WO2018174541A1

WO2018174541A1 - Video signal processing method and device

Info

Publication number: WO2018174541A1
Application number: PCT/KR2018/003261
Authority: WO
Inventors: 이배근
Original assignee: 주식회사 케이티
Priority date: 2017-03-21
Filing date: 2018-03-21
Publication date: 2018-09-27
Also published as: KR20180107006A

Abstract

An image decoding method, according to the present invention, may comprise the steps of: decoding, from a bitstream, information associated with a reference face; on the basis of the information, determining whether a face different from a current face comprising a current block may be used as a reference face; acquiring motion information of the current block; and performing motion compensation on the current block on the basis of the determination and the motion information.

Description

Video signal processing method and apparatus

The present invention relates to a video signal processing method and apparatus.

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 perform motion compensation in consideration of continuity between faces in encoding / decoding a video signal.

An object of the present invention is to derive coding parameters from neighboring faces in consideration of continuity between faces in encoding / decoding video signals.

An object of the present invention is to adaptively determine the size of an image stored in a decoded picture buffer in consideration of continuity between faces in encoding / decoding a video signal.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

An image decoding method and apparatus according to the present invention decodes reference face related information from a bitstream, and determines whether a face different from a current face including a current block is available as a reference face based on the information. , Motion information for the current block may be obtained, and motion compensation for the current block may be performed based on the determination and the motion information.

The video encoding method and apparatus according to the present invention determine whether a face different from the current face including the current block is available as a reference face, obtain motion information for the current block, and determine the determination and the motion information. Based on the motion compensation for the current block, the reference face related information may be encoded based on the determination.

In the image decoding / coding method and apparatus according to the present invention, the reference face related information may be information indicating whether a face located beyond a discontinuous face boundary from the current face can be used as a reference face.

The method and apparatus for image decoding / coding according to the present invention may reconstruct the current block by using the prediction sample obtained through the motion compensation and store the reconstructed current picture in a reconstructed picture buffer. have. In this case, when a face positioned beyond the discontinuous face boundary from the current face cannot be used as a reference face, only a part of the current picture may be stored in the reconstructed picture buffer.

In the image decoding / coding method and apparatus according to the present invention, the discontinuous face boundaries may indicate boundaries between faces that are adjacent to each other in the 2D plane but not adjacent to each other in 3D space.

In the image decoding / coding method and apparatus according to the present invention, the reference face related information may be information indicating whether a face having an index different from the current face can be used as the reference face.

In the image decoding / coding method and apparatus according to the present invention, the motion information of the current block may be derived from a face that is vertically or symmetrical with the current face.

In the image decoding / coding method and apparatus according to the present invention, the motion information includes a motion vector, and in the 2D plane, when the current face and the symmetrical face have different rotation angles, the motion vector of the current block is The motion vector of the block included in the symmetrical face may be derived from a value that compensates for the rotational difference between the current face and the symmetrical face.

The features briefly summarized above with respect to the present invention are merely exemplary aspects of the detailed description of the invention that follows, and do not limit the scope of the invention.

According to the present invention, by performing motion compensation in consideration of continuity between faces, there is an advantage that the encoding / decoding efficiency of a 360 degree video can be improved.

According to the present invention, there is an advantage that the encoding / decoding efficiency of a 360 degree video can be improved by allowing the coding parameter to be derived from a neighboring face according to the continuity between faces.

According to the present invention, by adaptively determining the image size stored in the decoded picture buffer, there is an advantage that the buffer size can be reduced.

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above may be clearly understood by those skilled in the art from the following description. will be.

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

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

3 is a diagram illustrating a partition mode that can be applied to a coding block when the coding block is encoded by inter-screen prediction.

4 to 6 are diagrams illustrating a camera apparatus for generating a panoramic image.

7 is a block diagram of a 360 degree video data generating device and a 360 degree video playing device.

8 is a flowchart illustrating operations of a 360 degree video data generating device and a 360 degree video playing device.

9 illustrates a 2D projection method using an isotonic method.

10 illustrates a 2D projection method using a cube projection technique.

11 illustrates a 2D projection method using a icosahedron projection technique.

12 illustrates a 2D projection method using an octahedron projection technique.

13 illustrates a 2D projection method using a truncated pyramid projection technique.

14 is a diagram for explaining the conversion between the face 2D coordinates and the three-dimensional coordinates.

15 and 16 illustrate an example in which frame packing is applied to a 360 degree projection image to which an OHP technique is applied.

17 illustrates a motion compensation method according to an embodiment of the present invention.

18 illustrates an example of a picture unit stored in a reconstructed picture buffer when motion compensation for a discontinuous face is limited.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may exist in the middle. Should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

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

Referring to FIG. 1, the image encoding apparatus 100 may include a picture splitter 110, a

predictor

120 and 125, a transformer 130, a quantizer 135, a realigner 160, and an entropy encoder. 165, an inverse quantizer 140, an inverse transformer 145, a filter 150, and a memory 155.

Each of the components shown in FIG. 1 is independently illustrated to represent different characteristic functions in the image encoding apparatus, and does not mean that each of the components is made of separate hardware or one software component unit. In other words, each component is included in each component for convenience of description, and at least two of the components may be combined into one component, or one component may be divided into a plurality of components to perform a function. Integrated and separate embodiments of the components are also included within the scope of the present invention without departing from the spirit of the 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.

The picture dividing unit 110 may divide the input picture into at least one processing unit. In this case, the processing unit may be a prediction unit (PU), a transform unit (TU), or a coding unit (CU). The picture dividing unit 110 divides one picture into a combination of a plurality of coding units, prediction units, and transformation units, and combines one coding unit, prediction unit, and transformation unit on a predetermined basis (eg, a cost function). You can select to encode the picture.

For example, one picture may be divided into a plurality of coding units. In order to split a coding unit in a picture, a recursive tree structure such as a quad tree structure may be used, and coding is divided into other coding units by using one image or a largest coding unit as a root. The unit may be split with as many child nodes as the number of split coding units. Coding units that are no longer split according to certain restrictions become leaf nodes. That is, when it is assumed that only square division is possible for one coding unit, one coding unit may be split into at most four other coding units.

