Color & Light Knowledge

Measuring Instruments

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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 1.7cm circle while a 10ذ field of view at the same distance would be an 8.8cm circle. Most of the information in this booklet is based on the 2ذ 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.
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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