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lilianam79461047
lilianam79461047
Participating Frequently
May 23, 2017
Answered

1px and 2px lines show incorrect thickness when converting a high resolution pdf into a lower resolution pdf.

  • May 23, 2017
  • 1 reply
  • 4148 views

Hi all,

Converting a higher resolution pdf into a lower resolution pdf file is causing 2px lines to appear in random different thicknesses. Sometimes they even disappear. I also have 1px strokes framing some photos and some of those lines disappear too. I have already changed the preferences of Acrobat Pro DC to uncheck "enhance thin lines" and "smooth line art" and has not made any difference.

Anyone out there know how to sort out this issue?

Many thanks

This topic has been closed for replies.
Correct answer Dov Isaacs

There is really no such thing as a high resolution PDF versus a low resolution PDF. What you are really doing is downsampling the images within the PDF file. Any text or vector content is fully scalable and has no inherent resolution!

If you are framing images, you should be using vector-based lines or shapes instead of incorporating such “line frames” into the images themselves. As part of the images, downsampling could in fact corrupt the apparent thickness of these lines, especially if “lossy” compression such as JPEG is used.

The Enhance thin lines and smooth line art are totally irrelevant to raster images such as your photographic images with embedded frames in raster format.

Bottom line is to change your workflow to frame your images with vector-based shapes and don't incorporate same into the image itself.

          - Dov

1 reply

Dov Isaacs
Dov IsaacsCorrect answer
Legend
May 23, 2017

There is really no such thing as a high resolution PDF versus a low resolution PDF. What you are really doing is downsampling the images within the PDF file. Any text or vector content is fully scalable and has no inherent resolution!

If you are framing images, you should be using vector-based lines or shapes instead of incorporating such “line frames” into the images themselves. As part of the images, downsampling could in fact corrupt the apparent thickness of these lines, especially if “lossy” compression such as JPEG is used.

The Enhance thin lines and smooth line art are totally irrelevant to raster images such as your photographic images with embedded frames in raster format.

Bottom line is to change your workflow to frame your images with vector-based shapes and don't incorporate same into the image itself.

          - Dov

- Dov Isaacs, former Adobe Principal Scientist (April 30, 1990 - May 30, 2021)
lilianam79461047
lilianam79461047Author
Participating Frequently
May 23, 2017

Thanks for your answer but you are assuming I'm doing things incorrectly, which is not the case.

All my line artwork is vector based (yes, even the frames around images), and when I say high resolution and low resolution is partly correct because when you are reducing the file size of a pdf, images need to be compressed drastically to enable the pdf to be much smaller than a PDF that has no compression at all. Therefore, this is reflected in the file size and quality of the PDF.

I am preparing these PDFs to be viewed digitally both on desktop and mobile, as they will be part of a digital campaign. I would expect that when a pdf is compressed, there will be some loss of image quality but I don't expect the pdf to change the appearance of any vector artwork, and this is my problem.

I have googled this many times and there does seem to be an issue for many people. The appearance of line artwork changes once you create a compressed pdf, and I was wondering if Adobe has an answer for this as I couldn't find any. It did look like if it was an acrobat bug.

Any other answers out there?

Dov Isaacs
Dov Isaacs
Legend
May 23, 2017

Contrary to what you may have been told and/or believe, there is absolutely no change in display or print quality in a PDF file for vector or text content when you do downsampling of the images! Vector is vector and is not measured in pixels which is resolution dependent. And FWIW, at Adobe we are not aware of any issues associated with downsampling images causing issues with vector and text content.

OK, assuming that your frames are indeed vector, one other thing to look at is ordering. If the image is above the frame, the boundary of the frame and the image may be the issue. Try putting the frame above the image and see if that helps. Also, make sure the frame is opaque.

If that isn't the case, we would appreciate it if you could post PDF file samples for us, one before downsampling and one after downsampling and we'll try to see what's going on.

          - Dov

- Dov Isaacs, former Adobe Principal Scientist (April 30, 1990 - May 30, 2021)
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