WO2020055611A1 - Method and apparatus for identity transform in multiple transform selection - Google Patents

Abstract

A method of controlling residual coding for decoding or encoding of a video sequence, is performed by at least one processor and includes determining whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT), based on whether either one or both of a block height and a block width meet a predetermined condition; and based on either one or both of the block height and the block width meeting the predetermined condition, replacing the transform type of MTS by using the IDT and keeping a syntax of the MTS unchanged, and the IDT is a linear transform process using an NxN transform core in which each coefficient is non-zero along a diagonal position, and wherein N is an integer.

Description

METHOD AND APPARATUS FOR IDENTITY TRANSFORM IN MULTIPLE

TRANSFORM SELECTION

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from U.S. Provisional Patent Application No.

62/731,773, filed on September 14, 2018 and U.S. Patent Application No. 16/393,289, filed on April 24, 2019, in the United States Patent and Trademark Office, which are incorporated herein by reference in their entirety.

BACKGROUND

1. Field

[0002] Methods and apparatuses consistent with embodiments relate to video coding, and more particularly, a method and an apparatus for applying identity transform in Multiple Transform Selection (MTS).

2. Description of Related Art

[0003] In High Efficiency Video Coding (HEVC), a coding tree unit (CTU) is split into coding units (CUs) by using a quadtree structure denoted as a coding tree to adapt to various local characteristics. A decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at a CU level. Each CU can be further split into one, two or four prediction units (PUs) according to a PU splitting type. Inside one PU, the same prediction process is applied and relevant information is transmitted to a decoder on a PU basis. After obtaining a residual block by applying a prediction process based on the PU splitting type, a CU can be partitioned into transform units (TUs) according to another quadtree structure similar to the coding tree for the CU. One of key features of an HEVC structure is that it has multiple partition conceptions including CU, PU, and TU. In HEVC, a CU or a TU can only be square shape, while a PU may be square or rectangular shape for an inter predicted block. In a later stage of HEVC, some contributions proposed to allow rectangular shape PUs for intra prediction and transform. At a picture boundary, HEVC imposes implicit a quadtree split so that a block will keep quadtree splitting until a size fits the picture boundary.

[0004] In Versatile Video Coding (VVC), a quadtree plus binary tree (QTBT) structure removes concepts of multiple partition types, i.e., removes a separation of CU, PU and TU concepts, and supports more flexibility for CU partition shapes. In the QTBT block structure, a CU can have either a square or rectangular shape. As shown in FIG. 1 A, a CTU is first partitioned by a quadtree structure. Quadtree leaf nodes are further partitioned by a binary tree structure. There are two splitting types, symmetric horizontal splitting and symmetric vertical splitting, in binary tree splitting. Binary tree leaf nodes are called CUs, and that segmentation is used for prediction and transform processing without any further partitioning. This means that a CU, a PU and a TU have the same block size in the QTBT coding block structure. In VVC, a CU sometimes consists of coding blocks (CBs) of different color components, e.g., one CU contains one luma CB and two chroma CBs in a case of P and B slices of a 4:2:0 chroma format, and a CU sometimes consists of a CB of a single component, e.g., one CU contains only one luma CB or just two chroma CBs in a case of I slices.

[0005] The following parameters are defined for a QTBT partitioning scheme.

[0006] - CTU size: a root node size of a quadtree, the same concept as in HEVC

[0007] - MinQTSize: a minimum allowed quadtree leaf node size

[0008] - MaxBTSize : a maximum allowed binary tree root node size [0009] - MaxBTDepth. a maximum allowed binary tree depth

[0010] - MinBTSize: a minimum allowed binary tree leaf node size

[0011] In an example of the QTBT partitioning structure, the CTU size is set as 128x 128 luma samples with two corresponding 64x64 blocks of chroma samples, the MinQTSize is set as 16x 16, the MaxBTSize is set as 64x64, the MinBTSize (for both width and height) is set as 4x4, and the MaxBTDepth is set as 4. The quadtree partitioning is applied to a CTU first to generate quadtree leaf nodes. The quadtree leaf nodes may each have a size from 16x 16 (i.e., the

MinQTSize ) to 128x 128 (i.e., the CTU size). If the leaf quadtree node is 128x 128, it will not be further split by a binary tree because the size exceeds the MaxBTSize (i.e., 64x64). Otherwise, the leaf quadtree node could be further partitioned by the binary tree. Therefore, the quadtree leaf node is also a root node for the binary tree, and has the binary tree depth as 0. When the binary tree depth reaches MaxBTDepth (i.e., 4), no further splitting is considered. When the binary tree node has the width equal to MinBTSize (i.e., 4), no further horizontal splitting is considered. Similarly, when the binary tree node has the height equal to MinBTSize, no further vertical splitting is considered. The leaf nodes of the binary tree are further processed by prediction and transform processing without any further partitioning. The maximum CTU size may be 256x256 luma samples.

[0012] Portion (a) of FIG. 1 A illustrates an example of block partitioning by using

QTBT, and Portion (b) of FIG. 1 A illustrates a corresponding tree representation. Solid lines indicate quadtree splitting and dotted lines indicate binary tree splitting. In each splitting (i.e., nondeaf) node of the binary tree, one flag is signaled to indicate which splitting type (i.e., horizontal or vertical) is used, where 0 indicates horizontal splitting and 1 indicates vertical splitting. For the quadtree splitting, there is no need to indicate the splitting type because quadtree splitting always splits a block both horizontally and vertically to produce 4 sub-blocks with an equal size.

[0013] In addition, the QTBT scheme supports an ability for a luma and a chroma to each have a separate QTBT structure. Currently, for P and B slices, luma and chroma CTBs in one CTU share the same QTBT structure. However, for I slices, a luma CTB is partitioned into CUs by a QTBT structure, and chroma CTBs are partitioned into chroma CUs by another QTBT structure. This means that a CU in an I slice consists of a coding block of a luma component or coding blocks of two chroma components, and a CU in a P or B slice consists of coding blocks of all three color components.

[0014] In HEVC, inter prediction for small blocks is restricted to reduce a memory access of motion compensation, such that bi-prediction is not supported for 4><8 and 8x4 blocks, and inter prediction is not supported for 4x4 blocks. In a QTBT of VVC, these restrictions are removed.

[0015] In addition to DCT-II and 4x4 DST-VII that are employed in HEVC, an Multiple

Transform Selection (MTS), or as known as a Adaptive Multiple Transform (AMT) or Enhanced Multiple Transform (EMT), scheme is used for residual coding for both inter and intra coded blocks. The MTS uses multiple selected transforms from DCT/DST families other than current transforms in HEVC. Newly introduced transform matrices are DST-VII, DCT-VIII, DST-I and

DCT-V. Table shows basis functions of a selected DST/DCT. Table 1: Transform basis functions of DCT-II/V/VIII and DST-I/VII for N-point input

[0016] To keep an orthogonality of a transform matrix, transform matrices are quantized more accurately than transform matrices in HEVC, with lO-bit representation instead of 8-bit in HEVC. To keep intermediate values of transformed coefficients within a range of l6-bit, after horizontal and after vertical transform, all the coefficients are right shifted by 2 more bits, comparing to a right shift used in current HEVC transforms.

[0017] The AMT applies to CUs each with both width and height smaller than or equal to

64, and whether AMT applies or not is controlled by a CU level flag. When the CU level flag is equal to 0, DCT-II is applied in a CU to encode a residue. For a luma coding block within an AMT enabled CU, two additional flags are signaled to identify the horizontal and vertical transform to be used. As in HEVC, a residual of a block can be coded with a transform skip mode in VVC. To avoid a redundancy of syntax coding, a transform skip flag is not signaled when a CU level AMT flag is not equal to zero.

[0018] For infra residue coding, due to different residual statistics of different intra prediction modes, a mode-dependent transform candidate selection process is used. Three transform subsets are defined as shown in Table 2, and a transform subset is selected based on an intra prediction mode, as specified in Table 3.

Table 2: Three pre-defined transform candidate sets

Table 3: Selected (H)orizontal and (V)ertical transform sets for each intra prediction mode

[0019] With a subset concept, a transform subset is first identified based on Table 3 using an intra prediction mode of a CU with a CU-level AMT flag that is equal to 1. After that, for each of horizontal and vertical transforms, one of two transform candidates in the identified transform subset, according to in Table 2, is selected based on explicitly-signaled flags. [0020] For an inter prediction residual, however, only one transform set, which consists of DST-VII and DCT-VIII, is used for all inter modes and for both horizontal and vertical transforms.

[0021] In VVC, only one transform set, which includes DST-VII and DCT-VIII, is adopted, and MTS is applied up to 32-point.

[0022] In VVC, a Transform Skip (TS) mode is applied for coding both intra and inter prediction residuals. For a coding block (both luma and chroma) with less than or equal to 16 samples, a flag is signaled to indicate whether TS mode is applied for current block. When TS mode is applied, the detailed modifications for each module are listed below.

(a) Prediction: No change.

(b) Transform: Skipped. Instead, for transform skipping TUs, a simple scaling process is used. To let transform skipping coefficients have similar magnitudes as other transform coefficients, a scaling-down process is performed, and the scaling factor is same with the scaling associated with other transforms (versus standard floating point transform with norm 1) of the same size.

(c) De-quantization and scaling. No change.

(d) Entropy coding: A flag is signaled to indicate if transform is bypassed or not.

(e) Deblocking, S AO and ALF : No change.

(f) A flag in the SPS to indicate whether transform skipping is enabled or not.

[0023] In VVC, a mode-dependent non-separable secondary transform (NSST) is applied between a forward core transform and quantization (at an encoder) and between de-quantization and an inverse core transform (at a decoder). To keep low complexity, NSST is only applied to low frequency coefficients after a primary transform. If both width (W) and height (H) of a transform coefficient block is larger than or equal to 8, then an 8x8 non-separable secondary transform is applied to a top-left 8x8 region of a transform coefficients block. Otherwise, if either W or H of a transform coefficient block is equal to 4, a 4x4 non-separable secondary transform is applied, and the 4x4 non-separable transform is performed on a top-left

min(8,W)xmin(8,H) region of the transform coefficient block. The above transform selection rule is applied for both luma and chroma components.

[0024] Matrix multiplication implementation of a non-separable transform is described as follows using a 4x4 input block as an example. To apply the non-separable transform, the 4x4 input block Xis represented as a vector X in Equations (1) and (2):

[0025] The non-separable transform is calculated as F = T X, where F indicates a transform coefficient vector, and Tis a 16x 16 transform matrix. The 16x 1 coefficient vector F is subsequently re-organized as a 4^c4 block using a scanning order for that block (horizontal, vertical or diagonal). Coefficients with a smaller index will be placed with a smaller scanning index in the 4x4 coefficient block. In VVC, a Hypercube-Givens Transform (HyGT) with butterfly implementation is used instead of matrix multiplication to reduce a complexity of non- separable transform.

[0026] There is a total of 35x3 non-separable secondary transforms for both 4x4 and 8x8 block sizes, where 35 is a number of transform sets specified by an intra prediction mode, denoted as set, and 3 is a number of NSST candidates for each intra prediction mode. A mapping from the intra prediction mode to the transform set is defined in Table 4. The transform set applied to luma/chroma transform coefficients is specified by corresponding luma/chroma intra prediction modes, according to Table 4. For intra prediction modes larger than 34 (diagonal prediction direction), a transform coefficient block is transposed before/after a secondary transform at an encoder/decoder.

Table 4: Mapping from intra prediction mode to transform set index

[0027] For each transform set, a selected non-separable secondary transform candidate is further specified by an explicitly signaled CU-level NS ST index. The index is signaled in a bitstream once per intra CU after transform coefficients and truncated unary binarization are used. A truncated value is 2 in case of planar or DC mode, and 3 for an angular intra prediction mode. This NSST index is signaled only when there is more than one non-zero coefficients in a CU. A default value is zero when it is not signaled. Zero value of this syntax element indicates a secondary transform is not applied to the current CU, and values 1-3 indicate which secondary transform from the set should be applied.

[0028] In VVC, NSST is not applied for a block coded with a transform skip mode.

When the NSST index is signaled for a CU and not equal to zero, NSST is not used for a block of a component that is coded with the transform skip mode in the CU. When a CU with blocks of all components are coded in the transform ski mode or a number of non-zero coefficients of non-transform-skip mode CBs is less than 2, the NSST index is not signaled for the CU.

[0029] Mixing NSST and EMT may be forbidden when using QTBT— effectively enforcing NSST to only be used with DCT-2 as a primary transform. [0030] The HyGT is used in a computation of a non-separable secondary transform.

Basic elements of this orthogonal transform are Givens rotations, which are defined by orthogonal matrices G(m, n, Q), which have elements defined by:

fc os Q , i = j = m or i = j = n,

sin Q, i = m,j = n,

Gi _jim. n ) = < —sin Q, i = n,j = m, (5)·

1, i = j and i ¹ m and i ¹ n,

f0, otherwise.

[0031] These transformations can be graphically represented in FIG. 1B.

[0032] HyGT is implemented by combining sets of Givens rotations in a hypercube arrangement. FIG. 1C shows a“butterfly” shape flowchart of HyGT for 16 elements (4x4 non- separable transform). Assuming that N is a power of two, a HyGT round is defined as a sequence of log2(N) passes, where in each pass, indexes in vectors m and n are defined by edges of a hypercube with a dimension log2(N), sequentially in each direction.

[0033] To obtain good compression, more than one HyGT round is used. As shown in

FIG. 1D, a full non-separable secondary transform is composed of R rounds HyGT, and may include an optional permutation pass, to sort transform coefficients according to their variance.

In VVC, a 2-round HyGT is applied for a 4x4 secondary transform, and a 4-round HyGT is applied for a 8x8 secondary transform.

SUMMARY

[0034] According to embodiments, a method of controlling residual coding for decoding or encoding of a video sequence, is performed by at least one processor and includes determining whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT), based on whether either one or both of a block height and a block width meet a predetermined condition. The method further includes, based on either one or both of the block height and the block width meeting the predetermined condition, replacing the transform type of Multiple Transform Selection (MTS) by using the IDT and keeping a syntax of the MTS unchanged, and the IDT is a linear transform process using an NxN transform core in which each coefficient is non-zero along a diagonal position, and N is an integer.

[0035] According to embodiments, an apparatus for controlling residual coding for decoding or encoding of a video sequence includes at least one memory configured to store computer program code, and at least one processor configured to access the at least one memory and operate according to the computer program code. The computer program code includes determining code configured to cause the at least one processor to determine whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT), based on whether either one or both of a block height and a block width meet a predetermined condition. The computer program code further includes replacing code configured to cause the at least one processor to, based on either one or both of the block height and the block width meeting the predetermined condition, replace the transform type of MTS by using the IDT and keeping a syntax of the MTS unchanged, and the IDT is a linear transform process using an NxN transform core in which each coefficient is non-zero along a diagonal position, and N is an integer.

[0036] According to embodiments, a non-transitory computer-readable storage medium stores instructions that cause at least one processor to determine whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT), based on whether either one or both of a block height and a block width meet a predetermined condition. The instructions further cause the at least one processor to based on either one or both of the block height and the block width meeting the predetermined condition, replace the transform type of MTS by using the IDT and keeping a syntax of the MTS unchanged, and the IDT is a linear transform process using an NxN transform core in which each coefficient is non-zero along a diagonal position, and N is an integer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 A is a diagram illustrating a QTBT structure.

[0038] FIG. 1B is a diagram illustrating a graphical representation of Givens rotations.

[0039] FIG. 1C is a diagram illustrating an HyGT that is defined by combinations of

Givens rotations in a hypercube arrangement.

[0040] FIG. 1D is another diagram illustrating an HyGT that is defined by combination of Givens rotations in a hypercube arrangement.

[0041] FIG. 2 is a simplified block diagram of a communication system according to an embodiment.

[0042] FIG. 3 is a diagram of a placement of a video encoder and a video decoder in a streaming environment, according to an embodiment.

[0043] FIG. 4 is a functional block diagram of a video decoder according to an embodiment.

[0044] FIG. 5 is a functional block diagram of a video encoder according to an embodiment.

[0045] FIG. 6 is a flowchart illustrating a method of controlling residual coding for decoding or encoding of a video sequence, according to an embodiment. [0046] FIG. 7 is a flowchart illustrating a method of controlling residual coding for decoding or encoding of a video sequence, according to an embodiment.

[0047] FIG. 8 is a simplified block diagram of an apparatus for controlling residual coding for decoding or encoding of a video sequence, according to an embodiment.

[0048] FIG. 9 is a diagram of a computer system suitable for implementing

embodiments.

DETAILED DESCRIPTION

[0049] FIG. 2 is a simplified block diagram of a communication system (200) according to an embodiment. The communication system (200) may include at least two terminals (210- 220) interconnected via a network (250). For unidirectional transmission of data, a first terminal (210) may code video data at a local location for transmission to the other terminal (220) via the network (250). The second terminal (220) may receive the coded video data of the other terminal from the network (250), decode the coded data and display the recovered video data.

Unidirectional data transmission may be common in media serving applications and the like.

[0050] FIG. 2 illustrates a second pair of terminals (230, 240) provided to support bidirectional transmission of coded video that may occur, for example, during

videoconferencing. For bidirectional transmission of data, each terminal (230, 240) may code video data captured at a local location for transmission to the other terminal via the network (250). Each terminal (230, 240) also may receive the coded video data transmitted by the other terminal, may decode the coded data and may display the recovered video data at a local display device. [0051] In FIG. 2, the terminals (210-240) may be illustrated as servers, personal computers and smart phones but the principles of embodiments are not so limited. Embodiments find application with laptop computers, tablet computers, media players and/or dedicated video conferencing equipment. The network (250) represents any number of networks that convey coded video data among the terminals (210-240), including for example wireline and/or wireless communication networks. The communication network (250) may exchange data in circuit- switched and/or packet-switched channels. Representative networks include telecommunications networks, local area networks, wide area networks and/or the Internet. For the purposes of the present discussion, the architecture and topology of the network (250) may be immaterial to the operation of embodiments unless explained herein below.

[0052] FIG. 3 is a diagram of a placement of a video encoder and a video decoder in a streaming environment, according to an embodiment. The disclosed subject matter can be equally applicable to other video enabled applications, including, for example, video

conferencing, digital TV, storing of compressed video on digital media including CD, DVD, memory stick and the like, and so on.

[0053] A streaming system may include a capture subsystem (313) that can include a video source (301), for example a digital camera, creating, for example, an uncompressed video sample stream (302). That sample stream (302), depicted as a bold line to emphasize a high data volume when compared to encoded video bitstreams, can be processed by an encoder (303) coupled to the camera (301). The encoder (303) can include hardware, software, or a

combination thereof to enable or implement aspects of the disclosed subject matter as described in more detail below. The encoded video bitstream (304), depicted as a thin line to emphasize the lower data volume when compared to the sample stream, can be stored on a streaming server (305) for future use. One or more streaming clients (306, 308) can access the streaming server (305) to retrieve copies (307, 309) of the encoded video bitstream (304). A client (306) can include a video decoder (310) which decodes the incoming copy of the encoded video bitstream (307) and creates an outgoing video sample stream (311) that can be rendered on a display (312) or other rendering device (not depicted). In some streaming systems, the video bitstreams (304, 307, 309) can be encoded according to certain video coding/compression standards. Examples of those standards include ITU-T Recommendation H.265. Under development is a video coding standard informally known as VVC. The disclosed subject matter may be used in the context of VVC.

[0054] FIG. 4 is a functional block diagram of a video decoder (310) according to an embodiment.

