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Transparency for Print Output in Adobe Creative Suite 3

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Table of Contents

  1. Introduction
  2. New transparency features in CS3
  3. The Adobe Print Engine
  4. New technology
  5. Creating transparency
  6. Transparency: live or flattened?
  7. Designers Guide to Transparency
  8. Creating and viewing transparency effects
  9. Best practices for working with transparency
  10. Transparency effects in Illustrator CS3
  11. Transparency effects in InDesign CS3
  12. Importing and placing files with transparency
  13. Building effects with transparency
  14. Saving and exporting files with transparency
  15. Printing files with transparency
  16. Delivering files with transparency to your print service provider
  17. Transparency-related resources
  18. Transparency: A Print Production Guide
  19. Best practices when flattening
  20. Flattening basics
  21. Advanced Flattener controls
  22. Flattening controls in Illustrator CS3
  23. Flattening controls in InDesign CS3
  24. Flattening controls in Acrobat 8 Professional
  25. Transparency and color
  26. Troubleshooting
  27. Glossary

Transparency: A Print Production Guide

Transparency and color

It’s important to properly configure the color settings in InDesign CS3 and Illustrator CS3 prior to flattening a job. During flattening, the Flattener may transform colors involved in transparency—and if the application’s color settings are not configured correctly, the colors affected by the Flattener may not match the actual press conditions.

Whether or not you use a color-managed workflow, be aware that transparency in your jobs can affect your color output. This section explains how the Transparency Flattener can affect your existing color workflows and how to configure the Flattener’s settings to achieve optimal color output.

The topic of color management is beyond the scope of this document. For information about color management in Adobe Creative Suite 3, see Color Workflows for Adobe Creative Suite 3.

See

Transparency Blend Space

To blend transparent objects together, the Flattener must use a single color space (RGB or CMYK) for the blending. Called the Transparency Blend Space (or simply, "blend space"), this space may be either the RGB or CMYK document color space. InDesign CS3 and Illustrator CS3 set the document color space in the Working Spaces section of the Color Settings dialog box (Edit > Color Settings). For example, if the Transparency Blend Space is set to CMYK, the color space profile used is the one defined as the document’s CMYK working space. If a document is not being color-managed, a generic RGB or CMYK color profile is assigned to the document color space.

The Transparency Blend Space setting is determined differently in InDesign CS3, Illustrator CS3, and Acrobat 8 Professional:

In InDesign CS3, a document can contain both RGB and CMYK color objects. You must choose whether to use the RGB or CMYK blending space (Edit > Transparency Blend Space).

In Illustrator CS3, documents are either in RGB or CMYK color mode. The blending space of a document is always the same as the document color mode (File > Document Color Mode). This document-based blend space differs from InDesign CS3.

In Acrobat 8 Professional, a PDF document can contain both RGB and CMYK color objects. When printing, Acrobat uses the Color Profile setting from the Output section of the Advanced Print Setup dialog box. Ideally, when printing to a CMYK output device this color profile will be the same color space in which CMYK objects in the PDF already reside. Using the same color space will prevent CMYK-to-CMYK conversions during flattening.

To display the Acrobat Color Profile settings:

  1. Choose File > Print.
  2. Click the Advanced button to get to the Advanced Print Setup dialog box.
  3. Select Output from the list on the left.

Transparency Blend Space and color management

The color conversions that the Flattener performs augment the conversions performed at output. When a job that contains live transparency is printed (or exported to a file format that doesn’t support live transparency), both the Flattener and the application’s print engine may convert colors, and the printer may further convert color.

Printing transparency: step-by-step

When printing a page containing live transparency from InDesign CS3, and the Transparency Blend Space is set to Document CMYK, the following steps will take place (steps 3 and 6 may perform color conversions):

  1. The Flattener detects transparency on a spread.
  2. The Flattener refers to the Transparency Blend Space setting to determine the appropriate color space in which to blend transparent objects. In this example, Document CMYK was selected. The Document CMYK color space is determined by the active color settings (Edit > Color Settings).
  3. Any image that is tagged with a color space that differs from the selected blend space is converted to Document CMYK.
  4. The Flattener flattens the transparency.
  5. The flattened data is passed to the print engine.
  6. The print engine compares the color information in the flattened data with the Printer Profile color space set in the Print dialog box. If the color settings don’t match, the print engine converts the colors to the color space indicated by the Printer Profile.
  7. The color-managed job is printed.

Example 1: No color conversion

Scenario: An InDesign document contains a single spread with one CMYK image and one element that contains transparency. The CMYK image contains a profile that matches both the InDesign document’s CMYK Working Space profile and the Printer Profile. The Transparency Blend Space setting is set to Document CMYK.

Using the step numbers from Printing transparency: step-by-step:

  1. Because the image’s color profile matches the profile of the transparency blending space, no conversion is necessary during the flattening process.
  2. Because the image’s color profile also matches the Printer Profile, no color conversion is performed by the print engine.

In this example, no color conversions take place.

Example 2: Unwanted color conversion due to incorrect Transparency Blending Space setting

Scenario: An InDesign document contains a single spread with one CMYK image and one element that contains transparency. The CMYK image contains a profile that matches both the InDesign document’s CMYK Working Space profile and the Printer Profile. Unlike Example 1, the Transparency Blending Space is set (incorrectly for this job) to Document RGB.

Using the step numbers from Printing transparency: step-by-step:

  1. Because the image’s color profile does not match the profile of the transparency blending space, the image is converted from the CMYK color space to the Document RGB space.
  2. Because the image’s color space has been converted to Document RGB by the Flattener and thus does not match the CMYK printing space, the print engine converts the image back to CMYK.

