Sub8×8 block processing

A method of coding a current block, comprising:

• generating a first block and a second block for the current block, the second block generated by subsampling the current block;
• dividing the first block into first sub-blocks comprising a first sub-block and a second sub-block, wherein the current block is an 8×8 block and each first sub-block is a 4×4 luma prediction block, wherein the second block is a 4×4 chroma block;
• determining a first prediction mode for the first sub-block and a second prediction mode for the second sub-block, the first prediction mode is an inter-mode or an intra-mode and the second prediction mode is the inter-mode or the intra-mode;
• and
• coding the second block based on a determination that the first prediction mode or the second prediction mode is the intra-mode by steps comprising:
• on a condition that the first prediction mode or the second prediction mode is determined to be the intra-mode, selecting the second prediction mode of the second sub-block as a prediction mode for the second block;
• and
• on a condition that neither one of the first prediction mode nor the second prediction mode is the intra-mode, performing steps comprising:
• dividing the second block into second sub-blocks;
• and
• predicting at least some of the second sub-blocks using the inter-mode.

An apparatus for coding a current block, comprising:

• a memory;
• and
• a processor configured to execute instructions stored in the memory to:
• generate a first block and a second block for the current block, the second block generated by subsampling the current block;
• divide the first block into first sub-blocks comprising a first sub-block and a second sub-block;
• determine a first prediction mode for the first sub-block and a second prediction mode for the second sub-block, the first prediction mode is an inter-mode or an intra-mode and the second prediction mode is the inter-mode or the intra-mode;
• and
• code the second block based on a determination that the first prediction mode or the second prediction mode is the intra-mode by instructions including:
• only on a condition that neither one of the first prediction mode nor the second prediction mode is determined to be the intra-mode:
• divide the second block into second sub-blocks;
• and
• predict at least some of the second sub-blocks using the inter-mode.