[0055] A receiver (410) may receive one or more codec video sequences to be decoded by the decoder (310); in the same or an embodiment, one coded video sequence at a time, where the decoding of each coded video sequence is independent from other coded video sequences. The coded video sequence may be received from a channel (412), which may be a

hardware/software link to a storage device which stores the encoded video data. The receiver (410) may receive the encoded video data with other data, for example, coded audio data and/or ancillary data streams, that may be forwarded to their respective using entities (not depicted).

The receiver (410) may separate the coded video sequence from the other data. To combat network jitter, a buffer memory (415) may be coupled in between receiver (410) and entropy decoder / parser (420) (“parser” henceforth). When receiver (410) is receiving data from a store/forward device of sufficient bandwidth and controllability, or from an isosychronous network, the buffer (415) may not be needed, or can be small. For use on best effort packet networks such as the Internet, the buffer (415) may be required, can be comparatively large and can advantageously of adaptive size.

[0056] The video decoder (310) may include a parser (420) to reconstruct symbols (421) from the entropy coded video sequence. Categories of those symbols include information used to manage operation of the decoder (310), and potentially information to control a rendering device such as a display (312) that is not an integral part of the decoder but can be coupled to it, as was shown in FIG. 4. The control information for the rendering device(s) may be in the form of Supplementary Enhancement Information (SEI messages) or Video Usability Information (VUI) parameter set fragments (not depicted). The parser (420) may parse / entropy-decode the coded video sequence received. The coding of the coded video sequence can be in accordance with a video coding technology or standard, and can follow principles well known to a person skilled in the art, including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, and so forth. The parser (420) may extract from the coded video sequence, a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder, based upon at least one parameter corresponding to the group. Subgroups can include Groups of Pictures (GOPs), pictures, tiles, slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) and so forth. The entropy decoder / parser may also extract from the coded video sequence information such as transform coefficients, quantizer parameter (QP) values, motion vectors, and so forth. [0057] The parser (420) may perform entropy decoding / parsing operation on the video sequence received from the buffer (415), so to create symbols (421). The parser (420) may receive encoded data, and selectively decode particular symbols (421). Further, the parser (420) may determine whether the particular symbols (421) are to be provided to a Motion

Compensation Prediction unit (453), a scaler / inverse transform unit (451), an Intra Prediction unit (452), or a loop filter unit (454).

[0058] Reconstruction of the symbols (421) can involve multiple different units depending on the type of the coded video picture or parts thereof (such as: inter and intra picture, inter and intra block), and other factors. Which units are involved, and how, can be controlled by the subgroup control information that was parsed from the coded video sequence by the parser (420). The flow of such subgroup control information between the parser (420) and the multiple units below is not depicted for clarity.

[0059] Beyond the functional blocks already mentioned, decoder (310) can be conceptually subdivided into a number of functional units as described below. In a practical implementation operating under commercial constraints, many of these units interact closely with each other and can, at least partly, be integrated into each other. However, for the purpose of describing the disclosed subject matter, the conceptual subdivision into the functional units below is appropriate.

[0060] A first unit is the scaler / inverse transform unit (451). The scaler / inverse transform unit (451) receives quantized transform coefficient as well as control information, including which transform to use, block size, quantization factor, quantization scaling matrices, etc. as symbol(s) (421) from the parser (420). It can output blocks comprising sample values that can be input into aggregator (455).

[0061] In some cases, the output samples of the scaler / inverse transform (451) can pertain to an intra coded block; that is: a block that is not using predictive information from previously reconstructed pictures, but can use predictive information from previously

reconstructed parts of the current picture. Such predictive information can be provided by an intra picture prediction unit (452). In some cases, the intra picture prediction unit (452) generates a block of the same size and shape of the block under reconstruction, using surrounding already reconstructed information fetched from the current (partly reconstructed) picture (456). The aggregator (455), in some cases, adds, on a per sample basis, the prediction information the intra prediction unit (452) has generated to the output sample information as provided by the scaler / inverse transform unit (451).

[0062] In other cases, the output samples of the scaler / inverse transform unit (451) can pertain to an inter coded, and potentially motion compensated block. In such a case, a Motion Compensation Prediction unit (453) can access reference picture memory (457) to fetch samples used for prediction. After motion compensating the fetched samples in accordance with the symbols (421) pertaining to the block, these samples can be added by the aggregator (455) to the output of the scaler / inverse transform unit (in this case called the residual samples or residual signal) so to generate output sample information. The addresses within the reference picture memory form where the motion compensation unit fetches prediction samples can be controlled by motion vectors, available to the motion compensation unit in the form of symbols (421) that can have, for example X, Y, and reference picture components. Motion compensation also can include interpolation of sample values as fetched from the reference picture memory when sub- sample exact motion vectors are in use, motion vector prediction mechanisms, and so forth.

[0063] The output samples of the aggregator (455) can be subject to various loop filtering techniques in the loop filter unit (454). Video compression technologies can include in-loop filter technologies that are controlled by parameters included in the coded video bitstream and made available to the loop filter unit (454) as symbols (421) from the parser (420), but can also be responsive to meta-information obtained during the decoding of previous (in decoding order) parts of the coded picture or coded video sequence, as well as responsive to previously reconstructed and loop-filtered sample values.

[0064] The output of the loop filter unit (454) can be a sample stream that can be output to the render device (312) as well as stored in the reference picture memory (456) for use in future inter-picture prediction.

[0065] Certain coded pictures, once fully reconstructed, can be used as reference pictures for future prediction. Once a coded picture is fully reconstructed and the coded picture has been identified as a reference picture (by, for example, parser (420)), the current reference picture (456) can become part of the reference picture buffer (457), and a fresh current picture memory can be reallocated before commencing the reconstruction of the following coded picture.

[0066] The video decoder (310) may perform decoding operations according to a predetermined video compression technology that may be documented in a standard, such as ITU-T Rec. H.265. The coded video sequence may conform to a syntax specified by the video compression technology or standard being used, in the sense that it adheres to the syntax of the video compression technology or standard, as specified in the video compression technology document or standard and specifically in the profiles document therein. Also necessary for compliance can be that the complexity of the coded video sequence is within bounds as defined by the level of the video compression technology or standard. In some cases, levels restrict the maximum picture size, maximum frame rate, maximum reconstruction sample rate (measured in, for example megasamples per second), maximum reference picture size, and so on. Limits set by levels can, in some cases, be further restricted through Hypothetical Reference Decoder (HRD) specifications and metadata for HRD buffer management signaled in the coded video sequence.

[0067] In an embodiment, the receiver (410) may receive additional (redundant) data with the encoded video. The additional data may be included as part of the coded video sequence(s). The additional data may be used by the video decoder (310) to properly decode the data and/or to more accurately reconstruct the original video data. Additional data can be in the form of, for example, temporal, spatial, or signal -to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, and so on.

[0068] FIG. 5 is a functional block diagram of a video encoder (303) according to an embodiment.

[0069] The encoder (303) may receive video samples from a video source (301) (that is not part of the encoder) that may capture video image(s) to be coded by the encoder (303).

[0070] The video source (301) may provide the source video sequence to be coded by the encoder (303) in the form of a digital video sample stream that can be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, ...), any colorspace (for example, BT.601 Y CrCB, RGB, ...) and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). In a media serving system, the video source (301) may be a storage device storing previously prepared video. In a videoconferencing system, the video source (301) may be a camera that captures local image information as a video sequence. Video data may be provided as a plurality of individual pictures that impart motion when viewed in sequence. The pictures themselves may be organized as a spatial array of pixels, wherein each pixel can comprise one or more samples depending on the sampling structure, color space, etc. in use. A person skilled in the art can readily understand the relationship between pixels and samples. The description below focuses on samples.

[0071] According to an embodiment, the encoder (303) may code and compress the pictures of the source video sequence into a coded video sequence (543) in real time or under any other time constraints as required by the application. Enforcing appropriate coding speed is one function of Controller (550). Controller controls other functional units as described below and is functionally coupled to these units. The coupling is not depicted for clarity. Parameters set by controller can include rate control related parameters (picture skip, quantizer, lambda value of rate-distortion optimization techniques, ...), picture size, group of pictures (GOP) layout, maximum motion vector search range, and so forth. A person skilled in the art can readily identify other functions of controller (550) as they may pertain to video encoder (303) optimized for a certain system design.

[0072] Some video encoders operate in what a person skilled in the art readily recognizes as a“coding loop.” As an oversimplified description, a coding loop can consist of the encoding part of an encoder (530) (“source coder” henceforth) (responsible for creating symbols based on an input picture to be coded, and a reference picture(s)), and a (local) decoder (533) embedded in the encoder (303) that reconstructs the symbols to create the sample data that a (remote) decoder also would create (as any compression between symbols and coded video bitstream is lossless in the video compression technologies considered in the disclosed subject matter). That reconstructed sample stream is input to the reference picture memory (534). As the decoding of a symbol stream leads to bit-exact results independent of decoder location (local or remote), the reference picture buffer content is also bit exact between local encoder and remote encoder. In other words, the prediction part of an encoder“sees” as reference picture samples exactly the same sample values as a decoder would“see” when using prediction during decoding. This fundamental principle of reference picture synchronicity (and resulting drift, if synchronicity cannot be maintained, for example because of channel errors) is well known to a person skilled in the art.

[0073] The operation of the“local” decoder (533) can be the same as of a“remote” decoder (310), which has already been described in detail above in conjunction with FIG. 4. Briefly referring also to FIG. 4, however, as symbols are available and en/decoding of symbols to a coded video sequence by entropy coder (545) and parser (420) can be lossless, the entropy decoding parts of decoder (310), including channel (412), receiver (410), buffer (415), and parser (420) may not be fully implemented in local decoder (533).

[0074] An observation that can be made at this point is that any decoder technology except the parsing/entropy decoding that is present in a decoder also necessarily needs to be present, in substantially identical functional form, in a corresponding encoder. The description of encoder technologies can be abbreviated as they are the inverse of the comprehensively described decoder technologies. Only in certain areas a more detail description is required and provided below. [0075] As part of its operation, the source coder (530) may perform motion compensated predictive coding, which codes an input frame predictively with reference to one or more previously-coded frames from the video sequence that were designated as“reference frames.” In this manner, the coding engine (532) codes differences between pixel blocks of an input frame and pixel blocks of reference frame(s) that may be selected as prediction reference(s) to the input frame.

