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WO2018131830A1 - Procédé et dispositif de traitement de signal vidéo - Google Patents

Procédé et dispositif de traitement de signal vidéo Download PDF

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Publication number
WO2018131830A1
WO2018131830A1 PCT/KR2017/015752 KR2017015752W WO2018131830A1 WO 2018131830 A1 WO2018131830 A1 WO 2018131830A1 KR 2017015752 W KR2017015752 W KR 2017015752W WO 2018131830 A1 WO2018131830 A1 WO 2018131830A1
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face
block
boundary
current
prediction
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PCT/KR2017/015752
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English (en)
Korean (ko)
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이배근
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주식회사 케이티
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/103—Selection of coding mode or of prediction mode
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/12—Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264
    • H04N19/122—Selection of transform size, e.g. 8x8 or 2x4x8 DCT; Selection of sub-band transforms of varying structure or type
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/157—Assigned coding mode, i.e. the coding mode being predefined or preselected to be further used for selection of another element or parameter
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/597—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding specially adapted for multi-view video sequence encoding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/70—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by syntax aspects related to video coding, e.g. related to compression standards

Definitions

  • the present invention relates to a video signal processing method and apparatus.
  • 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
  • An object of the present invention is to provide a method and apparatus capable of effectively encoding / decoding a 360 degree projection image in encoding / decoding a video signal.
  • An object of the present invention is to provide a method and apparatus capable of performing padding at an image boundary or a face boundary in encoding / decoding a video signal.
  • An object of the present invention is to provide a method and apparatus for performing padding in encoding / decoding a video signal in consideration of similarity between boundary samples.
  • An object of the present invention is to provide a method and apparatus for performing motion compensation by replacing a reference region outside an image or face boundary in encoding / decoding a video signal.
  • An object of the present invention is to provide a method and apparatus for performing motion compensation using samples generated due to padding or interpolation in encoding / decoding a video signal.
  • the video signal decoding method and apparatus determine whether a block outside the boundary of the current picture or face can be used as a reference block, and based on the determination result, determine a reference block of the current block, The prediction block of the current block may be generated using the reference block.
  • the video signal encoding method and apparatus determine whether a block outside the boundary of the current picture or face can be used as a reference block, and based on the determination result, determine a reference block of the current block, The prediction block of the current block may be generated using the reference block.
  • the reference block when the reference block is located adjacent to a first boundary of an image or a face, the reference block may include a first sample or the first sample adjacent to the first boundary.
  • the sample may include a sample generated based on at least one of the second samples adjacent to the second boundary having the boundary.
  • the reference block may include a sample generated by interpolating the first sample and the second sample.
  • the second boundary may be adjacent to the first boundary when the current picture is subjected to inverse projection transformation into three-dimensional space.
  • the reference block when the reference block is located adjacent to a first boundary of an image or a face, the reference block is a first sub-block adjacent to the first boundary or the It may include at least one of the second sub-blocks adjacent to the second boundary having an adjacency to the first boundary.
  • information indicating whether a block outside the boundary of the current picture or face can be used as a reference block may be signaled through a bitstream.
  • FIG. 1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.
  • FIG. 2 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present invention.
  • FIG. 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.
  • FIG. 7 is a diagram schematically illustrating a process of encoding / decoding and rendering of 360 degree video.
  • 11 shows an octahedral projection method among 2D projection methods.
  • FIG. 12 illustrates a truncated pyramid projection conversion method among 2D projection methods.
  • FIG. 13 is a diagram for explaining the conversion between face 2D coordinates and 3D coordinates.
  • FIG. 14 is a flowchart illustrating an inter prediction method of a 2D image according to an embodiment to which the present invention is applied.
  • 15 is a diagram illustrating a process of deriving motion information of a current block when a merge mode is applied to the current block.
  • 16 is a diagram illustrating a process of deriving motion information of a current block when an AMVP mode is applied to the current block.
  • 17 is a diagram illustrating a position of a reference block used to derive a prediction block of the current block.
  • FIG. 18 is a diagram illustrating an example in which a face including a reference block is identified by a reference face index in a 360 degree projection image based on TPP.
  • 19 is a diagram illustrating a motion vector when the current block and the reference block belong to the same face.
  • 20 is a diagram illustrating a motion vector when the current block and the reference block belong to different faces.
  • 21 is a diagram illustrating an example of modifying a reference face to match the current face.
  • 22 is a diagram illustrating a method of performing inter prediction of a current block in a 360 degree projection image according to the present invention.
  • FIG. 23 is a diagram illustrating an example of generating a reference block based on a sample belonging to a reference face.
  • 24 is a diagram illustrating an example of generating a motion compensation reference face by modifying a second face adjacent to a first face including a reference point of a reference block.
  • FIG. 25 is a diagram illustrating an example of determining whether a reference face is available based on proximity between faces.
  • FIG. 26 is a diagram illustrating a 360 degree projection image in a cube map format.
  • 27 is a diagram illustrating a method of performing motion compensation in consideration of directionality between faces.
  • 28 is a diagram illustrating an example of performing motion compensation when the current face and the reference face have different directions.
  • 29 is a diagram for explaining continuity of an ERP projection image.
  • FIG. 30 illustrates an example in which a length of a padding area is set differently according to an image boundary.
  • 31 is a diagram illustrating an example in which padding is performed at a boundary of a face.
  • 32 is a diagram illustrating an example of determining a sample value of a padding area between faces.
  • 33 and 34 illustrate examples of replacing an unavailable area among reference areas in a 360-degree projection image based on the ERP format.
  • 35 is a diagram illustrating a motion vector to be encoded.
  • 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.
  • 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.
  • FIG. 1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.
  • 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.
  • 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.
  • 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.
  • 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.
  • one picture may be divided into a plurality of coding units.
  • 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.
  • 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.
  • 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.
  • specific information eg, an intra prediction mode, a motion vector, a reference picture, etc.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • FBMA full search-based block matching algorithm
  • TSS three step search
  • NTS new three-step search algorithm
  • 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.
  • 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.
  • AMVP advanced motion vector prediction
  • 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.
  • 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.
  • intra prediction 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.
  • AIS adaptive intra smoothing
  • the type of AIS filter applied to the reference pixel may be different.
  • 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.
  • 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.
  • 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.
  • DCT discrete cosine transform
  • DST discrete sine transform
  • KLT KLT
  • 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.
  • 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).
