WO2015046866A1

WO2015046866A1 - Method and apparatus for encoding/decoding multilayer video signal

Info

Publication number: WO2015046866A1
Application number: PCT/KR2014/008872
Authority: WO
Inventors: 이배근; 김주영
Original assignee: 주식회사 케이티
Priority date: 2013-09-24
Filing date: 2014-09-24
Publication date: 2015-04-02
Also published as: KR20150133685A; WO2015046867A1; KR20150033577A; KR20150033576A

Abstract

A method for decoding a multilayer video signal, according to the present invention, is characterized by: determining a corresponding picture in a reference layer used for inter-layer prediction of a current picture in a current layer; generating an inter-layer reference picture by upsampling the determined corresponding picture; specifying a reference block in the inter-layer reference picture used for inter-layer prediction of the current block, based on spatial offset information; and conducting inter-layer prediction of the current block using the specified reference block.

Description

Method and apparatus for encoding / decoding multilayer video signal

The present invention relates to a method and apparatus for encoding / decoding multilayer video signals.

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.

Meanwhile, as the demand for high resolution video increases, the demand for stereoscopic video content also increases as a new video service. There is a discussion about a video compression technology for effectively providing high resolution and ultra high resolution stereoscopic image contents.

An object of the present invention is to provide a method and apparatus for determining a corresponding picture of a reference layer used for inter-layer prediction of a current picture in encoding / decoding a multilayer video signal.

An object of the present invention is to provide a method and apparatus for upsampling a corresponding picture of a reference layer in encoding / decoding a multilayer video signal.

An object of the present invention is to provide a method and apparatus for specifying a reference block of a reference layer used for inter-layer prediction of a current block in encoding / decoding a multilayer video signal.

An object of the present invention is to provide a method and apparatus for constructing a reference picture list using an inter-layer reference picture in encoding / decoding a multilayer video signal.

An object of the present invention is to provide a method and apparatus for effectively deriving texture information of a current layer through inter-layer prediction in encoding / decoding a multilayer video signal.

The method and apparatus for decoding a multilayer video signal according to the present invention determine a corresponding picture of a reference layer used for inter-layer prediction of a current picture in a current layer, and upsample the determined corresponding picture to generate an interlayer reference picture. And specifying a reference block in the interlayer reference picture used for inter-layer prediction of the current block based on spatial offset information, and performing inter-layer prediction of the current block using the specified reference block. .

In the method and apparatus for decoding a multi-layer video signal according to the present invention, the specification of the reference block is performed based on the inter-layer prediction limit flag.

In the method and apparatus for decoding a multi-layer video signal according to the present invention, the inter-layer prediction limit flag is a constraint that a reference block specified based on the spatial offset information is applied in inter-layer prediction of the current block. It is characterized by indicating whether or not.

In the method and apparatus for decoding a multilayer video signal according to the present invention, the reference block is specified as a block of a position moved by an offset according to the spatial offset information with respect to a call block belonging to the interlayer reference picture. do.

In the method and apparatus for decoding a multilayer video signal according to the present invention, the spatial offset information includes at least one of a segment offset and a block offset.

The method and apparatus for encoding a multilayer video signal according to the present invention determine a corresponding picture of a reference layer used for inter-layer prediction of a current picture in a current layer, and upsample the determined corresponding picture to generate an interlayer reference picture. And specifying a reference block in the interlayer reference picture used for inter-layer prediction of the current block based on spatial offset information, and performing inter-layer prediction of the current block using the specified reference block. .

In the method and apparatus for encoding a multi-layer video signal according to the present invention, the specification of the reference block is performed based on the inter-layer prediction limit flag.

In the method and apparatus for encoding a multi-layer video signal according to the present invention, whether the inter-layer prediction limit flag is applied in the inter-layer prediction of the current block, the constraint that a reference block specified based on the spatial offset information is applied is applied. It is characterized by indicating whether or not.

In the method and apparatus for encoding a multilayer video signal according to the present invention, the reference block is specified as a block of a position moved by an offset according to the spatial offset information with respect to a call block belonging to the interlayer reference picture. do.

In the method and apparatus for encoding a multilayer video signal according to the present invention, the spatial offset information includes at least one of a segment offset and a block offset.

According to the present invention, it is possible to effectively determine the corresponding picture of the reference layer used for inter-layer prediction of the current picture in the current layer.

According to the present invention, it is possible to effectively upsample a picture of a reference layer.

According to the present invention, a reference picture list including an interlayer reference picture can be effectively constructed.

According to the present invention, the reference block of the reference layer used for inter-layer prediction of the current block can be effectively determined.

According to the present invention, texture information of the current layer can be effectively derived through inter-layer prediction.

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 flowchart illustrating a process of performing inter prediction of a current layer using a corresponding picture of a reference layer according to an embodiment to which the present invention is applied.

4 illustrates a method of determining a corresponding picture of a reference layer based on a reference active flag according to an embodiment to which the present invention is applied.

5 illustrates a syntax table of a reference active flag according to an embodiment to which the present invention is applied.

FIG. 6 illustrates a method of obtaining inter-layer reference information for a current picture according to an embodiment to which the present invention is applied.

7 illustrates a syntax table of interlayer reference information according to an embodiment to which the present invention is applied.

8 is a flowchart illustrating a method of upsampling a corresponding picture of a reference layer according to an embodiment to which the present invention is applied.

FIG. 9 illustrates a method of specifying a near reference picture stored in a decoding picture buffer as an embodiment to which the present invention is applied.

FIG. 10 illustrates a method of specifying a long-term reference picture as an embodiment to which the present invention is applied.

FIG. 11 illustrates a method of constructing a reference picture list using a near reference picture and a long range reference picture as an embodiment to which the present invention is applied.

12 illustrates a process of performing inter-layer prediction of a current block based on spatial offset information according to an embodiment to which the present invention is applied.

13 to 15 illustrate a syntax table of spatial offset information according to an embodiment to which the present invention is applied.

FIG. 16 illustrates a method of specifying a reference block used for inter-layer prediction of a current block by using spatial offset information according to an embodiment to which the present invention is applied.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

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 video 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 encoding performance of an image. Performing prediction of the current layer using information of another layer is referred to as inter-layer prediction or inter-layer prediction in the following.

The plurality of layers may have different resolutions, where the resolution may mean at least one of spatial resolution, temporal resolution, and image quality. Resampling such as up-sampling or downsampling of a layer may be performed to adjust the resolution during inter-layer prediction.

