17 Replies Latest reply: Dec 13, 2013 6:49 AM by Test Screen Name RSS

    How to prevent PDF presets to alter image quality

    molezeen Community Member

      In experimenting with various PDF presets, I noticed that with grayscale images in Photoshop, saving as PDFs using different presets, alters image quality, specifically the contrast. 

       

      Therefore, it seems like saving an image in the "wrong" PDF preset could undo a lot of prepress work. Is there a better way/format?

       

      To get a crude idea: there is an 8.7% decrease in the percent black between 10% and 50% values (the range) on a step wedge between the original in Photoshop and the HighQuality PDF, which showed the same values, and the PDF/X-1a, which compressed the range by 4 percentage points (approximately a 8.7% decrease). 

       

      A visual, and idiosyncratic, assessment of four versions of the same image  (Photoshop grayscale, High Qualtiy PDF, PDF/X-1a, and PDF/X-3), which included a step wedge and color ramp, would rank the fidelity to the original from best, HighQuality, to worst, PDF/X-1a. 

       

      The same grayscale image in Photoshop CS6 was distilled (File > Print > Adobe PDF) to PDFs using unmodified PDF presets in Acrobat XI distiller.

       

      The following composit screen shot (all four images on the screen, screen print, reorganizing them, then reducing the image to a 120 dpi at 4.2" wide (including text) gives some idea of the differences, but a lot got lost getting it here. 

       

       

      Walton

        • 1. Re: How to prevent PDF presets to alter image quality
          Test Screen Name CommunityMVP

          Just a little more by way of questions

          - is the original in greyscale mode?

          - what product are you viewing the PDF in?

           

          Are you able to share a set of actual PDFs (you can't post the files here, only a link)?

          • 2. Re: How to prevent PDF presets to alter image quality
            molezeen Community Member

            The original grayscale is in grayscale mode. I created the PDFs from it. 

             

            The PDFs opened in Acrobat XI.

             

            I will get a zipped file of the PDFs uploaded as soon as I can.

             

            Thanks,
            Walton

            • 3. Re: How to prevent PDF presets to alter image quality
              molezeen Community Member

              Here is a zip file with the original grayscale image and the three PDFs:

              http://www.12on14.com/dpi/grayscale_images.zip

               

              Walton

              • 4. Re: How to prevent PDF presets to alter image quality
                Test Screen Name CommunityMVP

                All contain a greyscale image, with the same pixel values. There are important differences between them.  Especially the PDF/X-1a PDF is untagged, while the other two (PDF/X-3 and "High quality") are both tagged. This is to be expected, due to limitations in the older PDF/X-1a standard. Also, the PDF/X-3 and "High quality" files display differently for me). This is because PDF/X files must use the embedded output intent (Coated FOGRA27) rather than my default CMYK profile.

                 

                My immediate question to you is: what do you want to happen with a greyscale image? Do you want it to be applied to the black plate only, or treated as shades of rich black according to the profiles you have chosen (or defaulted)?

                 

                My second question: are you using PDF/X for any particular reason?

                • 5. Re: How to prevent PDF presets to alter image quality
                  molezeen Community Member

                  I do a lot of work with print-on-demand books (design and formatting), and I am active on the CreateSpace (the p-o-d division of Amazon.com). Although CS will accept work in virtually any PDF preset or origin (doPDF, cutePDF, etc.), PDF/X-1a is the recommended format, and for other companies it is the only accepted preset.

                   

                  Here is the dumb question:

                   

                  • On the monitor (as the screen shot shows) the four images (PS, HQ PDF, PDF/X-1a, PDF/X-4) appear quite different: i.e. my video/monitor system is representing the images differently.
                  • A screen shot of all four images on the screen at the same time, then with the info window open in Photoshop, I assessed their CMYK values in the exact same places on each image (lining the images up, using the measure tool and  guidelines, measuring at high magnification); here (the color original followed by the original grayscalse conversion) are the black values (C00 M00 Y00 K1-100):

                   

                  • The images display differently, and those displays measure differently.
                  • When I view the PDF images, they appear differently, but if i measure them (Output Preview set to Dot Gain 20%) the K values are the same. 

