dotted cross appears on tilted image

[Frits5C99]

I put a tif image on an Illustrator design and tilted it 15 degrees. After making a pdf a dotted cross at 15 degrees appeared on that image (not if it's not tilted). After zooming in far enough on the pdf, it disappeared. I made a low res screen capture of it:

screen capture of pdf file

My questions: will this have any effect on the printing in high resolution? (I can't see anything on my own print-out,) If so, what can I do to prevent this? If not so, same question, as I have it to explain it to my clients.

[Abambo · Accepted solution]

How do you create your PDF file? What is the PDF version?

What you see is Acrobat's tradeoff between speed and accuracy. When being scaled out, instead of showing a very accurate picture, you see a speed optimized screen. The seem you see is because the image has been split into sub-images. This happens, especially when you are using an older PDF file format or when you create the PDF by printing to a PostScript file and distilling that.

When you zoom in, you will see an accurate picture of what a print will look like. However, in some rare cases you will notice a colour shift with some elements.

You can avoid this, when exporting a PDF X/4 format. This format supports transparency and different other goodies, that will avoid splitting up the images. The overall result will be more accurate. https://en.wikipedia.org/wiki/PDF/X

[Frits5C99]

Thanks, Abambo. I already thought it had something to do with the screen output, as I used to have comparable problems with viewing thin lines in pdf's.

I always made my pdf's by printing to pdf. Then, the pdf x/4 format is not available. With saving to pdf it is, and it works for the problem I mentioned.

However, with pdf x/4 another problem turns up. Compare the images:

1. pdf at 200% with pdf x/42. pdf at 400% with pdf x/43. pdf at 200% with old settings

Left an image at 200% with pdf x/4: thin lines hardly visible. The problem disappears at 400% (middle). However (right image), with the old settings at 200% (and also at 100%) it is far better than the x/4 version!

[Abambo]

If your file is from Illustrator, you should "save as PDF". https://helpx.adobe.com/illustrator/using/creating-pdf-files.html

In InDesign use File->Export.

[Abambo]

If you want this to look good on screen, avoid the transparency alltogether. Share the Illustrator file here (at least the flower with the background, and I will check one or two things.

[Frits5C99]

There is no transparency. The ginkgo leaf is a tif image just existing of the 'lines' you see, it has no background.

Thank you for your offer, but I wouldn't like to bother you with something of little consequence. Problems with very thin lines on screen output are easy to explain to clients, dotted lines 'coming from nowhere' are less so. I just wanted to express my amazement that x/4 seems to be doing worse in this respect than the older settings, but that could well be the other way around with another image. So I consider this problem solved.

I'm familiar with 'export' in InDesign, but using 'print as pdf' in Illustrator instead of 'save as pdf' is just a habit of many years – maybe 'save as pdf' didn't exist 13 years ago, or I didn't notice at the time. I'll change my bad habits!