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WO2012128453A1 - Procédé et dispositif de codage/décodage d'images - Google Patents

Procédé et dispositif de codage/décodage d'images Download PDF

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Publication number
WO2012128453A1
WO2012128453A1 PCT/KR2011/010224 KR2011010224W WO2012128453A1 WO 2012128453 A1 WO2012128453 A1 WO 2012128453A1 KR 2011010224 W KR2011010224 W KR 2011010224W WO 2012128453 A1 WO2012128453 A1 WO 2012128453A1
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Prior art keywords
prediction mode
chroma
prediction
mode
index
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English (en)
Korean (ko)
Inventor
임재현
박승욱
헨드리헨드리
박준영
최영희
김정선
전병문
전용준
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LG Electronics Inc
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LG Electronics Inc
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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
    • H04N19/186—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 a colour or a chrominance component
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/103—Selection of coding mode or of prediction mode
    • H04N19/11—Selection of coding mode or of prediction mode among a plurality of spatial predictive coding modes
    • 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
    • H04N19/46—Embedding additional information in the video signal during the compression process
    • H04N19/463—Embedding additional information in the video signal during the compression process by compressing encoding parameters before transmission
    • 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 image processing, and more particularly, to an image encoding / decoding method and apparatus.
  • the demand for high resolution and high quality images such as high definition (HD) images and ultra high definition (UHD) images is increasing in various fields.
  • the higher the resolution and the higher quality of the image data the more information or bit rate is transmitted than the existing image data. Therefore, the image data can be transmitted by using a medium such as a conventional wired / wireless broadband line or by using a conventional storage medium.
  • the transmission cost and the storage cost are increased. High efficiency image compression techniques can be used to solve these problems.
  • Image compression technology includes an inter prediction technique for predicting pixel values included in a current picture from before and / or after a current picture, and for predicting pixel values included in a current picture by using pixel information in the current picture.
  • An object of the present invention is to provide an image encoding method and apparatus capable of improving image encoding / decoding efficiency.
  • Another object of the present invention is to provide an image decoding method and apparatus capable of improving image encoding / decoding efficiency.
  • Another technical problem of the present invention is to provide a method and apparatus for transmitting chroma prediction mode information capable of improving image encoding / decoding efficiency.
  • Another technical problem of the present invention is to provide a method and apparatus for deriving a chroma prediction mode capable of improving image encoding / decoding efficiency.
  • An embodiment of the present invention is an image decoding method based on a prediction unit to which a short distance intra prediction (SDIP) is applied.
  • the method includes generating a chroma prediction mode candidate list by assigning an index corresponding to a codeword to chroma prediction mode candidates and using the generated chroma prediction mode candidate list and chroma prediction mode index information transmitted from an encoder. Deriving a chroma prediction mode of the chroma prediction mode candidate list, wherein the chroma prediction mode candidate list is a set of chroma prediction mode candidates each having an index assigned thereto, and the chroma prediction mode index information includes candidates included in the chroma prediction mode candidate list.
  • SDIP short distance intra prediction
  • Luma component prediction unit Includes prediction modes.
  • the lowest index may be allocated to the LM mode.
  • the number of chroma prediction mode candidates included in the chroma prediction mode candidate list may be limited to a predetermined fixed number.
  • the predetermined fixed number may be five or six.
  • the chroma prediction mode candidate list may include only the LM mode and the luma prediction mode.
  • the highest index may be allocated to the LM mode.
  • a prediction mode candidate list by allocating an index corresponding to the codeword to the chroma prediction mode candidate, assigning an index lower than the LM mode to some prediction modes among the prediction modes included in the luma prediction mode.
  • An index higher than the LM mode may be allocated to the remaining prediction modes among the prediction modes included in the luma prediction mode.
  • the index may be allocated to the LM mode based on flag information transmitted from the encoder.
  • the luma prediction mode may include only some of the prediction modes of the plurality of luma component prediction units corresponding to the chroma component prediction unit.
  • the luma prediction mode may include sub-sampled prediction modes corresponding to each of the prediction modes of the plurality of luma component prediction units corresponding to the chroma component prediction unit.
  • Another embodiment of the present invention is an image decoding apparatus based on a prediction unit to which a short distance intra prediction (SDIP) is applied.
  • SDIP short distance intra prediction
  • the apparatus generates an chroma prediction mode candidate list by assigning an entropy decoder for entropy decoding chroma prediction mode index information transmitted from an encoder and an index corresponding to a codeword to the chroma prediction mode candidates, and generating the chroma prediction mode candidate.
  • An intra prediction unit for deriving a chroma prediction mode of a current block using a list and the entropy decoded chroma prediction mode index information, and performing intra prediction on a chroma component of the current block using the derived chroma prediction mode
  • the chroma prediction mode candidate list is a set of chroma prediction mode candidates to which an index is assigned, respectively, and the chroma prediction mode index information corresponds to a chroma prediction mode of the current block among candidates included in the chroma prediction mode candidate list.
  • the chroma prediction mode candidate list includes an LM mode and a luma prediction mode
  • the luma prediction mode includes prediction modes of a plurality of luma component prediction units corresponding to the chroma component prediction unit.
  • Another embodiment of the present invention is a method of deriving a chroma prediction mode based on a prediction unit to which a short distance intra prediction (SDIP) is applied.
  • the method includes generating a chroma prediction mode candidate list by assigning an index corresponding to a codeword to chroma prediction mode candidates and using the generated chroma prediction mode candidate list and chroma prediction mode index information transmitted from an encoder. Deriving a chroma prediction mode of the chroma prediction mode candidate list, wherein the chroma prediction mode candidate list is a set of chroma prediction mode candidates each having an index assigned thereto, and the chroma prediction mode index information includes candidates included in the chroma prediction mode candidate list.
  • SDIP short distance intra prediction
  • Luma component prediction unit Includes prediction modes.
  • the lowest index may be allocated to the LM mode.
  • the number of chroma prediction mode candidates included in the chroma prediction mode candidate list may be limited to a predetermined fixed number.
