WO2021049865A1 - Bdof를 수행하는 영상 부호화/복호화 방법, 장치 및 비트스트림을 전송하는 방법 - Google Patents
Bdof를 수행하는 영상 부호화/복호화 방법, 장치 및 비트스트림을 전송하는 방법 Download PDFInfo
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Definitions
- the present disclosure relates to an image encoding/decoding method, an apparatus, and a method of transmitting a bitstream, and more particularly, an image encoding/decoding method and apparatus for performing a bi-directional optical flow (BDOF), and an image encoding of the present disclosure. It relates to a method of transmitting a bitstream generated by a method/apparatus.
- BDOF bi-directional optical flow
- An object of the present disclosure is to provide a video encoding/decoding method and apparatus with improved encoding/decoding efficiency.
- an object of the present disclosure is to provide a video encoding/decoding method and apparatus for performing BDOF.
- an object of the present disclosure is to provide a method for transmitting a bitstream generated by an image encoding method or apparatus according to the present disclosure.
- an object of the present disclosure is to provide a recording medium storing a bitstream generated by an image encoding method or apparatus according to the present disclosure.
- an object of the present disclosure is to provide a recording medium storing a bitstream that is received and decoded by an image decoding apparatus according to the present disclosure and used for restoring an image.
- An image decoding method is an image decoding method performed by an image decoding apparatus, comprising: deriving a prediction sample of the current block based on motion information of the current block, and whether to apply BDOF to the current block. Determining whether or not, when applying the BDOF to the current block, deriving a gradient for the current subblock in the current block, and an improved motion vector for the current subblock based on the gradient (v x , v y ), deriving a BDOF offset based on the gradient and the improved motion vector, and an improved prediction sample for the current block based on the prediction sample and the BDOF offset of the current block. It may include the step of deriving.
- the step of deriving the gradient includes right-shifting the predicted sample of the current block by a first shift amount, and the first shift amount is the bit depth of the current block and It can be set to a fixed value regardless.
- the first shift amount may be 6.
- the deriving of the improved motion vector (v x , v y ) comprises: deriving a first intermediate parameter diff based on a predicted sample of the current block, and the gradient It may include the step of deriving the second intermediate parameters tempH and tempV based on.
- the step of deriving the first intermediate parameter diff includes right-shifting a prediction sample of the current block by a second shift amount, and the second shift amount is the current block It can be set to a fixed value regardless of the bit depth of.
- the second shift amount may be 4.
- the step of deriving the second intermediate parameters tempH and tempV includes right-shifting a value derived based on the gradient by a third shift amount, and the third shift amount May be set to a fixed value regardless of the bit depth of the current block.
- the third shift amount may be 1.
- the improved motion vectors (v x , v y ) may be clipped to a predetermined range.
- the predetermined range for clipping the improved motion vectors (v x , v y ) may be set to a fixed range irrespective of the bit depth of the current block.
- the step of deriving the BDOF offset includes right-shifting a value derived based on the gradient and the improved motion vector by a predetermined shift amount, and the predetermined shift The amount may be set to a fixed range irrespective of the bit depth of the current block.
- the step of deriving an improved prediction sample for the current block includes clipping the BDOF offset into a predetermined range, wherein the predetermined range is a bit depth of the current block. Can be set based on
- An image decoding apparatus includes a memory and at least one processor, wherein the at least one processor derives a prediction sample of the current block based on motion information of the current block, and It is determined whether to apply BDOF, and when BDOF is applied to the current block, a gradient for a current subblock in the current block is derived, and an improved motion vector for the current subblock (v derive x , v y ), derive a BDOF offset based on the gradient and the improved motion vector, and derive an improved prediction sample for the current block based on the prediction sample and the BDOF offset of the current block can do.
- An image encoding method is an image encoding method performed by an image encoding apparatus, comprising: deriving a predicted sample of the current block based on motion information of the current block, and applying a BDOF to the current block. Determining whether to apply or not, when applying BDOF to the current block, deriving a gradient for a current subblock in the current block, and an improved motion vector for the current subblock based on the gradient (v Deriving x , v y ), deriving a BDOF offset based on the gradient and the improved motion vector, and improved prediction for the current block based on a prediction sample of the current block and the BDOF offset It may include the step of deriving a sample.
- a transmission method may transmit a bitstream generated by the image encoding apparatus or image encoding method of the present disclosure.
- a computer-readable recording medium may store a bitstream generated by the image encoding method or image encoding apparatus of the present disclosure.
- an image encoding/decoding method and apparatus with improved encoding/decoding efficiency may be provided.
- an image encoding/decoding method and apparatus for deriving a BDOF offset may be provided.
- an image encoding/decoding method and apparatus for performing BDOF may be provided.
- a method for transmitting a bitstream generated by an image encoding method or an apparatus according to the present disclosure may be provided.
- a recording medium storing a bitstream generated by an image encoding method or apparatus according to the present disclosure may be provided.
- a recording medium may be provided that stores a bitstream that is received and decoded by the image decoding apparatus according to the present disclosure and used for image restoration.
- FIG. 1 is a diagram schematically illustrating a video coding system to which an embodiment according to the present disclosure can be applied.
- FIG. 2 is a diagram schematically illustrating an image encoding apparatus to which an embodiment according to the present disclosure can be applied.
- FIG. 3 is a schematic diagram of an image decoding apparatus to which an embodiment according to the present disclosure can be applied.
- FIG. 4 is a flowchart illustrating a video/video encoding method based on inter prediction.
- FIG. 5 is a diagram illustrating an exemplary configuration of an inter prediction unit 180 according to the present disclosure.
- FIG. 6 is a flowchart illustrating a video/video decoding method based on inter prediction.
- FIG. 7 is a diagram illustrating an exemplary configuration of an inter prediction unit 260 according to the present disclosure.
- FIG. 8 is a diagram illustrating neighboring blocks that can be used as spatial merge candidates.
- FIG. 9 is a diagram schematically illustrating a method of constructing a merge candidate list according to an example of the present disclosure.
- FIG. 10 is a diagram illustrating a pair of candidates for redundancy check performed on a spatial candidate.
- 11 is a diagram for describing a method of scaling a motion vector of a temporal candidate.
- FIG. 12 is a diagram for describing a location in which a temporal candidate is derived.
- FIG. 13 is a diagram schematically illustrating a method of constructing a motion vector predictor candidate list according to an example of the present disclosure.
- FIG. 14 is a diagram illustrating an extended CU to perform BDOF.
- 15 is a diagram for describing a process of deriving a prediction sample of a current block by applying BDOF.
- 16 is a diagram illustrating input and output of a BDOF process according to an embodiment of the present disclosure.
- 17 is a diagram for describing variables used in a BDOF process according to an embodiment of the present disclosure.
- FIG. 18 is a diagram for describing a method of generating a prediction sample for each subblock in a current CU based on whether or not BDOF is applied, according to an embodiment of the present disclosure.
- 19 is a diagram for describing a method of inducing a gradient, an auto-correlation relationship, and a cross-correlation relationship of a current subblock, according to an embodiment of the present disclosure.
- FIG. 20 is a diagram for describing a method of inducing improved motion vectors (motion refinement, v x , v y ), inducing a BDOF offset, and generating a prediction sample of a current subblock, according to an embodiment of the present disclosure. It is a drawing.
- 21 is a diagram for describing variables used in a BDOF process according to another embodiment of the present disclosure.
- FIG. 22 is a diagram for describing a method of inducing a gradient, an auto-correlation relationship, and a cross-correlation relationship of a current subblock according to another embodiment of the present disclosure.
- FIG. 23 is a diagram for describing a method of deriving an improved motion vector (motion refinement, v x , v y ), deriving a BDOF offset, and generating a prediction sample of a current subblock, according to another embodiment of the present disclosure. It is a drawing.
- FIG. 24 is a diagram for describing variables used in a BDOF process according to another embodiment of the present disclosure.
- 25 is a diagram for describing a method of inducing a gradient, an auto-correlation relationship, and a cross-correlation relationship of a current subblock according to another embodiment of the present disclosure.
- 26 is a diagram for describing variables used in a BDOF process according to another embodiment of the present disclosure.
- FIG. 27 is a diagram for describing a method of inducing a gradient, an auto-correlation relationship, and a cross-correlation relationship of a current subblock according to another embodiment of the present disclosure.
- FIG. 28 is a diagram illustrating a content streaming system to which an embodiment of the present disclosure can be applied.
- a component when a component is said to be “connected”, “coupled” or “connected” with another component, it is not only a direct connection relationship, but also an indirect connection relationship in which another component exists in the middle. It may also include.
- a certain component when a certain component "includes” or “have” another component, it means that other components may be further included rather than excluding other components unless otherwise stated. .
- first and second are used only for the purpose of distinguishing one component from other components, and do not limit the order or importance of the components unless otherwise noted. Accordingly, within the scope of the present disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment is referred to as a first component in another embodiment. It can also be called.
- components that are distinguished from each other are intended to clearly describe each feature, and do not necessarily mean that the components are separated. That is, a plurality of components may be integrated into one hardware or software unit, or one component may be distributed to form a plurality of hardware or software units. Therefore, even if not stated otherwise, such integrated or distributed embodiments are also included in the scope of the present disclosure.
- components described in various embodiments do not necessarily mean essential components, and some may be optional components. Accordingly, an embodiment consisting of a subset of components described in an embodiment is also included in the scope of the present disclosure. In addition, embodiments including other elements in addition to the elements described in the various embodiments are included in the scope of the present disclosure.
- the present disclosure relates to encoding and decoding of an image, and terms used in the present disclosure may have a common meaning commonly used in the technical field to which the present disclosure belongs unless newly defined in the present disclosure.
- a “picture” generally refers to a unit representing one image in a specific time period
- a slice/tile is a coding unit constituting a part of a picture
- one picture is one It may be composed of more than one slice/tile.
- a slice/tile may include one or more coding tree units (CTU).
- pixel or “pel” may mean a minimum unit constituting one picture (or image).
- sample may be used as a term corresponding to a pixel.
- a sample may generally represent a pixel or a value of a pixel, may represent only a pixel/pixel value of a luma component, or may represent only a pixel/pixel value of a chroma component.
- unit may represent a basic unit of image processing.
- the unit may include at least one of a specific area of a picture and information related to the corresponding area.
- the unit may be used interchangeably with terms such as “sample array”, “block”, or “area” depending on the case.
- the MxN block may include samples (or sample arrays) consisting of M columns and N rows, or a set (or array) of transform coefficients.
- current block may mean one of “current coding block”, “current coding unit”, “coding object block”, “decoding object block”, or “processing object block”.
- current block may mean “current prediction block” or “prediction target block”.
- transformation inverse transformation
- quantization inverse quantization
- current block may mean “current transform block” or “transform target block”.
- filtering is performed, “current block” may mean “block to be filtered”.
- FIG. 1 shows a video coding system according to this disclosure.
- a video coding system may include an encoding device 10 and a decoding device 20.
- the encoding device 10 may transmit the encoded video and/or image information or data in a file or streaming format to the decoding device 20 through a digital storage medium or a network.
- the encoding apparatus 10 may include a video source generator 11, an encoding unit 12, and a transmission unit 13.
- the decoding apparatus 20 may include a receiving unit 21, a decoding unit 22, and a rendering unit 23.
- the encoder 12 may be referred to as a video/image encoder, and the decoder 22 may be referred to as a video/image decoder.
- the transmission unit 13 may be included in the encoding unit 12.
- the receiving unit 21 may be included in the decoding unit 22.
- the rendering unit 23 may include a display unit, and the display unit may be configured as a separate device or an external component.
- the video source generator 11 may acquire a video/image through a process of capturing, synthesizing, or generating a video/image.
- the video source generator 11 may include a video/image capturing device and/or a video/image generating device.
- the video/image capture device may include, for example, one or more cameras, a video/image archive including previously captured video/images, and the like.
- the video/image generating device may include, for example, a computer, a tablet and a smartphone, and may (electronically) generate a video/image.
