2° Standard Observer and 10° Supplementary Standard Observer

2Δ Standard Observer and 10Δ Supplementary Standard ObserverThe 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 l964, the CIE defined an additional standard observer, this time based upon a l0° 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 φ1.7cm circle while a 10° field of view at the same distance would be φ8.8cm 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°.

Color-Matching Functions

Color-Matching FunctionsThe 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 Observer.

XYZ Tristimulus Values (CIE 1931)

Tristimulus values determined based on the colormatching functions x(λ),y(λ), and z(λ) defined in 1931 by CIE; also referred to as 2° XYZ tristimulus values. They are suitable for a viewing angle of 4° or less and are defined for reflecting objects by the following formulas:

XYZ Tristimulus Values (CIE 1931)

XYZ Tristimulus Values (CIE 1964)

Tristimulus values determined based on the colormatching functions x10(λ), y10(λ),and z10(λ) defined in 1964 by CIE; also referred to as l0° XYZ tristimulus values. They are suitable for a viewing angle of more than 4° and are defined for reflecting objects by the following formulas:

XYZ Tristimulus Valus (CIE 1964)