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 expressed as a current layer or an enhancement layer, and the lower layer may be expressed as an enhancement layer, a base layer, or a reference layer having a lower resolution than the upper layer. . The upper layer and the lower layer may have at least one of a spatial resolution, a temporal resolution according to a frame rate, and an image quality according to a color format or a quantization size. 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 may include a divider 110, a predictor 120, a transformer 130, a quantizer 140, a reorderer 150, an entropy encoder 160, and an inverse quantizer ( 170, an inverse transform unit 180, a filter unit 190, and a memory 195.

The encoder 100b of the lower layer includes a divider 111, a predictor 125, a transformer 131, a quantizer 141, a reordering unit 151, an entropy encoder 161, and an inverse quantizer ( 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. As a block for performing inter prediction, there is a prediction block partitioning method using Asymmetric Motion Partitioning (AMP), which is a square form such as 2Nx2N and NxN, or a rectangular form or asymmetric form such as 2NxN and Nx2N. 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, 127). The predictor 120 of the higher layer encoder 100a may further include an inter-layer predictor 123 that performs prediction on the higher 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. In performing the intra prediction, the process of determining the intra prediction mode in units of prediction blocks and performing the intra prediction based on the determined intra prediction mode may be performed in units of transform blocks. 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 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 have a directional prediction mode using a reference pixel according to a prediction direction and a non-directional mode without considering the prediction direction. 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, an intra prediction mode in which luma information is predicted or predicted luma information may be used. If a reference pixel is not available, the unusable reference pixel may be replaced with another pixel, and a prediction block may be generated using the reference 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 performed, and a plurality of transform blocks are included in the prediction block, intra prediction is performed by using neighboring pixels adjacent to the transform block as reference pixels. Can be done. Here, the neighboring pixel adjacent to the transform block may include at least one of the neighboring pixel adjacent to the prediction block and the pixels already decoded in the prediction block.

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 case of a 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 a motion vector predictor (MVP), may be used as the inter prediction method.

In inter prediction, motion information, that is, information such as a reference index, a motion vector, and a residual signal, is entropy coded and transmitted to a decoder. When the skip mode is applied, since the residual signal is not generated, the conversion and quantization processes for the residual signal may be omitted.

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 may perform inter-layer prediction using texture information, motion information, etc. of the lower layer.

In inter-layer prediction, prediction of a current block of an upper layer may be performed using motion information on a picture of a lower layer (reference layer) using a picture of a lower layer as a reference picture. The picture of the reference layer used as the reference picture in inter-layer prediction may be a picture sampled according to the resolution of the current layer. In addition, the motion information may include a motion vector and a reference index. In this case, the value of the motion vector for the picture of the reference layer may be set to (0,0).

As an example of inter-layer prediction, a prediction method using a picture of a lower layer as a reference picture has been described, but the present invention is not limited thereto. The inter-layer prediction unit 123 may perform inter-layer texture prediction, inter-layer motion prediction, inter-layer syntax prediction, and inter-layer difference prediction.

Inter-layer texture prediction may derive the texture of the current layer based on the texture of the reference layer. The texture of the reference layer may be sampled according to the resolution of the current layer, and the inter-layer predictor 123 may predict the texture of the current layer based on the sampled texture of the reference layer.

Inter-layer motion prediction may derive the motion vector of the current layer based on the motion vector of the reference layer. In this case, the motion vector of the reference layer may be scaled according to the resolution of the current layer. In inter-layer syntax prediction, the syntax of the current layer may be predicted based on the syntax of the reference layer. For example, the inter-layer prediction unit 123 may use the syntax of the reference layer as the syntax of the current layer. In addition, in the difference prediction between layers, the picture of the current layer may be reconstructed using the difference between the reconstructed image of the reference layer and the reconstructed image of the current layer.

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 coefficients 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 block from the

reordering units

150 and 151 and the

prediction units

120 and 125. Entropy encoding may be performed based on a predetermined encoding method by receiving various information such as unit information, motion information, reference frame information, block interpolation information, 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

filter units

190 and 191 may include at least one of a deblocking filter and an offset correction unit.

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 predetermined areas, and then, the area to be offset is determined and the offset is applied to the corresponding area, or the offset is applied considering the edge information of each pixel. Can be used.

The

filter units

190 and 191 may apply only the deblocking filter or both the deblocking filter and the offset correction without applying both the deblocking filter and the offset correction.

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 100a of the upper layer or the encoder 100b of the lower layer, or may be implemented as an independent device or module separate from the encoder 100.

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 obtained by entropy decoding by the

entropy decoders

210 and 211 is a reordering unit. It may be input to (220, 221).

Like the

entropy encoders

160 and 161, the

entropy decoders

210 and 211 may use 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 decoder

210 or 211 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 may be reconstructed by reconstructing the coefficients in a two-dimensional block form. The

reordering units

220 and 221 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 corresponding 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 or inverse DST on the DCT or 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 the 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 of the current block, and a prediction direction. The

inverse transformers

240 and 241 of the decoding apparatus may convert Inverse transformation may be performed based on the performed 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. In order to perform inter prediction, a motion prediction method of a prediction block included in a coding block based on a coding block uses a skip mode, a merge mode, a motion vector predictor (MVP) (AMVP). Mode) can be determined.

The intra prediction unit may generate a prediction block based on the reconstructed 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 pixel of the current block, a reference pixel interpolator that generates a reference pixel of an integer value or less by interpolating the reference pixel, 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 may perform inter-layer prediction using intra prediction mode information and motion information.

In inter-layer prediction, prediction of a current block of an upper layer may be performed using motion information of a lower layer (reference layer) picture using a picture of a lower layer as a reference picture.

The picture of the reference layer used as the reference picture in inter-layer prediction may be a picture sampled according to the resolution of the current layer. In addition, the motion information may include a motion vector and a reference index. In this case, the value of the motion vector for the picture of the reference layer may be set to (0,0).

As an example of inter-layer prediction, a prediction method using a picture of a lower layer as a reference picture has been described, but the present invention is not limited thereto. The inter-layer prediction unit 123 may further perform inter-layer texture prediction, inter-layer motion prediction, inter-layer syntax prediction, and inter-layer difference prediction.

Inter-layer texture prediction may derive the texture of the current layer based on the texture of the reference layer. The texture of the reference layer may be sampled according to the resolution of the current layer, and the inter-layer predictor may predict the texture of the current layer based on the sampled texture. Inter-layer motion prediction may derive the motion vector of the current layer based on the motion vector of the reference layer. In this case, the motion vector of the reference layer may be scaled according to the resolution of the current layer. In inter-layer syntax prediction, the syntax of the current layer may be predicted based on the syntax of the reference layer. For example, the inter-layer prediction unit 123 may use the syntax of the reference layer as the syntax of the current layer. In addition, in the difference prediction between layers, the picture of the current layer may be reconstructed using the difference between the reconstructed image of the reference layer and the reconstructed image of the current layer.

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 and an offset correction unit.

