WO2014189300A1 - Method and apparatus for coding video supporting plurality of layers - Google Patents

Abstract

Disclosed are a method and an apparatus for coding a video supporting a plurality of layers. The method for coding the video supporting the plurality of layers, according to the present invention, comprises the steps of: inducing a reference layer sample location from a reference layer picture used for inter-layer prediction of a current layer picture; resampling the reference layer picture, based on the reference layer sample location; and generating a prediction sample of a current block by inter-layer predicting the current block of the current layer picture, based on the resampled reference layer picture.

Description

Video coding method and apparatus supporting multiple layers

The present invention relates to video compression techniques, and more particularly, to a method and apparatus for performing video coding that supports multiple layers.

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

An inter-screen prediction technique for predicting pixel values included in the current picture from a picture before or after the current picture using an image compression technique, an intra prediction technique for predicting pixel values included in a current picture using pixel information in the current picture, Various techniques exist, such as an entropy encoding technique for allocating a short code to a high frequency of appearance and a long code to a low frequency of appearance, and the image data can be effectively compressed and transmitted or stored.

The present invention provides a method and apparatus for encoding / decoding an enhancement layer by performing interlayer prediction in scalable video coding.

The present invention provides a resampling method and apparatus for compensating for phase difference in scalable video coding.

According to an embodiment of the present invention, an image decoding method supporting a plurality of layers is provided. The image decoding method may include deriving a reference layer sample position from a reference layer picture used for inter-layer prediction of a current layer picture, resampling the reference layer picture based on the reference layer sample position, and resampling And generating a prediction sample of the current block by performing interlayer prediction on the current block of the current layer picture based on a reference layer picture.

The deriving of the reference layer sample position may include: in the reference layer corresponding to a top-left sample position of the current block based on information on a phase offset for compensating a phase difference between layers. Sample location can be derived.

The information on the phase shift may include at least one of a phase shift for a luma component and a phase shift for a chroma component.

According to another embodiment of the present invention, an image decoding apparatus supporting a plurality of layers is provided. The image decoding apparatus derives a reference layer sample position from a reference layer picture used for inter-layer prediction of a current layer picture, resamples the reference layer picture based on the reference layer sample position, and resamples the reference layer picture. And a predictor configured to generate predictive samples of the current block by performing interlayer prediction on a current block of the current layer picture based on a picture.

The predictor may derive the reference layer sample position corresponding to the top-left sample position of the current block based on information on a phase offset to compensate for the phase difference between layers.

The information on the phase shift may include at least one of a phase shift for a luma component and a phase shift for a chroma component.

In the case of performing interlayer prediction using the resampling method according to an embodiment of the present invention, the phase shift may be compensated for by inducing the phase shift to compensate for the phase difference that may occur during the resampling process. error) can be reduced. In addition, according to the embodiment of the present invention, the prediction accuracy can be increased by reducing the error in resampling according to the phase difference, and the encoding / decoding efficiency can be improved.

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

2 is a block diagram schematically illustrating a decoding apparatus according to an embodiment of the present invention.

3 is a diagram illustrating a resampling method for an inter-layer reference picture for compensating a difference between resampling phases between layers according to an embodiment of the present invention.

FIG. 4 is a flowchart schematically illustrating a method for performing interlayer prediction using a resampling method for compensating for a resampling phase difference between layers in a scalable video coding structure according to an embodiment of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described concretely with reference to drawings. In describing the embodiments of the present specification, when it is determined that a detailed description of a related well-known configuration or function may obscure the gist of the present specification, the description may be omitted.

When a component is referred to herein as being “connected” or “connected” to another component, it may mean that it is directly connected to or connected to that other component, or another component in between. It may also mean that an element exists. In addition, the description "includes" a specific configuration in this specification does not exclude a configuration other than the configuration, it means that additional configuration may be included in the scope of the technical spirit of the present invention or the present invention.

Terms such as first and second may be used to describe various configurations, but the configurations are not limited by the terms. The terms are used to distinguish one configuration from another. For example, without departing from the scope of the present invention, the first configuration may be referred to as the second configuration, and similarly, the second configuration may also be referred to as the first configuration.

In addition, the components shown in the embodiments of the present invention are independently shown to represent different characteristic functions, and do not mean that each component is made of separate hardware or one software component unit. In other words, each component is listed as a component for convenience of description, and at least two of the components may form one component, or one component may be divided into a plurality of components to perform a function. The integrated and separated embodiments of each component are also included in the scope of the present invention without departing from the spirit of the present invention.

In addition, some of the components may not be essential components for performing essential functions in the present invention, but may be optional components for improving performance. The present invention can be implemented including only the components essential for implementing the essentials of the present invention except for the components used for improving performance, and the structure including only the essential components except for the optional components used for improving performance. Also included in the scope of the present invention.

Encoding and decoding of video that supports multiple layers in a bitstream is called scalable coding. Since there is a strong correlation between the plurality of layers, the prediction may be performed by using this correlation to remove redundant elements of data and to improve the encoding performance of the image. Performing prediction of the current layer to be predicted by using information of another layer is referred to as inter-layer prediction or inter-layer prediction in the following.

At least one of the resolution, frame rate, and color format may be different from each other, and the up-sampling or downsampling of a layer may be performed to adjust the resolution when inter layer prediction is performed. Resampling such as down sampling may be performed.

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

The encoding apparatus 100 according to the present invention includes an encoder 100a for an upper layer and an encoder 100b for a lower layer.

The upper layer may be represented by a current layer or an enhancement layer and the lower layer may be represented by a reference layer or a base layer. The upper layer and the lower layer may have at least one of a resolution, a frame rate, and a color format. When a resolution change is necessary to perform inter-layer prediction, upsampling or downsampling of a layer may be performed.

The encoder 100a of the upper layer includes a splitter 110, a predictor 100, an intra prediction unit 121, an inter prediction unit 122, an inter layer prediction unit 123, and a transformer 130. , Quantization unit 140, reordering unit 150, entropy encoding unit 160, inverse quantization unit 170, inverse transform unit 180, filter unit 190 and memory 195, and MUX 197. can do.

The encoder 100b of the lower layer includes a splitter 111, a predictor 125, an intra prediction unit 126, an inter prediction unit 127, a transform unit 131, a quantizer 141, and a rearrangement. The unit 151 may include an entropy encoding unit 161, an inverse quantization unit 171, an inverse transform unit 181, a filter unit 191, and a memory 196.

