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                                                   570
         CHAPTER 7                                                                  Transparency



         achieved by specifying the fill and stroke with separate path objects and an ex-
         plicit transparency group.

         Note: Overprinting of the stroke over the fill does not work in the second case de-
         scribed above (although either the fill or the stroke can still overprint the backdrop).
         Furthermore, if the overprint graphics state parameter is true, the results are discon-
         tinuous at the transition between equal and unequal values of the stroking and non-
         stroking alpha constants. For this reason, it is best not to use overprinting for
         combined filling and stroking operations if the stroking and nonstroking alpha con-
         stants are being varied independently.


         Summary of Overprinting Behavior

         Tables 7.14 and 7.15 summarize the overprinting and erasing behavior in the
         opaque and transparent imaging models, respectively. Table 7.14 shows the over-
         printing rules used in the opaque model, as described in Section 4.5.6, “Overprint
         Control.” Table 7.15 shows the equivalent rules as implemented by the Compatib-
         leOverprint blend mode in the transparent model. The names OP and OPM in the
         tables refer to the overprint and overprint mode parameters of the graphics state.

                    TABLE 7.14 Overprinting behavior in the opaque imaging model


                                                               EFFECT ON COLOR COMPONENT
SOURCE COLOR SPACE       AFFECTED COLOR
                         COMPONENT
                                                    OP FALSE       OP TRUE, OPM 0       OP TRUE, OPM 1

DeviceCMYK,              C, M, Y, or K          Paint source       Paint source       Paint source if ≠ 0.0
specified directly,                                                                   Do not paint if = 0.0
not in a sampled image
                         Process colorant       Paint source       Paint source       Paint source
                         other than CMYK

                         Spot colorant          Paint 0.0          Do not paint       Do not paint

Any process color        Process colorant       Paint source       Paint source       Paint source
space (including other
cases of DeviceCMYK)     Spot colorant          Paint 0.0          Do not paint       Do not paint

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