WO2018128222A1

WO2018128222A1 - Method and apparatus for image decoding in image coding system

Info

Publication number: WO2018128222A1
Application number: PCT/KR2017/003687
Authority: WO
Inventors: 박내리; 남정학; 서정동; 이재호; 임재현; 장형문
Original assignee: 엘지전자 주식회사
Priority date: 2017-01-03
Filing date: 2017-04-04
Publication date: 2018-07-12

Abstract

A method for image decoding carried out by a decoding apparatus according to the present invention comprises the steps of: parsing a first flag which indicates whether the prediction mode carried out in the current block is an inter-merge-prediction mode; parsing a second flag for the current block if the value of the first flag is 0; deriving, on the basis of the second flag, one from among the intra-prediction mode and inter-prediction MVP mode as the prediction mode carried out in the current block; and generating a prediction sample of the current block on the basis of the derived prediction mode. According to the present invention, a merge flag of the current block can be parsed prior to a prediction mode flag, thereby reducing the number of bits generated when a merge mode is carried out in the current block, and thus allowing the overall coding efficiency to be improved.

Description

Method and apparatus for image decoding in image coding system

The present invention relates to an image coding technique, and more particularly, to an image decoding method and apparatus in an image coding system.

Recently, the demand for high resolution and high quality images such as high definition (HD) images and ultra high definition (UHD) images is increasing in various fields. The higher the resolution and the higher quality of the image data, the more information or bit rate is transmitted than the existing image data. Therefore, the image data can be transmitted by using a medium such as a conventional wired / wireless broadband line or by using a conventional storage medium. In the case of storage, the transmission cost and the storage cost are increased.

Accordingly, a high efficiency image compression technique is required to effectively transmit, store, and reproduce high resolution, high quality image information.

An object of the present invention is to provide a method and apparatus for improving image coding efficiency.

Another technical problem of the present invention is to provide a method and apparatus for deriving a prediction mode of a current block performed based on flag information.

Another technical problem of the present invention is to provide a method and apparatus for determining a parsing order of a plurality of flags regarding a prediction mode of a current block.

Another technical problem of the present invention is to provide a method and apparatus for deriving a context increase parameter for flag information about a current block.

According to an embodiment of the present invention, there is provided an image decoding method performed by a decoding apparatus. The method may include parsing a first flag indicating whether a prediction mode performed on a current block is an inter merge prediction mode, and when the value of the first flag is 0, setting a second flag for the current block. Parsing, deriving one of an intra prediction mode and an inter prediction motion vector prediction (MVP) mode as a prediction mode for the current block based on the second flag, and the current block based on the derived prediction mode And generating a predictive sample of.

According to another embodiment of the present invention, a decoding apparatus for performing image decoding is provided. The decoding apparatus parses a first flag indicating whether a prediction mode performed on a current block is an inter merge prediction mode, and when the value of the first flag is 0, a second flag for the current block. An entropy decoding unit for parsing, and a prediction mode for a current block among an intra prediction mode and an inter prediction motion vector prediction (MVP) mode based on the second flag, and deriving a prediction mode of the current block based on the derived prediction mode And a prediction unit generating a prediction sample.

According to another embodiment of the present invention, a video encoding method performed by an encoding apparatus is provided. The method includes determining a prediction mode for a current block, generating a prediction sample of the current block based on the prediction mode for the current block, and generating flag information indicating a prediction mode for the current block. And encoding and outputting the flag information.

According to another embodiment of the present invention, a video encoding apparatus is provided. The encoding apparatus determines a prediction mode for the current block, generates a prediction sample of the current block based on the prediction mode for the current block, and generates a flag information indicating a prediction mode for the current block. And an entropy encoding unit for encoding and outputting the flag information.

According to the present invention, the merge flag of the current block can be parsed before the prediction mode flag, thereby reducing the amount of bits generated when the merge mode is performed on the current block, thereby improving the overall coding efficiency.

According to the present invention, it is possible to adaptively parse a merge flag of a current block before a prediction mode flag based on an arbitrary condition, thereby reducing the amount of bits generated when a merge mode is performed on the current block, thereby overall coding. The efficiency can be improved.

1 is a diagram schematically illustrating a configuration of a video encoding apparatus to which the present invention may be applied.

2 is a diagram schematically illustrating a configuration of a video decoding apparatus to which the present invention may be applied.

3 shows an example of a parsing order of syntax elements for a CU.

4 shows another example of a parsing order of syntax elements for a CU.

5 schematically illustrates a video encoding method by an encoding device according to the present invention.

6 schematically illustrates a video decoding method by a decoding apparatus according to the present invention.

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the invention to the specific embodiments. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the spirit of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. The terms "comprise" or "having" in this specification are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features It is to be understood that the numbers, steps, operations, components, parts or figures do not exclude in advance the presence or possibility of adding them.

On the other hand, each configuration in the drawings described in the present invention are shown independently for the convenience of description of the different characteristic functions, it does not mean that each configuration is implemented by separate hardware or separate software. For example, two or more of each configuration may be combined to form one configuration, or one configuration may be divided into a plurality of configurations. Embodiments in which each configuration is integrated and / or separated are also included in the scope of the present invention without departing from the spirit of the present invention.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. Hereinafter, the same reference numerals are used for the same components in the drawings, and redundant description of the same components is omitted.

In the present specification, a picture generally refers to a unit representing one image of a specific time zone, and a slice is a unit constituting a part of a picture in coding. One picture may be composed of a plurality of slices, and if necessary, the picture and the slice may be mixed with each other.

A pixel or a pel may refer to a minimum unit constituting one picture (or image). Also, 'sample' may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a value of a pixel, and may only represent pixel / pixel values of the luma component, or only pixel / pixel values of the chroma component.

A unit represents the basic unit of image processing. The unit may include at least one of a specific region of the picture and information related to the region. The unit may be used interchangeably with terms such as block or area in some cases. In a general case, an M × N block may represent a set of samples or transform coefficients composed of M columns and N rows.

Referring to FIG. 1, the video encoding apparatus 100 may include a picture divider 105, a predictor 110, a subtractor 115, a transformer 120, a quantizer 125, a reordering unit 130, An entropy encoding unit 135, an inverse quantization unit 140, an inverse transform unit 145, an adder 150, a filter unit 155, and a memory 160 are included.

The picture divider 105 may divide the input picture into at least one processing unit. In this case, the processing unit may be a coding unit block (CU), a prediction unit (PU), or a transform unit (TU). A coding unit is a unit block of coding and may be split from a largest coding unit (LCU) into coding units of a deeper depth along a quad-tree structure. In this case, the maximum coding unit may be used as the final coding unit immediately based on coding efficiency according to the image characteristic, or if necessary, the coding unit is recursively divided into coding units of lower depths and optimized. A coding unit of size may be used as the final coding unit. If a smallest coding unit (SCU) is set, the coding unit may not be split into smaller coding units than the minimum coding unit.

Here, the final coding unit refers to a coding unit that is the basis of partitioning or partitioning into a prediction unit or a transform unit. The prediction unit is a block partitioning from the coding unit block and may be a unit block of sample prediction. In this case, the prediction unit may be divided into sub blocks. The transform unit may be divided along the quad tree structure from the coding unit block, and may be a unit block for deriving a transform coefficient and / or a unit block for deriving a residual signal from the transform coefficient.

Hereinafter, a coding unit may be called a coding block (CB), a prediction unit is a prediction block (PB), and a transform unit may be called a transform block (TB). A prediction block or prediction unit may mean a specific area in the form of a block within a picture, and may include an array of prediction samples. In addition, a transform block or a transform unit may mean a specific area in a block form within a picture, and may include an array of transform coefficients or residual samples.

Meanwhile, the current picture may be divided according to a quad-tree binary-tree (QTBT) structure. In this case, the coding unit, the prediction unit, and the transform unit may be used without being divided, and in this case, the integrated unit may be called a coding unit. In this case, the final coding unit may be square or non-square.

The prediction unit 110 may perform a prediction on a block to be processed (hereinafter, referred to as a current block) and generate a prediction block including prediction samples of the current block. The unit of prediction performed by the prediction unit 110 may be a coding block, a transform block, or a prediction block.

The prediction unit 110 may determine whether intra prediction or inter prediction is applied to the current block. As an example, the prediction unit 110 may determine whether intra prediction or inter prediction is applied on a CU basis.

