19 Replies Latest reply on Feb 10, 2016 7:03 AM by ASwin1

    Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.

    ASwin1

      When i export two identical pdf files from ID CS3 and bring them into Photoshop CS3, both files are identical when i overlay the layers and compare in detail, but if the pages move up or down on the pages panel in Indesign, after i export the same file again and bring it back into Photoshop, there are two very fine horizontal lines where the pixels are skewed/different to an identical pdf.  The line is there at full zoom.  The only variable is the exported page is different page number in the Indesign pages panel.  How is this possible?  My export settings are:

       

      High Quality Print, Acrobat 5 (pdf 1.4), No compression.

       

      Many thanks.

        • 2. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
          ASwin1 Level 1

          Hi Peter, hopefully you should be able to open these files in full res.  You can see 3 lines across the first image, and one across the 2nd.  (Screenshot captured at a higher zoom).  All lines are 1 pixel in depth, occasionally 2.  The only variable is the fact the page may have moved down or up the pages panel as more spreads are added in Indesign .. or they were exported at different times (days).  But this shouldn't affect anything - all pdf settings are the same, and both from exactly the same ID document.  The pdf's have the lines/artifacts in the same place.  The image itself is a high-res tif file, perhaps because they have been saved from Photoshop?  Although i doubt that.  Any help would be great on this, thank you!

           

          [Images removed by request]

          • 3. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
            Peter Spier Most Valuable Participant (Moderator)

            I don't see a difference on my screen....

            • 4. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
              Willi Adelberger Most Valuable Participant
              1. I don't see a difference neither.
              2. What kind of screen do you have? It might be an issue of the screen's resolution.
              3. Why do you bring InDesign PDFs to Photoshop? How? Is there a specific reason?
              • 5. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                ASwin1 Level 1

                Hi Peter/Willi, thanks for the reply.  If you download both screenshots (i've labelled them 1a/1b, 2a/2b) and bring them into photoshop as two layers and make the top layer visible and invisible (on/off).... you will see the discrepancies.  You won't see anything with the naked eye by comparing the screenshots.  The problem is that with the "phantom lines", both with and without can look ok, so it's difficult to tell which is the problem image.  However for high-end output, i need to identify why it's happening.  I have a late 2006 imac intel with 20" screen .. i'm not an expert, but i think the problem lies in the pdf export. I use slight 'trial and error' alterations with differences in position and size with objects, and bringing a pdf file helps me back-track and confirm two things i've been working with (usually via lot's of screenshots) are the same spread.

                • 6. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                  Willi Adelberger Most Valuable Participant

                  For high print output you should not use Photoshop here in any intermediate step.

                  • 7. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                    ASwin1 Level 1

                    So with this error in workflow taken into account, does that mean the prints with be 100% identical when inspected with a hig-end loupe, despite 2 pdf's having this issue? That's all i need to know. My only aim is to identify what the lines are and why it's happening.

                    • 8. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                      Peter Spier Most Valuable Participant (Moderator)

                      OK, I can confirm the difference in the screen shots, and I think I understand why you are doing what you are doing, but I have no explanation for why the images rasterize differently.

                      • 9. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                        Peter Spier Most Valuable Participant (Moderator)

                        The coordinates of the image placement on the page remain the same from page to page?

                        • 10. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                          ASwin1 Level 1

                          Hi Peter, thanks, yes both (all) images and screenshots exactly the same position.  Only difference is the top layer visibility being switched on/off.  Since Willi's reply, i had the idea to take two full-res pdf's, one with the line issue, one without.. and zoom in 100% in preview in OSX, then zoom out with one click.  I took close-up screenshots of both versions and brought them into photoshop to compare..... there doesn't seem to be any prominent line issue, which suggests that the problem i'm seeing could be bringing them into Photoshop? There are miniscule differences in pixels when the new OSX 'preview' screenshots are compared, but the are generally in uniform and nothing too untowards where the line issue is in Photoshop.

                          • 11. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                            Peter Spier Most Valuable Participant (Moderator)

                            I wouldn't rely on screen captures to compare. Can you stack actual prints on a light table?

                            • 12. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                              ASwin1 Level 1

                              I don't have to equipment to run off some prints to do that yet but i do have the lightbox ready.  I didn't want to get to the stage where i compared two prints with a one or two pixel width difference as the mind can play tricks on you, and of course none appears to be glaringly 'right' or 'wrong'....i'm really looking to identify the issue at this stage so i can proceed with a single pdf print confidently.  The images are full archival-resolution objects.... do you think the problem is solely the way in which Photoshop is rasterizing the pdf's?  Although i took a screeshot of one or two lines, i have checked and lines actually appear further down the image too.  If this is the issue, then there is no issue in a sense. Thanks Peter.