  • the predetermined fixed number may be five or six.
  • the index may be allocated to the LM mode based on flag information transmitted from the encoder.
  • the luma prediction mode may include only some of the prediction modes of the plurality of luma component prediction units corresponding to the chroma component prediction unit.
  • the luma prediction mode may include sub-sampled prediction modes corresponding to each of the prediction modes of the plurality of luma component prediction units corresponding to the chroma component prediction unit.
  • image encoding / decoding efficiency can be improved.
  • the image decoding method According to the image decoding method according to the present invention, the image encoding / decoding efficiency can be improved.
  • image encoding / decoding efficiency may be improved.
  • image encoding / decoding efficiency may be improved.
  • FIG. 1 is a block diagram schematically illustrating an image encoding apparatus according to an embodiment of the present invention.
  • FIG. 2 is a conceptual diagram schematically illustrating a prediction unit according to an embodiment of the present invention.
  • FIG. 3 is a block diagram schematically illustrating an image decoding apparatus according to an embodiment of the present invention.
  • FIG. 4 is a conceptual diagram schematically illustrating a prediction unit of an image decoding apparatus according to an embodiment of the present invention.
  • FIG. 5 is a conceptual diagram schematically illustrating an embodiment of a prediction unit used for intra prediction.
  • FIG. 6 is a conceptual diagram schematically illustrating an embodiment of a method of generating a chroma prediction mode candidate in SDIP.
  • FIG. 7 is a conceptual diagram schematically illustrating an embodiment of a method for generating a chroma prediction mode candidate when SDIP and LM mode are used at the same time.
  • FIG. 8 is a conceptual diagram schematically illustrating an embodiment of an index allocation method for a chroma prediction mode candidate.
  • FIG. 9 is a conceptual diagram schematically illustrating another embodiment of an index allocation method for chroma prediction mode candidates.
  • FIG. 10 is a flowchart illustrating an embodiment of a method for transmitting chroma prediction mode information when SDIP and LM modes are used at the same time.
  • FIG. 11 is a flowchart illustrating an embodiment of a chroma prediction mode derivation method when SDIP and LM modes are used simultaneously.
  • FIG. 12 is a flowchart schematically illustrating another embodiment of a method of generating a chroma prediction mode candidate when SDIP and LM modes are used at the same time.
  • FIG. 13 is a conceptual diagram schematically illustrating a method of deriving a final luma prediction mode through a mapping process.
  • each of the components in the drawings described in the present invention are shown independently for the convenience of the description of the different characteristic functions in the image encoding / decoding apparatus, each component is implemented by separate hardware or separate software It does not mean to be.
  • two or more of each configuration may be combined to form one configuration, or one configuration may be divided into a plurality of configurations.
  • Embodiments in which each configuration is integrated and / or separated are also included in the scope of the present invention without departing from the spirit of the present invention.
  • the components may not be essential components for performing essential functions in the present invention, but may be optional components for improving performance.
  • the present invention can be implemented including only the components essential for implementing the essentials of the present invention except for the components used for improving performance, and the structure including only the essential components except for the optional components used for improving performance. Also included within the scope of the present invention.
  • the image encoding apparatus 100 may include a picture splitter 105, a predictor 110, a transformer 115, a quantizer 120, a realigner 125, and an entropy encoder 130. , An inverse quantization unit 135, an inverse transform unit 140, a filter unit 145, and a memory 150.
  • the picture dividing unit 105 may divide the input picture into at least one processing unit.
  • the processing unit may be a prediction unit (PU), a transform unit (TU), or a coding unit (CU).
  • the predictor 110 may include an inter predictor that performs inter prediction and an intra predictor that performs intra prediction.
  • the prediction unit 110 may generate a prediction block by performing prediction on the processing unit of the picture in the picture division unit 105.
  • the processing unit of the picture in the prediction unit 110 may be a coding unit, a transformation unit, or a prediction unit.
  • the processing unit in which the prediction is performed may differ from the processing unit in which the prediction method and the details are determined.
  • the method of prediction and the prediction mode are determined in units of prediction units, and the performance of prediction may be performed in units of transform units.
  • the residual value (residual block) between the generated prediction block and the original block may be input to the converter 115.
  • prediction mode information and motion vector information used for prediction may be encoded by the entropy encoder 130 together with the residual value and transmitted to the decoder.
  • the transform unit 115 performs a transform on the residual block in transform units and generates transform coefficients.
  • the transform unit in the transform unit 115 may be a transform unit and may have a quad tree structure. In this case, the size of the transform unit may be determined within a range of a predetermined maximum and minimum size.
  • the transform unit 115 may transform the residual block using a discrete cosine transform (DCT) and / or a discrete sine transform (DST).
  • DCT discrete cosine transform
  • DST discrete sine transform
  • the quantization unit 120 may generate quantization coefficients by quantizing the residual values transformed by the transformation unit 115.
  • the value calculated by the quantization unit 120 may be provided to the inverse quantization unit 135 and the reordering unit 125.
  • the reordering unit 125 rearranges the quantization coefficients provided from the quantization unit 120. By rearranging the quantization coefficients, the efficiency of encoding in the entropy encoder 130 may be increased.
  • the reordering unit 125 may rearrange the quantization coefficients in the form of a two-dimensional block into a one-dimensional vector form through a coefficient scanning method.
  • the reordering unit 125 may increase the entropy coding efficiency of the entropy encoder 130 by changing the order of coefficient scanning based on probabilistic statistics of coefficients transmitted from the quantization unit.
  • the entropy encoder 130 may perform entropy encoding on the quantized coefficients rearranged by the reordering unit 125.
  • the entropy encoder 130 may include quantization coefficient information, block type information, prediction mode information, division unit information, prediction unit information, transmission unit information, and motion vector of the coding unit received from the reordering unit 125 and the prediction unit 110.
  • Various information such as information, reference picture information, interpolation information of a block, and filtering information can be encoded.
  • Entropy encoding may use encoding methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC).