- a virtual video/image may be generated through a computer or the like, and in this case, a video/image capturing process may be substituted as a process of generating related data.
- the encoder 12 may encode an input video/image.
- the encoder 12 may perform a series of procedures such as prediction, transformation, and quantization for compression and encoding efficiency.
- the encoder 12 may output encoded data (coded video/image information) in the form of a bitstream.
- the transmission unit 13 may transmit the encoded video/image information or data output in the form of a bitstream to the reception unit 21 of the decoding apparatus 20 through a digital storage medium or a network in a file or streaming form.
- Digital storage media may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD.
- the transmission unit 13 may include an element for generating a media file through a predetermined file format, and may include an element for transmission through a broadcast/communication network.
- the receiving unit 21 may extract/receive the bitstream from the storage medium or network and transmit it to the decoding unit 22.
- the decoder 22 may decode the video/image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoder 12.
- the rendering unit 23 may render the decoded video/image.
- the rendered video/image may be displayed through the display unit.
- FIG. 2 is a diagram schematically illustrating an image encoding apparatus to which an embodiment according to the present disclosure can be applied.
- the image encoding apparatus 100 includes an image segmentation unit 110, a subtraction unit 115, a transformation unit 120, a quantization unit 130, an inverse quantization unit 140, and an inverse transformation unit ( 150), an addition unit 155, a filtering unit 160, a memory 170, an inter prediction unit 180, an intra prediction unit 185, and an entropy encoding unit 190.
- the inter prediction unit 180 and the intra prediction unit 185 may be collectively referred to as a “prediction unit”.
- the transform unit 120, the quantization unit 130, the inverse quantization unit 140, and the inverse transform unit 150 may be included in a residual processing unit.
- the residual processing unit may further include a subtraction unit 115.
- All or at least some of the plurality of constituent units constituting the image encoding apparatus 100 may be implemented as one hardware component (eg, an encoder or a processor) according to embodiments.
- the memory 170 may include a decoded picture buffer (DPB), and may be implemented by a digital storage medium.
- DPB decoded picture buffer
- the image segmentation unit 110 may divide an input image (or picture, frame) input to the image encoding apparatus 100 into one or more processing units.
- the processing unit may be referred to as a coding unit (CU).
- the coding unit is a coding tree unit (CTU) or a largest coding unit (LCU) recursively according to a QT/BT/TT (Quad-tree/binary-tree/ternary-tree) structure ( It can be obtained by dividing recursively.
- one coding unit may be divided into a plurality of coding units of a deeper depth based on a quad tree structure, a binary tree structure, and/or a ternary tree structure.
- a quad tree structure may be applied first, and a binary tree structure and/or a ternary tree structure may be applied later.
- the coding procedure according to the present disclosure may be performed based on the final coding unit that is no longer divided.
- the largest coding unit may be directly used as the final coding unit, or a coding unit of a lower depth obtained by dividing the largest coding unit may be used as the final cornet unit.
- the coding procedure may include a procedure such as prediction, transformation, and/or restoration, which will be described later.
- the processing unit of the coding procedure may be a prediction unit (PU) or a transform unit (TU).
- the prediction unit and the transform unit may be divided or partitioned from the final coding unit, respectively.
- the prediction unit may be a unit of sample prediction
- the transform unit may be a unit for inducing a transform coefficient and/or a unit for inducing a residual signal from the transform coefficient.
- the prediction unit (inter prediction unit 180 or intra prediction unit 185) performs prediction on a block to be processed (current block), and generates a predicted block including prediction samples for the current block. Can be generated.
- the prediction unit may determine whether intra prediction or inter prediction is applied in units of a current block or CU.
- the prediction unit may generate various information on prediction of the current block and transmit it to the entropy encoding unit 190.
- the information on prediction may be encoded by the entropy encoding unit 190 and output in the form of a bitstream.
- the intra prediction unit 185 may predict the current block by referring to samples in the current picture.
- the referenced samples may be located in a neighborhood of the current block or may be located away from each other according to an intra prediction mode and/or an intra prediction technique.
- the intra prediction modes may include a plurality of non-directional modes and a plurality of directional modes.
- the non-directional mode may include, for example, a DC mode and a planar mode (Planar mode).
- the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes, depending on the degree of detail of the prediction direction. However, this is an example, and more or less directional prediction modes may be used depending on the setting.
- the intra prediction unit 185 may determine a prediction mode applied to the current block by using the prediction mode applied to the neighboring block.
- the inter prediction unit 180 may derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture.
- motion information may be predicted in units of blocks, subblocks, or samples based on a correlation between motion information between a neighboring block and a current block.
- the motion information may include a motion vector and a reference picture index.
- the motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information.
- the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block existing in the reference picture.
- the reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different from each other.
- the temporal neighboring block may be referred to by a name such as a collocated reference block and a collocated CU (colCU).
- a reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic).
- the inter prediction unit 180 constructs a motion information candidate list based on neighboring blocks, and provides information indicating which candidate is used to derive a motion vector and/or a reference picture index of the current block. Can be generated. Inter prediction may be performed based on various prediction modes.
- the inter prediction unit 180 may use motion information of a neighboring block as motion information of a current block.
- a residual signal may not be transmitted.
- MVP motion vector prediction
- a motion vector of a neighboring block is used as a motion vector predictor, and an indicator for a motion vector difference and a motion vector predictor ( indicator) to signal the motion vector of the current block.
- the motion vector difference may mean a difference between a motion vector of a current block and a motion vector predictor.
- the prediction unit may generate a prediction signal based on various prediction methods and/or prediction techniques to be described later.
- the prediction unit may apply intra prediction or inter prediction for prediction of the current block, and may simultaneously apply intra prediction and inter prediction.
- a prediction method in which intra prediction and inter prediction are applied simultaneously for prediction of the current block may be referred to as combined inter and intra prediction (CIIP).
- the prediction unit may perform intra block copy (IBC) for prediction of the current block.
- the intra block copy may be used for content image/movie coding such as games, such as, for example, screen content coding (SCC).
- IBC is a method of predicting a current block by using a reference block in a current picture at a distance from the current block by a predetermined distance. When IBC is applied, the position of the reference block in the current picture may be encoded as a vector (block vector) corresponding to the predetermined distance.
- the prediction signal generated through the prediction unit may be used to generate a reconstructed signal or may be used to generate a residual signal.
- the subtraction unit 115 subtracts the prediction signal (predicted block, prediction sample array) output from the prediction unit from the input image signal (original block, original sample array), and subtracts a residual signal (remaining block, residual sample array). ) Can be created.
- the generated residual signal may be transmitted to the converter 120.
- the transform unit 120 may generate transform coefficients by applying a transform technique to the residual signal.
- the transformation technique uses at least one of DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), KLT (Karhunen-Loeve Transform), GBT (Graph-Based Transform), or CNT (Conditionally Non-linear Transform).
- DCT Discrete Cosine Transform
- DST Discrete Sine Transform
- KLT Kerhunen-Loeve Transform
- GBT Graph-Based Transform
- CNT Conditionally Non-linear Transform
- GBT refers to the transformation obtained from this graph when the relationship information between pixels is expressed in a graph.
- CNT refers to a transformation obtained based on generating a prediction signal using all previously reconstructed pixels.
- the conversion process may be applied to a block of pixels having the same size of a square, or may be applied to a block of a variable size other than a square.
- the quantization unit 130 may quantize the transform coefficients and transmit the quantization to the entropy encoding unit 190.
- the entropy encoding unit 190 may encode a quantized signal (information on quantized transform coefficients) and output it as a bitstream. Information about the quantized transform coefficients may be called residual information.
- the quantization unit 130 may rearrange the quantized transform coefficients in a block form into a one-dimensional vector form based on a coefficient scan order, and the quantized transform coefficients in the form of the one-dimensional vector It is also possible to generate information about transform coefficients.
- the entropy encoding unit 190 may perform various encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC).
- the entropy encoding unit 190 may encode together or separately information necessary for video/image restoration (eg, values of syntax elements) in addition to quantized transform coefficients.
- the encoded information (eg, encoded video/video information) may be transmitted or stored in a bitstream form in units of network abstraction layer (NAL) units.
- the video/video information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS).
- the video/video information may further include general constraint information.
- the signaling information, transmitted information, and/or syntax elements mentioned in the present disclosure may be encoded through the above-described encoding procedure and included in the bitstream.
- the bitstream may be transmitted through a network or may be stored in a digital storage medium.
- the network may include a broadcasting network and/or a communication network
- the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD.
- a transmission unit (not shown) for transmitting the signal output from the entropy encoding unit 190 and/or a storage unit (not shown) for storing may be provided as an internal/external element of the image encoding apparatus 100, or transmission The unit may be provided as a component of the entropy encoding unit 190.
- the quantized transform coefficients output from the quantization unit 130 may be used to generate a residual signal.
- a residual signal residual block or residual samples
- inverse quantization and inverse transform residual transforms
- the addition unit 155 adds the reconstructed residual signal to the prediction signal output from the inter prediction unit 180 or the intra prediction unit 185 to obtain a reconstructed signal (a reconstructed picture, a reconstructed block, and a reconstructed sample array). Can be generated.
- a reconstructed signal (a reconstructed picture, a reconstructed block, and a reconstructed sample array).
- the predicted block may be used as a reconstructed block.
- the addition unit 155 may be referred to as a restoration unit or a restoration block generation unit.
- the generated reconstructed signal may be used for intra prediction of the next processing target block in the current picture, and may be used for inter prediction of the next picture through filtering as described later.
- LMCS luma mapping with chroma scaling
- the filtering unit 160 may improve subjective/objective image quality by applying filtering to the reconstructed signal.
- the filtering unit 160 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and the modified reconstructed picture may be converted to the memory 170, specifically, the DPB of the memory 170. Can be saved on.
- the various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.
- the filtering unit 160 may generate various information about filtering and transmit it to the entropy encoding unit 190 as described later in the description of each filtering method. Information about filtering may be encoded by the entropy encoding unit 190 and output in the form of a bitstream.
- the modified reconstructed picture transmitted to the memory 170 may be used as a reference picture in the inter prediction unit 180.
- the image encoding apparatus 100 may avoid prediction mismatch between the image encoding apparatus 100 and the image decoding apparatus, and may improve encoding efficiency.
- the DPB in the memory 170 may store a reconstructed picture modified to be used as a reference picture in the inter prediction unit 180.
- the memory 170 may store motion information of a block from which motion information in a current picture is derived (or encoded) and/or motion information of blocks in a picture that have already been reconstructed.
- the stored motion information may be transmitted to the inter prediction unit 180 in order to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block.
- the memory 170 may store reconstructed samples of reconstructed blocks in the current picture, and may be transmitted to the intra prediction unit 185.
- FIG. 3 is a schematic diagram of an image decoding apparatus to which an embodiment according to the present disclosure can be applied.
- the image decoding apparatus 200 includes an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an addition unit 235, a filtering unit 240, and a memory 250. ), an inter prediction unit 260 and an intra prediction unit 265.
- the inter prediction unit 260 and the intra prediction unit 265 may be collectively referred to as a “prediction unit”.
- the inverse quantization unit 220 and the inverse transform unit 230 may be included in the residual processing unit.
- All or at least some of the plurality of constituent units constituting the image decoding apparatus 200 may be implemented as one hardware component (eg, a decoder or a processor) according to embodiments.
- the memory 170 may include a DPB, and may be implemented by a digital storage medium.
- the image decoding apparatus 200 receiving a bitstream including video/image information may reconstruct an image by performing a process corresponding to the process performed by the image encoding apparatus 100 of FIG. 1.
- the image decoding apparatus 200 may perform decoding using a processing unit applied by the image encoding apparatus.
- the processing unit of decoding may be, for example, a coding unit.
- the coding unit may be a coding tree unit or may be obtained by dividing the largest coding unit.
- the reconstructed image signal decoded and output through the image decoding apparatus 200 may be reproduced through a reproducing apparatus (not shown).
- the image decoding apparatus 200 may receive a signal output from the image encoding apparatus of FIG. 1 in the form of a bitstream.
