Method and Apparatus of Encoding or Decoding Video Blocks with Constraints during Block Partitioning

A method of processing video data in a video coding system, comprising:

• receiving input data associated with a current block in a current slice;
• checking whether one or more components of the current block satisfy one or more predefined criteria during partitioning;
• setting the current block to be a root block if the one or more components of the current block satisfy the one or more predefined criteria;
• applying a chroma split constraint to the current block if the current block is set to be a root block, wherein the chroma split constraint prohibits chroma components of the current block to be further partitioned while a luma component of the current block is allowed to be further partitioned;
• and
• encoding or decoding the current block.

An apparatus of processing video data in a video coding system, the apparatus comprising one or more electronic circuits configured for:

• receiving input data associated with a current block in a current slice;
• determining whether one or more components of the current block satisfy one or more predefined criteria during partitioning;
• setting the current block to be a root block if the one or more components of the current block satisfy the one or more predefined criteria;
• applying a mode constraint, a chroma split constraint, or both the mode and chroma split constraints to the current block only if the current block is set to be a root block, wherein the mode constraint restricts all blocks split from the current block to be processed by a same prediction mode and the chroma split constraint prohibits further partitioning chroma components of the current block;
• and
• encoding or decoding the current block.

A non-transitory computer readable medium storing program instruction causing a processing circuit of an apparatus to perform a video processing method for video data, and the method comprising:

• receiving input data associated with a current block in a current slice;
• determining whether one or more components of the current block satisfy one or more predefined criteria during partitioning;
• setting the current block to be a root block if the one or more components of the current block satisfy the one or more predefined criteria;
• applying a mode constraint, a chroma split constraint, or both the mode and chroma split constraints to the current block only if the current block is set to be a root block, wherein the mode constraint restricts all blocks split from the current block to be processed by a same prediction mode and the chroma split constraint prohibits further partitioning chroma components of the current block;
• and
• encoding or decoding the current block.