When I put PNG images into an InDesign document, sometimes they have black borders on the exported PDF. Usually this doesn't seem to be a problem in print but in a recent proof, I did see some of the issue surfacing there too (albeit not quite as bad). However... Even if it's not as bad in print, it'd be nice to not occur in the PDFs too as these get sent out to customers via email too.
Now I know what people are going to say here... PNGs are a web format and not for print! I agree! I'm slowly converting people over to TIF/PSD here.
The catch here is that I don't get this problem with all of the PNG files. Some are absolutely fine. I've noticed that in the links panel of InDesign that some have black backgrounds and some have white backgrounds (presumably the alpha layer doesn't show up in the links panel). Why are some of these PNG files showing up perfect and others not? I can't seem to see the difference between the files in Photoshop.
To illustrate this issue, screenshots and photos follow:
Here's a PNG placed into an InDesign Document:
Note the black background that this file has in the links panel.
Here's the same section on a PDF export of this document (PDF/X-4:2014, Average downsampling to 300dpi for images over 350, compression:JPEG, quality:Maximum):
And here's what it looks like when zoomed in:
Finally, here it is on the proof:
The right side of the bottle has dark bits along the edge.
Now here is another PNG in the same document:
There's a white background in the links panel for this file.
And here's how it looks in the same PDF:
No black borders at all on the PDF and no black edge on the print either: