WO2020211769A1 - Clipping parameter derivation in adaptive loop filter - Google Patents

Clipping parameter derivation in adaptive loop filter Download PDF

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WO2020211769A1
WO2020211769A1 PCT/CN2020/084873 CN2020084873W WO2020211769A1 WO 2020211769 A1 WO2020211769 A1 WO 2020211769A1 CN 2020084873 W CN2020084873 W CN 2020084873W WO 2020211769 A1 WO2020211769 A1 WO 2020211769A1
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parameters
filter
current video
video block
coding
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French (fr)
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Li Zhang
Kai Zhang
Hongbin Liu
Yue Wang
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Beijing ByteDance Network Technology Co Ltd
ByteDance Inc
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Beijing ByteDance Network Technology Co Ltd
ByteDance Inc
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Priority to CN202080028109.XA priority Critical patent/CN113678462B/zh
Priority to CN202211656192.2A priority patent/CN115914627A/zh
Publication of WO2020211769A1 publication Critical patent/WO2020211769A1/en
Priority to US17/392,581 priority patent/US11303894B2/en
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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
    • H04N19/119—Adaptive subdivision aspects, e.g. subdivision of a picture into rectangular or non-rectangular coding blocks
    • 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
    • H04N19/132—Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
    • 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
    • H04N19/174—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 slice, e.g. a line of blocks or a group of blocks
    • 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
    • H04N19/184—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 bits, e.g. of the compressed video stream
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/70—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
    • 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
    • H04N19/82—Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation involving filtering within a prediction loop

Definitions

  • This patent document relates to video coding and decoding techniques, devices and systems.
  • Devices, systems and methods related to digital video coding, and specifically, to temporal prediction of parameters in non-linear adaptive loop filtering are described.
  • the described methods may be applied to both the existing video coding standards (e.g., High Efficiency Video Coding (HEVC) ) and future video coding standards (e.g., Versatile Video Coding (VVC) ) or codecs.
  • HEVC High Efficiency Video Coding
  • VVC Versatile Video Coding
  • the disclosed technology may be used to provide a method for visual media processing.
  • This method includes configuring, for a current video block, one or more parameters of a clipping operation that is part of a non-linear filtering operation; and performing, based on the one or more parameters, a conversion between the current video block and a bitstream representation of the current video block, wherein the one or more parameters is coded in accordance with a rule.
  • the disclosed technology may be used to provide a method for visual media processing.
  • This method includes determining, based on a characteristic of a current video block, one or more parameters of a non-linear filtering operation; and performing, based on the one or more parameters, a conversion between the current video block and a bitstream representation of the current video block.
  • the disclosed technology may be used to provide a method for visual media processing.
  • This method includes configuring, for a current video block, one or more parameters of a clipping operation that is part of a non-linear filtering operation; and performing, based on the one or more parameters, a conversion between the current video block and a bitstream representation of the current video block, wherein the one or more parameters are presented in the bitstream representation independently from values of at least one filter coefficient associated with the non-linear filtering operation.
  • the disclosed technology may be used to provide a method for visual media processing.
  • This method includes configuring, for a current video block, one or more parameters of a clipping operation that is part of a non-linear filtering operation; and performing, based on the one or more parameters, a conversion between the current video block and a bitstream representation of the current video block, wherein the current video block inherits filter coefficients from an i-th filter, and wherein a first rule associated with inheritance of the one or more parameters of the clipping operation is different from a second rule associated with inheritance of the filter coefficients.
  • the above-described method is embodied in the form of processor-executable code and stored in a computer-readable program medium.
  • a video encoder apparatus may implement a method as described herein.
  • a video decoder apparatus may implement a method as described herein.
  • FIG. 1 shows an example of an encoder block diagram for video coding.
  • FIGS. 2A, 2B and 2C show examples of geometry transformation-based adaptive loop filter (GALF) filter shapes.
  • GALF geometry transformation-based adaptive loop filter
  • FIG. 3 shows an example of a flow graph for a GALF encoder decision.
  • FIGS. 4A-4D show example subsampled Laplacian calculations for adaptive loop filter (ALF) classification.
  • ALF adaptive loop filter
  • FIG. 5 shows an example of neighboring samples utilized in a bilateral filter.
  • FIG. 6 shows an example of windows covering two samples utilized in a weight calculation.
  • FIG. 7 shows an example of a scan pattern.
  • FIGS. 8A-8C show flowcharts of exemplary methods for the temporal prediction of parameters in non-linear adaptive loop filtering.
  • FIG. 9 is a block diagram of an example of a hardware platform for implementing a video decoding or a video encoding technique described in the present document.
  • FIG. 10 is a block diagram of an example video processing system in which disclosed techniques may be implemented.
  • FIG. 11 shows a flowchart of an example method for visual media processing.
