Color correction is a process used in
stage lighting
Stage lighting is the craft of lighting as it applies to the production of theater, dance, opera, and other performance arts. ,
photography
Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed ...
,
television
Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertisin ...
,
cinematography
Cinematography (from ancient Greek κίνημα, ''kìnema'' "movement" and γράφειν, ''gràphein'' "to write") is the art of motion picture (and more recently, electronic video camera) photography.
Cinematographers use a lens to focu ...
, and other disciplines, which uses
color gel
Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
s, or filters, to alter the overall color of the light. Typically the light color is measured on a scale known as
color temperature
Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...
, as well as along a
green
Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 Nanometre, nm. In subtractive color systems, used in painting and color printing, it is created by ...
–
magenta
Magenta () is a color that is variously defined as pinkish- purplish-red, reddish-purplish-pink or mauvish-crimson. On color wheels of the RGB (additive) and CMY (subtractive) color models, it is located exactly midway between red and blue. I ...
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
Diegesis (; from the Greek from , "to narrate") is a style of fiction storytelling that presents an interior view of a world in which:
# Details about the world itself and the experiences of its characters are revealed explicitly through narra ...
) is the goal. Color gels may also be used to tint lights for artistic effect.
Correlated color temperature
![PlanckianLocus](https://upload.wikimedia.org/wikipedia/commons/b/ba/PlanckianLocus.png)
The particular color of a white light source can be simplified into a
correlated color temperature
Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...
(CCT). The higher the CCT, the bluer the light appears. Sunlight at 5600 K, for example, appears much bluer than tungsten light at 3200 K. Unlike a
chromaticity
Chromaticity is an objective specification of the quality of a color regardless of its luminance. Chromaticity consists of two independent parameters, often specified as hue (h) and colorfulness (s), where the latter is alternatively called ...
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.
Fluorescent light
A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet lig ...
s, for example, are typically very green in comparison with other types of lighting. However, some fluorescent lamps are designed to have a high faithfulness to an ideal light, as measured by its
color rendering index
A color rendering index (CRI) is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with a natural or standard light source. Light sources with a high CRI are desirable in ...
(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".
Gel nomenclature
The main color correction gels are color temperature blue (CTB) and color temperature orange (CTO). A CTB gel converts tungsten light to 'daylight' color. A CTO gel performs the reverse.
Note that different manufacturers' gels yield slightly different colors. As well, there is no precise definition of the color of daylight since it varies depending on the location (latitude, dust, pollution) and the time of day.
Gels that remove the green cast of fluorescent lights are called minus green. Gels that add a green cast are called plus green.
Fractions such as 3/4, 1/2, 1/4, and 1/8 indicate the strength of a gel. A 1/2 CTO gel is half the strength of a (full) CTO gel.
Process
Color Correction is a technical process that fixes color issues and makes footage appear as naturalistic as possible. The idea is for colors to look clean and real, as
human eye
The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm.
...
s would see them in the real world. Basically, correcting problems of the underlying image by balancing out the colors, making the whites appear white, the blacks appear black, and making sure that everything is even.
This process is usually used in stage lighting, photography, television, cinematography, and other disciplines, which uses color gels, or filters,
White balancing cameras
Color filters may be applied over a camera lens to adjust its white balance. In video systems, white balance can be achieved by digital or electronic manipulation of the signal and hence color correction filters are not entirely necessary. However, some digital cinema cameras can record an image without any digital filtering applied. Using physical color correction filters to white balance (instead of digital or electronic manipulation) can maximize the
dynamic range
Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of signals, like sound and light. It is measured either as a ratio or as a base-1 ...
of the captured image.
Some professional cameras designed for
ENG use filter wheels containing color correction filters and are designed to optimize performance for different color temperatures.
In film cameras, no electronic or digital manipulation of white balance is possible in the original camera negative. Color correction filters are an effective method of adjusting white balance. Without filtering, one must attempt to fix white balance through
color timing
Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are assoc ...
or by manipulating the film after it has been scanned or telecined.
Color Correction in Photoshop
Photoshop
Adobe Photoshop is a raster graphics editor developed and published by Adobe Inc. for Windows and macOS. It was originally created in 1988 by Thomas and John Knoll. Since then, the software has become the industry standard not only in raster ...
is an editing software that allows the users to edit and manipulate images, correct colors, create a clipping path, and more to achieve the desired results in an image. In Photoshop, there are multiple tools available to correct colors, match colors, or change colors of images or a part of images.
References
External links
* {{Commons category-inline
Cinematography
Photographic techniques
Stage lighting