(graymap-normalize! graymap)
This procedure applies a simple linear normalization to the 16 bit graymap.
The graymap is modfied.
The modified graymap is returned.
> (define graymap (mandelbrot 0.27085 0.27100 0.004640 0.004810 2000 640))
graymap
> (graymap-normalize! graymap)
#<graymap(16) orow:-1 ocol:-1 xres:-1 yres:-1 w:640 h:725>
>