  • 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).
  • a deblocking filter may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).
  • ALF adaptive loop filter
  • the deblocking filter may remove block distortion caused by boundaries between blocks in the reconstructed picture.
  • 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.
  • a strong filter or a weak filter may be applied according to the required deblocking filtering strength.
  • 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.
  • 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 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.
  • ALF Adaptive Loop Filtering
  • 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.
  • FIG. 2 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present invention.
  • 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.
  • 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.
  • 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.
  • a transform scheme eg, DCT, DST, KLT
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 'unit' may indicate a basic unit for performing a specific encoding / decoding process
  • 'block' may indicate a sample array having a predetermined size.
  • 'block' and 'unit' may be used interchangeably.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Part_mode partition mode
  • 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.
  • 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.
  • a partition candidate available to a coding block may be determined according to an encoding mode of the current block.
  • 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.
  • any one of eight partition modes may be applied to the coding block, as shown in the example illustrated in FIG. 3.
  • 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.
  • the minimum size of the coding block may be predefined in the encoder and the decoder.
  • information about the minimum size of the coding block may be signaled through the bitstream.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the size of the prediction block may have a size of 64x64 to 4x4.
  • the prediction block may not have a 4x4 size in order to reduce the memory bandwidth.
  • FIGS. 4 to 6 illustrate an example of capturing up, down, left, and right sides simultaneously using a plurality of cameras.
  • a video generated by stitching a plurality of videos may be referred to as a panoramic video.
  • an image having a degree of freedom of 360 degrees based on a predetermined central axis may be referred to as a 360 degree video.
  • 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.
  • a two-dimensional arrangement that is, a mixture of vertical and horizontal arrangements
  • a spherical device may be equipped with a plurality of cameras.
  • FIG. 7 is a diagram schematically illustrating a process of encoding / decoding and rendering of 360 degree video.
  • isotropic projection ERP
  • cube projection transformation Cube Map Projection, CMP
  • isosahedral projection transformation ISP
  • octahedron projection transformation Octahedron Projection, OHP
  • Truncated Pyramid Projection TPP
  • Sharp Segment Projection SSP
  • rotated sphere projection RSP
  • Isometric is a method of projecting a pixel corresponding to a sphere in a 2: 1 ratio rectangle, which is the most commonly used 2D transformation technique.
  • the actual length of the sphere corresponding to the unit length on the 2D plane becomes shorter toward the pole of the sphere.
  • 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.
  • 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.
  • the cube projection method is to approximate 3D data to correspond to a cube, and then convert the cube into 2D.
  • one face (or plane) is configured to be adjacent to 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.
  • encoding / decoding may be performed by rearranging the 2D projection-converted image into a quadrangle form. Reordering the 2D projection-converted image into a quadrangular shape may be referred to as frame reordering or frame packing.
  • the icosahedron projection method is a method of approximating 3D data to correspond to the icosahedron and converting it into 2D.
  • the icosahedral projection method is characterized by strong continuity between faces.
  • frame packing for rearranging the 2D projection-converted image may be performed.
  • 11 shows an octahedral projection method among 2D projection methods.
  • the octahedron projection method is a method of approximating 3D data so as to correspond to an octahedron, and converting it into 2D.
  • the octahedral projection method is characterized by strong continuity between faces.
  • frame packing for rearranging the 2D projection-converted image may be performed.
  • FIG. 12 illustrates a truncated pyramid projection conversion method among 2D projection methods.
  • the truncated pyramid projection transformation method is a method of approximating 3D data to correspond to the truncated pyramid, and converting it into 2D.
  • frame packing may be performed such that a face at a particular point in time has a different size than a neighboring face.
  • the front face may have a larger size than the side face and the back face.
  • SSP divides the sphere into high latitudes, low latitudes, and mid-latitudes, mapping two north-south high latitudes into two circles, and mapping mid-latitudes into rectangles, such as ERP.
  • RSP represents a method of mapping a sphere into two ellipses surrounding a tennis ball.
  • a 2D image constructed using 2D projection transformation will be referred to as a 360 degree projection image.
  • a 360 degree projection image a 2D image constructed using 2D projection transformation
  • 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.
  • FIG. 13 is a diagram illustrating a conversion between a face 2D coordinate and a 3D coordinate.
  • conversion between three-dimensional coordinates (x, y, z) and face 2D coordinates (f, m, n) may be performed using Equations 1 to 4 below. have.
  • the current picture in the 360 degree projection image may include at least one or more faces.
  • the number of faces may be 1, 2, 3, 4 or more natural numbers, depending on the projection method.
  • 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).
  • the number of faces constituting the current picture may be fixed or variable.
  • the number of faces constituting the current picture may be limited not to exceed a predetermined threshold.
  • the threshold value may be a fixed value previously promised by the encoder and the decoder.
  • 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.
  • Inter prediction in a 360 degree projection image may be performed based on motion information of a current block, such as encoding / decoding of a 2D image.
  • FIGS. 14 to 16 are flowcharts for describing an inter prediction method for a 2D image.
  • FIG. 14 is a flowchart illustrating an inter prediction method of a 2D image according to an embodiment to which the present invention is applied.
  • the motion information of the current block may be determined (S1410).
  • the motion information of the current block may include at least one of a motion vector of the current block, a reference picture index of the current block, or an inter prediction direction of the current block.
  • the motion information of the current block may be obtained based on at least one of information signaled through a bitstream or motion information of a neighboring block neighboring the current block.
  • 15 is a diagram illustrating a process of deriving motion information of a current block when a merge mode is applied to the current block.
  • a spatial merge candidate may be derived from the spatial neighboring block of the current block (S1510).
  • the spatial neighboring block may include at least one of a block adjacent to a top, left, or corner of the current block (eg, at least one of a top left corner, a top right corner, or a bottom left corner).
  • the motion information of the spatial merge candidate may be set to be the same as the motion information of the spatial neighboring block.
  • a temporal merge candidate may be derived from a temporal neighboring block of the current block (S1520).
  • a temporal neighboring block may mean a co-located block included in a collocated picture.
  • the collocated picture has a different temporal order (Picture Order Count, POC) than the current picture containing the current block.
  • the collocated picture may be determined by a picture having a predefined index in the reference picture list or by an index signaled from the bitstream.