- the received signal may be decoded through the entropy decoding unit 210.
- the entropy decoding unit 210 may parse the bitstream to derive information (eg, video/video information) necessary for image restoration (or picture restoration).
- the video/video information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS).
- the video/video information may further include general constraint information.
- the image decoding apparatus may additionally use information on the parameter set and/or the general restriction information to decode an image.
- the signaling information, received information, and/or syntax elements mentioned in the present disclosure may be obtained from the bitstream by decoding through the decoding procedure.
- the entropy decoding unit 210 decodes information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and a value of a syntax element required for image reconstruction, and a quantized value of a transform coefficient related to a residual. Can be printed.
- the CABAC entropy decoding method a bin corresponding to each syntax element is received in a bitstream, and information on the syntax element to be decoded, decoding information of a neighboring block and a block to be decoded, or information of a symbol/bin decoded in a previous step.
- the context model is determined by using and, according to the determined context model, the probability of occurrence of bins is predicted to perform arithmetic decoding of the bins to generate a symbol corresponding to the value of each syntax element. I can.
- the CABAC entropy decoding method may update the context model using information of the decoded symbol/bin for the context model of the next symbol/bin after the context model is determined.
- information about prediction is provided to the prediction unit (inter prediction unit 260 and intra prediction unit 265), and the register on which entropy decoding is performed by the entropy decoding unit 210
- the dual value that is, quantized transform coefficients and related parameter information may be input to the inverse quantization unit 220.
- information about filtering among information decoded by the entropy decoding unit 210 may be provided to the filtering unit 240.
- a receiving unit for receiving a signal output from the image encoding device may be additionally provided as an inner/outer element of the image decoding device 200, or the receiving unit is provided as a component of the entropy decoding unit 210 It could be.
- the video decoding apparatus may include an information decoder (video/video/picture information decoder) and/or a sample decoder (video/video/picture sample decoder).
- the information decoder may include an entropy decoding unit 210, and the sample decoder includes an inverse quantization unit 220, an inverse transform unit 230, an addition unit 235, a filtering unit 240, a memory 250, It may include at least one of the inter prediction unit 260 and the intra prediction unit 265.
- the inverse quantization unit 220 may inverse quantize the quantized transform coefficients and output transform coefficients.
- the inverse quantization unit 220 may rearrange the quantized transform coefficients in a two-dimensional block shape. In this case, the rearrangement may be performed based on a coefficient scan order performed by the image encoding apparatus.
- the inverse quantization unit 220 may perform inverse quantization on quantized transform coefficients using a quantization parameter (eg, quantization step size information) and obtain transform coefficients.
- a quantization parameter eg, quantization step size information
- the inverse transform unit 230 may inverse transform the transform coefficients to obtain a residual signal (residual block, residual sample array).
- the prediction unit may perform prediction on the current block and generate a predicted block including prediction samples for the current block.
- the prediction unit may determine whether intra prediction or inter prediction is applied to the current block based on the prediction information output from the entropy decoding unit 210, and determine a specific intra/inter prediction mode (prediction technique). I can.
- the prediction unit can generate the prediction signal based on various prediction methods (techniques) described later.
- the intra prediction unit 265 may predict the current block by referring to samples in the current picture.
- the description of the intra prediction unit 185 may be equally applied to the intra prediction unit 265.
- the inter prediction unit 260 may derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture.
- motion information may be predicted in units of blocks, subblocks, or samples based on correlation between motion information between neighboring blocks and the current block.
- the motion information may include a motion vector and a reference picture index.
- the motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information.
- the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block existing in the reference picture.
- the inter prediction unit 260 may construct a motion information candidate list based on neighboring blocks, and derive a motion vector and/or a reference picture index of the current block based on the received candidate selection information.
- Inter prediction may be performed based on various prediction modes (techniques), and the information on prediction may include information indicating a mode (technique) of inter prediction for the current block.
- the addition unit 235 is reconstructed by adding the obtained residual signal to the prediction signal (predicted block, prediction sample array) output from the prediction unit (including the inter prediction unit 260 and/or the intra prediction unit 265).
- a signal (restored picture, reconstructed block, reconstructed sample array) can be generated.
- the description of the addition unit 155 may be equally applied to the addition unit 235.
- LMCS luma mapping with chroma scaling
- the filtering unit 240 may improve subjective/objective image quality by applying filtering to the reconstructed signal.
- the filtering unit 240 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and the modified reconstructed picture may be converted to the memory 250, specifically, the DPB of the memory 250. Can be saved on.
- the various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.
- the reconstructed picture (modified) stored in the DPB of the memory 250 may be used as a reference picture in the inter prediction unit 260.
- the memory 250 may store motion information of a block from which motion information in a current picture is derived (or decoded) and/or motion information of blocks in a picture that have already been reconstructed.
- the stored motion information may be transmitted to the inter prediction unit 260 to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block.
- the memory 250 may store reconstructed samples of reconstructed blocks in the current picture, and may be transmitted to the intra prediction unit 265.
- embodiments described in the filtering unit 160, the inter prediction unit 180, and the intra prediction unit 185 of the encoding apparatus 100 are respectively The same or corresponding to the prediction unit 260 and the intra prediction unit 265 may be applied.
- the image encoding/decoding apparatus may derive a prediction sample by performing inter prediction in block units.
- Inter prediction may refer to a prediction technique derived in a method dependent on data elements of picture(s) other than the current picture.
- a prediction block for the current block may be derived based on a reference block specified by a motion vector on a reference picture.
- motion information of the current block may be derived based on the correlation of motion information between the neighboring block and the current block, and motion information in units of blocks, sub-blocks or samples Can be induced.
- the motion information may include a motion vector and a reference picture index.
- the motion information may further include inter prediction type information.
- the inter prediction type information may mean directional information of inter prediction.
- the inter prediction type information may indicate that the current block is predicted using one of L0 prediction, L1 prediction, and Bi prediction.
- the neighboring blocks of the current block may include a spatial neighboring block existing in the current picture and a temporal neighboring block existing in the reference picture.
- the reference picture including the reference block for the current block and the reference picture including the temporal neighboring block may be the same or different.
- the temporal neighboring block may be referred to as a collocated reference block, a colCU, and the like, and a reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). I can.
- a motion information candidate list may be constructed based on neighboring blocks of the current block.
- a flag or index information indicating which candidate is used to derive a motion vector and/or a reference picture index of the current block is provided. Can be signaled.
- the motion information may include L0 motion information and/or L1 motion information according to the inter prediction type.
- the motion vector in the L0 direction may be defined as an L0 motion vector or MVL0
- the motion vector in the L1 direction may be defined as an L1 motion vector or MVL1.
- the prediction based on the L0 motion vector may be defined as L0 prediction
- the prediction based on the L1 motion vector may be defined as the L1 prediction
- the prediction based on both the L0 motion vector and the L1 motion vector is bi-prediction (Bi- prediction).
- the motion vector L0 may mean a motion vector associated with the reference picture list L0
- the motion vector L1 may mean a motion vector associated with the reference picture list L1.
- the reference picture list L0 may include pictures prior to the current picture in an output order as reference pictures, and the reference picture list L1 may include pictures after the current picture in an output order.
- previous pictures may be defined as forward (reference) pictures, and subsequent pictures may be defined as backward (reference) pictures.
- the reference picture list L0 may further include pictures after the output order than the current picture.
- previous pictures in the reference picture list L0 may be indexed first, and pictures afterwards may be indexed next.
- the reference picture list L1 may further include previous pictures in output order than the current picture.
- subsequent pictures in the reference picture list L1 may be indexed first, and previous pictures may be indexed next.
- the output order may correspond to a picture order count (POC) order.
- POC picture order count
- FIG. 4 is a flowchart illustrating a video/video encoding method based on inter prediction.
- FIG. 5 is a diagram illustrating an exemplary configuration of an inter prediction unit 180 according to the present disclosure.
- the encoding method of FIG. 4 may be performed by the video encoding apparatus of FIG. 2. Specifically, step S410 may be performed by the inter prediction unit 180, and step S420 may be performed by the residual processing unit. Specifically, step S420 may be performed by the subtraction unit 115. Step S430 may be performed by the entropy encoding unit 190.
- the prediction information of step S430 may be derived by the inter prediction unit 180, and the residual information of step S430 may be derived by the residual processing unit.
- the residual information is information on the residual samples.
- the residual information may include information on quantized transform coefficients for the residual samples.
- the residual samples may be derived as transform coefficients through the transform unit 120 of the image encoding apparatus, and the transform coefficients may be derived as quantized transform coefficients through the quantization unit 130.
- Information on the quantized transform coefficients may be encoded by the entropy encoding unit 190 through a residual coding procedure.
- the image encoding apparatus may perform inter prediction on the current block (S410).
- the image encoding apparatus may derive the inter prediction mode and motion information of the current block and generate prediction samples of the current block.
- the procedure for determining the inter prediction mode, deriving motion information, and generating prediction samples may be performed simultaneously, or one procedure may be performed before the other procedure.
- the inter prediction unit 180 of the image encoding apparatus may include a prediction mode determination unit 181, a motion information derivation unit 182, and a prediction sample derivation unit 183. have.
- a prediction mode determination unit 181 determines a prediction mode for the current block
- a motion information derivation unit 182 derives motion information of the current block
- a prediction sample derivation unit 183 predicts the current block. Samples can be derived.
- the inter prediction unit 180 of the video encoding apparatus searches for a block similar to the current block within a predetermined area (search area) of reference pictures through motion estimation, and a difference between the current block and the current block. It is possible to derive a reference block that is less than the minimum or a certain criterion.
- a reference picture index indicating a reference picture in which the reference block is located may be derived, and a motion vector may be derived based on a position difference between the reference block and the current block.
- the image encoding apparatus may determine a mode applied to the current block from among various inter prediction modes.
- the image encoding apparatus may compare a rate-distortion (RD) cost for the various prediction modes and determine an optimal inter prediction mode for the current block.
- RD rate-distortion
- the method of determining the inter prediction mode for the current block by the image encoding apparatus is not limited to the above example, and various methods may be used.
- the inter prediction mode for the current block is a merge mode, a merge skip mode, an MVP mode (Motion Vector Prediction mode), a SMVD mode (Symmetric Motion Vector Difference), an affine mode, and Subblock-based merge mode, AMVR mode (Adaptive Motion Vector Resolution mode), HMVP mode (History-based Motion Vector Predictor mode), Pair-wise average merge mode, MMVD mode It may be determined at least one of (Merge mode with Motion Vector Differences mode), DMVR mode (Decoder side Motion Vector Refinement mode), CIIP mode (Combined Inter and Intra Prediction mode), and GPM (Geometric Partitioning mode).
- the image encoding apparatus may derive merge candidates from neighboring blocks of the current block and construct a merge candidate list using the derived merge candidates.
- the apparatus for encoding an image may derive a reference block in which a difference between the current block and the current block among reference blocks indicated by merge candidates included in the merge candidate list is a minimum or a predetermined reference or less.
- a merge candidate associated with the derived reference block is selected, and merge index information indicating the selected merge candidate may be generated and signaled to the image decoding apparatus.
- Motion information of the current block may be derived using motion information of the selected merge candidate.
- the video encoding apparatus when the MVP mode is applied to the current block, derives motion vector predictor (MVP) candidates from neighboring blocks of the current block, and uses the derived MVP candidates to perform MVP. Can construct a candidate list.
- the video encoding apparatus may use a motion vector of an MVP candidate selected from among MVP candidates included in the MVP candidate list as the MVP of the current block.
- a motion vector indicating a reference block derived by the above-described motion estimation may be used as the motion vector of the current block, and among the MVP candidates, the difference between the motion vector of the current block and the current block is the smallest.
- An MVP candidate having a motion vector may be the selected MVP candidate.
- a motion vector difference which is a difference obtained by subtracting the MVP from the motion vector of the current block, may be derived.
- index information indicating the selected MVP candidate and information about the MVD may be signaled to the video decoding apparatus.
- the value of the reference picture index may consist of reference picture index information and may be separately signaled to the video decoding apparatus.
