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Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!uw-beaver!tektronix!tekcae!kurtk
From: kurtk@tekcae.CAX.TEK.COM (Kurt Krueger)
Newsgroups: comp.graphics,rec.photo
Subject: Re: photographing computer screens
Message-ID: <2236@tekcae.CAX.TEK.COM>
Date: 17 Nov 88 17:58:06 GMT
References: <18196@ames.arc.nasa.gov>
Reply-To: kurtk@tekcae.CAX.TEK.COM (Kurt Krueger)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 21

I've seen some good advice here, but thought I would add some more info.

Notice that camera systems designed for this work are set up to photograph
a black and white screen through 3 different color filters (i.e. the red
part is displayed and photographed through a red filter, etc.)

This solves a few problems.

1. The mismatch of the color phosphor's output spectrum vs. the film's
   spectral response is fixed by the color filters.

2. Gamma correction can be done, as well as differing sensitivity to the
   three primary colors.

3. If you take a magnifying glass to the color screen, you will notice that
   if you have an entire green image (for example) that only 1/3 of the
   screen is actually lit up (the red and blue dots are black in this case).
   A well focussed photograph will be 1/3 green and 2/3 black.  The results
   will be a muddy green.  By photographing a b&w screen through a green
   filter you can get 100% green.
   (Note: you can help this situation by overexposing or defocusing).