13 Replies Latest reply on Nov 29, 2014 6:52 AM by rob day

    Grayscale images with alpha channel get lighter?

    gaphic2 Level 1

      Hi,

       

      I'm placing grayscale tiffs to which I've added an alpha channel in Photoshop. Using the channel in Indesign causes the images to become a lot lighter, also in the pdf output.

       

      What do you think is causing this and how can I avoid it?

        • 1. Re: Grayscale images with alpha channel get lighter?
          [Jongware] Most Valuable Participant

          InDesign uses a different drawing algorithm for items that contain transparency. See also this thread: http://forums.adobe.com/thread/1020620?tstart=0

           

          If you switch to Preview/Overprint Mode, you'll see no difference.

          • 2. Re: Grayscale images with alpha channel get lighter?
            gaphic2 Level 1

            Thanks, I know about that issue. But turning preview on/of does not make a difference.

             

            What does make a difference is if I set the transparancy blend space to RGB instead of CMYK. The resulting PDF has the grayscale images in RGB then, but I can change that back outside of Indesign. Still, I wonder what I'm doing wrong.

            • 3. Re: Grayscale images with alpha channel get lighter?
              Peter Spier Most Valuable Participant (Moderator)

              OVERPRINT preview (or Separations Preview active, which turns on Overprint Preview) not Preview Mode.

               

              Without overprint preview, your grayscales are previews as gamma 2.2, I believe. With it turned on you are seeing the gray values as they will print on the black channel of the current CMYK space (which is where they end up when you print or export). That could be darker or lighter than gamma 2.2, depending on the dot gain in the working profile.

              • 4. Re: Grayscale images with alpha channel get lighter?
                gaphic2 Level 1

                Thanks Peter.

                 

                So how do I keep the images with an alpha channel at the same level as the ones where no transparancy is used?

                • 5. Re: Grayscale images with alpha channel get lighter?
                  Peter Spier Most Valuable Participant (Moderator)

                  I'm not really sure I unserstand what you are asking. The transparency shouldn't be affecting the PDF output -- the gray numbers are always put on the black plate in ID -- so ity's the output space that sould be controlling the final appearing in the PDF. Overprint preview should match that output (presuming you don't convert to some other space during export) for both transparent and non-transparent grayscale images.

                  • 6. Re: Grayscale images with alpha channel get lighter?
                    gaphic2 Level 1

                    Well, I'm using Fogra 27 as my CMYK working space and I don't convert on export. The levels of non-transparent grayscale images in the PDF look the same as on the screen in Photoshop. I'm using Gray Gamma 2.2 in Acrobat and Photoshop as Grayscale working spaces. The jobs I send to the press come back looking the same as well.

                     

                    What do I need to change so that the overprint preview matches the levels I've set in Photoshop?

                    • 7. Re: Grayscale images with alpha channel get lighter?
                      Peter Spier Most Valuable Participant (Moderator)

                      Probaly the best bet would be to creat a custom gray space using the Black Ink channel from Fogra 27. Gamma 2.2 is a screen profile.

                      LoadGray.png

                       

                      In Photoshop, Edit > Color Settings... and clcike the More Options button. You should see the Load Gray.... option inthe dropdown for the gray profile. Click that and it should open your folder of color profiles. Pick the Fogra 27 and say OK.

                      • 8. Re: Grayscale images with alpha channel get lighter?
                        gaphic2 Level 1

                        Yeah thanks, Peter. I had come across that suggestion in a related post somewhere.

                         

                        I tried it out and it works.

                         

                        However, won't this lead to serious wider problems? My pdf's end up with a whole lot of people. They will all need to have that gray space set up in Acrobat, or they'll see the images either too dark or too light. They get files from other designers as well, so they'll probably need several setups. Is that workable?

                         

                        And what will happen at the printer's?

                         

                        Wouldn't I be better off just working in the RGB workspace for Grayscale jobs and convert the finished PDF to grayscale post Indesign?

                        • 9. Re: Grayscale images with alpha channel get lighter?
                          Peter Spier Most Valuable Participant (Moderator)

                          For print it's not a problem at all. There is no gray space in InDesign, only RGB or CMYK, and all of your grayscale images are placed directly on the K plate using the numbers in the gray channel. Using the K channel from the CMYK space guarantees the number will be correct for the dnsity you are trying to achieve.

