16 Replies Latest reply on Mar 9, 2014 10:34 PM by d3athcarb4fatty

    Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)

    opusmarketing

      Hello,

       

      i am trying to describe a problem which persists since version CS3 of InDesign. It's about aliased edges in images in a certain angle; occuring when exporting the brochure as PDF file (at 300 ppi). The placed images are always at a higher quality than needed (for example 780 ppi effective). The aliasing is not there when opening the original image files in photoshop (viewing at 100%).

       

      The PDF export settings are:

      - Compression: Bicubic downsampling to300 ppi for images above 350 ppi (for color images, grayscale images and monochrome images)

      - Crop Image data to frames

      - Marks: Crop Marks and Page Information

      - Output: No Color Conversion

      - Advanced: Transparency Flattener: High Resolution

      - Compatibility: Acrobat 4 (PDF 1.3)

      - PDF /X-3:2002

       

      Below are two screenshots

      - The left one was the original image, downsampled to 216 mm in width using automatic bicubic downsampling

      - The right one is the result when exporting a InDesign Document with the same width to a PDF with the mentioned settings

       

      Downsampled in Photoshop CS6 to 216 mm widthExported from InDesign CS6 with mentioned settings
      image_ps_downsampled.pngimage_indesign_pdf_downsampled.png

       

      I have no clue what happens here, but it looks like the internal downsampling of InDesign CS6 is not very good.

      When i write a PostScript file of the brochure and put it in Distiller (with the same PDF Preset as above), the image looks like the one made with Photoshop. So this problem has to lie somwhere deep in InDesign or it's settings.

       

      Anybody with similar experiences?

        • 1. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
          Laubender Adobe Community Professional & MVP

          @OctupusMarketing – I'm no friend of downsampling.
          I know it's taking a few more seconds to minutes for output, but I'll leave the pixels untouched when writing a PDF.

           

          If you need it for presentation purposes at smaller size, just try Acrobat Pro.
          Or, if you want transparency flattened use the PostScript - Distiller combination.

           

          For printing on the press  I'll never do downsampling.

           

          Uwe

          • 2. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
            Peter Spier Most Valuable Participant (Moderator)

            I suspect if you save the Photoshop image directly to PDF and open it in Acrobat you are going to see the same thing. It may improve on screen with Smooth Edges enabled in Acrobat, but you are not looking at a 1:1 pixel representation on screen in Acrobat as you are in Photoshop, so some stair-stepping is pretty typical on slopes at some magnifications.

            • 3. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
              opusmarketing Level 1

              If i do the downsampling on the original image in Photoshop, the aliasing effect is gone. The output format does not matter here (PDF, TIF, JPEG) because it simply saves the data instead of altering it again. To me, it looks like Photoshop and Distiller are downsampling with a higher quality than InDesign.

              • 4. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                opusmarketing Level 1

                I should mention that this problem is not only a display related issue, the aliasing is also visible when printing from the InDesgin Document with a professional digital printer.

                • 5. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                  d3athcarb4fatty

                  OctopusMarketing,

                   

                  I'm having the same problem, did you ever find a solution?  I've tried creating PDFs downsampled from the same image within InDesign, Acrobat, and Photoshop, and Photoshop is the only one that seems to work.  Acrobat and InDesign seem to have some downsampling quality issues.

                   

                  Quality downsampling is essential because my PDFs will be viewed online, and they have lots of sharp, straight edges or rasterized line drawings so quality anti-aliasing is a must.

                  • 6. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                    rob day Adobe Community Professional & MVP

                    I think this issue has more to do with the way the three programs scale and anti alias for display zooming. A 100% view in ID CS6 and Acrobat is different than Photoshop's 100% view—Photoshop's is a 1:1 actual pixel view.

                     

                    So if you take resampling out of the mix and simply display the same image  at 100% you get different anti-aliasing qualities. Acrobat has a Preference that handles the way 100% is scaled and anti-aliased, which you can't control on the end user's machine:

                     

                    compare.png

                    • 7. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                      rob day Adobe Community Professional & MVP

                      If you compare PDF export downsampling vs. Photoshop downsampling at the highest magnifications there are some differences in the pixel structure but nothing that would show up in print if all the data is being sent to the printer (ID>Print>Graphics>Send Data).

                       

                      Here are 1 point lines sampled from 1000ppi to 300ppi in PS and via export without compression on the left:

                       

                      Screen Shot 2014-03-09 at 11.55.42 AM.png

                      • 8. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                        d3athcarb4fatty Level 1

                        Hello Rob, thanks for the reply.  The differences in the Photoshop downsampling vs Photoshop PDF export downsampling is slightly noticeable like you said, but that looks acceptable to me too. 

                         

                        I did a few tests to try to illustrate the problem I'm having better.  These are four PDFs, each zoomed to 1200% in Acrobat so that you can clearly see the pixels.  The differences here are big enough that they are noticeable in print, especially with high contrast images or rasterized line drawings.  The two PDFs on the right side look much better in Acrobat at various zoom levels as well, despite Acrobat's zooming display qualities. 

                         

                        PDF settings comparison.jpg

                        • 9. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                          rob day Adobe Community Professional & MVP

                          Is there any transparency on your InDesign pages? Does it happen if you export via PDF/X-4 so there are no color conversions or flattening?

