TITLE

METHOD AND APPARATUS FOR STILL PICTURE AND VIDEO CODING

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims the right of priority to international patent application PCT/RU2019/000469 filed on June 28, 2019, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

Embodiments of the present application (disclosure) generally relate to the field of picture processing and more particularly to shape-adaptive resampling of residual blocks for still image and video coding.

BACKGROUND

Video coding (video encoding and decoding) is used in a wide range of digital video applications, for example broadcast digital TV, video transmission over internet and mobile networks, real-time conversational applications such as video chat, video conferencing, DVD and Blu-ray discs, video content acquisition and editing systems, and camcorders of security applications.

The amount of video data needed to depict even a relatively short video can be substantial, which may result in difficulties when the data is to be streamed or otherwise communicated across a communications network with limited bandwidth capacity. Thus, video data is generally compressed before being communicated across modern day telecommunications networks. The size of a video could also be an issue when the video is stored on a storage device because memory resources may be limited. Video compression devices often use software and/or hardware at the source to code the video data prior to transmission or storage, thereby decreasing the quantity of data needed to represent digital video images. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and ever increasing demands of higher video quality, improved compression and decompression techniques that improve compression ratio with little to no sacrifice in picture quality are desirable. SUMMARY

Embodiments of the present application aim to provide apparatuses and methods for improving and enhancing efficiency of prediction coding (encoding and/or decoding), in particular with shape-adaptive resampling of a picture or video sequence, in particular, improving and enhancing efficiency of the related signaling.

The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect the invention relates to a method for still picture and/or video residual coding. The method comprises the steps of determining if a syntax element belongs to an initial syntax element group Fi which belongs to a dependent syntax element group FRC and is obtained in dependence of confirmative values of one or more correlative syntax elements belonging to a syntax element group Fo which are unconditionally present in a bit stream, inferring the syntax element to be zero if the syntax element does not belong to the initial syntax element group Fi, and/or encoding into or parsing from the bit stream, the syntax element for coding a current block if the syntax element belongs to the initial syntax element group Fi.

According to a second aspect the invention relates to an apparatus for still picture and/or video residual coding. The apparatus comprises means for determining if a syntax element belongs to an initial syntax element group Fi which belongs to a dependent syntax element group FRC and is obtained in dependence of confirmative values of one or more correlative syntax elements belonging to a syntax element group Fo which are unconditionally present in a bit stream. The apparatus further comprises means for inferring the syntax element to be zero if the syntax element does not belong to the initial syntax element group Fi, and/or means for encoding into or parsing from the bit stream, the syntax element for coding a current block if the syntax element belongs to the initial syntax element group Fi.

It is the particular approach of the present invention to implement a residual coding parameter signaling scheme, wherein only a limited number of syntax elements (syntax element group Fo) is unconditionally signaled, whereas other syntax elements are only conditionally signaled if necessary. Whether or not a particular syntax element is signaled, is determined depending on values of syntax elements that are unconditionally signaled, based on a predetermined principle (in particular: a function, mapping table or operation). An element for which a condition to be signaled is not fulfilled is inferred to be zero. This may enhance overall coding efficiency. A particular field of application may be harmonization of signaling when both partial transform (PT) and sub block transform (SBT) may be used.

In particular, on the encoding side (encoder), a syntax element to be signaled, i.e. a syntax element that belongs to the initial syntax element group Fi may be encoded, in order to be transferred to the decoding side (decoder). On the other hand, on the decoding side (decoder) the respective syntax element that belongs to the initial syntax element group Fi may be’s parsed from the bitstream (that has been received from the encoding side).

According to exemplary embodiments, the dependent syntax element group FRC comprises one or several of the following syntax elements:

part_trans_flag, which is a flag indicating whether or not Partial Transform, PT, is enabled;

part_trans_idx, which is an index value, that is used to indicate parameters of partial transform, wherein the parameters of partial transform comprise at least one of the following elements:

- Log2[tbWidth],

- Log2[tbHeight], tbWidth and tbHeight being a width and a height of a transform unit, respectively,

- MergeTriangleFlag, which is a flag that identifies whether triangular partitioning mode, TPM, is selected or not, or

geo_partition_idx, which specifies the geometric splitting type of the geometric partitioning mode;

tu_mts_idx, which is a flag indicating a transform type used for the residual signal;

transform_skip_flag, which is a flag indicating that transform is not performed on the residual signal;

lfnst_flag, which is a flag indicating that a part of transformed residual are further transformed to obtain secondary transformed residual; and

cu_sbt_flag, which is a flag indicating, whether or not, subblock transform, SBT, is used for a current coding unit.

In accordance with exemplary embodiments, obtaining the initial syntax element group Fi includes deriving the initial syntax element group Fi by using a predefined mapping operation. The mapping operation may, for example, be implemented in form of a mapping table, alternatively, other principles functions, operations are possible in embodiments. More specifically, the predefined mapping operation comprises at least one of the following: when cu_sbt_flag is 1 , part_trans_flag is not included into Fi\

when MergeTriangleFlag is 1 , lfnst_flag is not included into Fi\

when geo_flag is 1 , lfnst_flag is not included into Fi,

when cbf is 0, part_trans_flag is not included into Fi,

when skip_flag is 1 , part_trans_flag is not included into Fi, wherein geo_flag specifies whether the geometric partitioning inter-picture merge prediction is applied for the current coding unit, cbf is the Coded Block Flag that signals the information whether at least one non-zero transform coefficient level is transmitted for a coding unit, CU, and skip_flag is a flag that specifies whether for a CU motion data is inferred instead of explicitly signaled and that the prediction residual is zero. Hence, it is possible to reduce signaling overhead by omitting flags that are superfluous in a certain situation. For instance, if subblock transform is used, partial transform is not used at the same time and so on.

According to exemplary embodiments, the method further comprises redefining the initial syntax element group Fi based on a predefined dependency rule. A respective apparatus further comprises means for redefining the initial syntax element group Fi based on a predefined dependency rule. By using such a redefinition, further dependencies may be taken into account, according to which the need for signaling may depend not only on the unconditionally signaled syntax elements of group Fo but also on values of syntax elements of group Fi that were signaled in the bitstream.

More specifically, the dependency rule may comprise at least one of the following:

- when cu_sbt_flag is 1 , part_trans_flag is removed from Fi,

- when part_trans_flag is 1 , lfnst_flag is removed from Fi,

- when part_trans_flag is 1 , tu_mts_idx is removed from Fi.

According to exemplary embodiments, the group Fo of syntax elements that are unconditionally signaled, in a bit stream, on SPS/PPS level comprises a triangle prediction related flag which indicates whether a triangle prediction is allowed for a video sequence or a picture of the video or not or a geometric partitioning related flag which indicates whether geometric partitioning prediction is allowed for a video sequence or a picture of the video or not, the group Fo of syntax elements that are unconditionally signaled, in the bit stream, on the SPS/PPS level further comprises a first partial transform related flag which indicates whether a partial transform is allowed for a video sequence or a picture of the video or not and the method comprises/the apparatus comprises means for, in response to a confirmative value (e.g.1 ) of the triangle prediction related flag or the geometric partitioning related flag and a confirmative value (e.g.1 ) of the first partial transform related flag, signaling, in the bit stream, on the SPS/PPS level a second partial transform related flag which indicates if a partial transform is allowed for coding blocks that the triangle prediction or the geometric partitioning prediction is applied to, as a syntax element belonging to said initial syntax element group Fi.

In accordance with exemplary embodiments, the method is applied to decoding and comprises/the apparatus is configured for decoding and comprises means for parsing, from a bit stream, on SPS/PPS level a triangle prediction related flag which indicates whether a triangle prediction is allowed for a video sequence or a picture of the video or not or a geometric partitioning related flag which indicates whether geometric partitioning prediction is allowed for a video sequence or a picture of the video or not, said flags belonging to said group Fo of syntax elements that are unconditionally signaled, parsing, from a bit stream, on the SPS/PPS level a first partial transform related flag which indicates if a partial transform is allowed for a video sequence or a picture of the video or not, said flag belonging to said group Fo of syntax elements that are unconditionally signaled, and in response to a confirmative value (e.g. 1 ) of the triangle prediction related flag or the geometric partitioning related flag and a confirmative value (e.g.1 ) of the first partial transform related flag, parsing, from a bit stream, on the SPS/PPS level a second partial transform related flag which indicates if a partial transform is allowed for coding blocks that the triangle prediction or the geometric partitioning prediction is applied to, as a syntax element belonging to said initial syntax element group Fi.

In accordance with alternative exemplary embodiments, the group Fo of syntax elements that are unconditionally signaled, in a bit stream, on a SPS/PPS level comprises a triangle prediction related flag which indicates whether a triangle prediction is allowed for a video sequence or a picture of the video or not or a geometric partitioning related flag which indicates whether geometric partitioning prediction is allowed for a video sequence or a picture of the video or not, and the method comprises/the apparatus comprises means for, in response to a confirmative value (e.g. 1 ) of the triangle prediction related flag or the geometric partitioning related flag, signaling, in the bit stream, on a slice level (slice header) a second partial transform related flag which indicates if a partial transform is allowed for coding blocks that the triangle prediction or the geometric partitioning prediction is applied to, as a syntax element belonging to said initial syntax element group Fi.

According to further exemplary embodiments, the method is applied to decoding and comprises/the apparatus is configured for decoding and comprises means for parsing, from a bit stream, on SPS/PPS level a triangle prediction related flag which indicates if a triangle prediction is allowed for a video sequence or a picture of the video or not or a geometric partitioning related flag which indicates whether geometric partitioning prediction is allowed for a video sequence or a picture of the video or not, said flags belonging to said group Fo of syntax elements that are unconditionally signaled and, in response to a confirmative value (e.g. 1 ) of the triangle prediction related flag or the geometric partitioning related flag, parsing, from a bit stream, on a slice level (slice header) a second partial transform related flag which indicates if a partial transform is allowed for coding blocks that the triangle prediction or the geometric partitioning is applied to, as a syntax element belonging to said initial syntax element group Fi.

According to exemplary embodiments, a syntax element is signaled for indicating a height or a width of a region to be resampled, if the second partial transform flag indicates that partial transform is allowed.

In the above, the triangle prediction related flag may, in particular, be a flag indicating whether or not triangle prediction mode (TPM) is enabled such as the sps_triangle_enabled_flag discussed further below. The geometric partitioning related flag is a respective flag indicating whether or not geometric partitioning prediction is enabled. The first partial transform related flag may be a high level flag for enabling or disabling partial transform such as the flag sps_partial_transform_enabled_flag discussed further below. The second partial transform related flag that is conditionally signaled may be a flag indicating whether partial transform is enabled for blocks that triangle prediction mode or geometric partition prediction mode, respectively, are applied to, such as the below discussed sps_partial_transform_enabled_for_triangle_flag or the respective flag for the geometric partitioning prediction.

According to exemplary embodiments, the method of the first aspect or any of its embodiments is implemented by an encoding device.

According to exemplary embodiments, the method of the first aspect or any of its embodiments is implemented by a decoding device.

According to a third aspect, the invention relates to an encoder comprising processing circuitry for carrying out the method according to the first aspect or any of its embodiments.

According to a fourth aspect, the invention relates to a decoder comprising processing circuitry for carrying out the method according to the first aspect or any of its embodiments. According to a fifth aspect, the invention relates to a computer program product comprising program code for performing the method according to the first aspects or any of its embodiments.

According to a sixth aspect, the invention relates to a decoder comprising one or more processors and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the decoder to carry out the method according to the first aspect or any of its embodiments.

According to a seventh aspect, the invention relates to an encoder comprising one or more processors and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the encoder to carry out the method according to the first aspect or any of its embodiments.

According to an eighth aspect, the invention relates to a non-transitory computer-readable medium carrying a program code which, when executed by a computer device, causes the computer device to perform the method of the first aspect or any of its embodiments.

The method according to the first aspect of the invention can be performed by the apparatus according to the second to fourth, sixth and seventh aspects of the invention. Further features and implementation forms of the method according to the first aspect of the invention correspond to the features and implementation forms of the apparatus according to the second aspect of the invention.

According to another aspect the invention relates to an apparatus for decoding a video stream including a processor and a memory. The memory is storing instructions that cause the processor to perform the method according to the first aspect or its embodiments.

According to another aspect the invention relates to an apparatus for encoding a video stream including a processor and a memory. The memory is storing instructions that cause the processor to perform the method according to the first aspect or its embodiments.

According to another aspect, a computer-readable storage medium having stored thereon instructions that when executed cause one or more processors configured to code video data is proposed. The instructions cause the one or more processors to perform a method according to the first or aspect or any possible embodiment of the first aspect.

According to another aspect, the invention relates to a computer program comprising program code for performing the method according to the first aspect or any possible embodiment of the first aspect when executed on a computer.

Further, embodiments of the present application facilitate an efficient illumination compensation.

Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the invention are described in more detail with reference to the attached figures and drawings, in which:

Fig. 1 A is a block diagram showing an example of a video coding system configured to implement embodiments of the invention;

Fig. 1 B is a block diagram showing another example of a video coding system configured to implement embodiments of the invention;

Fig. 2 is a block diagram showing an example of a video encoder configured to

implement embodiments of the invention;

Fig. 3 is a block diagram showing an example structure of a video decoder configured to implement embodiments of the invention;

Fig. 4 is a block diagram illustrating an example of an encoding apparatus or a decoding apparatus;

Fig. 5 is a block diagram illustrating another example of an encoding apparatus or a decoding apparatus;

Fig. 6 is an illustration of the steps required at encoder side to obtain a set of transform blocks for used color components marked as a transform unit according to an embodiment of the invention;

Fig. 7 is an illustration of an alternative way to resample residual blocks for obtaining a set of transform blocks for used color components marked as a transform unit according to an embodiment of the invention; Fig. 8 is a flowchart to illustrate the processing steps of the invention applied to a unit predicted using TPM at both decoder and encoder sides according to an embodiment of the invention;

Fig. 9 is an illustration of a resampling process within a unit where the GMP technique is used according to an embodiment of the invention;

Fig. 10 is a flowchart to illustrate the processing steps of an embodiment of the invention at both decoder and encoder side if the resampling process is applied to a unit where the GMP technique is used;

Fig. 11 is a flowchart showing the signaling of flags according to an embodiment of the invention;

Fig. 12 is a flowchart showing the signaling of flags according to an embodiment of the invention, including explicit signaling of the size of a resampled transform block; Fig. 13 is an illustration of the smoothing process that uses one-dimensional padding of the samples adjacent to the near-boundary region;

Fig. 14 is an illustration of the smoothing process that uses two-dimensional spatial filter of the samples adjacent to the near-boundary region;

Fig. 15 is an illustration of obtaining the near-boundary region for the case of GMP using column-wise scan;

Fig. 16 is an illustration of obtaining the near-boundary region for the case of GMP using a row-wise scan;

Fig. 17 is a flowchart showing the signaling of residual coding tool flags in the presence of lossless coding flag, for being used on the decoding side; and

Fig. 18 is a separate flowchart showing the signaling of residual coding tool flags in the presence of lossless coding flag, for being used on the encoding side.

In the following identical reference signs refer to identical or at least functionally equivalent features if not explicitly specified otherwise.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the invention or specific aspects in which embodiments of the present invention may be used. It is understood that embodiments of the invention may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Video coding typically refers to the processing of a sequence of pictures, which form the video or video sequence. Instead of the term“picture” the term“frame” or“image” may be used as synonyms in the field of video coding. Video coding (or coding in general) comprises two parts video encoding and video decoding. Video encoding is performed at the source side, typically comprising processing (e.g. by compression) the original video pictures to reduce the amount of data required for representing the video pictures (for more efficient storage and/or transmission). Video decoding is performed at the destination side and typically comprises the inverse processing compared to the encoder to reconstruct the video pictures. Embodiments referring to“coding” of video pictures (or pictures in general) shall be understood to relate to“encoding" or“decoding” of video pictures or respective video sequences. The combination of the encoding part and the decoding part is also referred to as CODEC (Coding and Decoding).

In case of lossless video coding, the original video pictures can be reconstructed, i.e. the reconstructed video pictures have the same quality as the original video pictures (assuming no transmission loss or other data loss during storage or transmission). In case of lossy video coding, further compression, e.g. by quantization, is performed, to reduce the amount of data representing the video pictures, which cannot be completely reconstructed at the decoder, i.e. the quality of the reconstructed video pictures is lower or worse compared to the quality of the original video pictures. Several video coding standards belong to the group of“lossy hybrid video codecs” (i.e. combine spatial and temporal prediction in the sample domain and 2D transform coding for applying quantization in the transform domain). Each picture of a video sequence is typically partitioned into a set of non-overlapping blocks and the coding is typically performed on a block level. In other words, at the encoder the video is typically processed, i.e. encoded, on a block (video block) level, e.g. by using spatial (intra picture) prediction and/or temporal (inter picture) prediction to generate a prediction block, subtracting the prediction block from the current block (block currently processed/to be processed) to obtain a residual block, transforming the residual block and quantizing the residual block in the transform domain to reduce the amount of data to be transmitted (compression), whereas at the decoder the inverse processing compared to the encoder is applied to the encoded or compressed block to reconstruct the current block for representation. Furthermore, the encoder duplicates the decoder processing loop such that both will generate identical predictions (e.g. intra- and inter predictions) and/or re-constructions for processing, i.e. coding, the subsequent blocks. In the following embodiments of a video coding system 10, a video encoder 20 and a video decoder 30 are described based on Figs. 1 to 3.

Fig. 1A is a schematic block diagram illustrating an example coding system 10, e.g. a video coding system 10 (or short coding system 10) that may utilize techniques of this present application. Video encoder 20 (or short encoder 20) and video decoder 30 (or short decoder 30) of video coding system 10 represent examples of devices that may be configured to perform techniques in accordance with various examples described in the present application.

As shown in Fig. 1A, the coding system 10 comprises a source device 12 configured to provide encoded picture data 21 e.g. to a destination device 14 for decoding the encoded picture data 13.

The source device 12 comprises an encoder 20, and may additionally, i.e. optionally, comprise a picture source 16, a pre-processor (or pre-processing unit) 18, e.g. a picture preprocessor 18, and a communication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturing device, for example a camera for capturing a real-world picture, and/or any kind of a picture generating device, for example a computer-graphics processor for generating a computer animated picture, or any kind of other device for obtaining and/or providing a real-world picture, a computer generated picture (e.g. a screen content, a virtual reality (VR) picture) and/or any combination thereof (e.g. an augmented reality (AR) picture). The picture source may be any kind of memory or storage storing any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed by the pre-processing unit 18, the picture or picture data 17 may also be referred to as raw picture or raw picture data 17.

Pre-processor 18 is configured to receive the (raw) picture data 17 and to perform preprocessing on the picture data 17 to obtain a pre-processed picture 19 or pre-processed picture data 19. Pre-processing performed by the pre-processor 18 may, e.g., comprise trimming, color format conversion (e.g. from RGB to YCbCr), color correction, or de-noising.

It can be understood that the pre-processing unit 18 may be optional component.

The video encoder 20 is configured to receive the pre-processed picture data 19 and provide encoded picture data 21 (further details will be described below, e.g., based on Fig. 2). Communication interface 22 of the source device 12 may be configured to receive the encoded picture data 21 and to transmit the encoded picture data 21 (or any further processed version thereof) over communication channel 13 to another device, e.g. the destination device 14 or any other device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g. a video decoder 30), and may additionally, i.e. optionally, comprise a communication interface or communication unit 28, a post-processor 32 (or post-processing unit 32) and a display device 34.

The communication interface 28 of the destination device 14 is configured to receive the encoded picture data 21 (or any further processed version thereof), e.g. directly from the source device 12 or from any other source, e.g. a storage device, e.g. an encoded picture data storage device, and provide the encoded picture data 21 to the decoder 30.

The communication interface 22 and the communication interface 28 may be configured to transmit or receive the encoded picture data 21 or encoded data 13 via a direct

communication link between the source device 12 and the destination device 14, e.g. a direct wired or wireless connection, or via any kind of network, e.g. a wired or wireless network or any combination thereof, or any kind of private and public network, or any kind of combination thereof. The communication interface 22 may be, e.g., configured to package the encoded picture data 21 into an appropriate format, e.g. packets, and/or process the encoded picture data using any kind of transmission encoding or processing for transmission over a

communication link or communication network.

The communication interface 28, forming the counterpart of the communication interface 22, may be, e.g., configured to receive the transmitted data and process the transmission data using any kind of corresponding transmission decoding or processing and/or de-packaging to obtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may be configured as unidirectional communication interfaces as indicated by the arrow for the communication channel 13 in Fig. 1A pointing from the source device 12 to the destination device 14, or bidirectional communication interfaces, and may be configured, e.g. to send and receive messages, e.g. to set up a connection, to acknowledge and exchange any other information related to the communication link and/or data transmission, e.g. encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 and provide decoded picture data 31 or a decoded picture 31 (further details will be described below, e.g., based on Fig. 3 or Fig. 5).

The post-processor 32 of destination device 14 is configured to post-process the decoded picture data 31 (also called reconstructed picture data), e.g. the decoded picture 31 , to obtain post-processed picture data 33, e.g. a post-processed picture 33. The postprocessing performed by the post-processing unit 32 may comprise, e.g. color format conversion (e.g. from YCbCr to RGB), color correction, trimming, or re-sampling, or any other processing, e.g. for preparing the decoded picture data 31 for display, e.g. by display device 34.

The display device 34 of the destination device 14 is configured to receive the post- processed picture data 33 for displaying the picture, e.g. to a user or viewer. The display device 34 may be or comprise any kind of display for representing the reconstructed picture, e.g. an integrated or external display or monitor. The displays may, e.g. comprise liquid crystal displays (LCD), organic light emitting diodes (OLED) displays, plasma displays, projectors , micro LED displays, liquid crystal on silicon (LCoS), digital light processor (DLP) or any kind of other display. Although Fig. 1A depicts the source device 12 and the destination device 14 as separate devices, embodiments of devices may also comprise both or both functionalities, the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality. In such embodiments the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality may be implemented using the same hardware and/or software or by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, the existence and (exact) split of functionalities of the different units or functionalities within the source device 12 and/or destination device 14 as shown in Fig. 1A may vary depending on the actual device and application.

The encoder 20 (e.g. a video encoder 20) or the decoder 30 (e.g. a video decoder 30) or both encoder 20 and decoder 30 may be implemented via processing circuitry as shown in Fig. 1 B, such as one or more microprocessors, digital signal processors (DSPs), application- specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, hardware, video coding dedicated or any combinations thereof. The encoder 20 may be implemented via processing circuitry 46 to embody the various modules as discussed with respect to encoder 20of Fig. 2 and/or any other encoder system or subsystem described herein. The decoder 30 may be implemented via processing circuitry 46 to embody the various modules as discussed with respect to decoder 30 of Fig. 3 and/or any other decoder system or subsystem described herein. The processing circuitry may be configured to perform the various operations as discussed later. As shown in fig. 5, if the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the

instructions in hardware using one or more processors to perform the techniques of this disclosure. Either of video encoder 20 and video decoder 30 may be integrated as part of a combined encoder/decoder (CODEC) in a single device, for example, as shown in Fig. 1 B.

Source device 12 and destination device 14 may comprise any of a wide range of devices, including any kind of handheld or stationary devices, e.g. notebook or laptop computers, mobile phones, smart phones, tablets or tablet computers, cameras, desktop computers, set-top boxes, televisions, display devices, digital media players, video gaming consoles, video streaming devices(such as content services servers or content delivery servers), broadcast receiver device, broadcast transmitter device, or the like and may use no or any kind of operating system. In some cases, the source device 12 and the destination device 14 may be equipped for wireless communication. Thus, the source device 12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in Fig. 1A is merely an example and the techniques of the present application may apply to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between the encoding and decoding devices. In other examples, data is retrieved from a local memory, streamed over a network, or the like. A video encoding device may encode and store data to memory, and/or a video decoding device may retrieve and decode data from memory. In some examples, the encoding and decoding is performed by devices that do not communicate with one another, but simply encode data to memory and/or retrieve and decode data from memory.

For convenience of description, embodiments of the invention are described herein, for example, by reference to High-Efficiency Video Coding (HEVC) or to the reference software of Versatile Video coding (WC), the next generation video coding standard developed by the Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG). One of ordinary skill in the art will understand that embodiments of the invention are not limited to HEVC or WC.

Encoder and Encoding Method

Fig. 2 shows a schematic block diagram of an example video encoder 20 that is configured to implement the techniques of the present application. In the example of Fig. 2, the video encoder 20 comprises an input 201 (or input interface 201), a residual calculation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, and inverse transform processing unit 212, a reconstruction unit 214, a loop filter unit 220, a decoded picture buffer (DPB) 230, a mode selection unit 260, an entropy encoding unit 270 and an output 272 (or output interface 272). The mode selection unit 260 may include an inter prediction unit 244, an intra prediction unit 254 and a partitioning unit 262. Inter prediction unit 244 may include a motion estimation unit and a motion compensation unit (not shown). A video encoder 20 as shown in Fig. 2 may also be referred to as hybrid video encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206, the quantization unit 208, the mode selection unit 260 may be referred to as forming a forward signal path of the encoder 20, whereas the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the buffer 216, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244 and the intra-prediction unit 254 may be referred to as forming a backward signal path of the video encoder 20, wherein the backward signal path of the video encoder 20 corresponds to the signal path of the decoder (see video decoder 30 in Fig. 3). The inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244 and the intra-prediction unit 254 are also referred to forming the“built-in decoder” of video encoder 20.

Pictures & Picture Partitioning (Pictures & Blocks)

The encoder 20 may be configured to receive, e.g. via input 201 , a picture 17 (or picture data 17), e.g. picture of a sequence of pictures forming a video or video sequence. The received picture or picture data may also be a pre-processed picture 19 (or pre-processed picture data 19). For sake of simplicity the following description refers to the picture 17. The picture 17 may also be referred to as current picture or picture to be coded (in particular in video coding to distinguish the current picture from other pictures, e.g. previously encoded and/or decoded pictures of the same video sequence, i.e. the video sequence which also comprises the current picture).