In the case of intra prediction, the prediction unit 110 may derive a prediction sample for the current block based on reference samples outside the current block in the picture to which the current block belongs (hereinafter, referred to as the current picture). In this case, the prediction unit 110 may (i) derive the prediction sample based on the average or interpolation of neighboring reference samples of the current block, and (ii) the neighbor reference of the current block. The prediction sample may be derived based on a reference sample present in a specific (prediction) direction with respect to the prediction sample among the samples. In case of (i), it may be called non-directional mode or non-angle mode, and in case of (ii), it may be called directional mode or angular mode. In intra prediction, the prediction mode may have, for example, 33 directional prediction modes and at least two non-directional modes. The non-directional mode may include a DC prediction mode and a planner mode (Planar mode). The prediction unit 110 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

In the case of inter prediction, the prediction unit 110 may derive the prediction sample for the current block based on the sample specified by the motion vector on the reference picture. The prediction unit 110 may apply one of a skip mode, a merge mode, and a motion vector prediction (MVP) mode to derive a prediction sample for the current block. In the skip mode and the merge mode, the prediction unit 110 may use the motion information of the neighboring block as the motion information of the current block. In the skip mode, unlike the merge mode, the difference (residual) between the prediction sample and the original sample is not transmitted. In the MVP mode, the motion vector of the current block can be derived using the motion vector of the neighboring block as a motion vector predictor.

In the case of inter prediction, the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block present in the reference picture. A reference picture including the temporal neighboring block may be called a collocated picture (colPic). The motion information may include a motion vector and a reference picture index. Information such as prediction mode information and motion information may be encoded (entropy) and output in the form of a bitstream.

When the motion information of the temporal neighboring block is used in the skip mode and the merge mode, the highest picture on the reference picture list may be used as the reference picture. Reference pictures included in a reference picture list may be sorted based on a difference in a picture order count (POC) between a current picture and a corresponding reference picture. The POC corresponds to the display order of the pictures and may be distinguished from the coding order.

The subtraction unit 115 generates a residual sample which is a difference between the original sample and the prediction sample. When the skip mode is applied, residual samples may not be generated as described above.

The transform unit 120 generates a transform coefficient by transforming the residual sample in units of transform blocks. The transform unit 120 may perform the transformation according to the size of the transform block and the prediction mode applied to the coding block or the prediction block that spatially overlaps the transform block. For example, if intra prediction is applied to the coding block or the prediction block that overlaps the transform block, and the transform block is a 4 × 4 residual array, the residual sample uses a discrete sine transform (DST). In other cases, the residual sample may be transformed by using a discrete cosine transform (DCT).

The quantization unit 125 may quantize the transform coefficients to generate quantized transform coefficients.

The reordering unit 130 rearranges the quantized transform coefficients. The reordering unit 130 may reorder the quantized transform coefficients in the form of a block into a one-dimensional vector form through a coefficient scanning method. Although the reordering unit 130 has been described in a separate configuration, the reordering unit 130 may be part of the quantization unit 125.

The entropy encoding unit 135 may perform entropy encoding on the quantized transform coefficients. Entropy encoding may include, for example, encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), and the like. The entropy encoding unit 135 may encode information necessary for video reconstruction other than the quantized transform coefficients (for example, a value of a syntax element) together or separately. Entropy encoded information may be transmitted or stored in units of network abstraction layer (NAL) units in the form of bitstreams.

The inverse quantization unit 140 inverse quantizes the quantized values (quantized transform coefficients) in the quantization unit 125, and the inverse transform unit 145 inversely transforms the inverse quantized values in the inverse quantization unit 135 to obtain a residual sample. Create

The adder 150 reconstructs the picture by combining the residual sample and the predictive sample. The residual sample and the predictive sample may be added in units of blocks to generate a reconstructed block. Although the adder 150 has been described in a separate configuration, the adder 150 may be part of the predictor 110.

The filter unit 155 may apply a deblocking filter and / or a sample adaptive offset to the reconstructed picture. Through deblocking filtering and / or sample adaptive offset, the artifacts of the block boundaries in the reconstructed picture or the distortion in the quantization process can be corrected. The sample adaptive offset may be applied on a sample basis and may be applied after the process of deblocking filtering is completed. The filter unit 155 may apply an adaptive loop filter (ALF) to the reconstructed picture. ALF may be applied to the reconstructed picture after the deblocking filter and / or sample adaptive offset is applied.

The memory 160 may store information necessary for reconstruction picture or encoding / decoding. Here, the reconstructed picture may be a reconstructed picture after the filtering process is completed by the filter unit 155. The stored reconstructed picture may be used as a reference picture for (inter) prediction of another picture. For example, the memory 160 may store (reference) pictures used for inter prediction. In this case, pictures used for inter prediction may be designated by a reference picture set or a reference picture list.

Referring to FIG. 2, the video decoding apparatus 200 includes an entropy decoding unit 210, a reordering unit 220, an inverse quantization unit 230, an inverse transform unit 240, a predictor 250, and an adder 260. , A filter unit 270, and a memory 280.

When a bitstream including video information is input, the video decoding apparatus 200 may reconstruct the video in response to a process in which the video information is processed in the video encoding apparatus.

For example, the video decoding apparatus 200 may perform video decoding using a processing unit applied in the video encoding apparatus. Thus, the processing unit block of video decoding may be a coding unit block, a prediction unit block, or a transform unit block. The coding unit block may be divided along the quad tree structure from the largest coding unit block as a unit block of decoding. The prediction unit block is a block partitioned from the coding unit block and may be a unit block of sample prediction. In this case, the prediction unit block may be divided into sub blocks. The transform unit block may be divided along the quad tree structure from the coding unit block, and may be a unit block for deriving a transform coefficient or a unit block for deriving a residual signal from the transform coefficient.

The entropy decoding unit 210 may parse the bitstream and output information necessary for video reconstruction or picture reconstruction. For example, the entropy decoding unit 210 decodes information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, quantized values of syntax elements required for video reconstruction, and transform coefficients for residuals. Can be output.

More specifically, the CABAC entropy decoding method receives a bin corresponding to each syntax element in a bitstream, and decodes syntax element information and decoding information of neighboring and decoding target blocks or information of symbols / bins decoded in a previous step. The context model may be determined using the context model, the probability of occurrence of a bin may be predicted according to the determined context model, and arithmetic decoding of the bin may be performed to generate a symbol corresponding to the value of each syntax element. have. In this case, the CABAC entropy decoding method may update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bean after determining the context model.

The information related to the prediction among the information decoded by the entropy decoding unit 210 is provided to the prediction unit 230, and the residual value on which the entropy decoding has been performed by the entropy decoding unit 210, that is, the quantized transform coefficient, is used as a reordering unit ( 220).

The reordering unit 220 may rearrange the quantized transform coefficients in the form of a two-dimensional block. The reordering unit 220 may perform reordering in response to coefficient scanning performed by the encoding apparatus. Although the reordering unit 220 has been described in a separate configuration, the reordering unit 220 may be a part of the quantization unit 230.

The inverse quantization unit 230 may output the transform coefficients by inversely quantizing the transform coefficients quantized based on the (inverse) quantization parameter. In this case, information for deriving a quantization parameter may be signaled from the encoding apparatus.

The inverse transform unit 240 may induce residual samples by inversely transforming the transform coefficients.

The prediction unit 250 may perform prediction on the current block and generate a prediction block including prediction samples for the current block. The unit of prediction performed by the prediction unit 250 may be a coding block, a transform block, or a prediction block.

The prediction unit 250 may determine whether to apply intra prediction or inter prediction based on the information about the prediction. In this case, a unit for determining which of intra prediction and inter prediction is to be applied and a unit for generating a prediction sample may be different. In addition, the unit for generating a prediction sample in inter prediction and intra prediction may also be different. For example, whether to apply inter prediction or intra prediction may be determined in units of CUs. In addition, for example, in inter prediction, a prediction mode may be determined and a prediction sample may be generated in PU units, and in intra prediction, a prediction mode may be determined in PU units and a prediction sample may be generated in TU units.

