Patent Application
20210105506
This disclosure relates to video coding and more particularly to techniques for performing deblocking of reconstructed video data.
Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, laptop or desktop computers, tablet computers, digital recording devices, digital media players, video gaming devices, cellular telephones, including so-called smartphones, medical imaging devices, and the like. Digital video may be coded according to a video coding standard. Video coding standards define the format of a compliant bitstream encapsulating coded video data. A compliant bitstream is a data structure that may be received and decoded by a video decoding device to generate reconstructed video data. Video coding standards may incorporate video compression techniques. Examples of video coding standards include ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC) and High-Efficiency Video Coding (HEVC). HEVC is described in High Efficiency Video Coding (HEVC), Rec. ITU-T H.265, December 2016, which is incorporated by reference, and referred to herein as ITU-T H.265. Extensions and improvements for ITU-T H.265 are currently being considered for the development of next generation video coding standards. For example, the ITU-T Video Coding Experts Group (VCEG) and ISO/IEC (Moving Picture Experts Group (MPEG) (collectively referred to as the Joint Video Exploration Team (JVET)) are working to standardized video coding technology with a compression capability that significantly exceeds that of the current HEVC standard. The Joint Exploration Model 7 (JEM 7), Algorithm Description of Joint Exploration Test Model 7 (JEM 7), ISO/IEC JTC1/SC29/WG11 Document: JVET-G1001, July 2017, Torino, IT, which is incorporated by reference herein, describes the coding features that were under coordinated test model study by the JVET as potentially enhancing video coding technology beyond the capabilities of ITU-T H.265. It should be noted that the coding features of JEM 7 are implemented in JEM reference software. As used herein, the term JEM may collectively refer to algorithms included in JEM 7 and implementations of JEM reference software. Further, in response to a “Joint Call for Proposals on Video Compression with Capabilities beyond HEVC,” jointly issued by VCEG and MPEG, multiple descriptions of video coding tools were proposed by various groups at the 10th Meeting of ISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018, San Diego, Calif. From the multiple descriptions of video coding tools, a resulting initial draft text of a video coding specification is described in “Versatile Video Coding (Draft 1),” 10th Meeting of ISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018, San Diego, Calif., document JVET-J1001-v2, which is incorporated by reference herein, and referred to as JVET-J1001. The current development of a next generation video coding standard by the VCEG and MPEG is referred to as the Versatile Video Coding (VVC) project. “Versatile Video Coding (Draft 5),” 14th Meeting of ISO/IEC JTC1/SC29/WG11 19-27 Mar. 2019, Geneva, CH, document JVET-N1001-v8, which is incorporated by reference herein, and referred to as JVET-N1001, represents an iteration of the draft text of a video coding specification corresponding to the VVC project.
Video compression techniques enable data requirements for storing and transmitting video data to be reduced. Video compression techniques may reduce data requirements by exploiting the inherent redundancies in a video sequence. Video compression techniques may sub-divide a video sequence into successively smaller portions (i.e., groups of pictures within a video sequence, a picture within a group of pictures, regions within a picture, sub-regions within regions, etc.). Intra prediction coding techniques (e.g., spatial prediction techniques within a picture) and inter prediction techniques (i.e., inter-picture techniques (temporal)) may be used to generate difference values between a unit of video data to be coded and a reference unit of video data. The difference values may be referred to as residual data. Residual data may be coded as quantized transform coefficients. Syntax elements may relate residual data and a reference coding unit (e.g., intra-prediction mode indices, and motion information). Residual data and syntax elements may be entropy coded. Entropy encoded residual data and syntax elements may be included in data structures forming a compliant bitstream.
In one example, a method of filtering reconstructed video data, the method comprising: receiving a slice header; parsing a syntax element, from the slice header, specifying a first offset for a deblocking parameter applied to a luma component for a current slice, wherein the first offset is distinct from a second offset for a deblocking parameter applied to a chroma component; determining a threshold value based on the syntax element; and applying a deblocking filter based on the threshold value.
In one example, a device for decoding video data, the device comprising one or more processors configured to: receive a slice header; parse a syntax element, from the slice header, specifying a first offset for a deblocking parameter applied to a luma component for a current slice, wherein the first offset is distinct from a second offset for a deblocking parameter applied to a chroma component; determine a threshold value based on the syntax element; and apply a deblocking filter based on the threshold value.
In general, this disclosure describes various techniques for coding video data. In particular, this disclosure describes techniques for performing deblocking of reconstructed video data. It should be noted that although techniques of this disclosure are described with respect to ITU-T H.264, ITU-T H.265, JEM, and JVET-N1001 the techniques of this disclosure are generally applicable to video coding. For example, the coding techniques described herein may be incorporated into video coding systems, (including video coding systems based on future video coding standards) including video block structures, intra prediction techniques, inter prediction techniques, transform techniques, filtering techniques, and/or entropy coding techniques other than those included in ITU-T H.265, JEM, and JVET-N1001. Thus, reference to ITU-T H.264, ITU-T H.265, JEM, and/or JVET-N1001 is for descriptive purposes and should not be construed to limit the scope of the techniques described herein. Further, it should be noted that incorporation by reference of documents herein is for descriptive purposes and should not be construed to limit or create ambiguity with respect to terms used herein. For example, in the case where an incorporated reference provides a different definition of a term than another incorporated reference and/or as the term is used herein, the term should be interpreted in a manner that broadly includes each respective definition and/or in a manner that includes each of the particular definitions in the alternative.
In one example, a device for video coding comprises one or more processors configured to receive arrays of sample values including adjacent reconstructed video blocks for respective luma and chroma channels of video data, for each of a horizontal and vertical direction, determine whether the number of chroma samples is half of or equal to the number of luma samples, select lines for computing gradients for determining blockiness for chroma based on the determination, determine blockiness based on the selected lines, and modify sample values in the adjacent reconstructed video blocks based on the determined blockiness according to a deblocking filter.
In one example, a non-transitory computer-readable storage medium comprises instructions stored thereon that, when executed, cause one or more processors of a device to receive arrays of sample values including adjacent reconstructed video blocks for respective luma and chroma channels of video data, for each of a horizontal and vertical direction, determine whether the number of chroma samples is half of or equal to the number of luma samples, select lines for computing gradients for determining blockiness for chroma based on the determination, determine blockiness based on the selected lines, and modify sample values in the adjacent reconstructed video blocks based on the determined blockiness according to a deblocking filter.
In one example, an apparatus comprises means for receiving arrays of sample values including adjacent reconstructed video blocks for respective luma and chroma channels of video data, means for determining whether the number of chroma samples is half of or equal to the number of luma samples for each of a horizontal and vertical direction, means for selecting lines for computing gradients for determining blockiness for chroma based on the determination, means for determining blockiness based on the selected lines, and means for modifying sample values in the adjacent reconstructed video blocks based on the determined blockiness according to a deblocking filter.
The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.
Video content includes video sequences comprised of a series of frames (or pictures). A series of frames may also be referred to as a group of pictures (GOP). Each video frame or picture may be divided into one or more regions. Regions may be defined according to a base unit (e.g., a video block) and sets of rules defining a region. For example, a rule defining a region may be that a region must be an integer number of video blocks arranged in a rectangle. Further, video blocks in a region may be ordered according to a scan pattern (e.g., a raster scan). As used herein, the term video block may generally refer to an area of a picture or may more specifically refer to the largest array of sample values that may be predictively coded, sub-divisions thereof, and/or corresponding structures. Further, the term current video block may refer to an area of a picture being encoded or decoded. A video block may be defined as an array of sample values. It should be noted that in some cases pixel values may be described as including sample values for respective components of video data, which may also be referred to as color components, (e.g., luma (Y) and chroma (Cb and Cr) components or red, green, and blue components). It should be noted that in some cases, the terms pixel value and sample value are used interchangeably. Further, in some cases, a pixel or sample may be referred to as a pel. A video sampling format, which may also be referred to as a chroma format, may define the number of chroma samples included in a video block with respect to the number of luma samples included in a video block.
