		COLOR PHENOMENA				Page: 10. 01
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
	X-Y-Z TRISTIMULUS on page 10.00
	HUNTER VERSUS CIE on this page
	CIE-1931 CHROMATICITY DIAGRAM on page 10.02
	CIE-1976 CHROMATICITY DIAGRAM on page 10.03

HUNTER versus CIE

10-01-01

Mathematical relationships for the standard illuminant C between
Hunter-color-system and CIE 2^oStandard Observer.

10-01-02

.	L a b	X_% Y_% Z_%	X Y Z
L a b	.	Y_% = 0.01 L²	Y = 0.01 L²
		X_% = 0.01 L² + ( a*L / 175 )	X = 0.9804 ( 0.01L² + a*L / 175 )
		Z_% = 0.01 L²- ( b*L / 70 )	Z = 1.181 ( 0.01L²- b*L / 70 )
X_% Y_% Z_%	L = 10 * Y_%^-1/2	.	Y = Y_%
	a = 17.5 ( X_%- Y_%) / Y_%^-1/2		X = 0.9084 * X_% = X_%/ 1.02
	b = 7.0 ( Y_% - Z_% ) / Y_%^-1/2		Z = 1.181 * Z_% = Z_% / 0.847
X Y Z	L = 10 * Y^-1/2	Y_% = Y	.
	a = 17.5 ( 1.02 X - Y ) / Y^-1/2	X_% = X / 0.9804 = 1.02 X
	b = 7.0 ( Y - 0.847 Z ) / Y^-1/2	Z_% = Z / 1.181 = 0.847 Z

The tristimulus values X, Y and Z are limited as color specifications because they correlate poorly with any of the visible attributes.
Only Y correlates with Lightness, X and Z do not correlate with Hue, Saturation, vividness etc.
or with any visually meaningful attribute of color appearance.

The CIE recommended a chromaticity system to identify those aspects of color appearance separate from Lightness,
and proposed the trichromatic coefficients as x, y and z.

10-01-03

THE CIE 1931 (x,y) CHROMATICITY DIAGRAM

This (xy) chromaticity diagram is used to designate hues and chromas of colors.
Color values (darkness/lightness) are represented separately from the chromaticity chart.
Hue designations are show on the diagram as locations around the periphery.
Wavelength notation are in italic numerals just outside the periphery.
For example, red is near 650 nanometers; blue is near 475 nanometers.
Chroma designations are show by locations outward from the center of the diagram.
The dominate wavelength of a color can be determined by drawing a line from a radiation source,
though the color location, to the wavelength notation on the periphery.
Color temperatures of radiation sources are show on the temperature (black) line.
Sources, such as A, B, E, D65 and C are noted.
The Hunter coordinates (ab) are show as +a for red, -a for green, +b for yellow and -b for blue.

Mathematical relationships for the standard illuminant C between
trichromatic coefficients and tristimulus values.

.	x y z	X Y Z	The sum of x, y and z will always be unity and for that reason only two of the chromatic coefficients are needed to specify chromaticity. x + y + z = 1.0000 z = 1.0000 - ( x + y )
x y z	.	X = x ( X + Y + Z )
		Y = y ( X + Y + Z )
		Z = z ( X + Y + Z )
X Y Z	x = X / (X + Y + Z )	.
	y = Y / ( X + Y + Z )
	z = Z / (X + Y + Z )

E X P L A N A T I O N
L a b Hunter System	L = Lightness
	+a = redness	-a = greenness
	+b = yellowness	-b = blueness
X_% Y_% Z_%	X_%= ....................
	Y_%= Y = Lightness
	Z_%= ....................
X Y Z CIE System	X = ....................
	Y = Y_%= Lightness
	Z = ....................
CIE	Means: Commission Internationale de l'�clairage. 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