A warning for graphic designers using InDesign, PSD files and InstantPDF

The strangest thing just happened (twice!) last week and with atwork for a large client. This artwork got send out as Certified PDF. An Art Director set up a quick design and a pre-press guy added the final corrections, made sure everything aligned and he exported a PDF using the presets in InDesign. It got certified using InstantPDF and the App approved the PDF. When we saw the printed Ad several days later it contained an image with a very low resolution. That is NOT suppose to happen! InstantPDF can detect low resolution images and will definitely not approve any Certified PDF containing a low res image. But somehow it had approved this PDF and the other one. What the hell was going on here?

I created a test. A 72 dpi transparent Photoshop file was placed in InDesign and got placed at 800%. This was definitely a low resolution image now. The document was exported to PDF using the Gent Work Group presets. I opened the PDF in Acrobat and selected ‘Save as Certified PDF…’ It got approved! That’s crazy! What was going on? At first I blamed InstantPDF but Jimmy Hartington from Denmark read my complaint in the Enfocus email-list and helped me out.

It was the transparency in the PSD. I had noticed the PDF did not get approved if I placed a low res TIFF. Somehow it had to be the PSD format. And it was. InDesign uses a transparency-setting and in my presets it is set to at least 300 dpi when objects with transparency are flattened. This is for things like ‘transparency-effects’ like blend modes or drop-shadows and glows. But the placed PSD contained transparency as well and Indesign upscaled the 18 dpi image (effective resolution) to 300 dpi! Instant PDF never saw the danger…