The encoder may be implemented by the image encoding method described in the following embodiments of the present invention, but operations in some components may not be performed to reduce the complexity of the encoding apparatus or for fast real time encoding. For example, in performing the intra prediction in the prediction unit, some limited number of methods are used without selecting the optimal intra intra coding method using all intra prediction modes in order to perform encoding in real time. A method of selecting one intra prediction mode among them as a final intra prediction mode using the intra prediction mode of the image may be used. As another example, it is possible to limit the use of the type of prediction block used in performing intra prediction or inter prediction.

The unit of a block processed by the encoding apparatus may be a coding unit that performs encoding, a prediction unit that performs prediction, or a transformation unit that performs transformation. A coding unit may be represented by a term such as a coding unit (CU), a prediction unit is a prediction unit (PU), and a transformation unit is a transform unit (TU).

The splitters 110 and 111 divide a layer image into a combination of a plurality of coding blocks, prediction blocks, and transform blocks, and one of the coding blocks, prediction blocks, and transform blocks according to a predetermined criterion (for example, a cost function). You can split the layer by selecting the combination of. For example, to split a coding unit in a layer image, a recursive tree structure such as a quad tree structure may be used. Hereinafter, in the embodiment of the present invention, the meaning of the coding block may be used not only as a block for encoding but also as a block for decoding.

The prediction block may be a unit for performing prediction such as intra prediction or inter prediction. The block for performing intra prediction may be a block having a square shape such as 2N × 2N or N × N. Predictive block partitioning is performed by using 2NxN, Nx2N, or asymmetric Asymmetric Motion Partitioning (AMP), which splits a square or square type prediction block into the same form. There is a way. Depending on the shape of the prediction block, the transform unit 115 may change a method of performing the transform.

The prediction units 120 and 125 of the encoders 100a and 100b may include the intra prediction units 121 and 126 performing intra prediction and the inter prediction unit performing inter prediction. (122, 126). The predictor 120 of the higher layer encoder 100a further includes an inter-layer predictor 123 that performs prediction on the upper layer by using information of the lower layer.

The prediction units 120 and 125 may determine whether to use inter prediction or intra prediction on the prediction block. The processing unit in which the prediction is performed and the processing block in which the prediction method is determined may be different. For example, in performing intra prediction, a prediction mode is determined based on a prediction block, and a process of performing prediction may be performed based on a transform block. The residual value (residual block) between the generated prediction block and the original block may be input to the transformers 130 and 131. In addition, prediction mode information and motion vector information used for prediction may be encoded by the entropy encoder 130 together with the residual value and transmitted to the decoding apparatus.

When using the Pulse Coded Modulation (PCM) coding mode, the original block may be encoded as it is and transmitted to the decoder without performing prediction through the prediction units 120 and 125.

The intra prediction units 121 and 126 may generate an intra prediction block based on reference pixels present around the current block (the block to be predicted). In the intra prediction method, the intra prediction mode may include a directional prediction mode using reference pixel information according to a prediction direction and a non-directional mode using no directional information when performing prediction. The mode for predicting luma information and the mode for predicting color difference information may be different. In order to predict the color difference information, intra prediction mode information or predicted luma signal information may be used. If the reference pixel is not available, the prediction block may be generated by replacing the unavailable reference pixel with another pixel.

The prediction block may include a plurality of transform blocks. If the prediction block has the same size as the transform block when the intra prediction is performed, pixels present on the left side of the prediction block, pixels present on the upper left side, and top Intra-prediction of the prediction block may be performed based on the pixels present in the. However, when the prediction block is different from the size of the transform block when the intra prediction is included, and a plurality of transform blocks are included in the prediction block, the intra prediction is performed using a reference pixel determined based on the transform block. can do.

The intra prediction method may generate a prediction block after applying a mode dependent intra smoothing (MDIS) filter to a reference pixel according to the intra prediction mode. The type of MDIS filter applied to the reference pixel may be different. The MDIS filter is an additional filter applied to the predicted block in the picture by performing the intra prediction and may be used to reduce the residual present in the predicted block in the picture generated after performing the prediction with the reference pixel. In performing MDIS filtering, filtering on a reference pixel and some columns included in the predicted block in the screen may perform different filtering according to the direction of the intra prediction mode.

The inter prediction units 122 and 127 may perform prediction by referring to information of a block included in at least one of a previous picture or a subsequent picture of the current picture. The inter prediction units 122 and 127 may include a reference picture interpolator, a motion predictor, and a motion compensator.

The reference picture interpolation unit may receive reference picture information from the memories 195 and 196 and generate pixel information of an integer pixel or less in the reference picture. In the luma pixel, a DCT-based 8-tap interpolation filter having different filter coefficients may be used to generate pixel information of integer pixels or less in units of 1/4 pixels. In the case of a chrominance signal, a DCT-based interpolation filter having different filter coefficients may be used to generate pixel information of an integer pixel or less in units of 1/8 pixels.

The inter prediction units 122 and 127 may perform motion prediction based on the reference picture interpolated by the reference picture interpolator. As a method for calculating a motion vector, various methods such as a full search-based block matching algorithm (FBMA), a three step search (TSS), and a new three-step search algorithm (NTS) may be used. The motion vector may have a motion vector value of 1/2 or 1/4 pixel units based on the interpolated pixels. The inter prediction units 122 and 127 may perform prediction on the current block by applying one inter prediction method among various inter prediction methods.

For example, various methods, such as a skip method, a merge method, and an MVP (Motion Vector Prediction) method, may be used as the inter prediction method.

In inter prediction, motion information, that is, information such as an index of a reference picture, a motion vector, and a residual signal, is entropy coded and transmitted to a decoder. When the skip mode is applied, residuals may not be generated, transformed, quantized, or transmitted.

The interlayer prediction unit 123 performs interlayer prediction for predicting an upper layer by using information of a lower layer. The inter-layer prediction unit 123 uses inter-layer texture prediction and inter-layer inter prediction by using textures of lower layers, intra prediction mode information, motion information, and syntax information. ), Inter-layer syntax prediction, and the like.

Inter-layer texture prediction means using the texture of the reference block in the lower layer as a prediction sample of the current block of the upper layer. In this case, the texture of the reference block may be scaled by upsampling.

Inter-layer texture prediction includes the intra BL and upsampled lower layers, which upsample the reconstructed values of the reference blocks in the lower layers and encode the residuals with the current blocks using the upsampled reference blocks as predictions for the current block. There may be a reference index method that stores the in memory and uses the stored lower layer as a reference index.

