This sounds like a transparency flattening artifact called stitching. What settings did you use to make the PDF? Stitching doesn't normally show up if the PDF keeps the transparency live and flattens at output, but it is printer dependent.
Despite it is in portuguese, this is the setup we usually use. PDF/X-1a:2001 with compatibility with Acrobat 5 (PDF 1.4)
It isn't always that this happens, it is quite randomic, and, as I said, it doesn't show up on PDF files. I look around the forum and found people saying ghost lines showing up on PDF that were nonexistent in Indesign and Illustrator, and people mentioned it to be the same issue you named, so I'm a little unsure if it is the same problem.
Thank you again for your patience
PDF/X-1a flattens transparency, so it sounds like this really is stitching. Try PDF/X-4 and see if the problem disappears.
Thanks! I'll try and let know what'll be the result
This looks like a different issue than the original post and obviously is not a flattening stitching artifact. It looks like the fill on the image's parent container could be something other than None or [Paper]?
Image is placed directly to InDesign, creating its own frame with default (no fill no stroke).
It gets even weirder: if I crop the image from Illustrator in InDesign, so I am certain there is no edge proximity I see the same. I have this issue on two different computers, however, a colleague of mine exported the PDF X-4 from the files I gave him with no problem...
I am using predefined PDF export option and so did he. I am really clueless.
If you can help here are all the test files: https://we.tl/DXrSSCLNaS
I think the line is a preview artifact and is coming over from Illustrator where the black background image aligns with the transparency above. I was able to ad a 1pt [Paper] centered stroke to the ID boxes an it went away.
Something tells me it wouldn't print on a high res device because it responds to AcrobatPro's Page Display preferences. It's kind of like a PDF/X-4 version of a flattened transparency artifact:
Smooth Line Art and Enhance Thin Lines off:
I came up with the same work around with stroke as a quick and dirty solution to replace files for printing.
The printing house claims it would be (is?) visible after printing (which I find very hard to believe, since at 6400% zoom the line is a micron thick!), so they had to prepare new plates, which means extra costs. I will investigate that in details tomorrow, as well as the mystery of the ghost lines.
At least one mystery is solved! My colleague simply has different preview options in Acrobat, turning these two options off helps.
In that case is it some sort of Illustrator bug?
Anyways, thank you very much for spending your time on this issue and helping me out!
In that case is it some sort of Illustrator bug?
It could be in the way you constructed the AI file. The background image is low res @ 86ppi, so even though you have all of the objects lined up with matching width and heights, I'm wondering if the large pixel dimension is creating problems—there can't be a partial pixel, so the stroke over in ID creates a mask.
Try making a clipping mask for your background .jpg in Illustrator. That worked for me, so I think it is the low res bitmap not in perfect alignment.
Clipping mask in Illustrator was the first thing I tried when I first spotted the ghost lines and it didn't help. Also doesn't work with the test files in my case. In real life we have 300ppi images/photoshop files, so the resolution is not an issue here.
1. exporting PDF directly from AI and placing it in ID then exporting again to PDF X-4 - result: ghost lines
2. exporting AI with clipping mask containing entire artwork on a larger artboard to PDF X-4 - result: ghost lines
3. creating a mask around the artboard which is 210 x 210 mm and the mask makes it 209 x 209 mm or option B 200 x 200 mm - result: ghost lines
- like so (the mask is white, the color in the screenshot is only to visualise it better):
4. creating AI with 210 x 210 mm with 5 mm bleed and extending artwork to bleed, then importing without bleed to ID - same result
5. creating AI as above and importing with bleed and keeping it in the frame or outside, adding the mask, using image at 100% size (falls outside the AI artboard) mask and no mask, all the combinations - same result
I am trying to develop some sort of good practice, but I seem to fail. The best solution and the easiest one so far is to add the paper stroke in ID, which is kind of disappointing. Why then all the options to import page, artboard, bleed, etc if they all result in the same frustrating outcome?
The point on scaling images in Illustrator is interesting. If that is the case, then we are talking about 1.25 pt difference in width, which would be visible after printing, even if divided by 5! I am getting really confused...
I think you should clarify with your printer if they are seeing it in full resolution print. I tried printing part of your PDF/X-4 where the artifact shows at 300% and it did not print.