  • the temporal neighboring block may be determined as any block in the block having the same position and size as the current block in the collocated picture or a block adjacent to a block having the same position and size as the current block. For example, at least one of a block including a center coordinate of a block having the same position and size as the current block in the collocated picture, or a block adjacent to a lower right boundary of the block may be determined as a temporal neighboring block.
  • the motion information of the temporal merge candidate may be determined based on the motion information of the temporal neighboring block.
  • the motion vector of the temporal merge candidate may be determined based on the motion vector of the temporal neighboring block.
  • the inter prediction direction of the temporal merge candidate may be set to be the same as the inter prediction direction of the temporal neighboring block.
  • the reference picture index of the temporal merge candidate may have a fixed value.
  • the reference picture index of the temporal merge candidate may be set to '0'.
  • a merge candidate list including a spatial merge candidate and a temporal merge candidate may be generated (S1530). If the number of merge candidates included in the merge candidate list is smaller than the maximum merge candidate number, a merge candidate having a combination of two or more merge candidates or a merge candidate having a (0,0) zero motion vector It may be included in the merge candidate list.
  • At least one of the merge candidates included in the merge candidate list may be specified based on the merge candidate index (S1540).
  • the motion information of the current block may be set to be the same as the motion information of the merge candidate specified by the merge candidate index (S1550). For example, when the spatial merge candidate is selected by the merge candidate index, the motion information of the current block may be set to be the same as the motion information of the spatial neighboring block. Alternatively, when the temporal merge candidate is selected by the merge candidate index, the motion information of the current block may be set to be the same as the motion information of the temporal neighboring block.
  • 16 is a diagram illustrating a process of deriving motion information of a current block when an AMVP mode is applied to the current block.
  • At least one of the inter prediction direction or the reference picture index of the current block may be decoded from the bitstream (S1610). That is, when the AMVP mode is applied, at least one of the inter prediction direction or the reference picture index of the current block may be determined based on information encoded through the bitstream.
  • a spatial motion vector candidate may be determined based on the motion vector of the spatial neighboring block of the current block (S1620).
  • the spatial motion vector candidate may include at least one of a first spatial motion vector candidate derived from an upper neighboring block of the current block and a second spatial motion vector candidate derived from a left neighboring block of the current block.
  • the upper neighboring block includes at least one of the blocks adjacent to the upper or upper right corner of the current block
  • the left neighboring block of the current block includes at least one of the blocks adjacent to the left or lower left corner of the current block.
  • the block adjacent to the upper left corner of the current block may be treated as the upper neighboring block, or may be treated as the left neighboring block.
  • the spatial motion vector may be obtained by scaling the motion vector of the spatial neighboring block.
  • a temporal motion vector candidate may be determined based on the motion vector of the temporal neighboring block of the current block (S1630). If the reference picture is different between the current block and the temporal neighboring block, the temporal motion vector may be obtained by scaling the motion vector of the temporal neighboring block.
  • a motion vector candidate list including a spatial motion vector candidate and a temporal motion vector candidate may be generated (S1640).
  • At least one of the motion vector candidates included in the motion vector candidate list may be specified based on information for specifying at least one of the motion vector candidate lists (S1650).
  • the motion vector candidate specified by the information may be set as a motion vector prediction value of the current block, and the motion vector difference value is added to the motion vector prediction value to obtain a motion vector of the current block (S1660).
  • the motion vector difference value may be parsed through the bitstream.
  • motion compensation for the current block may be performed based on the obtained motion information (S1420).
  • motion compensation for the current block may be performed based on the inter prediction direction, the reference picture index, and the motion vector of the current block.
  • inter prediction of a 360 degree projection image may be performed in units of blocks, and may be performed based on motion information of a current block.
  • the prediction block of the current block to be encoded / decoded in the current picture may be derived from a region most similar to the prediction block in the reference picture.
  • the reference block in the reference picture used to derive the prediction block of the current block may be located at the same face or at a different face than the current block.
  • 17 is a diagram illustrating a position of a reference block used to derive a prediction block of the current block.
  • the reference block in the reference picture used to derive the predictive block of the current block may exist at the same face as the current block in the current picture (see (b)), or the current block in the current picture. May be at a different face than (see (c)). Or, the reference block may span two or more faces (see (a)).
  • the reference picture including the reference block may be a picture different from the current picture in a temporal order or output order (POC).
  • POC output order
  • the current picture may be used as a reference picture.
  • a block encoded / decoded before a current block in a current picture including the current block may be set as a reference block of the current block.
  • the predictive block of the current block may be derived from a reference block included in the same face as the current block or a reference block included in a different face from the current block.
  • the position of the reference block may be specified through a motion vector between the reference block from the corresponding position block corresponding to the position of the current block in the reference picture.
  • the current block using information for specifying a face including a reference block and / or a motion vector for specifying a position of a reference block within the face. It is also possible to perform the motion compensation of.
  • a face including a reference block in the reference picture may be referred to as a 'reference face'.
  • the information for specifying a face including a reference block includes information indicating whether the reference block belongs to the same face as the current block and / or information for identifying a face including the reference block (eg, a reference face index). It may include at least one. For example, a 1-bit flag can be used to determine whether the reference block belongs to the same face as the current block. In addition, a reference face index may be used to specify a face including a reference block in the reference picture.
  • FIG. 18 is a diagram illustrating an example in which a face including a reference block is identified by a reference face index in a 360 degree projection image based on TPP.
  • a reference face index 'mc_face_idx' (or 'ref_face_idx') for identifying a face including a reference block may be defined.
  • the reference face index may be encoded / decoded through the bitstream.
  • a reference face index may be derived from a neighboring block neighboring the current block.
  • the reference face index of the current block may be derived from the merge candidate merged with the current block.
  • the face index of the current block may be encoded / decoded through the bitstream.
  • the reference face index may specify the face that contains the reference position of the reference block.
  • the reference position may include the position of a specific corner (eg, the upper left sample) in the reference block or the center point of the reference block.
  • the position of the reference block in the face may be specified based on the vector value from the reference position of the reference face to the reference position of the reference block.
  • the reference position of the reference face may be a position of a specific corner (eg, the position of the upper left reference sample) or the center point of the face.
  • the reference position of the reference face may be variably determined according to the index of the face including the current block (ie, the current face index), the reference face index, the relative position between the current face and the reference face, or the position of the current block in the face. have.
  • the index of the face including the current block (ie, the current face index), the reference face index, the relative position between the current face and the reference face, or the position of the current block in the face.
