How to know if you have the problem. If you are using a Silicon Graphics workstation or a machine running NeXTStep, your hardware will apply the necessary gamma correction. For most other workstations, you must configure your external viewers to apply correction. Otherwise, our images will look too dark to you.
What to do about it. As an example of how to configure an external viewer to apply gamma correction, suppose that your image viewer (e.g. the viewer used for displaying .tif and .jpg files) is xv and the gamma of your display monitor is 2.0. You can ask xv to apply gamma correction as it displays an image by placing the following line in your .mailcap file:
image/*; xv -gamma 2.0 %sTo find out the gamma of your monitor, look at the hardware specifications that you threw away on the day you unpacked the monitor. Most monitors have a gamma between 1.7 and 2.7.
A subtlety. Silicon Graphics workstation monitors have a gamma of 2.4, but they correct as if the monitor had a gamma of 1.7. This yields a residual gamma of 2.4 / 1.7 = 1.4. This is called the system gamma, and it is intended to compensate for the fact that the images you are viewing typically represent brightly illuminated scenes, but you are viewing them while seated in a dimly illuminated room, which changes the transfer characteristics of your eye. The bottom line is that, if you are forced to apply gamma correction, you should experiment to find a gamma that suits your tastes. For more detail on this fascinating subject, see Pearson, D.E., Transmission and Display of Pictorial Information, Halsted Press, 1975.
The catch. There is currently no way to configure Mosaic or Netscape to gamma correct the .gif images embedded in .html files. These images will therefore look dark on uncorrected monitors.