11 Replies Latest reply on Mar 17, 2012 1:20 PM by Peter Spier

    Resize image

    steve barker Level 1

      Hi,

       

      what happens when I resize an image in InDesign. If I have an image that is 100 px x 200 px and then I resize to 200 px x 400 px it will be larger (size) on screen but what happens to the image itself? The pixels can't be stretched (made bigger) as my monitor pixel size is constant so does this mean the image is being resampled (pixels added) ?

       

      thank you

        • 1. Re: Resize image
          Peter Spier Most Valuable Participant (Moderator)

          No, the image pixels ARE stretched. ID doesn't really DO pixels, it just lets you use the standard 72 pts = 1 inch and labels the rulers as pixels instead of points, but you're really working in points. Pixels, until you print them, don't have a physical size, so as you change image dimensions without resampling (and ID doesn't know how to resample except to downsample during output) you are changing the size that the pixels will be printed.

          • 2. Re: Resize image
            steve barker Level 1

            Thank you Peter,

             

            I am a bit lost here. On my monitor the pixels are set with the display as 1680 x 1050 they are all the pixels I have and the monitor size remains the same and the pixel size on my display remains the same (hope that makes sense).

             

            I take my 100 x 200 pixel image which is using 20,000 of my screen pixels. I then make it 200 x 400 so now it is using 80,000 of my screen pixels. Those 60,000 pixels came from somewhere ? I cant have 20,000 bigger pixels (stretched) because my display pixel is the same size (it did not get bigger).

             

            So I guessed the 60,0000 pixels were added by upsampling from ID ?

             

            thanks again

            • 3. Re: Resize image
              Peter Spier Most Valuable Participant (Moderator)

              The size and resolution of the monitor have nothing to do with it, other than to determine how large a pixel is displayed at any particular zoom level. When you zoom in or out, the number of monitor pixels used to display an image pixel changes. You can show your 200 px image full screen, in which case each pixel in the image will use about 64 monitor pixels (8 x 8), with some interpolation becuse you can't use or dispaly partial pixels, or you can shrink it down to a very small area onthe screen and use only 200 x 400 monitor pixels, or even less.

               

              The zoom level only affects how the monitor shows you the image, not the number of pixels that make the image. If you zoom in enough you see the individual pixel edges. Same thing happens on paper when you print. Scaling the image up on your ID page is the equivalent of zooming in on screen (what you see on screen in ID is a rendering of the page, not the actual image pixels that you would see in Photoshop). If you scale up enough, the individual pixels become visible in your print. It's like blowing up a balloon with something printed on it. The more you blow it up, the bigger the printed image becomes, but nothing new is added.

              • 4. Re: Resize image
                steve barker Level 1

                Thanks again Peter.

                 

                So what you are saying (if I am correct) is that if I am zoomed to 100% and I have my 100 x 200 pixel image and I make it twice the size then it is still 100 x 200 pixels and without changing the zoom size (remains at 100%) the image 'appears' bigger as the resize has the effect of zooming that image so let's say I am 100% zoomed but the image appears 200% zoomed ?

                • 5. Re: Resize image
                  rob day Adobe Community Professional & MVP

                  If I have an image that is 100 px x 200 px and then I resize to 200 px x 400 px it will be larger (size) on screen but what happens to the image itself?

                  Also, if you fit your 100px x 200px image exactly into a 1" x 2" frame it's output resolution (effective res in the info panel) is 100 pixels per inch. If you scale the  image to 200%, the image output res is now  50 ppi.

                   

                  Zooming has no effect on the output (via print or export), but scaling does.

                  • 6. Re: Resize image
                    Peter Spier Most Valuable Participant (Moderator)

                    Disregarding that 100% zoom is a misnomer in ID (that's a different discussion), when you zoom to any percentage view in ID what you are zooming in on is the size of the page you laid out. This is totally independent of the size of any object you place on the page. You can create a page  in ID that is 6 inches by 6 inches, and on one that is 18 inches by 18 inches, and you can place your image on both pages at the same scale. Adjusting the zoom on both pages to the same percentage value should show you your placed image at exactly the same size, but zooming to fit the page on screen  would make the images appear in proportion to page sizes.

