(19)
(11)EP 3 707 898 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
17.03.2021 Bulletin 2021/11

(21)Application number: 19744635.4

(22)Date of filing:  10.07.2019
(51)Int. Cl.: 
H04N 19/12  (2014.01)
H04N 19/186  (2014.01)
H04N 19/61  (2014.01)
H04N 19/159  (2014.01)
H04N 19/176  (2014.01)
(86)International application number:
PCT/EP2019/068548
(87)International publication number:
WO 2020/011860 (16.01.2020 Gazette  2020/03)

(54)

TRANSFORM SELECTION IN A VIDEO ENCODER AND/OR VIDEO DECODER

TRANSFORMATIONSAUSWAHL BEI EINEM VIDEOCODIERER UND/ODER VIDEODECODIERER

SÉLECTION DE TRANSFORMÉE DANS UN CODEUR VIDÉO ET/OU UN DÉCODEUR VIDÉO


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 13.07.2018 US 201862697484 P

(43)Date of publication of application:
16.09.2020 Bulletin 2020/38

(60)Divisional application:
21155559.4

(73)Proprietor: Telefonaktiebolaget LM Ericsson (publ)
164 83 Stockholm (SE)

(72)Inventors:
  • YU, Ruoyang
    183 39 Täby (SE)
  • ZHANG, Zhi
    170 66 Solna (SE)
  • SJÖBERG, Rickard
    113 62 Stockholm (SE)

(74)Representative: Ericsson 
Patent Development Torshamnsgatan 21-23
164 80 Stockholm
164 80 Stockholm (SE)


(56)References cited: : 
  
  • CHEN J ET AL: "JVET-G1001- Algorithm description of Joint Exploration Test Model 7 (JEM7)", JOINT VIDEO EXPLORATION TEAM (JVET)OF ITU-T SG 16 WP 3 AND ISO/IEC JTC 1/SC 29/WG 11, 7TH MEETING, 13-7-2017 - 21-7-2017; TORINO , 19 August 2017 (2017-08-19), pages i-iv, 1, XP030150980, Retrieved from the Internet: URL:http://phenix.int-evry.fr/jvet/doc_end _user/documents/7_Torino/wg11/JVET-G0001-v 1.zip
  • LIN Y ET AL: "Prediction dependent transform for intra and inter frame coding", 10. JVET MEETING; 10-4-2018 - 20-4-2018; SAN DIEGO; (THE JOINT VIDEO EXPLORATION TEAM OF ISO/IEC JTC1/SC29/WG11 AND ITU-T SG.16 ); URL: HTTP://PHENIX.INT-EVRY.FR/JVET/,, no. JVET-J0064-v2, 15 April 2018 (2018-04-15), XP030151254,
  • Z Zhang ET AL: "Non-CE6: On LFNST transform set selection for a CCLM coded block", Joint Video Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11 15th Meeting: Gothenburg, SE, 3-12 July 2019, JVET-O0219-v1, 24 June 2019 (2019-06-24), pages 1-4, XP055638157, Retrieved from the Internet: URL:http://phenix.it-sudparis.eu/jvet/doc_ end_user/documents/15_Gothenburg/wg11/JVET -O0219-v1.zip [retrieved on 2019-10-31]
  • ZHAO (TENCENT) X: "BoG report on CE6 related transforms and transform signalling contributions", 127. MPEG MEETING; 20190708 - 20190712; GOTHENBURG; (MOTION PICTURE EXPERT GROUP OR ISO/IEC JTC1/SC29/WG11), , no. m49750 7 July 2019 (2019-07-07), XP030208259, Retrieved from the Internet: URL:http://phenix.int-evry.fr/mpeg/doc_end _user/documents/127_Gothenburg/wg11/m49750 -JVET-O1115-v3-JVET-O1115.zip JVET-O1115-v3.docx [retrieved on 2019-07-07]
  • CHUOHAO YEO ET AL: "Mode-Dependent Transforms for Coding Directional Intra Prediction Residuals", IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS, US, vol. 22, no. 4, 1 April 2012 (2012-04-01), pages 545-554, XP011440420, ISSN: 1051-8215, DOI: 10.1109/TCSVT.2011.2168291
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

TECHNICAL FIELD



[0001] This disclosure relates to video encoding and/or decoding.

BACKGROUND



[0002] This disclosure relates to the encoding and/or decoding of a video sequence, which consists of a sequence of pictures.

Components



[0003] Each picture of the video sequence consists of one or more components. Each component can be described as a two-dimensional rectangular array of sample values. It is common that a picture in a video sequence consists of three components: i) a luma component (Y), where the sample values are luma values; ii) a first chroma component (Cb), where the sample values are chroma values; and iii) a second chroma component (Cr), where the sample values are chroma values.

[0004] Other examples include Y' Cb Cr, YUV and ICTCP. In ICTCP, I is the "intensity luma" component. For the remainder of this document we may refer to any luma component Y', Y or I as Y or simply luma. It is common that the dimensions of the chroma components are smaller than the luma components by a factor of two in each dimension. For example, the size of the luma component of an HD picture would be 1920x1080 and the chroma components would each have the dimension of 960x540. Components are sometimes referred to as color components.