[0076] The local video decoder (533) may decode coded video data of frames that may be designated as reference frames, based on symbols created by the source coder (530).

Operations of the coding engine (532) may advantageously be lossy processes. When the coded video data may be decoded at a video decoder (not shown in FIG. 4), the reconstructed video sequence typically may be a replica of the source video sequence with some errors. The local video decoder (533) replicates decoding processes that may be performed by the video decoder on reference frames and may cause reconstructed reference frames to be stored in the reference picture cache (534). In this manner, the encoder (303) may store copies of reconstructed reference frames locally that have common content as the reconstructed reference frames that will be obtained by a far-end video decoder (absent transmission errors).

[0077] The predictor (535) may perform prediction searches for the coding engine (532).

That is, for a new frame to be coded, the predictor (535) may search the reference picture memory (534) for sample data (as candidate reference pixel blocks) or certain metadata such as reference picture motion vectors, block shapes, and so on, that may serve as an appropriate prediction reference for the new pictures. The predictor (535) may operate on a sample block-by- pixel block basis to find appropriate prediction references. In some cases, as determined by search results obtained by the predictor (535), an input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (534).

[0078] The controller (550) may manage coding operations of the video coder (530), including, for example, setting of parameters and subgroup parameters used for encoding the video data.

[0079] Output of all aforementioned functional units may be subjected to entropy coding in the entropy coder (545). The entropy coder translates the symbols as generated by the various functional units into a coded video sequence, by loss-less compressing the symbols according to technologies known to a person skilled in the art as, for example Huffman coding, variable length coding, arithmetic coding, and so forth.

[0080] The transmitter (540) may buffer the coded video sequence(s) as created by the entropy coder (545) to prepare it for transmission via a communication channel (560), which may be a hardware/software link to a storage device that may store the encoded video data. The transmitter (540) may merge coded video data from the video coder (530) with other data to be transmitted, for example, coded audio data and/or ancillary data streams (sources not shown).

[0081] The controller (550) may manage operation of the encoder (303). During coding, the controller (550) may assign to each coded picture a certain coded picture type, which may affect the coding techniques that may be applied to the respective picture. For example, pictures often may be assigned as one of the following frame types:

[0082] An Intra Picture (I picture) may be one that may be coded and decoded without using any other frame in the sequence as a source of prediction. Some video codecs allow for different types of Intra pictures, including, for example Independent Decoder Refresh Pictures. A person skilled in the art is aware of those variants of I pictures and their respective applications and features.

[0083] A Predictive picture (P picture) may be one that may be coded and decoded using intra prediction or inter prediction using at most one motion vector and reference index to predict the sample values of each block.

[0084] A Bi-directionally Predictive Picture (B Picture) may be one that may be coded and decoded using intra prediction or inter prediction using at most two motion vectors and reference indices to predict the sample values of each block. Similarly, multiple-predictive pictures can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0085] Source pictures commonly may be subdivided spatially into a plurality of sample blocks (for example, blocks of 4 x 4, 8 x 8, 4 x 8, or 16 x 16 samples each) and coded on a block- by-block basis. Blocks may be coded predictively with reference to other (already coded) blocks as determined by the coding assignment applied to the blocks’ respective pictures. For example, blocks of I pictures may be coded non-predictively or they may be coded predictively with reference to already coded blocks of the same picture (spatial prediction or intra prediction).

Pixel blocks of P pictures may be coded non-predictively, via spatial prediction or via temporal prediction with reference to one previously coded reference pictures. Blocks of B pictures may be coded non-predictively, via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures.

[0086] The video coder (303) may perform coding operations according to a

predetermined video coding technology or standard, such as ITU-T Rec. H.265. In its operation, the video coder (303) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancies in the input video sequence. The coded video data, therefore, may conform to a syntax specified by the video coding technology or standard being used.

[0087] In an embodiment, the transmitter (540) may transmit additional data with the encoded video. The video coder (530) may include such data as part of the coded video sequence. Additional data may comprise temporal/spatial/SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, Supplementary Enhancement

Information (SEI) messages, Visual Usability Information (VUI) parameter set fragments, and so on.

[0088] In VVC, there are separate syntaxes and semantics for TS mode and MTS, however, these two tools are both related to transform selection, and the syntaxes and semantics can be harmonized.

[0089] Separate signaling of TS mode and MTS increases the complexity for both the encoder and the decoder. For the encoder, an additional TS mode should be checked if MTS is not used. For the decoder, TS mode is implemented separately from MTS.

[0090] In TS mode, both horizontal and vertical transforms are skipped. However, it is more flexible to have transform skipped for either horizontal or vertical, or both horizontal and vertical.

[0091] TS mode is applied for blocks with area size smaller than or equal to 16, for 4x2 and 2x4 blocks, since the area size is not a power of 2, to re-use the same quantization scheme, multiplication operations are needed in TS mode, which are additional computation cost comparing to 4-point transform skip which does not involve multiplications.

[0092] Thus, according to embodiments, certain transform types of MTS are replaced by

Identity transform (IDT), but keeping the syntax of MTS unchanged. An N-point IDT is a linear transform process using an NxN transform core which has only non-zero coefficient along the diagonal positions, the diagonal positions refer to positions having equal horizontal and vertical coordinate values.

[0093] According to an embodiment, certain transform types of MTS, (namely trType) are replaced by IDT (or certain transform types of MTS are replaced by IDT if the certain transform types of MTS are applied on the smaller side of block) if the block width and/or height meets pre-defmed conditions.

[0094] The following conditions may be used separately or combined in any order.

(a) In an example, the certain transform types of MTS include, but not limited to DCT-l, DCT-2, ... DCT-8, DST-l, DST-2, ... DST-8. This bullet applies to below a.ii ~ a.ix.

(b) In an example, the certain transform types of MTS can be DCT-8 or DCT-4.

(c) In an example, it is further restricted that when selecting the primary transform type, intra prediction mode information is not used. That is, there is no intra prediction mode dependency on selecting the primary transform type.

(d) In an example, the condition is whether the said certain transform types of MTS are applied as the horizontal transform and block width is smaller than or equal to a pre-defmed threshold. Example values (T) include but not limited to 2, 4, 8, 16, 32, 64, 128, 256. (e) In another example, the condition is whether the said certain transform types of MTS are applied as the vertical transform and block height is smaller than or equal to a pre-defmed threshold. Example values (T) include but are not limited to 2, 4, 8, 16, 32, 64, 128, 256.

(f) In an example, the condition is whether the block area size is smaller than or equal to a pre-defmed value, example values (T) include but are not limited to 8, 16, 32, 64, 128, 256, 512, 1024.

(f) In another example, the condition is whether max(width/height, height/width) ratio is smaller than or larger than a pre-defmed threshold value. Example values of the threshold values (T) include, but not limited to 2, 4, 8, 16, 32.

(g) In another example, the condition is whether min(height, width) is smaller than a pre- defmed threshold.

(h) In an embodiment, the threshold values (T) mentioned above, or Log2(T) or Log2(T)-l, or Log2(T-2) can be signaled in Slice header, PPS, SPS, VPS.

(i) In another example, transform type trType is replaced by IDT if horizontal and transform types are different. That is, if transform type trType is used only on horizontal direction or vertical direction, but not both, then transform type trType is replaced by IDT.

(j) In an example, the horizontal and vertical transform combinations used in MTS, i.e., (DST-7, DST-7}, (DST-7, DCT-8}, (DCT-8, DST-7}, (DCT-8, DCT-8}, are replaced by a different set of horizontal and vertical transform combinations, including: (DST-7, DST-7}, (DST-7, IDT}, (IDT, DST-7} and (DCT-8, DCT-8}. [0095] In an embodiment, the transform core of IDT has only non-zero elements 2^M* sqrt(N), where M is integers, example values of M include, but not limited to -20, -19, ..., 0, 1, 2, ... 19, 20.

[0096] In an embodiment, the transform core of IDT has only non-zero elements

Floor(2^M * sqrt(N)+0.5), where M is integers, example values of M include, but are not limited to -20, -19, ..., 0, 1, 2, ... 19, 20, Floor(.) is the floor function which returns the largest integer which is smaller than the input value.

[0097] In another embodiment, the transform core of IDT has only non-zero elements values being 2^M, where values of M depend on transform size.

[0098] According to an embodiment a different quantization matrix is applied for different primary and/or secondary transform types.

[0099] Depending on whether IDT is applied on horizontal direction, vertical direction or both horizontal and vertical direction, different quantization matrices are used.

[0100] In an example, if IDT is applied as both horizontal and vertical transform, a flat quantization matrix (with identical elements) is used.

[0101] In another example, if IDT is only applied as the horizontal transform, then a quantization matrix with identical elements along the horizontal direction is used.

[0102] In another example, if IDT is only applied as the vertical transform, then a quantization matrix with identical elements along the vertical direction is used.

[0103] Depending on which MTS candidates are applied on horizontal direction, vertical direction or both horizontal and vertical direction, different quantization matrices are used. [0104] According to an embodiment, when signaling the MTS transform index, if the number of non-zero coefficients is less than or equal to a pre-defmed threshold value, then MTS transform index is not signaled but implicitly derived as 0. The threshold value may depend on the primary and/or secondary transform types.

[0105] The following conditions may be used separately or combined in any order.

(a) In an example, if IDT is applied as both horizontal and vertical transform, the threshold value is -1 or 0 or 1.

(b) In another example, if IDT is applied as either horizontal and vertical transform, but not both horizontal and vertical transform, the threshold value is -1 or 0 or 1, and the value is different from the threshold value used in MTS transform index signaling when IDT is not applied.

(c) According to an embodiment, it is determined whether and which NSST transform cores are used depending on whether IDT is applied as the horizontal transform, vertical transform or both horizontal and vertical transforms.

[0106] The following conditions may be used separately or combined in any order.

