bitmap->greymap

(bitmap->greymap <bitmap>) converts the supplied bitmap to a greymap and returns this new generated greymap. Each black pixel in the bitmap becomes a greymap pixel with greylevel 255, each white pixel becomes a greymap pixel with greylevel 0.

[1] (bitmap->greymap (bitmap-create 500 500))
#<greymap orow:-1 ocol:-1 xres:-1 yres:-1 h:500 w:500>
[2]