WO2024026098A1 - Procédé et appareil de prédiction inter-composantes pour codage vidéo - Google Patents

Procédé et appareil de prédiction inter-composantes pour codage vidéo Download PDF

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WO2024026098A1
WO2024026098A1 PCT/US2023/028992 US2023028992W WO2024026098A1 WO 2024026098 A1 WO2024026098 A1 WO 2024026098A1 US 2023028992 W US2023028992 W US 2023028992W WO 2024026098 A1 WO2024026098 A1 WO 2024026098A1
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sample values
filter shape
chroma
luma
chroma sample
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PCT/US2023/028992
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Che-Wei Kuo
Hong-Jheng Jhu
Xiaoyu XIU
Ning Yan
Wei Chen
Xianglin Wang
Bing Yu
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Beijing Dajia Internet Information Technology Co., Ltd
Xianglin Wang
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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
    • H04N19/117—Filters, e.g. for pre-processing or post-processing
    • 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
    • H04N19/105—Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/136—Incoming video signal characteristics or properties
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/154—Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion
    • 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
    • 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
    • H04N19/70—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
    • 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
    • H04N19/80—Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation

Definitions

  • aspects of the present disclosure relate generally to iniage/video coding and compression, and more particularly, to methods and apparatus for cross-component prediction technology.
  • Video coding is performed according to one or more video coding standards.
  • video coding standards include versatile video coding (VVC), high -efficiency video coding (H.265/HEVC), advanced video coding (H.264/AVC), moving picture expert group (MPEG) coding, orthe like.
  • Video coding generally utilizes prediction methods (c.g., inter-prediction, intra-prcdiction, or the like) that take advantage of redundancy present in video images or sequences.
  • An important goal of video coding techniques is to compress video data into a form that uses a lower bit rate, while avoiding or minimizing degradations to video quality.
  • a method for decoding video data comprising: obtaining a video block from a bitstream; obtaining internal luma sample values of the video block, external luma sample values of an external region of the video block and external chroma sample values of the external region; selecting, based on the external luma sample values and the external chroma sample values, one fdter shape candidate from a plurality of fdter shape candidates for predicting internal chroma sample values of the video block, wherein the plurality of filter shape candidates correspond to different sets of weighting coefficients for predicting chorma sample values based on corresponding luma sample values; predicting, with the selected fdter shape candidate, the internal chroma sample values based on the internal luma sample values; and obtaining decoded video block using the predicted internal chroma sample values.
  • a method for encoding video data comprising: obtaining a video block; obtaining internal luma sample values of the video block, external luma sample values of an external region of the video block and external chroma sample values of the external region; selecting, based on the external luma sample values and the external chroma sample values, one filter shape candidate from a plurality of filter shape candidates for predicting internal chroma sample values of the video block, wherein the plurality of filter shape candidates correspond to different sets of weighting coefficients for predicting chorma sample values based on corresponding luma sample values; predicting, with the selected filter shape candidate, the internal chroma sample values based on the internal luma sample values; and generating a bitstream comprising encoded video block by using the predicted internal chroma sample values .
  • a computer system comprising: one or more processors; and one or more storage devices storing computer-executable instructions that, when executed, cause the one or more processors to perform the operations of the method of the present disclosure.
  • a computer program product storing computer-executable instructions that, when executed, cause one or more processors to perform the operations of the method of the present disclosure.
  • a computer readable medium storing computer-executable instructions that, when executed, cause one or more processors to receive a bitstream and perform the operations of the method of the present disclosure based on the bitstream.
  • a computer readable medium storing computer-executable instructions that, when executed, cause one or more processors to perform the operations of the method of the present disclosure and transmit a bitstream comprising encoded video information associated with the predicted chroma samples.
  • a computer readable medium storing a bitstream, wherein the bitstream is to be decoded by performing the operations of the method of the present disclosure.
  • a computer readable medium storing a bitstream, wherein the bitstream is obtained by performing the operations of the method of the present disclosure.
  • Figure 1 illustrates a block diagram of a generic block -based hybrid video encoding system.
  • Figures 2A to 2E illustrate five splitting types, comprising quaternary partitioning, horizontal binary partitioning, vertical binary partitioning, horizontal ternary partitioning, and vertical ternary partitioning.
  • Figure 3 illustrates a general block diagram of a block-based video decoder.
  • Figure 4 illustrates an example of the locations of the left and above samples and the sample of the current block involved in the CCLM mode .
  • Figures 5A to 5C illustrate examples of deriving CCLM parameters.
  • Figure 6 illustrates an example of classifying the neighboring samples into two groups based on the value Threshold.
  • Figure 7 illustrates an example of classifying the neighboring samples into two groups based on a knee point.
  • Figures 8A and 8B illustrate the effect of the scale adjustment parameter “u”.
  • Figure 8C illustrates the collocated reconstructed luma samples.
  • Figure 8D illustrates the neighboring reconstructed samples.
  • Figures 8E to 8H illustrate the steps of decoder-side intra mode derivation.
  • Figure 9 illustrates an example of four reference lines neighboring to a prediction block.
  • Figure 10A illustrates an exemplary pattern for convolutional cross-component model
  • Figure 10B illustrates an exemplary reference area which consists of 6 lines of chroma samples above and left of the PU.
  • Figures 10C and 10D illustrate schematic diagrams for correlation among a chroma sample and one or more luma samples.
  • FIG 11 illustrates an example that 6-tap is used in multiple linear regression (MLR) model according to one or more aspects of the present disclosure.
  • Figure 12 illustrates exemplary different filter shapes and/or numbers of taps according to one or more aspects of the present disclosure.
  • Figure 13 illustrates an example in which FLM can only use top or left luma and/or chroma samples (extended) for parameter derivation.
  • Figure 14 illustrates an example in which FLM can use different lines for parameter derivation.
  • Figures 15A to 15D illustrate some examples for l-tap/2-tap prc-opcrations.
  • Figure 16 illustrates examples of different shape/number of filter taps.
  • Figure 17 illustrates examples of different shape/number of filter taps.
  • Figures 18A and 18B illustrate examples of different shape/number of filter taps.
  • Figures 19A to 19G illustrate examples of different set of filter taps.
  • Figure 20 illustrates a workflow of a method for decoding video data according to one or more aspects of the present disclosure.
  • Figure 21 illustrates a workflow of a method for encoding video data according to one or more aspects of the present disclosure.
  • Figure 22 illustrates an exemplary computing system according to one or more aspects of the present disclosure.
  • the first version of the VVC standard was finalized in July, 2020, which offers approximately 50% bit-rate saving or equivalent perceptual quality compared to the prior generation video coding standard HEVC.
  • the VVC standard provides significant coding improvements than its predecessor, there is evidence that superior coding efficiency can be achieved with additional coding tools.
  • Joint Video Exploration Team JVET
  • ISO/IEC MPEG started the exploration of advanced technologies that can enable substantial enhancement of coding efficiency over VVC.
  • ECM Enhanced Compression Model
  • VTM VVC Test Model
  • CTCs JVET common test conditions
  • FIG. 1 illustrates a block diagram of a generic block -based hybrid video encoding system.
  • the input video signal is processed block by block (called coding units (CUs)).
  • CUs coding units
  • a CU can be up to 128x128 pixels.
  • one coding tree unit (CTU) is split into CUs to adapt to varying local characteristics based on quad/binary/temary-tree.
  • each quad-tree leaf node can be further partitioned by a binary and ternary tree structure.
  • FIGs 2A, 2B, 2C, 2D, and 2E there are five splitting types, quaternary partitioning, vertical binary partitioning, horizontal binary partitioning, vertical extended quaternary partitioning, and horizontal extended quaternary partitioning.
  • Spatial prediction uses pixels from the samples of already coded neighboring blocks (which are called reference samples) in the same video picture/slice to predict the current video block. Spatial prediction reduces spatial redundancy inherent in the video signal.
  • Temporal prediction also referred to as “inter prediction” or “motion compensated prediction” uses reconstructed pixels from the already coded video pictures to predict the current video block. Temporal prediction reduces temporal redundancy inherent in the video signal.
  • Temporal prediction signal for a given CU is usually signaled by one or more motion vectors (MVs) which indicate the amount and the direction of motion between the current CU and its temporal reference.
  • MVs motion vectors
  • one reference picture index is additionally sent, which is used to identify from which reference picture in the reference picture store the temporal prediction signal comes.
  • the mode decision block in the encoder chooses the best prediction mode, for example based on the rate-distortion optimization method.
  • the prediction block is then subtracted from the current video block; and the prediction residual is de-correlated using transform and quantized.
  • the quantized residual coefficients are inverse quantized and inverse transformed to form the reconstructed residual, which is then added back to the prediction block to fonn the reconstructed signal of the CU
  • Further inloop filtering such as deblocking filter, sample adaptive offset (SAG) and adaptive in-loop filter (ALF) may be applied on the reconstructed CU before it is put in the reference picture store and used to code future video blocks.
  • coding mode inter or intra
  • prediction mode information, motion information, and quantized residual coefficients arc all sent to the entropy coding unit to be further compressed and packed to fonn the bit-stream.
  • block or video block may be a portion, in particular a rectangular (square or non- square) portion, of a frame or a picture.
  • the block or video block may be or correspond to a Coding Tree Unit (CTU), a CU, a Prediction Unit (PU) or a Transform Unit (TU) and/or may be or correspond to a corresponding block, e g., a Coding Tree Block (CTB), a Coding Block (CB), a Prediction Block (PB) or a Transform Block (TB) and/or to a sub-block.
  • CTU Coding Tree Unit
  • PU Prediction Unit
  • TU Transform Unit
  • a corresponding block e g., a Coding Tree Block (CTB), a Coding Block (CB), a Prediction Block (PB) or a Transform Block (TB) and/or to a sub-block.
  • CTB Coding Tree Block
  • PB Prediction Block
  • TB Transform Block
  • FIG. 3 illustrates a general block diagram of a block -based video decoder.
  • the video bitstream is first entropy decoded at entropy decoding unit.
  • the coding mode and prediction information arc sent to cither the spatial prediction unit (if intra coded) or the temporal prediction unit (if inter coded) to form the prediction block.
  • the residual transform coefficients are sent to inverse quantization unit and inverse transform unit to reconstruct the residual block.
  • the prediction block and the residual block are then added together.
  • the reconstructed block may further go through in -loop filtering before it is stored in reference picture store.
  • the reconstructed video in reference picture store is then sent out to drive a display device, as well as used to predict future video blocks.
