Fixing Gamma

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Background reading

Fixing Gamma on a Sun

Sun's SX hardware does about all you can 
without going to more than eight bits per 
channel.. use their command 
 cg14config -g _gammavalue_ 

to setup a gamma lookup table (in the 
SX aka cg14 hardware) for the gamma you
give, or use 
 cg14config -U _filename_

to load your table with whatever (8-bit)
values you want for each of the 256 
non-negative integer intensities.

Oh, their 3D hardware called ZX (or sometimes
called leo), they have the command 
 leoconfig -G _gamma_value_

to setup this hardware with whatever gamma 
value you want. The leo hardware may not 
have the ability to load arbitrary correction
tables. 

Note that all this correction works in the 
display hardware.. no speed cost. Could be
that Sun did something right. Why I hear that
Sun is even active in some standards for 
color (and gamma) management software. Sun 
had some sort of calibration probe on 
display with an SX workstation at the last 
Siggraph.
Thanks to Carl F. Diegert for this contribution.

Fixing Gamma on a Macintosh

Macintoshes tend to do graphics right so pictures should look pretty good. If a photo looks a little washed-out, it is probably because it was prepared on a Unix box or PC with a higher gamma than your Mac. Get the Knoll Gamma Corrector control panel, which comes with Adobe PhotoShop, and set the gamma to 2.2 for a somewhat richer look.

You may also want to use the Knoll corrector set to 2.2 if you are producing images for others to view on the Web.

Fixing Gamma on an IBM PC-compatible

I have no idea how to do this and wish someone would write this section for me.
"It's problematic.

"In several Compuserve libraries, there's a file called MONCAL.GIF which, when viewed with a non-gamma-correcting gif viewer, will give you an idea of your monitor's native gamma.. a place to start. While viewing MONCAL, Brightness and Contrast controls on the monitor can be adjusted, which may or may not get you closer to a 1.8 - 2.2 range.

"Aldus Photostyler and Adobe Photoshop/WIN both include monitor calibration sw routines. You mention Knoll's GAMMA in the MAC discussion and it's included in the PC version (although there's a bug which makes it seem like the utility doesn't work-it does, it just doesn't look like it's storing user settings.. but it does)."

Sam Merrell

Fixing Gamma on a Silicon Graphics (SGI)

The default system gamma value of 1.7 is stored in /etc/config/system.glGammaVal. You can also set a new gamma value as root using the gamma command: /usr/sbin/gamma [newvalue]. Unless you have a very old SGI, you should not need to restart the X server.

You can calibrate your monitor using the Monitor Confidence Test (part of the sysadmdesktop subsystem), accessible from Toolchest (System > Run Confidence Tests), or via the command line: /usr/sbin/Confidence/monitor -test monitor. This includes focus, raster regulation, grey scale, and convergence; if you're like me, having the owner's manual for the monitor is handy for explaining those icons.

An alternate method is to set gamma at 2.4 and run /usr/sbin/gamcal. Consult the UNIX man page man 6 gamcal for more detailed instructions. After calibration, change the gamma back to 1.7 for regular use.

philg@mit.edu