I am having issues with ghost lines that show up on my work in preview and sometimes PDF. The lines don’t come out in print but are quite disconcerting for clients. Sometimes they’re related to empty layers or shapes in Illustrator, but in this case it’s different.
The image above is a photo that was edited in Photoshop then brought into Illustrator and then saved as PDF.
How do I get rid of them?
Thank you!!
Those lines are usually related to transparency effect atomic areas.
Especially if used in conjunction with spot colors.
Either don’t allow flattening to occur, or try saving as a PDF-x1a
^Right.
Those lines are known as “stitching” and they are the result of one of Adobe’s titling methods for resolving flattened transparency in the screen rendering of PDF. As you’ve seen, they are a display anomaly, and not really there; i.e., they don’t print.
PrintDriver’s given you the right advice for prevention, and I would add that Apple’s Preview may be the least reliable PDF viewer of all.
Ok I did use a gradient in Illustrator over the bottom half of the image but not anywhere near where the ghost lines are appearing, would this be a transparency effect? I have not assigned spot colours in this doc and it is a PDF x1.
Where do I find the flattening option so I know not to allow it?
Folks, I think there’s two different things going on here.
There is the stitching issue. You can find info about that online. Here’s one page talking about it.
https://helpx.adobe.com/indesign/kb/thin-white-dark-lines-stitching.html
If you render the PDF into Photoshop, and the white lines disappear, it’s a stitching issue. Another test is to zoom in on the white lines. If they stay the same size as you zoom in more and more, it’s a stitching issue.
Every once and a while, I’ll render an Illustrator file into Photoshop (usually because the client has requested a high res JPEG file), and a thing white line will show up. Look at the attached screen captures. This is a logo that was created in Illustrator. It’s a solid black color – no spot color, not gradient, no transparency – just straight black. I rendered this into Photoshop and then added solid colors on a layer underneath the logo. You’ll see either white or yellow showing through a misrendering (for lack of a better word).
Further complicating the situation is that I can render the same file twice and one time it will be fine and the next time I’ll get a line.
To my eye, what Rebekah posted looks like the rendering issue I get sometimes – sort of like those white lines are semi-transparent – not pure white.
I wish I had an answer as it’s an issue for me.
The problem with transparency is the effect extends way beyond the shapes involved. What’s call the atomic area might extend all the way across the graphic.
The OP says they used a gradient. That shouldn’t be an issue as gradients aren’t transparent. But I’m seeing a gradient fade, which is.
If using PDF-x1a, sometimes setting the Flattener to Highest Resolution (in the Advanced tab) works. Any PDF format over 1.4 should preserve the transparency without flattening anyway.
When clients can’t ignore the stitching, a screenshot of the file, rather than a PDF, can solve the problem. 
To further on Steve’s observation, Illustrator Bevel-Extrude effect can introduce all sorts of printable stitch artifacts. That isn’t what’s happening here, but when you expand a fully rendered 3D object in illustrator, if you see stitch lines between the color facets, likely they will print, and they will scale larger if the vector file is enlarged in any way.