  • a second position corresponding to the first position in the reference face may be determined as the reference position.
  • the reference position of the reference face is set to the upper left corner
  • the reference position of the reference face is set to the top center.
  • the motion vector from the reference position in the face to the reference block may be referred to as a face vector.
  • Whether the motion vector is a face vector may be determined based on whether the current face and the reference face are the same (ie, whether the current face index and the reference face index are the same). For example, when the current face index and the reference face index are the same, the motion vector may indicate a vector from the current block to the reference block. On the other hand, when the current face index and the reference face index are different, the motion vector may indicate a vector from the reference position in the reference face to the reference block.
  • information indicating whether a motion vector is a face vector may be encoded / decoded through a bitstream.
  • the motion vector (eg, the face vector or non-face vector) of the current block may be encoded / decoded through the bitstream.
  • the motion vector value may be encoded / decoded through the bitstream as it is.
  • the motion vector may be encoded / decoded through a bitstream or a motion vector of the current block may be derived from a neighboring block.
  • the inter prediction mode of the current block is an AMVP mode
  • the motion vector of the current block may be encoded / decoded using differential coding.
  • differential coding refers to encoding / decoding a difference between a motion vector of a current block and a motion vector prediction value through a bitstream.
  • the motion vector prediction value may be derived from the spatial / temporal neighboring block of the current block.
  • the motion vector of the current block may be derived in the same manner as the spatial / temporal neighboring block of the current block.
  • the inter prediction mode of the current block is the merge mode
  • the motion vector of the current block may be set to be the same as the motion vector of the spatial / temporal neighboring block of the current block.
  • the motion vector of the current block may be derived according to the motion vector of the current block. For example, if the motion vector of the current block is a non-face vector, while the motion vector of the neighboring block is a face vector, the neighboring block, using the vector between the neighboring block and the reference face reference point of the neighboring block and the face vector of the neighboring block, The face vector of can be converted to a non-face vector. According to the inter prediction mode of the current block, the motion vector of the current block may be derived based on the transformed non-face vector of the neighboring block.
  • the encoding / decoding method of the motion vector of the current block may be differently determined according to whether the motion vector of the current block is a face vector or a non-face vector. For example, when the motion vector of the current block is a non-face vector, the motion vector of the current block is derived using the motion vector of the neighboring block, whereas if the motion vector of the current block is a face vector, the face vector value is bit-changed as it is. It may also be encoded / decoded through a stream.
  • motion compensation of the current block may be performed through a reference block belonging to a different face from the current block.
  • a phase, a size, or a shape of a face including a current block and a face including a reference block is different, it is difficult to search for a reference block that matches the prediction block of the current block within the reference face.
  • TPP it is difficult to have similarities between blocks belonging to the front face and blocks belonging to the right face because the front face and the right face have different sizes and shapes. Accordingly, when it is desired to perform motion estimation or motion compensation from a reference face having a phase, magnitude or shape different from that of the current face, a transformation that matches the phase, magnitude or shape of the current face and the reference face needs to be performed.
  • 19 is a diagram illustrating a motion vector when the current block and the reference block belong to the same face.
  • the motion vector is the coordinate difference between the starting point between the current block and the starting point of the reference block, as in a 2D image. Can be used as a motion vector.
  • 20 is a diagram illustrating a motion vector when the current block and the reference block belong to different faces.
  • the face that contains the current block and the reference block is different (that is, the current face index and the reference face index are different), and at least one of the size, shape, or phase between the current face and the reference face is different, the face to which the reference block belongs. May be modified according to the size, shape, or phase of the face to which the prediction block belongs.
  • the reference face may be transformed using at least one of phase warping, interpolation and / or padding.
  • FIG. 21 is a diagram illustrating an example of modifying a reference face to a current face. If the size and / or shape of the current face and the reference face are different, apply phase transformation, padding or interpolation to the reference face, as in the example shown in FIG.
  • the reference face to make the reference face the same size and / or shape as the current face. It can be modified to have a.
  • modifying the reference face at least one of phase modification, padding, and / or interpolation may be omitted, and modification of the reference face may be performed in a different order than that shown in FIG. 21.
  • a reference face modified for the current face may be referred to as a reference face for motion compensation.
  • the motion compensation reference face can be interpolated with a predefined precision (eg, quarter pel or integer pel, etc.).
  • a block most similar to the prediction block of the current block in the interpolated motion compensation reference face may be generated as the prediction block of the current block.
  • the motion vector of the current block may indicate a coordinate difference between the start position of the current block and the start position of the reference block (ie, encoding / decoding a non-face vector).
  • the reference face is modified to match the phase, size, or shape of the current face.
  • the inter prediction is performed by modifying at least one of the phase, magnitude, or shape between the current face and the reference face. Can be.
  • 22 is a diagram illustrating a method of performing inter prediction of a current block in a 360 degree projection image according to the present invention.
  • information about a reference face may be decoded from a bitstream (S2210).
  • the information about the reference face is decoded, it may be determined whether the current block and the reference block belong to the same face based on the decoded information (S2220).
  • the information about the reference face may include at least one of whether the current block and the reference block belong to the same face or a reference face index.
  • 'isSameFaceFlag' indicating whether a face to which a current block belongs and a face to which a reference block belongs to each other or whether the current face index and the reference face index are the same may be signaled through the bitstream.
  • a value of isSameFaceFlag of 1 may mean that the current face index and the reference face index have the same value, or that the face to which the current block belongs and the face to which the reference block belongs correspond to each other.
  • a value of isSameFaceFlag of 0 may mean that the current face and the reference face index have different values or that the face to which the current block belongs and the face to which the reference block belongs do not correspond to each other.
  • the reference face index may be signaled only when the value of isSameFaceFlag is 0. Alternatively, signaling of the isSameFaceFlag may be omitted and the reference face index may be signaled essentially. If signaling of isSameFaceFlag is omitted, it may be determined whether the current block and the reference block belong to the same face by comparing the current face index and the reference face index.
  • a motion vector indicating a coordinate difference between the current block and the reference block in the reference face is obtained (S2230), and motion compensation is performed using the obtained motion vector. It may be performed (S2240).
  • a motion compensation reference face obtained by modifying at least one of a phase, a size, or a shape of the reference face to the current face may be generated (S2250).
  • a motion vector indicating a coordinate difference between the current block and the reference block in the motion compensation reference face may be obtained, and motion compensation may be performed using the obtained motion vector.
