Posted: 2006-10-20T19:27:20-07:00
The only way to accomplish want you want is to create a map image with only 80 entries and use the -map option.
You can find out all about what -colors and -map does in the new IM Color Quantization section.
http://www.cit.gu.edu.au/~anthony/graph ... ze/#colors
Especially note the major warning
Quantization does NOT Preserve Colors
http://www.cit.gu.edu.au/~anthony/graph ... _not_exact
NOTE: GIF images have a 256 color limit of only Q8 colors, and can make ONE of those the fully transparent color.