Changing Gamma Settings on Your Mac (OS X and Debian)

One of the things about having an older Mac like an iBook or a Sawtooth running a pre-Snow Leopard system is that the default gamma values on the monitor are too bright. I've found this true under both OS X and Debian Linux. Long story short on the Apple side is the default setting of gamma 1.8 on systems before Snow Leopard was a relic from the black and white monitor days of early Macs, and they never bothered changing along with the rest of the computer world till Snow Leopard. As a result, colors on the web and in photos can look too washed out compared with being viewed on Windows computers, which they were likely calibrated from in the first place.

So to fix this and have photos and web pages display in Tiger and Leopard the way they were intended, simply go into System Preferences-->Displays and click the Color tab, then the Calibrate button. It will ask you to adjust a bunch of settings, and when you get to the "Select a target gamma" section, select "2.2 Television Gamma" and then continue through to the end and save. Afterward, you'll find that pictures look less washed out and have more depth, but you may also find that black text on a white background looks a little harder on the eyes. Try it out and see which setting you prefer.

On Debian, I also noticed the dafault gamma values seemed a little too aggressively bright, so--this being Linux--after extensive research I found you can tone it down a bit by editing your xorg.conf file (if you don't have a xorg.conf file by default and need to create one, learn how here). First you want to find the best setting to your eyes. You test this by using the xgamma application in the terminal. For example:

xgamma -gamma 0.9

will reset your gamma settings 1/10th of a point off the default of 1.0, and will slightly darken your screen's gamma output. You can play around with it, entering 1.1, 0.8, etc. until you settle on a setting you like best (I chose 0.9, slightly off the original too-bright default). Then you open your xorg.conf file and, under the section "Monitor," add the line:

Gamma 0.9 #or whatever value you settle on, and with a tab between Gamma and 0.9.

This will keep your settings on restart, and you can confirm it worked by running xgamma again with no arguments, and it will display the current gamma settings.

UPDATED for clarity.