For graphics on the Internet to look the way the creator intended them to, it is important that you have your monitor correctly calibrated. A standard setup has been decided by the W3C, which has been named sRGB for short, or sRGB IEC61966-2.1 if you want to be precise.
This setup includes using a gamma of 2.2. At gamma 1.0 things are fairly straight forward; a pixel value of 128/256 (50%, for example grey #808080) would equal a luminance on the screen of 50%. However, at gamma 2.2 things get a little more complicated. Now a pixel value of 128/256 only gives a luminance of 21%, and you need a pixel value of 188/256 (73%) to get 50% luminance. Put simply, higher gamma values make all pixel values between 0 (black) and 255 (white) darker.
Why gamma 2.2? Well, I'm not exactly sure of the answer to that. Gamma 2.2 has been the standard for PC CRT screens for a very long time, and is the standard for Macs too these days. (Macs were previously setup to gamma 1.8.) However, since it is a proposed standard I will adhere to it here and recommend you do so too. (Although, I'll have to admit I find my photos turn out a little on the dark side.)
If you adjust your screen according to the instructions on the following page you will be setup to a gamma of 2.2, and you will see graphics all over the Internet as they were meant to be viewed.
On to the screen calibration page.
All content © 2010 David Naylor.