7 Replies Latest reply on Dec 31, 2013 7:39 PM by leonardeprio

    Resizing images through dpi or WxH dimension

    leonardeprio

      I edit pictures but it seems no significant difference between changing dpi or not. In naked eye, it's almost the same!

      My question: What is the difference when the image size changes via dpi resolution rather than changing the WxH simply ignoring dpi?

      Can anyone explain me which one is best? Thanks in advance.

       

       

      Note: If I choose first to dpi, it's usually followed by changing the WxH that must be corrected.

        • 1. Re: Resizing images through dpi or WxH dimension
          gener7 Adobe Community Professional & MVP

          Well there is resampling.

           

          If you have that checked in the Image Size dialog, you can change the ppi without changing the document size.

           

          You basically add or subtract pixels to your image changing the pixel dimensions changing the resolution, but you won't change the document size.

           

          If you uncheck resample, then you are scaling. if you change the ppi resolution, then your document size will change,but the pixel dimensions remain the same.

           

          So you want to resample if you want to change your resolution and keep your W x H.

           

          Gene

          • 2. Re: Resizing images through dpi or WxH dimension
            leonardeprio Level 1

            Gene, thanks for quick reply.

            Yes, I've tried, it doesn't change the file size or pixel dimensions if unchecked resample.

            I tried to change dpi from 72 to 200 with the same dimensions, but apparently there was no difference in the picture quality. Or maybe will have an effect on the print out? (haven't try yet). Can you tell me?

            • 3. Re: Resizing images through dpi or WxH dimension
              JJMack Most Valuable Participant

              Yes if you do not resample not a single pixel is changed.  The number of pixels remain the same as does the File size and image aspect ratio. All that changes is the size of a pixel the resolution the pixel density the dpi.  Pixels have no size till you specify the resolution. 300dpi means that there are 9000 pixel per square inch each is square 1/300"x1/300" when the resolution is 100DPI there are 1000 pixels per inch each is 1/100"x1/100" the 100DPI image is 9 times larger then the 300DPI image it is 3 times wider and 3 times higher.

               

              When you resample an image not a single pixel remains intact.  You wind up with an entirely new image with a different number of pixels so the file size will go up or down depending on the how you resample.  Not a single pixel was made using a lens, sensor and firmware.  If you do not constrain the aspect ratio during the resampling the image will also distort.  When you resample you will always loose some image quality. A print image of the new generated image the number of pixel and resolution may look better close up then the original image still the detail was not captured from the scene. It was generated from some other image by  a computer algorithm. Or the number of pixels may have just been reduced so it will fix on a web page,  Web page image display at the display devices dpi resolution,  The Image dpi is not used for displays are run at a single resolution.   Web image display size depends on the display.  On a high resolution display the image will be smaller then on a low resolution display.

              • 4. Re: Resizing images through dpi or WxH dimension
                leonardeprio Level 1

                Thanks JJMack. Yeah.. So, if I prioritize the number of pixels in the image in a fixed state, should I change the print dimensions or resolution, deselect Resample..is it right? Because there is worst on the active Resample to increase/decrease ppi resolution, please correct me if wrong, thank you!

                • 5. Re: Resizing images through dpi or WxH dimension
                  JJMack Most Valuable Participant

                  If resample is not checked all values are linked to each other.  Change width or height or dpi and you will see Photoshop calculate and set the other two values.

                  • 6. Re: Resizing images through dpi or WxH dimension
                    gener7 Adobe Community Professional & MVP

                    Thanks for getting this discussion, JJMack. I got very busy and could not get back to the topic.

                    • 7. Re: Resizing images through dpi or WxH dimension
                      leonardeprio Level 1

                      OK, my problem has been solved - thread can be closed. Thank you all..