Color correction
Encyclopedia
Color correction by using color gel
s, 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 http://www.etconsult.com/papers/White%20Paper%20Matt%20Cowan.pdf. 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".
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.
of the captured image http://www.cinematography.net/Pages%20DW/Viper_Magenta_Filter.htm.
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
or by manipulating the film after it has been scanned or telecined.
Color gel
A color gel or color filter , also known as lighting gel or simply gel, is a transparent colored material that is used in theatre, event production, photography, videography and cinematography to color light and for color correction...
s, or filters, is a process used in stage lighting
Stage lighting
Modern stage lighting is a flexible tool in the production of theatre, dance, opera and other performance arts. Several different types of stage lighting instruments are used in the pursuit of the various principles or goals of lighting. Stage lighting has grown considerably in recent years...
, photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
, television
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
, cinematography
Cinematography
Cinematography is the making of lighting and camera choices when recording photographic images for cinema. It is closely related to the art of still photography...
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
Color temperature
Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, and other fields. The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of...
, as well as along a green
Green
Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...
–magenta
Magenta
Magenta is a color evoked by light stronger in blue and red wavelengths than in yellowish-green wavelengths . In light experiments, magenta can be produced by removing the lime-green wavelengths from white light...
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.
Correlated color temperature
Chromaticity
Chromaticity is an objective specification of the quality of a color regardless of its luminance, that is, as determined by its hue and colorfulness ....
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 http://www.etconsult.com/papers/White%20Paper%20Matt%20Cowan.pdf. 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".
Gel nomenclature
The main color correction gels are CTB (color temperature blue) and CTO (color temperature orange). A CTB gel converts tungsten light of 3200K 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.
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 rangeDynamic range
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...
of the captured image http://www.cinematography.net/Pages%20DW/Viper_Magenta_Filter.htm.
Some professional cameras designed for ENG
Electronic news gathering
ENG is a broadcasting industry acronym which stands for electronic news gathering. It can mean anything from a lone broadcast journalist reporter taking a single professional video camera out to shoot a story, to an entire television crew taking a production truck or satellite truck on location...
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 grading
Color grading or colour painting, is the process of altering and enhancing the color of a motion picture, video image, or still image either electronically, photo-chemically or digitally. The photo-chemical process is also referred to as color timing and is typically performed at a photographic...
or by manipulating the film after it has been scanned or telecined.