A video encoder may perform predictive encoding on video blocks and sub-divisions thereof. Video blocks and sub-divisions thereof may be referred to as nodes. ITU-T H.264 specifies a macroblock including 16×16 luma samples. That is, in ITU-T H.264, a picture is segmented into macroblocks. ITU-T H.265 specifies an analogous Coding Tree Unit (CTU) structure (which may be referred to as a largest coding unit (LCU)). In ITU-T H.265, pictures are segmented into CTUs. In ITU-T H.265, for a picture, a CTU size may be set as including 16×16, 32×32, or 64×64 luma samples. In ITU-T H.265, a CTU is composed of respective Coding Tree Blocks (CTB) for each component of video data (e.g., luma (Y) and chroma (Cb and Cr). It should be noted that video having one luma component and the two corresponding chroma components may be described as having two channels, i.e., a luma channel and a chroma channel. Further, in ITU-T H.265, a CTU may be partitioned according to a quadtree (QT) partitioning structure, which results in the CTBs of the CTU being partitioned into Coding Blocks (CB). That is, in ITU-T H.265, a CTU may be partitioned into quadtree leaf nodes. According to ITU-T H.265, one luma CB together with two corresponding chroma CBs and associated syntax elements are referred to as a coding unit (CU). In ITU-T H.265, a minimum allowed size of a CB may be signaled. In ITU-T H.265, the smallest minimum allowed size of a luma CB is 8×8 luma samples. In ITU-T H.265, the decision to code a picture area using intra prediction or inter prediction is made at the CU level.
In ITU-T H.265, a CU is associated with a prediction unit (PU) structure having its root at the CU. In ITU-T H.265, PU structures allow luma and chroma CBs to be split for purposes of generating corresponding reference samples. That is, in ITU-T H.265, luma and chroma CBs may be split into respective luma and chroma prediction blocks (PBs), where a PB includes a block of sample values for which the same prediction is applied. In ITU-T H.265, a CB may be partitioned into 1, 2, or 4 PBs. ITU-T H.265 supports PB sizes from 64×64 samples down to 4×4 samples. In ITU-T H.265, square PBs are supported for intra prediction, where a CB may form the PB or the CB may be split into four square PBs. In ITU-T H.265, in addition to the square PBs, rectangular PBs are supported for inter prediction, where a CB may be halved vertically or horizontally to form PBs. Further, it should be noted that in ITU-T H.265, for inter prediction, four asymmetric PB partitions are supported, where the CB is partitioned into two PBs at one quarter of the height (at the top or the bottom) or width (at the left or the right) of the CB. Intra prediction data (e.g., intra prediction mode syntax elements) or inter prediction data (e.g., motion data syntax elements) corresponding to a PB is used to produce reference and/or predicted sample values for the PB.
JEM specifies a CTU having a maximum size of 256×256 luma samples. JEM specifies a quadtree plus binary tree (QTBT) block structure. In JEM, the QTBT structure enables quadtree leaf nodes to be further partitioned by a binary tree (BT) structure. That is, in JEM, the binary tree structure enables quadtree leaf nodes to be recursively divided vertically or horizontally. In JVET-N1001, CTUs are partitioned according a quadtree plus multi-type tree (QTMT or QT+MTT) structure. The QTMT in JVET-N1001 is similar to the QTBT in JEM. However, in JVET-N1001, in addition to indicating binary splits, the multi-type tree may indicate so-called ternary (or triple tree (TT)) splits. A ternary split divides a block vertically or horizontally into three blocks. In the case of a vertical TT split, a block is divided at one quarter of its width from the left edge and at one quarter its width from the right edge and in the case of a horizontal TT split a block is divided at one quarter of its height from the top edge and at one quarter of its height from the bottom edge. Referring again to
As described above, each video frame or picture may be divided into one or more regions. For example, according to ITU-T H.265, each video frame or picture may be partitioned to include one or more slices and further partitioned to include one or more tiles, where each slice includes a sequence of CTUs (e.g., in raster scan order) and where a tile is a sequence of CTUs corresponding to a rectangular area of a picture. It should be noted that a slice, in ITU-T H.265, is a sequence of one or more slice segments starting with an independent slice segment and containing all subsequent dependent slice segments (if any) that precede the next independent slice segment (if any). A slice segment, like a slice, is a sequence of CTUs. Thus, in some cases, the terms slice and slice segment may be used interchangeably to indicate a sequence of CTUs arranged in a raster scan order. Further, it should be noted that in ITU-T H.265, a tile may consist of CTUs contained in more than one slice and a slice may consist of CTUs contained in more than one tile. However, ITU-T H.265 provides that one or both of the following conditions shall be fulfilled: (1) All CTUs in a slice belong to the same tile; and (2) All CTUs in a tile belong to the same slice.
With respect to JVET-N1001, slices are required to consist of an integer number of bricks instead of only being required to consist of an integer number of CTUs. In JVET-N1001, a brick is a rectangular region of CTU rows within a particular tile in a picture. Further, in JVET-N1001, a tile may be partitioned into multiple bricks, each of which consisting of one or more CTU rows within the tile. A tile that is not partitioned into multiple bricks is also referred to as a brick. However, a brick that is a true subset of a tile is not referred to as a tile. As such, a slice including a set of CTUs which do not form a rectangular region of a picture may or may not be supported in some video coding techniques. Further, it should be noted that in some cases, a slice may be required to consist of an integer number of complete tiles and in this case is referred to as a tile group. The techniques described herein may be applicable to bricks, slices, tiles, and/or tile groups.
For intra prediction coding, an intra prediction mode may specify the location of reference samples within a picture. In ITU-T H.265, defined possible intra prediction modes include a planar (i.e., surface fitting) prediction mode, a DC (i.e., flat overall averaging) prediction mode, and 33 angular prediction modes (predMode: 2-34). In JEM, defined possible intra-prediction modes include a planar prediction mode, a DC prediction mode, and 65 angular prediction modes. It should be noted that planar and DC prediction modes may be referred to as non-directional prediction modes and that angular prediction modes may be referred to as directional prediction modes. It should be noted that the techniques described herein may be generally applicable regardless of the number of defined possible prediction modes.
For inter prediction coding, a reference picture is determined and a motion vector (MV) identifies samples in the reference picture that are used to generate a prediction for a current video block. For example, a current video block may be predicted using reference sample values located in one or more previously coded picture(s) and a motion vector is used to indicate the location of the reference block relative to the current video block. A motion vector may describe, for example, a horizontal displacement component of the motion vector (i.e., MVx), a vertical displacement component of the motion vector (i.e., MVy), and a resolution for the motion vector (e.g., one-quarter pixel precision, one-half pixel precision, one-pixel precision, two-pixel precision, four-pixel precision). Previously decoded pictures, which may include pictures output before or after a current picture, may be organized into one or more to reference pictures lists and identified using a reference picture index value. Further, in inter prediction coding, uni-prediction refers to generating a prediction using sample values from a single reference picture and bi-prediction refers to generating a prediction using respective sample values from two reference pictures. That is, in uni-prediction, a single reference picture and corresponding motion vector are used to generate a prediction for a current video block and in bi-prediction, a first reference picture and corresponding first motion vector and a second reference picture and corresponding second motion vector are used to generate a prediction for a current video block. In bi-prediction, respective sample values are combined (e.g., added, rounded, and clipped, or averaged according to weights) to generate a prediction. Pictures and regions thereof may be classified based on which types of prediction modes may be utilized for encoding video blocks thereof. That is, for regions having a B type (e.g., a B slice), bi-prediction, uni-prediction, and intra prediction modes may be utilized, for regions having a P type (e.g., a P slice), uni-prediction, and intra prediction modes may be utilized, and for regions having an I type (e.g., an I slice), only intra prediction modes may be utilized. As described above, reference pictures are identified through reference indices. For example, for a P slice, there may be a single reference picture list, RefPicList0 and for a B slice, there may be a second independent reference picture list, RefPicList1, in addition to RefPicList0. It should be noted that for uni-prediction in a B slice, one of RefPicList0 or RefPicList1 may be used to generate a prediction. Further, it should be noted that during the decoding process, at the onset of decoding a picture, reference picture list(s) are generated from previously decoded pictures stored in a decoded picture buffer (DPB). Further, a coding standard may support various modes of motion vector prediction. Motion vector prediction enables the value of a motion vector for a current video block to be derived based on another motion vector. For example, a set of candidate blocks having associated motion information may be derived from spatial neighboring blocks and temporal neighboring blocks to the current video block. Further, generated (or default) motion information may be used for motion vector prediction. Examples of motion vector prediction include advanced motion vector prediction (AMVP), temporal motion vector prediction (TMVP), so-called “merge” mode, and “skip” and “direct” motion inference. Further, other examples of motion vector prediction include advanced temporal motion vector prediction (ATMVP) and Spatial-temporal motion vector prediction (STMVP). For motion vector prediction, both a video encoder and video decoder perform the same process to derive a set of candidates. Thus, for a current video block, the same set of candidates is generated during encoding and decoding.
