Its one of those annoying facts of life is that display devices convert a video signal to light in a nonlinear way (think curve instead of a straight line). The light intensity output by the display is actually related to the incoming video source voltage by a power law (a number raised to a power – approximately 2.2 for a CRT). The value of the power used is the gamma of the particular display device. If no gamma correction is applied video colors displayed appear either to light or dark compared to the original.

Television and display manufacturers correct this problem by modifying the incoming video signal so the video displayed has the correct brightness levels. This process is known as gamma correction. The gamma correction curve applied to the incoming video signal is designed to precisely distort the incoming video signal so that when it is further distorted by the nonlinear output relationship of the display the final output will be to a linear scale matching the original incoming signal. Display manufacturers develop the gamma correction from the known intensity to voltage response curve of each particular display.

LCDs actually have a very nonlinear signal voltage to intensity relationship which is somewhat of an S-shaped curve rather than a power law curve like CRTs. To make this simpler all LCDs have a built-in electronic correction to make them behave as if there was a power law relationship.