(a) In an example, if IDT is applied as both horizontal and vertical transform, NSST is not applied.

(b) In an example, if IDT is applied as either horizontal and vertical transform, NSST is not applied.

(c) In an embodiment, whether NSST is applied may not only depend on the usage of IDT in MTS, but also depend on other coded information or any information that is available to both encoder and decoder, including, but not limited to block width, block height, block area size, block width to height ratio, intra prediction mode.

[0107] The below syntax descriptions illustrate changes to the VVC spec text draft version 2, according to an embodiment. Text that is added is shown in underline and text that is deleted is shown in strikethrough.

[0108] Picture parameter set RBSP syntax

[0109] Residual coding syntax

[0110] Picture parameter set RBSP semantics pps_pie_parameter_set_id identifies the PPS for reference by other syntax elements. The value of pps_pic_parameter_set_id shall be in the range of 0 to 63, inclusive.

pps seq parameter set id specifies the value of sps_seq_j)arameter_set_id for the active SPS. The value of pps_seq_parameter_set_id shall be in the range of 0 to 15, inclusive.

transform_slap_enabled_flag equal to 1 Specifies that transform_sfcip_flag may be present in the residual coding syntax. transform_skip_enabled_flag equal to Q specifies that trahsform_skip_flag is not present in the residual coding syntax.

[0111] Residual coding semantics

The array AbsLevel[ xC ][ yC ] represents an array of absolute values of tran form coefficient levels for the current transform block and the at ray AbsLevel Pass l f xC ][ yC ] represents an array of partially reconstructed absolute values of transform coefficient levels for the current transform block. The array indices \C and yC specify the transform coefficient location ( xC, yC ) within the current transform block. When the value of AbsLevel[ xC ][ yC ] is not specified in clause 7.3.4.8, it is inferred to be equal to 0. When the value of AbsLevelPassl[ xC ][ yC ] is not specified in clause 7. .4 8, it is inferred to be equal to 0.

The variables CoeffMin and CoeffMax specifying the minimum and maximum transform coefficient values are derived by the following Equations (3) and (4): CoeffMin = -( 1 « 15 ) (3)

CoeffMax = ( 1 « 15 ) - 1 (4)

The array QStateTransTable[ ][ ] is specified by the following Equation:

QStateTransTable[ ][ ] = { { 0, 2 }, { 2, 0 }, { 1, 3 }, { 3, 1 } } (5)

transform_skip_flag[ x0 ][ y0 ][ cldx ]— specifies whether— a transform— is— applied to the associated transform block or not: The array indices xO, yO specify the location ( xO, yO ) of the top left luma sample of the considered transform block relative to the top left luma sample of the picture. The array index cldx specifies an indicator for the colour component; it is equal to 0 for luma, equal to 1 for Cb and equal to 2 for Cr. transform_skip_flag[ xO ][ yO ][ cldx ] equal to 1 specifies - that - no - transform - is - applied - to - the - current - transform - block. transform_skip_flag[ xO ][ yO ][ cldx ] equal to 0 specifics that the decision whether transform is applied to the current transform block or not depends on other syntax elements. When transform_skip_flag[ xO ][ yO ][ cldx ] is not present, it is inferred to be equal to 0.

last sig coeff x prefix specifies the prefix of the column position of the last significant coefficient in scanning order within a transform block. The values of last_sig_coeff_x_prefix shall be in the range of 0 to ( log2TbWidth « 1 ) - 1, inclusive.

last sig coeff y prefix specifies the prefix of the row position of the last significant coefficient in scanning order within a transform block. The values of last_sig_coeff_y_prefix shall be in the range of 0 to ( log2TbHeight « 1 ) - 1, inclusive.

last sig coeff x suffix specifies the suffix of the column position of the last significant coefficient in scanning order within a transform block. The values of last sig coeff x suffix shall be in the range of 0 to ( 1 « ( ( last_sig_coeff_x_prefix » 1 )— 1 ) )— 1, inclusive.

The column position of the last significant coefficient in scanning order within a transform block LastSignificantCoeffX is derived as follows:

[0112] Scaling and transformation process

Inputs to this process are:

- a luma location ( xTbY, yTbY ) specifying the top-left sample of the current luma transform block relative to the top-left luma sample of the current picture,

- a variable cldx specifying the colour component of the current block,

- a variable nTbW specifying the transform block width,

- a variable nTbH specifying the transform block height.

Output of this process is the (nTbW)x(nTbH) array of residual samples resSamples[ x ][ y ] with x = O.mTbW - 1, y = O.mTbH - 1. The variables bitDepth, bdShift and tsShift are derived by the following equations: bitDepth = ( cldx = = 0 ) ? BitDepthy : BitDepthc (6)

bdShift = Max( 22 - bitDepth, 0 ) (7)

ts Shift = 5 + ( ( Log2( nTbW ) + Log2( nTbH ) ) / 2 ) - (8)

The (nTbW)x(nTbH) array of residual samples resSamples is derived as follows:

(1) The scaling process for transform coefficients as specified in clause 8.3.3 is invoked with the transform block location ( xTbY, yTbY ), the transform width nTbW and the transform height nTbH, the colour component variable cldx and the bit depth of the current colour component bitDepth as inputs, and the output is an (nTbW)x(nTbH) array of scaled transform coefficients d.

(2) - The (nTbW)x(nTbH) array of residual samples r is derived as follows:

- If transform_skip_flag[ xTbY ][ yTbY ][ cldx ] is equal to 1, the residual sample array values r[ x ][ y ] with with x O.mTbW - 1, y O.mTbH - 1 are derived as follows: r[ ^x ][ Y ] ~ d[ x ][ y ] « tsShift - (9)

- Otherwise— (transform_skip_flag[ xTbY ][ yTbY ][ cldx ]— is— equal— to— <¾ the transformation process for scaled transform coefficients as specified in clause 8.3.4.1 is invoked with the transform block location ( xTb Y, yTbY ), the transform width nTbW and the transform height nTbH, the colour component variable cldx and the (nTbW)x(nTbH) array of scaled transform coefficients d as inputs, and the output is an (nTbW)x(nTbH) array of residual samples r.

(3) The residual samples resSamples[ x ][ y ] with x = O.mTbW - 1, y = O.mTbH - 1 are derived by the following Equation:

resSamples[ x ][ y ] = ( r[ x ][ y ] + ( 1 « ( bdShift - 1 ) ) ) » bdShift (10)

[0113] Transformation matrix derivation process

Inputs to this process are:

- a variable nTbS specifying the horizontal sample size of scaled transform coefficients,

- the transformation kernel type trType.

Output of this process is the transformation matrix transMatrix.

The transformation matrix transMatrix is derived based on trType and nTbs as follows:

- If trType is equal to 0, the following Equations apply: transMatrix[ m ][ n ] = transMatrixCol0tol5[ m ][ n ] with m = 0..15, n = 0..63 (11) transMatrixColOto 15 (12)

{ 256 256 256 256 256 256 256 256 256 256 256 256 256 256 256 256 } { 362 361 359 357 353 349 344 338 331 323 315 306 296 285 274 262 } { 362 358 351 341 327 311 291 268 243 216 186 155 122 88 53 18 } { 361 353 338 315 285 250 208 163 114 62 9 -44 -97 -147 -194 236 } { 360 346 319 280 230 171 105 35 -35 105 -171 -230 280 -319 -346 360 } { 359 338 296 236 163 79 -9 -97 -178 250 -306 -344 361 -357 -331 285 } { 358 327 268 186 88 -18 122 -216 -291 341 -362 -351 311 -243 -155 -53 } { 357 315 236 130 9 -114 223 -306 -353 359 -323 -250 147 -27 97 208 } { 355 301 201 71 -71 -201 301 -355 -355 301 -201 -71 71 201 301 355 } { 353 285 163 9 -147 -274 349 -357 -296 178 -27 130 262 344 359 306 } { 351 268 122 -53 -216 -327 362 -311 -186 -18 155 291 358 341 243 88

{ 349 250 79 114 -274 -357 338 -223 -44 147 296 361 323 194 9 178 } { 346 230 35 171 -319 -360 280 -105 105 280 360 319 171 -35 -230 346 } { 344 208 -9 223 -349 -338 194 27 236 353 331 178 -44 -250 -357 323 } { 341 186 -53 268 -362 -291 -88 155 327 351 216 -18 243 -358 -311 122

{ 338 163 -97 306 -357 -223 27 262 362 274 44 -208 353 -315 -114 147 } { 334 139 -139 334 -334 -139 139 334 334 139 -139 -334 334 -139 139 334 } { 331 114 -178 353 -296 -44 236 362 250 -27 -285 -357 194 97 323 338 } { 327 88 -216 362 -243 53 311 341 122 186 -358 -268 18 291 351 155 } { 323 62 -250 359 -178 147 353 274 -27 306 -338 -97 223 362 208 114 } { 319 35 -280 346 -105 230 360 171 -171 360 -230 105 346 280 -35 319 } { 315 9 -306 323 -27 296 331 44 -285 338 -62 274 344 79 -262 349 } { 311 -18 -327 291 53 341 268 -88 -351 243 122 358 216 -155 -362 186 } { 306 -44 -344 250 130 361 178 -208 -357 -97 274 331 9 -323 -285 79 } { 301 -71 -355 201 201 355 71 -301 -301 71 355 201 201 -355 -71 301 } { 296 -97 -361 147 262 323 -44 -353 -194 223 344 9 338 -236 178 357 } { 291 -122 -362 -88 311 268 155 -358 -53 327 243 -186 351 -18 341 216 } { 285 -147 -357 -27 344 194 250 -315 97 362 79 -323 236 208 338 -44 } { 280 -171 -346 35 360 105 319 -230 230 319 -105 -360 -35 346 171 280 } { 274 -194 -331 97 359 9 357 -114 323 208 -262 -285 178 338 -79 361 } { 268 -216 -311 155 341 -88 358 18 362 53 -351 -122 327 186 -291 243 } { 262 -236 -285 208 306 -178 323 147 338 114 -349 79 357 -44 -361 9 } { 256 -256 -256 256 256 -256 256 256 256 256 -256 256 256 -256 -256 256 } { 250 -274 -223 296 194 -315 163 331 130 344 -97 353 62 -359 -27 362 } { 243 -291 -186 327 122 -351 -53 362 -18 358 88 341 155 -311 216 268 } { 236 -306 -147 349 44 -362 62 344 -163 296 250 223 315 -130 353 27 } { 230 -319 -105 360 -35 -346 171 280 -280 171 346 35 360 105 319 230 } { 223 -331 -62 361 -114 -306 262 178 -349 -9 353 -163 274 296 130 359 } { 216 -341 -18 351 -186 -243 327 53 -358 155 268 -311 -88 362 -122 291 } { 208 -349 27 331 -250 -163 359 -79 -306 285 114 -362 130 274 -315 -62 } { 201 -355 71 301 -301 -71 355 -201 -201 355 -71 -301 301 71 -355 201