- the image encoding apparatus may derive residual samples based on the prediction samples (S420).
- the image encoding apparatus may derive the residual samples by comparing the original samples of the current block with the prediction samples. For example, the residual sample may be derived by subtracting a corresponding prediction sample from an original sample.
- the image encoding apparatus may encode image information including prediction information and residual information (S430).
- the image encoding apparatus may output the encoded image information in the form of a bitstream.
- the prediction information is information related to the prediction procedure and may include prediction mode information (eg, skip flag, merge flag or mode index, etc.) and information on motion information.
- the prediction mode information e.g, skip flag, merge flag or mode index, etc.
- the skip flag is information indicating whether the skip mode is applied to the current block
- the merge flag is information indicating whether the merge mode is applied to the current block.
- the prediction mode information may be information indicating one of a plurality of prediction modes, such as a mode index. When the skip flag and the merge flag are each 0, it may be determined that the MVP mode is applied to the current block.
- the information on the motion information may include candidate selection information (eg, merge index, mvp flag, or mvp index) that is information for deriving a motion vector.
- candidate selection information eg, merge index, mvp flag, or mvp index
- the merge index may be signaled when a merge mode is applied to the current block, and may be information for selecting one of merge candidates included in the merge candidate list.
- the MVP flag or the MVP index may be signaled when the MVP mode is applied to the current block, and may be information for selecting one of MVP candidates included in the MVP candidate list.
- the MVP flag may be signaled using the syntax element mvp_l0_flag or mvp_l1_flag.
- the information on the motion information may include information on the above-described MVD and/or reference picture index information.
- the information on the motion information may include information indicating whether L0 prediction, L1 prediction, or pair (Bi) prediction is applied.
- the residual information is information on the residual samples.
- the residual information may include information on quantized transform coefficients for the residual samples.
- the output bitstream may be stored in a (digital) storage medium and transmitted to an image decoding device, or may be transmitted to an image decoding device through a network.
- the image encoding apparatus may generate a reconstructed picture (a picture including reconstructed samples and a reconstructed block) based on the reference samples and the residual samples. This is because the video encoding apparatus derives the same prediction result as that performed by the video decoding apparatus, and coding efficiency can be improved through this. Accordingly, the apparatus for encoding an image may store a reconstructed picture (or reconstructed samples, and a reconstructed block) in a memory and use it as a reference picture for inter prediction. As described above, an in-loop filtering procedure or the like may be further applied to the reconstructed picture.
- FIG. 6 is a flowchart illustrating a video/video decoding method based on inter prediction.
- FIG. 7 is a diagram illustrating an exemplary configuration of an inter prediction unit 260 according to the present disclosure.
- the image decoding apparatus may perform an operation corresponding to an operation performed by the image encoding apparatus.
- the image decoding apparatus may perform prediction on the current block and derive prediction samples based on the received prediction information.
- the decoding method of FIG. 6 may be performed by the video decoding apparatus of FIG. 3.
- Steps S610 to S630 may be performed by the inter prediction unit 260, and the prediction information of step S610 and the residual information of step S640 may be obtained from the bitstream by the entropy decoding unit 210.
- the residual processing unit of the image decoding apparatus may derive residual samples for the current block based on the residual information (S640).
- the inverse quantization unit 220 of the residual processing unit derives transform coefficients by performing inverse quantization based on the quantized transform coefficients derived based on the residual information
- the inverse transform unit of the residual processing unit ( 230) may derive residual samples for the current block by performing inverse transform on the transform coefficients.
- Step S650 may be performed by the addition unit 235 or the restoration unit.
- the image decoding apparatus may determine a prediction mode for the current block based on the received prediction information (S610).
- the video decoding apparatus may determine which inter prediction mode is applied to the current block based on prediction mode information in the prediction information.
- the skip mode is applied to the current block based on the skip flag.
- one of various inter prediction mode candidates may be selected based on the mode index.
- the inter prediction mode candidates may include a skip mode, a merge mode, and/or an MVP mode, or may include various inter prediction modes to be described later.
- the image decoding apparatus may derive motion information of the current block based on the determined inter prediction mode (S620). For example, when a skip mode or a merge mode is applied to the current block, the video decoding apparatus may configure a merge candidate list to be described later, and select one merge candidate from among merge candidates included in the merge candidate list. The selection may be performed based on the aforementioned candidate selection information (merge index). Motion information of the current block may be derived using motion information of the selected merge candidate. For example, motion information of the selected merge candidate may be used as motion information of the current block.
- the video decoding apparatus may configure an MVP candidate list and use a motion vector of an MVP candidate selected from among MVP candidates included in the MVP candidate list as the MVP of the current block. have.
- the selection may be performed based on the aforementioned candidate selection information (mvp flag or mvp index).
- the MVD of the current block may be derived based on the information on the MVD
- a motion vector of the current block may be derived based on the MVP of the current block and the MVD.
- a reference picture index of the current block may be derived based on the reference picture index information.
- a picture indicated by the reference picture index in the reference picture list for the current block may be derived as a reference picture referenced for inter prediction of the current block.
- the image decoding apparatus may generate prediction samples for the current block based on motion information of the current block (S630).
- the reference picture may be derived based on the reference picture index of the current block, and prediction samples of the current block may be derived using samples of the reference block indicated on the reference picture by the motion vector of the current block.
- a prediction sample filtering procedure may be further performed on all or part of the prediction samples of the current block.
- the inter prediction unit 260 of the image decoding apparatus may include a prediction mode determination unit 261, a motion information derivation unit 262, and a prediction sample derivation unit 263. have.
- the inter prediction unit 260 of the video decoding apparatus determines a prediction mode for the current block based on the prediction mode information received from the prediction mode determination unit 261, and motion information received from the motion information derivation unit 262.
- the motion information (motion vector and/or reference picture index, etc.) of the current block may be derived based on the information about and prediction samples of the current block may be derived by the prediction sample derivation unit 263.
- the image decoding apparatus may generate residual samples for the current block based on the received residual information (S640).
- the image decoding apparatus may generate reconstructed samples for the current block based on the prediction samples and the residual samples, and generate a reconstructed picture based on the prediction samples (S650). Thereafter, as described above, an in-loop filtering procedure or the like may be further applied to the reconstructed picture.
- the inter prediction procedure may include determining an inter prediction mode, deriving motion information according to the determined prediction mode, and performing prediction based on the derived motion information (generating a prediction sample).
- the inter prediction procedure may be performed in an image encoding apparatus and an image decoding apparatus.
- inter prediction may be performed using motion information of a current block.
- the video encoding apparatus may derive optimal motion information for the current block through a motion estimation procedure. For example, the video encoding apparatus can search for a similar reference block with high correlation using the original block in the original picture for the current block in units of fractional pixels within a predetermined search range in the reference picture, and derive motion information through this. can do.
- Block similarity can be calculated based on the sum of absolute differences (SAD) between the current block and the reference block.
- SAD sum of absolute differences
- motion information may be derived based on the reference block having the smallest SAD in the search area.
- the derived motion information may be signaled to the video decoding apparatus according to various methods based on the inter prediction mode.
- motion information of the current block is not directly transmitted, and motion information of the current block is derived using motion information of a neighboring block. Accordingly, motion information of the current prediction block may be indicated by transmitting flag information indicating that the merge mode has been used and candidate selection information indicating which neighboring blocks have been used as merge candidates (eg, merge index).
- flag information indicating that the merge mode has been used
- candidate selection information indicating which neighboring blocks have been used as merge candidates (eg, merge index).
- the current block since the current block is a unit of performing prediction, the current block is used in the same meaning as the current prediction block, and the neighboring block may be used in the same meaning as the neighboring prediction block.
- the video encoding apparatus may search for a merge candidate block used to induce motion information of a current block. For example, up to five merge candidate blocks may be used, but the number of merge candidate blocks is not limited thereto. The maximum number of merge candidate blocks may be transmitted in a slice header or a tile group header, but is not limited thereto.
- the image encoding apparatus may generate a merge candidate list, and among them, a merge candidate block having the lowest RD cost may be selected as a final merge candidate block.
- the present disclosure provides various embodiments of a merge candidate block constituting the merge candidate list.
- the merge candidate list may use, for example, five merge candidate blocks.
- four spatial merge candidates and one temporal merge candidate can be used.
- FIG. 8 is a diagram illustrating neighboring blocks that can be used as spatial merge candidates.
- FIG. 9 is a diagram schematically illustrating a method of constructing a merge candidate list according to an example of the present disclosure.
- the image encoding apparatus/image decoding apparatus may insert spatial merge candidates derived by searching for spatial neighboring blocks of the current block into the merge candidate list (S910).
- the spatial neighboring blocks are a block around the lower left corner of the current block (A0), a neighboring block on the left (A1), a block around the upper right corner (B0), and a neighboring block at the top (B1) ), may include blocks B2 around the upper left corner.
- additional neighboring blocks such as a right peripheral block, a lower peripheral block, and a right lower peripheral block may be further used as the spatial neighboring blocks.
- the image encoding apparatus/image decoding apparatus may detect available blocks by searching for the spatial neighboring blocks based on priority, and derive motion information of the detected blocks as the spatial merge candidates. For example, the video encoding apparatus/video decoding apparatus may construct a merge candidate list by searching the five blocks shown in FIG. 8 in the order of A1, B1, B0, A0, B2 and sequentially indexing the available candidates. have.
- the image encoding apparatus/image decoding apparatus may insert a temporal merge candidate derived by searching for a temporal neighboring block of the current block into the merge candidate list (S920).
- the temporal neighboring block may be located on a reference picture that is a picture different from the current picture in which the current block is located.
- the reference picture in which the temporal neighboring block is located may be referred to as a collocated picture or a col picture.
- the temporal neighboring block may be searched in the order of a lower-right corner neighboring block and a lower-right center block of a co-located block with respect to the current block on the col picture. Meanwhile, when motion data compression is applied to reduce the memory load, specific motion information for the col picture may be stored as representative motion information for each predetermined storage unit.
- the predetermined storage unit may be previously determined as, for example, a 16x16 sample unit or an 8x8 sample unit, or size information on the predetermined storage unit may be signaled from an image encoding apparatus to an image decoding apparatus.
- motion information of the temporal neighboring block may be replaced with representative motion information of the predetermined storage unit in which the temporal neighboring block is located.
- the temporal merge candidate may be derived based on motion information of a covered prediction block.
- the coordinates of the temporally neighboring blocks (xTnb, yTnb) If la, the ((xTnb >> n) ⁇ n ) the modified position, ( Motion information of a prediction block located at yTnb>>n) ⁇ n)) may be used for the temporal merge candidate.
- the predetermined storage unit is a 16x16 sample unit
- the modified positions ((xTnb>>4) ⁇ 4)
- (yTnb) The motion information of the prediction block located at >>4) ⁇ 4) may be used for the temporal merge candidate.
- the predetermined storage unit is an 8x8 sample unit
- the coordinates of the temporal neighboring block are (xTnb, yTnb)
- the modified positions ((xTnb>>3) ⁇ 3), (yTnb> Motion information of the prediction block located at >3) ⁇ 3)) may be used for the temporal merge candidate.
- the image encoding apparatus/image decoding apparatus may check whether the number of current merge candidates is less than the number of maximum merge candidates (S930).
- the number of the maximum merge candidates may be predefined or may be signaled from the image encoding apparatus to the image decoding apparatus.
- the image encoding apparatus may generate information on the number of the maximum merge candidates, encode, and transmit the information to the image decoding apparatus in the form of a bitstream.
- a subsequent candidate addition process (S940) may not proceed.
- the video encoding apparatus/video decoding apparatus may induce an additional merge candidate according to a predetermined method and then insert it into the merge candidate list. Yes (S940).
- the additional merge candidate is, for example, history based merge candidate(s), pair-wise average merge candidate(s), ATMVP, combined bi-predictive merge candidate (the slice/tile group type of the current slice/tile group is B type. Case) and/or a zero vector merge candidate.
- the image encoding apparatus/image decoding apparatus may terminate the construction of the merge candidate list.
