Method and Apparatus of Encoding or Decoding Using Reference Samples Determined by Predefined Criteria

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 picture;
• checking if the current block satisfies two or more predefined criteria during partitioning;
• and
• if the current block satisfies the two or more predefined criteria during partitioning:
• encoding or decoding one or more chroma color components of the current block without further partitioning and using neighboring reconstructed samples of the one or more chroma color components of the current block as reference samples, and encoding or decoding the luma color component of each subblock in the current block using neighboring reconstructed samples of the luma color components of each subblock in the current block as reference samples,
• wherein the two or more predefined criteria correspond to block size, width, height or partitioning of the current block or one or more children block, wherein one of the two or more predefined criteria corresponds to the condition that the partitioning of the current block or one or more children block is quad-tree partition or ternary-tree partition.