As described above, for inter prediction coding, reference samples in a previously coded picture are used for coding video blocks in a current picture. Previously coded pictures which are available for use as reference when coding a current picture are referred as reference pictures. It should be noted that the decoding order does not necessary correspond with the picture output order, i.e., the temporal order of pictures in a video sequence. In ITU-T H.265, when a picture is decoded it is stored to a decoded picture buffer (DPB) (which may be referred to as frame buffer, a reference buffer, a reference picture buffer, or the like). In ITU-T H.265, pictures stored to the DPB are removed from the DPB when they have been output and are no longer needed for coding subsequent pictures. In ITU-T H.265, a determination of whether pictures should be removed from the DPB is invoked once per picture, after decoding a slice header, i.e., at the onset of decoding a picture. For example, referring to
As described above, intra prediction data or inter prediction data is used to produce reference sample values for a block of sample values. The difference between sample values included in a current PB, or another type of picture area structure, and associated reference samples (e.g., those generated using a prediction) may be referred to as residual data. Residual data may include respective arrays of difference values corresponding to each component of video data. Residual data may be in the pixel domain. A transform, such as, a discrete cosine transform (DCT), a discrete sine transform (DST), an integer transform, a wavelet transform, or a conceptually similar transform, may be applied to an array of difference values to generate transform coefficients. It should be noted that in ITU-T H.265 and JVET-N1001, a CU is associated with a transform unit (TU) structure having its root at the CU level. That is, an array of difference values may be partitioned for purposes of generating transform coefficients (e.g., four 8×8 transforms may be applied to a 16×16 array of residual values). For each component of video data, such sub-divisions of difference values may be referred to as Transform Blocks (TBs). It should be noted that in some cases, a core transform and a subsequent secondary transforms may be applied (in the video encoder) to generate transform coefficients. For a video decoder, the order of transforms is reversed.
A quantization process may be performed on transform coefficients or residual sample values directly (e.g., in the case, of palette coding quantization). Quantization approximates transform coefficients by amplitudes restricted to a set of specified values. Quantization essentially scales transform coefficients in order to vary the amount of data required to represent a group of transform coefficients. Quantization may include division of transform coefficients (or values resulting from the addition of an offset value to transform coefficients) by a quantization scaling factor and any associated rounding functions (e.g., rounding to the nearest integer). Quantized transform coefficients may be referred to as coefficient level values. Inverse quantization (or “dequantization”) may include multiplication of coefficient level values by the quantization scaling factor, and any reciprocal rounding or offset addition operations. It should be noted that as used herein the term quantization process in some instances may refer to division by a scaling factor to generate level values and multiplication by a scaling factor to recover transform coefficients in some instances. That is, a quantization process may refer to quantization in some cases and inverse quantization in some cases. Further, it should be noted that although in some of the examples below quantization processes are described with respect to arithmetic operations associated with decimal notation, such descriptions are for illustrative purposes and should not be construed as limiting. For example, the techniques described herein may be implemented in a device using binary operations and the like. For example, multiplication and division operations described herein may be implemented using bit shifting operations and the like.
Quantized transform coefficients and syntax elements (e.g., syntax elements indicating a coding structure for a video block) may be entropy coded according to an entropy coding technique. An entropy coding process includes coding values of syntax elements using lossless data compression algorithms. Examples of entropy coding techniques include content adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), probability interval partitioning entropy coding (PIPE), and the like. Entropy encoded quantized transform coefficients and corresponding entropy encoded syntax elements may form a compliant bitstream that can be used to reproduce video data at a video decoder. An entropy coding process, for example, CABAC, may include performing a binarization on syntax elements. Binarization refers to the process of converting a value of a syntax element into a series of one or more bits. These bits may be referred to as “bins.” Binarization may include one or a combination of the following coding techniques: fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, k-th order exponential Golomb coding, and Golomb-Rice coding. For example, binarization may include representing the integer value of 5 for a syntax element as 00000101 using an 8-bit fixed length binarization technique or representing the integer value of 5 as 11110 using a unary coding binarization technique. As used herein each of the terms fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, k-th order exponential Golomb coding, and Golomb-Rice coding may refer to general implementations of these techniques and/or more specific implementations of these coding techniques. For example, a Golomb-Rice coding implementation may be specifically defined according to a video coding standard. In the example of CABAC, for a particular bin, a context provides a most probable state (MPS) value for the bin (i.e., an MPS for a bin is one of 0 or 1) and a probability value of the bin being the MPS or the least probably state (LPS). For example, a context may indicate, that the MPS of a bin is 0 and the probability of the bin being 1 is 0.3. It should be noted that a context may be determined based on values of previously coded bins including bins in the current syntax element and previously coded syntax elements. For example, values of syntax elements associated with neighboring video blocks may be used to determine a context for a current bin.
Further, as illustrated in
As described above, a video sampling format, which may also be referred to as a chroma format, may define the number of chroma samples included in a video block with respect to the number of luma samples included in a video block. For example, for the 4:2:0 sampling format, the sampling rate for the luma component is twice that of the chroma components for both the horizontal and vertical directions. As a result, for a CU formatted according to the 4:2:0 format, the width and height of an array of samples for the luma component are twice that of each array of samples for the chroma components.
It should be noted that for a sampling format, e.g., a 4:2:0 sample format, a chroma location type may be specified. That is, for example for the 4:2:0 sample format, horizontal and vertical offset values which indicate relative spatial positioning may be specified for chroma samples with respect to luma samples. Table 2 provides a definition of HorizontalOffsetC and VerticalOffsetC for the 5 chroma location types provided in JVET-N1001. Further,
With respect to the equations used herein, the following arithmetic operators may be used:
Used to denote division in mathematical equations where no truncation or rounding is intended.
Further, the following logical operators may be used:
Further, the following relational operators may be used:
Further, the following bit-wise operators may be used:
Further, the following assignment operators may be used:
Further, the following defined mathematical functions may be used:
As described above, with respect to the examples illustrated in
Deblocking (or de-blocking), deblock filtering, or applying a deblocking filter refers to the process of smoothing the boundaries of neighboring reconstructed video blocks (i.e., making boundaries less perceptible to a viewer). Smoothing the boundaries of neighboring reconstructed video blocks may include modifying sample values included in rows or columns adjacent to a boundary. ITU-T H.265 provides where a deblocking filter is applied to reconstructed sample values as part of an in-loop filtering process. ITU-T H.265 includes two types deblocking filters that may be used for modifying luma samples: a Strong Filter which modifies sample values in the three adjacent rows or columns to a boundary and a Weak Filter which modifies sample values in the immediately adjacent row or column to a boundary and conditionally modifies sample values in the second row or column from the boundary. Further, ITU-T H.265 includes one type of filter that may be used for modifying chroma samples: Normal Filter. JVET-N1001 similarly provides where a deblocking filter is applied to reconstructed sample values as part of an in-loop filtering process.
Inputs to this process are:
Outputs of this process are:
Depending on the value of dE, the following applies:
When nDp is greater than 0 and one or more of the following conditions are true, nDp is set equal to 0:
When nDq is greater than 0 and one or more of the following conditions are true, nDq is set equal to 0:
JVET-N1001 specifies the luma long filter process as follows:
Inputs to this process are:
Outputs of this process are:
The variable refMiddle is derived as follows:
The variables refP and refQ are derived as follows:
The variables fi and tCPDi are defined as follows:
The variables gj and tCQDj are defined as follows:
The filtered sample values p1′ and qj′ with i=0..maxFilterLengthP−1 and j=0..maxFilterLengthQ−1 are derived as follows:
pi′=Clip3(pi−(tC*tCPDi)>>1, pi+(tC*tCPDi)>>1, (refMiddle*fi+refP*(64−fi)+32)>>6)
qj′=Clip3(qj−(tC*tCQDj)>>1, qi+(tC*tCQDj)>>1, (refMiddle*gj+refQ*(64−gj)+32)>>6)
When one or more of the following conditions are true, the filtered sample value, pi′ is substituted by the corresponding input sample value piwith i=0..maxFilterLengthP−1:
When one or more of the following conditions are true, the filtered sample value, qi′ is substituted by the corresponding input sample value qj with j=0..maxFilterLengthQ 1:
JVET-N1001 further specifies a chroma filter process a follows:
This process is only invoked when ChromaArrayType is not equal to 0.
Inputs to this process are:
Outputs of this process are the filtered sample values p1′ and q1′ with i=0..maxFilterLengthCbCr−1.