In this example, two unnecessary color conversions took place due to the improper setting of the Transparency Blend Space. These unwanted color conversions would very likely result in an noticeable shift in the color of the image.

Color-managed images and the Flattener

Keep the following in mind when preparing color-managed images (tagged with an ICC profile) for use in an InDesign or Illustrator CS3 job that contains transparency: an image’s color space must match the Transparency Blend Space, and if it does not, will be converted to the blend space. Thus, an image (with or without transparency) placed in an InDesign CS3 spread or Illustrator CS3 page containing transparency will be converted to the color space of the Transparency Blend Space.

Converting the colors of all objects on a spread to the color space of the Transparency Blend Space yields consistent color across any two same-colored objects on a spread, and prevents visible color shifts at the edges of transparency.

Untagged images and the Flattener

When Illustrator CS3 or InDesign CS3 encounter untagged (not color-managed) images that use the same color model as the blend space, the application assumes those images are saved in the same color space as the blend space. Thus, no color conversion will occur.

Settings for color-managed images

When placing images into InDesign CS3 and Illustrator CS3, it's always best to use images that have been prepared for the same color space as the Transparency Blend Space. This makes color conversion unnecessary when flattening occurs.

Settings for images to be used in both CMYK and RGB workflows

When creating an image for use in both RGB and CMYK workflows such as for print and web, it's best to save the image as a color-managed RGB file. Image appearance changes only slightly on converting from one RGB color space to another RGB color space, or from an RGB color space to a CMYK color space.

Avoiding CMYK-to-CMYK conversions

Do not place a color-managed CMYK image that is saved in a color space that differs from the Transparency Blend Space, especially if the blend space is CMYK. CMYK-to-CMYK conversions often noticeably change the image appearance due to the nature of the conversion. CMYK-to-RGB conversions are somewhat better in this respect, but also not desired.

In-RIP color management and transparency

If you want to use your RIP’s color management features, you may have to change the way you work. This is necessary because of the way the Transparency Flattener works: if a page or spread contains a transparent item, the Flattener has to convert all graphics and images on that page to the Transparency Blend Space. The color transformation for graphics on these pages is handled by the Flattener before the RIP gets the data. If you want to use your RIP’s color management function for jobs that contain transparency, you can either let the RIP partially color-manage your job or work in a large color space.

Letting the RIP partially color-manage your job

The Flattener converts color only on those pages containing transparency. In this scenario, you let the Flattener convert the colors for graphics on pages with transparency, and you let the RIP convert the colors on pages without transparency.

To use this method, your document working space in Illustrator CS3 or InDesign CS3 should be the same as the output device’s color space. This ensures that the Flattener and the RIP converts all elements to the same color space.

Working in a large color space

Some digital output devices are capable of print colors that are not available in a standard press CMYK gamut (for example, by using more than four ink colors). In some cases, RIPs for these devices have built-in color management that optimizes the colors of the graphics for the device’s gamut. To take advantage of the RIP’s color optimization, you can work in a large color space (such as AdobeRGB) in your Adobe Creative Suite 3 application.

This method works well if you have control over the creation of the images and graphics that you print. If you control how the graphics are created, make sure that they are created in a large color space such as AdobeRGB. After placing the AdobeRGB images into your CS3 application, be sure to set your blend space to Document RGB, and your RGB working space to AdobeRGB. Because your graphics’ color profiles match that of the working space, no color transformation takes place—even on pages with transparency.

Spot colors in exported Illustrator files

In Illustrator 10, CS, CS2, or CS3 artwork, a file with transparency and spot colors must be exported in specific formats to get correct spot color separations:

  • Native Illustrator 10, CS, CS2, or CS3 (in which transparency remains live).
  • Illustrator 10, CS, CS2, or CS3 EPS (in which transparency has been flattened).
  • PDF 1.4, 1.5, 1.6, or 1.7 (in which transparency remains live).

In the case of other flattened formats, such as EPS files that were created by using Illustrator version 9 or earlier and PDF 1.3 and earlier, spot colors may convert to process when you save the file and transparency will be lost.

See also Saving and exporting files with transparency.

The Flattener and spot colors

Adobe Creative Suite 3 applications fully support using spot colors with transparency. For most jobs, no special treatment is needed for spot colors. But in a few special cases in a print workflow, spot colors may be converted to process: the use of certain blending modes, conversion of spot colors of placed graphics to process, and the use of the Simulate Overprint feature.

Blending modes that affect spot colors

Certain blending modes, such as Difference, Exclusion, Saturation, and Luminosity, can introduce unexpected process colors, or convert spot colors to process. If these blending modes are used in your files, create a flattened PDF file and use the Separations Preview feature in Acrobat 8 Professional to determine what colors will print.

Converting placed graphics with live transparency and spot colors to process colors

If you place a graphic (such as a native Illustrator file that contains spot colors and live transparency into InDesign CS3) and then use InDesign to convert the spot color to process when printing or exporting, color discrepancies may occur between the spot color in the placed graphic and the element created in InDesign that use the same spot color. This difference is caused by the way the Flattener processes live transparency in placed graphics, compared to how it processes live transparency in the application in which the Flattener is running.

Previewing separations

Be sure to use the Separations Preview (Figure 63) available in InDesign CS3 and Output Preview in Acrobat 8 Professional to confirm your expectations prior to output. Use these panels to turn on and off the display of individual separations, and display color values at the position of your mouse on the page.

See also Printing files with transparency.

Previewing separations: Acrobat 8 Professional Output Preview dialog box (left) and InDesign CS3 Separations Preview panel (right).

(+) view larger
Figure 63. Previewing separations: Acrobat 8 Professional Output Preview dialog box (left) and InDesign CS3 Separations Preview panel (right).

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