  • the entropy encoder 130 may store a table for performing entropy coding, such as a variable length coding (VLC) table, and the entropy encoder 130. ) May perform entropy encoding using the stored VLC table.
  • VLC variable length coding
  • the entropy encoder 130 converts a symbol into a bin and binarizes the symbol, and then performs an arithmetic encoding on the bin according to the occurrence probability of the bin to generate a bitstream. You can also create
  • a low value index and a corresponding short codeword are assigned to a symbol having a high probability of occurrence, and a high value index is assigned to a symbol having a low probability of occurrence.
  • Corresponding long codewords may be assigned. Accordingly, the bit amount of the symbols to be encoded may be reduced, and image compression performance may be improved by entropy encoding.
  • the inverse quantization unit 135 may inverse quantize the quantized values in the quantization unit 120, and the inverse transformer 140 may inversely transform the inverse quantized values in the inverse quantization unit 135.
  • the residual value generated by the inverse quantization unit 135 and the inverse transformer 140 may be combined with the prediction block predicted by the prediction unit 110 to generate a reconstructed block.
  • the filter unit 145 may apply a deblocking filter and / or an adaptive loop filter (ALF) to the reconstructed picture.
  • ALF adaptive loop filter
  • the deblocking filter may remove block distortion generated at the boundary between blocks in the reconstructed picture.
  • the adaptive loop filter may perform filtering based on a value obtained by comparing a reconstructed image with an original image after the block is filtered through a deblocking filter. ALF may be performed only when high efficiency is applied.
  • the filter unit 145 may not apply filtering to the reconstructed block used for inter prediction.
  • the memory 150 may store the reconstructed block or the picture calculated by the filter unit 145.
  • the reconstructed block or picture stored in the memory 150 may be provided to the predictor 110 that performs inter prediction.
  • a coding unit is a unit in which coding / decoding of a picture is performed and may be divided with a depth based on a quad tree structure.
  • the coding unit may have various sizes, such as 64x64, 32x32, 16x16, and 8x8.
  • the encoder may transmit information about a largest coding unit (LCU) and a minimum coding unit (SCU) to the decoder.
  • Information (depth information) regarding the number of splittable times together with information about the maximum coding unit and / or the minimum coding unit may be transmitted to the decoder.
  • Information on whether the coding unit is split based on the quad tree structure may be transmitted from the encoder to the decoder through flag information such as a split flag.
  • the predictor 200 may include an inter predictor 210 and an intra predictor 220.
  • the inter prediction unit 210 may generate a prediction block by performing prediction based on information of at least one picture of a previous picture or a subsequent picture of the current picture.
  • the intra predictor 220 may generate a prediction block by performing prediction based on pixel information in the current picture.
  • the inter prediction unit 210 may select a reference picture with respect to the prediction unit and select a reference block having the same size as the prediction unit in integer pixel sample units. Subsequently, the inter prediction unit 210 is most similar to the current prediction unit in sub-integer sample units such as 1/2 pixel sample unit and 1/4 pixel sample unit, so that the residual signal is minimized and the size of the motion vector to be encoded is also minimized. Can generate a predictive block.
  • the motion vector may be expressed in units of integer pixels or less, for example, in units of 1/4 pixels for luma pixels and in units of 1/8 pixels for chroma pixels.
  • Information about the index and the motion vector of the reference picture selected by the inter prediction unit 210 may be encoded and transmitted to the decoder.
  • the image decoder 300 includes an entropy decoder 310, a reordering unit 315, an inverse quantizer 320, an inverse transformer 325, a predictor 330, and a filter 335. And a memory 340.
  • the input bit stream may be decoded according to a procedure in which image information is processed by the image encoder.
  • the entropy decoding unit 310 may perform entropy decoding on the input bitstream, and the entropy decoding method is similar to the entropy encoding method described above.
  • VLC variable length coding
  • the entropy decoder 310 may also be identical to the VLC table used in the encoder. Entropy decoding can be performed by implementing a VLC table. Even when CABAC is used to perform entropy encoding in the image encoder, the entropy decoder 310 may perform entropy decoding using CABAC correspondingly.
  • a low value index and a corresponding short codeword are assigned to a symbol having a high probability of occurrence, and a high value index is assigned to a symbol having a low probability of occurrence.
  • Corresponding long codewords may be assigned. Accordingly, the bit amount of the symbols to be encoded may be reduced, and image compression performance may be improved by entropy encoding.
  • Information for generating a prediction block among the information decoded by the entropy decoder 310 may be provided to the predictor 330, and a residual value of which entropy decoding is performed by the entropy decoder may be input to the reordering unit 315.
  • the reordering unit 315 may reorder the bit stream deentropy decoded by the entropy decoding unit 310 based on a method of reordering the image encoder.
  • the reordering unit 315 may reorder the coefficients expressed in the form of a one-dimensional vector by restoring the coefficients in the form of a two-dimensional block.
  • the reordering unit 315 may be realigned by receiving information related to coefficient scanning performed by the encoder and performing reverse scanning based on the scanning order performed by the corresponding encoder.
  • the inverse quantization unit 320 may perform inverse quantization based on the quantization parameter provided by the encoder and the coefficient values of the rearranged block.
  • the inverse transform unit 325 may perform inverse DCT and / or inverse DST on DCT and DST performed by the transform unit of the encoder with respect to the quantization result performed by the image encoder.
  • the inverse transform may be performed based on a transmission unit determined by the encoder or a division unit of an image.
  • the DCT and / or DST may be selectively performed according to a plurality of pieces of information, such as a prediction method, a size and a prediction direction of the current block, and the inverse transformer 325 of the decoder is performed by the transformer of the encoder.
  • Inverse transformation may be performed based on the transformation information.
  • the prediction unit 330 may generate the prediction block based on the prediction block generation related information provided by the entropy decoding unit 310 and the previously decoded block and / or picture information provided by the memory 340.
  • the reconstruction block may be generated using the prediction block generated by the predictor 330 and the residual block provided by the inverse transform unit 325.
  • the reconstructed block and / or picture may be provided to the filter unit 335.