Blocks and Units



[0005] A block is one two-dimensional array of samples corresponding to an area of a picture, and a unit consists of one or more blocks. In video coding, each component is split into blocks and the coded video bit stream consist of a series of blocks. A "transform block" is a block to which a transform is applied. A "prediction block" is a block to which a single prediction mode is applied.

[0006] It is common in video coding that the picture is split into units that cover a specific area of the picture, referred to as a "picture area." Each unit consists of all blocks that make up that picture area and each block belongs fully to one unit. The Coding Unit (CU) in HEVC is an example of a unit.

[0007] In HEVC, some decoding processes are done at the Coding Unit level, some are done at the prediction blocks, and some at the transform blocks.

[0008] In HEVC, there are two kinds of prediction types for a prediction block: intra prediction, which only uses prediction from previous decoded samples of the current picture for prediction, and inter prediction, which uses prediction from at least one previously decoded picture. A prediction block that is generated using intra prediction can be called an "intra block," and a prediction block generated using inter prediction can be called an "inter block."

[0009] In the current versatile video coding (WC) standardization development, a CU can implicitly be divided into multiple of transform blocks. Implicit transform blocks can however only appear when the CU size has a width or height that is larger than the maximum transform size. When a CU prediction type is intra prediction, the same transform block implicit split mechanism is applied to prediction block. The size of transform block is the same as the size of prediction block when CU prediction type is intra prediction. In other words, the transform and prediction operate on the same two-dimensional array when CU prediction type is intra prediction.

Intra prediction



[0010] In HEVC, the intra prediction generates the samples for a prediction block based on samples from previously decoded CUs of the same picture. These samples are referred to as "reference samples." When a previously decoded CU is not available, the corresponding reference samples are padded from the nearest available left-bottom or right-top reference samples.

[0011] In HEVC, there are 35 intra prediction modes: DC, planar and 33 angular modes. Each of these 33 angular modes represent a pre-defined prediction direction. The intra prediction then follows the direction to predict samples for a prediction block corresponding to an area of the picture based on spatial extrapolation of reference samples corresponding to a neighboring area of the picture.

[0012] The current WC development defines a set of tools called bench mark sets (BMS). The BMS consists of tools that are likely for inclusion in the standard. The BMS extends the existing HEVC's intra directions to support up to 67 intra prediction modes.

Residual, primary transform and quantization



[0013] A residual block consists of residual samples that are obtained by taking the sample value difference between the original samples ("original block") corresponding to an area of the picture and the predicted samples corresponding to the area of the picture (i.e., the predicted block for the area of the picture). The residual block is further processed by using a spatial core transform to produce primary-transformed (DCT/DST transformed) transform coefficients. The transform is a process to decorrelate the information of the residual block into frequency domain. In HEVC, the types of spatial core transform include DCT-II and 4x4 DST-VII. The spatial core transform is sometimes referred to as primary transform.

[0014] The resulting primary-transformed (DCT/DST transformed) transform coefficients (or simply "transform coefficients" for short) are then quantized according to a quantization parameter (QP) which controls the precision of the quantized coefficients. The quantized coefficients can be referred to as residual coefficients. A high QP would result in low precision of the coefficients and thus low fidelity of the residual block. The non-zero residual coefficients are signaled in the video bit stream. A decoder then receives the non-zero residual coefficients, applies inverse quantization and inverse transform to derive the residual block. If all residual coefficients are 0 after quantization, a flag is signaled in the video bit stream, therefore a decoder does not need to apply inverse quantization and inverse transform for the block.

Non-separable secondary transform (NSST)



[0015] NSST is applied for intra blocks (i.e., is applied when the residual block is generated using a predicted block that was generated suing intra prediction). It is a secondary transform which operates on the transform coefficients. On the encoder side, a forward NSST is applied between forward core transform and quantization. On the decoder side, an inverse NSST is applied between de-quantization and inverse core transform. In the current WC, the NSST is applied only on the low-frequency transformed coefficients, i.e. top-left 4x4 transformed coefficients.

[0016] BMS tools improve the adaptability of transform process since the DCT/DST-based transform cannot fully decorrelate the residual signal, especially when there are strong directional information present.

[0017] For each of the angular modes, a NSST transform set of 3 different matrices is defined. For DC or planar mode, a NSST transform set of 2 different matrices is defined. In BMS, each NSST transform set is assigned an index, which identifies the transform set. A mapping between the intra prediction modes and the NSST transform set indices is defined using a look-up table. That is, a look-up table is used to map each of the intra prediction modes to an transform set index, thereby mapping each of the intra prediction modes to the transform set identified by the index to which the intra prediction mode is mapped.

Cross-component prediction



[0018] BMS includes cross-component linear model (CCLM) prediction modes. CCLM is a special intra prediction method for the chroma component. The chroma samples are predicted based on the reconstructed luma samples by using a linear model as follows: pred_C(i,j) = α·rec_L'(i,j)+β, where pred_C(i,j) represents the predicted chroma samples in a CU and rec_L'(i,j) represents the downsampled reconstructed luma samples (in case chroma has reduced resolution compared to luma). Parameters α and β are derived by minimizing the regression error between the neighboring reconstructed luma and chroma samples around the prediction block.