In the case of intra prediction, the prediction unit 250 may derive the prediction sample for the current block based on the neighbor reference samples in the current picture. The prediction unit 250 may derive the prediction sample for the current block by applying the directional mode or the non-directional mode based on the neighbor reference samples of the current block. In this case, the prediction mode to be applied to the current block may be determined using the intra prediction mode of the neighboring block.

In the case of inter prediction, the prediction unit 250 may derive the prediction sample for the current block based on the sample specified on the reference picture by the motion vector on the reference picture. The prediction unit 250 may induce a prediction sample for the current block by applying any one of a skip mode, a merge mode, and an MVP mode. In this case, motion information required for inter prediction of the current block provided by the video encoding apparatus, for example, information about a motion vector, a reference picture index, and the like may be obtained or derived based on the prediction information.

In the skip mode and the merge mode, the motion information of the neighboring block may be used as the motion information of the current block. In this case, the neighboring block may include a spatial neighboring block and a temporal neighboring block.

The predictor 250 may construct a merge candidate list using motion information of available neighboring blocks, and may use information indicated by the merge index on the merge candidate list as a motion vector of the current block. The merge index may be signaled from the encoding device. The motion information may include a motion vector and a reference picture. When the motion information of the temporal neighboring block is used in the skip mode and the merge mode, the highest picture on the reference picture list may be used as the reference picture.

In the skip mode, unlike the merge mode, the difference (residual) between the prediction sample and the original sample is not transmitted.

In the MVP mode, the motion vector of the current block may be derived using the motion vector of the neighboring block as a motion vector predictor. In this case, the neighboring block may include a spatial neighboring block and a temporal neighboring block.

For example, when the merge mode is applied, a merge candidate list may be generated by using a motion vector of a reconstructed spatial neighboring block and / or a motion vector corresponding to a Col block, which is a temporal neighboring block. In the merge mode, the motion vector of the candidate block selected from the merge candidate list is used as the motion vector of the current block. The information about the prediction may include a merge index indicating a candidate block having an optimal motion vector selected from candidate blocks included in the merge candidate list. In this case, the prediction unit 250 may derive the motion vector of the current block by using the merge index.

As another example, when the Motion Vector Prediction (MVP) mode is applied, a motion vector predictor candidate list may be generated using a motion vector of a reconstructed spatial neighboring block and / or a motion vector corresponding to a Col block which is a temporal neighboring block. Can be. That is, the motion vector of the reconstructed spatial neighboring block and / or the Col vector, which is a temporal neighboring block, may be used as a motion vector candidate. The prediction information may include a prediction motion vector index indicating an optimal motion vector selected from the motion vector candidates included in the list. In this case, the prediction unit 250 may select the predicted motion vector of the current block from the motion vector candidates included in the motion vector candidate list using the motion vector index. The prediction unit of the encoding apparatus may obtain a motion vector difference (MVD) between the motion vector of the current block and the motion vector predictor, and may encode the output vector in a bitstream form. That is, MVD may be obtained by subtracting the motion vector predictor from the motion vector of the current block. In this case, the prediction unit 250 may obtain a motion vector difference included in the information about the prediction, and derive the motion vector of the current block by adding the motion vector difference and the motion vector predictor. The prediction unit may also obtain or derive a reference picture index or the like indicating a reference picture from the information about the prediction.

The adder 260 may reconstruct the current block or the current picture by adding the residual sample and the predictive sample. The adder 260 may reconstruct the current picture by adding the residual sample and the predictive sample in block units. Since the residual is not transmitted when the skip mode is applied, the prediction sample may be a reconstruction sample. Although the adder 260 is described in a separate configuration, the adder 260 may be part of the predictor 250.

The filter unit 270 may apply the deblocking filtering sample adaptive offset, and / or ALF to the reconstructed picture. In this case, the sample adaptive offset may be applied in units of samples and may be applied after deblocking filtering. ALF may be applied after deblocking filtering and / or sample adaptive offset.

The memory 280 may store information necessary for reconstruction picture or decoding. Here, the reconstructed picture may be a reconstructed picture after the filtering process is completed by the filter unit 270. For example, the memory 280 may store pictures used for inter prediction. In this case, pictures used for inter prediction may be designated by a reference picture set or a reference picture list. The reconstructed picture can be used as a reference picture for another picture. In addition, the memory 280 may output the reconstructed picture in an output order.

As described above, the current picture may be reconstructed by performing intra prediction and / or inter prediction. Further, whether to perform inter prediction or intra prediction may be determined in units of a coding unit (CU) in the current picture, and when it is determined that inter prediction is performed on the current CU, the prediction unit in the current CU The Prediction Unit (PU) may determine a prediction mode of one of a skip mode, a merge mode, and a motion vector prediction (MVP) mode. Here, the MVP mode may be referred to as an advanced motion vector prediction (AMVP) mode. In addition, the current picture may not be divided into separate units such as a CU and a PU, or may be divided into one unit integrating the CU and the PU. For example, the CU and the PU may be integrated into a CU, and the current picture may be divided into only a CU in which the CU and the PU are integrated. In this case, a prediction mode of the current picture may be determined in units of the CU, and the prediction mode may be determined as one of an intra prediction mode, a merge mode among inter prediction modes, a skip mode, and an AMVP mode. The merge mode may be called an inter prediction merge mode, the skip mode is an inter prediction skip mode, and the AMVP mode may be called an inter prediction AMVP mode. In other words, the prediction mode determined in the CU unit may be one of an intra prediction mode, an inter prediction merge mode, an inter prediction skip mode, and an inter prediction AMVP mode.

Meanwhile, when the type of a slice including the current block is not an I slice, an occurrence frequency when the inter prediction merge mode is performed on the current block may be high. In this case, the decoding apparatus indicates whether the inter prediction merge mode is performed on the current block before parsing a prediction mode flag indicating whether the prediction mode performed on the current block is an intra prediction mode or an inter prediction mode. By parsing a merge mode flag, the amount of bits generated when the inter prediction merge mode is performed on the current block can be reduced. In other words, the merge flag may be parsed in preference to the prediction mode flag, and if the inter prediction merge mode is applied, the prediction mode flag may not be signaled. Accordingly, the amount of bits generated when the inter prediction merge mode is performed on the current block having a high frequency of occurrence can be reduced, thereby improving the overall coding efficiency. Here, the syntax element of the merge flag may be merge_flag, and the syntax element of the prediction mode flag may be pred_mode_flag. In addition, the merge flag may be referred to as a first flag, and the prediction mode flag may be referred to as a second flag.

3 shows an example of a parsing order of syntax elements for a CU. Referring to FIG. 3, when the current slice is not an I slice, the decoding apparatus may receive and parse a skip flag for the current CU, and determine whether a skip mode is performed on the current CU based on the skip flag. (S305). The syntax element representing the skip flag may be cu_skip_flag. Only intra prediction modes may be applied to blocks in an I slice, and thus a prediction mode may not be determined based on the skip flag.

When it is determined that a skip mode is performed on the current CU based on the skip flag, the decoding apparatus may receive and parse a merge index for the current CU, and determine a candidate block in the merge candidate list indicated by the merge index. The motion information on the current CU may be derived based on the motion information (S310).

In addition, when it is determined that the current slice is not an I slice and a skip mode is not performed on the current CU based on the skip flag, the decoding apparatus may receive and parse a prediction mode flag for the current CU. Based on the prediction mode flag, it may be determined which prediction mode of inter prediction mode and intra prediction mode is performed in the current CU (S315). For example, when the value of the prediction mode flag is 1, the current CU may be determined to perform an inter prediction mode, and when the value of the prediction mode flag is 0, the current CU may have an intra prediction mode. It may be judged to be performed.

When it is determined that the inter prediction mode among the inter prediction mode and the intra prediction mode is performed on the current CU based on the prediction mode flag, the decoding apparatus transmits to the current CU based on partitioning information on the current CU. One or more corresponding PUs may be derived (S320). The syntax element representing the partitioning information for the current CU may be part_mode. Meanwhile, when the current picture is divided into a unit in which the CU and the PU are integrated, for example, when the CU and the PU are integrated into the CU to distinguish the current picture, partitioning information for the CU does not exist. You may not. Also, the decoding apparatus may determine one prediction mode among an intra prediction mode, an inter prediction merge mode, an inter prediction skip mode, and an inter prediction AMVP mode.

