WO2020009460A1 - Procédé de réagencement de signaux résiduels, et appareil de décodage d'image - Google Patents
Procédé de réagencement de signaux résiduels, et appareil de décodage d'image Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
- H04N19/129—Scanning of coding units, e.g. zig-zag scan of transform coefficients or flexible macroblock ordering [FMO]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
- H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
- H04N19/176—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
- H04N19/625—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding using discrete cosine transform [DCT]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/70—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by syntax aspects related to video coding, e.g. related to compression standards
Definitions
- the present invention relates to encoding and decoding of an image, and more particularly, to a residual signal rearrangement method and an image decoding apparatus that rearranges residual signals to improve encoding and decoding efficiency.
- moving image data has a larger amount of data than audio data or still image data
- a large amount of hardware resources including a memory, are required to store or transmit itself without processing for compression.
- the video data when storing or transmitting video data, the video data is compressed and stored or transmitted using an encoder, and the decoder receives the compressed video data, decompresses, and plays the video data.
- video compression techniques include H.264 / AVC and HEVC (High Efficiency Video Coding), which improves coding efficiency by about 40% compared to H.264 / AVC.
- an aspect of the present invention is to encode and decode a residual signal by adaptively rearranging the residual signal according to the characteristics of the current block. Relates to techniques for improving the efficiency of the.
- a method comprising: decoding from a bitstream a transform type information indicating transform coefficients in a transform block of a current block and a transform type applied to the transform block; Deriving a residual block from the transform coefficients according to the transform type indicated by the transform type information; And rearranging the residual signals in the residual block according to one of the one or more rearrangement types.
- a decoding unit for decoding transform coefficients in the transform block of the current block and transform type information indicating the transform type applied to the transform block from the bitstream;
- An inverse transform unit for deriving a residual block from the transform coefficients according to the transform type indicated by the transform type information;
- control means for rearranging residual signals in the residual block according to any one or more types of rearrangement.
- the residual signal is rearranged in a form suitable for the conversion type, compression performance for image encoding and decoding may be improved.
- FIG. 1 is an exemplary block diagram of an image encoding apparatus that may implement techniques of this disclosure.
- FIG. 2 is a diagram for explaining a method of dividing a block using a QTBTTT structure.
- 3 is a diagram for describing a plurality of intra prediction modes.
- FIG. 4 is an exemplary block diagram of an image decoding apparatus that may implement techniques of this disclosure.
- 5 is a view for explaining a waveform of the basis functions of the transform type.
- FIG. 6 is a diagram for describing a conversion type suitable for energy distribution of residual signals.
- FIG. 7 is a flowchart illustrating an embodiment of the present invention for rearranging residual signals.
- FIGS. 8 and 9 are diagrams for describing two examples of the rearrangement type.
- FIG. 10 is a diagram for describing an example of rearranging residual signals according to the rearrangement types described with reference to FIGS. 8 and 9.
- 11 is a diagram for describing an example of classifying intra prediction according to a prediction direction.
- FIG. 14 is a flowchart for explaining an embodiment of rearranging residual signals based on error values of reference blocks.
- FIG. 15 is a diagram for describing an example of rearranging residual signals using the embodiment described with reference to FIG. 14.
- FIG. 1 is an exemplary block diagram of an image encoding apparatus that may implement techniques of this disclosure.
- an image encoding apparatus and subcomponents thereof will be described with reference to FIG. 1.
- the image encoding apparatus may include a block divider 110, a predictor 120, a subtractor 130, a transformer 140, a quantizer 145, an encoder 150, an inverse quantizer 160, and an inverse transform unit ( 165, an adder 170, a filter unit 180, and a memory 190.
- Each component of the image encoding apparatus may be implemented in hardware or software, or a combination of hardware and software.
- the functions of each component may be implemented in software and the microprocessor may be implemented to execute the functions of the software corresponding to each component.
- One image is composed of a plurality of pictures. Each picture is divided into a plurality of regions, and encoding is performed for each region. For example, one picture is divided into one or more tiles or slices. Here, one or more tiles may be defined as a tile group. Each tile or / slice is divided into one or more coding tree units (CTUs). Each CTU is divided into one or more coding units (CUs) by a tree structure. Information applied to each CU is encoded as the syntax of the CU, and information commonly applied to the CUs included in one CTU is encoded as the syntax of the CTU.
- CTUs coding tree units
- information commonly applied to all blocks in one tile is encoded as a syntax of a tile or as a syntax of a tile group in which a plurality of tiles are collected.
- Information applied to all blocks constituting one picture is It is encoded in a picture parameter set (PPS) or picture header.
- PPS picture parameter set
- SPS sequence parameter set
- VPS video parameter set
- the block divider 110 determines the size of a coding tree unit (CTU).
- CTU size Information on the size of the CTU (CTU size) is encoded as a syntax of the SPS or PPS and transmitted to the image decoding apparatus.
- the block dividing unit 110 After dividing each picture constituting an image into a plurality of coding tree units (CTUs) having a predetermined size, the block dividing unit 110 iteratively divides the CTUs using a tree structure. split (recursively) A leaf node in the tree structure becomes a CU (coding unit) which is a basic unit of coding.
- CU coding unit
- the tree structure is QuadTree (QT) in which the parent node (or parent node) is divided into four child nodes (or child nodes) of the same size, or BinaryTree in which the parent node is divided into two child nodes. , BT), or a ternary tree (TernaryTree, TT) in which a parent node is divided into three child nodes in a 1: 2: 1 ratio, or a mixture of two or more of these QT structures, BT structures, and TT structures.