SUMMARY



[0019] When CCLM is used to generate a particular prediction block comprising chroma components (i.e., a chroma component prediction block), the current solution uses the intra planar mode as the entry for selecting the transform set (e.g., NSST transform set) for the particular prediction block - - i.e., the transform set that is used to transform the transform coefficients that were generated by transforming the residual block that was generated based on the particular prediction block. The selected transform set, however, might not be well suitable because there can be a directional pattern present in the prediction block (e.g., in the chroma component).

[0020] To overcome this problem, this disclosure describes an improved process for selecting the transform set for a prediction block. The process can be used in both an encoder and a decoder. For example, the process can be used in both an encoder and a decoder for a prediction block that has been predicted from a reference block. In some embodiments, both the prediction block and the reference block are intra blocks.

[0021] A first aspect of the embodiments defines a method for encoding a video sequence comprising a plurality of pictures. The method comprises determining a directional pattern in a chroma prediction block of one of the pictures in the video sequence wherein the chroma prediction block is created by cross-component linear model (CCLM) mode. The determining comprises using information from a luma reference block from which the chroma prediction block is generated to determine the directional pattern, wherein the luma reference block is coded using an intra prediction mode and wherein determining the directional pattern comprises or consists of determining the intra prediction mode of the luma reference block. The method comprises selecting a transform set for the chroma prediction block based on the determined directional pattern. The method comprises, using the selected transform set, transforming data derived from the chroma prediction block, wherein transforming data using the transform set selected based on the determined directional pattern comprises transforming a residual block using the selected transform set.

[0022] A second aspect of the embodiments defines a method for decoding a video sequence comprising a plurality of pictures. The method comprises determining a directional pattern in a chroma prediction block of one of the pictures in the video sequence, wherein the chroma prediction block is created by cross-component linear model (CCLM) mode. The determining comprises using information from a luma reference block from which the chroma prediction block is generated to determine the directional pattern, wherein the luma reference block is coded using an intra prediction mode and wherein determining the directional pattern comprises or consists of determining the intra prediction mode of the luma reference block. The method comprises selecting an inverse transform set for the chroma prediction block based on the determined directional pattern. The method comprises inverse transforming data using the inverse transform set selected based on the determined directional pattern, wherein inverse transforming data using the inverse transform set selected based on the determined directional pattern comprises inverse transforming a coefficient block after dequantization.

[0023] A third aspect of the embodiments defines a computer program, the computer program comprising instructions which, when executed by processing circuity, cause the processing circuity to carry out the method of any one of the first and the second aspect.

[0024] A fourth aspect of the embodiments defines a carrier containing the computer program according to the third aspect, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

[0025] A fifth aspect of the embodiments defines an encoder for encoding a video sequence comprising a plurality of pictures, the encoder being adapted to perform a method according to the first aspect.

[0026] A sixth aspect of the embodiments defines a decoder for decoding a video sequence comprising a plurality of pictures, the decoder being adapted to perform a method according to the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS



[0027] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

FIG. 1 illustrates a system according to an embodiment.

FIG. 2 illustrates an example table mapping intra prediction modes to a particular transform set index.

FIG. 3 illustrates a 4x4 block.

FIG. 4 illustrates a process according to one embodiment.

FIG. 5 illustrates a process according to one embodiment.

FIG. 6 illustrates processes according to one embodiment.

FIG. 7 is a block diagram of an apparatus according to one embodiment.

FIG 8. illustrates functional units of an encoder according to an embodiment.

FIG 9. illustrates functional units of an encoder according to an embodiment.


DETAILED DESCRIPTION



[0028] FIG. 1 illustrates a system 100 according to an example embodiment. System 100 includes an encoder 102 in communication with a decoder 104 via a network 110 (e.g., the Internet or other network).

[0029] Encoder 102 includes a primary transform unit (PTU) 111, a secondary transform unit (STU) 112 (e.g., an NSST unit), and a quantization unit (QU) 113. As explained above, primary transform unit 111 may implement a spatial core transform that performs a process to decorrelate a residual block into frequency domain (i.e., produce transform coefficients), secondary transform unit 112 may be applied for intra blocks and may operate on the transform coefficients (i.e., the output of primary transform unit 111) to produce coefficients that will be quantized by quantization unit 113 according to a QP which controls the precision of the quantized coefficients. Likewise, decoder 104 includes a de-quantization unit 123, an inverse second transform unit 122, and an inverse primary transform unit 121.

[0030] As further shown in FIG. 1, each of the encoder 102 and the decoder 104 may include a selector 114, 124 that functions to select a transform set (e.g., a primary transform set or a secondary transform set) or an inverse-transform set, respectively, for a prediction block. Advantageously, in some scenarios, the selector 114, 124 determines a directional pattern in the prediction block using information from the reference block from which the prediction block is predicted and then selects the transform set (or inverse-transform) based on the determined directional pattern. In some embodiments, both the prediction block and the reference block are intra blocks. In some embodiments, determining the directional pattern comprises or consists of the transform selector 114, 124 determining the intra prediction mode of the reference block and/or reconstructed sample values of the reference block.

