Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!rutgers!ames!amdcad!cae780!leadsv!eps2!jon From: jon@eps2.UUCP Newsgroups: sci.physics,comp.graphics,comp.sys.ibm.pc Subject: Re: Color questions Message-ID: <82@eps2.UUCP> Date: Fri, 12-Jun-87 04:34:50 EDT Article-I.D.: eps2.82 Posted: Fri Jun 12 04:34:50 1987 Date-Received: Sat, 13-Jun-87 20:06:40 EDT References: <1937@druhi.ATT.COM> <725@bsu-cs.UUCP> <6861@mimsy.UUCP> <943@elrond.CalComp.COM> Distribution: comp Organization: DuPont Design Technologies/Via Video Lines: 49 Xref: utgpu sci.physics:1564 comp.graphics:721 comp.sys.ibm.pc:4202 Summary: Sigh. Not in the real world. In article <943@elrond.CalComp.COM>, amamaral@elrond.CalComp.COM (Alan Amaral) writes: > It's trivial. Oh come on. Everyone who reads this newsgroup knows how to translate between the RGB and CMY color spaces. And I'm sure everyone could figure out how to do the crude undercolor removal... The question Ed asks is not the simple one that you think he is asking. From his posting it is obvious that he knows about how real inks used by printers work, and that they do not absorb light like ideal cyan, magenta, and yellow inks. None of the simple solutions I've posted to the net are adequate. I have a Pantone color simulator in front of me. Just looking at the front page, I can see that there is no way you can print a bright orange color on paper without using ink that is actually bright orange. I asked this same question about a year ago. One useful piece of information I received was from someone at the University of Utah. He told me that Maureen Stone at Xerox PARC has done work in this area. I found out she has published papers and she recently gave a talk out here. Ed, one thing you may want to do is buy a Pantone color simulator. You can get a feel for what the different inks look like when mixed together. The book consists of about 500 of the Pantone process colors, and then a color chip next to them showing a close approximation using CMYK ink. There are three more CMYK color chips which can be torn out next to the big chip. You can find this at most any art store. The price is a bit steep, $200. The other four Pantone books which make up the rest of the set are only $250 total. Of course the colors printed are dependent on the ink, paper, screen angles, etc, but you can get an idea of how things work from this book. I know that Eikonix has a lot of people who are experts in this area, but they're not going to divulge a lot of the information because it is proprietary. My personal opinion is that if Eikonix ever gets around to announcing a Sun-3 prepress machine (if they haven't already), one of their big features will be their expertise in color fidelity. Our systems are targeted at design, not production, so our "big features" are our tools for graphic designers. I made an error in a previous posting about halftone dot sizes. Although prepress machines store their pixels as 8-bit quantities, typically dot size is controllable on an output scanner only to 2% increments, so there are only 50 different dot sizes. The top of the line Hell scanner generates dots electronically at a maximum of 146 dots/mm. If you are doing 12 halftone dots/mm, that gives you about a 12x12 grid of dots to simulate your halftone dot, so I guess you could assume 144 dot sizes. Jonathan Hue DuPont Design Technologies/Via Visuals leadsv!eps2!jon