- QTBT QuadTree plus BinaryTree
- QTBTTT QuadTree plus BinaryTree TernaryTree
- the BTTT may be collectively referred to as a multiple-type tree (MTT).
- the CTU may first be divided into a QT structure. Quadtree splitting may be repeated until the size of the splitting block reaches the minimum block size (MinQTSize) of the leaf nodes allowed in QT.
- MinQTSize minimum block size
- the first flag QT_split_flag indicating whether each node of the QT structure is divided into four nodes of a lower layer is encoded by the encoder 150 and signaled to the image decoding apparatus. If the leaf node of the QT is not larger than the maximum block size (MaxBTSize) of the root node allowed in BT, it may be further divided into one or more of the BT structure or the TT structure.
- MaxBTSize maximum block size
- a plurality of division directions there may be a plurality of division directions. For example, there may be two directions in which a block of a corresponding node is divided horizontally and a direction divided vertically.
- a second flag indicating whether nodes are partitioned
- a flag indicating additional partitioning direction vertical or horizontal
- / or partition type Boary or Ternary
- the CU split flag (split_cu_flag) indicating that the split is performed first and the QT split flag (split_qt_flag) information indicating whether the split type is a QT split are provided by the encoder 150. ) And is signaled to the image decoding apparatus.
- the CU split flag (split_cu_flag) value is not split, the block of the corresponding node becomes a leaf node in the split tree structure to become a coding unit (CU) which is a basic unit of encoding.
- split_cu_flag When indicating that the CU split flag (split_cu_flag) value is split, it is distinguished whether the split type is QT or MTT through the QT split flag (split_qt_flag) value. If the partition type is QT, there is no additional information. If the partition type is MTT, additionally, a flag indicating the MTT splitting direction (vertical or horizontal) (mtt_split_cu_vertical_flag) and / or a flag indicating the MTT splitting type (Binary or Ternary) (mtt_split_cu_binary_flag) is encoded by the encoder 150 and signaled to the image decoding apparatus.
- split_flag split flag indicating whether each node of the BT structure is divided into blocks of a lower layer and split type information indicating a split type are encoded by the encoder 150 and transmitted to the image decoding apparatus. Meanwhile, there may further be a type in which blocks of the corresponding node are further divided into two blocks having an asymmetric shape.
- the asymmetric form may include a form of dividing a block of a node into two rectangular blocks having a size ratio of 1: 3, or a form of dividing a block of a node in a diagonal direction.
- the CU may have various sizes depending on the QTBT or QTBTTT splitting from the CTU.
- a block corresponding to a CU that is, a leaf node of QTBTTT
- a 'current block' a block corresponding to a CU (that is, a leaf node of QTBTTT) to be encoded or decoded.
- the prediction unit 120 predicts the current block and generates a prediction block.
- the predictor 120 includes an intra predictor 122 and an inter predictor 124.
- current blocks within a picture may each be predictively coded.
- prediction of the current block uses an intra prediction technique (using data from a picture containing the current block) or an inter prediction technique (using data from a picture coded before a picture containing the current block). Can be performed.
- Inter prediction includes both unidirectional prediction and bidirectional prediction.
- the intra predictor 122 predicts pixels in the current block by using pixels (reference pixels) positioned around the current block in the current picture including the current block.
- the plurality of intra prediction modes may include a non-directional mode including a planar mode and a DC mode and 65 directional modes.
- the surrounding pixels to be used and the expressions are defined differently for each prediction mode.
- the intra predictor 122 may determine an intra prediction mode to use to encode the current block.
- intra prediction unit 122 may encode the current block using several intra prediction modes and select an appropriate intra prediction mode to use from the tested modes. For example, intra predictor 122 calculates rate distortion values using rate-distortion analysis for several tested intra prediction modes, and has the best rate distortion characteristics among the tested modes. Intra prediction mode may be selected.
- the intra prediction unit 122 selects one intra prediction mode from among the plurality of intra prediction modes, and predicts the current block by using a neighboring pixel (reference pixel) and an operation formula determined according to the selected intra prediction mode.
- Information about the selected intra prediction mode is encoded by the encoder 150 and transmitted to the image decoding apparatus.
- the inter prediction unit 124 generates a prediction block for the current block through a motion compensation process.
- the block most similar to the current block is searched in the coded and decoded reference picture before the current picture, and a predicted block for the current block is generated using the searched block.
- a motion vector corresponding to a displacement between the current block in the current picture and the prediction block in the reference picture is generated.
- motion estimation is performed on a luma component, and a motion vector calculated based on the luma component is used for both the luma component and the chroma component.
- the motion information including the information about the reference picture and the motion vector used to predict the current block is encoded by the encoder 150 and transmitted to the image decoding apparatus.
- the subtractor 130 generates a residual block by subtracting the prediction block generated by the intra predictor 122 or the inter predictor 124 from the current block.
- the transformer 140 converts the residual signal in the residual block having pixel values of the spatial domain into a transform coefficient of the frequency domain.
- the transform unit 140 may transform the residual signals in the residual block by using the entire size of the residual block as a conversion unit, or divide the residual block into two subblocks, a transform region and a non-conversion region, Residual signals may be transformed using only blocks as transform units.