Intra-prediction of the upper layer may be performed using intra-prediction mode information of the lower layer. In this case, the intra-prediction mode of the lower layer may be referred to as a BL intra mode.

Inter-layer motion prediction is also called inter-layer inter prediction, and according to inter-layer motion prediction, prediction of a current block of an upper layer may be performed using motion information of a lower layer. The motion information may include a motion vector and a reference picture index.

The inter-layer prediction unit 123 may also perform inter-layer syntax prediction for predicting or generating a texture of the current block by using syntax information of the lower layer. In this case, the syntax information of the lower layer used for the prediction of the current block may be information about an intra prediction mode, motion information, and the like.

As another example of inter-layer prediction, according to the difference prediction between layers, the prediction of the current block is performed by using the difference image generated as a difference value between the reconstructed image of the upper layer and the upsampled reconstructed image of the lower layer. Can be.

As an example of the inter-layer prediction, the inter-layer texture prediction, the inter-layer motion prediction, the inter-layer syntax prediction, and the inter-layer differential prediction have been described, but the inter-layer prediction applicable to the present invention is not limited thereto.

A residual block including residual information, which is a difference between the predicted block generated by the predictors 120 and 125 and the reconstructed block of the predicted block, is generated, and the residual block is input to the transformers 130 and 131.

The transform units 130 and 131 may transform the residual block using a transform method such as a discrete cosine transform (DCT) or a discrete sine transform (DST). Whether DCT or DST is applied to transform the residual block may be determined based on intra prediction mode information of the prediction block used to generate the residual block and size information of the prediction block. That is, the transformers 130 and 131 may apply the transformation method differently according to the size of the prediction block and the prediction method.

The quantizers 140 and 141 may quantize the values transformed by the transformers 130 and 131 into the frequency domain. The quantization coefficient may change depending on the block or the importance of the image. The values calculated by the quantizers 140 and 141 may be provided to the dequantizers 170 and 17 and the reordering units 150 and 151.

The reordering units 150 and 151 may reorder coefficient values with respect to the quantized residual value. The reordering units 150 and 151 may change the two-dimensional block shape coefficients into a one-dimensional vector form through a coefficient scanning method. For example, the realignment units 150 and 151 may scan DC coefficients to coefficients in the high frequency region by using a Zig-Zag scan method and change them into one-dimensional vectors. Depending on the size of the transform block and the intra prediction mode, a vertical scan method for scanning two-dimensional block shape coefficients in a column direction, not a zig-zag scan method, and a horizontal scan method for scanning two-dimensional block shape factors in a row direction Can be used. That is, according to the size of the transform block and the intra prediction mode, it is possible to determine which scan method among zigzag-scan, vertical scan and horizontal scan is used.

The entropy encoders 160 and 161 may perform entropy encoding based on the values calculated by the reordering units 150 and 151. Entropy encoding may use various encoding methods such as, for example, Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC).

The entropy encoders 160 and 161 transmit residual value coefficient information, block type information, prediction mode information, partition unit information, prediction block information, and the like of the coding blocks from the reordering units 150 and 151 and the predictors 120 and 125. Entropy encoding may be performed based on a predetermined encoding method by receiving various information such as unit information, motion vector information, reference frame information, interpolation information of a block, and filtering information. In addition, the entropy encoder 160 or 161 may entropy-encode coefficient values of coding units input from the reordering unit 150 or 151.

The entropy encoders 160 and 161 may encode the intra prediction mode information of the current block by performing binarization on the intra prediction mode information. The entropy encoder 160 or 161 may include a codeword mapping unit for performing such a binarization operation, and may perform different binarization according to the size of a prediction block for performing intra prediction. In the codeword mapping unit, the codeword mapping table may be adaptively generated or stored in advance through a binarization operation. As another embodiment, the entropy encoders 160 and 161 may express prediction mode information in the current screen using a codenum mapping unit for performing codenum mapping and a codeword mapping unit for performing codeword mapping. In the codenum mapping unit and the codeword mapping unit, a codenum mapping table and a codeword mapping table may be generated or stored.

The inverse quantizers 170 and 171 and the inverse transformers 180 and 181 inverse quantize the quantized values in the quantizers 140 and 141 and inversely transform the converted values in the transformers 130 and 131. The residual values generated by the inverse quantizers 170 and 171 and the inverse transformers 180 and 181 may be predicted by the motion estimator, the motion compensator, and the intra prediction unit included in the predictors 120 and 125. It may be combined with the prediction block to generate a reconstructed block.

The filters 190 and 191 may include at least one of a deblocking filter, an offset corrector, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion caused by boundaries between blocks in the reconstructed picture. In order to determine whether to perform deblocking, it may be determined whether to apply a deblocking filter to the current block based on the pixels included in several columns or rows included in the block. When the deblocking filter is applied to the block, a strong filter or a weak filter may be applied according to the required deblocking filtering strength. In addition, in applying the deblocking filter, horizontal filtering and vertical filtering may be performed in parallel when vertical filtering and horizontal filtering are performed.

The offset correction unit may correct the offset with respect to the original image on a pixel-by-pixel basis for the deblocking image. In order to perform offset correction for a specific picture, the pixels included in the image are divided into a predetermined number of areas, and then, an area to be offset is determined, an offset is applied to the corresponding area, or offset considering the edge information of each pixel. You can use this method.

The adaptive loop filter (ALF) may perform filtering based on a value obtained by comparing the filtered reconstructed image with the original image. After dividing the pixels included in the image into at least one group, one filter to be applied to the group may be determined and filtering may be performed for each group.

The filter units 190 and 191 may apply only the deblocking filter, only the deblocking filter and the ALF, or may apply only the deblocking filter and the offset correction unit without applying all of the deblocking filter, the ALF, and the offset correction unit.

The memories 195 and 196 may store reconstructed blocks or pictures calculated by the filters 190 and 191, and the stored reconstructed blocks or pictures may be provided to the predictors 120 and 125 when performing inter prediction. have.

The information output from the entropy encoder 100b of the lower layer and the information output from the entropy encoder 100a of the upper layer may be multiplexed by the MUX 197 and output as a bitstream.

The MUX 197 may be included in the encoder 100b of the lower layer or may be implemented as an independent device or module separate from the encoder 100.

