Independent subpicture film grain

1 . A method for applying film grain to regions of a picture, the method comprising

decoding region information from syntax elements in a bitstream;

deriving, based on the region information, a number of regions in the picture, wherein the number of regions is at least two;

deriving, based on the region information, a first region raster-scan order for a first region of the at least two regions;

deriving a first region identifier value for the first region;

generating a first seed value for the first region based on the first region identifier value, and

decoding the first region, wherein

decoding the first region comprises applying film grain to the first region using the first seed value and in accordance with the first region raster-scan order.

2 . The method of claim 1 , wherein a region is one of a subpicture or a slice of the picture.

3 . The method of claim 1 , wherein a region is a rectangular region.

4 . The method of claim 1 , further comprising:

deriving, based on the region information, a second region raster-scan order for a second region of the at least two regions; and

decoding the second region, wherein

decoding the second region comprises applying film grain to the second region in accordance with the second region raster-scan order, and

the second region raster-scan order is different than the first region raster-scan order.

5 . The method of claim 1 , wherein

the method further comprises:

obtaining a second seed value for a second region of the picture; and

applying film grain to the second region using the second seed value.

6 . The method of claim 1 , wherein the region raster-scan order comprises a block-based raster-scan order for a plurality of blocks in the first region, the method further comprising:

applying film grain to the plurality of blocks in the first region in accordance with the block-based raster-scan order.

7 . The method of claim 1 , wherein the region raster-scan order comprises: (i) a block-based raster-scan order for a plurality of blocks in the first region and (ii) a respective raster-scan order within each block of the plurality of blocks in the first region, the method further comprising:

applying film grain to a first block of the plurality of blocks in the first region in accordance with the block-based raster-scan order and the respective raster-scan order within the first block.

8 . The method of claim 1 , further comprising:

determining whether a first block and a second block share a common block edge within the picture;

determining whether the first block and the second block that share the common block edge within the picture belong to a same region; and

in response to a determination that the first block and the second block belong to the same region, applying a film grain deblocking filter to the common block edge.

9 . The method of claim 8 , further comprising:

in response to a determination that the first block and the second block that share the common block edge do not belong to the same region, determining not to apply a film grain deblocking filter to the common block edge.

10 . The method of claim 1 , wherein the applying film grain to the first region comprises:

generating a first seed value for the first region; and

initializing a pseudo-random number generator with the first seed value for the first region for use in the applying film grain to the first region.

11 . The method of claim 10 , further comprising:

generating a second seed value for a second region of the at least two regions, wherein the second seed value is different than the first seed value;

initializing a pseudo-random number generator with the second seed value for the second region; and

decoding the second region, wherein the decoding the second region comprises applying film grain to the second region using the pseudo-random number generator initialized with the second seed value.

12 . The method of claim 10 , further comprising:

initializing the pseudo-random number generator with the first seed value for a second region of the at least two regions; and

decoding the second region of the at least two regions, wherein the decoding the second region comprises applying film grain to the second region using the pseudo-random number generator initialized with the first seed value.

13 . The method of claim 1 , the method further comprising:

deriving a first mode value from syntax elements in the bitstream, wherein the first mode value is equal to a first value or a second value,

wherein the first value indicates to apply film grain treating each region of the at least two regions in the picture individually using a respective region raster-scan order for each region, and

wherein the second value indicates to apply film grain to each region of the at least two regions in the picture as a whole using a raster-scan order for the picture.

14 . The method of claim 13 , further comprising:

in response to a determination that the first mode value equals the first value, determining whether a first block and a second block that share a common block edge within the picture belong to a same region; and

in response to a determination that the first block and the second block belong to the same region, applying a film grain deblocking filter to the common block edge.

15 . The method of claim 1 , further comprising:

deriving a region mode value for each region of the at least two regions from syntax elements in the bitstream, wherein the region mode value is equal to a first value or a second value,

wherein the first value indicates to apply a film grain deblocking filter to each block edge within a region except for block edges between neighboring regions, and

wherein the second value indicates to apply a film grain deblocking filter to each block edge within a region inclusive of block edges between neighboring regions.

16 . The method of claim 15 , further comprising:

deriving a first region mode value for a first block belonging to the first region;

deriving a second region mode value for a second block belonging to a second region, wherein the first block and the second block share a common block edge within the picture;

determining whether the first region mode value equals the second value and the second region mode value equals the second value; and

in response to a determination that the first region mode value equals the second value and the second region mode value equals the second value, applying a film grain deblocking filter to the common block edge.

17 . The method claim 1 , further comprising:

deriving a second region identifier value for a second region of the at least two regions;

generating a second seed value for the second region based on the second region identifier value; and

decoding the second region, wherein the decoding the second region comprises applying film grain to the second region using the second seed value.

18 . The method of claim 17 , wherein the first region and the second region share a common vertical region edge.

19 . The method of claim 1 , wherein the first seed value is further based on a picture order count value for the picture.

20 . The method of claim 1 , wherein the first region is a subpicture and the first region identifier is a subpicture identifier.

21 . The method of claim 1 , wherein the first region identifier value is obtained from a syntax element in one or more of:

a picture parameter set,

a sequence parameter set,

a picture header, or

a slice header.

22 . A computer program product comprising a non-transitory computer-readable medium carrying instructions which when executed by processing circuitry of a decoder, causes the decoder to perform a method comprising:

decoding region information from syntax elements in a bitstream;

deriving, based on the region information, a number of regions in the picture, wherein the number of regions is at least two;

deriving, based on the region information, a first region raster-scan order for a first region of the at least two regions;

deriving a first region identifier value for the first region;

generating a first seed value for the first region based on the first region identifier value; and

decoding the first region, wherein

decoding the first region comprises applying film grain to the first region using the first seed value and in accordance with the first region raster-scan order.

23 . A decoding apparatus, the apparatus comprising:

memory; and

processing circuitry, wherein the decoding apparatus is configured to perform a process comprising:

decoding region information from syntax elements in a bitstream;

deriving, based on the region information, a number of regions in the picture, wherein the number of regions is at least two;

deriving, based on the region information, a first region raster-scan order for a first region of the at least two regions;

deriving a first region identifier value for the first region;

generating a first seed value for the first region based on the first region identifier value; and

decoding the first region, wherein

decoding the first region comprises applying film grain to the first region using the first seed value and in accordance with the first region raster-scan order.