- the transform region subblock may be one of two rectangular blocks having a size ratio of 1: 1 on the horizontal axis (or vertical axis).
- a flag (cu_sbt_flag), directional (vertical / horizontal) information (cu_sbt_horizontal_flag) and / or position information (cu_sbt_pos_flag) indicating that only a subblock has been converted are encoded by the encoder 150 and signaled to the video decoding apparatus.
- the size of the transform region subblock may have a size ratio of 1: 3 based on the horizontal axis (or vertical axis).
- a flag (cu_sbt_quad_flag) for distinguishing the division is additionally encoded by the encoder 150 to decode the image. Signaled to the device.
- the converter 140 may select one of a plurality of conversion types and convert residual signals.
- the plurality of transformation types may include cosine-based transformations (eg, DCT-II, DCT-VIII, etc.) and sine-based transformations (eg, DST-VII). Further, the transform unit 140 may skip the transform and output the residual signal of the spatial domain to the quantizer 145 as it is.
- the quantization unit 145 quantizes the transform coefficients output from the transform unit 140, and outputs the quantized transform coefficients to the encoder 150.
- the encoder 150 generates a bitstream by encoding the quantized transform coefficients by using a coding scheme such as CABAC (Context-based Adaptive Binary Arithmetic Code).
- the encoder 150 may encode information such as a CTU size, a CU division flag, a QT division flag, an MTT division direction, and an MTT division type related to block division, so that the image decoding apparatus may divide the block in the same manner as the image encoding apparatus. Make sure
- the encoder 150 encodes information about a prediction type indicating whether the current block is encoded by intra prediction or inter prediction, and intra prediction information (that is, intra prediction mode) according to the prediction type. Information) or inter prediction information (information about a reference picture and a motion vector) is encoded. Also, the encoder 150 may encode syntax elements related to the transform. As an example, the encoding unit 150 may include a transform skip flag indicating whether a transform on the residual signal is skipped, and a transform indicating a transform type used to transform the residual signal among a plurality of transform types when the transform is not skipped. Type information and the like can be encoded.
- the inverse quantizer 160 inversely quantizes the quantized transform coefficients output from the quantizer 145 to generate transform coefficients.
- the inverse transformer 165 restores the residual block by converting the transform coefficients output from the inverse quantizer 160 from the frequency domain to the spatial domain.
- the adder 170 reconstructs the current block by adding the reconstructed residual block and the predicted block generated by the predictor 120.
- the pixels in the reconstructed current block are used as reference pixels when intra prediction of the next order of blocks.
- the filter unit 180 filters the reconstructed pixels to reduce blocking artifacts, ringing artifacts, blurring artifacts, and the like caused by block-based prediction and transformation / quantization. Do this.
- the filter unit 180 may include a deblocking filter 182 and a sample adaptive offset (SAO) filter 184.
- the deblocking filter 180 filters the boundaries between the reconstructed blocks to remove blocking artifacts caused by block-by-block encoding / decoding, and the SAO filter 184 adds an additional block to the deblocking filtered image. Perform filtering.
- the SAO filter 184 is a filter used to compensate for the difference between the reconstructed pixel and the original pixel caused by lossy coding.
- the reconstructed blocks filtered through the deblocking filter 182 and the SAO filter 184 are stored in the memory 190.
- the reconstructed picture is used as a reference picture for inter prediction of a block in a picture to be encoded later.
- the apparatus for encoding an image may further include control means for rearranging residual signals (samples) in the residual block.
- This control means may be implemented in the same physical configuration (processor or the like) together with the subcomponents represented in FIG. 1 or in a different physical configuration than the subcomponents represented in FIG. Details of the control means will be described later.
- FIG. 4 is an exemplary block diagram of an image decoding apparatus that may implement techniques of this disclosure.
- an image decoding apparatus and subcomponents thereof will be described with reference to FIG. 4.
- the image decoding apparatus may include a decoder 410, an inverse quantizer 420, an inverse transformer 430, a predictor 440, an adder 450, a filter 460, and a memory 470. have.
- each component of the image decoding apparatus may be implemented in hardware or software, or a combination of hardware and software.
- the functions of each component may be implemented in software and the microprocessor may be implemented to execute the functions of the software corresponding to each component.
- the decoder 410 decodes the bitstream received from the image encoding apparatus, extracts information related to block division, determines a current block to be decoded, and includes information on prediction information and residual signal necessary for reconstructing the current block. Extract
- the decoder 410 extracts information on the CTU size from a Sequence Parameter Set (SPS) or Picture Parameter Set (PPS) to determine the size of the CTU, and divides the picture into a CTU of the determined size.
- SPS Sequence Parameter Set
- PPS Picture Parameter Set
- the CTU is determined as the highest layer of the tree structure, that is, the root node, and the CTU is partitioned using the tree structure by extracting the partition information for the CTU.
- a first flag (QT_split_flag) related to splitting of QT is extracted, and each node is divided into four nodes of a lower layer.
- QT_split_flag For the node corresponding to the leaf node of the QT, a second flag (MTT_split_flag), a splitting direction (vertical / horizontal) and / or a splitting type (binary / ternary) information related to splitting of the MTT is extracted, and the corresponding leaf node is MTT.
- MTT_split_flag a splitting direction (vertical / horizontal) and / or a splitting type (binary / ternary) information related to splitting of the MTT
- a CU split flag indicating whether to split a CU is extracted, and when a corresponding block is split, a QT split flag (split_qt_flag) is extracted.
