Chroma deblocking harmonization for video coding

1 . A method for processing video, comprising:

deriving, for a conversion between a video processing unit of the video and a bitstream of the video processing unit, at least one decision result associated with decisions in a chroma deblocking filter decision process of the video processing unit;

applying a same decision result from the at least one decision result for all chroma components of the video processing unit; and

performing the conversion based on the same decision result,

wherein the chroma components of the video processing unit include a first chroma component and a second chroma component,

wherein information of only one colour component is utilized to derive a decision for both the first chroma component and the second chroma component;

wherein the decision made for the first chroma component is applied to the second chroma component; or

wherein the decision made for the second chroma component is applied to the first chroma component.

2 . The method of claim 1 , wherein the first chroma component is a blue difference chroma (Cb) colour component and the second chroma component is a red difference chroma (Cr) colour component when the video processing unit is in a luma (Y), Cb, Cr (YCbCr) format; or

wherein the first chroma component is a green (G) colour component and the second chroma component is a blue (B) colour component when the video processing unit is in an red (R), G, B (RGB) format.

3 . The method of claim 2 , wherein the decision result indicates a decision that deblocking filter shall be performed to chroma block boundaries.

4 . The method of claim 3 , wherein the decision result indicates a decision whether applying deblocking filter for one chroma component, and when the decision indicates that applying deblocking filter for one chroma component, the decision is applied to all chroma components; or

wherein the decision result indicates a decision whether to apply a deblocking filter for one colour component, and when the decision indicates applying the deblocking filter for one colour component, the decision is applied to all colour components.

5 . The method of claim 3 , wherein the decision result indicates a decision whether to apply a strong deblocking filter for one chroma component, and when the decision indicates to apply a strong deblocking filter for one chroma component, the decision is applied to all chroma components; or

wherein the decision result indicates a decision whether to apply a strong deblocking filter for one colour component, and when the decision indicates to apply the strong deblocking filter for one colour component, the decision is applied to all colour components.

6 . The method of claim 2 , wherein the decision result indicates a decision of boundary strength.

7 . The method of claim 6 , wherein when at least one of an adjacent first chroma component block and an adjacent second chroma component block has non-zero transform coefficients, the boundary strength for the adjacent first chroma component block and the adjacent second chroma component block are set to 1; or

wherein when at least one of the adjacent first chroma component block and the adjacent second chroma component block has non-zero transform coefficients and none of the adjacent first chroma component block and the adjacent second chroma component block is intra coded, the boundary strength for the adjacent first chroma component block and the adjacent second chroma component block is set to 1.

8 . The method of claim 6 , wherein when at least one of an adjacent first chroma component block or an adjacent second chroma component block has non-zero transform coefficients and at least one of the adjacent second chroma component blocks has non-zero transform coefficients, the boundary strength for the adjacent first chroma component block and the adjacent second chroma component block is set to 1; or

wherein when both adjacent first chroma component blocks do not have non-zero transform coefficients, or both adjacent second chroma component blocks do not have non-zero transform coefficients, the boundary strength for the adjacent first chroma component block and the adjacent second chroma component block is set to 0; or

wherein when at least one of the adjacent first chroma component block or the adjacent second chroma component block has non-zero transform coefficients and at least one of the adjacent second chroma component blocks has non-zero transform coefficients and none of the adjacent first chroma component block and adjacent second chroma component block is intra coded, the boundary strength for the adjacent first chroma component block and adjacent second chroma component block is set to 1.

9 . The method of claim 2 , wherein information of both the first chroma component and the second chroma component is utilized to derive the decision for both the first chroma component and the second chroma component;

wherein the decision is applied to both the first chroma component and the second chroma component; or

wherein the decision includes a first decision and a final decision, wherein the first decision is made for the first chroma component and the second chroma component, respectively, and the final decision applied to both the first chroma component and the second chroma component is based on the first decision.

10 . The method of claim 1 , further comprising:

deriving at least one deblocking filter associated with a chroma deblocking filter process of the video processing unit;

applying a same deblocking filter from the at least one deblocking filter for all chroma components of the video processing unit; and

performing the conversion based on the same deblocking filter.