A (digital) picture is or can be regarded as a two-dimensional array or matrix of samples with intensity values. A sample in the array may also be referred to as pixel (short form of picture element) or a pel. The number of samples in horizontal and vertical direction (or axis) of the array or picture define the size and/or resolution of the picture. For representation of color, typically three color components are employed, i.e. the picture may be represented or include three sample arrays. In RBG format or color space a picture comprises a

corresponding red, green and blue sample array. However, in video coding each pixel is typically represented in a luminance and chrominance format or color space, e.g. YCbCr, which comprises a luminance component indicated by Y (sometimes also L is used instead) and two chrominance components indicated by Cb and Cr. The luminance (or short luma) component Y represents the brightness or grey level intensity (e.g. like in a grey-scale picture), while the two chrominance (or short chroma) components Cb and Cr represent the chromaticity or color information components. Accordingly, a picture in YCbCr format comprises a luminance sample array of luminance sample values (Y), and two chrominance sample arrays of chrominance values (Cb and Cr). Pictures in RGB format may be converted or transformed into YCbCr format and vice versa, the process is also known as color transformation or conversion. If a picture is monochrome, the picture may comprise only a luminance sample array. Accordingly, a picture may be, for example, an array of luma samples in monochrome format or an array of luma samples and two corresponding arrays of chroma samples in 4:2:0, 4:2:2, and 4:4:4 colour format.

Embodiments of the video encoder 20 may comprise a picture partitioning unit (not depicted in Fig. 2) configured to partition the picture 17 into a plurality of (typically non-overlapping) picture blocks 203. These blocks may also be referred to as root blocks, macro blocks (H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU) (H.265/HEVC and WC). The picture partitioning unit may be configured to use the same block size for all pictures of a video sequence and the corresponding grid defining the block size, or to change the block size between pictures or subsets or groups of pictures, and partition each picture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receive directly a block 203 of the picture 17, e.g. one, several or all blocks forming the picture 17. The picture block 203 may also be referred to as current picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or can be regarded as a two-dimensional array or matrix of samples with intensity values (sample values), although of smaller dimension than the picture 17. In other words, the block 203 may comprise, e.g., one sample array (e.g. a luma array in case of a monochrome picture 17, or a luma or chroma array in case of a color picture) or three sample arrays (e.g. a luma and two chroma arrays in case of a color picture 17) or any other number and/or kind of arrays depending on the color format applied. The number of samples in horizontal and vertical direction (or axis) of the block 203 define the size of block 203. Accordingly, a block may, for example, an MxN (M-column by N-row) array of samples, or an MxN array of transform coefficients.

Embodiments of the video encoder 20 as shown in Fig. 2 may be configured to encode the picture 17 block by block, e.g. the encoding and prediction is performed per block 203.

Embodiments of the video encoder 20 as shown in Fig. 2 may be further configured to partition and/or encode the picture by using slices (also referred to as video slices), wherein a picture may be partitioned into or encoded using one or more slices (typically nonoverlapping), and each slice may comprise one or more blocks (e.g. CTUs).

Embodiments of the video encoder 20 as shown in Fig. 2 may be further configured to partition and/or encode the picture by using tile groups (also referred to as video tile groups) and/or tiles (also referred to as video tiles), wherein a picture may be partitioned into or encoded using one or more tile groups (typically non-overlapping), and each tile group may comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g. may be of rectangular shape and may comprise one or more blocks (e.g. CTUs), e.g.

complete or fractional blocks.

Residual Calculation

The residual calculation unit 204 may be configured to calculate a residual block 205 (also referred to as residual 205) based on the picture block 203 and a prediction block 265 (further details about the prediction block 265 are provided later), e.g. by subtracting sample values of the prediction block 265 from sample values of the picture block 203, sample by sample (pixel by pixel) to obtain the residual block 205 in the sample domain.

The present invention broadly relates to improvements in residual calculation and preforming the necessary parameter signaling.

Transform

The transform processing unit 206 may be configured to apply a transform, e.g. a discrete cosine transform (DCT) or discrete sine transform (DST), on the sample values of the residual block 205 to obtain transform coefficients 207 in a transform domain. The transform coefficients 207 may also be referred to as transform residual coefficients and represent the residual block 205 in the transform domain.

The transform processing unit 206 may be configured to apply integer approximations of DCT/DST, such as the transforms specified for H.265/HEVC. Compared to an orthogonal DCT transform, such integer approximations are typically scaled by a certain factor. In order to preserve the norm of the residual block which is processed by forward and inverse transforms, additional scaling factors are applied as part of the transform process. The scaling factors are typically chosen based on certain constraints like scaling factors being a power of two for shift operations, bit depth of the transform coefficients, tradeoff between accuracy and implementation costs, etc. Specific scaling factors are, for example, specified for the inverse transform, e.g. by inverse transform processing unit 212 (and the

corresponding inverse transform, e.g. by inverse transform processing unit 312 at video decoder 30) and corresponding scaling factors for the forward transform, e.g. by transform processing unit 206, at an encoder 20 may be specified accordingly.

Embodiments of the video encoder 20 (respectively transform processing unit 206) may be configured to output transform parameters, e.g. a type of transform or transforms, e.g.

directly or encoded or compressed via the entropy encoding unit 270, so that, e.g., the video decoder 30 may receive and use the transform parameters for decoding. Quantization

The quantization unit 208 may be configured to quantize the transform coefficients 207 to obtain quantized coefficients 209, e.g. by applying scalar quantization or vector quantization. The quantized coefficients 209 may also be referred to as quantized transform coefficients 209 or quantized residual coefficients 209.

The quantization process may reduce the bit depth associated with some or all of the transform coefficients 207. For example, an n-bit transform coefficient may be rounded down to an m-bit Transform coefficient during quantization, where n is greater than m. The degree of quantization may be modified by adjusting a quantization parameter (QP). For example for scalar quantization, different scaling may be applied to achieve finer or coarser quantization. Smaller quantization step sizes correspond to finer quantization, whereas larger quantization step sizes correspond to coarser quantization. The applicable quantization step size may be indicated by a quantization parameter (QP). The quantization parameter may for example be an index to a predefined set of applicable quantization step sizes. For example, small quantization parameters may correspond to fine quantization (small quantization step sizes) and large quantization parameters may correspond to coarse quantization (large

quantization step sizes) or vice versa. The quantization may include division by a

quantization step size and a corresponding and/or the inverse dequantization, e.g. by inverse quantization unit 210, may include multiplication by the quantization step size.

Embodiments according to some standards, e.g. HEVC, may be configured to use a quantization parameter to determine the quantization step size. Generally, the quantization step size may be calculated based on a quantization parameter using a fixed point approximation of an equation including division. Additional scaling factors may be introduced for quantization and dequantization to restore the norm of the residual block, which might get modified because of the scaling used in the fixed point approximation of the equation for quantization step size and quantization parameter. In one example implementation, the scaling of the inverse transform and dequantization might be combined. Alternatively, customized quantization tables may be used and signaled from an encoder to a decoder, e.g. in a bitstream. The quantization is a lossy operation, wherein the loss increases with increasing quantization step sizes.

Embodiments of the video encoder 20 (respectively quantization unit 208) may be configured to output quantization parameters (QP), e.g. directly or encoded via the entropy encoding unit 270, so that, e.g., the video decoder 30 may receive and apply the

quantization parameters for decoding. Inverse Quantization

The inverse quantization unit 210 is configured to apply the inverse quantization of the quantization unit 208 on the quantized coefficients to obtain dequantized coefficients 21 1 , e.g. by applying the inverse of the quantization scheme applied by the quantization unit 208 based on or using the same quantization step size as the quantization unit 208. The dequantized coefficients 21 1 may also be referred to as dequantized residual coefficients 21 1 and correspond - although typically not identical to the transform coefficients due to the loss by quantization - to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply the inverse transform of the transform applied by the transform processing unit 206, e.g. an inverse discrete cosine transform (DCT) or inverse discrete sine transform (DST) or other inverse transforms, to obtain a reconstructed residual block 213 (or corresponding dequantized coefficients 213) in the sample domain. The reconstructed residual block 213 may also be referred to as transform block 213.

Reconstruction

The reconstruction unit 214 (e.g. adder or summer 214) is configured to add the transform block 213 (i.e. reconstructed residual block 213) to the prediction block 265 to obtain a reconstructed block 215 in the sample domain, e.g. by adding - sample by sample - the sample values of the reconstructed residual block 213 and the sample values of the prediction block 265.

Filtering

The loop filter unit 220 (or short“loop filter” 220), is configured to filter the reconstructed block 215 to obtain a filtered block 221 , or in general, to filter reconstructed samples to obtain filtered samples. The loop filter unit is, e.g., configured to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit 220 may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, e.g. a bilateral filter, an adaptive loop filter (ALF), a sharpening, a smoothing filter or a collaborative filter, or any combination thereof. Although the loop filter unit 220 is shown in Fig. 2 as being an in loop filter, in other configurations, the loop filter unit 220 may be implemented as a post loop filter. The filtered block 221 may also be referred to as filtered reconstructed block 221. Embodiments of the video encoder 20 (respectively loop filter unit 220) may be configured to output loop filter parameters (such as sample adaptive offset information), e.g. directly or encoded via the entropy encoding unit 270, so that, e.g., a decoder 30 may receive and apply the same loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that stores reference pictures, or in general reference picture data, for encoding video data by video encoder 20. The DPB 230 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The decoded picture buffer (DPB) 230 may be configured to store one or more filtered blocks 221. The decoded picture buffer 230 may be further configured to store other previously filtered blocks, e.g. previously reconstructed and filtered blocks 221 , of the same current picture or of different pictures, e.g. previously reconstructed pictures, and may provide complete previously reconstructed, i.e. decoded, pictures (and corresponding reference blocks and samples) and/or a partially reconstructed current picture (and corresponding reference blocks and samples), for example for inter prediction. The decoded picture buffer (DPB) 230 may be also configured to store one or more unfiltered reconstructed blocks 215, or in general unfiltered

reconstructed samples, e.g. if the reconstructed block 215 is not filtered by loop filter unit 220, or any other further processed version of the reconstructed blocks or samples.

Mode Selection (Partitioning & Prediction)

The mode selection unit 260 comprises partitioning unit 262, inter-prediction unit 244 and intra-prediction unit 254, and is configured to receive or obtain original picture data, e.g. an original block 203 (current block 203 of the current picture 17), and reconstructed picture data, e.g. filtered and/or unfiltered reconstructed samples or blocks of the same (current) picture and/or from one or a plurality of previously decoded pictures, e.g. from decoded picture buffer 230 or other buffers (e.g. line buffer, not shown).. The reconstructed picture data is used as reference picture data for prediction, e.g. inter-prediction or intra-prediction, to obtain a prediction block 265 or predictor 265.

Mode selection unit 260 may be configured to determine or select a partitioning for a current block prediction mode (including no partitioning) and a prediction mode (e.g. an intra or inter prediction mode) and generate a corresponding prediction block 265, which is used for the calculation of the residual block 205 and for the reconstruction of the reconstructed block 215. Embodiments of the mode selection unit 260 may be configured to select the partitioning and the prediction mode (e.g. from those supported by or available for mode selection unit 260), which provide the best match or in other words the minimum residual (minimum residual means better compression for transmission or storage), or a minimum signaling overhead (minimum signaling overhead means better compression for transmission or storage), or which considers or balances both. The mode selection unit 260 may be configured to determine the partitioning and prediction mode based on rate distortion optimization (RDO), i.e. select the prediction mode which provides a minimum rate distortion. Terms like“best”, “minimum”,“optimum” etc. in this context do not necessarily refer to an overall“best”, “minimum”,“optimum”, etc. but may also refer to the fulfillment of a termination or selection criterion like a value exceeding or falling below a threshold or other constraints leading potentially to a“sub-optimum selection” but reducing complexity and processing time.

In other words, the partitioning unit 262 may be configured to partition the block 203 into smaller block partitions or sub-blocks (which form again blocks), e.g. iteratively using quadtree-partitioning (QT), binary partitioning (BT) or triple-tree-partitioning (TT) or any combination thereof, and to perform, e.g., the prediction for each of the block partitions or sub-blocks, wherein the mode selection comprises the selection of the tree-structure of the partitioned block 203 and the prediction modes are applied to each of the block partitions or sub-blocks.

In the following the partitioning (e.g. by partitioning unit 260) and prediction processing (by inter-prediction unit 244 and intra-prediction unit 254) performed by an example video encoder 20 will be explained in more detail.

Partitioning

The partitioning unit 262 may partition (or split) a current block 203 into smaller partitions, e.g. smaller blocks of square or rectangular size. These smaller blocks (which may also be referred to as sub-blocks) may be further partitioned into even smaller partitions. This is also referred to tree-partitioning or hierarchical tree-partitioning, wherein a root block, e.g. at root tree-level 0 (hierarchy-level 0, depth 0), may be recursively partitioned, e.g. partitioned into two or more blocks of a next lower tree-level, e.g. nodes at tree-level 1 (hierarchy-level 1 , depth 1 ), wherein these blocks may be again partitioned into two or more blocks of a next lower level, e.g. tree-level 2 (hierarchy-level 2, depth 2), etc. until the partitioning is terminated, e.g. because a termination criterion is fulfilled, e.g. a maximum tree depth or minimum block size is reached. Blocks which are not further partitioned are also referred to as leaf-blocks or leaf nodes of the tree. A tree using partitioning into two partitions is referred to as binary-tree (BT), a tree using partitioning into three partitions is referred to as ternary- tree (TT), and a tree using partitioning into four partitions is referred to as quad-tree (QT).

