Information Technology Reference
In-Depth Information
⎛
⎞
⎛
⎞
⎛
⎞
X
Y
Z
0
.
607 0
.
174 0
.
201
0
.
299 0
.
587 0
.
114
0
.
000 0
.
066 1
.
117
R
G
B
⎝
⎠
=
⎝
⎠
⎝
⎠
.
(9)
The Y component is intentionally defined to match closely to luminance, while X
and Z components give color information. As this system is a linear combination
of the RGB components, it inherits all the dependencies on the imaging conditions
from the RGB color system. Furthermore, it is commonly considered as a system of
transition from RGB to another color system and rarely used directly.
3.1.2
Luminance-Chrominance Systems
Luminance-chrominance systems divide color into one luminance component and
two chrominance components. The main advantage of these color models is that
the luminance and the chrominance information are independent. Thus, the lumi-
nance component can be processed without affecting the color contents. Among the
mostly used luminance-chrominance systems, we mainly distinguish between the
perceptually uniform systems Luv and Lab [25], proposed by CIE, and the YC
r
C
b
system devoted for television and video transmission. Perceptual uniformity of Luv
and Lab color systems means that the Euclidean distance between two colors in
these spaces models the human perception of color differences. Chrominance com-
ponents are (u,v) for the Luv space, and (a,b) in Lab. Both color spaces are derived
from the XYZ color space, as follows:
⎧
⎨
⎩
116
Y
n
1
3
Y
−
16
,
if
Y
n
>
0
.
01
L
=
(10)
903
.
3
Y
n
1
3
,
otherwise
,
4
X
X
+ 15
Y
+ 3
Z
,
u
= 13
L
(
u
u
n
)
,
u
=
−
where
(11)
9
Y
X
+ 15
Y
+ 3
Z
,
v
= 13
L
(
v
v
n
)
,
v
=
−
where
(12)
a
= 500
f
X
X
n
f
Y
Y
n
,
−
(13)
b
= 200
f
Y
Y
n
f
Z
Z
n
,
−
(14)
where
f
(
t
)=
t
3
,
if
t
>
0
.
008856
16
7
.
787
t
+
116
,
otherwise.
Here
Y
n
= 1
.
0 is the luminance, and
X
n
= 0
.
312713 and
Y
n
= 0
.
329016 are the
chrominances of the white point of the system. The values of the L component are