  • CCLM cross-component linear model
  • a cross-component linear model (CCLM) prediction mode is used in the VVC, for which the chroma samples are predicted based on the reconstructed luma samples of the same CU by using a linear model as follows: (1) where pred c (i, j) represents the predicted chroma samples in a CU, and rec L '(i,j) represents the down-sampled reconstructed luma samples of the same CU which are obtained by performing downsampling on the reconstructed luma samples rec L (i,j) .
  • pred c (i, j) represents the predicted chroma samples in a CU
  • rec L '(i,j) represents the down-sampled reconstructed luma samples of the same CU which are obtained by performing downsampling on the reconstructed luma samples rec L (i,j) .
  • the above a and p are linear model parameters which arc derived from at most four neighboring chroma samples and their corresponding down-sampled luma samples, which may be referred to as neighboring luma-chroma sample pairs.
  • W and FT are obtained as follows: where in the LM mode, above samples and left samples of the CU are used together to calculate the linear model coefficients; in the LM_A mode, only the above samples of the CU are used to calculate the linear model coefficients; and in the LM_L mode, only the left samples of the CU are used to calculate the linear model coefficients.
  • positions of four neighboring chroma samples are selected as follows: are selected as the positions of the four neighboring chroma samples when LM mode is applied and both above and left neighboring samples are available; are selected as the positions of the four neighboring chroma samples when LM-A mode is applied or only the above neighboring samples arc available; are selected as the positions of the four neighboring chroma samples when LM-L mode is applied or only the left neighboring samples are available
  • the four neighboring luma samples corresponding to the selected locations are obtained by a down-sampling operation and the obtained four neighboring luma samples are compared four times to find two larger values: and and two smaller values: x° B and x l B .
  • Chroma sample values corresponding to the two larger values and the two smaller values are denoted as y°A, y l A, y° B and y l B respectively.
  • X, X. Y a and Yt are derived as: (2)
  • the linear model parameters a and /? are obtained according to the following equations. (4)
  • Figure 4 illustrates an example of the locations of the left and above samples and the sample of the current block involved in the CCLM mode, including locations of left and above samples of an NxN chroma block in the CU and locations of left and above samples of an 2Nx 2N luma block in the CU.
  • the division operation to calculate parameter a is implemented with a look-up table.
  • the dfff value difference between maximum and minimum values
  • the parameter a are expressed by an exponential notation. For example, diff xs approximated with a 4-bit significant part and an exponent. Consequently, the table for 1/diff is reduced into 16 elements for 16 values of the significand as follows:
  • LM_T mode only the above template is used to calculate the linear model coefficients. To get more samples, the above template is extended to (W+H) samples.
  • LM_L mode only left template is used to calculate the linear model coefficients. To get more samples, the left template is extended to (H+W) samples.
  • This parameter computation is performed as part of the decoding process, and is not just as an encoder search operation. As a result, no syntax is used to convey the a and p values to the decoder.
  • chroma intra mode coding a total of 8 intra modes are allowed for chroma intra mode coding. Those modes include five traditional intra modes and three cross -component linear model modes (CCLM, LM_A, and LM_L). Chroma mode signalling and derivation process are shown in Table 1. Chroma mode coding directly depends on the intra prediction mode of the corresponding luma block.
  • one chroma block may correspond to multiple luma blocks. Therefore, for Chroma DM mode, the intra prediction mode of the corresponding luma block covering the center position of the current chroma block is directly inherited.
  • the first bin indicates whether it is regular (0) or LM modes (1). If it is LM mode, then the next bin indicates whether it is LM_CHROMA (0) or not. If it is not LM_CHROMA, next 1 bin indicates whether it is LM_L (0) or LM_A (1). For this case, when sps_cclm_enabled_flag is 0, the first bin of the binarization table for the corresponding intra_chroma_prcd_modc can be discarded prior to the entropy coding. Or, in other words, the first bin is inferred to be 0 and hence not coded. This single binarization table is used for both sps_cclm_enabled_flag equal to 0 and 1 cases. The first two bins in Table 2 are context coded with its own context model, and the rest bins are bypass coded.
  • the chroma CUs in 32x32 / 32x16 chroma coding tree node are allowed to use CCLM in the following way:
  • all chroma CUs in the 32x16 chroma node can use CCLM.
  • CCLM is not allowed for chroma CU.
  • the LM A, LM L modes are also called Multi-Directional Linear Model (MDLM).
  • MDLM Multi-Directional Linear Model
  • Figure 5A illustrates an example that MDLM works when the block content cannot be predicted from the L- shape reconstructed region.
  • Figure 5B illustrates MDLM L which only uses left reconstructed samples to derive CCLM parameters.
  • Figure 5C illustrates MDLM T which only uses top reconstructed samples to derive CCLM parameters.
  • the integerization design utilizes the linear relationship to modelize the correlation of luma signal and chroma signal.
  • the chroma values are predicted from reconstructed luma values of collocated block.
  • Luma and chroma components have different sampling ratios in YUV420 sampling.
  • Tire sampling ratio of chroma components is half of that of luma component and has 0.5 pixel phase difference in vertical direction.
  • Reconstructed luma needs down-sampling in vertical direction and subsample in horizontal direction to match size of chroma signal.
  • the down-sampling may be implemented by: (10)
  • Equation (1) Float point operation is necessary in equation (8) to calculate linear model parameters ⁇ to keep high data accuracy.
  • float point multiplication is involved in equation (1) when ⁇ is represented by float point value.
  • the integer implementation of this algorithm is designed. Specifically, fractional part of parameter ⁇ is quantized with n ⁇ bits data accuracy. Parameter ⁇ value is represented by an up-scaled and rounded integer value . Then the linear model of equation (1) is changed to: (11)
  • equation (12) can be rewritten as following.
  • the constant parameters are set as: equals to 13, which value is tradeoff between data accuracy and computational cost. equals to 6, results in lookup table size as 64, table size can be further reduced to 32 by up- scaling
  • an intra prediction mode called LM is applied to predict chroma PU based on a linear model using the reconstruction of the collocated luma PU.
  • the parameters of the linear model consist of slope (a»k) and y-intercept (b), which are derived from the neighboring luma and chroma pixels using the least mean square solution.
  • variables a, b and k can be derived as: where ImDiv is specified in a 63-entry look-up table, i.e. Table 3, which is online generated by: (20) Table 3-Specifi cation of ImDiv
  • Equation (19-6) als is a 16-bit signed integer and ImDiv is a 16-bit unsigned integer. Therefore, 16-bit multiplier and 16-bit storage are needed. It is proposed to reduce the bit depth of multipliers to the internal bit depth, as well as the size of the look-up table, as detailed below.
  • Table 4 shows the example of internal bit depth 10.
  • Multi -model LM (MMLM) prediction mode for which the chroma samples are predicted based on the reconstructed luma samples of the same CU by using two linear models as follows: where pred c (i, j) represents the predicted chroma samples in a CU and rec L ' (i,j) represents the down-sampled reconstructed luma samples of the same CU. Threshold is calculated as the average value of the neighboring reconstructed luma samples.
  • Figure 6 illustrates an example of classifying the neighboring samples into two groups based on the value Threshold.
  • parameter a and PRON with i equal to 1 and 2 respectively, are derived from the straight-line relationship between luma values and chroma values from two samples, which are minimum luma sample and maximum luma sample B (X B , Y B ) inside the group.
  • X B , Y B are the x-coordinate and y- coordinate value for sample B.
  • the linear model parameters a and /? are obtained according to the following equations. (26) [0089] Such a method is also called min-max method. The division in the equation above could be avoided and replaced by a multiplication and a shift.
  • the two templates also can be used alternatively in the other two MMLM modes, called MMLM_A. and MMLM L modes.
  • MMLM A mode only pixel samples in the above template are used to calculate the linear model coefficients. To get more samples, the above template is extended to the size of (W+W).
  • MMLM L mode only pixel samples in the left template are used to calculate the linear model coefficients. To get more samples, the left template is extended to the size of (H+H).
  • Chroma mode signaling and derivation process are shown in Table 6.
  • Chroma mode coding directly depends on the intra prediction mode of the corresponding luma block. Since separate block partitioning stmeture for luma and chroma components is enabled in I slices, one chroma block may correspond to multiple luma blocks. Therefore, for Chroma DM mode, the intra prediction mode of the corresponding luma block covering the center position of the current chroma block is directly inherited.
  • MMLM and LM modes may also be used together in an adaptive manner.
  • two linear models are as follows: where pred c (i, j) represents the predicted chroma samples in a CU and represents the down-sampled reconstructed luma samples of the same CU. Threshold can be simply determined based on the luma and chroma average values together with their minimum and maximum values.
  • Figure 7 shows an example of classifying the neighboring samples into two groups based on the knee point, T, indicated by an arrow.
  • Linear model parameter and [f arc derived from the straight-line relationship between luma values and chroma values from two samples which arc minimum luma sample A (X A , Y A ) and the Threshold (X T , Y T ).
  • the linear model parameters and for each group, with i equal to 1 and 2 respectively, are obtained according to the following equations. (28)
  • the two templates also can be used alternatively in the other two MMLM modes, called MMLM A, and MMLM_L modes respectively.
  • MMLM A mode only pixel samples in the above template are used to calculate the linear model coefficients. To get more samples, the above template is extended to the size of (W+W).
  • MMLM L mode only pixel samples in the left template are used to calculate the linear model coefficients. To get more samples, the left template is extended to the size of (H+H).
  • condition check used to select LM modes (CCLM, LM_A, and LM_L) or multi -model LM modes (MMLM, MMLM_A, and MMLM_L).
  • LM modes CCLM, LM_A, and LM_L
  • MMLM, MMLM_A, and MMLM_L multi -model LM modes
  • d represents a pre -determined threshold value. In one example, d may take a value of 0. In another example, d may take a value of 8.
  • d may take a value of 8.
  • chroma intra mode coding a total of 8 intra modes are allowed for chroma intra mode coding. Those modes include five traditional intra modes and three cross -component linear model modes. Chroma mode signaling and derivation process are shown in Table 1 . It is worth noting that for a given CU, if it is coded under linear model mode, whether it is a conventional single model LM mode or a MMLM mode is determined based on the condition check above.
  • Chroma mode coding directly depends on the intra prediction mode of the corresponding luma block. Since separate block partitioning structure for luma and chroma components is enabled in 1 slices, one chroma block may correspond to multiple luma blocks. Therefore, for Chroma DM mode, the intra prediction mode of the corresponding luma block covering the center position of the current chroma block is directly inherited.
  • CCLM uses a model with 2 parameters to map luma values to chroma values.
  • the scale parameter “a” and the bias parameter “b” define the mapping as follows: (30)
  • mapping function is tilted or rotated around the point with luminance value y It is proposed to use the average of the reference luma samples used in the model creation as in order to provide a meaningful modification to the model.