As mentioned before, the term“block” as used herein may be a portion, in particular a square or rectangular portion, of a picture. With reference, for example, to HEVC and WC, the block may be or correspond to a coding tree unit (CTU), a coding unit (CU), prediction unit (PU), and transform unit (TU) and/or to the corresponding blocks, e.g. a coding tree block (CTB), a coding block (CB), a transform block (TB) or prediction block (PB).

For example, a coding tree unit (CTU) may be or comprise a CTB of luma samples, two corresponding CTBs of chroma samples of a picture that has three sample arrays, or a CTB of samples of a monochrome picture or a picture that is coded using three separate colour planes and syntax structures used to code the samples. Correspondingly, a coding tree block (CTB) may be an NxN block of samples for some value of N such that the division of a component into CTBs is a partitioning. A coding unit (CU) may be or comprise a coding block of luma samples, two corresponding coding blocks of chroma samples of a picture that has three sample arrays, or a coding block of samples of a monochrome picture or a picture that is coded using three separate colour planes and syntax structures used to code the samples. Correspondingly a coding block (CB) may be an MxN block of samples for some values of M and N such that the division of a CTB into coding blocks is a partitioning.

In embodiments, e.g., according to HEVC, a coding tree unit (CTU) may be split into CUs by using a quad-tree structure denoted as coding tree. The decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the CU level. Each CU can be further split into one, two or four PUs according to the PU splitting type. Inside one PU, the same prediction process is applied and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the 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.

In embodiments, e.g., according to the latest video coding standard currently in

development, which is referred to as Versatile Video Coding (WC), a combined Quad-tree and binary tree (QTBT) partitioning is for example used to partition a coding block. In the QTBT block structure, a CU can have either a square or rectangular shape. For example, a coding tree unit (CTU) is first partitioned by a quadtree structure. The quadtree leaf nodes are further partitioned by a binary tree or ternary (or triple) tree structure. The partitioning tree leaf nodes are called coding units (CUs), and that segmentation is used for prediction and transform processing without any further partitioning. This means that the CU, PU and TU have the same block size in the QTBT coding block structure. In parallel, multiple partition, for example, triple tree partition may be used together with the QTBT block structure.

In one example, the mode selection unit 260 of video encoder 20 may be configured to perform any combination of the partitioning techniques described herein.

As described above, the video encoder 20 is configured to determine or select the best or an optimum prediction mode from a set of (e.g. pre-determined) prediction modes. The set of prediction modes may comprise, e.g., intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 different intra-prediction modes, e.g. non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined in HEVC, or may comprise 67 different intra-prediction modes, e.g. non- directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined for WC.

The intra-prediction unit 254 is configured to use reconstructed samples of neighboring blocks of the same current picture to generate an intra-prediction block 265 according to an intra-prediction mode of the set of intra-prediction modes.

The intra prediction unit 254 (or in general the mode selection unit 260) is further configured to output intra-prediction parameters (or in general information indicative of the selected intra prediction mode for the block) to the entropy encoding unit 270 in form of syntax

elements 266 for inclusion into the encoded picture data 21 , so that, e.g., the video decoder 30 may receive and use the prediction parameters for decoding.

Inter-Prediction

The set of (or possible) inter-prediction modes depends on the available reference pictures (i.e. previous at least partially decoded pictures, e.g. stored in DBP 230) and other interprediction parameters, e.g. whether the whole reference picture or only a part, e.g. a search window area around the area of the current block, of the reference picture is used for searching for a best matching reference block, and/or e.g. whether pixel interpolation is applied, e.g. half/semi-pel and/or quarter-pel interpolation, or not.

Additional to the above prediction modes, skip mode and/or direct mode may be applied. The inter prediction unit 244 may include a motion estimation (ME) unit and a motion compensation (MC) unit (both not shown in Fig.2). The motion estimation unit may be configured to receive or obtain the picture block 203 (current picture block 203 of the current picture 17) and a decoded picture 231 , or at least one or a plurality of previously

reconstructed blocks, e.g. reconstructed blocks of one or a plurality of other/different previously decoded pictures 231 , for motion estimation. E.g. a video sequence may comprise the current picture and the previously decoded pictures 231 , or in other words, the current picture and the previously decoded pictures 231 may be part of or form a sequence of pictures forming a video sequence.

The encoder 20 may, e.g., be configured to select a reference block from a plurality of reference blocks of the same or different pictures of the plurality of other pictures and provide a reference picture (or reference picture index) and/or an offset (spatial offset) between the position (x, y coordinates) of the reference block and the position of the current block as inter prediction parameters to the motion estimation unit. This offset is also called motion vector (MV).

The motion compensation unit is configured to obtain, e.g. receive, an inter prediction parameter and to perform inter prediction based on or using the inter prediction parameter to obtain an inter prediction block 265. Motion compensation, performed by the motion compensation unit, may involve fetching or generating the prediction block based on the motion/block vector determined by motion estimation, possibly performing interpolations to sub-pixel precision. Interpolation filtering may generate additional pixel samples from known pixel samples, thus potentially increasing the number of candidate prediction blocks that may be used to code a picture block. Upon receiving the motion vector for the PU of the current picture block, the motion compensation unit may locate the prediction block to which the motion vector points in one of the reference picture lists.

The motion compensation unit may also generate syntax elements associated with the blocks and video slices for use by video decoder 30 in decoding the picture blocks of the video slice. In addition or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be generated or used.

Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, an entropy encoding algorithm or scheme (e.g. a variable length coding (VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmetic coding scheme, a binarization, a context adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique) or bypass (no compression) on the quantized coefficients 209, inter prediction parameters, intra prediction parameters, loop filter parameters and/or other syntax elements to obtain encoded picture data 21 which can be output via the output 272, e.g. in the form of an encoded bitstream 21 , so that, e.g., the video decoder 30 may receive and use the parameters for decoding. The encoded bitstream 21 may be transmitted to video decoder 30, or stored in a memory for later transmission or retrieval by video decoder 30.

Other structural variations of the video encoder 20 can be used to encode the video stream. For example, a non-transform based encoder 20 can quantize the residual signal directly without the transform processing unit 206 for certain blocks or frames. In another

implementation, an encoder 20 can have the quantization unit 208 and the inverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

Fig. 3 shows an example of a video decoder 30 that is configured to implement the techniques of this present application. The video decoder 30 is configured to receive encoded picture data 21 (e.g. encoded bitstream 21 ), e.g. encoded by encoder 20, to obtain a decoded picture 331. The encoded picture data or bitstream comprises information for decoding the encoded picture data, e.g. data that represents picture blocks of an encoded video slice (and/or tile groups or tiles) and associated syntax elements.

In the example of Fig. 3, the decoder 30 comprises an entropy decoding unit 304, an inverse quantization unit 310, an inverse transform processing unit 312, a reconstruction unit 314 (e.g. a summer 314), a loop filter 320, a decoded picture buffer (DBP) 330, a mode application unit 360, an inter prediction unit 344 and an intra prediction unit 354. Inter prediction unit 344 may be or include a motion compensation unit. Video decoder 30 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 100 from Fig. 2.

As explained with regard to the encoder 20, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214 the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 344 and the intra prediction unit 354 are also referred to as forming the“built-in decoder” of video encoder 20. Accordingly, the inverse quantization unit 310 may be identical in function to the inverse quantization unit 1 10, the inverse transform processing unit 312 may be identical in function to the inverse transform processing unit 212, the reconstruction unit 314 may be identical in function to reconstruction unit 214, the loop filter 320 may be identical in function to the loop filter 220, and the decoded picture buffer 330 may be identical in function to the decoded picture buffer 230. Therefore, the explanations provided for the respective units and functions of the video 20 encoder apply correspondingly to the respective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21 (or in general encoded picture data 21) and perform, for example, entropy decoding to the encoded picture data 21 to obtain, e.g., quantized coefficients 309 and/or decoded coding parameters (not shown in Fig. 3), e.g. any or all of inter prediction parameters (e.g. reference picture index and motion vector), intra prediction parameter (e.g. intra prediction mode or index), transform parameters, quantization parameters, loop filter parameters, and/or other syntax elements. Entropy decoding unit 304 maybe configured to apply the decoding algorithms or schemes corresponding to the encoding schemes as described with regard to the entropy encoding unit 270 of the encoder 20. Entropy decoding unit 304 may be further configured to provide inter prediction parameters, intra prediction parameter and/or other syntax elements to the mode application unit 360 and other parameters to other units of the decoder 30.

Video decoder 30 may receive the syntax elements at the video slice level and/or the video block level. In addition or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be received and/or used.

Inverse Quantization

The inverse quantization unit 310 may be configured to receive quantization parameters (QP) (or in general information related to the inverse quantization) and quantized coefficients from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) and to apply based on the quantization parameters an inverse quantization on the decoded quantized coefficients 309 to obtain dequantized coefficients 311 , which may also be referred to as transform coefficients 311. The inverse quantization process may include use of a quantization parameter determined by video encoder 20 for each video block in the video slice (or tile or tile group) to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied. Inverse Transform

Inverse transform processing unit 312 may be configured to receive dequantized coefficients 31 1 , also referred to as transform coefficients 31 1 , and to apply a transform to the dequantized coefficients 31 1 in order to obtain reconstructed residual blocks 213 in the sample domain. The reconstructed residual blocks 213 may also be referred to as transform blocks 313. The transform may be an inverse transform, e.g., an inverse DCT, an inverse DST, an inverse integer transform, or a conceptually similar inverse transform process. The inverse transform processing unit 312 may be further configured to receive transform parameters or corresponding information from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) to determine the transform to be applied to the dequantized coefficients 31 1 .

Reconstruction

The reconstruction unit 314 (e.g. adder or summer 314) may be configured to add the reconstructed residual block 313, to the prediction block 365 to obtain a reconstructed block 315 in the sample domain, e.g. by adding the sample values of the reconstructed residual block 313 and the sample values of the prediction block 365.

Filtering

The loop filter unit 320 (either in the coding loop or after the coding loop) is configured to filter the reconstructed block 315 to obtain a filtered block 321 , e.g. to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit 320 may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, e.g. a bilateral filter, an adaptive loop filter (ALF), a sharpening, a smoothing filters or a collaborative filters, or any combination thereof. Although the loop filter unit 320 is shown in Fig. 3 as being an in loop filter, in other configurations, the loop filter unit 320 may be implemented as a post loop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decoded picture buffer 330, which stores the decoded pictures 331 as reference pictures for subsequent motion compensation for other pictures and/or for output respectively display.

The decoder 30 is configured to output the decoded picture 31 1 , e.g. via output 312, for presentation or viewing to a user. Prediction

The inter prediction unit 344 may be identical to the inter prediction unit 244 (in particular to the motion compensation unit) and the intra prediction unit 354 may be identical to the inter prediction unit 254 in function, and performs split or partitioning decisions and prediction based on the partitioning and/or prediction parameters or respective information received from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304). Mode application unit 360 may be configured to perform the prediction (intra or inter prediction) per block based on reconstructed pictures, blocks or respective samples (filtered or unfiltered) to obtain the prediction block 365.

When the video slice is coded as an intra coded (I) slice, intra prediction unit 354 of mode application unit 360 is configured to generate prediction block 365 for a picture block of the current video slice based on a signaled intra prediction mode and data from previously decoded blocks of the current picture. When the video picture is coded as an inter coded (i.e., B, or P) slice, inter prediction unit 344 (e.g. motion compensation unit) of mode application unit 360 is configured to produce prediction blocks 365 for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit 304. For inter prediction, the prediction blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder 30 may construct the reference frame lists, List 0 and List 1 , using default construction techniques based on reference pictures stored in DPB 330. The same or similar may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices), e.g. a video may be coded using I, P or B tile groups and /or tiles.

Mode application unit 360 is configured to determine the prediction information for a video block of the current video slice by parsing the motion vectors or related information and other syntax elements, and uses the prediction information to produce the prediction blocks for the current video block being decoded. For example, the mode application unit 360 uses some of the received syntax elements to determine a prediction mode (e.g., intra or inter prediction) used to code the video blocks of the video slice, an inter prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more of the reference picture lists for the slice, motion vectors for each inter encoded video block of the slice, inter prediction status for each inter coded video block of the slice, and other information to decode the video blocks in the current video slice. The same or similar may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices), e.g. a video may be coded using I, P or B tile groups and/or tiles.

Embodiments of the video decoder 30 as shown in Fig. 3 may be configured to partition and/or decode the picture by using slices (also referred to as video slices), wherein a picture may be partitioned into or decoded using one or more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g. CTUs).

Embodiments of the video decoder 30 as shown in Fig. 3 may be configured to partition and/or decode the picture by using tile groups (also referred to as video tile groups) and/or tiles (also referred to as video tiles), wherein a picture may be partitioned into or decoded using one or more tile groups (typically non-overlapping), and each tile group may comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g. may be of rectangular shape and may comprise one or more blocks (e.g. CTUs), e.g. complete or fractional blocks.

