Have you ever seen fine white lines appear when you print out a PDF proof of a page, and are afraid that they will appear in your final product when your commercial printer prints it? In the example below, notice the fine white lines on the right side of the man on the purple background.
What Causes White Lines in a PDF File?
These are screen artifacts that are called stitching. Even though you can see them on your computer monitor, they should not be a problem when printed at high resolution on a printing press. They are caused when your artwork contains transparency. In the picture above you see that an outer glow has been applied to the image, which is a form of transparency. If you choose a method of creating a PDF file which requires transparency to be flattened these artifacts will appear because the flattening process breaks artwork into sections. This could happen if you created a PostScript file and then used Adobe Acrobat Distiller to create the PDF, or if you had chosen Acrobat 4 compatibility when you export to PDF. Both of these methods require transparency to be flattened.
How to Fix Them
You can avoid flattening transparency and artifacts if you export a PDF directly from your application and if you choose Acrobat 5 compatibility or higher in your export settings. Check with your commercial printer about the proper PDF presets to use for their production process. But, in any case, even though you see the artifacts, they should not print.
Need help with preparing your files for printing? Talk to a live print expert today: 800-930-7978.