[0031] For example, in one embodiment, selector 114 selects the transform set for the prediction block by determining the intra prediction mode of the reference block used to generate the prediction block (i.e., the prediction block's reference block) and then uses information (e.g., a table) that maps each intra prediction mode included in a set of intra prediction modes to a particular transform set (e.g., to a transform set index that identifies a transform set) to select the transform set to which the determined intra prediction mode is mapped.

[0032] FIG. 2 illustrates an example table mapping each one of intra prediction modes 0 to 66 to a transform set index. Thus, for example, if selector 114 determines that the intra prediction mode of the prediction block's reference block is 66, then selector 114 will select for the prediction block the transform set identified by transform set index 2. In other words, in one embodiment, selecting the transform set for the prediction block using the determined directional pattern consists of using the intra prediction mode for the reference block as the entry for selecting the transform set.

[0033] The selected transform set is then applied by the primary transform unit 111 or secondary transform unit 112, and the selected inverse-transform is then applied by the primary inverse transform unit 121 or the secondary inverse transform unit 122. An advantage of this process is that is provides better de-correlation of chroma components' residual signal when, for example, CCLM is used.

[0034] In one embodiment, the selected transform set is a NSST transform set or any other directional-dependent transform set. The selected transform set for the prediction block can be used either as a primary transform which operates on the residual block generated based on the prediction block and the original block corresponding to the prediction block or used as a secondary transform which operates on the transform coefficients produced as a result of the primary transform unit transforming the residual block. The process can be applied for a single color component or to all color components. Examples of color components are luma, Cb and Cr.

[0035] In some embodiments, the prediction block belongs to a chroma color component and the reference block belongs to a luma color component. One example is when CCLM mode is used. In some embodiments, both the prediction block and reference block belong to the same color component. One example is when the intra block copy (IBC) tool in range extension of HEVC is used. The tool creates a prediction block by referencing previously coded blocks in the same picture or slice. Preferably, this embodiment is applied when the picture or slice is intra.

[0036] In some embodiments, determining the directional pattern in the prediction block using information from the reference block comprises selector 114, 124 selecting an intra prediction mode using both the reference block's intra prediction mode and the prediction block. Selector 114 (124) then uses the selected intra prediction mode to directly select the transform set (inverse transform set). For example, when CCLM is used, the generation process for the prediction block involves downsampling and linear mapping of the referenced luma block's reconstructed samples.

[0037] In one embodiment, the following steps are performed by selector 114 (124) to select the intra prediction mode that will be used to select the transform set (inverse-transform set):

[0038] Firstly, a set of intra prediction modes is defined. The set includes the reference block's intra prediction mode (L_dir) and includes a few additional modes. The additional modes can contain the adjacent modes to L_dir, it can also contain non-adjacent intra prediction mode DC or planar.

[0039] For each mode included in the set, the selector 114, 124 uses samples from the first row and first column of the prediction block (P) (assuming the size is MxN) to predict the remaining samples (size of (M-1)x(N-1)) inside P. An example is shown in FIG. 3. In other words, for each mode included in the set, a temporary block T with (M-1)x(N-1) is generated using intra prediction method.

[0040] After the block T is generated, the samples in T are compared against the corresponded samples of P. The comparison can be done by calculating the sum of absolute difference (SAD), as shown below.



[0041] The intra prediction mode that gives the smallest SAD is selected to represent the directional pattern (i.e., is the selected intra prediction mode that is used to directly select the transform (inverse-transform) set.

[0042] FIG. 4 is a flow chart illustrating a process 400, according to an embodiment, that is performed by encoder 102.

[0043] Process 400 may begin in step s402 in which selector 114 determines a directional pattern in a prediction block of one of the pictures in the video sequence, wherein the determining comprises using information from a reference block from which the prediction block is generated to determine the directional pattern.

[0044] In some embodiments, determining the directional pattern comprises or consists of the selector 114 determining the reference block's intra prediction mode.

[0045] In step s404, selector 114 selects a transform set for the prediction block based on the determined directional pattern (e.g., based on the reference block's intra prediction mode).

[0046] In step s406, a transform unit of encoder 102 (e.g., primary transform unit 111 or secondary transform unit 112) uses the transform set selected for the prediction block based on the determined directional pattern to transform data derived from the prediction block (e.g., a residual block derived from the prediction block and an original block or transform coefficients generated as a result of transforming the residual block derived from the prediction block). For example, primary transform unit 111 transforms the residual block using the selected transform set or secondary transform unit 112 transforms the output of primary transform unit 111 using the selected transform set.

[0047] FIG. 5 is a flow chart illustrating a process 500, according to an embodiment, that is performed by decoder 104.

[0048] Process 500 may begin in step s502 in which selector 124 determines a directional pattern in a prediction block of one of the pictures in the video sequence, wherein the determining comprises using information from a reference block from which the prediction block is generated to determine the directional pattern.