- a flag indicating the MTT splitting direction (vertical or horizontal) and / or a flag (mtt_split_cu_binary_flag) indicating the MTT splitting type (Binary or Ternary) is additionally extracted.
- each node may generate zero or more repetitive MTT splits after 0 or more repetitive QT splits.
- the CTU may directly generate MTT splitting or vice versa.
- the first flag QT_split_flag related to the splitting of the QT is extracted to divide each node into four nodes of the lower layer. Then, for the node corresponding to the leaf node of the QT, a split flag (split_flag) indicating splitting or splitting direction information indicating whether to be split further by BT is extracted.
- the decoder 410 determines the current block to be decoded by splitting the tree structure, the decoder 410 extracts information about a prediction type indicating whether the current block is intra predicted or inter predicted.
- the prediction type information indicates intra prediction
- the decoder 410 extracts a syntax element for intra prediction information (intra prediction mode) of the current block.
- the prediction type information indicates inter prediction
- the decoder 410 extracts a syntax element for inter prediction information, that is, a motion vector and information representing a reference picture to which the motion vector refers.
- the decoder 410 extracts information about quantized transform coefficients of the current block as information on the residual signal.
- the decoder 410 extracts syntax elements related to the transform. For example, if the transform skip flag is extracted and the transform skip flag indicates that the transform is not skipped, transform type information or the like may be extracted.
- the inverse quantizer 420 inverse quantizes the quantized transform coefficients, and the inverse transformer 430 inversely transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain to generate a residual block for the current block. .
- the inverse transform may be performed based on the transform related syntax elements extracted by the decoder 410. For example, if the transform skip flag indicates a transform skip, an inverse transform by the inverse transform unit 430 is skipped. In this case, a block that has undergone inverse quantization (a block composed of dequantized transform coefficients) is output as a residual block. If the transform skip flag indicates that the transform is to be performed, the inverse transform unit 430 performs inverse transform according to the transform type indicated by the transform type information.
- the inverse transform unit 430 generates a residual block by performing an inverse transform using a DCT-II based transform matrix, and generates a residual block based on DST-VII if the transform type indicates DST-VII.
- a residual block is generated by performing inverse transform using a transform matrix of.
- the inverse transform unit 430 indicates a flag (cu_sbt_flag) indicating that only a subblock of the transform block has been transformed, and vertical / horizontal information (cu_sbt_horizontal_flag) of the subblock. ) And / or the position information (cu_sbt_pos_flag) of the subblock is extracted, and the residual signals are restored by inversely transforming transform coefficients of the corresponding subblock from the frequency domain to the spatial domain, and a value of "0" as a residual signal for the region not inversely transformed. Fill in to create the last residual block for the current block.
- the predictor 440 may include an intra predictor 442 and an inter predictor 444.
- the intra predictor 442 is activated when the prediction type of the current block is intra prediction
- the inter predictor 444 is activated when the prediction type of the current block is inter prediction.
- the intra predictor 442 determines the intra prediction mode of the current block among the plurality of intra prediction modes from the syntax element for the intra prediction mode extracted from the decoder 410, and references pixels around the current block according to the intra prediction mode. Predict the current block using
- the inter prediction unit 444 determines the motion vector of the current block and the reference picture to which the motion vector refers by using syntax elements of the intra prediction mode extracted from the decoder 410, and uses the motion vector and the reference picture. To predict the current block.
- the adder 450 reconstructs the current block by adding the residual block output from the inverse transformer and the prediction block output from the inter predictor or the intra predictor.
- the pixels in the reconstructed current block are utilized as reference pixels when intra prediction of a block to be decoded later.
- the filter unit 460 may include a deblocking filter 462 and a SAO filter 464.
- the deblocking filter 462 deblocks and filters the boundary between reconstructed blocks in order to remove blocking artifacts caused by block-by-block decoding.
- the SAO filter 464 performs additional filtering on the reconstructed block after the deblocking filtering to compensate for the difference between the reconstructed pixel and the original pixel caused by lossy coding.
- the reconstructed blocks filtered through the deblocking filter 462 and the SAO filter 464 are stored in the memory 470. When all the blocks in a picture are reconstructed, the reconstructed picture is used as a reference picture for inter prediction of a block in a picture to be encoded later.
- the image decoding apparatus may further include a control means for rearranging the residual signals in the residual block.
- This control means may be implemented in the same physical configuration (processor or the like) together with the subcomponents represented in FIG. 4 or in a different physical configuration than the subcomponents represented in FIG. Details of the control means will be described later.
- control means included in the video decoding apparatus corresponds to the above-described control means included in the video encoding apparatus and a configuration corresponding in function thereof.
- control means included in the video decoding apparatus is referred to as decoding control means, and the control included in the video encoding apparatus.
- the means is referred to as encoding control means.
- the HEVC standard (conventional method) performs transformation / inverse transformation using three kinds of transformation types (DCT, DST, and transform skip).
- DCT transformation / inverse transformation using three kinds of transformation types
- DST transformation type
- transform skip transform skip
- the basis functions represented in Fig. 5A are used to convert the input signal value into a count signal value.
- the basis functions represented in FIG. 5 (b) are used to convert the input signal value into a count signal value.
- the conversion can be efficiently processed. That is, when the input signal is similar to the waveform of the basis function, the total amount of the output count signal values may be reduced to improve the compression performance.