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

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.

In SVC (Scalable Video Coding) supporting multi-layer structure, there is an association between layers. Prediction using this association can remove redundant elements of data and improve the encoding performance of the image.

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 inter-layer prediction is performed, the current layer may generate a prediction sample of the current layer by using a decoded picture of a reference layer used for inter-layer prediction as a reference picture.

In this case, since the current layer and the reference layer may have at least one of spatial resolution, temporal resolution, and image quality different from each other (that is, due to scalability differences between layers), the picture of the decoded reference layer matches 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 specification, 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. A picture (ie, a reference picture) of a reference layer used for inter layer prediction of the current layer may be referred to as an inter layer reference picture or an inter layer reference picture.

Referring to FIG. 3, a corresponding picture of a reference layer used for inter-layer prediction of the current picture of the current layer may be determined (S300).

The reference layer may mean a base layer or another enhancement layer having a lower resolution than the current layer. The corresponding picture may mean a picture located at the same time zone as the current picture of the current layer.

For example, the corresponding picture may be a picture having the same picture order count (POC) information as the current picture of the current layer. The corresponding picture may belong to the same Access Unit (AU) as the current picture of the current layer. The corresponding picture may have the same temporal level ID (TemporalID) as the current picture of the current layer. Here, the temporal level identifier may mean an identifier for specifying each of a plurality of layers that are coded scalable according to temporal resolution.

The current block may use corresponding pictures of one or more reference layers for inter-layer prediction, and a method of specifying the corresponding picture will be described with reference to FIGS. 4 to 7.

The interlayer reference picture may be generated by upsampling the corresponding picture determined in operation S300 (S310).

Here, the interlayer reference picture may be used as a reference picture for inter-layer prediction of the current picture.

In more detail, the interlayer reference picture may include at least one of a first interlayer reference picture and a second interlayer reference picture. The first interlayer reference picture may mean a reference picture that has been filtered for the integer position, and the second interlayer reference picture may mean a reference picture that has not been filtered for the integer position.

Here, the integer position may refer to pixels of an integer unit of the corresponding picture to be upsampled. Alternatively, in the upsampling process, when interpolating in units of integer pixels or less, that is, in units of 1 / n pixels, n phases are generated, and at this time, zero phase positions (that is, n-fold integer pixels after interpolation) are generated. It may mean). Filtering on the integer position may be performed using the surrounding integer position. The surrounding integer position may be located in the same row or the same column as the currently filtered integer position. The surrounding integer position may include a plurality of integer positions belonging to the same row or the same column. Here, the plurality of integer positions may be sequentially arranged in the same column or the same row. A detailed upsampling method will be described below with reference to FIG. 8.

However, when the current layer and the reference layer have the same resolution, the above upsampling process can be omitted. That is, the corresponding picture of the reference layer may be used as the interlayer reference picture.

A reference picture list including an interlayer reference picture and a temporal reference picture generated in step S310 may be generated (S320).

First, the reference picture list may include a reference picture (hereinafter, referred to as a temporal reference picture) belonging to the same layer as the current picture. The temporal reference picture may mean a picture having an output order different from the current picture (eg, picture order count, POC). A method of generating a reference picture list composed of temporal reference pictures will be described with reference to FIGS. 9 to 11.

Meanwhile, when the current picture performs inter-layer prediction, the reference picture list may further include an interlayer reference picture. That is, in a multilayer structure (eg, scalable video coding and multi-view video coding), a reference picture of the same layer as well as a reference picture of another layer may be used as a reference picture of the enhancement layer.

In more detail, a picture belonging to a reference layer may be used as a reference picture. Here, the reference layer may be identified by a reference layer identifier RefPiclayerId. The reference layer identifier may be derived based on the syntax inter_layer_pred_layer_idc (hereinafter referred to as an interlayer indicator) of the slice header. The interlayer indicator may indicate a layer of a picture used by the current picture for inter-layer prediction. In this manner, a reference picture list including the interlayer reference picture of the reference layer specified by the reference layer identifier can be generated.

Meanwhile, as described in operation S310, the interlayer reference picture may include at least one of the first interlayer reference picture and the second interlayer reference picture. Accordingly, a reference picture list including any one of a first interlayer reference picture and a second interlayer reference picture may be generated, and a reference picture list including both the first interlayer reference picture and the second interlayer reference picture is generated. You may.

For selective use of the first interlayer reference picture and the second interlayer reference picture, whether to use both the first interlayer reference picture and the second interlayer reference picture on a picture basis, or any one of the interlayer reference pictures You can choose whether to use only. Furthermore, when only one of the first interlayer reference picture and the second interlayer reference picture is selected and used, it is possible to select which interlayer reference picture to use. To this end, the encoding apparatus may signal information about which of the two layer reference pictures to use.

Alternatively, a reference index may be used for the selective use. Specifically, only the first interlayer reference picture may be selected by the reference index on a prediction block basis, or only the second interlayer reference picture may be selected, and both the first and second interlayer reference pictures are selected. May be

When an interlayer reference picture is added to the reference picture list, it is necessary to change the range of the number of reference pictures arranged in the reference picture list or the number of reference indices allocated for each reference picture.

Herein, it is assumed that the ranges of num_ref_idx_l0_active_minus1 and num_ref_idx_l1_active_minus1, which are syntaxes of the slice header indicating the maximum reference index of the reference picture list for the base layer, have a value between 0 and 14.

When using either the first interlayer reference picture or the second interlayer reference picture, the ranges of num_ref_idx_l0_active_minus1 and num_ref_idx_l1_active_minus1, which are the syntaxes representing the maximum reference index values of the reference picture list for the current layer, range from 0 to 15. Can be defined. Alternatively, even when both the first interlayer reference picture and the second interlayer reference picture are used, when two interlayer reference pictures are added to different reference picture lists, the range of num_ref_idx_l0_active_minus1 and num_ref_idx_l1_active_minus1 is a value between 0 and 15. Can be defined.

For example, if the number of temporal reference pictures in the reference picture list L0 is 15, when the first or second interlayer reference picture is added to the reference picture list, 16 reference pictures exist in total, and the value of num_ref_idx_l0_active_minus1 is 15 do.

Alternatively, when both the first interlayer reference picture and the second interlayer reference picture are used, and when two interlayer reference pictures are added to the same reference picture list, the reference index maximum value of the reference picture list for the current layer is maximum. The ranges of num_ref_idx_l0_active_minus1 and num_ref_idx_l1_active_minus1, which are syntaxes that represent NNs, may be defined as values between 0 and 16.

For example, if the number of temporal reference pictures in the reference picture list L0 is 15, and the first interlayer reference picture and the second interlayer reference picture are added to the reference picture list L0, a total of 17 reference pictures exist and num_ref_idx_l0_active_minus1 The value is 16.