  • Figures 8A to 8B illustrate the effect of the scale adjustment parameter “u”, wherein Figure 8 A illustrates the model created without the scale adjustment parameter and Figure 8B illustrates the model created with the scale adjustment parameter “u”.
  • the scale adjustment parameter is provided as an integer between -4 and 4, inclusive, and signaled in the bitstream.
  • the unit of the scale adjustment parameter is l/8th of a chroma sample value per one luma sample value (for 10-bit content).
  • adjustment is available for the CCLM models that are using reference samples both above and left of the block ( LM CHROMA IDX' and “MMLM_CHROMA_IDX”), but not for the “single side” modes. This selection is based on coding efficiency vs. complexity tradeoff considerations.
  • the encoder may perform an SATD based search for the best value of the scale update for Cr and a similar SATD based search for Cb. If either one results as anon-zero scale adjustment parameter, the combined scale adjustment pair (SATD based update for Cr, SATD based update for Cb) is included in the list of RD checks for the TU.
  • JVET-Y0092/Z0051 proposed fusion of chroma intra modes.
  • the intra prediction modes enabled for the chroma components in ECM -4.0 are six crosscomponent linear model (LM) modes including CCLM LT, CCLM L, CCLM T, MMLM_LT, MMLM L and MMLM T modes, the direct mode (DM), and four default chroma intra prediction modes.
  • the four default modes are given by the list ⁇ 0, 50, 18, 1 ⁇ and if the DM mode already belongs to that list, the mode in the list will be replaced with mode 66.
  • a decoder-side intra mode derivation (DIMD) method for luma mtra prediction is included in ECM-4.0.
  • a horizontal gradient and a vertical gradient are calculated for each reconstructed luma sample of the L-shaped template of the second neighboring row and column of the current block to build a Histogram of Gradients (HoG).
  • HoG Histogram of Gradients
  • the two intra prediction modes with the largest and the second largest histogram amplitude values are blended with the Planar mode to generate the final predictor of the current luma block.
  • DIMD chroma dccodcr-sidc derived chroma intra prediction mode
  • a DIMD chroma mode uses the DIMD derivation method to derive the chroma intra prediction mode of the current block based on the collocated reconstnrcted luma samples. Specifically, a horizontal gradient and a vertical gradient are calculated for each collocated reconstructed luma sample of the current chroma block to build a HoG, as shown in Figure 8C. Then the intra prediction mode with the largest histogram amplitude values is used for performing chroma intra prediction of the current chroma block.
  • the intra prediction mode derived from the DIMD chroma mode is the same as the intra prediction mode derived from the DM mode, the intra prediction mode with the second largest histogram amplitude value is used as the DIMD chroma mode.
  • a CU level flag is signaled to indicate whether the proposed DIMD chroma mode is applied as shown in Table 7.
  • a fusion of chroma intra prediction modes is proposed, wherein the DM mode and the four default modes can be fused with the MMLM_LT mode as follows: where s the predictor obtained by applying the non-LM mode, predl is the predictor obtained by applying the MMLM_LT mode and pred is the final predictor of the current chroma block
  • the two weights, w0 and w1 are determined by the intra prediction mode of adjacent chroma blocks and shift is set equal to 2. Specifically, when the above and left adjacent blocks are both coded with LM modes, when the above and left adjacent blocks are both coded with non- LM modes ; otherwise, ⁇ ⁇ ⁇ ⁇
  • the DIMD chroma mode and the fusion of chroma intra prediction modes are combined. Specifically, the DIMD chroma mode described in the first embodiment is applied, and for I slices, the DM mode, the four default modes and tire DIMD chroma mode can be fused with the MMLM_LT mode using the weights described in the second embodiment, while for non-I slices, only the DIMD chroma mode can be fused with the MMLM LT mode using equal weights.
  • the DIMD chroma mode with reduced processing and the fusion of chroma intra prediction modes are combined. Specifically, the DIMD chroma mode with reduced processing derives the intra mode based on the neighboring reconstructed Y, Cb and Cr samples in the second neighboring row and column as shown in Figure 8D. Other parts are the same as the third embodiment.
  • two intra modes are derived from the reconstructed neighbor samples, and those two predictors are combined with the planar mode predictor with the weights derived from the gradients as described in JVET -00449.
  • the division operations in weight derivation is performed utilizing the same lookup table (LUT) based integerization scheme used by the CCLM.
  • LUT lookup table
  • the division operation in the orientation calculation is computed by the following LUT-based scheme :
  • FIG. 8E to 8H illustrate the steps of decoder-side intra mode derivation, wherein intra prediction direction is estimated without intra mode signaling.
  • the first step as shown in Figure 8E includes estimating gradient per sample (for light-grey samples as illustrated in Figure 8E).
  • the second step as shown in Figure 8F includes mapping gradient values to closest prediction direction within [2,66]
  • the third step as shown in Figure 8G includes selecting 2 prediction directions, wherein for each prediction direction, all absolute gradients Gx and Gy of neighboring pixels with that direction are summed up, and top 2 directions are selected.
  • the fourth step as shown in Figure 8H includes enabling weighted intra prediction with the selected directions.
  • MRL Multiple reference line
  • HEVC intra-picture prediction uses the nearest reference line (i.e., reference line 0).
  • 2 additional lines reference line 1 and reference line 3 are used.
  • the index of selected reference line (mrl idx) is signaled and used to generate intra predictor.
  • reference line idx which is greater than 0, only include additional reference line modes in MPM list and only signal mpm index without remaining mode.
  • the reference line index is signaled before intra prediction modes, and Planar mode is excluded from intra prediction modes in case a nonzero reference line index is signaled.
  • MRL is disabled for the first line of blocks inside a CTU to prevent using extended reference samples outside the current CTU line. Also, PDPC is disabled when additional line is used.
  • MRL mode the derivation of DC value in DC intra prediction mode for non -zero reference line indices is aligned with that of reference line index 0.
  • MRL requires the storage of 3 neighboring luma reference lines with a CTU to generate predictions.
  • the Cross-Component Linear Model (CCLM) tool also requires 3 neighboring luma reference lines for its down -sampling filters. The definition of MRL to use the same 3 lines is aligned as CCLM to reduce the storage requirements for decoders.
  • CCCM convolutional cross-component model
  • CCCM convolutional cross-component model
  • Multi-model CCCM mode can be selected for PUs which have at least 128 reference samples available.
  • the proposed convolutional 7-tap filter consists of a 5-tap plus sign shape spatial component, a nonlinear term and a bias term.
  • the input to the spatial 5-tap component of the filter consists of a center (C) luma sample which is collocated with the chroma sample to be predicted and its above/north (N), below/south (S), left/west (W) and right/east (E) neighbors as illustrated in Figure 10A.
  • the nonlinear term P is represented as power of two of the center luma sample C and scaled to the sample value range of the content:
  • the bias term B represents a scalar offset between the input and output (similarly to the offset term in CCLM) and is set to middle chroma value (512 for 10-bit content).
  • Output of the filter is calculated as a convolution between the filter coefficients Ci and the input values and clipped to the range of valid chroma samples:
  • the filter coefficients Ci are calculated by minimising MSE between predicted and reconstructed chroma samples in the reference area.
  • Figure 10B illustrates the reference area which consists of 6 lines of chroma samples above and left of the PU. Reference area extends one PU width to the right and one PU height below the PU boundaries. Area is adjusted to include only available samples. The extensions to the area shown in blue are needed to support the “side samples” of the plus shaped spatial filter and are padded when in unavailable areas.
  • the MSE minimization is performed by calculating autocorrelation matrix for the luma input and a cross-correlation vector between the luma input and chroma output.
  • Autocorrelation matrix is LDL decomposed and the final filter coefficients arc calculated using back-substitution.
  • the process follows roughly the calculation of the ALF filter coefficients in ECM, however LDL decomposition was chosen instead of Cholesky decomposition to avoid using square root operations.
  • the proposed approach uses only integer arithmetic.
  • CCCM Usage of the mode is signalled with a CABAC coded PU level flag.
  • CABAC context was included to support this.
  • CCCM is considered a sub-mode of CCLM. That is, the CCCM flag is only signalled if intra prediction mode is LM CHROMA IDX (to enable single mode CCCM) or MMLM CHROMA IDX (to enable multi -model CCCM).
  • the encoder performs two new RD checks in the chroma prediction mode loop, one for checking single model CCCM mode and one for checking multi-modcl CCCM mode.
  • the neighboring reconstructed luma-chroma sample pairs are classified into one or more sample groups based on the value Threshold, which only considers the luma DC values. That is, a luma-chroma sample pair is classified by only considering the intensity of the luma sample.
  • Threshold which only considers the intensity of the luma sample.
  • luma component usually preserves abundant textures, and the current luma sample may be highly correlated with neighboring luma samples, such inter-sample correlation (AC correlation) may benefit the classification of luma-chroma sample pairs and can bring additional coding efficiency.
  • the CCLM assumes a given chroma sample only correlates to a corresponding luma sample (L0.5, which can be taken as the fractional luma sample position), and a simple linear regression (SLR) with ordinary least squares (OLS) estimation is used to predict the given chroma sample.
  • SLR simple linear regression
  • OLS ordinary least squares
  • one chroma sample may simultaneously correlate to multiple luma samples (AC or DC correlation), so a multiple linear regression (MLR) model may further improve the prediction accuracy.
  • the CCCM mode can enhance the intra prediction efficiency, there is room to further improve its performance. Meanwhile, some parts of the existing CCCM mode also need to be simplified for efficient codec hardware implementations or improved for better coding efficiency. Furthermore, the tradeoff between its implementation complexity and its coding efficiency benefit needs to be further improved.
  • classifiers considering luma edge or AC information is introduced, in contrast to the above implementations wherein only luma DC values are considered.
  • the present disclosure provides exemplary classifiers.
  • Tire process of generating linear prediction models for different sample groups may be similar as CCLM or MMLM (c.g., via a least square method, or a simplified min -max method, etc.), but with different metrices for classification.
  • Different classifiers may be used to classify the neighboring luma samples (e.g., of the neighboring luma-chroma sample pairs) and/orthe luma samples corresponding to chroma samples to be predicted.
  • the luma samples corresponding to the chroma samples may be obtained by a down-sampling operation to match the locations of the corresponding chroma samples for 4:2:0 video sequences.
  • a luma sample corresponding to a chroma sample may be obtained by performing a down -sampling operation on more than one (e.g., 4) reconstructed luma samples corresponding to the chroma sample (e.g., located around the chroma sample).
  • the luma samples may obtained directly from the reconstructed luma samples in a case of 4:4:4 video sequences, for example.
