Transparency


InDesign's ability to create transparent effects has great appeal for designers. It's easy to make objects translucent, feather the edges of vector components, and add drop shadows to anything. But the introduction of transparency in InDesign 2.0 caused printers to grumble. The short story is that transparency effects, such as blend modes and opacity settings utilize an imaging model that goes beyond what PostScript understands. And since PostScript is the native tongue of imagesetters, platesetters, and many of our desktop printers, this presents a challenge. But InDesign converts new-fangled transparency content to a form that can be correctly handled by PostScript devices and processes by performing transparency flattening. Flattening occurs during any of the following procedures:

  • Choosing File > Print and then selecting a desktop printer or PostScript as the target.

  • Choosing File > Export and then selecting the EPS format.

  • Choosing File > Export to create a PDF and then selecting Acrobat 4 (PDF 1.3) compatibility.

Transparency Flattening

Nothing within InDesign is flattened by Transparency Flattening. Your layers remain intact, and all transparency effects are still live. Instead, it's the output stream that is flattened. Content is cut apart, recreated, and reassembled in a form acceptable to PostScript (Figure 12.23). And this jigsaw puzzle will image as you expectif you provide the correct ingredients and the right recipe.

Figure 12.23. During print or export, InDesign starts with transparency involving graphics and text (left), then takes it apart, creating opaque stunt doubles (right) that look like the original effect. Note where the glass cup interacts with text: A text-shaped clipping path is created, which contains a generated image to portray the color interaction of the cup with the text.


Taking some relatively simple precautions when you build a document containing transparency will ensure that it produces predictable results when flattened and processed by the RIP. And there are some changes that print service providers must make to correctly handle transparent content. The following sections present some best practices for handling transparency as you create documents.

Put Text on Top

When text and vector elements fall beneath transparent elements in InDesign, those elements may be rasterized or converted to outlines during printing or exporting. Bring text and vector elements to the top of the pile, and they'll be safe from rasterization (well, until they hit the RIP). Putting such elements at the top of the stacking order should be sufficient. But it's not a bad idea to think in layers, just as a reminder of the issue (Figure 12.24).

Figure 12.24. Placing text and vector art on a topmost layer ensures that such content will not be rasterized by interaction with any transparent content.


Choose the Appropriate Transparency Blend Space

As InDesign flattens transparent overlapping objects, it must create new objects to replace the overlap area (Figure 12.25). While this may sound like extra work, it's necessary as part of creating an output file that PostScript understands. To create the most faithful color in the replacement area, InDesign looks to the Transparency Blend Space setting to determine how it should do the color math. To control the Transparency Blend Space settings, choose Edit > Transparency Blend Space.

Figure 12.25. It's easy to create interesting effects by using opacity settings and blend modes (top, before flattening). During the transparency-flattening process, InDesign creates replacement objects for overlapping areas (bottom, after flattening). The Transparency Blend Space needs to match the color space (RGB or CMYK) of the objects so that InDesign can properly match the color of the overlapping areas. It may look messy, but it's easily digested by devices that speak fluent PostScript.


The default setting for Transparency Blend Space is CMYK, and you should leave it that way for print. When generating a PDF for the Web or an onscreen presentation, you can reduce file size by choosing a PDF preset such as Smallest File Size, which uses the RGB color space. In that situation, change the Transparency Blend Space to RGB in keeping with the fact that content will become RGB in the outgoing PDF. This will result in a more satisfactory rendering of the color in overlapped areas in the resulting PDF.

Choose the Appropriate Transparency Flattener Preset

As InDesign performs flattening, it needs a recipe for generating two important componentsrasterized text and vector art and soft-edged effects. That recipe is contained in the Transparency Flattener Preset (Figure 12.26). Before we discuss appropriate flattener settings, it's helpful to consider some of the functions that take place during flattening.

Figure 12.26. Transparency flattener presets are invoked during output or export to govern the generation of shadows and feathered effects. They also govern any necessary rasterizing of text and vector art. The default flattener presets in InDesign are only a starting point. Custom presets are necessary for proper imaging.


Rasterizing Text and Vector Content

The interaction of transparent images with text and vector art is one of the most challenging combinations to image. Text and vector content must sometimes be rasterized during export or output to satisfy PostScript requirements. While it may be disturbing to hear the words rasterize and text in the same sentence, rasterizing text is not inherently a bad thing (you are no doubt gasping in distaste as you read this).

