Method and apparatus for intra prediction using an interpolation filter

An encoding device, comprising:

• at least one processor;
• and
• one or more memories coupled to the at least one processor and storing programming instructions for execution by the at least one processor to cause the encoding device to:
• perform an intra-prediction process of a block to obtain predicted sample values of the block,
• wherein an interpolation filter is applied to reference samples of the block during the intra-prediction process of the block;
• obtain residual information according to sample values of the block and the predicted sample values of the block;
• and
• perform transformation, quantization, and entropy coding on the residual information, to obtain an encoded bitstream,
• wherein the interpolation filter is selected on the basis of a subpixel offset between the reference samples and the predicated samples, and
• wherein a size of a main reference side used in the intra-prediction process is determined as a sum of:
• an integer part of a greatest non-integer value of the subpixel offset, wherein an intra-prediction mode provides, out of a set of available intra-prediction modes, the greatest non-integer value of said subpixel offset,
• a size of a side of the block, and
• a half of the length of the interpolation filter.

A non-transitory computer readable medium having an encoded bitstream for a video signal stored therein, the encoded bitstream is generated by a video encoding method, wherein the method comprises:

• performing an intra-prediction process of a block to obtain predicted sample values of the block, wherein an interpolation filter is applied to reference samples of the block during the intra-prediction process of the block;
• obtaining residual information according to sample values of the block and predicted sample values of the block;
• and
• performing transformation, quantization, and entropy coding on the residual information, to obtain the encoded bitstream;
• wherein the interpolation filter is selected on the basis of a subpixel offset between the reference samples and the predicted samples, and
• wherein a size of a main reference side used in the intra-prediction process is determined as a sum of:
• an integer part of a greatest non-integer value of the subpixel offset, wherein an intra-prediction mode provides, out of a set of available intra-prediction modes, the greatest non-integer value of said subpixel offset,
• a size of a side of the block, and
• a half of the length of the interpolation filter.