  • FIG. 12 shows a flowchart of an example method for visual media processing.
  • FIG. 13 shows a flowchart of an example method for visual media processing.
  • FIG. 14 shows a flowchart of an example method for visual media processing.
  • Video codecs typically include an electronic circuit or software that compresses or decompresses digital video, and are continually being improved to provide higher coding efficiency.
  • a video codec converts uncompressed video to a compressed format or vice versa.
  • the compressed format usually conforms to a standard video compression specification, e.g., the High Efficiency Video Coding (HEVC) standard (also known as H. 265 or MPEG-H Part 2) , the Versatile Video Coding (VVC) standard to be finalized, or other current and/or future video coding standards.
  • HEVC High Efficiency Video Coding
  • VVC Versatile Video Coding
  • Video coding standards have evolved primarily through the development of the well-known ITU-T and ISO/IEC standards.
  • the ITU-T produced H. 261 and H. 263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the two organizations jointly produced the H. 262/MPEG-2 Video and H. 264/MPEG-4 Advanced Video Coding (AVC) and H. 265/HEVC standards.
  • AVC H. 264/MPEG-4 Advanced Video Coding
  • H. 265/HEVC High Efficiency Video Coding
  • the video coding standards are based on the hybrid video coding structure wherein temporal prediction plus transform coding are utilized.
  • Joint Video Exploration Team JVET was founded by VCEG and MPEG jointly in 2015.
  • JVET Joint Exploration Model
  • Embodiments of the disclosed technology may be applied to existing video coding standards (e.g., HEVC, H. 265) and future standards to improve runtime performance.
  • Section headings are used in the present document to improve readability of the description and do not in any way limit the discussion or the embodiments (and/or implementations) to the respective sections only.
  • Color space also known as the color model (or color system)
  • color model is an abstract mathematical model which simply describes the range of colors as tuples of numbers, typically as 3 or 4 values or color components (e.g. RGB) .
  • color space is an elaboration of the coordinate system and sub-space.
  • YCbCr, Y′CbCr, or Y Pb/Cb Pr/Cr also written as YCBCR or Y'CBCR, is a family of color spaces used as a part of the color image pipeline in video and digital photography systems.
  • Y′ is the luma component and CB and CR are the blue-difference and red-difference chroma components.
  • Y′ (with prime) is distinguished from Y, which is luminance, meaning that light intensity is nonlinearly encoded based on gamma corrected RGB primaries.
  • Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance.
  • Each of the three Y'CbCr components have the same sample rate, thus there is no chroma subsampling. This scheme is sometimes used in high-end film scanners and cinematic post production.
  • the two chroma components are sampled at half the sample rate of luma, e.g. the horizontal chroma resolution is halved. This reduces the bandwidth of an uncompressed video signal by one-third with little to no visual difference.
  • Cb and Cr are cosited horizontally.
  • Cb and Cr are sited between pixels in the vertical direction (sited interstitially) .
  • Cb and Cr are sited interstitially, halfway between alternate luma samples.
  • Cb and Cr are co-sited in the horizontal direction. In the vertical direction, they are co-sited on alternating lines.
  • FIG. 1 shows an example of encoder block diagram of VVC, which contains three in-loop filtering blocks: deblocking filter (DF) , sample adaptive offset (SAO) and ALF.
  • DF deblocking filter
  • SAO sample adaptive offset
  • ALF utilize the original samples of the current picture to reduce the mean square errors between the original samples and the reconstructed samples by adding an offset and by applying a finite impulse response (FIR) filter, respectively, with coded side information signaling the offsets and filter coefficients.
  • FIR finite impulse response
  • ALF is located at the last processing stage of each picture and can be regarded as a tool trying to catch and fix artifacts created by the previous stages.
  • GAF geometry transformation-based adaptive loop filter
  • For the luma component one among 25 filters is selected for each 2 ⁇ 2 block, based on the direction and activity of local gradients.
  • up to three diamond filter shapes (as shown in FIGS. 2A, 2B and 2C for the 5 ⁇ 5 diamond, 7 ⁇ 7 diamond and 9 ⁇ 9 diamond, respectively) can be selected for the luma component.
  • An index is signalled at the picture level to indicate the filter shape used for the luma component.
  • the 5 ⁇ 5 diamond shape is always used.
  • Each 2 ⁇ 2 block is categorized into one out of 25 classes.
  • the classification index C is derived based on its directionality D and a quantized value of activity as follows:
  • Indices i and j refer to the coordinates of the upper left sample in the 2 ⁇ 2 block and R (i, j) indicates a reconstructed sample at coordinate (i, j) .
  • D maximum and minimum values of the gradients of horizontal and vertical directions are set as:
  • Step 1 If both and are true, D is set to 0.
  • Step 2 If continue from Step 3; otherwise continue from Step 4.
