HP IndiChrome, Руководство пользователя

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96 Chapter A Special options, basic concepts, and spare parts (all presses)
ENWW
Basic concepts
Color space
Every color can be represented by the CIELab coordinates: L*, a*, and b*.
The lightness, L*, indicates whether a color is light, such as Yellow, or dark, such as
Dark Blue. An L* value close to 100 indicates a very light color, whereas a value close to
zero indicates a very dark color.
The coordinate a* indicates the green or red content of a color. A negative value of a*
indicates a green color, whereas a positive value indicates a red color. Most colors used in
printing have values of a* between -80 and 80.
The coordinate b* indicates the blue or yellow content of a color. A negative value of b*
indicates a blue color, whereas a positive value indicates a yellow color. Most colors used
in printing have values of b* between -80 and 120.
The three coordinates L*, a*, and b* form a color space, which is a three-dimensional
space where every color is represented by a point in the space.
The chroma C* is a measure of the brightness of a color. Colors with large C* values are
referred to as bright (saturated) colors, whereas colors with small C* values are referred to
as dull colors.
C* is defined as:
∆
E*
94
As a default, the HP IndiChrome ink mixing system uses
∆
E*
94
to quantify differences
between colors. If the value of
∆
E*
94
is small, the two colors being compared are similar. If
the value of
∆
E*
94
is large, the two colors being compared are not similar.
The CIE 1994 Color Difference Model defines
∆
E*
94
as a replacement of the more familiar
CIELab
∆
E*. The
∆
E*
94
color difference improves upon the CIELab
∆
E* for color matching
of saturated colors. Furthermore,
∆
E*
94
is more uniform than
∆
E* in the sense that the
perception of the difference between two colors is a direct function of
∆
E*
94
and not
dependant upon L*a*b*.
In the IMS software,
∆
E*
94
and
∆
E* refer to the color difference between the actual mix or
best mix and the target color. The
∆
E*
94
color difference is defined by:
The
∆
E* color difference is defined by:
where:
L*, a*, and b* are the color coordinates of either best mix or actual mix.
C
∗
a
∗
( )
2
b
∗
( )
2
+ =
2
*
*
2
*
*
2 * *
015 . 0 1 045 . 0 1
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
∆
+
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
∆
+ ∆ ≡ ∆
target target
94
C
H
C
C
L E
2 * 2 * 2 * *
b a L E
∆ + ∆ + ∆ ≡ ∆
* * *
target
L L L
− ≡ ∆
* * *
target
a a a
− ≡ ∆
* * *
target
b b b
− ≡ ∆
* * *
target
C C C
− ≡ ∆
2 * 2 * 2 * *
C b a H
∆ − ∆ + ∆ ≡ ∆