{ 194 -359 114 262 -338 27 315 -296 -62 349 -236 -147 362 -163 -223 353 } { 186 -362 155 216 -358 122 243 -351 88 268 -341 53 291 -327 18 311 } { 178 -362 194 163 -361 208 147 -359 223 130 -357 236 114 -353 250 97 } { 171 -360 230 105 -346 280 35 -319 319 -35 -280 346 105 -230 360 171 } { 163 -357 262 44 -315 331 -79 -236 361 194 -130 349 285 -9 296 344 } { 155 -351 291 -18 -268 358 186 -122 341 311 53 243 362 216 88 327 } { 147 -344 315 -79 -208 359 274 9 262 361 223 62 306 349 -163 130 } { 139 -334 334 139 -139 334 334 139 139 334 334 -139 139 334 -334 139 } { 130 -323 349 194 -62 285 361 250 -9 236 359 -296 79 178 -344 331 } { 122 -311 358 243 18 216 351 327 -155 -88 291 -362 268 -53 -186 341 } { 114 -296 362 285 97 130 306 361 -274 79 147 -315 359 -262 62 163 } { 105 -280 360 319 171 35 230 346 -346 230 -35 -171 319 -360 280 105 } { 97 -262 353 344 236 -62 130 285 -359 331 -208 27 163 -306 362 315 } { 88 -243 341 358 291 -155 -18 186 -311 362 -327 216 -53 -122 268 351 } { 79 -223 323 362 331 -236 97 62 -208 315 -361 338 250 114 44 194 } { 71 -201 301 355 355 -301 201 -71 -71 201 -301 355 355 301 -201 71 } { 62 -178 274 338 362 -344 285 -194 79 44 -163 262 331 361 -349 296 } { 53 -155 243 311 351 -362 341 -291 216 122 18 88 186 268 -327 358 } { 44 -130 208 274 323 -353 362 -349 315 262 194 -114 27 62 -147 223 } { 35 -105 171 230 280 -319 346 -360 360 346 319 -280 230 -171 105 -35 } { 27 -79 130 178 223 -262 296 -323 344 357 362 -359 349 -331 306 274 } { 18 -53 88 122 155 -186 216 -243 268 291 311 -327 341 -351 358 362 } 9 -27 44 -62 79 -97 114 -130 147 -163 178 -194 208 -223 236 -250

},

transMatrix[ m ][ n ] = transMatrixColl6to3l[ m - 16 ][ n ] with m = 16..31, n = 0..63 (13) transMatrixColl6to3l = (14)

{ 256 256 256 256 256 256 256 256 256 256 256 256 256 256 256 256 }

{ 250 236 223 208 194 178 163 147 130 114 97 79 62 44 27 9 }

{ -18 -53 -88 -122 -155 -186 -216 -243 -268 -291 -311 -327 -341 -351 358 -362 }

{-274 -306 -331 -349 -359 -362 -357 -344 -323 -296 -262 -223 -178 -130 -79 -27 }

{-360 -346 -319 -280 -230 -171 -105 -35 35 105 171 230 280 319 346 360 }

{-223 -147 -62 27 114 194 262 315 349 362 353 323 274 208 130 44 }

{ 53 155 243 311 351 362 341 291 216 122 18 -88 -186 -268 327 -358 }

{ 296 349 361 331 262 163 44 -79 -194 -285 -344 -362 -338 -274 178 -62 }

{ 355 301 201 71 -71 -201 -301 -355 -355 -301 -201 -71 71 201 301 355 }

{ 194 44 -114 -250 -338 -361 -315 -208 -62 97 236 331 362 323 223 79 }

{ -88 -243 -341 -358 -291 -155 18 186 311 362 327 216 53 -122 268 -351 }

{-315 -362 -306 -163 27 208 331 359 285 130 -62 -236 -344 -353 262 -97 }

{-346 -230 -35 171 319 360 280 105 -105 -280 -360 -319 -171 35 230 346 }

{-163 62 262 359 315 147 -79 -274 -361 -306 -130 97 285 362 296 114 }

{ 122 311 358 243 18 -216 -351 -327 -155 88 291 362 268 53 186 -341 }

{ 331 344 178 -79 -296 -359 -236 9 250 361 285 62 -194 -349 323 -130 }

{ 334 139 -139 -334 -334 -139 139 334 334 139 -139 -334 -334 -139 139 334 }

{ 130 -163 -349 -306 -62 223 361 262 -9 -274 -359 -208 79 315 344 147 }

{-155 -351 -291 -18 268 358 186 -122 -341 -311 -53 243 362 216 -88 -327 }

{-344 -296 -9 285 349 130 -194 -361 -236 79 331 315 44 -262 357 -163 }

{-319 -35 280 346 105 -230 -360 -171 171 360 230 -105 -346 -280 35 319 }

{ -97 250 353 114 -236 -357 -130 223 359 147 -208 -361 -163 194 362 178 }

{ 186 362 155 -216 -358 -122 243 351 88 -268 -341 -53 291 327 18 -311 }

{ 353 223 -163 -362 -147 236 349 62 -296 -315 27 338 262 -114 359 -194 }

{ 301 -71 -355 -201 201 355 71 -301 -301 71 355 201 -201 -355 -71 301 }

{ 62 -315 -274 130 362 114 -285 -306 79 359 163 -250 -331 27 349 208 }

{-216 -341 18 351 186 -243 -327 53 358 155 -268 -311 88 362 122 -291 }

{-359 -130 296 274 -163 -353 -9 349 178 -262 -306 114 361 62 331 -223 }

{-280 171 346 -35 -360 -105 319 230 -230 -319 105 360 35 -346 171 280 }

{ -27 353 130 -315 -223 250 296 -163 -344 62 362 44 -349 -147 306 236 }

{ 243 291 -186 -327 122 351 -53 -362 -18 358 88 -341 -155 311 216 -268 }

{ 362 27 -359 -62 353 97 -344 -130 331 163 -315 -194 296 223 274 -250 }

{ 256 -256 -256 256 256 -256 -256 256 256 -256 -256 256 256 -256 256 256 }

{ -9 -361 44 357 -79 -349 114 338 -147 -323 178 306 -208 -285 236 262 }

{-268 -216 311 155 -341 -88 358 18 -362 53 351 -122 -327 186 291 -243 }

{-361 79 338 -178 -285 262 208 -323 -114 357 9 -359 97 331 194 -274 }

{-230 319 105 -360 35 346 -171 -280 280 171 -346 -35 360 -105 319 230 }

{ 44 338 -208 -236 323 79 -362 97 315 -250 -194 344 27 -357 147 285 }

{ 291 122 -362 88 311 -268 -155 358 -53 -327 243 186 -351 18 341 -216 }

{ 357 -178 -236 338 9 -344 223 194 -353 44 323 -262 -147 361 -97 -296 }

{ 201 -355 71 301 -301 -71 355 -201 -201 355 -71 -301 301 71 355 201 }

{ -79 -285 323 9 -331 274 97 -357 208 178 -361 130 250 -344 44 306 }

{-311 -18 327 -291 -53 341 -268 -88 351 -243 -122 358 -216 -155 362 -186 }

{-349 262 79 -344 274 62 -338 285 44 -331 296 27 -323 306 9 -315 }

{-171 360 -230 -105 346 -280 -35 319 -319 35 280 -346 105 230 360 171 }

{ 114 208 -362 223 97 -338 306 -27 -274 353 -147 -178 359 -250 -62 323 }

{ 327 -88 -216 362 -243 -53 311 -341 122 186 -358 268 18 -291 351 -155 }

{ 338 -323 97 194 -357 285 -27 -250 362 -236 -44 296 -353 178 114 -331 }

{ 139 -334 334 -139 -139 334 -334 139 139 -334 334 -139 -139 334 334 139 }

{-147 -114 315 -353 208 44 -274 362 -262 27 223 -357 306 -97 163 338 }

{-341 186 53 -268 362 -291 88 155 -327 351 -216 -18 243 -358 311 -122 }

{-323 357 -250 44 178 -331 353 -236 27 194 -338 349 -223 9 208 -344 }

{-105 280 -360 319 -171 -35 230 -346 346 -230 35 171 -319 360 280 105 }

{ 178 9 -194 323 -361 296 -147 -44 223 -338 357 -274 114 79 250 349 }

{ 351 -268 122 53 -216 327 -362 311 -186 18 155 -291 358 -341 243 -88 }

{ 306 -359 344 -262 130 27 -178 296 -357 349 -274 147 9 -163 285 -353 }

{ 71 -201 301 -355 355 -301 201 -71 -71 201 -301 355 -355 301 201 71 }

{-208 97 27 -147 250 -323 359 -353 306 -223 114 9 -130 236 315 357 }

{-358 327 -268 186 -88 -18 122 -216 291 -341 362 -351 311 -243 155 -53 }

{-285 331 -357 361 -344 306 -250 178 -97 9 79 -163 236 -296 338 -359 }

{ -35 105 -171 230 -280 319 -346 360 -360 346 -319 280 -230 171 105 35 }

{ 236 -194 147 -97 44 9 -62 114 -163 208 -250 285 -315 338 353 361 }

{ 362 -358 351 -341 327 -311 291 -268 243 -216 186 -155 122 -88 53 -18 } { 262 -274 285 -296 306 -315 323 -331 338 -344 349 -353 357 359 361 -362 }

transMatrix[ m][n] = (n&l?-l : 1)* transMatrixColl6to3l[47 -m ][ n ] (15) with m =32..47, n = 0..63

transMatrix[ m][n] = (n&l?-l : 1)* transMatrixCol0tol5[63 -m ][ n ] (16) with m =48..63, n = 0..63