  • Step 3 If D is set to 2; otherwise D is set to 1.
  • the activity value A is calculated as:
  • A is further quantized to the range of 0 to 4, inclusively, and the quantized value is denoted as For both chroma components in a picture, no classification method is applied, i.e. a single set of ALF coefficients is applied for each chroma component.
  • K is the size of the filter and 0 ⁇ k, l ⁇ K-1 are coefficients coordinates, such that location (0, 0) is at the upper left corner and location (K-1, K-1) is at the lower right corner.
  • the transformations are applied to the filter coefficients f (k, l) depending on gradient values calculated for that block.
  • Table 1 The relationship between the transformation and the four gradients of the four directions are summarized in Table 1.
  • GALF filter parameters are signaled for the first CTU, i.e., after the slice header and before the SAO parameters of the first CTU. Up to 25 sets of luma filter coefficients could be signaled. To reduce bits overhead, filter coefficients of different classification can be merged. Also, the GALF coefficients of reference pictures are stored and allowed to be reused as GALF coefficients of a current picture. The current picture may choose to use GALF coefficients stored for the reference pictures, and bypass the GALF coefficients signaling. In this case, only an index to one of the reference pictures is signaled, and the stored GALF coefficients of the indicated reference picture are inherited for the current picture.
  • a candidate list of GALF filter sets is maintained. At the beginning of decoding a new sequence, the candidate list is empty. After decoding one picture, the corresponding set of filters may be added to the candidate list. Once the size of the candidate list reaches the maximum allowed value (i.e., 6 in current JEM) , a new set of filters overwrites the oldest set in decoding order, and that is, first-in-first-out (FIFO) rule is applied to update the candidate list. To avoid duplications, a set could only be added to the list when the corresponding picture doesn’t use GALF temporal prediction. To support temporal scalability, there are multiple candidate lists of filter sets, and each candidate list is associated with a temporal layer.
  • each array assigned by temporal layer index may compose filter sets of previously decoded pictures with equal to lower TempIdx.
  • the k-th array is assigned to be associated with TempIdx equal to k, and it only contains filter sets from pictures with TempIdx smaller than or equal to k. After coding a certain picture, the filter sets associated with the picture will be used to update those arrays associated with equal or higher TempIdx.
  • Temporal prediction of GALF coefficients is used for inter coded frames to minimize signaling overhead.
  • temporal prediction is not available, and a set of 16 fixed filters is assigned to each class.
  • a flag for each class is signaled and if required, the index of the chosen fixed filter.
  • the coefficients of the adaptive filter f (k, l) can still be sent for this class in which case the coefficients of the filter which will be applied to the reconstructed image are sum of both sets of coefficients.
  • the filtering process of luma component can controlled at CU level.
  • a flag is signaled to indicate whether GALF is applied to the luma component of a CU.
  • chroma component whether GALF is applied or not is indicated at picture level only.
  • each sample R (i, j) within the block is filtered, resulting in sample value R′ (i, j) as shown below, where L denotes filter length, f m, n represents filter coefficient, and f (k, l) denotes the decoded filter coefficients.
  • VTM4.0 the filtering process of the Adaptive Loop Filter, is performed as follows:
  • L denotes the filter length
  • w (i, j) are the filter coefficients in fixed point precision.
  • Equation (11) can be reformulated, without coding efficiency impact, in the following expression:
  • w (i, j) are the same filter coefficients as in equation (11) [excepted w (0, 0) which is equal to 1 in equation (13) while it is equal to 1- ⁇ (i, j) ⁇ (0, 0) w (i, j) in equation (11) ] .
  • the ALF filter is modified as follows:
  • O′ (x, y) I (x, y) + ⁇ (i, j) ⁇ (0, 0) w (i, j) ⁇ K (I (x+i, y+j) -I (x, y) , k (i, j) ) (14)
  • K (d, b) min (b, max (-b, d) ) is the clipping function, and k (i, j) are clipping parameters, which depends on the (i, j) filter coefficient.
  • the encoder performs the optimization to find the best k (i, j) . Note that for implementation in integer precision, shifting with rounding ⁇ (i, j) ⁇ (0, 0) w (i, j) ⁇ K (I (x+i, y+j) -I (x, y) , k (i, j) ) is applied.
  • the clipping parameters k (i, j) are specified for each ALF filter, one clipping value is signaled per filter coefficient. It means that up to 12 clipping values can be signalled in the bitstream per Luma filter and up to 6 clipping values for the Chroma filter.
  • the sets of clipping values used in the JVET-N0242 tests are provided in the Table 2.
  • the 4 values have been selected by roughly equally splitting, in the logarithmic domain, the full range of the sample values (coded on 10 bits) for Luma, and the range from 4 to 1024 for Chroma.
