Color and grayscale display

[avenues at sonnet.com]

I am trying to register some 256-color aerial photos to grayscale
orthophotos using the i.ortho.photo routines. Registration is difficult
because of the poor color and grayscale representation of the images in
GRASS-Linux. I have tried using the float colormode. This improves the
greyscale image but not the color image. I have also tried using the 24-bit
x-driver, but that does not result in any better color or greyscale
representation. Are there any other techniques which might give better
resuilts? Thank you for your help.

Note: I can export the images from GRASS using r.out.ppm and display them
with xv in Linux, and the color is improved. Is there some internal limit
in GRASS that does not allow display of all 256 colors?

Jim Schmidt
USDA Forest Service
Sonora, California