Other variations of the video decoder 30 can be used to decode the encoded picture data 21. For example, the decoder 30 can produce the output video stream without the loop filtering unit 320. For example, a non-transform based decoder 30 can inverse-quantize the residual signal directly without the inverse-transform processing unit 312 for certain blocks or frames. In another implementation, the video decoder 30 can have the inverse-quantization unit 310 and the inverse-transform processing unit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, a processing result of a current step may be further processed and then output to the next step. For example, after interpolation filtering, motion vector derivation or loop filtering, a further operation, such as Clip or shift, may be performed on the processing result of the interpolation filtering, motion vector derivation or loop filtering.

It should be noted that further operations may be applied to the derived motion vectors of current block (including but not limited to control point motion vectors of affine mode, subblock motion vectors in affine, planar, ATMVP (advanced temporal motion vector prediction) modes, temporal motion vectors, and so on). For example, the value of motion vector is constrained to a predefined range according to its representing bit. If the representing bit of motion vector is bitDepth, then the range is -2 ^A (bitDepth-1 ) ~ 2 ^A (bitDepth-1 )-1 , where “ ^A ” means exponentiation. For example, if bitDepth is set equal to 16, the range is -32768 ~ 32767; if bitDepth is set equal to 18, the range is -131072~131071. For example, the value of the derived motion vector (e.g. the MVs of four 4x4 sub-blocks within one 8x8 block) is constrained such that the max difference between integer parts of the four 4x4 sub-block MVs is no more than N pixels, such as no more than 1 pixel. Here provides two methods for constraining the motion vector according to the bitDepth.

Method 1 : remove the overflow MSB (most significant bit) by flowing operations ux= ( mvx+2 ^bitDepth ) % 2 ^bitDepth (1 ) mvx = ( ux >= 2 ^{bitDepth 1} ) ? (ux - 2 ^bitDepth ) : ux (2) uy= ( mvy+2 ^bitDepth ) % 2 ^bitDepth (3) mvy = ( uy >= 2 ^{bitDepth 1} ) ? (uy - 2 ^bitDepth ) : uy (4) where mvx is a horizontal component of a motion vector of an image block or a sub-block, mvy is a vertical component of a motion vector of an image block or a sub-block, and ux and uy indicates an intermediate value;

For example, if the value of mvx is -32769, after applying formula (1) and (2), the resulting value is 32767. In computer system, negative decimal numbers are stored as two’s complement. The two’s complement of -32769 is 1 ,011 1 ,1 11 1 ,11 11 ,11 11 (17 bits), then the MSB is discarded, so the resulting two’s complement is 01 11 ,11 11 ,1 11 1 ,1 11 1 (decimal number is 32767), which is same as the output by applying formula (1) and (2). ux= ( mvpx + mvdx +2 ^bitDepth ) % 2 ^bitDepth (5) mvx = ( ux >= 2 ^{bitDepth 1} ) ? (ux - 2 ^bitDepth ) : ux (6) uy= ( mvpy + mvdy +2 ^bitDepth ) % 2 ^bitDepth (7) mvy = ( uy >= 2 ^bitDepth - ¹ ) ? (uy - 2 ^bitDepth ) : uy (8)

The operations may be applied during the sum of mvp (motion vector predictor) and mvd (motion vector difference), as shown in formula (5) to (8).

Method 2: remove the overflow MSB by clipping the value vx = Clip3(-2 ^{bitDepth 1} , 2 ^{bitDepth 1} -1 , vx) vy = Clip3(-2 ^{bitDepth 1} , 2 ^{bitDepth 1} -1 , vy) where vx is a horizontal component of a motion vector of an image block or a sub-block, vy is a vertical component of a motion vector of an image block or a sub-block; x, y and z respectively correspond to three input value of the MV clipping process, and the definition of function Clip3 is as follows: x Z < X

Clip3( x, y, z ) y z > y

.z otherwise

Fig. 4 is a schematic diagram of a video coding device 400 according to an embodiment of the disclosure. The video coding device 400 is suitable for implementing the disclosed embodiments as described herein. In an embodiment, the video coding device 400 may be a decoder such as video decoder 30 of Fig. 1 A or an encoder such as video encoder 20 of Fig. 1A.

The video coding device 400 comprises ingress ports 410 (or input ports 410) and receiver units (Rx) 420 for receiving data; a processor, logic unit, or central processing unit (CPU) 430 to process the data; transmitter units (Tx) 440 and egress ports 450 (or output ports 450) for transmitting the data; and a memory 460 for storing the data. The video coding device 400 may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports 410, the receiver units 420, the transmitter units 440, and the egress ports 450 for egress or ingress of optical or electrical signals.

The processor 430 is implemented by hardware and software. The processor 430 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), FPGAs, ASICs, and DSPs. The processor 430 is in communication with the ingress ports 410, receiver units 420, transmitter units 440, egress ports 450, and memory 460. The processor 430 comprises a coding module 470. The coding module 470 implements the disclosed embodiments described above. For instance, the coding module 470

implements, processes, prepares, or provides the various coding operations. The inclusion of the coding module 470 therefore provides a substantial improvement to the functionality of the video coding device 400 and effects a transformation of the video coding device 400 to a different state. Alternatively, the coding module 470 is implemented as instructions stored in the memory 460 and executed by the processor 430. The memory 460 may comprise one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 460 may be, for example, volatile and/or non-volatile and may be a read-only memory (ROM), random access memory (RAM), ternary content-addressable memory (TCAM), and/or static random-access memory (SRAM).

Fig. 5 is a simplified block diagram of an apparatus 500 that may be used as either or both of the source device 12 and the destination device 14 from Fig. 1 according to an exemplary embodiment.

A processor 502 in the apparatus 500 can be a central processing unit. Alternatively, the processor 502 can be any other type of device, or multiple devices, capable of manipulating or processing information now-existing or hereafter developed. Although the disclosed implementations can be practiced with a single processor as shown, e.g., the processor 502, advantages in speed and efficiency can be achieved using more than one processor.

A memory 504 in the apparatus 500 can be a read only memory (ROM) device or a random access memory (RAM) device in an implementation. Any other suitable type of storage device can be used as the memory 504. The memory 504 can include code and data 506 that is accessed by the processor 502 using a bus 512. The memory 504 can further include an operating system 508 and application programs 510, the application programs 510 including at least one program that permits the processor 502 to perform the methods described here. For example, the application programs 510 can include applications 1 through N, which further include a video coding application that performs the methods described here.

The apparatus 500 can also include one or more output devices, such as a display 518. The display 518 may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display 518 can be coupled to the processor 502 via the bus 512.

Although depicted here as a single bus, the bus 512 of the apparatus 500 can be composed of multiple buses. Further, the secondary storage 514 can be directly coupled to the other components of the apparatus 500 or can be accessed via a network and can comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. The apparatus 500 can thus be implemented in a wide variety of configurations. Triangular partitioning mode (TPM) and geometric motion partitioning (GMP) are partitioning techniques that enable non-horizontal and non-vertical boundaries between prediction partitions, as exemplarily shown in Fig. 6, where prediction unit PU1 601 and prediction unit PU1 602 are combined in region 603 using a weighted averaging procedure of subsets of their samples related to different color components. TMP enables boundaries between prediction partitions only along a rectangular block diagonals, whereas boundaries according to GMP maybe located at arbitrary positions as Fig. 9 illustrates. In region 603 of Fig. 6, integer numbers within squares denote weights W _PUI applied to luma component of prediction unit PU1. In an example, weights WPUå applied to luma component of prediction unit PU2 are calculated as follows:

Wpu2— 8— Wpui

Weights applied to chroma components of corresponding prediction units may differ from weights applied to luma components of corresponding prediction units.

The details on the current syntax for TPM are presented in Table 1 , where 4 syntax elements are used to signal information on TPM:

MergeTriangleFlag is a flag that identifies whether TPM is selected or not (“0” means that TPM is not selected; otherwise, TPM is chosen); merge_triangle_split_dir is a split direction flag for TPM (“0” means the split direction from top-left corner to the below-right corner; otherwise, the split direction is from top-right corner to the below-left corner; i.e., in Fig. 6, the flag is 0); merge_triangle_idxO and merge_triangle_idx1 are indices of merge candidates 0 and 1 used for TPM. Here, the merge candidates are motion vectors associated with the prediction units PU1 and PU2in the list of reference motion vectors (reference picture list).

Table 1. Merge data syntax including syntax for TPM

In more detail, TPM is described in the following proposal: R-L. Liao and C.S. Lim “CE10.3.1.b: Triangular prediction unit mode,” contribution JVET-L0124 to the 12 ^th JVET meeting, Macao, China, October 2018. GMP is explained in the following paper: M. Blaser,

J. Schneider, Johannes Sauer, and Mathias Wien,“Geometry-based Partitioning for Predictive Video Coding with Transform Adaptation,” Picture Coding Symposium (PCS), San Francisco, California, USA, June 2018.

Increasing compression efficiency of TPM and GMP by reducing bitrate needed to encode blocks, the blocks are predicted using these and similar partitioning techniques.

Prediction errors are localized only in near-boundary region that covers the boundary between partitions to use a more compact representation. Transform and quantization are performed only for this near-boundary region.

In an exemplary embodiment, a near-boundary region is defined by start and end side positions, wherein the first of the side positions is located on a first side of the block, a side of the block is top, left, right or bottom; and the second side position is located on the second side of the block, and wherein the first side of the block is not the same as the second side of the block. For instance, in the example of Fig. 6, the first position is on the left side of the block, at the boundary between regions 602 and 603 in the left hand drawing (corresponding to the boundary between a left hand pixel marked as“0” and a left hand pixel marked with “1” in the upper right hand drawing) and the second position is on the right side of the block, at the boundary between regions 603 and 601 in the left hand drawing (corresponding to the boundary between a right hand pixel marked“7” and a right hand pixel marked“8” in the upper right hand drawing. The near-boundary region could be defined by a curve that connects the first and the second positions and including to the near-boundary region the samples with the distance to the curve not exceeding a distance threshold. This threshold is set to 2 so that subsampled block obtained from the samples of a near-boundary region have sides lengths that are a power of two values.

For example, rows of a subsampled block are obtained by selecting a set of samples from a range of rows of a block of residual signal, wherein the start position is for the first row of the range is specified as the first side position and the end position specified for the last row of the range as the end position, and wherein a sampling position is specified for each of the rows between the first row and the last row of the range so that the sampling position is a monotonic function of the row position within a block, and wherein the set of samples comprises the samples for which the distance to the sampling position of the row is not greater than the distance threshold.

In another example, columns of subsampled block are obtained by selecting a set of samples from a range of columns of a block of residual signal, wherein the start position is for the first column of the range is specified as the first side position and the end position is specified for the last column of the range as the end position, and wherein a sampling position is specified for each of the columns between the first column and the last column of the range so that the sampling position is a monotonic function of the column position within a block, and wherein the set of samples comprises the samples for which the distance to the sampling position of the column is not greater than the distance threshold.

It’s understood, that the distance threshold is smaller than corresponding block side length, i.e. it could be set to half of the height or half of the width of the block.

Embodiments of this application disclose a mechanism of resampling a block to obtain this near-boundary region that is processed as a transform block / transform unit.

In an embodiment of the present invention, as shown in Fig. 6, prediction unit PU1 601 and prediction unit PU2 602 are combined using TPM technique to get a predictor. The prediction error is calculated for these units. A residue block contains 2 zero-residue regions 61 1 and 612, and region 613 is resampled into a transform block (TB) 623, so that the TB 623 represents residues for a color component of a transform unit (TU). In regions 61 1 and 612, residues are assumed to be zero, whereas residual should be non zero in region 613.

In Fig. 6, region 613 covers the area where weights at least for one prediction unit PU1 or PU2 are non-zero. In an example, residue signal from region 613 can be resampled into transform block 623 by reading samples from memory row-wise or column-wise. In another example, as shown in Fig. 7, non-zero residuals shown in region 701 cover a part of the area where weights at least for one prediction unit PU1 or PU2 are non-zero. In regions 702 and 703, residues are assumed to be quantized out to zero. So, transform block 704 that represents residues for a color component of a transform unit (TU) is the result of resampling region 701.

In another example, as shown in Fig. 8, processing steps for the TPM case are presented as 2 flow-charts for decoder and encoder, respectively. In step 801 , residual data are decoded, inverse quantization and inverse transform (if any) are performed to obtain transform blocks (TBs) of a TU. Then, inverse resampling 802 restores residues within each transform block (TB) of a TU by placing samples of a transform blocks at corresponding positions within a residue block. The correspondence between samples positions in region 613 and sample positions in transform block 623 of a TU is demonstrated in Fig. 6. Similarly, this

correspondence is also shown in Fig. 7. Regions 611 and 612 in Fig. 6 or regions 702 and 703 in Fig. 7 are filled in by zero. Step 803 corresponds to PU reconstruction using the restored residues and TPM predictor.