  • Luma table of clipping values More precisely, the Luma table of clipping values have been obtained by the following formula:
  • Chroma tables of clipping values is obtained according to the following formula:
  • the selected clipping values are coded in the “alf_data” syntax element by using a Golomb encoding scheme corresponding to the index of the clipping value in the above Table 2.
  • This encoding scheme is the same as the encoding scheme for the filter index.
  • Adaptive parameter set was adopted in VTM4.
  • Each APS contains one set of signalled ALF filters, up to 32 APSs are supported.
  • slice-level temporal filter is tested.
  • a tile group can re-use the ALF information from an APS to reduce the overhead.
  • the APSs are updated as a first-in-first-out (FIFO) buffer.
  • For luma component when ALF is applied to a luma CTB, the choice among 16 fixed, 5 temporal or 1 signaled filter sets (signalled in slice level) is indicated. Only the filter set index is signalled. For one slice, only one new set of 25 filters can be signaled. If a new set is signalled for a slice, all the luma CTBs in the same slice share that set. Fixed filter sets can be used to predict the new slice-level filter set and can be used as candidate filter sets for a luma CTB as well. The number of filters is 64 in total.
  • chroma component when ALF is applied to a chroma CTB, if a new filter is signalled for a slice, the CTB used the new filter, otherwise, the most recent temporal chroma filter satisfying the temporal scalability constrain is applied.
  • the APSs are updated as a first-in-first-out (FIFO) buffer.
  • diffusion filter is proposed, wherein the intra/inter prediction signal of the CU may be further modified by diffusion filters.
  • the Uniform Diffusion Filter is realized by convolving the prediction signal with a fixed mask that is either given as h I or as h IV , defined below. Besides the prediction signal itself, one line of reconstructed samples left and above of the block are used as an input for the filtered signal, where the use of these reconstructed samples can be avoided on inter blocks.
  • pred be the prediction signal on a given block obtained by intra or motion compensated prediction.
  • the prediction signal needs to be extended to a prediction signal pred ext .
  • This extended prediction can be formed in two ways:
  • one line of reconstructed samples left and above the block are added to the prediction signal and then the resulting signal is mirrored in all directions. Or only the prediction signal itself is mirrored in all directions.
  • the latter extension is used for inter blocks. In this case, only the prediction signal itself comprises the input for the extended prediction signal pred ext .
  • the filter mask h I is given as
  • h IV h I *h I *h I *h I .
  • Directional diffusion filter Instead of using signal adaptive diffusion filters, directional filters, a horizontal filter h hor and a vertical filter h ver , are used which still have a fixed mask. More precisely, the uniform diffusion filtering corresponding to the mask h I of the previous section is simply restricted to be either applied only along the vertical or along the horizontal direction.
  • the vertical filter is realized by applying the fixed filter mask
  • Bilateral filter is proposed in JVET-L0406, and it is always applied to luma blocks with non-zero transform coefficients and slice quantization parameter larger than 17. Therefore, there is no need to signal the usage of the bilateral filter.
  • Bilateral filter if applied, is performed on decoded samples right after the inverse transform.
  • the filter parameters i.e., weights are explicitly derived from the coded information.
  • the filtering process is defined as:
  • P 0, 0 is the intensity of the current sample and P′ 0, 0 is the modified intensity of the current sample, P k, 0 and W k are the intensity and weighting parameter for the k-th neighboring sample, respectively.
  • weight W k (x) associated with the k-th neighboring sample is defined as follows:
  • ⁇ d is dependent on the coded mode and coding block sizes.
  • the described filtering process is applied to intra-coded blocks, and inter-coded blocks when TU is further split, to enable parallel processing.
  • weights function resulted from Equation (2) are being adjusted by the ⁇ d parameter, tabulated in Table 4 as being dependent on coding mode and parameters of block partitioning (minimal size) .
  • Table 4 Value of ⁇ d for different block sizes and coding modes
  • P k, m and P 0, m represent the m-th sample value within the windows centered at P k, 0 and P 0, 0 , respectively.
  • the window size is set to 3 ⁇ 3.
  • An example of two windows covering P 2, 0 and P 0, 0 are depicted in FIG. 6.
  • JVET-K0068 in-loop filter in 1D Hadamard transform domain which is appl ied on CU level after reconstruction and has multiplication free implementation. Proposed filter is applied for all CU blocks that meet the predefined condition and filter parameters are derived from the coded information.
  • Proposed filtering is always applied to luma reconstructed blocks with non-zero transform coefficients, excluding 4x4 blocks and if slice quantization parameter is larger than 17.
  • the filter parameters are explicitly derived from the coded information.
  • Proposed filter, if applied, is performed on decoded samples right after inverse transform.
