Patent ID: 11882284
Assignee: FRAUNHOFER GESELLSCHAFT ZUR FÖRDERUNG DER ANGEWANDTEN FORSCHUNG E.V.
Field: Audio-visual technology (Electrical engineering)
Classification: CPC H | IPC H

Claim 16:
17. A video decoder for decoding a picture into a data stream using block-based prediction and block-based residual coding, the video decoder comprising:
at least one processor configuredto:
determine a set of transform candidates for a current residual block out of a set of transforms based on a height and a width of the current residual block and positions of significant transform coefficients, the determined set including a reverse transform of a primary transform, the set of transforms including reverse transforms of a plurality of multi-stage transforms and the reverse transform of the primary transform, each of the multi-stage transforms including the primary transform and a respective non-separable secondary transform applied to primary transform coefficients resulting in respective secondary transform coefficients,
wherein the at least one processor is configured to determine the set of transform candidates by:
determining whether at least one transform coefficient outside a sub-group of transform coefficient positions is significant;
in response to a determination that no transform coefficient outside the sub-group is significant, including the reverse transforms for the plurality of multi-stage transforms in the determined set; and
in response to a determination that at least one transform coefficient outside the sub-group is significant, omitting the reverse transforms for the plurality of multi-stage transforms from the determined set;

select a transform from the determined set of transform candidates and decode a prediction residual within the current residual block, wherein the at least one processor is configured to select a transform by selectively decoding the transform by:
when the determined set of transform candidates includes the reverse transforms for the plurality of multi-stage transforms, decoding an index from the data stream, and
when the reverse transforms for the plurality of multi-stage transforms are excluded from the determined set of transform candidates, not decoding the index from the data stream.