The filtered sample values p1′ and q1′ with i=0..maxFilterLengthCbCr 1 are derived as follows:
p0′=Clip3(p0−tC, p0+tC, (p3+p2+p1+2*p0+q0+q1+q2+4)>>3)
p1′=Clip3(p1−tC, p1+tC, (2*p3+p2+2*p1+p0+q0+q1+4)>>3)
p2′=Clip3(p2−tC, p2+tC, (3*p3+2*p2+p1+p0+q0+4)>>3)
q0′=Clip3(q0−tC, q0+tC, (p2+p1+p02*q0+q1+q2+q3+4)>>3)
q1′=Clip3(q1−tC, q1+tC, (p1+p0+q0+2*q1+q2+2*q3+4)>>3)
q2′=Clip3(q2−tC, q2+tC, (p0+q0+q1+2*q2+3*q3+4)>>3)
When one or more of the following conditions are true, the filtered sample value, pi′ is substituted by the corresponding input sample value pi with i=0..maxFilterLengthCbCr−1:
When one or more of the following conditions are true, the filtered sample value, q1′ is substituted by the corresponding input sample value qi with i=0..maxFilterLengthCbCr−1:
As indicated in the filter processes above, a variable tc, and, in the case of the luma long filter, a variable dE, and the variables dEp and dEq are used as input. In JVET-N1001, for luma, the variable tc, a variable dE, and the variables dEp and dEq are determined according to a decision process for block edge as follows:
Inputs to this process are:
Outputs of this process are:
The sample values pi,k and qj,k with i=0..maxFilterLengthP, j=0..maxFilterLengthQ and k=0 and 3 are derived as follows:
The variable qpOffset is derived as follows:
The variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,0, respectively.
The variable qP is derived as follows:
The value of the variable β′ is determined as specified in the Table illustrated in
where slice_beta_offset_div2 is the value of the syntax element slice_beta_offset_div2 for the slice that contains sample q0,0.
The variable 6 is derived as follows:
The value of the variable tC′ is determined as specified Table the illustrated in
where slice_tc_offset_div2 is the value of the syntax element slice_tc_offset_div2 for the slice that contains sample q0,0.
The variable tC is derived as follows:
The following ordered steps apply:
Decision Process for a Luma Sample
Inputs to this process are:
Output of this process is the variable dSam containing a decision.
The variables sp and sq are modified as follows:
The variable sThr is derived as follows:
The variable dSam is specified as follows:
In JVET-N1001, for chroma, the variable tC is determined according to a decision process for block edge as follows:
This process is only invoked when ChromaArrayType is not equal to 0.
Inputs to this process are:
Outputs of this process are
The values pi and qi with i=0.. maxFilterLengthCbCr and k=0..1 are derived as follows:
The variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,0 respectively.
The variable QpC is derived as follows:
If ChromaArrayType is equal to 1, the variable QpC is determined as specified in Table 3 based on the index qPi derived as follows:
NOTE—The variable cQpPicOffset provides an adjustment for the value of pps_cb_qp_offset or pps_cr_qp_offset, according to whether the filtered chroma component is the Cb or Cr component. However, to avoid the need to vary the amount of the adjustment within the picture, the filtering process does not include an adjustment for the value of slice_cb_qp_offset or slice_cr_qp_offset.
The value of the variable β is determined as specified in the Table illustrated in
where slice_beta_offset_div2 is the value of the syntax element slice_beta_offset_div2 for the slice that contains sample q0,0.
The variable β is derived as follows:
The value of the variable tC′ is determined as specified in the Table illustrated in
where slice_tc_offset_div2 is the value of the syntax element slice_tc_offset_div2 for the slice that contains sample q0,0.
The variable tC is derived as follows:
When maxFilterLengthCbCr is equal to 1 and bS is not equal to 2, maxFilterLengthCbCr is set equal to 0.
When maxFilterLengthCbCr is equal to 3, the following ordered steps apply:
1. The variables dpq0, dpq1, dp, dq and d are derived as follows:
dp0=Abs(p2,0−2*p1,0+p0,0)
dp1=Abs(p2,1−2*p1,1+p0,1)
dq0=Abs(q2,0−2*q1,0+q0,0)
dq1=Abs(q2,1−2*q1,1+q0,1)
dpq0=dp0+dq0
dpql=dp 1+dq1
dp=dp0+dp1
dq=dq0+dq1
d=dpq0+dpq1
2. The variables dSam0 and dSam1 are both set equal to 0.
3. When d is less than β, the following ordered steps apply:
4. The variable maxFilterLengthCbCr is modified as follows:
Decision Process for a Chroma Sample
Inputs to this process are:
Output of this process is the variable dSam containing a decision.
The variable dSam is specified as follows:
As provided above, the decision process for the variable tc, a variable dE, and the variables dEp and dEq for luma and the decision process for the variable tC for chroma applied for a block edge. In JVET-N1001, a block edge is derived as follows:
Where,
cIdx==0, indicates the luma channel;
cIdx==1, indicates the chroma channel;
edgeType==EDGE_VER indicates a vertical deblocking edge, and when not true indicates a horizontal deblocking edge.
And blocks edges are provided at xDk with k=0..xN and yDm with m=0..yN
Thus, the decision process for the variable tC, a variable dE, and the variables dEp and dEq for luma and the decision process for the variable tC for chroma applied is applied on a four lines-by-four line basis (i.e., lines are rows for a vertical deblocking edge and columns for a horizontal deblocking edge). Further, referring to the decision process for the variable tC, a variable dE, and the variables dEp and dEq for luma, the decision is based on variables dp0, dp3, dq0 and dq3, which as provided above, is based on lines 0 and 3 with respect to the block edge. Further, referring to the decision process for the variable tC for chroma, the decision is based on variables dp0, dp 1, dq0 and dq1, which as provided above, is based on lines 0 and 1 with respect to the block edge. Essentially, the variables dp0, dp3, dq0 and dq3, and dp0, dp 1, dq0 and dq1 are used to compute gradients, i.e., between a Q block and a P block, in order to detect blockiness at a deblocking boundary.
The computation of gradients for determining blockiness in JVET-N1001 may be less than ideal. That is, with respect to FIGS.
It should be noted that in addition to applying a deblocking filter as part of an in-loop filtering process, Sample Adaptive Offset (SAO) filtering may be applied in the in-loop filtering process. In ITU-T H.265, SAO is a process that modifies the deblocked sample values in a region by conditionally adding an offset value. ITU-T H.265 provides two types of SAO filters that may be applied to a CTB: band offset or edge offset. For each of band offset and edge offset, four offset values are included in a bitstream. For band offset, the offset which is applied depends on the amplitude of a sample value (e.g., amplitudes are mapped to bands which are mapped to the four signaled offsets). For edge offset, the offset which is applied depends on a CTB having one of a horizontal, vertical, first diagonal, or second diagonal edge classification (e.g., classifications are mapped to the four signaled offsets). Another type of filtering process includes the so-called adaptive loop filter (ALF). An ALF with block-based adaption is specified in JEM. In JEM, the ALF is applied after the SAO filter. It should be noted that an ALF may be applied to reconstructed samples independently of other filtering techniques. The process for applying the ALF specified in JEM at a video encoder may be summarized as follows: (1) each 2×2 block of the luma component for a reconstructed picture is classified according to a classification index; (2) sets of filter coefficients are derived for each classification index; (3) filtering decisions are determined for the luma component; (4) a filtering decision is determined for the chroma components; and (5) filter parameters (e.g., coefficients and decisions) are signaled. Further, it should be noted that JVET-N1001 specifies SAO, and ALF filters which can be described as being generally based on the SAO and ALF filters provided in ITU-T H.265 and JEM.
Communications medium 110 may include any combination of wireless and wired communication media, and/or storage devices. Communications medium 110 may include coaxial cables, fiber optic cables, twisted pair cables, wireless transmitters and receivers, routers, switches, repeaters, base stations, or any other equipment that may be useful to facilitate communications between various devices and sites. Communications medium 110 may include one or more networks. For example, communications medium 110 may include a network configured to enable access to the World Wide Web, for example, the Internet. A network may operate according to a combination of one or more telecommunication protocols. Telecommunications protocols may include proprietary aspects and/or may include standardized telecommunication protocols. Examples of standardized telecommunications protocols include Digital Video Broadcasting (DVB) standards, Advanced Television Systems Committee (ATSC) standards, Integrated Services Digital Broadcasting (ISDB) standards, Data Over Cable Service Interface Specification (DOCSIS) standards, Global System Mobile Communications (GSM) standards, code division multiple access (CDMA) standards, 3rd Generation Partnership Project (3GPP) standards, European Telecommunications Standards Institute (ETSI) standards, Internet Protocol (IP) standards, Wireless Application Protocol (WAP) standards, and Institute of Electrical and Electronics Engineers (IEEE) standards.