- the video encoding apparatus may select an optimal merge candidate from among merge candidates constituting the merge candidate list based on RD cost, and use candidate selection information (ex. merge candidate index, merge index) indicating the selected merge candidate as a video image. It can be signaled by the decoding device.
- the video decoding apparatus may select the optimal merge candidate based on the merge candidate list and the candidate selection information.
- motion information of the selected merge candidate may be used as motion information of the current block, and prediction samples of the current block may be derived based on the motion information of the current block.
- the image encoding apparatus may derive residual samples of the current block based on the prediction samples, and may signal residual information about the residual samples to the image decoding apparatus.
- the image decoding apparatus may generate reconstructed samples based on residual samples derived based on the residual information and the prediction samples, and generate a reconstructed picture based on the residual samples.
- motion information of the current block may be derived in the same manner as when the merge mode is applied previously. However, when the skip mode is applied, the residual signal for the corresponding block is omitted, and thus prediction samples can be directly used as reconstructed samples.
- the skip mode may be applied when the value of cu_skip_flag is 1, for example.
- the spatial candidate may represent the spatial merge candidate described above.
- the derivation of the spatial candidate may be performed based on spatial neighboring blocks. For example, up to four spatial candidates may be derived from candidate blocks existing at the location shown in FIG. 8.
- the order of deriving the spatial candidate may be the order of A1 -> B1 -> B0 -> A0 -> B2.
- the order of deriving the spatial candidate is not limited to the above order, and may be, for example, B1 -> A1 -> B0 -> A0 -> B2.
- the last position in the order (position B2 in the above example) may be considered when at least one of the preceding four positions (in the example, A1, B1, B0, and A0) is not available.
- the fact that the block at the predetermined location is not available may include a case in which the corresponding block belongs to a different slice or a different tile from the current block, or the corresponding block is an intra-predicted block.
- a spatial candidate is derived from a first position (A1 or B1 in the above example) in order
- a redundancy check may be performed on spatial candidates of a subsequent position. For example, when motion information of a subsequent spatial candidate is the same as motion information of a spatial candidate already included in the merge candidate list, the subsequent spatial candidate is not included in the merge candidate list, thereby improving encoding efficiency.
- the redundancy check performed on subsequent spatial candidates is not performed on all possible candidate pairs, but only on some candidate pairs, thereby reducing computational complexity.
- FIG. 10 is a diagram illustrating a pair of candidates for redundancy check performed on a spatial candidate.
- the redundancy check for the spatial candidate at the location B0 may be performed only on the spatial candidate at the A0 location.
- the redundancy check for the spatial candidate at the location B1 may be performed only on the spatial candidate at the location B0.
- the redundancy check for the spatial candidate at the A1 position may be performed only on the spatial candidate at the A0 position.
- the redundancy check for the spatial candidate of the B2 position may be performed only on the spatial candidate of the A0 position and the B0 position.
- the example shown in FIG. 10 is an example in which the order of deriving the spatial candidate is the order of A0 -> B0 -> B1 -> A1 -> B2.
- the present invention is not limited thereto, and even if the order of inducing spatial candidates is changed, as in the example illustrated in FIG. 10, the redundancy check may be performed for only some candidate pairs.
- the temporal candidate may represent the temporal merge candidate described above.
- the motion vector of the temporal candidate may correspond to the temporal candidate of the MVP mode.
- the motion vector of the temporal candidate may be scaled.
- the scaling is performed on a co-located CU (hereinafter, referred to as a'col block') belonging to a collocated reference picture (colPic) (hereinafter, referred to as a'collocated picture'). It can be done on the basis of.
- the reference picture list used for derivation of the collocated block may be explicitly signaled in the slice header.
- 11 is a diagram for describing a method of scaling a motion vector of a temporal candidate.
- curr_CU and curr_pic represent a current block and a current picture
- col_CU and col_pic represent a collocated block and a collated picture
- curr_ref indicates a reference picture of the current block
- col_ref indicates a reference picture of a collocated block
- tb denotes a distance between the reference picture of the current block and the current picture
- td denotes the distance between the reference picture of the collocated block and the collocated picture.
- the tb and td may be expressed as values corresponding to a difference in picture order count (POC) between pictures.
- Scaling of the motion vector of the temporal candidate may be performed based on tb and td.
- the reference picture index of the temporal candidate may be set to 0.
- FIG. 12 is a diagram for describing a location in which a temporal candidate is derived.
- a block with a thick solid line indicates a current block.
- the temporal candidate may be derived from a block in the collocated picture corresponding to the position C0 (lower right position) or the position C1 (center position) of FIG. 12.
- a temporal candidate may be derived based on the location C0. If the C0 location is not available, a temporal candidate may be derived based on the C1 location. For example, when the block in the collocated picture at the position C0 is an intra-predicted block or exists outside the current CTU row, it may be determined that the position C0 is not available.
- a motion vector of a collocated block may be stored for each predetermined unit block.
- the C0 position or the C1 position may be modified to induce a motion vector of a block covering the C0 position or the C1 position.
- the predetermined unit block is an 8x8 block
- the C0 position or the C1 position is (xColCi, yColCi)
- the position for inducing a temporal candidate is ((xColCi >> 3) ⁇ 3, (yColCi >> It can be modified as 3) ⁇ 3 ).
- a history-based candidate can be expressed as a history-based merge candidate.
- the history-based candidate may be added to the merge candidate list after the spatial and temporal candidates are added to the merge candidate list.
- motion information of a previously encoded/decoded block is stored in a table, and may be used as a history-based candidate of the current block.
- the table may store a plurality of history-based candidates during the encoding/decoding process.
- the table can be initialized when a new CTU row is started. Initializing a table may mean that all history-based candidates stored in the table are deleted and the table is emptied. Whenever there is an inter-predicted block, related motion information may be added to the table as a last entry. In this case, the inter-predicted block may not be a block predicted based on a subblock. Motion information added to the table can be used as a new history-based candidate.
- the table of history-based candidates may have a predetermined size.
- the size may be 5.
- the table can store up to five history-based candidates.
- a limited first-in-first-out (FIFO) rule may be applied in which a redundancy check is first performed to see if the same candidate exists in the table. If the same candidate already exists in the table, the same candidate is deleted from the table, and positions of all subsequent history-based candidates may be moved forward.
- FIFO first-in-first-out
- History-based candidates can be used in the process of constructing a merge candidate list. At this time, history-based candidates recently included in the table are checked in order, and may be included in positions after temporal candidates of the merge candidate list. When a history-based candidate is included in a merge candidate list, a redundancy check with a spatial candidate or a temporal candidate already included in the merge candidate list may be performed. If a history-based candidate and a spatial or temporal candidate already included in the merge candidate list overlap, the corresponding history-based candidate may not be included in the merge candidate list. By simplifying the redundancy check as follows, the amount of computation can be reduced.
- N denotes the number of candidates already included in the merge candidate list
- M denotes the number of available history-based candidates stored in the table. That is, when 4 or less candidates are included in the merge candidate list, the number of history-based candidates used to generate the merge candidate list is M, and the merge candidate list includes more than 4 N candidates. In this case, the number of history-based candidates used to generate the merge candidate list may be set to (8-N).
- the construction of the merge candidate list using the history-based candidate may be terminated.
- the pair-wise average candidate may be expressed as a pair-wise average merge candidate or a pair-wise candidate.
- the pair-wise average candidate may be generated by obtaining a predefined pair of candidates from candidates included in the merge candidate list and averaging them.
- the predefined candidate pairs are ⁇ (0, 1), (0, 2), (1, 2), (0, 3), (1, 3), (2, 3) ⁇ and constitute each candidate pair.
- the number may be an index of the merge candidate list. That is, the predefined candidate pair (0, 1) means a pair of the index 0 candidate and the index 1 candidate of the merge candidate list, and the pair-wise average candidate can be generated by the average of the index 0 candidate and the index 1 candidate. have. Pair-wise average candidates may be derived in the order of the predefined candidate pairs.
- a pair-wise average candidate derivation process may be performed in the order of the candidate pair (0, 2) and the candidate pair (1, 2). have.
- the pair-wise average candidate derivation process may be performed until configuration of the merge candidate list is completed.
- the pair-wise average candidate derivation process may be performed until the number of merge candidates included in the merge candidate list reaches the maximum number of merge candidates.
- Pair-wise average candidates can be calculated individually for each of the reference picture list.
- an average of these two motion vectors may be calculated. In this case, even if the two motion vectors indicate different reference pictures, the average of the two motion vectors may be performed. If only one motion vector is available for one reference picture list, the available motion vector may be used as a motion vector of the pair-wise average candidate. If both motion vectors are not available for one reference picture list, it may be determined that the corresponding reference picture list is not valid.
- a zero vector may be added to the merge candidate list until the maximum number of merge candidates is reached.
- a motion vector of a reconstructed spatial neighboring block eg, a neighboring block shown in FIG. 8 and/or a motion vector corresponding to a temporal neighboring block (or Col block) are used.
- a motion vector predictor (mvp) candidate list may be generated. That is, a motion vector of the reconstructed spatial neighboring block and/or a motion vector corresponding to the temporal neighboring block may be used as a motion vector predictor candidate of the current block.
- an mvp candidate list for deriving L0 motion information and an mvp candidate list for deriving L1 motion information may be separately generated and used.
- Prediction information (or information on prediction) for the current block is candidate selection information indicating an optimal motion vector predictor candidate selected from among motion vector predictor candidates included in the mvp candidate list (ex. MVP flag or MVP index). It may include.
- the prediction unit may select a motion vector predictor of the current block from among motion vector predictor candidates included in the mvp candidate list using the candidate selection information.
- the prediction unit of the video encoding apparatus may obtain a motion vector difference (MVD) between the motion vector of the current block and the motion vector predictor, encode the motion vector, and output it in the form of a bitstream. That is, MVD may be obtained by subtracting the motion vector predictor from the motion vector of the current block.
- MVD motion vector difference
- the prediction unit of the image decoding apparatus may obtain a motion vector difference included in the prediction information, and derive the motion vector of the current block by adding the motion vector difference and the motion vector predictor.
- the prediction unit of the video decoding apparatus may obtain or derive a reference picture index indicating a reference picture from the prediction-related information.
- FIG. 13 is a diagram schematically illustrating a method of constructing a motion vector predictor candidate list according to an example of the present disclosure.
- an available candidate block may be inserted into the MVP candidate list by searching for a spatial candidate block of the current block (S1010). Thereafter, it is determined whether there are less than two MVP candidates included in the MVP candidate list (S1020), and if there are two, the configuration of the MVP candidate list may be completed.
- step S1020 when there are less than two available spatial candidate blocks, the available candidate blocks may be inserted into the MVP candidate list by searching for a temporal candidate block of the current block (S1030).
- the configuration of the MVP candidate list may be completed by inserting a zero motion vector into the MVP candidate list (S1040).
- a reference picture index may be explicitly signaled.
- a reference picture index for L0 prediction (refidxL0) and a reference picture index for L1 prediction (refidxL1) may be differentiated and signaled.
- the MVP mode when the MVP mode is applied and BI prediction is applied, both information on refidxL0 and information on refidxL1 may be signaled.
- information on the MVD derived from the video encoding apparatus may be signaled to the video decoding apparatus.
- the information on the MVD may include, for example, information indicating the absolute value of the MVD and the x and y components of the sign. In this case, information indicating whether the absolute MVD value is greater than 0 or greater than 1, and the remainder of the MVD may be signaled in stages. For example, information indicating whether the absolute MVD value is greater than 1 may be signaled only when a value of flag information indicating whether the absolute MVD value is greater than 0 is 1.
- step S410 of FIG. 4 or step S630 of FIG. 6.
- a predicted block for the current block may be generated based on motion information derived according to the prediction mode.
- the predicted block may include prediction samples (prediction sample array) of the current block.
- prediction samples prediction sample array
- an interpolation procedure may be performed, and through this, prediction samples of the current block are calculated based on the reference samples in the fractional sample unit within the reference picture. Can be derived.
