Chroma processing for video encoding and decoding

1. A method for encoding picture information, the method comprising:

determining a first scaling factor varying with a first granularity to scale a chroma prediction residual associated with chroma information included in the picture information;

determining a second scaling factor varying with a second granularity finer than the first granularity;

scaling the chroma prediction residual based on a combination of the first scaling factor and the second scaling factor to provide a scaled chroma prediction residual with the second granularity; and

encoding at least a portion of the picture information based on the scaled chroma prediction residual.

2. The method of claim 1 , wherein the second scaling factor is determined based on luma information included in the picture information and located in a vicinity of the chroma information;

determining the first scaling factor comprises determining a scaling index referring to an entry in a table of a plurality of scaling factors; and

encoding the at least a portion of the picture information includes encoding the scaling index.

3. The method of claim 2 , wherein encoding the scaling index comprises including the scaling index as a syntax element of an encoded bitstream produced by the encoding.

4. The method of claim 2 , wherein encoding the scaling index comprises encoding the scaling index for at least one structural entity.

5. A method for decoding picture information, the method comprising:

determining a first scaling factor varying with a first granularity to scale a chroma prediction residual associated with chroma information included in the picture information;

determining a second scaling factor varying with a second granularity finer than the first granularity;

scaling the chroma prediction residual based on a combination of the first scaling factor and the second scaling factor to provide a scaled chroma prediction residual with the second granularity; and

decoding at least a portion of the picture information based on the scaled chroma prediction residual.

6. The method of claim 5 , wherein the second scaling factor is determined based on luma information included in the picture information and located in a vicinity of the chroma information;

determining the first scaling factor comprises determining a scaling index referring to an entry in a table of a plurality of scaling factors; and

decoding the at least a portion of the picture information is based on the scaling index.

7. The method of claim 6 , wherein determining the scaling index comprises determining the scaling index from a syntax element of an encoded bitstream including the picture information.

8. The method of claim 6 , wherein determining the scaling index comprises determining the scaling index for at least one structural entity.

9. The method of claim 8 , wherein the at least one structural entity comprises at least one of a CTU, or a VDPU, or a CU, or a TU, or a slice, or a tile, or a brick, or a quantization group, or a plurality of non-overlapping areas of size Wc*Hc, where Wc and Hc are either pre-defined values or values signaled in the bitstream.

10. The method of claim 6 , wherein the second scaling factor being determined based on luma information located in a vicinity of the chroma information comprises one of

a. an average value of prediction or reconstructed luma samples, collocated with the chroma area, or

b. a median value of prediction or reconstructed luma samples, collocated with the chroma area, or

c. a percentage of the largest values of the prediction or reconstructed luma samples, collocated with the chroma area, or

d. a percentage of the lowest values of the prediction or reconstructed luma samples, collocated with the chroma area.

11. A non-transitory computer readable medium storing executable program instructions to cause a computer executing the instructions to perform a method according to claim 5 .

12. Apparatus for encoding picture information comprising:

one or more processors configured to

determine a first scaling factor varying with a first granularity to scale a chroma prediction residual associated with chroma information included in the picture information;

determine a second scaling factor varying with a second granularity finer than the first granularity;

scale the chroma prediction residual based on a combination of the first scaling factor and the second scaling factor to provide a scaled chroma prediction residual with the second granularity; and

encode at least a portion of the picture information based on the scaled chroma prediction residual.

13. The apparatus of claim 12 , wherein the one or more processors are further configured to

determine the second scaling factor based on luma information included in the picture information and located in a vicinity of the chroma information; and

determine a scaling index referring to an entry in a table of a plurality of scaling factors; and

encode the scaling index.

14. The apparatus of claim 13 , wherein the one or more processors being configured to encode the scaling index comprises the one or more processors being further configured to include the scaling index as a syntax element of an encoded bitstream produced by the encoding.

15. The apparatus of claim 13 , wherein the one or more processors being configured to encode the scaling index comprises the one or more processors being further configured to encode the scaling index for at least one structural entity.

16. Apparatus for decoding picture information comprising:

one or more processors configured to

determine a first scaling factor varying with a first granularity to scale a chroma prediction residual associated with chroma information included in the picture information;

determine a second scaling factor varying with a second granularity finer than the first granularity;

scale the chroma prediction residual based on a combination of the first scaling factor and the second scaling factor to provide a scaled chroma prediction residual with the second granularity; and

decode at least a portion of the picture information based on the scaled chroma prediction residual.

17. The apparatus of claim 16 , wherein the one or more processors are further configured to

determine the second scaling factor based on luma information included in the picture information and located in a vicinity of the chroma information; and

determine a scaling index referring to an entry in a table of a plurality of scaling factors; and decode the at least a portion of the picture information based on the scaling index.

18. The apparatus of claim 17 , wherein the one or more processors are further configured to determine the scaling index from a syntax element of an encoded bitstream including the picture information.

19. The apparatus of claim 17 , wherein the one or more processors being configured to determine the scaling index comprises the one or more processors being configured to determine the scaling index for at least one structural entity.

20. The apparatus of claim 19 , wherein the at least one structural entity comprises at least one of a CTU, or a VDPU, or a CU, or a TU, or a slice, or a tile, or a brick, or a quantization group, or a plurality of non-overlapping areas of size Wc*Hc, where Wc and Hc are either pre-defined values or values signaled in the bitstream.

21. The apparatus of claim 17 , wherein the second scaling factor being determined based on luma information located in a vicinity of the chroma information comprises one of

a. an average value of prediction or reconstructed luma samples, collocated with the chroma area, or

b. a median value of prediction or reconstructed luma samples, collocated with the chroma area, or

c. a percentage of the largest values of the prediction or reconstructed luma samples, collocated with the chroma area, or

d. a percentage of the lowest values of the prediction or reconstructed luma samples, collocated with the chroma area.

22. The apparatus of claim 16 , further comprising at least one of (i) an antenna configured to receive a signal, the signal including data representative of the image information, (ii) a band limiter configured to limit the received signal to a band of frequencies that includes the data representative of the image information, and (iii) a display configured to display an image from the image information.

23. The apparatus of claim 22 , wherein the apparatus comprises one of a television, a television signal receiver, a set-top box, a gateway device, a mobile device, a cell phone, a tablet, or other electronic device.