When the PU corresponding to the current CU is derived, the decoding apparatus may receive and parse a merge flag, and among the inter prediction merge mode and the inter prediction AMVP mode of the current PU corresponding to the current CU based on the merge flag. It may be determined whether one prediction mode is performed (S325). For example, when the value of the merge flag is 1, the current PU may be determined to perform an inter prediction merge mode, and when the value of the prediction mode flag is 0, the current PU may be an inter prediction AMVP mode. Can be determined to be performed.

When it is determined that the inter prediction merge mode is performed on the current PU based on the merge flag, the decoding apparatus may receive and parse a merge index and based on the motion information of the candidate block in the merge candidate list indicated by the merge index. In operation S330, motion information of the current PU may be derived.

In addition, when it is determined that the inter prediction AMVP mode is performed on the current PU based on the merge flag, the decoding apparatus may perform uni-prediction or bi-prediction on the current PU based on an inter prediction indicator. It may be determined whether to perform (S335). For example, when the value of the inter prediction indicator is 0, the current PU may be determined to be uni-predicted based on motion information included in the motion vector predictor candidate list L0, and the inter prediction indicator may be determined. When the value is 1, the current PU may be determined to be uni-predicted based on motion information included in the motion vector predictor candidate list L1. When the value of the inter prediction indicator is 2, the current PU is determined. May be determined to perform pair prediction based on the motion information in the motion vector predictor candidate list L0 and the motion information in the motion vector predictor candidate list L1.

The decoding apparatus may receive and parse a reference picture index indicating a reference picture for the current PU included in the reference picture list L0, information about a motion vector difference (MVD) L0, and a motion vector predictor (MVP) L0 flag ( In operation S345, a reference picture index indicating the reference picture for the current PU included in the reference picture list L1, information on MVDL1, and an MVP L1 flag may be received and parsed (S345).

Based on the above-described steps, motion information for one or a plurality of PUs may be sequentially derived, and the decoding apparatus may determine whether the current PU is the last PU in decoding order among the PUs corresponding to the current CU. (S350). When the current PU is the last PU, the prediction procedure for the CU may be terminated, and when the current PU is not the last PU, a PU that is next to the current PU in decoding order among PUs corresponding to the current CU. The above-described process can be performed.

On the other hand, when it is determined in step S315 that the intra prediction mode of the inter prediction mode and the intra prediction mode is performed on the current CU based on the prediction mode flag, the decoding apparatus derives one or more PUs for the current CU. In operation S355, it may be determined whether the most probable mode (MPM) based intra luma prediction mode is applied to the current PU based on the previous intra luma prediction flag. The previous intra luma prediction flag may be represented by a prev_intra_luma_pred_flag syntax element. The decoding apparatus may configure the MPM list based on the prediction mode of the left neighboring block and the intra mode of the upper neighboring block. In this case, an additional intra mode may be determined according to a predetermined specific condition and further included in the MPM list.

If it is determined that the intra luma prediction mode included in the MPM list is applied to the current PU, the decoding apparatus may receive and parse an MPM index to derive the intra luma prediction mode for the current PU from the MPM list ( S360). On the other hand, when it is determined that the intra luma prediction mode included in the MPM for the current PU is not applied, the decoding apparatus derives the intra luma prediction mode for the current PU based on the main intra luma prediction mode information. Can be (S365).

After deriving the intra luma prediction mode for the current PU, the decoding apparatus may derive the intra chroma prediction mode for the current PU based on the intra chroma prediction mode information (S370).

On the other hand, it may be necessary to rearrange the position on the syntax of the syntax element representing the inter prediction merge mode having a relatively high frequency of occurrence among the prediction modes. That is, the parsing order between syntax elements for deriving a prediction mode for the current block may be changed. The decoding apparatus may reduce the amount of bits for prediction of an image by parsing a syntax element representing a relatively high frequency prediction mode before other syntax elements, thereby improving overall coding efficiency.

For example, a 2N × 2N size CU may have a very high frequency of skip mode. Accordingly, when the slice type of the slice including the CU is not an I slice, the skip flag for the CU may be parsed preferentially. Specifically, for example, when the value of the skip flag is 1, that is, when a skip mode is performed in the CU, the decoding apparatus may parse a merge index for the CU. Through this, a bit amount for indicating a skip mode is performed to the CU having a high frequency of occurrence can be allocated as the minimum bit, and the overall coding efficiency can be improved.

In a case similar to the above example, the occurrence frequency when the inter prediction merge mode is performed on the current CU may be higher than the occurrence frequency when the inter prediction AMVP mode and the intra prediction mode are performed on the current CU. In this case, the decoding apparatus may parse the merge flag for the current CU preferentially rather than the prediction mode flag for distinguishing whether the prediction mode performed on the current CU is an intra prediction mode or an inter prediction mode. The amount of bits generated when the inter prediction merge mode is performed on the current CU can be reduced.

4 shows another example of a parsing order of syntax elements for a CU. Referring to FIG. 4, when the current slice is not an I slice, the decoding apparatus may receive and parse a skip flag for the current CU, and determine whether a skip mode is performed on the current CU based on the skip flag. (S405).

When it is determined that a skip mode is performed on the current CU based on the skip flag, the decoding apparatus may receive and parse a merge index for the current block, and the movement of the candidate block in the merge candidate list indicated by the merge index may be performed. The motion information on the current block may be derived based on the information (S410). The decoding apparatus may derive one or a plurality of PUs for the current CU. In this case, the current block may be a PU for the current CU. In addition, when the current picture is divided into one unit in which the CU and the PU are integrated, the decoding apparatus may not derive one or a plurality of PUs with respect to the current CU. In this case, the current block may be one unit integrating the CU and the PU, and one unit integrating the CU and the PU may be called a CU.

On the other hand, if it is determined that the current slice is not an I slice and a skip mode is not performed on the current CU based on the skip flag, the decoding apparatus determines the current block before parsing a prediction mode flag for the current block. The merge flag may be received and parsed (S415). When one or a plurality of PUs are derived for the current CU, the current block may be a PU for the current CU, and when the current picture is divided into one unit integrating the CU and the PU. The current block may be one unit integrating the CU and the PU, and one unit integrating the CU and the PU may be called a CU.

In detail, the decoding apparatus may parse the merge flag prior to the prediction mode flag. For example, when the merge flag has a value of 1, the current block may be determined that the inter prediction merge mode is performed. When the merge flag has a value of 0, the current block may have an inter prediction merge mode. It may be determined that is not performed.

Meanwhile, when it is determined in step S415 that the inter prediction merge mode is performed on the current block based on the merge flag, the decoding apparatus may receive and parse a merge index for the current block, and the merge index may be The motion information of the current block may be derived based on the motion information of the candidate block in the pointed merge candidate list (S420).

On the other hand, when it is determined in step S415 that the inter prediction merge mode is not performed on the current block based on the merge flag, the decoding apparatus may receive and parse the prediction mode flag for the current block, and the prediction may be performed. Based on the mode flag, it may be determined which prediction mode of the inter prediction AMVP mode and the intra prediction mode is performed in the current block (S425). As shown in FIG. 4, the amount of bits generated when the inter prediction merge mode is performed on the current block can be reduced and the overall coding efficiency can be improved by changing the parsing order between the syntax elements of the current block. .

If it is determined in step S425 that the inter prediction AMVP mode is performed on the current block based on the prediction mode flag, the decoding apparatus uni-prediction or pair prediction on the current block based on an inter prediction indicator. It may be determined whether a (bi-prediction) is performed (S430). For example, when the value of the inter prediction indicator is 0, the current block may be determined to be unipredicted based on motion information included in the motion vector predictor candidate list L0, and the inter prediction indicator may be determined. When the value is 1, the current block may be determined to be unipredicted based on motion information included in the motion vector predictor candidate list L1. When the value of the inter prediction indicator is 2, the current block may be determined. May be determined to perform pair prediction based on the motion information in the motion vector predictor candidate list L0 and the motion information in the motion vector predictor candidate list L1.

The decoding apparatus may receive and parse a reference picture index indicating a reference picture for the current block included in the reference picture list L0, information about a motion vector difference (MVD) L0, and a motion vector predictor (MVP) L0 flag ( In operation S440, a reference picture index indicating the reference picture for the current block included in the reference picture list L1, information about MVDL1, and an MVP L1 flag may be received and parsed.

