COLOR  PHENOMENA Page: 10. 00
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Color Scales

X-Y-Z TRISTIMULUS on this page

HUNTER VERSUS CIE on page 10.01
CIE-1931 CHROMATICITY DIAGRAM on page 10.02
CIE-1976 CHROMATICITY DIAGRAM on page  10.03
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X-Y-Z  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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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 an arm length a 2° field 
of view would be about a 2 cm circle while a 10° field of view at the same distance would be about a 10 cm circle.  

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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
XYZ
Tristimulus Values

or

"CIE" 1931 
X2Y2Z2  
Tristimulus Values

Tristimulus values determined based on the color matching functions 
x (λ), y (λ) and z (λ) defined by CIE in 1931 
and 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:

X = K 380 780 S (λ) x (λ) R (λ) d (λ)
Y = K 380 780 S (λ) y
(λ) R (λ) d (λ)
Z = K 380 780 S (λ) z
(λ) R (λ) d (λ)
K = 100 /
{ 380 780 S (λ) y (λ) d (λ)}

where S (λ) is the relative spectral power distribution of the illuminant;
x
(λ), y (λ), z (λ) are the color matching functions for CIE-1931 2° Standard Observer 
and R
(λ) as the spectral reflectance of the specimen.

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"CIE" 1964
X10Y10Z10
 Tristimulus Values

Tristimulus values determined based on the color matching functions 
x10 (λ), y10 (λ) and z10 (λ) defined by CIE in 1964 
and also referred to as 10° XYZ tristimulus values. 

They are suitable for a viewing angle of more than 4° and are defined 
for reflecting objects by the following formulas:

X10 = K 380 780 S (λ) x10 (λ) R (λ) d (λ)
Y10 = K 380 780 S (λ) y10
(λ) R (λ) d (λ)
Z10 = K 380 780 S (λ) z10
(λ) R (λ) d (λ)
K = 100 /
{ 380 780 S (λ) y10 (λ) d (λ)}

where S (λ) is the relative spectral power distribution of the illuminant;
x10
(λ), y10 (λ), z10 (λ) are the color matching functions for CIE-1964 10°  Supplementary Standard Observer 
and R
(λ) as the spectral reflectance of the specimen.

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E X P L A N A T I O N

"2° Standard Observer" 


10-00-01

" 10° Supplementary Standard Observer"


10-00-02

"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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 Last update
2010-05-18