Methods and apparatus on transform and coefficient signaling

An electronic apparatus comprising:

• one or more processing units;
• and
• a memory coupled to the one or more processing units and configured to store a plurality of programs executable by the one or more processing units,
• wherein the one or more processing units are configured to:
• receive bitstream encoding a transform block, wherein the transform block includes a non-zero region and a zero-out region;
• check whether there is any non-zero coefficient within the zero-out region;
• in accordance with a determination that there is no non-zero coefficient within the zero-out region of the transform block:
• determine a scan order index of a last non-zero coefficient of the transform block along a scanning direction;
• in accordance with a determination that the scan order index of the last non-zero coefficient is greater than a predefined threshold:
• receive, from the bitstream, a value for multiple transform selection (MTS) index;
• and
• apply respective transforms to transform coefficients of the transform block in both horizontal and vertical directions based on the value of the MTS index.

A non-transitory computer readable storage medium storing a plurality of programs for execution by an electronic apparatus having one or more processing units, wherein the plurality of programs, when executed by the one or more processing units, cause the electronic apparatus to perform a method of decoding video data, the method including:

• receiving bitstream encoding a transform block, wherein the transform block includes a non-zero region and a zero-out region;
• checking whether there is any non-zero coefficient within the zero-out region;
• in accordance with a determination that there is no non-zero coefficient within the zero-out region of the transform block:
• determining a scan order index of a last non-zero coefficient of the transform block along a scanning direction;
• in accordance with a determination that the scan order index of the last non-zero coefficient is greater than a predefined threshold:
• receiving, from the bitstream, a value for multiple transform selection (MTS) index;
• and
• applying respective transforms to transform coefficients of the transform block in both horizontal and vertical directions based on the value of the MTS index.