On the other hand, when it is determined in step S425 that an intra prediction mode of an inter prediction mode and an intra prediction mode is performed on the current block based on the prediction mode flag, the decoding apparatus determines that the current block is based on a previous intra luma prediction flag. It may be determined whether the most probable mode (MPM) based intra luma prediction mode is applied (S445). The previous intra luma prediction flag may be represented by a prev_intra_luma_pred_flag syntax element. The decoding apparatus may configure the MPM list based on the prediction mode of the left neighboring block and the intra mode of the upper neighboring block. In this case, an additional intra mode may be determined according to a predetermined specific condition and further included in the MPM list.

If it is determined that the intra luma prediction mode included in the MPM list is applied to the current block, the decoding apparatus may receive and parse an MPM index to derive an intra luma prediction mode for the current block from the MPM list ( S450). On the other hand, if it is determined that the intra luma prediction mode included in the MPM for the current block is not applied, the decoding apparatus determines an intra luma prediction mode for the current block based on the information of the main intra luma prediction mode. Can be derived (S455). After deriving the intra luma prediction mode for the current block, the decoding apparatus may derive the intra chroma prediction mode for the current block based on the intra chroma prediction mode information (S460).

Meanwhile, the generation rate between the inter prediction merge mode and the intra prediction mode may vary according to a slice or a sequence including the current block. Accordingly, the above-described method of minimizing the amount of bits generated when the inter prediction merge mode is performed on the current block can be adaptively applied to each slice based on an arbitrary condition, thereby maximizing the effect of the method. Can be improved. For example, a method of changing the parsing order between the syntax elements in slice units according to the following conditions may be applied, and a method of changing the parsing order between the syntax elements according to each combination of conditions may be applied. You may.

As an example, the decoding apparatus may signal a flag for determining a parsing order of the prediction mode flag and the merge flag on a slice basis. The flag may be called a third flag. For example, when the value of the third flag is 0, the decoding apparatus may first parse the merge flag and parse the prediction mode flag based on the value of the merge flag. In addition, when the value of the third flag is 1, the decoding apparatus may parse the prediction mode flag, and when the value of the prediction mode flag indicates the inter prediction mode, may parse the merge flag. Or, as another example, when the value of the third flag is 1, the decoding apparatus may parse the merge flag in preference to the prediction mode flag, and parse the prediction mode flag based on the value of the merge flag. Can be. In addition, when the value of the third flag is 0, the decoding apparatus may parse the prediction mode flag, and when the value of the prediction mode flag indicates the inter prediction mode, may parse the merge flag.

As another example, the decoding apparatus may determine the parsing order of the prediction mode flag and the merge flag according to whether a slice including a current block corresponds to a generalized bi-prediction (GBP) slice. Here, the GBP slice may have up to two motion information for each block in the slice based on the L0 reference picture list and the L1 reference picture list, similarly to the B-prediction slice. However, the L0 reference picture list and the L1 reference picture list for the GBP slice may consist of only reference pictures located in the past than the GBP slice on the time axis. The decoding apparatus may parse the merge flag in preference to the prediction mode flag when the slice including the current block is the GBP slice, and when the slice including the current block is not the GBP slice, the prediction The mode flag may be parsed prior to the merge flag. In detail, when the slice including the current block is the GBP slice, the decoding apparatus may parse the merge flag and parse the prediction mode flag based on the merge flag value. In addition, when the slice including the current block is not the GBP slice, the decoding apparatus may parse the prediction mode flag, and when the prediction mode flag indicates the inter prediction mode, the decoding apparatus parses the merge flag. can do.

As another example, the decoding apparatus may determine the parsing order of the prediction mode flag and the merge flag according to a temporal level of a slice including the current block. When the temporal level of the slice including the current block is greater than or equal to a specific value, the decoding apparatus may parse the merge flag preferentially over the prediction mode flag, and the temporal level of the slice including the current block is smaller than a specific value. In this case, the prediction mode flag may be parsed prior to the merge flag. In detail, when the temporal level of the slice including the current block is equal to or greater than a specific value, the decoding apparatus may parse the merge flag and parse the prediction mode flag based on the value of the merge flag. In addition, when the temporal level of the slice including the current block is smaller than a specific value, the decoding apparatus may parse the prediction mode flag, and when the prediction mode flag indicates the inter prediction mode, parse the merge flag. Can be.

As another example, the decoding apparatus may determine the parsing order of the prediction mode flag and the merge flag according to a quantization parameter (QP) value of the slice including the current block. When the QP value of the slice including the current block is greater than or equal to a specific value, the decoding device may parse the merge flag preferentially than the prediction mode flag, and the QP value of the slice including the current block is smaller than a specific value. In this case, the prediction mode flag may be parsed prior to the merge flag. In detail, when the QP value of the slice including the current block is equal to or greater than a specific value, the decoding apparatus may parse the merge flag and parse the prediction mode flag based on the merge flag value. Also, when the QP value of the slice including the current block is smaller than a specific value, the decoding apparatus may parse the prediction mode flag, and when the prediction mode flag indicates the inter prediction mode, parse the merge flag. Can be.

As another example, the third flag for determining the parsing order of the prediction mode flag and the merge flag may be not only a slice unit but also a picture parameter set (PPS) unit, a sequence parameter set (SPS) unit, or a video parameter set (VPS) unit It may be signaled via higher levels. In addition, a fourth flag indicating whether the third flag is signaled in a slice unit may be signaled in a picture parameter set (PPS) unit, a sequence parameter set (SPS) unit, or a video parameter set (VPS) unit. When the value of the fourth flag is 1, the third flag may be adaptively signaled for each slice.

Meanwhile, the decoding apparatus may change and apply context modeling for the merge flag. That is, the decoding apparatus may change and apply context modeling for entropy decoding the merge flag. The merge flag may be entropy decoded based on the context index for the merge flag. In addition, the merge flag may be entropy decoded based on a context increase parameter for the merge flag.

In detail, the context index may be derived by adding a context increment parameter and a context index offset. For example, the context index may be derived using the following equation.

Here, ctxIdx represents the context index, ctxInc represents the context increase parameter, and ctxIdxOffset represents the context index offset.

The context increase parameter may be derived based on a syntax element of a left neighboring block of the current block and a syntax element of an upper neighboring block of the current block. For example, the context increase parameter may be derived based on a merge flag of the left neighboring block of the current block and a merge flag of the upper neighboring block of the current block. Specifically, the context increase parameter may be derived based on the following table.

Here, condL is a condition value of the left neighboring block, condA is a condition value of the upper neighboring block, merge_flag [x0] [y0] is a merge flag of the current block, and merge_flag [xNbL] [yNbL] is of the left neighboring block. A merge flag, merge_flag [xNbA] [yNbA], is a merge flag of the upper neighboring block, availableL indicates whether the left neighboring block is available, and availableA indicates whether the upper neighboring block is available. If the condition is satisfied, the condition value may indicate 1, and if the condition is not satisfied, the condition value may indicate 0. Availability may indicate 1 if available and 0 if not available.

In this case, the condition value of the left neighboring block may be the same as the value of the merge flag of the left neighboring block, and the condition value of the upper neighboring block may be the same as the value of the merge flag of the upper neighboring block. The context increase parameter may be derived based on a merge flag of the left neighboring block, a merge flag of the upper neighboring block, whether the left neighboring block is available, and whether the upper neighboring block is available. The value of the increment parameter can be derived as one of zero, one and two. The decoding apparatus may entropy decode a merge flag of the current block based on the context increase parameter.

Specifically, for example, when the merge flag value of the left neighboring block is 1 and the left neighboring block is available, the merge flag value of the upper neighboring block is 1 and the upper neighboring block is available, the context The value of the increment parameter may be two.

Further, when the merge flag value of the left neighbor block is 1 and the left neighbor block is not available, and the merge flag value of the upper neighbor block is 1 and the upper neighbor block is available, the value of the context increase parameter May be 1.

Further, when the merge flag value of the left neighboring block is 1 and the left neighboring block is available, and the merge flag value of the upper neighboring block is 1 and the upper neighboring block is not available, the value of the context increase parameter May be 1.

Further, when the merge flag value of the left neighboring block is 0 and the left neighboring block is available, and the merge flag value of the upper neighboring block is 1 and the upper neighboring block is available, the value of the context increase parameter is May be one.

