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Contracted from the term micro reciprocal degree, the mired is a unit of measurement used to express
A blue sky, which has a color temperature ''T'' of about , has a mired value of ''M'' = 40 mireds, while a standard electronic
Contracted from the term micro reciprocal degree, the mired is a unit of measurement used to express 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 ...
. Values in mireds are calculated by the formula:
:
where ''T'' is the colour temperature in units of kelvins
The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and ph ...
and ''M'' denotes the resulting mired dimensionless number. The constant is one million kelvins.
For convenience, ''decamireds'' are sometimes used, with each decamired equaling ten mireds. The SI term for this unit is the reciprocal megakelvin (MK−1), shortened to ''mirek'', but this term has not gained traction.
The use of the term ''mired'' dates back to Irwin G. Priest's observation in 1932 that the just noticeable difference
In the branch of experimental psychology focused on sense, sensation, and perception, which is called psychophysics, a just-noticeable difference or JND is the amount something must be changed in order for a difference to be noticeable, detectable ...
between two illuminant
A standard illuminant is a theoretical source of visible light with a spectral power distribution that is published. Standard illuminants provide a basis for comparing images or colors recorded under different lighting.
CIE illuminants
The Inter ...
s is based on the difference of the reciprocals of their temperatures, rather than the difference in the temperatures themselves.
Examples
A blue sky, which has a color temperature ''T'' of about , has a mired value of ''M'' = 40 mireds, while a standard electronic photography
Photography is the visual art, 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 i ...
flash
Flash, flashes, or FLASH may refer to:
Arts, entertainment, and media
Fictional aliases
* Flash (DC Comics character), several DC Comics superheroes with super speed:
** Flash (Barry Allen)
** Flash (Jay Garrick)
** Wally West, the first Kid F ...
, having a color temperature ''T'' of 5000 K, has a mired value of ''M'' = 200 mireds.
In photography
Photography is the visual art, 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 i ...
, mireds are used to indicate the color temperature shift provided by a filter or gel for a given film and light source. For instance, to use daylight film (5700 K) to take a photograph under a tungsten light source (3200 K) without introducing a color cast, one would need a corrective filter or gel providing a mired shift
:
This corresponds to a color temperature blue (CTB) filter.{{cite book , url=https://books.google.com/books?id=1JL2jFbNPNAC&q=ctb+159+mired&pg=PA172 , title=Cinematography: Theory and Practice : Imagemaking for Cinematographers , first=Blain , last=Brown , isbn=0-240-80500-3 , page=172 , publisher=Focal Press , year=2002
Color gels with negative mired values appear green or blue, while those with positive values appear amber or red.
References