  • the filter unit 335 may apply deblocking filtering, sample adaptive offset (SAO), and / or adaptive loop filtering (ALF) to the reconstructed block and / or picture.
  • deblocking filtering sample adaptive offset (SAO)
  • ALF adaptive loop filtering
  • the memory 340 may store the reconstructed picture or block to use as a reference picture or reference block, and may provide the reconstructed picture to the output unit.
  • FIG. 4 is a conceptual diagram schematically illustrating a prediction unit of an image decoding apparatus according to an embodiment of the present invention.
  • the predictor 400 may include an intra predictor 410 and an inter predictor 420.
  • the intra prediction unit 410 may generate a prediction block based on pixel information in the current picture when the prediction mode for the corresponding prediction unit is an intra prediction mode (intra prediction mode).
  • the inter prediction unit 420 may include information necessary for inter prediction of the current prediction unit provided by the image encoder, eg, a motion vector, Inter-prediction of the current prediction unit may be performed based on information included in at least one of a previous picture or a subsequent picture of the current picture including the current prediction unit by using information about the reference picture index.
  • the motion information may be derived in response to the skip flag, the merge flag, and the like of the coding unit received from the encoder.
  • a "picture” or a “picture” can represent the same meaning as a “picture” according to the configuration or expression of the invention, the “picture” may be described as a “picture” or a “picture”.
  • inter prediction and inter prediction have the same meaning
  • intra prediction and intra prediction have the same meaning.
  • FIG. 5 is a conceptual diagram schematically illustrating an embodiment of a prediction unit used for intra prediction.
  • One coding unit may be divided into a plurality of prediction units.
  • a prediction mode may be determined in units of prediction units, and prediction may be performed in units of prediction units.
  • a prediction mode may be determined in units of prediction units, and intra prediction may be performed in units of transform units.
  • a prediction unit may have a size of 2N ⁇ 2N or N ⁇ N (N is an integer).
  • N is an integer
  • a N ⁇ N size prediction unit may be determined to be applied only to a minimum size coding unit or may be determined to be applied only to intra prediction.
  • a 64x64 size prediction unit may exist for a 64x64 size coding unit
  • a 32x32 size prediction unit may exist for a 32x32 size coding unit.
  • a 16x16 sized prediction unit may exist for a 16x16 sized coding unit
  • an 8x8 and / or 4x4 sized prediction unit may exist for an 8x8 sized coding unit.
  • the prediction unit used for intra prediction may have the form of a rectangle as well as a square.
  • the prediction unit may be a (1/4) hNx2N sized block in which a hNx2N sized block is divided again, and a 2Nx (1/4) hN sized block in which a 2NxhN sized block is divided again. It may be.
  • Intra prediction when a rectangular prediction unit is used as shown in 520 and 530 of FIG. 5 may be referred to as short distance intra prediction (SDIP).
  • SDIP short distance intra prediction
  • 8x32 and / or 32x8 size prediction units may exist for 32x32 size coding units, and 4x16 and / or 16x4 size prediction units may exist for 16x16 size coding units. There may be 2x8 and / or 8x2 prediction units for an 8x8 coding unit.
  • SDIP may not be applied to a 64x64 coding unit, and a 1x16 and / or 16x1 prediction unit may be additionally provided for a 16x16 coding unit.
  • each prediction unit having a rectangular shape obtained by dividing one square encoding unit may have an independent intra prediction mode.
  • each prediction mode may have one of the mode values assigned to the Unified Directional Intra (UDI) mode.
  • UDI Unified Directional Intra
  • each prediction unit in which one square coding unit is divided into four may have an independent intra prediction mode.
  • each of the prediction units in which one square coding unit is divided into four and the prediction units in four is further allowed to have the same prediction mode.
  • the intra predictor may generate a prediction block for the current block by performing prediction based on pixel information in the current picture. For example, the intra predictor may predict pixel values in the current block by using pixels in the reconstructed block located at the top, left, top left and / or top right with respect to the current block.
  • vertical, horizontal, DC, planar, and angular modes may be used according to the position and / or prediction method of reference pixels used for pixel value prediction of the current block. There may be.
  • the prediction may be performed in the vertical direction using the pixel values of the adjacent blocks
  • the prediction block may be generated by an average of pixel values in the current block.
  • the angular mode prediction may be performed according to a predetermined angle and / or direction for each mode.
  • a predetermined prediction direction and prediction mode value may be used for intra prediction, and the number of intra prediction modes used for intra prediction may vary depending on the size of the current block.
  • the prediction mode for the luma component may be encoded using the prediction mode of the neighboring block adjacent to the current block.
  • Most Probable Mode MPM
  • MPM Most Probable Mode
  • chroma prediction mode candidates When performing intra prediction on the chroma mode, prediction may be performed in one prediction mode among the chroma prediction mode candidates.
  • the chroma prediction mode candidate may include five candidates of LM, vertical, horizontal, DC, and DM modes.
  • the chroma prediction mode candidate may include six candidates of LM, vertical, horizontal, DC, vertical-8, and DM modes.
  • the chroma prediction mode candidate may include six candidates of DM, LM, planner, vertical, horizontal, and DC modes. At this time, if the prediction mode indicated by the DM mode is the same as one of the planner, vertical, horizontal, or DC modes, the vertical + 8 mode is chroma instead of the same prediction mode as the prediction mode indicated by the DM mode.
  • the chroma prediction mode candidate is not limited to the above embodiment and may vary depending on implementation and / or need.
  • the LM mode is a prediction mode in which the prediction value of the chroma component pixel is determined from the pixels of the neighboring block adjacent to the current block and the reconstructed luma component pixels of the current block
  • the DM mode is the prediction mode of the chroma component as it is. Prediction mode used as.
  • the prediction mode information of the chroma component When the prediction mode information of the chroma component is transmitted, information on whether the prediction value is used as the prediction mode of the current block, unlike the luma component, may not be transmitted. Since the chroma component and the luma component in the current block are correlated with each other, the prediction mode of the chroma component may be encoded using the prediction mode of the corresponding luma component.
