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Flattening transparency for high - resolution output
Transparency has been a feature of image editors such as Adobe Photoshop for many years.
The design advantages of transparency are so compelling that customers have long requested
a similar capability in vector drawing and page layout programs. While some drawing pro-
grams support transparency for a limited range of objects, Adobe supports transparency at a
fundamental level so that it can be used for any practical application, from true semi-trans-
parent drop shadows to changing the opacity of any object. To make this happen, Adobe
includes support for transparency in the Adobe Graphics Manager (AGM) graphics engine
to provide high-quality display of transparency effects. Integrated support for transparency
allows transparency effects to be preserved from Illustrator and Photoshop files and applied
to InDesign objects.
Native
transparency
or
live transparency
are terms for the data that describe transpar-
ency, such as specifying 25% opacity or a Screen blend mode. However, Adobe PostScript
thinks in terms of solid or screened color and grayscale values, with no support for native
transparency data. For this reason, native transparency must be
flattened
—converted to the
ink values required to reproduce the appearance of transparency on press. Flattening can
be done by a RIP or by the application generating output data. RIPs are available that can
process native transparency data directly, by supporting PDF 1.4 and flattening transpar-
ency data in-RIP. But many RIPs in use today can’t process transparency data directly, so
before sending them to such a device, documents that use transparency must be flattened in
advance.
It may seem that transparency creates a special case for a service provider to handle.
However, this situation continues to improve with time. Transparency is already part of
the PDF 1.4 and 1.5 specifications supported by Adobe InDesign (starting from version 2),
Acrobat (starting from version 5), and Illustrator (starting from version 9). And as noted
above, RIPs are available that can receive native transparency. As device manufacturers and
service providers upgrade RIPs, software, and workflows, flattening in advance becomes less
necessary. Adobe’s goal is to make working with native transparency as routine as it is to
work with line screens today (which were a challenge in the early days of desktop publish-
ing).
For devices that don’t yet have the ability to process native transparency, Adobe InDesign
includes tools that help you efficiently prepare transparency for high-quality output. The
Flattener Preview palette works together with transparency flattener presets so that you can
evaluate, customize, and apply them. Also, the Pages palette indicate the spreads on which
transparency (from Adobe Illustrator 9 and up; InDesign, or Photoshop) is used, by display-
ing those pages with a checkerboard pattern.
