Refined entropy coding for level maps

A method for coding a current block, comprising:

• obtaining a transform class for coding a transform block for the current block, wherein the transform class corresponding to a transform type and a direction;
• selecting, based on the transform class, a coding context for coding a value of a non-zero map,
• wherein the non-zero map indicating which coefficients of the transform block have non-zero values,
• wherein the transform class partitions the non-zero map into regions, and
• wherein the coding context is selected based on a region of the value;
• and
• coding the value of the non-zero map based on the coding context.

An apparatus for decoding a current block, comprising:

• a memory;
• and
• a processor, the processor configured to execute instructions stored in the memory to:
• obtain a transform class for decoding a transform block for the current block, the transform class corresponding to a transform type and a direction;
• select, based on the transform type, a template for coding a value of a non-zero map, the non-zero map indicating which coefficients of the transform block have non-zero values;
• obtain, using the template, a context value, wherein the context value is obtained by combining values of the non-zero map corresponding to positions of the template;
• obtain, using the transform class, a region of the non-zero map, wherein the region includes the value of the non-zero map;
• obtain a coding context for coding the value of the non-zero map using the context value and the region;
• and
• decode, from a compressed bitstream, the value of the non-zero map based on the coding context.