Inter-prediction of the current picture may be performed based on the reference picture list generated in step S320 (S330).

Specifically, a reference picture corresponding to the reference index of the current block is selected from the reference picture list. The selected reference picture may be a temporal reference picture or an inter-layer reference picture (ie, a corresponding picture of the reference layer or an upsampled corresponding picture) in the same layer as the current block.

A reference block in the reference picture may be specified based on the motion vector of the current block, and the sampled value or texture information of the current block may be predicted using the reconstructed sample value or texture information of the specified reference block.

When the reference picture corresponding to the reference index of the current block is an interlayer reference picture, the reference block may be a block at the same position as the current block (hereinafter, referred to as a call block). To this end, when the reference picture of the current block is an interlayer reference picture, the motion vector of the current block may be set to (0,0).

Alternatively, when the reference picture corresponding to the reference index of the current block is an interlayer reference picture, a block of a position shifted by a predetermined offset in the call block may be used as a reference block, and this will be described with reference to FIGS. 12 to 16. Let's take a closer look.

4 illustrates a method of determining a corresponding picture of a reference layer based on a reference active flag as an embodiment to which the present invention is applied, and FIG. 5 is an embodiment to which the present invention is applied. A syntax table is shown.

Referring to FIG. 4, a reference active flag may be obtained from a bitstream (S400).

The reference active flag all_ref_layers_active_flag may indicate whether a constraint that the corresponding picture of all layers having direct dependency with the current layer is used for inter-layer prediction of the current picture is applied. Referring to FIG. 5, the reference active flag may be obtained from a video parameter set.

Here, whether the layer has a direct dependency on the current layer may be determined based on the direct dependency flag direct_dependency_flag [i] [j]. The direct dependency flag direct_dependency_flag [i] [j] may indicate whether the j th layer is used for inter-layer prediction of the i th current layer.

For example, when the value of the direct dependency flag is 1, the j th layer may be used for inter-layer prediction of the i th current layer. When the value of the direct dependency flag is 0, the j th layer may be used. It may not be used for inter-layer prediction of the i th current layer.

It may be checked whether the value of the reference active flag is 1 (S410).

When the value of the reference active flag is 1, the constraint that the corresponding picture of all layers having direct dependency with the current layer is used for inter-layer prediction of the current picture is applied. In this case, corresponding pictures of all layers having direct dependency on the current layer may be included in a reference picture list of the current picture. Accordingly, the corresponding picture of all layers having direct dependency on the current layer may be determined as the corresponding picture used for inter-layer prediction of the current picture (S420).

On the other hand, when the value of the reference active flag is 0, the constraint that the corresponding picture of all layers having direct dependency with the current layer is used for inter-layer prediction of the current picture is not applied. That is, the current picture of the current layer may perform inter-layer prediction using corresponding pictures of all layers having direct dependency on the current layer, and only some corresponding pictures of all layers having direct dependency on the current layer may be used. Inter-layer prediction may be performed selectively. That is, when the value of the reference active flag is 0, the corresponding picture of all layers having direct dependency with the current layer may be included in the reference picture list of the current picture, or only some corresponding pictures may be selectively included. Therefore, it is necessary to specify the corresponding picture used for inter-layer prediction of the current picture among the layers having the current layer and direct dependency. To this end, interlayer reference information about the current picture may be obtained (S430).

Here, the interlayer reference information may include at least one of an interlayer prediction flag, information on the number of reference pictures, or a reference layer identifier.

In detail, the interlayer prediction flag may indicate whether inter-layer prediction is used in the decoding process of the current picture. The number information of the reference picture may indicate the number of corresponding pictures used for inter-layer prediction of the current picture. Information about the number of reference pictures may be encoded and signaled by subtracting 1 from the number of corresponding pictures used for inter-layer prediction of the current picture for coding efficiency. The reference layer identifier may mean a layer identifier (layerId) of a layer including a corresponding picture used for inter-layer prediction of the current picture.

A method of obtaining the interlayer reference information will be described with reference to FIGS. 6 and 7.

A corresponding picture used for inter-layer prediction may be determined based on the interlayer reference information obtained in S430 (S440).

For example, when the value of the interlayer prediction flag of the current picture is 1, it means that the current picture performs inter-layer prediction. In this case, among the layers having direct dependency on the current layer, the corresponding picture of the layer specified by the reference layer identifier may be determined as the corresponding picture used for inter-layer prediction of the current picture.

On the other hand, when the value of the inter-layer prediction flag of the current picture is 0, since the current picture does not perform inter-layer prediction, corresponding pictures of all layers having direct dependency on the current layer are applied to inter-layer prediction of the current picture. Will not be used.

FIG. 6 is a diagram illustrating a method of obtaining interlayer reference information on a current picture, according to an embodiment to which the present invention is applied; FIG. It is shown.

Referring to FIG. 6, an interlayer prediction flag may be obtained based on a reference active flag (S600).

Referring to FIG. 7, the interlayer prediction flag inter_layer_pred_enabled_flag may be obtained only when the value of the reference active flag all_ref_layers_active_flag is 0 (S700).

When the value of the reference active flag is 1, this may mean that corresponding pictures of all layers having direct dependency on the current layer are used for inter-layer prediction of the current picture. Thus, in this case, there is no need to signal the interlayer prediction flag in the header information (eg, slice segment header) of the current picture.

In addition, referring to FIG. 7, when the layer identifier nuh_layer_id of the current layer including the current picture is greater than 0, the interlayer prediction flag may be obtained. This is because, when the layer identifier of the current layer is 0, the current layer corresponds to a base layer which does not perform inter-layer prediction in the multilayer.

In addition, referring to FIG. 7, the interlayer prediction flag may be obtained when the number NumDirectRefLayers of the layers having direct dependency with the current layer is at least one. This is because when there is no layer having direct dependency on the current layer, all pictures of the current layer do not perform inter-layer prediction.

Referring to FIG. 6, it may be determined whether the value of the interlayer prediction flag acquired in S600 is 1 (S610).

As a result of checking in S610, when the value of the interlayer prediction flag is 1, information about the number of reference pictures may be obtained (S620).

As illustrated in FIG. 4, the number information of the reference picture may indicate the number of corresponding pictures used for inter-layer prediction of the current picture among the corresponding pictures of the layer having direct dependency with the current layer.

Therefore, referring to FIG. 7, when the number of layers (NumDirectRefLayers) having direct dependency is one, the number of corresponding pictures used for inter-layer prediction of the current picture cannot exceed one. It is not necessary to signal the number information (num_inter_layer_ref_pics_minus1) of the reference picture. In this case, the number information of the reference picture may not be obtained, and the number of corresponding pictures used for inter-layer prediction of the current picture may be derived as one.

