CIE 1960 color space

The CIE 1960 color space ("CIE 1960 UCS", variously expanded "Uniform Color Space", "Uniform Color Scale", "Uniform Chromaticity Scale", "Uniform Chromaticity Space") is another name for the (u,v) chromaticity space devised by David MacAdam. [cite journal|authorlink=David MacAdam|first=David Lewis|last=MacAdam|title=Projective transformations of I.C.I. color specifications| journal=JOSA|volume=27|issue=8|month=August|year=1937|pages=294–299| url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-27-8-294]

The CIE 1960 UCS does not define a luminance or lightness component, but the Y tristimulus value of the XYZ color space or a lightness index similar to W^* of the CIE 1964 color space are sometimes used. [cite book|title=Digital Pictures: Representation, Compression, and Standards|publisher=Springer|isbn=030642195X|author=Arun N. Netravali, Barry G. Haskell|authorlink=Arun Netravali|edition=2E|page=288| url=http://books.google.com/books?id=-TXYfZrCBuQC&pg=PA288&vq=1960+CIE-UCS+coordinate+system&dq=Riemannian+munsell&source=gbs_search_s&sig=ep8zmQbO7sFBfjJbmOnYiA9mmmI]

Today, the CIE 1960 UCS is mostly used to calculate correlated color temperature, where the isothermal lines are perpendicular to the Planckian locus. As a uniform chromaticity space, it has been superseded by the CIE 1976 UCS.

Background

Judd determined that a more uniform color space could be found by a simple projective transformation of the CIEXYZ tristimulus values: [cite journal|title=A Maxwell Triangle Yielding Uniform Chromaticity Scales|journal=JOSA|first=Deane B.|last=Judd|volume=25|issue=1|year=1935|month=January|pages=24–35| url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-25-1-24| quote=An important application of this coordinate system is its use in finding from any series of colors the one most resembling a neighboring color of the same brilliance, for example, the finding of the nearest color temperature for a neighboring non-Planckian stimulus. The method is to draw the shortest line from the point representing the non-Planckian stimulus to the Planckian locus.]

Judd was the first to employ this type of transformation, and many others were to follow. Converting this RGB space to chromaticities one finds [cite journal|journal=JOSA|title=Quantitative data and methods for colorimetry|volume=34|issue=11|month=November|year=1944|author=OSA Committee on Colorimetry| pages=633–688|url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-34-11-633 (recommended reading)]

$u=frac\{0.4661x+0.1593y\}\{y-0.15735x+0.2424\}$

$v=frac\{0.6581y\}\{y-0.15735x+0.2424\}$

or equivalently (for comparative purposes with the equations to follow):

$u=frac\{5.5932x+1.9116y\}\{12y-1.882x+2.9088\}$

$v=frac\{7.8972y\}\{12y-1.882x+2.9088\}$

MacAdam simplified Judd's UCS for computational purposes:

$u\; =\; 4x\; /\; (12y\; -\; 2x\; +\; 3)$

$v\; =\; 6y\; /\; (12y\; -\; 2x\; +\; 3)$

The Colorimetry committee of the CIE considered MacAdam's proposal at its 14th Session in Brussels for use in situations where more perceptual uniformity was desired than the (x,y) chromaticity space, [cite journal| url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-50-1-87| title=Brussels Session of the International Commission on Illumination|authorlink=International Commission on Illumination|journal=JOSA|volume=50|issue=1|month=January|year=1960|pages=89–90|author=CIE|quote=The use of the following chromaticity diagram is provisionally recommended whenever a diagram yielding color spacing perceptually more nearly uniform than the (xy) diagram is desired. The chromaticity diagram is produced by plotting 4X/(X+15Y+3Z) as abscissa and 6Y/(X+15Y+3Z) as ordinate, in which X, Y, Z are the tristimulus values corresponding to the 1931 CIE Standard Observer and Coordinate System.] and officially adopted it as the standard UCS the next year. [citation|location=Brussels|year=1960|author=CIE|authorlink=International Commission on Illumination|contribution=Official Recommendations|page=36|series=14th Session|title=Publication № 004: Proceedings of the CIE Session 1959 in Bruxelles|volume=A|url=http://cie.kee.hu/newcie/main/withdrawn.html]

Relation to CIEXYZ

:$U=(2/3)X$:$V=Y$:$W=(-X+3Y+Z)/2$:$Z=(3U-3V+2W)/2$

:$u\; =\; 4X\; /\; (X\; +\; 15Y\; +3Z)$:$v\; =\; 6Y\; /\; (X\; +\; 15Y\; +\; 3Z)$

:$u\; =\; 4x\; /\; (-2x\; +\; 12y\; +\; 3)$:$v\; =\; 6y\; /\; (-2x\; +\; 12y\; +\; 3)$

:$x\; =\; 3u\; /\; (2u\; -\; 8v\; +\; 4)$:$y\; =\; 2v\; /\; (2u\; -\; 8v\; +\; 4)$

Relation to CIELUV

:$u\text{'}\; =\; u$:$2v\text{'}\; =\; 3v$

Reference

External links

* [http://www.efg2.com/Lab/Graphics/Colors/Chromaticity.htm Free Windows utility to generate chromaticity diagrams.] Delphi source included.