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                                                       978
             CHAPTER 10                                                         Document Interchange




                 TABLE 10.53 Additional entries specific to a trap network appearance stream
KEY                       TYPE          VALUE

PCM                       name          (Required) The name of the process color model that was assumed when
                                        this trap network was created; equivalent to the PostScript page device
                                        parameter ProcessColorModel (see Section 6.2.5 of the PostScript Lan-
                                        guage Reference, Third Edition). Valid values are DeviceGray, DeviceRGB,
                                        DeviceCMYK, DeviceCMY, DeviceRGBK, and DeviceN.

SeparationColorNames      array         (Optional) An array of names identifying the colorants that were assumed
                                        when this network was created; equivalent to the PostScript page device
                                        parameter of the same name (see Section 6.2.5 of the PostScript Language
                                        Reference, Third Edition). Colorants implied by the process color model
                                        PCM are available automatically and need not be explicitly declared. If this
                                        entry is absent, the colorants implied by PCM are assumed.

TrapRegions               array         (Optional) An array of indirect references to TrapRegion objects defining
                                        the page’s trapping zones and the associated trapping parameters, as de-
                                        scribed in Adobe Technical Note #5620, Portable Job Ticket Format.
                                        These references are to objects comprising portions of a PJTF job ticket
                                        that is embedded in the PDF file. When the trapping zones and parame-
                                        ters are defined by an external job ticket (or by some other means, such
                                        as with JDF), this entry is absent.

TrapStyles                text string   (Optional) A human-readable text string that applications can use to de-
                                        scribe this trap network to the user (for example, to allow switching be-
                                        tween trap networks).

             Note: Preseparated PDF files (see Section 10.10.3, “Separation Dictionaries”) can-
             not be trapped because traps are defined along the borders between different colors
             and a preseparated file uses only one color. Preseparation must therefore occur after
             trapping, not before. An application preseparating a trapped PDF file is responsible
             for calculating new Version arrays for the separated trap networks.


10.10.6 Open Prepress Interface (OPI)
             The workflow in a prepress environment often involves multiple applications in
             areas such as graphic design, page layout, word processing, photo manipulation,
             and document construction. As pieces of the final document are moved from one
             application to another, it is useful to separate the data of high-resolution images,
             which can be quite large—in some cases, many times the size of the rest of the
             document combined—from that of the document itself. The Open Prepress Inter-
             face (OPI) is a mechanism, originally developed by Aldus Corporation, for cre-

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