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

The prediction unit may be split in the form of at least one square or rectangle having the same size in one coding unit, or the prediction unit of any one of the prediction units split in one coding unit is different from one another. It may be divided to have a different shape and / or size than the unit.

When generating the prediction unit that performs the intra prediction based on the coding unit, when the prediction unit is not the minimum coding unit, the intra prediction may be performed without splitting into a plurality of prediction units NxN.

The

predictors

120 and 125 may include an inter predictor 120 that performs inter prediction and an intra predictor 125 that performs intra prediction. Whether to use inter prediction or intra prediction on the prediction unit may be determined, and specific information (eg, an intra prediction mode, a motion vector, a reference picture, etc.) according to each prediction method may be determined. In this case, the processing unit in which the prediction is performed may differ from the processing unit in which the prediction method and the details are determined. For example, the method of prediction and the prediction mode may be determined in the prediction unit, and the prediction may be performed in the transform unit. The residual value (residual block) between the generated prediction block and the original block may be input to the transformer 130. In addition, prediction mode information and motion vector information used for prediction may be encoded by the entropy encoder 165 together with the residual value and transmitted to the decoder. When a specific encoding mode is used, the original block may be encoded as it is and transmitted to the decoder without generating the prediction block through the

prediction units

120 and 125.

The inter prediction unit 120 may predict the prediction unit based on the information of at least one of the previous picture or the next picture of the current picture. In some cases, the inter prediction unit 120 may predict the prediction unit based on the information of the partial region in which the encoding is completed in the current picture. You can also predict units. The inter predictor 120 may include a reference picture interpolator, a motion predictor, and a motion compensator.

The reference picture interpolator may receive reference picture information from the memory 155 and generate pixel information of an integer pixel or less in the reference picture. In the case of luminance pixels, 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 motion predictor 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 full search-based block matching algorithm (FBMA), three step search (TSS), and 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 motion prediction unit may predict the current prediction unit by using a different motion prediction method. As the motion prediction method, various methods such as a skip method, a merge method, an advanced motion vector prediction (AMVP) method, an intra block copy method, and the like may be used.

The intra predictor 125 may generate a prediction unit based on reference pixel information around the current block, which is pixel information in the current picture. If the neighboring block of the current prediction unit is a block that has performed inter prediction, and the reference pixel is a pixel that has performed inter prediction, the reference pixel of the block that has performed intra prediction around the reference pixel included in the block where the inter prediction has been performed Can be used as a substitute for information. That is, when the reference pixel is not available, the unavailable reference pixel information may be replaced with at least one reference pixel among the available reference pixels.

In intra prediction, a prediction mode may have a directional prediction mode using reference pixel information according to a prediction direction, and a non-directional mode using no directional information when performing prediction. The mode for predicting the luminance information and the mode for predicting the color difference information may be different, and the intra prediction mode information or the predicted luminance signal information used for predicting the luminance information may be utilized to predict the color difference information.

When performing intra prediction, if the size of the prediction unit and the size of the transform unit are the same, the intra prediction on the prediction unit is performed based on the pixels on the left of the prediction unit, the pixels on the upper left, and the pixels on the top. Can be performed. However, when performing intra prediction, if the size of the prediction unit is different from that of the transform unit, intra prediction may be performed using a reference pixel based on the transform unit. In addition, intra prediction using NxN division may be used only for a minimum coding unit.

The intra prediction method may generate a prediction block after applying an adaptive intra smoothing (AIS) filter to a reference pixel according to a prediction mode. The type of AIS filter applied to the reference pixel may be different. In order to perform the intra prediction method, the intra prediction mode of the current prediction unit may be predicted from the intra prediction mode of the prediction unit existing around the current prediction unit. When the prediction mode of the current prediction unit is predicted by using the mode information predicted from the neighboring prediction unit, if the intra prediction mode of the current prediction unit and the neighboring prediction unit is the same, the current prediction unit and the neighboring prediction unit using the predetermined flag information If the prediction modes of the current prediction unit and the neighboring prediction unit are different, entropy encoding may be performed to encode the prediction mode information of the current block.

Also, a residual block may include a prediction unit performing prediction based on the prediction units generated by the

prediction units

120 and 125 and residual information including residual information that is a difference from an original block of the prediction unit. The generated residual block may be input to the transformer 130.

The transform unit 130 converts the residual block including residual information of the original block and the prediction unit generated by the

prediction units

120 and 125 into a discrete cosine transform (DCT), a discrete sine transform (DST), and a KLT. You can convert using the same conversion method. Whether to apply DCT, DST, or KLT to transform the residual block may be determined based on intra prediction mode information of the prediction unit used to generate the residual block.

The quantization unit 135 may quantize the values converted by the transformer 130 into the frequency domain. The quantization coefficient may change depending on the block or the importance of the image. The value calculated by the quantization unit 135 may be provided to the inverse quantization unit 140 and the reordering unit 160.

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

The reordering unit 160 may change the two-dimensional block shape coefficients into a one-dimensional vector form through a coefficient scanning method. For example, the reordering unit 160 may scan from 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 unit and the intra prediction mode, a vertical scan that scans two-dimensional block shape coefficients in a column direction instead of a zig-zag scan may be used, and a horizontal scan that scans two-dimensional block shape coefficients in a row direction. That is, according to the size of the transform unit and the intra prediction mode, it is possible to determine which scan method among the zig-zag scan, the vertical scan, and the horizontal scan is used.

The entropy encoder 165 may perform entropy encoding based on the values calculated by the reordering unit 160. 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 encoder 165 receives residual value coefficient information, block type information, prediction mode information, partition unit information, prediction unit information, transmission unit information, and motion of the coding unit from the reordering unit 160 and the

prediction units

120 and 125. Various information such as vector information, reference frame information, interpolation information of a block, and filtering information can be encoded.

The entropy encoder 165 may entropy encode a coefficient value of a coding unit input from the reordering unit 160.