[0049] In step s504, selector 124 selects an inverse transform set (e.g., an inverse NSST transform set) for the prediction block based on the determined directional pattern.

[0050] In step s506, an inverse transform unit of decoder 104 (e.g., primary inverse transform unit 121 or secondary inverse transform unit 122) inverse transforms data using the inverse transform set selected based on the determined directional pattern. For example, primary transform unit 121 inverse transforms the output of secondary transform unit 122 using the selected inverse transform set or secondary inverse transform unit 122 inverse transforms the output of the de-quantization unit 123 using the selected inverse transform set.

[0051] In some embodiments, process 400 and/or 500 further comprises maintaining mapping information (e.g., a table) that maps each intra prediction mode included in a particular set of intra prediction modes (e.g., modes 0 to 66) to a transform set index that identifies a transform set. The reference block's intra prediction mode is included in the particular set of intra prediction modes, and selecting the transform set (or inverse transform set) comprises using the mapping information to identify the transform set index to which the reference block's intra prediction mode is mapped.

[0052] In some embodiments, the prediction block belongs to a chroma color component and the reference block belongs to a luma color component.

[0053] In some embodiments, the process further includes generating the prediction block using the reference block and a cross-component linear model (CCLM) prediction mode.

[0054] In some embodiments, the prediction block belongs to a color component and the reference block belongs to the same color component.

[0055] In some embodiments, the process also includes generating the prediction block using the reference block and an intra block copy (IBC) tool.

[0056] In some embodiments, determining the directional pattern comprises: defining a set of two or more intra prediction modes, the set of set of two or more intra prediction modes comprising the intra prediction mode of the reference block and a second intra prediction mode; for each intra prediction mode included in the set of intra prediction modes, generating a temporary block; and using the generated temporary blocks and the prediction block to select one of the intra prediction modes from the set of intra prediction modes, wherein the selected intra prediction mode represents the directional pattern such that the transform set is selected based on the selected intra prediction mode.

[0057] As illustrated in FIG. 6, in some embodiments, process 400 and 500 further include determining that a set of one or more conditions is satisfied (see steps s601a and s601b, respectively), wherein the data is transformed (inverse transformed) using the transform (inverse transform) set selected in step s404 (s504) as a result of determining that the set of conditions is satisfied. That is, if the set of conditions are not satisfied, the data will be transformed using the transform set selected in the conventional manner (e.g., selected based on the prediction block's intra prediction mode) (see steps s602a and s602b).

[0058] In some embodiments, determining that the set of conditions is satisfied comprises: determining the prediction block's intra prediction mode; and determining that the prediction block's intra prediction mode satisifies a certain condition (e.g., is above a first threshold (T1), where T1 may equal 66).

[0059] In some embodiments, determining that the set of conditions is satisfied comprises determining that the prediction block was generated using CCLM.

[0060] In some embodiments, determining that the set of conditions is satisfied comprises: determining the number of non-zero transform coefficients (N) of the reference block; and determining that N satisfies a certain condition (e.g., N is at or below a certain threshold (T2)).

[0061] In some embodiments, determining that the set of conditions is satisfied comprises: determining the QP used for the reference block; and determining that the QP satisfies a certain condition (e.g., QP is at or above a certain threshold (T3)).

[0062] In some embodiments, determining that the set of conditions is satisfied comprises determining that a particular flag received from an encoder is set to a certain value.

[0063] FIG. 7 is a block diagram of an apparatus 701 for implementing encoder 102 or decoder 104, according to some embodiments. As shown in FIG. 7, network apparatus 701 may comprise: processing circuitry (PC) 702, which may include one or more processors (P) 755 (e.g., one or more general purpose microprocessors and/or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or data center or may be geographically distributed; a network interface 748 comprising a transmitter (Tx) 745 and a receiver (Rx) 747 for enabling apparatus 701 to transmit data to and receive data from other nodes connected to network 110 (e.g., an Internet Protocol (IP) network) to which network interface 748 is connected; and a local storage unit (a.k.a., "data storage system") 708, which may include one or more non-volatile storage devices and/or one or more volatile storage devices. In embodiments where PC 702 includes a programmable processor, a computer program product (CPP) 741 may be provided. CPP 741 includes a computer readable medium (CRM) 742 storing a computer program (CP) 743 comprising computer readable instructions (CRI) 744. CRM 742 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 744 of computer program 743 is configured such that when executed by PC 702, the CRI causes apparatus 701 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, apparatus 701 may be configured to perform steps described herein without the need for code. That is, for example, PC 702 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

[0064] An advantage of the processes described herein is that they provide better de-correlation of chroma components' residual signal, particularly when CCLM is used. One example is when the luma and chroma components are using the same CU split. The method is applied on chroma components which are predicted by CCLM. The luma intra prediction mode is used to select the NSST transform set. The reference is VVC with BMS setting. The BD rate performance with all intra configuration is provided as follows:
 YUV
Class A1 -0,07% -0,51% -0,77%
Class A2 -0,01% -0,31% -0,32%
Class B -0,01% -0,24% -0,24%
Class C 0,04% -0,23% -0,35%
Class E 0,02% -0,32% 0,04%
Overall 0,00% -0,30% -0,32%
Class D 0,04% -0,31% -0,35%


[0065] While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments.

