Screen Gamma Test

Gamma is the non-proportional rate at which a monitor screen "gets brighter" as the electrical signal applied to it increases. Increasing gamma value makes the darkest parts of a picture get brighter faster than the lighter areas. This brings out shadow detail without burning out the highlights. Most PC-based image-editing applications assume your monitor has a gamma of 2.2 and make corrections to the image data as they send it to your screen. If gamma is being over-corrected for your monitor, the dark areas will be pale and washed out looking (too light). If gamma is being under-corrected, the dark areas will look excessively dark; trying to fix this by turning up the brightness will merely wash out the highlights.

This test pattern can reveal the actual monitor gamma. Once you have determined this, a (very) few monitors and some programs will allow you to make compensating adjustments. To use the test, blur your eyes or move far enough away from your monitor so that you can't see the textured pattern in the background of this image. The square whose brightness most closely matches the background shows the current gamma of your monitor.  

Note that on LCD (flat panel) monitors, that the results will be wildly affected by your viewing angle relative to the screen. For the most accurate results, your line of sight to the monitor must be absolutely perpendicular to the monitor surface. 

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