Xref: utzoo sci.electronics:3927 rec.audio:8476 Path: utzoo!utgpu!attcan!uunet!tank!ncar!ames!lll-tis!lll-winken!arisia!tow From: tow@arisia.Xerox.COM (Rob Tow) Newsgroups: sci.electronics,rec.audio Subject: Re: Looking for Blue LEDs Summary: Cease bogus postings, please - go read some references Keywords: blue blue blue, not yellow or red or green Message-ID: <428@arisia.Xerox.COM> Date: 28 Sep 88 01:55:08 GMT References: <1138@nmtsun.nmt.edu> <862@ritcv.UUCP> <255@rna.UUCP> <4422@lynx.UUCP> <871@ritcv.UUCP> <262@rna.UUCP> Reply-To: tow@arisia.UUCP (Rob Tow) Distribution: misc.flame Organization: Xerox PARC Lines: 64 In article <262@rna.UUCP> dan@rna.UUCP (Dan Ts'o) writes: >In article <871@ritcv.UUCP> cep4478@ritcv.UUCP (Christopher E. Piggott) writes: >> >>Question: why are R.G.B. monitors Red, GREEN, blue, when GREEN is not one of >>the primary colors (being a combination of blue and yellow)? Why shouldn't >>it be red, YELLOW, blue? > > You are confusing additive colors with subtractive colors. Yes, if >you add blue paint to yellow paint, you get green paint. But if you add >red light to green light, you get yellow light, not brown paint. I am stirred from my dogmatic slumbers, to paraphrase Hume... Wrong. In the "paint" world, adding *cyan* to yellow yields green. Cyan is often confused with blue. In the world of "paint" - subtractive colors, actually - cyan is blue plus green. Adding a really blue paint to a really yellow paint would produce a grey or a black! On a monitor, yellow is made by lighting up the green and red phosphor dots; adding blue then makes white. The entire discussion of color up to this point has been filled with misinformation, with the sole exception of one gentleman who actually quoted sources for cone pigment sensitivity curves. This discussion does not belong in this group. It should be moved elsewhere. The closest match would be comp.graphics - where it gets regularly revived every year or so. A few sources for those who really do wish to explore human color perception and color reproduction (quickly looking at my bookshelf): "The Reproduction of Colour in Photography, Printing, and Television", by Dr. R. W. G. Hunt, Fourth Edition, Fountain Press, England, 1987, ISBN o 86343 088 0. This is perhaps the ultimate reference for color reproduction. Warning: this, and the next book, are rather expensive: on the close order of $100. "Color Science: Concepts and Methods, Quantitative Data and Formulae", Gunter Wyszecki and W. S. Stiles, 2nd Edition, John Wiley and Sons, 1982, ISBN 0-471-02106-7. This is the ultimate deskside reference for psychophics/radiometry/color measurement. "Colour: Why the World Isn't Grey", Hazel Rossotti, Princeton University Press, 1985, ISBN 0-691-08369-X. An entertaining yet informative exploration of color perception and the physics of color. Color perception is not a completely understood area. There are useful engineering models; after all, we find utility in color printing, television, photography, etc. All of these are actually clever illusions which exploit aspects of the human visual system. --- Rob Tow Member Research Staff Electronic Document Lab Xerox PARC 3333 Coyote Hill Drive Palo Alto, CA 94304 (415)-494-4087