Storage devices may include any type of device or storage medium capable of storing data. A storage medium may include a tangible or non-transitory computer-readable media. A computer readable medium may include optical discs, flash memory, magnetic memory, or any other suitable digital storage media. In some examples, a memory device or portions thereof may be described as non-volatile memory and in other examples portions of memory devices may be described as volatile memory. Examples of volatile memories may include random access memories (RAM), dynamic random access memories (DRAM), and static random access memories (SRAM). Examples of non-volatile memories may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. Storage device(s) may include memory cards (e.g., a Secure Digital (SD) memory card), internal/external hard disk drives, and/or internal/external solid state drives. Data may be stored on a storage device according to a defined file format.
Referring again to
Referring again to
Display 126 may comprise one of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display. Display 126 may include a High Definition display or an Ultra High Definition display. It should be noted that although in the example illustrated in
As illustrated in
Coefficient quantization unit 206 may be configured to perform quantization of the transform coefficients. As described above, the degree of quantization may be modified by adjusting a quantization parameter. Coefficient quantization unit 206 may be further configured to determine quantization parameters and output QP data (e.g., data used to determine a quantization group size and/or delta QP values) that may be used by a video decoder to reconstruct a quantization parameter to perform inverse quantization during video decoding. It should be noted that in other examples, one or more additional or alternative parameters may be used to determine a level of quantization (e.g., scaling factors). The techniques described herein may be generally applicable to determining a level of quantization for transform coefficients corresponding to a component of video data based on a level of quantization for transform coefficients corresponding another component of video data.
Referring again to
As described above, a video block may be coded using an intra prediction. Intra prediction processing unit 212 may be configured to select an intra prediction mode for a video block to be coded. Intra prediction processing unit 212 may be configured to evaluate a frame and/or an area thereof and determine an intra prediction mode to use to encode a current block. As illustrated in
Referring again to
According to the techniques herein, filter unit 216 may be configured to compute gradients for determining blockiness where the number of chroma gradient computations is reduced compared to JVET-N1001 and where the selection of lines for gradient computation is aligned for luma and chroma, when luma and chroma have the same dimension in a direction.
In particular, in one example, according to the techniques herein, filter unit 216 may be configured to compute gradients for determining blockiness with respect to chroma as follows: when the number of chroma samples is half the number of luma samples in a direction, for each block edge, compute a gradient at a single line corresponding to the block edges, and when the number of chroma samples is the same as the number of luma samples, compute a gradient at each line corresponding to a line where a luma gradient is computed.
With respect to JVET-N1001, in one example, this example of computing gradients for determining blockiness with respect to chroma may be express as follows:
Thus, according to the techniques herein, filter unit 216 may be configured to perform a decision process for a block edge based on the following:
This process is only invoked when ChromaArrayType is not equal to 0.
Inputs to this process are:
Outputs of this process are
The values pi and qi with i=0.. maxFilterLengthCbCr and k=0..1 are derived as follows:
subSampling=SubHeightC
subSampling=SubWidthC
The variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,o, respectively.
The variable QpC is derived as follows:
If ChromaArrayType is equal to 1, the variable Qpc is determined as specified in Table 3 based on the index qPi derived as follows:
Otherwise (ChromaArrayType is greater than 1), the variable QpC is set equal to Min(qPi, 63).
NOTE—The variable cQpPicOffset provides an adjustment for the value of pps_cb_qp_offset or pps_cr_qp_offset, according to whether the filtered chroma component is the Cb or Cr component. However, to avoid the need to vary the amount of the adjustment within the picture, the filtering process does not include an adjustment for the value of slice_cb_qp_offset or slice_cr_qp_offset.
The value of the variable β′ is determined as specified in the Table illustrated in
where slice_beta_offset_div2 is the value of the syntax element slice_beta_offset_div2 for the slice that contains sample q0,0.
The variable 6 is derived as follows:
The value of the variable tC′ is determined as specified in the Table illustrated in
where slice_tc_offset_div2 is the value of the syntax element slice_tc_offset_div2 for the slice that contains sample q0,0.
The variable tC is derived as follows:
When maxFilterLengthCbCr is equal to 1 and bS is not equal to 2, maxFilterLengthCbCr is set equal to 0.
When maxFilterLengthCbCr is equal to 3, the following ordered steps apply:
1. The variables dpq0, dpq3, dp, dq and d are derived as follows:
In one example, dp3 and dq3 may be respectively computed as follows:
dp3=(subSampling==2) ? Abs(p2,1−2*p1,1+p0,1):Abs(p2,3−2*p1,3+p0,3)
dq3=(subSampling==2) ? Abs(q2,1−2*q1,1+q0,1):Abs(q2,3−2*q1,3+q0,3)
2. The variables dSam0 and dSam3 are both set equal to 0.
3. When d is less than β, the following ordered steps apply:
4. The variable maxFilterLengthCbCr is modified as follows:
It should be noted that in the above process, the phrase “The variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,0, respectively,” may be ambiguous. That is, in cases where dual trees are used for partitioning (i.e., DUAL_TREE_CHROMA in JVET-N1001) samples q0,0 and p0,0, belong to a chroma-only coding unit. As a result, no corresponding value is defined for QpY, in these cases.
In one example, according to the techniques herein, a luma location corresponding to samples q0,0 and p0,0 may be used for predictor derivation. That is, in one example, according to the techniques herein, in the process above, the phrase
“The variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,0, respectively.”
May be replaced with the following:
When treeType is equal to DUAL_TREE_CHROMA, the variables QpQ and QpP are derived using the following ordered steps:
Otherwise, the variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,0
Further, in one example, according to the techniques herein, luma location corresponding to center of chroma coding block of q0,0 and p0,0 may be used for predictor derivation. That is, in one example, according to the techniques herein, in the process above, the phrase
“The variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,0, respectively.”
May be replaced with the following:
When treeType is equal to DUAL_TREE_CHROMA, the variables QpQ and QpP are derived using the following ordered steps:
Otherwise, the variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,0
Further, in one example, according to the techniques herein, luma location corresponding to center of chroma coding block of q0,0 and p0,0 may be used for predictor derivation, with the computation units being luma samples. That is, in one example, according to the techniques herein, in the process above, the phrase
“The variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,o, respectively.”
May be replaced with the following:
When treeType is equal to DUAL_TREE_CHROMA, the variables QpQ and QpP are derived using the following ordered steps:
Otherwise, the variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,0
Versatile Video Coding (Draft 6), 15th Meeting of ISO/IEC JTC1/SC29/WG11 3-12 Jul. 2019, Gothenburg, SE, document JVET-O2001-vE, which is incorporated by reference herein, and referred to as JVET-O2001, represents the current iteration of the draft text of a video coding specification corresponding to the VVC project. In JVET-O2001, determining candidate boundaries for deblocking may be performed using the following approach:
It should be noted that sub-blocks on an 8×8 grid within their CU may correspond to boundaries resulting from affine or ATMVP modes. Such sub-blocks, in some cases, may be referred to as motion boundaries. Determining candidate boundaries for deblocking in this manner is less than ideal. In particular, there is a design inconsistency for CUs that use coding sub-blocks and transform sub-blocks. Specifically, the transform sub-blocks may create boundaries that are not on a 8×8 grid, but that are on the 4×4 grid. In this case, the process in JVET-O2001 would cause a decoder to consider deblocking motion boundaries within a CU on an 8×8 grid and also consider deblocking the transform boundaries within the CU on the 4×4 grid. This requires additional computational logic and increases complexity. It also creates some unexpected design inconsistency.
According to the techniques herein, the deblocking inconsistences are resolved by limiting how a CU may utilize coding sub-blocks and transform sub-blocks. In one example, a CU is not allowed to have transform sub-blocks that create a transform boundary on the 4×4 grid, when coding sub-blocks are present. Such a condition can be realized by not allowing a transform sub-block of one quarter size when the CU dimension is equal to 16 samples or smaller. A CU dimension, in this case may refer to a corresponding width or height of a corresponding block structure, e.g., an sub-block width or height, a CB width or height, etc. Table 4 illustrates an example of relevant CU syntax, according to the techniques herein, that does not allow a transform sub-block of one quarter size to occur when the CU dimension is equal to 16 samples or smaller.