But consider this: Your text and vector content will be rasterized eventually when it is processed by a RIPa raster image processor. The RIP ultimately converts everything to pixels, but at such a high resolution (usually 2400 ppi or above) that pixels are not apparent in the output. So it isn't the rasterization process itself that's problematic. It's the choice of incorrect resolution during rasterization that can lead to undesirable results.

Similarly, when you scan signatures, maps, or drawings, you set the scanning resolution to a high value, such as 1200 ppi, to smoothly render drawn lines. Pixels are not apparent in the final artwork because of the high resolution. See? Pixels aren't a problem, as long as the resolution of an image is sufficient to fool the eye into seeing a smooth line.

Generating Shadows and Feathered Edges

All those festive drop shadows you're tempted to create in InDesign must be expressed in pixels. Similarly, feathering effects (Object > Feather) applied to InDesign objects or placed artwork are also accomplished with pixels. The feather and drop shadow aren't literal pixels until you export or printthey're just live effects for display until output makes them real. And the resolution of those effects is determined by the flattener preset chosen at the moment of export or print.

Appropriate Flattener Settings

To create and edit flattener presets, choose Edit > Transparency Flattener Presets. The dialog offers three default flattener presets, but since you're creating content for print, the Low and Medium resolution settings are fairly useless. To create a worthwhile flattener preset for print, select the High Resolution option as a starting point, and then click New (Figure 12.27).

Figure 12.27. The default flattener presets are a bit like the Goldilocks fairy tale, except there's no "just right" setting. Start with High Resolution and then select New to create a custom style.


The two key values in the flattener options dialog are Line Art and Text Resolution and Gradient and Mesh Resolution. There isn't a one-size-fits-all transparency flattener setting. The settings should be dictated by the resolution of the output device.

The Line Art and Text Resolution option governs the rasterization of text and vector content. It should equal the resolution of the output device. For example, if you're printing to a desktop printer with a resolution of 600 ppi, set the Line Art Resolution to 600 ppi. On the other hand, a prepress technician preparing to generate PostScript for a 2400 ppi imagesetter would choose 2400 ppi, and so on. If you're creating PDF/X-1a files to send to a print service provider, ask them to give you specific instructions for creating a flattener preset. Be concerned if your contact responds, "Oh, I don't know. Just make a PDF." Push your way past that person, and ask to speak to a prepress technician for guidance.

The Gradient and Mesh Resolution value governs the generation of drop shadows and soft feathered edges created in InDesign. A prepress technician would usually choose 300 ppi for general output, although lower resolutions might be sufficient for low line-screen jobs such as newspaper work. If you're printing to your 600 ppi desktop printer, 150 ppi is probably a sufficient gradient setting for printing comps. By the way, this setting has no effect on the resolution of placed imagesonly on the shadows and feathered edges generated by InDesign (Figure 12.28).

Figure 12.28. Flattener options should be in keeping with the resolution of the output device. For output on an imagesetter (film) or platesetter (plates), a typical setting might be 2400 ppi for line art and 300 ppi for gradients (top).

For a desktop printer with an imaging resolution of 600 ppi (bottom), the line-art resolution should be 600. Setting the gradient resolution to 150 saves a little time in the print process.


Invoking Transparency Flattener Presets

Although you may have created custom flattener presets, they don't actually do anything until you invoke them during print or export. You'll need to pick the proper flattener preset when you print, export an EPS, or generate a PDF with Acrobat 4 compatibility (Figure 12.29). Flattener presets are located in the Advanced section of print and export dialogs.

Figure 12.29. When exporting a PDF with Acrobat 4 compatibility, such as PDF/X-1a, select the appropriate flattener preset in the Advanced section of the Print and Export dialogs.


Chances are, you'll be invoking flattener presets in two situations: Printing to your desktop printer and generating PDFs for submission to the print service provider. Revisit Figure 12.28 to see suggested settings for both of those situations: Your actual settings will depend on output resolution. We'll wait here while you look up your desktop printer resolution. You can do that while you're on hold, waiting to talk to a technician in the print service provider's prepress department so you can inquire about their RIP resolution.

Special Case: Spot Color Content

In addition to performing the jigsaw trickery of flattening during output or export, InDesign instructs some components to overprint in order to render such blending modes as Multiply.

What is overprint? Here's a simple example: Create a solid yellow square, and then place a solid cyan circle on top of the yellow square. The cyan circle knocks out (covers up) the portion of the yellow square underneath it, because shapes are usually opaque in PostScript reality. Like pieces of construction paper, they completely cover up anything underneath them.

