Context adaptive transform set

1. A method performed by at least one processor, the method comprising:

receiving a coded bitstream; and

decoding a block of a picture from the coded bitstream, the decoding comprising:

selecting a transform set based on at least one neighboring reconstructed sample from one or more previously decoded neighboring blocks or from a previously decoded picture; and

inverse transforming coefficients of the block using a transform from the transform set,

wherein the selecting the transform set comprises:

selecting a sub-group of transform sets from a group of transform sets based on coded information of an intra prediction mode or an inter prediction mode; and

selecting the transform set from the sub-group,

the selecting the transform set from the sub-group comprises selecting the transform set based on coded information of a type of the intra prediction mode or the inter prediction mode, a block size, prediction block samples of the block, or the at least one neighboring reconstructed sample, and

the method further comprises selecting a transform candidate from the transform set based on an index value signaled in the coded bitstream.

2. The method of claim 1 , wherein the selecting the transform set from the sub-group comprises selecting the transform set based on the coded information of the type of the intra prediction mode or the inter prediction mode.

3. The method of claim 2 , wherein the selecting the transform set from the sub-group comprises selecting the transform set based on the coded information of the type of the inter prediction mode.

4. The method of claim 1 , wherein the at least one neighboring reconstructed sample includes a reconstructed sample from the one or more previously decoded neighboring blocks.

5. The method of claim 1 , wherein

the group of transform sets includes only secondary transform kernels.

6. The method of claim 5 , wherein the second transform kernels are non-separable.

7. The method of claim 1 , wherein the transform set is a secondary transform.

8. A system comprising:

at least one memory configured to store computer program code; and

at least one processor configured to access the computer program code and operate as instructed by the computer program code, the computer program code comprising decoding code that is configured to cause the at least one processor to decode a block of a picture from a coded bitstream that is received,

wherein the decoding code comprises:

transform set selecting code configured to cause the at least one processor to select a transform set based on at least one neighboring reconstructed sample from one or more previously decoded neighboring blocks or from a previously decoded picture; and

transforming code configured to cause the at least one processor to inverse transform coefficients of the block using a transform from the transform set,

wherein the transform set selecting code is configured to cause the at least one processor to:

select a sub-group of transform sets from a group of transform sets based on coded information of an intra prediction mode or an inter prediction mode; and

select the transform set from the sub-group,

the transform set selecting code is configured to cause the at least one processor to select the transform set based on coded information of a type of the intra prediction mode or the inter prediction mode, a block size, prediction block samples of the block, or the at least one neighboring reconstructed sample, and

the decoding code further comprises transform selecting code configured to cause the at least one processor to select a transform candidate from the transform set based on an index value signaled in the coded bitstream.

9. The system of claim 8 , wherein the transform set selecting code is configured to cause the at least one processor to select the transform set based on the coded information of the type of the intra prediction mode or the inter prediction mode.

10. The system of claim 9 , wherein the transform set selecting code is configured to cause the at least one processor to select the transform set based on the coded information of the type of the inter prediction mode.

11. The system of claim 8 , wherein the at least one neighboring reconstructed sample includes a reconstructed sample from the one or more previously decoded neighboring blocks.

12. The system of claim 8 , wherein

the group of transform sets includes only secondary transform kernels.

13. The system of claim 12 , wherein the second transform kernels are non-separable.

14. A non-transitory computer-readable medium storing computer instructions that are configured to, when executed by at least one processor, cause the at least one processor to decode a block of a picture from a received coded bitstream by:

selecting a transform set based on at least one neighboring reconstructed sample from one or more previously decoded neighboring blocks or from a previously decoded picture; and

inverse transforming coefficients of the block using a transform from the transform set,

wherein the selecting the transform set comprises:

selecting a sub-group of transform sets from a group of transform sets based on coded information of an intra prediction mode or an inter prediction mode; and

selecting the transform set from the sub-group,

the selecting the transform set from the sub-group comprises selecting the transform set based on coded information of a type of the intra prediction mode or the inter prediction mode, a block size, prediction block samples of the block, or the at least one neighboring reconstructed sample, and

the computer instructions are further configured to, when executed by the at least one processor, cause the at least one processor to decode the block by selecting a transform candidate from the transform set based on an index value signaled in the coded bitstream.

15. The method of claim 1 , wherein the selecting the transform set from the sub-group comprises selecting the transform set based on the coded information of the block size.

16. The method of claim 1 , wherein the selecting the transform set from the sub-group comprises selecting the transform set based on the coded information of the prediction block samples of the block.

17. The method of claim 1 , wherein the selecting the transform set from the sub-group comprises selecting the transform set based on the coded information of the at least one neighboring reconstructed sample.