With respect to Table 4 the semantics of the illustrated syntax elements may be based on the following:
cu_cbf equal to 1 specifies that the transform_tree( )syntax structure is present for the current coding unit. cu_cbf equal to 0 specifies that the transform_tree( )syntax structure is not present for
the current coding unit.
When cu_cbf is not present, it is inferred as follows:
cu_sbt_flag equal to 1 specifies that for the current coding unit, subblock transform is used.
cu_sbt_flag equal to 0 specifies that for the current coding unit, subblock transform is not used.
When cu_sbt_flag is not present, its value is inferred to be equal to 0.
cu_sbt_quad_flag equal to 1 specifies that for the current coding unit, the subblock transform includes a transform unit of 1/4 size of the current coding unit. cu_sbt_quad_flag equal to 0 specifies that for the current coding unit the subblock transform includes a transform unit of 1/2 size of the current coding unit.
When cu_sbt_quad_flag is not present, its value is inferred to be equal to 0.
cu_sbt_horizontal_flag equal to 1 specifies that the current coding unit is split horizontally into 2 transform units. cu_sbt_horizontal_flag[x0][y0] equal to 0 specifies that the current coding unit is split vertically into 2 transform units.
When cu_sbt_horizontal_flag is not present, its value is derived as follows:
cu_sbt_pos_flag equal to 1 specifies that the tu_cbf luma, tu_cbf cb and tu_cbf cr of the first transform unit in the current coding unit are not present in the bitstream. cu_sbt_pos_flag equal to 0 specifies that the tu_cbf luma, tu_cbf cb and tu_cbf cr of the second transform unit in the current coding unit are not present in the bitstream.
The variable SbtNumFourthsTb0 is derived as follows:
Further, ciip_flag may be included in a merge-data syntax structure of a CU and have the following semantics:
ciip_flag[x0][y0] specifies whether the combined inter-picture merge and intra-picture prediction is applied for the current coding unit. The array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
When ciip_flag[x0][y0] is not present, it is inferred as follows:
When ciip_flag[x0] [y0] is equal to 1, the variable IntraPredModeY[x ][y ] with x=x0..×0+cbWidth−1 and y=y0..y0+cbHeight−1 is set to be equal to INTRA_PLANAR.
The variable MergeTriangleFlag[x0][y0], which specifies whether triangular shape based motion compensation is used to generate the prediction samples of the current coding unit, when decoding a B slice, is derived as follows:
Further,
Variable cbWidth is the width of the current coding block;
Variable cbHeight is the height of the current coding block; and
Variable MaxSbtSize is the maximum sub-block size
Further, sps_sbtmvp_enabled_flag, sps_affine_enabled_flag, sps_sbt_enabled_flag, sps_sbt_max_size_64_flag and sps_max_luma_transform_size_64_flag are in the SPS and have the following semantics:
sps_sbtmvp_enabled_flag equal to 1 specifies that subblock-based temporal motion vector predictors may be used in decoding of pictures with all slices having slice_type not equal to I in the CVS. sps_sbtmvp_enabled_flag equal to 0 specifies that subblock-based temporal motion vector predictors are not used in the CVS. When sps_sbtmvp_enabled_flag is not present, it is inferred to be equal to 0.
sps_affine_enabled_flag specifies whether affine model based motion compensation can be used for inter prediction. If sps_affine_enabled_flag is equal to 0, the syntax shall be constrained such that no affine model based motion compensation is used in the CVS, and inter_affine_flag and cu_affine_type_flag are not present in coding unit syntax of the CVS. Otherwise (sps_affine_enabled_flag is equal to 1), affine model based motion compensation can be used in the CVS.
sps_sbt_enabled_flag equal to 0 specifies that subblock transform for inter-predicted CUs is disabled. sps_sbt_enabled_flag equal to 1 specifies that subblock transform for inter-predicteds CU is enabled.
sps_sbt_max_size_64_flag equal to 0 specifies that the maximum CU width and height for allowing subblock transform is 32 luma samples. sps_sbt_max_size_64_flag equal to 1 specifies that the maximum CU width and height for allowing subblock transform is 64 luma samples. MaxSbtSize=Min(MaxTbSizeY, sps_sbt_max_size_64_flag ? 64:32),
sps_max_luma_transform_size_64_flag equal to 1 specifies that the maximum transform size in luma samples is equal to 64. sps_max_luma_transform_size_64_flag equal to 0 specifies that the maximum transform size in luma samples is equal to 32.
When CtbSizeY is less than 64, the value of sps_max_luma_transform_size_64_flag shall be equal to 0.
The variables MinTbLog2SizeY, MaxTbLog2SizeY, MinTbSizeY, and MaxTbSizeY are derived as follows:
Table 5 illustrates an example of relevant CU syntax, according to the techniques herein, that does not allow a transform sub-block of one quarter size to occur when the CU dimension is greater equal to 16 samples or smaller when coding sub-blocks may be present.
With respect to Table 5 the semantics of the illustrated syntax elements may be based on those provided above with respect to Table 4.
It should be noted that CU syntax includes syntax element inter_affine_flag having the following semantics:
inter_affine_flag[x0][y0] equal to 1 specifies that for the current coding unit, when decoding a P or B slice, affine model based motion compensation is used to generate the prediction samples of the current coding unit. inter_affine_flag[x0][y0] equal to 0 specifies that the coding unit is not predicted by affine model based motion compensation. When inter_affine_flag[x0] [y0] is not present, it is inferred to be equal to 0.
In one example, sps_affine_enabled_flag in Table 5 may be replaced with inter_affine_flag. It should be noted that CU syntax includes syntax element merge_subblock_flag having the following semantics:
merge_subblock_flag[x0] [y0] specifies whether the subblock-based inter prediction parameters for the current coding unit are inferred from neighbouring blocks. The array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture. When merge_subblock_flag[x0] [y0] is not present, it is inferred to be equal to 0.
In one example, sps_sbtmvp_enabled_flag in Table 5 may be replaced with merge_subblock_flag.
In one example, according to the techniques herein, anytime it is possible for a coding block to have associated motion vectors stored at subblock level, then there may be a limitation on whether subblock transforms can be used on that coding subblock. In one example, the limitation may be based on block size. For example, in one example, if it is possible for a coding block to have associated motion vectors stored at subblock level and a coding block dimension is less than (or greater than) a threshold value, then subblock transforms may be disabled. It should be noted that such a limitation is based on how data is stored and the corresponding prediction process may actually operate in a different manner, e.g., at a sample level.
As described above, a variable, bS, specifies the boundary filtering strength. As further described above, a boundary strength determination may be used to determine whether to skip computations for a particular block e.g., with respect to determining the blockiness of a particular block (i.e., based on a computed gradient). In general, the boundary filtering strength is used in JVET-O2001 to determine if/how to apply deblocking. JVET-O2001 provides the following with respect to determining a variable bS specifying the boundary filtering strength:
Inputs to this process are:
Output of this process is a two-dimensional (nCbW)x(nCbH) array bS specifying the boundary filtering strength.
The variables xDi, yDj, xN and yN are derived as follows:
xDi=(i*gridSize)
yN=cIdx==0 ? (nCbH/4)−1:(nCbH/2)−1
xDi=cIdx==0 ? (i<<2):(i<<1)
yDj=(j*gridSize)
xN=cIdx==0 ? (nCbW/4)−1 (nCbW/2)−1
For xDi with i=0..xN and yD, with j=0..yN, the following applies:
As described above, in JVET-O2001, the variable MergeTriangleFlag[x0][y0] may specify whether triangular shape based motion compensation is used to generate the prediction samples of a current coding unit. In triangular shape based motion compensation, a rectangular video block is predicted using two triangular shaped predictions. Two weighting processes may be specified that assign equal or nearly equal weights to the reference prediction samples either about the diagonal (from top-left corner to bottom-right corner) or about the inverse diagonal (from top-right corner to bottom-left corner) direction. Each reference rectangular prediction is generated using its own motion vector(s) and reference frame index. Each prediction sample of a current coding unit is obtained using a weighting of two reference prediction sample values and as such motion discontinuity may be smoothened by the weighting process. As such, deblocking internal edges based on motion discontinuity for a coding unit with triangular shape based weighting process may be less than ideal.
