6 Replies Latest reply: Jul 16, 2013 10:41 AM by Test Screen Name RSS

    How to determine and alter dpi of a PDF?

    cicorporation1 Community Member

      I have a 70 page PDF and would like it to be searchable, and to run OCR on it.  The error message is:

       

      Acrobat could not run Paper Capture because of the following error: This page is of unsupported resolution, so it cannot be captured.  Supported resolutions are 200-600 dpi for b/w and 200-400 dpi for gray/color.  

       

      How do I determine the dots per inch (dpi) of the  document and how to increase or decrease it?

        • 1. Re: How to determine and alter dpi of a PDF?
          MichaelKazlow ACP/MVPs

          PDF files do not have a resolution. Only images do. You should be able to find out with the Preflight tool. But you cannot fruitfully increase or decrease the dpi. You need to rescan at the proper dpi using the scanner's settings to determine what dpi you want to scan with.

          • 2. Re: How to determine and alter dpi of a PDF?
            cicorporation1 Community Member

            The PDF was created from 70 JPGs scanned at 150 dpi. 

             

            Since there as no way to convert the PDF to 200+ dpi, I had to take the 70 JPGs that made from the scanner. 

             

            1. I opened each of the 70 JPGs with Microsoft's free Photo Editor *

            2. select File Properties to convert them from 150 dbi to 200 dpi

            3. Resave them as 200 dpi.

            4. Then I recombined the 70 JPGs into a new PDF.

             

            It worked. Acrobat's Paper Capture processed all the 200 dpi pages.

             

            Indeed, as an experiment I left 2 JPGs as 150 dpi, and Adobe Acrobat stopped on those 2 pages and gave the message that it could not run Paper Capture on them.

             

            Thanks for your reply which sent me in the right direction.

            If there is a faster way than the above steps, let me know.

             

            However, I see why Adobe insists on at least 200 dpi original scanning.  The 150 dpi saved as 200 dpi JPGs did not get recognized well by Adobe - with many character errors.  Lighter typed sections were not picked up at all.  Google would not be able to pick up much from it, but a lot of garbled words (assuming they require 200 dpi too - anyone know?) 

             

            So I will have to go back to the scanner and rescan all 70 pages at 200 dpi , then make a new PDF to be fully readable by Adobe Acrobat.

             

            In the mean time, to get the text OCR scanned quickly, I used PDFOCR from www.pdfocr.net which recognized the characters on the 150 dpi pages very well.

             

            Lesson: Always scan text documents at least at 200 dpi.

             

            * This process was made less tedious thanks to Aldo's Macro Recorder from www.AldosTools.org

             

             

            Document is at www.CICorp.com/TM/Research/CTOMEEG

            • 3. Re: How to determine and alter dpi of a PDF?
              nuitgoddess Community Member

              What do you use in preflight to check the dpi of images?

              Thanks.

              • 4. Re: How to determine and alter dpi of a PDF?
                MichaelKazlow ACP/MVPs

                You can create a custom profile that will list what you want.2013-07-16_11-37-38.png

                • 5. Re: How to determine and alter dpi of a PDF?
                  nuitgoddess Community Member

                  How does ppi translate to dpi?

                   

                  My print vendor says I have a PDF file with images printing  at 150 and

                  usually we print at 300 dpi.

                  How can I tell what I have sent to him?

                   

                  ~~~~~~~~~~~~~~~~~

                  Deborah  :->

                  • 6. Re: How to determine and alter dpi of a PDF?
                    Test Screen Name MVP

                    ppi and dpi are basically interchangeable (ppi is more correct for an image, dpi for a scanner setting).

                     

                    You can find the lowest limit of the ppi used by adjusting your preflight rules, and test it. Bear in mind there isn't a DPI value for a PDF. Each image is potentially different.