Methods and devices for decoder-side intra mode derivation

1 . A method for video decoding, comprising:

determining, by a decoder, a unified fusion scheme applied in decoder-side intra mode derivation (DIMD) mode and template-based intra mode derivation (TIMD) mode, wherein the unified fusion scheme is applied as a weighted average of predictors in the DIMD mode and the TIMD mode; and

wherein determining, by the decoder, the unified fusion scheme applied in the DIMD mode and the TIMD mode comprises:

applying, by the decoder, a fusion scheme adopted in the DIMD mode to the TIMD mode, such that a fusion scheme in the TIMD mode is determined via following operations:

selecting, by the decoder, a planar mode and two modes with a smallest sum of absolute transformed differences (SATD) cost in the TIMD mode as predictors for the fusion scheme in the TIMD mode; and

determining, by the decoder, a weighted average of the planar mode and the two modes with the smallest SATD cost, wherein a weight of the planar mode is fixed in the fusion scheme in the TIMD mode, and a remaining weight is shared between the two modes based on a SATD cost of each of the two modes.

2 . The method for video decoding of claim 1 , further comprising:

receiving, by the decoder, a selection of the fusion scheme in the TIMD mode or in the DIMD mode.

3 . The method for video decoding of claim 2 , further comprising:

receiving, by the decoder, a signaled flag indicating whether the DIMD mode is applied to a block; and

in response to determining, by the decoder, that the DIMD mode is applied to the block, receiving, by the decoder, another signaled flag to indicate the fusion scheme to be applied to the block.

4 . The method for video decoding of claim 1 , further comprising:

determining, by the decoder, whether to add intra modes derived from the DIMD mode into a list of intra most probable modes (MPMs) based on whether the fusion scheme is applied in the DIMD mode.

5 . The method for video decoding of claim 4 , wherein determining whether to add intra modes derived from the DIMD mode into the list of MPMs comprises:

in response to determining that the fusion scheme is applied in the DIMD mode, adding the intra modes derived from the DIMD mode as a candidate for the list of MPMs; and

in response to determining that the fusion scheme is not applied in the DIMD mode, not adding the intra modes derived from the DIMD mode as the candidate for the list of MPMs.

6 . The method for video decoding of claim 1 , further comprising:

determining, by the decoder, whether to add intra modes derived from the TIMD mode into a list of intra most probable modes (MPMs).

7 . The method for video decoding of claim 6 , further comprising:

in response to determining, by the decoder, that intra modes derived from the DIMD mode is not added as a candidate for the list of the MPMs, adding the intra modes derived from the TIMD mode as the candidate for the list of MPMs.

8 . The method for video decoding of claim 6 , further comprising:

determining, by the decoder, whether to add intra modes derived from the TIMD mode into a list of MPMs based on whether the fusion scheme is applied in the TIMD mode.

9 . The method for video decoding of claim 8 , further comprising:

in response to determining, by the decoder, that the fusion scheme is applied in the TIMD mode, adding the intra modes derived from the TIMD mode as a candidate for the list of MPMs; and

in response to determining, by the decoder, that the fusion scheme is not applied in the TIMD mode, not adding the intra modes derived from the TIMD mode as the candidate for the list of MPMs.

10 . An apparatus for video decoding, comprising:

one or more processors; and

a memory configured to store instructions executable by the one or more processors and a bitstream to be decoded; wherein the one or more processors, upon execution of the instructions, are configured to perform operations with the bitstream, the operations comprising:

determining a unified fusion scheme applied in decoder-side intra mode derivation (DIMD) mode and template-based intra mode derivation (TIMD) mode, wherein the unified fusion scheme is applied as a weighted average of predictors in the DIMD mode and the TIMD mode; and

wherein determining the unified fusion scheme applied in the DIMD mode and the TIMD mode comprises:

applying a fusion scheme adopted in the DIMD mode to the TIMD mode, such that a fusion scheme in the TIMD mode is determined via following operations:

selecting a planar mode and two modes with a smallest sum of absolute transformed differences (SATD) cost in the TIMD mode as predictors for the fusion scheme in the TIMD mode; and

determining a weighted average of the planer mode and the two modes with the smallest SATD cost, wherein a weight of the planar mode is fixed in the fusion scheme in the TIMD mode, and a remaining weight is shared between the two modes based on a SATD cost of each of the two modes.

11 . The apparatus for video decoding of claim 10 , wherein the operations further comprise:

determining whether to add intra modes derived from the DIMD mode into a list of intra most probable modes (MPMs) based on whether the fusion scheme is applied in the DIMD mode.

12 . The apparatus for video decoding of claim 10 , wherein the operations further comprise:

determining whether to add intra modes derived from the TIMD mode into a list of intra most probable modes (MPMs).

13 . A method for storing a bitstream, comprising:

storing the bitstream to be decoded on a non-transitory computer-readable storage medium, the bitstream is generated by operations comprising:

determining a unified fusion scheme applied in decoder-side intra mode derivation (DIMD) mode and template-based intra mode derivation (TIMD) mode, wherein the unified fusion scheme is applied as a weighted average of predictors in the DIMD mode and the TIMD mode; and

wherein determining the unified fusion scheme applied in the DIMD mode and the TIMD mode comprises:

applying a fusion scheme adopted in the DIMD mode to the TIMD mode, such that a fusion scheme in the TIMD mode is determined via:

selecting a planar mode and two modes with a smallest sum of absolute transformed differences (SATD) cost in the TIMD mode as predictors for the fusion scheme in the TIMD mode; and

determining a weighted average of the planer mode and the two modes with the smallest SATD cost, wherein a weight of the planar mode is fixed in the fusion scheme in the TIMD mode, and a remaining weight is shared between the two modes based on a SATD cost of each of the two modes.

14 . The method of claim 13 , wherein the operations further comprise:

determining whether to add intra modes derived from the DIMD mode into a list of intra most probable modes (MPMs) based on whether the fusion scheme is applied in the DIMD mode.

15 . The method of claim 13 , wherein the operations further comprise:

determining whether to add intra modes derived from the TIMD mode into a list of intra most probable modes (MPMs).