BR122023025774A2 - CROSS-COMPONENT ADAPTIVE LOOP FILTERING FOR VIDEO CODING - Google Patents

Abstract

A method in an image encoding and/or an image decoding is provided, in which image header entries for CCALF are introduced which define the common CCALF data and all slices can then inherit this common information. The signaling overhead, in particular the slice header overhead (in terms of number of bits) is reduced.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application (disclosure) generally relate to the field of image processing and, more particularly, to a cross-component adaptive loop filter (CC-ALF) as an in-loop filter or as a post-loop filter and high-level syntax for Cross-Component ALF (CCALF).

FUNDAMENTALS

[0002] Image coding (encoding and decoding) is used in a wide range of digital imaging applications, e.g., digital TV broadcasting, video transmission over the Internet and mobile networks, real-time conversational applications such as video chat video, video conferencing, DVD and Blu-ray discs, video content acquisition and editing systems, and security applications camcorders.

[0003] Since the development of the block-based hybrid video coding approach in the H.261 standard in 1990, new video coding techniques and tools have been developed and have formed the basis for new video coding standards. One of the goals of most video coding standards was to achieve a reduction in bitrate compared to its predecessor without sacrificing image quality. Other video coding standards include MPEG-1 video, MPEG-2 video, ITU-T H.262/MPEG-2, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Coding Advanced Video Coding (AVC), ITU-T H.265, High Efficiency Video Coding (HEVC), ITU-T H.266/Versatile Video Coding (VVC) and extensions, e.g. scalability and/or three-dimensional extensions (3D), of these patterns.

[0004] Block-based image coding schemes have in common that along block edges, edge artifacts may appear. These artifacts are due to the independent coding of the coding blocks. These edge artifacts are often easily visible to a user. One goal in block-based image coding is to reduce edge artifacts below a visibility threshold. This is done by performing loop filtering such as deblocking filter, SAO, and adaptive loop filter (ALF). The order of the filtering process is unblocking filter, then SAO, then ALF. Furthermore, the cross-component adaptive loop filter (CC-ALF) is additionally used.

[0005] Especially for cross-component adaptive loop filter (CC-ALF), luma sample values are used to refine each chroma component. The process needs to be done on both Cb and Cr components, cross-component adaptive loop filtering can be computationally complex and therefore can add additional pipeline latency, especially for hardware implementations.

SUMMARY

[0006] In view of the challenges mentioned above, the present disclosure aims to improve cross-component adaptive loop filtering and syntax elements for CCALF. The present disclosure may, among others, pertain to the object of providing an apparatus, an encoder, a decoder and corresponding methods that can perform cross-component adaptive loop filtering with reduced signaling overhead, particularly, the slice header overhead (in terms number of bits) can be reduced, so filtering can be more efficient.

[0007] Examples of the present disclosure provide apparatus and methods for encoding and decoding an image that can improve coding performance, thereby improving the coding efficiency of a video signal. The revelation is elaborated on the examples and claims contained in this file.

[0008] Embodiments of the present application provide apparatus and methods for encoding and decoding according to the independent claims, thus the complexity of the Cross-Component ALF can be reduced and the performance of the Cross-Component Adaptive Loop Filter (CC-ALF) as a in-loop filter or as post-loop filter, respectively, can be improved.

[0009] The above and other objectives can be achieved by the subject matter of independent claims. Additional forms of implementation are evident in the dependent claims, the description and the figures.

[0010] Particular embodiments are described in the attached independent claims, with other embodiments in the dependent claims.

[0011] According to a first aspect, the disclosure relates to a coding method implemented by a coding device, comprising: performing a filtering process (such as a cross-component filtering process) by applying a component adaptive loop filter crossed (CC-ALF); generate a bitstream including a plurality of CC-ALF-related syntax elements (such as M CC-ALF-related syntax elements and M>=1 and M is an integer), wherein the plurality of related syntax elements CC-ALF indicates CC-ALF related information, wherein the plurality of CC-ALF related syntax elements is signaled at any one or more of a Video Parameter Set (VPS) level, a Video Parameter Set (VPS) level a sequence parameter set (SPS), an image parameter set (PPS) level, an image header, a slice header, or a tile header; or wherein the plurality of syntax elements related to CC-ALF are signaled at a sequence parameter set (SPS) level and/or an image header.

[0012] This bitstream can be reduced in size while providing relevant information on the structure of the bitstream for the levels at which this request is actually applied or belongs, and allows performing cross-component adaptive loop filtering with signaling overhead reduced, thus filtering can be more efficient, and coding efficiency improvement is achieved.

[0013] According to a second aspect, the disclosure relates to a decoding method implemented by a decoding device, comprising: analyzing one or more syntax elements from a bit stream of a video signal, wherein syntax elements indicate information related to the Cross-Component Adaptive Loop Filter (CC-ALF), where the syntax elements are obtained from any one or more of a video parameter set (VPS) level, a level sequence parameter set (SPS), a picture parameter set (PPS) level, an image header, a slice header, or a bitstream tile header; or wherein the syntax elements are obtained from a string parameter set (SPS) level and/or an image header; and performing a filtering process (such as a cross-component filtering process) by applying a CC-ALF based on the syntax elements or based on the value of the syntax elements.

[0014] This method can allow obtaining relevant information from the bitstream during decoding, in which the bitstream is reduced in size, allowing for better data compression, and allows cross-component adaptive loop filtering to be performed with overhead of reduced signaling, therefore filtering can be more efficient, and improved coding efficiency is achieved.

[0015] According to a third aspect, the invention relates to an apparatus for decoding video data. The apparatus comprises: processing circuitry for carrying out the method in accordance with the first aspect of the disclosure.

[0016] According to a fourth aspect, the invention relates to an apparatus for encoding video data. The apparatus comprises: processing circuitry for carrying out the method according to the second aspect of the disclosure.

[0017] The method according to the first aspect of the present disclosure can be carried out by the apparatus according to the third aspect of the disclosure. Additional features and ways of implementing the method according to the third aspect of the disclosure correspond to the features and ways of implementing the apparatus according to the first aspect of the disclosure.

[0018] The method according to the second aspect of the disclosure can be carried out by the apparatus according to the fourth aspect of the invention. Additional features and ways of implementing the method according to the fourth aspect of the disclosure correspond to the features and ways of implementing the apparatus according to the second aspect of the disclosure.

[0019] According to a fifth aspect, the disclosure relates to an apparatus for decoding a video stream that includes a processor and a memory. The memory is storing instructions that make the processor perform the method according to the first aspect.

[0020] According to a sixth aspect, the disclosure relates to an apparatus for encoding a video stream that includes a processor and a memory. The memory is storing instructions that make the processor perform the method according to the second aspect.

[0021] According to a seventh aspect, a computer-readable storage medium is proposed having instructions stored thereon that, when executed, cause one or more processors to be configured to encode video data. The instructions cause one or more processors to perform a method in accordance with the first or second aspect or any possible embodiment of the first or second aspect.

[0022] According to an eighth aspect, the disclosure relates to a computer program comprising program code for carrying out the method according to the first or second aspect or any possible embodiment of the first or second aspect when executed on a computer.

[0023] The present disclosure provides a coding method implemented by a coding device, the method comprising: applying a cross-component adaptive loop filter, CC-ALF to refine a chroma component; generate a bit stream including a plurality of ALF-related syntax elements (CC-ALF-related syntax elements, used below), wherein the plurality of CC-ALF-related syntax elements indicates ALF-related information (related information the CC-ALF, used below); wherein the plurality of syntax elements related to CC-ALF are signaled at any one or more of a sequence parameter set (SPS) level, an image header, or a slice header; wherein the plurality of syntax elements related to CC-ALF comprise a first syntax element that indicates whether or not an adaptive loop filter (ALF) comprising the cross-component adaptive loop filter is enabled or not at a sequence level, and the first element syntax element is signaled at the SPS level, and a second syntax element that indicates whether the cross-component adaptive loop filter is enabled or not at a sequence level, and the second syntax element is signaled at the SPS level.

[0024] Although it is generally specified here that a first and a second syntax element are signaled at the SPS level, this does not mean that the signaling of at least the second syntax element is unconditional. Instead, this embodiment also encompasses embodiments in which the second syntax element is signaled, for example, based on a value of the first syntax element and/or depending on a value of another syntax element as will be further described below.

[0025] The first syntax element may be called sps_alf_enabled_flag below, while the second syntax element may be called sps_ccalf_enabled_flag. This is, however, just a nomenclature used here. The invention is not limited to a specific name of the first or second syntax element or any other syntax element referred to herein.

[0026] It can be understood that CC-ALF is a special type of ALF, CC-ALF may depend on whether ALF is enabled or not, therefore the first syntax element, that is, sps_alf_enabled_flag is also related to CC-ALF, and, therefore, syntax elements related to CC-ALF can be used below. Similarly, the information indicated by the first syntax element i.e. sps_alf_enabled_flag is also related to CC-ALF, so information related to CC-ALF can be used below.

[0027] Information that can be used, for example, for all images in a sequence can thus be efficiently signaled at the SPS level, reducing the size of the bit stream, reducing the amount of redundant information, and allows to perform cross-component adaptive loop filtering with reduced signaling overhead, thus filtering can be more efficient and improved coding efficiency is achieved.

[0028] In one embodiment, the plurality of syntax elements related to CC-ALF comprise a third syntax element when the second syntax element indicates that CC-ALF is enabled, wherein the third syntax element is signaled in the header of image and the third syntax element indicates whether CC-ALF is enabled for a current image comprising a plurality of slices.

[0029] This third syntax element can also be referred to as pic_ccalf_enabled_flag. With this embodiment, relevant CC-ALF information relative to a complete image can be signaled while keeping the bitstream size small. In an example, Slice 1.. Slice N share the same CCALF information, so common information can be inherited directly from the image header instead of each slice header transmitting it redundantly.

[0030] In a further embodiment, the plurality of syntax elements related to CC-ALF comprise a fourth syntax element when the second syntax element indicates that CC-ALF is enabled, wherein the fourth syntax element is signaled in the header and the fourth syntax element indicates whether CC-ALF for a Cb color component is enabled for a current image of a video sequence associated with the bitstream.

[0031] The fourth syntax element can, for example, be indicated with pic_cross_component_alf_cb_enabled_flag. However, this is not mandatory. The fourth syntax element can efficiently signal CC-ALF for a Cb color component, keeping the amount of redundant information, for example in a slice header, small.

[0032] It may further be provided that if the fourth syntax element has a value of 1, this indicates that CC-ALF for the Cb color component is enabled for the current image and/or if the fourth syntax element has a value of 0, it indicates that CC-ALF for the Cb color component is disabled for the current image.

[0033] In one embodiment, the plurality of syntax elements related to CC-ALF comprises a fifth syntax element when the fourth syntax element indicates that CC-ALF for the Cb color component is enabled for the current image, wherein the fifth syntax element is flagged in the image header, and the fifth syntax element indicates a set of parameters that the Cb color component of all slices in the current image refers to. This syntax element can be indicated with pic_cross_component_alf_cb_aps_id. This, however, is just a nomenclature and is not construed to limit the present disclosure. This embodiment can allow sets of signaling parameters that are provided for all slices of an image already at an image level, thus reducing the amount of redundant information.

[0034] It may further be provided that the plurality of syntax elements associated with CC-ALF comprise a seventh syntax element when the second syntax element indicates that CC-ALF is enabled, wherein the seventh syntax element is signaled in the header image and the seventh syntax element specifies whether CC-ALF for a Cr color component is enabled for a current image of a video sequence associated with the bitstream. This syntax element may, for example, be indicated with pic_cross_component_alf_cr_enabled_flag without limiting the present disclosure. With this syntax element, the enabling of CC-ALF for Cr color components can be signaled reliably.

[0035] It may further be provided that if the seventh syntax element has a value of 1, this indicates that CC-ALF for the Cr color component is enabled for the current image and/or if the seventh syntax element has a value of 0, it indicates that CC-ALF for the Cr color component is disabled for the current image.

[0036] In one embodiment, the plurality of syntax elements associated with CC-ALF comprises an eighth syntax element when the seventh syntax element indicates that CC-ALF for the Cr color component is enabled for the current image, wherein the eighth syntax element is signaled in the image header and the eighth syntax element indicates a set of parameters that is associated with the Cr color component of all slices in the current image. The eighth syntax element can be denoted with pic_cross_component_alf_cr_aps_id, although this is just an example. This syntax element can provide information about relevant parameters to use during filtering.

[0037] It may further be provided that the fourth syntax element, the fifth syntax element, the sixth syntax element, the seventh syntax element, the eighth syntax element and the ninth syntax element are signaled when the third syntax element syntax indicate that CC-ALF is enabled for the current image of a video sequence associated with the bitstream. If CC-ALF is disabled, these elements can be set to a default value and still signaled in the bitstream. Alternatively, if CC-ALF is disabled, these syntax elements may not be flagged in the bitstream, thereby reducing its size because unused information is deleted from the bitstream.

[0038] In another embodiment, the plurality of syntax elements related to CC-ALF comprises a tenth syntax element when the second syntax element indicates that CC-ALF is enabled, wherein the tenth syntax element is signaled in a slice header and the tenth syntax element indicates whether CCALF for a Cb color component is enabled for a current slice of a current image of a video sequence associated with the bitstream. This syntax element may, without intending to limit the present disclosure, be referred to as slice_cross_component_alf_cb_enabled_flag. Thus, efficient signaling can be provided whether CC-ALF should be enabled for Cb color components.

[0039] It may further be provided that if the tenth syntax element has a value of 1, this indicates that CCALF for the Cb color component is enabled for the current slice and/or the tenth syntax element has a value of 0, this indicates that CCALF for the Cb color component is disabled for the current slice.

[0040] In a further embodiment, the plurality of syntax elements related to CC-ALF comprises an eleventh syntax element when the tenth syntax element indicates that CC-ALF for the Cb color component is enabled for the current slice, wherein the tenth syntax element is flagged in a slice header and the tenth syntax element specifies a set of parameters to which the Cb color component of the current slice refers. This syntax element may be indicated with pic_cross_component_alf_cb_aps_id, although this is not intended to limit the present disclosure.

[0041] In a further embodiment, the plurality of syntax elements related to CC-ALF comprises a twelfth syntax element when the second syntax element indicates that CC-ALF is enabled, wherein the twelfth syntax element is signaled in a slice header and the twelfth syntax element indicates whether CCALF for a Cr color component is enabled for a current slice of a current image of a video sequence associated with the bitstream. The twelfth syntax element can, for example, be indicated with slice_cross_component_alf_cr_enabled_flag.

[0042] In a further embodiment, it is provided that if the twelfth syntax element has a value of 1, this indicates that CCALF for the Cr color component is enabled for the current slice and/or if the twelfth syntax element syntax has a value of 0, this indicates that CCALF for the Cr color component is disabled for the current slice.

[0043] It may also be provided that the plurality of syntax elements related to CC-ALF comprise a thirteenth syntax element when the twelfth syntax element indicates that CC-ALF for the Cr color component is enabled for the current slice , where the thirteenth syntax element is flagged in a slice header and the thirteenth syntax element specifies a set of parameters to which the Cr color component of the current slice refers. The thirteenth syntax element can, for example, be indicated with slice_cross_component_alf_cr_aps_id. This can efficiently provide information about the parameter to be used for filtering associated with the Cr color component.

[0044] It may be provided that the second syntax element is signaled if the first syntax element has a first value, or the second syntax element is conditionally signaled at least based on a value of the first syntax element. If ALF is not enabled (which is signaled by the first syntax element), CC-ALF will also not be enabled. By not providing the second syntax element in this case, the size of the bitstream can be further reduced.

[0045] In one embodiment, the plurality of syntax elements related to CC-ALF comprise a fourteenth syntax element that is signaled at the SPS level, wherein the fourteenth syntax element indicates the type of input to the CC-ALF. ALF. The fourteenth syntax element may be indicated with ChromaArrayType, although this does not limit the present disclosure.

[0046] More specifically, the second syntax element is signaled when the first syntax element has a first value and the fourteenth syntax element has a second value. The second value can be any value other than a specific value that would indicate that CC-ALF should not be enabled.

[0047] In another specific embodiment, the second syntax element is signaled when the first syntax element has a value that is equal to 1 and the fourteenth syntax element has a value that is not equal to 0.

[0048] For any of the above embodiments, it may be provided that the CC-ALF operates as part of the adaptive loop filter process and makes use of luma sample values to refine at least one chroma component.

[0049] The present disclosure further provides a decoding method implemented by a decoding device, the method comprising: analyzing a plurality of syntax elements related to cross-component adaptive loop filters, CC-ALF, from a stream of bits, wherein the plurality of syntax elements, wherein the plurality of syntax elements related to CC-ALF is obtained from any one or more of a sequence parameter set (SPS) level, an image header or a slice header; wherein the plurality of syntax elements related to CC-ALF comprise a first syntax element that indicates whether or not an adaptive loop filter (ALF) comprising the cross-component adaptive loop filter is enabled or not at a sequence level, and the first element syntax element is signaled at the SPS level, and a second syntax element that indicates whether the cross-component adaptive loop filter is enabled or not at a sequence level, and the second syntax element is signaled at the SPS level; perform a CC-ALF process using at least one of the plurality of syntax elements related to CC-ALF.

[0050] Although it is generally specified here that a first and a second syntax element are provided at the SPS level, this does not mean that at least the second syntax element is provided in the bitstream unconditionally. Instead, this embodiment also encompasses embodiments in which the second syntax element is part of the bit stream, for example, based on a value of the first syntax element and/or depending on a value of another syntax element as will be additionally described below.

[0051] The first syntax element may be called sps_alf_enabled_flag below, while the second syntax element may be called sps_ccalf_enabled_flag. This is, however, just a nomenclature used here. The invention is not limited to a specific name of the first or second syntax element or any other syntax element referred to herein.

[0052] Information that can be used, for example, for all images in a sequence can thus be provided to the decoder efficiently at the SPS level, reducing the size of the bit stream, reducing the amount of redundant information , and allows performing cross-component adaptive loop filtering with reduced signaling overhead, thus filtering can be more efficient and improved coding efficiency is achieved.

[0053] It may be provided that the plurality of syntax elements related to CC-ALF comprise a third syntax element when the second syntax element is obtained as indicating that CC-ALF is enabled, wherein the third syntax element is obtained from the image header and the third syntax element indicates whether CC-ALF is enabled for a current image comprising a plurality of slices. This third syntax element can also be referred to as pic_ccalf_enabled_flag. With this embodiment, relevant CC-ALF information relative to a complete image can be provided while keeping the bitstream size small.

[0054] In a further embodiment, the plurality of syntax elements related to CC-ALF comprise a fourth syntax element when the second syntax element is obtained as indicating that CC-ALF is enabled, wherein the fourth syntax element is obtained from the image header and the fourth syntax element indicates whether CC-ALF is enabled for a Cb color component for a current image of a video sequence. The fourth syntax element can, for example, be indicated with pic_cross_component_alf_cb_enabled_flag. However, this is not mandatory. The fourth syntax element can cause the decoder to enable CC-ALF for a Cb color component, keeping the amount of redundant information, for example in a slice header, small.

[0055] In a further embodiment, it may be provided that if the fourth syntax element has a value of 1, this indicates that the CC-ALF for a Cb color component is enabled for the current image and/or if the fourth syntax element has a value of 0, this indicates that the CC-ALF for a Cb color component is disabled for the current image.

[0056] Furthermore, the plurality of syntax elements related to CC-ALF may comprise a fifth syntax element when the fourth CC-ALF syntax element for the color component Cb is enabled for the current image, wherein the fifth syntax element is obtained from the image header and the fifth syntax element indicates a set of parameters that is associated with the Cb color component of all slices in the current image. This syntax element can be indicated with pic_cross_component_alf_cb_aps_id. This, however, is only a nomenclature and is not construed to limit the present disclosure. This modality can allow the provision of parameter sets that are provided for all slices of an image already at the image level, thus reducing the amount of redundant information.

[0057] In a further embodiment, the plurality of syntax elements associated with CC-ALF comprise a seventh syntax element when the second syntax element is obtained as indicating that CC-ALF is enabled, wherein the seventh syntax element is obtained from the image header and the seventh syntax element specifies whether CC-ALF is enabled for a Cr color component for a current image of a video sequence associated with the bitstream. This syntax element may, for example, be indicated with pic_cross_component_alf_cr_enabled_flag without limiting the present disclosure. With this syntax element, the CC-ALF decoder can reliably determine whether CC-ALF is enabled for Cr color components.

[0058] It may be provided that if the seventh syntax element has a value of 1, this indicates that CC-ALF for the Cr color component is enabled for the current image and/or if the seventh syntax element has a value of 0, this indicates that CC-ALF for the Cr color component is disabled for the current image.

[0059] In a further embodiment, the plurality of syntax elements associated with CC-ALF comprises an eighth syntax element when the seventh syntax element is obtained as indicating that CC-ALF for the Cr color component is image enabled. current, where the eighth syntax element is taken from the image header and the eighth syntax element indicates a set of parameters that is associated with the Cr color component of all slices in the current image. The eighth syntax element can be denoted with pic_cross_component_alf_cr_aps_id, although this is just an example. This syntax element can provide information about relevant parameters to use during filtering.

[0060] It may be further provided that the fourth syntax element, the fifth syntax element, the sixth syntax element, the seventh syntax element, the eighth syntax element and the ninth syntax element are obtained when the third syntax element syntax is taken to indicate that CC-ALF is enabled for the current image of a video sequence associated with the bitstream.

