Adobe InDesign CS5 - Manual (Page 466)

460 USING INDESIGN
Transparency effects
Last updated 11/16/2011
Best practices when creating transparency
In most cases, flattening produces excellent results when you use an appropriate predefined flattener preset, or create
a preset with settings appropriate for your final output. For a complete reference and troubleshooting guide on how
transparency affects output, see the document “Achieving Reliable Print Output with Transparency” (English only) on
the Adobe website.
However, if your document contains complex, overlapping areas and you require high-resolution output, you can
achieve more reliable print output by following a few basic guidelines:
Important: If you’re applying transparency to documents intended for high-resolution output, be sure to discuss your
plans with your service provider. Good communication between you and your service provider will help you achieve the
results you expect.
Overprinting objects
Although flattened objects may look transparent, they are actually opaque and don’t allow other objects beneath them
to show through. However, if you don’t apply overprint simulation, the transparency flattener may be able to preserve
basic overprinting of objects when exporting to PDF or printing. In this case, recipients of the resulting PDF file should
select Overprint Preview in Acrobat 5.0 or later to accurately view the results of overprinting.
Conversely, if you apply overprint simulation, the transparency flattener provides a simulation of what the overprints
look like, and this simulation results in all opaque objects. In PDF output, this simulation converts spot colors to
process color equivalents. Therefore, Simulate Overprint should not be selected for output that will be color separated
later.
Spot colors and blending modes
Using spot colors with certain blending modes sometimes produces unexpected results. This is because InDesign uses
process color equivalents on screen, but uses spot colors in print. In addition, isolated blending in an imported graphic
could create knockouts in the active document.
If you use blending, check your design periodically using Overprint Preview in the View menu. Overprint Preview
gives an approximation of how spot inks that overprint or interact with transparent objects will appear. If the visual
effect is not what you want, do any of the following:
• Use a different blending mode or no blending mode. Avoid these blending modes when working with spot colors:
Difference, Exclusion, Hue, Saturation, Color, and Luminosity.
• Use a process color where possible.
Blend space
If you apply transparency to objects on a spread, all colors on that spread convert to the transparency blend space
you’ve chosen (Edit > Transparency Blend Space), either Document RGB or Document CMYK, even if they’re not
involved with transparency. Converting all the colors results in consistency across any two same-colored objects on a
spread, and avoids more dramatic color behavior at the edges of transparency. Colors are converted “on the fly” as you
draw objects. Colors in placed graphics that interact with transparency are also converted to the blend space. This
affects how the colors appear on-screen and in print, but not how the colors are defined in the document.
Depending on your workflow, do one of the following:
• If you create documents for print only, choose Document CMYK for the blend space.
• If you create documents for web only, choose Document RGB.
• If you create documents for both print and web, decide which is more important, and then choose the blend space
that matches the final output.