cyrus@hi.unm.edu (Tait Cyrus) (08/29/88)
I am working on a utility that takes an RGB image (3 files, 1 for R, 1 for G and 1 for B), converts it halftones, and then converts it to CMY so that I can print it on a color CMYB versatec printer we have. My problem is that the colors don't seem to be coming out looking correct. Cyan comes out looking blue, blue comes out looking purple, green comes out too dark, etc..... Several people have suggested looking into using chromaticity. Looking at Foley and Van Dam's "Fundamentals of Interactive Computer Graphics", as well as Roger's "Procedural Elements for Computer Graphics", I find that I am totally lost. Are there scale factors I need to multiply with my colors to get them to come out looking correct on my CMY printer? Can I use chromaticity concepts to solve my problem? Thanks in advance for any comments, pointers to other books, pointers to PD software that already does this, etc.... The solution is probably staring me right in the face, all I need is someone to shove my face in it. :^) --- Tait Cyrus (505) 277-0806 University of New Mexico Dept of Electrical & Computer Engineering Albuquerque, New Mexico 87131 e-mail: cyrus@hi.unm.edu or cyrus%hi.unm.edu@ariel.unm.edu
pickel@polyof.UUCP ( Prof. Pickel ) (09/08/88)
In article <23632@hi.unm.edu>, cyrus@hi.unm.edu (Tait Cyrus) writes: > > I am working on a utility that takes an RGB image (3 files, 1 for R, 1 > for G and 1 for B), converts it halftones, and then converts it to CMY > so that I can print it on a color CMYB versatec printer we have. > > My problem is that the colors don't seem to be coming out looking > correct. Cyan comes out looking blue, blue comes out looking purple, > green comes out too dark, etc..... we have been working on 512 by 512 by 8bits RGB to 2560 by 2560 CYMB for a shinko thermal tranfer plotter there is a major difference in the colors printed depending on the rate at which the data is sent to the plotter at slower speeds it was necessary to shift the RGB to get more saturated colors at the highest speed straight C = 255 - R etc Black = min CYM seems to work quite well (followed by ordered dither) currently we use a sharpened gaussian filter to go from 512 to 2560 total processing time for each picture is about 27 minutes on a VAX class machine (16 min CPU) I'm working on faster approaches.