  • the luma samples may be obtained from respective ones of the reconstructed luma samples that are at respective collocated positions for the corresponding chroma samples.
  • a luma sample to be classified may be obtained from one of four reconstructed luma samples corresponding to the chroma sample that is at a left-top position of the four reconstructed luma samples, which may be considered as a collocated position for the chroma sample.
  • a first classifier may classify luma samples according to their edge strengths. For example, one direction (c.g., 0-dcgrcc, 45-dcgrcc, or 90-dcgrcc, etc.) may be selected to calculate the edge strength.
  • a direction may be formed by a current sample and a neighboring sample along the direction (e.g., a neighboring sample located at the right-top of the current sample for 45-degree).
  • An edge strength may be calculated by subtracting the neighbor sample from the current sample.
  • the edge strength may be quantized into one of M segments by M-l thresholds, and the first classifier may use M classes to classify the current sample.
  • N directions may be formed by a current sample and N neighboring samples along the N directions.
  • N edge strengths maybe calculated by subtracting N neighboring samples from the current sample, respectively.
  • the first classifier may use MN classes to classify the current sample.
  • a second classifier may be used to classify according to a local pattern. For example, a current luma sample Y0 may be compared with its neighboring N luma samples Yi. A score may be added by one if the value of Y0 is greater than that of Yi, otherwise, the score may be reduced by one. The sore may be quantized to form K classes. The second classifier may classify a current sample into one of the K classes. For example, the neighboring luma samples may be obtained from four neighbors that are located above, left, right and below the current luma samples, i.e., without diagonal neighbors.
  • first classifier may be combined with the existing MMLM threshold-based classifier.
  • instance A of the first classifier may be combined with another instance B of the first classifier, where the instance A and B employ different directions (e g., employing vertical and horizontal directions, respectively).
  • the proposed cross-component method described in the disclosure can also be applied to other prediction coding tools with similar design spirits.
  • the proposed method can also be applied by dividing luma-chroma sample pairs into multiple sample groups.
  • Y/Cb/Cr also can be denoted as Y/U/V in video coding area. If video data is of RGB format, the proposed method can also be applied by simply mapping YUV notation to GBR, for example .
  • a filter-based linear model which utilizes the MLR model is introduced as follows, to take into account the possibilities that one chroma sample may simultaneously correlate to multiple luma samples.
  • the reconstructed collocated and neighboring luma samples can be used to predict the chroma sample, to capture the intcr-samplc correlation among the collocated luma sample, neighboring luma samples, and the chroma sample.
  • the reconstructed luma samples are linear weighted and combined with one “offset” to generate the predicted chroma sample (C: predicted chroma sample reconstructed collocated or neighboring luma samples filter coefficients, offset, N: filter taps), as shown in the following equation (32-1). Note the linear weighted plus offset value directly forms the predicted chroma sample (can be low pass, high pass adaptively according to video content), and it is then added by the residual to form the reconstructed chroma sample.
  • the offset term can also be implemented as middle chroma value B (512 for 10-bit content) multiplied by another coefficient, as shown in the following equation (32-2).
  • the top and left reconstructed luma and chroma samples can be used to derive or train the FLM parameters
  • CCLM can be derived via OLS.
  • the top and left training samples are collected, and one pseudo inverse matrix is calculated at both encoder and decoder sides to derive the parameters, which are then used to predict the chroma samples in the given CU.
  • N denotes the number of filter taps applied on luma samples
  • M denotes the total top and left reconstructed luma-chroma sample pairs used for training parameters
  • Figure 11 shows an example that N is 6 (6-tap), M is 8, top 2 rows and left 3 columns luma samples and top 1 row and left 1 column chroma samples are used to derive ortrainthe parameters.
  • ELM/FLM/GLM (as discussed below) can be extended straightforwardly to the CfL design in the AV I standard, which transmits model parameters (a, P) explicitly. For example, (1-tap case) deriving and/or at encoder at SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblcok/Sample levels, and signaled to decoder for the CfL mode.
  • a 6-tap luma filter is used for the FLM prediction.
  • training data e.g., top and left neighboring reconstructed luma and chroma samples
  • it may result in overfitting and may not predict well on testing data i.e., the to-be-predicted chroma block samples.
  • different filter shapes may adapt well to different video block content, leading to more accurate prediction.
  • the filter shape and number of filter taps can be predefined or signaled or switched in Sequence Parameter Set (SPS), Adaptation Parameter Set (APS), Picture Parameter Set (PPS), Picture Header (PH), Slice Header (SH), Region, CTU, CU, Subblock, or Sample level.
  • SPS Sequence Parameter Set
  • APS Adaptation Parameter Set
  • PPS Picture Parameter Set
  • PH Picture Header
  • SH Slice Header
  • Region CTU
  • CU Subblock
  • Sample level Sample level
  • a set of filter shape candidates can be predefined, and a selection on the set of filter shape candidates may be signaled or switched in SPS, APS, PPS, PH, SH, Region, CTU, CU, Subblock, or Sample level.
  • Different components e.g., U and V
  • a set of filter shape candidates may be predefined, and a filter shape (1, 2) may denote a 2-tap luma filter, a filter shape (1, 2, 4) may denote a 3-tap luma filter and the like, as shown in Figure 11 .
  • Tire filter shape selection of U and V components can be switched in PH or in CU or CTU level.
  • N-tap can represent N-tap with or without the offset P as described herein.
  • Table 8 One example is given as below in Table 8.
  • Different chroma types and/or color formats can have different predefined filter shapes and/or taps.
  • a predefined filter shape (1, 2, 4, 5) may be used for 4:2:0 type-0
  • a predefined filter shape (0, 1, 2, 4, 7) may be used for 4:2:0 type-2
  • a predefined filter shape (1, 4) may be used for 4:2:2
  • a predefined filter shape (0, 1, 2, 3, 4, 5) may be used for 4:4:4, as shown in Figure 12.
  • unavailable luma and chroma samples for deriving the MLR model can be padded from available reconstructed samples. For example, if using a 6-tap (0, 1 , 2, 3, 4, 5) filter as in Figure 12, for a CU located at tire left picture boundary, the left columns including samples (0, 3) are not available (out of picture boundary), so samples (0, 3) are repetitive padding from samples (1, 4) to apply the 6-tap filter. Note that the padding process may be applied in both training data (top and left neighboring reconstructed luma and chroma samples) and testing data (the luma and chroma samples in the CU(s)).
  • One or more shape/number of filter taps may be used for FLM prediction, examples being shown in Figure 16, Figure 17, and Figures 18A to 18B.
  • One or more sets of filter taps may be used for FLM prediction, examples being shown in Figures 19A to 19G.
  • the filter shape candidates can be implicitly derived without explicitly signaling bits.
  • the filter shape candidates can be the filter shape candidates for FLM or GLM (as discussed below).
  • the filter shape candidates can be the cross shape filter for CCCM, any of the filters shown in Figure 16, Figure 17, Figure 18A, Figure 18B, and Figures 19A to 19G, or other filters mentioned in this disclosure.
  • the well-known N-fold training technique in machine learning area can be used fortraining filter coefficients.
  • Step 1 determining M filter shape candidates for predicting the chroma sample values of the current CU
  • Step 2 dividing the available L-shapcd template area external to the CU into N regions, denoted as i.e., dividing the training data into N sets for N-fold training, wherein the luma sample values and the chroma sample values of the available template area are known values;
  • Step 3 applying each of the M filter shape candidates respectively to a part of the available template area, i.e., one or more regions among all the N regions
  • Step 4 deriving M filter coefficient sets corresponding to the M filter shape candidates, denoted as
  • Step 5 applying the derived filter coefficient sets to another part of the available template area to predict the chroma sample values based on corresponding luma sample values, wherein the another part of the available template area is different from the part of the available template area mentioned in Step 3;
  • Step 6 accumulating, for each of the M filter shapes respectively, the errors between the predicted chroma sample values and the known chroma sample values in the another part of the available template area by Sum of Absolute Difference (SAD), Sum of Squared Difference (SSD), or Sum of Absolute Transformed Difference (SATD), denoted as
  • Step 7 sorting and selecting K smallest errors, denoted as which correspond to K filter shapes and K filter coefficient sets.
  • Step 8 selecting one filter shape candidate from the K filter shape candidates, to apply to the current CU for chroma prediction. If K is more than 1, then the decoder may still receive signal from the encoder indicating the applied filter. However, if K is 1, then the signaling can be omitted and the filter with the smallest accumulated error is determined to be the applied filter.
  • one of 4 filter shape candidates is to be selected as the applied filter, while the L-shapcd template area is divided into cvcn-numbcrcd and odd-numbered rows or columns.
  • the steps include: predefining 4 filter shape candidates for the current CU (for example, 4 filter shape candidates from Figure 16); dividing the available L-shaped template area (for example, 6 chroma rows and columns for CCCM) into 2 regions denoted as wherein, for example, is composed of the even rows or columns, and Ri is composed of the odd rows or columns; applying 4 filter shape candidates independently to a part of the available template area (for example, region ); deriving 4 filter coefficient sets for the 4 filter shapes respectively, denoted as Fo, Fi, ...
  • the steps include: determining 4 filter shape candidates for the current CU; dividing the available L-shaped template area (for example, 6 chroma rows or columns for CCCM) into 2 regions denoted as Ro, Ri, wherein the luma samples in Ro and Ri are for example interleaved as shown in the following tables: or applying 4 filter shape candidates independently to a part of the available template area (for example, region Ro); deriving 4 filter coefficient sets for the 4 filter shapes respectively, denoted as applying the derived filter coefficient sets to the other part of the available template area (for example, region ) respectively, to predict the corresponding chroma sample values; accumulating, for each of the 4 filter shapes respectively, the errors between the predicted chroma sample values and the known chroma sample values in the other part of the available template area (for example, region R, ) by SAD, SSD, or SATD, denoted a sorting and
  • the steps of dividing the available L-shapcd template area may be omitted.
  • the M filter coefficient sets may be derived based on the sample values from the available template area and then applied back to the available template area respectively, to predict the corresponding chroma sample values for accumulating the errors.
  • an MLR model linear equations
  • several methods are proposed to derive the pseudo inverse matrix or to directly solve the linear equations.
  • Other known methods like Newton's method, Cayley-Hamilton method, and Eigendecomposition as mentioned in https://en.wikipedia.org/wiki/Invertible_matrix can also be applied.
  • linear equations can be solved using Gauss-Jordan elimination, by an augmented matrix and a series of elementary row operation to obtain the reduced row echelon form
  • Gauss-Jordan elimination by an augmented matrix and a series of elementary row operation to obtain the reduced row echelon form
  • default values can be used to fill the chroma prediction values.