2 is a block diagram schematically illustrating a decoding apparatus according to an embodiment of the present invention.

As shown in FIG. 2, the decoding apparatus 200 includes a decoder 200a of an upper layer and a decoder 200b of a lower layer.

The decoder 200a of the upper layer includes an entropy decoder 210, a reordering unit 220, an inverse quantization unit 230, an inverse transform unit 240, a prediction unit 250, a filter unit 260, and a memory 270. ) May be included.

The lower layer decoding unit 200b includes an entropy decoding unit 211, a reordering unit 221, an inverse quantization unit 231, an inverse transform unit 241, a prediction unit 251, a filter unit 261, and a memory 271. ) May be included.

When a bitstream including a plurality of layers is transmitted from the encoding apparatus, the DEMUX 280 may demultiplex information for each layer and transmit the information to the decoders 200a and 200b for each layer. The input bitstream may be decoded in a procedure opposite to that of the encoding apparatus.

The entropy decoders 210 and 211 may perform entropy decoding in a procedure opposite to that of the entropy encoder in the encoding apparatus. Information for generating a prediction block among the information decoded by the entropy decoders 210 and 211 is provided to the predictors 250 and 251, and the residual value of the entropy decoding performed by the entropy decoder is the reordering unit 220 or 221. Can be entered.

Like the entropy encoders 160 and 161, the entropy decoders 210 and 211 may perform inverse transform using at least one of CABAC and CAVLC.

The entropy decoders 210 and 211 may decode information related to intra prediction and inter prediction performed by the encoding apparatus. The entropy decoding unit may include a codeword mapping unit and include a codeword mapping table for generating a received codeword as an intra prediction mode number. The codeword mapping table may be stored in advance or generated adaptively. When using the codenum mapping table, a codenum mapping unit for performing codenum mapping may be additionally provided.

The reordering units 220 and 221 may reorder the bitstreams entropy decoded by the entropy decoding units 210 and 211 based on a method of rearranging the bitstreams by the encoder. Coefficients expressed in the form of a one-dimensional vector can be rearranged by restoring the coefficients in a two-dimensional block form. The reordering unit may be realigned by receiving information related to coefficient scanning performed by the encoder and performing reverse scanning based on the scanning order performed by the encoder.

The inverse quantization units 230 and 231 may perform inverse quantization based on quantization parameters provided by the encoding apparatus and coefficient values of the rearranged block.

The inverse transformers 240 and 241 may perform inverse DCT and inverse DST on the DCT and DST performed by the transformers 130 and 131 with respect to the quantization result performed by the encoding apparatus. The inverse transform may be performed based on a transmission unit determined by the encoding apparatus. The DCT and DST may be selectively performed by the transform unit of the encoding apparatus according to a plurality of pieces of information, such as a prediction method, a size and a prediction direction of the current block, and the inverse transform unit 225 of the decoding apparatus may be performed by the transform unit of the encoding apparatus. Inverse transformation may be performed based on the transformation information. When the transform is performed, the transform may be performed based on the coding block rather than the transform block.

The prediction units 250 and 251 may generate the prediction blocks based on the prediction block generation related information provided by the entropy decoding units 210 and 211 and previously decoded blocks or picture information provided by the memories 270 and 271. .

The predictors 250 and 251 may include a prediction unit determiner, an inter prediction unit, and an intra prediction unit.

The prediction unit discriminator receives various information such as prediction unit information input from the entropy decoder, prediction mode information of the intra prediction method, and motion prediction related information of the inter prediction method, and distinguishes the prediction block from the current coding block. It is possible to determine whether to perform this inter prediction or intra prediction.

The inter prediction unit uses information required for inter prediction of the current prediction block provided by the encoding apparatus to the current prediction block based on information included in at least one of a previous picture or a subsequent picture of the current picture including the current prediction block. Inter prediction can be performed. Whether the motion prediction method of the prediction block included in the coding block is skip mode, merge mode, or AMVP mode to perform inter prediction. Can be determined.

The intra prediction unit may generate a prediction block based on pixel information in the current picture. When the prediction block is a prediction block that performs intra prediction, intra prediction may be performed based on intra prediction mode information of the prediction block provided by the encoding apparatus. The intra prediction unit is an MDIS filter that performs filtering on the reference pixels of the current block, a reference pixel interpolator which generates reference pixels in pixel units smaller than an integer value by interpolating the reference pixels, and filters when the prediction mode of the current block is DC mode. It may include a DC filter for generating a prediction block through.

The predictor 250 of the upper layer decoder 200a may further include an inter-layer predictor that performs inter-layer prediction for predicting an upper layer by using information of the lower layer.

The inter-layer prediction unit uses inter-layer texture prediction, inter-layer inter prediction, and inter-layer prediction by using textures of lower layers, intra prediction mode information, motion information, and syntax information. Inter-layer syntax prediction may be performed.

According to the inter-layer texture prediction, prediction may be performed using the texture of the reference block in the lower layer as a prediction value of the current block of the upper layer. The texture of the reference block can be scaled by upsampling.

Inter-layer texture prediction includes the intra BL and upsampled base layers that upsample the reconstructed values of the reference blocks in the lower layers and encode residuals with the current blocks using the upsampled reference blocks as predictions for the current block. Is stored in memory and uses the stored base layer as a reference index.

Intra-prediction of the upper layer may be performed using intra-prediction mode information of the lower layer, and in this case, the intra-prediction mode of the lower layer may be expressed as a BL intra mode.

According to inter-layer motion prediction, prediction of a current block of an upper layer may be performed using motion information of a lower layer.

The inter-layer prediction unit may also perform inter-layer syntax prediction for predicting or generating a texture of the current block using syntax information of the lower layer. In this case, the syntax information of the lower layer used for the prediction of the current block may be information about an intra prediction mode, motion information, and the like.

In addition, the inter-layer prediction unit may perform differential prediction between layers predicting the current block by using the difference image generated as a difference value between the reconstructed image of the upper layer and the resampled image of the lower layer.

As an example of the inter-layer prediction, the inter-layer texture prediction, the inter-layer motion prediction, the inter-layer syntax prediction, and the inter-layer differential prediction have been described, but the inter-layer prediction applicable to the present invention is not limited thereto.

The reconstructed block or picture may be provided to the filter units 260 and 261. The filter units 260 and 261 may include a deblocking filter, an offset corrector, and an ALF.