[0066] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.


Claims

1. A method (400) for encoding a video sequence comprising a plurality of pictures, the method comprising:

determining (s402) a directional pattern in a chroma prediction block of one of the pictures in the video sequence, wherein the chroma prediction block is created by cross-component linear model (CCLM) mode, wherein the determining comprises using information from a luma reference block from which the chroma prediction block is generated to determine the directional pattern, wherein the luma reference block is coded using an intra prediction mode and wherein determining the directional pattern comprises or consists of determining the intra prediction mode of the luma reference block;

selecting (s404) a transform set for the chroma prediction block based on the determined directional pattern; and

using (s406) the selected transform set, transforming data derived from the chroma prediction block, wherein transforming data using the transform set selected based on the determined directional pattern comprises transforming a residual block using the selected transform set.


 
2. A method (500) for decoding a video sequence comprising a plurality of pictures, the method comprising:

determining (s502) a directional pattern in a chroma prediction block of one of the pictures in the video sequence, wherein the chroma prediction block is created by cross-component linear model (CCLM) mode, wherein the determining comprises using information from a luma reference block from which the chroma prediction block is generated to determine the directional pattern, wherein the luma reference block is coded using an intra prediction mode and wherein determining the directional pattern comprises or consists of determining the intra prediction mode of the luma reference block;

selecting (s504) an inverse transform set for the chroma prediction block based on the determined directional pattern; and

inverse transforming (s506) data using the inverse transform set selected based on the determined directional pattern, wherein inverse transforming data using the inverse transform set selected based on the determined directional pattern comprises inverse transforming a coefficient block after dequantization.


 
3. The method of claims 1 or 2, wherein
the method further comprises maintaining mapping information that maps each intra prediction mode included in a particular set of intra prediction modes to a transform set index,
the luma reference block's intra prediction mode is included in the particular set of intra prediction modes, and
selecting the transform set or inverse transform set comprises using the mapping information to identify the transform set index to which the luma reference block's intra prediction mode is mapped.
 
4. The method of any one of claims 1-3, wherein the chroma prediction block belongs to a chroma color component and the luma reference block belongs to a luma color component.
 
5. The method of any one of claims 1 or 3-4, further comprising determining that a set of conditions is satisfied, wherein the step of transforming the data using the transform set selected based on the determined directional pattern is performed as a result of determining that the set of conditions is satisfied.
 
6. The method of any one of claims 2 or 3-4, further comprising determining that a set of conditions is satisfied, wherein the step of inverse transforming the data using the inverse transform set selected based on the determined directional pattern is performed as a result of determining that the set of conditions is satisfied.
 
7. The method of claim 5 or 6, wherein determining that the set of conditions is satisfied comprises:

determining the number of non-zero transform coefficients (N) of the luma reference block; and

determining that N satisfies a certain condition.


 
8. A computer program, the computer program comprising instructions which, when executed by processing circuity (702), cause the processing circuity to carry out the method of any one of claims 1-7.
 
9. A carrier containing the computer program of claim 8, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.
 
10. An encoder (102) for encoding a video sequence comprising a plurality of pictures, the encoder being adapted to perform a method according to any of claims 1, 3-4 and 7.
 
11. A decoder (104) for decoding a video sequence comprising a plurality of pictures, the decoder being adapted to perform a method according to any of claims 2-4 and 6-7.
 


Ansprüche

1. Verfahren (400) zum Codieren einer Videosequenz, die eine Vielzahl von Bildern umfasst, wobei das Verfahren umfasst:

Bestimmen (s402) eines Richtungsmusters in einem Chroma-Vorhersageblock eines der Bilder in der Videosequenz, wobei der Chroma-Vorhersageblock durch einen Kreuzkomponenten-Linearmodell (CCLM)-Modus erzeugt wird, wobei das Bestimmen das Verwenden von Informationen von einem Luma-Referenzblock umfasst, aus dem der Chroma-Vorhersageblock erzeugt wird, um das Richtungsmuster zu bestimmen, wobei der Luma-Referenzblock unter Verwendung eines Intra-Vorhersagemodus codiert wird und wobei das Bestimmen des Richtungsmusters das Bestimmen des Intra-Vorhersagemodus des Luma-Referenzblocks umfasst oder daraus besteht;

Auswählen (s404) eines Transformationssatzes für den Chroma-Vorhersageblock basierend auf dem bestimmten Richtungsmuster; und

Verwenden (s406) des ausgewählten Transformationssatzes, wobei Daten, die von dem Chroma-Vorhersageblock abgeleitet sind, transformiert werden, wobei das Transformieren von Daten unter Verwendung des auf der Grundlage des bestimmten Richtungsmusters ausgewählten Transformationssatzes das Transformieren eines Restblocks unter Verwendung des ausgewählten Transformationssatzes umfasst.


