jfjr@mbunix.mitre.org (Jerome Freedman) (03/03/89)
I am writing this for a co-worker who does not have access to
usenet please attribute mistakes and dumbnesses to my mis transcription:
I am new to the world of color graphics and I am writing (or
trying to write) a program to display a color image. I am working on
a Sun 3/160, Sun Os 3.2 - 4.2 BSD, using smalltalk-80, 8-bit RGB.
I have two requests
1) Does anyone have adescription of a good "basic" RGB color table.
My color table can have a maximum of 256 colors in it and I want to
select that group of RGB values which gives a "good" cross section of
colors.
2) I also need an alogorithm that takes a given RGB value and chooses
which entry in the basic color table described above that best approximates
a given color.
Also any suggestions, references, pointers will be appreciated
Jerry Freedman, Jr
jfjr@mbunix.mitre.org
Jerry Freedman, Jr "Why did
jfjr@mbunix.mitre.org Unix come from the east?"
(617)271-8398 mac@trantor.harris-atd.com (Mike McDonald) (03/05/89)
>1) Does anyone have adescription of a good "basic" RGB color table. >My color table can have a maximum of 256 colors in it and I want to >select that group of RGB values which gives a "good" cross section of >colors. > There was a decent article in the Sept. 88 issue of IEEE Computer Graphics and Applications on how to pick good color map. Mike McDonald mac@trantor.harris-atd.com postmaster@trantor.harris-atd.com (407) 727-5060 Advanced Technology Dept. Harris Corp. M.S. 3A-1912 P.O. Box 37 Melbourne, Florida 32902
jonathan@jvc.UUCP (Jonathan Hue) (03/07/89)
In article <45570@linus.UUCP>, jfjr@mbunix.mitre.org (Jerome Freedman) writes: > 2) I also need an alogorithm that takes a given RGB value and chooses > which entry in the basic color table described above that best approximates > a given color. The best method I know of (which means it isn't the best method, with 99% certainty) is to minimize the CIELUV color difference. This is defined as: delta E*uv = sqrt((delta L*)^2 + (delta u*)^2 + (delta v*)^2) where L* = 116(Y/Yn)^(1/3) - 16 for Y > 0.008856, and L* = 903.3 * (Y/Yn) if not and u* = (u' - un')13L* and v* = (v' - vn')13L* un' is the u' for your reference white and vn' is the v' for your reference white, and Yn is the Y for your reference white. Y, u', and v' can be derived from RGB and your monitors chromaticity coordinates and reference white by the equations I posted here recently. I used this method to convert 24-bit color images to Amiga HAM format. However, I found that combining this with error diffusion (F-S) dithering was tricky, and am still working on a good solution. It does work well for just straight mapping. -Jonathan uunet!jvc!jonathan