11 . The method of claim 10 , further comprising:

deriving deblocking parameters associated with the chroma deblocking filter decision process or the chroma deblocking filter process of the video processing unit;

applying a same deblocking parameters from the deblocking parameters for all chroma components of the video processing unit; and

performing the conversion based on the same deblocking parameters,

wherein the deblocking parameters include at least one of parameters β and t C involved in the chroma deblocking filter decision process and the chroma deblocking filter process, and wherein the parameters β and t C are derived based on quantization parameters of blocks on both sides of a boundary.

12 . The method of claim 11 , wherein the parameters β and t C for all chroma components follow one chroma component.

13 . The method of claim 11 , wherein the parameters β and t C for all chroma components depend on an average of pps_cb_qp_offset or pps_cr_qp_offset, and wherein the pps_cb_qp_offset and pps_cr_qp_offset are syntax elements which specify offsets to a luma quantization parameter used for deriving chroma quantization parameter of Cb and Cr components, respectively.

14 . The method of claim 11 , wherein the parameters β and t C for all chroma components depend on pps_joint_cbcr_qp_offset, wherein pps_joint_cbcr_qp_offset is a syntax element which specifies an offset to a luma quantization parameter used for deriving joint chroma quantization parameter, or wherein the parameters β and t C for all chroma components depend on an average of (pps_cb_qp_offset+slice_cb_qp_offset) and (pps_cr_qp_offset+slice_cr_qp_offset);

wherein the pps_cb_qp_offset and pps_cr_qp_offset are syntax elements signaled in a sequence parameter set (SPS), which specifies the offsets to the luma quantization parameter used for deriving a chroma quantization parameter of Cb and Cr components, respectively; and

wherein the slice_cb_qp_offset and slice_cr_qp_offset are syntax elements signaled in a slice header, which specifies a difference to be added to a value of pps_cb_qp_offset and a value of pps_cr_qp_offset when determining a value of the chroma quantization parameter of Cb and Cr components, respectively, or wherein the parameters β and t C for all chroma components depend on slice_joint_cbcr_qp_offset, wherein the slice_joint_cbcr_qp_offset is a syntax element signaled in the slice header, which specifies a difference to be added to a value of pps_joint_cbcr_qp_offset_value when determining a value of joint chroma quantization parameter, and the pps_joint_cbcr_qp_offset is a syntax element signaled in the SPS, which specifies the offset to the luma quantization parameter used for deriving joint chroma quantization parameter.

15 . The method of claim 11 , wherein the decision process of whether to apply the chroma deblocking filter or the chroma deblocking filter process depends on whether a colour format of the video processing unit is 4:2:0 and/or 4:2:2, and wherein indications of usage of the chroma deblocking filter decision process or the chroma deblocking filter process are signaled in at least one of sequence, picture, slice, tile group, tile, brick and a video region-level, or signaled in at least one of video parameter set (VPS), sequence parameter set (SPS), picture parameter set (PPS), picture header, slice header, and tile group header.

16 . The method of claim 1 , wherein the conversion includes encoding the video processing unit of the video into the bitstream.

17 . The method of claim 1 , wherein the conversion includes decoding the bitstream from the video processing unit of the video.

18 . An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

derive, for a conversion between a video processing unit of the video and a bitstream of the video processing unit, at least one decision result associated with decisions in a chroma deblocking filter decision process of the video processing unit;

apply a same decision result from the at least one decision result for all chroma components of the video processing unit; and

perform the conversion based on the same decision result,

wherein the chroma components of the video processing unit include a first chroma component and a second chroma component,

wherein information of only one colour component is utilized to derive a decision for both the first chroma component and the second chroma component;

wherein the decision made for the first chroma component is applied to the second chroma component; or

wherein the decision made for the second chroma component is applied to the first chroma component.

19 . A method for storing a bitstream of a video, comprising:

deriving, for a video processing unit of the video, at least one decision result associated with decisions in a chroma deblocking filter decision process of the video processing unit;

applying a same decision result from the at least one decision result for all chroma components of the video processing unit;

generating the bitstream based on the same decision result; and

storing the bitstream in a non-transitory computer-readable recording medium,

wherein the chroma components of the video processing unit include a first chroma component and a second chroma component,

wherein information of only one colour component is utilized to derive a decision for both the first chroma component and the second chroma component;

wherein the decision made for the first chroma component is applied to the second chroma component; or

wherein the decision made for the second chroma component is applied to the first chroma component.