Further, when the merge flag value of the left neighbor block is 1, the left neighbor block is available, the merge flag value of the upper neighbor block is 0, and the upper neighbor block is available, the value of the context increase parameter is May be one.

Further, when neither the left neighboring block nor the upper neighboring block is available, or the merge flag of the left neighboring block and the merge flag of the upper neighboring block are both 0, the value of the context increase parameter may be 0. have.

As another example, the context increase parameter may be derived based on a merge flag and a skip flag of the left neighboring block, a merge flag and a skip flag of the upper neighboring block. Specifically, the context increase parameter may be derived based on the following table.

Here, cu_skip_flag [xNbL] [yNbL] represents a skip flag of the left neighboring block, and cu_skip_flag [xNbA] [yNbA] represents a skip flag of the upper neighboring block. The context increase parameter may include a merge flag of the left neighboring block, a skip flag of the left neighboring block, a merge flag of the upper neighboring block, a skip flag of the upper neighboring block, availability of the left neighboring block, and the upper neighbor. The block may be derived based on the availability of the block, and the value of the context increase parameter may be derived as one of 0, 1, and 2. FIG. The decoding apparatus may entropy decode a merge flag of the current block based on the context increase parameter.

Specifically, for example, when the merge flag of the left neighboring block and the skip flag of the left neighboring block are all 1, the condition value of the left neighboring block may be derived as 1.

In addition, when the merge flag of the upper neighboring block and the skip flag of the upper neighboring block are both 1, the condition value of the upper neighboring block may be derived as 1. After deriving the condition value of the left neighboring block and the condition value of the upper neighboring block, the condition value of the left neighboring block and the availability of the left neighboring block, the condition value of the upper neighboring block and the upper neighboring block The value of the context increase parameter may be derived based on availability.

For example, when the condition value of the left neighboring block is 1, the left neighboring block is available, the condition value of the upper neighboring block is 1, and the upper neighboring block is available, the value of the context increase parameter is 2 days. Can be.

Further, when the condition value of the left neighboring block is 1 and the left neighboring block is not available, and the condition value of the upper neighboring block is 1 and the upper neighboring block is available, the value of the context increase parameter may be 1. have.

Further, when the condition value of the left neighboring block is 1 and the left neighboring block is available, and the condition value of the upper neighboring block is 1 and the upper neighboring block is not available, the value of the context increase parameter may be 1. have.

In addition, when the condition value of the left neighboring block is 0, the left neighboring block is available, the condition value of the upper neighboring block is 1, and the upper neighboring block is available, the value of the context increase parameter may be 1. .

In addition, when the condition value of the left neighboring block is 1, the left neighboring block is available, the condition value of the upper neighboring block is 0, and the upper neighboring block is available, the value of the context increase parameter may be 1. .

In addition, when neither the left neighboring block nor the upper neighboring block is available, or the condition value of the left neighboring block and the condition value of the upper neighboring block are both zero, the value of the context increase parameter may be zero.

The context increasing parameter may include a slice type of a slice including the current block, a prediction mode flag transmitted in a slice unit, a flag for determining a parsing order of a merge flag, a GBP slice corresponding to a slice including the current block, It may be derived based on a temporal level value for the current block or a QP value of a slice including the current block. In addition, the context increase parameter may be derived through a combination of the above-described conditions.

5 schematically illustrates a video encoding method by an encoding device according to the present invention. The method disclosed in FIG. 5 may be performed by the encoding apparatus disclosed in FIG. 1. Specifically, for example, S500 to S510 of FIG. 5 may be performed by the prediction unit of the encoding apparatus, and S520 to S530 may be performed by the entropy encoding unit of the encoding apparatus.

The encoding apparatus determines a prediction mode for the current block (S500). The encoding apparatus may perform prediction based on various prediction modes, and may determine a prediction mode having the highest prediction accuracy among the prediction modes as the prediction mode performed on the current block. In detail, the encoding apparatus may determine a prediction mode of one of an intra prediction mode, an inter prediction skip mode, an inter prediction merge mode, and an inter prediction AMVP mode as the prediction mode for the current block.

The encoding apparatus generates a prediction sample of the current block based on the prediction mode for the current block (S510). The encoding apparatus may generate a prediction sample of the current block through an intra prediction mode, an inter prediction skip mode, an inter prediction merge mode, or an inter prediction AMVP mode. In addition, the encoding apparatus may generate a reconstruction sample for the current block based on the prediction sample.

The encoding apparatus generates flag information indicating a prediction mode for the current block (S520). The flag information may include a first flag indicating whether a prediction mode for the current block is an inter merge prediction mode. The first flag may be called a merge flag. In addition, the flag information may include a second flag indicating whether a prediction mode performed on the current block is an intra prediction mode or an inter prediction mode. The second flag may be called a prediction mode flag.

Meanwhile, the first flag may be a flag parsed before the second flag. The first flag may be a flag which is parsed before the second flag when the current block satisfies an arbitrary condition. For example, a flag parsed first of the first flag and the second flag may be determined based on a condition described below, or a combination of conditions.

As an example, the encoding apparatus may generate a flag indicating a flag parsed first of the first flag and the second flag. The flag indicating the first parsed flag may be called a third flag. The third flag may be included in the flag information. In detail, a flag that is first parsed among the first flag and the second flag may be determined based on the value of the third flag. For example, when the value of the third flag is 1, the first parsed flag may be determined as the first flag, and when the value of the third flag is 0, the first parsed flag may be the second flag. Can be determined. The third flag may be signaled in units of slices through a slice header. In addition, the third flag may be signaled through a higher level such as a picture parameter set (PPS) unit, a sequence parameter set (SPS) unit, or a video parameter set (VPS) unit.

Alternatively, a fourth flag indicating whether the third flag is signaled in a slice unit may be signaled through a higher level such as a picture parameter set (PPS) unit, a sequence parameter set (SPS) unit, or a video parameter set (VPS) unit. When the value of the fourth flag is 1, the third flag may be signaled in units of slices through a slice header.

As another example, the first parsed flag among the first flag and the second flag may be determined based on a slice type (or picture type) of the current slice (or current picture) including the current block. Specifically, for example, when the current slice is a Generalized Bi-Prediction (GBP) slice (or GBP picture), the first parsed flag may be determined as the first flag, and the current slice is not a GBP slice. In this case, the first parsed flag may be determined as the second flag.

As another example, the first parsed flag among the first flag and the second flag may be determined based on a temporal level of the current slice (or current picture) including the current block. Specifically, for example, when the temporal level of the current slice is equal to or greater than a specific value, the first parsed flag may be determined as the first flag, and when the temporal level of the current slice is smaller than a specific value, the first parsed A flag may be determined as the second flag.

As another example, a flag parsed first among the first flag and the second flag may be determined based on a quantization parameter (QP) of a current slice (or current picture) including the current block. Specifically, for example, when the QP of the current slice is greater than or equal to a specific value, the first parsed flag may be determined as the first flag, and when the QP of the current slice is smaller than a specific value, the first parsed flag may be The second flag may be determined.

Meanwhile, the encoding apparatus may change and apply context modeling for the first flag. In other words, the encoding apparatus may change and apply a method of deriving a context index or a context increment parameter for entropy encoding the first flag. Here, the context index may indicate an index indicating a context applied to the current block, and the context index may be derived as a value obtained by adding a context increase parameter and a context index offset. In addition, the context index may be calculated through Equation 1 described above. The encoding apparatus may entropy encode the first flag for the current block based on the derived context index or context increment parameter.

As an example of deriving the context increasing parameter for the first flag, the context increasing parameter may be derived based on a syntax element of a left neighboring block of the current block and a syntax element of an upper neighboring block of the current block. Can be. The syntax element of the left neighboring block may include a merge flag of the left neighboring block, and the syntax element of the upper neighboring block may include a merge flag of the upper neighboring block. The syntax element of the left neighboring block may further include a skip flag of the left neighboring block, and the syntax element of the upper neighboring block may further include a skip flag of the upper neighboring block.

In detail, the context increase parameter may be derived based on the merge flag of the left neighboring block and the merge flag of the upper neighboring block. The value of the context increase parameter may be derived from one of 0, 1, and 2. The context increase parameter may be derived through Table 1 described above.

