Flatten transparent artwork

If your document or artwork contains transparency, to be output it usually needs to undergo a process called flattening. Flattening divides transparent artwork into vector-based areas and rasterized areas. As artwork becomes more complex (mixing images, vectors, type, spot colors, overprinting, and so on), so does the flattening and its results.

Flattening may be necessary when you print or when you save or export to other formats that don’t support transparency. To retain transparency without flattening when you create PDF files, save your file as Adobe PDF 1.4 (Acrobat 5.0) or later.

You can specify flattening settings and then save and apply them as transparency flattener presets. Transparent objects are flattened according to the settings in the selected flattener preset.

About transparency flattener presets

If you regularly print or export documents that contain transparency, you can automate the flattening process by saving flattening settings in a transparency flattener preset. You can then apply these settings for print output as well as for saving and exporting files to PDF 1.3 (Acrobat 4.0) and EPS and PostScript formats. In addition, in Illustrator you can apply them when saving files to earlier versions of Illustrator or when copying to the clipboard; in Acrobat, you can also apply them when optimizing PDFs.

These settings also control how flattening occurs when you export to formats that don’t support transparency.

You can choose a flattener preset in the Advanced panel of the Print dialog box or of the format-specific dialog box that appears after the initial Export or Save As dialog box. You can create your own flattener presets or choose from the default options provided with the software. The settings of each of these defaults are designed to match the quality and speed of the flattening with an appropriate resolution for rasterized transparent areas, depending on the document’s intended use:

is for final press output and for high-quality proofs, such as separations-based color proofs.

is for desktop proofs and print-on-demand documents that will be printed on PostScript color printers.

is for quick proofs that will be printed on black-and-white desktop printers and for documents that will be published on the web or exported to SVG.

Apply a flattener preset for output

You can choose a flattener preset in the Print dialog box, or in the format-specific dialog box that appears after the initial Export dialog box.

If you regularly export or print documents that contain transparency, you can automate the flattening process by saving flattener settings in a transparency flattener preset. You can then apply these settings when you print or export to PDF 1.3 (Acrobat 4.0) or EPS formats.

Create or edit a transparency flattener preset

You can save transparency flattener presets in a separate file, making it easy to back them up or to make them available to your service providers, clients, or others in your workgroup. In InDesign, transparency flattener preset files have an .flst extension.

Export and import a custom transparency flattener preset

You can export and import transparency flattener presets in order to share them with your service providers, your clients, or others in your workgroup.

Rename or delete a custom transparency flattener preset

Flatten an individual spread

You can apply flattener settings to individual spreads in a document, overriding the flattener preset you’ve set for the entire document or book. This is useful for controlling the flattening quality in documents with a mix of high-resolution images with lots of transparency and low-resolution images. In this case, you can flatten the complex spread at a high quality, and use a faster and lower-quality flattener preset on the other spreads.

At print or export time, you can revert to the flattener settings for the document or book.

Ignore the flattener preset on an individual spread

Transparency Flattener options

You can set Transparency Flattener options when creating, editing, or previewing flattener presets in Illustrator, InDesign, or Acrobat.

Highlight (preview) options

Disables previewing.

Highlights the areas that will be rasterized for performance reasons (as determined by the Rasters/Vectors slider). Keep in mind that the boundary of the highlight area has a higher probability of producing stitching problems (depending on the print-driver settings and the rasterization resolution). To minimize stitching problems, select Clip Complex Regions.

Highlights the objects that are sources of transparency, such as objects with partial opacity (including images with alpha channels), objects with blending modes, and objects with opacity masks. In addition, note that styles and effects may contain transparency, and overprinted objects may be treated as sources of transparency if they are involved in transparency or if the overprint needs to be flattened.

Highlights all objects that are involved in transparency, including transparent objects and objects that are overlapped by transparent objects. The highlighted objects will be affected by the flattening process—their strokes or patterns will be expanded, portions of them may get rasterized, and so on.

Highlights all linked EPS files that are affected by transparency.