Meanwhile, the number information of the reference picture may be obtained limitedly based on the maximum active reference flag.

Here, the maximum active reference flag may indicate whether only at least one corresponding picture is used for inter-layer prediction of the current picture. For example, when the value of the maximum active reference flag is 1, the current picture performs inter-layer prediction using only at least one corresponding picture. When the value of the maximum active reference flag is 0, the current picture is one or more corresponding. Inter-layer prediction may be performed using a picture.

Referring to FIG. 7, the number information of the reference picture may be obtained only when the value of the maximum active reference flag max_one_active_ref_layer_flag is 0. That is, when the value of the maximum active reference flag is 1, since the number of corresponding pictures used for inter-layer prediction of the current picture is limited to one, it is not necessary to signal the number information of the reference picture.

Referring to FIG. 6, a reference layer identifier may be obtained based on the number information of the reference pictures obtained in S620 (S630).

Specifically, referring to FIG. 7, the number of corresponding pictures (NumActiveRefLayerPics) used for inter-layer prediction of the current picture among the corresponding pictures of the layer having the direct dependency with the current layer, and the layer having the direct dependency with the current layer. When the number NumDirectRefLayers is different, a reference layer identifier may be obtained. Here, the variable NumActiveRefLayerPics may be derived from the number information of the reference picture. For example, when information on the number of reference pictures is encoded by subtracting 1 from the number of corresponding pictures used for inter-layer prediction of the current picture, the variable NumActiveRefLayerPics adds 1 to the information on the number of reference pictures acquired in S620. Can be derived from a value.

If the variable NumActiveRefLayerPics and the variable NumDirectRefLayers are the same, this means that the corresponding picture of the layer having direct dependency on the current layer becomes the corresponding picture used for inter-layer prediction of the current picture. Thus, there is no need to signal the reference layer identifier.

Referring to FIG. 8, a reference sample position of a reference layer corresponding to the current sample position of the current layer may be derived (S800).

Since the resolutions of the current layer and the reference layer may be different, the reference sample position corresponding to the current sample position may be derived in consideration of the resolution difference between the two. That is, the aspect ratio may be considered between the picture of the current layer and the picture of the reference layer. In addition, since a case where an upsampled picture of the reference layer does not match the size of the picture of the current layer may occur, an offset for correcting this may be required.

For example, the reference sample position may be derived in consideration of the scale factor and the upsampled reference layer offset.

Here, the scale factor may be calculated based on a ratio of the width and the height between the current picture of the current layer and the corresponding picture of the reference layer.

The upsampled reference layer offset may mean position difference information between any one sample located at the edge of the current picture and any one sample located at the edge of the interlayer reference picture. For example, the upsampled reference layer offset includes horizontal position information in the horizontal / vertical direction between the upper left sample of the current picture and the upper left sample of the interlayer reference picture, and the lower right sample of the current picture and the lower right sample of the interlayer reference picture. Position difference information in the horizontal / vertical direction of the liver may be included.

The upsampled reference layer offset may be obtained from the bitstream. For example, the upsampled reference layer offset may be obtained from at least one of a video parameter set, a sequence parameter set, a picture parameter set, and a slice header. Can be.

The filter coefficient of the upsampling filter may be determined in consideration of the phase of the reference sample position derived in S800 (S810).

Here, the upsampling filter may be any one of a fixed upsampling filter and an adaptive upsampling filter.

1. Fixed Upsampling Filter

The fixed upsampling filter may mean an upsampling filter having a predetermined filter coefficient without considering the feature of the image. A tap filter may be used as the fixed upsampling filter, which may be defined for the luminance component and the chrominance component, respectively. Hereinafter, a fixed upsampling filter having an accuracy of 1/16 sample units will be described with reference to Tables 1 to 2.

Table 1

Phase p	Interpolation filter coefficients
Phase p	f [p, 0]	f [p, 1]	f [p, 2]	f [p, 3]	f [p, 4]	f [p, 5]	f [p, 6]	f [p, 7]
0	0	0	0	64	0	0	0	0
One	0	One	-3	63	4	-2	One	0
2	-One	2	-5	62	8	-3	One	0
3	-One	3	-8	60	13	-4	One	0
4	-One	4	-10	58	17	-5	One	0
5	-One	4	-11	52	26	-8	3	-One
6	-One	3	-3	47	31	-10	4	-One
7	-One	4	-11	45	34	-10	4	-One
8	-One	4	-11	40	40	-11	4	-One
9	-One	4	-10	34	45	-11	4	-One
10	-One	4	-10	31	47	-9	3	-One
11	-One	3	-8	26	52	-11	4	-One
12	0	One	-5	17	58	-10	4	-One
13	0	One	-4	13	60	-8	3	-One
14	0	One	-3	8	62	-5	2	-One
15	0	One	-2	4	63	-3	One	0

Table 1 is a table that defines the filter coefficients of the fixed upsampling filter for the luminance component.

As shown in Table 1, in the case of upsampling the luminance component, an 8-tap filter is applied. That is, interpolation may be performed using a reference sample of a reference layer corresponding to the current sample of the current layer and a neighboring sample adjacent to the reference sample. Here, the neighbor sample may be specified according to the direction in which interpolation is performed. For example, when performing interpolation in the horizontal direction, the neighboring sample may include three consecutive samples to the left and four consecutive samples to the right based on the reference sample. Alternatively, when performing interpolation in the vertical direction, the neighboring sample may include three consecutive samples at the top and four consecutive samples at the bottom based on the reference sample.

In addition, since interpolation is performed with an accuracy of 1/16 samples, there are 16 phases in total. This is to support resolutions of various magnifications such as 2 times and 1.5 times.

In addition, the fixed upsampling filter may use different filter coefficients for each phase p. Except in the case where phase p is zero, the magnitude of each filter coefficient may be defined to fall in the range of 0 to 63. This means that the filtering is performed with a precision of 6 bits. Here, a phase p of 0 means a position of an integer multiple of n times when interpolated in units of 1 / n samples.

TABLE 2

Phase p	Interpolation filter coefficients
Phase p	f [p, 0]	f [p, 1]	f [p, 2]	f [p, 3]
0	0	64	0	0
One	-2	62	4	0
2	-2	58	10	-2
3	-4	56	14	-2
4	-4	54	16	-2
5	-6	52	20	-2
6	-6	46	28	-4
7	-4	42	30	-4
8	-4	36	36	-4
9	-4	30	42	-4
10	-4	28	46	-6
11	-2	20	52	-6
12	-2	16	54	-4
13	-2	14	56	-4
14	-2	10	58	-2
15	0	4	62	-2

Table 2 is a table that defines the filter coefficients of the fixed upsampling filter for the chrominance components.