The inverse quantizer 140 and the inverse transformer 145 inverse quantize the quantized values in the quantizer 135 and inversely transform the transformed values in the transformer 130. The residual value generated by the inverse quantizer 140 and the inverse transformer 145 is reconstructed by combining the prediction units predicted by the motion estimator, the motion compensator, and the intra predictor included in the

predictors

120 and 125. You can create a Reconstructed Block.

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

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

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

Adaptive Loop Filtering (ALF) may be performed based on a value obtained by comparing the filtered reconstructed image with the original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the group may be determined and filtering may be performed for each group. For information related to whether to apply ALF, a luminance signal may be transmitted for each coding unit (CU), and the shape and filter coefficient of an ALF filter to be applied may vary according to each block. In addition, regardless of the characteristics of the block to be applied, the same type (fixed form) of the ALF filter may be applied.

The memory 155 may store the reconstructed block or picture calculated by the filter unit 150, and the stored reconstructed block or picture may be provided to the

predictors

120 and 125 when performing inter prediction.

Referring to FIG. 2, the image decoder 200 includes an entropy decoder 210, a reordering unit 215, an inverse quantizer 220, an inverse transformer 225, a

predictor

230, 235, and a filter unit ( 240, a memory 245 may be included.

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

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

The entropy decoder 210 may decode information related to intra prediction and inter prediction performed by the encoder.

The reordering unit 215 may reorder the entropy decoded bitstream by the entropy decoding unit 210 based on a method of rearranging the bitstream. 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 unit 215 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 unit 220 may perform inverse quantization based on the quantization parameter provided by the encoder and the coefficient values of the rearranged block.

The inverse transform unit 225 may perform an inverse transform, i.e., an inverse DCT, an inverse DST, and an inverse KLT, for a quantization result performed by the image encoder, that is, a DCT, DST, and KLT. Inverse transformation may be performed based on a transmission unit determined by the image encoder. The inverse transform unit 225 of the image decoder may selectively perform a transform scheme (eg, DCT, DST, KLT) according to a plurality of pieces of information such as a prediction method, a size of a current block, and a prediction direction.

The

prediction units

230 and 235 may generate the prediction block based on the prediction block generation related information provided by the entropy decoder 210 and previously decoded blocks or picture information provided by the memory 245.

As described above, when performing the intra prediction in the same manner as the operation in the image encoder, when the size of the prediction unit and the size of the transformation unit are the same, the pixel present on the left side, the pixel present on the upper left side, and the upper part exist Intra prediction is performed on a prediction unit based on a pixel, but when intra prediction is performed, when the size of the prediction unit and the size of the transformation unit are different, intra prediction may be performed using a reference pixel based on the transformation unit. Can be. In addition, intra prediction using NxN division may be used only for a minimum coding unit.

The

predictors

230 and 235 may include a prediction unit determiner, an inter predictor, and an intra predictor. The prediction unit determiner receives various information such as prediction unit information input from the entropy decoder 210, prediction mode information of the intra prediction method, and motion prediction related information of the inter prediction method, and distinguishes the prediction unit from the current coding unit, and predicts It may be determined whether the unit performs inter prediction or intra prediction. The inter prediction unit 230 predicts the current prediction based on information included in at least one of a previous picture or a subsequent picture of the current picture including the current prediction unit by using information required for inter prediction of the current prediction unit provided by the image encoder. Inter prediction may be performed on a unit. Alternatively, inter prediction may be performed based on information of some regions pre-restored in the current picture including the current prediction unit.

In order to perform inter prediction, a motion prediction method of a prediction unit included in a coding unit based on a coding unit includes a skip mode, a merge mode, an AMVP mode, and an intra block copy mode. It can be determined whether or not it is a method.

The intra predictor 235 may generate a prediction block based on pixel information in the current picture. When the prediction unit is a prediction unit that has performed intra prediction, intra prediction may be performed based on intra prediction mode information of the prediction unit provided by the image encoder. The intra predictor 235 may include an adaptive intra smoothing (AIS) filter, a reference pixel interpolator, and a DC filter. The AIS filter is a part of filtering the reference pixel of the current block and determines whether to apply the filter according to the prediction mode of the current prediction unit. AIS filtering may be performed on the reference pixel of the current block by using the prediction mode and the AIS filter information of the prediction unit provided by the image encoder. If the prediction mode of the current block is a mode that does not perform AIS filtering, the AIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on a pixel value interpolating the reference pixel, the reference pixel interpolator may generate a reference pixel having an integer value or less by interpolating the reference pixel. If the prediction mode of the current prediction unit is a prediction mode for generating a prediction block without interpolating the reference pixel, the reference pixel may not be interpolated. The DC filter may generate the prediction block through filtering when the prediction mode of the current block is the DC mode.

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

Information about whether a deblocking filter is applied to a corresponding block or picture, and when the deblocking filter is applied to the corresponding block or picture, may be provided with information about whether a strong filter or a weak filter is applied. In the deblocking filter of the image decoder, the deblocking filter related information provided by the image encoder may be provided and the deblocking filtering of the corresponding block may be performed in the image decoder.

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 ALF may be applied to a coding unit based on ALF application information, ALF coefficient information, and the like provided from the encoder. Such ALF information may be provided included in a specific parameter set.

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

As described above, in the embodiment of the present invention, a coding unit is used as a coding unit for convenience of description, but may also be a unit for performing decoding as well as encoding.

In addition, the current block represents a block to be encoded / decoded, and according to the encoding / decoding step, a coding tree block (or a coding tree unit), an encoding block (or a coding unit), a transform block (or a transform unit), or a prediction block. (Or prediction unit) or the like. In the present specification, 'unit' may indicate a basic unit for performing a specific encoding / decoding process, and 'block' may indicate a sample array having a predetermined size. Unless otherwise specified, 'block' and 'unit' may be used interchangeably. For example, in the embodiments described below, the coding block (coding block) and the coding unit (coding unit) may be understood to have the same meaning.

One picture may be divided into square or non-square basic blocks and encoded / decoded. In this case, the basic block may be referred to as a coding tree unit. A coding tree unit may be defined as the largest coding unit allowed in a sequence or slice. Information regarding whether the coding tree unit is square or non-square or the size of the coding tree unit may be signaled through a sequence parameter set, a picture parameter set or a slice header. The coding tree unit may be divided into smaller sized partitions. In this case, when the partition generated by dividing the coding tree unit is called depth 1, the partition generated by dividing the partition having depth 1 may be defined as depth 2. That is, a partition generated by dividing a partition that is a depth k in a coding tree unit may be defined as having a depth k + 1.

