11 Replies Latest reply on Jan 23, 2013 5:40 AM by rob day

    Jpeg recompress?

    ConnyO Level 1

      If I place a picture in Indesign that are already compressed with jpeg maximum quality, and then create a pdf, again with jpeg maximum quality, will the picture be recompressed, or will it keep the original pixels?

       

       

      I will of course not downsample the picture, but it will be cropped.

        • 1. Re: Jpeg recompress?
          Eugene Tyson Adobe Community Professional & MVP

          Here's a note that Dov Isaacs wrote on JPEG compressions - I hope it helps

           

          With the JPEG option, compression is always lossy JPEG compression using the chosen quality setting.

           

          With the Automatic(JPEG) option, each image is analyzed and depending upon the image content, JPEG or ZIP compression would be used. If the image is “photographic” in nature, lossy JPEG compression is used with the quality setting chosen. If the image is effectively a raster representation of mostly text and/or vector content (such as many screen shots, especially of menus or dialog boxes), lossless ZIP compression, using indexed color if less than 256 distinct colors, is chosen to avoid imaging artifacts that JPEG compression can introduce for such content.

           

          Automatic(JPEG2000) works similarly, except that lossy JPEG2000 compression is used for the photographic images. (JPEG2000 compression in PDF requires at least PDF 1.5 compliance).

           

          In general we recommend Automatic(JPEG) with quality set to Maximum as the best compromise for image quality and file size, including for most critical high resolution printing. My personal high quality printing experience confirms this recommendation. (Note that there are purists who never allow any “lossy” compression such as JPEG for any content, but I have yet to see any real world benefit of that unless you examine you images with very high power magnifiers!)

           

          So - no it won't be recompressed.

          • 2. Re: Jpeg recompress?
            ConnyO Level 1

            Thank you! But I'm not sure that it realyy answers my question. I don't mind jpeg compression, but I don't want to many generations of it.

             

            Maybe I should make a real test in InDesign. With low enough quality it should be visible if the picture is recompressed or not...

            • 3. Re: Jpeg recompress?
              Eugene Tyson Adobe Community Professional & MVP

              I said at the end that

               

              no it won't be recompressed.
              • 4. Re: Jpeg recompress?
                Michael Witherell Adobe Community Professional

                An interesting test: Open the first jpg in Photoshop, then add the second post-PDF jpg (right-click and Edit from Acrobat) as a layer on top of the original layer and set its blend mode to Difference in order to see (while zoomed in) what has changed. I will bet that little will change. Or in other words, not enough to really be visible. But mathematically, it probably will make a few pixels change.

                 

                Remember, you are asking this question essentially: If I don't compress my jpg hardly at all, and then make a PDF where I don't compress my jpg hardly at all, will the file stay the same? Likely the difference will remain well below the threshold of visibility.

                • 5. Re: Jpeg recompress?
                  ConnyO Level 1

                  No, my question is if InDesign will recompress or not. I know that in most cases it will not be visble anyway, but there are exceptions.

                   

                  And, Eugene, just because you write it, it's not the the truth :-)

                   

                  I will get back with the result of the test...

                  • 6. Re: Jpeg recompress?
                    Peter Spier Most Valuable Participant (Moderator)

                    I've pinged Dov about this thread. Hopefully when the sun rises on the west coast he'll chime in with an authoritative comment. In case you don't already know, his job title is Principal Scientist for  PDF Workflow or some such.

                    • 7. Re: Jpeg recompress?
                      Michael Witherell Adobe Community Professional

                      I just tested my own test. It does change the picture ever so slightly in the PDF jpg. You have to really zoom in to see it. Of course, the original jpg placed into InDesign, being a linked, separate graphic, has not changed.

                      • 8. Re: Jpeg recompress?
                        Eugene Tyson Adobe Community Professional & MVP

                        ConnyO wrote:

                         

                        No, my question is if InDesign will recompress or not. I know that in most cases it will not be visble anyway, but there are exceptions.

                         

                        And, Eugene, just because you write it, it's not the the truth :-)

                         

                        I will get back with the result of the test...

                         

                        Good luck.

                        • 9. Re: Jpeg recompress?
                          rob day Adobe Community Professional & MVP

                          If you try the same difference test in Photoshop, the Histogram panel will tell you exactly how many pixels change and by how much, and multiple compressions have surprisingly little cumulative effect.

                           

                          Screen shot 2013-01-22 at 1.09.52 PM.png

                           

                          This is one save with max quality—if there was no change all the pixels would be at 0

                           

                          Screen shot 2013-01-22 at 1.26.19 PM.png

                          This is 4 saves at max quality and the mean and deviation have barely changed.

                           

                          Screen shot 2013-01-22 at 1.33.30 PM.png

                           

                          This a medium compression where you can actualy see the changes

                           

                          Screen shot 2013-01-22 at 1.41.50 PM.png

                          • 10. Re: Jpeg recompress?
                            ConnyO Level 1

                            I have now completed my small test. There is no doubt that InDesign recompresses the pictures. It doesn't matter that the picture is the same size, and not cropped.

                            Too bad :-(

                             

                            Thank you for your help!

                            • 11. Re: Jpeg recompress?
                              rob day Adobe Community Professional & MVP

                              Right, it's the same as Photoshop where if you open and save a jpeg it's recompressed. The good news is that if the compression is always maximum quality there won't be a problem.