Previous Next

                                                    235
           SECTION 4.5                                                                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.

—             W*           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.

           Note: In addition to path objects, text objects can also be used for clipping; see Sec-
           tion 5.2.5, “Text Rendering Mode.”

           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.

Previous Next