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I was wondering if anyone knows how to avoid vector created patterns (from Illustrator) looking terrible (a sort of harsh, jagged looking moire pattern) when viewing a saved pdf in Acrobat. If you view the same pdf in a web browser it looks fine. I create a lot of downloadable pdf:s and often people will choose to view them in Acrobat. I have seen pdf:s with beautiful smooth vector patterns so I know it can be done, just don't know how to do it.

I would be extremely grateful for advise on this. I wanted to attach my pdf so you can see for yourselves but couldn't find an option to do so...

Thanks

  • Viewing at 100%, or "fit page", or some other zoom level in Acrobat? – Scott Apr 9 '14 at 12:15
  • Screen capture of your PDF would probably work, did you try Preferences > Page display > Smooth line art? – curious Apr 9 '14 at 13:39
  • Thank you for your replies. The problem is that it has to look good straight away for my clients when they view the PDF. I can't give them a list of instructions on how to set their preferences. I know it can be done as I have seen pdf:s containing vector patterns which look good straight away. – Michelle Apr 9 '14 at 14:16
  • If I copy the pattern from Illustrator into Photoshop and save it as a jpg and then place it back in again it helps. The pattern looks much smoother but... it's annoying having to do that + it then get that slightly pixelated look. I know that pdf:s created in Illustrator often looks a bit weird (thickness of lines, certain letters etc.) but when you print it, it looks perfect. But surely there much be a way to save a pdf for on-line viewing and make sure it looks good. : ( – Michelle Apr 9 '14 at 14:17
  • I should re-phrase my question to "how to save Illustrator vector patterns for optimal online PDF viewing in Acrobat" – Michelle Apr 9 '14 at 14:19
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For your particular problem, you need to figure out what the target screen sizes are (probably mostly between 1920x1080 and 1366x768) along with the default zoom options and then increase those pattern sizes in your art to get out of the danger zone where moire is created.

Note that Acrobat/Distiller/whatever-they-call-it-now has a "default view" setting in "file > properties." While there is no gurantee of client software honoring it, you can set the view there and then save it. I like to set it to the "full-page, spread, with cover" setting so that it simulates a book.


The problem here is that you have a dynamic zoom and multiple client display devices with variant capabilities. You cannot avoid moire, you can only try and mitigate first impressions.

Moire patterns are a function of the content of the art and the sampling rate. On screen, the sampling rate is more or less the size of the grid of pixels (the desktop's pixel dimensions).

When patterns within the art are close to the grid size (and especially not strictly parallel to the x and y axes) you run the risk of moire. For any sample to be properly reconstructed you need the sample rate to be approximately 2x the frequency. ( http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem#Application_to_multivariable_signals_and_images )

Incidentally, this sampling 2x (really 1.5-2) number is the reason for "300dpi" standard in commercial printing. High-quality-but-common halftone screens are around 150 lines per inch. You need 300dpi to get above the 150lpi sampling frequency. But if you work for a screen door company, you need to be careful about your choice of art.

  • agreed. The designer can not control how the user agent does sampling. Not agreeing with the screens. – joojaa Apr 9 '14 at 15:23
  • Thanks a lot for this info, I will look into it. When I opened the AI PDF in Photoshop and re-saved it as a PS PDF the problem of moire looking pattern was solved but this is obviously not a solution for multi page documents created in Illustrator or inDesign... – Michelle Apr 9 '14 at 16:36

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