In an example, at the encoder side, the order of actions shown in Fig. 8 for TPM is as follows. In step 811 , prediction process is fulfilled to get a predictor for a unit, residues are obtained according to the predictor. In step 812, samples corresponds to region 613 in Fig. 6 or region 701 in Fig. 7 are fetched from memory either row-wise or column-wise to get transform blocks of a TU. Forward transform, quantization and residual coding are performed as in step 813.

Similarly, resampling and inverse resampling are used in the case of GMP as shown by way of example in Fig. 9. In regions 902, 904, 912 and 914, residues are assumed to be zero. The boundary between regions 902 and 904 is shown by line 903, whereas the boundary between regions 912 and 914 is shown by line 913. The near-boundary regions 901 or 911 cover the area between regions 902 and 904 as well as 912 and 914 in different ways as Fig. 9 illustrates, respectively. Besides, regions 901 or 91 1 are resampled into transform blocks of different shapes 905 and 915, respectively.

In Fig. 10, processing steps for the GMP case are presented as 2 flow-charts for decoder and encoder. In step 1001 , residual are decoded, inverse quantization and inverse transform (if any) are performed to obtain transform blocks of a TU. Then, inverse resampling 1002 should restore residues within each transform block of a TU, placing samples of a transform blocks at corresponding positions within a residue blocks. The correspondence between samples positions within regions 901 and 91 1 and transform blocks 905 and 915 of TUs is demonstrated in Fig. 9. Regions 902, 904, 912 and 914 in Fig. 9 are filled in by zero. Final step 1003 corresponds to PU reconstruction using the restored residues and GMP predictor.

At the encoder side, the order of actions shown in Fig. 10 for GMP is as follows. In step 101 1 , prediction process is fulfilled to get a predictor for a unit and then residues are obtained. In step 1012, samples corresponds to regions 901 and 911 in Fig. 9 are fetched from memory either row-wise or column-wise to get transform blocks of a TU. Finally, forward transform, quantization and residual coding are performed as in step 1013.

The proposed mechanism adds one more state flags that should be signaled. In Fig. 1 1 , we disclose a signaling mechanism for the proposed method exemplarily applied to TPM. In steps 1101 and 1102, the value of the flags MergeTriagleFlag and cbf (Coded Block Flag) are checked. If the values of both MergeTriagleFlag and cbf flags is set to 1 , then the flag ShapeAdaptiveResamplingFlag (a flag indicating whether or not Partial Transform (PT), i.e. the process of selecting a near-boundary region is enabled, also known as part_trans_flag) should be checked. At the encoder side, its value can be iterated in Rate-Distortion

Optimization procedure. So, its set value should be read from memory. At the decoder side, a value of ShapeAdaptiveResamplingFlag should be parsed from a bit-stream. If

ShapeAdaptiveResamplingFlag equals 1 , resampling for transform blocks is applied.

Note that in the current design of H.266A/VC, there are several syntax elements that have meanings of cbf flags, namely: cu_cbf for an entire coding unit (CU), tu_cbf_luma, tu_cbf_cb and tu_cbf_cr are CBFs for luma, Cb, and Cr components of TU, respectively. For the sake of generality, the abbreviation cbf in step 1 102 may denote any of these flags. Of course, the meaning of this flag is different in each case. If cu_cbf is checked, then the proposed resampling is applied to each color component. Otherwise, it is used only for a concrete color component (luma, Cb, or Cr).

As mentioned above, the height of a region to be resampled and, therefore, the height of a TB can be different. In particular, the height of region 613 in Fig. 6 differs from the height of region 701 in Fig. 7. To make the design of the proposed technique flexible, the height of a region to be resampled and, therefore, the height of a TB should be adjustable. The 1 ^st mechanism to adjust the height of a region to be resampled and, therefore, the height of a TB is to derive it using an entire block shape and size. For example, a values of heightr _B of a region to be resampled and, therefore, the height of a TB can be calculated as follows: heightrB = max{width, height} / 2, where width and height are horizontal and vertical lengths of a block. The 2 ^nd mechanism to adjust the height of a region to be resampled and, therefore, the height of a TB is to signal it in a bit-stream as shown in Fig. 12. Steps 1201-1203 are same as steps 1 101 -1 103 in Fig. 1 1. At step 1204, the value of ShapeAdaptiveResamplingFlag is checked whether it equals 1 or not. If ShapeAdaptiveResamplingFlag equals 1 , then the syntax element ShapeAdaptiveResamplingSize should be read from memory (at the encoder side) or parsed from a bit-stream (at the decoder side) at step 1205. Different codes can be used to encode or decode the syntax element ShapeAdaptiveResamplingSize. For example, if it is necessary to choose only between 2 values of the heights of a region to be resampled and, therefore, the height of a TB, 1 bin flag (binary flag) can be used. If more options (3 or more variants of the height) are available, unary truncated code, fixed-length code, exponential Golomb-Rice code, etc. might be used as codes. It is noted that ShapeAdaptiveResampling is another term for partial transform. As indicated above, ShapeAdaptiveTransformFlag has the same meaning as part_trans_flag. The syntax element ShapeAdaptiveResamplingSize has the same meaning as the above introduced part_trans_idx.

One of the difficulties in using the proposed technique is how to perform deblocking filtering on the boundaries of a region when its boundaries are not horizontal or vertical. In Fig. 13, region 1301 is resampled into a TB and then transform (if any) and quantization are performed. So, blocking artifacts might appear near boundary between region 1301 and region 1302 as well as near boundary between region 1301 and region 1303. To deblock these 2 boundaries, we propose using the following mechanism:

1. Fetch sample p[x][y] located within region 1301 immediately on block boundaries and marked by black circles in Fig. 13;

2. Assign value of (p[x][y] » k) to samples at position (x, y - k) if k <= 3

3. Fetch sample p[x][y] located within region 1301 immediately on block boundaries and marked by white circles in Fig. 13;

4. Assign value of (p[x][y] » k) to samples at position (x, y + k) if k <= 3.

The proposed deblocking filter is directional. The propagation directions are marked by arrows 1304 and 1305 in Fig. 13.

Another mechanism to deblock boundaries between regions 1401 and 1402 as well as 1401 and 1403 is presented in Fig. 14. Spatial filter of (2 ^w +1)x(2 ^M +1) size (where N and M are non-zero integer values) are applied on the boundaries between regions 1401 and 1402 as well as 1401 and 1403 so that the spatial filter is fed by a group of samples that contains at least one sample belonging to region 1401 and at least one sample belonging to region 1402 or 1403. In the example shown in Fig. 14, regions where spatial filter is applied have sizes of 3x3 and are denoted by 1404 and 1405. This spatial filter should relate to the type of low- pass smoothing filters. If a 3x3 Gaussian filter is used, its coefficients can be as follows:

In another embodiment of the invention illustrated in Fig. 15 and Fig. 16 a near boundary region is defined by the partitioning process of GMP that subdivides a PU onto two regions using a straight line. This line has an intersection with the PU boundary in two points corresponding to two integer positions. There are 6 cases of partitioning, four of these cases split PU into one triangle and 1 pentagon area, and the rest two cases split PU into two trapeze areas.

For the trapeze cases these two positions are located on top and bottom side, or on the left and right sides of the PU.

The near-boundary region is obtained by either a row-wise or column-wise scan, wherein for each iteration sampling position is shifted onto a step value, that could be defined as:

s = _E ~ ys + ^S TB )/(* _£ - Xs - 1) . when the scan is column-wise; and

s = (x _E - x _s + S _TB )/(y _E — y _s — 1) , when the scan is row-wise.

In the equations above {x ₅ , y ₅ } and {x _E ,y _E } denote start and end positions, shown in Fig 15 and Fig 16 respectively, for a colomn-wise and a row-wise scans. Depending on the scan, STB denotes heightr _B (Fig 15) or widttvrB (Fig 16) of the subsampled block and is further referred to as a subsampling width Sw-

For a row-wise scan, samples of the subsampled block B(x,y ) are obtained from PU samples p(x,y) as follows:

B{x,y ) = p(x + x _s + s y - S _w ,y _s + y)

For a column-wise scan, samples of the subsampled block B(x,y ) are obtained from PU samples p(x,y) as follows:

B(x,y ) = p(x _s + x ,y + y _s + s - x - S _w ).

For the cases when split results in one triangle and one pentagon, selection of the scan depends on whether a horizontal or vertical component of the start and end positions are closer to the corner that is aligned with the resulting triangle. When horizontal component is closer to the corner of the split case, x _s - x _E is quantized to the closest power-of-two value and a column-wise scan is applied. When vertical component is closer to the corner of the split case, y _s - y _E is quantized to the closest power-of-two value and a row-wise scan is applied.

In both cases, S _w is selected in such a way that the resulting near-boundary region is inside the PU. cu_sbt_flag equal to 1 specifies that for the current coding unit, subblock transform (SBT) is used. cu_sbt_flag equal to 0 specifies that for the current coding unit, subblock transform is not used. When cu_sbt_flag is not present, its value is inferred to be equal to 0.

When subblock transform is used, a coding unit is split into two transform units; one transform unit has residual data, the other does not have residual data. The present disclosure may provide a harmonization in signalling for the alternatives of resampling (Partial Transform PT) and subblock transform SBT.

Exemplary signaling of a“cu_sbt_flag” is given in Table 2.

Table 2. Signaling of cu_sbt_flag.

sps_sbt_enabled_flag equal to 0 specifies that subblock transform for inter-predicted CUs is disabled. sps_sbt_enabled_flag equal to 1 specifies that subblock transform for inter- predicteds CU is enabled. ciip_flag[ xO ][ yO ] specifies whether the combined inter-picture merge and intra-picture prediction is applied for the current coding unit. The array indices xO, yO specify the location ( xO, yO ) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.

When ciip_flag[ xO ][ yO ] is not present, it is inferred to be equal to 0.

When ciip_flag[ xO ][ yO ] is equal to 1 , the variable lntraPredModeY[ x ][ y ] with x = xCb..xCb + cbWidth - 1 and y = yCb..yCb + cbHeight - 1 is set to be equal to INTRA_PLANAR. cbWidth and cbHeight correspondingly denote a width or a height of a coding block. Intermediate variables allowSbtVerH, allowSbtHorH, allowSbtVerQ , allowSbtHorQ correspondingly stand for the conditions of whether a CU could be:

- vertically spilt into 2 TUs (“allowSbtVerH”) ,

- horizontally split into 2 TUs (“allowSbtHorH”),

- vertically spilt into 4 TUs (“allowSbtVerQ”) , or

- horizontally split into 4 TUs (“allowSbtHorQ”). Exemplary GMP partitioning could be performed as disclosed in the following part of the specification: geo_flag[ xO ][ yO ] specifies whether the geometric partitioning inter-picture merge prediction is applied for the current coding unit. The array indices xO, yO specify the location ( xO, yO ) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture. When geo_flag[ xO ][ yO ] is not present, it is inferred to be equal to 0. geo_partition_idx[ xO ][ yO ] specifies the geometric splitting type of the geometric partitioning mode. The array indices xO, yO specify the location ( xO, yO ) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture. When geo_partition_idx[ xO ][ yO ] is not present, it is inferred to be equal to 0. Table 3 shows a lookup-table to derive angleldx and distanceldx parameters from geo_partition_idx.

Table 3. A lookup-table to derive angleldx and distanceldx parameters from geo_partition_idx.

Sample weight derivation process for geometric partitioning merge mode

Inputs to this process are:

- two variables nCbW and nCbH specifying the width and the height of the current coding block,

- two variables angleldx and distanceldx which specify the angle and distance lookup values of the current geometric partitioning mode.

Further, the following arrays have to be allocated in memory:

- a (nCbW)x(nCbH) array sampleWeighti., - a (nCbW/2)x(nCbH/2) array sampleWeightc,

- a (nCbW/4)x(nCbH/4) array motionWeight.

Output of this process are the three arrays sampleWeighti., sampleWeightc and motionWeight of per-sample weight values having a range from 0 ... 8.

1. The luma blending weights stored in sampleWeighti. for the current geometric partitioning mode are derived as follows:

The value of the following variables are set:

- wldx is set to log2(nCbW) - 3,

- hldx is set to log2(nCbH) - 3,

- stepOffset is set to 64,

- the following variables are set according to the comparison of (wldx >= hldx):

whRratio = (wldx >= hldx) ? wldx - hldx : hldx - wldx

wlsLargerH = (wldx >= hldx) ? true : false

scaleStep = (wldx >= hldx) ? (1 « hldx) : (1 « wldx)

- displacement is set to angleldx

- displacementY is set to (displacement + 8)%32

- angleN is set to:

angleN = angleldx if angleldx >= 0 && angleldx <=8,

angleN = 16 - angleldx if angleldx > 8 && angleldx<= 16,

angleN = angleldx - 16 if angleldx > 16 && angleldx <=24,

angleN = 32 - angleldx otherwise,

- further, angleN is set to the following value, depending on wlsLargerH:

angleN = (wlsLargerH) ? 8 - angleN : angleN

stepDis is set according to the values of whRatio and angleN as specified in Table4 and further,

stepSize = stepDis + stepOffset

- rho is set to the following value using the look-up table denoted as Dis, specified in Table4:

rho = distanceldx*stepSize*scaleStep + nCbW*Dis[displacementX] + nCbH*Dis[displacementY] . For each sample position x=0... nCbW - 1 and y=0... nCbH - 1 the value of sampleWeighti _. ! x ][ y ] is derived in the following manner:

- a distance distFromLine is calculated using the look-up table denoted as Dis, specified in Table5 as follows:

distFromLine = ((x«1) + 1)*Dis[displacementX] + ((y«1) + 1))*Dis[displacementY] - rho.