  • Table 1 schematically shows an embodiment of the relationship between the luma component prediction mode and the chroma component prediction mode.
  • n / a is a mode that has not been used to avoid duplication with cases handled in DM mode.
  • the prediction mode of the luma component is 0 and the prediction mode index of the chroma component is 2, the corresponding value in Table 1 is 1. Therefore, at this time, the prediction may be performed in the prediction mode having the mode value of 1 with respect to the chroma component of the current block. If the prediction mode having the mode value of 1 is the horizontal mode, the prediction may be performed in the horizontal mode on the chroma component of the current block.
  • Table 2 schematically shows another embodiment of the relationship between the luma component prediction mode and the chroma component prediction mode.
  • n / a is a mode that has not been used to avoid duplication with cases handled in DM mode.
  • the prediction mode of the luma component is 0 and the prediction mode index of the chroma component is 2, the corresponding value in Table 1 is 1. Therefore, at this time, the prediction may be performed in the prediction mode having the mode value of 1 with respect to the chroma component of the current block. If the prediction mode having the mode value of 1 is the vertical mode, the prediction may be performed in the vertical mode on the chroma component of the current block.
  • a mode value of 0 may indicate a vertical mode
  • a mode value 1 indicates a horizontal mode
  • a mode value 2 indicates a DC mode
  • a mode value 3 indicates a vertical-8 mode
  • a mode value 35 indicates an LM mode.
  • mode value 0 may represent a planner mode
  • mode value 1 may be a vertical mode
  • mode value 2 may be a horizontal mode
  • mode value 3 may be a DC mode
  • mode value 35 may be an LM mode.
  • the relationship between the luma component prediction mode and the chroma component prediction mode is not limited to the embodiments of Tables 1 and 2 and may vary depending on implementation and / or needs.
  • the encoder may generate a bit stream by performing code entropy encoding by assigning a codeword to a chroma component prediction mode index according to a luma component prediction mode.
  • the coder may reduce the amount of bits transmitted to the decoder by varying the length of the codewords allocated to the chroma component prediction mode indexes according to the prediction mode of the luma component.
  • the decoder may derive the actual prediction mode used for intra prediction on the chroma component of the current block from the received codeword information and luma component prediction mode information.
  • FIG. 6 is a conceptual diagram schematically illustrating an embodiment of a method of generating a chroma prediction mode candidate in SDIP.
  • the LM mode is not used for the chroma component, and the number of chroma prediction mode candidates is limited to five.
  • each prediction unit in a rectangular form in which one square block is divided in the SDIP may have an independent intra prediction mode.
  • the prediction unit of the chroma component may be one square unit, and only one prediction mode may be assigned to the prediction unit of the chroma component.
  • the four luma component prediction units obtained by dividing one square coding unit may have independent prediction modes, and thus each other in one coding unit There may be four other luma component prediction modes.
  • the prediction unit of the chroma component corresponding to the luma component of the one coding unit may be one square prediction unit, and one chroma component prediction mode may exist in one chroma component prediction unit.
  • the prediction mode of the luma component may be used as the prediction mode of the chroma component as it is, but when the SDIP is used, the prediction mode of the luma component that may be used as the prediction mode of the chroma component is It can be up to four. In this case, the chroma component prediction mode may be difficult to be determined by the method shown in the embodiment of Table 1 above. Therefore, a chroma prediction mode candidate may be generated according to a method described below.
  • prediction mode values used in each of four luma component prediction units may be listed in ascending order. Following prediction mode values used in each prediction unit, prediction mode values from 0 to 3 may be listed in ascending order. At this time, in one embodiment, 0 may be a mode value of a vertical mode, 1 of a horizontal mode, 2 of a DC mode, and 3 of a vertical-8 mode. In another embodiment, 0 may be a planar mode, 1 may be a vertical mode, 2 may be a horizontal mode, and 3 may be a mode value of a DC mode. By selecting five prediction modes from the front in the list configured in this manner, a chroma prediction mode candidate can be generated.
  • prediction mode values used in each of four luma component prediction units may be listed in ascending order.
  • prediction mode values from 0 to 3 may be arranged in ascending order after the prediction mode values used in each prediction unit.
  • the overlapped prediction modes may be eliminated.
  • the prediction mode value 0 is a prediction mode value used in the luma component prediction unit
  • the prediction mode values listed next to the prediction mode values used in each prediction unit may start from 1.
  • prediction may be performed in one prediction mode among the chroma prediction mode candidates.
  • the method for generating a chroma prediction mode candidate according to the embodiment of FIG. 6 may be applied to a case where an NxN prediction unit is used in some cases. This is because up to four prediction modes used for luma component intra prediction may exist within a coding unit in which an N ⁇ N prediction unit is used.
  • the chroma prediction mode candidate generation method according to the embodiment of FIG. 6 may be applied even when an 8x8 coding unit is split into a 4x4 prediction unit.
  • the SDIP and the LM mode may be used together for intra prediction on the chroma component.
  • the SDIP and LM modes are separated and may be used independently instead of simultaneously using each other. SDIP and LM modes can also be combined and used simultaneously.
  • the LM mode may not be used for the coding unit in which the SDIP is used.
  • the LM mode may also be applied only to prediction units of 2N ⁇ 2N or N ⁇ N size in which SDIP is not used.
  • FIG. 7 is a conceptual diagram schematically illustrating an embodiment of a method for generating a chroma prediction mode candidate when SDIP and LM mode are used at the same time.
  • the prediction mode used in each luma component prediction unit to which SDIP is applied is called a luma prediction mode.
  • a luma prediction mode, an LM mode, a UDI mode corresponding to a mode value of 0 to 3, and / or a combination of the above modes may be used to generate a chroma prediction mode candidate.
  • the number of luma prediction modes corresponding to chroma components in one coding unit may be plural.
  • 0 may be a mode value of a vertical mode, 1 of a horizontal mode, 2 of a DC mode, and 3 of a vertical-8 mode.
  • 0 may be a planner mode
  • 1 may be a vertical mode
  • 2 may be a horizontal mode
  • 3 may be a mode value of a DC mode.
