(graymap-maximum graymap)
The maximum pixel value (gray level) of the graymap is returned as a number.
> (define graymap (mandelbrot 0.27085 0.27100 0.004640 0.004810 2000 640))
graymap
> (graymap-maximum graymap)
2000
> (graymap-normalize! graymap)
2000
> (graymap-maximum graymap)
65535
>