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Actual PPI vs. Effective PPI

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    • #115839
      Anonymous
      Inactive

      Hi there guys, how are you?

      I have an intriguing issue. I am making tons of redimensions of the same layout, some big and some small. The Indesign files for these layouts consists of a very heavy linked image (sometimes with the .PSB reaching 9GBs) in the TIFF format (as the Indesign would never read .PSBs).

      Our goal is to make all the layout redimensions without having to open too much .PSBs files so this would consume a lot of time, so for some files, I can just scale the image for the right size as I am working with lots of bleed. The problem is, in the Link window, there are Actual PPI and Effective PPI. I know that when you scale down, the Effective PPI will increase and when you scale up it will decrease, and the Actual PPI shows you the original PPI.

      The doubt is: When I choose whatever PDF format I’m going to send for press (X1/A, X4/A, etc), do I have to care for the Actual PPI or the Effective PPI? Does all the PDF exporting methods respect Actual PPI or Effective PPI?

      Thank you very much for your attention guys!

      Raphael.

    • #115843
      David Blatner
      Keymaster

      When you export to PDF, InDesign downsamples from the current image resolution (“effective ppi”) to the resolution you specify in the “Compression” pane of the Export PDF dialog box. For example, if the Effective PPI is 3500 ppi, then it will be downsampled to 300 ppi when you export the PDF (or whatever you have the compression set to).

      The problem is that the Export PDF process does not downsample as well as Photoshop. So a 10 or 20% downsample is probably not a big problem. But if you downsample from 3500 ppi to 300 ppi, the image may get much softer in InDesign; Photoshop has better-quality downsampling algorithms.

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