  • the chroma prediction mode candidate may include all of the luma prediction mode, the LM mode, and the UDI mode corresponding to the mode values of 0 to 3.
  • the amount of bits transmitted from the encoder to the decoder may be large. Therefore, in order to reduce the amount of information to be transmitted, a method of limiting the maximum number of prediction modes that can be included in the chroma prediction mode candidate or selectively selecting only a portion of the LM, horizontal, DC, and vertical-8 modes as the chroma prediction mode candidate May be provided.
  • the maximum number of chroma prediction mode candidates allowed including the luma prediction mode, the LM mode, the vertical mode, the horizontal mode, the DC mode, and the vertical-8 mode may be limited to five or six.
  • the LM mode may be used only if the number of prediction mode candidates, including luma prediction mode, vertical mode, horizontal mode, DC mode, vertical-8 mode, is less than five or only less than six.
  • the chroma prediction mode candidate may be generated only by the combination of the luma prediction mode and the LM mode.
  • the number of chroma prediction mode candidates may be five when prediction units of size hNx2N are used and the luma prediction mode values for each prediction unit are all different.
  • a chroma prediction mode candidate may be generated by a combination of the above methods.
  • FIG. 7 illustrates an embodiment of a method of generating a chroma prediction mode candidate when the maximum number of chroma prediction mode candidates is limited to six among the above embodiments.
  • the maximum number of chroma prediction mode candidates may be limited to six.
  • luma prediction modes used in each prediction unit are 5, 7, 9, and 10. Therefore, prediction mode values of 5, 7, 9, and 10 may be listed in ascending order.
  • the LM modes may be listed after 5, 7, 9, and 10, and the mode values 0, 1, 2, and 3 may be listed in ascending order after the LM mode.
  • the encoder and the decoder may store a table for performing entropy encoding such as a VLC table, and the encoder and the decoder may perform entropy encoding using the stored VLC table.
  • the encoder and the decoder may generate a bitstream by performing arithmetic encoding on the basis of the occurrence probability after binarizing the symbol.
  • a symbol having a high occurrence probability is assigned a low value index and a corresponding short codeword, and a symbol having a low occurrence probability is assigned a high value index and a corresponding long codeword. Can be. Therefore, the bit amount of the symbols to be encoded may be reduced.
  • the coding efficiency may be improved by assigning shorter codewords to the prediction mode with a higher frequency of occurrence.
  • a lower index may be mapped to a shorter codeword, so in this case a lower index may be assigned to a more frequent prediction mode.
  • the generated chroma prediction mode candidate may be assigned a codeword variably according to the frequency of occurrence.
  • Table 3 shows an embodiment of a codeword allocation method according to the number and index of chroma prediction mode candidates.
  • the codeword allocated to the current prediction mode may be '01'.
  • the codeword allocated to the current prediction mode may be '01'.
  • the current prediction mode may be estimated as it is.
  • Table 4 shows another embodiment of a codeword allocation method according to the number and indexes of chroma prediction mode candidates.
  • the codeword allocated to the current prediction mode may be '10'.
  • the codeword allocated to the current prediction mode may be inferred as it is.
  • an index may also be assigned to the LM mode. Since lower indices may be mapped to shorter codewords, if the chroma prediction mode candidates are listed in ascending order of the index assigned to each candidate, the index and / or codeword information assigned to the LM mode is determined by the chroma prediction mode candidates. It can also be viewed as information about the location of the LM mode.
  • Information on whether the LM mode is applied may be transmitted from the encoder to the decoder through a separate flag.
  • index information allocated to the LM mode and / or information about the location of the LM mode may be transmitted from the encoder to the decoder.
  • the LM mode may always be assigned a certain fixed index.
  • the position of the LM mode may be fixed to a specific position within the chroma prediction mode candidate.
  • the LM mode may always be assigned the lowest index and / or shortest codeword.
  • the LM mode may always be assigned the highest index and / or longest codeword.
  • the LM mode may always be assigned the second lowest index and / or second shortest codeword. A specific embodiment in the case where the lowest index is allocated to the LM mode will be described later.
  • the index assigned to the LM mode may be selectively determined according to the value of the luma prediction mode.
  • the position of the LM mode may be selectively determined according to the value of the luma prediction mode.
  • some indexes may be assigned lower indexes than the LM mode and others may be assigned higher indexes than the LM mode.
  • a mode value of a candidate to which an index lower than the LM mode is allocated among candidates obtained from the luma prediction mode is set to 0, 1, and 2.
  • the order of the chroma prediction mode candidates may be 0, 2, LM, 10, 17 in the ascending order of the index assigned to each candidate.
  • 8 is a conceptual diagram schematically illustrating an embodiment of an index allocation method for a chroma prediction mode candidate. 8 illustrates an index allocation method when SDIP and LM modes are used at the same time.
  • a, b, c, and d represent mode values of the luma prediction mode.
  • chroma prediction mode candidates are listed in descending order of index.
  • the lowest index may be assigned to chroma prediction mode candidates obtained from the luma prediction mode.
  • the number of luma prediction modes in the SDIP may be plural, for example, four. When the number of luma prediction modes is four, four indexes of 0, 1, 2, and 3 may be allocated to chroma prediction mode candidates obtained from the luma prediction mode. The next lower index may be assigned to the LM mode. The remaining indices may be assigned to the prediction mode having the mode values of 0 to 2 in low order.
  • the number of chroma prediction mode candidates may be limited to six, so a prediction mode to which indexes 0 to 5 are assigned may be used for chroma component intra prediction.
  • a lower index may be allocated to the luma prediction mode than the LM mode. That is, shorter codewords may be assigned to the luma prediction mode. In the LM mode, a relatively long codeword may be assigned.
  • 9 is a conceptual diagram schematically illustrating another embodiment of an index allocation method for chroma prediction mode candidates. 9 illustrates an index allocation method when SDIP and LM modes are used at the same time.
  • a, b, c, and d represent mode values of the luma prediction mode.