  • For each pixel from reconstructed block pixel processing comprises the following steps:
  • (i) is index of spectrum component in Hadamard spectrum
  • R (i) is spectrum component of reconstructed pixels corresponding to index
  • ⁇ is filtering parameter deriving from codec quantization parameter QP using following equation:
  • A is the current pixel and ⁇ B, C, D ⁇ are surrounding pixels.
  • the scan pattern is adjusted ensuring all required pixels are within current CU.
  • Virtual pipeline data units are defined as non-overlapping MxM-luma (L) /NxN-chroma (C) units in a picture.
  • L latitude
  • C NxN-chroma
  • VPDU size is roughly proportional to the buffer size in most pipeline stages, so it is said to be very important to keep the VPDU size small.
  • the VPDU size is set to the maximum transform block (TB) size.
  • Enlarging the maximum TB size from 32x32-L/16x16-C (as in HEVC) to 64x64-L/32x32-C (as in the current VVC) can bring coding gains, which results in 4X of VPDU size (64x64-L/32x32-C) expectedly in comparison with HEVC.
  • TT and BT splits can be applied to 128x128-L/64x64-C coding tree blocks (CTUs) recursively, which is said to lead to 16X of VPDU size (128x128-L/64x64-C) in comparison with HEVC.
  • the VPDU size is defined as 64x64-L/32x32-C.
  • the non-linear ALF (NLALF) design in JVET-N0242 has the following problems:
  • the classification process in GALF relies on the gradient and Laplacian activities which utilize the reconstructed samples before applying ALF.
  • the classification results may be inaccurate. For example, for one sample, differences between it and its neighbors may be quite similar while for another sample, difference between it and one neighbor may be too different and for all others, difference may be too small. For these two cases, they may be classified to one class index which may be unreasonable.
  • the clipping parameters are associated with the filter coefficient.
  • one filter may be utilized for multiple classes due to filter merging process.
  • the filter coefficients and clipping parameters are the same.
  • the two blocks may have different characteristics, for example, the selected geometric transformation may be different. Using same clipping parameters may be suboptimal.
  • one block may inherit the filter coefficients from previously coded frames. How to handle the clipping parameters need to be studied.
  • the clipping function K (d, b) min (b, max (-b, d) ) with b as the upper bounder and -b as the lower bound, d as the input.
  • the restriction of equal magnitudes for the upper and lower bounder may be suboptimal.
  • Embodiments of the presently disclosed technology overcome the drawbacks of existing implementations, thereby providing video coding with higher coding efficiencies.
  • the examples of the disclosed technology provided below explain general concepts, and are not meant to be interpreted as limiting. In an example, unless explicitly indicated to the contrary, the various features described in these examples may be combined.
  • one filter may be associated with multiple filter coefficients.
  • One set of filters represents multiple filters. Denote the i-th filter by F i and its associated filter coefficients by F i k, such as the variable k denotes the k-th filter coefficient associated with F i , e.g., it may be corresponding to Ck in FIG. 2.
  • NLALF parameters e.g., on/off control flag, clipping parameters
  • the NLALF parameters may be dependent on coded mode information.
  • NLALF parameters to be selected may be determined by the coded mode, such as intra or non-intra mode.
  • NLALF parameters to be selected may be determined by the coded mode, such as intra or inter mode.
  • NLALF parameters to be selected may be determined by the coded mode, such as IBC or non-IBC mode.
  • the NLALF parameters may be dependent on transform information.
  • they may be dependent on whether transform skip is applied or not.
  • the NLALF parameters may be dependent on residual information.
  • they may be dependent on whether the block contains non-zero coefficients.
  • the NLALF parameters may be dependent on tile group types/picture types.
  • the NLALF parameters may be dependent on temporal layer information/reference picture information associated with one tile/tile group/slice etc. al.
  • they may be dependent on whether all reference pictures are associated with smaller POC values compared to current picture.
  • ii may be dependent on whether all reference pictures are associated with smaller or equal POC values compared to current picture.
  • NLALF parameters e.g., on/off control flag, clipping parameters
  • NLALF parameters e.g., on/obiff control flag, clipping parameters
  • the associated NLALF parameters may be different.
  • indications of more than one clipping parameter may be signaled.
  • how many clipping parameters/or indices of clipping parameters or other representations of clipping parameters may be dependent on the number of allowed geometric transformations.
  • predictive coding of clipping parameters/indices of clipping parameters associated with one filter parameter may be applied.
  • a clipping parameter of one filter for one sample or block may be predicted by another clipping parameter of another filter used for a spatial/temporal adjacent or non-adjacent neighbouring sample or block.
  • indications of both upper bound and lower bound for one clipping function may be signaled.
  • each of them may be coded with N-bits (e.g., N is set to 2) .
  • N may be fixed
  • N may be signaled
  • N may depend on coding information, such as QP, picture dimensions and so on.
  • N may be fixed
  • N may be signaled
  • N may depend on coding information, such as QP, picture dimensions and so on.
