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The color sensitivity of the eye changes according to the angle of view (object size).
The CIE originally defined the standard observer in 1931 using a 2° field of view, hence the name 2° Standard Observer.
In 1964, the CIE defined an additional standard observer, this time based upon a 10° field of view;
this is referred to as the 10° Supplementary Standard Observer. To give an idea of what a 2° field of view is
like compared to a 10° field of view, at a viewing distance of 50cm a 2° field of view would be a Ø1.7cm circle
while a 10° field of view at the same distance would be an Ø8.8cm circle. Most of the information in this booklet is
based on the 2° Standard Observer. The 2° Standard Observer should be used for viewing angles of 1° to 4°;
the 10° Supplementary Standard Observer should be used for viewing angles of more than 4°. |
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The color matching functions are the tristimulus values of the equal-energy spectrum as a function of wavelength.
These functions are intended to correspond to the sensitivity of the human eye.
Separate sets of three color matching functions are specified for the 2° Standard Observer
and 10° Supplementary Standard Observers.
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