As shown in Table 2, in the case of upsampling for the chrominance component, a 4-tap filter may be applied unlike the luminance component. That is, interpolation may be performed using a reference sample of a reference layer corresponding to the current sample of the current layer and a neighboring sample adjacent to the reference sample. Here, the neighbor sample may be specified according to the direction in which interpolation is performed. For example, when performing interpolation in the horizontal direction, the neighboring sample may include one sample to the left and two samples to the right based on the reference sample. Alternatively, when performing interpolation in the vertical direction, the neighboring sample may include one sample continuous to the top and two samples continuous to the bottom based on the reference sample.

Meanwhile, since the interpolation is performed with the accuracy of 1/16 sample unit like the luminance component, a total of 16 phases exist, and different filter coefficients may be used for each phase p. And, except for the case where the phase p is 0, the magnitude of each filter coefficient may be defined to be in the range of 0 to 62. This also means filtering with 6bits precision.

Although an example in which an 8-tap filter is applied to the luminance component and a 4-tap filter to the chrominance component has been described as an example, the present invention is not limited thereto, and the order of the tap filter may be variably determined in consideration of coding efficiency. Of course.

2. Adaptive Upsampling Filter

Instead of using fixed filter coefficients, an optimal filter coefficient may be determined by an encoder in consideration of characteristics of an image, signaled, and transmitted to a decoder. In this way, the adaptive upsampling filter uses the filter coefficients that are adaptively determined in the encoder. Since the characteristics of the image are different in picture units, coding efficiency can be improved by using an adaptive upsampling filter that can express the characteristics of the image better than using a fixed upsampling filter in all cases.

The interlayer reference picture may be generated by applying the filter coefficient determined in operation S810 to the corresponding picture of the reference layer (S820).

Specifically, interpolation may be performed by applying the determined filter coefficients of the upsampling filter to samples of the corresponding picture. Here, the interpolation may be performed primarily in the horizontal direction, and may be performed in the vertical direction secondary to the sample generated after the horizontal interpolation.

The temporal reference picture may be stored in a decoded picture buffer (DPB) and used as a reference picture when necessary for inter prediction of the current picture. The temporal reference picture stored in the decoding picture buffer may include a short-term reference picture. The near reference picture refers to a picture in which the difference between the current picture and the POC value is not large.

The information specifying the near reference picture that should be stored in the decoding picture buffer at the present time is composed of the output order (POC) of the reference picture and a flag indicating whether the current picture is directly referenced (for example, used_by_curr_pic_s0_flag and used_by_curr_pic_s1_flag). This is called a reference picture set. Specifically, when the value of the used_by_curr_pic_s0_flag [i] is 0, when the i-th near-reference picture of the near-reference picture set has a value smaller than the output order (POC) of the current picture, the i-th near-reference picture is the reference picture of the current picture. Not used. When the value of the used_by_curr_pic_s1_flag [i] is 0, when the i th near reference picture of the near reference picture set has a value larger than the output order (POC) of the current picture, the i th near reference picture is the reference picture of the current picture. Not used.

Referring to FIG. 9, in the case of a picture having a POC value of 26, all three pictures (that is, pictures having POC values of 25, 24, and 20) may be used as a near reference picture in inter prediction. However, since the used_by_curr_pic_s0_flag value of a picture having a POC value of 25 is 0, a picture having a POC value of 25 is not directly used for inter prediction of a picture having a POC value of 26.

In this way, the near-field reference picture can be specified based on the output order (POC) of the reference picture and a flag indicating whether the reference picture is used as the reference picture.

On the other hand, for a picture not shown in the reference picture set for the current picture, an indication (eg, unused for reference) that is not used as a reference picture can be made, and further removed from the decoding picture buffer.

In the case of a long-range reference picture, since the difference between the current picture and the POC value is large, it can be expressed using a least significant bit (LSB) and a most significant bit (MSB) of the POC value.

Accordingly, the POC value of the long range reference picture may be derived using a difference between the LSB value of the POC value of the reference picture, the POC value of the current picture, and the MSB of the POC value of the current picture and the MSB of the POC value of the reference picture.

For example, it is assumed that a POC value of the current picture is 331, a maximum value that can be represented by the LSB is 32, and a picture having a POC value of 308 is used as the long distance reference picture.

In this case, 331, which is a POC value of the current picture, may be expressed as 32 * 10 + 11, where 10 is an MSB value and 11 is an LSB value. The POC value of the long range reference picture 308 is expressed as 32 * 9 + 20, where 9 is an MSB value and 20 is an LSB value. In this case, the POC value of the long range reference picture may be derived as shown in FIG. 10.

Referring to FIG. 11, a reference picture list including a temporal reference picture may be generated in consideration of whether the temporal reference picture is a near reference picture and a POC value of the near reference picture. Here, the reference picture list may include at least one of reference picture list 0 for L0 prediction and reference picture list 1 for L1 prediction.

Specifically, in reference picture list 0, a near reference picture (RefPicSetCurr0) having a POC value smaller than the current picture, a near reference picture (RefPicSetCurr1) having a POC value larger than the current picture, and a long distance reference picture (RefPicSetLtCurr) may be arranged in this order. have.

Meanwhile, in reference picture list 1, a near reference picture (RefPicSetCurr1) having a larger POC value than the current picture, a near reference picture (RefPicSetCurr0) having a POC value smaller than the current picture, and a long distance reference picture (RefPicSetLtCurr) may be arranged in this order. .

In addition, a plurality of temporal reference pictures included in the reference picture list may be rearranged in order to improve encoding efficiency of the reference index of the temporal reference picture. This may be adaptively performed based on the list rearrangement flag list_modification_present_flag. Here, the list rearrangement flag is information specifying whether or not the reference pictures in the reference picture list are rearranged. The list rearrangement flag may be signaled with respect to reference picture list 0 and reference picture list 1, respectively.

For example, when the value of the list rearrangement flag list_modification_present_flag is 0, the reference pictures in the reference picture list are not rearranged, and only when the value of the list rearrangement flag list_modification_present_flag is 1. Reference pictures may be rearranged.

If the value of the list rearrangement flag list_modification_present_flag is 1, reference pictures in the reference picture list may be rearranged using list entry information list_entry [i]. Here, the list entry information list_entry [i] may specify a reference index of the reference picture located at the current position (that is, the i-th entry) in the reference picture list.

In detail, a reference picture corresponding to the list entry information list_entry [i] may be specified in a previously generated reference picture list, and the specified reference picture may be rearranged to an i-th entry in the reference picture list.

