SECTION 4.5
235
Color Spaces
TABLE 4.11 Clipping path operators
OPERANDS
OPERATOR
DESCRIPTION
—
W
Modify the current clipping path by intersecting it with the current path, using the
nonzero winding number rule to determine which regions lie inside the clipping
path.
Modify the current clipping path by intersecting it with the current path, using the
even-odd rule to determine which regions lie inside the clipping path.
—
W*
Note:
In addition to path objects, text objects can also be used for clipping; see Sec-
The
n
operator (see Table 4.10) is a no-op path-painting operator; it causes no
marks to be placed on the page, but can be used with a clipping path operator to
establish a new clipping path. That is, after a path has been constructed, the se-
quence
W n
intersects that path with the current clipping path to establish a new
clipping path.
There is no way to enlarge the current clipping path or to set a new clipping path
without reference to the current one. However, since the clipping path is part of
the graphics state, its effect can be localized to specific graphics objects by en-
closing the modification of the clipping path and the painting of those objects
between a pair of
q
and
Q
operators (see Section 4.3.1, “Graphics State Stack”).
Execution of the
Q
operator causes the clipping path to revert to the value that
was saved by the
q
operator before the clipping path was modified.
4.5 Color Spaces
PDF includes powerful facilities for specifying the colors of graphics objects to be
painted on the current page. The color facilities are divided into two parts:
•
Color specification.
A PDF file can specify abstract colors in a device-
independent way. Colors can be described in any of a variety of color systems,
or
color spaces.
Some color spaces are related to device color representation
(grayscale,
RGB, CMYK),
others to human visual perception (CIE-based). Cer-
tain special features are also modeled as color spaces: patterns, color mapping,
separations, and high-fidelity and multitone color.