A partition of any size generated as the coding tree unit is split may be defined as a coding unit. The coding unit may be split recursively or split into basic units for performing prediction, quantization, transform, or in-loop filtering. For example, an arbitrary size partition generated as a coding unit is divided may be defined as a coding unit or a transform unit or a prediction unit that is a basic unit for performing prediction, quantization, transform, or in-loop filtering.

Alternatively, when the coding block is determined, a prediction block having the same size as the coding block or a size smaller than the coding block may be determined through prediction division of the coding block. Predictive partitioning of a coding block may be performed by a partition mode (Part_mode) indicating a partition type of a coding block. The size or shape of the prediction block may be determined according to the partition mode of the coding block. The division type of the coding block may be determined through information specifying any one of partition candidates. In this case, the partition candidates available to the coding block may include an asymmetric partition shape (eg, nLx2N, nRx2N, 2NxnU, 2NxnD) according to the size, shape, or coding mode of the coding block. As an example, a partition candidate available to a coding block may be determined according to an encoding mode of the current block. As an example, FIG. 3 is a diagram illustrating a partition mode that may be applied to a coding block when the coding block is encoded by inter prediction.

When the coding block is encoded by inter prediction, any one of eight partition modes may be applied to the coding block, as shown in the example illustrated in FIG. 3.

On the other hand, when a coding block is encoded by intra prediction, partition mode PART_2Nx2N or PART_NxN may be applied to the coding block.

PART_NxN may be applied when the coding block has a minimum size. Here, the minimum size of the coding block may be predefined in the encoder and the decoder. Alternatively, information about the minimum size of the coding block may be signaled through the bitstream. As an example, the minimum size of the coding block is signaled through the slice header, and accordingly, the minimum size of the coding block may be defined for each slice.

As another example, the partition candidates available to the coding block may be determined differently according to at least one of the size or shape of the coding block. For example, the number or type of partition candidates that a coding block may use may be differently determined according to at least one of the size or shape of the coding block.

Alternatively, the type or number of asymmetric partition candidates among partition candidates available to the coding block may be limited according to the size or shape of the coding block. As an example, the number or type of asymmetric partition candidates that a coding block may use may be differently determined according to at least one of the size or shape of the coding block.

In general, the size of the prediction block may have a size of 64x64 to 4x4. However, when the coding block is encoded by inter prediction, when the motion compensation is performed, the prediction block may not have a 4x4 size in order to reduce the memory bandwidth.

The field of view of the camera limits the field of view of the video taken by the camera. In order to overcome this problem, a plurality of cameras may be used to capture an image, and the captured image may be stitched to configure one video or one bitstream. For example, FIGS. 4 to 6 illustrate an example of capturing up, down, left, and right sides simultaneously using a plurality of cameras. As such, a video generated by stitching a plurality of videos may be referred to as a panoramic video. In particular, an image having a degree of freedom based on a predetermined central axis may be referred to as 360 degree video. For example, the 360 degree video may be an image having rotation degrees of freedom for at least one of Yaw, Roll, and Pitch.

The camera structure (or camera arrangement) for acquiring 360-degree video has a circular arrangement, as in the example shown in FIG. 4, or a one-dimensional vertical / horizontal arrangement, as in the example shown in FIG. 5A. Alternatively, as in the example shown in FIG. 5B, a two-dimensional arrangement (that is, a mixture of vertical and horizontal arrangements) may be used. Alternatively, as shown in FIG. 6, a spherical device may be equipped with a plurality of cameras.

An embodiment to be described later will be described based on 360 degree video, but it will be included in the technical scope of the present invention to apply the embodiment to be described later to a panoramic video which is not a 360 degree video.

FIG. 7 is a block diagram of a 360 degree video data generating apparatus and a 360 degree video playing apparatus, and FIG. 8 is a flowchart illustrating operations of the 360 degree video data generating apparatus and 360 degree video playing apparatus.

Referring to FIG. 7, the 360-degree video data generating apparatus includes a projection unit 710, a frame packing unit 720, an encoding unit 730, and a transmission unit 740. It may include a parser 750, a decoder 760, a frame depacking unit 770, and a reverse projection unit 780. The encoding unit and the decoding unit illustrated in FIG. 7 may correspond to the image encoding apparatus and the image decoding apparatus illustrated in FIGS. 1 and 2, respectively.

The data generating apparatus may determine a projection conversion technique of the 360 degree image generated by stitching the images photographed by the plurality of cameras. The projection unit 710 may determine the 3D form of the 360 degree video according to the determined projection transformation technique, and project the 360 degree video onto the 2D plane according to the determined 3D form (S801). Here, the projection transformation technique may represent an aspect in which the 360 degree video is developed on the 3D form and the 2D plane of the 360 degree video. The 360-degree image may be approximated as having a form of sphere, cylinder, cube, octahedron or icosahedron in 3D space, according to a projection transformation technique. According to a projection transformation technique, an image generated by projecting a 360 degree video onto a 2D plane may be referred to as a 360 degree projection image.

The 360 degree projection image may be composed of at least one face according to a projection conversion technique. For example, when the 360 degree video is approximated as a polyhedron, each face constituting the polyhedron may be defined as a face. Alternatively, the specific surface constituting the polyhedron may be divided into a plurality of regions, and the divided regions may be set to form separate faces. The 360 degree video approximated in the shape of a sphere may have a plurality of faces according to the projection transformation technique.

In order to increase the encoding / decoding efficiency for the 360 degree video, the frame packing may be performed in the frame packing unit 720 (S802). Frame packing may include at least one of reordering, resizing, warping, rotating, or flipping a face. Through frame packing, the 360-degree projection image may be converted into a form (eg, a rectangle) having high encoding / decoding efficiency, or discontinuity data between faces may be removed. Frame packing may also be referred to as frame reordering or region-wise packing. Frame packing may be selectively performed to improve encoding / decoding efficiency for the 360 degree projection image.