- A scaled distance distScaled is derived as:

distScaled = min((abs(distFroml_ine) + 8) » 4, 14).

The value of sampleWeighti.! x ][ y ] is set according to the filter weight look-up table, denoted as GeoFilter specified in

- Table 6 as:

sampleWeighti_[ x ][ y ] = GeoFilter[distScaled] if distFromLine <= 0 sampleWeighti_[ x ][ y ] = 8 - GeoFilter[distScaled] if distFromLine > 0

2. The chroma weights stored in sampleWeightc for the current geometric partitioning mode are derived as follows:

For each sample position x=0... (nCbW/2) - 1 and y=0... (nCbH/2) - 1 the value of sampleWeightc[ x ][ y ] is derived in the following manner:

sampleWeightc! x ][ y ] = sampleWeighti_[ (x«1) ][ (y«1) ]

3. The motion weights stored in the array motionWeight for the current geometric partitioning mode are derived as follows:

- The following variables are set:

threshScaler = ((log2(nCbW) + log2(nCbH)) » 1)— 1

threshLower = 32 » threshScaler

threshUpper = 32 - threshLower

For each sample position x=0... (nCbW/4) - 1 and y=0... (nCbH/4) - 1 the value of motionWeight[ x ][ y ] is derived in the following manner:

Cnt = sampleWeighti.! (x«2) ][ (y«2) ]

+ sampleWeighti.! ( ^x<< 2) + 3 ][ (y«2) ]

+ sampleWeighti.! ( ^x<< 2) ][ (y«2) + 3 ]

+ sampleWeighti.! ( ^x<< 2) + 3 ][ (y«2) + 3 ]

The value of motionWeight! x ][ y ] is set to: motionWeight[ x ][ y ] = 0 if Cnt <= threshLower

motionWeight[ x ][ y ] = 1 if Cnt >= threshllpper

motionWeight[ x ][ y ] = 2 otherwise Table 4 Specification of the step distance stepDis according to the values of whRatio and angleN.

Table 5 - Look-up table Dis for derivation of geometric partitioning distance.

Table 6 - Filter weight look-up table GeoFilter for derivation of geometric partitioning filter weights.

As indicated above, the process of selecting a near-boundary region is also referred to as Partial Transform (PT). PT process may be applied to blocks predicted using TPM mode, GMP mode. Another mandatory requirement for enabling PT process is that residual coding process is performed for the block. An exemplary signaling of whether PT is performed for the coded block at position (xO, yO) is given in Table 7. In Table 7,“tbWidth” denotes width of the TU (or a PU),“tbHeight” denotes height of the transform block TU (or a PU),“geo_flag” is a syntax element value indicating whether a GMP mode is applied to the PU,“cu_transquant_bypass_flag” is a flag indicating whether a CU is encoded in a lossless mode,“part_trans_flag” is a syntax element value indicating whether a PT is performed for the coded block,“part_trans_idx_present” is a lookup table that provides a boolean value for an index value that may comprise the following elements:

- Log2[tbWidth],

- Log2[tbHeight],

- “MergeTriangleFlag”, or

- “geo_partition_idx”.

The condition“partial_transform_enabled” verifies a set of conditions that should be so be true to determine whether TP could be applied to one or several PUs of a CU. The set of conditions may comprise one or several of the following conditions:

- (tbWidth < sideLenConstr && tbHeight < sideLenConstr), where sideLenConstr is a threshold value for a side length of a PU; an exemplary value of sideLenConstr may comprise be equal to 16,32, 64 or 128;

- tbWidth * tbHeight >= sizeConstr, where sizeConstr is a PU size threshold, an

exemplary values of sizeConstr are 32, 64, 128 or 256;

- TU is a part of luminance component of coded picture

Table 7. PT signaling syntax

Another way to harmonize partial transform with other tools used in codec (for example, with screen-content tools) is to have a high-level flag for enabling or disabling partial transform. As exemplarily shown in Table 8, this high-level flag sps_partial_transform_enabled_flag can be signaled in sequence parameter set (SPS). If its value equals 1 , partial transform is enabled. Otherwise, it is disabled. Besides, if TPM is enabled (i.e. the flag sps_triangle_enabled_flag, an example of a “triangle prediction related flag”, equals 1), the flag sps_partial_transform_enabled_flag (an example of a first partial transform related flag) is used to check whether the flag sps_partial_transform_enabled_for_triangle_flag (an example of a second partial transform related flag) should be present in a bit-stream or not. The flag sps_partial_transform_enabled_for_triangle_flag indicates whether partial transform is enabled for blocks that TPM is applied to. If a value of the flag sps_partial_transform_enabled_for_triangle_flag equals 1 , partial transform is enabled for blocks where TPM is used. Otherwise, it is disabled.

Table 8. PT flag in sequence parameter set RBSP (raw byte sequence payload) syntax

The foregoing table relates to RBSP, which is a syntax structure containing an integer number of bytes that is encapsulated in a NAL (network abstraction layer) unit and is either empty or has the form of a string of data bits containing syntax elements followed by an RBSP stop bit and zero or more subsequent bits equal to 0. A NAL unit is a syntax structure containing an indication of the type of data to follow and bytes containing that data in the form of an RBSP interspersed as necessary with emulation prevention bytes. Definitions and explanations of the syntax elements used in the specific examples of Table 8 and Table 9 below can be inferred from document“Versatile Video Coding (Draft 5)” of Joint Video Experts Team (JVET), Geneva, March 2019, available under http://phenix.it- sudparis.eu/ivet/doc end user/documents/14 Geneva/wq11/JVET-N1001 -v10.zip.

For mixed content where natural video is interleaved with screen content, it can be useful to have a flag (slice_partial_transform_enabled_flag) for enabling or disabling partial transform in a slice or tile header. It allows applying partial transform, for example, to slices (tiles) containing natural video and disabling it, e.g., for slices (tiles) with screen content. As exemplarily shown in Table 9, if a value of the flag sps_partial_transform_enabled_flag (an example of a first partial transform related flag) equals 1 , the flag slice_partial_transform_enabled_flag (another example of a second partial transform related flag) should present in a bit-stream. If its value is “1”, the flag slice_partial_transform_enabled_flag indicates that partial transform is enabled in a given slide (tile). Otherwise, ii is disabled there. Table 9. PT related signaling in general slice header syntax

Fig. 17 illustrates, on a general level, the steps that are performed in the decoding process to conditionally indicate whether residual coding tools are enabled in the presence of a lossless coding mode flag (“isLossless”). The steps are performed for the following set of flags:

- a set Fo, which is a set of flags that are non-conditionally signalled within a bitstream, i.e. these flags are present in a bitstream with any“isLossless” flag value and with any combination of the values of the flags belonging to one or any of the sets;

- a set FRC, which is a set of flags indicating whether residual coding tools are applied and the presence of these flags in bitstream is determined by“isLossless” flag value; - a set Fi, FI ^ FRC, which is a set of flags that are conditionally signalled in a bitstream, so that their presence is determined by“isLossless” flag value and a combination of other residual coding tools flags. In an exemplary embodiment, the set FRC may comprise the following flags:

- part_trans_flag;

- part_trans_idx;

- tu_mts_idx, i.e. a flag indicating a transform type used for the residual signal;

- transform_skip_flag, i.e. a flag indicating that transform is not performed on the

residual signal;

- Ifnst_flag, i.e. a flag indicating that a part of transformed residual are further

transformed to obtain a secondary transformed residual;

- cu_sbt_flag

In particular, “isLossless” flag value may be set equal to“cu_transquant_bypass_flag”. In another embodiment, “isLossless” flag value may be set equal to 1 when quantization parameter (QP) for a CU is set equal to 0.

The processing of Fig. 17 starts with step 1701 , in which the non-conditionally signalled flags fo _,i out of set Fo are parsed from a received bitstream. Subsequently, in step 1702, it is checked whether lossless video coding mode is applied, for example by checking the“isLossless” flag.

The step 1703“Fi =0” which is performed when“isLossless” flag value is set toone (1702: yes), determines that all the flags of FRC should be inferred to 0 and are not signalled in a bitstream.

On the other hand, in case the“isLossless” flag is set to zero (1702: no), the step 1704“Derive dependent set of flags” determines, what residual coding tools flags should be signalled based on the values of the non-conditionally signalled flags (those belonging to the set Fo). Particular embodiments may define the following set of mapping operations“M()” to define the set Fi.

- when cu_sbt_flag is 1 , part_trans_flag is not included into Fi\

- when MergeTriangleFlag is 1 or geo_flag is 1 , lfnst_flag is not included into Fi\

More generally, the above mapping operations are an example of more general principles for defining the set Fi, including but not being limited to mapping operations or functions, such as tables (look-up tables).

In case set Fi is not empty, i.e. there are flags in the set, for each flag fi out of set FRC (1705) it is checked in step 1706, whether the flag belongs to set Fi If not, it is inferred that the flag is zero (step 1707). On the other hand, if yes, it is inferred that the flag is signaled in the bitstream and it is obtained from parsing the bitstream in step 1708. Thus, presence of residual coding tools flags (those belonging to a set Fi) may additionally depend on the values of the Fi flags that were signalled in the bitstream. This dependency is shown in the“redefine Fi” step 1709, wherein some of the elements are removed from the set Fi based on the value fi that was signalled and parsed in the previous step 1708“parse fi’.

An exemplary embodiment may comprise any combination of the following dependencies:

- when cu_sbt_flag is 1 , part_trans_flag is removed from Fi\

- when part_trans_flag is 1 , lfnst_flag is removed from Fi

- when part_trans_flag is 1 , tu_mts_idx is removed from Fi.

In Fig.18 a general level flowchart for conditional indication of used residual coding tools on the encoding side is shown. In this figure, a set Fo is a set of flags that are non-conditionally signalled in step 1801 within a bitstream for a CU or a PU. The set Fo may comprise the following syntax elements: MergeTriangleFlag, geo_flag, cbf, transform_skip_flag.

Depending on the values of the flags signalled in step 1801 , the set off the dependent residual coding flags is obtained in step 1802. A set Fi F _RC is a set of flags that are conditionally signalled in a bitstream so that the presence of their indication in the bitstream depends on the values of syntax elements {fo} signalled in step 1801.

In an exemplary embodiment, the set F _RC may comprise the following flags:

- part_trans_flag;

- part_trans_idx;

- tu_mts_idx;

- transform_skip_flag, i.e. a flag indicating that transform is not performed on the

residual signal;

lfnst_flag, i.e. a flag indicating that a part of transformed residual are further transformed to obtain secondary transformed residual;

- cu_sbt_flag wherein cu_sbt_flag is a syntax element indicating the usage of subblock transform (SBT) for the current coding unit; part_trans_flag is a syntax element value indicating whether a partial transform (PT) is performed for the coded block; lfnst_flag is a flag indicating that a part of transformed residual signal is further transformed to obtain secondary transformed residual; tu_mts_idx is a syntax element indicating a type of the transform applied to the residual signal to obtain transformed residual; i.e. integer sine transform, integer cosine transform, etc.

Step 1802 uses a mapping function M() to define a subset Fi out of the set F _RC . Mapping function M() could be defined as follows: C F _I ,F _O ) ) ® fiSFi. Here check function C(fi,Fo) verifies any combination of the following exceptions for a residual coding tool flag†i and a set of signalled non-conditional elements Fo.

- when cu_sbt_flag is 1 , part_trans_flag is not included into Fi\

when MergeTriangleFlag is 1 , lfnst_flag is not included into Fi

when geo_flag is 1 , lfnst_flag is not included into Fi,

when cbf is 0, part_trans_flag is not included into Fi,

- when skip_flag is 1 , part_trans_flag is not included into Fi.

Step 1803 iterates over the set of flags belonging to the set FRC defined in step 1802, so that steps 1804 .. 1807 are performed for a flag that is currently selected for iteration at step 1803.

Step 1804 infers the currently iterated flag fi to be equal to 0 when the check 1805 verifies whether the flag does not belong to the set Fi. If step 1805 verifies the currently iterated flag fi does belong to Ft its value is signaled in a bitstream.

In step 1807, flag fi is used to refine the set Fi so that some of the flags further iterated in step 1803 could be skipped by step 1805 depending in the value that is signaled in step 1806. An exemplary embodiment of step 1807 may comprise any combination of the following dependencies:

- when cu_sbt_flag is 1 , part_trans_flag is removed from Fi

- when part_trans_flag is 1 , lfnst_flag is removed from Fi

- when part_trans_flag is 1 , tu_mts_idx is removed from F*.

Mathematical Operators

The mathematical operators used in this application are similar to those used in the C

programming language. However, the results of integer division and arithmetic shift

operations are defined more precisely, and additional operations are defined, such as exponentiation and real-valued division. Numbering and counting conventions generally begin from 0, e.g., "the first" is equivalent to the 0-th, "the second" is equivalent to the 1 -th, etc.