Information about whether a deblocking filter is applied to the corresponding block or picture and when the deblocking filter is applied to the block or picture may be provided from the encoding apparatus as to whether a strong filter or a weak filter is applied. The deblocking filter of the decoding apparatus may receive the deblocking filter related information provided by the encoding apparatus and perform the deblocking filtering on the corresponding block in the decoding apparatus.

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

The adaptive loop filter (ALF) may perform filtering based on a value obtained by comparing the restored image with the original image after performing the filtering. The ALF may be applied to the coding unit based on the ALF application information, the ALF coefficient information, and the like provided from the encoding apparatus. Such ALF information may be provided included in a specific parameter set.

The memories 270 and 271 may store the reconstructed picture or block to be used as the reference picture or the reference block, and output the reconstructed picture.

The encoding apparatus and the decoding apparatus may encode three or more layers instead of two layers. In this case, a plurality of encoders for a higher layer and a decoder for a higher layer may be provided in correspondence to the number of upper layers. Can be.

As described above, in the scalable high efficiency video codec (SHVC) technology that supports the multi-layer structure, since there is a strong association between layers, prediction using this association can remove redundant elements of data and encode an image. It can improve performance.

Therefore, when predicting a picture (image) of a current layer (enhanced layer) to be encoded / decoded, not only inter prediction or intra prediction using information of the current layer, but also inter layer prediction using information of another layer may be performed. .

When performing inter-layer prediction, the current layer predicts the current layer by using a decoded picture of a reference layer (or reference layer) used for inter-layer prediction as a reference picture. Samples can be generated.

In this case, since the current layer and the reference layer may have at least one of a resolution, a frame rate, a color format, and a viewpoint (ie, due to scalability differences between layers), the decoded reference layer picture may be matched to the scalability of the current layer. Resampling may be performed and then used as a reference picture for inter-layer prediction of the current layer. Resampling means up-sampling or downsampling samples of a reference layer picture according to a picture size of a current layer.

In the present invention, the current layer refers to a layer on which current encoding or decoding is performed, and may be an enhancement layer or an upper layer. The reference layer refers to a layer referenced by the current layer for inter-layer prediction and may be a base layer or a lower layer. The picture of the reference layer (ie, the reference picture) used for inter-layer prediction of the current layer may be referred to as an inter-layer reference picture.

In general, the SHVC standard defines a resampling filter (eg, an upsampling filter) used for resampling in a decoding process, but a resampling filter (eg, a downsampling filter) used in a resampling process in a coding process. Not. Thus, different (arbitrary) resampling filters may be used in the encoding of layers, and resampling filters defined in the standard are used in the decoding of layers. In this case, since a different resampling filter may be used during encoding and decoding, there is a case where the phase between the sample of the reference layer (base layer) picture and the sample of the current layer (enhancement layer) picture does not match during decoding. May occur.

In other words, the resampling filter (upsampling filter) of the decoding process defined in the current SHVC standard is designed on the assumption that a phase difference does not occur with the resampling filter (downsampling filter) of the coding process. If an undefined resampling filter is used, a phase difference occurs between the current layer and the reference layer when resampling is performed during decoding.

In order to solve the above problems, the present invention provides a method for compensating the phase difference between the current layer and the reference layer that may occur during the resampling process of the inter-layer reference picture.

3 is a diagram illustrating a resampling method for an inter-layer reference picture for compensating a difference between resampling phases between layers according to an embodiment of the present invention.

Referring to FIG. 3, when interlayer prediction is performed on a current layer, the current block 315 of the current layer picture 310 to be predicted is the current block 315 using the interlayer reference picture 320. The predictive sample values of may be obtained.

In this case, the interlayer reference picture 320 may be resampled according to the size of the current layer picture 310. Hereinafter, a resampling process for the interlayer reference picture 320 according to an embodiment of the present invention will be described in detail.

First, a sample position (xRef, yRef) of the reference layer picture 320 corresponding to the sample position (xP, yP) of the current layer picture 310 to be predicted may be derived. In this case, the reference layer sample positions (xRef, yRef) may be derived as sample positions with 1/16 accuracy.

Equation 1 shows that the reference layer sample positions (xRef, yRef) are derived to a 1/16 accuracy reference sample position.

Equation 1

Here, (xRef16, yRef16) means a reference layer sample position in units of 1/16 samples corresponding to the sample positions (xP, yP) of the current layer picture 310.

The phase values (xPhase, yPhase) of the resampling filter used in the resampling process may be derived using Equation 2 using reference layer sample positions (xRef16, yRef16) in units of 1/16 samples.

Equation 2

According to an embodiment of the present invention, when inducing reference layer sample positions (xRef16 and yRef16) in units of 1/16 samples, phase difference between layers may be compensated. For example, the phase difference between layers may be compensated using phase offset information for compensating the phase difference between layers.

Reference layer sample positions xRef16 and yRef16 in units of 1/16 samples for deriving the reference layer sample positions xRef and yRef with 1/16 accuracy may be calculated as shown in Equations 3 and 4 below.

Equation 3 shows an equation for deriving reference layer sample positions (xRef16 and yRef16) in units of 1/16 samples for a luma component. In this case, the reference layer sample positions (xRef16 and yRef16) of the 1/16 sample unit for the luminance component may be derived based on phase shift information for compensating the phase difference between the layers for the luminance component.

Equation 3

Equation 4 shows an equation for deriving reference layer sample positions (xRef16 and yRef16) in units of 1/16 samples for a chroma component. In this case, reference layer sample positions xRef16 and yRef16 in units of 1/16 samples with respect to the color difference component may be derived based on phase shift information for compensating the phase difference between layers with respect to the color difference component.

Equation 4

In equations (3) and (4), (xP, yP) represents a sample position of the current layer picture 310, and indicates the position of the sample at the top left in the current block 315 of the current layer picture 310. it means.

shiftX = 16, shiftY = 16.

luma_phase_offseX, luma_phase_offseY, chorma_phase_offseX, and chroma_phase_offseY are variable values for compensating for phase differences between layers during resampling. For example, luma_phase_offseX and luma_phase_offseY may be variable values for compensating for phase differences between layers in the case of luminance components, and chorma_phase_offseX and chroma_phase_offseY may be variable values for compensating for phase differences between layers in the case of chrominance components. In this case, the variable values luma_phase_offseX, luma_phase_offseY, chorma_phase_offseX, and chroma_phase_offseY for compensating for the phase difference between the current layer and the reference layer may be determined in picture units or slice units, and are signaled through the picture parameter set, slice header, etc. for each determined unit. Can be.