- Otherwise, if trType is equal to 1 and nTbs is equal to 4, the following Equation applies:

transMatrix[ m ][ n ] = (17)

{ 117 219 296 336 }

{ 296 296 0 -296 }

{ 336 -117 -296 219 }

{ 219 -336 296 -117 }

},

- Otherwise, if trType is equal to 1 and nTbs is equal to 8, the following applies:

transMatrix[ m ][ n ] = (18)

{ 65 127 185 237 280 314 338 350 }

{ 185 314 350 280 127 -65 -237 -338 }

{ 280 338 127 -185 -350 -237 65 314 }

{ 338 185 -237 -314 65 350 127 -280 }

{ 350 -65 -338 127 314 -185 -280 237 }

{ 314 -280 -65 338 -237 -127 350 -185 }

{ 237 -350 280 -65 -185 338 -314 127 }

{ 127 -237 314 -350 338 -280 185 -65 }

},

- Otherwise, if trType is equal to 1 and nTbs is equal to 16, the following Equation applies:

transMatrix[ m ][ n ] = (19)

{ 34 67 100 133 163 193 220 246 269 290 309 324 337 346 353 356 }

{ 100 193 269 324 353 353 324 269 193 100 0 -100 -193 -269 -324 -353 }

{ 163 290 353 337 246 100 -67 -220 -324 -356 -309 -193 -34 133 269 346 }

{ 220 346 324 163 -67 -269 -356 -290 -100 133 309 353 246 34 -193 -337 }

{ 269 353 193 -100 -324 -324 -100 193 353 269 0 -269 -353 -193 100 324 }

{ 309 309 0 -309 -309 0 309 309 0 -309 -309 0 309 309 0 -309 }

{ 337 220 -193 -346 -34 324 246 -163 -353 -67 309 269 -133 -356 -100 290 }

{ 353 100 -324 -193 269 269 -193 -324 100 353 0 -353 -100 324 193 -269 }

{ 356 -34 -353 67 346 -100 -337 133 324 -163 -309 193 290 -220 -269 246 }

{ 346 -163 -269 290 133 -353 34 337 -193 -246 309 100 -356 67 324 -220 }

{ 324 -269 -100 353 -193 -193 353 -100 -269 324 0 -324 269 100 -353 193 }

{ 290 -337 100 220 -356 193 133 -346 269 34 -309 324 -67 -246 353 -163 }

{ 246 -356 269 -34 -220 353 -290 67 193 -346 309 -100 -163 337 -324 133 }

{ 193 -324 353 -269 100 100 -269 353 -324 193 0 -193 324 -353 269 -100 }

{ 133 -246 324 -356 337 -269 163 -34 -100 220 -309 353 -346 290 -193 67 }

{ 67 -133 193 -246 290 -324 346 -356 353 -337 309 -269 220 -163 100 -34 }

- Otherwise, if trType is equal to 1 and nTbs is equal to 32, the following Equations apply: transMatrix[ m ][ n ] = transMatrixCol0tol5[ m ][ n ] with m = 0..15, n = 0..31 (20)

transMatrix[ m ][ n ] = transMatrixColl6to3 l [ m - 16 ] [ n ] with m = 16..31, n = 0..31 (22)

- Otherwise, if trType is equal to 2 and nTbs is equal to 4, the following Equation applies:

transMatrix[ m ][ n ] = (24)

- Otherwise, if trType is equal to 2 and nTbs is equal to 8, the following Equation applies:

transMatrix[ m ][ n ] = (25)

{ 350 338 314 280 237 185 127 65 }

{ 338 237 65 -127 280 -350 314 -185 }

{ 314 65 -237 -350 185 127 338 280 }

{ 280 127 -350 - 65 314 237 185 -338 }

{ 237 280 -185 314 127 -338 - 65 350 }

{ 185 350 127 237 338 65 280 -314 }

{ 127 314 338 -185 - 65 280 350 237 }

{ 65 185 280 -338 350 -314 237 -127 }

} , Otherwise, if trType is equal to 2 and nTbs is equal to 16, the following applies: transMatrix[ m ][ n ] (26)

Otherwise, if trType is equal to 2 and nTbs is equal to 32, the following applies:

transMatrix[ m ][ n ] = transMatrixCol0tol5[ m ][ n ] with m = 0..15, n = 0..31 (27)

transMatrix[ m ][ n ] = transMatrixColl6to3 l[ m - 16 ][ n ] with m = 16..31, n = 0..31 (29)

[0114] FIG. 6 is a flowchart illustrating a method (600) of controlling residual coding for decoding or encoding of a video sequence, according to an embodiment. In some

implementations, one or more process blocks of FIG. 6 may be performed by the decoder (310).

In some implementations, one or more process blocks of FIG. 6 may be performed by another device or a group of devices separate from or including the decoder (310), such as the encoder

(303).

[0115] Referring to FIG. 6, in a first block (610), the method (600) includes determining whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT). Based on whether either one or both of a block height and a block width meet a predetermined condition (610-No), the method (600) ends.

[0116] In a second block (620), the method (600) includes, based on either one or both of the block height and the block width meeting the predetermined condition, replacing the transform type of MTS by using the IDT (6lO-Yes).

[0117] In a third block (630), the method (600) includes keeping a syntax of the MTS unchanged.

[0118] The determining whether the first intra prediction direction of the luma coding block is aligned with the second intra prediction direction of the chroma coding block may include determining that the first intra prediction direction is aligned with the second intra prediction direction, based on both the first intra prediction direction and the second intra prediction direction corresponding to one of angular prediction modes, a planar mode and a DC mode.

[0119] The transform type of the MTS may be discrete cosine transform DCT-4 or DCT-

8

[0120] FIG. 7 is a flowchart illustrating a method (700) of controlling residual coding for decoding or encoding of a video sequence, according to another embodiment. In some implementations, one or more process blocks of FIG. 7 may be performed by the decoder (310). In some implementations, one or more process blocks of FIG. 7 may be performed by another device or a group of devices separate from or including the decoder (310), such as the encoder (303). [0121] Referring to FIG. 7, in a first block (710), the method (700) includes determining whether the transform type of the MTS is applied as a horizontal transform or a vertical transform.

[0122] Based on the transform type of the MTS being applied as a horizontal transform

(710-Horizontal), the method (700) includes, in a second block (720), the predetermined condition is that the block width is smaller than a predetermined threshold.

[0123] Based on the transform type of the MTS being applied as a vertical transform

(7lO-Vertical), the method (700) includes, in a third block (730), the predetermined condition is that the block height is smaller than a predetermined threshold.

[0124] The predetermined threshold may be one from among 2, 4, 8, 16, 32, 64, 128, and

156.

[0125] The predetermined condition may be that the transform type of the MTS is used on a horizontal direction or a vertical direction, but is not used on both the horizontal direction and the vertical direction.

[0126] Although FIGS. 6 and 7 show example blocks of the methods (600) and (700), in some implementations, the methods (600) and (700) may include additional blocks, fewer blocks, different blocks, or differently arranged blocks than those depicted in FIGS. 6 and 7. Additionally, or alternatively, two or more of the blocks of the methods (600) and (700) may be performed in parallel.

[0127] Further, the proposed methods may be implemented by processing circuitry (e.g., one or more processors or one or more integrated circuits). In an example, the one or more processors execute a program that is stored in a non-transitory computer-readable medium to perform one or more of the proposed methods.

[0128] FIG. 8 is a simplified block diagram of an apparatus (800) for controlling residual coding for decoding or encoding of a video sequence, according to an embodiment.

[0129] Referring to FIG. 8, the apparatus (800) includes determining code (810) and replacing code (820).

[0130] The determining code (810) is configured to cause at least one processor to determine whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT), based on whether either one or both of a block height and a block width meet a predetermined condition.

[0131] The replacing code (820) is configured to cause the at least one processor to, based on either one or both of the block height and the block width meeting the predetermined condition, replace the transform type of Multiple Transform Selection (MTS) by using the IDT and keeping a syntax of the MTS unchanged.

[0132] The techniques described above, can be implemented as computer software using computer-readable instructions and physically stored in one or more computer-readable media.

[0133] FIG. 9 is a diagram of a computer system (900) suitable for implementing embodiments.

[0134] The computer software can be coded using any suitable machine code or computer language, that may be subject to assembly, compilation, linking, or like mechanisms to create code comprising instructions that can be executed directly, or through interpretation, micro-code execution, and the like, by computer central processing units (CPUs), Graphics Processing Units (GPUs), and the like.

[0135] The instructions can be executed on various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smartphones, gaming devices, internet of things devices, and the like.

[0136] The components shown in FIG. 9 for computer system (900) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing embodiments. Neither should the configuration of components be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary embodiment of a computer system (900).

[0137] Computer system (900) may include certain human interface input devices. Such a human interface input device may be responsive to input by one or more human users through, for example, tactile input (such as: keystrokes, swipes, data glove movements), audio input (such as: voice, clapping), visual input (such as: gestures), olfactory input (not depicted). The human interface devices can also be used to capture certain media not necessarily directly related to conscious input by a human, such as audio (such as: speech, music, ambient sound), images (such as: scanned images, photographic images obtain from a still image camera), video (such as two-dimensional video, three-dimensional video including stereoscopic video).