                          • 10. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                            d3athcarb4fatty Level 1

                            Just to be sure, I copied this particular image (flattened PSD) to a new InDesign document and tried PDF/X-4, which gave me the same low-quality result.

                             

                            One thing I should note about my test is that the image actually had an effective ppi of 650.  At exactly 600ppi, the downsampling looks much better, probably because it's a simple 2:1 ratio.  (Of course I could always resize all of my links to be the ID layout size @ 300ppi, but that would mean giving up entirely on InDesign downsamping which would add a ton of work).

                            • 11. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                              rob day Adobe Community Professional & MVP

                              Something about your test looks off. The export from ID and export from PS PDFs are both zoomed at 1200%, but the export from ID vrsion is 90% smaller.

                              • 12. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                                rob day Adobe Community Professional & MVP

                                The differences here are big enough that they are noticeable in print

                                 

                                The diagonal lines in your test are 1 pixel so at 300ppi to an offset press at 150lpi, the lines would be less than a halftone dot so I'm pretty sure you would need a loupe to see any difference. Maybe with a stochastic screen there would be better resolution but still difficult to see. So if the printing is that good I would just export without down sampling. With disk space running at 15 cents a gigabyte there's not much to gain with a downsample.

                                • 13. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                                  d3athcarb4fatty Level 1

                                  Rob Day wrote:

                                   

                                  Something about your test looks off. The export from ID and export from PS PDFs are both zoomed at 1200%, but the export from ID vrsion is 90% smaller.

                                   

                                  Yeah I noticed that I actually had the image in InDesign scaled @ 90%, so the effective ppi was around 650.  I get the same jagged results when I use anything other than a 300 or 600 effective ppi.  Whereas if I use a 650ppi image in Photoshop and export to PDF, it downsamples smoothly.

                                   

                                   

                                  Rob Day wrote:

                                   

                                  The diagonal lines in your test are 1 pixel so at 300ppi to an offset press at 150lpi, the lines would be less than a halftone dot so I'm pretty sure you would need a loupe to see any difference. Maybe with a stochastic screen there would be better resolution but still difficult to see. So if the printing is that good I would just export without down sampling. With disk space running at 15 cents a gigabyte there's not much to gain with a downsample.

                                   

                                  It becomes noticeable with some images more than others, but I'm printing a lot of images of buildings and drawings with sharp lines that converge to a point, or are distinguishable in the full size image but indistinguishable when downsampled.  This can introduce distracting patterns when they aren't downsampled smoothly, something like this:

                                   

                                  http://oclc.org/content/dam/research/publications/library/visguides/visguide3fig6.gif

                                   

                                  Unfortunately the printers near me aren't very good, so I'm having things printed online, and this particular printer (blurb.com - for a small job) won't accept large PDFs without compressed/downsampled images :/  I'm making 300dpi versions of the really crucial images for the time being, but I'm hoping there is a better solution!

                                   

                                  The other issue is exporting the PDF for use on the web, either as a download or on an online PDF viewer like issuu.com.  The two PDFs on the right side of my test look much better in these situations.  Is there any disadvantage to using Distiller to make my PDFs for this purpose using the Device Independent setting?  I don't have any special interactive elements. 

                                  • 14. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                                    rob day Adobe Community Professional & MVP

                                    I see it's like a fabric or screen moire—I think in this case you would have to manually downsample.

                                     

                                    On the web I don't see how you control it—your clients could be using different readers–Preview, Acrobat Reader, AcrobatPro—set with different page display preferences and zoom scales.

                                     

                                    I don't think there's a problem with Distiller in your work flow. For print it's going to flatten transparency, but Blurb might be asking for that anyway.

                                    • 15. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                                      d3athcarb4fatty Level 1

                                      Okay I am going to try the Distiller route.  Thanks for the input!

                                      • 16. Re: Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)
                                        d3athcarb4fatty Level 1

                                        One last bit of information for anyone else who stumbles upon this thread: I've learned that even Distiller has downsampling limitations.  The short summary is that there is a bug/limitation with Distiller, where if you try to use bicubic downsampling at any less than a 2:1 ratio (e.g. downsampling an image from an effective 301-599ppi to 300ppi), Distiller will switch from using bicubic to "average" downsampling, which is much less smooth.  For images such as these, manually downsampling in Photoshop first is the only (tedious) solution.

                                         

                                        There is a good explanation with examples here:

                                        http://kaiser-edv.de/tmp/Downsampling-Verdeutlichung/

                                         

                                        And someone on another forum posted what they said was Adobe's official respose to this "bug":

                                         

                                        First of all, Distiller never switches from bicubic to subsampling.

                                        The code simply cannot do that. However, I think there is a need

                                        for clarification about how Distiller performs bicubic downsampling.

                                        For bicubic downsampling Distiller can only do 2:1 downsampling.

                                        That's how the code is designed. Therefore, if you try to downsample

                                        from for example 400dpi to 150dpi, Distiller first downsamples the

                                        image with "Average" downsampling to two times the target resulution

                                        which is 300dpi. Then it applies bicubic downsampling from 300 to

                                        150dpi.

                                        This also means that if you try to downsample with bicubic from

                                        400 to 300 dpi, then Distiller won't do bicubic, but it switches

                                        to Average downsampling to go from 400dpi to 300dpi in one step.