At first, it was just the occasional shadow, and that
was kind of novel. But then everyone got carried
away—show me a headline, and I’ll show you text
with a drop shadow (figure 1). There’s something
fundamentally appealing about transparency: Start
with simple elements, throw in a little peekaboo and
things are more interesting. But, to paraphrase your
mother, it’s all fun and games until somebody can’t
print his job.
Of course, we’ve had transparency in Adobe
Photoshop for many years. But its introduction in
Adobe Illustrator 9.0 meant that vectors could play
along. Adobe InDesign 2.0 brought transparency to
page layout, and designers cheered. Printers, on the
other hand, hid under their light tables, hoping it
would go away. But the see-through cat is out of the
bag—even QuarkXPress 7.0 contains transparency
effects now.
What could be scary about transparency?
Well, for starters, PostScript—the page-description
programming language that powers many desktop
printers and the imaging devices used by commercial
printers—doesn’t understand transparency at all. As
you’ll see, there are some accommodations you must
make when creating transparent artwork, and some
small modifications your printer needs to make to
standard imaging workflows.
How applications handle transparency
Popular graphics applications create and handle
transparency effects differently, with differences in
imaging models and limitations. Within a single
application, things aren’t too scary. It’s when you
start cross-pollinating between applications that you
hit some roadblocks.
For example, it’s easy to stack up multiple layers
in a Photoshop file, assigning opacity settings
and blending modes to allow the layers to visually
interact. Shadows created within Photoshop correctly
darken content underneath using the Multiply blending
mode—as long as you remain in Photoshop.
But place that Photoshop file into Illustrator,
InDesign or QuarkXPress, and the shadow knocks
out what’s underneath—not the effect you want
(figure 2). For some work-arounds, see the sidebar
“Making Shadows Image Correctly” on page 28.
Although opacity in a Photoshop-layered,
native file is honored by other applications, Photoshop blending modes—such as Multiply—are
not translated correctly. Why is this? Photoshop’s
internal imaging model differs somewhat from the
model used in other Adobe applications and in
QuarkXPress. The situation is much better for native
Illustrator (.ai) files placed in InDesign because the
two applications share the same imaging model.
Happily, opacity and blending modes in Illustrator
files—including shadows—are fully supported by
InDesign. Whoopee!
QuarkXPress solves this dilemma by offering no
support for native Illustrator files. Even version 7.0
allows only Illustrator EPS files, which cannot contain
any transparency.
What do you mean,
you flattened my file?
Because our primary print-imaging model,
PostScript, doesn’t understand native transparency,
applications that allow transparency have
to “predigest” transparent content, turning it into
PostScript-legal content that looks transparent.
When transparency first appeared in Illustrator
9.0, that digestion process—called flattening—wasn’t
as sophisticated as current versions, and printers
didn’t know quite how to image such content. The
flattening process assumed that RIPs (Raster Image
Processors) would be sophisticated enough to use
the full complement of PostScript Level 3 operators,
and a print file was generated based on that assumption.
The flattener was counting on the RIP to “Do
the Right Thing.” However, even RIP vendors who
licensed PostScript from Adobe didn’t necessarily
implement every single arcane programming command
and were caught short by this newfangled stew,
allowing instances of rasterized text and other unattractive
artifacts to occur.
Fast-forward to present day: Flattening procedures
currently used by Illustrator, InDesign and
QuarkXPress are much more elegant and more effective,
and major vendors have updated their RIPs to
handle transparency.
Curious about what happens during flattening?
InDesign, Illustrator and QuarkXPress analyze
transparent content at the time of print or export,
replace that content with opaque “stunt doubles” that
PostScript understands and assign overprint attributes
to polish it off (figure 3). In some cases, text must
be converted to outlines to preserve a visual effect,
but output correctly. Some situations may require
that some objects are rasterized. It’s a pretty amazing
engineering feat.
Best practices
You can develop some healthy habits as you create
transparency effects. Herewith, a checklist:
General Guidelines
1. Convert all unnecessary spot colors to process
before output.
2. If possible, put text and linework above transparent
effects in stacking order.
3. Don’t use opacity when a simple tint will suffice.
4. Avoid mixing RGB and CMYK content in a
single document.
5. If you are working in an OPI workflow (low res/
high res swap), the high-resolution images must be
in place before export/output. (If this doesn’t ring a
bell, you’re probably not using an OPI workflow.)
Illustrator:
1. Before creating shadows or other soft-edged
effects, set the appropriate resolution: Effect >
Document Raster Effects Settings. A value of 200-
300 ppi at final size is appropriate. Where possible,
use Effects rather than Filters. Effects are live effects
that can be edited at any time, whereas Filters create
literal content that’s more difficult to modify.
2. Embed any images involved in transparency.
3. Lastly, save as native Illustrator files for placement
in InDesign.
InDesign:
>1. Use InDesign’s forensic tools to see a more faithful
rendition of content: Choose Window > Output
> Separations Preview, and you can view individual
separations as well as color percentage values of all
content (figure 4).