                     

                    I'm guessing, based partly on your choice of pixels as the dimension, that you are not a print designer, and don't have a lot of experience in ID yet. ID started as a traditonal print layout tool -- everything you designed was presumed to have a physical dimension corresponding to some printed sheet of paper. That's still true, but the size of the sheet is "elastic," like that ballon, when you start designing for the screen. An 800 x 600 pt (px) layout will have the same aspect ratio on any screen, but it's apparent "physical" size will vary with the size and resolution of the monitor that is being used for viewing, even as the objects and their "sizes" remain constant in the layout. You also need to remember that you can use content at any scale inside the ID page. The page dimensions set a relative framework for how large objects are rendered. Your pixel-based page is really a 72 points per inch layout. How large or small the 100 x 200 pixel image appears @ 100% object scale (as distinct from view scale of the page) and how much of the area of your document it occupies will depend on what the image dimensions and resolution were set for when the image was saved. If it was saved at 72 ppi, it will be 200 points wide, but if it was save at 200 ppi it will be only 72 points wide in your document, but in both cases it is exactly the same image. Scaling in ID is the equivalent of changing the dimensions or the resolution in Photoshop without resampling -- no pixels are altered, just the apparent size of the rendering on the page.

                    • 7. Re: Resize image
                      steve barker Level 1

                      Hi Rob, yes for print but I thought ppi (dpi) has no bearing when viewed on screen. I am totally struggling with this concept of 'on screen'. I just can't get my head around it. I have 1.8M pixels for my screen and they are a constant size. This is what is throwing me totally. I just can't see how making the image bigger stretches pixels. The pixels on screen (1.8M) cannot in any way be stretched.

                       

                      I am at a loss to understand what is happening when I make the image bigger. I know it looks more blurry (not sure if it is pixelated but certainly blurry) and so I thought it was being resampled (pixels added) but then thought that ID doesn't do that (not like PS for example) so what is happening.

                       

                      Thank you

                      • 8. Re: Resize image
                        steve barker Level 1

                        Thanks Peter,

                         

                        dpi (ppi) on screen should not be relevant should it? I have 72 ppi and thats it on my screen no matter what I do to the image an inch on the screen will always be an inch with 72 pixels in it.

                         

                        Correct I am not a print designer, I am creating my first DPS doc

                         

                        Trying to understand this is fundamental for me. Yes it is the case that DPI/PPI matters for print and I would keep an eye on effective ppi if printing but in my case I am not. PPI just doesn't count for the screen as far as I have read that is.

                         

                        I am probably stuck with one idea in my head and its difficult to get rid of it

                         

                        thanks

                        • 9. Re: Resize image
                          Peter Spier Most Valuable Participant (Moderator)

                          Essentially that's correct. What's happening here is that you aren't REALLY working in pixel dimsions, as you would be in Photoshop or Dreamweaver, becasue ID is really a print program. What happens to your image if you scale it in Dreamweaver ( I don't design for screen. )?

                           

                          In the scenario you have now in ID, if your image is saved at 72 ppi, and placed at 100%, I think that would be roughly what you expect. The problem is that scaling is not resampling and is not the same as changing the monitor resolution.

                          • 10. Re: Resize image
                            steve barker Level 1

                            Thanks Peter,

                             

                            I think I may finally have it if this is correct that is:

                             

                            I have an image that is 100 x 200 and is represented on screen by 100 x 200 screen pixels. I make it 200 x 400 by resizing. What happens (I think) is that it is not resampling it is indeed stretching my pixels. The image is still 100 x 200 pixels but is now represented on screen by 200 x 400 pixels. So 1 image pixel now = 2 screen pixels so it is stretched and looks blurry/pixelated

                             

                            Am I in the right area ?

                             

                            thanks

                            • 11. Re: Resize image
                              Peter Spier Most Valuable Participant (Moderator)

                              I think so.