Color and grayscale display

Andrew M McDermott mcdermam at
Mon Dec 21 05:32:04 EST 1998

avenues at wrote:
> I am trying to register some 256-color aerial photos to grayscale
> orthophotos using the 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
perhaps you are running X in 8 bit color and running out of colors to
allocate. Have you tried 16 or 24 bit mode (startx -- -bpp 16  (or 24) 
) to see if the display looks better?

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