The encoding unit 730 may perform encoding on the 360 degree projection image or the 360 degree projection image on which the frame packing is performed (S803). In this case, the encoder 730 may encode information indicating a projection transformation technique for the 360 degree video. Here, the information indicating the projection transformation technique may be index information indicating any one of the plurality of projection transformation techniques.

In addition, the encoder 730 may encode information related to frame packing for the 360 degree video. Here, the information related to the frame packing may include at least one of whether frame packing is performed, the number of faces, the position of the face, the size of the face, the shape of the face, or the rotation information of the face.

The transmitter 740 may encapsulate and transmit the encapsulated data to the player terminal (S804).

The file parsing unit 750 may parse the file received from the content providing device (S805). The decoding unit 760 may decode the 360 degree projection image using the parsed data (S806).

When frame packing is performed on the 360-degree projection image, the frame depacking unit 760 may perform frame depacking (Region-wise depacking) opposite to the frame packing performed on the content providing side (S807). Frame depacking may be to restore the frame packed 360 degree projection image to before frame packing is performed. For example, frame depacking may be to reverse the reordering, resizing, warping, rotation, or flipping of a face performed in the data generating device.

The inverse projection unit 780 may inversely project the 360 degree projection image on the 2D plane in a 3D form according to a projection transformation technique of the 360 degree video (S808).

Projection transformation techniques include isotropic rectangular projection (ERP), cubic projection transformation (Cube Map Projection, CMP), isosahedral projection transformation (ISP), octahedron projection transformation (Octahedron Projection, OHP), truncated pyramid It may include at least one of a projection transform (Truncated Pyramid Projection (TPP)), a Sharpe Segment Projection (SSP), an Equatorial cylindrical projection (ECP), or a rotated sphere projection (RSP).

9 illustrates a 2D projection method using an isotonic method.

The isotropic method is a method of projecting a pixel corresponding to a sphere into a rectangle having an aspect ratio of N: 1, which is the most widely used 2D transformation technique. Here, N may be two, and may be two or less or two or more real numbers. With isotonicity, the actual length of the sphere corresponding to the unit length on the 2D plane becomes shorter toward the pole of the sphere. For example, the coordinates of both ends of the unit length on the 2D plane may correspond to a distance difference of 20 cm near the equator of the sphere, while corresponding to a distance difference of 5 cm near the pole of the sphere. As a result, the isotropic rectangular method has a disadvantage in that the image distortion is large and coding efficiency is lowered near the poles of the sphere.

10 illustrates a 2D projection method using a cube projection technique.

The cube projection technique involves approximating a 360-degree video to a cube and then converting the cube into 2D. When projecting a 360 degree video onto a cube, one face (or plane) is configured to adjoin four faces. The continuity between the faces is high, and the cube projection method has an advantage of higher coding efficiency than the isotonic diagram method. After projection-converting the 360-degree video to 2D, encoding / decoding may be performed by rearranging the 2D projection-converted image into a quadrangle form.

11 illustrates a 2D projection method using a icosahedron projection technique.

The icosahedron projection technique is a method of approximating a 360 degree video to an icosahedron and converting it into 2D. The icosahedral projection technique is characterized by strong continuity between faces. As in the example shown in FIG. 11, encoding / decoding may be performed by rearranging faces in the 2D projection-converted image.

12 illustrates a 2D projection method using an octahedron projection technique.

The octahedral projection method is a method of approximating a 360 degree video to an octahedron and converting it into 2D. The octahedral projection technique is characterized by strong continuity between faces. As in the example shown in FIG. 12, encoding / decoding may be performed by rearranging faces in the 2D projection-converted image.

The truncated pyramid projection technique is a method of approximating a 360 degree video to a truncated pyramid and converting it into 2D. Under a truncated pyramid projection technique, frame packing may be performed such that the face at a particular point in time has a different size than the neighboring face. For example, as in the example shown in FIG. 13, the front face may have a larger size than the side face and the back face. When the truncated pyramid projection technique is used, image data of a specific viewpoint is large, and thus the encoding / decoding efficiency of the specific viewpoint is higher than that of other viewpoints.

SSP is a method of dividing a spherical 360-degree video into high- and mid-latitude regions and performing 2D projection transformation. Specifically, when the SSP is followed, the two high latitude regions of the sphere may be mapped to two circles on the 2D plane, and the mid-latitude regions of the sphere may be mapped to the rectangles on the 2D plane like the ERP.

ECP converts spherical 360-degree video into cylindrical form and then converts cylindrical 360-degree video into 2D projection. Specifically, when the ECP is followed, the top and bottom of the cylinder can be mapped to two circles on the 2D plane, and the body of the cylinder can be mapped to the rectangle on the 2D plane.

RSP represents a method of converting a spherical 360 degree video of a tennis ball into two ellipses on a 2D plane.

Each sample of the 360 degree projection image may be identified by face 2D coordinates. The face 2D coordinates may include an index f for identifying the face where the sample is located, a coordinate (m, n) representing a sample grid in a 360 degree projection image.

Through the transformation between the face 2D coordinates and the 3D coordinates, 2D projection transformation and image rendering may be performed. As an example, FIG. 14 is a diagram illustrating a conversion between a face 2D coordinate and a 3D coordinate. When a 360 degree projection image is generated based on the ERP, conversion between three-dimensional coordinates (x, y, z) and face 2D coordinates (f, m, n) may be performed using Equations 1 to 3 below. have.

The current picture in the 360 degree projection image may include at least one or more faces. In this case, the number of faces may be 1, 2, 3, 4 or more natural numbers, depending on the projection method. Among the face 2D coordinates, f may be set to a value equal to or smaller than the number of faces. The current picture may include at least one or more faces having the same temporal order or output order (POC).

Alternatively, the number of faces constituting the current picture may be fixed or variable. For example, the number of faces constituting the current picture may be limited not to exceed a predetermined threshold. Here, the threshold value may be a fixed value previously promised by the encoder and the decoder. Alternatively, information about the maximum number of faces constituting one picture may be signaled through a bitstream.

