Xref: utzoo comp.graphics:3631 rec.photo:3661
Path: utzoo!attcan!uunet!ubvax!ames!watson
From: watson@ames.arc.nasa.gov (John S. Watson)
Newsgroups: comp.graphics,rec.photo
Subject: Re: photographing computer screens
Message-ID: <18196@ames.arc.nasa.gov>
Date: 15 Nov 88 19:08:12 GMT
Reply-To: watson@ames.arc.nasa.gov (John S. Watson)
Organization: NASA Ames Research Center, Moffett Field, CA
Lines: 56


[this discussion started in comp.graphics]
 
Here's how I get 24 bit photographs of my images from my 8 bit Sun screen
(The basic idea is to triple expose the film, once with each R,G,B channels).
 
First I set up my 35mm camera in front of the our Sun's 8-bit color monitor,
on a tripod.  I level the Sun screen and make sure the camera is pointed
at the center of the Sun screen.  A good sturdy tripod is best, but I
use my ultra-cheap ultra-lite backpacking tripod.
I also connect my remote shutter controller, and turn on the 2 second delay
to minimize vibrations.
 
I use a telephoto lens of about 100mm to minimize the "wide-angle" distortion.
 
Once everything is set up I run a program I wrote that take the three
red, green and blue image files and make a grey scale "intensity" file.
Then I display this intensity image.  Next, I turn out all the lights in
the room and take a meter reading of the intensity image.
 
I have a fancy camera that has all sorts of automatic modes, 
but I just use it's light meter to tell me the right exposure. 
I use as slow a film as 100 ISO or less, usually Kodak.
I want a long shutter speed to avoid flicker, 
on the order of 10 seconds, so I set the aperture to 8 or more.
 
Next I set my camera to expose the same frame 3 times, and set the 
exposure to 1/3 of the meter reading I got from above (so for the 10 second
example I'd expose with three 3.33 second exposures).
 
I have 3 little programs with display each of the red, green and blue file
separately, each with it's respective "red scale", "blue scale" and
"green scale" colormap (i.e., for the "red scale" the red values in the
colormap are from 0 to 255, and the green and blue are 0). 
 
So then I:
Display the red channel.    Expose the film.
Display the green channel.  Expose the film.
Display the blue channel.   Expose the film.
 
That's it.  I also redo the whole process at with a slightly longer 
and at a slightly shorter exposure (bracketing), just in case.
 
Turn on the lights, go home, have a beer. 
 
I'm sure there are lots of nitty gritty details that I ignore; 
things like gamma corrections of the monitor and all that sort of stuff,
but what the heck, the results are fine. 
 
Have fun,

-- 
John "Crash" Watson, Civil Servent from Hell  ARPA: watson@ames.arc.nasa.gov 
NASA Ames Research Center                     UUCP:  ...!ames!watson
Any opinions expressed herein are, like, solely the responsibility of, like, the
author and do not, like, represent the opinions of NASA or the U.S. Government.