  • the process of generating a motion vector reference face may be omitted if the phase, magnitude, or shape between the current face and the reference face are the same.
  • the motion compensation of the current block in the 360 degree projection image may be limited to using only reference blocks belonging to the same face as the current block.
  • Motion estimation and motion compensation for the current block may be performed on a reference block belonging to the same face as the current block.
  • motion compensation may not be performed, such as when the current block and the reference block belong to different faces.
  • the face to which the reference block belongs may be determined based on the position of the reference point of the reference block.
  • the reference point of the reference block may be a corner sample, a center point, or the like of the reference block. For example, even when the reference block is located over the boundary of two faces, if the reference point of the reference block belongs to the same face as the current face, it may be determined that the reference block belongs to the same face as the current block.
  • Whether motion compensation may be performed using a reference block belonging to a different face from the current block may be adaptively determined based on the projection method, the size / shape of the face, the size difference between the faces, and the like.
  • information eg, a flag
  • indicating whether motion compensation can be performed using a reference block belonging to a different face from the current block may be signaled through the bitstream.
  • the motion compensation of the current block may be performed based on a reference block generated by interpolation, padding, or phase shifting of pixels belonging to the reference face corresponding to the current face.
  • a reference block spans two or more faces, and a reference point of the reference block belongs to a reference face corresponding to the current face, the reference block corresponds to a reference face corresponding to the current face (hereinafter referred to as a first face). It may include a first region belonging to and a second region belonging to a reference face outside the current face (hereinafter referred to as a second face).
  • the pixels of the second region may be generated by copying or interpolating the samples included in the first face, or a predetermined filter may be applied to the samples and / or the pixels of the second face. You can also create pixels.
  • the predetermined filter may mean a weighted filter, an average filter, an interpolation filter, or the like.
  • the pixel region to which the filter is applied may be all regions belonging to the first face and / or the second face, or may be some regions.
  • the partial region may be the first region and the second region, or may be a region of a size / type predefined by the encoder / decoder.
  • the filter may be applied to one or more pixels adjacent to the boundary of the first and second faces.
  • FIG. 23 is a diagram illustrating an example of generating a reference block based on a sample belonging to a reference face.
  • a sample included in a boundary of a reference face (first face) corresponding to a current face is padded (or copied) and / or interpolated, or a sample included in a first face, Based on the reference block generated by applying a filter between samples included in the second face adjacent to the first face, motion compensation for the current block may be performed.
  • a padding area is generated by padding a sample included in a front face to which a reference point of a reference block belongs, and using the sample included in the padding area, motion compensation is performed for the current block. It became.
  • motion compensation for the current block may be performed using the generated motion compensation reference face.
  • 24 is a diagram illustrating an example of generating a motion compensation reference face by modifying a second face adjacent to a first face including a reference point of a reference block.
  • a motion compensation reference face may be generated. Accordingly, motion compensation for the current block may be performed using a sample belonging to the motion compensation reference face.
  • Information indicating whether to use a reference block generated based on a sample value belonging to a reference face corresponding to the current face for motion compensation may be encoded / decoded through a bitstream.
  • the information is a 1-bit flag. For example, a flag value of 0 indicates that a reference block generated based on a sample value belonging to a reference face corresponding to the current face is not used for motion compensation. 1 may indicate that a reference block generated based on a sample value belonging to a reference face corresponding to the current face may be used for motion compensation of the current block.
  • the size / shape between faces may be different.
  • the front face may be larger than the residual face.
  • Small faces have a relatively small amount of information compared to large faces.
  • the motion vector accuracy at the small face can be increased, and the coding efficiency can be increased. That is, the motion vector precision may be adaptively determined according to the size / shape of the reference face in which the reference block is included.
  • motion compensation is performed using a quarter pel (1 / 4pel), while the reference block has a smaller right face and left than the front face.
  • motion compensation may be performed using an octopel.
  • the reference block of the current block may be derived from a face having a neighbor with the current face. That is, a face that does not have a neighbor with the current face cannot be used as a reference face, and blocks belonging to the face cannot be used as reference blocks of the current block.
  • Whether the current face and the predetermined face have contiguity includes whether the current face and the reference face are spatially neighboring or whether the difference between the index of the current face and the index of the reference face is larger than a predetermined threshold. Can be determined on the basis.
  • whether the current face and the reference face are spatially neighboring may be determined based on the 3D space or may be determined based on the 2D plane.
  • neighbors between faces may be predefined in the encoder and the decoder.
  • a face that does not spatially neighbor a current face cannot be used as a reference face.
  • the face corresponding to the opposite face of the current face may not be used as a reference face as it is not spatially neighboring the current face.
  • FIG. 25 is a diagram illustrating an example of determining whether a reference face is available based on proximity between faces.
  • the back face opposite to the front face cannot be used as the reference face of the current block.
  • the front face cannot be used as the reference face.
  • motion compensation may be performed by using a predetermined position region in a picture different from the current picture.
  • the predetermined location area may mean a block that is the same location as the current block or a block adjacent to the same location block in a specific direction.
  • availability of the motion vector, the merge candidate, or the motion vector candidate may be determined according to the position of the motion vector of the current block or the reference block indicated by the merge candidate. For example, when the motion vector of the current block or the reference block indicated by the merge candidate of the current block is located at a face that does not have a neighbor with the current face, it may be determined that the motion vector or the merge candidate is unavailable.
  • the unusable merge candidate may be excluded from the merge candidate list.
  • the faces may have different directions from each other, depending on the projection conversion format.
  • frame packing may be performed by modifying or rotating faces.
  • FIG. 26 is a diagram illustrating a 360 degree projection image in a cube map format.
  • the faces (faces 0, 1, 2) included in the bottom row are rotated 90 degrees clockwise relative to the faces (faces 3, 4, 5) included in the top row.
  • the faces have different directions from each other.
  • motion compensation for the current block may be performed by rotating the reference face or the reference block according to the directionality of the reference face. Referring to FIG. 27, a method of performing motion compensation in consideration of inter-face directionality will be described in more detail.
  • 27 is a diagram illustrating a method of performing motion compensation in consideration of directionality between faces.
  • a reference face or reference block of a current block may be specified (S2710).
  • the reference face of the current block may be specified by a reference face index or by a reference block specified by the motion vector of the current block.
  • the reference face or the reference block of the current block it may be determined whether the current face and the reference face have the same direction (S2720). Whether the current face and the reference face have the same direction may be determined based on rotation information related to the rotation of the face.