The faces may be determined by partitioning the current picture using at least one of a horizontal line, a vertical line, or a diagonal line, depending on the projection method.

Each face within a picture may be assigned an index to identify each face. Each face may be parallelized, such as a tile or a slice. Accordingly, when performing intra prediction or inter prediction of the current block, neighboring blocks belonging to different faces from the current block may be determined to be unavailable.

Paces (or non-parallel regions) where parallelism is not allowed may be defined, or faces with interdependencies may be defined. For example, faces that do not allow parallel processing or faces with interdependencies may be coded / decoded sequentially instead of being parallel coded / decoded. Accordingly, even neighboring blocks belonging to different faces from the current block may be determined to be available for intra prediction or inter prediction of the current block, depending on whether parallel processing between faces or dependencies is possible.

In the embodiments described below, although the embodiments are described based on the specific projection method, the embodiments described below may be extended to the projection methods other than the specific projection method.

By performing frame packing in which consecutive faces are disposed adjacent to each other in the 3D space, the encoding / decoding efficiency of the 360 degree projection image may be increased.

When the frame packing is performed on the 360 degree projection image to which the OHP technique is applied, the frame packing may be performed such that a continuous face is disposed adjacent to each other in the horizontal and horizontal directions. For example, as in the example shown in FIG. 15, the top faces 2, 3, and 4 positioned at the top of the 2D development view may be arranged to have mutual continuity. At this time, in order to make the upper faces 2, 3 and 4 have continuity, the upper faces 2 and 4 of the upper and lower faces 3 may be rotated. Thereafter, the two or more faces may be mutually continuous, thereby placing at least some of the remaining faces. For example, as shown in the example shown in FIG. 15, the bottom faces 5 and 6 positioned at the bottom on the 2D development view may be arranged to have mutual continuity, and the bottom faces 7 and 8 may be arranged to have mutual continuity.

As another example, frame packing may be performed such that a face continuous in a vertical direction in a 3D space is disposed adjacent to each other. For example, as shown in FIG. 16, faces 2 and 6 having continuity in 3D space may be arranged to have continuity. In addition, the

face

1 and 3 which have the continuity of the face 2 and the horizontal direction can be arrange | positioned to the left and right of the face 2, and the

face

5 and 7 which have the continuity of the face 6 and the horizontal direction can be arrange | positioned to the left and right of the face 6.

In order to convert a 360-degree projection image into a quadrangular picture, a triangular face located at the left, right, top or bottom boundary of the image may be divided into two parts. For example, as in the example illustrated in FIG. 15, the face 7 may be divided into two regions, and each divided region may be disposed on the left and right sides of the image. Alternatively, as in the example illustrated in FIG. 16, faces 4 and 8 may be divided into two regions, and each divided region may be disposed at the top and bottom of the image.

Faces continuous in the left and right or horizontal directions in 3D space or faces continuous in the vertical and vertical directions in 3D space may be defined as symmetrical faces. For example, in the example illustrated in FIG. 16, face 2 and face 6 may be defined as vertically symmetrical faces.

Even if frame packing is performed, cases where neighboring faces do not have continuity in 3D space may occur. For example, in the 360-degree projection image based on the OHP technique shown in FIG. 15, Face 5 in the frame-packed 360-degree projection image is adjacent to Face 7, whereas in the 360-degree image restored to the octahedron, Face 5 and Face 7 are You can see that you cannot neighbor each other. As described above, boundaries between faces that are adjacent to each other in the frame-packed 360 degree projection image but do not have continuity in the 3D reconstructed 360 degree image may be defined as discontinuous face boundaries.

On the other hand, in the example of FIG. 15, it can be seen that Face 3 and Face 2 neighboring each other in the frame-packed 360-degree projection image also neighbor each other in the 360-degree image restored to the octahedron. As such, the boundary between faces having continuity in both the frame-packed 360 degree projection image and the 3D reconstructed image may be defined as a continuous face boundary.

The frame-packed 360 degree projection image may be divided into a plurality of regions by a predetermined boundary represented by a vertical line, a horizontal line, or an angular line having a predetermined angle. . In this case, the predetermined boundary may be at least one of a discontinuous face boundary, a continuous face boundary determined based on the continuity of the image, or a straight line extending from the discontinuous face boundary or the continuous face boundary toward a predetermined direction (eg, vertical or horizontal direction). Can be.

As an example, the frame packed image shown in FIG. 15 may include a discrete face boundary between 7-R and face 5, a discrete face boundary between face 6 and face 2, a discrete face boundary between face 4 and face 1 or face 1. And divided into two or more regions based on at least one of the discontinuous face boundaries between face 8.

In addition, the frame packed image shown in FIG. 16 has a discontinuous face boundary between faces 8-L and 4-R and faces 1 and 5, and a discontinuous face boundary between

faces

3 and 7 and faces 8-R and 4-L. It may be divided into two or more regions based on at least one of the.

Each divided area may consist of one or more faces.

According to the projection transformation technique or the frame packing method, segmentation related information of the 360 degree projection image may be predefined. The segmentation related information may include at least one of a position, a number, an interval, and an angle of a predetermined boundary for dividing the 360 degree projection image. As another example, the segmentation related information of the 360 degree projection image may be signaled through the bitstream.

The 360 degree projection image may be encoded / decoded in units of regions divided by a predetermined boundary. In this case, encoding / decoding may be performed with interdependencies between regions, or encoding / decoding may be performed independently without interdependencies between regions. In this case, the dependency may indicate that the encoding / decoding parameter in the predetermined region is determined by referring to the encoding / decoding parameter of the previously encoded / decoded region. As an example, encoding / decoding of a predetermined region may include reconstructed texture data (eg, pixel value, residual value, or prediction value) of the region previously encoded / decoded, intra prediction related information (eg, mode candidate list, intra prediction). Mode or splitting technique), inter prediction related information (eg, a motion vector, a reference picture index, a prediction direction, a reference picture list, or a motion candidate list), a quantization parameter, or a transformation technique. .

If there is interdependence between regions, information indicating inter-region dependencies may be signaled through the bitstream. For example, at least one of a flag indicating whether a predetermined region has a dependency on another region, an index for identifying another region having a dependency on the predetermined region, or information indicating symmetry between faces may be signaled through the bitstream.