[0061] In one embodiment, the plurality of syntax elements related to CC-ALF comprises a tenth syntax element when the second syntax element is obtained as indicating that CC-ALF is enabled, wherein the tenth syntax element is obtained from a slice header and the tenth syntax element indicates whether CCALF for a Cb color component is enabled for a current slice of a current image of a video sequence associated with the bitstream. This syntax element may, without intending to limit the present disclosure, be referred to as slice_cross_component_alf_cb_enabled_flag. Thus, the decoder can determine whether CC-ALF should be enabled so that Cb color components can be provided.

[0062] It may further be provided that if the tenth syntax element has a value of 1, this indicates that CCALF for the color component Cb is enabled for the current slice and/or if the tenth syntax element has a value of 0, this indicates that CCALF for the Cb color component is disabled for the current slice.

[0063] In one embodiment, the plurality of syntax elements related to CC-ALF comprises an eleventh syntax element when the tenth syntax element is obtained as indicating that CC-ALF for the Cb color component is enabled for the slice current, where the tenth syntax element is taken from the slice header and the tenth syntax element specifies a set of parameters that the Cb color component of the current slice refers to. This syntax element may be indicated with pic_cross_component_alf_cb_aps_id, although this is not intended to limit the present disclosure.

[0064] It may be provided that the plurality of syntax elements related to CC-ALF comprise a twelfth syntax element when the second syntax element is obtained as indicating that CC-ALF is enabled, wherein the twelfth syntax element is obtained from the slice header and the twelfth syntax element indicates whether CCALF for a Cr color component is enabled for a current slice of a current image of a video sequence associated with the bitstream. The twelfth syntax element can, for example, be indicated with slice_cross_component_alf_cr_enabled_flag.

[0065] In a more specific embodiment, if the twelfth syntax element has a value of 1, this indicates that CCALF for the Cr color component is enabled for the current slice and/or if the twelfth syntax element has a value of 0, this indicates that CCALF for the Cr color component is disabled for the current slice.

[0066] It may further be provided that the plurality of syntax elements related to CC-ALF comprise a thirteenth syntax element when the twelfth syntax element is obtained as indicating that CC-ALF for the Cr color component is enabled for the current slice, where the thirteenth syntax element is obtained from a slice header and the thirteenth syntax element specifies a set of parameters to which the Cr color component of the current slice refers. The thirteenth syntax element can, for example, be indicated with slice_cross_component_alf_cr_aps_id. This can efficiently provide information about the parameter to be used for filtering associated with the Cr color component.

[0067] In one embodiment, the second syntax element is obtained if the first syntax element has a first value, or the second syntax element is obtained at least based on a value of the first syntax element.

[0068] It may further be provided that the plurality of syntax elements related to CC-ALF comprise a fourteenth syntax element that is obtained from the SPS level, wherein the fourteenth syntax element indicates the type of input to the CC-ALF. The fourteenth syntax element may be indicated with ChromaArrayType, although this does not limit the present disclosure.

[0069] More specifically, the second syntax element can be obtained when the first syntax element has a first value and the fourteenth syntax element has a second value. This second value can be any value other than a value that indicates that CC-ALF should not be enabled or that can be used to indicate so.

[0070] More specifically, it can be provided that the second syntax element is obtained when the first syntax element has a value that is equal to 1 and the fourteenth syntax element has a value that is different from 0.

[0071] For any of the above embodiments, it may be further provided that the CC-ALF operates as part of the adaptive loop filter process and makes use of luma sample values to refine at least one chroma component.

[0072] The present disclosure further relates to a device for encoding video data, comprising: a video data memory; and a video encoder, wherein the video encoder is configured to: apply a cross-component adaptive loop filter, CC-ALF to refine a chroma component; generating a bitstream including a plurality of CC-ALF-related syntax elements, wherein the plurality of CC-ALF-related syntax elements indicates CC-ALF-related information; wherein the plurality of syntax elements related to CC-ALF are signaled at any one or more of a sequence parameter set (SPS) level, an image header, or a slice header; wherein the plurality of syntax elements related to CC-ALF comprise a first syntax element that indicates whether or not an adaptive loop filter (ALF) comprising the cross-component adaptive loop filter is enabled or not at a sequence level, and the first element syntax element is signaled at the SPS level, and a second syntax element that indicates whether the cross-component adaptive loop filter is enabled or not at a sequence level, and the second syntax element is signaled at the SPS level. With this, the advantages of the coding methods mentioned above are provided to coders for coding, for example, videos.

[0073] The present disclosure also relates to a device for decoding video data, comprising: a video data memory; and a video decoder, wherein the video decoder is configured to: parse a plurality of cross-component adaptive loop filter, CC-ALF, related syntax elements from a bit stream, wherein the plurality of elements of syntax, wherein the plurality of syntax elements related to CC-ALF are obtained from any one or more of a sequence parameter set (SPS) level, an image header, or a slice header; wherein the plurality of syntax elements related to CC-ALF comprise a first syntax element that indicates whether or not an adaptive loop filter (ALF) comprising the cross-component adaptive loop filter is enabled or not at a sequence level, and the first element syntax element is signaled at the SPS level, and a second syntax element that indicates whether the cross-component adaptive loop filter is enabled or not at a sequence level, and the second syntax element is signaled at the SPS level; and performing a CC-ALF process using at least one of the plurality of syntax elements related to CC-ALF.

[0074] Thereby, the advantages of reduced bitstream size are realized when achieving reliable decoding of a video.

[0075] Furthermore, an encoder is provided for encoding a video, the encoder comprising processing circuitry for carrying out a method in accordance with any of the above embodiments. With this, the advantages of the coding methods mentioned above are provided to coders for coding, for example, videos.

[0076] Furthermore, a decoder for decoding a bit stream is provided, the decoder comprising processing circuitry for carrying out a method in accordance with any of the above embodiments. By doing so, the advantages of reduced bitstream size are realized when achieving reliable decoding of a video.

[0077] Furthermore, there is provided in this disclosure a computer-readable storage medium comprising thereon computer-executable instructions which, when executed by a computing device, cause the computing device to perform a method in accordance with any of the above embodiments.

[0078] The present disclosure further provides an encoded bitstream for the video signal including a plurality of syntax elements related to CC-ALF, wherein the plurality of syntax elements related to CC-ALF indicates information related to CC-ALF. ALF; wherein the plurality of syntax elements related to CC-ALF are signaled at any one or more of a sequence parameter set (SPS) level, an image header, or a slice header; wherein the plurality of syntax elements related to CC-ALF comprise a first syntax element that indicates whether or not an adaptive loop filter (ALF) comprising the cross-component adaptive loop filter is enabled or not at a sequence level, and the first element syntax element is signaled at the SPS level, and a second syntax element that indicates whether the cross-component adaptive loop filter is enabled or not at a sequence level, and the second syntax element is signaled at the SPS level.

[0079] The bit stream can be reduced in size while providing information to be used in decoding when reliably applying CC-ALF.

[0080] Details of one or more embodiments are presented in the attached drawings and in the description below. Other features, objects and advantages will be apparent from the description, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] In the following, embodiments of the invention are described in more detail with reference to the accompanying figures and drawings, in which:

[0082] Figure 1A is a block diagram showing an example of a video coding system configured to implement embodiments of the invention;

[0083] Figure 1B is a block diagram showing another example of a video coding system configured to implement embodiments of the invention;

[0084] Figure 2 is a block diagram showing an example of a video encoder configured to implement embodiments of the invention;

[0085] Figure 3 is a block diagram showing an example structure of a video decoder configured to implement embodiments of the invention;

[0086] Figure 4 is a block diagram illustrating an example of an encoding apparatus or a decoding apparatus;

[0087] Figure 5 is a block diagram illustrating another example of an encoding apparatus or a decoding apparatus;

[0088] Figure 6 includes Figures 6a, 6b and 6c, in which (6a) Placement of CC ALF in relation to other loop filters (6b and 6c) Diamond-shaped filter;

[0089] Figure 7 is a diagram illustrating all slice headers that must transmit CCALF data in the prior art;

[0090] Figure 8 is a diagram illustrating an example of enhanced CC-ALF syntax elements;

[0091] Figure 9A is a conceptual diagram illustrating the relative nominal vertical and horizontal locations of luma and chroma samples;

[0092] Figure 9B is a schematic diagram illustrating a co-located luma block and a chroma block;

[0093] Figure 10 is a block diagram showing an example structure of a content delivery system 3100 that performs a content delivery service;

[0094] Figure 11 is a block diagram showing a structure of an example of a terminal device;

[0095] Figure 12 is a block diagram showing an example of an encoder;

[0096] Figure 13 is a block diagram showing an example of a decoder;

[0097] Figure 14 shows a flowchart of a method of encoding a video according to an embodiment;

[0098] Figure 15 shows a flowchart of a method of decoding a video according to one embodiment.

[0099] Figure 16 is a schematic diagram of a data structure 5000, i.e., a video bit stream 500.

[0100] In the following, identical reference signals refer to identical or at least functionally equivalent resources, if not explicitly specified otherwise.

DETAILED DESCRIPTION OF MODALITIES

[0101] The following definition is for reference: □ coding block: An MxN block of samples for some values of M and N such that dividing a CTB into coding blocks is a partitioning. □ coding tree block (CTB): An NxN block of samples for some value of N such that dividing a component into CTBs is a partitioning. □ coding tree unit (CTU): One CTB of luma samples, two corresponding CTBs of chroma samples from an image that has three sample arrays, or one CTB of samples from a monochrome image or an image encoded using three planes of Separate colors and syntax structures used to encode the samples. □ coding unit (CU): A coding block of luma samples, two corresponding coding blocks of chroma samples of an image that has three sample arrays, or a coding block of samples of a monochrome image or a encoded using three separate color planes and syntax structures used to encode the samples. □ component: A single arrangement or sample of one of the three arrangements (luma and two chroma) that make up an image in 4:2:0, 4:2:2 or 4:4:4 color format or the arrangement or a single sample of the arrangement that makes up an image in monochrome format.

[0102] In the following description, reference is made to the attached figures, which form part of the disclosure and which show, by way of illustration, specific aspects of the embodiments of the invention or specific aspects in which the embodiments of the present invention can be used. It is understood that embodiments of the invention can be used in other aspects and comprise structural or logical changes not represented in the figures. The following detailed description, therefore, should not be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

[0103] For example, it is understood that a disclosure in connection with a described method may also be true for a corresponding device or system configured to carry out 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, for carrying out the described or plurality of method steps (e.g., a unit performing the 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 images. 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 a step for realizing the functionality of one or plurality of units (e.g., a 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 images. Furthermore, it is understood that features of the various exemplary embodiments and/or aspects described herein may be combined with each other unless specifically indicated otherwise.

[0104] Video coding typically refers to the processing of a sequence of images, which form the video or video sequence. Instead of the term “image” (“picture”), the term “frame” or “image” (“image”) can 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 coding is performed on the source side, typically comprising processing (e.g. by compression) of the original video images to reduce the amount of data required to represent the video images (for more efficient storage and/or transmission) . Video decoding is performed on the target side and typically comprises inverse processing compared to the encoder to reconstruct the video images. Embodiments that refer to "coding" of video images (or images in general) should be understood as relating to "encoding" or "decoding" of video images or respective video sequences. The combination of encoding part and decoding part is also known as CODEC (Encoding and Decoding).

[0105] In the case of lossless video coding, the original video images can be reconstructed, i.e., the reconstructed video images have the same quality as the original video images (assuming no transmission loss or other data loss during storage or transmission). In the case of lossy video coding, additional compression, for example by quantization, is performed, to reduce the amount of data representing the video images, which cannot be completely reconstructed in the decoder, i.e. the quality of the images reconstructed video images is inferior or worse compared to the quality of the original video images.

[0106] Various 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 to apply quantization in the transform domain). Each image in a video sequence is typically partitioned into a set of non-overlapping blocks, and encoding is typically performed at a block level. In other words, in the encoder, the video is typically processed, i.e. encoded, at a block level (video block), for example, by using spatial prediction (intra image) and/or temporal prediction (inter image) to generate a prediction block, subtract the prediction block from the current block (block currently processed/to be processed) to obtain a residual block, transform the residual block and quantize the residual block in the transform domain to reduce the amount of data to be transmitted (compression), while in the decoder, 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 so that both will generate identical predictions (e.g., intra- and inter-predictions) and/or reconstructions for processing, i.e., coding of subsequent blocks.

[0107] In the following embodiments of a video coding system 10, a video encoder 20 and a video decoder 30 are described based on Figures 1 to 3.

[0108] Figure 1A is a schematic block diagram illustrating an example coding system 10, for example, a video coding system 10 (or coding system 10 for short) that may utilize techniques of the present application. The video encoder 20 (or encoder 20 for short) and the video decoder 30 (or decoder 30 for short) of the video coding system 10 represent examples of devices that can be configured to perform techniques in accordance with various examples described in this request.

[0109] As shown in Figure 1A, the encoding system 10 comprises a source device 12 configured to provide encoded image data 21, for example, to a destination device 14 for decoding the encoded image data 13.

[0110] The source device 12 may comprise an encoder 20 and may additionally, i.e. optionally, comprise an image source 16, a preprocessor (or preprocessing unit) 18, e.g. image processor 18, and a communication interface or communication unit 22.

[0111] The image source 16 may comprise or be any type of image capturing device, e.g., a camera for capturing a real-world image and/or any type of an imaging device, e.g., a computer graphics processor to generate a computer-animated image, or any type of other device to obtain and/or provide a real-world image, a computer-generated image (e.g., a screen content, a virtual reality image ( VR)) and/or any combination thereof (e.g. an augmented reality (AR) image). The image source can be any type of memory or storage storing any of the above-mentioned images.

[0112] In distinction to the preprocessor 18 and the processing performed by the preprocessing unit 18, the image or image data 17 may also be referred to as the raw image or raw image data 17.

[0113] The preprocessor 18 may be configurable to receive the (raw) image data 17 and to perform preprocessing on the image data 17 to obtain a preprocessed image 19 or preprocessed image data 19. Preprocessing performed by preprocessor 18 may, for example, comprise cropping, color format conversion (e.g., from RGB to YCbCr), color correction, or noise elimination. It can be understood that the preprocessing unit 18 can be an optional component.

[0114] The video encoder 20 may be configured to receive the preprocessed image data 19 and provide encoded image data 21 (more details will be described below, for example, based on Figure 2).

[0115] Communication interface 22 of the source device 12 may be configured to receive the encoded image data 21 and to transmit the encoded image data 21 (or any further processed version thereof) over the communication channel 13 to another device , for example, the target device 14 or any other device, for storage or direct reconstruction.

[0116] The target device 14 may comprise 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.

[0117] The communication interface 28 of the destination device 14 may be configured to receive the encoded image data 21 (or any further processed version thereof), for example, directly from the source device 12 or from any another source, e.g., a storage device, e.g., an encoded image data storage device, and providing the encoded image data 21 to the decoder 30.

[0118] The communication interface 22 and the communication interface 28 may be configured to transmit or receive the encoded image data 21 or encoded data 13 via a direct communication link between the source device 12 and the destination device 14 , for example, a direct wired or wireless connection, or through any type of network, for example, a wired or wireless network or any combination thereof, or any type of private and public network, or any type of combination thereof same.

[0119] Communication interface 22 may be, for example, configured to package the encoded image data 21 into an appropriate format, e.g. packets, and/or process the encoded image data using any type of encoding or processing. transmission for transmission over a communications link or communications network.

[0120] The communication interface 28, forming the counterpart of the communication interface 22, may be, for example, configured to receive the transmitted data and process the transmission data using any type of decoding or processing and/or corresponding transmission unpacking to obtain the encoded image data 21.

[0121] Both, or at least one of, the communication interface 22 and the communication interface 28 can be configured as unidirectional communication interfaces, as indicated by the arrow for communication channel 13 in Figure 1A pointing from the communication device. source 12 to destination device 14, or as bidirectional communication interfaces, and may be configured, for example, to send and receive messages, for example, to configure a connection, to recognize and exchange any other information related to the communication link and/or data transmission, for example, transmission of encoded image data.

[0122] The decoder 30 may be configured to receive the encoded image data 21 and provide decoded image data 31 or a decoded image 31 (more details will be described below, for example, based on Figure 3 or Figure 5).

[0123] The post-processor 32 of the target device 14 may be configured to post-process the decoded image data 31 (also called reconstructed image data), e.g., the decoded image 31, to obtain post-image data. -processed 33, for example, a post-processed image 33. The post-processing performed by the post-processing unit 32 may comprise, for example, color format conversion (e.g., from YCbCr to RGB), color correction , cropping, or resampling, or any other processing, for example, to prepare the decoded image data 31 for display, for example, by the display device 34.

[0124] The display device 34 of the target device 14 may be configured to receive the post-processed image data 33 to display the image, for example, to a user or viewer. The display device 34 may be or comprise any type of display for representing the reconstructed image, e.g., an integrated or external display or monitor. The displays may, for example, comprise liquid crystal displays (LCD), organic light emitting diode (OLED) displays, plasma displays, projectors, microLED displays, liquid crystal on silicon (LCoS), digital light processor ( DLP) or any other type of display.

[0125] Although Figure 1A depicts the source device 12 and the destination device 14 as separate devices, device embodiments may also comprise both or both functionality, 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 target 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.

[0126] The source device and/or target device may further be implemented using dedicated hardware and/or software. For example, one or both of these devices may be implemented using hardware specifically designed to perform one or more of the functionalities mentioned above and below. Alternatively or additionally, one or more of the functionalities described above and below may be implemented using specifically designed software that can run on general purpose hardware, such as processors. Furthermore, combinations of the above are also envisioned, wherein the source device and/or the target device may be implemented using a combination of hardware specifically dedicated to performing one or more functionalities and software to performing one or more other functionalities.

[0127] As will be apparent to the skilled person based on the description, the existence and (exact) division of functionalities of the different units or functionalities within the source device 12 and/or target device 14, as shown in Figure 1A, may vary depending on the actual device and application.

[0128] Encoder 20 (e.g., a video encoder 20) or decoder 30 (e.g., a video decoder 30) or both, encoder 20 and decoder 30 may be implemented through processing circuits such as shown in Figure 1B, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, hardware, dedicated video coding, or any combination of the same. Encoder 20 may be implemented through processing circuitry 46 to incorporate the various modules as discussed in connection with encoder 20 of Figure 2 and/or any other encoder system or subsystem described herein. Decoder 30 may be implemented through processing circuitry 46 to incorporate the various modules as discussed with respect to decoder 30 of Figure 3 and/or any other decoder system or subsystem described herein. The processing circuits can be configured to perform the various operations, as discussed later. As shown in Figure 5, if the techniques are implemented partially in software, a device may store instructions for the software on 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 revelation. Any 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 Figure 1B.

[0129] The source device 12 and the target device 14 may comprise any of a wide range of devices, including any type of portable or stationary devices, e.g., notebook or laptop computers, mobile phones, smartphones, tablets or computers tablets, cameras, desktop computers, set-top boxes, televisions, display devices, digital media players, video game consoles, video streaming devices (such as content services servers or content delivery servers), broadcast receiving device, broadcast transmitting device, or similar and may use no or any type 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.

[0130] In some cases, the video coding system 10 illustrated in Figure 1A is only an example and the techniques of the present application can be applied 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 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, encoding and decoding are performed by devices that do not communicate with each other, but simply encode data into memory and/or retrieve and decode data from memory.

[0131] For convenience of description, embodiments of the invention are described herein, for example, by reference to High Efficiency Video Coding (HEVC) or the Versatile Video Coding (VVC) reference software, the next generation video developed by the Joint Video Coding Collaboration Team (JCT-VC) of the ITU-T Video Coding Specialist Group (VCEG) and ISO/IEC Moving Figure Specialist Group (MPEG). A person skilled in the art will understand that the embodiments of disclosure are not limited to HEVC or VVC.

Encoder and Coding Method

[0132] Figure 2 shows a schematic block diagram of an example video encoder 20 that can be configured to implement the techniques of the present disclosure. In the example of Figure 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 coding unit 270, and an output 272 (or 272 output interface). The mode selection unit 260 may include an intra prediction unit 244, an intra prediction unit 254, and a partitioning unit 262. The intra prediction unit 244 may include a motion estimation unit and a motion compensation unit. (not shown). A video encoder 20, as shown in Figure 2, may also be referred to as a hybrid video encoder or a video encoder according to a hybrid video codec.

[0133] The residual calculation unit 204, the transform processing unit 206, the quantization unit 208, and the mode selection unit 260 may be referred to as forming a direct signal path of the encoder 20, while the inverse quantization 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 reverse signal path of the video encoder 20, wherein the reverse signal path of the video encoder 20 corresponds to the signal path of the decoder (see video decoder 30 in Figure 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 to form the “built-in decoder” of the video encoder 20. Images and Image Partitioning (Images and Blocks)

[0134] The encoder 20 can be configured to receive, for example, through input 201, an image 17 (or image data 17), for example, an image of a sequence of images forming a video or video sequence. The received image or image data may also be a preprocessed image 19 (or preprocessed image data 19). For simplicity, the following description refers to image 17. Image 17 may also be referred to as the current image or image to be encoded (in particular in video coding to distinguish the current image from other images, e.g. images previously encoded and/or decoded from the same video sequence, i.e. the video sequence that also includes the current image).

[0135] A (digital) image is or can be considered as a two-dimensional array or matrix of samples with intensity values. A sample in the array may also be referred to as a pixel (short for picture element) or pel. The number of samples in the horizontal and vertical direction (or axis) of the array or image defines the size and/or resolution of the image. For color representation, three color components are typically employed, i.e., the image can be represented as or include three sample arrangements. In the RBG format or color space, an image comprises an arrangement of corresponding red, green, and blue samples. 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 denoted by Y (sometimes also L is used instead) and two chrominance components indicated by Cb and Cr. The luminance component (or luma for short) Y represents the brightness or gray level intensity (e.g. as in a grayscale image), while the two chrominance components (or chroma for short) Cb and Cr represent the chromaticity or components of color information. Consequently, an image in YCbCr format comprises one luminance sample array of luminance sample values (Y) and two chrominance sample arrays of chrominance values (Cb and Cr). Images in RGB format can be converted or transformed into YCbCr format and vice versa, the process is also known as color transformation or conversion. If an image is monochromatic, the image may comprise only one luminance sample array. Consequently, an image can be, for example, a luma sample array in monochrome format or a luma sample array and two corresponding chroma sample arrays in color format 4:2:0, 4:2:2 and 4:4:4.

