Tektronix LumaColor II J18, Instruction Manual

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Appendix B: Chromaticity Reference
B–2 J18 Photometer Instruction Manual
The 1931 CIE Chromaticity Diagram
The 1931 CIE chromaticity diagram, also known as a Kelly chart, is
shown in Figure B–1. The diagram can be used to categorize
chromaticity measurements expressed as x, y values. The x, y values
are determined from the spectral tristimulus values (X, Y, Z), by the
following equations:
x
X
X Y Z
y
Y
X Y Z
The main features of the 1931 CIE chromaticity diagram include:
H
All colors perceptible to the average human eye fall within the
bounded area of the chart.
H
A straight line drawn through two colors, and passing through the
equal energy point (x = 0.333, y = 0.333), indicates complimenta-
ry colors.
H
Saturated colors, which are located on the periphery of the
bounded area, are monochromatic, except on the purple to red
boundary. Colors become progressively less saturated toward the
white achromatic region in the center. The degree of saturation is
a measure of color purity.
H
Boundaries between colors are not distinct; one color blends
gradually into the next.
H
The ratio of distances between two colors to a third color located
on a line drawn between them is proportional to the ratio of
intensities of a mixture of those two colors required to produce
the third color.
The principal disadvantage of the x,y chart is that equal distances on
the diagram do not represent equal perceived color distances.
Appendix B: Chromaticity Reference
B–2 J18 Photometer Instruction Manual
The 1931 CIE Chromaticity Diagram
The 1931 CIE chromaticity diagram, also known as a Kelly chart, is
shown in Figure B–1. The diagram can be used to categorize
chromaticity measurements expressed as x, y values. The x, y values
are determined from the spectral tristimulus values (X, Y, Z), by the
following equations:
x
X
X Y Z
y
Y
X Y Z
The main features of the 1931 CIE chromaticity diagram include:
H
All colors perceptible to the average human eye fall within the
bounded area of the chart.
H
A straight line drawn through two colors, and passing through the
equal energy point (x = 0.333, y = 0.333), indicates complimenta-
ry colors.
H
Saturated colors, which are located on the periphery of the
bounded area, are monochromatic, except on the purple to red
boundary. Colors become progressively less saturated toward the
white achromatic region in the center. The degree of saturation is
a measure of color purity.
H
Boundaries between colors are not distinct; one color blends
gradually into the next.
H
The ratio of distances between two colors to a third color located
on a line drawn between them is proportional to the ratio of
intensities of a mixture of those two colors required to produce
the third color.
The principal disadvantage of the x,y chart is that equal distances on
the diagram do not represent equal perceived color distances.