2. When printing or exporting to PDF or EPS,
choose the High Resolution Flattener setting (under
the Advanced controls in print and export dialogs).
This ensures that any shadows or feathered edges
have adequate resolution.
3. Ask the printer how you should submit your files,
and whether special considerations exist because of
the imaging workflow. Some printers want PDFs,
and some want the packaged InDesign files plus
fonts and support art. Never assume.
QuarkXPress 7.0:
1. Earlier builds of QuarkXPress 7.0 may struggle
with even moderately complex transparency, crashing
when you attempt to print or export. Update
your installation to the current build, 7.1. On the
Mac, you’ll have to install the 7.01 patch first. On
Windows, you can apply the 7.1 update to the base
7.0 install without intermediate patches.
2. If you’re applying the same type of shadow to
several objects on a page, group them first and then
apply the shadow to the group as a whole. Looks the
same, but prints and RIPs faster.
3. If you want a soft-edged silhouette on a Photoshop
image, don’t use the Alpha Channel clipping approach. It just creates a harsh vector edge based on
the pixels of the alpha channel. Instead, use a Layer
Mask in Photoshop for true, soft-edged transparency.
White line fever:
misleading display in Acrobat
InDesign and Illustrator use an internal PDF Library
to generate PDFs. QuarkXPress uses a non-Adobe
solution from Global Graphics. Both methods make
legal PDFs. Your print service provider should provide
specifications for PDF creation. (If they say, “just
send any old PDF,” that’s not a good sign.)
Acrobat versions 5.0 and later support live,
unflattened transparency because the imaging model
goes beyond PostScript limitations. Sounds great,
doesn’t it? However, most current imaging devices
are going to convert such PDFs into PostScript anyway,
using their own recipes. So, unless your printer
explicitly sanctions late-model PDFs, you should create
PDF/x-1a files, which are Acrobat 4.0-flavored.
Sounds fancy, but it’s a one-click preset choice in
QuarkXPress and InDesign (File > Export), as well as
Illustrator (File > Save).
Be forewarned: Your PDF may not appear correctly
when viewed in Acrobat, for several reasons.
Because the flattening process requires overprint to
render some transparency effects in a PostScriptlegal
form, you’ll need to turn on Overprint Preview
in Acrobat (figure 5). In Acrobat 7.0, choose
Advanced > Overprint Preview. In Acrobat 8.0,
choose Advanced > Print Production > Overprint
Preview. You’ll find this necessary when transparency
(such as drop shadows) interacts with spot
color content.
As figure 3 shows, the flattening process cuts
content into little puzzle pieces. When you view such
a PDF in Acrobat, you’re appalled by what seem to
be gaps between those pieces, an artifact called stitching.
There’s actually no gap: The pieces really touch
and fit perfectly. But Acrobat anti-aliases vector edges
to improve display, and the white lines are an unfortunate
side effect of that effort. You can turn off the effect in Acrobat preferences (Acrobat > Preferences
for Mac or Edit > Preferences for PC) by unchecking
“Smooth line art.” But then you’ll encounter another
side effect: Any text that was converted to outlines
during flattening will look very rough (although it
images fine). So you have to decide which irks you
more—imaginary white lines or imaginary rough
edges (figure 6).
What your printer needs to do
While RIPs have matured and flattening is much
more sophisticated than it was at the dawn of transparency,
a few tweaks by the print service provider
are still necessary to ensure proper imaging.
Remember how you had to turn on Overprint
Preview in Acrobat for correct display of transparency
involved with spot colors? Well, your printer has to
turn on PostScript overprint in the RIP to correctly
image such effects. (In most workflows, it’s turned
off.) If you receive a contact proof with Dreaded
White Box Syndrome, remind your printer to turn
on PostScript overprint.
Some RIPs think they need to trap the flattened
puzzle pieces to each other, leading to unnecessary
visible trap lines. Your printer may have to create a
modified queue to prevent this. And, on Rampage
RIPs, it may be necessary to turn off something
called Dual Rasterization to prevent an effect similar
to Acrobat’s White Line Fever. Each RIP has its own
hardware and software, and thus its own particular
set of issues. The RIP’s vendor can help your printer
find patches and a work-around to correctly image
challenging files.
Additionally, if your printer is a member of
Adobe Solutions Network, the company is eligible
for extensive tech support directly from Adobe to
help deal with any software issues. If the company
isn’t a member, it should join to receive the great
resources available.
A postscript: beyond PostScript
After all these years, PostScript may be ready to
retire. Adobe’s new PDF Print Engine goes beyond
the capabilities of PostScript, allowing live transparency
and true PDF-native workflows. It will soon
begin appearing in commercial RIPs and will eventually
make its way into our desktop printers. Just
imagine—no more problems with transparency!
Don’t worry; we’ll come up with something else
to challenge the new technology. We always do!
