Basic Concepts; Color Space - HP IndiChrome User Manual

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*
As a default, the HP IndiChrome ink mixing system uses ∆E*
between colors. If the value of ∆E*
the value of ∆E*
The CIE 1994 Color Difference Model defines ∆E*
CIELab ∆E*. The ∆E*
of saturated colors. Furthermore, ∆E*
perception of the difference between two colors is a direct function of ∆E*
dependant upon L*a*b*.
In the IMS software, ∆E*
best mix and the target color. The ∆E*
The ∆E* color difference is defined by:
where:
L*, a*, and b* are the color coordinates of either best mix or actual mix.
96 Chapter A Special options, basic concepts, and spare parts (all presses)
C ∗
=
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is large, the two colors being compared are not similar.
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color difference improves upon the CIELab ∆E* for color matching
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⎛
⎜
∆ * ≡ ∆ 2 * +
E L
⎜
94
+
1 . 0
⎝
∆ ≡ ∆ + ∆ +
* 2 * 2 *
E L a
∆ ≡ − ∆
* * *
L L L
target
∆ ≡ −
* * *
C C C
∆
target
a ∗ 2 b ∗ 2
( ) ( )
+
is small, the two colors being compared are similar. If
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is more uniform than ∆E* in the sense that the
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and ∆E* refer to the color difference between the actual mix or
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color difference is defined by:
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2
⎞ ⎛
∆
*
C
⎟ ⎜
+
⎟ ⎜
+
*
045 C 1 . 0
⎠ ⎝
target
∆
2 *
b
≡ −
* * *
a a a
target
* ≡ ∆ 2 * + ∆ 2 * − ∆
H a b C
to quantify differences
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as a replacement of the more familiar
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2
⎞
∆
*
H
⎟
⎟
*
015 C
⎠
target
∆ ≡ −
* * *
b b b
target
2 *
and not
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ENWW