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