- an input signal to be converted becomes a residual signal after prediction. Accordingly, depending on the shape / shape / waveform of the residual signal (shape / shape / waveforms of the residual signal values), there may be a conversion type among which the conversion can be efficiently processed. An example for explaining this in detail is represented in FIG. 6.
- a difference value (error value) between a value of encoding / decoding target pixels (a, b, c, d) and a reference sample (circle indicated by hatching) May increase based on the distance from the reference sample.
- an error value is relatively small as a pixel adjacent to the reference sample has a higher prediction accuracy, and a error value is relatively larger as a pixel farther from the reference sample has a lower prediction accuracy.
- the difference of the error value is expressed based on the distance from the reference sample, it may be expressed as a straight upward line as shown by the dashed-dotted line in FIG.
- FIG. 6 (b) An example of comparing the two-dot chain line with the waveforms of the DCT basis functions is shown in FIG. 6 (b), and an example of comparing the two-dot chain line with the waveforms of the DST basis functions is shown in FIG. 6 (c).
- the two-dot dashed line shows the magnitude of magnitude as distance increases, and the waveform of DCT basis function decreases as the distance increases. As it increases, the size increases. Accordingly, it can be seen that a conversion type suitable for residual signal values whose error value gradually increases is a DST conversion type.
- a form in which the distribution of residual signal values becomes smaller from the upper left side to the lower right side of the residual block may be appropriate. This is because the conventional method of encoding the transform coefficient is suitable when the coefficient values are distributed in the low frequency region and the coefficient values are not distributed in the high frequency region.
- the present invention focuses on this characteristic (correlation between the magnitude distribution of the residual signal values and the transform type), and proposes methods for rearranging the residual signals to be a more suitable arrangement for the transform type.
- the image encoding apparatus may derive a residual block for the current block by differentiating the current block and the prediction block of the current block.
- the derived residual block may include one or more residual signals (samples).
- the video encoding apparatus may adjust or rearrange the arrangement or distribution of the residual signals so as to be suitable for the transform type to be applied to the residual block.
- the rearrangement type may include an exchange type, a move type, and the like, and the move type may include one or more of various types of inversion type and shifting type.
- the exchange type can be understood as being included in the mobile type or in the same rearrangement as the mobile type. Specific examples of the rearrangement type will be described later.
- the image encoding apparatus may derive the transform coefficients (transform blocks) by applying the rearranged residual signals to the transform type.
- the conversion type is a Skip type
- the conversion coefficients may correspond to residual signals.
- the video encoding apparatus 150 may include information (transformation type information) and transform coefficients (quantized transform coefficients) indicating a transform type applied to the transform block and signal the image decoding apparatus to the bitstream. .
- the decoder 410 may decode the transform type information and the transform coefficients from the bitstream (S710).
- the inverse transform unit 430 inversely transforms the transform coefficients (conversion block) according to the transform type (conversion type indicated by the transform type information) indicated by the transform type information among the transform types (DCT, DST, and Skip). It can be derived (S720).
- the decoding control means may rearrange the residual signals in the residual block according to one of the one or more rearrangement types (S730).
- the rearranged residual signals (rearranged residual blocks) may have the same arrangement or distribution as the residual signals before being rearranged in the image encoding apparatus.
- the rearranged residual block is summed with the prediction block derived from the prediction unit 440 to restore the current block.
- a method of rearranging the residual signals may include a type (moving type) for exchanging (exchanging type) or moving the residual signals, and in the moving type, the residual signals are inverted or moved.
- moving type for exchanging type
- moving type the residual signals are inverted or moved.
- shift shift There may be types that shift shift. Examples of the type of inverting and moving the residual signals (inverting type) and the type of shifting (shifting type) are shown in FIGS. 8 to 10.
- the positions of the respective samples are represented using the numbers represented in the respective samples. It was.
- a horizontal flip (H-flip) (FIG. 8A), which inverts and moves the upper and lower samples based on a horizontal center line (horizontal center axis, dotted line) of the residual block
- a residual Vertical flip (V-flip) (Fig. 8 (b)) for inverting and shifting the left and right samples with respect to the vertical center line of the block (vertical center axis, dashed line)
- V-flip Fig. 8 (b)
- a type that inverts the upper left and lower right samples based on a dotted line (diagonal-up flip (Dup-flip), FIG. 8 (c)), and the lower left sample based on the right downward diagonal line (dashed line) of the residual block.
- the inversion type may further include an inversion type (N-flip, FIG. 8E) in which the residual signal is not inverted (no change occurs).
- FIGS. 10A and 10B An example of rearranging the residual signals using the Dup-flip type among various inversion types is illustrated in FIGS. 10A and 10B.
- the hatched samples represent samples having a relatively large value (relatively high energy) of the residual signal.
- the values of the residual signals increase in both the horizontal axis direction and the vertical axis direction.
- the residual signals are rearranged in an energy form suitable for DST.
- the positions of the respective samples are determined using the numbers represented in the respective samples. Expressed.
- a horizontal shift (H-shift) for shifting the upper and lower samples with respect to the horizontal center line (horizontal center axis, dashed line) of the residual block, FIG. 9 (a)
- a vertical shifting type for shifting left and right samples based on a vertical center line (vertical center axis, dotted line) of the residual block.