 
2. Verfahren (500) zum Decodieren einer Videosequenz, die eine Vielzahl von Bildern umfasst, wobei das Verfahren umfasst:

Bestimmen (s502) eines Richtungsmusters in einem Chroma-Vorhersageblock eines der Bilder in der Videosequenz, wobei der Chroma-Vorhersageblock durch einen Kreuzkomponenten-Linearmodell (CCLM)-Modus erzeugt wird, wobei das Bestimmen das Verwenden von Informationen von einem Luma-Referenzblock umfasst, aus dem der Chroma-Vorhersageblock erzeugt wird, um das Richtungsmuster zu bestimmen, wobei der Luma-Referenzblock unter Verwendung eines Intra-Vorhersagemodus codiert wird und wobei das Bestimmen des Richtungsmusters das Bestimmen des Intra-Vorhersagemodus des Luma-Referenzblocks umfasst oder daraus besteht;

Auswählen (s504) eines inversen Transformationssatzes für den Chroma-Vorhersageblock basierend auf dem bestimmten Richtungsmuster; und

inverses Transformieren (s506) von Daten unter Verwendung des auf der Grundlage des bestimmten Richtungsmusters ausgewählten inversen Transformationssatzes, wobei das inverse Transformieren von Daten unter Verwendung des auf der Grundlage des bestimmten Richtungsmusters ausgewählten inversen Transformationssatzes das inverse Transformieren eines Koeffizientenblocks nach Dequantisierung umfasst.


 
3. Verfahren nach Anspruch 1 oder 2, wobei

das Verfahren ferner das Aufrechterhalten von Abbildungsinformationen umfasst, die jeden Intra-Vorhersagemodus, der in einem bestimmten Satz von Intra-Vorhersagemodi enthalten ist, auf einen Transformationssatzindex abbilden,

der Intra-Vorhersagemodus des Luma-Referenzblocks in dem bestimmten Satz von Intra-Vorhersagemodi enthalten ist, und

Auswählen des Transformationssatzes oder inversen Transformationssatzes das Verwenden der Abbildungsinformationen umfasst, um den Transformationssatzindex zu identifizieren, auf den der Intra-Vorhersagemodus des Luma-Referenzblocks abgebildet wird.


 
4. Verfahren nach einem der Ansprüche 1 bis 3, wobei der Chroma-Vorhersageblock zu einer Chroma-Farbkomponente gehört und der Luma-Referenzblock zu einer Luma-Farbkomponente gehört.
 
5. Verfahren nach einem der Ansprüche 1 oder 3 bis 4, das ferner das Bestimmen umfasst, dass ein Satz von Bedingungen erfüllt ist, wobei der Schritt des Transformierens von Daten unter Verwendung des auf der Grundlage des bestimmten Richtungsmusters ausgewählten Transformationssatzes als Ergebnis des Bestimmens, dass der Satz von Bedingungen erfüllt ist, durchgeführt wird.
 
6. Verfahren nach einem der Ansprüche 2 oder 3 bis 4, das ferner das Bestimmen umfasst, dass ein Satz von Bedingungen erfüllt ist, wobei der Schritt des inversen Transformierens von Daten unter Verwendung des auf der Grundlage des bestimmten Richtungsmusters ausgewählten inversen Transformationssatzes als Ergebnis des Bestimmens, dass der Satz von Bedingungen erfüllt ist, durchgeführt wird.
 
7. Verfahren nach Anspruch 5 oder 6, wobei das Bestimmen, dass der Satz von Bedingungen erfüllt ist, umfasst:

Bestimmen der Anzahl von Nicht-Null-Transformationskoeffizienten (N) des Luma-Referenzblocks; und

Bestimmen, dass N eine bestimmte Bedingung erfüllt.


 
8. Computerprogramm, wobei das Computerprogramm Anweisungen umfasst, die beim Ausführen durch eine Verarbeitungsschaltung (702) die Verarbeitungsschaltung dazu veranlassen, das Verfahren nach einem der Ansprüche 1 bis 7 durchzuführen.
 
9. Träger, der das Computerprogramm nach Anspruch 8 enthält, wobei der Träger eines von einem elektronischen Signal, einem optischen Signal, einem Funksignal oder einem computerlesbaren Speichermedium ist.
 
10. Codierer (102) zum Codieren einer Videosequenz, die eine Vielzahl von Bildern umfasst, wobei der Codierer angepasst ist, um ein Verfahren gemäß einem der Ansprüche 1, 3 bis 4 und 7 durchzuführen.
 
11. Decodierer (104) zum Decodieren einer Videosequenz, die eine Vielzahl von Bildern umfasst, wobei der Decodierer angepasst ist, um ein Verfahren gemäß einem der Ansprüche 2 bis 4 und 6 bis 7 durchzuführen.
 