Arithmetic operators

The following arithmetic operators are defined as follows:

+ Addition

Subtraction (as a two-argument operator) or negation (as a unary prefix operator) * Multiplication, including matrix multiplication Exponentiation. Specifies x to the power of y. In other contexts, such notation is used for superscripting not intended for interpretation as exponentiation.

Integer division with truncation of the result toward zero. For example, 7 / 4 and -7 / -4 are truncated to 1 and -7 / 4 and 7 / -4 are truncated to -1.

Used to denote division in mathematical equations where no truncation or rounding is intended.

x Used to denote division in mathematical equations where no truncation or rounding y is intended.

y

f( i ) The summation of f ( i ) with i taking all integer values from x up to and including y. i = x

Modulus. Remainder of x divided by y, defined only for integers x and y with x >= 0 x % y

and y > 0.

Logical operators

The following logical operators are defined as follows:

x && y Boolean logical "and" of x and y

x 1 1 y Boolean logical "or" of x and y

! Boolean logical "not"

x ? y : z If x is TRUE or not equal to 0, evaluates to the value of y; otherwise, evaluates

to the value of z.

Relational operators

The following relational operators are defined as follows:

> Greater than

>: Greater than or equal to

Less than

C Less than or equal to

Equal to

Not equal to

When a relational operator is applied to a syntax element or variable that has been assigned the value "na" (not applicable), the value "na" is treated as a distinct value for the syntax element or variable. The value "na" is considered not to be equal to any other value. Bit-wise operators

The following bit-wise operators are defined as follows:

& Bit-wise "and". When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.

I Bit-wise "or". When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.

^L Bit-wise "exclusive or". When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0. x » y Arithmetic right shift of a two's complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted into the most significant bits (MSBs) as a result of the right shift have a value equal to the MSB of x prior to the shift operation. x « y Arithmetic left shift of a two's complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted into the least significant bits (LSBs) as a result of the left shift have a value equal to 0.

Assignment operators

The following arithmetic operators are defined as follows:

= Assignment operator

+ + Increment, i.e., x+ + is equivalent to x = x + 1 ; when used in an array index, evaluates to the value of the variable prior to the increment operation.

Decrement, i.e., x- - is equivalent to x = x - 1 ; when used in an array index, evaluates to the value of the variable prior to the decrement operation.

+= Increment by amount specified, i.e., x += 3 is equivalent to x = x + 3, and

x += (-3) is equivalent to x = x + (-3).

-= Decrement by amount specified, i.e., x -= 3 is equivalent to x = x - 3, and x -= (-3) is equivalent to x = x - (-3). Range notation

The following notation is used to specify a range of values: x = y..z x takes on integer values starting from y to z, inclusive, with x, y, and z being integer numbers and z being greater than y. Mathematical functions

The following mathematical functions are defined: x >= 0

x < 0

Asin( x ) the trigonometric inverse sine function, operating on an argument x that is in the range of -1.0 to 1 .0, inclusive, with an output value in the range of

-TT÷2 to TT÷2, inclusive, in units of

radians

Atan( x )the trigonometric inverse tangent function, operating on an argument x, with an output value in the range of -TT÷2 to TT÷2, inclusive, in units of radians

Ceil( x ) the smallest integer greater than or equal to x.

Clipl _Y ( X ) = Clip3( 0, ( 1 « BitDepthy ) - 1 , x

Clipl c( x ) = Clip3( 0, ( 1 « BitDepthc ) - 1 , x

( x ; z < x

Clip3( x, y, z ) = y ; z > y

_< z otherwise

Cos( x ) the trigonometric cosine function operating on an argument x in units of radians. Floor( x ) the largest integer less than or equal to

x.

GetCurrMsb(

Ln( x ) the natural logarithm of x (the base-e logarithm, where e is the natural

logarithm base constant

2.718 281 828...).

Log2( x ) the base-2 logarithm of

x.

Log10( x ) the base-10 logarithm of x.

Min( x, y ) = { y :

Max( x, y ) = { y :

Round( x ) = Sign( x ) * Floor( Abs( x ) + 0.5

)

Sign(

Sin( x ) the trigonometric sine function operating on an argument x in units of radians Sqrt( x ) = Vx Swap( x, y ) = ( y, x )

Tan( x ) the trigonometric tangent function operating on an argument x in units of

radians Order of operation precedence

When an order of precedence in an expression is not indicated explicitly by use of parentheses, the following rules apply:

- Operations of a higher precedence are evaluated before any operation of a lower precedence. - Operations of the same precedence are evaluated sequentially from left to right.

The table below specifies the precedence of operations from highest to lowest; a higher position in the table indicates a higher precedence.

For those operators that are also used in the C programming language, the order of precedence used in this Specification is the same as used in the C programming language. Table: Operation precedence from highest (at top of table) to lowest (at bottom of table)

Text description of logical operations

In the text, a statement of logical operations as would be described mathematically in the following form: if( condition 0 )

statement 0 else if( condition 1 )

statement 1 else /* informative remark on remaining condition */

statement n may be described in the following manner:

... as follows / ... the following applies:

- If condition 0, statement 0

- Otherwise, if condition 1 , statement 1

- Otherwise (informative remark on remaining condition), statement n.

Each "If ... Otherwise, if ... Otherwise, ..." statement in the text is introduced with "... as follows" or "... the following applies" immediately followed by "If ... ". The last condition of the "If ... Otherwise, if ... Otherwise, ..." is always an "Otherwise, Interleaved "If ... Otherwise, if ... Otherwise, ..." statements can be identified by matching "... as follows" or "... the following applies" with the ending "Otherwise,

In the text, a statement of logical operations as would be described mathematically in the following form: if( condition 0a && condition Ob )

statement 0

else if( condition 1 a 1 1 condition 1 b )

statement 1 else

statement n may be described in the following manner:

... as follows / ... the following applies:

- If all of the following conditions are true, statement 0:

- condition 0a

- condition Ob

- Otherwise, if one or more of the following conditions are true, statement 1 :

- condition 1 a condition 1 b

- Otherwise, statement n

In the text, a statement of logical operations as would be described mathematically in the following form: if( condition 0 )

statement 0

if( condition 1 )

statement 1 may be described in the following manner:

When condition 0, statement 0

When condition 1 , statement 1.

According to a further particular aspect of the present invention, a method for still picture and/or video coding is provided. The method comprises the steps of

determining if a syntax element belongs to an initial syntax element group Fi which belongs to a dependent syntax element group F _RC and is derived by using a predefined mapping table/principle/function/operation predefined and referring a confirmative value of a correlative syntax element Fo which is unconditionally presented in a bit stream,

inferring the syntax element to be zero if the syntax element belongs to the initial syntax element group Fi, and or

encoding into/parsing from the bit stream, the syntax element for coding a current block if the syntax element does not belong to the initial syntax element group Fi.

According to still a further particular aspect of the present invention, a method for still picture and/or video coding is provided. The method comprises the steps of

determining if a syntax element belongs to an initial syntax element group Fi which belongs to a dependent syntax element group FRC and is derived by using a predefined mapping table/principle/function/operation predefined and referring a confirmative value of a correlative syntax element Fo which is unconditionally presented in a bit stream,

inferring the syntax element to be zero if the syntax element does not belong to the initial syntax element group Fi, and or

encoding into/parsing from the bit stream, the syntax element for coding a current block if the syntax element belongs to the initial syntax element group Fi. According to one or more embodiments of the above further or still further particular aspects, the method further comprises the step of refining the initial syntax element group Fi based on a predefined dependency rule.

According to one or more embodiments, the dependency rule comprises at least one of the following:

- when cu_sbt_flag is 1 , part_trans_flag is removed from Fi,

- when part_trans_flag is 1 , lfnst_flag is removed from F

- when part_trans_flag is 1 , tu_mts_idx is removed from Fi.

According to one or more embodiments of the above further or still further particular aspect, the predefined mapping table/principle/function/operation predefined comprises at least one of the following:

when cu_sbt_flag is 1 , part_trans_flag is not included into Fi,

when MergeTriangleFlag is 1 , lfnst_flag is not included into F ,

when geo_flag is 1 , lfnst_flag is not included into Fi,

when cbf is 0, part_trans_flag is not included into Fi,

when skip_flag is 1 , part_trans_flag is not included into Fi.

According to one or more embodiments of the above further or still further particular aspect, wherein the dependent syntax element group F _RC comprises the following flags:

part_trans_flag;

part_trans_idx;

tu_mts_idx;

transform_skip_flag, i.e. a flag indicating that transform is not performed on the residual signal;

lfnst_flag, i.e. a flag indicating that a part of transformed residual are further transformed to obtain secondary transformed residual;

cu_sbt_flag.

According to yet a further particular aspect of the present invention, a method for still picture and/or video coding is provided. The method comprises the steps of

signaling, in a bit stream, in SPS/PPS level a triangle prediction related flag which indicates if a triangle prediction is allowed for a video sequence or a picture of the video or not,

signaling, in the bit stream, in the SPS/PPS level a first partial transform related flag which indicates if a partial transform is allowed for a video sequence or a picture of the video or not, and in response to a confirmative value (e.g. 1 ) of triangle prediction related flag and a confirmative value (e.g.1 ) of the first partial transform related flag, signaling, in the bit stream, in the SPS/PPS level a second partial transform related flag which indicates if a partial transform is allowed for coding blocks that the triangle prediction is applied.

According to another particular aspect of the present invention, a method for still picture and/or video decoding is provided. The method comprises the steps of

parsing, from a bit stream, in SPS/PPS level a triangle prediction related flag which indicates if a triangle prediction is allowed for a video sequence or a picture of the video or not,

parsing, from a bit stream, in the SPS/PPS level a first partial transform related flag which indicates if a partial transform is allowed for a video sequence or a picture of the video or not, and

in response to a confirmative value (e.g. 1 ) of triangle prediction related flag and a confirmative value (e.g.1 ) of the first partial transform related flag, parsing, from a bit stream, in the SPS/PPS level a second partial transform related flag which indicates if a partial transform is allowed for coding blocks that the triangle prediction is applied.

According to still another particular aspect of the present invention, a method for still picture and/or video coding is provided. The method comprises the steps of

signaling, in a bit stream, in a SPS/PPS level a first partial transform related flag which indicates if a partial transform is allowed for a video sequence or a picture of the video or not and

in response to a confirmative value (e.g. 1 ) of triangle prediction related flag, signaling, in the bit stream, in a slice level (slice header) a second partial transform related flag which indicates if a partial transform is allowed for coding blocks that the triangle prediction is applied.

According to a still different particular aspect of the present invention, a method for still picture and/or video coding is provided. The method comprises the steps of

signaling, in a bit stream, in a SPS/PPS level a triangle prediction related flag which indicates if a partial transform is allowed for a video sequence or a picture of the video or not and

in response to a confirmative value (e.g. 1 ) of triangle prediction related flag, signaling, in the bit stream, in a slice level (slice header) a second partial transform related flag which indicates if a partial transform is allowed for coding blocks that the triangle prediction is applied. According to yet another particular aspect of the present invention, a method for still picture and/or video decoding is provided. The method comprises

parsing, from a bit stream, in SPS/PPS level a triangle prediction related flag which indicates if a triangle prediction is allowed for a video sequence or a picture of the video or not and

in response to a confirmative value (e.g. 1 ) of triangle prediction related flag, parsing, from a bit stream, in a slice level (slice header) a second partial transform related flag which indicates if a partial transform is allowed for coding blocks that the triangle prediction is applied.

According to a further aspect, a method according to any of the above particular aspects or its embodiments is implemented by an encoding device.

According to still a further aspect, a method according to any of the above particular aspects or its embodiments is implemented by a decoding device.

According to yet a further aspect, an encoder is provided comprising processing circuitry for carrying out the method according to any one of the above particular aspects or its embodiments.

According to still another aspect, a decoder is provided comprising processing circuitry for carrying out the method according to any one of the above particular aspects or its embodiments.

According to yet another aspect, a computer program product comprising a program code for performing the method according to any one of the above particular aspects or its embodiments is provided.

Also, according to an aspect, a decoder is provided. The decoder comprises one or more processors and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the decoder to carry out the method according to any one of the above particular aspects or its embodiments.

Further, according to an aspect, an encoder is provided. The decoder comprises one or more processors and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the encoder to carry out the method according to any one of the above particular aspects or its embodiments.

Still further, according to an aspect, a non-transitory computer-readable medium is provided, carrying a program code which, when executed by a computer device, causes the computer device to perform the method of any one of the above particular aspects or its embodiments.

Embodiments, e.g. of the encoder 20 and the decoder 30, and functions described herein, e.g. with reference to the encoder 20 and the decoder 30, may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on a computer-readable medium or transmitted over communication media as one or more instructions or code and executed by a hardware-based processing unit.

Computer-readable media may include computer-readable storage media, which

corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limiting, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers.

Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term“processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (1C) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

In summary, the present invention relates to a method and apparatus for still picture or video residual coding, wherein certain syntax elements for residual coding tools are conditionally signaled upon conditions depending on values of one or more other syntax elements that are unconditionally signaled. Syntax elements that are decided not to be signaled in you of the conditions may be inferred to zero. This may enhance coding efficiency by reducing signaling overhead.