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PDF HandShake UB+ User manual |
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12 PDF-native OPI workflow
HELIOS ImageServer is well-known as a reliable, color-true and fast OPI workflow solution. For more information about OPI workflows see the ImageServer manual. All classic OPI workflows use the print function of page layout applications like InDesign to produce PostScript output with OPI references. These OPI references are placeholders for high-resolution images. To obtain a full-resolution document, e.g. for the generation of a printing plate, the OPI references within the PostScript output are resolved, i.e. replaced with high-resolution images. Then this resolved PostScript output is used for further processing with a trapping, imposition or rasterizing solution.
The basic idea behind PDF HandShake's new PDF-native OPI workflow is to use the File > Export- > Adobe PDF function in InDesign to produce PDF output with OPI references instead of PostScript output with OPI references. As mentioned above, to obtain a full-resolution document, the OPI references within the exported PDF document are resolved, i.e. replaced with high-resolution images, and the result is a new PDF document containing the high-resolution images. The command line utility "pdfresolve" (see 6.7 "pdfresolve") provides this new OPI image replacement functionality for PDF documents. This functionality can also be used by means of a hot folder utilizing the Script Server example script "pdfresolve.pl".
For more information on Script Server and the example script "pdfresolve.pl" see the ImageServer manual. This workflow needs neither PostScript documents nor conversions from PDF to PostScript or vice versa. The development of "pdfresolve" follows the current trend in workflow design to replace PostScript with PDF.
One major benefit of using PDF instead of PostScript is that InDesign offers many features that can be expressed in PDF but not in PostScript. If you use a classic OPI workflow based on PostScript, much valuable information like transparency, ICC profiles, PDF/X output intents, metadata, and trapping information cannot be embedded within the document file. It is a difficult and nearly impossible task to store and maintain this information elsewhere, and once this information is lost somewhere within the workflow, it is often gone for good. Another major advantage of PDF over PostScript is that PDF viewing applications are available for many platforms whereas viewing PostScript accurately enough for prepress needs is a sophisticated task which involves high software costs.
12.1 Choosing the file format to place in InDesign
You can place both high-resolution and layout images in InDesign. When you generate layout images via ImageServer, you can choose between EPSF and TIFF layouts. It is strongly recommended not to use high-resolution images and to generate TIFF layouts only in a PDF-native OPI workflow. You can force the recommended generation of TIFF layouts by copying the high-resolution images to a folder in a HELIOS volume with automatic layout generation enabled and using the "%t" folder naming option (see the chapter "Defining folder-specific OPI settings" in the ImageServer manual.
What are the benefits of placing layouts instead of high-resolution images in InDesign? First of all, layouts are nearly always much smaller than high-resolution images, making production possible on a limited bandwidth network or making production substantially faster. This is also the main reason why OPI is used in the first place. Moreover, ImageServer generates layouts that contain the Mac file ID of their high-resolution image.
When you place TIFF layouts in InDesign and export an InDesign document as PDF using the Omit For OPI options described below, InDesign embeds these Mac file IDs in the exported PDF document. When "pdfresolve" resolves OPI references of exported PDF documents, it uses the Mac file IDs of high-resolution image files to locate them in the desktop database of HELIOS volumes. The file search via Mac file ID is a very powerful mechanism that can locate files that have been renamed or moved within a volume.
What are the benefits of placing TIFF layouts rather than EPSF layouts in InDesign? First of all, the current versions of InDesign do not embed the Mac file ID of high-resolution images in the exported PDF documents when using EPSF layouts. Furthermore, ImageServer generates TIFF and EPSF layouts from high-resolution images with clipping paths while preserving these clipping paths, but InDesign copies the clipping path to the embedded PDF documents only if TIFF layouts are used. "pdfresolve" does not insert clipping paths during OPI image replacement currently either. Hence clipping paths are lost within the PDF-native OPI workflow when using EPSF layouts.
The preference PDFNativeWorkflow (see 14.1 "Global PDF preferences") enforces the generation of PDF-native workflow compatible layout images from vector-based EPS images, even if TIFF layout images are supposed to be generated, e.g. via a "%t" folder syntax.
12.2 Exporting PDF from InDesign
When you have loaded an InDesign document in InDesign and want to export it as PDF for a PDF-native OPI workflow, you have to specify certain options in the Export PDF options dialog.
If you want to use the transparency features in InDesign, which include drop shadow and feather effects, you must select Acrobat 5 (PDF 1.4) or higher from the Compatibility pop-up menu in the "General" settings section of the Export PDF options dialog (Fig. 37). Prior versions of PDF do not support transparencies.
If you use TIFF layout files only as recommended, you must check the Omit for OPI checkbox for Bitmap images in the "Advanced" settings section of the Export PDF options dialog (Fig. 38):
If you want to use EPSF layouts despite their disadvantages, you must check the EPS checkbox here, too.
12.3 Using printer queue settings to configure "pdfresolve"
By default, "pdfresolve" adopts all of its image replacement options from a specified printer queue. Additional command line options override printer queue settings. Printer queue settings can be edited using HELIOS Admin, but two "pdfresolve" options can only be specified via the command line, they cannot be specified in HELIOS Admin. These are the TagReplacedImages option and the options to compress replaced images with JPEG 2000 compression format. For more information on the command line options of "pdfresolve" please refer to 6.7 "pdfresolve". Here is a short overview of the TagReplacedImages option:
Using "pdfresolve" with settings of different printer queues allows easy generation of PDF output documents for a broad range of applications, from a single PDF document exported by InDesign:
12.3.1 Downsampling and output compression
In a PDF-native OPI workflow with large high-resolution images it is advantageous to specify downsampling and compression options for the used printer queue. These options can easily be specified in HELIOS Admin (Fig. 39):
In the HELIOS Admin printer queue settings select the OPI tab and from the Downsampling pop-up menu choose a resolution (in dpi) which will be applied to objects in the PDF document that exceed the specified value.
Likewise, specify an output compression method from the Bitmap, Monochrome, and Color pop-up menus.
It is recommended to choose a lossless compression type such as "ZIP" or "CCITT Group 4".
12.3.2 Hot folder setup
Please refer to the ImageServer manual how to set up the Script Server and how to use the example script "pdfresolve.pl" to set up a PDF-native OPI hot folder.
12.4 Limitations
- Raster images are supported as high-resolution images only, object-based EPSF and PDF documents are not supported as high-resolution images.
- Using EPSF layouts leads to reduced high-resolution image file search functionality and loss of clipping paths and transparency, see above.
- Ultimately all PDF documents need to be rastered, e.g. for the generation of a printing plate. All current RIP solutions can rasterize PDF documents with transparencies, alternatively Adobe Acrobat Professional can be used to print and flatten PDF documents with transparencies.
12.5 Remote PDF-native OPI workflows
The basic concept of a remote PDF-native OPI workflow is:
- Generate TIFF layout images from high-resolution images on a server system running ImageServer and PDF HandShake
- Transfer the layout images only to the designers, e.g. via Internet and HELIOS WebShare
- The designers place these layout images in InDesign documents and export them as PDF
- The designers transfer the exported PDF documents back to the server system, e.g. via Internet using HELIOS WebShare
- The exported PDF documents are resolved via PDF-native OPI "hot folders" for different applications, e.g. for offset printing plate generation, for website publishing, etc.
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