Usage of templates for decoder-side intra mode derivation

An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

• construct, during a conversion between a current video block of a video and a bitstream of the video, at least one template set for the current video block from a plurality of sub-templates;
• derive at least one intra-prediction mode (IPM) based on cost calculations, wherein the cost calculations are determined based on the at least one template set and the current block;
• determine, based on the at least one IPM, a final predictor of the current video block;
• and
• perform the conversion based on the final predictor,
• wherein the at least one template set is selected from the plurality of sub-templates based on a coding information for the current video block, wherein the coding information includes a block dimension of the current video block, and the at least one template set is selected from the plurality of sub-templates based on a relationship between the block dimension of the current video block and a pre-defined threshold, and wherein a BW represents a block width of the current video block and a BH represents a block height of the current video block, and
• wherein a left sub-template is not selected in a case that the BW divided by the BH is greater than or equal to a first threshold.

A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:

• constructing, during a conversion between a current video block of a video and a bitstream of the video, at least one template set for the current video block from a plurality of sub-templates;
• deriving at least one intra-prediction mode (IPM) based on cost calculations, wherein the cost calculations are determined based on the at least one template set and the current block;
• determining, based on the at least one IPM, a final predictor of the current video block;
• and
• generating the bitstream based on the final predictor,
• wherein the at least one template set is selected from the plurality of sub-templates based on a coding information for the current video block, wherein the coding information includes a block dimension of the current video block, and the at least one template set is selected from the plurality of sub-templates based on a relationship between the block dimension of the current video block and a pre-defined threshold, and wherein a BW represents a block width of the current video block and a BH represents a block height of the current video block, and
• wherein a left sub-template is not selected in a case that the BW divided by the BH is greater than or equal to a first threshold.

A non-transitory computer-readable storage medium storing instructions that cause a processor to:

• construct, during a conversion between a current video block of a video and a bitstream of the video, at least one template set for the current video block from a plurality of sub-templates;
• derive at least one intra-prediction mode (IPM) based on cost calculations, wherein the cost calculations are determined based on the at least one template set and the current block;
• determine, based on the at least one IPM, a final predictor of the current video block;
• and
• perform the conversion based on the final predictor,
• wherein the at least one template set is selected from the plurality of sub-templates based on a coding information for the current video block, wherein the coding information includes a block dimension of the current video block, and the at least one template set is selected from the plurality of sub-templates based on a relationship between the block dimension of the current video block and a pre-defined threshold, and wherein a BW represents a block width of the current video block and a BH represents a block height of the current video block, and
• wherein a left sub-template is not selected in a case that the BW divided by the BH is greater than or equal to a first threshold.