The C.I.E Primaries

The Commission Internationale d'Eclairage derived a new set of primaries using the blue, green, and red primaries in both positive and negative combinations. This new set of primaries, called X, Y, and Z, have the following properties:

  1. They always produce positive tristimulus values.
  2. It is possible to represent any color in terms of these primaries.
  3. They were derived so that equal values of X, Y, and Z produce white.
  4. They were arranged so that a single parameter Y determines the luminance of the color.
  5. They are related to the sensitivity of the human eye by the use of color matching functions which match to the C.I.E. 1931 Standard Observer.
Index

CIE concepts

Vision concepts

Color vision concepts

Reference
Williamson & Cummins
Ch 3
 
HyperPhysics***** Light and Vision R Nave
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The C.I.E. Color Matching Functions

If the spectral power distribution (SPD) for a colored object is weighted by these curves, the CIE chromaticity coordinates can be calculated.

Calculation of coordinatesCompare with RGB
Index

CIE concepts

Vision concepts

Color vision concepts

Reference
Williamson & Cummins
 
HyperPhysics***** Light and Vision R Nave
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Additive Color Mixing with CIE

The result of adding two colors of light can be worked out as a weighted average of the CIE chromaticity coordinates for the two colors. The weighting factors involve the brightness parameters Y. If the coordinates of the two colors are

then the additive mixture color coordinates are

This linear procedure is valid only if the colors are relatively close to each other in value.

Various ways to achieve the same hue: color perception
Additive mixing of primary colorsAdditive color with Newton color circle
Index

CIE concepts

Vision concepts

Color vision concepts

Reference
Williamson & Cummins
Ch 3
 
HyperPhysics***** Light and Vision R Nave
Go Back