In one example, according to the techniques herein, motion discontinuity for internal edges may not be considered for deblocking in cases where triangular shape based weighting process is used to generate the prediction samples of a current coding unit. Whether an edge is an internal edge may be determined based on edge type being filtered and distance from a corresponding coding unit edge (e.g., distance from left and/or right coding unit edge when performing deblocking for a vertical edge type; distance from top and/or bottom coding unit edge when performing deblocking for a horizontal edge type). In one example, not considering motion discontinuity for internal edges for deblocking in cases where triangular shape based weighting process is used to generate the prediction samples of a current coding unit, may be achieved by deriving a bS value according to the following process: Inputs to this process are:
Output of this process is a two-dimensional (nCbW)x(nCbH) array bS specifying the boundary filtering strength.
The variables xDi, yDj, xN and yN are derived as follows:
xDi=(i*gridSize)
yN=cIdx==0 ? (nCbH/4)−1:(nCbH/2)−1
xDi=cIdx==0 ? (i<<2) (i<<1)
yDj=(j*gridSize)
xN=cIdx==0 ? (nCbW/4)−1:(nCbW/2)−1
For xDi with i=0..xN and yDj with j=0..yN, the following applies:
In one example, according to the techniques herein, motion discontinuity for internal edges may not be considered for deblocking in cases where a CU makes use of affine mode, and the edge is not a 8×8 CU grid. In one example, not considering motion discontinuity for internal edges for deblocking in cases where a CU makes use of affine mode, and the edge is not a 8×8 CU grid, may be achieved by deriving a bS value according to the following process:
Inputs to this process are:
Output of this process is a two-dimensional (nCbW)x(nCbH) array bS specifying the boundary filtering strength.
The variables xDi, yDj, xN and yN are derived as follows:
xDi=(i*gridSize
yN=cIdx==0 ? (nCbH/4)−1:(nCbH/2)−1
xDi=cIdx==0 ? (i<<2): (i<<1)
yD,=(j*gridSize)
xN=cIdx==0 ? (nCbW/4)−1:(nCbW/2)−1
For xDi with i=0..xN and yD, with j=0..yN, the following applies:
As described above, in the case of the luma long filter for luma, a variable dSam containing a decision is determined according to a decision process for block edge based on B as follows:
The variable sThr is derived as follows:
The variable dSam is specified as follows:
Where,
The variable β is derived as follows:
β=β′*(1<<(BitDepthY−8))
The value of the variable β′ is determined as specified in the Table illustrated in
where slice_beta_offset_div2 is the value of the syntax element slice_beta_offset_div2 for the slice that contains sample q0,0.
The variable qP is derived as follows:
qP=((QpQ+QpP+1)>>1)+qpOffset
The variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,o, respectively.
Thus, it is difficult to adjust sThr in a flexible and independent manner. For example, adjusting sThr by adjusting the level of quantization of blocks Q and P may be less than ideal. Further, more independent control of long filters may be desirable for example, when for a video sequence the application of long filters is too aggressive and smoothing out true edges. In one example, according to the techniques herein, a syntax element used to adjust the control threshold of the long filter deblocking independent of non-long filter deblocking operations may be included in the bitstream.
In one example, according to the techniques herein, in the case of the luma long filter for luma, a variable dSam containing a decision is determined according to a decision process for block edge based on βL as follows:
The variable sThr is derived as follows:
The variable dSam is specified as follows:
Where,
The variable βL is derived as follows:
The value of the variable βL′=β′, which is determined as specified in the Table illustrated in
where slice_betaL_offset_div2 is the value of the syntax element slice_betaL_offset_div2 for the slice that contains sample q0,0.
The variable qP is derived as follows:
qP=((QpQ+QpP+1)>>1)+qpOffset
The variables QpQ and QpP are set equal to the QpY values of the coding units which include the coding blocks containing the sample q0,0 and p0,o, respectively.
In one example, syntax element slice_betaL_offset_div2 may be signaled in a slice header. Table 6 illustrates an example of the relevant syntax of a slice header including slice_betaL_offset_div2.
With respect to Table 6, in one example the semantics may be based on the following:
deblocking_filter_override_flag equal to 1 specifies that deblocking parameters are present in the slice header. deblocking_filter_override_flag equal to 0 specifies that deblocking parameters are not present in the slice header. When not present, the value of deblocking_filter_override_flag is inferred to be equal to 0.
slice_deblocking_filter_disabled_flag equal to 1 specifies that the operation of the deblocking filter is not applied for the current slice. slice_deblocking_filter_disabled_flag equal to 0 specifies that the operation of the deblocking filter is applied for the current slice. When slice_deblocking_filter_disabled_flag is not present, it is inferred to be equal to pps_deblocking_filter_disabled_flag.
slice_beta_offset_div2 and slice_tc_offset_div2 specify the deblocking parameter offsets for B and tC (divided by 2) for the current slice. The values of slice_beta_offset_div2 and slice_tc_offset_div2 shall both be in the range of 6 to 6, inclusive. When not present, the values of slice_beta_offset_div2 and slice_tc_offset_div2 are inferred to be equal to pps_beta_offset_div2 and pps_tc_offset_div2, respectively.
slice_betaL_offset_div2 specifies the deblocking parameter offsets for BL divided by 2 for the current slice. The values of slice_betaL_offset_div2 shall both be in the range of 6 to 6, inclusive. When not present, the values of slice_betaL_offset_div2 are inferred to be equal to pps_betaL_offset_div2.
Alternatively, in other examples, syntax element slice_betaL_offset_div2 may be signaled at another high level signaling location e.g., picture header, picture parameter set, sequence parameter set, etc. Table 7 illustrates an example of the relevant syntax of a picture parameter set including slice_betaL_offset_div2.
With respect to Table 7, in one example the semantics may be based on the following:
deblocking_filter_control_present_flag equal to 1 specifies the presence of deblocking filter control syntax elements in the PPS. deblocking_filter_control_present_flag equal to 0 specifies the absence of deblocking filter control syntax elements in the PPS.
deblocking_filter_override_enabled_flag equal to 1 specifies the presence of deblocking_filter_override_flag in the slice headers for pictures referring to the PPS. deblocking_filter_override_enabled_flag equal to 0 specifies the absence of deblocking_filter_override_flag in the slice headers for pictures referring to the PPS. When not present, the value of deblocking_filter_override_enabled_flag is inferred to be equal to 0.
pps_deblocking_filter_disabled_flag equal to 1 specifies that the operation of deblocking filter is not applied for slices referring to the PPS in which slice_deblocking_filter_disabled_flag is not present. pps_deblocking_filter_disabled_flag equal to 0 specifies that the operation of the deblocking filter is applied for slices referring to the PPS in which slice_deblocking_filter_disabled_flag is not present. When not present, the value of pps_deblocking_filter_disabled_flag is inferred to be equal to 0.
pps_beta_offset_div2 and pps_tc_offset_div2 specify the default deblocking parameter offsets for B and tC (divided by 2) that are applied for slices referring to the PPS, unless the default deblocking parameter offsets are overridden by the deblocking parameter offsets present in the slice headers of the slices referring to the PPS. The values of pps_beta_offset_div2 and pps_tc_offset_div2 shall both be in the range of 6 to 6, inclusive. When not present, the value of pps_beta_offset_div2 and pps_tc_offset_div2 are inferred to be equal to 0.
pps_betaL_offset_div2 specifies the default deblocking parameter offsets for BL divided by 2 that are applied for slices referring to the PPS, unless the default deblocking parameter offsets are overridden by the deblocking parameter offsets present in the slice headers of the slices referring to the PPS. The value of pps_betaL_offset_div2 shall both in the range of 6 to 6, inclusive. When not present, the value of pps_betaL_offset_div2 is inferred to be equal to 0.
In some examples, according to the techniques herein, the signaling of syntax element pps_betaL_offset_div2 or syntax element slice_betaL_offset_div2 may be controlled by higher level syntax. For example, syntax elements colour_primaries and transfer_characteristics may be signaled in the VUI (Video Usability Information) parameters syntax if colour_description_present_flag is true. In one example, syntax element pps_betaL_offset_div2 or syntax element slice_betaL_offset_div2 may be present if colour_description_present_flag is true and/or if syntax elements colour_primaries and transfer_characteristics have a particular value. For example, in one example, syntax element
pps_betaL_offset_div2 or syntax element slice_betaL_offset_div2 may be signaled only for High Dynamic Range (HDR) (e.g., Perceptual Quantizer (PQ) or Hybrid Log-Gamma (HLG)) sequences. In one example, syntax element pps_betaL_offset_div2 or syntax element slice_betaL_offset_div2 may be signaled only when the container is BT.2020. Further, in one example, the signaling of syntax element pps_betaL_offset_div2 or syntax element slice_betaL_offset_div2 may be controlled by a flag in SPS.