[0136] Embodiments of the video encoder 20 may comprise an image partitioning unit (not depicted in Figure 2) configured to partition the image 17 into a plurality of image blocks 203 (normally non-overlapping). These blocks may also be referred to as root blocks, macroblocks (H.264/AVC), or coding tree blocks (CTB) or coding tree units (CTU) (H.265/HEVC and VVC). The image partitioning unit can be configured to use the same block size for all images in a video sequence and the corresponding grid defining the block size, or to change the block size between images or subsets or groups of images , and partition each image into corresponding blocks.

[0137] In additional embodiments, the video encoder may be configured to directly receive a block 203 of image 17, e.g., one, several, or all of the blocks forming image 17. Image block 203 may also be referred to as current image block or image block to be encoded.

[0138] Like image 17, image block 203, again, is or may be considered as a two-dimensional array or array of samples with intensity values (sample values), albeit of smaller dimension than image 17. In In other words, block 203 may comprise, for example, a sample array (e.g., a luma array in the case of a monochrome image 17, or a luma or chroma array in the case of a color image) or three sample arrays ( for example, one luma and two chroma array in the case of a color image 17) or any other number and/or type of arrays depending on the color format applied. The number of samples in horizontal and vertical direction (or axis) of block 203 defines the size of block 203. Therefore, a block may, for example, be an MxN (M columns by N rows) array of samples, or an MxN array of transform coefficients.

[0139] Embodiments of the video encoder 20, as shown in Figure 2, can be configured to encode the image 17 block by block, for example, coding and prediction are performed per block 203.

[0140] Embodiments of the video encoder 20, as shown in Figure 2, may be further configured to partition and/or encode the image using slices (also called video slices), wherein an image may be partitioned or encoded using a or more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g., CTUs) or one or more groups of blocks (e.g., tiles (H.265/HEVC and VVC) or bricks (VVC) ).

[0141] Embodiments of the video encoder 20, as shown in Figure 2, may be further configured to partition and/or encode the image using groups of slices/tiles (also referred to as groups of video tiles) and/or tiles (also referred to as referred to as video tiles), wherein an image may be partitioned or encoded using one or more groups of slices/tiles (typically non-overlapping), and each group of slices/tiles may comprise, for example, one or more blocks (e.g. e.g., CTUs) or one or more tiles, wherein each tile, for example, may be rectangular in shape and may comprise one or more blocks (e.g., CTUs), e.g., full or fractional blocks.

Residual Calculation

[0142] The residual calculation unit 204 may be configured to calculate a residual block 205 (also referred to as residual 205) based on the image block 203 and a prediction block 265 (additional details about the prediction block 265 are provided later ), for example, subtracting sample values from the prediction block 265 from sample values from the image block 203, sample by sample (pixel by pixel) to obtain the residual block 205 in the sample domain.

Transformed

[0143] The transform processing unit 206 may be configured to apply a transform, e.g., a discrete cosine transform (DCT) or discrete sine transform (DST), to the sample values of the residual block 205 to obtain coefficients of transform 207 into a transform domain. Transform coefficients 207 may also be referred to as transform residual coefficients and represent the residual block 205 in the transform domain.

[0144] The transform processing unit 206 can 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 that is processed by the forward and inverse transforms, additional scaling factors are applied as part of the transform process. Scaling factors are typically chosen based on certain constraints, such as scaling factors being a power of two for shift operations, bit depth of transform coefficients, tradeoff between accuracy and implementation costs, etc. Specific scaling factors are, for example, specified for the inverse transform, for example, by the inverse transform processing unit 212 (and the corresponding inverse transform, for example, by the inverse transform processing unit 312 in the video decoder 30). and corresponding scaling factors for the direct transform, for example, by the transform processing unit 206, in an encoder 20 may be specified accordingly.

[0145] 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 through the unit entropy coding 270, such that, for example, video decoder 30 can receive and use the transform parameters for decoding.

Quantization

[0146] The quantization unit 208 can be configured to quantize the transform coefficients 207 to obtain quantized coefficients 209, for example, by applying scalar quantization or vector quantization. Quantized coefficients 209 may also be referred to as quantized transform coefficients 209 or quantized residual coefficients 209.

[0147] 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 can be modified by adjusting a quantization parameter (QP). For example, for scalar quantization, different scaling can be applied to achieve finer or coarser quantization. Smaller quantization step sizes correspond to finer quantization, while larger quantization step sizes correspond to coarser quantization. The applicable quantization step size can be indicated by a quantization parameter (QP). The quantization parameter may, for example, be an index for 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. Quantization may include division by a quantization step size and a corresponding dequantization and/or 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 can be calculated based on a quantization parameter using a fixed-point approximation of an equation including division. Additional scaling factors can be introduced for quantization and dequantization to restore the residual block norm, which can be modified because of the scaling used in the fixed-point approximation of the equation for the quantization step size and quantization parameter. In an example implementation, inverse transform scaling and dequantization can be combined. Alternatively, custom quantization tables can be used and signaled from an encoder to a decoder, for example in a bitstream. Quantization is a lossy operation, where the loss increases with increasing quantization step sizes.

[0148] 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 coding unit 270, so that, e.g. For example, video decoder 30 can receive and apply quantization parameters for decoding.

Inverse Quantization

[0149] The inverse quantization unit 210 may be configured to apply the inverse quantization of the quantization unit 208 on the quantized coefficients to obtain dequantized coefficients 211, for example, 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 211 may also be referred to as dequantized residual coefficients 211 and correspond - although normally not identical to the transform coefficients due to quantization loss - to the transform coefficients 207.

Inverse Transform

[0150] The inverse transform processing unit 212 may be 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 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

[0151] The reconstruction unit 214 (e.g., adder or adder 214) may be 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 domain of sample, for example, by adding - sample by sample - the sample values from the reconstructed residual block 213 and the sample values from the prediction block 265.

Filtering

[0152] The loop filter unit 220 (or "loop filter" for short 220), may be configured to filter the reconstructed block 215 to obtain a filtered block 221 or, in general, to filter reconstructed samples to obtain filtered sample values . The loop filter unit is, for example, configured to smooth pixel transitions or improve video quality. The loop filter unit 220 may comprise one or more loop filters, such as an deblocking filter, an adaptive sample shift (SAO) filter, or one or more other filters, e.g., an adaptive loop filter (ALF), an noise suppression filter (NSF), or any combination thereof. In one example, the loop filter unit 220 may comprise a deblocking filter, an SAO filter, and an ALF filter. The order of the filtering process can be unblocking filter, SAO and ALF. In another example, a process called luma mapping with chroma scaling (LMCS) (i.e., the adaptive in-loop reshaper) is added. This process is carried out before unlocking. In another example, the deblocking filter process can also be applied to internal edges of subblocks, e.g., affine subblock edges, ATMVP subblock edges, subblock transform (SBT) edges, and intra subpartition (ISP) edges.

[0153] To effectively remove blocking artifacts that occur in large “blocks,” VVC uses a longer bypass deblocking filter. Here the term “blocks” is used very generically and can refer to a “transform block (TB), prediction block (PB) or coding unit block (CU)”. The longer bypass filter is applied to the Luma and Chroma components. The longest bypass filter for Luma components modifies a maximum of 7 samples for each line of samples perpendicular and adjacent to the edge and is applied for blocks whose size is >=32 samples in the unblocking direction, i.e. for vertical edges, the block width must be >=32 samples and for horizontal edges, the block height must be >=32 samples.

[0154] The longest chroma drift filter is applied to Chroma blocks when both blocks adjacent to a given edge have a size >=8 samples and modifies a maximum of three samples on each side of the edge. Therefore, for vertical edges the block width of both blocks adjacent to the edge must be >=8 samples and for horizontal edges the block height of both blocks adjacent to the edge must be >=8 samples. Although the loop filter unit 220 is shown in Figure 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 the filtered rebuilt block 221.

[0155] Embodiments of the video encoder 20 (respectively loop filter unit 220) can be configured to output loop filter parameters (such as SAO filter parameters or ALF filter parameters or LMCS parameters), for example, directly or encoded through the entropy coding unit 270, such that, for example, a decoder 30 can receive and apply the same loop filter parameters or respective loop filters for decoding.

Decoded Image Buffer

[0156] The decoded picture buffer (DPB) 230 may be a memory that stores reference images, or in general reference picture data, for encoding video data by the video encoder 20. The DPB 230 may be formed by any one 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 image or different images, e.g. previously reconstructed images, and can provide complete previously reconstructed images, i.e. decoded images (and corresponding reference blocks and samples) and/or a partially reconstructed current image (and reference blocks and corresponding samples), for example, for inter prediction. The decoded picture buffer (DPB) 230 may also be configured to store one or more unfiltered reconstructed blocks 215 or, in general, unfiltered reconstructed samples, for example, if the reconstructed block 215 is not filtered by the loop filter unit 220 or any other additional processed version of the reconstructed blocks or samples. Mode selection (partitioning and prediction)

[0157] 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 image data, e.g., an original block 203 (current block 203 of the current image 17), and reconstructed image data, e.g. filtered and/or unfiltered reconstructed samples or blocks of the same (current) image and/or of one or a plurality of previously decoded images, e.g. from the buffer decoded image buffer 230 or other buffers (e.g., line buffer, not shown). The reconstructed image data is used as reference image data for prediction, e.g., inter prediction or intra prediction, to obtain a prediction block 265 or predictor 265.

[0158] 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.

[0159] Embodiments of the mode selection unit 260 may be configured to select the partitioning and prediction mode (e.g., from those supported by or available to the mode selection unit 260) that provide the best combination or in other words the minimum residual (minimum residual means best compression for transmission or storage), or a minimum signaling overhead (minimum signaling overhead means best 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., selecting the prediction mode that provides a minimum rate distortion. Terms such as "best", "minimum", "optimal", etc. in this context do not necessarily refer to an overall "best", "minimum", "optimal", etc., but may also refer to the fulfillment of a termination or selection criterion such as a value exceeding or falling below a threshold or other constraints potentially leading to "suboptimal selection" but reducing complexity and processing time.

[0160] In other words, the partitioning unit 262 may be configured to partition an image from a video sequence into a sequence of coding tree units (CTUs), and the CTU 203 may be further partitioned into partitions of smaller blocks or sub-blocks (which again form blocks), for example 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 selecting the tree structure of the partitioned block 203 and the prediction modes are applied to each of the block partitions or sub-blocks .

[0161] In the following, the partitioning (e.g., per partitioning unit 260) and prediction processing (per inter prediction unit 244 and intra prediction unit 254) performed by an example video encoder 20 will be explained in more detail .

Partitioning

[0162] The partitioning unit 262 may be configured to partition an image of a video sequence into a sequence of coding tree units (CTUs), and the partitioning unit 262 may partition (or divide) a coding tree unit. coding (CTU) 203 in smaller partitions, for example smaller blocks of square or rectangular size. For an image that has three sample arrays, a CTU consists of an NxN block of luma samples along with two corresponding blocks of chroma samples. The maximum allowable luma block size in a CTU is specified as 128 x 128 in Versatile Video Coding (VVC), but may be specified as a value instead of 128 x 128 in the future, for example, 256 x 256. The CTUs of an image can be clustered as groups of slices/tiles, tiles or bricks. A tile covers a rectangular region of an image and a tile can be divided into one or more bricks. A brick consists of a number of CTU lines within a tile. A tile that is not partitioned into multiple bricks can be called a brick. However, a brick is a true subset of a tile and is not referred to as a tile. There are two tile group modes supported in VVC, namely raster scan tile/slice group mode and rectangular slice mode. In raster scan tile group mode, a slice/tile group contains a sequence of tiles in the tile raster scan of an image. In rectangular slice mode, a slice contains multiple bricks of an image that collectively form a rectangular region of the image. The bricks within a rectangular slice are in the raster scan order of the slice's bricks. These smaller blocks (which can also be called sub-blocks) can be partitioned into even smaller partitions. This is also referred to as tree partitioning or hierarchical tree partitioning, where a root block, for example at root tree level 0 (hierarchy level 0, depth 0), can be recursively partitioned, e.g. partitioned into two or more blocks of a next lower tree level, for example, nodes at tree level 1 (hierarchy level 1, depth 1), where these blocks may be further partitioned into two or more blocks of a next lower level, e.g. example, tree level 2 (hierarchy level 2, depth 2), etc. until partitioning is terminated, for example because a termination criterion is met, for example, a maximum tree depth or minimum block size is reached. Blocks, which are not additionally partitioned, are also called leaf blocks or leaf nodes of the tree. A tree using two-partitioning is called a binary tree (BT), a tree using three-partitioning is called a ternary tree (TT), and a tree using four-partitioning is called a quadtree (QT).

[0163] For example, a coding tree unit (CTU) may be or comprise a CTB of luma samples and two corresponding CTBs of chroma samples of an image that has three sample arrays or a CTB of samples of an image monochrome or an image that is encoded using three separate color planes and syntax structures used to encode the samples. Correspondingly, a coding tree block (CTB) can be an NxN block of samples for some value of N such that dividing 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 an image having three sample arrays, or a coding block of samples of a monochrome image. or an image that is encoded using three separate color planes and syntax structures used to encode the samples. Correspondingly, a coding block (CB) can be an MxN block of samples for some values of M and N so that dividing a CTB into coding blocks is a partitioning.

[0164] In embodiments, for example, according to HEVC, a coding tree unit (CTU) can be divided into CUs using a quadtree structure denoted as coding tree. The decision to encode an image area using inter-image (temporal) or intra-image (spatial) prediction is made at the leaf CU level. Each sheet CU can be divided into one, two or four PUs according to the PU division type. Within a PU, the same prediction process is applied and relevant information is transmitted to the decoder based on the PU. After obtaining the residual block by applying the prediction process based on 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.

[0165] In embodiments, for example, according to the latest video coding standard currently under development, which is referred to as Versatile Video Coding (VVC), a nested Quad-tree multi-type tree combined using segmentation of binary and ternary divisions, for example, used to partition a coding tree unit. In the coding tree structure within a coding tree unit, a CU can have a square or rectangular shape. For example, the coding tree unit (CTU) is first partitioned by a quaternary tree. Then, the leaf nodes of the quaternary tree can be partitioned by a multi-type tree structure. There are four types of splitting in the multitype tree structure, vertical binary splitting (SPLIT_BT_VER), horizontal binary splitting (SPLIT_BT_HOR), vertical ternary splitting (SPLIT_TT_VER), and horizontal ternary splitting (SPLIT_TT_HOR). Tree leaf nodes of multiple types are called coding units (CUs), and unless the CU is too large for the maximum transform length, this segmentation is used for transform prediction and processing without any additional partitioning. This means that in most cases, CU, PU and TU have the same block size in the quadtree with nested multi-type tree coding block structure. The exception occurs when the maximum supported transform length is less than the width or height of the CU color component. VVC develops a unique signaling mechanism of partition division information in quadtree with multi-type tree coding tree structure nested. In the signaling mechanism, a coding tree unit (CTU) is treated as the root of a quaternary tree and is first partitioned by a quaternary tree structure. Each quaternary tree leaf node (when large enough to allow) is then partitioned by a multi-type tree structure. In the multi-type tree structure, a first flag (mtt_split_cu_flag) is signaled to indicate whether the node is additionally partitioned; When a node is additionally partitioned, a second flag (mtt_split_cu_vertical_flag) is flagged to indicate the direction of the split, and then a third flag (mtt_split_cu_binary_flag) is flagged to indicate whether the split is a binary split or a ternary split. Based on the values of mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag, the multi-type tree splitting mode (MttSplitMode) of a CU can be derived by a decoder based on a predefined rule or a table. It should be noted that for a certain design, e.g. 64x64 Luma block and 32x32 Chroma pipelining design in VVC hardware decoders, TT splitting is prohibited when the width or height of a luma encoding block is greater than 64 as shown in Figure 6. TT splitting is also prohibited when the width or height of a chroma encoding block is greater than 32. The pipeline design will split an image into virtual pipeline data units ( VPDUs) which are defined as non-overlapping units in an image. In hardware decoders, successive VPDUs are processed by multiple pipeline stages simultaneously. The size of the VPDU is roughly proportional to the buffer size in most pipeline stages, so it is important to keep the VPDU size small. In most hardware decoders, the VPDU size can be set to the maximum transform block size (TB). However, in VVC, the partition of ternary tree (TT) and binary tree (BT) can lead to the increase in the size of VPDUs.

[0166] Additionally, it should be noted that when a portion of a tree node block exceeds the bottom or right boundary of the image, the tree node block is forced to be split until all samples from each encoded CU are located within the image boundaries.

[0167] As an example, the Intra SubPartitions (ISP) tool can divide predicted intra luma blocks vertically or horizontally into 2 or 4 subpartitions depending on the size of the block.

[0168] In one example, the mode selection unit 260 of the video encoder 20 may be configured to perform any combination of the partitioning techniques described herein.

[0169] As described above, video encoder 20 is configured to determine or select the best or an optimal prediction mode from a set of prediction modes (e.g., predetermined). The set of prediction modes may comprise, for example, intra prediction modes and/or inter prediction modes.

Intra Prediction

[0170] The set of intra prediction modes may comprise 35 different intra prediction modes, for example, non-directional modes such as DC (or average) mode and planar mode, or directional modes, for example, as defined in HEVC, or may comprise 67 intra prediction modes, for example, non-directional modes, such as DC (or average) mode and planar mode, or directional modes, for example, as defined for VVC. As an example, several conventional intra-angle prediction modes are adaptively replaced by wide-angle intra prediction modes for the non-square blocks, for example, as defined in VVC. As another example, to avoid division operations for DC prediction, only the longest side is used to calculate the average of non-square blocks. And, the planar mode intra prediction results can be further modified by a position dependent intra prediction combination (PDPC) method.

[0171] The intra prediction unit 254 is configured to use reconstructed samples from neighboring blocks of the same current image to generate an intra prediction block 265 according to an intra prediction mode from the set of intra prediction modes.

[0172] The intra prediction unit 254 (or, in general, the mode selection unit 260) is further configured to output intra prediction parameters (or general information indicative of the intra prediction mode selected for the block) to the entropy coding unit 270 in the form of syntax elements 266 for inclusion in the encoded image data 21 so that, for example, the video decoder 30 can receive and use the prediction parameters for decoding.

Inter Prediction

[0173] The set of (or possible) inter prediction modes depends on the available reference images (i.e., previous at least partially decoded images, e.g., stored in DBP 230) and other inter prediction parameters, e.g., whether the entire reference image or just a part, for example, a search pane around the current block area, of the reference image is used to search for the best matching reference block, and/or for example, if the pixel interpolation is applied, for example, half/semi-pel interpolation, quarter-pel interpolation and/or 1/16-pel interpolation, or not.

[0174] In addition to the above prediction modes, skip mode, direct mode and/or other inter prediction mode can be applied.

[0175] For example, extended merge prediction, the merge candidate list is thus constructed by including the following five candidate types in order: spatial MVP from spatial neighboring CUs, temporal MVP from co-located CUs, MVP based on history from a table FIFO, average MVP in pairs and MVs Zero. And a decoder lateral motion vector refinement based on bilateral correspondence (DMVR) can be applied to increase the accuracy of merge mode MVs. Merge mode with MVD (MMVD), which comes from merge mode with motion vector differences. An MMVD flag is signaled immediately after sending a skip flag and a merge flag to specify whether MMVD mode is used for a CU. And an adaptive motion vector resolution (AMVR) scheme at the CU level can be applied. AMVR allows the MVD of the CU to be encoded at different precisions. Depending on the prediction mode of the current CU, the MVDs of the current CU can be selected adaptively. When a CU is coded in merge mode, the combined inter/intra prediction (CIIP) mode can be applied to the current CU. The weighted average of the inter and intra prediction signals is performed to obtain the CIIP prediction. Compensated Affine Motion Prediction,The affine motion field of the block is described by,motion information of two control points (4 parameters) or,three control point motion vectors (6 parameters). Subblock-based temporal motion vector prediction (SbTMVP), which is similar to temporal motion vector prediction (TMVP) in HEVC, but predicts the motion vectors of the sub-CUs within the current CU. Bidirectional optical flow (BDOF), formerly known as BIO, is a simpler version that requires much less computation, particularly in terms of number of multiplications and multiplier size. Triangular partition mode, in this mode, a CU is evenly divided into two triangle-shaped partitions using either diagonal splitting or antidiagonal splitting. Furthermore, the biprediction mode is extended beyond simple averaging to allow weighted averaging of the two prediction signals.

[0176] The inter prediction unit 244 may include a motion estimation (ME) unit and a motion compensation (MC) unit (both not shown in Figure 2). The motion estimation unit may be configured to receive or obtain image block 203 (current image block 203 of current image 17) and a decoded image 231, or at least one or a plurality of previously reconstructed blocks, e.g. reconstructed blocks of one or a plurality of previously decoded 231 other/different images, for motion estimation. For example, a video sequence may comprise the current image and previously decoded images 231, or in other words, the current image and previously decoded images 231 may be part of or form a sequence of images forming a video sequence.

[0177] Encoder 20, for example, may be configured to select a reference block from a plurality of reference blocks of the same or different images from the plurality of other images and provide a reference image (or image index of reference) 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 for the motion estimation unit. This displacement is also called motion vector (MV).