  • the default values can be predefined or signaled or switched in SPS/ DPS/VPS/SEUAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels, for example, when predefined l «(bitDepth-l), meanC, meanL, or meanC-meanL (mean current chroma or other chroma, luma values from available, or subset of FLM reconstructed neighboring region).
  • Figure 11 shows atypical case that the FLM parameters are derived using top 2 and/or left 3 luma lines and top 1 and/or left 1 chroma lines.
  • using different region for parameter derivation may bring coding benefit because of different block content and the reconstructive quality of different neighboring samples, as mentioned above.
  • Several ways to choose the applied region for parameter derivation are proposed below:
  • the FLM derivation can only use top or left luma and/or chroma samples to derive the parameters.
  • FLM_L, or FLM_T can be predefined or signaled or switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblcok/Sample levels.
  • W’ and H’ arc obtained as follows:
  • the number of extended luma/chroma samples can be predefined, or signaled or switched in SPS/ DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • Figure 13 shows an illustration of FLM_L and FLM_T (c.g., under 4 tap).
  • FLM L or FLM_T When FLM L or FLM_T is applied, only H’ or W’ luma/chroma samples are used for parameter derivation, respectively.
  • different line index can be predefined, or signaled or switched in SPS/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels, to indicate the selected lumachroma sample pair line. This may benefit from different reconstructive quality of different line samples.
  • FIG 14 shows that similar to MRL, FLM can use different lines for parameter derivation (e.g., under 4 tap).
  • FLM can use light blue/yellow luma and/or chroma samples in index 1.
  • the luma sample values of an external region of the video block to be decoded may be referred to as “the external luma sample values”, and the chroma sample values of the external region may be referred to as “the external chroma sample values” throughout the disclosure .
  • Corresponding syntax may be defined as below in Table 9 for the FLM prediction.
  • FLC represents fixed length code
  • TU represents truncated unary code
  • EGk represents cxponcntial- golomb code with order k, where k can be fixed or signaled/switched in SPS/ DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblcok/Sample levels
  • SVLC represents signed EGO
  • UVLC represents unsigned EGO.
  • a new method for cross-component prediction is proposed on the basis of the existing linear model designs, in order to further improve coding accuracy and efficiency.
  • Main aspects of the proposed method arc detailed as follows.
  • reference samples/training template/reconstructed neighboring region usually refers to the luma samples used for deriving the MLR model parameters, which are then applied to the inner luma samples in one CU, to predict the chroma samples in the CU.
  • pre-operations e.g., pre linear weighted, sign, scale/abs, thresholding, ReLU
  • the pre- operations may comprise calculating sample differences based on the luma sample values.
  • the sample differences may be characterized as gradients, and thus this new method is also referred to as gradient linear model (GLM) in certain embodiments.
  • FIGS 15A to 15D show some examples for l-tap/2-tap (with offset) pre-operations, where 2-tap coefficients are denoted as (a, b).
  • each circle as illustrated in Figures 15 A to 15D represent an illustrative chroma position in the YUV 4:2:0 format.
  • a luma sample corresponding to a chroma sample may be obtained by performing a down -sampling operation on more than one (e.g., 4) reconstructed luma samples corresponding to the chroma sample (e g., located around the chroma sample).
  • the chroma position may correspond to corresponding to one or more luma samples comprising a collocated luma sample.
  • the different 1-tap patterns are designed for different gradient directions and using different “interpolated” luma samples (weighting to different luma location) for gradient calculation. For example, one typical filter 1 1 , 0, -1 ; 1, 0, -1 1 is shown in Figures 15A, 15C and 15D, which represents the following operations:
  • rec L represents the reconstructed luma sample values and Rec L "(i,j) represents the preoperated luma sample values.
  • tire 1-tap filters as shown in Figures 15A, 15C and 15D may be understood as alternatives for the down-sampling filters as used in CCLM (please refer to equations (6)-(7)), with changed filter coefficients.
  • Pre-operations can be according to gradients, edge direction (detection), pixel intensity, pixel variation, pixel variance, Roberts/Prewitt/compass/Sobel/Laplacian operator, high-pass filter (by calculating gradients or other relevant operators), low-pass filter (by performing weighted-average operations)... etc.
  • the edge direction detectors listed in the examples can be extended to different edge directions. For example, 1 -tap (1 , -1 ) or 2-tap (a, b) applied along different directions to detect different edge gradients.
  • the filter shape/coeff can be symmetric with respect to the chroma position, as the Figures 15A to 15D examples (420 type-0 case).
  • the pre-operation parameters can be fixed or signalcd/switchcd in SPS/DPS/VPS/SEl/APS/PPS/PH/SH/Rcgion/CTU/CU/Subblcok/Samplc levels. Note in the examples, if multiple coefficients apply on one sample (e.g., -1, 4), then they can be merged (e.g., 3) to reduce operations.
  • the pre-operations may relate to calculating sample differences of the luma sample values.
  • the pre-operations may comprise performing down-sampling by weighted-average operations. Tn certain cases, the pre-operations can be applied repeatedly. For example, one may apply one template filtering to template to remove outliers using the low-pass smoothing FIR filter 1 1, 2, 1
  • the pre-operation coefficients (finally applied (e.g., 3), or middle applied (e.g., -1, 4) to per luma sample) can be limited to power -of-2 values to save multipliers.
  • the proposed new method may be reused for/combined with tire above discussed CCLM, which utilizing a simple linear regression (SLR) model and using one corresponding luma sample value to predict the chroma sample value .
  • SLR simple linear regression
  • deriving the linear model further comprises deriving a scale parameter a and an offset parameter ⁇ 3 by using the pre-operated neighboring luma sample values and the neighboring chroma sample values.
  • the linear model may be re-writen as: (35)
  • L here represents “pre-operated” luma samples.
  • the parameter derivation of 1-tap GLM can reuse CCLM design, but taking directional gradient into consideration (may be with high -pass filter).
  • the scale parameter a may be derived by utilizing a division look-up table, as detailed below, to enable simplification
  • the scale parameter and the offset paremeter may be derived by utilizing the above-discussed min-max method.
  • the scale parameter and the offset paremeter may be derived by: comparing the pre-operated neighboring luma sample values to determine a minimum luma samle value and a maximum luma sample value determining corresponding choma samples values for the minimum luma samle value Y A and the maximum luma sample value Y B , respectively; and deriving the scale parameter a and the offset paremeter based on the minimum luma samle value the maximum luma sample value and the corresponding choma samples values according to the following equations: (36)
  • the encoder may determine a scale adjustment value (for example, “u”) to be signaled in the bitstream and add the scale adjustment value to the derived scale parameter a.
  • the decoder may dertermine the scale adjustment value (for example, “u”) from the bitstream and add the scale adjustment value to the derived scale parameter a.
  • the added value arc finally used to predict the internal chroma sample values.
  • the proposed new method may be reused for/combined with FLM, which utilizing a multiple linear regression (MLR) model and using multiple luma sample values to predict the chroma sample value.
  • FLM which utilizing a multiple linear regression (MLR) model and using multiple luma sample values to predict the chroma sample value.
  • MLR multiple linear regression
  • the linear model may be re-writen as:
  • multiple scale parameters a and an offset parameter may be derived by using the pre-operated neighboring luma sample values and the neighboring chroma sample values.
  • the offset parameter is optional.
  • at least one of the multiple scale parameters a may be derived by utilizing the sample differences.
  • another of the multiple scale parameters a may be derived by utilizing the down -sampled luma sample value.
  • at least one of the multiple scale parameters a may be derived by utilizing horizontal or vertical sample differences calculated on the basis of down-sampled neighboring luma sample values.
  • the linear model may combine multiple scale parameters a asscosicatcd with different pre -opertaions.
  • the used direction oriented filter shape can be derived at decoder to save bit overhead. For example, at the decoder, a number of directional gradient filters may be applied for each reconstructed luma sample of the L-shaped template of the i-th neighboring row and column of the current block. Then the filtered values (gradients) may be accumulated for each direction of the number of directional gradient filters respectively. In an example, the accumulated value is an accumulated value of absolute values of corresponding filtered values. After the accumulation, the direction of the directional gradient filter for which the accumulated value is the largest may be determined as the derived (luma) gradient direction. For example, a Histogram of Gradients (HoG) may be built to determine the largest value. The derived direction can be further applied as the direction for predicting chroma samples in the current block.
  • HoG Histogram of Gradients
  • DIMD decoder-side intra mode derivation
  • Step 1 applying 2 kinds of directional gradient filters (3x3 hor/ver Sobel) for each reconstructed luma sample of the L-shaped template of the 2 nd neighboring row and column of the current block;
  • Step 2 accumulating filtered values (gradients) by SAD (sum of absolute differences) for each of the directional gradient filters;
  • Step 3 Build a Histogram of Gradients (HoG) based on the accumulating filtered values; and Step 4: The largest value in HoG is determined to be the derived (luma) gradient direction, based on which the GLM filter may be determined.
  • HoG Histogram of Gradients
  • shape candidates are [-1, 0, 1; -1, 0, 1] (horizontal) and [1, 2, 1; -1, - 2, -1] (vertical)
  • shape [-1, 0, 1; -1, 0, 1] for GLM based chroma prediction.
  • the gradient filter used for deriving the gradient direction can be the same or different with the GLM filter in shape.
  • both of the filters may be horizontal [-1, 0, 1; -1, 0, 1], orthe two filters may have different shapes, while the GLM filter may be determined based on the gradient filter.
  • the proposed GLM can be combined with above discussed MMLM or ELM.
  • each group can share or have its own filter shape, with syntaxes indicating shape for each group.
  • horiontal grandients grad_hor may be classified into a first group, which correspond to a first linear model
  • vertical grandients grad_ver may be classified into a second group, which correspond to a second linear model.
  • the horiontal luma patterns may be generated only once.
  • the neighboring and internal luma-chroma sample pairs of the current video block may be classified into muitple groups based on one or more thresholds.
  • each neighboring/intemal chroma sample and its corresponding luma sample may be referred to as a lumachroma sample pair.
  • the one or more thresholds are associated with intensities of neighboring/ internal luma samples.
  • each of the multiple groups corresponds to a respective one of the plurality of linear models.
  • the following operations may be performed: classifying neighboring reconstructed luma-chroma sample pairs of the current video block into 2 groups based on Threshold; deriving different linear models for different groups, wherein the deriving process may be GLM simplified, i.e., with the above pre -operations to reduce the number of taps; classifying luma-chroma sample pairs inside the CU (internal luma-chroma sample pairs, wherein each of the internal luma-chroma sample pairs comprises an internal chroma sample value to be predicted with the derived linear model) into 2 groups similarly based on Threshold; applying different linear models to the reconstructed luma samples in different groups; and predicting chroma samples in the CU based on different classified linear models.
