Gamma correction, gamma nonlinearity, gamma encoding, or often simply gamma, is the name of a nonlinear operation used to code and decode luminance or tristimulus values in video or still image systems.

Richard S. Hunter has written:

'Photoelectric tristimulus colorimetry with three filters' -- subject(s): Colorimetry, Photoelectric cells

The retina contains two types of photoreceptors, rods and cones. The rods are more numerous, some 120 million, and are more sensitive than the cones. However, they are not sensitive to color. The 6 to 7 million cones provide the eye's color sensitivity and they are much more concentrated in the central yellow spot known as the macula. In the center of that region is the " fovea centralis ", a 0.3 mm diameter rod-free area with very thin, densely packed cones.

The experimental evidence suggests that among the cones there are three different types of color reception. Response curves for the three types of cones have been determined. Since the perception of color depends on the firing of these three types of nerve cells, it follows that visible color can be mapped in terms of three numbers called tristimulus values. Color perception has been successfully modeled in terms of tristimulus values and mapped on the CIE chromaticity diagram.

1. Densitometer

A densitometer is a type of colorimeter that helps control color by measuring the darkness and lightness of a printed material during the printing process. A densitometer evaluates color by placing a test strip or print control strip along the edge of a proof.

Color Temperature Meter

Photographers and cinematographers opt for a color temperature meter, a type of colorimeter, to balance the color in photos and cinematograph's flash and continuous light.

§ Viscosity Meter

Precise Lab & Process Viscometers. Get Engineering

Tristimulus Colorimeter A tristimulus colorimeter measures color from primary light resources such as light signals, lamps, filters, displays and monitors.

Spectroradiometer

A spectroradiometer is a type of colorimeter that measures the intensity and irradiance of color.

The two kinds of values are intrinsic values, which are values that are inherently important or worthwhile, and extrinsic values, which are values that are based on external factors such as rewards or approval from others.