thrapp@cod.NOSC.MIL (Gary R. Thrapp) (04/14/88)
I am very interested in obtaining a set of RGB (or convertible to RGB)
values to construct a 64, 128, or 256 element color table with a wide
variety of colors including things like shades of brown?
If someone could supply such a database it would be greatly appreciated.
Thank you very much.
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Gary R. Thrapp
Code 443
Naval Ocean Systems Center
San Diego, CA 92152-5000
(619) 553-4131
DDN: thrapp@nosc.mil
UUCP: {ihnp4,akgua,decvax,dcdwest,ucbvax}!sdcsvax!nosc!thrappoltz@batcomputer.tn.cornell.edu (Michael Oltz) (04/14/88)
In article <1059@cod.NOSC.MIL> thrapp@cod.NOSC.MIL (Gary R. Thrapp) writes: >I am very interested in obtaining a set of RGB (or convertible to RGB) >values to construct a 64, 128, or 256 element color table with a wide >variety of colors including things like shades of brown? I have a similar situation. I will need to grab many video images of color distributions which I cannot predict, and quantize them down to 256 colors. All of them must use exactly the same color table. The question is, does anyone out there have experience with what is a good table for doing this? All I know about the images is that in some cases there will be people in them and we don't want them to come out orange, but it is all right if they look a little 'Sunday funnies'. P.S. I cannot take samples and calculate a table from that. This procedure would be used in many different situations, so I don't know what I'm getting. -- Mike Oltz oltz@tcgould.tn.cornell.UUCP (607)255-8312 Cornell Computer Services 215 Computing and Communications Center Ithaca NY 14853
oj@apollo.uucp (Ellis Oliver Jones) (04/18/88)
In article <1059@cod.NOSC.MIL> thrapp@cod.NOSC.MIL (Gary R. Thrapp) writes: >I am very interested in obtaining a set of RGB (or convertible to RGB) >values to construct a 64, 128, or 256 element color table with a wide >variety of colors including things like shades of brown? I've had pretty good success reducing 24-plane TrueColor images for display on 8 planes by constructing a color map with coarse, but uniform, ramps for each of the primary colors. One such color map (originally dreamed up by Allen Akin at DEC, and suggested as a standard shared color map for X11) provides six levels each of red, green, and blue, using a total of 216 (6x6x6) color cells. This is handy in an 8-plane workstation context because it leaves forty cells free). Another scheme I've used has seven levels of red and green, and five of blue (245 cells). This gives slightly better image quality for some color images, but is bad for gray ramps -- they change color slightly. Of course, there's always 8 shades of red, 8 of green, and 4 of blue (in other words 3 bits each of red and green, and 2 bits of blue). To fit your color map to your image adaptively (rather than just coarsening the colors of your image) see Color Image Quantization for Frame Buffer Display by Paul Heckbert on p 297ff of the 1982 SIGgraph proceedings (from Heckbert's Pre-Jello Period :-) If you are going to use as simple a color-space reduction as this, you probably should consider dithering your image into the coarser color space. If you have less than eight planes (256 color cells) to work with, you definitely should dither. (see Rogers, Procedural Elements for Computer Graphics, p107). /Ollie Jones (speaking for myself, not necessarily for Apollo Computer, Inc.)