  • Threshold may be average value of the neighboring reconstructed luma samples.
  • the number of classes (2) can be extended to multiple classes by increasing the number of Threshold (e g., equally divided based on min/max of neighboring reconstructed (down-sampled) luma samples, fixed or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblcok/Sample levels).
  • the filtered values of FLM/GLM apply on neighboring luma samples are used for classification. For example, if 1-tap (1, -1) GLM is applied, average AC values are used (physical meaning).
  • the processing can be: classifying neighboring reconstructed luma-chroma sample pairs into K groups based on one or more filter shapes, one or more filtered values, and K-l Threshold Ti; deriving different MLR models for different groups, wherein the deriving process may be GLM simplified, i.e., with the above pre -operations to reduce the number of taps; classifying luma-chroma sample pairs inside the CU (internal luma-chroma sample pairs, wherein each of the internal luma-chroma sample pairs comprises an internal chroma sample value to be predicted with the derived linear model) into K groups similarly based on one or more filter shapes, one or more filtered values, and K-l Threshold Ti; applying different linear models to die reconstructed luma samples in different groups, predicting chroma samples in the CU based on different classified linear models.
  • Threshold can be predefined (e.g., 0, or can be a tabic) or signalcd
  • Threshold can be the average AC value (filtered value) (2 groups), or equally divided based on min/max AC (K groups), of neighboring reconstructed (can be down-sampled) luma samples.
  • one filter shape (e g., 1-tap) may be selected to calculate edge strengths.
  • the direction is determined as a direction along which a sample difference between samples of the current and N neighboring samples (e.g., all 6 luma samples) is calculated.
  • the filter shape [1, 0, -1; 1, 0, -1]
  • the filter at the upper middle in Figure 15A indicates a horizontal direction since a sample difference may be calculated between samples in the horizontal direction
  • the filter below it shape 1 1 1 , 2, 1 ; -1 , -2, - 1 1 1 1
  • the positive and negative coefficients in each of the filters enable the calculation of the sample differences.
  • the filter shape used for classification can be the same or different with the filter shape used for MLR prediction.
  • Both and the number of thresholds M-l, the thresholds values Ti can be fixed or signaled/switched in SPS/DPS/VPS/SET/APS/PPS/PH/SH/Region/CTU/CU/Subblcok/Sample levels.
  • other classificrs/combincd-classificrs as discussed in ELM can also be used for GLM.
  • the matrix/parameter derivation in FLM requires floating-point operation (e.g., division in closed-form), which is expensive for decoder hardware, so a fixed-point design is required.
  • floating-point operation e.g., division in closed-form
  • CCLM modified luma reconstructed sample generation of CCLM
  • the original CCLM process can be reused for GLM, including fixed-point operation, MDLM downsampling, division table, applied size restriction, min-max approximation, and scale adjustment.
  • 1-tap GLM can have its own configurations or share the same design as CCLM.
  • each group can apply the same or different simplification operation. For example, samples for each group are padded respectively to the target sample number before applying right shift, and then apply the same derivation process, same division table.
  • the 1 -tap case can reuse the CCLM design, dividing by n may be implemented by right shift, dividing by A 2 may be implemented by by a LUT.
  • the integerization parameters including n table invloved in the integerization design of LMS CCLM and intermediate parameters for deriving the linear model (equations (19)-(20)) can be the same as CCLM or have different values, to have more precision.
  • the integerization parameters can be predefined or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblcok/Sample levels, can be conditioned on sequence bitdepth. For example,
  • the padding method for GLM can be the same or different with that of CCLM.
  • Division LUT proposed for CCLM/LIC Long Illumination Compensation
  • AVC/HEVC/AV1/WC/AVS can be used for GLM division.
  • CCLM/LIC Large Illumination Compensation
  • the division LUT can be different from CCLM.
  • CCLM uses min-max with DivTable as in equation 5, but GLM uses 32- entries LMS division LUT as in Table 5.
  • the meanL values may not always be positive (e.g., using filtered/gradient values to classify groups), so sgn(meanL) needs to be extracted, and use abs(mcanL) to look-up the division LUT.
  • division LUT used for MMLM classification and parameter derivation can be different. For example, using lower precision LUT (as the LUT in min- max) for mean classification, and using higher precision LUT (as in the LMS) for parameter derivation.
  • ELM/FLM/GLM Similar to the CCLM design, some size restrictions can be applied for ELM/FLM/GLM. For example, same constraint for luma-chroma latency in dual tree may be applied.
  • the size restriction can be according to the CU area/width/height/depth.
  • the threshold can be predefined or signaled in SPS/DPS/VPS/SEI/APS/PPS/PI I/SI I/Rcgion/CTU/CU/Subblcok/Sample levels.
  • the predefined threshold may be 128 for chroma CU area.
  • the at least one prc-opcration is performed in response to determining that the video block meets an enabling threshold, wherein the enabling threshold is associated with area, width, height or partition depth of the video block.
  • the enabling threshold may define a minium or maximum area, width, height or partition depth of the video block.
  • the video block may comprise a current chroma block and its collocated luma block. It is also proposed to apply the above enabling threshold for the current chroma block and its collocated luma block jointly.
  • the at least one pre-operation is performed in response to determining the enabling threshold is met for both the current chroma block and its collocated luma block.
  • the top template samples generation can be limited to 1 row, to reduce CTU row line buffer storage. Note that only one luma line (general line buffer in intra prediction) is used to make the down-sampled luma samples when the upper reference line is at the CTU boundary.
  • top template can be limited to only use 1 row (but not 2) for parameter derivation (other CUs can still use 2 rows).
  • [00227] For example, take the 1-tap filter [1, 0, -1; 1, 0, -1] shown in Figure 15 A as an example for illustration. This filter can be reduced to [0, 0, 0; 1, 0, -1], i.e., only use below row coefficients. Alternatively, the limited upper row luma samples can be padded (repetitive, mirror, 0, meanL, meanC...etc.) from the bellow row luma samples.
  • top 4 rows of neighboring luma sample values and corresponding chroma sample values are used for deriving the linear model.
  • the corresponding chroma sample values may refer to corresponding top 4 rows of neighboring chroma sample values (for example, for the YUV 4:4:4 format).
  • the corresponding chroma sample values may refer to corresponding top 2 rows of neighboring chroma sample values (for example, for the YUV 4:2:0 format).
  • the top 4 rows of neighboring luma sample values and corresponding chroma sample values may be divided into two regions - a first region comprising valid sample values (for example, the one nearest row of luma sample values and corresponding chroma sample values) and a second region comprising invalid sample values (for example, the other three rows of luma sample values and corresponding chroma sample values). Then coefficients of the filter corresponding to sample positions not belonging to the first region may be set as zeros, such that only sample values from the first region arc used for calculating the sample differences.
  • the filter [1, 0, -1; 1, 0, -1] can be reduced to [0, 0, 0; 1, 0, -1],
  • the nearest sample values in the first region may be padded to the second region, such that the padded sample values may be used to calculate the sample differences.
  • GLM can be taken as one special CCLM mode
  • the fusion design can be reused or have its own way.
  • Multiple (two or more) weights can be applied to generation the final predictor. For example, wherein is the predictor based on non-LM mode, while predl is the predictor based on GLM, or predO is the predictor based on one of CCLM (including all MDLM/MMLM), while predl is the predictor based on GLM, or predO is the predictor based on GLM, while predl is the predictor based on GLM.
  • Different I/P/B slices can have different designs for weights, wO and wl, depending on if neighboring blocks is coded with CCLM/GLM/other coding mode or the block size/width/height.
  • the designs for weights can be determined by the intra prediction mode of adjacent chroma blocks and shift is set equal to 2. Specifically, when the above and left adjacent blocks are both coded with LM modes, then ; when the above and left adjacent blocks are both coded with non inodes, then ⁇ , otherwise, For non-I slices, can both be set equal to 2.
  • GLM has good gain complexity trade-off since it can reuse the existing CCLM module without introducing additional derivation.
  • Such 1-tap design can be extended or generalized further according to one or more aspects of the present disclosure.
  • one single corresponding luma sample L may be generated by combining collocated luma sample and neighboring luma samples.
  • the combination may be a combination of different linear filters, e.g., a combination of a high-pass gradient filter (GLM) and a low-pass smoothing filter (e.g., 1 1, 2, 1 ; 1 , 2, 1 1/8 FIR down-sampling filter that may be generally used in CCLM); and/or a combination of a linear filter and a non-linear filter (e.g., with power of n, e.g., L n , n can be positive, negative, or +- fractional number (e.g., +1/2, square root or +3, cube, which can rounding and rescale to bitdepth dynamic range)).
  • a combination of different linear filters e.g., a combination of a high-pass gradient filter (GLM) and a low-pass smoothing filter (e.g., 1 1, 2, 1 ; 1 , 2,
  • the combination may be repeatedly applied.
  • a combination of GLM and [1, 2, 1; 1, 2, l]/8 FIR may be applied on the reconstructed luma samples, and then a non-linear power of 1/2 may be applied.
  • the non-linear filter may be implemented as LUT 0 3, where 5 is to scale to bitdepth— 10 dynamic range.
  • the nonlinear filter may provide options when linear filter cannot handle the luma-chroma relationship efficiently Whether to use nonlinear term can be predefined or signale d/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblcok/Sample levels.
  • the GLM may refer to Generalized Linear Model (may be used to generate one single luma sample linearly or nonlincarly, and the generated one single luma sample may be fed into the CCLM linear model to derive parameters of the CCLM linear model), linear/nonlinear generation may be called general patterns. Different gradient or general patterns can be combined to form another pattern.
  • Generalized Linear Model may be used to generate one single luma sample linearly or nonlincarly, and the generated one single luma sample may be fed into the CCLM linear model to derive parameters of the CCLM linear model
  • linear/nonlinear generation may be called general patterns. Different gradient or general patterns can be combined to form another pattern.
  • a gradient pattern may be combined with a CCLM down-sampled value; a gradient pattern may be combined with a non-linear L 2 value; a gradient pattern may be combined with another gradient pattern, the two gradient patterns to be combined may have different directions or the same direction, e.g., [1, 1, 1; -1, -1, -1] and [1, 2, 1; -1, -2, -1], which both have a vertical direction, may be combined, also [1, 1, 1; -1, -1, -1] and [1, 0, -1; 1, 0, -1], which have a vertical and horizontal directions, may be combined, as shown in Figures 15A to 15D.
  • the combination may comprise plus, minus, or linear weighted.
