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.
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.
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.
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.
Printing PDF documents with transparencies via “pdfprint” or the Acrobat PDF HandShake plug-in to a PrintPreview queue is fully supported.
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.
Printing PDF documents with transparencies to printer queues with output color space CIELab is not allowed and will result in an error.
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.
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.
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.
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.