                   

                  When the same image is prepared using different PDF presets (a previous set of test using different images and looking for something different) they will print (printed in a black & white book by CreateSpace) differently.

                   

                  How can one predict how a grayscale image will print? How can one prepare it and safely convert it to PDF?

                   

                  Walton

                  • 6. Re: How to prevent PDF presets to alter image quality
                    Test Screen Name CommunityMVP

                    Well, the reason they are different is that you are asking for quite different things.The difference is all to do with colour management. You have files with an output intent and none; files with the greyscale tagged and not.

                     

                    You say you are measuring with output preview set to the profile Dot Gain 20%. I can imagine that in many cases this will bring them back. PDF/X is mainly of interest to control colour, and if you have a true greyscale workflow it is only going to complicate things. If you are making PDF/X for a greyscale workflow, then set a greyscale output intent or you could easily see multiple conversions (calibrated greyscale to calibrated CMYK then back again).

                    • 7. Re: How to prevent PDF presets to alter image quality
                      molezeen Community Member

                      If you could take a moment more . . .

                       

                      If I am confused, then there is no hope for most of the tens of thousands of CS members (several of us have estimated 50,000 new titles each year), who have to deal with this one way or another.

                       

                      The original grayscale (which appears to be working gray: dot gain 20%) was converted Acrobat Distiller.  I left all settings at their defaults with no modifications, except to set the PDF output size. 

                       

                      I have no idea what to do next or how to understand it.  Can you recommend a source/book/site . . . when this sort of things is explained.

                       

                      Thank you,

                       

                      Walton

                      • 8. Re: How to prevent PDF presets to alter image quality
                        Test Screen Name CommunityMVP

                        Do you understand colour management, and the use of colour profiles, and how profiles will change colours as you see/print them? That is behind all of this, and you can't get anywhere without that.

                        • 9. Re: How to prevent PDF presets to alter image quality
                          Test Screen Name CommunityMVP

                          And by the way, how did you pick "dot gain 20%"? I don't know print-on-demand technology, but is it ink-based, and does it really have this level of dot gain?

                          • 10. Re: How to prevent PDF presets to alter image quality
                            molezeen Community Member

                            Yes, I do understand basic color management and the use of color profiles.  One might, for example, use a printer's profile for a job, and all/most of this becomes moot. 

                             

                            In this case the assigned source space in Photoshop was Gray-Dot Gain 20%; the rendering intent was Relative Colorimetric. The PDF were created with unmodified presets.

                             

                            The expert approach in the CS community would be to convert the image to DeviceGray.

                             

                            CS for example does not share any information about the who, what, where, when, and how of their printing. I can demonstrate that CS uses non-traditional process colors (compared to Pantone Process Colors); they use their own proprietary profiles. They strip off some to all color information and replace it with whatever they do.  Although the profile for the grayscale is Dot Gain 20%, I know the dot gain for CS should be between 9%-12%. I believe they strip off more from RGB files than from CMYK (but I do not know for sure). 

                             

                            If I want to work on an image in Grayscale and that will be printed on a black only press, I will convert the image to Grayscale > Monotone > custom CMYK (Separation type GCR, Black generation Maximum, Black Ink Limit 100%), after working on it, I convert to PDF using High Pass or PDF/X-3, without changing anything. 

                             

                            Obviously, I am weak in this area.

                             

                            Walton

                            • 11. Re: How to prevent PDF presets to alter image quality
                              Test Screen Name CommunityMVP

                              I can't pretend it's simple. There have been many choices made to accommodate the many different requirements of pre-press professionals. Even experienced people can struggle to get colour matching to work as they know it should.

                               

                               

                              The essential thing to remember is that in colour management, there is never just one profile involved. There is always two (or four, or six...). One, the source profile, describes the colours in your document. The other, the destination profile, describes a device. This device might be the screen you view on, the printer you print on, or a device that is being simulated.

