Transparency flattening overview

Transparency flattening is the process InDesign uses to prepare transparent artwork for print and export. Effects such as drop shadows, opacity changes, and blend modes may need to be flattened when the output format or printer does not support live transparency.

Flattening divides a transparent artwork into vector and raster areas while preserving its visual appearance. This helps preserve the artwork's appearance, even when the file format does not support transparency natively.

When flattening occurs

InDesign automatically flattens transparent artwork when you:

• Print to a PostScript device
• Create a PostScript file
• Export to PDF 1.3 (Acrobat 4)
• Export to EPS or other older formats
• Save to earlier InDesign versions that don't support transparency

To avoid flattening, export to Adobe PDF 1.4 (Acrobat 5) or later. These formats keep transparency live and editable.

How flattening works

The flattener looks at overlapping transparent objects and divides them into separate opaque pieces. These pieces work together to recreate the original transparent effect.

For example, if a transparent blue circle overlaps a yellow rectangle, InDesign may split the artwork into three parts: the yellow rectangle, the blue circle outside the overlap, and a green overlap area. Each area becomes opaque, but together they still look transparent.

Documents with more complex artwork, such as images, gradients, text, spot colors, and blend modes, may require more rasterization to maintain quality.

Vector and raster divisions

Flattening keeps vector artwork whenever possible. Text, simple paths, and solid colors often stay as vectors because they are easier to reproduce cleanly.

Some effects require rasterization. Feathered edges, transparent gradients, and complex blend modes often render as raster images because vector graphics cannot reproduce these effects accurately.

The quality of rasterized areas depends on the flattener preset you choose.

Flattener presets

Flattener presets control how much artwork remains vector and how much is rasterized.

• Low Resolution: Creates smaller files and works well for proofs
• Medium Resolution: Balances quality and file size for most print jobs
• High Resolution: Produces the best quality for final print output

The selected preset controls raster image resolution, how complex areas are handled, and whether text or shapes convert to outlines or images.

Special considerations

Spot colors

If transparent objects overlap spot colors, InDesign may convert those overlap areas to process colors. This preserves the appearance but may affect spot color printing.

Overprinting

Transparency and overprint settings can interact in unexpected ways. InDesign may need to simulate or change overprint behavior in transparent areas.

High-resolution requirements

For commercial printing or large-format output, use the High Resolution flattener preset. Complex transparency may increase processing time, so test your output early.

Understanding transparency flattening helps you choose the right export format and settings for your workflow. This helps maintain the appearance of your artwork from screen to final output.