[magick-users] Reducing output range

[Illtud Daniel]

Anthony Thyssen wrote:

> In the mean time you can use a LUT to reduce the number of colors
> 
>    http://www.cit.gu.edu.au/~anthony/graphics/imagick6/color/#color_lut

Thanks - that's really useful. It also pointed me to a simpler way of
doing it:

If I have a 256c greyscale image with range 0-255, $image.pgm, then
this:

convert -fx 'r/8' -depth 8 image.pgm out.pgm

gives me the same image but with the levels squashed into 0-31.

However, If I do:

$image->Fx(expression=>'r/8');

In my perl, it makes no change to the image at all. Where am I going
wrong?