                           

                          Acrobat is a bit more complex, and I honestly don't have a perfect understanding of when Acrobat seems to to know how to render the numbers in the file in a particular space, and when it displays using the correct numbers, but the wrong profile. I believe it depends on whether or not a rendering intent is embedded in the file. BUT, and this is a big but, the rendering problem isn't restricted to your grayscales. Remember, there is no grayscale support in ID (except for exporting to a grayscale profile in CS6, but I don't get the sense we are talking about that), so your grayscales are now being output with the K in the CMYK. If you've used the balck ink from your CMYK space and your grayscales don't look right in Acrobat, nothing is going to look right.

                          • 10. Re: Grayscale images with alpha channel get lighter?
                            gaphic2 Level 1

                            Thanks for all your help, Peter.

                             

                            I think I'm going to avoid this problem for now by prepping the images in Photoshop in a way so I don't need the alpha channel in Indesign.

                            • 11. Re: Grayscale images with alpha channel get lighter?
                              rob day Adobe Community Professional & MVP

                              I think I'm going to avoid this problem for now by prepping the images in Photoshop in a way so I don't need the alpha channel in Indesign.

                               

                              It's not the alpha channel that's changing the preview.

                               

                              For documents that will never be printed Indesign gives you the option to preview place grayscale objects in a typical screen color space (Gamma 2.2, the sRGB profile is Gamma 2.2). So for screen projects you can set your Transparency Blend Space to RGB, leave Overprint and Separation Setups Off and gray objects will display as sRGB.

                               

                              For print projects you want the preview of grayscale objects to be managed by the document's CMYK profile because they will be output to the black plate unchanged—a 50% grayscale object should look the same as a 0|0|0|50 swatch. To get the accurate CMYK/grayscale preview, the blend space has to be CMYK and Overprint/Separation Setup need to be on.

                               

                              Same goes for Photoshop. If your grayscale is headed for a Fogra 27 profiled press the Gamma 2.2 gray profile will preview grayscales as too dark—a press can't have 2 different profiles.

                              • 12. Re: Grayscale images with alpha channel get lighter?
                                gaphic2 Level 1

                                Thanks for your reply, rob day.

                                 

                                "For documents that will never be printed ... For print projects"

                                 

                                That's the whole argument in a nutshell, though, isn't it? I can't say that any project I work on these days is purely for print. Apart from the book itself nowadays there's always either a downloadable pdf, an epub, a website or an iPad app, and frequently all of the above.

                                 

                                I really wonder what happens at the different printer's with my pdf's? During the last couple of years I've set several hundreds of books, most of them with grayscale illustrations. What you say makes perfect sense, and so they should have all come out far too light when printed, and yet everything looks fine.

                                 

                                Is this because I'm not including any profiles on export? Or do they have a workflow that can deal with my seriously lacking color management?

                                • 13. Re: Grayscale images with alpha channel get lighter?
                                  rob day Adobe Community Professional & MVP

                                  InDesign ignores grayscale profiles—you can save a grayscale out of PS with a gray profile but it has no affect on the ID preview or output.

                                   

                                  So if the preview you are seeing in ID is too light then the Fogra 27 profile is wrong for the destination press (or your monitor profile isn't an accurate profile of your monitor).

                                   

                                  Here's a ramp of grayscale patches with corresponding black tints below in ID, and Fogra27 as the document CMYK profile. With Separation Preview off the top grayscale object is displaying differently even though the output values are identical, so if the top version is a better preview, your ID CMYK profile (and black tint display) are wrong:

                                   

                                  Screen shot 2012-06-11 at 12.43.04 PM.png

                                   

                                   

                                  Sep Preview On:

                                   

                                  Screen shot 2012-06-11 at 12.44.32 PM.png

                                   

                                  It maybe the press is printing closer to the US Sheetfed Coated profile which produces darker black tints in ID when it is chosen as the document CMYK profile:

                                   

                                  Screen shot 2012-06-11 at 12.44.17 PM.png

                                   

                                  It should be noted that Photoshop grayscale profiles are never perfectly accurate because the color of the black ink is not considered in a grayscale profile. CMYK profiles don't preview black as absolute because 60|60|50|100 would be blacker than 0|0|0|100 on press. Both the Fogra and US Sheetfed profiles are displaying that effect.