Method and apparatus for identity transform in mulitple transform selection

An apparatus for controlling residual coding for decoding or encoding of a video sequence, the apparatus comprising:

• at least one memory configured to store computer program code;
• and
• at least one processor configured to access the at least one memory and operate according to the computer program code, the computer program code comprising:
• determining code configured to cause the at least one processor to determine whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT), based on whether either one or both of a block height and a block width meet a predetermined condition;
• and
• replacing code configured to cause the at least one processor to, based on either one or both of the block height and the block width meeting the predetermined condition, replace the transform type of MTS by using the IDT and keeping a syntax of the MTS unchanged,
• wherein the IDT is a linear transform process using an N×N transform core in which each coefficient is non-zero along a diagonal position, and wherein N is an integer.

A non-transitory computer-readable storage medium storing instructions that cause at least one processor to:

• determine whether to replace a transform type of Multiple Transform Selection (MTS) by using Identity transform (IDT), based on whether either one or both of a block height and a block width meet a predetermined condition;
• and
• based on either one or both of the block height and the block width meeting the predetermined condition, replace the transform type of MTS by using the IDT and keeping a syntax of the MTS unchanged,
• wherein the IDT is a linear transform process using an N×N transform core in which each coefficient is non-zero along a diagonal position, and wherein N is an integer.