[0178] The motion compensation unit can be configured to obtain, for example, receive an inter prediction parameter and perform inter prediction based on or using the inter prediction parameter to obtain an inter prediction block 265. Motion compensation Motion, 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 for subpixel accuracy. Interpolation filtering can generate additional pixel samples from known pixel samples, thereby potentially increasing the number of candidate prediction blocks that can be used to encode an image block. Upon receiving the motion vector for the PU from the current image block, the motion compensation unit can locate the prediction block to which the motion vector points in one of the reference image lists.

[0179] The motion compensation unit may also generate syntax elements associated with the video blocks and slices for use by the video decoder 30 in decoding the image blocks of the video slice. In addition to or as an alternative to slices and their syntax elements, groups of tiles and/or tiles and their syntax elements can be generated or used.

Entropy Coding

[0180] The entropy coding unit 270 is configured to apply, for example, an entropy coding algorithm or scheme (e.g., a variable length coding scheme (VLC), 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 coding (PIPE), or other methodology or entropy coding technique) or shift (without compression) in the quantized coefficients 209, inter prediction parameters, intra prediction parameters, loop filter parameters and/or other syntax elements to obtain encoded image data 21 that can be output through of the output 272, for example, in the form of a coded bit stream 21, so that, for example, the video decoder 30 can receive and use the decoding parameters. The bit stream may, for example, have a shape as further specified in Figure 16 below. The embodiments described in relation to this figure are thus considered to also encompass the bit stream 21 described here. Furthermore, any structure of a bit stream referred to herein may be provided as bit stream 21 in the sense of this embodiment. The encoded bit stream 21 may be transmitted to the video decoder 30 or stored in a memory for later transmission or retrieval by the video decoder 30.

[0181] Other structural variations of video encoder 20 may be used to encode the video stream. For example, a non-transform based encoder 20 may quantize the residual signal directly without the transform processing unit 206 for certain blocks or frames. In another implementation, an encoder 20 may have the quantization unit 208 and the inverse quantization unit 210 combined into a single unit.

Decoder and decoding method

[0182] Figure 3 shows an example of a video decoder 30 that can be configured to implement the techniques of this present disclosure. Video decoder 30 may be configured to receive encoded image data 21 (e.g., encoded bitstream 21), e.g., encoded by encoder 20, to obtain a decoded image 331. The encoded image data or bitstream comprise information for decoding the encoded image data, for example, data representing image blocks of an encoded video slice (and/or groups of tiles or tiles) and associated syntax elements.

[0183] In the example of Figure 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., an adder 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. The inter prediction unit 344 may be or include a motion compensation. The video decoder 30 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to the video encoder 100 of Figure 2.

[0184] As explained with respect 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 the video encoder 20. Therefore, the inverse quantization unit 310 may be identical in function to the inverse quantization unit 110, 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 the 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 encoder 20 apply correspondingly to the respective units and functions of the video decoder 30.

Entropy decoding

[0185] The entropy decoding unit 304 may be configured to analyze the bit stream 21 (or generally encoded image data 21) and perform, for example, entropy decoding for the encoded image data 21 to obtain, e.g., quantized coefficients 309 and/or decoded encoding parameters 366, (not shown in Figure 3), e.g., any or all inter prediction parameters (e.g., reference image 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. The entropy decoding unit 304 may be configured to apply decoding algorithms or schemes corresponding to the encoding schemes as described with respect to the entropy coding unit 270 of the encoder 20. The 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. The video decoder 30 may receive the syntax elements at the level of video slice and/or video block level. In addition to or as an alternative to slices and their syntax elements, groups of tiles and/or tiles and their syntax elements may be received and/or used.

Inverse Quantization

[0186] The inverse quantization unit 310 may be configured to receive quantization parameters (QP) (or in general information related to inverse quantization) and quantized coefficients from the encoded image data 21 (e.g., by analysis and/or decoding, for example, by entropy decoding unit 304) and applying, 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 process Inverse quantization may include using a quantization parameter determined by video encoder 20 for each video block in the video slice (or tile or groups of tiles) to determine a degree of quantization and, likewise, a degree of inverse quantization that must be applied.

Inverse Transform

[0187] The inverse transform processing unit 312 may be configured to receive dequantized coefficients 311, also referred to as transform coefficients 311, and to apply a transform to the dequantized coefficients 311 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 further be configured to receive transform parameters or corresponding information from the encoded image data 21 (e.g., by analysis and/or decoding, e.g., by entropy decoding unit 304). to determine the transform to be applied to the dequantized coefficients 311.

Reconstruction

[0188] The reconstruction unit 314 (e.g., adder or adder 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 values sample values from the reconstructed residual block 313 and the sample values from the prediction block 365.

Filtering

[0189] The loop filter unit 320 (in the encoding loop or after the encoding loop) may be configured to filter the reconstructed block 315 to obtain a filtered block 321, for example, to smooth pixel transitions or improve quality of video. The loop filter unit 320 may comprise one or more loop filters, such as an deblocking filter, an adaptive sample offset (SAO) filter, or one or more other filters, e.g., an adaptive loop filter (ALF), an noise suppression filter (NSF), or any combination thereof. In one example, the loop filter unit 220 may comprise a deblocking filter, an SAO filter, and an ALF filter. The order of the filtering process can be unblocking filter, SAO and ALF. In another example, a process called luma mapping with chroma scaling (LMCS) (i.e., the adaptive in-loop reshaper) is added. This process is carried out before unlocking. In another example, the deblocking filter process can also be applied to internal edges of subblocks, e.g., affine subblock edges, ATMVP subblock edges, subblock transform (SBT) edges, and intra subpartition (ISP) edges. Although the loop filter unit 320 is shown in Figure 3 as being an in-loop filter, in other configurations, the loop filter unit 320 may be implemented as a post-loop filter.

[0190] JVET-P0080 and JVET-O0630 propose a new in-loop filter called cross-component ALF filter, also referred to here as CC-ALF or CCALF. CC-ALF operates as part of the adaptive loop filter process and makes use of luma sample values to refine each chroma component (i.e., Cr or Cb component, as a first chroma component is called a Cb component and a second component of chroma is called the Cr component). CC-ALF operates by applying a diamond-shaped filter to the Luma component for each Chroma sample of the Chroma component, and then the output filtered value is used as a correction to the output of the Chroma ALF process.

[0191] The cross-component adaptive loop filter (CC-ALF) can be used as a loop filter and as a post-processing step, respectively.

Decoded Image Buffer

[0192] The decoded video blocks 321 of an image are then stored in decoded image buffer 330, which stores the decoded images 331 as reference images for subsequent motion compensation for other images and/or for output, respectively, display.

[0193] Decoder 30 may be configured to output the decoded image 311, for example, via output 312, for presentation or viewing to a user.

Prediction

[0194] The inter prediction unit 344 may be identical to the inter prediction unit 244 (in particular the motion compensation unit) and the intra prediction unit 354 may be identical to the inter prediction unit 254 in function, and perform decisions of division or partitioning and prediction based on the partitioning and/or prediction parameters or respective information received from the encoded image data 21 (e.g., by analysis and/or decoding, e.g., by entropy decoding unit 304) . Mode application unit 360 can be configured to perform prediction (intra or inter prediction) per block based on reconstructed images, blocks or respective samples (filtered or unfiltered) to obtain prediction block 365.

[0195] When the video slice is encoded as an intra (I) coded slice, the intra prediction unit 354 of the mode application unit 360 is configured to generate the prediction block 365 for an image block of the video slice current based on an intra-signaled prediction mode and data from previously decoded blocks of the current image. When the video image is encoded as an inter coded slice (i.e., B or P), the inter prediction unit 344 (e.g., motion compensation unit) of the mode application unit 360 is configured to produce blocks of prediction 365 for a video block of the current video slice based on the motion vectors and other syntax elements received from the entropy decoding unit 304. For inter prediction, the prediction blocks may be produced from one of the reference images within one of the reference image lists. Video decoder 30 may construct lists of reference frames, List 0 and List 1, using standard construction techniques based on reference images stored in DPB 330. The same or similar may be applied to or across modalities using groups of tiles (e.g. groups of video tiles) and/or tiles (e.g. video tiles) in addition to or alternatively to slices (e.g. video slices), e.g. a video may be encoded using groups of tiles I, P or B and/or tiles.

[0196] The mode application unit 360 may be configured to determine the prediction information for a video block of the current video slice by analyzing 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 encode the video blocks of the video slice, a type of prediction slice. inter (e.g., B-slice, P-slice, or GPB-slice), construction information for one or more of the reference image lists for the slice, motion vectors for each inter-encoded video block of the slice, inter-prediction status for each inter encoded 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 to or across embodiments using groups of tiles (e.g., groups of video tiles) and/or tiles (e.g., video tiles), in addition to or alternatively to slices (e.g., video slices). video), for example, a video can be encoded using I, tile groups and/or P or B tiles.

[0197] Embodiments of the video decoder 30, as shown in Figure 3, may be configured to partition and/or decode the image using slices (also referred to as video slices), wherein an image may be partitioned or decoded using one or more more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g., CTUs) or one or more groups of blocks (e.g., tiles (H.265/HEVC and VVC) or bricks (VVC)) .

[0198] Embodiments of the video decoder 30, as shown in Figure 3, may be configured to partition and/or decode the image using groups of slices/tiles (also referred to as groups of video tiles) and/or tiles (also referred to as such as video tiles), wherein an image may be partitioned or decoded using one or more groups of slices/tiles (typically non-overlapping), and each group of slices/tiles may comprise, for example, one or more blocks (e.g. , CTUs) or one or more tiles, wherein each tile, for example, may be rectangular in shape and may comprise one or more blocks (e.g., CTUs), for example, full or fractional blocks.

[0199] Other variations of the video decoder 30 may be used to decode the encoded image data 21. For example, the decoder 30 may produce the output video stream without the loop filtering unit 320. For example, a decoder does not transform-based 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 may have the inverse quantization unit 310 and the inverse transform processing unit 312 combined into a single unit.

[0200] 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 sent to the next step. For example, after interpolation filtering, motion vector derivation, or loop filtering, an additional operation such as Cut or shift can be performed on the processing result of interpolation filtering, motion vector derivation, or loop filtering.

[0201] It should be noted that additional operations may be applied to motion vectors derived from the current block (including but not limited to affine mode control point motion vectors, sub-block motion vectors in affine modes, planes , ATMVP, temporal motion vectors, and so on). For example, the motion vector value is restricted to a predefined range according to its representation bit. If the motion vector representation bit is bitDepth, then the range is -2A(bitDepth-1) ~ 2A(bitDepth-1) -1, where “A” stands for 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 an 8x8 block) is restricted such that the max difference between the integer parts of the four MVs of the 4x4 sub-block is no more than N pixels, with a maximum of 1 pixel. Here provides two methods to constrain the motion vector according to bitDepth.

[0202] Figure 4 is a schematic diagram of a video encoding device 400 in accordance with one embodiment of the disclosure. The video encoding device 400 is suitable for implementing the disclosed embodiments as described herein. In one embodiment, the video encoding device 400 may be a decoder, such as video decoder 30 of Figure 1A, or an encoder, such as video encoder 20 of Figure 1A.

[0203] Video encoding device 400 comprises ingress ports 410 (or input ports 410) and receiver (Rx) units 420 for receiving data; a processor, logical unit, or central processing unit (CPU) 430 for processing the data; transmitting 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 encoding 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 to egress. or ingress of optical or electrical signals.

[0204] Processor 430 is implemented by hardware and software. 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, receiving units 420, transmitting units 440, egress ports 450, and memory 460. The processor 430 comprises an encoding module 470. The encoding module 470 implements the disclosed embodiments described. above. For example, the coding module 470 implements, processes, prepares or provides the various coding operations. The inclusion of the encoding module 470 therefore provides a substantial improvement to the functionality of the video encoding device 400 and effects a transformation of the video encoding device 400 to a different state. Alternatively, encoding module 470 is implemented as instructions stored in memory 460 and executed by processor 430.

[0205] Memory 460 may comprise one or more disks, tape drives, and solid state drives and may be used as an overflow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that is read during program execution. 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 access memory static random (SRAM).

[0206] Figure 5 is a simplified block diagram of an apparatus 500 that can be used as either or both the source device 12 and the destination device 14 of Figure 1A in accordance with an exemplary embodiment.

[0207] A processor 502 in apparatus 500 may be a central processing unit. Alternatively, processor 502 may be any other type of device, or multiple devices, capable of manipulating or processing information now existing or developed in the future. Although the disclosed implementations can be implemented with a single processor, as shown, for example, processor 502, advantages in speed and efficiency can be achieved by using more than one processor.

[0208] A memory 504 in apparatus 500 may be a read-only memory device (ROM) or a random access memory device (RAM) in one implementation. Any other suitable type of storage device may be used as memory 504. Memory 504 may include code and data 506 that are accessed by processor 502 using a bus 512. Memory 504 may further include an operating system 508 and application programs 510, the application programs 510 including at least one program that allows the processor 502 to perform the methods described herein. For example, application programs 510 may include applications 1 through N, which further include a video encoding application that performs the methods described herein.

[0209] Apparatus 500 may also include one or more output devices, such as a display 518. Display 518 may be, in one example, a touch-sensitive display that combines a display with a touch-sensitive element that is operable to detect touch inputs. Display 518 may be coupled to processor 502 via bus 512.

[0210] Although represented herein as a single bus, bus 512 of apparatus 500 may be composed of multiple buses. Furthermore, secondary storage 514 may be directly coupled to other components of apparatus 500 or may be accessed via a network and may 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.

Detailed description of the embodiments of the present disclosure

[0211] Video coding can be performed based on color space and color format. For example, color video plays an important role in multimedia systems, where multiple color spaces are used to represent colors efficiently. A color space specifies colors with numerical values using multiple components. A popular color space is the RGB color space, where color is represented as a combination of three primary color component values (i.e., red, green, and blue). For color video compression, the YCbCr color space has been widely used, as described in A. Ford and A. Roberts, “Color space conversions,” University of Westminster, London, Tech. Rep., August 1998.

[0212] YCbCr can be easily converted from the RGB color space through a linear transformation and the redundancy between different components, i.e., cross-component redundancy, is significantly reduced in the YCbCr color space. An advantage of YCbCr is backward compatibility with black and white TV, as the Y signal transmits luminance information. Furthermore, chrominance bandwidth can be reduced by subsampling the Cb and Cr components in the 4:2:0 chroma sampling format with significantly less subjective impact than subsampling in the RGB color space. Because of these advantages, YCbCr has been the main color space in video compression. There are also other color spaces such as YCoCg used in video compression. In this disclosure, regardless of the actual color space used, the luma (or L or Y) and two chroma (Cb and Cr) are used to represent the three color components in the video compression scheme.

[0213] For example, when the chroma format sampling frame is 4:2:0 sampling, each of the two chroma arrays is half the height and half the width of the luma array. The nominal vertical and horizontal relative locations of the luma and chroma samples in the images are shown in Figure 9A. Figure 9B illustrates an example of 4:2:0 sampling. Figure 9B illustrates an example of a co-located luma block and a chroma block. If the video format is YUV4:2:0, there will be one 16x16 luma block and two 8x8 chroma blocks.

[0214] Specifically, a coding block or a transform block contains one luma block and two chroma blocks.

[0215] As shown, the luma block contains four times as many samples as the chroma block. Specifically, the chroma block contains N number of samples by N number of samples, while the luma block contains 2N number of samples by 2N number of samples. Therefore, the luma block is four times the resolution of the chroma block. For example, when the YUV4:2:0 format is used, luma samples can be reduced by a factor of four (for example, width by two and height by two). YUV is a color coding system that employs a color space in terms of luma components Y and two chrominance components U and V.

Image header:

[0216] The image header concept has recently been introduced into the VVC standard (as presented in JVET-P1006, P0095, P0120, P0239). See section 7.3.2.6 in JVET-P2001-VE for image header syntax.

[0217] In the current VVC design, a mandatory image header concept is proposed to be transmitted once per image as the first VCL NAL unit of an image. The current VVC design also moves some of the syntax elements currently present in the slice header to this image header. Syntax elements that functionally only need to be passed once per image are moved to the image header instead of being passed multiple times for a given image, for example, syntax elements in the slice header are passed once per slice. There is a benefit noted when moving syntax elements from the slice header, as the computation required for slice header processing can be a limiting factor for overall throughput.

[0218] For the adaptive loop filter (ALF), the following syntax elements (ALF-related syntax elements) have been introduced into the image header: 7.3.2.6 Image header RBSP syntax

[0219] Here, the syntax elements are pic_alf_enabled_present_flag, pic_alf_enabled_flag, pic_num_alf_aps_ids_luma, pic_alf_aps_id_luma[i], pic_alf_chroma_idc, pic_alf_aps_id_chroma. These syntax elements are provided in the image header, where their presence potentially depends on other syntax elements that have been signaled previously or otherwise. For example, sps_alf_enabled_flag and ChromaArrayType are other syntax elements.

[0220] In the following, any syntax element indicated with a descriptor in a table and/or provided in bold letters is a syntax element that is signaled or provided in the current syntax structure.

[0221] In the slice header, the following syntax changes are introduced for ALF 7.3.7.1 General slice header syntax

[0222] The semantics of the ALF image header entries and slice header entries are as follows:

[0223] pic_alf_enabled_present_flag equal to 1 specifies that pic_alf_enabled_flag, pic_num_alf_aps_ids_luma, pic_alf_aps_id_luma [i], pic_alf_chroma_idc and pic_alf_aps_id_chroma are present in the PH. pic_alf_enabled_present_flag equal to 0 specifies that pic_alf_enabled_flag, pic_num_alf_aps_ids_luma, pic_alf_aps_id_luma[i], pic_alf_chroma_idc, and pic_alf_aps_id_chroma are not present in the PH. When pic_alf_enabled_present_flag is not present, it is inferred to be equal to 0.

[0224] pic_alf_enabled_flag equal to 1 specifies that the adaptive loop filter is enabled for all slices associated with the PH and can be applied to the Y, Cb, or Cr color component in the slices. pic_alf_enabled_flag equal to 0 specifies that the adaptive loop filter can be disabled for one, or more, or all slices associated with the PH. When not present, pic_alf_enabled_flag is inferred to be equal to 0.

[0225] pic_num_alf_aps_ids_luma specifies the number of ALF APSs to which the PH-associated slices refer.

[0226] pic_alf_aps_id_luma [i] specifies the adapter_parameter_set_id of the ith ALF APS to which the luma component of the slices associated with the PH refers.

[0227] The value of alf_luma_filter_signal_flag of the APS NAL unit having aps_params_type equal to ALF_APS and adapter_parameter_set_id equal to pic_alf_aps_id_luma [i] must be equal to 1.

[0228] pic_alf_chroma_idc equal to 0 specifies that the adaptive loop filter is not applied to the Cb and Cr color components. pic_alf_chroma_idc equal to 1 indicates that the adaptive loop filter is applied to the Cb color component. pic_alf_chroma_idc equal to 2 indicates that the adaptive loop filter is applied to the Cr color component. pic_alf_chroma_idc equal to 3 indicates that the adaptive loop filter is applied to the Cb and Cr color components. When pic_alf_chroma_idc is not present, it is inferred to be equal to 0.

[0229] pic_alf_aps_id_chroma specifies the adapter_parameter_set_id of the ALF APS to which the chroma component of the slices associated with the PH refers.

[0230] The value of alf_chroma_filter_signal_flag of the APS NAL unit having aps_params_type equal to ALF_APS and adapter_parameter_set_id equal to pic_alf_aps_id_chroma must be equal to 1.

[0231] slice_alf_enabled_flag equal to 1 specifies that the adaptive loop filter is enabled and can be applied to the Y, Cb, or Cr color component in a slice. slice_alf_enabled_flag equal to 0 specifies that the adaptive loop filter is disabled for all color components in a slice. When not present, the value of slice_alf_enabled_flag is inferred to be equal to pic_alf_enabled_flag.

[0232] slice_num_alf_aps_ids_luma specifies the number of ALF APSs to which the slice refers. When slice_alf_enabled_flag is equal to 1 and slice_num_alf_aps_ids_luma is not present, the value of slice_num_alf_aps_ids_luma is inferred to be equal to the value of pic_num_alf_aps_ids_luma.

[0233] slice_alf_aps_id_luma [i] specifies the adapter_parameter_set_id of the ith ALF APS to which the slice's luma component refers. The TemporalId of the APS NAL unit having aps_params_type equal to ALF_APS and adapter_parameter_set_id equal to slice_alf_aps_id_luma[i] must be less than or equal to the TemporalId of the encoded slice NAL unit. When slice_alf_enabled_flag is equal to 1 and slice_alf_aps_id_luma[i] is not present, the value of slice_alf_aps_id_luma[i] is inferred to be equal to the value of pic_alf_aps_id_luma[i].

[0234] The value of alf_luma_filter_signal_flag of the APS NAL unit having aps_params_type equal to ALF_APS and adapter_parameter_set_id equal to slice_alf_aps_id_luma [i] must be equal to 1.

[0235] slice_alf_chroma_idc equal to 0 specifies that the adaptive loop filter is not applied to the Cb and Cr color components. slice_alf_chroma_idc equal to 1 indicates that the adaptive loop filter is applied to the Cb color component. slice_alf_chroma_idc equal to 2 indicates that the adaptive loop filter is applied to the Cr color component. slice_alf_chroma_idc equal to 3 indicates that the adaptive loop filter is applied to the Cb and Cr color components. When slice_alf_chroma_idc is not present, it is inferred to be equal to pic_alf_chroma_idc.

