prediction mode of the current coding block according to the index value. Decide

Table 7 is an example of a table for determining the specified number of times.

The index value in Table 7 is calculated as follows.

11 is a flowchart illustrating an explicit run / level mode encoding method according to an embodiment of the present invention.

As described above with reference to FIGS. 5 and 6, explicit run / level mode encoding is performed when the current number of encodings is less than a threshold value.

Referring to FIG. 11, in the run_level_sel_flag loading step (S1110), run_level_sel_flag, which is a syntax for selecting a run mode and a level mode, is loaded.

In the encoding mode selection step (S1120), run mode encoding or level mode encoding is selected according to run_level_sel_flag. For example, when run_level_sel_flag is 0, the run mode encoding step S1130 is performed. When run_level_sel_flag is 1, the level mode encoding step SS1140 is performed.

Although the above-described embodiments are described through a series of steps or a flowchart represented by blocks, the present invention is not limited to the order of the steps described above, and some steps may occur in different steps, different orders, or concurrently. In addition, one of ordinary skill in the art will appreciate that the steps shown in the flowcharts are not exclusive, that other steps may be included or some steps may be deleted.

In addition, the above-described embodiments include examples of various aspects. In order to represent various aspects, not all possible combinations may be described, but one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (1)

In the entropy encoding method in a video encoding apparatus,
Scanning the coefficients of the differential signal from high frequency components to low frequency components and sorting the coefficients of the differential signal into a one-dimensional array;
Encoding the one-dimensional array in a run mode to generate a first encoded one-dimensional array;
Determining a specified number of bits for indicating an entropy encoding mode of the first coded one-dimensional array;
Comparing a current encoding number with the specified number of times; And
And encoding the first coded one-dimensional array in an encoding mode indicated by the bits when the current number of encoding times is smaller than the specified number of times.

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