[0138] Input human interface devices may include one or more of (only one of each depicted): keyboard (901), mouse (902), trackpad (903), touch screen (910), data-glove (904), joystick (905), microphone (906), scanner (907), camera (908). [0139] Computer system (900) may also include certain human interface output devices.

Such human interface output devices may be stimulating the senses of one or more human users through, for example, tactile output, sound, light, and smell/taste. Such human interface output devices may include tactile output devices (for example tactile feedback by the touch-screen (910), data-glove (904), or joystick (905), but there can also be tactile feedback devices that do not serve as input devices), audio output devices (such as: speakers (909), headphones (not depicted)), visual output devices (such as screens (910) to include cathode ray tube (CRT) screens, liquid-crystal display (LCD) screens, plasma screens, organic light-emitting diode (OLED) screens, each with or without touch-screen input capability, each with or without tactile feedback capability— some of which may be capable to output two dimensional visual output or more than three dimensional output through means such as stereographic output; virtual-reality glasses (not depicted), holographic displays and smoke tanks (not depicted)), and printers (not depicted).

[0140] Computer system (900) can also include human accessible storage devices and their associated media such as optical media including CD/DVD ROM/RW (920) with CD/DVD or the like media (921), thumb-drive (922), removable hard drive or solid state drive (923), legacy magnetic media such as tape and floppy disc (not depicted), specialized ROM/ASIC/PLD based devices such as security dongles (not depicted), and the like.

[0141] Those skilled in the art should also understand that term“computer readable media” as used in connection with the presently disclosed subject matter does not encompass transmission media, carrier waves, or other transitory signals. [0142] Computer system (900) can also include interface(s) to one or more communication networks. Networks can for example be wireless, wireline, optical. Networks can further be local, wide-area, metropolitan, vehicular and industrial, real-time, delay-tolerant, and so on. Examples of networks include local area networks such as Ethernet, wireless LANs, cellular networks to include global systems for mobile communications (GSM), third generation (3G), fourth generation (4G), fifth generation (5G), Long-Term Evolution (LTE), and the like, TV wireline or wireless wide area digital networks to include cable TV, satellite TV, and terrestrial broadcast TV, vehicular and industrial to include CANBus, and so forth. Certain networks commonly require external network interface adapters that attached to certain general purpose data ports or peripheral buses ((949)) (such as, for example universal serial bus (ETSB) ports of the computer system (900); others are commonly integrated into the core of the computer system (900) by attachment to a system bus as described below (for example Ethernet interface into a PC computer system or cellular network interface into a smartphone computer system). Easing any of these networks, computer system (900) can communicate with other entities. Such communication can be uni-directional, receive only (for example, broadcast TV), uni -directional send-only (for example CANbus to certain CANbus devices), or bi-directional, for example to other computer systems using local or wide area digital networks. Certain protocols and protocol stacks can be used on each of those networks and network interfaces as described above.

[0143] Aforementioned human interface devices, human-accessible storage devices, and network interfaces can be attached to a core (940) of the computer system (900). [0144] The core (940) can include one or more Central Processing Units (CPU) (941),

Graphics Processing Units (GPU) (942), specialized programmable processing units in the form of Field Programmable Gate Areas (FPGA) (943), hardware accelerators (944) for certain tasks, and so forth. These devices, along with Read-only memory (ROM) (945), Random-access memory (RAM) (946), internal mass storage such as internal non-user accessible hard drives, solid-state drives (SSDs), and the like (947), may be connected through a system bus (948). In some computer systems, the system bus (948) can be accessible in the form of one or more physical plugs to enable extensions by additional CPUs, GPU, and the like. The peripheral devices can be attached either directly to the core’s system bus (948), or through a peripheral bus (949). Architectures for a peripheral bus include peripheral component interconnect (PCI), USB, and the like.

[0145] CPUs (941), GPUs (942), FPGAs (943), and accelerators (944) can execute certain instructions that, in combination, can make up the aforementioned computer code. That computer code can be stored in ROM (945) or RAM (946). Transitional data can also be stored in RAM (946), whereas permanent data can be stored for example, in the internal mass storage (947). Fast storage and retrieve to any of the memory devices can be enabled through the use of cache memory, that can be closely associated with one or more CPU (941), GPU (942), mass storage (947), ROM (945), RAM (946), and the like.

[0146] The computer readable media can have computer code thereon for performing various computer-implemented operations. The media and computer code can be those specially designed and constructed for the purposes of embodiments, or they can be of the kind well known and available to those having skill in the computer software arts. [0147] As an example and not by way of limitation, the computer system having architecture (900), and specifically the core (940) can provide functionality as a result of processor(s) (including CPUs, GPUs, FPGA, accelerators, and the like) executing software embodied in one or more tangible, computer-readable media. Such computer-readable media can be media associated with user-accessible mass storage as introduced above, as well as certain storage of the core (940) that are of non-transitory nature, such as core-internal mass storage (947) or ROM (945). The software implementing various embodiments can be stored in such devices and executed by core (940). A computer-readable medium can include one or more memory devices or chips, according to particular needs. The software can cause the core (940) and specifically the processors therein (including CPU, GPU, FPGA, and the like) to execute particular processes or particular parts of particular processes described herein, including defining data structures stored in RAM (946) and modifying such data structures according to the processes defined by the software. In addition or as an alternative, the computer system can provide functionality as a result of logic hardwired or otherwise embodied in a circuit (for example: accelerator (944)), which can operate in place of or together with software to execute particular processes or particular parts of particular processes described herein. Reference to software can encompass logic, and vice versa, where appropriate. Reference to a computer- readable media can encompass a circuit (such as an integrated circuit (IC)) storing software for execution, a circuit embodying logic for execution, or both, where appropriate. Embodiments encompass any suitable combination of hardware and software.

[0148] While this disclosure has described several exemplary embodiments, there are alterations, permutations, and various substitute equivalents, which fall within the scope of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise numerous systems and methods which, although not explicitly shown or described herein, embody the principles of the disclosure and are thus within the spirit and scope thereof.

Claims

CLAIMS:

1. A method of controlling residual coding for decoding or encoding of a video sequence, the method being performed by at least one processor, and the method comprising: determining whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT), based on whether either one or both of a block height and a block width meet a predetermined condition; and

based on either one or both of the block height and the block width meeting the predetermined condition, replacing the transform type of MTS by using the IDT and keeping a syntax of the MTS unchanged,

wherein the IDT is a linear transform process using an NxN transform core in which each coefficient is non-zero along a diagonal position, and wherein N is an integer.

2. The method of claim 1, wherein the transform type of the MTS is discrete cosine transform DCT-4 or DCT-8.

3. The method of claim 1, wherein the transform type of the MTS is applied as a horizontal transform and the predetermined condition is that the block width is smaller than a predetermined threshold.

4. The method of claim 3, wherein the predetermined threshold is one from among 2, 4, 8, 16, 32, 64, 128, and 156.

5. The method of claim 1, wherein the transform type of the MTS is applied as a vertical transform and the predetermined condition is that the block height is smaller than a predetermined threshold.

6. The method of claim 5, wherein the predetermined threshold is one from among 2, 4, 8, 16, 32, 64, 128, and 156.

7. The method of claim 1, wherein the predetermined condition is that the transform type of the MTS is used on a horizontal direction or a vertical direction, but is not used on both the horizontal direction and the vertical direction.

8. An apparatus for controlling residual coding for decoding or encoding of a video sequence, the apparatus comprising:

at least one memory configured to store computer program code; and

at least one processor configured to access the at least one memory and operate according to the computer program code, the computer program code comprising:

determining code configured to cause the at least one processor to determine whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT), based on whether either one or both of a block height and a block width meet a predetermined condition; and replacing code configured to cause the at least one processor to, based on either one or both of the block height and the block width meeting the predetermined condition, replace the transform type of MTS by using the IDT and keeping a syntax of the MTS unchanged,

wherein the IDT is a linear transform process using an NxN transform core in which each coefficient is non-zero along a diagonal position, and wherein N is an integer.

9. The apparatus of claim 8, wherein the transform type of the MTS is discrete cosine transform DCT-4 or DCT-8.

10. The apparatus of claim 8, wherein the transform type of the MTS is applied as a horizontal transform and the predetermined condition is that the block width is smaller than a predetermined threshold.

11. The apparatus of claim 10, wherein the predetermined threshold is one from among 2, 4, 8, 16, 32, 64, 128, and 156.

12. The apparatus of claim 8, wherein the transform type of the MTS is applied as a vertical transform and the predetermined condition is that the block height is smaller than a predetermined threshold.

13. The apparatus of claim 12, wherein the predetermined threshold is one from among 2, 4, 8, 16, 32, 64, 128, and 156.

14. The apparatus of claim 8, wherein the predetermined condition is that the transform type of the MTS is used on a horizontal direction or a vertical direction, but is not used on both the horizontal direction and the vertical direction.

15. A non-transitory computer-readable storage medium storing instructions that cause at least one processor to:

determine whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT), based on whether either one or both of a block height and a block width meet a predetermined condition; and

based on either one or both of the block height and the block width meeting the predetermined condition, replace the transform type of MTS by using the IDT and keeping a syntax of the MTS unchanged,

wherein the IDT is a linear transform process using an NxN transform core in which each coefficient is non-zero along a diagonal position, and wherein N is an integer.

16. The non-transitory computer-readable storage medium of claim 15, wherein the transform type of the MTS is discrete cosine transform DCT-4 or DCT-8.

17. The non-transitory computer-readable storage medium of claim 15, wherein the transform type of the MTS is applied as a horizontal transform and the predetermined condition is that the block width is smaller than a predetermined threshold.

18. The non-transitory computer-readable storage medium of claim 17, wherein the predetermined threshold is one from among 2, 4, 8, 16, 32, 64, 128, and 156.

19. The non-transitory computer-readable storage medium of claim 15, wherein the transform type of the MTS is applied as a vertical transform and the predetermined condition is that the block height is smaller than a predetermined threshold.

20. The non-transitory computer-readable storage medium of claim 19, wherein the predetermined threshold is one from among 2, 4, 8, 16, 32, 64, 128, and 156.