In Equations 3 and 4, scaleFactorX and scaleFactorY may be defined as in Equation 5.

Equation 5

In Equations 3 and 4, addX and addY may be defined as in Equation 6.

Equation 6

In Equations 5 and 6, scaledW may be defined as 1.5 * PicWRL or 2.0 * PicWRL, and scaledH may be defined as 1.5 * PicHRL or 2.0 * PicHRL. PicWRL can be defined as the width of the reference layer, PicHRL can be defined as the height of the reference layer.

As described above, in order to compensate for the phase difference between layers when deriving a reference layer sample position, as expressed in Equations 3 to 6, addX, addY, phaseX, phaseY, luma_phase_offsetX, luma_phase_offsetY, chroma_phase_offsetX, Phase shift information such as chroma_phase_offsetY may be used.

Here, when inducing a reference layer sample position of a 1/16 sample unit with respect to the chrominance component, phase shift information on the chrominance component may be used, or phase shift information on the luminance component may be used. For example, phase shift information for a chrominance component, such as addX, addY, phaseX, phaseY, chroma_phase_offsetX, chroma_phase_offsetY, is 1/2 of each of the phase shift information addX, addY, phaseX, phaseY, luma_phase_offsetX, luma_phase_offsetY values for the luminance component. Can be induced.

Next, as described above, the current layer picture 310 is based on the reference layer sample positions (xRef, yRef) and phase values (xPhase, yPhase) derived using 1/16 accuracy sample positions (xRef16, yRef16). Interpolation may be performed on the sample positions (xP, yP) of

In this case, an 8-tap filter may be used as the luminance component in the interpolation process, and a 4-tap filter may be used as the chrominance component. Different filter coefficients may be used for each phase value.

Table 1 shows an example of 8-tap filters (filter coefficients) for luminance components according to 1/16 phases used in the resampling process, and Table 2 shows 1/16 phases used in the resampling process. An example of a 4-tap filter (filter coefficient) for the chrominance component is shown.

Table 1

TABLE 2

As described above, based on the reference layer sample positions (xRef, yRef) and phase values (xPhase, yPhase), the sample positions of the current layer picture 310 using filter coefficients as shown in Tables 1 and 2 above. By performing interpolation on (xP, yP), resampled sample values (resampled interlayer reference picture) can be obtained. The obtained resampled interlayer reference picture may be used to perform interlayer prediction (motion compensation) on the current block 315 of the current layer picture 310, and as a result, the current block 315 may be performed. Prediction sample values may be obtained.

As described above, in order to compensate for the phase difference between layers in the resampling process for the interlayer reference picture, according to an embodiment of the present invention, phase offset information for compensating for phase difference between layers may be provided in units of pictures, Signaling was determined in units of slices, and the reference layer sample position was derived based on the signaled phase shift information.

In this case, the phase shift information on the luminance component and the phase shift information on the color difference component may be signaled, respectively, or the phase shift information on the color difference component may be derived based on the phase shift information on the luminance component.

Hereinafter, a method of deriving phase shift information for compensating for phase difference between layers of color difference components according to an embodiment of the present invention will be described.

In the method for deriving the phase shift information for the chrominance component according to an embodiment of the present invention, 1) using the phase shift information for the luminance component as phase shift information for the chrominance component, 2) the phase for the luminance component 3) a method of deriving phase shift information for a color difference component based on the shift information; and 3) signaling whether there is a difference between phase shift information for a luminance component and phase shift information for a color difference component. There is a way to derive.

1) Method of using phase shift information on luminance component as phase shift information on color difference component

The phase shift information for the color difference component can be used as the same value as the phase shift information for the luminance component. For example, when deriving a reference layer sample position (xRef16, yRef16) in units of 1/16 samples corresponding to the current sample position (xP, yP) of the current layer picture, both the reference component position for the luminance component and the chrominance component It can be calculated using Equation 3.

2) A method of deriving the phase shift information on the chrominance component based on the phase shift information on the luminance component

The phase shift information for the color difference component may be derived from the phase shift information for the luminance component using a predetermined condition. For example, the phase shift for the color difference component may be derived using arithmetic conditions such as dividing or multiplying the phase shift for the luminance component by a specific value (for example, 1/2, 1/4, etc.).

3) a method of deriving phase shift information for the chrominance component by signaling whether there is a difference between phase shift information for the luminance component and phase shift information for the chrominance component

Whether the phase shift for the chrominance component is the same as the phase shift for the luminance component may be signaled through a picture parameter set, a slice header, and the like.

If the phase shift for the chrominance component and the luminance component are the same, the phase shift for the luminance component can be used as the phase shift for the chrominance component.

Otherwise, if the phase shift for the chrominance component and the luminance component is different, the phase shift for the chrominance component may be signaled, or the phase shift difference between the luminance component and the chrominance component may be signaled.

Table 3 shows an example of syntax for determining phase shift information for compensating for phase difference between layers in picture units and signaling the same through a picture parameter set.

TABLE 3

Referring to Table 3, luma_phase_offsetX represents the x-axis component phase value of the luminance component luma. luma_phase_offsetY represents a y-axis component phase value of the luminance component luma.

isSameLumaPhaseX indicates whether the x-axis component phase value of the chrominance component chroma is equal to the x-axis component phase value of the luminance component luma. An isSameLumaPhaseX value of 1 indicates that the x-axis component phase value of the chrominance component (chroma) is equal to the x-axis component phase value of the luminance component (luma). It is different from the x-axis component phase value of the luminance component luma.

isSameLumaPhaseY indicates whether or not the y-axis component phase value of the chrominance component chroma is equal to the y-axis component phase value of the luminance component luma. isSameLumaPhaseY value of 1 indicates that the y-axis component phase value of the chrominance component (chroma) is equal to y-axis component phase value of the luminance component (luma). isSameLumaPhaseY value of 0 indicates that the y-axis component phase value of the chrominance component (chroma) It is different from the y-axis component phase value of the luminance component luma.

chroma_phase_offsetX represents the x-axis component phase value of the chroma component (chroma). chroma _phase_offsetY represents a y-axis component phase value of a chrominance component (chroma).

Table 4 shows another example of syntax for determining phase shift information for compensating for phase difference between layers in picture units and signaling the same through a picture parameter set.

