Best practices when creating transparency

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.

• If you create a high-resolution print piece that you’ll also publish as a high-profile PDF document on a website, you may need to switch the blending space back and forth before final output. In this case, be sure to reproof the color on every spread that has transparency, and avoid using the Difference and Exclusion blend modes—these modes can change the appearance dramatically.

Type

When type is close to transparent objects, it may interact with transparent objects in unexpected ways. For example, type that wraps around a transparent object may not actually overlap the object, but the glyphs may be close enough to interact with the transparency. In this case, the flattener may convert the glyphs to outlines, resulting in thickened stroke widths on the glyphs only.

If this happens, do either of the following:

• Move the text to the top of the stacking order. Use the Selection tool to select the text frame, and then choose Object > Arrange > Bring to Front.

• Expand all text to outlines for a consistent effect throughout the document. To expand all text to outlines, select Convert All Text To Outlines in the Transparency Flattener Preset Options dialog box. Selecting this option may affect processing speed.

Image replacement

The flattener requires high-resolution data to accurately process a document with transparency. However, in an OPI proxy workflow, placeholder or proxy images are used, for later replacement with high-resolution versions by an OPI server. If the flattener doesn’t have access to the high-resolution data, then no OPI comments are produced and only the low-resolution proxy images are output, resulting in low-resolution images at final output.

If you work in an OPI workflow, consider using InDesign to substitute images before saving the document as PostScript. To do this, you must specify settings both when you place the EPS graphic and when you output it. When you place the EPS graphic, select Read Embedded OPI Image Links in the EPS Import Options dialog box. When you output, select OPI Image Replacement in the Advanced area of either the Print or Export EPS dialog box.

Color conversions

If a transparent object overlaps a spot color object, undesirable results may occur when you export to EPS format, and then convert spot colors to process colors upon printing or create color separations in an application other than InDesign.

To prevent problems in these cases, use the Ink Manager to convert spot colors to process color equivalents as necessary prior to exporting from InDesign. Another way to prevent problems is to make sure that your spot inks are consistent in both the original application (for example, Adobe Illustrator) and InDesign. This may mean that you’ll need to open an Illustrator document, convert a spot color to process color, export it again to EPS, and then place the EPS file in your InDesign layout.

Adobe PDF files

Exporting to Acrobat 4.0 (Adobe PDF 1.3) always flattens a document with transparency, which may affect the appearance of its transparent objects. Nontransparent content is not flattened unless Simulate Overprint is selected in the Output area of the Export Adobe PDF dialog box. Therefore, when you export an InDesign document with transparency to Adobe PDF, do any of the following:

• Whenever possible, choose Acrobat 5.0 (Adobe PDF 1.4), Acrobat 6.0 (Adobe PDF 1.5), or Acrobat 7.0 (Adobe PDF 1.6) compatibility in the Export Adobe PDF dialog box to preserve transparency in a live and fully editable form. Make sure that your service provider can handle Acrobat 5.0, Acrobat 6.0, or Acrobat 7.0 files.

• If you must use Acrobat 4.0 compatibility, your document contains spot colors, and you want to create a PDF file for on-screen viewing (such as a client review), you may want to select the Simulate Overprint option in the Output area of the Export Adobe PDF dialog box. This option properly simulates the spot and transparent areas; recipients of the PDF file won’t have to select Overprint Preview in Acrobat to see how the document will look when printed. However, the Simulate Overprint option converts all spot colors to process color equivalents in the resulting PDF file, so be sure to deselect this option when you create the PDF for final production.

• Consider using the predefined [Press Quality] Adobe PDF preset. This preset contains flattener settings appropriate for complex documents intended for high-resolution output.

Trapping

Flattening may convert vectors to rasterized areas. Traps applied to artwork in Adobe Illustrator using strokes and placed in InDesign will be preserved. Traps applied to vector artwork drawn in InDesign and then rasterized may not be preserved.

To keep as many objects vector as possible, select the [High Resolution] transparency flattener preset in the Advanced area of the Print or Export Adobe PDF dialog box.