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teresa.a.
Participant
April 29, 2019
Answered

Is there such thing as «too many ppi»?

  • April 29, 2019
  • 4 replies
  • 4931 views

Hi, everyone.

I'm working on a project (Indesign CC) that will be printed in offset.

The one hundred images have been delivered to me by the client (already converted to grey) and I'm not supposed to do anything to them. They will appear in small dimensions (30 x 20 mm). My preflight is telling me that all of the images have too many ppi. The maximum is 1200 (The message the preflight gives me is «Grey images must be at most 1200 ppi.). In fact, some of them have almost 3000 effective ppi. But, the actual ppi is 300.

My problem is: I really don't want to change the images because it is such a difficult client that prefers to do it himself.

On the other hand, I don't want to ask him unless it is not absolutely necessary.

So, my question is: do I really need to be worried about this?

Will this mean that the images will have problems when being printed? Will too many ppi affect the quality of the printing images? Or will the printing house ask me later to reduce the ppi?

Or is it just a warning that can be ignored since the PDF looks perfect?

Thank you so much!

t.a.

    Correct answer @mj

    It means that you have scaled down images to around 10% their original size. So the resolution has gone up to 3000dpi.

    The nett result is your computer will take longer to create the PDF because it needs to resample your images.

    Ensure that you create a PDF/x file as this is the ISO standard for print.

    ID will resample the file to 300dpi for color and grayscale respectively.

    Bitmaps will be resampled to 1200dpi.

    HTH

    4 replies

    L
    Community Expert
    LaubenderCommunity Expert
    Community Expert
    May 1, 2019

    Hi together,

    in the sense of the headline of this thread::

    Is there such thing as «too many ppi»?

    my answer would be: no

    But. It could happen that a one bit image with very high effective ppi has details, very thin lines perhaps, only one or a couple of pixels thin, that could not be reproduced well or at all when a plate is made for e.g. offset printing.

    Example: Construction plans for architecture scanned 1:1 at high resolution with fine lines, later scaled in the layout to effective ppi more than e.g. 10,000 ppi ( this value is just an example ). Usually a plate for printing is done with e.g. 2540 dots per inch. If a thin line of the raster data results in a dot range of 1 to perhaps 10 dots ( ? ) width it could become problematic to see such a line reproduced on paper. This of course depends on the printing paper and other factors like the condition the rubber blanket of the printing press is in.

    FWIW: The same basically goes with vector graphics that are scaled down tremendously with thin lines, but for that the process for doing the raster work for imaging the plates can artifically make them thicker. Don't know if current RIP technology can do that with pixel images.

    Also see this:

    Minimum line width for a print project

    Regards,
    Uwe

      Stephen Marsh
      Community Expert
      Stephen MarshCommunity Expert
      Community Expert
      April 29, 2019

      Yes, there is such a thing as having too much resolution. It is not as bad as not having enough resolution. It generally just makes the images look a little bit soft. Resampling will very likely happen somewhere. If it is not done in Photoshop on copies of the originals and if it is not done using the PDF export settings – then it will very likely happen in the service providers RIP, which may or may not do as good a job.

      The upper image had an effective ppi of 3000, while the lower had an original/effective ppi of 300, the PDF page was rasterized to 300 ppi for evaluation with no further post-processing. The lower image with the lower "correct" resolution has more detail:

      You can also take a look here for a recent discussion on the same topic:

      Re: Do I need to resize images before importing them in Adobe InDesign?

        rob day
        Community Expert
        rob dayCommunity Expert
        Community Expert
        April 29, 2019

        I think you have to consider the resampling that is happening to fit the comparison images on screen—the real test would be halftone screen output from a RIP that is not downsampling.

        The preview of the 3000ppi image has to get downsampled in order to fit it on the screen for the 10% view, and that‘s not necessarily an accurate preview of the output. In this comparison of 3000ppi (top) vs. 300ppi, the 3000ppi version is displayed at 10% vs. the 100% 1:1 view for the 300ppi version:

        The 100% 1:1 actual view for the 3000ppi version vs. the 10X view for the 300ppi version.

          Stephen Marsh
          Community Expert
          Stephen MarshCommunity Expert
          Community Expert
          May 1, 2019

          I think you have to consider the resampling that is happening to fit the comparison images on screen—the real test would be halftone screen output from a RIP that is not downsampling.

          Rob I agree that the final AM/FM screening for a real world test is better than pixel peeping and would take it a step further to ink on paper. That being said, I believe that a "correctly" prepared file will deliver better results than an "incorrectly" prepared file.

          Even if the image is not being resampled and all of this data makes it through to the screening algorithm intact, I think it is a gamble to provide excessive reduction and crazy high resolution as being discussed here with 3000 ppi effective resolution.

          rob day
          Community Expert
          rob dayCommunity Expert
          Community Expert
          April 29, 2019

          So, my question is: do I really need to be worried about this?

          Will this mean that the images will have problems when being printed?

          Or is it just a warning that can be ignored since the PDF looks perfect?

          No.

          If you export a PDF for the final print, the Export Compression tab lets you control if and how images are sampled down.

          Also, if you are delivering a PDF you might want to preflight from AcrobatPro rather than ID, because that’s the document that will be printed.

            @mj
            Community Expert
            @mjCommunity ExpertCorrect answer
            Community Expert
            April 29, 2019

            It means that you have scaled down images to around 10% their original size. So the resolution has gone up to 3000dpi.

            The nett result is your computer will take longer to create the PDF because it needs to resample your images.

            Ensure that you create a PDF/x file as this is the ISO standard for print.

            ID will resample the file to 300dpi for color and grayscale respectively.

            Bitmaps will be resampled to 1200dpi.

            HTH

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