  • the rotation information may include information about whether to rotate, the rotation direction, the rotation angle, or the order / position of allocating a sample of the reference block to the prediction block.
  • the rotation information may be encoded in the encoder and signaled through the bitstream, or may be derived based on the inter-face directionality.
  • whether the face rotates or the rotation angle may be predefined in the encoder and the decoder according to the position of the face.
  • a prediction block for the current block may be generated using the reference block included in the reference face (S2730).
  • the reference face or the reference block included in the reference face may be rotated to have the same direction as the current face (S2740).
  • the prediction block for the current block may be generated using the reference block or the rotated reference block included in the rotated reference face.
  • 28 is a diagram illustrating an example of performing motion compensation when the current face and the reference face have different directions.
  • the reference face is specified by the reference face index or the motion vector of the current block, it may be determined whether the reference face has the same direction as the current face. For example, in the example illustrated in FIG. 28, since the reference face 1 is rotated 90 degrees with respect to the current face 4, it may be determined that the current face and the reference face have different directions.
  • the reference face or the reference block included in the reference face may be rotated to have the same direction as the current face. For example, after rotating the reference face according to the direction of the current face, a reference block can be obtained from the rotated reference face. When the reference block is obtained, the prediction block of the current block may be generated using the obtained reference block.
  • the obtained reference block may be rotated according to the direction of the current face.
  • the predicted block of the current block may be generated using the rotated reference block.
  • the reference face or reference block is illustrated as being rotated in accordance with the direction of the current block. Unlike in the illustrated example, it is also possible to perform motion compensation by rotating the reference picture or by rotating the current face or the current block in the direction of the reference face. Alternatively, it is possible to rotate both the current face and the reference face according to the predefined direction.
  • motion compensation may be performed by padding outside the picture boundary in which the pixel value does not exist.
  • Padding may be performed by copying samples adjacent to the picture boundary or interpolating samples adjacent to the picture boundary.
  • padding may be performed by setting a region in which no pixel value outside the picture boundary exists to a predefined value. For example, padding may be performed to set a pixel value outside a picture boundary to an intermediate value of the available pixel value range (for example, 128 for an 8-bit image).
  • padding may be performed at a picture boundary or a face boundary.
  • the padding at the picture boundary or the face boundary may be performed in consideration of the continuity of the 360 degree image.
  • back-projecting a 360 degree projection image into a sphere or a polyhedron it is possible to determine continuity between picture boundaries or continuity between faces.
  • the boundary of the 360 degree projection image or the boundary of the face in the 360 degree projection image may be performed using samples adjacent to the boundary adjacent to the boundary in three-dimensional space.
  • 29 is a diagram for explaining continuity of an ERP projection image.
  • a 360-degree projection image approximated by a sphere can be expanded into a rectangle having a 2: 1 ratio to obtain a two-dimensional 360-degree projection image.
  • the left boundary of the 360 degree projection image has continuity with the right boundary.
  • pixels A, B, and C outside the left boundary may be expected to have values similar to pixels A ', B', and C 'inside the right boundary, and outside the right boundary. It can be expected that the pixels D, E and F of have values similar to the pixels D ', E' and F 'inside the left boundary line.
  • the upper boundary on the left has continuity with the upper boundary on the right.
  • pixels G and H outside the upper left boundary can be predicted to be similar to the inner pixels G 'and H' of the upper right boundary, and pixels I and J outside the right upper boundary. Can be expected to be similar to the inner pixels I 'and J' of the upper left boundary.
  • the upper boundary on the left has continuity with the upper boundary on the right.
  • pixels K and L outside the lower left boundary can be predicted to be similar to pixels K 'and L' inside the right lower boundary, and pixels M and N outside the lower right boundary. Can be expected to be similar to the inner pixels M 'and N' of the lower left boundary.
  • padding may be performed at the boundary of the 360 degree projection image or the boundary between faces.
  • padding may be performed using samples included inside the boundary having continuity with the boundary.
  • padding is performed using samples adjacent to the right boundary at the left boundary of the 360 degree projection image
  • padding is performed using samples adjacent to the left boundary at the right boundary of the 360 degree projection image.
  • padding may be performed using samples of the positions of D ′, E ′, and F ′ included inside the left boundary.
  • padding may be performed using samples adjacent to the upper right boundary at the upper left boundary, and padding may be performed using samples adjacent to the upper left boundary at the upper right boundary. That is, at G and H positions of the upper left boundary, padding is performed using samples of G 'and H' positions contained inside the right upper boundary, and at I and J positions of the upper right boundary, the upper left boundary Padding may be performed using samples of the I 'and J' positions contained inside of.
  • padding may be performed using samples adjacent to the lower right boundary at the lower left boundary, and padding may be performed using samples adjacent to the lower left boundary at the lower right boundary. That is, at the K and L positions of the lower left boundary, padding is performed using samples of the K 'and L' positions contained inside the right upper boundary, and at the M and N positions of the upper right boundary, the upper left boundary Padding may be performed using samples of the M 'and N' positions contained inside of.
  • the padding area may be referred to as a padding area, and the number of sample lines generated by the padding may be referred to as a length of the padding area.
  • k sample lines may be generated in the padding area, and the length of the padding area may be considered to be k.
  • the length of the padding area may be set differently according to the horizontal direction or the vertical direction, or differently according to the face boundary.
  • the closer to the region where distortion occurs the more padding is performed using more pixels, or the smoothing filter (Smoothing Filter) can be considered to smooth the boundary of the image.
  • FIG. 30 illustrates an example in which a length of a padding area is set differently according to an image boundary.
  • the length of the arrow indicates the length of the padding area.
  • the length of the padding area performed in the horizontal direction and the length of the padding area performed in the vertical direction may be set differently. For example, if k columns of samples are generated through padding in the horizontal direction, padding may be performed such that 2k rows of samples are generated in the vertical direction.
  • padding may be performed with the same length in both the vertical direction and the horizontal direction, but in at least one of the vertical direction and the horizontal direction, the length of the padding area may be post-expanded through interpolation.
  • k sample lines may be generated in the vertical direction and the horizontal direction, and k sample lines may be additionally generated in the vertical direction through interpolation. That is, after generating k sample lines in both the horizontal and vertical directions (see FIG. 29), k sample lines may be additionally generated in the vertical direction, so that the length in the vertical direction is 2k (see FIG. 30). .