Specifically, for example, when the left neighboring block and the upper neighboring block are available, and the value of the merge flag of the left neighboring block and the merge flag of the upper neighboring block is 1, the value of the context increase parameter Can be derived as 2. Further, when the merge flag value of the left neighbor block is 1 and the left neighbor block is not available, and the merge flag value of the upper neighbor block is 1 and the upper neighbor block is available, the context increase parameter. The value of can be derived as 1. The context increasing parameter when the merge flag value of the left neighbor block is 1 and the left neighbor block is available, and the merge flag value of the upper neighbor block is 1 and the upper neighbor block is not available. The value of can be derived as 1. Further, when the value of the merge flag of the left neighboring block is 0 and the left neighboring block is available, the value of the merge flag of the upper neighboring block is 1 and the upper neighboring block is available, The value can be derived as one. Further, when the merge flag value of the left neighbor block is 1 and the left neighbor block is available, the merge flag value of the upper neighbor block is 0, and the upper neighbor block is available, The value can be one. Further, when neither the left neighboring block nor the upper neighboring block is available, or the merge flag of the left neighboring block and the merge flag of the upper neighboring block are both 0, the value of the context increase parameter is 0. Can be.

As another example, the context increase parameter may be derived based on the merge flag and the skip flag of the left neighboring block, the merge flag and the skip flag of the upper neighboring block. The value of the context increase parameter may be derived from one of 0, 1, and 2. The context increase parameter may be derived through Table 2 described above.

Specifically, for example, the left peripheral block and the upper peripheral block are available, and the merge flag of the left peripheral block, the skip flag of the left peripheral block, the merge flag of the upper peripheral block, and the upper peripheral block are available. When the skip flag value of the block is 1, the value of the context increase parameter may be derived as 2. Further, one of the left peripheral block and the upper peripheral block is not available, and the merge flag of the left peripheral block, the skip flag of the left peripheral block, the merge flag of the upper peripheral block and the upper peripheral block are not available. When the skip flag value of the block is 1, the value of the context increase parameter may be derived as 1. In addition, one of the merge flag and the skip flag of the left peripheral block is 0 and the left peripheral block is available, and the value of the merge flag and the skip flag of the upper peripheral block is 1 and the upper peripheral block. If this is available, the value of the context increase parameter may be derived as one. Further, the merge flag and the skip flag of the left neighbor block have a value of 1 and the left neighbor block is available, and one of the merge flag and the skip flag of the upper neighbor block has a value of 0 and the upper neighbor block. If this is available, the value of the context increase parameter may be derived as one. Further, neither the left neighboring block nor the upper neighboring block is available, or the merge flag of the left neighboring block, the skip flag of the left neighboring block, the merge flag of the upper neighboring block, and the upper neighboring block. When the value of the skip flag is 0, the value of the context increase parameter may be 0.

The context increasing parameter may be a slice type of a slice including the current block, the third flag, a GBP slice corresponding to a slice including the current block, a temporal level value for the current block, or the current block. It may be derived based on the QP value of the included slice. In addition, the context increase parameter may be derived through a combination of the above-described conditions.

The encoding apparatus encodes and outputs the flag information (S530). The encoding device may entropy encode the flag information and output the bit information in the form of a bitstream. The bitstream may be transmitted to a decoding apparatus via a network or a storage medium.

Although not shown, the encoding apparatus may encode and output information about the residual sample for the current block. The information about the residual sample may include transform coefficients regarding the residual sample.

6 schematically illustrates a video decoding method by a decoding apparatus according to the present invention. The method disclosed in FIG. 6 may be performed by the decoding apparatus disclosed in FIG. 2. Specifically, for example, S600 to S610 may be performed by the entropy decoding unit of the decoding apparatus, and S620 to S630 may be performed by the prediction unit of the decoding apparatus.

The decoding apparatus parses a first flag indicating whether the prediction mode performed on the current block is an inter merge prediction mode (S600). The decoding apparatus may parse a first flag indicating whether a prediction mode performed on the current block is an inter merge prediction mode through a bitstream. The first flag may be called a merge flag.

Meanwhile, the decoding apparatus may determine a flag that is first parsed among the first flag for the current block and the prediction mode flag for the current block according to an arbitrary condition. The prediction mode flag may be a flag indicating whether a prediction mode performed on the current block is an intra prediction mode or an inter prediction mode, and the prediction mode flag may be called a second flag. Specifically, for example, a flag parsed first of the first flag and the second flag may be determined based on a condition described below, or a combination of conditions.

For example, the decoding apparatus may parse a flag indicating a flag that is first parsed among the first flag and the second flag. The flag indicating the first parsed flag may be called a third flag. In detail, the decoding apparatus may parse a third flag for the current block, and determine a flag that is first parsed among the first flag and the second flag based on the value of the third flag. For example, when the value of the third flag is 1, the first parsed flag may be determined as the first flag, and when the value of the third flag is 0, the first parsed flag may be the second flag. Can be determined.

Meanwhile, the third flag may be signaled in units of slices through a slice header. In addition, the third flag may be signaled through a higher level such as a picture parameter set (PPS) unit, a sequence parameter set (SPS) unit, or a video parameter set (VPS) unit.

As another example, the decoding apparatus may determine a flag that is first parsed among the first flag and the second flag based on the slice type (or picture type) of the current slice (or current picture) including the current block. Specifically, for example, when the current slice is a Generalized Bi-Prediction (GBP) slice (or GBP picture), the first parsed flag may be determined as the first flag, and the current slice is not a GBP slice. In this case, the first parsed flag may be determined as the second flag.

As another example, the decoding apparatus may determine a flag that is first parsed among the first flag and the second flag based on a temporal level of the current slice (or current picture) including the current block. Specifically, for example, when the temporal level of the current slice is equal to or greater than a specific value, the first parsed flag may be determined as the first flag, and when the temporal level of the current slice is smaller than a specific value, the first parsed A flag may be determined as the second flag.

As another example, the decoding apparatus may determine a flag that is first parsed among the first flag and the second flag based on a quantization parameter (QP) of the current slice (or current picture) including the current block. Specifically, for example, when the QP of the current slice is greater than or equal to a specific value, the first parsed flag may be determined as the first flag, and when the QP of the current slice is smaller than a specific value, the first parsed flag may be The second flag may be determined.

Meanwhile, the decoding apparatus may change and apply context modeling for the first flag. In other words, the decoding apparatus may change and apply a method of deriving a context index or a context increment parameter for entropy decoding the first flag. Here, the context index may indicate an index indicating a context applied to the current block, and the context index may be derived as a value obtained by adding a context increase parameter and a context index offset. In addition, the context index may be calculated through Equation 1 described above. The decoding apparatus may entropy decode the first flag for the current block based on the derived context index or context increment parameter.

As an example of deriving the context increase parameter based on the first flag, the decoding apparatus may be configured to perform a syntax element of a left neighboring block of the current block and a syntax element of an upper neighboring block of the current block. The context increment parameter for the context may be derived, and the context index for the current block may be derived based on the context increment parameter. The syntax element of the left neighboring block may include a merge flag of the left neighboring block, and the syntax element of the upper neighboring block may include a merge flag of the upper neighboring block. The syntax element of the left neighboring block may further include a skip flag of the left neighboring block, and the syntax element of the upper neighboring block may further include a skip flag of the upper neighboring block.

In detail, the context increase parameter may be derived based on the merge flag of the left neighboring block and the merge flag of the upper neighboring block. The value of the context increase parameter may be derived from one of 0, 1, and 2. The context increase parameter may be derived through Table 1 described above. The decoding apparatus may entropy decode the first flag for the current block based on the context increase parameter.

Specifically, for example, when the left neighboring block and the upper neighboring block are available, and the value of the merge flag of the left neighboring block and the merge flag of the upper neighboring block is 1, the value of the context increase parameter Can be derived as 2.

Further, when the merge flag value of the left neighbor block is 1 and the left neighbor block is not available, and the merge flag value of the upper neighbor block is 1 and the upper neighbor block is available, the context increase parameter. The value of can be derived as 1. The context increasing parameter when the merge flag value of the left neighbor block is 1 and the left neighbor block is available, and the merge flag value of the upper neighbor block is 1 and the upper neighbor block is not available. The value of can be derived as 1. Further, when the value of the merge flag of the left neighboring block is 0 and the left neighboring block is available, the value of the merge flag of the upper neighboring block is 1 and the upper neighboring block is available, The value can be derived as one. Further, when the merge flag value of the left neighbor block is 1 and the left neighbor block is available, the merge flag value of the upper neighbor block is 0, and the upper neighbor block is available, The value can be one.