- prediction samples may be generated based on MV per sample/subblock.
- prediction samples derived based on L0 prediction i.e., prediction using a reference picture in a reference picture list L0 and MVL0
- L1 prediction i.e., a reference in a reference picture list L1
- Prediction samples derived through a weighted sum (according to a phase) or a weighted average of prediction samples derived based on prediction using a picture and MVL1 may be used as prediction samples of the current block.
- L0 prediction i.e., prediction using a reference picture in a reference picture list L0 and MVL0
- L1 prediction i.e., a reference in a reference picture list L1
- Prediction samples derived through a weighted sum (according to a phase) or a weighted average of prediction samples derived based on prediction using a picture and MVL1 may be used as prediction samples of the current block.
- reconstructed samples and reconstructed pictures may be generated based on the derived prediction samples, and then a procedure such as in-loop filtering may be performed.
- residual samples may be derived based on the derived prediction samples, and encoding of image information including prediction information and residual information may be performed.
- BDOF may be used to refine (improve) a bi-prediction signal.
- BDOF is for generating prediction samples by calculating improved motion information when bi-prediction is applied to a current block (ex. CU). Accordingly, the process of calculating the improved motion information by applying the BDOF may be included in the motion information derivation step described above.
- BDOF can be applied at the 4x4 subblock level. That is, BDOF may be performed in units of 4x4 subblocks in the current block.
- BODF may be applied to a CU that satisfies at least one or all of the following conditions, for example.
- BDOF can only be applied to the luma component.
- the present invention is not limited thereto, and the BDOF may be applied only to the chroma component, or may be applied to both the luma component and the chroma component.
- the BDOF mode is based on the concept of optical flow. That is, it is assumed that the movement of the object is smooth.
- an improved motion vector motion refinement (v x , v y ) may be calculated for each 4x4 subblock.
- the improved motion vector motion refinement
- the improved motion vector can be calculated by minimizing the difference between the L0 prediction sample and the L1 prediction sample.
- the improved motion vector motion refinement
- the horizontal gradient of the two prediction signals And vertical gradient can be calculated.
- k may be 0 or 1.
- the gradient can be calculated by directly calculating the difference between two adjacent samples.
- the gradient can be calculated as follows.
- I (0) (i, j) refers to the sample value at the (i, j) position in the L0 prediction block
- I (1) (i, j) is the (i, j) position in the L1 prediction block. It can mean a sample value.
- the first shift amount shift1 may be determined based on the bit depth (bit depth) of the luma component. For example, when the bit depth of the luma component is referred to as bitDepth, shift1 may be determined as max(6, bitDepth-6).
- n a and n b may be set to min(1, bitDepth-11) and min(4, bitDepth-8), respectively.
- the motion refinement (v x , v y ) improved by using the auto-correlation and cross-correlation between gradients described above can be derived as follows.
- n S2 may be 12. Based on the derived motion refinement and gradients, the following adjustment may be performed for each sample in a 4x4 subblock. .
- predicted samples (pred BDOF ) of a CU to which BDOF is applied may be calculated by adjusting the bi-prediction samples of the CU as follows.
- n a , n b and n S2 may be 3, 6 and 12, respectively. These values may be selected so that the multiplier in the BDOF process does not exceed 15 bits, and the bit-width of intermediate parameters is maintained within 32 bits.
- 14 is a diagram illustrating an extended CU to perform BDOF.
- a row/column extended around a boundary of a CU may be used.
- prediction samples in the extended area are generated using a bilinear filter, and CU (gray area in FIG. 14).
- Region prediction samples may be generated using a normal 8-tap motion compensation interpolation filter.
- the sample values of the extended position can be used only for gradient calculation.
- the nearest neighbor sample value and/or a gradient value may be padded (repeated) and used.
- the CU When the width and/or height of the CU is greater than 16 luma samples, the CU may be divided into sub-blocks having a width and/or height of 16 luma samples.
- the boundary of each sub-block may be treated the same as the CU boundary described above in the BDOF process.
- the maximum unit size in which the BDOF process is performed may be limited to 16x16.
- whether to perform BDOF may be determined. That is, the BDOF process for each subblock may be skipped. For example, when the SAD value between the initial LO prediction sample and the initial L1 prediction sample is less than a predetermined threshold, the BDOF process may not be applied to the corresponding subblock. At this time, when the width and height of the corresponding subblock are W and H, respectively, the predetermined threshold may be set to (8 * W*( H >> 1 ). In consideration of the complexity of additional SAD calculation, DMVR The SAD between the initial L0 prediction sample and the initial L1 prediction sample calculated in the process may be reused.
- luma_weight_lx_flag may be information indicating whether weighting factors of WP for the luma component of lx prediction (x is 0 or 1) are present in the bitstream. Alternatively, it may be information indicating whether WP is applied to the luma component of the lx prediction.
- SMVD Symmetric MVD
- CIIP CIIP
- BDOF is applied in the inter prediction process to improve the reference sample in the motion compensation process, thereby improving the compression performance of an image.
- BDOF can be performed in the normal mode. That is, in the Matte mode, the GPM mode, the CIIP mode, etc., the BDOF is not performed.
- the present disclosure prevents potential errors of BDOF and improves performance by applying normalization and clipping when inducing a BDOF offset (bdofOffset, b(x, y)) for improvement of a reference sample in the BDOF process.
- BDOF offset bdofOffset, b(x, y)
- normalization may mean unifying a value expressed in various units (eg, 1/64-pel, 1/32-pel, 2-pel, etc.) into a value of a predetermined unit (eg, 1-pel). have.
- [a, b] means a range of values from a to b, and that a certain value x is clipped to the range of [a, b] means that when x is less than a, the value of a, x When is greater than b, it may mean that the range of x is limited to have a value of b, and in other cases, a value of x.
- the bit depth is not limited to the bit depth of the luma component, and may include, for example, a bit depth when the bit depth of the luma component and the chroma component are the same.
- 15 is a diagram for describing a process of deriving a prediction sample of a current block by applying BDOF.
- the BDOF-based inter prediction procedure of FIG. 15 may be performed in an image encoding apparatus and an image decoding apparatus.
- motion information of the current block may be derived.
- Motion information of the current block may be derived by various methods described in this disclosure.
- the motion information of the current block may be derived by a regular merge mode, an MMVD mode, or an AMVP mode.
- the motion information may include bi-prediction motion information (L0 motion information, L1 motion information).
- the L0 motion information may include MVL0 (L0 motion vector) and refIdxL0 (L0 reference picture index)
- the L1 motion information may include MVL1 (L1 motion vector) and refIdxL1 (L1 reference picture index). have.
- a prediction sample of the current block may be derived based on the derived motion information of the current block (S1520). Specifically, L0 prediction samples for the current block may be derived based on the L0 motion information. In addition, L1 prediction samples for the current block may be derived based on the L1 motion information.
- a BDOF offset may be derived based on the derived prediction samples (S1530).
- BDOF of step S1530 may be performed according to the method described in the present disclosure.
- a BDOF offset may be derived based on a gradient (according to a phase) of the L0 prediction samples and a gradient (according to a phase) of the L1 prediction samples.
- the improved prediction samples may be used as a final prediction block of the current block.
- the image encoding apparatus may derive residual samples through comparison with original samples based on prediction samples of the current block generated according to the method of FIG. 15.
- information about the residual samples may be included in the image/video information, encoded, and output in the form of a bitstream.
- the image decoding apparatus can generate the reconstructed current block based on the residual samples obtained based on the prediction samples of the current block generated according to the method of FIG. 15 and residual information in the bitstream. As shown.
- 16 is a diagram illustrating input and output of a BDOF process according to an embodiment of the present disclosure.
- the input of the BDOF process includes a width (nCbW), a height (nCbH) of the current block, a prediction subblock (predSamplesL0, predSamplesL1) in which the boundary region is extended by a predetermined length (ex, 2), and a prediction direction. It may include indexes (predFlagL0, predFlagL1) and reference picture indexes (refIdxL0, refIdxL1).
- the input of the BDOF process may further include a BDOF use flag (bdofUtilizationFlag).
- the BDOF use flag is input in units of subblocks within the current block, and may indicate whether or not BDOF is applied to the corresponding subblock.
- the BDOF process may generate improved prediction blocks pbSamples by applying BDOF based on the input information.
- FIG. 17 is a diagram for describing variables used in a BDOF process according to an embodiment of the present disclosure.
- FIG. 17 may be a process following FIG. 16.
- the input bit depth (bitDepth) of the current block may be set to BitDepth Y.
- BitDepth Y may be derived based on information about the bit depth signaled through the bitstream.
- various right shift amounts may be set based on the bit depth. For example, a first shift amount (shift1), a second shift amount (shift2), a third shift amount (shift3), and a fourth shift amount (shift4) may be respectively derived as shown in FIG. 17 based on the bit depth. have.
- an offset (offset4) may be set based on shift4.
- a variable mvRefineThres for specifying the clipping range of the improved motion vector may be set based on the bit depth. The use of the various variables described in FIG. 17 will be described later.
- 18 is a diagram for describing a method of generating a prediction sample for each subblock in a current CU based on whether or not BDOF is applied, according to an embodiment of the present disclosure. 18 may be a process subsequent to FIG. 17.
- the process disclosed in FIG. 18 is performed for each subblock in the current CU, and in this case, the size of the subblock may be 4x4.
- the BDOF use flag (bdofUtilizationFlag) for the current subblock is the first value (False, '0')
- the BDOF may not be applied to the current subblock.
- the prediction sample of the current subblock is derived by a weighted sum of the L0 prediction sample and the L1 prediction sample, and in this case, the weight applied to the L0 prediction sample and the weight applied to the L1 prediction sample may be the same.
- Shift4 and offset4 used in Equation (1) of FIG. 18 may be values set in FIG. 17.
- BDOF may be applied to the current subblock.
- the prediction sample of the current subblock may be generated by the BDOF process according to the present disclosure to be described later.
- FIG. 19 is a diagram for describing a method of inducing a gradient, an auto-correlation relationship, and a cross-correlation relationship of a current subblock, according to an embodiment of the present disclosure.
- FIG. 19 may be a process following FIG. 18.
- the process disclosed in FIG. 19 is performed for each subblock in the current CU, and in this case, the size of the subblock may be 4x4.
- positions (h x , h y ) for each sample position (x, y) in the current subblock may be derived.
- a horizontal gradient and a vertical gradient for each sample position may be derived according to Equations (3) to (6).
- variables (first intermediate parameter diff and second intermediate parameters tempH and tempV) for inducing autocorrelation and cross-correlation according to Equations (7) to (9) may be derived.
- the first intermediate parameter diff may be derived using a value obtained by applying a right shift by a second shift amount (shift2) to the prediction samples (predSamplesL0, predSamplesL1) of the current block.
- the second intermediate parameters tempH and tempV apply a right shift by a third shift amount (shift3) to the sum of the gradient in the L0 direction and the gradient in the L1 direction, as shown in Equations (8) and (9). Can be induced. Thereafter, an auto-correlation relationship and a cross-correlation relationship may be derived according to Equations (10) to (16) based on the derived first intermediate parameter and the second intermediate parameter.
- FIG. 20 is a diagram for describing a method of inducing improved motion vectors (motion refinement, v x , v y ), inducing a BDOF offset, and generating a prediction sample of a current subblock, according to an embodiment of the present disclosure. It is a drawing. FIG. 20 may be a process following FIG. 19.
- the process disclosed in FIG. 20 is performed for each subblock in the current CU, and in this case, the size of the subblock may be 4x4.
- improved motion vectors (v x , v y ) can be derived according to Equations (1) and (2).
- the improved motion vector can be clipped to the range specified by mvRefineThres.
- a BDOF offset (bdofOffset) may be derived according to Equation (3) based on the improved motion vector and gradient.
- prediction samples (pbSamples) of the current subblock may be generated according to Equation (4).
- the methods described with reference to FIGS. 16 to 20 are successively performed to implement the BDOF process according to the first embodiment of the present disclosure.
