Minolta CL-200, Instruction Manual

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51
Reference
<CHROMATICITY AND CORRELATED COLOR TEMPERATURE>
Chromaticity (xy)
The CIE (Commission Internationale de
l’Éclairage), an international organization
set up to establish worldwide standards re-
lating to light and color, established the
XYZ
color space
in 1931. This color space
makes it possible to express colors as nu-
merical values. Various improvements and
additional systems have been introduced
in the years since. At present a number of
different color spaces (coordinate systems)
are commonly used for communicating
color information.
The XYZ space was adapted from the prin-
ciples of basic trichromatic theory, which
expressed color as the sum of Red, Green,
and Blue components. The XYZ space uses
a two-dimensional chromaticity diagram
with “x” and “y” as coordinates, as shown
in the illustration below. The center of the
graph corresponds to a no-color condition;
colorfulness increases with movement to-
ward the periphery.
XYZ Color Space
Correlated Color Temperature (Tcp)
The concept of
color temperature
is based
on radiation from a
black body
—an ideal
“perfect radiator” that absorbs all radiant
energy that falls upon it. As the tempera-
ture of this body rises, the body changes
color continuously: starting with red, then
moving through yellow, and finally becom-
ing white. The body temperature at which a
given color appears is referred to as that
color’s color temperature (absolute tem-
perature, measured in Kelvin).
The chart below shows how color tempera-
ture and the block-body locus can be ex-
pressed on an xy chromaticity diagram. In
cases where the source’s color is not found
on the locus, the temperature nearest to it
is taken as the color’s
correlated color tem-
perature . In general, the correlated color
temperature is shown in combination with
the differential (
∆
uv) from the locus.
xy Chromaticity Diagram with Black-Body Locus,
Color Temperature Lines, and Color Difference
Lines
0.50
0.40
0.45
0.35
0.30
0.25
0.20
0.25 0.30 0.35 0.40 0.45 0.50 0.55
50000
+ 0.02uv
+ 0.01uv
+ 0.00uv
– 0.01uv
– 0.02uv
30000
20000
15000
13000
10000
9000
8000
7000
6000
5000
4500
4000
3500
3000
2500
y
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
0.10 0.20 0.30 0.40 0.50 0.60 0.70
x
520
530
540
550
560
570
590
600
610
620
650
680~780
510
500
490
480
470
460
450
380~440
2000 2500
3000
3500
4000
4500
10000
* *
*
*
*
*
B
C
A
D55
D65
D75
580
1500