What is the correct gamma value?

What is the correct gamma value?

Post by Wes Barr » Thu, 24 Dec 1992 08:04:29



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?

===============================================================================
Wes Barris                                                   PH: (612) 626-8090

 
 
 

What is the correct gamma value?

Post by David Blyt » Fri, 01 Jan 1993 19:47:48



>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?

the correct gamma value is theoretically a property of the monitor (CRT
and associated electronics).  gamcal will help you determine what this
value should be.  In practice asthetics, religious beliefs, the application
itself, etc,  perturb this value.  I believe the two values you have seen
reflect two different opinions of SGI engineers (I think they bracket the
typical range of values).  I believe 1.7 is the installed default regardless
of the monitor shipped with the system.
        -db

- Show quoted text -

>===============================================================================
>Wes Barris                                                   PH: (612) 626-8090



 
 
 

1. Method needed to correct gamma value

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

2. FS Axon AX100.

3. O2 Gamma value resetting & video DAC LUT's

4. root account automatically created for a "GCW" host???

5. what is correct value of /etc/config/system.glGammaVal ?

6. File C:\OS2\INSTALL\CLEANUP.EXE

7. gamma util

8. IT specialists

9. Gamma on GR2 board

10. IMPACT gamma?

11. gamma question

12. fixing gamma

13. Question about StarterVideo gamma map.