Alternatively, the encoding parameter of the current face may be derived from the adjacent face according to whether or not it has symmetry with the adjacent face.

For example, when a particular object in the 360 degree image is in contact with both faces, the motion information between the two faces may be expected to have a large correlation. Accordingly, the motion information of the block belonging to the predetermined face can be derived from the face symmetrical with the predetermined face. Here, the motion information may include at least one of a motion vector, a reference picture index, or prediction direction information. In detail, the motion information of a block belonging to a predetermined face may be derived from a block belonging to a face that is left or right or up and down symmetrical while having a continuous face boundary.

For example, in the example illustrated in FIG. 15, motion information of a block belonging to face 3 may be derived from motion information of a block belonging to face 2, which is a symmetrical face. In the example shown in FIG. 16, motion information of a block belonging to face 2 may be derived from motion information of a block belonging to face 6, which is a vertically symmetrical face.

In this case, when the rotation angles between the faces are different, the motion vector of the block belonging to the predetermined face may be obtained by compensating the rotation angle difference to the motion vector of the block belonging to the symmetrical face. For example, in the example shown in FIG. 15, the motion vector of the block belonging to face 3 may be derived based on a value of the angular rotation of the motion vector of the block belonging to face 2.

A motion vector of a block belonging to a predetermined face may be derived in the same manner as a motion vector of a block belonging to a symmetrical face, or may be derived by multiplying a motion vector of a block belonging to a symmetrical face by scaling, offsetting, or weighting. When encoding / decoding is performed using a symmetrical face, information specifying a position of a face having a dependency may not be signaled separately.

Intra / intra prediction of a block belonging to a given face may be performed using a sample belonging to a face different from the given face. For example, motion compensation of the current block may be performed using a reference block belonging to a face different from the current face in the reference picture (that is, a face different from the current face and the face index). However, if there is a discontinuous face boundary between the current face and the other face, the relationship between the other face and the current face may be very low. Accordingly, in performing intra / inter prediction of a block belonging to a predetermined face, continuity of a face boundary may be considered. For example, in encoding / decoding a 360 degree projection image, motion prediction, motion compensation, or intra prediction may be limited based on continuity of a face boundary.

In detail, the motion compensation for the current block may be limited such that the motion compensation is not performed through the face located beyond the discontinuous face boundary from the current face including the current block. That is, a block belonging to a face located beyond the discontinuous face boundary from the co-located face corresponding to the current face in the reference picture may be restricted from being used as a reference block of the current block. Accordingly, the motion vector of the current block may also be restricted so as not to point to a face located beyond the discrete face boundary from the current face.

On the other hand, a block belonging to a face located beyond the continuous face boundary from the current face may be used as a reference block of the current block without limitation.

For convenience of explanation, a face located beyond the discontinuous boundary from the current face will be referred to as a discontinuous face.

First, referring to FIG. 17, it may be determined whether motion compensation may be performed using a discontinuous face (S1701).

The image encoding apparatus may encode information indicating whether motion compensation using a discontinuous face is limited to the bitstream. In detail, the apparatus for encoding an image may determine whether to use a discontinuous face during motion compensation by comparing cost values when the motion compensation using the discontinuous face is limited and the motion compensation using the discontinuous face. have.

As an example, isDisConti_MC_enabled_flag may be a syntax indicating whether motion compensation is limited through discontinuous paces. Decoding may decode isDisConti_MC_enabled_flag from the bitstream, and determine whether motion compensation through discontinuous faces is limited based on the value of the decoded isDisConti_MC_enabled_flag. For example, an isDisConti_MC_enabled_flag of 0 (or 1) may indicate that motion compensation using a discontinuous face is limited, and an isDisConti_MC_enabled_flag of 1 (or 0) may indicate that motion compensation using a discontinuous face is allowed. The information may be encoded in a sequence unit, picture unit, slice unit, face unit, or block unit.

As another example, for each face, information indicating a referenceable face may be signaled. For example, a syntax inter_face_idc [i] [j] indicating whether a face of index i can be referred to from a face of index i may be signaled. A value of 0 (or 1) of inter_face_idc [i] [j] indicates that blocks included in face i cannot refer to blocks included in face j, and a value of inter_face_idc [i] [j] is 1 (Or 0) indicates that blocks included in face i may perform motion compensation with reference to blocks included in face j. Here, face j may be an adjacent face of face i, having a discontinuous face boundary with face i. Alternatively, when face i is adjacent to a plurality of faces, inter_face_idc information may be signaled for each of the plurality of faces. Alternatively, inter_face_idc information may be signaled for a face that is not adjacent to face i.

Next, motion information on the current block may be obtained (S1702).

The motion information of the current block may be derived from a block included in a face associated with the current face including the current block. For example, the motion information of the current block may be derived from a block included in a face that is symmetrical with the current face. The reference block in the symmetrical face used to derive the motion information of the current block may have the same position as the current block in the symmetrical face or a position symmetrical with the current block based on the symmetry point of the current face and the symmetrical face.

Alternatively, it is also possible to derive the motion information of the current block from the block of the predefined position in the symmetrical face. The predefined position is a block adjacent to the boundary of the symmetrical face, and may be a block located on the same horizontal line as the current block or on the same vertical line as the current block.

As another example, the motion information of the current block may be derived based on the merge or the AMVP mode.

For example, under the merge mode, the motion information of the current block may be derived in the same manner as the motion information of the merge candidate specified by the merge index among the plurality of merge candidates. Here, the merge candidate may be derived from at least one of a neighboring block and a collocated block neighboring the current block. Here, the neighboring block may include at least one of neighboring blocks on the left side, the upper side, the upper left side, the upper right side, and the lower left side of the current block.

Or, under the AMVP mode, the reference picture index and the motion prediction direction of the current block may be determined based on the information signaled through the bitstream. The motion vector of the current block may be derived based on a motion vector prediction value specified by a prediction index (or a prediction flag) among a plurality of motion vector prediction candidates. For example, the motion vector of the current block may be derived based on the motion prediction value and the motion vector difference signaled through the bitstream. The motion vector prediction candidate may be derived from at least one of a neighboring block and a collocated block neighboring the current block. Here, the neighboring block may include at least one of neighboring blocks on the left side, the upper side, the upper left side, the upper right side, and the lower left side of the current block.

