4 Replies Latest reply on Dec 4, 2014 3:14 PM by Mary Lou Frost

    understanding resizing for projection

    Mary Lou Frost Level 1

      If there is any topic upon which one hears conflicting information it is this one.  It is my understanding that when an image will be viewed on a computer or projected via a digital projector, the factors which matter are:   1. pixel dimensions, and 2. jpeg quality options in saving the image.  The information in the "document" section of the Image/Image Size window is only used when preparing images for printing.


      In spite of this information, I continuously meet photographers who try to say that you must also set the resolution of this file to 300 dpi//ppi.


      I listened to the Adobe TV presentation on this topic and it confirms my understanding.


      Why is this topic such a problem area?  e.g. I have students who are submitting digital copies of an image for consideration for exhibit.  They are told to send the digital file at 800 pixels on the long side and they are told to make the resolution of 300 dpi!

      I need an Adobe professional to reply so that I can print it out and hand it to people who insist that a higher resolution (with the same pixel dimensions) will make the image project better in a digital competition.


      Thanks for your input.


      Mary Lou

        • 1. Re: understanding resizing for projection
          gener7 Adobe Community Professional & MVP

          Unfortunately the ppi myth won't die.  You hear 72 and 96 for screen resolutions that were common in low resolution 1990s monitors.


          Only pixels count and you just need to be sure they match your target, the projector screen. I would say experiment until you find the dimensions you that look sharp on the screen


          300 ppi is a standard and basically for an offset press.  It is a print, not screen specification. Inches refer to paper not screen.


          800 pixels divided by 300 ppi = 2.66 inches if they want to print it at that setting on paper.


          Add to the confusion caused when shops use dpi (device units) and ppi (screen units) interchangeably.


          Dpi, misunderstandings and explanation, what is dpi



          • 2. Re: understanding resizing for projection
            Semaphoric Adobe Community Professional

            I was wondering about this sort of thing the other day: can you make a Photoshop document that has NO resolution - just pixel dimension, no physical units. I tried, but Photoshop wouldn't let me create such a doc.


            So, if the resolution has to be something, might as well humor these competition people, and make it 300.

            • 3. Re: understanding resizing for projection
              gener7 Adobe Community Professional & MVP

              Semaphoric, actually Photoshop will.


              Save for web takes out the ppi spec in the Metadata. Thus Photoshop will fill in 72, but Windows properties will fill in 96.


              I use Exiftool by Phil Harvey and the ppi field is not there. So some programs "fills in the blank."


              I found this out when a user was confused why Photoshop Mac version reported 72 ppi but Windows files properties reported 96 ppi, based on the old 640 x 480 Windows standard. He was in a contest and the spec was given as 72 ppi and he didn't know what was going on. Saving directly to jpeg and png will include that spec in the metadata to avoid "the changing ppi."


              I agree. Humor them especially if they get bureaucratic about the rules they set.



              • 4. Re: understanding resizing for projection
                Mary Lou Frost Level 1

                Thanks for putting this issue to rest.  The link in your email is just what I have always wanted.


                Mary Lou