[0236] slice_alf_aps_id_chroma specifies the adapter_parameter_set_id of the ALF APS to which the slice's chroma component refers. The TemporalId of the APS NAL unit having aps_params_type equal to ALF_APS and adapter_parameter_set_id equal to slice_alf_aps_id_chroma must be less than or equal to the TemporalId of the encoded slice NAL unit. When slice_alf_enabled_flag is equal to 1 and slice_alf_aps_id_chroma is not present, the value of slice_alf_aps_id_chroma is inferred to be equal to the value of pic_alf_aps_id_chroma.

[0237] The value of alf_chroma_filter_signal_flag of the APS NAL unit having aps_params_type equal to ALF_APS and adapter_parameter_set_id equal to slice_alf_aps_id_chroma must be equal to 1.

[0238] As described above, when all slices have the same ALF filtering data, instead of transmitting the ALF filtering data separately in each of the slice headers, the common ALF filtering data in all slices is transmitted only once in the image header and as a result, all slices inherit the ALF filtering data from the image header. In this way, the overhead of the slice header (in terms of number of bits) is reduced.

[0239] The present disclosure brings together all of the common syntax elements of CCALF that are signaled in each slice header of an image and are defined in the image header. The present disclosure attempts to extend the same ALF signaling principle also to cross-component ALF (CCALF). Currently, for CCALF, each slice header must convey the following information in the conventional way: 7.3.7.1 General slice header syntax

[0240] Therefore, each slice must convey all of the above syntax elements, even if the information is the same in all slices of a given image.

[0241] Therefore, to reduce slice header overhead, the present invention defines image header entries for CCALF as well. 1.1 Technical problem(s) to be resolved by this disclosure

[0242] The present disclosure introduces image header entries to CCALF to reduce slicing overhead. As shown in Figure 7, slice 1 through slice N contain the same CCALF 7001 filter information. Therefore, each slice header has to transmit the same data resulting in redundancy and slice bit signaling overhead. As shown in Figure 8, to remove this redundancy in the CCALF data, image header entries 8001 are introduced for CCALF that define the common CCALF data (also called CCALF-related information) and all slices can then inherit this information common 8002. Therefore, this removes redundancy in signaling and reduces the overhead of parsing slice headers. 1.2 Embodiments of the technical implementation of the present disclosure

[0243] Note that each of the embodiments disclosed below as "alternatives" may be provided in combination with any of the other (alternative) embodiments and may be specifically implemented using any of the devices described above, such as an encoder and/or a decoder as referred to in the figures above. 1.2.1. Alternative Modality 1

[0244] In the first step, a new sequence parameter set (SPS) syntax element called “second syntax element” (denoted below, for example, with sps_ccalf_enabled_flag) is introduced that controls whether CCALF is enabled or not. The syntax is shown below: The second syntax element (sps_ccalf_enabled_flag) decouples the ALF operation and the CCALF operation completely and therefore allows ALF and CCALF to be turned on and off separately at the sequence level. 7.3.2.3 String Parameter Set RBSP Syntax

[0245] Here, sps_alf_enabled_flag is an example of a first syntax element that is also provided in the SPS level syntax. The first and second syntax element can be signaled independently of each other, as provided exemplarily in the table above. However, as for example provided in alternative embodiment 5 below, the second syntax element may also be signaled depending, for example, on a value that the first syntax element has or receives.

[0246] The new image header entries (marked in bold italics) are shown below: 7.3.2.6 Image Header RBSP Syntax

[0247] Here, additional syntax elements are introduced into the image header, wherein these additional syntax elements can only be present if the first and/or second syntax elements take on specific values. This is indicated with the “if” syntax, depending on the value of the first syntax element and/or the second syntax element.

[0248] Specifically, in the image header, a third syntax element (indicated here with pic_ccalf_enabled_flag) may be provided depending on the value of the second syntax element. This syntax element can indicate (as explained below) whether CCALF should be enabled for the current image.

[0249] A fourth syntax element (such as pic_cross_component_alf_cb_enabled_flag) may be additionally provided in the image header depending on the second syntax element.

[0250] Depending, for example, on the value of the second syntax element and/or the value of the third syntax element and/or the fourth syntax element, a fifth syntax element may be provided, such as pic_cross_component_alf_cb_aps_id. Additionally, a sixth syntax element, denoted here with pic_cross_component_cb_filters_signalled_minus1 , may be provided in the image header, potentially also depending on the second syntax element and/or the third syntax element and/or the fourth syntax element.

[0251] In parallel to this, a seventh syntax element, denoted above with pic_cross_component_alf_cr_enabled_flag, may be provided, depending on the second syntax element and/or the third syntax element.

[0252] Depending, for example, on the value of the seventh syntax element, but potentially also depending on the second syntax element and/or the third syntax element, an eighth (such as pic_cross_component_alf_cr_aps_id) and/or a ninth syntax element (such as pic_cross_component_cr_filters_signalled_minus1) can be provided.

[0253] The meaning of the first to ninth syntax element and also the meaning of the tenth to fourteenth syntax element specified below will be explained later.

[0254] The slice header syntax is as follows: 7.3.7.1 General slice header syntax

[0255] As provided above, in some embodiments, additional syntax elements provided in the slice header syntax may be provided only if the first and/or second syntax element and/or one or more additional syntax elements provided in the header images assume appropriate values.

[0256] Specifically, as shown above, a tenth syntax element, such as slice_cross_component_alf_cb_enabled_flag , may be provided depending on the value of the second syntax element and potentially also depending on a fourteenth syntax element (optionally provided at the SPS level and indicated here with ChromaArrayType) not being equal to 0. Additionally, an eleventh syntax element that is indicated above with slice_cross_component_alf_cb_aps_id may be provided, depending on the value of the second syntax element and/or depending on the value of the tenth syntax element.

[0257] Correspondingly, a twelfth syntax element, such as slice_cross_component_alf_cr_enabled_flag , may be provided depending on the value of the second syntax element and potentially also depending on the fourteenth syntax element not being equal to 0. Additionally, a thirteenth syntax element of syntax can be provided, indicated above with slice_cross_component_alf_cr_aps_id , depending on the value of the second syntax element and/or depending on the value of the twelfth syntax element.

[0258] However, it is also included that the syntax elements (specifically the tenth through thirteenth syntax elements) provided in the slice header may be present independently of the value of other syntax elements, such as the second syntax element or the fourteenth syntax element. Specifically, it may be provided that syntax elements belonging to CC-ALF in the slice header (such as, for example, the tenth through thirteenth syntax elements) take a default value whether the first syntax element or the second syntax element or other syntax element indicates that CC-ALF is not enabled.

[0259] The semantics of the newly introduced syntax elements are as follows:

[0260] The second syntax element is indicated here with sps_ccalf_enabled_flag. This is just an example and does not limit the revelation. In embodiments, the value of the second syntax element equal to 0 specifies that the cross-component adaptive loop filter is disabled for a current video sequence. The second syntax element's value of 1 specifies that the cross-component adaptive loop filter is enabled for a current video sequence.

[0261] pic_ccalf_enabled_present_flag equal to 1 specifies that pic_ccalf_enabled_flag, pic_cross_component_alf_cb_enabled_flag, pic_cross_component_alf_cb_aps_id, pic_cross_component_alf_cb_filter_count_minus1, pic_cross_component_alf_cr_enabled_flag, alf_cr_aps_id and pic_cross_component_alf_cr_filter_count_minus1 are present in the PH (image header). pic_alf_enabled_present_flag equal to 0 specifies that pic_ccalf_enabled_flag, pic_cross_component_alf_cb_enabled_flag, pic_cross_component_alf_cb_aps_id, pic_cross_component_alf_cb_filter_count_minus1, pic_cross_component_alf_cr_enabled_flag, s_id and pic_cross_component_alf_cr_filter_count_minus1 are not present in the PH. When pic_ccalf_enabled_present_flag is not present, it is inferred to be equal to 0.

[0262] The value of the third syntax element (denoted here with pic_ccalf_enabled_flag) equal to 1 specifies that the cross-component adaptive loop filter is enabled for all slices associated with the PH and can be applied to the Cb or Cr color component in the slices . The value of the third syntax element equal to 0 specifies that the cross-component adaptive loop filter can be disabled for one, or more, or all slices associated with the PH (image header). When not present, the value of the third syntax element can be inferred to be 0.

[0263] A fourth syntax element was mentioned above and may be denoted here with pic_cross_component_alf_cb_enabled_flag . The fourth syntax element's value of 0 specifies that the cross-component Cb filter is not applied to the Cb color component of all slices associated with the PH. When the value of the fourth syntax element is equal to 1, it indicates that the cross-component Cb filter is applied to the Cb color component of all slices associated with the PH. When the fourth syntax element is not present, it is inferred to be equal to 0.

[0264] A fifth syntax element may be denoted here with pic_cross_component_alf_cb_aps_id . The fifth syntax element specifies the adapter_parameter_set_id which is the Cb color component of all slices associated with the PH.

[0265] A sixth syntax element may be denoted here with pic_cross_component_cb_filters_signalled_minus1 . The value of the sixth syntax element plus 1 specifies the number of cross-component Cb filters of all slices associated with the PH. The value of the sixth syntax element must be in the range 0 to 3.

[0266] When the fourth syntax element is equal to 1, it is a bitstream compliance requirement that the sixth syntax element must be less than or equal to the value of alf_cross_component_cb_filters_signalled_minus1 in the ALF APS referred to by the fifth syntax element of the current image .

[0267] A seventh syntax element mentioned above is indicated with pic_cross_component_alf_cr_enabled_flag. The value of the seventh syntax element of 0 specifies that the cross-component Cr filter is not applied to the Cr color component of all slices associated with the PH. The value of the seventh syntax element equal to 1 indicates that the cross-component Cr filter is applied to the Cr color component of all slices associated with the PH. When the seventh syntax element is not present, it is inferred to be equal to 0.

[0268] An eighth syntax element was also mentioned and exemplarily denoted with pic_cross_component_alf_cr_aps_id. The value of the eighth syntax element is intended to specify the adapter_parameter_set_id that the Cr color component of all slices associated with the PH.

[0269] Furthermore, a ninth syntax element is mentioned which can be denoted with pic_cross_component_cr_filters_signalled_minus1 . The value of the ninth syntax element plus 1 specifies the number of cross-component Cr filters of all slices associated with the PH. The value of the ninth syntax element must be in the range 0 to 3.

[0270] When the value of the seventh syntax element is equal to 1, it is a bitstream compliance requirement that the value of the ninth syntax element must be less than or equal to the value of alf_cross_component_cr_filters_signalled_minus1 in the ALF APS referred to by the eighth syntax element. current image syntax.

[0271] The semantics of the CCALF slice header syntax elements are refined as follows:

[0272] slice_ccalf_enabled_flag equal to 1 specifies that the cross-component adaptive loop filter is enabled and can be applied to the Cb or Cr color component in a slice. slice_alf_enabled_flag equal to 0 specifies that the cross-component adaptive loop filter is disabled for all color components in a slice. When not present, the value of slice_ccalf_enabled_flag is inferred to be equal to the third syntax element.

[0273] The tenth syntax element mentioned above can be indicated with slice_cross_component_alf_cb_enabled_flag and it can be provided that the value of the tenth syntax element equal to 0 specifies that the cross-component Cb filter is not applied to the Cb color component. The tenth syntax element of 1 indicates that the cross-component Cb filter is applied to the Cb color component. When the tenth syntax element is not present, it is inferred to be equal to the fourth syntax element (such as pic_cross_component_alf_cb_enabled_flag).

[0274] An eleventh syntax element mentioned above may be referred to as slice_cross_component_alf_cb_aps_id. The value of the eleventh syntax element specifies the adapter_parameter_set_id that the slice's Cb color component refers to.

[0275] When the tenth syntax element has a value that is equal to 1, it is a bitstream compliance requirement that, for all slices of the current image, the ALF APS referred to by the eleventh syntax element is the same .

[0276] When the tenth syntax element is equal to 1 and the eleventh syntax element is not present, the value of the eleventh syntax element is inferred to be equal to the value of the fifth syntax element.

[0277] slice_cross_component_cb_filters_signalled_minus1 plus 1 specifies the number of cross-component Cb filters. The value of slice_cross_component_cb_filters_signalled_minus1 must be in the range 0 to 3.

[0278] When the tenth syntax element is equal to 1, it is a bitstream compliance requirement that slice_cross_component_cb_filters_signalled_minus1 must be less than or equal to the value of alf_cross_component_cb_filters_signalled_minus1 in the ALF APS referred to by the eleventh of the current slice.

[0279] When the tenth syntax element is equal to 1 and the eleventh is not present, the value of slice_cross_component_cb_filters_signalled_minus1 is inferred to be equal to the value of pic_cross_component_cb_filters_signalled_minus1

[0280] A twelfth mentioned syntax element may be referred to as slice_cross_component_alf_cr_enabled_flag . The twelfth syntax element value of 0 specifies that the cross-component Cr filter is not applied to the Cr color component. The value of the twelfth syntax element equal to 1 indicates that the cross-component adaptive loop filter is applied to the Cr color component. When the twelfth syntax element is not present, it is inferred to be the same as the seventh syntax element, such as pic_cross_component_alf_cr_enabled_flag .

[0281] A thirteenth syntax element was mentioned and may be further referred to as slice_cross_component_alf_cr_aps_id . The value of the thirteenth syntax element specifies the adapter_parameter_set_id that the slice's Cr color component refers to.

[0282] When the value of the twelfth syntax element is equal to 1, it is a bitstream compliance requirement that, for all slices of the current image, the ALF APS referred to by the thirteenth syntax element is the same.

[0283] When the value of the twelfth syntax element is equal to 1 and the thirteenth syntax element is not present, the value of the thirteenth syntax element is inferred to be equal to the value of the eighth syntax element.

[0284] slice_cross_component_cr_filters_signalled_minus1 plus 1 specifies the number of cross-component Cr filters. The value of slice_cross_component_cr_filters_signalled_minus1 must be in the range 0 to 3.

[0285] When the twelfth syntax element is equal to 1, it is a bitstream compliance requirement that slice_cross_component_cr_filters_signalled_minus1 must be less than or equal to the value of alf_cross_component_cr_filters_signalled_minus1 in the referenced ALF APS referred to by the thirteenth syntax element of the current slice.

[0286] When the twelfth syntax element is equal to 1 and the thirteenth syntax element is not present, the value of slice_cross_component_cr_filters_signalled_minus1 is inferred to be equal to the value of pic_cross_component_cr_filters_signalled_minus1.

Alternative Modality 2:

[0287] In alternative 2, the second syntax element at the SPS level (such as sps_ccalf_enabled_flag) is no longer introduced, therefore the first syntax element (such as sps_alf_enabled_flag) also controls the application of the ccalf filter.

[0288] The syntax for alternative 2 is as follows: 7.3.2.6 Image Header RBSP Syntax

[0289] In this second embodiment, the second syntax element, which may be sps_ccalf_enabled_flag, may be provided at the SPS level. Whether or not CCALF is to be enabled can, in this embodiment, be specified based on an additional syntax element, such as pic_ccalf_enabled_present_flag, which specifies whether CCALF than other syntax elements belonging to CCALF are present and from which it can be additionally obtained that , for the current image to which pic_ccalf_enabled_present_flag belongs, CCALF must be enabled.

[0290] The slice header syntax is as follows: 7.3.7.1 General slice header syntax

[0291] As seen above, the presence of syntax elements in the slice header, such as slice_ccalf_enabled_flag, slice_cross_component_alf_cb_enabled_flag, slice_cross_component_alf_cb_aps_id, slice_cross_component_cb_filters_signalled_minus1, slice_cross_component_alf_cr_enabled_flag, _alf_cr_aps_id and slice_cross_component_cr_filters_signalled_minus1 , and/or the tenth to thirteenth syntax elements already mentioned above may depend on the first syntax element provided at the SPS level, such as sps_alf_enabled_flag, and a syntax element provided in the image header, such as pic_ccalf_enabled_present_flag, and potentially another syntax element provided in the slice header, such as slice_ccalf_enabled_flag.

Alternative Modality 3:

[0292] The other alternative for the CCALF image header entries is as follows: in this pic_alf_enabled_present_flag alternative, pic_alf_enabled_flag controls the CCALF image header and CCALF slice header entries, respectively. 7.3.2.6 Image Header RBSP Syntax

[0293] The slice header syntax is as follows: 7.3.7.1 General slice header syntax

[0294] It can be noted that !(0) = 1 or !(1) = 0.

Alternative Modality 4:

[0295] Since, in the current design of CCALF, there is a restriction that slice_cross_component_alf_cb_aps_id, slice_cross_component_alf_cr _aps_id must be the same in all slices, it makes no sense to repeat this syntax element in the slice header, but just flag the pic_cross_component_alf_cb_aps_id and pic_cross_component_alf_cr_aps_id in the image header. The values of the slice_cross_component_alf_cb_aps_id and slice_cross_component_alf_cr syntax elements can then be inferred to be the same as pic_cross_component_alf_cb_aps_id and pic_cross_component_alf_cr_aps_id. Thus, the amount of information in the bit stream can be further reduced.

[0296] The possible syntax is as follows: 7.3.2.6 Image Header RBSP Syntax

[0297] Here, the other syntax elements that belong to CCALF (i.e., at least the syntax elements that comprise a ccalf or cross_component_alf or cc_alf element are provided depending on a value of the second syntax element signaled at the SPS level, that is, in this modality sps_ccalf_enabled_flag.

[0298] Specifically, depending on the value of the second syntax element, a third syntax element, such as pic_ccalf_enabled_flag, may be provided in the image header, wherein this third syntax element may indicate whether CCALF is enabled for the image slices current.

[0299] Additionally, a fourth syntax element, such as pic_cross_component_alf_cb_enabled_flag, and a seventh syntax element, such as pic_cross_component_alf_cb_enabled_flag, may be provided in the image header depending on the value of the second syntax element.

[0300] The slice header syntax may be as follows: 7.3.7.1 General slice header syntax

[0301] Also for this embodiment, it may be provided that the syntax elements in the slice header that belong to CCALF are provided depending on the value of the second syntax element provided at the SPS level and/or depending on a value of one or more syntax elements belonging to CCALF provided in the image header, such as pic_ccalf_enabled_present_flag.

[0302] slice_cross_component_alf_cb_aps_id can always be inferred to be the same value as pic_cross_component_alf_cb_aps_id.

[0303] slice_cross_component_alf_cr_aps_id can always be inferred to be the same value as pic_cross_component_alf_cr_aps_id.

[0304] The other possible syntax is as follows: 7.3.2.6 Image Header RBSP Syntax

[0305] In the syntax according to the table above, the presence of syntax elements that belong to CCALF depends on the value of the first syntax element provided at the SPS level, such as sps_alf_enabled_flag. The second syntax element, such as sps_ccalf_enabled_flag, may or may not be provided at the SPS level in this embodiment.

[0306] The slice header syntax may be as follows: 7.3.7.1 General slice header syntax

[0307] slice_cross_component_alf_cb_aps_id is always inferred to be the same as the value of pic_cross_component_alf_cb_aps_id.

[0308] slice_cross_component_alf_cr_aps_id is always inferred to be the same as the value of pic_cross_component_alf_cr_aps_id.

[0309] The other possible syntax is as follows: Image Header RBSP Syntax

[0310] The slice header syntax is as follows: 7.3.7.1 General slice header syntax

[0311] In this embodiment, slice_cross_component_alf_cb_aps_id is always inferred to be the same as the value of pic_cross_component_alf_cb_aps_id.

[0312] In this embodiment, a twelfth syntax element, such as slice_cross_component_alf_cr_aps_id, is always inferred to be the same as the value of the eighth syntax element, such as pic_cross_component_alf_cr_aps_id).

[0313] Alternative Modality 5:

[0314] The other alternative syntax is the one possible below: In this syntax, CCALF parameters are signaled conditionally based on a value of the second syntax element, as already mentioned above. This second syntax element can be provided as or can include a flag, such as sps_ccalf_enabled_flag. String Parameter Set RBSP Syntax

[0315] As seen in the table above, the second syntax element sps_ccalf_enabled_flag is provided depending on the value of the first syntax element sps_alf_enabled_flag, and optionally depending on a fourteenth syntax element such as ChromaArrayType. Specifically, the second syntax element may, in some embodiments, be signaled if the fourteenth syntax element takes on a non-zero value. 7.3.2.3 String Parameter Set RBSP Syntax

[0316] Notes: ChromaArrayType != 0, that is, it is not a luma component and Cb, Cr a chroma component

[0317] ChromaArrayType indicates chroma sampling relative to luma sampling as specified in the following table.

[0318] In monochromatic sampling there is only one sample arrangement, which is nominally considered the luma arrangement.

[0319] In 4:2:0 sampling, each of the two chroma arrays is half the height and half the width of the luma array.

[0320] In 4:2:2 sampling, each of the two chroma arrays is the same height and half the width of the luma array.

[0321] In 4:4:4 sampling, each of the two chroma arrays has the same height and width as the luma array.

