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An illuminant is characterized by its relative spectral power distribution (SPD). The white point of an illuminant is the chromaticity of a white object under the illuminant, and can be specified by chromaticity coordinates, such as the x, y coordinates on the CIE 1931 chromaticity diagram (hence the use of the relative SPD and not the absolute SPD, because the white point is only related to ...
The spectrum of a standard illuminant, like any other profile of light, can be converted into tristimulus values. The set of three tristimulus coordinates of an illuminant is called a white point. If the profile is normalized, then the white point can equivalently be expressed as a pair of chromaticity coordinates.
A list of standardized illuminants, their CIE chromaticity coordinates (x,y) of a perfectly reflecting (or transmitting) diffuser, and their correlated color temperatures (CCTs) are given below.
For example, the white point of an sRGB display is an x, y chromaticity of (0.3127, 0.3290), where x and y coordinates are used in the xyY space. ( u′ , v′ ) , the chromaticity in CIELUV , is a fairly perceptually uniform presentation of the chromaticity as (another than in CIE 1931) planar Euclidean shape.
The chromaticity components U* and V* are defined such that the white point maps to the origin, as in Adams chromatic valence color spaces. This arrangement has the benefit of being able to express the loci of chromaticities with constant saturation simply as ( U *) 2 + ( V *) 2 = C for a constant C .
The white point, which defaults to D50, can be changed by ICC profile. CIELAB D50 is available in ICC profiles as a profile connection space named "Lab color space". [2] CIELAB (any white point) is a supported color space in TIFF image files. [17] CIELAB (any white point) is available in PDF documents, where it is called the "Lab color space ...
Image:Map of USA-bw.png – Black and white outlines for states, for the purposes of easy coloring of states. Image:BlankMap-USA-states.PNG – US states, grey and white style similar to Vardion's world maps. Image:Map of USA with county outlines.png – Grey and white map of USA with county outlines.
A comparison between a typical normalized M cone's spectral sensitivity and the CIE 1931 luminosity function for a standard observer in photopic vision. In the CIE 1931 model, Y is the luminance, Z is quasi-equal to blue (of CIE RGB), and X is a mix of the three CIE RGB curves chosen to be nonnegative (see § Definition of the CIE XYZ color space).