In one example, syntax element slice_betaL_offset_div2 may represent an offset with respect to slice beta offset div2. That is, in one example, the semantics of syntax element slice_betaL_offset_div2 may be based on the following:
slice_betaL_offset_div2 and slice_beta_offset_div2 specifies the deblocking parameter offsets for βL divided by 2 for the current slice. The values of slice_betaL_offset_div2 shall both be in the range of −6 to 6, inclusive. When not present, the values of slice_betaL_offset_div2 are inferred to be equal to pps_betaL_offset_div2.
And the quantization parameter Q may be derived as follows:
Q=Clip3(0, 63, Qpc+((slice betaL offset div2+slice beta offset div2) <<1)) where slice betaL offset div2 is the value of the syntax element slice betaL offset div2 for the slice that contains sample q0,0.
In one example, syntax element slice_betaL_offset may represent an offset with respect to 13. That is, in one example, the semantics of syntax element slicebetaL_offset may be based on the following:
slice_betaL_offset specifies the deblocking parameter offsets for BL for the current slice from β. The values of slice_betaL_offset shall both be in the range of −12 to 12, inclusive. When not present, the values of slice_betaL_offset are inferred to be equal to pps_betaL_offset.
The variabe BL is derived as follows:
βL=β+slice_betaL_offset
In one example, syntax element slice_betaL_offset may be signaled in a slice header. For example, syntax element slice_betaL_offset may replace syntax element slice_betaL_offset_div2 in Table 6. Alternatively, in other examples, syntax element slice_betaL_offset may be signaled at another high level signaling location e.g., picture header, picture parameter set, sequence parameter set, etc. For example, syntax element slice_betaL_offset may replace syntax element slice_betaL_offset_div2 in Table 7.
In one example, according to the techniques herein, similar to signaling syntax element slice_betaL_offset_div2 to independently control the activation threshold for long filter deblocking, a syntax element, e.g., slice_tcL_offset_div2 may be signaled to independently control the clipping threshold for long filter deblocking. That is, for example, a syntax element, e.g., slice_tcL_offset_div2, may replace the existing use of slice_tc_offset_div2 for long filters. In one example, according to the techniques herein, similar to signaling pps_betaL_offset_div2 to independently control the activation threshold for long filter deblocking, a syntax element, e.g., pps_tcL_offset_div2, may be signaled to independently control the clipping threshold for long filter deblocking. That is, for example, a syntax element, e.g., pps_tcL_offset_div2, may replace the existing use of pps_tc_offset_div2 for long filters. In one example, syntax element pps_tcL_offset_div2 and syntax element slice_tcL_offset_div2 may be based on the following semantics:
pps_tcL_offset_div2 specify the default deblocking parameter offsets for tcL (divided by 2) that are applied for slices referring to the PPS, unless the default deblocking parameter offsets are overridden by the deblocking parameter offsets present in the slice headers of the slices referring to the PPS. The value of pps_tcL_offset_div2 shall both be in the range of 6 to 6, inclusive. When not present, the value of pps_tcL_offset_div2 is inferred to be equal to 0.
slice_betaL_offset_div2 and slice_tcL_offset_div2 specify the deblocking parameter offsets for tcL (divided by 2) for the current slice. The value of slice_tcL_offset_div2 shall both be in the range of −6 to 6, inclusive. When not present, the values of slice_tcL_offset_div2 are inferred to be equal to pps_tcL_offset_div2
In one example, the value of the variable tCL′ is determined as specified in the Table illustrated in
where slice_tcL_offset_div2 is the value of the syntax element slice_tcL_offset_div2 for the slice that contains sample q0,0.
The variable tCL is derived as follows: tCL=BitDepthY<10 ? (tCL′+2)>>(10−BitDepthY): tCL′* (1<<(BitDepthY−10))
Further, in an example, a decision process for a luma sample may be based on the following:
Inputs to this process are:
Output of this process is the variable dSam containing a decision.
The variables sp and sq are modified as follows:
The variable sThr is derived as follows:
The variable dSam is specified as follows:
In another example, in the the invocation of long filters, the parameter is tCL instead of tC. For example, as follows:
When dE is equal to 3, for each sample location (xCb+xBl, yCb+yBl+k), k=0..3, the following ordered steps apply:
And
When dE is equal to 3, for each sample location (xCb+xBl+k, yCb+yBl), k=0..3, the following ordered steps apply:
Referring again to
As illustrated in
Referring again to
Intra prediction processing unit 508 may be configured to receive intra prediction syntax elements and retrieve a predictive video block from reference buffer 516. Reference buffer 516 may include a memory device configured to store one or more frames of video data. Intra prediction syntax elements may identify an intra prediction mode, such as the intra prediction modes described above. In one example, intra prediction processing unit 308 may reconstruct a video block using according to one or more of the intra prediction coding techniques described herein. Inter prediction processing unit 510 may receive inter prediction syntax elements and generate motion vectors to identify a prediction block in one or more reference frames stored in reference buffer 516. Inter prediction processing unit 510 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used for motion estimation with sub-pixel precision may be included in the syntax elements. Inter prediction processing unit 510 may use interpolation filters to calculate interpolated values for sub-integer pixels of a reference block.
Filter unit 514 may be configured to perform filtering on reconstructed video data. For example, Filter unit 514 may be configured to perform deblocking and/or SAO filtering, as described above with respect to filter unit 216. Further, it should be noted that in some examples, filter unit 514 may be configured to perform proprietary discretionary filter (e.g., visual enhancements). As illustrated in
In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.
By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.
Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.
The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.
Moreover, each functional block or various features of the base station device and the terminal device used in each of the aforementioned embodiments may be implemented or executed by a circuitry, which is typically an integrated circuit or a plurality of integrated circuits. The circuitry designed to execute the functions described in the present specification may comprise a general-purpose processor, a digital signal processor (DSP), an application specific or general application integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gates or transistor logic, or a discrete hardware component, or a combination thereof. The general-purpose processor may be a microprocessor, or alternatively, the processor may be a conventional processor, a controller, a microcontroller or a state machine. The general-purpose processor or each circuit described above may be configured by a digital circuit or may be configured by an analogue circuit. Further, when a technology of making into an integrated circuit superseding integrated circuits at the present time appears due to advancement of a semiconductor technology, the integrated circuit by this technology is also able to be used. Various examples have been described. These and other examples are within the scope of the following claims.
In one example, a method of filtering reconstructed video data, the method comprising: receiving arrays of sample values including adjacent reconstructed video blocks for respective luma and chroma channels of video data; for each of a horizontal and vertical direction, determining whether the number of chroma samples is half of or equal to the number of luma samples; selecting lines for computing gradients for determining blockiness for chroma based on the determination; determining blockiness based on the selected lines; and modifying sample values in the adjacent reconstructed video blocks based on the determined blockiness according to a deblocking filter. In one example, the method, wherein the video data has a chroma format selected from: 4:2:0, 4:2:2, and 4:4:4.
In one example, a device for coding video data, the device comprising one or more processors configured to perform any and all combinations of the steps.
In one example, the device, wherein the device includes a video encoder.
In one example, the device, wherein the device includes a video decoder.
In one example, a system comprising: the device includes a video encoder; and the device includes a video decoder.
In one example, an apparatus for coding video data, the apparatus comprising means for performing any and all combinations of the steps.
In one example, a non-transitory computer-readable storage medium comprising instructions stored thereon that, when executed, cause one or more processors of a device for coding video data to perform any and all combinations of the steps.
In one example, a method of filtering reconstructed video data, the method comprising: receiving a slice header; parsing a syntax element, from the slice header, specifying a first offset for a deblocking parameter applied to a luma component for a current slice, wherein the first offset is distinct from a second offset for a deblocking parameter applied to a chroma component; determining a threshold value based on the syntax element; and applying a deblocking filter based on the threshold value.
In one example, a device for decoding video data, the device comprising one or more processors configured to: receive a slice header; parse a syntax element, from the slice header, specifying a first offset for a deblocking parameter applied to a luma component for a current slice, wherein the first offset is distinct from a second offset for a deblocking parameter applied to a chroma component; determine a threshold value based on the syntax element; and apply a deblocking filter based on the threshold value.
This Nonprovisional application claims priority under 35 U.S.C. § 119 on provisional Application No. 62/911,802 on Oct. 7, 2019, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62911802 | Oct 2019 | US |
