Color correction

Color correction by using color gels, or filters, is a process used in stage lighting, photography, television, cinematography, and other disciplines, the intention of which is to alter the overall color of the light; typically the light color is measured on a scale known as color temperature, as well as along a green–magenta axis orthogonal to the color temperature axis.

Without color correction gels, a scene may have a mix of various colors. Applying color correction gels in front of light sources can alter the color of the various light sources to match. Mixed lighting can produce an undesirable aesthetic when displayed on a television or in a theatre.

Conversely, gels may also be used to make a scene appear more natural by simulating the mix of color temperatures that occur naturally. This application is useful, especially where motivated lighting (lending the impression that it is diegetic) is the goal. Color gels may also be used to tint lights for artistic effect.

The particular color of a white light source can be simplified into a correlated color temperature (CCT). The higher the CCT, the bluer the light appears. Sunlight at 5600K, for example, appears much bluer than tungsten light at 3200K. Unlike a chromaticity diagram, the Kelvin scale reduces the light source's color into one dimension. Thus, light sources of the same CCT may appear green or magenta in comparison with one another [1]. Fluorescent lights, for example, are typically very green in comparison with other types of lighting. However, some fluorescents are designed to have a high faithfulness to an ideal light, as measured by its color rendering index (CRI). This dimension, along lines of constant CCT, is sometimes measured in terms of green–magenta balance; this dimension is sometimes referred to as "tint" or "CC".

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