The value of gamma varies depending on the CRT, but is usually close to 2.5. The gamma response of a CRT is caused by electrostatic effects in the electron gun. Since most sensors used in television cameras produce output voltages proportional to scene intensity, a correction for CRT gamma must be applied to the camera signal to avoid having midtones in the scenes being too dark on the TV set. This value was chosen to simultaneously correct for the CRT gamma of 2.5 and compensate for the apparent reduction of contrast which occurs when a TV is viewed against the dim background typically found in a living room. Applying the correction at the studio was more economical than applying the correction in every TV set.
Many computer displays ignore the effect of monitor gamma.
The frame buffer values provided by the application software are converted linearly into voltages that drive the CRT in the display. The values in the frame buffer are not proportional to the resulting intensity. Some display systems such as NeXT's and SGI's contain hardware lookup tables that correct for monitor gamma. On these systems the frame buffer values provided by the application are corrected for the gamma of the CRT by a lookup table in the display controller, producing a display system gamma of 1.0 which linearly maps frame buffer values into intensity. Macintosh computers contain lookup tables in their display hardware which can be used to correct for CRT gamma.