- the first shift amount shift1 is set to Max(6, bitDepth-6)
- mvRefineThres is set to 1 ⁇ Max(, bitDepth-7). Therefore, the bit width of each parameter of predSample and BDOF according to BitDepth can be derived as shown in the table below.
- each parameter can have a more accurate value, and furthermore, a memory overflow issue in the BDOF process can be solved.
- a gradient (gradientHLX, gradientVLX, where X is 0 or 1) represents a slope at a distance of 2-pixels up and down and left and right of the current sample position, respectively.
- v x and v y are 1/32-pel precision and have a range of values of [-32, 31] or [-32, 32]
- 1 value of v x and v y is actually 1 Represents the /32-pel distance. Therefore, v x and v y can be viewed as applying the "1 ⁇ 5" operation to the 1-pixel unit value.
- each parameter (horizontal gradient, vertical gradient, v x , v y ) used for calculating the BDOF offset may be normalized to values in 1-pixel units. For example, for a gradient that is a slope of a 2-pixel distance, normalization may be performed in a 1-pixel unit value by applying an operation of ">>1". In addition, for v x and v y of 1/32-pel precision, normalization may be performed in 1-pixel units by applying an operation of ">>5". In consideration of this, as shown in Equation (3) of FIG. 23, a value obtained by multiplying the gradient and v x , v y for the normalization may be right-shifted by a first shift amount (shift1).
- shift1 may be set to a fixed value (eg, 7) regardless of the bit depth.
- v x and v y may also be clipped to a range of values set regardless of the bit depth.
- a variable mvRefineThres that specifies the clipping ranges of v x and v y may be set to a value of "1 ⁇ 5".
- normalization according to the second embodiment of the present disclosure may be performed by considering a gradient and v x , v y together.
- the second embodiment of the present disclosure can be implemented by improving Figs. 17, 19 and 20 of the first embodiment of the present disclosure.
- 21 is a diagram for describing variables used in a BDOF process according to another embodiment of the present disclosure. 21 may be a modified example of the example of FIG. 17. Accordingly, descriptions of common parts in FIGS. 17 and 21 may be omitted.
- the input bit depth (bitDepth) of the current block may be set to BitDepth Y.
- BitDepth Y may be derived based on information about the bit depth signaled through the bitstream.
- the first shift amount shift1, the second shift amount shift2, and the third shift amount shift3 may be set to fixed values regardless of the bit depth.
- the first shift amount shift1, the second shift amount shift2, and the third shift amount shift3 may be set to 7, 4, and 1, respectively.
- the fourth shift amount (shift4) and the offset (offset4) may be derived in the same manner as in the example of FIG. 17.
- the variable mvRefineThres may be set to a fixed value regardless of the bit depth.
- the variable mvRefineThres may be set to "1 ⁇ 5".
- 22 is a diagram for describing a method of inducing a gradient, an auto-correlation relationship, and a cross-correlation relationship of a current subblock according to another embodiment of the present disclosure. 22 may be a modified example of the example of FIG. 19. Accordingly, descriptions of common parts in FIGS. 19 and 22 may be omitted.
- the right shift operation (“>>shift1") may not be performed. According to the present embodiment, a gradient with higher accuracy can be obtained by omitting the right shift operation.
- FIG. 23 is a diagram for describing a method of deriving an improved motion vector (motion refinement, v x , v y ), deriving a BDOF offset, and generating a prediction sample of a current subblock, according to another embodiment of the present disclosure. It is a drawing. 23 may be a modified example of the example of FIG. 20. Accordingly, descriptions of common parts in FIGS. 20 and 23 may be omitted.
- the right shift operation ">>1" may be changed to ">>shift1". That is, it is possible to shift right by, gradient and v x, v y and v for the normalization of the gradient x, v values a first amount of shift (shift1) multiplied by y as described above. In this case, as described above, shift1 can be set to a fixed value (eg, 7) regardless of the bit depth.
- the second embodiment of the present disclosure may be implemented.
- bit width of each parameter of predSample and BDOF according to BitDepth may be derived as shown in the table below.
- the gradient having a high correlation with the bit depth changes according to the bit depth.
- the accuracy of the gradient value may increase.
- the bit widths of v x and v y that are not related to the bit depth may have a fixed value regardless of the bit depth. According to Table 2, instead of increasing the range of the gradient value, the range of the values of v x and v y decreases, so the range of the bdofOffset value is not affected.
- the gradient and v x , v y may be normalized to values in 1-pixel units.
- a bit overflow may occur in the gradient calculation process. For example, as shown in Equations (3) to (6) of FIG. 22, when a shift operation is not performed in the gradient calculation process, a 32-bit operation may be performed to calculate the gradient. That is, a bit overflow may occur when calculating a gradient.
- normalization for a gradient may be applied when calculating the gradient.
- the gradient may not exceed 16 bits.
- normalization for v x and v y may be performed by applying a right shift operation by the adjusted shift 1.
- shift1 may be set to a fixed value (eg, 6) regardless of the bit depth.
- the third embodiment of the present disclosure can be implemented by improving Figs. 21 and 22 of the second embodiment of the present disclosure.
- 24 is a diagram for describing variables used in a BDOF process according to another embodiment of the present disclosure. 24 may be a modified example of the example of FIG. 21. Accordingly, descriptions of common parts in FIGS. 21 and 24 may be omitted.
- the input bit depth of the current block may be set to BitDepth Y.
- BitDepth Y may be derived based on information about the bit depth signaled through the bitstream.
- the first shift amount shift1, the second shift amount shift2, and the third shift amount shift3 may be set to fixed values regardless of the bit depth.
- the first shift amount shift1, the second shift amount shift2, and the third shift amount shift3 may be set to 6, 4, and 1, respectively.
- the fourth shift amount (shift4) and the offset (offset4) may be derived in the same manner as in the example of FIG. 17.
- the variable mvRefineThres may be set to a fixed value regardless of the bit depth.
- the variable mvRefineThres may be set to "1 ⁇ 5".
- 25 is a diagram for describing a method of inducing a gradient, an auto-correlation relationship, and a cross-correlation relationship of a current subblock according to another embodiment of the present disclosure. 25 may be a modified example of the example of FIG. 22. Accordingly, descriptions of common parts in FIGS. 22 and 25 may be omitted.
- a right shift operation (“>>1") may be performed. In this way, the occurrence of bit overflow can be prevented by performing a right shift operation in the gradient calculation process.
- the third embodiment of the present disclosure may be implemented.
- bit width of each parameter of predSample and BDOF according to BitDepth may be derived as shown in the table below.
- the gradient having a high correlation with the bit depth changes according to the bit depth.
- the accuracy of the gradient value may increase.
- the bit widths of v x and v y that are not related to the bit depth may have a fixed value regardless of the bit depth.
- the gradient and v x , v y may be normalized to values in 1-pixel units.
- a bit overflow may occur in the gradient calculation process. For example, as shown in Equations (3) to (6) of FIG. 22, when a shift operation is not performed in the gradient calculation process, a 32-bit operation may be performed to calculate the gradient. That is, a bit overflow may occur when calculating a gradient.
- a bit overflow can be prevented by performing clipping when calculating a gradient.
- the gradient may not exceed 16 bits.
- the gradient and normalization for v x , v y may be performed in the same manner as in the second embodiment of the present disclosure.
- a value obtained by multiplying the gradient by v x and v y may be shifted right by a first shift amount (shift1).
- shift1 may be set to a fixed value (eg, 7) regardless of the bit depth.
- the fourth embodiment of the present disclosure can be implemented by improving Figs. 21 and 22 of the second embodiment of the present disclosure.
- 26 is a diagram for describing variables used in a BDOF process according to another embodiment of the present disclosure. 26 may be a modified example of the example of FIG. 21. Accordingly, descriptions of common parts in FIGS. 21 and 26 may be omitted.
- the input bit depth (bitDepth) of the current block may be set to BitDepth Y.
- BitDepth Y may be derived based on information about the bit depth signaled through the bitstream.
- the first shift amount shift1, the second shift amount shift2, and the third shift amount shift3 may be set to fixed values regardless of the bit depth.
- the first shift amount shift1, the second shift amount shift2, and the third shift amount shift3 may be set to 7, 4, and 1, respectively.
- the fourth shift amount (shift4) and the offset (offset4) may be derived in the same manner as in the example of FIG. 17.
- variable mvRefineThres may be set to a fixed value regardless of the bit depth.
- the variable mvRefineThres may be set to "1 ⁇ 5".
- a variable gradLimit for specifying the clipping range of the gradient value may be set. In this case, the gradLimit may be set based on the bit depth, for example, may be set to "1 ⁇ Max(15, BitDepth+3)".
- FIG. 27 is a diagram for describing a method of inducing a gradient, an auto-correlation relationship, and a cross-correlation relationship of a current subblock according to another embodiment of the present disclosure. 27 may be a modified example of the example of FIG. 22. Accordingly, descriptions of common parts in FIGS. 22 and 27 may be omitted.
- a clipping operation may be performed. That is, the calculated gradient value may be clipped to a value in the range specified by gradLimit.
- the clipping range may be [-gradLimit, gradLimit-1].
- the occurrence of bit overflow can be prevented by performing a clipping operation in the gradient calculation process as described above.
- the fourth embodiment of the present disclosure may be implemented.
- bit width of each parameter of predSample and BDOF according to BitDepth may be derived as shown in the table below.
- the gradient having a high correlation with the bit depth changes according to the bit depth.
- the accuracy of the gradient value may increase.
- the bit widths of v x and v y that are not related to the bit depth may have a fixed value regardless of the bit depth.
- the value range of the predicted sample (predSample) generated by interpolation of inter prediction is determined by the input bit depth and the coefficient of the interpolation filter, and in the worst case, has a value range of [-16830, 33150].
- the value of predSample can be adjusted in the range of [-25022, 24958].
- predSample has a value of 16 bit range when the bit depth is 8 to 12, and when the bit depth is 14 and 16, predSample has a value of 18 bit range and 20 bit range, respectively.
- the clipping range of bdofOffset may also be defined in consideration of the bit depth. For example, a variable OffsetLimit specifying a clipping range of bdofOffset is defined based on a bit depth, and clipping of bdofOffset may be additionally applied to embodiments of the present disclosure.
- bdofOffset may be clipped to a range of [-OffsetLimit, OffsetLimit-1].
- bdofOffset may be replaced by Clip3 (-OffsetLimit, OffsetLimit-1, bdofOffset).
- OffsetLimit may be defined based on bit depth. For example, OffsetLimit may be set to "1 ⁇ Max(12, BitDepth Y)".
- a right shift operation in a gradient calculation process can be minimized.
- the accuracy of bdofOffset may be further increased by adding an offset value.
- the offset value may be determined based on the right shift amount.
- shift1 may be set to "6", and offset may be set based on shift1 such as "1 ⁇ (shift1-1)".
- Equation (3) is not limited to being applied to the third embodiment of the present disclosure, and may be applied to other embodiments of the present disclosure.
- the modification of Equation (3) can be applied to the fourth embodiment of the present disclosure.
- shift1 may be set to "7”
- offset may be set based on shift1 such as "1 ⁇ (shift1-1)".
- the accuracy of bdofOffset can be improved by minimizing a right shift operation in a gradient calculation process and adding an offset value when performing a right shift operation in the bdofOffset calculation process.
- the bit range of the gradient value may vary.
- Table 1 in the first embodiment of the present disclosure, a gradient of 11 bit-range can be calculated by applying ">>6" to a prediction sample of 16 bit-range.
- the gradient Can in the case of applying ">>1" or clipping to a prediction sample of 16 bit-range according to the third or fourth embodiment of the present disclosure, as shown in Table 3 or Table 4, the gradient Can have a value of 16 bit-range.
- equations (8) and (9) of FIGS. 25 and 27 can be modified as follows.
- tempV[ x ][ y ] (gradientVL0[ x ][ y ]>> shift3)+ (gradientVL1[ x ][ y ] >> shift3)
- shift3 may be set to Max(1, bitDepth-11) or a fixed value of 1.
- 16 Bit overflow may occur.
