PDF HandShake UB64 User manual (Version 5.0.0)  

17 PDF Transparency

The PDF standard supports transparency since PDF Reference 1.4 and Acrobat 5 and is continuously enhanced by Adobe. Recent versions of page layout applications such as Adobe InDesign, Adobe Illustrator, QuarkXPress1 or Esko ArtPro generate PDF documents with transparencies for overlapping transparent objects and drop shadows.

When PDF documents with transparencies are printed on PostScript printers, the printing application must flatten the transparencies, since PostScript does not support transparency. Acrobat Distiller2 can process PostScript input and supports transparency using the “pdfmark” constructs extension of the PostScript language defined in “pdfmark Reference, Adobe Acrobat SDK Version 8.0” from 2006.

PDF HandShake can convert PDF documents with transparencies to PostScript files with “pdfmark” constructs, and Acrobat Distiller can convert these files back to PDF documents with transparencies. Furthermore, both ImageServer and PrintPreview can convert PostScript with “pdfmark” constructs to raster images with correct visualization of transparencies.

If you want to use PostScript printers or PostScript processing software other than Acrobat Distiller 8, PrintPreview and ImageServer, you probably cannot use PostScript with “pdfmark” constructs as input.

17.1 Control transparency processing in PDF HandShake

17.1.1 PDF transparency in printing

The PDF Transparency checkbox in the HELIOS Admin printer settings determines whether printing PDF documents with transparencies (via the HELIOS Acrobat plug-in, the “pdfprint” command, or from an OPI process with layouts replaced by PDF high-resolution images) results in an error or whether PostScript with “pdfmark” constructs is generated. The PDF Transparency option of printer queues is disabled by default. Please note that there is a very limited number of printers and PostScript processing applications which can process PostScript with “pdfmark” constructs correctly. Nearly all printers and PostScript processing software will ignore the “pdfmark” transparency constructs and silently replace transparent objects with non-transparent objects, resulting in substantially wrong visual output.

17.1.2 PDF to EPSF conversion and EPSF layout generation from PDF documents

PDF documents can be converted to both vector-based and raster-based EPSF files using the HELIOS ImageServer “layout” program in convert mode, i.e. using the -l option. Conversion of PDF documents with transparencies to raster-based EPSF files or other raster image formats is supported by PDF HandShake with ImageServer. Conversion of PDF documents with transparencies to vector-based EPSF files will produce EPSF files using “pdfmark” constructs by default. Since the number of printers or PostScript processing applications that can properly process these EPSF files is limited, you can prevent the generation of “pdfmark” constructs in vector-based EPSF output by option -o PDFTransparency=FALSE. If this option is used, “layout” aborts conversion with an error if a source PDF document contains transparencies. The same rules apply to EPSF layout generation from PDF documents with transparencies.

17.1.3 High-resolution PDF documents with transparencies in OPI workflows

PDF documents with transparencies can be used as high-resolution image files in OPI workflows if the intended output device or processing software supports “pdfmark” constructs, e.g. with a “Create PDF” queue. But you should configure the OPI server to generate raster layouts for PDF high-resolution image files since page layout applications such as InDesign and QuarkXPress cannot display vector-based EPSF layouts with “pdfmark” constructs correctly. If you want to exclude PDF documents with transparencies from OPI workflows, you can set the preference Global/Opi/PDFTransparency to FALSE.

17.1.4 Previews of PDF documents with transparencies in PrintPreview

Printing PDF documents with transparencies via “pdfprint” or the Acrobat PDF HandShake plug-in to a PrintPreview queue is fully supported.

17.2 Configure Distiller 8 for processing PDF HandShake output with transparencies

Acrobat Distiller versions before version 8 are not suitable for PDF HandShake output with transparencies. By default, in Distiller 8 (and later), support for “pdfmark” constructs for transparencies is not enabled. The transparency feature of Distiller 8 cannot be changed in its Edit Adobe PDF Settings... dialog. The transparency feature of Distiller is determined by the Adobe PDF Settings file selected in the Distiller user interface. The Adobe PDF Settings files for Mac are usually located in “/​Library/​Application Support/​Adobe/​Adobe PDF/​Settings/​”. The shipped Adobe PDF Settings files all disable Distiller’s transparency feature. To enable it, you need to edit these text files and change the default setting of /AllowTransparency from FALSE to TRUE. When Distiller processes a PostScript file containing “pdfmark” transparency features and /AllowTransparency is FALSE, Distiller generates an error.

17.3 Limitations of PDF Transparency support in ImageServer and PrintPreview

  1. Printing PDF documents with transparencies to printer queues with output color space CIELab is not allowed and will result in an error.

  2. Separated printing of PDF documents with transparencies may result in wrong visual output when non-separable blend modes are used. Non-separable blend modes are part of the PDF transparency imaging model.

  3. PDF HandShake has a sophisticated built-in color management. PDF HandShake converts the color of objects in PDF documents to the color space of the selected output device before they are used for transparency computations. This combination of color management and transparency computation may result in unwanted variations with regards to visual output color.

  4. Combinations of PDF transparencies with spot colors or overprints are critical. You cannot expect PDF documents with such combinations to have consistent visual appearance using different PDF viewing or processing applications, or using different options in just one PDF viewing or processing application.

17.4 Troubleshooting with PDF transparencies

Different workflows, different PDF and raster image viewing applications or different settings used in one viewing application tend to produce substantially different results for these critical features. OS X Preview, Adobe Acrobat and Photoshop often produce substantially different output for these critical features. Here is one important advice if you experience missing transparent objects for a particular PDF document with PDF HandShake.

The Overprint Preview flag in Adobe Acrobat can have significant influence on how the document is displayed. If you have a critical PDF document with transparencies, please view it in Adobe Acrobat and toggle the Overprint Preview flag. If some elements appear with one setting and disappear with the other, you will probably need to set the DeviceN/PostScript 3 (HELIOS Admin) or PreserveDeviceN (Acrobat PDF HandShake plug-in) options, and if that does not help, you will probably have to re-create the PDF document in its page layout application with different settings.

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HELIOS Manuals April 1, 2020