  • chroma prediction mode candidates are listed in descending order of index.
  • the lowest index (eg, 0) may be assigned to the LM mode.
  • the next lower index may be assigned to the chroma prediction mode candidates obtained from the luma prediction mode.
  • the number of luma prediction modes in the SDIP may be plural, for example, four. When the number of luma prediction modes is four, four indices of 1, 2, 3, and 4 may be allocated to chroma prediction mode candidates obtained from the luma prediction mode. The remaining indices may be assigned to the prediction mode having the mode values of 0 to 2 in low order.
  • the number of chroma prediction mode candidates may be limited to six, so a prediction mode to which indexes 0 to 5 are assigned may be used for chroma component intra prediction.
  • a lower index may be allocated to the LM mode than the luma prediction mode. That is, shorter codewords can be assigned to the LM mode.
  • each luma prediction mode occurrence probability may be lower than an LM mode occurrence probability. Therefore, coding efficiency can be improved by allocating shorter codewords to the LM mode.
  • An input for the processing may include a position of a current block and a size of a current coding unit in a current picture, and the output is an intra prediction mode for a current chroma component. This can be represented as follows.
  • the chroma prediction mode is derived by the following table 5 and 6 as an example of the relationship between the luma component prediction mode and the chroma component prediction mode. Can be.
  • the table according to the embodiment of Table 5 is used when the LM mode is applied, and the table according to the embodiment of Table 6 may be used when the LM mode is not applied.
  • Whether the LM mode is applied may be indicated by a flag sent from the encoder, and in one embodiment, the flag may be chroma_pred_from_luma_enabled_flag.
  • 34 may indicate an LM mode, 0 may be a vertical mode, 1 may be a horizontal mode, and 2 may be a DC mode.
  • the relationship between the luma component prediction mode and the chroma component prediction mode is not limited to the embodiments of Tables 5 and 6 described above, and may vary according to implementation and / or needs.
  • the chroma prediction mode may be derived by following Tables 7 and 8.
  • the table according to the embodiment of Table 7 is used when the LM mode is applied, and the table according to the embodiment of Table 8 may be used when the LM mode is not applied. Whether the LM mode is applied may be indicated by a flag sent from the encoder, and in one embodiment, the flag may be chroma_pred_from_luma_enabled_flag. Also in the embodiments of Tables 7 and 8, for example, LM is LM mode, 0 is planar mode, 1 is vertical mode, 2 is horizontal mode, 3 is DC mode, 7 is vertical + 8 8) It can indicate a mode.
  • the decoder may derive the chroma prediction mode through the relationship between the chroma component prediction mode and the luma component prediction mode shown in Tables 7 and 8. This can be represented as follows.
  • intra_chroma_pred_mode may be a prediction mode index of the chroma component
  • IntraPredMode may be a prediction mode of the luma component.
  • the decoder When the size of the current prediction unit is 2NxhN or hNx2N, that is, when SDIP is applied, the decoder generates a separate chroma prediction mode candidate without using Table 7 and / or Table 8 above, and assigns an index to the generated candidate. Can be.
  • the decoder may specify the position or size of each prediction unit, which may be represented as follows.
  • the decoder can assign the lowest index to the LM mode, which can be represented as follows.
  • the decoder may search for a luma prediction mode used in the current coding unit, which may be represented as follows.
  • the decoder may assign the lowest index after the index assigned to the LM mode to the luma prediction mode.
  • the remaining indices may also be assigned to the prediction modes of 0 to 3 in low order under conditions not overlapping with the luma prediction mode. In this case, when all six indexes are not allocated, the remaining indexes may be allocated to the prediction mode of seven. This can be represented as follows.
  • the decoder may derive the chroma prediction mode based on the prediction mode index information of the chroma component transmitted from the encoder.
  • the prediction mode index information of the chroma component may be, for example, intra_chroma_pred_mode. This can be represented as follows.
  • Table 9 below is a simulation result showing the BD-rate measured as a result of the experiment using the index allocation method according to the embodiment of FIG.
  • Y is a luma component
  • U and V are two chroma components.
  • the encoding time and the decoding time may represent complexity for performing encoding and decoding.
  • the experiments were performed in intra mode and were performed in High Efficiency (HE) configuration and Low Complexity (LC) configuration, respectively.
  • HE High Efficiency
  • LC Low Complexity
  • the BD-rate for chroma components is reduced on average in HE and LC to improve coding efficiency.
  • the complexity may be maintained without increasing the complexity.
  • FIG. 10 is a flowchart illustrating an embodiment of a method for transmitting chroma prediction mode information when SDIP and LM modes are used at the same time.
  • the encoder generates a chroma prediction mode candidate for the current coding unit (S1010).
  • a method of generating a chroma prediction mode candidate is as described above in the embodiment of FIG. 7.
  • the maximum number of chroma prediction mode candidates may be limited to five or six.
  • a chroma prediction mode candidate may be generated with only a combination of luma prediction mode and LM mode.
  • the chroma prediction mode candidates may be generated by the aforementioned various methods.
  • the encoder generates a chroma prediction mode candidate list by assigning an index corresponding to the codeword to the generated chroma prediction mode candidates (S1020).
  • the chroma prediction mode candidate list may mean a set of chroma prediction mode candidates to which an index is assigned.
  • the encoder can improve coding efficiency by assigning a low index and / or a short codeword to a prediction mode with a high probability of occurrence.
  • the index allocation method is as described above in the embodiments of Tables 3 to 9, 8 and 9.
  • the encoder After determining the chroma prediction mode of the current block, the encoder transmits information about an index assigned to the same candidate as the chroma prediction mode of the current block among candidates included in the chroma prediction mode candidate list (S1030).
  • the information about the index assigned to the same chroma prediction mode candidate as the chroma prediction mode of the current block is referred to as chroma prediction mode index information.
  • FIG. 11 is a flowchart illustrating an embodiment of a chroma prediction mode derivation method when SDIP and LM modes are used simultaneously.
  • the decoder generates a chroma prediction mode candidate for the current coding unit (S1110).
