Adjustments applied during the display of a digital representation of colour on a screen in order to compensate for the fact that the Cathode Ray Tubes used in computer monitors (and televisions) produce a light intensity which is not proportional to the input voltage. The light intensity is actually proportional to the input voltage raised to the inverse power of some constant, called gamma. Its value varies from one display to another, but is usually around 2.5.
Because it is more intuitive for the colour components (red, green and blue) to be varied linearly in the computer, the actual voltages sent to the monitor by the display hardware must be adjusted in order to make the colour component intensity on the screen proportional to the value stored in the computer's display memory. This process is most easily achieved by a dedicated module in the display hardware which simply scales the outputs of the display memory before sending them to the digital-to-analogue converters.
More expensive graphics cards and workstations (particularly those used for CAD applications) will have a gamma correction facility.
In combination with the "white-point" gamma correction is used to achieve precise colour matching.
Robert Berger's explanation of monitor gamma.
["Digital Imaging in C and the World Wide Web", W. David Schwaderer].