Intra video coding using multiple reference filters

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:

• determine, for a conversion between a first video block of a video and a bitstream of the video, that a first coding tool is applied for the first video block, wherein in the first coding tool, the first video block is split into multiple sub-regions in horizontal direction or vertical direction;
• generate prediction samples for at least one of the multiple sub-regions based on a first reference interpolation filtering process;
• and
• perform the conversion based on the prediction samples,
• wherein in the first reference interpolation filtering process, a first 4-tap interpolation filter is applied, and wherein the multiple sub-regions share a same intra mode,
• wherein for a second video block without applying the first coding tool, a second reference interpolation filtering process is used, and wherein in the second reference interpolation filtering process, one of the first 4-tap interpolation filter and a second 4-tap interpolation filter is selected based on at least one of the following:
• an intra mode of the second video block, positions of reference samples of the second video block and a size of the second video block, and the second 4-tap interpolation filter is different from the first 4-tap interpolation filter, and
• wherein in a case that an index of the intra mode of the second video block is one of a first indices set, the first 4-tap interpolation filter is selected, and the first indices set includes −14, −12, −10, −6, 2, 34, 66, 72, 76, 78, 80.

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

• determine, for a conversion between a first video block of a video and a bitstream of the video, that a first coding tool is applied for the first video block, wherein in the first coding tool, the first video block is split into multiple sub-regions in horizontal direction or vertical direction;
• generate prediction samples for at least one of the multiple sub-regions based on a first reference interpolation filtering process;
• and
• perform the conversion based on the prediction samples,
• wherein in the first reference interpolation filtering process, a first 4-tap interpolation filter is applied, and wherein the multiple sub-regions share a same intra mode,
• wherein for a second video block without applying the first coding tool, a second reference interpolation filtering process is used, and wherein in the second reference interpolation filtering process, one of the first 4-tap interpolation filter and a second 4-tap interpolation filter is selected based on at least one of the following:
• an intra mode of the second video block, positions of reference samples of the second video block and a size of the second video block, and the second 4-tap interpolation filter is different from the first 4-tap interpolation filter, and
• wherein in a case that an index of the intra mode of the second video block is one of a first indices set, the first 4-tap interpolation filter is selected, and the first indices set includes −14, −12, −10, −6, 2, 34, 66, 72, 76, 78, 80.

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:

• determining that a first coding tool is applied for a first video block of the video, wherein in the first coding tool, the first video block is split into multiple sub-regions in horizontal direction or vertical direction;
• generating prediction samples for at least one of the multiple sub-regions based on a first reference interpolation filtering process;
• and
• generating the bitstream based on the prediction samples,
• wherein in the first reference interpolation filtering process, a first 4-tap interpolation filter is applied, and wherein the multiple sub-regions share a same intra mode,
• wherein for a second video block without applying the first coding tool, a second reference interpolation filtering process is used, and wherein in the second reference interpolation filtering process, one of the first 4-tap interpolation filter and a second 4-tap interpolation filter is selected based on at least one of the following:
• an intra mode of the second video block, positions of reference samples of the second video block and a size of the second video block, and the second 4-tap interpolation filter is different from the first 4-tap interpolation filter, and
• wherein in a case that an index of the intra mode of the second video block is one of a first indices set, the first 4-tap interpolation filter is selected, and the first indices set includes −14, −12, −10, −6, 2, 34, 66, 72, 76, 78, 80.