- intermediate parameters such as sGx2, sGy2, sGxGy, sGxdI, sGydI, etc. calculated based on the variables tempH and tempV.
- the modified Equations (8) and Equations ( The amount of right shift (shift3) applied to 9) can be adjusted.
- shift3 may be set to Max(6, bitDepth-6) or a fixed value of 6. .
- shift3 is set to Max(6, bitDepth-6)+1 or a fixed value of 7 I can. According to the present embodiment, it is possible to prevent the occurrence of bit overflow in the calculation of not only variables tempH and tempV, but also intermediate parameters such as sGx2, sGy2, sGxGy, sGxdI, and sGydI.
- the embodiments of the present disclosure are not limited to the above-described examples, and the embodiments described in the present disclosure may be used in combination with other embodiments or modifications.
- the fifth embodiment of the present disclosure may be implemented by changing the step of FIG. 17 among steps constituting the first embodiment of the present disclosure described with reference to FIGS. 16 to 20.
- FIG. 17 of the first embodiment of the present disclosure to FIG. 24 of the third embodiment of the present disclosure, a fifth embodiment of the present disclosure may be derived.
- the exemplary methods of the present disclosure are expressed as a series of operations for clarity of description, this is not intended to limit the order in which steps are performed, and each step may be performed simultaneously or in a different order if necessary.
- the exemplary steps may include additional steps, other steps may be included excluding some steps, or may include additional other steps excluding some steps.
- an image encoding apparatus or an image decoding apparatus performing a predetermined operation may perform an operation (step) of confirming an execution condition or situation of a corresponding operation (step). For example, when it is described that a predetermined operation is performed when a predetermined condition is satisfied, the video encoding apparatus or the video decoding apparatus performs an operation to check whether the predetermined condition is satisfied, and then performs the predetermined operation. I can.
- various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof.
- one or more ASICs Application Specific Integrated Circuits
- DSPs Digital Signal Processors
- DSPDs Digital Signal Processing Devices
- PLDs Programmable Logic Devices
- FPGAs Field Programmable Gate Arrays
- general purpose It may be implemented by a processor (general processor), a controller, a microcontroller, a microprocessor, or the like.
- the image decoding device and the image encoding device to which the embodiment of the present disclosure is applied include a multimedia broadcasting transmission/reception device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video chat device, and a real-time communication device such as video communication.
- Mobile streaming devices storage media, camcorders, video-on-demand (VoD) service providers, OTT video (Over the top video) devices, Internet streaming service providers, three-dimensional (3D) video devices, video telephony video devices, and medical use. It may be included in a video device or the like, and may be used to process a video signal or a data signal.
- an OTT video (Over the top video) device may include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smartphone, a tablet PC, and a digital video recorder (DVR).
- DVR digital video recorder
- FIG. 28 is a diagram illustrating a content streaming system to which an embodiment of the present disclosure can be applied.
- a content streaming system to which an embodiment of the present disclosure is applied may largely include an encoding server, a streaming server, a web server, a media storage device, a user device, and a multimedia input device.
- the encoding server serves to generate a bitstream by compressing content input from multimedia input devices such as a smartphone, a camera, and a camcorder into digital data, and transmits it to the streaming server.
- multimedia input devices such as smart phones, cameras, camcorders, etc. directly generate bitstreams
- the encoding server may be omitted.
- the bitstream may be generated by an image encoding method and/or an image encoding apparatus to which an embodiment of the present disclosure is applied, and the streaming server may temporarily store the bitstream while transmitting or receiving the bitstream.
- the streaming server may transmit multimedia data to a user device based on a user request through a web server, and the web server may serve as an intermediary for notifying the user of a service.
- the web server transmits the request to the streaming server, and the streaming server transmits multimedia data to the user.
- the content streaming system may include a separate control server, and in this case, the control server may play a role of controlling a command/response between devices in the content streaming system.
- the streaming server may receive content from a media storage and/or encoding server. For example, when content is received from the encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.
- Examples of the user device include a mobile phone, a smart phone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation system, a slate PC, and Tablet PC (tablet PC), ultrabook (ultrabook), wearable device (e.g., smartwatch, glass terminal (smart glass), HMD (head mounted display)), digital TV, desktop There may be computers, digital signage, etc.
- PDA personal digital assistant
- PMP portable multimedia player
- slate PC slate PC
- Tablet PC Tablet PC
- ultrabook ultrabook
- wearable device e.g., smartwatch, glass terminal (smart glass), HMD (head mounted display)
- digital TV desktop There may be computers, digital signage, etc.
- Each server in the content streaming system may be operated as a distributed server, and in this case, data received from each server may be distributedly processed.
- the scope of the present disclosure is software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that cause operations according to the methods of various embodiments to be executed on a device or computer, and such software It includes a non-transitory computer-readable medium (non-transitory computer-readable medium) which stores instructions and the like and is executable on a device or a computer.
- a non-transitory computer-readable medium non-transitory computer-readable medium
- An embodiment according to the present disclosure may be used to encode/decode an image.
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Abstract
Description
Claims (15)
- 영상 복호화 장치에 의해 수행되는 영상 복호화 방법으로서, 상기 영상 복호화 방법은,현재 블록의 움직임 정보에 기반하여 상기 현재 블록의 예측 샘플을 도출하는 단계;상기 현재 블록에 BDOF(Bi-directional optical flow)를 적용할지 여부를 결정하는 단계;상기 현재 블록에 BDOF를 적용하는 경우,상기 현재 블록 내 현재 서브블록에 대한 그래디언트를 도출하는 단계;상기 그래디언트에 기반하여 상기 현재 서브블록에 대한 개선된 움직임 벡터(vx, vy)를 도출하는 단계;상기 그래디언트 및 상기 개선된 움직임 벡터에 기반하여 BDOF 오프셋을 도출하는 단계; 및상기 현재 블록의 예측 샘플 및 상기 BDOF 오프셋에 기반하여 상기 현재 블록에 대한 개선된 예측 샘플을 도출하는 단계를 포함하는 영상 복호화 방법.
- 제1항에 있어서,상기 그래디언트를 도출하는 단계는 상기 현재 블록의 예측 샘플을 제1 쉬프트량만큼 우쉬프트하는 단계를 포함하고,상기 제1 쉬프트량은 상기 현재 블록의 비트 뎁스와 무관하게 고정된 값으로 설정되는 영상 복호화 방법.
- 제2항에 있어서,상기 제1 쉬프트량은 6인 영상 복호화 방법.
- 제1항에 있어서,상기 개선된 움직임 벡터(vx, vy)를 도출하는 단계는,상기 현재 블록의 예측 샘플에 기반하여 제1 중간 파라미터 diff를 도출하는 단계; 및상기 그래디언트에 기반하여 제2 중간 파라미터 tempH 및 tempV를 도출하는 단계를 포함하는 영상 복호화 방법.
- 제4항에 있어서,상기 제1 중간 파라미터 diff를 도출하는 단계는 상기 현재 블록의 예측 샘플을 제2 쉬프트량만큼 우쉬프트하는 단계를 포함하고,상기 제2 쉬프트량은 상기 현재 블록의 비트 뎁스와 무관하게 고정된 값으로 설정되는 영상 복호화 방법.
- 제5항에 있어서,상기 제2 쉬프트량은 4인 영상 복호화 방법.
- 제4항에 있어서,상기 제2 중간 파라미터 tempH 및 tempV를 도출하는 단계는 상기 그래디언트에 기반하여 유도된 값을 제3 쉬프트량만큼 우쉬프트하는 단계를 포함하고,상기 제3 쉬프트량은 상기 현재 블록의 비트 뎁스와 무관하게 고정된 값으로 설정되는 영상 복호화 방법.
- 제7항에 있어서,상기 제3 쉬프트량은 1인 영상 복호화 방법.
- 제1항에 있어서,상기 개선된 움직임 벡터(vx, vy)는 소정의 범위로 클리핑되는 영상 복호화 방법.
- 제9항에 있어서,상기 개선된 움직임 벡터(vx, vy)를 클리핑하는 상기 소정의 범위는 상기 현재 블록의 비트 뎁스와 무관하게 고정된 범위로 설정되는 영상 복호화 방법.
- 제1항에 있어서,상기 BDOF 오프셋을 도출하는 단계는 상기 그래디언트와 상기 개선된 움직임 벡터에 기반하여 유도된 값을 소정의 쉬프트량만큼 우쉬프트하는 단계를 포함하고,상기 소정의 쉬프트량은 상기 현재 블록의 비트 뎁스와 무관하게 고정된 범위로 설정되는 영상 복호화 방법.
- 제1항에 있어서,상기 현재 블록에 대한 개선된 예측 샘플을 도출하는 단계는 상기 BDOF 오프셋을 소정의 범위로 클리핑하는 단계를 포함하고,상기 소정의 범위는 상기 현재 블록의 비트 뎁스에 기반하여 설정되는 영상 복호화 방법.
- 메모리 및 적어도 하나의 프로세서를 포함하는 영상 복호화 장치로서,상기 적어도 하나의 프로세서는현재 블록의 움직임 정보에 기반하여 상기 현재 블록의 예측 샘플을 도출하고, 상기 현재 블록에 BDOF를 적용할지 여부를 결정하고, 상기 현재 블록에 BDOF를 적용하는 경우, 상기 현재 블록 내 현재 서브블록에 대한 그래디언트를 도출하고, 상기 그래디언트에 기반하여 상기 현재 서브블록에 대한 개선된 움직임 벡터(vx, vy)를 도출하고, 상기 그래디언트 및 상기 개선된 움직임 벡터에 기반하여 BDOF 오프셋을 도출하고, 상기 현재 블록의 예측 샘플 및 상기 BDOF 오프셋에 기반하여 상기 현재 블록에 대한 개선된 예측 샘플을 도출하는 영상 복호화 장치.
- 영상 부호화 장치에 의해 수행되는 영상 부호화 방법으로서, 상기 영상 부호화 방법은,현재 블록의 움직임 정보에 기반하여 상기 현재 블록의 예측 샘플을 도출하는 단계;상기 현재 블록에 BDOF를 적용할지 여부를 결정하는 단계;상기 현재 블록에 BDOF를 적용하는 경우,상기 현재 블록 내 현재 서브블록에 대한 그래디언트를 도출하는 단계;상기 그래디언트에 기반하여 상기 현재 서브블록에 대한 개선된 움직임 벡터(vx, vy)를 도출하는 단계;상기 그래디언트 및 상기 개선된 움직임 벡터에 기반하여 BDOF 오프셋을 도출하는 단계; 및상기 현재 블록의 예측 샘플 및 상기 BDOF 오프셋에 기반하여 상기 현재 블록에 대한 개선된 예측 샘플을 도출하는 단계를 포함하는 영상 부호화 방법.
- 제14항의 영상 부호화 방법에 의해 생성된 비트스트림을 전송하는 방법.
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US17/639,837 US20220337842A1 (en) | 2019-09-10 | 2020-09-09 | Image encoding/decoding method and device for performing bdof, and method for transmitting bitstream |
JP2022515879A JP2022547988A (ja) | 2019-09-10 | 2020-09-09 | Bdofを行う画像符号化/復号化方法、装置、及びビットストリームを伝送する方法 |
CN202080063601.0A CN114365485A (zh) | 2019-09-10 | 2020-09-09 | 用于执行bdof的图像编码/解码方法和装置及用于发送比特流的方法 |
EP20863214.1A EP4030760A4 (en) | 2019-09-10 | 2020-09-09 | IMAGE CODING/DECODING METHOD AND APPARATUS FOR PERFORMING BDOF AND METHOD FOR TRANSMITTING A BIT STREAM |
AU2020347025A AU2020347025B2 (en) | 2019-09-10 | 2020-09-09 | Image encoding/decoding method and device for performing bdof, and method for transmitting bitstream |
KR1020227005733A KR20220036966A (ko) | 2019-09-10 | 2020-09-09 | Bdof를 수행하는 영상 부호화/복호화 방법, 장치 및 비트스트림을 전송하는 방법 |
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