One would think that in this day and age, viewing color images on a computer monitor in a consistent way would be very straight forward. Alas, this is not the case. The same image can end up looking quite different depending on the particular brand of graphics card, monitor, and operating system you are using. This is due to the different methods that vendors use for correcting the non-linearity of the computer display, also known as "gamma correction." Some vendors, such as Silicon Graphics, provide gamma lookup tables that can be loaded with values to do the proper gamma correction. Other vendors, such as Microsoft, don't do anything about gamma correction. The result is that images that were created on a Silicon Graphics workstation, for example, will look too dark when viewed on PCs running Windows and images that were created on other systems not having gamma correction will look too light when viewed on an SGI workstation. Unfortunately, there is no standard solution to this problem (which is why the problem still exists after all these years).
If you are using a computer that doesn't provide a means of doing gamma correction, you can adjust the brightness and contrast on your monitor as a means of doing rudimentary gamma correction. Two web sites are available to assist with this adjustment:
On UNIX workstations that have the "xv" viewing program, you can directly control the gamma correction factor (we suggest you set it to a value of 2.0). To do this, go to the "controls" menu panel in xv and pick the "ColEdit" button to bring up the Color Editor panel. Then in the "Intensity" field, click the "Gam" button and type in a value of 2.0.
- Paul Haeberli's Grafica Obscura includes a brightness test pattern that can be used to optimize the adjustment of both your workstation's gamma factor and/or monitor brightness and contrast.
- Rick Rodger's site at NLM [LINK GOES HERE]
If you are aware of other web sites that have good methods for adjusting gamma correction factors, please drop a note to firstname.lastname@example.org and let us know the URL of these sites.
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