4 Replies Latest reply on Oct 19, 2012 12:30 AM by Silkrooster

    Changing dpi changes resolution

    lnllakewood

      Does changing the dpi of an image change the resolution of the image without changing the size?

      I have an image that is 300 dpi that I need to enlarge 400% changing the dpi to 75.

      I don't think manually changing the dpi to 600 will actually change the clarity of the image when enlarged 400%.

      Is that correct?

       

      Thanks

      Cindy

        • 1. Re: Changing dpi changes resolution
          conroy Level 5

          First, DPI (dots per inch) is different to PPI (pixels per inch) despite the terms very often being wrongly interchanged. Photoshop works with pixels, not printer output dots.

           

          http://www.google.com/search?q=dpi+v+ppi

           

          Changing resolution with "Resample" enabled will result in changed pixels, but no change in the physical size (inches/cm/etc.) of the document.

           

          Changing resolution with "Resample" disabled will result in unchanged pixels, but there will be a change to the physical size of the document.

           

          You will not increase the clarity of an image by enlarging it.

           

          The best way to learn what happens is to try things and observe the results.

          • 2. Re: Changing dpi changes resolution
            Silkrooster Adobe Community Professional & MVP

            To help you understand, take a look at these formulas...

             

            1) width in pixels / ppi = width in inches  {Ex. 1200 px/300 ppi = 4"}

            2) width in inches x ppi = width in pixels {Ex. 6" x 300 ppi = 1800 px}

            3) width in pixels / width in inches = ppi {Ex. 1000 px /8 " = 125 ppi}

             

            Exchange Width with Height and repeat for the rest of the equation...

             

            The resample enabled box allows the pixels to be altered

            If the pixels are changed then the quality will be effected.

             

            With resample disabled, the pixels are lock so they can not be changed.

            So the quality can not be effected.

            • 3. Re: Changing dpi changes resolution
              Level 5

              Silkrooster wrote:

               

              ...If the pixels are changed then the quality will be effected...

               

              The quality will definitely be affected, always adversely.

               

               

              Silkrooster wrote:

               

              ...With resample disabled, the pixels are lock so they can not be changed.

              So the quality can not be effected...

               

              Again, you mean affected.  It's a meaningful typo.

              • 4. Re: Changing dpi changes resolution
                Silkrooster Adobe Community Professional & MVP

                Oops, sorry about that.