/* alpha modes, convenience mostly */
/* if you have alpha, pick constant appropriate to the
number of channels (1 for I8, 2 for I8A8, 4 for R8G8B8A8, etc */
/* alpha modes, convenience mostly */
/* if you have alpha, pick constant appropriate to the
number of channels (1 for I8, 2 for I8A8, 4 for R8G8B8A8, etc */