This is bits per channel - per color for truecolor or grey and per pixel for palette.
Indexed ones can have depth of 1,2,4, or 8,
Greyscale can be 1,2,4,8,16
Everything else must be 8 or 16.
See Implementation
This is bits per channel - per color for truecolor or grey and per pixel for palette.
Indexed ones can have depth of 1,2,4, or 8,
Greyscale can be 1,2,4,8,16
Everything else must be 8 or 16.