Table 4

Referring to Table 4, luma_phase_offsetX represents the x-axis component phase value of the luminance component luma. luma_phase_offsetY represents a y-axis component phase value of the luminance component luma.

isSameLumaPhaseX indicates whether the x-axis component phase value of the chrominance component chroma is equal to the x-axis component phase value of the luminance component luma. An isSameLumaPhaseX value of 1 indicates that the x-axis component phase value of the chrominance component (chroma) is equal to the x-axis component phase value of the luminance component (luma); an isSameLumaPhaseX value of 0 indicates that the x-axis component phase value of the chrominance component It is different from the x-axis component phase value of the luminance component luma.

isSameLumaPhaseY indicates whether or not the y-axis component phase value of the chrominance component chroma is equal to the y-axis component phase value of the luminance component luma. isSameLumaPhaseY value of 1 indicates that the y-axis component phase value of the chrominance component (chroma) is equal to y-axis component phase value of the luminance component (luma). isSameLumaPhaseY value of 0 indicates that the y-axis component phase value of the chrominance component (chroma) It is different from the y-axis component phase value of the luminance component luma.

delta_phase_offsetX represents luma_phase_offsetX-chroma_phase_offsetX value. delta_phase_offsetY represents a luma_phase_offsetY-chorma_phase_offsetY value.

FIG. 4 is a flowchart schematically illustrating a method for performing interlayer prediction using a resampling method for compensating for a resampling phase difference between layers in a scalable video coding structure according to an embodiment of the present invention.

The method of FIG. 4 may be performed by the encoder of FIG. 1 and the decoder of FIG. 2, and more specifically, by the predictor of the encoder of FIG. 1 and the predictor of the decoder of FIG. 2. In addition, in FIG. 4, for convenience of description, the decoding apparatus will be described as performing the interlayer prediction method according to the embodiment of the present invention.

The scalable video coding structure may include a plurality of layers. For example, it may include a current layer on which current decoding is performed and a reference layer used for inter-layer prediction of the current layer. The current layer may be an enhancement layer, and the reference layer may be a base layer or a lower layer that provides lower scalability than the current layer.

Referring to FIG. 4, the decoding apparatus derives a reference layer sample position from a reference layer picture used for interlayer prediction of a current layer picture (S400).

The reference layer sample position is a sample position in the reference layer picture corresponding to the top-left sample position of the current block in the current layer picture, and may be a sample position used when resampling the reference layer.

As described above, since the phase difference between layers may occur during the resampling process, the phase difference between the layers should be compensated for during the resampling process.

Accordingly, the reference layer sample position may be derived based on phase offset information for compensating for phase differences between layers. The phase shift information may include at least one of phase shift information on the luminance component and phase shift information on the color difference component.

For example, the decoding apparatus may induce a reference layer sample position in units of 1/16 samples, and may match phases between layers by compensating phase shifts for reference layer sample positions in units of 1/16 samples. As described above, the decoding apparatus may derive the reference layer sample position in units of 1/16 samples whose phase shift is compensated by using Equations 3 to 6.

In this case, the decoding apparatus may induce a reference layer sample position based on phase shift information on the luminance component or the chrominance component according to the color component of the reference layer picture. For example, when the color component of the reference layer picture is a luminance component, the decoding apparatus may derive a reference layer sample position of a 1/16 sample unit for the luminance component based on phase shift information on the luminance component. Can be obtained as shown in 3. When the color component of the reference layer picture is a chrominance component, the decoding apparatus may derive a reference layer sample position in units of 1/16 samples for the chrominance component based on phase shift information on the chrominance component. It can be obtained as

Phase shift information for compensating the phase difference between layers may be signaled from the encoding apparatus. The encoding apparatus may determine the phase shift in a picture unit, a slice unit, and the like, and signal information about the phase shift to the decoding apparatus through the picture parameter set, the slice header, and the like for each determined unit. When signaling the phase shift information, the encoding apparatus may signal phase shift information for the luminance component and phase shift information for the color difference component, respectively, and phase shift information for the color difference component based on the phase shift information for the luminance component. Information may be signaled that may lead to.

As described above, the decoding apparatus may obtain phase shift information for the luminance component and phase shift information for the chrominance component based on the phase shift information signaled by the encoding apparatus.

For example, the decoding apparatus may use the phase shift value for the luminance component as the phase shift value for the color difference component.

Alternatively, the decoding apparatus may derive the phase shift value for the color difference component based on the phase shift value for the luminance component. For example, certain conditions can be used to derive from the phase shift value for the luminance component. The predetermined condition may be an operation condition such as dividing or multiplying a phase shift value for the luminance component by a specific value (for example, 1/2, 1/4, etc.).

Alternatively, the decoding apparatus may obtain variation information on the luminance component and the chrominance component based on flag information indicating whether the phase shift value for the luminance component and the phase shift value for the chrominance component are the same. For example, if the flag information indicates that the phase shift values for the chrominance component and the luminance component are the same (for example, when the flag value is 1), the decoding apparatus sets the phase shift value for the luminance component to the phase for the chrominance component. Can be used as a mutation value. If the flag information indicates that the phase shift values for the chrominance component and the luminance component are not the same (for example, when the flag value is 0), the decoding apparatus sets the phase shift value for the chrominance component to the picture parameter set and slice. It may be obtained from a header or the like, or based on a difference between the phase shift value for the color difference component and the phase shift value for the luminance component. For example, the encoding apparatus may signal the syntax as in Table 3 or Table 4, and the decoding apparatus may acquire the variation information on the luminance component and the chrominance component through the syntax.

The decoding apparatus resamples the reference layer picture based on the reference layer sample position (S410).

More specifically, the decoding apparatus may derive the phase value of the resampling filter used in the resampling process. The phase value may be derived using a reference layer sample position in units of 1/16 samples. For example, the phase value may be calculated as in Equation 2 above.

Next, the decoding apparatus may interpolate the upper left sample position of the current block of the current layer picture based on the derived reference layer sample position and phase value.

In this case, in the case of the luminance component, the decoding apparatus may interpolate the luminance component sample using, for example, an 8-tap interpolation filter as shown in Table 1 above. In the case of a chrominance component, the decoding apparatus may perform interpolation on a chrominance component sample using, for example, a 4-tap interpolation filter as shown in Table 2 above.

In other words, the decoding apparatus may obtain interpolated sample values by performing interpolation on the upper left sample of the current block using different interpolation filter coefficients according to the reference layer sample position and phase value.