[0322] As provided in the table above, the second syntax element is provided if the first syntax element indicates “true”, that is, in case the first syntax element is sps_alf_enabled_flag and indicates that ALF should be enabled. Additionally, the second syntax element is provided if the fourteenth syntax element has a value other than 0. 1.1.1.1 String Parameter Set RBSP Syntax 7.3.3.2 General restriction information syntax

[0323] Notes:

[0324] !(0) = 1

[0325] !(1) = 0 7.3.2.4 Image Parameter Set RBSP Syntax Image Header RBSP Syntax

[0326] alf_present_in_ph_flag equal to 1 specifies that syntax elements to enable the use of ALF may be present in the PHs (image headers) referring to the PPS. alf_present_in_ph_flag equal to 0 specifies that syntax elements to enable the use of ALF can be present in the PPS-referred slice headers. 7.3.2.6 Image Header RBSP Syntax

[0327] As provided in the table above, the presence of other syntax elements belonging to CCALF in the image header, such as a fourth syntax element (such as pic_cross_component_alf_cb_enabled_flag) and a seventh syntax element (such as, for example, pic_cross_component_alf_cr_enabled_flag), may depend on the presence and/or value of the second syntax element. The presence of a fifth syntax element such as pic_cross_component_alf_cb_aps_id may then depend on the second syntax element and/or the presence and/or value of the fourth syntax element, while the presence and/or value of an eighth syntax element such as pic_cross_component_alf_cr_aps_id , may depend on the presence and/or value of the second syntax element and/or the presence and/or value of the seventh syntax element. 7.3.7.1 General slice header syntax

[0328] In the table above, other syntax elements belonging to CCALF may additionally depend on the presence and/or value of the second syntax element. For example, a tenth syntax element, such as slice_cross_component_alf_cb_enabled_flag, may be provided depending on the second syntax element. Depending on the presence and/or value of this tenth syntax element and/or the second syntax element, an eleventh syntax element, such as slice_cross_component_alf_cb_aps_id, may be provided. Additionally, a twelfth syntax element such as slice_cross_component_alf_cr_enabled_flag may be provided in the slice header depending on the value of the second syntax element. Depending on the presence and/or value of the twelfth syntax element and/or depending on the second syntax element, a thirteenth syntax element, such as slice_cross_component_alf_cr_aps_id, may be provided in the slice header.

[0329] Notes:

[0330] !(0) = 1

[0331] !(1) = 0

[0332] if(sps_alf_enabled_flag && !alf_present_in_ph_flag) means “if sps_alf_enabled_flag is true (and) if alf_present_in_ph_flag is false)” Slice header syntax General slice header syntax

[0333] In the table above, some elements are shown as strikethrough. This means that, in a first embodiment, these elements may be present. In an alternative embodiment, these elements can be canceled, leaving the remaining syntax as is. For example, the ChromaArrayType element may not be provided. Correspondingly, any dependency on this element, including also the conditional presence of other syntax elements, can be provided in a first embodiment. In an alternative embodiment, this dependency does not exist, resulting, for example, in the presence of syntax elements in any case, while in the alternative embodiment they were present only if ChromaArrayType had a specific value.

[0334] Likewise, syntax elements such as slice_cross_component_cr_filters_signalled_minus1 and slice_cross_component_cb_filters_signalled_minus1 may not be provided (regardless of whether a syntax element such as ChromaArrayType is present).

[0335] The semantics of the newly introduced syntax elements are as follows:

[0336] The value of the second syntax element, such as (sps_ccalf_enabled_flag) equal to 0 specifies that the cross-component adaptive loop filter is disabled. The first syntax element's value of 1 specifies that the cross-component adaptive loop filter is enabled. This can also be provided in reverse, i.e. if the second syntax element has a value of 1, CCALF can be disabled while if the second syntax element has a value of 0, CCALF can be enabled.

[0337] no_ccalf_constraint_flag equal to 1 specifies that the first syntax element (such as sps_ccalf_enabled_flag) must be equal to 0. no_ccalf_constraint_flag equal to 0 does not impose such a restriction.

[0338] In embodiments, a filtering process is presented as below in detail.

[0339] For the embodiments discussed above, some general observations are made below regarding the meaning of specific syntax elements and the consequences of those syntax elements taking on specific values. The disclosure set forth below is intended to be encompassed by any of the above modalities, specifically alternative modalities 1 to 5.

8.8 In-loop filter process 8.8.1 General

[0340]

[0341] 4. When the first syntax element (indicated above as sps_alf_enabled_flag) equals 1, the following applies: - When the second syntax element (such as sps_ccalf_enabled_flag) equals 1, the image sample array reconstructed (before adaptive loop filter) SL' is set equal to the SL reconstructed image sample array - The adaptive loop filter process as specified in clause 8.8.5.1 is invoked with the SL reconstructed image sample array, and when the fourteenth syntax element (in the tables above, this is denoted as ChromaArrayType) is not equal to 0, the SCb and SCr arrays as inputs, and the modified reconstructed image sample array S'L, and when the fourteenth element syntax is not equal to 0, the S'Cb and S'Cr arrangements after the adaptive loop filter as outputs. - The S'L array and, when the fourteenth syntax element is not equal to 0, the S'Cb and S'Cr arrays are assigned to the SL array, and when the fourteenth syntax element is not equal to 0, the SCb and SCr arrays (which represent the decoded image), respectively. - When the second syntax element (such as sps_ccalf_enabled_flag) is equal to 1, the following applies: - The cross-component adaptive loop filter process as specified in the xxxx clause is invoked with the SL reconstructed image sample array, and then when the fourteenth syntax element (such as ChromaArrayType) is not equal to 0, the SCb and SCr arrays as inputs, and the modified reconstructed image sample array S'L, and when the fourteenth syntax element is not equal to 0, the S'Cb and S'Cr arrays after the cross-component adaptive loop filter as outputs. - The S'L array and, when the fourteenth syntax element is not equal to 0, the S'Cb and S'Cr arrays are assigned to the SL array, and when the fourteenth syntax element is not equal to 0, the SCb and SCr arrays (which represent the decoded image), respectively.

[0342] It should be noted that the present invention is not limited to the alternatives presented here, but rather the invention in a very general way allows the CCALF data present in the slice header to be conditionally signaled in the image header. The main advantage of using CCALF data in the image header is that the signal overhead in the slice header is reduced.

[0343] The invention also covers the case where a particular CCALF syntax element signaled in the slice header has the same value in all slices (e.g., due to some bitstream compliance requirements), then that syntax element Specific syntax is no longer flagged in the slice header, but rather flagged only once in the image header associated with all slices.

[0344] The cross-component adaptive loop filter (CC-ALF) can be used as a loop filter and as a post-processing step, respectively.

[0345] CC-ALF uses luma sample values to refine each chroma component. CC_ALF is applied to the luma samples to derive a correction factor for chroma sample filtering.

[0346] JVET-P0080 and JVET-O0630 propose a new in-loop filter called cross-component ALF filter. CC-ALF operates as part of the adaptive loop filter process and makes use of luma sample values to refine each chroma component (Cr or Cb component). The tool is controlled by information in the bitstream, and this information includes (a) filter coefficients for each chroma component and (b) a mask that controls filter application to sample blocks. Filter coefficients are signaled at the adaptation parameter set (APS), while block sizes and mask are signaled at the slice level.

[0347] It can be understood that Mask is a bit (0 or 1). Here the mask indicates whether the sample block should be filtered or not (mask = 1 means it is filtered) and (mask=0 means it is not filtered). Basically APS ports the coefficients to ALF and other information.

[0348] The general design of the CC-ALF is shown in Figure 6 (a), Figure 6(b) and Figure 6(c). This general project can be applied to any of the above modalities that refer to issues related to CC-ALF. Specifically, what is described here is intended to be encompassed by each of alternative embodiments 1 to 5.

[0349] Filter placement is as shown in Figure 6a (see left side). The shape of the filter is shown in Figures 6b and 6c.

[0350] CC-ALF operates by applying a diamond-shaped linear filter (Figure 6b and 6c) to the luma channel for each chroma component, which is expressed as , where (%, y) is chroma component location í being refined (xc,yc) is luma location based on (%, y) 5, is luma filter support for chroma component i Ci( x0,y0) represents the filter coefficients

[0351] Note that there is a first chroma component (such as the cb color component) when i=1 for the i chroma component, and there is a second chroma component (such as the cr color component) when i=2 for the chroma component i.

[0352] Key features of CC-ALF include: • The luma location (xc,yc), around which the support region is centered, is calculated based on the spatial scaling factor between the luma and chroma planes . Basically, CCALF uses the Luma samples to refine the Chroma samples. Therefore, the filter is applied to the Luma samples and then the correction factor for Chroma is derived. • All filter coefficients are transmitted in the APS and have a dynamic range of 8 bits. • An APS can be referenced in the slice header. • The CC-ALF coefficients used for each chroma component of a slice are also stored in a buffer corresponding to a temporal sublayer. Reuse of these sets of temporal subshell filter coefficients is facilitated using slice-level flags. It can be understood that temporal sublayers are basically defined based on reference information. • The application of CC-ALF filters is controlled at a variable block size and signaled by a context-encoded flag received for each block of samples. The block size along with a CC-ALF enable flag is received at the slice level for each chroma component. • Boundary padding for horizontal virtual boundaries makes use of repetition. For the remaining borders, the same padding type is used as for regular ALF.

[0353] Figure 8 is a block diagram showing image header entries for CCALF that are introduced that define the common data of CCALF and all slices can then inherit this common information compared to Figure 7.

[0354] Figure 16 is a schematic diagram of a data structure 5000, the data structure 5000 may represent a portion of a bit stream 21 generated by an encoder in Figure 2 and received by a decoder in Figure 3. The structure data stream 5000 (i.e., video bitstream 5000) may comprise a VPS 5005; an SPS 5010; a PPS 5015; and at least four slices 5020, 5025, 5030 and 5035. Slice 5020 may comprise a header 5040 and data 5045. Slices 5025, 5030, 5035 are similar to slice 5020. Data 5045 may comprise at least three blocks 5050, 5055 and 5060, that is, an encoded representation of at least three blocks 5050, 5055 and 5060. Although four slices 5020-5035 are shown, the video bit stream 5000 comprises any suitable number of slices. Although three blocks 5050-5060 are shown, data 5045 comprises any suitable number of blocks. Furthermore, each remaining slice 5025, 5030, 5035 also comprises blocks. Thus, while the video bitstream 5000 comprises, i.e., an encoded representation of multiple blocks, the video bitstream 5000 comprises an SPS 5010 and significantly fewer slice headers than blocks. It can be understood that the bit stream including a plurality of syntax elements related to CC-ALF can also be shown in Figure 16. As shown by the syntax above and below, a plurality of syntax elements related to CC-ALF are clearly specified. Furthermore, the process for encoding or decoding the bit stream is clearly specified in the syntax and/or semantics mentioned above and below.

[0355] The bit stream shown here can be obtained by encoding a video sequence using any of the modalities described above. Specifically, this bitstream may be obtained from or may include the syntax elements and specifically the syntax elements related to CC-ALF as explained in alternative embodiments 1 to 5 above.

[0356] Figure 14 shows a flowchart of a method 4200 of encoding, for example, a video. This method can, for example, be implemented using the encoder according to Figure 12, but also any other encoder and coding device disclosed in this document can be used to realize this method.

[0357] Coding method 4200 comprises applying 4201 a cross-component adaptive loop filter, CC-ALF to refine a chroma component and generating 4202 a bit stream including a plurality of syntax elements related to CC-ALF, wherein the plurality of syntax elements related to CC-ALF indicates Information related to CC-ALF. Within the bitstream generated in step 4202, the plurality of CC-ALF-related syntax elements are signaled at any one or more of a sequence parameter set (SPS) level, an image header, or a slice header. . The plurality of syntax elements related to CC-ALF comprise a first syntax element that indicates whether an adaptive loop filter (ALF) comprising the cross-component adaptive loop filter is enabled or not at a sequence level, and the first syntax element is signaled at the SPS level, and a second syntax element that indicates whether the cross-component adaptive loop filter is enabled or not at a sequence level, and the second syntax element is signaled at the SPS level.

[0358] Figure 15 shows a flowchart of a method 4300 of decoding, for example, a video from a bitstream or the like. This method 4300 can, for example, be implemented using the decoder according to Figure 13. Furthermore, any other decoder and decoding device disclosed herein can be used to carry out the method 4300.

[0359] Method 4300 comprises analyzing 4301 a plurality of syntax elements related to cross-component adaptive loop filters, CC-ALF, from a bit stream, wherein the plurality of syntax elements related to CC-ALF is obtained from any one or more of a sequence parameter set (SPS), an image header, or a slice header. The plurality of syntax elements related to CC-ALF comprise a first syntax element that indicates whether an adaptive loop filter (ALF) comprising the cross-component adaptive loop filter is enabled or not at a sequence level, and the first syntax element is signaled at the SPS level, and a second syntax element that indicates whether the cross-component adaptive loop filter is enabled or not at a sequence level, and the second syntax element is signaled at the SPS level. Method 4300 further comprises a step of performing 4302 a CC-ALF process using at least one of the plurality of syntax elements related to CC-ALF.

[0360] In one embodiment, there is provided a coding method implemented by a coding device, the method comprising: performing a filtering process (such as a cross-component filtering process) by applying a cross-component adaptive loop filter (CC- ALF); generate a bitstream including a plurality of CC-ALF related syntax elements (such as M CC-ALF related syntax elements and M>=1 and M is an integer), wherein the plurality of related syntax elements CC-ALF indicates information related to CC-ALF, wherein the plurality of syntax elements related to CC-ALF are signaled at any one or more of a video parameter set (VPS) level, a video parameter set level sequence parameters (SPS), an image parameter set (PPS) level, an image header, a slice header, or a tile header; or wherein the plurality of syntax elements related to CC-ALF are signaled at a sequence parameter set (SPS) level and/or an image header.

[0361] With this method, a bit stream can be provided that is reduced in size, as information relevant to, for example, all slices of an image can be provided in the image header only once.

[0362] In one embodiment, the plurality of CC-ALF-related syntax elements comprises: a first syntax element (e.g., a first indicator, such as sps_ccalf_enabled_flag or sps_alf_enabled_flag), wherein the first syntax element (e.g., a first flag, such as sps_ccalf_enabled_flag) is signaled at a sequence parameter set (SPS) level. This indicator can indicate whether ALF or CC-ALF or both can be enabled or not for the entire sequence.

[0363] In a further embodiment, the first syntax element (e.g., a first indicator, such as sps_ccalf_enabled_flag) indicates whether or not the cross-component adaptive loop filter (CC-ALF) is enabled at a sequence level, or wherein the first syntax element (e.g., a first indicator, such as sps_alf_enabled_flag) indicates whether the adaptive loop filter (ALF) comprising the cross-component adaptive loop filter (CC-ALF) is enabled or not at a sequence level . With this first syntax element, adaptive loop filter modes can be provided specifically at the sequence level for all images or parts of the sequence.

[0364] Additionally, it may be provided that the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is set to a first value (true or 1) or the first syntax element has a first value (true or 1). With this value, it can be indicated whether ALF and/or CC-ALF is/is enabled using, preferably, just a single bit value.

[0365] In one embodiment, the plurality of syntax elements related to CC-ALF further comprises: a second syntax element (e.g., a second indicator, such as pic_ccalf_enabled_present_flag) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is set to a first value (true or 1) or the first syntax element has a first value (true or 1), where the second syntax element (such as pic_ccalf_enabled_present_flag) is flagged in an image header; or a ninth syntax element (for example, a ninth indicator, such as pic_alf_enabled_present_flag) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is set to a first value (true or 1) or the first syntax element has a first value (true or 1), where the ninth syntax element (such as pic_alf_enabled_present_flag) is flagged in an image header.

[0366] That the second syntax element is provided if the first syntax element is set to a first value (and correspondingly for the ninth syntax element) can be understood to mean that the respective syntax element is provided only or at least if the first syntax element has the first value and is not provided in any other case. This embodiment may, however, encompass the second and ninth syntax elements being provided or present independently of the value of the first syntax element. This meaning may be applied to the presence or absence of all other syntax elements referred to herein, provided that those syntax elements are referred to as present if another syntax element takes on a specific value.

[0367] With the second and ninth syntax element, it can be specified whether ALF and/or CC-ALF are enabled for image slices using a reduced amount of bits.

[0368] In one embodiment, the second syntax element (e.g., a second indicator, such as pic_ccalf_enabled_present_flag) indicates whether a third syntax element and/or a fourth set of syntax elements are present in an image header.

[0369] It may further be provided that the plurality of CC-ALF-related syntax elements further comprises: a third syntax element (e.g., a third indicator, such as pic_ccalf_enabled_flag or pic_alf_enabled_flag) and the second syntax element (such as pic_ccalf_enabled_present_flag) or the ninth syntax element (such as pic_alf_enabled_present_flag) is set to a first value (true or 1) or the second syntax element or the ninth syntax element has a first value (true or 1), where the third syntax element (like pic_ccalf_enabled_flag or pic_alf_enabled_flag) is flagged in an image header.

[0370] In a further embodiment, the third syntax element (e.g., a third flag, such as pic_ccalf_enabled_flag) indicates whether the cross-component adaptive loop filter (CCALF) is enabled for all slices associated with the image header or not , or wherein the third syntax element (e.g., a third indicator such as pic_alf_enabled_flag) indicates whether the adaptive loop filter comprising the cross-component adaptive loop filter (CCALF) is enabled for all slices associated with the image header or no. Information about the application of ALF or CC-ALF can thus be signaled to all slices of an image using a reduced amount of information.

[0371] In a further embodiment, the plurality of syntax elements related to CC-ALF further comprises: a fourth set of syntax elements if the third syntax element (e.g., a third indicator such as pic_ccalf_enabled_flag or pic_alf_enabled_flag) is defined as a first value (true or 1) or the third syntax element has a first value (true or 1), where the fourth set of syntax elements is signaled in an image header (for example, at a header level image) or the fourth set of syntax elements is carried by image header entries.

[0372] Specifically, in one embodiment, the fourth set of syntax elements comprises:

[0373] It may additionally or alternatively be provided that the fourth set of syntax elements comprises:

[0374] Furthermore, additionally or alternatively, the fourth set of syntax elements comprises:

[0375] With the above embodiments, information relevant to the filters to be applied can be provided for all slices already in the image header, potentially reducing the size of the bit stream.

[0376] In a further embodiment, it is provided that for all slices of the same image, the same CC-ALF related information (such as aps_ids) is inherited from the image header. Information provided in the image header therefore need not be included in slice headers or the like in addition, thus potentially reducing the amount of information that is provided in the bitstream.

[0377] In one embodiment, the plurality of CC-ALF-related syntax elements comprises: a first syntax element (e.g., a first indicator, such as sps_ccalf_enabled_flag or sps_alf_enabled_flag), wherein the first syntax element (e.g., a first indicator, such as sps_ccalf_enabled_flag) is signaled at a sequence parameter set (SPS) level, a second syntax element (for example, a second indicator, such as pic_ccalf_enabled_present_flag) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is set to a first value (true or 1) or has a first value (true or 1) where the second syntax element (such as pic_ccalf_enabled_present_flag) is flagged in an image header.

[0378] Furthermore, the plurality of syntax elements related to CC-ALF may comprise: a fifth syntax element (e.g., a fifth indicator, such as slice_ccalf_enabled_flag or slice_alf_enabled_flag) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is set to a first value (true or 1) or has a first value (true or 1) and if the second syntax element (such as pic_ccalf_enabled_present_flag or pic_alf_enabled_present_flag) is set to a second value (false or 0) or has a second value (false or 0), where the fifth syntax element (such as slice_ccalf_enabled_flag or slice_alf_enabled_flag) is flagged in a slice header.

[0379] It may also be provided that the plurality of syntax elements related to CC-ALF further comprises: a sixth set of syntax elements if the fifth syntax element (e.g., a fifth indicator such as slice_ccalf_enabled_flag or slice_alf_enabled_flag) is defined as a first value (true or 1) or the fifth syntax element has a first value (true or 1), where the sixth set of syntax elements is signaled in a slice header or the sixth set of syntax elements is carried by slice header entries. This set of syntax elements can, for example, indicate parameters to be used in ALF or CC-ALF. By providing this potentially value-dependent set of the fifth syntax element, the size of the bit stream can be further reduced.

[0380] Specifically, it can be provided that the sixth set of syntax elements comprises:

[0381] Additionally or alternatively, it may be provided that the sixth set of syntax elements comprises:

[0382] Furthermore, it can be provided that the sixth set of syntax elements comprises:

[0383] In a further embodiment, the plurality of syntax elements related to CC-ALF further comprises: a seventh syntax element (e.g., a seventh indicator, such as pic_cross_component_alf_cb_aps_id) and an eighth syntax element (e.g., an eighth indicator, such as pic_cross_component_alf_cr_aps_id) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is set to a first value (true or 1) or has a first value (true or 1).

[0384] In one embodiment, the plurality of syntax elements related to CC-ALF further comprises: a seventh syntax element (e.g., a seventh indicator, such as pic_cross_component_alf_cb_aps_id) and an eighth syntax element (e.g., an eighth indicator , such as pic_cross_component_alf_cr_aps_id) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is defined as a first value (true or 1) or has a first value (true or 1) and if a ninth syntax element (such as pic_alf_enabled_present_flag) is defined as a first value (true or 1) or has a first value (true or 1).

[0385] In one embodiment, the plurality of syntax elements related to CC-ALF further comprises: a seventh syntax element (e.g., a seventh indicator, such as pic_cross_component_alf_cb_aps_id), an eighth syntax element (e.g., an eighth indicator , such as pic_cross_component_alf_cr_aps_id) and the second syntax element (such as pic_ccalf_enabled_present_flag) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is set to a first value (true or 1) or has a first value (true or 1) and whether a ninth syntax element (such as pic_alf_enabled_present_flag) is set to a first value (true or 1) or has a first value (true or 1).

[0386] It may also be provided that the plurality of syntax elements related to CC-ALF further comprises: a seventh syntax element (e.g., a seventh indicator, such as pic_cross_component_alf_cb_aps_id), an eighth syntax element (e.g., an eighth indicator, such as pic_cross_component_alf_cr_aps_id) and the ninth syntax element (such as pic_alf_enabled_present_flag) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is set to a first value (true or 1) or has a first value (true or 1).

[0387] Additionally, in one embodiment, CC-ALF is applied to perform filter processing on one or more luma samples of a luma component of a current image block, to refine a chroma sample (such as each chroma sample) of a chroma component of the current image block.