                               

                               

                              So, looking at the three PDFs on screen.

                              "High quality". Source: 20% dot gain. Target: your screen. This is probably closest to the colour displayed by Photoshop, which will do something similar.

                               

                              PDF/X3. Source: 20% dot gain. Target: the output intent, Coated FOGRA27. Then this will have to be further converted using two more profiles to see it on screen.

                               

                              PDF/X-1a. DeviceGray (no tagging). This (by the rules of PDF/X, but not PDF in general) is the grey channel of the output intent, Coated FOGRA27. So no converson so far, but this will be converted using two more profiles to see it on screen.

                               

                              Why FOGRA27? Because you chose it, or defaulted it, in your Distiller settings. This is not a good idea unless you know that it is the correct output device for your print requirements. This information should come from your printer, and you CANNOT make really good PDF/X files without it. If you choose it at random, you can expect further and unpredictable colour shifts.

                              • 12. Re: How to prevent PDF presets to alter image quality
                                molezeen Community Member

                                Thank you! 

                                 

                                As for FOGRA27 . . . I touched nothing, set nothing, by trying to keep to whatever Adobe does by defualt, I thought I was removing some of the many variables that you alluded to.

                                 

                                My general goal is this . . . given that CS and other print on demand companies are not forthcoming with things like profiles, or even much technical information, even as basic as what kind of press they are using . . . to determine how best to prepare grayscale images for print in black and white books (1 color black). 

                                 

                                The "expert" method is to work in grayscale then distill to PDF/X-1a (Save as PDF/X-1a does no seem to produce a PDF/X-1a compliant file), presumably selecting the working space that matches the image's working space.  I'm trying to figure out if this PDF, can be trusted to print an image as close to the source image in Photoshop, inasmuch as when I view it on the screen it appears different. 

                                 

                                It seems that working in PS is kind of blind if I convert to PDF/X-1a.  At least that is my feeling.

                                 

                                Walton

                                • 13. Re: How to prevent PDF presets to alter image quality
                                  Quickcut Dude

                                  team, Im curious as to what effect compression has on the Ink density in images.

                                   

                                  So Ive placed a fairly heavily Saturated TIFF with no LZW compression in an Indesign Page. I then export that to PDFX-1a preset, destination profile ISO Web coated.icc. By default it uses JPG compression on my image in the resulting PDF. I then use the same export preset but change the compression to ZIP. So I have 2 PDFs, 1 with a JPG compressed embedded image and the other with a ZIP compressed embedded imaged.

                                   

                                  The result in ink density between the 2 PDFs is what Im interested in here. The JPG compressed PDF has way more pixels up to the ICC profiles max ink of 300. The ZIP PDF far fewer.

                                   

                                  My question is why ?

                                   

                                   

                                  ZIP:

                                  ZIPComp.png

                                  JPG:

                                  JPGComp.png

                                  • 14. Re: How to prevent PDF presets to alter image quality
                                    Test Screen Name CommunityMVP

                                    The extra dots you see just look like compression artifacts in JPEG. When JPEG is used pixel values can vary a bit - how much they can vary will depend on the JPEG qualiy setings. If parts of the image are at the very edge of acceptable ink density, this could push them over. By contrast, LZW does not change the pixel values at all. LZW by the way is obsolete. Use Flate.

                                    • 15. Re: How to prevent PDF presets to alter image quality
                                      Test Screen Name CommunityMVP

                                      Correction: LZW for PDFs is obsolete but I see you are already using Flate for PDFs (called "ZIP"). LZW is in no sense obsolete for TIFFs so ignore that part of reply!

                                      • 16. Re: How to prevent PDF presets to alter image quality
                                        Phillip Jones Community Member

                                        Would he have less issues if the Images were PNG?

                                        • 17. Re: How to prevent PDF presets to alter image quality
                                          Test Screen Name CommunityMVP

                                          Using PNG shouldn't make any difference at all.  What is happening s just perfectly normal.