(colormap-difference colormap1 colormap2)
This procedure creates a new colormap by computing the absolute difference for each color channel of each pixel. The two suppied colormaps need to have the same dimensions, otherwise an error is signalled. The absolute difference for each single RGB channel is computed by subtracting the smaller value from the larger.
The resulting colormap is returned.
> (colormap-difference frame1 frame2) #<colormap orow:-1 ocol:-1 xres:-1 yres:-1 w:640 h:480> >