  • they may be coded with Exponential-Golomb method but with fixed order for one filter/for one filter set.
  • d may be coded with run-length coding.
  • the index of a clipping parameter may be firstly coded as ‘run’ , and the number of consecutive same clipping parameter as ‘length’ .
  • the index of a clipping parameter associated with F i may be firstly coded as ‘run’ , and the number of same clipping parameter in other filters as ‘length’ .
  • predictive coding of indications of clipping parameters may be applied.
  • predictive coding may be applied for clipping parameters within one filter.
  • predictive coding may be applied for clipping parameters among different filters.
  • predictive coding may be applied for clipping parameters among different filters for one color component.
  • predictive coding may be applied for clipping parameters among different filters for multiple color component.
  • predictive coding may be applied for clipping parameters of filters used for different samples or blocks.
  • predictive coding may be applied for clipping parameters signaled in different APSs.
  • the parsing of clipping parameters is independent from the values of filter coefficients.
  • indication of the associated clipping parameter may be still signaled.
  • the associated clipping parameters with the i-th filter may be not inherited.
  • temporal prediction when temporal prediction is enabled for one block, instead of directly inheriting the associated clipping parameters, whether to use non-local ALF or not (applying clipping or not) may be signaled.
  • the associated clipping parameters may be also inherited.
  • the clipping parameters are inherited/predicted from the j-th filter, i may be unequal to j.
  • the filter coefficients are inherited/predicted from the i-th filter
  • the clipping parameters are inherited/predicted from the j-th filter
  • the i-th and j-th filter may be associated with different filter set.
  • the i-th filter may be associated with a first picture/tile group/tile/slice and the j-th filter may be associated with a second picture/tile group/tile/slice.
  • i is unequal to j.
  • i is equal to j.
  • indications of clipping parameters associated with which filter may be signaled such as the filter index.
  • indications of clipping parameters associated with which filter set may be signaled such as the APS index.
  • the filter index may be further signalled.
  • the clipped sample difference may be utilized.
  • clipped sample difference or clipped gradients may be used.
  • clipped sample difference or clipped gradients may be used.
  • V k, l
  • clip1 and clip2 are two clipping functions.
  • clip1 and clip2 are two clipping functions.
  • Whether to apply the clipping operations may depend on the locations of the samples (such as I (x+i, y+j) in Section 5.2) to be used in the filtering process.
  • clipping may be disabled if the sample in a filter support is not located a CU/PU/TU/picture/tile/tile group boundary.
  • VPDU Virtual Pipelining Data Unit
  • whether to apply the clipping operations may depend on the distance of the samples (such as I (x+i, y+j) in Section 5.2) to be used in the filtering process from the CU/PU/TU/picture/tile/tile group/CTU/VPDU boundary.
  • the distance may be pre-defined (e.g., N-pel) .
  • the distance may be signaled.
  • the filter shape (a.k.a. filter support) used in adaptive loop filter process may depend on the color representation.
  • the filter support for all components should be the same when the color format is 4: 4: 4.
  • the filter support is 7*7 diamond as shown in FIG. 2B.
  • the filter support is 5*5 diamond as shown in FIG. 2A.
  • the support area for all components when the color format is RGB.
  • the filter support is 7*7 diamond as shown in FIG. 2B.
  • the filter support is 5*5 diamond as shown in FIG. 2A.
  • methods 800, 810 and 820 may be implemented at a video decoder or a video encoder.
  • FIG. 8A shows a flowchart of an exemplary method for video processing.
  • the method 800 includes, at step 802, determining, based on a characteristic of a current video block, one or more parameters of a non-linear filtering operation.
  • the method 800 includes, at step 804, performing, based on the one or more parameters, a conversion between the current video block and a bitstream representation of the current video block.
  • the characteristic of the current video block is a coding mode of the current video block.
  • the coding mode of the current video block is an intra mode, a non-intra mode, an intra block copy (IBC) mode or a non-IBC mode.
  • the characteristic is transform information.
  • the transform information comprises an indication of transform skip being applied to the current video block.
  • the characteristic is residual information.
  • the residual information comprises zero-valued coefficients in the current video block.
  • the characteristic is a tile group type or a picture type of a tile group or a picture comprising the current video block.
  • the characteristic is temporal layer information or reference information associated with a tile, a tile group, a picture or a slice comprising the current video block.
  • the characteristic is a reference picture or motion information associated with the current video block.
  • the characteristic is a geometric transformation.
  • the one or more parameters comprises an on/off control flag or one or more parameters of a clipping function.
  • a magnitude of an upper bound of the clipping function is different from a magnitude of a lower bound of the clipping function.
  • predictive coding is applied between the upper bound and the lower bound of the clipping function.
  • FIG. 8B shows a flowchart of an exemplary method for video processing.
