Bio-medical Ontologies Maintenance and Change Management

Multimedia Medical Databases 93
3.4.4 XYZ Color System
It was one of the first mathematically defined color spaces. Created by CIE in
1931, the CIE XYZ color space is special, because it is based on direct measurements
of the human eye, and serves as the basis from which many other color
spaces are defined [14, 29].
This color system was derived from a series of experiments done in the late
1920s by W. David Wright and John Guild. Their experimental results were combined
into the specification of the CIE RGB color space, from which the CIE XYZ
color space was derived.
This system is based on the additive mixture of the values X, Y, Z, the imaginary
primaries introduced by CIE. The values of X, Y, Z are calculated with the
next transformation [14, 29]:
X=0.607R+ 0.174G+0.200B
Y=0.299R+0.587G+0.114B
(3.4)
Z=0.000R+0.066G+1.116B
These color features cannot be seen by a human eye, or produced, because are
too saturated. The luminance is represented only by the Y value. This system is
device dependent, because the RGB color system is device dependent.
It has the next characteristics [29]: device independent, not perceptual uniform,
not intuitive, linear transformation, dependent on viewing direction, object geometry,
direction, intensity or color of the illumination and highlights.
3.4.5 CIE L*u*v* and CIE L*a*b* Color Systems
The CIE 1976 (L*, u*, v*) color space, also known as the CIELUV color space,
was adopted by the International Commission on Illumination (CIE) in 1976, as a
simple method to compute transformation of the 1931 CIE XYZ color space, but
which attempted perceptual uniformity [29, 52].
The color model L* is based on the scaling of luminance and it is determined
only by Y value.
The conversion from XYZ color space to the L*u*v* color space is [29]:
L* = 116 ( Y/Y ) n 1/3 - 16 if Y/Y > 0.008856
n
L* = 903.3 ( Y/Y ) if Y/Y