COLOR PHENOMENA  Page: 10. 00  
Introduction  Ingredients  Spectra  Attributes  The Human Eye  Color Mixing  General Terms 
Color Spaces  How to measure  Color Scales  Color Effects  After Images  Contents 
Color Scales 

XYZ TRISTIMULUS on this page  
HUNTER VERSUS CIE on page 10.01  
CIE1931 CHROMATICITY DIAGRAM on page 10.02  
CIE1976 CHROMATICITY DIAGRAM on page 10.03 
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XYZ TRISTIMULUS 
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Standard Observer 
In 1931, the CIE originally defined the standard Observer 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 and this is referred to as the "10° Supplementary Standard Observer"  
The 2° standard Observer should be used for viewing angles of 1° to 4° and the 10° supplementary standard Observer should be used for viewing angles of more than 4°. 
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Color Matching Functions 
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 the 10° Supplementary Standard Observer. 
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"CIE"
1931

Tristimulus
values determined based on the color matching functions
They are suitable for a viewing angle of 4° or less and
are defined
X = K _{380 }∫^{ 780} S (λ) x (λ) R (λ) d (λ) where S (λ) is the
relative spectral power distribution of the illuminant; 
. 
"CIE"
1964 
Tristimulus
values determined based on the color matching functions
They are suitable for a viewing angle of more than 4°
and are defined
X_{10}
= K _{380 }∫^{ 780} S (λ) x_{10 }(λ) R (λ) d (λ) where S (λ) is
the relative spectral power distribution of the
illuminant; 
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E X P L A N A T I O N 

"2° Standard Observer" 

" 10° Supplementary Standard Observer" 

"CIE" 
CIE means: Commission Internationale de
l'Éclairage. in English: The International Commission on Illuminant. The main international organization concerned with problems of color and color measurement. 
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