- a type for shifting the upper left sample and the lower right sample based on the right diagonal line (dotted line) of the block (diagonal-up shift (Dup-shift), FIG.
- FIGS. 10C and 10D An example of rearranging the residual signals using the Ddw-shift type among various shifting types is illustrated in FIGS. 10C and 10D.
- the hatched samples represent samples having a relatively large value (relatively high energy) of the residual signal.
- the values of the residual signals are increased in the horizontal axis direction so that the residual signals are rearranged in an energy form suitable for DST, and the residual signals are decreased in the vertical axis direction. It can be seen that they are rearranged in energy form suitable for DCT.
- the distribution or arrangement of the residual signals may vary depending on the prediction mode and / or the prediction direction of the current block.
- a rearrangement type suitable for a specific conversion type may also vary.
- the prediction mode may mean whether the prediction mode of the current block is inter prediction or intra prediction
- the prediction direction may mean an intra prediction direction when the prediction mode of the current block is intra prediction.
- the distribution form of the residual signals may be divided into three categories ((A), (B) and (C)) according to the intra prediction direction.
- (A) is a horizontal direct mode (Horizontal intra, up-diagonal intra), in which residual signal values gradually increase from left to right in the residual block.
- (C) is a vertical intra mode (down-diagonal intra), and the residual signal values may gradually increase from the upper side to the lower side in the residual block.
- (B) is a diagonal intra mode, and the residual signal values may increase from the upper left to the lower right in the residual block.
- non-directional mode and inter prediction may be classified into separate categories.
- the image encoding apparatus determines the distribution or arrangement of the residual signals based on the prediction mode and / or the prediction direction of the current block, determines the rearrangement type suitable for the arrangement and / or transformation type of the residual signals, and then determines the rearrangement.
- the type can be applied to the residual block to rearrange the residual signals.
- prediction information about the prediction mode and / or the prediction direction of the current block may be included in the bitstream and signaled from the image encoding apparatus to the image decoding apparatus.
- the image decoding apparatus may further decode the prediction information from the bitstream in addition to the transform type information and the transform coefficients. Also, the image decoding apparatus may determine one or more rearrangement types that may be applied to the rearrangement of the residual block based on one or more of the transform type information and the prediction information. Specifically, the image decoding apparatus determines the distribution or arrangement of the residual signals based on the prediction mode and / or the prediction direction of the current block, and determines the rearrangement type suitable for the arrangement and / or transformation type of the residual signals. The residual signals may be rearranged by applying the determined rearrangement type to the residual block.
- the image encoding / decoding apparatus may classify and categorize applicable rearrangement types according to prediction information and / or transform type information in advance.
- the apparatus for encoding an image selects a category corresponding to the prediction information and / or transform type information of the current block, and information about the rearrangement type applied to the rearrangement among one or more rearrangement types included in the selected category. May be signaled to the video decoding apparatus.
- the image decoding apparatus selects a category corresponding to the signaled prediction information and / or transform type information among predefined categories, and the signaled rearrangement type information is indicated from one or more rearrangement types included in the selected category.
- the residual signals may be rearranged.
- the conversion type is a skip type
- a form in which the value of the residual signals decreases from the upper left side to the lower right side of the residual block may be suitable.
- the transform type is the Skip type and the intra prediction direction is the horizontal directivity mode (A)
- a rearrangement type for exchanging or shifting the residual signals located on the left side and the residual signals located on the right side may be suitable.
- the transform type is the Skip type and the intra prediction direction is the vertical directing mode (C)
- a rearrangement type for exchanging or moving the residual signals located above and the residual signals located below the residual block may be suitable.
- the transform type is the Skip type and the intra prediction direction is the diagonal direction mode (B)
- a rearrangement type for exchanging or moving the residual signals located at the upper left side of the residual block and the residual signals located at the lower right side may be suitable. Can be.
- the rearrangement types suitable for the Skip type are shown in Tables 2 to 6 below based on the aforementioned categories.
- the inversion type and the shifting type of rearrangement types are taken as examples.
- Dup-flip can be replaced with Ddw-flip or HV-flip for diagonal directional mode (B), and Dup-flip and Ddw-flip for non-directional / inter mode (D). Can be replaced with HV-flip.
- Dup-flip can be replaced by Ddw-flip or HV-flip in the case of horizontal orientation mode (A) and vertical orientation mode (C), and diagonal orientation mode (B) and non-directional / inter mode (D ), Dup-flip and Ddw-flip can be replaced with HV-flip.
- N-flips are not included in Tables 2, 4, and 6, but N-flips are included in Tables 3 and 5. Due to such a difference, a difference may occur in a manner of signaling rearrangement type information. A method of signaling rearrangement type information will be described later.
- the conversion type is the DST type
- a form in which the value of the residual signals increases from the left to the right direction of the residual block or from the top to the bottom direction may be appropriate.
- the transform type when the transform type is DST and the intra prediction direction is the horizontal directivity mode (A), a rearrangement type for exchanging or moving the residual signals located above and the residual signals located below the residual block may be suitable.
- the transform type when the transform type is DST and the intra prediction direction is the vertical direction mode (C), a rearrangement type for exchanging or shifting the residual signals located on the left side and the residual signals located on the right side may be suitable.
- the rearrangement types suitable for the DST type are shown in Tables 7 to 9 below based on the aforementioned categories.
- Tables 7 to 9 the inversion type and the shifting type among the rearrangement types are taken as examples.