                              • 13. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                                Peter Spier Most Valuable Participant (Moderator)

                                I don't know what the issue is, but it wouldn't surprise me if moving the image on the screen before making the screen capture results in a different set of anomalies.

                                 

                                And how do you know which version is right?

                                • 14. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                                  ASwin1 Level 1

                                  The screenshots above were exactly the same position on screen.  Do you mean which pdf is the 'problem image'? I don't know. The lines appear in exactly the same place though if i export a fresh identical pdf spread.  They are either there or not there.  I'm now not looking at them as 'problem lines' as i did when i asked the question, but rather Photoshop doesn't feel there's a problem when rasterizing with the occasional 1 pixel line difference, especially taking into account what Willi said about the pdf having no place to be there in the first place.  Does this sound like it could be the culprit taking everything into account? The import settings bringing the pdf into photoshop is at 300 dpi and 8bit (these pdf's are not print-ready, they are full-res, i have not resized/resampled the images for print). They are just for my own reference at the moment.  But two identical images/spreads/documents "should be" identical no matter what the settings. But of course everyday's a school day.

                                  • 15. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                                    Peter Spier Most Valuable Participant (Moderator)

                                    I'm curious if you see a difference in the SAME PDF if you make two screen captures, nudging the PDF very slightly up or down on screen before making the second capture.

                                     

                                    The image data should give identical results for output unless there is some sort of interpolation required, as there could be in viewing on screen, or if the image coordinates on your page in ID change. Jpeg compression might be a factor, too. Try exporting with zip compression or no compression, along with no downsampling, and compare the PDFs (NOT screen captures of the PDFs) as you have been in Photoshop and see if you see the same anomalies.

                                    • 16. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                                      ASwin1 Level 1

                                      Ok, slowly getting to the bottom of it (i hope).  Firstly, i took several screen shots of the *same* pdf zoomed in fully in Photoshop, i nudged the image around the screen a little in different places and i can confirm that the line is in the same place and the image is 100% rock solid the same no matter it's position on the screen. ( and confirmed this by overlapping the screenshots in the right place).

                                       

                                      Next i looked into compression, my settings (bearing in mind these pdf's are currently just for reference) are 'no downsampling > Automatic jpeg compression, maximum quality'.  I then exported the spread with no downsampling > compression 'none', and no downsampling > compression 'zip'.  All looked totally identical and fine (aside from slight variations in quality).  I then tried the page panel variable.  I exported a spread in Indesign with zero downsampling and zero compression, then deleted some empty pages/spreads preceding the spread, then exported the spread again to pdf (now a different page number, i.e 34-35), and unfortunately when i compare this spread with the spread prior to deleting some empty pages, the line is there again.  The pixel order is not the same order as the previous lines, but the lines are in exactly the same place. The only variable is the spread position in the pages panel, and it is exported as a different spread number.

                                      • 17. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                                        Peter Spier Most Valuable Participant (Moderator)

                                        I meant you should take your screen captures for comparison in Acrobat, not Photoshop, then look at them in Photoshop.

                                         

                                        It's entirely possible this is a bug in CS3 (and it might still be there in newer versions for all I know). I may do some playing myself in newer versions.

                                        • 18. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                                          Peter Spier Most Valuable Participant (Moderator)

                                          I've done two experiments in CS6 and CS3 and cannot, so far, reproduce what you see.

                                           

                                          In CS6 I set up a one-page file and imported a page from a PDF that contains a number of raster, vector, and type objects. I then duplicated the page, exported to PDF/X-4 and opened both pages at 300 ppi in Photoshop. I copied the layer from the second page onto the first page in Photoshop and set the blend mode to Difference to make any differences jump out. The two layers are identical.

                                           

                                          In CS3 I started the same way, but instead of duplicating the page I made two PDFs, on with a single page after placing the PDF, and a second after adding two blank pages at the start of the doc, and a third after deleting one blank page so the same page appears on both left and right sides of the spine and as pages 1, 2 and 3. Again, I cannot detect a difference in the images.

                                           

                                          There ARE differences between the PDFs produced by CS6 and CS3, but that isn't so surprising and are most likely do to differences in the versions of  the PDF libraries used in the two versions of ID.

                                          • 19. Re: Identical Indesign pdf spreads, one has lines of skewed pixels, one doesn't.
                                            ASwin1 Level 1

                                            I've just ran some tests using Acrobat Pro 8 with some clearer results.  Importing two separate 'identical' pdf's (one had the the  line problem one didn't, or visa-versa) and i did some screen capture exports (fully zoomed in) and exported them both as tiff  and pdf/a files.  There appears to be no line problem now whatsoever when comparing the two Acrobat screen grabs.  This suggests that it's all about bringing the files into Photoshop as previously suspected and not a bug in Indesign.  Really appreciate the help from yourself and Willi, thanks.