  • pre -operations can be applied repeatedly and GLM can be applied on pre linear weighted/pre-operated samples.
  • GLM can be applied on pre linear weighted/pre-operated samples.
  • one template filtering can be applied to luma samples, in order to remove outliers using the low -pass smoothing FIR filter [1, 2, 1; 1, 2, l]/8 (i.e., CCLM down-sampling smoothing filter) and to generate down-sampled luma samples (one down- sampled luma sample corresponding to one chroma sample).
  • 1-tap GLM can be applied on smoothed down-sampled luma samples to derive the MLR model.
  • Some gradient filter patterns such as 3x3 Sobel or Prewitt operators, can be applied on down-sampled luma samples.
  • the following table shows some of the gradient filter patterns.
  • the gradient filter patterns can be combined with other gradient/general filter patterns in the down-sampled luma domain.
  • a combined filter pattern may be applied on down- sampled luma samples.
  • the combined filter pattern may be derived by performing addition or subtraction operations to respective coefficients of the gradient filter pattern and a DC/low-pass based filter pattern, such as filter pattern [0, 0, 0; 0, 1, 0; 0, 0, 0], or [1, 2, 1; 2, 4, 1; 1, 2, 1],
  • the combined filter pattern is derived by performing addition or subtraction operations to a coefficient of the gradient filter pattern and a non-linear value such as L 2 .
  • the combined filter pattern is derived by performing addition or subtraction operations to respective coefficients of the gradient filter pattern and another gradient filter pattern having a different or the same direction.
  • the combined filter pattern is derived by performing linear weighted operations to the coefficients of the gradient filter pattern.
  • GLM applied on down-sampled domain can fit in CCCM framework but may sacrifice high frequency accuracy since low -pass smoothing is applied before applying GLM.
  • GLM serves as input of CCCM
  • CCCM applies luma down-sampling before convolution as with CCLM.
  • the reconstructed luma samples are down-sampled to match the lower resolution chroma grid when chroma sub-sampling is used.
  • 1-tap GLM can also be taken as changing CCLM downsample filter coefficients (e g., from [1, 2, 1; 1, 2, 1]/ 8 to [1, 2, 1, -1, -2, -1], i.e., from low-pass to high- pass), the GLM can serve as the input of CCCM.
  • the gradient filter of GLM replaces luma down-sampling filter (
  • CCCM operation becomes “linear/non-linear combination of gradients”, as shown by the following equation:
  • C, N, S, E, W, P arc gradients of current or neighboring samples (compared to original downsample values for CCCM).
  • Related GLM methods described in this disclosure can be applied in the same way before entering CCCM convolution, e.g., classification, separate Cb/Cr control, syntax, pattern combining, PU size restriction etc.
  • the gradient-based coefficients replacement can apply to specific CCCM taps. Also, not only high-pass but low-pass/band-pass/all-pass coefficients replacement can be used. Tire replacement can be combined with FLM/CCCM shape switch discussed above (leading to different number of taps). For example, gradient patterns in Figures 15A to 15D can be used for replacement.
  • the operations for applying GLM as input of CCCM includes: predefining one or more coefficients candidates for CCCM/FLM down-sampling; determining CCCM/FLM filter shape and number of filter taps for this CU; applying different CCLM down-sample coefficients to different filter taps, wherein the coefficients can be high-pass filters (GLM), or low-pass/band-pass/all-pass filters; generating the down-sampled luma samples (using the applied coefficients) for CCCM input samples; and feeding the generated down-sampled luma samples into CCCM process.
  • GLM high-pass filters
  • Which CCCM/FLM taps to apply the coefficients replacement can be predefined (as above examples) or signaled/switched in
  • the coefficients candidate for CCCM/FLM down-sampling can be predefined or signaled/switched in
  • Example 5 [00260]
  • GLM syntaxes may be introducedo indicate information on the GLM.
  • An example of GLM syntaxes is illustrated in the following Table 10.
  • EGk exponential-golomb code with order k, where k can be fixed or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Rcgion/CTL7CU/Subblcol ⁇ /Samplc levels.
  • the GLM on/off control for Cb/Cr components may be jointly or separately.
  • 1 flag may be used to indicate if GLM is active for this CU. If active, 1 flag may be used to indicate if Cb/Cr are both active. If not both active, 1 flag to indicate either Cb or Cr is active.
  • Filter index/gradient (general) pattern may be signaled separately when Cb and/or Cr is active. All flags may have its own context model or be bypass coded.
  • whether to signal GLM on/off flags may depend on luma/chroma coding modes, and/or CU size.
  • GLM may be inferred off when MMLM or MMLM_L or MMLM_T is applied; when CU area ⁇ A, where A can be predefined or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels: If combined with CCCM, GLM may be inferred off when CCCM is on.
  • CCCM requires to process down-sampled luma reference values before the calculation of model parameters and applying the CCCM model, which burden decoder processing cycles.
  • CCCM without down-sampling process is proposed, including utilizing non-down-sampled luma reference values and/or different selection of non-down-sampled luma reference.
  • One or more filter shapes may be used for the purpose as described below.
  • reference samples/training template s/reconstructed neighboring regions usually refer to the luma samples used for deriving the MLR model parameters, which are then applied to the inner luma samples in one CU, to predict the chroma samples in the CU.
  • One or more shape/number of filter taps may be used for CCCM prediction, as shown in Figure 16, Figure 17, and Figures 18A to 18B.
  • One or more sets of filter taps may be used for FLM prediction, examples being shown in Figures 19A to 19G.
  • the selected luma reference values are non- down-sampled.
  • One or more predefined shape/number of filter taps may be used for CCCM prediction based on previous decoded information on TB/CB/slice/picture/sequence level.
  • a multiple tap filter can fit well on training data (i.e., top/left neighboring reconstructed luma/chroma samples), in some cases, that training data do not capture full characteristics of the testing data, and it may result in overfitting and may not predict well on the testing data (i.e., the to-bc -predicted chroma block samples).
  • different filter shapes may adapt well to different video block content, leading to more accurate prediction.
  • the filter shape/number of filter taps can be predefined or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Rcgion/CTU/CU/Subblock/Samplc levels.
  • a set of filter shape candidates can be predefined or signaled/switched in
  • Different components may have different filter switch control.
  • the filter shape selection of U/V components can be switched in PH or in CU/CTU levels.
  • N-tap can represent N-tap with or without the offset P as described above.
  • Different chroma types/color formats can have different predefined filter shapes/taps. For example, using predefined filter shape for 420 type-0: (1, 2, 4, 5), 420 type-2: (0, 1, 2, 4, 7), 422: (1, 4), 444: (0, 1, 2, 3, 4, 5) as shown in Figure 12.
  • the unavailable luma/chroma samples for deriving the MLR model can be padded from available reconstructed samples. For example, if using a 6-tap (0, 1, 2, 3, 4, 5) filter as in Figure 12, for a CU located at the left picture boundary, the left columns including (0, 3) are not available (out of picture boundary), so (0, 3) are repetitive padding from (1, 4) to apply the 6-tap filter. Note the padding process applied in both training data (top/left neighboring reconstructed luma/chroma samples) and testing data (the luma/chroma samples in the CU).
  • the unavailable luma/chroma samples for deriving the MLR model can be skipped and not used. Then the padding process is not needed for the unavailable luma/chroma samples.
  • CCCM requires to process LDL decomposition to calculate the model parameters of CCCM model, avoiding using square root operations and only integer arithmetic is required.
  • CCLM/MMLM with LDL decomposition are proposed.
  • LDL decomposition may also be used in ELM/FLM/GLM, as described above.
  • reference samplcs/training template s/rcconstructcd neighboring regions usually refer to the luma samples used for deriving the MLR model parameters, which are then applied to the inner luma samples in one CU, to predict the chroma samples in the CU.
  • One or more reference samples may be used for CCLM/MMLM prediction, i.e., as shown in Figure 10B, the reference area may be the same as the reference area in CCCM. Different reference areas may be used for CCLM/MMLM prediction based on previous decoded information on TB/ CB/slice/picture/ sequence level .
  • training data with multiple reference areas can fit well on the calculation of model parameters, in some cases that training data do not capture full characteristics of testing data, it may result in overfitting and may not predict well on testing data (i.e., the to-be-predicted chroma block samples). Also, different reference areas may adapt well to different video block content, leading to more accurate prediction. To address this issue, the reference shapc/numbcr of reference areas can be predefined or signaled/switched in
  • a set of reference area candidates can be predefined or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • the unavailable luma/chroma samples for deriving the MLR model can be padded from available reconstructed samples, the padding process being applied in both training data (top/left neighboring reconstructed luma/chroma samples) and testing data (the luma/chroma samples in the CU).
  • the unavailable luma/chroma samples for deriving the MLR model can be skipped and not used. Then the padding process is not needed for the unavailable luma/chroma samples.
  • FLM requires to process down-sampled luma reference values and calculate model parameters, which burden decoder processing cycles, especially for small blocks.
  • FLM with minimal samples restriction is proposed, for example, FLM is only used for samples larger than predefined number, such as 64, 128.
  • predefined number such as 64, 128.
  • FLM is only used in single model for samples larger than a predefined number, such as 256, and FLM is only used in multi model for samples larger than a predefined number, such as 128.
  • the number of predefined minimal samples for single model may be larger than or equal to the number of predefined minimal samples for multi model.
  • FLM/GLM/ELM/CCCM is only used in single model for samples larger than or equal to a predefined number, such as 128, and FLM/GLM/ELM/CCCM is only used in multi model for samples larger than or equal to a predefined number, such as 256.
  • the number of predefined minimal samples for FLM/GLM/ELM may be larger than or equal to the number of predefined minimal samples for CCCM.
  • CCCM is only used in single model for samples larger than or equal to a predefined number, such as 0, and CCCM is only used in multi model for samples larger than or equal to a predefined number, such as 128.
  • FLM is only used in single model for samples larger than or equal to a predefined number, such as 128, and FLM is only used in multi model for samples larger than or equal to a predefined number, such as 256.
  • Figure 20 illustrates a workflow of a method 2000 for decoding video data according to one or more aspects of the present disclosure.
  • the method 2000 comprises obtaining a video block from a bitstream.
  • the method 2000 comprises obtaining internal luma sample values of the video block, external luma sample values of an external region of the video block and external chroma sample values of the external region.
  • the method 2000 comprises selecting, based on the external luma sample values and the external chroma sample values, one filter shape candidate from a plurality of filter shape candidates for predicting internal chroma sample values of the video block, wherein the plurality of filter shape candidates correspond to different sets of weighting coefficients for predicting chorma sample values based on corresponding luma sample values.