- Dup-flip and Ddw-flip can be replaced with HV-flip in the case of non-directional / inter mode (D).
- all inversion types can be replaced with shifting types in the same manner.
- N-flips may be added to all categories.
- N-flip is not included in Table 7 and Table 9, but N-flip is included in Table 8. Due to this difference, a difference may occur in a method of signaling rearrangement type information, which will be described later.
- the conversion type is a DCT type
- a form in which the values of the residual signals decrease in a left to right direction or from an upper side to a lower side of the residual block may be suitable.
- the transform type is DCT and the intra prediction direction is the horizontal directivity mode (A)
- a rearrangement type for exchanging or shifting the residual signals located on the left side and the residual signals located on the right side may be suitable.
- the transform type is DCT and the intra prediction direction is the vertical direction mode (C)
- a rearrangement type for exchanging or moving the residual signals located above and the residual signals located below the residual block may be suitable.
- the transform type is DCT and the intra prediction direction is a diagonal direction mode (B)
- a rearrangement type for exchanging or moving the residual signals located at the upper left side of the residual block and the residual signals located at the lower right side may be suitable. have.
- the rearrangement type used in the present invention may include an exchange type and a move type
- the move type may include an inversion type and a shifting type.
- the image decoding apparatus may receive rearrangement type information from the image encoding apparatus (signaling) to determine the rearrangement type applied to the residual block, or the rearrangement type applied to the residual block without providing rearrangement type information.
- An example in which no rearrangement type information is provided may include a case in which a rearrangement type to be applied to the residual block is previously set in the image encoding / decoding apparatus.
- the rearrangement type information may not be provided.
- the rearrangement type information may not be provided.
- reordering type information examples include: 1) when only reordering type information is signaled, 2) enable information indicating whether reordering is allowed, reordering type information, and whether reordering is applied or not. When the application information is signaled, 3) the enable information and rearrangement type information may be signaled.
- the rearrangement type information may be formed in various forms such as an index and a flag according to the number of applicable rearrangement type information (one or more rearrangement types).
- the image encoding apparatus may signal the image decoding apparatus by including information on the rearrangement type applied to the residual block in the bitstream.
- the image decoding apparatus may decode rearrangement type information and rearrange residual signals according to the rearrangement type indicated by the decoded rearrangement type information among the one or more rearrangement type information.
- the image encoding apparatus may signal enable information (eg, residual_flipping_enabled_flag) indicating whether rearrangement is allowed.
- Enable information may be defined and signaled by a high-level syntax.
- the image encoding apparatus may apply application information (eg, residual_flipping_flag) indicating whether or not the rearrangement is applied to a corresponding residual block (or transform block). Or may be defined and signaled for each conversion block).
- Application information may be defined in the header position of the corresponding transform block.
- the image encoding apparatus may signal rearrangement type information (for example, residual_flipping_idx) applied to a corresponding residual block (or transform block).
- the image decoding apparatus may determine whether the enable information decoded from the bitstream is on / off (S1210). When the enable information is on, the image decoding apparatus may decode application information from the bitstream (S1220). If the application information is on (S1230), the image decoding apparatus may decode rearrangement type information from the bitstream (S1240). The image decoding apparatus may rearrange the residual signals according to the rearrangement type indicated by the rearrangement type information among one or more rearrangement types applicable (S1250).
- the video encoding apparatus may signal enable information.
- Enable information may be defined and signaled by a high-level syntax.
- the image encoding apparatus may signal rearrangement type information applied to the residual block (or transform block).
- the enable information is on (S1310)
- the image decoding apparatus may decode the rearrangement type information from the bitstream (S1320).
- the image decoding apparatus may rearrange the residual signals according to the rearrangement type indicated by the rearrangement type information among one or more rearrangement types applicable (S1330).
- the applicable rearrangement types may include an N-rearrangement type (eg, N-flip, N-shift) indicating that no rearrangement occurs.
- N-rearrangement type e.g, N-flip, N-shift
- the image encoding apparatus signals rearrangement type information indicating the N-rearrangement type, and the image decoding apparatus reconstructs the residual signals when the rearrangement type information indicates the N-rearrangement type. You may not perform the array.
- the rearrangement type divisions of Tables 3, 5, and 8 include the N-rearrangement type, but the remaining rearrangement type divisions (Tables 2, 4, 6, 7 and 9 do not include the N-rearrangement type. Accordingly, the rearrangement type classification of Tables 3, 5, and 8 may be suitable for the embodiment (c embodiment) in which the application information is not signaled, and in Table 2, Table 4, Table 6, Table 7, and Table 9 The rearrangement type classification may be suitable for the embodiment (b embodiment) in which the application information is signaled.
- Embodiment 2 corresponds to a method of rearranging residual signals in a residual block by using a correlation between an error value between respective reference blocks and an energy distribution of a residual block in bidirectional prediction of inter prediction. .
- the image encoding / decoding apparatus In bi-prediction of inter prediction, the image encoding / decoding apparatus generates a prediction block by averaging or weighting the reference blocks (reference block L0 and reference block L1) of each of the bidirectional directions (L1 direction and L0 direction), and The residual block may be generated by differentiating the prediction block.
- the region having a large error value between the reference block L0 and the reference block L1 corresponds to a region in which the prediction is relatively inaccurate
- the region having a small error value between the reference block L0 and the reference block L1 is a region with relatively accurate prediction It may correspond to.
