How to flatten a transparency in InDesign, Illustrator or Photoshop?

What is transparency in artwork?

Transparency in artwork is an effect where any object or image is not set at 100% opacity. Common effects that apply transparency are any stylising effects like shadows, glows and feathering. And of course applying ‘transparency’ to any object or image from the menu.

What is flattening?

The process of converting complex artwork into vector-based and rasterised areas is referred to as ‘flattening.’ Examples of objects that may require flattening include: text, gradients, spot colours, vectors, images and overprinting.

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Why is flattening necessary?

Flattening of transparencies is vitally important. Processing artwork becomes particularly complex when transparent objects and/or images overlap. If different colour modes have been used, unpredictable results can occur. For example, if an image is RGB and has overlapping graphics set in CMYK.

Flattening helps the final print output match what you see on your screen. Part of the print process involves converting the file information into ‘printer language.’ It is during this process that some printing software may interpret the file differently than intended, producing unexpected and unwanted results. Flattening the file properly greatly reduces the risk of this type of error, but always check the flattened PDF before you send it.

Flattening of files is best done in Acrobat Pro, even when the artwork has been created in InDesign, Illustrator or Photoshop.

1. Open the file in Acrobat Pro. Initially we need to check what Colour Separations are contained in the file. To preview the separations, open the Output Preview dialog box:

In Acrobat Pro, open All tools, then select Use print production > Output preview. From the Preview menu, choose Separations.

NOTE: The location of Print Production varies with the version of Acrobat. Older versions had it under View > Tools. In current Acrobat Pro it is listed under All tools as Use print production.

2. Check for Spot Colours

IMPORTANT: If spot colours are present, go back to the source file and either remove the spot colour objects or convert them to CMYK Process Colour.

For instructions on how to do this, check our guide 

Note: A dieline is the one exception. It is set to a spot colour on purpose so it doesn't print (see our dieline guide), so leave that one as it is.

Repeat step 1 as many times as necessary to ensure there are no Spot Colours left. Then the file is ready to be flattened using the following steps:

3. Open the Flattener Preview dialog box:

In All tools, select Use print production > Flattener preview.

4. Match the settings to the screenshot. The important settings are outlined in red: Raster/Vector Balance 100, Line Art and Text Resolution 1200 ppi, Gradient and Mesh Resolution 300 ppi, Convert All Text to Outlines, Convert All Strokes to Outlines and Preserve Overprint ticked, and Color Space showing DeviceCMYK.

Note: Adobe recommends 600 to 1200 ppi for line art and text, and 150 to 300 ppi for gradients and mesh. Higher gradient settings only add file size.

5. Under Apply to PDF, choose All pages in document (or set a page range), then click Apply.

Check the PDF before you send it, to make sure no elements dropped out in the flattening process.

6. Save the flattened file under a new name, and you're done!

IMPORTANT: Flattening can't be undone once the file is saved, so keep your original, unflattened file.