  • the method 2000 comprises predicting, with the selected filter shape candidate, the internal chroma sample values based on the internal luma sample values
  • the method 2000 comprises obtaining decoded video block using the predicted internal chroma sample values.
  • the method 2000 further comprises: determining the plurality of filter shape candidates for predicting the internal chroma sample values.
  • the plurality of filter shape candidates comprise at least one gradient filter candidate enabling calculation of sample differences between luma sample values.
  • selecting one filter shape candidate from a plurality of filter shape candidates for predicting the internal chroma sample values comprises: applying each of the sets of weighting coefficients for the plurality of filter shape candidates to the external region respectively, to predict chroma sample values in the external region based on corresponding luma sample values for the chroma sample values in the external region; accumulating, for each of the plurality of filter shape candidates respectively, errors between the predicted chroma sample values and corresponding external chroma sample values in the external region; and selecting one filter shape candidate from the plurality of filter shape candidates based on the accumulated errors for predicting the internal chroma sample values.
  • the method 2000 further comprises: applying each of the plurality of filter shape candidates to the external region respectively to derive a set of weighting coefficients corresponding to each of the plurality of filter shape candidates based on external luma sample values and corresponding external chroma sample values in the external region.
  • selecting one filter shape candidate from a plurality of filter shape candidates for predicting the internal chroma sample values comprises: dividing the external region into two or more parts; applying each of the plurality of filter shape candidates to a first part of the external region respectively to derive a set of weighting coefficients corresponding to each of the plurality of filter shape candidates based on external luma sample values and corresponding external chroma sample values in the first part of the external region; applying each of the derived sets of weighting coefficients for the plurality of filter shape candidates to a second part of the external region respectively, to predict chroma sample values in the second part of the external region based on corresponding luma sample values for the chroma sample values in the second part of the external region; accumulating, for each of the plurality of filter shape candidates respectively, errors between the predicted chroma sample values and corresponding external chroma sample values in the second part of the external region; selecting one filter shape candidate from the plurality of filter shape candidates based on the accumulated
  • the first part of the external region includes even-numbered rows or columns of the external region, and the second part of the external region includes remaining odd- numbered rows or columns of the external region.
  • the first part of the external region and the second part of the external region are interleaved parts of the external region.
  • accumulating errors between the predicted chroma sample values and corresponding external chroma sample values comprises: accumulating the errors by Sum of Absolute Difference (SAD), Sum of Squared Difference (SSD), or Sum of Absolute Transformed Difference (SATD).
  • selecting one filter shape candidate from the plurality of filter shape candidates based on the accumulated errors for predicting the internal chroma sample values comprises: selecting one filter shape candidate from the plurality of filter shape candidates with the smallest accumulated error for predicting the internal chroma sample values.
  • selecting one filter shape candidate from the plurality of filter shape candidates based on the accumulated errors for predicting the internal chroma sample values comprises: sorting and selecting two or more filter shape candidates from the plurality of filter shape candidates with the smallest errors; and selecting one filter shape candidate from the two or more filter shape candidates based on a received signal indicating an applied filter shape candidate for predicting the internal chroma sample values.
  • Figure 21 illustrates a workflow of a method 2100 for encoding video data according to one or more aspects of the present disclosure.
  • the method 2100 comprises obtaining a video block.
  • the method 2100 comprises obtaining internal luma sample values of the video block, external luma sample values of an external region of the video block and external chroma sample values of the external region.
  • the method 2100 comprises selecting, based on the external luma sample values and the external chroma sample values, one filter shape candidate from a plurality of filter shape candidates for predicting internal chroma sample values of the video block, wherein the plurality of filter shape candidates correspond to different sets of weighting coefficients for predicting chorma sample values based on corresponding luma sample values.
  • the method 2100 comprises predicting, with the selected filter shape candidate, the internal chroma sample values based on the internal luma sample values.
  • the method 2100 comprises generating a bitstream comprising encoded video block by using the predicted internal chroma sample values.
  • the method 2100 further comprises: determining the plurality of filter shape candidates for predicting the internal chroma sample values.
  • the plurality of filter shape candidates comprise at least one gradient filter candidate enabling calculation of sample differences between luma sample values.
  • selecting one filter shape candidate from a plurality of filter shape candidates for predicting the internal chroma sample values comprises: applying each of the sets of weighting coefficients for the plurality of filter shape candidates to the external region respectively, to predict chroma sample values in the external region based on corresponding luma sample values for the chroma sample values in the external region; accumulating, for each of the plurality of filter shape candidates respectively, errors between the predicted chroma sample values and corresponding external chroma sample values in the external region; and selecting one filter shape candidate from the plurality of filter shape candidates based on the accumulated errors for predicting the internal chroma sample values.
  • the method 2100 further comprises: applying each of the plurality of filter shape candidates to the external region respectively to derive a set of weighting coefficients corresponding to each of the plurality of filter shape candidates based on external luma sample values and corresponding external chroma sample values in the external region.
  • selecting one filter shape candidate from a plurality of filter shape candidates for predicting the internal chroma sample values comprises: dividing the external region into two or more parts; applying each of the plurality of filter shape candidates to a first part of the external region respectively to derive a set of weighting coefficients corresponding to each of the plurality of filter shape candidates based on external luma sample values and corresponding external chroma sample values in the first part of the external region; applying each of the derived sets of weighting coefficients for the plurality of filter shape candidates to a second part of the external region respectively, to predict chroma sample values in the second part of the external region based on corresponding luma sample values for the chroma sample values in the second part of the external region; accumulating, for each of the plurality of filter shape candidates respectively, errors between the predicted chroma sample values and corresponding external chroma sample values in the second part of the external region; selecting one filter shape candidate from the plurality of filter shape candidates based on the accumulated
  • the first part of the external region includes even-numbered rows or columns of the external region, and the second part of the external region includes remaining odd- numbered rows or columns of the external region.
  • the first part of the external region and the second part of the external region are interleaved parts of the external region.
  • accumulating errors between the predicted chroma sample values and corresponding external chroma sample values comprises: accumulating the errors by Sum of Absolute Difference (SAD), Sum of Squared Difference (SSD), or Sum of Absolute Transformed Difference (SATD).
  • SAD Sum of Absolute Difference
  • SSD Sum of Squared Difference
  • SATD Sum of Absolute Transformed Difference
  • selecting one filter shape candidate from the plurality of filter shape candidates based on the accumulated errors for predicting the internal chroma sample values comprises: selecting one filter shape candidate from the plurality of filter shape candidates with the smallest accumulated error for predicting the internal chroma sample values.
  • selecting one filter shape candidate from the plurality of filter shape candidates based on the accumulated errors for predicting the internal chroma sample values comprises: sorting and selecting two or more filter shape candidates from the plurality of filter shape candidates with the smallest errors; and selecting one filter shape candidate from the two or more filter shape candidates for predicting the internal chroma sample values
  • the method 2100 further comprises: signaling a syntax element indicating the selected filter shape candidate in the bitstream.
  • FIG. 22 illustrates an exemplary computing system 2200 according to one or more aspects of the present disclosure.
  • the computing system 2200 may compnse at least one processor 2210.
  • the computing system 2200 may further comprise at least one storage device 2220.
  • the storage device 2220 may store computer-executable instructions that, when executed, cause the processor 2210 to perform the steps of methods described above.
  • the processor 2210 may be a general-purpose processor, or may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
  • the storage device 2220 may store the input data, output data, data generated by processor 2210, and/or instructions executed by processor 2210.
  • the storage device 2220 may store computer-executable instructions that, when executed, cause the processor 2210 to perform any operations according to the embodiments of the present disclosure.
  • the embodiments of the present disclosure may be embodied in a computer-readable medium such as non-transitory computer-readable medium.
  • the non-transitory computer-readable medium may comprise instructions that, when executed, cause one or more processors to perform any operations according to the embodiments of the present disclosure.
  • the instructions when executed, may cause one or more processors to receive a bitstream and perform the decoding operations as described above.
  • the instractions when executed, may cause one or more processors to perform the encoding operations and transmit a bitstream comprising the encoded video information associated with the predicted chroma sample as described above.
  • modules in the methods described above may be implemented in various approaches. These modules may be implemented as hardware, software, or a combination thereof. Moreover, any of these modules may be further functionally divided into submodules or combined together.

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  • Multimedia (AREA)
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  • Compression Or Coding Systems Of Tv Signals (AREA)

Abstract

La présente invention propose un procédé de décodage de données vidéo, comprenant les étapes suivantes : obtenir un bloc vidéo à partir d'un flux binaire ; obtenir des valeurs d'échantillon luma interne du bloc vidéo, des valeurs d'échantillon luma externe d'une région externe du bloc vidéo et des valeurs d'échantillon chroma externe de la région externe ; sélectionner, sur la base des valeurs d'échantillon luma externe et des valeurs d'échantillon chroma externe, un candidat de forme de filtre parmi une pluralité de candidats de forme de filtre pour prédire les valeurs d'échantillon chroma interne du bloc vidéo, la pluralité de candidats de forme de filtre correspondant à différents ensembles de coefficients de pondération pour prédire les valeurs d'échantillon chroma sur la base des valeurs d'échantillon luma correspondantes ; prédire, avec le candidat de forme de filtre sélectionné, les valeurs d'échantillon chroma interne sur la base des valeurs d'échantillon luma interne ; et obtenir un bloc vidéo décodé à l'aide des valeurs d'échantillon chroma interne prédites.
PCT/US2023/028992 2022-07-28 2023-07-28 Procédé et appareil de prédiction inter-composantes pour codage vidéo WO2024026098A1 (fr)

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WO2021138354A1 (fr) * 2019-12-30 2021-07-08 Beijing Dajia Internet Information Technology Co., Ltd. Détermination trans-composantes de composantes chroma et luma de données vidéo
US20210274184A1 (en) * 2018-08-24 2021-09-02 Samsung Electronics Co., Ltd. Video decoding method and apparatus, and video encoding method and apparatus
US20210314581A1 (en) * 2018-12-13 2021-10-07 Huawei Technologies Co., Ltd. Chroma block prediction method and apparatus
US20220159307A1 (en) * 2019-08-08 2022-05-19 Panasonic Intellectual Property Corporation Of America System and method for video coding
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US20210274184A1 (en) * 2018-08-24 2021-09-02 Samsung Electronics Co., Ltd. Video decoding method and apparatus, and video encoding method and apparatus
US20210314581A1 (en) * 2018-12-13 2021-10-07 Huawei Technologies Co., Ltd. Chroma block prediction method and apparatus
US20220159307A1 (en) * 2019-08-08 2022-05-19 Panasonic Intellectual Property Corporation Of America System and method for video coding
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