Further, when neither the left neighboring block nor the upper neighboring block is available, or the merge flag of the left neighboring block and the merge flag of the upper neighboring block are both 0, the value of the context increase parameter is 0. Can be.

Specifically, for example, the left peripheral block and the upper peripheral block are available, and the merge flag of the left peripheral block, the skip flag of the left peripheral block, the merge flag of the upper peripheral block, and the upper peripheral block are available. When the skip flag value of the block is 1, the value of the context increase parameter may be derived as 2.

Further, one of the left peripheral block and the upper peripheral block is not available, and the merge flag of the left peripheral block, the skip flag of the left peripheral block, the merge flag of the upper peripheral block and the upper peripheral block are not available. When the skip flag value of the block is 1, the value of the context increase parameter may be derived as 1. In addition, one of the merge flag and the skip flag of the left peripheral block is 0 and the left peripheral block is available, and the value of the merge flag and the skip flag of the upper peripheral block is 1 and the upper peripheral block. If this is available, the value of the context increase parameter may be derived as one. Further, the merge flag and the skip flag of the left neighbor block have a value of 1 and the left neighbor block is available, and one of the merge flag and the skip flag of the upper neighbor block has a value of 0 and the upper neighbor block. If this is available, the value of the context increase parameter may be derived as one.

Further, neither the left neighboring block nor the upper neighboring block is available, or the merge flag of the left neighboring block, the skip flag of the left neighboring block, the merge flag of the upper neighboring block, and the upper neighboring block. When the value of the skip flag is 0, the value of the context increase parameter may be 0.

If the value of the first flag is 0, the decoding apparatus parses the second flag for the current block (S610). The decoding apparatus may determine a prediction mode of one of an inter prediction Motion Vector Prediction (MVP) mode and an intra prediction mode as a prediction mode performed on the current block based on the second flag.

Meanwhile, when it is determined that the first flag of the first flag and the second flag is parsed first based on any of the above conditions, the decoding apparatus parses the first flag, and the first flag is parsed. When the value of the flag is 0, the second flag for the current block may be parsed. Also, when it is determined that the second flag of the first flag and the second flag is parsed first based on the above-described arbitrary condition, the decoding apparatus parses the second flag, and the second flag When the value of the flag indicates the inter prediction mode, the first flag for the current block may be parsed.

The decoding apparatus derives one of the intra prediction mode and the inter prediction MVP mode as the prediction mode performed on the current block based on the second flag (S620). The value of the second flag may indicate one prediction mode of the intra prediction mode and the inter prediction MVP mode, and the decoding apparatus may determine one of the intra prediction mode and the inter prediction MVP mode based on the second flag. A prediction mode of may be derived as a prediction mode performed on the current block.

The decoding apparatus generates a prediction sample of the current block based on the derived prediction mode (S630). When the derived prediction mode is the intra prediction mode, the decoding apparatus may generate a prediction sample of the current block by performing intra prediction on the current block. In addition, when the derived prediction mode is the inter prediction MVP mode, the decoding apparatus may generate the prediction block of the current block by performing inter prediction on the current block.

Although not shown, the decoding apparatus may generate a reconstruction sample for the current block based on the prediction sample. The decoding apparatus may reconstruct the current block based on the prediction block. The decoding apparatus may generate a reconstructed picture based on the reconstructed sample.

In addition, the decoding apparatus may receive residual information on the current block from the bitstream. The residual information may include transform coefficients for the residual sample of the current block.

The decoding apparatus may derive the residual sample (or residual sample array) for the current block based on the residual information. The decoding apparatus may generate a reconstructed sample based on the prediction sample and the residual sample, and may derive a reconstructed block or a reconstructed picture based on the reconstructed sample. Thereafter, as described above, the decoding apparatus may apply an in-loop filtering procedure, such as a deblocking filtering and / or SAO procedure, to the reconstructed picture in order to improve subjective / objective picture quality as necessary.

According to the present invention described above, the merge flag of the current block can be parsed before the prediction mode flag, thereby reducing the amount of bits generated when the merge mode is performed on the current block, thereby improving the overall coding efficiency.

According to the present invention, it is possible to adaptively parse a merge flag of a current block before a prediction mode flag based on an arbitrary condition, thereby reducing the amount of bits generated when merge mode is performed on the current block. Overall coding efficiency can be improved.

In the above-described embodiment, the methods are described based on a flowchart as a series of steps or blocks, but the present invention is not limited to the order of steps, and any steps may occur in a different order or simultaneously from other steps as described above. have. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

The above-described method according to the present invention may be implemented in software, and the encoding device and / or the decoding device according to the present invention may perform image processing of, for example, a TV, a computer, a smartphone, a set-top box, a display device, and the like. It can be included in the device.

When embodiments of the present invention are implemented in software, the above-described method may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor by various well known means. The processor may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processing devices. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and / or other storage device.

Claims

In the video decoding method performed by the video decoding apparatus,

Parsing a first flag indicating whether the prediction mode performed on the current block is the inter prediction merge mode;

Parsing a second flag for the current block when the value of the first flag is 0;

Deriving one of an intra prediction mode and an inter prediction motion vector prediction (MVP) mode as a prediction mode for the current block based on the second flag; And

Generating a predictive sample of the current block based on the derived prediction mode.
The method of claim 1,

Parsing a third flag for the current block; And

Determining a first parsed flag of the first flag and the second flag based on a value of the third flag,

And when the value of the third flag is 1, the first parsed flag is determined as the first flag.
The method of claim 1,

And determining a first parsed flag among the first flag and the second flag based on a slice type of a current slice including the current block.
The method of claim 3,

And if the current slice is a Generalized Bi-Prediction (GBP) slice, the first parsed flag is determined as the first flag.
The method of claim 1,

And determining a first parsed flag among the first flag and the second flag based on a temporal level of the current slice including the current block.
The method of claim 1,

And determining a first parsed flag among the first flag and the second flag based on a quantization parameter of the current slice including the current block.
The method of claim 1,

Deriving a context increase parameter for the current block based on a syntax element of a left neighboring block of the current block and a syntax element of an upper neighboring block of the current block;

And entropy decoding the first flag based on the context increment parameter.
The method of claim 7, wherein

And the value of the context increment parameter is derived from one of 0, 1, and 2.
The method of claim 7, wherein

The syntax element of the left neighboring block includes a merge flag of the left neighboring block,

The syntax element of the upper neighboring block includes a merge flag of the upper neighboring block.
The method of claim 9,

When the left neighboring block and the upper neighboring block are available, and the merge flag of the left neighboring block and the merge flag of the upper neighboring block are both 1, the value of the context increase parameter is 2 Decoding method characterized in that derived.
The method of claim 9,

The syntax element of the left neighboring block further includes a skip flag of the left neighboring block,

The syntax element of the upper neighboring block further includes a skip flag of the upper neighboring block.
The method of claim 11,

The left neighboring block and the upper neighboring block are available, and values of the merge flag of the left neighboring block, the skip flag of the left neighboring block, the merge flag of the upper neighboring block, and the skip flag of the upper neighboring block are available. Is 1, the value of the context increase parameter is derived as 2.
In the decoding apparatus for performing image decoding,

Parsing a first flag indicating whether the prediction mode performed on the current block is an inter merge prediction mode, and entropy decoding parsing a second flag for the current block when the value of the first flag is 0. part; And

A prediction unit configured to derive a prediction mode for the current block among the intra prediction mode and the inter prediction motion vector prediction (MVP) mode based on the second flag, and generate a prediction sample of the current block based on the derived prediction mode Decoding apparatus comprising a.
The method of claim 13,

The entropy decoding unit parses a third flag for the current block,

The prediction unit determines a flag that is first parsed among the first flag and the second flag based on the value of the third flag,

And when the value of the third flag is 1, the first parsed flag is determined as the first flag.
The method of claim 13,

And the entropy decoding unit determines a flag that is first parsed among the first flag and the second flag based on a slice type of a current slice including the current block.