8 Replies Latest reply on Jun 12, 2016 10:53 AM by JustyR

    When images all change colour unexpectedly

    JustyR Level 1

      Hello,

       

      Wondering if there are any pre-press people out there that could help me.

       

      I have a group of greyscale images on a spread. They're all greyscale mode in Photoshop. But saved as PSDs.

       

      When placing one of those PSDs that has the image as a layer (i.e. not flattened), all the images on the page change brightness.

       

      I know this is to do with the transparency blend space. However, when making a Press Quality PDF, this also shows the change in tone.

       

      Only when choosing an output profile, e.g. Fogra39, do all images stay the same tone. But, they're not as 'rich' as I'd like.

       

      I don't want to change the blend space to RGB, because it's being printed.

       

      The only option I had was to flatten all images so they showed up nice and strong. Using a Press Quality setting with no colour conversion or output profile.

       

      I'm starting to learn about colour management. But what worries me is if I needed to layer an image for editing purposes. This would shift the greys of all other images on the spread.

       

      Can you please help me understand the issue and how to resolve it?

       

      Many thanks

        • 1. Re: When images all change colour unexpectedly
          rob day Adobe Community Professional & MVP

          This comes up often. Check these two threads:

           

          Re: Grayscale images showing up too dark

           

          https://forums.adobe.com/message/4482662#4482662#4482662

           

           

          When placing one of those PSDs that has the image as a layer (i.e. not flattened), all the images on the page change brightness.

          You would also see the change with no transparency when Overprint/Separation Preview is turned on.

           

          InDesign provides different ways of handling grayscale images depending on whether you are designing for screen or print. If you are designing for screen you can set the blend space to RGB, keep Overprint off, and set your Appearance of Black preference to Display All Blacks as Rich Blacks. In that case you will get an sGray or sRGB (2.2 Gamma) preview of the gray values.

           

          For print you want Overprint on, CMYK Blend Space, and Accurate Blacks. In that case grayscale objects preview via the document's CMYK profile. Most CMYK profiles attempt to preview black as it will appear on press, which is something less than absolute black—with most press conditions there is a visual difference between 0|0|0|100 and 65|50|50|100

          • 2. Re: When images all change colour unexpectedly
            JustyR Level 1

            Thanks, Rob, for such a quick and comprehensive reply. That's extremely helpful. Looks like I've got a bit reading to do.

            • 3. Re: When images all change colour unexpectedly
              rob day Adobe Community Professional & MVP

              Looks like I've got a bit reading to do.

              Keep in mind that it is just a preview change—the output numbers are not changing.

               

              Assuming your monitor is well calibrated and profiled, and your assigned document CMYK profile is correct, the InDesign preview is probably more accurate than Photoshop's default 20% Dot Gain grayscale profile. The other threads explain how to use the CMYK Black Ink as a grayscale profile over in PS, which will get you a close match in previews when Overprint is turned on in ID.

               

              It is possible to go the other way and emulate Photoshop's 20% Dot Gain in InDesign by assigning the legacy Photoshop 5 Default CMYK profile, but I wouldn't recommend that especially if you have color on the pages.

              • 4. Re: When images all change colour unexpectedly
                JustyR Level 1

                I haven't had time to look into it today, but from what you've said, the assumption is that any change on screen doesn't transfer to output, e.g. Press pdf.

                 

                However, that's not what I found. One spread of pics (without transparency) was darker than another spread (one pic with transparency amongst a bunch of others without it). That PDF would have gone to print and shown a clear difference between spreads.

                • 5. Re: When images all change colour unexpectedly
                  rob day Adobe Community Professional & MVP

                  One spread of pics (without transparency) was darker than another spread (one pic with transparency amongst a bunch of others without it)

                  Did you check the output numbers in AcrobatPro's Output Preview? The AcrobatPro preview depends on how you've setup the simulation preview. Try exporting to PDF/X-4 which uses the document's output intent/CMYK profile over in AcrobatPro as the Output Preview Simulation profile.

                   

                  InDesign doesn't recognize grayscale profiles so it always outputs and exports grayscale object values unchanged, unless you force a conversion from grayscale into a different CMYK space. In that case the gray values would be converted into 4-color blacks, which you would be able to see in Acrobat's output preview panel.

                  • 6. Re: When images all change colour unexpectedly
                    JustyR Level 1

                    Thanks for your continued help. I think I'm beginning to understand it.

                     

                    So, Acrobat Pro is simply showing a screen representation (let's say, in RGB), until you choose overprint preview? At which point it's then showing more accurately how it will print?

                     

                    This is what I see in Acrobat with a Press Quality PDF (before using Output Preview).

                    Press Quality no profiles or conversion.png

                     

                    This is what I see in Acrobat with a PDF/X-4 PDF (before using Output Preview).

                    PDFx4 no profiles or conversion.png

                     

                    Then when using the Output Preview and choosing a Simulation profile, both the PDF/X-4 and Press Quality PDFs show the same tones. They also show the same percentages of black, e.g. k97, to the right of the shirt collar.

                     

                    This all means that whilst we were trying to make all the blacks look darker, as per the Press Quality PDF screenshot, they will almost certainly come out the press looking like the PDF/X-4? Because we were only seeing Acrobat's this-is-how-it-looks-on-screen representation - not its this-is-really-what-it-looks-like representation?

                    • 7. Re: When images all change colour unexpectedly
                      rob day Adobe Community Professional & MVP

                      Then when using the Output Preview and choosing a Simulation profile, both the PDF/X-4 and Press Quality PDFs show the same tones. They also show the same percentages of black, e.g. k97, to the right of the shirt collar.

                      That's right, when you check files in AcrobatPro, you always want to open Output Preview and choose your document CMYK profile as the Simulation profile. The same 97% values confirm that the grayscale has exported unchanged.

                       

                      PDF/X-4 is a better export preset than Press Quality. It includes your document CMYK profile as the  output intent so that the simulation defaults to document CMYK.

                       

                      There can't be two different profiles simulating the black plate preview because matching gray and black values will print the same on press. The press profile can't be both 20% Dot Gain and Fogra39 Black Ink, it has to be one or the other. With Overprint on InDesign always uses the document CMYK profile's black ink for the preview. If you don't want the confusion of mismatched previews between ID and PS use your InDesign CMYK profile as the Gray profile in Photoshop.

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                      • 8. Re: When images all change colour unexpectedly
                        JustyR Level 1

                        Awesome. You're a star.