SECTION 4.5
265
Color Spaces
bined—on a printing press, for example—and the proper inks or other colorants
are applied to them, the result is a full-color page.
A
Separation
color space
(PDF 1.2)
provides a means for specifying the use of
additional colorants or for isolating the control of individual color components of
a device color space for a subtractive device. When such a space is the current
color space, the current color is a single-component value, called a
tint,
that con-
trols the application of the given colorant or color components only.
Note:
The term
separation
is often misused as a synonym for an individual device
colorant. In the context of this discussion, a printing system that produces separa-
tions generates a separate piece of physical medium (generally film) for each color-
ant. It is these pieces of physical medium that are correctly referred to as separations.
A particular colorant properly constitutes a separation only if the device is generat-
ing physical separations, one of which corresponds to the given colorant. The
Separation
color space is so named for historical reasons, but it has evolved to the
broader purpose of controlling the application of individual colorants in general, re-
gardless of whether they are actually realized as physical separations.
Note also that the operation of a
Separation
color space itself is independent of the
characteristics of any particular output device. Depending on the device, the space
may or may not correspond to a true, physical separation or to an actual colorant.
For example, a
Separation
color space could be used to control the application of a
single process colorant (such as cyan) on a composite device that does not produce
physical separations, or could represent a color (such as orange) for which no specif-
ic colorant exists on the device. A
Separation
color space provides consistent, pre-
dictable behavior, even on devices that cannot directly generate the requested color.
A
Separation
color space is defined as follows:
[ /Separation
name alternateSpace tintTransform
]
In other words, it is a four-element array whose first element is the color space
family name
Separation
. The remaining elements are parameters that a
Separation
color space requires; their meanings are discussed below.
A color value in a
Separation
color space consists of a single tint component in
the range 0.0 to 1.0. The value 0.0 represents the minimum amount of colorant
that can be applied; 1.0 represents the maximum. Tints are always treated as
subtractive
colors, even if the device produces output for the designated compo-
nent by an additive method. Thus, a tint value of 0.0 denotes the lightest color