Revendications

1. Procédé (400) de codage d'une séquence vidéo comprenant une pluralité d'images, le procédé comprenant :

la détermination (s402) d'un motif directionnel dans un bloc de prédiction de chrominance d'une des images dans la séquence vidéo, dans lequel le bloc de prédiction de chrominance est créé par un mode de modèle linéaire à composantes croisées (CCLM), dans lequel la détermination comprend l'utilisation d'informations provenant d'un bloc de référence de luminance à partir duquel le bloc de prédiction de chrominance est généré pour déterminer le motif directionnel, dans lequel le bloc de référence de luminance est codé en utilisant un mode de prédiction intra et dans lequel la détermination du motif directionnel comprend ou consiste en la détermination du mode de prédiction intra du bloc de référence de luminance ;

la sélection (s404) d'un ensemble de transformation pour le bloc de prédiction de chrominance sur la base du motif directionnel déterminé ; et

l'utilisation (s406) de l'ensemble de transformation sélectionné en transformant des données dérivées du bloc de prédiction de chrominance, dans lequel la transformation de données en utilisant l'ensemble de transformation sélectionné sur la base du motif directionnel déterminé comprend la transformation d'un bloc résiduel en utilisant l'ensemble de transformation sélectionné.


 
2. Procédé (500) de décodage d'une séquence vidéo comprenant une pluralité d'images, le procédé comprenant :

la détermination (s502) d'un motif directionnel dans un bloc de prédiction de chrominance d'une des images dans la séquence vidéo, dans lequel le bloc de prédiction de chrominance est créé par un mode de modèle linéaire à composantes croisées (CCLM), dans lequel la détermination comprend l'utilisation d'informations provenant d'un bloc de référence de luminance à partir duquel le bloc de prédiction de chrominance est généré pour déterminer le motif directionnel, dans lequel le bloc de référence de luminance est codé en utilisant un mode de prédiction intra et dans lequel la détermination du motif directionnel comprend ou consiste en la détermination du mode de prédiction intra du bloc de référence de luminance ;

la sélection (s504) d'un ensemble de transformation inverse pour le bloc de prédiction de chrominance sur la base du motif directionnel déterminé ; et

la transformation inverse (s506) des données en utilisant l'ensemble de transformation inverse sélectionné sur la base du motif directionnel déterminé, dans lequel la transformation inverse de données en utilisant l'ensemble de transformation inverse sélectionné sur la base du motif directionnel déterminé comprend la transformation inverse d'un bloc de coefficient après déquantification.


 
3. Procédé selon les revendications 1 ou 2, dans lequel
le procédé comprend en outre la conservation d'informations de mappage qui mappent chaque mode de prédiction intra inclus dans un ensemble particulier de modes de prédiction intra à un indice d'ensemble de transformation,
le mode de prédiction intra du bloc de référence de luminance est inclus dans l'ensemble particulier de modes de prédiction intra, et
la sélection de l'ensemble de transformation ou de l'ensemble de transformation inverse comprend l'utilisation des informations de mappage pour identifier l'indice d'ensemble de transformation auquel le mode de prédiction intra du bloc de référence de luminance est mappé.
 
4. Procédé selon l'une quelconque des revendications 1 à 3, dans lequel le bloc de prédiction de chrominance appartient à une composante de couleur de chrominance et le bloc de référence de luminance appartient à une composante de couleur de luminance.
 
5. Procédé selon l'une quelconque des revendications 1 ou 3 ou 4, comprenant en outre le fait de déterminer qu'un ensemble de conditions est rempli, dans lequel l'étape de transformation des données en utilisant l'ensemble de transformation sélectionné sur la base du motif directionnel déterminé est mise en œuvre en conséquence du fait de déterminer que l'ensemble de conditions est rempli.
 
6. Procédé selon l'une quelconque des revendications 2 ou 3 ou 4, comprenant en outre le fait de déterminer qu'un ensemble de conditions est rempli, dans lequel l'étape de transformation inverse des données en utilisant l'ensemble de transformation inverse sélectionné sur la base du motif directionnel déterminé est mise en œuvre en conséquence du fait de déterminer que l'ensemble de conditions est rempli.
 
7. Procédé selon la revendication 5 ou 6, dans lequel le fait de déterminer que l'ensemble de conditions est rempli comprend : la détermination du nombre de coefficients de transformation différents de zéro (N) du bloc de référence de luminance ; et le fait de déterminer que N remplit une certaine condition.
 
8. Programme informatique, le programme informatique comprenant des instructions qui, lorsqu'elles sont exécutées par un circuit de traitement (702), amènent le circuit de traitement à effectuer le procédé selon l'une quelconque des revendications 1 à 7.
 
9. Porteuse contenant le programme d'ordinateur selon la revendication 8, dans laquelle la porteuse est l'un parmi un signal électronique, un signal optique, un signal radio ou un support de stockage lisible par ordinateur.
 
10. Codeur (102) pour coder une séquence vidéo comprenant une pluralité d'images, le codeur étant conçu pour mettre en œuvre un procédé selon l'une quelconque des revendications 1, 3 ou 4 et 7.
 
11. Décodeur (104) pour décoder une séquence vidéo comprenant une pluralité d'images, le décodeur étant conçu pour mettre en œuvre un procédé selon l'une quelconque des revendications 2 à 4 et 6 ou 7.
 




Drawing