- the image encoding / decoding apparatus can grasp the distribution of the residual signal values in the residual block based on the magnitude of the error value between the reference block L0 and the reference block L1, and use the obtained result to distribute the residual signals suitable for the conversion type. Can be rearranged.
- additional information signaled from the image encoding apparatus to the image decoding apparatus may not be required to rearrange the residual signals. This is because the image decoding apparatus may also grasp information about each reference block in both directions by itself, and calculate an error value between the two reference blocks to use as a reordering criterion.
- the unit to be rearranged may be a residual signal or a subblock obtained by (virtually) dividing a residual block or reference blocks.
- the residual block or reference blocks may be divided into one or more (M ⁇ N) subblocks.
- the residual block or reference blocks may be divided into a total of four subblocks bisected on the horizontal and vertical axes, respectively.
- the second embodiment will be described based on the rearrangement of the subblock units.
- the image encoding apparatus may calculate an error value between the reference block L0 and the reference block L1.
- the error value may be calculated separately for each subblock, and when there are a plurality of pixels included in a specific subblock, the error value may be an error representative value obtained by averaging or summating error values of each of the pixels.
- the image encoding apparatus may rearrange subblocks in the residual block based on error values.
- the subblocks may be rearranged such that the distribution of the subblocks (residual signals) is suitable for the transform type to be applied to the residual block among the transform types DCT, DST, and Skip.
- the subblocks may be rearranged by sequentially sorting based on each error value and then scanning according to the conversion type to be applied.
- a method of sequentially ordering subblocks may include a descending order, an ascending order, etc.
- the method of scanning the aligned subblocks may include horizontal scanning, vertical scanning, diagonal-up scanning, zig-zag scanning, and the like.
- the image decoding apparatus may determine respective reference blocks in both directions (S1410), and calculate an error value between the reference blocks with respect to each of the subblocks (S1420). In addition, the image decoding apparatus may rearrange the residual signals by rearranging the subblocks based on the calculated error values (S1430).
- the above-described transform type may serve as a reference for the rearrangement of the subblocks, and the above-described sorting method and scanning method may be used as a method for rearranging the subblocks into a form suitable for the transform type. That is, the selection of the alignment scheme to be applied among the one or more alignment schemes and the selection of the scanning scheme to be applied among the one or more scanning schemes may be determined based on whether or not it is suitable for the conversion type.
- Table 10 shows the sorting method and the scanning method suitable for a specific conversion type.
- the descending order alignment method may be suitable, and the diagonal-up or zig-zag scanning method may be suitable.
- an ascending order alignment method may be suitable, and a horizontal or vertical scanning method may be suitable.
- the descending order alignment method may be suitable, and the horizontal or vertical scanning method may be suitable.
- an error block may correspond to a block including error values between two reference blocks.
- the error block may be divided into one or more subblocks, and an error (representative) value may be calculated for each subblock constituting the error block.
- the step of sorting the subblocks may be performed on the subblocks included in the error block, and the step of scanning the subblocks corresponds to the sorted order of the subblocks included in the error block. It may be performed on the subblocks included in the residual block.
- FIG. 15 (a) shows subblocks of an error block before rearrangement
- FIG. 15 (b) shows subblocks of the rearranged error block.
- Numbers in parentheses included in each of the subblocks indicate an error (representative) value
- numbers not represented in parentheses indicate the positions of the subblocks.
- subblocks before rearrangement may have a higher error value toward the lower side. If the subblocks are sorted before being rearranged using the descending order alignment method and the 'sorted subblocks' are scanned using the diagonal-up scanning method, the rearrangement becomes larger as the error value increases toward the upper left side and becomes smaller toward the lower right side. This can be implemented (Fig. 15 (b)). Accordingly, it can be seen that by sorting and scanning subblocks based on an error value, the subblocks can be rearranged into an array form suitable for a specific transform type (see FIG. 15, a skip type).
- the aforementioned inversion type and shifting type can be used in the rearrangement manner of Example 2.
- the image encoding / decoding apparatus determines an inversion type or shifting type to be applied to the residual block based on the error value between the reference blocks and the transform type to be applied (applied), and the residual signal according to the determined type. You can rearrange them.
- the image encoding / decoding apparatus calculates error values for the upper and lower subblocks based on the center horizontal axis of the residual block and then applies H-flip / H-shift based on the calculated error values. Can be determined.
- the image encoding / decoding apparatus calculates error values for left and right subblocks based on the central vertical axis of the residual block, and then determines whether to apply V-flip / V-shift based on the calculated error value. Can be.
- the image encoding / decoding apparatus compares the inversion types / shifting types with respect to the rearrangement results for each of the inversion types / shifting types and compares them with each other. Can be determined.
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Abstract
L'invention concerne un procédé de réagencement de signaux résiduels, et un appareil de décodage d'image. Selon un mode de réalisation de la présente invention, un procédé de réagencement de signaux résiduels comprend les étapes consistant à : décoder, à partir d'un flux binaire, des coefficients de transformée dans un bloc de transformée d'un bloc courant et des informations de type de transformée indiquant un type de transformée appliqué au bloc de transformée; déduire un bloc résiduel à partir des coefficients de transformée, selon le type de transformée indiqué par les informations de type de transformée; et réagencer des signaux résiduels dans le bloc résiduel selon l'un quelconque d'un ou plusieurs types de réagencement.
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