  • Interpolation may be performed using at least one of a sample included inside the boundary of the image or a sample included outside the boundary of the image.
  • an additional padding area may be generated by copying samples adjacent to the bottom boundary outside the padding area adjacent to the top boundary and then interpolating the copied samples and the samples included in the padding area adjacent to the top boundary.
  • the interpolation filter may include at least one of a vertical filter and a horizontal filter. Depending on the position of the generated pixel, one of the filter in the vertical direction and the filter in the horizontal direction may be selectively used. Alternatively, a sample included in the additional padding area may be generated using a filter in the vertical direction and a filter in the horizontal direction at the same time.
  • the length n in the horizontal direction of the padding area and the length m in the vertical direction of the padding area may have the same value or may have different values.
  • n and m are natural numbers greater than or equal to 0, and may have the same value, or one of m and n may have a smaller value than the other.
  • m and n may be encoded by the encoder and signaled through the bitstream.
  • the length n in the horizontal direction and the length m in the vertical direction may be predefined in the encoder and the decoder.
  • the sample value of the padding area may be generated by copying samples located inside the image.
  • a padding area positioned at the left boundary of the image may be generated by copying a sample adjacent to the right boundary of the image.
  • the sample value of the padding area may be determined using at least one sample included inside the boundary to be padded and a sample included outside the boundary. For example, samples that are spatially contiguous with a boundary to be padded are copied to the outside of the boundary, and then the sample of the padding region is weighted average or averaged between the copied samples and the samples contained inside the boundary. The value can be determined.
  • the padding area located at the left boundary of the image is a weighted average of at least one sample inside the left boundary of the image and at least one sample inside the right boundary of the image. Or on average.
  • the weight applied to each sample may be determined based on a distance from an image boundary. For example, the closer to the left boundary of the image, the greater the weight given to samples located inside the left boundary of the image, and the farther away from the left boundary of the image, the more samples are located outside the left boundary of the image (i.e. Weights given to samples located inside the right boundary may be increased.
  • frame packing may be performed by adding a padding area to the face boundary.
  • a 360 degree projection image in which a padding area is added to a boundary area between faces may be obtained.
  • 31 is a diagram illustrating an example in which padding is performed at a boundary of a face.
  • the 360 degree projection image is projection converted based on the ISP.
  • the upper face and the lower face will be distinguished based on the drawing shown in FIG. 31A.
  • the upper face may represent any one of faces 1, 2, 3, and 4
  • the lower face may represent any one of faces 5, 6, 7, and 8.
  • a padding area having a shape surrounding the predetermined face can be set.
  • a padding area including m samples may be generated for a triangular face.
  • the frame packing may be performed by adding a padding area only at the boundary of an image or by adding a padding area only between faces.
  • frame packing may be performed by adding a padding area only between faces in which discontinuity of an image occurs in consideration of inter-face continuity.
  • the length of the padding area between the faces may be set identically or differently depending on the position.
  • the length (i.e., horizontal length) n of the padding area where a given face is located on the left or right side and the horizontal length m of the padding area, which is located at the top or bottom of the predetermined face may have the same value or be different May have a value.
  • n and m are natural numbers greater than or equal to 0, and may have the same value, or one of m and n may have a smaller value than the other.
  • m and n may be encoded by the encoder and signaled through the bitstream.
  • the length n in the horizontal direction and the length m in the vertical direction may be predefined in the encoder and the decoder according to the projection transformation method, the position of the face, the size of the face or the shape of the face.
  • the sample value of the padding area may be determined based on a sample included in a predetermined face or a sample included in a sample included in a predetermined face and a face adjacent to the predetermined face.
  • the sample value of the padding area adjacent to a boundary of a predetermined face may be generated by copying a sample included in the face or interpolating the samples included in the face.
  • the upper extension region U of the upper face is generated by copying a sample adjacent to the boundary of the upper face or interpolating a predetermined number of samples adjacent to the boundary of the upper face.
  • the lower extension region D of the lower face may be generated by copying a sample adjacent to the boundary of the lower face or interpolating a predetermined number of samples adjacent to the boundary of the lower face.
  • the sample value of the padding area adjacent to the boundary of the predetermined face may be generated using the sample value of the face spatially adjacent to the face.
  • the inter-face proximity may be determined whether or not the face-to-face continuity is obtained when the 360-degree projection image is back projected on the 3D space.
  • a sample value of a padding area adjacent to a boundary of a predetermined face is generated by copying a sample included in a face spatially adjacent to the face, or included in a sample included in the face and a face spatially adjacent to the face. Samples can be generated by interpolating. For example, the left part of the upper extension region of the second face may be generated based on the samples included in the first face, and the right part may be generated based on the samples included in the third face.
  • 32 is a diagram illustrating an example of determining a sample value of a padding area between faces.
  • the padding area between the first face and the second face may be obtained by weighted averaging at least one sample included in the first face and at least one sample included in the second face.
  • the padding area between the upper face and the lower face may be obtained by weighted averaging the upper extension area U and the lower extension area D.
  • the weight w may be determined based on information encoded and signaled by the encoder. Alternatively, the weight w may be variably determined according to the position of the sample in the padding area. For example, the weight w may be determined based on the distance from the position of the sample in the padding area to the first face and the distance from the position of the sample in the padding area to the second face.
  • Equations 5 and 6 are diagrams showing examples in which the weight w is variably determined according to the position of the sample.
  • a sample value of the padding area is generated based on Equation 5 in an area close to the upper face and an area of the padding area based on Equation 6 in an area close to the lower face. Sample values can be generated.
  • the filter for weighting operation may have a vertical direction, a horizontal direction, or a predetermined angle.
  • a sample included in the first face and a sample included in the second face may be used to determine the sample value of the sample from the sample in the padding area.
  • the padding area may be generated using only samples included in one of the first and second faces. For example, when one of the samples included in the first face or the sample included in the second face is not available, padding may be performed using only the available samples. Alternatively, padding may be performed by replacing unused samples with surrounding available samples.
  • the area specified by the motion vector may be derived as a reference spare block, and then a block generated by padding or interpolating the reference spare block may be used as a reference block of the current block.
  • the reference region of the current block may be defined as the region referenced for intra prediction or inter prediction of the current block.
  • the availability of the reference area can be determined. For example, the availability of the reference area is determined based on whether the reference area spans a face boundary, whether the reference area spans an image boundary, or whether the reference area exists in an area between faces (ie, a padding area). can do.