[0388] Specifically, it may be provided that the CC-ALF is configured to refine each chroma component using luma sample values.

[0389] In one embodiment, the CC-ALF operates as part of the adaptive loop filter process.

[0390] It can also be provided that the image block comprises a luma block and chroma blocks, wherein a first chroma block is a first chroma component (such as Cb component) of the image block and a second block of Chroma is a second chroma component (such as Cr component) of the image block.

[0391] The present disclosure further relates to a coding method implemented by a coding device, comprising: determining whether the Cross-Component ALF (CC-ALF) is enabled or not; generate a bitstream including one or more syntax elements (e.g., CC-ALF-related syntax element such as pic_ccalf_enabled_flag, pic_cross_component_alf_cb_enabled_flag, or pic_cross_component_alf_cr_enabled_flag), wherein the one or more syntax elements indicate whether the Cross-Component ALF ( CC-ALF) is enabled or not at an image header level and corresponding CC-ALF related information, where syntax elements are flagged at an image header level. Thus, information relevant for subsequent decoding can be provided in a reduced size in the bit stream.

[0392] It may also be provided that CC-ALF is applied to perform filter processing on one or more luma samples of a luma component of a current image block, to refine a chroma sample (such as each chroma) of a chroma component of the current image block.

[0393] In one embodiment, the method further comprises: performing filtering processing on a luma component of a current image block belonging to an image using the CC-ALF filter, wherein one or more luma samples of the image component luma of the current image block are used to refine at least one chroma sample (as each chroma sample) of a chroma component of the current image block.

[0394] It may also be provided that the CC-ALF is configured to refine each chroma component using luma sample values.

[0395] In a further embodiment, the CC-ALF operates as part of the adaptive loop filter process.

[0396] It may also be provided that the image block comprises a luma block and chroma blocks, wherein a first chroma block is a first chroma component (such as Cb component) of the image block and a second block of Chroma is a second chroma component (such as Cr component) of the image block.

[0397] The present disclosure further relates to a decoding method implemented by a decoding device, the method comprising: analyzing one or more syntax elements from a bit stream of a video signal, wherein the one or more more syntax elements indicate information related to Cross-Component Adaptive Loop Filter (CC-ALF), where the one or more syntax elements are obtained from any one or more of a video parameter set (VPS) level , a sequence parameter set (SPS) level, an image parameter set (PPS) level, an image header, a slice header, or a bitstream tile header; or wherein the one or more syntax elements are obtained from a sequence parameter set (SPS) level and/or an image header; and performing a filtering process (such as a cross-component filtering process) by applying a CC-ALF based on the syntax elements or based on the value of the syntax elements.

[0398] Information that may be needed to determine the filtering method to be applied and how it should be applied can be provided therewith in a bit stream that is reduced in size and still allows reliable decoding.

[0399] The present disclosure further describes a decoding method implemented by a decoding device, the method comprising: analyzing a plurality of syntax elements from a bit stream of a video signal, wherein the syntax elements are obtained from any one or more of a video parameter set (VPS) level, a sequence parameter set (SPS) level, a picture parameter set (PPS) level), an image header, a slice header or a bitstream tile header; or wherein the syntax elements are obtained from a string parameter set (SPS) level and/or an image header; determining Cross-Component Adaptive Loop Filter (CC-ALF) related information based on one or more syntax elements of the plurality of syntax elements, wherein performing a filtering process (such as a cross-component filtering process) by applying a CC-ALF based on information related to CC-ALFs.

[0400] Information that may be needed to determine the filtering method to be applied and how it should be applied can be provided therewith in a bit stream that is reduced in size and still allows reliable decoding.

[0401] It may be provided that the one or more syntax elements or the plurality of syntax elements (such as CC-ALF-related syntax elements) comprise: a first syntax element (e.g., a first indicator, such as sps_ccalf_enabled_flag or sps_alf_enabled_flag), where the first syntax element (for example, a first flag such as sps_ccalf_enabled_flag) is taken from a sequence parameter set (SPS) level.

[0402] Specifically, it may be further provided that the first syntax element (e.g., a first indicator, such as sps_ccalf_enabled_flag) indicates whether or not the cross-component adaptive loop filter (CC-ALF) is enabled at a sequence level, or wherein the first syntax element (e.g., a first flag, such as sps_alf_enabled_flag) indicates whether or not the adaptive loop filter (ALF) comprising the cross-component adaptive loop filter (CC-ALF) is enabled or not at a level of sequence.

[0403] Thus, information about which filter method should be applied can be provided with a reduced amount of information to the decoder in the bit stream.

[0404] In one embodiment, the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is derived as a first value (true or 1) or the first syntax element has a first value (true or 1).

[0405] It may also be provided that the plurality of syntax elements (such as CC-ALF-related syntax elements) further comprises: a second syntax element (e.g., a second indicator, such as pic_ccalf_enabled_present_flag) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is derived as a first value (true or 1) or the first syntax element has a first value (true or 1), where the second syntax element (such as pic_ccalf_enabled_present_flag) is derived from a image header; or a ninth syntax element (for example, a ninth indicator, such as pic_alf_enabled_present_flag) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is derived as a first value (true or 1) or the first syntax element has a first value (true or 1), where the ninth syntax element (such as pic_alf_enabled_present_flag) is taken from an image header.

[0406] In a further embodiment, the second syntax element (e.g., a second indicator, such as pic_ccalf_enabled_present_flag) indicates whether a third syntax element and/or a fourth set of syntax elements are present in an image header.

[0407] The plurality of syntax elements (such as CC-ALF-related syntax elements) may further comprise: a third syntax element (e.g., a third indicator, such as pic_ccalf_enabled_flag or pic_alf_enabled_flag) if the second syntax element (such as pic_ccalf_enabled_present_flag) or the ninth syntax element (such as pic_alf_enabled_present_flag) is derived as a first value (true or 1) or the second syntax element or the ninth syntax element has a first value (true or 1), where the third element syntax (such as pic_ccalf_enabled_flag or pic_alf_enabled_flag) is obtained from an image header.

[0408] Specifically, it may be provided that the third syntax element (e.g., a third indicator such as pic_ccalf_enabled_flag) indicates whether the cross-component adaptive loop filter (CCALF) is enabled for all slices associated with the image header or not , or wherein the third syntax element (e.g., a third indicator such as pic_alf_enabled_flag) indicates whether the adaptive loop filter comprising the cross-component adaptive loop filter (CCALF) is enabled for all slices associated with the image header or no.

[0409] In one embodiment, the plurality of syntax elements (such as CC-ALF-related syntax elements) further comprises: a fourth set of syntax elements and the third syntax element (e.g., a third indicator, such as pic_ccalf_enabled_flag or pic_alf_enabled_flag) is derived as a first value (true or 1) or the third syntax element has a first value (true or 1), where the fourth set of syntax elements is obtained from an image header (e.g. example, at an image header level) or the fourth set of syntax elements is carried by image header entries.

[0410] This set of syntax elements may only be provided if the third syntax element takes or is derived as the first value and is not otherwise present or the values of the set of syntax elements may be set to a default value , as 0, if the third syntax element takes a different value. In both cases, reliable provision of decoding-relevant information can be ensured at reduced bitstream size.

[0411] Specifically, the fourth set of syntax elements may comprise:

[0412] Alternatively or additionally, the fourth set of syntax elements may comprise:

[0413] In a further embodiment, the fourth set of syntax elements may comprise:

[0414] It can be provided that, for all slices of the same image, the same CC-ALF related information (such as, aps_ids) is inherited from the image header. In this way, the amount of information provided in the bitstream to indicate to the decoder CC-ALF related information for slices of an image can be reduced.

[0415] In one embodiment, the plurality of syntax elements (such as CC-ALF-related syntax elements) comprises: a first syntax element (e.g., a first indicator, such as sps_ccalf_enabled_flag or sps_alf_enabled_flag), wherein the first element syntax element (for example, a first indicator such as sps_ccalf_enabled_flag) is obtained from a string parameter set (SPS) level, a second syntax element (for example a second indicator such as pic_ccalf_enabled_present_flag) if the first element syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is derived as a first value (true or 1) or has a first value (true or 1) where the second syntax element (such as pic_ccalf_enabled_present_flag) is obtained from an image header .

[0416] In a further embodiment, the plurality of syntax elements (such as CC-ALF-related syntax elements) further comprises: a fifth syntax element (e.g., a fifth indicator, such as slice_ccalf_enabled_flag or slice_alf_enabled_flag) if the first element syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is derived as a first value (true or 1) or has a first value (true or 1) and the second syntax element (such as pic_ccalf_enabled_present_flag or pic_alf_enabled_present_flag) is derived as a second value (false or 0) or has a second value (false or 0), where the fifth syntax element (such as slice_ccalf_enabled_flag or slice_alf_enabled_flag) is obtained from a slice header.

[0417] It may be provided that the plurality of syntax elements (such as CC-ALF-related syntax elements) further comprises: a sixth set of syntax elements and the fifth syntax element (e.g., a fifth indicator, such as slice_ccalf_enabled_flag or slice_alf_enabled_flag) is derived as a first value (true or 1) or the fifth syntax element has a first value (true or 1), where the sixth set of syntax elements is obtained from a slice header or the sixth set of syntax elements are carried by slice header entries.

[0418] Specifically, it can be provided that the sixth set of syntax elements comprises:

[0419] It may alternatively or additionally be provided that the sixth set of syntax elements comprises:

[0420] Likewise, it can be provided that the sixth set of syntax elements comprises:

[0421] In one embodiment, the plurality of syntax elements (such as CC-ALF-related syntax elements) further comprises: a seventh syntax element (e.g., a seventh indicator, such as pic_cross_component_alf_cb_aps_id) and an eighth syntax element ( for example, an eighth indicator, such as pic_cross_component_alf_cr_aps_id) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is derived as a first value (true or 1) or has a first value (true or 1).

[0422] It may also be provided that the plurality of syntax elements (such as syntax elements related to CC-ALF) further comprises: a seventh syntax element (e.g., a seventh indicator, such as pic_cross_component_alf_cb_aps_id) and an eighth syntax element (for example, an eighth indicator, such as pic_cross_component_alf_cr_aps_id) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is derived as a first value (true or 1) or has a first value (true or 1) and if a ninth element of syntax (such as pic_alf_enabled_present_flag) is derived as a first value (true or 1) or has a first value (true or 1).

[0423] In a further embodiment, the plurality of syntax elements (such as CC-ALF-related syntax elements) further comprises: a seventh syntax element (e.g., a seventh indicator, such as pic_cross_component_alf_cb_aps_id), an eighth syntax element (for example, an eighth indicator, such as pic_cross_component_alf_cr_aps_id) and the second syntax element (such as pic_ccalf_enabled_present_flag) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is derived as a first value (true or 1) or has a first value ( true or 1) and if a ninth syntax element (such as pic_alf_enabled_present_flag) is derived as a first value (true or 1) or has a first value (true or 1).

[0424] It may also be provided that the plurality of syntax elements (such as syntax elements related to CC-ALF) further comprises: a seventh syntax element (e.g., a seventh indicator, such as pic_cross_component_alf_cb_aps_id), an eighth syntax element (for example, an eighth indicator, such as pic_cross_component_alf_cr_aps_id) and the ninth syntax element (such as pic_alf_enabled_present_flag) if the first syntax element (such as sps_ccalf_enabled_flag or sps_alf_enabled_flag) is derived as a first value (true or 1) or has a first value ( true or 1).

[0425] In one embodiment, CC-ALF is applied to perform filter processing on one or more luma samples of a luma component of a current image block, to refine a chroma sample (such as each chroma sample ) of a chroma component of the current image block.

[0426] The CC-ALF can be configured to refine each chroma component using luma sample values.

[0427] It may also be provided that the CC-ALF operates as part of the adaptive loop filter process.

[0428] In one embodiment, the image block comprises a luma block and chroma blocks, wherein a first chroma block is a first chroma component (such as Cb component) of the image block and a second chroma block is is a second chroma component (such as Cr component) of the image block.

[0429] The present disclosure further relates to a decoding method implemented by a decoding device, comprising: analyzing from a bit stream of a video signal one or more syntax elements (e.g., M syntax elements related to CC-ALF, M is an integer and M>=1, such as pic_ccalf_enabled_flag, pic_cross_component_alf_cb_enabled_flag, or pic_cross_component_alf_cr_enabled_flag), where the one or more syntax elements indicate whether or not Cross Component ALF (CCALF) is enabled on a image header level and corresponding CCALF-related information, wherein the one or more syntax elements are obtained from an image header level. perform a filtering process (such as a cross-component filtering process) by applying a CC-ALF in response to determining that CC-ALF is enabled.

[0430] This method can appropriately apply CC-ALF during decoding, while allowing to reduce the size of the bit stream

[0431] In one embodiment, CC-ALF is applied to perform filter processing on one or more luma samples of a luma component of a current image block, to refine a chroma sample (such as each chroma sample ) of a chroma component of the current image block.

[0432] It may also be provided that the CC-ALF is configured to refine each chroma component using luma sample values.

[0433] In a further embodiment, the CC-ALF operates as part of the adaptive loop filter process.

[0434] Embodiments may further encompass that the image block comprises a luma block and chroma blocks, wherein a first chroma block is a first chroma component (such as Cb component) of the image block and a second block chroma component is a second chroma component (such as Cr component) of the image block.

[0435] The present disclosure further provides a device for encoding video data, the device comprising: a video data memory; and a video encoder, wherein the video encoder is configured to: perform a filtering process (such as a cross-component filtering process) by applying a cross-component adaptive loop filter (CC-ALF); generate a bitstream for the video signal including a plurality of syntax elements (such as CC-ALF-related syntax elements), wherein the plurality of syntax elements indicates the CC-ALF-related information, wherein the plurality of syntax elements related to CC-ALF is obtained from any one or more of a video parameter set (VPS) level, a sequence parameter set (SPS) level, a image (PPS), an image header, a slice header, or a tile header; or wherein the plurality of syntax elements related to CC-ALF are obtained from a sequence parameter set (SPS) level and/or an image header.

[0436] This device can perform encoding that results in a bit stream being reduced in size.

[0437] Furthermore, a device for decoding video data is provided, the device comprising: a video data memory; and a video decoder, wherein the video decoder is configured to: parse a plurality of syntax elements from a bit stream of a video signal, wherein the plurality of syntax elements is obtained from any one or more of a video parameter set (VPS) level, a sequence parameter set (SPS) level, a picture parameter set (PPS) level, an image header, a slice header, or a tile header of the bitstream, or wherein the plurality of syntax elements are obtained from a sequence parameter set (SPS) level, and/or an image header of the bitstream; determining Cross-Component Adaptive Loop Filter (CC-ALF) related information based on one or more syntax elements from the plurality of syntax elements; and performing a filtering process (such as a cross-component filtering process) by applying a CC-ALF based on information related to CC-ALFs.

[0438] This decoder may be capable of performing reliable decoding while requiring a reduced size bit stream to obtain information regarding the filter to be applied during decoding.

[0439] The present disclosure further provides an encoder, the encoder comprising processing circuitry for carrying out the method in accordance with any of the above embodiments.

[0440] The present disclosure also relates to a decoder, the decoder comprising processing circuitry for carrying out the method in accordance with any of the above embodiments.

[0441] Furthermore, a computer program product comprising program code for carrying out the method according to any of the above embodiments is provided.

[0442] The present disclosure further relates to a decoder, the 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 perform the method in accordance with any of the above embodiments.

[0443] Furthermore, an encoder is provided in the present disclosure, the 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 perform the method in accordance with any of the above embodiments.

[0444] Additionally, a non-transitory recording medium is provided that includes a coded bit stream decoded by an image decoding device, the bit stream being generated by dividing a frame of a video signal or a signal image in a plurality of blocks and including a plurality of syntax elements (such as CC-ALF-related syntax elements), wherein the plurality of syntax elements indicates CC-ALF-related information, wherein the plurality of elements (such as CC-ALF-related syntax elements) is obtained from any one or more of a video parameter set (VPS) level, a sequence parameter set (SPS) level, a image parameter set (PPS), an image header, a slice header or a tile header or wherein the plurality of syntax elements (such as CC-ALF related syntax elements) are obtained from at least least one sequence parameter set (SPS) level or an image header.

[0445] The present disclosure also relates to an apparatus, the apparatus comprising: a non-transitory computer-readable medium having stored instructions thereon that, when executed by one or more processors, cause the one or more processors to perform operations to generate data image data corresponding to a video bitstream, the image data comprising: a plurality of images in the video bitstream including an image comprising N slices; and an image header associated with the N slices of the image, wherein one or more of or each of the N slices comprises a plurality of sample blocks that are entropy encoded, wherein the CC-ALF filtering information or CC-ALF filter are inherited by the N slices from the image header or the N slices inherit the ALF filtering data from the image header.

[0446] According to any of the above embodiments, it may be further provided that slice_cross_component_alf_cr_aps_id and slice_cross_component_alf_cb_aps_id values are equal to pic_cross_component_alf_cb_aps_id and pic_cross_component_alf_cr_aps_id values.

[0447] In a further embodiment, pic_cross_component_alf_cb_aps_id and pic_cross_component_alf_cr_aps_id are obtained from the image header.

[0448] It may also be provided that a syntax element related to CCALF is obtained only once in the image header associated with all N slices.

[0449] In one embodiment, N is a positive integer and greater than 1.

[0450] In one embodiment, a method for encoding a video bitstream implemented by an encoding device is provided, the encoding method comprising: generating a bitstream for the video signal including a plurality of syntax elements (e.g., an ALF-related syntax element such as sps_alf_enabled_flag and/or a CCALF-related syntax element such as sps_ccalf_enabled_flag), wherein the plurality of syntax elements comprises a cross-component adaptive loop filter (CC) enabled flag -ALF) (such as sps_ccalf_enabled_flag) and where CC-ALF related parameters are signaled conditionally at least based on a value of the CC-ALF enabled flag (such as sps_ccalf_enabled_flag).

[0451] This can provide a bit stream comprising information relevant to decoding but being reduced in size.

[0452] Furthermore, a method for decoding a video bit stream implemented by a decoding device is provided in accordance with the present disclosure, the decoding method comprising: obtaining (S110) a plurality of syntax elements from of the video bit stream; wherein the plurality of syntax elements comprises a cross-component adaptive loop filter (CC-ALF) enabled flag (such as sps_ccalf_enabled_flag), and wherein CC-ALF related parameters are conditionally signaled at least based on a value of the CCALF enabled flag (like sps_ccalf_enabled_flag).

[0453] This method allows you to perform reliable decoding even when the bit stream is reduced in size.

[0454] In one embodiment, in the event that one or more conditions are satisfied, the CCALF enabled flag (such as sps_ccalf_enabled_flag) is signaled at a sequence parameter set (SPS) level of the bit stream, where one or more conditions comprise: when the value of a first flag (such as sps_alf_enabled_flag) that is signaled at a sequence parameter set (SPS) level of the bitstream is an enable value (such as a first value, for example, true or 1 ), and where the CCALF enabled flag indicates whether or not the cross-component adaptive loop filter (CCALF) is enabled at a sequence level or SPS level.

[0455] It may also be provided that the syntax elements comprise a third flag (such as alf_present_in_ph_flag) and the third flag is flagged as a bitstream picture parameter set (PPS) level and wherein the third flag indicates whether one or more syntax elements to enable use of ALF is present in the PHs (image headers) referring to the PPS or not.

[0456] It may also be provided that the third flag (alf_present_in_ph_flag) equal to 1 specifies that syntax elements to enable the use of ALF may be present in the PHs (image headers) relating to the PPS. The third flag (alf_present_in_ph_flag) equal to 0 specifies that syntax elements to enable the use of ALF can be present in the PPS-related slice headers.

[0457] In one embodiment, it is provided that if the value of the first flag (such as sps_alf_enabled_flag) is an enabling value (such as a first value, e.g., true or 1) and the value of the third flag (alf_present_in_ph_flag) is a enable value (as a first value, for example, true or 1), and if the value of the CCALF enabled flag (such as sps_ccalf_enabled_flag) is an enable value (as a first value, for example, true or 1), the Cross-Component Adaptive Loop Filtering (CCALF) related parameters (such as the syntax elements to enable use of CCALF) are signaled at a bitstream picture_header level.

[0458] In a further embodiment, it is provided that if the value of the first flag (such as sps_alf_enabled_flag) is an enabling value (such as a first value, e.g., true or 1) and the value of the third flag (alf_present_in_ph_flag) is a disable value (such as a second value, for example, false or 0), and if the value of the CCALF enabled flag (such as sps_ccalf_enabled_flag) is an enable value (such as a first value, for example, true or 1), Cross-Component Adaptive Loop Filtering (CCALF) related parameters (such as syntax elements to enable CCALF use) are signaled at the slice_header level of the bitstream.

[0459] In a further embodiment, it is provided that the CC-ALF enabled flag (such as sps_ccalf_enabled_flag) equal to 0 specifies that the cross-component adaptive loop filter is disabled; or the CC-ALF enabled flag (such as sps_ccalf_enabled_flag) equal to 1 specifies that the cross-component adaptive loop filter is enabled.

[0460] It may be further provided that the syntax elements comprise: a second flag (such as no_ccalf_constraint_flag) equal to 1 specifies that the CCALF enabled flag (such as sps_ccalf_enabled_flag) is equal to 0; or the second flag (such as no_ccalf_constraint_flag) equal to 0 does not impose such a restriction.

[0461] In one embodiment, the method further comprises: performing a filtering process (such as a cross-component adaptive loop filter process) on a reconstructed image (such as an SL reconstructed chroma sample array, a reconstructed chroma sample array SCb and/or, a reconstructed chroma sample array SCr), to obtain a filtered reconstructed image (such as, a modified reconstructed chroma sample array S'L, a modified reconstructed chroma sample array S 'Cb and/or, a modified reconstructed chroma sample array S'Cr).