  • a method of generating a chroma prediction mode candidate is as described above in the embodiment of FIG. 7.
  • the decoder generates a chroma prediction mode candidate list by assigning an index corresponding to the codeword to the generated chroma prediction mode candidate (S1120).
  • the chroma prediction mode candidate list may mean a set of chroma prediction mode candidates to which an index is assigned.
  • the decoder may assign an index to the chroma prediction mode candidate in the same manner as the encoder.
  • the index allocation method is as described above in the embodiments of Tables 3 to 9, 8 and 9.
  • the decoder derives a chroma prediction mode using the chroma prediction mode candidate list and the chroma prediction mode index information transmitted from the encoder (S1130).
  • FIG. 12 is a flowchart schematically illustrating another embodiment of a method of generating a chroma prediction mode candidate when SDIP and LM modes are used at the same time.
  • all luma prediction modes included in the current coding unit may be used as candidates when generating a chroma prediction mode candidate.
  • a method of reducing the number of final luma prediction modes used for generating chroma prediction mode candidates may be provided.
  • the encoder and the decoder derive a final luma prediction mode used as a chroma prediction mode candidate (S1210).
  • the encoder and the decoder may use only some prediction modes of the luma prediction modes included in the current coding unit to generate the chroma prediction mode candidates.
  • the encoder and the decoder may use the luma prediction mode of the first prediction unit among the prediction units to which SDIP is applied in the current coding unit, for generating the chroma prediction mode candidate.
  • the encoder and the decoder may use the luma prediction mode of the last prediction unit among the prediction units to which the SDIP is applied in the current coding unit, for generating the chroma prediction mode candidate.
  • the encoder and the decoder may use the prediction mode assigned the lowest index among the luma prediction modes to generate the chroma prediction mode candidates, and select the plurality of prediction modes in the order of the lowest indexes to generate the chroma prediction mode candidates. Can also be used. Prediction modes that are assigned low indexes can generally be more frequent.
  • the encoder and the decoder may select only the luma prediction mode of two or more prediction units among the prediction units included in the current coding unit, and use the same to generate a chroma prediction mode candidate.
  • the size of the prediction unit may be 2NxhN, hNx2N, 2Nx (1/4) hN, (1/4) hNx2N, and the like.
  • the encoder and the decoder may apply a separate mapping process to the luma prediction mode to reduce the number of final luma prediction modes used for generating a chroma prediction mode candidate.
  • a method of deriving the final luma prediction mode through the mapping process will be described later in the embodiment of FIG. 13.
  • the encoder and the decoder generate a chroma prediction mode candidate using the derived final luma prediction mode (S1220).
  • FIG. 13 is a conceptual diagram schematically illustrating a method of deriving a final luma prediction mode through a mapping process.
  • the number of final luma prediction modes used for generating a chroma prediction mode candidate may be reduced through the mapping process.
  • a prediction mode having one representative value may be used for generating a chroma prediction mode candidate.
  • the representative value may be a mode value of the prediction mode to which the lowest index among the prediction modes having similar angles is assigned.
  • the representative value may be a mode value of the prediction mode to which the highest index among the prediction modes having similar angles is assigned.
  • the representative value may be a mode value of a prediction mode to which an index corresponding to a median value among prediction modes having similar angles is assigned.
  • the representative value may be a mode value of one of the sub-sampled prediction modes after all the prediction modes that the prediction unit may have in the intra mode are sub-sampled according to an angle.
  • a prediction mode that a prediction unit may have in an intra mode may include prediction modes having various angles.
  • the prediction modes having the A, B, and C angles may be subsampled and mapped to the prediction modes having all of the C angles. Therefore, when the prediction unit has a luma prediction mode of A angle, B angle, or C angle, the prediction mode of C angle may be used for generating a chroma prediction mode candidate.
  • the methods for determining the above-described chroma prediction mode candidates are the current block and / or It can be selectively applied according to the size of the coding unit.
  • the coding unit may be recursively split from the LCU based on a quad tree structure. Therefore, the above-described methods of determining the chroma prediction mode candidate may be selectively applied according to the split count information indicating how many times the current coding unit is split from the LCU.
  • a method of reducing the number of final luma prediction modes used for generating chroma prediction mode candidates may be used by applying a mapping process according to the embodiment of FIG. 13. .
  • a prediction mode having one representative value may be used for generating a chroma prediction mode candidate. Specific examples of representative values used at this time are omitted.
  • SDIP may not be applied when the current coding unit is an LCU. If SDIP is not applied, prediction units of 2NxhN, hNx2N, 2Nx (1/4) hN, and (1/4) hNx2N sizes may not be used.
  • the prediction mode of the chroma component may be determined as one of LM, vertical, horizontal, DC, and DM modes, and prediction of one of LM, vertical, horizontal, vertical-8, DC, and DM modes. The mode may be determined.
  • the prediction mode of the chroma component may be determined as one of the prediction modes of the DM, LM, planner, vertical, horizontal, and DC modes. At this time, if the prediction mode indicated by the DM mode is the same as one of the planner, vertical, horizontal, or DC modes, the vertical + 8 mode is used instead of the same prediction mode as the prediction mode indicated by the DM mode. It may be.

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Abstract

La présente invention concerne un procédé de décodage d'images basé sur une unité de prédiction dans laquelle il est appliqué un SDIP. Le procédé de décodage d'images d'après la présente invention comprend une étape consistant à établir une liste des modes potentiels de prédiction de chromie en attribuant un indice correspondant à un mot codé aux modes potentiels de prédiction de chromie, ainsi qu'une étape consistant à déduire le mode de prédiction de chromie d'un bloc actuel en utilisant les informations des indices des modes de prédiction de chromie provenant de la liste établie des modes potentiels de prédiction de chromie et d'un dispositif de codage. La présente invention permet d'accroître l'efficacité d'un codage/décodage d'images.
PCT/KR2011/010224 2011-03-21 2011-12-28 Procédé et dispositif de codage/décodage d'images Ceased WO2012128453A1 (fr)

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