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Profiles can be further classified according to their gamut, or
the range of colors that can be expressed using the profile.
Gamut is conventionally expressed by means of chromaticity, a
measure of color developed by the Commission Internationale
de l'Éclairage (CIE). The CIE system, which is modeled on hu-
man color perception, maps the physical wavelengths of light to
three coordinates (known as CIE X, Y, and Z) that give unique
numerical expression to the full range of color differences that
can be perceived by humans. Chromaticity is a measure of color
from which considerations of brightness have been factored out,
giving a two-coordinate system.
In the chromaticity diagram at right, the complete gamut of col-
ors visible to humans is in the area enclosed by the green line.
The curved portion of the line gives the chromaticity of "pure,"
unmixed colors with wavelengths in the visible spectrum of 380–
780 nm. The blue end of the spectrum (380 nm) is at the bot-
tom left corner, the red end of the spectrum (780 nm) at the
bottom right corner. The straight diagonal line connecting these
two points represents the different shades of purple created by
combining red and blue light. The colors inside the area en-
closed by these lines are created by mixing light of different
wavelengths.
Reference: Preferences
No color profile is capable of expressing the full range of colors
visible to the human eye. The diagram below compares the
gamut of colors visible to the eye with the colors that can be
expressed in each of the RGB profiles provided with Nikon CMS.
The gamut for each profile is contained in the triangle defined
by the three points that mark the extremes of red, green, and
blue for that profile (red is at the bottom right corner, green at
the top of the triangle, and blue at the bottom left corner). The
white point for each profile is shown by the symbol in the cen-
ter of the triangle.
y
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.1
0.2
0.3
0.4
0.5
Apple RGB
Color Match RGB
sRGB
NTSC (1953)
Bruce RGB
Adobe RGB (1998)
CIE RGB
Wide Gamut RGB
Human
x
0.6
0.7
0.8
0.9
1
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