  • the reference area spans the face boundary means that the reference area spans the boundary of the 360-degree projection image when the reference area is the face boundary, the reference area spans two or more faces, or the reference area spans the face boundary and the padding area. It can represent the case, etc. over.
  • the entire reference region may be treated as available, or the entire reference region may be treated as unavailable. For example, when the reference region spans the face boundary, the entire reference region may be treated as unavailable.
  • the reference area may be divided into an available area and an unavailable area according to the position of the reference area. For example, when the reference region spans the face boundary, the region located inside the predetermined face may be determined to be available, and the region located outside the predetermined face may be determined to be unavailable.
  • the unavailable area may not be used in inter prediction of the current block, or the unavailable area may be replaced with the available area.
  • a sample value generated by padding or interpolating a sample included in an available area may be replaced with an unavailable area, and motion compensation of the current block may be performed using the replaced area.
  • Whether to use the unavailable region for motion compensation of the current block may be determined based on information signaled through the bitstream.
  • the information may be a flag of 1 bit. For example, according to the value of the flag, the motion compensation of the current block is excluded and the unavailable area is replaced based on the available area, and then the motion compensation of the current block is performed using the replaced unavailable area. Can be performed.
  • the unavailable area may be replaced with a sample value generated by padding or interpolating samples located inside the predetermined face. For example, a sample value generated by padding or interpolating a sample included in the usable area may be replaced with the unavailable area.
  • the unavailable area may be replaced with an area located at a boundary of a face different from a predetermined face.
  • the region located inside the predetermined face may be determined to be available, and the region located outside the predetermined face may be determined to be unavailable.
  • the unavailable area may be replaced by an area located inside a face different from the predetermined face, or may be replaced by a sample located inside the face different from the predetermined face or a sample value generated by interpolation.
  • the face including the replacement area or the replacement sample of the unavailable area may be determined in consideration of the proximity to the predetermined face.
  • Proximity may be determined in consideration of whether it is adjacent to a predetermined face or 2D space, or whether or not it is adjacent to a predetermined face when the 360-degree projection image is reversely projected on the 3D space.
  • the replacement area or replacement sample may be determined from a face located on the same vertical / horizontal line as the available area.
  • the unavailable region may be replaced with a sample value obtained based on interpolation or weighting operation between the sample included in the available region and the sample included in the region different from the available region.
  • the above-described method of processing the unavailable image is selectively used. It may be.
  • 33 and 34 illustrate examples of replacing an unavailable area among reference areas in a 360-degree projection image based on the ERP format.
  • the prediction of the current block may be performed using a reference block including a first sub block Ref 1 in the reference picture and a second sub block Ref 2 outside the reference picture.
  • the area beyond the boundary of the projected image may be replaced with an area adjacent to a boundary having a continuity with the boundary over which the reference area spans in the 3D space.
  • the outer region of the left boundary is a boundary having an adjacency with the left boundary in 3D space (ie, the right boundary). It can be replaced by an area adjacent to.
  • the outer region of the left boundary may be replaced with a copy of an area adjacent to the right boundary, or may be replaced with a sample value generated by padding or interpolating a sample included in the region adjacent to the right boundary.
  • the outer region of the upper left boundary is a boundary (i.e., the upper right boundary) adjacent to the upper left boundary in 3D space. Can be replaced by an adjacent area.
  • the outer region of the upper left boundary may be replaced by a copy of the region adjacent to the upper right boundary, or may be replaced by a sample value generated by padding or interpolating a sample included in the region adjacent to the upper right boundary.
  • the outer region of the right boundary can be replaced with an area adjacent to the left boundary; if the reference region spans the upper right boundary, the upper right outer region is the upper left. It can be replaced by an area adjacent to the boundary.
  • the reference region of the current block may be composed of a first sub block adjacent to the first boundary and a second sub block adjacent to the second boundary, which has continuity with the first boundary.
  • the encoder may selectively encode a small amount of information among the first motion vector MVRef0 up to the first subblock and the second motion vector MVRef1 up to the second subblock. For example, when the amount of information of the second motion vector is smaller than that of the first motion vector, the second motion vector may be encoded.
  • 35 is a diagram illustrating a motion vector to be encoded.
  • the first motion vector from the current block to the first sub block has a smaller value than the second motion vector from the current block to the second sub block. Accordingly, information about the first motion vector for specifying the position of the first subblock with respect to the current block may be encoded.
  • the motion vector of the current block may be derived based on the spatial / temporal neighboring blocks of the current block.
  • the derived motion vector may be set as the motion vector of the current block, or the motion vector of the current block may be determined by resizing the derived motion vector.
  • the resizing may represent at least one of an addition, a subtraction, or a scaling operation based on a predetermined parameter.
  • the predetermined parameter may be determined based on at least one of the size (eg, width and / or height) of the projection image and / or face or the motion vector precision (eg, an integer, half, quarter, etc.). Can be.
  • Information indicating whether to resize the derived motion vector may be encoded and transmitted.
  • the information may be a flag of 1 bit, and the information may be signaled in at least one unit of a picture, slice, tile, face, or block.
  • Resizing of the motion vector may be selectively performed based on at least one of a method of deriving the motion vector (eg, merge mode or AMVP mode) or motion jitter precision.
  • the resizing of the motion vector may be applied to both the x-axis component and the y-axis component of the motion vector or may be selectively applied to only one of the x-axis component and the y-axis component. If the motion vector is resized, the resized motion vector can be used to derive the motion vector of the neighboring block.
  • a picture composed of a plurality of faces can be used as a reference picture.
  • each face may be used as a reference picture, or a predetermined number of face sets may be used as the reference picture.
  • only the front face may be used as the reference picture, or the front face may be used as the reference picture and other sets of faces may be used as the reference picture.
  • 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.

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Abstract

La présente invention concerne un procédé de décodage d'image pouvant comprendre les étapes consistant à : déterminer si un bloc extérieur à une limite d'une image courante ou une phase peut être utilisé comme bloc de référence; d'après un résultat de la détermination, déterminer un bloc de référence du bloc actuel; et générer un bloc de prédiction du bloc actuel à l'aide du bloc de référence.
PCT/KR2017/015752 2017-01-11 2017-12-29 Procédé et dispositif de traitement de signal vidéo WO2018131830A1 (fr)

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