@property<EOL><INDENT>@array_util.Memoizer()<EOL>def sub_to_regular(self):<DEDENT>
return mapping_util.sub_to_regular_from_mask(self.mask, self.sub_grid_size).astype('<STR_LIT:int>')<EOL>
The mapping between every sub-pixel and its host regular-pixel.

        For example:

        - sub_to_pixel[8] = 2 -  The ninth sub-pixel is within the 3rd regular pixel.
        - sub_to_pixel[20] = 4 -  The twenty first sub-pixel is within the 5th regular pixel.