The list entry information may be obtained by the number of reference pictures included in the reference picture list or by the maximum reference index of the reference picture list. In addition, the list entry information may be obtained in consideration of the slice type of the current picture. That is, if the slice type of the current picture is a P slice, the list entry information (list_entry_l0 [i]) for the reference picture list 0 is obtained. If the slice type of the current picture is a B slice, the list for the reference picture list 1 is obtained. Entry information list_entry_l1 [i] may be additionally obtained.

Referring to FIG. 12, spatial offset information may be obtained (S1200).

The spatial offset information may indicate a position difference between the call block and the reference block of the current block. The call block is a block belonging to the corresponding picture of the reference layer and may mean a block having the same position as the current block. The reference block is a block belonging to a corresponding picture of the reference layer and may mean a block used for inter-layer prediction of the current block.

In more detail, the spatial offset information may include at least one of a segment offset and a block offset. The segment offset is an offset in units of slice segments, tiles, or coding tree unit columns (CTU rows), and may indicate a spatial region that is not used for inter-layer prediction of the picture of the current layer in the picture of the reference layer. Alternatively, the segment offset is an offset in units of slice segments, tiles, or coding tree units (CTU rows), and specifies a spatial region for specifying a reference block used for inter-layer prediction of the picture of the current layer in the picture of the reference layer. You can also indicate. The block offset is an offset in units of blocks, and may indicate a spatial region that is not used for inter-layer prediction of the picture of the current layer in the picture of the reference layer together with the segment offset. Alternatively, the block offset may be an offset in units of blocks and may indicate a spatial region for specifying a reference block used for inter-layer prediction of the picture of the current layer in the picture of the reference layer. Here, the block unit may mean a coding tree unit, and the coding tree unit may mean a maximum coding unit of a video sequence.

The spatial offset information may be obtained from video usability information (VUI) belonging to a video parameter set. The video usability information may not be used to decode the luminance component or the chrominance component, but may refer to information used for decoder conformance or output timing conformance. A detailed method of obtaining spatial offset information will be described below with reference to FIGS. 13 to 15.

First embodiment

Referring to FIG. 13, an inter-layer prediction restriction flag ilp_restricted_ref_layers_flag may be obtained (S1300).

Here, the inter-layer prediction limit flag may indicate whether a constraint that a reference block of a reference layer specified based on spatial offset information is applied in inter-layer prediction of the current block is applied. For example, when the value of the inter-layer prediction limit flag is 1, this may mean that a constraint that inter-layer prediction of the current block is performed using a reference block specified based on spatial offset information is applied. On the contrary, when the value of the inter-layer prediction limit flag is 0, this means that the constraint is not applied. Thus, the current block may perform inter-layer prediction using a reference block specified based on spatial offset information. It may not be performed.

If the value of the inter-layer prediction limit flag is 1, a segment offset min_spatial_segment_offset_plus1 [i] [j] may be obtained (S1310).

Here, the segment offset min_spatial_segment_offset_plus1 [i] [j] is not used for inter-layer prediction of a picture belonging to the i th current layer in each picture of the j th reference layer having direct dependency on the i th current layer. It can indicate a spatial domain.

A block offset flag ctu_based_offset_enable_flag [i] [j] may be obtained based on the segment offset obtained in step S1310 (S1320).

Here, the block offset flag (ctu_based_offset_enable_flag [i] [j]) indicates whether to use a block offset in indicating a spatial region that is not used for inter-layer prediction of the picture belonging to the i th current layer from the picture of the j th reference layer. Can be specified. For example, when the value of the block offset flag is 1, this means that the spatial region that is not used for inter-layer prediction of the picture belonging to the i th current layer in the picture of the j th reference layer uses the block offset together with the segment offset. It may mean indicated. In contrast, when the value of the block offset flag is 0, this may mean that a spatial region that is not used for inter-layer prediction of a picture belonging to the i th current layer in the picture of the j th reference layer is indicated only by the segment offset.

On the other hand, the block offset flag may be obtained when the value of the segment offset obtained in step S1310 is greater than zero. If the value of the segment offset is greater than 0, it is because there is a spatial region in the picture of the j th reference layer that is not used for inter-layer prediction of the picture belonging to the i th current layer.

A block offset min_horizontal_ctu_offset_plus1 may be obtained based on the block offset flag acquired in step S1320 (S1330).

Specifically, when a spatial region that is not used for inter-layer prediction of a picture belonging to the i th current layer in the picture of the j th reference layer according to the block offset flag is indicated using the block offset together with the segment offset (that is, the block Block offset may be obtained in the case where the value of the offset flag is 1).

Second embodiment

Referring to FIG. 14, an inter-layer prediction restriction flag ilp_restricted_ref_layers_flag may be obtained (S1400).

As described above with reference to FIG. 13, the inter-layer prediction limit flag may indicate whether a constraint that a reference block of a reference layer specified based on spatial offset information is applied in inter-layer prediction of the current block is applied. Detailed description will be omitted.

When the value of the inter-layer prediction limit flag acquired in step S1400 is 1, a segment offset min_spatial_segment_offset_plus1 [i] [j] may be obtained (S1410).

A block offset min_horizontal_ctu_offset [i] [j] may be obtained based on the segment offset obtained in step S1410 (S1420).

In detail, the block offset may be obtained when the value of the segment offset obtained in step S1410 is greater than zero. If the value of the segment offset is greater than 0, it is because there is a spatial region in the picture of the j th reference layer that is not used for inter-layer prediction of the picture belonging to the i th current layer.

Instead of the syntax min_horizontal_ctu_offset_plus1 described above with reference to FIG. 13, a block offset (min_horizontal_ctu_offset [i] [j]) that determines the size of a spatial region that is not used for inter-layer prediction may be signaled. If the value of the block offset (min_horizontal_ctu_offset [i] [j]) is 0, it means that there is no spatial region that is not used for inter-layer prediction in the picture of the j th layer, as in the syntax ctu_based_offset_enable_flag [i ] [j] may not be used.

Third embodiment

Referring to FIG. 15, an inter-layer prediction restriction flag ilp_restricted_ref_layers_flag may be obtained (S1500).

Here, the inter-layer prediction limit flag may indicate whether a constraint that a reference block of a reference layer specified based on spatial offset information is applied in inter-layer prediction of the current block is applied, as described above with reference to FIG. 13. Detailed description will be omitted.

When the value of the inter-layer prediction limit flag is 1, a segment offset min_spatial_segment_offset_plus1 [i] [j] may be obtained (S1510).

A block offset flag ctu_based_offset_enable_flag [i] [j] may be obtained based on the segment offset obtained in step S1510 (S1520).

On the other hand, the block offset flag may be obtained when the value of the segment offset obtained in step S1510 is greater than zero. If the value of the segment offset is greater than 0, it is because there is a spatial region in the picture of the j th reference layer that is not used for inter-layer prediction of the picture belonging to the i th current layer.