[0462] The present disclosure further provides an encoded bitstream for the video signal including a plurality of syntax elements (e.g., an ALF-related syntax element such as sps_alf_enabled_flag and/or a CCALF-related syntax element, such as sps_ccalf_enabled_flag), wherein the plurality of syntax elements comprise a cross-component adaptive loop filter (CCALF) enabled flag (such as sps_ccalf_enabled_flag) and wherein CCALF-related parameters are conditionally signaled at least based on a value of the flag enabled from CCALF (like sps_ccalf_enabled_flag).

[0463] The bit stream can be reduced in size while providing information to be used in decoding by reliably applying CC-ALF.

[0464] Figure 12 shows an embodiment of an encoder 4000. The encoder 4000 can be implemented using any processing circuits indicated herein with 4001 to perform a method of encoding a video. Specifically, processing circuitry 4001 may be adapted to apply a cross-component adaptive loop filter, CC-ALF to refine a chroma component. The processing circuitry may be further adapted to generate a bit stream including a plurality of CC-ALF related syntax elements, wherein the plurality of CC-ALF related syntax elements indicates CC-ALF related information, wherein the plurality of syntax elements related to CC-ALF are signaled at any one or more of a sequence parameter set (SPS) level, an image header, or a slice header.

[0465] The plurality of syntax elements related to CC-ALF in this context comprise a first syntax element that indicates whether or not an adaptive loop filter (ALF) comprising the cross-component adaptive loop filter is enabled at a sequence level and the first syntax element is signaled at the SPS level, and a second syntax element that indicates whether the cross-component adaptive loop filter is enabled or not at a sequence level, and the second syntax element is signaled at the SPS level.

[0466] The encoder may further comprise a receiver 4002 for receiving a video to be encoded and a transmitter 4003 for transmitting a bit stream comprising at least the plurality of syntax elements.

[0467] Figure 13 shows an embodiment of a decoder 4100. The decoder 4100 may be implemented using any processing circuitry 4101 to perform a method of decoding a video. Specifically, processing circuitry 4101 may be adapted to parse a plurality of syntax elements related to cross-component adaptive loop filters, CC-ALF, from a bit stream, wherein the plurality of syntax elements related to CC-ALF is obtained from any one or more of a sequence parameter set (SPS) level, an image header, or a slice header.

[0468] Specifically, the plurality of syntax elements related to CC-ALF comprise a first syntax element that indicates whether or not an adaptive loop filter (ALF) comprising the cross-component adaptive loop filter is enabled at a sequence level and the first syntax element is signaled at the SPS level, and a second syntax element that indicates whether the cross-component adaptive loop filter is enabled or not at a sequence level, and the second syntax element is signaled at the SPS level.

[0469] The processing circuitry may further be adapted to perform a CC-ALF process using at least one of the plurality of syntax elements related to CC-ALF.

[0470] Additionally, decoder 4100 may comprise a receiver 4102 for receiving a bit stream. Additionally, the decoder may comprise a transmitter 4103 for sending the decoded video, for example, to an output device not shown here.

[0471] The following is an explanation of the applications of the encoding method as well as the decoding method as shown in the aforementioned embodiments, and a system that uses them.

[0472] Figure 10 is a block diagram showing a content supply system 3100 for performing the content distribution service. This content delivery system 3100 includes capture device 3102, terminal device 3106, and optionally includes display 3126. The capture device 3102 communicates with the terminal device 3106 via communication link 3104. The communication link may include the communication 13 described above. The 3104 communication link includes, but is not limited to, WIFI, Ethernet, Cable, wireless (3G/4G/5G), USB or any type of combination thereof, or similar.

[0473] The capture device 3102 generates data and can encode the data by the encoding method as shown in the above embodiments. Alternatively, the capture device 3102 may distribute the data to a streaming server (not shown in the Figures) and the server encodes the data and transmits the encoded data to the terminal device 3106. The capture device 3102 includes, but is not limited to, a, camera, smartphone or Pad, computer or laptop, video conferencing system, PDA, vehicle-mounted device or a combination of any of them, or the like. For example, capture device 3102 may include source device 12 as described above. When the data includes video, the video encoder 20 included in the capture device 3102 can actually perform video encoding processing. When the data includes audio (i.e., voice), an audio encoder included in the capture device 3102 may actually perform audio encoding processing. For some practical scenarios, the capture device 3102 distributes the encoded audio and video data by multiplexing them together. For other practical scenarios, for example in video conferencing system, the encoded audio data and encoded video data are not multiplexed. The capture device 3102 distributes the encoded audio data and the encoded video data to the terminal device 3106 separately.

[0474] In the content supply system 3100, the terminal device 310 receives and reproduces the encoded data. Terminal device 3106 may be a device capable of receiving and retrieving data, such as a smartphone or Pad 3108, computer or laptop 3110, network video recorder (NVR)/digital video recorder (DVR) 3112, TV 3114, set-top box (STB) 3116, video conferencing system 3118, video surveillance system 3120, personal digital assistant (PDA) 3122, vehicle-mounted device 3124, or a combination of any of them, or the like capable of decoding the aforementioned encoded data. For example, terminal device 3106 may include destination device 14 as described above. When the encoded data includes video, the video decoder 30 included in the terminal device is prioritized to perform video decoding. When the encoded data includes audio, an audio decoder included in the terminal device is prioritized to perform audio decoding processing.

[0475] To a terminal device with its display, e.g., smartphone or Pad 3108, computer or laptop 3110, network video recorder (NVR)/digital video recorder (DVR) 3112, TV 3114, personal digital assistant (PDA ) 3122 or vehicle-mounted device 3124, the terminal device can feed the decoded data to its display. For a terminal device equipped without a display, e.g., STB 3116, video conferencing system 3118, or video surveillance system 3120, an external display 3126 is contacted to receive and display the decoded data.

[0476] When each device in this system performs encoding or decoding, the image encoding device or the image decoding device as shown in the above-mentioned embodiments may be used.

[0477] Figure 11 is a diagram showing a structure of an example terminal device 3106. After the terminal device 3106 receives the stream from the capture device 3102, the protocol procedure unit 3202 analyzes the stream transmission protocol . The protocol includes but is not limited to Real-time Streaming Protocol (RTSP), Hypertext Transfer Protocol (HTTP), HTTP real-time streaming protocol (HLS), MPEG-DASH, Real-time Transport Protocol (RTP), Real-Time Messaging Protocol (RTMP)), or any type of combination thereof, or similar.

[0478] After the protocol procedure unit 3202 processes the stream, the stream file is generated. The file is sent to a demultiplexing unit 3204. The demultiplexing unit 3204 can separate the multiplexed data into encoded audio data and encoded video data. As described above, for some practical scenarios, for example in video conferencing system, the encoded audio data and encoded video data are not multiplexed. In this situation, the encoded data is transmitted to the video decoder 3206 and the audio decoder 3208 other than through the demultiplexing unit 3204.

[0479] Through demultiplexing processing, elementary video stream (ES), audio ES and, optionally, subtitles are generated. The video decoder 3206, which includes the video decoder 30 as explained in the above-mentioned embodiments, decodes the video ES by the decoding method as shown in the above-mentioned embodiments to generate the video frame, and feeds this data to the synchronous unit 3212. Audio decoder 3208 decodes the audio IO to generate the audio frame, and feeds this data to the synchronous unit 3212. Alternatively, the video frame may be stored in a buffer (not shown in Figure Y) before feeding it to the synchronous unit 3212. Similarly, the audio frame can be stored in a buffer (not shown in Figure Y) before feeding it to the synchronous unit 3212.

[0480] The synchronous unit 3212 synchronizes the video frame and the audio frame, and supplies the video/audio to a video/audio display 3214. For example, the synchronous unit 3212 synchronizes the presentation of video and audio information. Information can be encoded in syntax using timestamps relative to the presentation of encoded audio and visual data and timestamps relative to the delivery of the data stream itself.

[0481] If the caption is included in the stream, the caption decoder 3210 decodes the caption, and synchronizes it with the video frame and the audio frame, and supplies the video/audio/caption to a video/audio/display. caption 3216.

[0482] The present invention is not limited to the above-mentioned system, and both the image encoding device and the image decoding device in the above-mentioned embodiments can be incorporated into another system, for example, a car system.

Mathematical operators

[0483] 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 division of real value. Numbering and counting conventions generally start at 0, for example, "the first" is equivalent to the 0th, "the second" is equivalent to the 1st, etc.

Arithmetic operators

[0484] The following arithmetic operators are defined as follows: + Addition - Subtraction (as a two-argument operator) or negation (as a unary prefix operator) * Multiplication, including xy matrix multiplication Exponentiation. Specifies x to the power of y. In other contexts, this notation is used for superscript, not intended to be interpreted as exponentiation. / Integer division with truncation of the result towards 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 in which no truncation or rounding is intended. x/y Used to denote division in mathematical equations in which no truncation or rounding is intended. The sum of f(i) with i taking all integer values from x up to and including y. x%y Module. Remainder of x divided by y, defined only for integers x and y with x >= 0 and y > 0.

Logical operators

[0485] The following logical operators are defined as follows: x && y Logical Boolean "and" of x and y x || y Logical Boolean "or" of x and y ! Logical Boolean "not" x ? y: z If x is TRUE or different from 0, evaluates the value of y; otherwise, it evaluates the value of z.

Relational operators

[0486] The following relational operators are defined as follows: > Greater than >= Greater than or equal to < Less than <= Less than or equal to == Equal to != Not equal to

[0487] When a relational operator is applied to an element or syntax variable that has been assigned the value "na" (not applicable), the value "na" is treated as a distinct value for the element or syntax variable. The value "na" is not considered equal to any other value.

Bitwise Operators

[0488] The following Bitwise operators are defined as follows: &"and" Bitwise. 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. | " or " Bitwise. 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. A"or exclusive"Bitwise. 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 only defined for non-negative integer values of y. The bits shifted to the most significant bits (MSBs) as a result of the right shift have a value equal to the MSB of x before the shift operation. x << y Arithmetic left shift of a two's complement integer representation of x by y binary digits. This function is only defined for non-negative integer values of y. Bits shifted to least significant bits (LSBs) as a result of left shifting have a value of 0.

Assignment Operators

[0489] 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 the value of the variable before the increment operation. - - Decrement, that is, x - - is equivalent to x = x - 1; when used in an array index, evaluates the value of the variable before the decrement operation. + = Increment by the specified amount, that is, x + = 3 is equivalent to x = x + 3 and x + = (−3) is equivalent to x = x + (−3). - = Decrement by the specified amount, that is, x - = 3 is equivalent to x = x – 3, and x - = (−3) is equivalent to x = x - (−3).

Strip notation

[0490] The following notation is used to specify a range of values: x = y..z x takes integer values starting from y to z, inclusive, with x, y and z being integers and z being greater than y.

Mathematical functions

[0491] The following mathematical functions are defined: Asin(x) the trigonometric inverse sine function, operating on an argument x that is in the range -1.0 to 1.0, inclusive, with an output value in the range -π*2 to π*2, inclusive, in units of radians Atan (x) the trigonometric inverse tangent function, operating on one argument x, with an output value in the range -π - 2 to π - 2, inclusive, in units of radians Ceil (x) the smallest integer greater than or equal to x. Clip1Y (x) = Clip3 (0, (1 << BitDepth Y) - 1, x) Clip1C (x) = Clip3 (0, (1 << BitDepth C) - 1, x) Cos(x) the cosine trigonometric function operating on an argument x in units of radians. Floor (x) the largest integer less than or equal to x. Ln (x) the natural logarithm of x (the logarithm of base e, where e is the constant natural logarithm of base 2.718 281 828...). Log2 (x) the base 2 logarithm of x. Log10 (x) the base 10 logarithm of x. Sin(x) the trigonometric sine function operating on an argument x in units of radians Tan(x) the trigonometric tangent function operating on an argument x in units of radians Order of operation precedence

[0492] When an order of precedence in an expression is not explicitly indicated by the use of parentheses, the following rules apply: - Higher precedence operations are evaluated before any lower precedence operations. - Operations of the same precedence are evaluated sequentially from left to right.

[0493] The table below specifies the precedence of operations from highest to lowest; a higher position in the table indicates higher precedence.

[0494] For operators that are also used in the C programming language, the order of precedence used in this Descriptive Report is the same as that used in the C programming language. Table: operation precedence from highest (at the top of the table) to lowest (at the bottom of the table)

Text description of logical operations

[0495] In the text, a statement of logical operations that would be described mathematically as follows: if (condition 0) statement 0 else if (condition 1) statement 1 ... else / * informative remark on remaining condition * / statement n can be described as follows: ... as follows /... the following applies: - If condition 0, statement 0 - Otherwise, if condition 1, statement 1 - Otherwise (informative note about the remaining condition ), statement n

[0496] 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 "If... Otherwise, if... Otherwise,..." is always an "Otherwise,...". The interspersed statements "If... If Otherwise, if... Otherwise..." can be identified by matching "... as follows" or "... the following applies" with the ending "Otherwise...".

[0497] In the text, a statement of logical operations that would be described mathematically as follows: if (condition 0a && condition 0b) statement 0 else if (condition 1a | | condition 1b) statement 1 else statement n may be described as follows : ... as follows /... the following applies: - If all of the following conditions are true, statement 0: - condition 0a - condition 0b - Otherwise, if one or more of the following conditions are true, statement 1 : - condition 1a - condition 1b - Otherwise statement n

[0498] In the text, a statement of logical operations that would be described mathematically as follows: if (condition 0) statement 0 if (condition 1) statement 1 can be described as follows: When condition 0, statement 0 When condition 1, statement 1

[0499] Although embodiments of the invention have been described primarily on the basis of video coding, it should be noted that embodiments of the encoding system 10, encoder 20, and decoder 30 (and correspondingly the system 10) and the other embodiments described herein they can also be configured for image processing or coding, that is, the processing or coding of an individual image independent of any preceding or consecutive image as in video coding. In general, only inter prediction units 244 (encoder) and 344 (decoder) may not be available in case image processing coding is limited to a single image 17. All other features (also referred to as tools or technologies) of video encoder 20 and video decoder 30 may also be used for still image processing, e.g., residual calculation 204/304, transform 206, quantization 208, inverse quantization 210/310, (inverse) transform 212/312, partitioning 262/362, intra prediction 254 / 354 and/or loop filtering 220, 320 and entropy coding 270 and entropy decoding 304.

[0500] Embodiments of, for example, encoder 20 and decoder 30, and functions described herein, for example, with reference to encoder 20 and decoder 30, may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, functions can be stored on a computer-readable medium or transmitted via communication as one or more instructions or code, and executed by a hardware-based processing unit. Computer-readable medium may include computer-readable storage media, which corresponds to a tangible medium, such as data storage media or communication medium, including any medium that facilitates the transfer of a computer program from one place to another, for example, according to a communication protocol. In this way, computer-readable medium generally can correspond to (1) tangible computer-readable storage media that is non-transitory or (2) a communication medium, such as a signal or carrier wave. The data storage media may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementing the techniques described in this disclosure. A computer program product may include computer-readable media.

[0501] By way of example, and not limitation, such computer-readable storage media may 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. Furthermore, any connection is appropriately called a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave , then 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 transient media, but are directed to non-transitory tangible storage media. Disk and disc as used herein include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc, where disks are generally reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above must also be included in the scope of computer-readable media.

[0502] 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 others equivalent integrated or discrete logic circuits. Accordingly, the term "processor" as used herein may refer to any of the foregoing frameworks or any other framework suitable for implementing the techniques described herein. Additionally, in some aspects, the functionality described in this document may be provided in dedicated hardware and/or software modules configured for encoding and decoding, or incorporated into a combined codec. Furthermore, the techniques can be fully implemented in one or more circuits or logic elements.

[0503] The techniques of this disclosure can be implemented in a wide variety of devices or apparatus, including a portable wireless device, an integrated circuit (IC), or a set of ICs (e.g., a chip set). Various components, modules or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require performance by different hardware units. Instead, as described above, multiple units may be combined into a codec hardware unit or provided by a collection of interoperating hardware units, including one or more processors, as described above, in conjunction with suitable software and/or firmware. .

Claims (15)

1. Encoding method implemented by an encoding device, CHARACTERIZED by the fact that it comprises: generating a bit stream including a plurality of ALF-related syntax elements, wherein the plurality of ALF-related syntax elements comprises a first element syntax that indicates whether an adaptive loop filter (ALF) is enabled or not; a second syntax element is conditionally signaled in ALF-related syntax elements when the first syntax element has a first value, where the second syntax element indicates whether a cross-component adaptive loop filter (CC-ALF) is enabled or not. 2. Method according to claim 1, CHARACTERIZED by the fact that the plurality of ALF syntax elements comprises a seventh syntax element when the second syntax element indicates that CC-ALF is enabled, wherein the seventh syntax element syntax is signaled in the image header and the seventh syntax element specifies whether CC-ALF for a Cr color component is enabled for a current image of a video sequence associated with the bitstream. 3. Method, according to claim 2, CHARACTERIZED by the fact that if the seventh syntax element has a value of 1, this indicates that CC-ALF for the Cr color component is enabled for the current image and/or if If the seventh syntax element has a value of 0, this indicates that CC-ALF for the Cr color component is disabled for the current image. 4. Method according to claim 2 or 3, CHARACTERIZED by the fact that the plurality of ALF syntax elements comprises an eighth syntax element when the seventh syntax element is obtained as indicating that CC-ALF for the component of Cr color is enabled for the current image, where the eighth syntax element is obtained from the image header and the eighth syntax element indicates a set of parameters that is associated with the Cr color component of all slices in the current image . 5. Method according to any one of claims 1 to 4, CHARACTERIZED by the fact that the plurality of syntax elements related to ALF comprises a tenth syntax element when the second syntax element is obtained as indicating that CC-ALF is enabled, where the tenth syntax element is taken from a slice header and the tenth syntax element indicates whether CC-ALF for a Cb color component is enabled for a current slice of a current image of a video sequence associated with the bit stream. 6. Decoding method (4300) implemented by a decoding device, CHARACTERIZED by the fact that it comprises: analyzing (4301) a plurality of syntax elements related to ALF from a bit stream, wherein the plurality of syntax elements ALF-related syntax comprises a first syntax element that indicates whether an adaptive loop filter (ALF) is enabled or not; a second syntax element is conditionally signaled in ALF-related syntax elements when the first syntax element has a first value, where the second syntax element indicates whether a cross-component adaptive loop filter (CC-ALF) is enabled or not. 7. Method according to claim 6, CHARACTERIZED by the fact that the plurality of ALF syntax elements comprises a seventh syntax element when the second syntax element indicates that CC-ALF is enabled, wherein the seventh syntax element syntax is signaled in the image header and the seventh syntax element specifies whether CC-ALF for a Cr color component is enabled for a current image of a video sequence associated with the bitstream. 8. Method, according to claim 7, CHARACTERIZED by the fact that if the seventh syntax element has a value of 1, this indicates that CC-ALF for the Cr color component is enabled for the current image and/or if If the seventh syntax element has a value of 0, this indicates that CC-ALF for the Cr color component is disabled for the current image. 9. Method according to claim 7 or 8, CHARACTERIZED by the fact that the plurality of ALF syntax elements comprises an eighth syntax element when the seventh syntax element is obtained as indicating that CC-ALF for the component of Cr color is enabled for the current image, where the eighth syntax element is obtained from the image header and the eighth syntax element indicates a set of parameters that is associated with the Cr color component of all slices in the current image . 10. Method according to any one of claims 6 to 9, CHARACTERIZED by the fact that the plurality of syntax elements related to ALF comprises a tenth syntax element when the second syntax element is obtained as indicating that CC-ALF is enabled, where the tenth syntax element is taken from a slice header and the tenth syntax element indicates whether CC-ALF for a Cb color component is enabled for a current slice of a current image of a video sequence associated with the bit stream. 11. Device for encoding video data, CHARACTERIZED by the fact that it comprises: a video data memory; and a video encoder, wherein the video encoder is configured to: generate a bitstream including a plurality of ALF-related syntax elements, wherein the plurality of ALF-related syntax elements comprises a first syntax element that indicates whether an adaptive loop filter (ALF) is enabled or not; a second syntax element is conditionally signaled in ALF-related syntax elements when the first syntax element has a first value, where the second syntax element indicates whether a cross-component adaptive loop filter (CC-ALF) is enabled or not. 12. Device for decoding video data, CHARACTERIZED by the fact that it comprises: a video data memory; and a video decoder, wherein the video decoder is configured to: parse a plurality of ALF-related syntax elements from a bit stream, wherein the plurality of ALF-related syntax elements comprises a first syntax that indicates whether an adaptive loop filter (ALF) is enabled or not; a second syntax element is conditionally signaled in ALF-related syntax elements when the first syntax element has a first value, where the second syntax element indicates whether a cross-component adaptive loop filter (CC-ALF) is enabled or not. 13. Computer-readable storage media, CHARACTERIZED by the fact that it comprises thereon computer-executable instructions that, when executed by a computing device, cause the computing device to perform a method as defined in any one of claims 1 to 10. 14. Non-transitory storage media, CHARACTERIZED by the fact that it comprises a stream of bits encoded/decoded by the method as defined in any of the preceding claims. 15. Coded bit stream, CHARACTERIZED by the fact that the bit stream comprises: including a plurality of ALF-related syntax elements, wherein the plurality of ALF-related syntax elements comprises a first syntax element that indicates whether a adaptive loop filter (ALF) is enabled or not; a second syntax element is conditionally signaled in ALF-related syntax elements when the first syntax element has a first value, where the second syntax element indicates whether a cross-component adaptive loop filter (CC-ALF) is enabled or not.