Method needed to correct gamma value

Method needed to correct gamma value

Post by Larry Singlet » Thu, 05 Aug 1993 02:31:50



I would like to set up an experiment to test the gamma value on my SGI machine.
I need some help with the details.

I now have a photometer, that gives reading in "New Foot Candles".
1 NFC = 10.78 LUX

So now what I want to do is set up the experiment.
The first thing I realize is that it should be conducted in
fairly absolute darkness.  

as dark an environment as can be obtained.

How do I associate the value read from the photometer (Which as noted
above can be converted to LUX), to the gamma value.

In other words, I can I tell from the photometer reading, that

In other words, how can tell from the photometer reading, that
the gamma value must be increased or decreased in order to obtain
a fairly linear output.

Thank you very much,

        Larry Singleton

        Dept. Computing & Info Science
        Queen's University
        RPL

 
 
 

1. What is the correct gamma value?

The man page for gamcal says:

   "Normally the gamma of the display should be set to
    2.4 using the program /usr/sbin/gamma."

However, the following lines are found in /usr/lib/X11/xdm:

   Xlogin:glGammaDefault="1.7"
   Xstartup:glGammaDefault="1.7"

NOTE: These files (Xlogin and Xstartup) do not seem to be setting the gamma
      anyway but that is a separate issue.

Using the gamcal program to help calibrate the gamma leads me to believe
that 2.4 is the "correct" value.

I am running IRIX 4.0.5 on a 4D/35.  Is there a reason for the two
different gamma values found on my system?

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