  • the method 810 includes, at step 812, configuring, for a current video block, one or more parameters of a clipping operation that is part of a non-linear filtering operation.
  • the method 810 includes, at step 814, performing, based on the one or more parameters, a conversion between the current video block and a bitstream representation of the current video block.
  • the one or more parameters is coded with a fixed length of N bits. In other embodiments, the one or more parameters is coded with a truncated unary method with a maximum value of N. In an example, N is fixed. In another example, N is signaled. In yet another example, N is based on coded information of the current video block that comprises a quantization parameter or a dimension of the picture comprising the current video block.
  • the one or more parameters is coded with an Exponential-Golomb method with a fixed order for one filter or filter set.
  • the one or more parameters is coded with run-length coding.
  • the one or more parameters is signaled independently from values of at least one filter coefficient.
  • the one or more parameters further comprises filter coefficients, wherein the current video block inherits the filter coefficients from an i-th filter, and wherein the one or more parameters of the clipping function are inherited from a j-th filter that is different from the i-th filter.
  • FIG. 8C shows a flowchart of an exemplary method for video processing.
  • the method 820 includes, at step 822, configuring a non-linear filtering operation that comprises a clipping operation.
  • the method 820 includes, at step 824, performing, based on the non-linear filtering operation, a conversion between a current video block and a bitstream representation of the current video block.
  • the method 820 further includes the step of performing a gradient calculation process that uses a clipped sample difference or a clipped gradient generated using the clipping operation. In other embodiments, the method 820 further includes the step of performing an activity calculation process that uses a clipped sample difference or a clipped gradient generated using the clipping operation.
  • performing the conversion comprises filtering one or more samples of the current video block, and an operation of the clipping operation is configured based on a location of the one or more samples.
  • the location of the one or more samples is a boundary of a coding unit (CU) , a prediction unit (PU) , a transform unit (TU) , a picture, a tile, a tile group, a coding tree unit (CTU) or a virtual pipelining data unit (VPDU) .
  • CU coding unit
  • PU prediction unit
  • TU transform unit
  • CTU coding tree unit
  • VPDU virtual pipelining data unit
  • a shape of a filter used in the non-linear filtering operation is based on a color representation.
  • the color representation comprises a 4: 4: 4 color format or an RGB color format.
  • the filter is a diamond shaped filter.
  • the non-linear filtering operation is a non-linear adaptive loop filtering operation.
  • FIG. 9 is a block diagram of a video processing apparatus 900.
  • the apparatus 900 may be used to implement one or more of the methods described herein.
  • the apparatus 900 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on.
  • the apparatus 900 may include one or more processors 902, one or more memories 904 and video processing hardware 906.
  • the processor (s) 902 may be configured to implement one or more methods (including, but not limited to, methods 800, 810 and 820) described in the present document.
  • the memory (memories) 904 may be used for storing data and code used for implementing the methods and techniques described herein.
  • the video processing hardware 906 may be used to implement, in hardware circuitry, some techniques described in the present document.
  • the video coding methods may be implemented using an apparatus that is implemented on a hardware platform as described with respect to FIG. 9.
  • FIG. 10 is a block diagram showing an example video processing system 1000 in which various techniques disclosed herein may be implemented.
  • the system 1000 may include input 1002 for receiving video content.
  • the video content may be received in a raw or uncompressed format, e.g., 8 or 10 bit multi-component pixel values, or may be in a compressed or encoded format.
  • the input 1002 may represent a network interface, a peripheral bus interface, or a storage interface. Examples of network interface include wired interfaces such as Ethernet, passive optical network (PON) , etc. and wireless interfaces such as Wi-Fi or cellular interfaces.
  • PON passive optical network
  • the system 1000 may include a coding component 1004 that may implement the various coding or encoding methods described in the present document.
  • the coding component 1004 may reduce the average bitrate of video from the input 1002 to the output of the coding component 1004 to produce a coded representation of the video.
  • the coding techniques are therefore sometimes called video compression or video transcoding techniques.
  • the output of the coding component 1004 may be either stored, or transmitted via a communication connected, as represented by the component 1006.
  • the stored or communicated bitstream (or coded) representation of the video received at the input 1002 may be used by the component 1008 for generating pixel values or displayable video that is sent to a display interface 1010.
  • the process of generating user-viewable video from the bitstream representation is sometimes called video decompression.
  • certain video processing operations are referred to as “coding” operations or tools, it will be appreciated that the coding tools or operations are used at an encoder and corresponding decoding tools or operations that reverse the results of the coding will be performed by
  • peripheral bus interface or a display interface may include universal serial bus (USB) or high definition multimedia interface (HDMI) or Displayport, and so on.
  • storage interfaces include SATA (serial advanced technology attachment) , PCI, IDE interface, and the like.