However, if you set the cyan circle to overprint, it's no longer opaque. It allows the yellow square underneath to show through, and the overlap area becomes green (cyan plus yellow, as shown in (Figure 12.30).

Figure 12.30. By default, opaque shapes knock out everything underneath (left). Overprinting allows a shape to intermix with everything underneath (right).


Overprint is not a complicated concept, and it's been part of PostScript forever. InDesign counts on the RIP to understand overprint in order to properly image transparency effects. However, many desktop printers don't implement overprint, which is why you may see ugly white or discolored boxes around drop shadows that fall on spot-color areas when you print on a desktop printer (Figure 12.31). It's just One of Those Things. To eliminate (or at least subdue) this problem, make some changes in the Output tab of the Print dialog.

Figure 12.31. To image correctly, a drop shadow on a spot color background (left) requires that the RIP understand how to handle PostScript overprint. A white or discolored box around the shadow (right) indicates that the RIP is not correctly processing PostScript overprint. Many desktop printers suffer from this shortfall, but a print service provider's RIP should handle the shadow correctly.


Choose Composite CMYK and select the Simulate Overprint option (Figure 12.32). You may still see some discoloration, but the white box should be eliminated. Don't freak out: This is due to some limitations of many desktop printers, and doesn't foretell how the effect will be processed by your print service provider's RIP.

Figure 12.32. To subdue the dreaded white-box-under-a-shadow syndrome on a desktop printer, choose Composite CMYK and select the Simulate Overprint option.


Spot Colors and Transparency: Overprinting at the Print Service Provider

InDesign exploits the overprint capability of PostScript to allow shadows and other transparency effects to interact correctly with spot-color content. If you intend to print spot colors, you certainly don't want to convert spot colors to process on your final print job to avoid the dreaded white box syndrome, andwhew!you don't have to. To correctly process shadows and other transparency effects that interact with spot color areas, the print service provider will have to enable PostScript overprint on their RIP (in the past, it was usually turned off). This isn't something you can do from within InDesign. It's the responsibility of the prepress department to make this change. But it's helpful for you to know, so that you can communicate with the print service provider. Different RIP vendors label the function slightly differently, but the gist of it is, "Hey! Honor any PostScript overprint instructions!"

Note that, just as correct rendering of overprinting is crucial to imaging transparent effects correctly, being able to preview overprinting is necessary for correct display of such content on a monitor. By default, Adobe Acrobat does not show overprinting effects, but you can turn on this feature in Acrobat 6.0 Professional and Acrobat 7.0 Professional by choosing Advanced > Overprint Preview. Adobe Reader 7.0 also offers overprint preview, but the setting is lurking in Preferences > Page Display. Note that the Macintosh OS X application Preview cannot display overprint in PDF files.

Drop Shadows: The Sun Never Moves

In the real world, if you rotate a box sitting on a table, the shadow doesn't rotate with the box because the light source remains stationary. The same rules apply in InDesign. Its imaginary sun doesn't move either. This doesn't seem unreasonable until you begin rotating objects to which you've applied drop shadows in InDesign. If you rotate the objects, their shadows do not rotate with them. While it's logical, it may not produce the effect you want. In home-brewed imposition, for example (Figure 12.33), a shadow's relationship with its parent object will change. In the example, the SmithcoMatic logo is supposed to have a drop shadow that's positioned down and to the right of the logo. However, rotating the art 180 degrees causes the shadow to be positioned up and to the left of the art. Oops.

Figure 12.33. This looks fine, doesn't it? Try standing on your head, and you'll see what's wrong with this picture.


InDesign doesn't offer the option to turn off the global light source position (as Photoshop does). The only cure is to manually change the position of the shadow by choosing Object > Drop Shadow, and then entering a new value for the shadow position (Figure 12.34). In the example, the correct shadow position is .04 of an inch for both X and Y offsets. To correct for the rotation, the shadow for the rotated artwork is set to -.04 of an inch for both X and Y offsets (that's a minus sign in front of the number, indicating a negative value).

Figure 12.34. To compensate for InDesign's single-sun approach to drop shadows, you may have to alter the X and Y Offset values for rotated objects (for example, during manual imposition).





Real World(c) Print Production
Real World Print Production
ISBN: 0321410181
EAN: 2147483647
Year: 2007
Pages: 132
Authors: Claudia McCue

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