A block offset min_horizontal_ctu_offset_minus1 [i] [j] may be obtained based on the block offset flag acquired in step S1520 (S1530).

Referring to FIG. 12, a reference block used for inter-layer prediction of a current block may be specified based on spatial offset information (S1210).

Specifically, the reference block may be specified as a block of a position moved by an offset according to spatial offset information based on the position of the call block, which will be described below with reference to FIG. 16.

Referring to FIG. 16, colCtbAddr [i] [j] of the j th reference layer refers to a block having the same position as the current block belonging to the i th current layer, that is, a call block. The j th reference layer may be a layer having direct dependency on the i th current layer. refCtbAddr [i] [j] means the position of the reference block used for inter-layer prediction of the current block. refCtbAddr [i] [j] may be determined based on colCtbAddr [i] [j] and spatial offset information (eg, min_spatial_segment_offset_plus1 and min_horizontal_ctu_offset_plus1). Here, the location of the call block or reference block may be represented by a raster scan address. Specific methods for determining refCtbAddr [i] [j] will be described based on the first to third embodiments described above.

RefCtbAddr [i] [j] derivation method according to the first embodiment

Specifically, refCtbAddr [i] [j] may be derived as in Equation 1 below.

Equation 1

In Equation 1, xOffset [i] [j] and yOffset [i] [j] may be derived as in Equation 2 below.

Equation 2

In Equation 2, xColCtb [i] [j] corresponds to the x component of the coordinate values of the call block belonging to the picture of the j th layer. refPicWidthInCtbY [i] [j] represents the number of coding tree units included in a coding tree unit column in a picture of a j-th layer.

In addition, minHorizontalCtbOffset [i] [j] may be derived based on the block offset min_horizontal_ctu_offset_plus1. For example, as shown in Equation 3, when the value of the block offset is 0, minHorizontalCtbOffset [i] [j] may be derived as (refPicWidthInCtbY [i] [j] -1), and the value of the block offset is 0. If larger, minHorizontalCtbOffset [i] [j] may be derived as (min_horizontal_ctu_offset_plus1-1).

Equation 3

Alternatively, minHorizontalCtbOffset [i] [j] may be derived as shown in Equation 4 not only considering whether the value of the block offset is greater than 0 but also considering whether the value of the block offset is 1 or more.

Equation 4

RefCtbAddr [i] [j] derivation method according to the second embodiment

Specifically, refCtbAddr [i] [j] may be derived as shown in Equation 5 below.

Equation 5

In Equation 5, xOffset [i] [j] and yOffset [i] [j] may be derived as in Equation 6 below.

Equation 6

In Equation 6, xColCtb [i] [j] and refPicWidthInCtbY [i] [j] have been described in Equation 2, and a detailed description thereof will be omitted.

RefCtbAddr [i] [j] derivation method according to the third embodiment

Specifically, refCtbAddr [i] [j] may be derived as shown in Equation 7 below.

Equation 7

In Equation 7, xOffset [i] [j] and yOffset [i] [j] may be derived as shown in Equation 8 below.

Equation 8

In Equation 8, xColCtb [i] [j] and refPicWidthInCtbY [i] [j] have been described in Equation 2, and a detailed description thereof will be omitted.

12, inter-layer prediction of the current block may be performed based on the reference block specified in step S1210 (S1220).

The present invention can be used to code a multilayer video signal.

Claims

Determining a corresponding picture of the reference layer used for inter-layer prediction of the current picture in the current layer;

Generating an interlayer reference picture by upsampling the determined corresponding picture;

Specifying a reference block in the interlayer reference picture used for inter-layer prediction of the current block based on spatial offset information; And

And performing inter-layer prediction of the current block using the specified reference block.
The method of claim 1, wherein the specifying of the reference block is performed based on an inter-layer prediction limit flag.

The inter-layer prediction limit flag indicates whether or not a constraint that a reference block specified based on the spatial offset information is used is applied in inter-layer prediction of the current block.
The method of claim 2, wherein the reference block is specified as a block of a position moved by an offset according to the spatial offset information based on a call block belonging to the interlayer reference picture.
4. The method of claim 3, wherein the spatial offset information comprises at least one of a segment offset and a block offset.
Determines the corresponding picture of the reference layer used for inter-layer prediction of the current picture in the current layer, generates an inter-layer reference picture by upsampling the determined corresponding picture, and uses the inter-layer prediction of the current block based on spatial offset information. And a predictor configured to specify a reference block in the interlayer reference picture to be used, and to perform inter-layer prediction of the current block by using the specified reference block.
The method of claim 5, wherein the specification of the reference block is performed based on an inter-layer prediction limit flag.

The inter-layer prediction limit flag indicates whether or not a constraint that a reference block specified based on the spatial offset information is used is applied in inter-layer prediction of the current block.
The apparatus of claim 6, wherein the reference block is specified as a block of a position shifted by an offset according to the spatial offset information based on a call block belonging to the interlayer reference picture.
The apparatus of claim 7, wherein the spatial offset information comprises at least one of a segment offset and a block offset.
Determining a corresponding picture of the reference layer used for inter-layer prediction of the current picture in the current layer;

Generating an interlayer reference picture by upsampling the determined corresponding picture;

Specifying a reference block in the interlayer reference picture used for inter-layer prediction of the current block based on spatial offset information; And

And performing inter-layer prediction of the current block by using the specified reference block.
The method of claim 9, wherein the specifying of the reference block is performed based on an inter-layer prediction limit flag.

The inter-layer prediction limit flag indicates whether or not a constraint that a reference block specified based on the spatial offset information is used is applied in inter-layer prediction of the current block.
The method of claim 10, wherein the reference block is specified as a block of a position moved by an offset according to the spatial offset information based on a call block belonging to the interlayer reference picture.
12. The method of claim 11, wherein the spatial offset information comprises at least one of a segment offset and a block offset.
Determines the corresponding picture of the reference layer used for inter-layer prediction of the current picture in the current layer, generates an inter-layer reference picture by upsampling the determined corresponding picture, and uses the inter-layer prediction of the current block based on spatial offset information. And a predictor configured to specify a reference block in the interlayer reference picture to be used, and to perform inter-layer prediction of the current block by using the specified reference block.
The method of claim 13, wherein the specification of the reference block is performed based on an inter-layer prediction limit flag.

The inter-layer prediction limit flag indicates whether or not a constraint that a reference block specified based on the spatial offset information is used is applied in inter-layer prediction of the current block.
The method of claim 14, wherein the reference block is specified as a block of a position moved by an offset according to the spatial offset information based on a call block belonging to the interlayer reference picture,

The spatial offset information includes at least one of a segment offset and a block offset.