Next, the decoding apparatus may obtain resampled sample values (resampled interlayer reference picture) for the reference layer picture from the interpolated sample values.

The decoding apparatus may perform interlayer prediction on the current block of the current layer picture based on the resampled sample values (resampled interlayer reference picture), and as a result, may generate prediction samples of the current block (S420). .

The decoding apparatus may reconstruct the current block based on the prediction samples of the current block generated through the inter-layer prediction and the residual samples of the current block.

Meanwhile, in the encoding process, the residual samples of the current block may be derived based on the prediction samples of the current blocks generated through the above-described steps S400 to S420, and after transform / quantization is performed on the residual samples of the current block. The result can be entropy encoded.

When the inter-layer prediction is performed using the resampling method according to the embodiment of the present invention as described above, the phase difference that occurs during the resampling process may be compensated by inducing the phase shift so as to compensate the phase difference that may occur during the resampling process It is possible to reduce the error (error). In addition, according to the embodiment of the present invention, the prediction accuracy can be increased by reducing the error in resampling according to the phase difference, and the encoding / decoding efficiency can be improved.

The method according to the present invention described above may be stored in a computer-readable recording medium that is produced as a program for execution on a computer, and examples of the computer-readable recording medium include ROM, RAM, CD-ROM, magnetic tape , Floppy disks, optical data storage devices, and the like, and also include those implemented in the form of carrier waves (eg, transmission over the Internet).

The computer readable recording medium can be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. In addition, functional programs, codes, and code segments for implementing the method can be easily inferred by programmers in the art to which the present invention belongs.

In the above embodiments, 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 certain steps may occur in a different order or at the same time than other steps described above. Can be. Also, one of ordinary skill in the art appreciates that the steps shown in the flowcharts are not exclusive, that other steps may be included, or that one or more steps in the flowcharts may be deleted without affecting the scope of the present invention. I can understand.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims (20)

In the image decoding method that supports a plurality of layers, Deriving a reference layer sample position from a reference layer picture used for inter-layer prediction of the current layer picture; Resampling for the reference layer picture based on the reference layer sample position; And Generating prediction samples of the current block by performing interlayer prediction on a current block of the current layer picture based on the resampled reference layer picture, Deriving the reference layer sample position, Derive a sample position in the reference layer corresponding to a top-left sample position of the current block based on information on a phase offset to compensate for a phase difference between layers, And the information about the phase shift includes at least one of a phase shift for a luma component and a phase shift for a chroma component. The method of claim 1, Deriving the reference layer sample position, Derive the reference layer sample position in units of 1/16 samples, And inducing the reference layer sample position by the 1/16 sample unit, compensating for the phase difference between the layers by using the information about the phase shift. The method of claim 1, The information about the phase shift is signaled through a picture parameter set or a slice header. The method of claim 1, And the phase shift for the chrominance component is derived based on the phase shift for the luminance component. The method of claim 4, wherein And the phase shift for the chrominance component is derived to the same value as the phase shift for the luminance component. The method of claim 4, wherein And the phase shift with respect to the chrominance component is derived as a half value of the phase shift with respect to the luminance component. The method of claim 1, Obtaining information indicating whether a phase shift for the luminance component and a phase shift for the chrominance component are the same; If the phase shift for the luminance component and the phase shift for the chrominance component are indicated to be the same, the phase shift for the chrominance component uses the phase shift for the luminance component, If the phase shift for the chrominance component and the phase shift for the chrominance component are indicated to be not equal, the phase shift for the chrominance component is obtained through a picture parameter set or slice header, or for the chrominance component And a phase shift and a phase shift for the luminance component. The method of claim 1, Resampling the reference layer picture may include: Derive a phase value used in the resampling process, And interpolating the top-left sample position of the current block based on the reference layer sample position and the phase value. The method of claim 8, Resampling the reference layer picture may include: And performing an interpolation using an 8-tap interpolation filter on the top-left luminance component sample position of the current block based on the reference layer sample position and the phase value. The method of claim 8, Resampling the reference layer picture may include: And performing interpolation using a 4-tap interpolation filter on the top-left color difference component sample position of the current block based on the reference layer sample position and the phase value. In an image decoding apparatus supporting a plurality of layers, Derive the reference layer sample position from the reference layer picture used for inter-layer prediction of the current layer picture, Resample the reference layer picture based on the reference layer sample position, A predictor configured to generate predictive samples of the current block by performing interlayer prediction on the current block of the current layer picture based on the resampled reference layer picture, The prediction unit, Derive the reference layer sample position corresponding to the top-left sample position of the current block based on information about a phase offset to compensate for the phase difference between layers, And the information on the phase shift includes at least one of a phase shift for a luma component and a phase shift for a chroma component. The method of claim 11, The prediction unit, Derive the reference layer sample position in units of 1/16 samples, And inducing the reference layer sample position in units of 1/16 samples, compensating for the phase difference between the layers by using the information about the phase shift. The method of claim 11, And the information on the phase shift is signaled through a picture parameter set or a slice header. The method of claim 11, The prediction unit, And inducing a phase shift with respect to the color difference component based on the phase shift with respect to the luminance component. The method of claim 14, The prediction unit, And inducing a phase shift with respect to the chrominance component to a value equal to a phase shift with respect to the luminance component. The method of claim 14, The prediction unit, And inducing a phase shift with respect to the chrominance component to a half value of the phase shift with respect to the luminance component. The method of claim 11, The prediction unit, Obtaining information indicating whether a phase shift with respect to the luminance component and a phase shift with respect to the color difference component are the same; If the phase shift for the luminance component and the phase shift for the chrominance component are indicated to be the same, the phase shift for the luminance component is derived as a phase shift for the chrominance component, If it is indicated that the phase shift for the luminance component and the phase shift for the chrominance component are not equal, obtain a phase shift for the chrominance component through a picture parameter set or slice header, or phase for the chrominance component And obtaining a phase shift for the chrominance component based on a difference between the shift and the phase shift for the luminance component. The method of claim 11, The prediction unit, Derive a phase value used in the resampling process, And interpolating the top-left sample position of the current block based on the reference layer sample position and the phase value. The method of claim 18, The prediction unit, And an 8-tap interpolation filter is performed on the top-left luminance component sample position of the current block based on the reference layer sample position and the phase value. The method of claim 18, The prediction unit, And a 4-tap interpolation filter is performed on a top-left color difference component sample position of the current block based on the reference layer sample position and the phase value.

Images