The Greek letter gamma is used in image capture and image display for the tonal range or tonal gradation. The tonal value gradation, known as gradation, is device-specific and manifests itself in digital cameras, displays, projectors and printers in different, non-linear gradations in hue, color saturation and brightness
. Different color gradations cause the distinctions in dark image areas to be different from those in light image areas. The viewer recognizes this by the non-linearity of the gradations. Gamma correction straightens out the non-linearities and thus the gamma curve becomes linear. Gamma is then 1 and the output brightness or the output color tone corresponds to the input brightness or the input color tone.