Me and my friend are kinda struggling a lot. We have a "overlay" PDF file containing a PNG bitmap image (no vectors). We use this PDF for automatic montages in PDFlib together with generic photos to create another print PDF. This PDF is printed afterwards.
However, the source overlay PDF seems to have issues with transparency. On screen, everything looks ok, even the PDFlib output PDF looks alright, but after printing the document out, there are artefacts clearly visible on the transparent part of the overlay PDF. Other parts on the photo do not have any artifact issues, except these transparent ones.
Is there a way to prevent these artifacts from appearing? Now, as I said, we put a PNG image into inDesign and export it to PDF (v1.6) afterwards.
I will attach 2 images of, one is before the actual printing (no artifacts visible at all) and the other one is scanned picture of the printed document. Artifacts are clearly visible in that one. (Sorry for the crappy scanner quality that darkened the photo, but it will do. It looks exactly like the input, except the artifacts.)