Gamma is the relationship between the numerical value of a pixel stored in an image file (think JPG or TIFF)  and the brightness of that pixel when viewed on-screen.

  • A computer translates the numerical values in an image file into voltages that are sent to pixels on a monitor. A higher voltage means a brighter pixel.
  • This relationship between stored value and appearance is non-linear, so a change in voltage does not translate directly into an equivalent change in brightness.
  • For many TVs and computer monitors, to double the apparent brightness of a pixel might require 2.5 times more voltage.
  • In the above example the gamma for such a device is said to be 2.5.