In deriving the motion information of the current block, the neighboring block belonging to the face located beyond the discontinuous boundary from the current face including the current block may be determined to be unavailable as a motion vector candidate for the current block. Here, the motion vector candidate may indicate a merge candidate under a merge mode or a motion prediction candidate under an AMVP mode. An unavailable motion vector candidate may be replaced with a block included in a face that is continuous with the current face in 3D space.

Thereafter, based on the motion information of the current block, a prediction sample for the current block may be obtained (S1703), and the current block may be reconstructed using the prediction sample of the current block (S1704).

The reconstructed picture may be stored in a reconstructed picture buffer (DPB) and used as a reference picture. In this case, the picture unit stored in the decoded picture buffer may be adaptively determined according to whether motion compensation for the discontinuous face is limited. For example, when it is determined whether motion compensation for discontinuous faces is limited in units of sequences, the reconstructed picture buffer may be adaptively used according to the determination in units of sequences.

When motion compensation for a discontinuous face is limited, only a part of the entire picture, not the entire picture, may be stored in the reconstructed picture buffer. For example, as shown in the example shown in FIG. 17, a rectangular sub picture including a continuous face boundary between

faces

5 and 6 and a continuous face boundary between

faces

2, 3, and 4 is stored in the reconstructed picture buffer. Can be. On the other hand, a rectangular sub picture including phases 1-R, 8, and 7-L may not be stored in the reconstructed picture buffer.

Instead of storing the entire picture in the reconstructed picture buffer, only a portion of the picture is stored, thereby reducing the size of the reconstructed picture buffer. For blocks belonging to regions not stored in the reconstructed picture buffer, inter prediction may be set not to be allowed, or only inter prediction in which a reference picture is a current picture is allowed.

Unlike the illustrated example, when motion compensation for discontinuous faces is allowed, the entire picture can be stored in the reconstructed picture buffer.

In performing intra prediction of the current block, the continuity of the face boundary may be considered. For example, a sample belonging to a face located beyond a discontinuous boundary from a current face including a current block may be determined to be unavailable as a reference sample for intra prediction of the current block. An unavailable sample may be replaced with a sample included in a face that is continuous with the current face in 3D space.

Although the above-described embodiments are described based on a series of steps or flowcharts, this does not limit the time-series order of the invention and may be performed simultaneously or in a different order as necessary. In addition, in the above-described embodiment, each component (for example, a unit, a module, etc.) constituting the block diagram may be implemented as a hardware device or software, and a plurality of components are combined into one hardware device or software. It may be implemented. The above-described embodiments may be implemented in the form of program instructions that may be executed by various computer components, and may be recorded in a computer-readable recording medium. The computer-readable recording medium may include program instructions, data files, data structures, etc. alone or in combination. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks and magnetic tape, optical recording media such as CD-ROMs, DVDs, and magneto-optical media such as floptical disks. media), and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. The hardware device may be configured to operate as one or more software modules to perform the process according to the invention, and vice versa.

The present invention can be applied to an electronic device capable of encoding / decoding an image.

Claims

Decoding, from the bitstream, reference face related information;

Based on the information, determining whether a face different from the current face including the current block is available as a reference face;

Obtaining motion information for the current block; And

And performing motion compensation on the current block based on the determination and the motion information.
According to claim 1,

And the reference face related information is information indicating whether a face located beyond the discontinuous face boundary from the current face can be used as the reference face.
The method of claim 2,

Reconstructing the current block by using the prediction sample obtained through the motion compensation; And

Storing the reconstructed current picture in a reconstructed picture buffer.

When the reference face related information indicates that a face located beyond the discontinuous face boundary from the current face cannot be used as the reference face, only a part of the current picture is stored in the reconstructed picture buffer. A video decoding method.
The method of claim 2,

The discontinuous face boundary represents a boundary between faces which are adjacent to each other in a 2D plane but not adjacent to each other in 3D space.
According to claim 1,

The reference face related information is information indicating whether or not a face having an index different from the current face can be used as a reference face.
According to claim 1,

And the motion information of the current block is derived from a face that is vertically or symmetrical with the current face.
The method of claim 6,

The motion information includes a motion vector,

In the 2D plane, when the current face and the symmetrical face have different rotation angles, the motion vector of the current block includes the motion vector of the block included in the symmetrical face by the rotational difference between the current face and the symmetrical face. The image decoding method, characterized in that it is derived from the compensated value.
Determining whether a face different from the current face including the current block is available as a reference face;

Obtaining motion information for the current block;

Performing motion compensation on the current block based on the determination and the motion information; And

And based on the determination, encoding the reference face related information.
The method of claim 8,

And the reference face related information is information indicating whether a face located beyond a discontinuous face boundary from the current face can be used as a reference face.
The method of claim 9,

Reconstructing the current block by using the prediction sample obtained through the motion compensation; And

Storing the reconstructed current picture in a reconstructed picture buffer.

And when a face located beyond the discontinuous face boundary from the current face is not available as a reference face, only a part of the current picture is stored in the reconstructed picture buffer.
The method of claim 9,

And the discontinuous face boundary represents a boundary between faces that are adjacent to each other in a 2D plane but not adjacent to each other in 3D space.
The method of claim 8,

And the reference face related information is information indicating whether or not a face having an index different from the current face can be used as a reference face.
The method of claim 8,

And the motion information of the current block is derived from a face that is vertically or symmetrical with the current face.
A decoder which decodes reference face related information from the bitstream;

Based on the information, it is determined whether a face different from the current face including the current block is available as a reference face, obtains motion information for the current block, and based on the determination and the motion information, the current And an inter predictor configured to perform motion compensation on the block.
Determining whether a face different from the current face including the current block is available as a reference face;

Obtaining motion information for the current block;

Performing motion compensation on the current block based on the determination and the motion information; And

And based on the determination, encoding the reference face related information.