Highlights all placed content affected by transparency or transparency effects. This option is useful for service providers who need to see graphics that require attention to print properly.

Highlights all patterns that will be expanded if involved in transparency.

Highlights all strokes that will be outlined if involved in transparency or because Convert All Strokes To Outlines is selected.

Highlights all text that will be outlined if involved in transparency or because Convert All Text To Outlines is selected.

Highlights text and strokes that have rasterized fills as a result of flattening.

Highlights objects and intersections of objects that will be rasterized because there is no other way of representing them in PostScript or because they are more complex than the threshold specified by the Rasters/Vectors slider. For example, the intersection of two transparent gradients will always be rasterized, even if the Rasters/Vectors value is 100. The All Rasterized Regions option also shows raster graphics (such as Photoshop files) involved in transparency, and raster effects such as drop shadows and feathers. Note that this option takes longer to process than the others.

Transparency Flattener Preset options

Specifies the name of the preset. Depending on the dialog box, you can type a name in the Name text box or accept the default. You can enter the name of an existing preset to edit that preset. However, you can’t edit the default presets.

Specifies the amount of vector information that will be preserved. Higher settings preserve more vector objects, while lower settings rasterize more vector objects; intermediate settings preserve simple areas in vector form and rasterize complex ones. Select the lowest setting to rasterize all the artwork.

Rasterizes all objects, including images, vector artwork, text, and gradients, to the specified resolution. Acrobat and InDesign allow a maximum of 9600 pixels per inch (ppi) for line art, and 1200 ppi for gradient mesh. Illustrator allows a maximum of 9600 ppi for both line art and gradient mesh. The resolution affects the precision of intersections when flattened. Line Art and Text Resolution should generally be set to 600‑1200 to provide high-quality rasterization, especially on serif or small point sized type.

Specifies the resolution for gradients and Illustrator mesh objects rasterized as a result of flattening, from 72 to 2400 ppi. The resolution affects the precision of intersections when flattened. Gradient and mesh resolution should generally be set between 150 and 300 ppi, because the quality of the gradients, drop shadows, and feathers do not improve with higher resolutions, but printing time and file size increase.

Converts all type objects (point type, area type, and path type) to outlines and discards all type glyph information on pages containing transparency. This option ensures that the width of text stays consistent during flattening. Note that enabling this option will cause small fonts to appear slightly thicker when viewed in Acrobat or printed on low-resolution desktop printers. It doesn’t affect the quality of the type printed on high-resolution printers or imagesetters.

Converts all strokes to simple filled paths on pages containing transparency. This option ensures that the width of strokes stays consistent during flattening. Note that enabling this option causes thin strokes to appear slightly thicker and may degrade flattening performance.

Ensures that the boundaries between vector artwork and rasterized artwork fall along object paths. This option reduces stitching artifacts that result when part of an object is rasterized while another part of the object remains in vector form. However, selecting this option may result in paths that are too complex for the printer to handle.

Preserves the overall opacity of flattened objects. With this option, blending modes and overprints are lost, but their appearance is retained within the processed artwork, along with the level of alpha transparency (as when you rasterize artwork using a transparent background). Preserve Alpha Transparency can be useful if you are exporting to SWF or SVG, since both of these formats support alpha transparency.

Generally preserves spot colors. It also preserves overprinting for objects that aren’t involved in transparency. Select this option when printing separations if the document contains spot colors and overprinted objects. Deselect this option when saving files for use in page-layout applications. With this option selected, overprinted areas that interact with transparency are flattened, while overprinting in other areas is preserved. The results are unpredictable when the file is output from a page-layout application.

Blends the color of transparent artwork with the background color to create an overprint effect.

Preview which areas of artwork will be flattened

Use the preview options in the Flattener Preview to highlight areas that are affected by flattening. You can use this color-coded information to adjust flattening options.

Refresh the preview in the Flattener Preview panel

• To automatically update the display whenever it is out of date and idle, select Auto Refresh Highlight.
• To manually update the display, click Refresh.

  In both cases, the display is updated in the document window according to the transparency flattening settings you chose.

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:

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.