Path: utzoo!utgpu!water!watmath!clyde!wtr@moss.ATT.COM
From: wtr@moss.ATT.COM
Newsgroups: sci.electronics
Subject: Re: Looking for Blue LEDs
Message-ID: <34669@clyde.ATT.COM>
Date: 12 Oct 88 01:51:00 GMT
References: <1138@nmtsun.nmt.edu> <862@ritcv.UUCP> <255@rna.UUCP> <4422@lynx.UUCP> <871@ritcv.UUCP> <870@dlhpedg.co.uk> <795@wheaton.UUCP>
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Reply-To: wtr@moss.UUCP (Bill Rankin)
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Organization: AT&T Bell Laboratories, Whippany NJ
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In article <795@wheaton.UUCP> fwells@wheaton.UUCP (Frank Wells) 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)?

>Somebody's probably already said it, but the primary PIGMENTS are Red,
>Yellow, Blue (as opposed to COLORS, tints if you will.).
>Hope this helps.
>Frank Wells

Now wait a minute.... :-)

In printing (ink), the three pigments used are: yellow,
cyan (*not* blue), and magenta (*not* red).  there is a 
pseudo fourth pigment (black), but this is just used because
it is a combination of the first three, and much easier to use
in everyday printing.

In printing, remember that the colors that you see are
what is *not* absorbed by the individule pigments.
the color green is (are?) the wavelengths that cyan and 
yellow have in common.  likewise blue is the intersection
of cyan/magenta and red is the intersection of yellow/magenta.
remember that this is a subtractive (is that an adjective :-)
effect.  green is cyan minus all but the 'yellow' components.

light, on the otherhand, is additive.  blue *plus* green give
you back the cyan. ( a gross generalization at best, but
suitable for the moment) if you look at it like red/green/blue
are three disjoint sets whose union make up the color
'universe'.  then magenta/cyan/yellow are the union of two specific
colors. ie


    |-- red --||-- blue -||- green -|

    |------ magenta -----|
               |------- cyan -------|
  <- yellow --|           |-- yellow ->


that's why tv/monitors/etc use red/green/blue for the guns,
and why printers use cyan/magenta/yellow.

critical review welcome, i'll bring the marshmellows ;-)

=====================================================================
Bill Rankin
Bell Labs, Whippany NJ
(201) 386-4154 (cornet 232)

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