  • FIG. 11 shows a flowchart of an example method for visual media processing. Steps of this flowchart are discussed in connection with example 4 in Section 10 of this document.
  • the process configures, for a current video block, one or more parameters of a clipping operation that is part of a non-linear filtering operation.
  • the process performs, based on the one or more parameters, a conversion between the current video block and a bitstream representation of the current video block, wherein the one or more parameters is coded in accordance with a rule.
  • FIG. 12 shows a flowchart of an example method for visual media processing. Steps of this flowchart are discussed in connection with example 1 in Section 10 of this document.
  • the process determines, based on a characteristic of a current video block, one or more parameters of a non-linear filtering operation.
  • the process performs, based on the one or more parameters, a conversion between the current video block and a bitstream representation of the current video block.
  • FIG. 13 shows a flowchart of an example method for visual media processing. Steps of this flowchart are discussed in connection with example 5 in Section 10 of this document.
  • the process configures, for a current video block, one or more parameters of a clipping operation that is part of a non-linear filtering operation.
  • the process performs, based on the one or more parameters, a conversion between the current video block and a bitstream representation of the current video block, wherein the one or more parameters are presented in the bitstream representation independently from values of at least one filter coefficient associated with the non-linear filtering operation.
  • FIG. 14 shows a flowchart of an example method for visual media processing. Steps of this flowchart are discussed in connection with example 6 in Section 10 of this document.
  • the process configures, for a current video block, one or more parameters of a clipping operation that is part of a non-linear filtering operation.
  • the process performs, based on the one or more parameters, a conversion between the current video block and a bitstream representation of the current video block, wherein the current video block inherits filter coefficients from an i-th filter, and wherein a first rule associated with inheritance of the one or more parameters of the clipping operation is different from a second rule associated with inheritance of the filter coefficients.
  • a method for visual media processing comprising:
  • N is based on coded information of the current video block that comprises a quantization parameter or a dimension of the picture comprising the current video block.
  • non-linear filtering operation is an adaptive loop filter (ALF) operation which comprises determining a filter index based on gradient calculations in different directions.
  • ALF adaptive loop filter
  • a method for visual media processing comprising:
  • non-linear filtering operation is an adaptive loop filter (ALF) operation which comprises determining a filter index based on gradient calculations in different directions.
  • ALF adaptive loop filter
  • a video encoder apparatus comprising a processor configured to implement a method recited in any one or more of clauses A1-B25.
  • a video decoder apparatus comprising a processor configured to implement a method recited in any one or more of clauses A1-B25.
  • a method for visual media processing comprising:
  • non-linear filtering operation is an adaptive loop filter (ALF) operation which comprises determining a filter index based on gradient calculations in different directions.
  • ALF adaptive loop filter
  • a method for visual media processing comprising:
  • V_ (k, l)
  • H_ (k, l)
  • non- linear filtering operation is an adaptive loop filtering (ALF) operation which comprises determining a filter index based on gradient calculations in different directions.
  • ALF adaptive loop filtering
  • a video encoder apparatus comprising a processor configured to implement a method recited in any one or more of clauses C1-D26.
  • a video decoder apparatus comprising a processor configured to implement a method recited in any one or more of clauses C1-D26.
  • a computer readable medium having code stored thereon, the code embodying processor-executable instructions for implementing a method recited in any of or more of clauses C1-D26.
  • video processing or “visual media processing” or “processing of visual media” may refer to video encoding, video decoding, video compression or video decompression.
  • video compression algorithms may be applied during conversion from pixel representation of a video to a corresponding bitstream representation or vice versa.
  • the bitstream representation of a current video block may, for example, correspond to bits that are either co-located or spread in different places within the bitstream, as is defined by the syntax.
  • a macroblock may be encoded in terms of transformed and coded error residual values and also using bits in headers and other fields in the bitstream.
  • a decoder may parse a bitstream with the knowledge that some fields may be present, or absent, based on the determination, as is described in the above solutions.
  • an encoder may determine that certain syntax fields are or are not to be included and generate the coded representation accordingly by including or excluding the syntax fields from the coded representation.
  • Implementations of the subject matter and the functional operations described in this patent document can be implemented in various systems, digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible and non-transitory computer readable medium for execution by, or to control the operation of, data processing apparatus.
  • the computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them.
  • data processing unit or “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers.
  • the apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.
  • a computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.
  • a computer program does not necessarily correspond to a file in a file system.
  • a program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document) , in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code) .
  • a computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.
  • the processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output.
  • the processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit) .
  • processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer.
  • a processor will receive instructions and data from a read only memory or a random access memory or both.
  • the essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data.
  • a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks.
  • mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks.
  • a computer need not have such devices.
  • Computer readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices.
  • semiconductor memory devices e.g., EPROM, EEPROM, and flash memory devices.
  • the processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

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