15 Replies Latest reply: Dec 16, 2009 7:34 AM by John Smith for example RSS

    Working space settings for Grayscale?

    John Smith for example Community Member

      (Preliminary remark: I'm using the German version of PS, so some items may be called differently in the English version.)

       

      In the colour settings of PS CS4 I can define a working space for gray scale pictures. What does this setting actually do?

       

      I know that there is no ICC colour management for grayscale pictures, so what do the dot gain settings do? Do they just darken the display or is there more? What do the gamma settings do? What does "Black&White mean? What does sGray mean? Does Photoshop somehow add ICC profiles to grayscale pictures? If yes, which and what does it do?

       

      So far I decided to just set "no adjustment". The reasoning is that this should display the true greyscale values on the screen. I then can add dot gain as needed manually as a final step. Does this make sense or am I misunderstanding something?

       

      Bonus question: What about the spot colour settings? Are they applied to multichannel pictures?

        • 1. Re: Working space settings for Grayscale?
          c.pfaffenbichler Community Member

          I know that there is no ICC colour management for grayscale pictures

          How do You know this? There are grayscale-icc-profiles, after all.

           

          But basically Your assumption that those profiles darken the image (to simulate the selected dot-gain) sounds right, the darkening effect varying over the whole range though.

           

          The reasoning is that this should display the true greyscale values on the screen.

          What do You mean by »true greyscale values«?

          If a grayscale image is printed the result depends on the printing-process, paper, etc.; so X% grey in a digital image correlates to an L*a*b-value by virtue of its appearance being determined by a profile.

          How firm is Your grasp on color management-concepts generally?

           

          Are they applied to multichannel pictures?

          Yes, as far as I know, the Grayscale Working Space is used in displaying any additional channels.

          • 2. Re: Working space settings for Grayscale?
            John Smith for example Community Member

            There are grayscale-icc-profiles, after all.

             

            Well, sort of. As I understand, color space conversions are always done using Lab as intermediary. So my grayscale would be converted to Lab, which is fine, but on the way to the printer the CM Engine would take the Lab values and happily optimise the image by adding undercolours according to the printer profile, transforming my nice grayscale image to CMYK. As I understand further, this can only be circumvented by using device link profiles, which is no option for me.

             

            What do You mean by »true greyscale values«?

            If a grayscale image is printed the result depends on the printing-process, paper, etc.; so X% grey in a digital image correlates to an L*a*b-value by virtue of its appearance being determined by a profile.

             

            I mean the grayscale values which the consumer will see. As I said above, I'm reluctant look at them as Lab values, because I don't want to end up with a quadruplex.

             

            How firm is Your grasp on color management-concepts generally?

             

            I did some reading, but until now only theoretically. I "left" photoshop with version 7 and no colour management and am now confronted with CS4 with colour management. Unluckily, when it comes to colour management, the Photoshop manual is mediocre at best, and the existence of grayscale images is even completely ignored.

            • 3. Re: Working space settings for Grayscale?
              c.pfaffenbichler Community Member

              I mean the grayscale values which the consumer will see.

              How would Photoshop calculate what to display if one does not provide the relevant information about dot gain?

               

              As I understand, color space conversions are always done using Lab as intermediary.

              And why should grayscale-to-grayscale conversions not utilize the profile connection space?

               

              By the way, I think this has often been recommended as reading about Color Management:

              http://www.gballard.net/psd/cmstheory.html

              • 4. Re: Working space settings for Grayscale?
                p_d_f Community Member

                "I know that there is no ICC colour management for grayscale pictures, so what do the dot gain settings do? Do they just darken the display or is there more? What do the gamma settings do? What does "Black&White mean? What does sGray mean? Does Photoshop somehow add ICC profiles to grayscale pictures? If yes, which and what does it do?

                 

                So far I decided to just set "no adjustment". The reasoning is that this should display the true greyscale values on the screen. I then can add dot gain as needed manually as a final step. Does this make sense or am I misunderstanding something?

                 

                Bonus question: What about the spot colour settings? Are they applied to multichannel pictures?"

                 

                Photoshop always has to assume something in order to display your images. You can't ever really turn off color management. Yes, there really are Grayscale ICC profiles. They can be theoretical profiles like the ones that use a simple gamma curve to define the tonal response, profiles that use a simple dot gain figure or profiles that use actual measurement data to calculate the profile. An ICC profile is basically just a lookup table formatted to the ICC spec, and can specify one, three, four or more channels.

                 

                The Grayscale profiles loaded in Ps control how your GS image is displayed but just as important to me at least, they control how your RGB or CMYK individual channels are displayed as well, which can have repercussions when dealing with images on a channel by channel basis.

                 

                And yes, you still need both your Monitor profile AND your Grayscale profile (source and destination) in order to properly display your Grayscale file.

                • 5. Re: Working space settings for Grayscale?
                  c.pfaffenbichler Community Member

                  Well said.

                   

                  An ICC profile is basically just a lookup table formatted to the ICC spec, and can specify one, three, four or more channels.

                  Wasn’t one of the problems of the Hexachrome-process that failed to catch on a couple of years ago that it could not be separated with an icc-profile (and not edited as a layered six-channels-file …)?

                  So is support for more than four channels a more recent addition to the icc-standard or was I just missing something back then?

                  • 6. Re: Working space settings for Grayscale?
                    p_d_f Community Member

                    It was not an ICC limitation, just a limitation of Photoshop. I know that my copy of ProfileMaker has been able to generate up to eight channel profiles for several years now.

                    • 7. Re: Working space settings for Grayscale?
                      John Smith for example Community Member

                      p_d_f wrote:

                       

                      Yes, there really are Grayscale ICC profiles...

                       

                      Thank you. After contemplating a bit, I think I've finally understood where my confusion originated. But the more I understand, the more new questions arise.

                       

                      So far I've understood that if a picture is to be displayed on an internet site or used in an office application, then I best work with the gamma 2.2 profile. If the target computer honours ICC profiles, then it desn't matter anyway which profile I use, but if the target computer ignores ICC profiles, then most computers out there will display the picture with a gamma of 2.2 (more or less) because this tends to be the default setting on most computers.

                       

                      But when it comes to pictures for print, some questions remain.

                       

                      To begin with, I could continue to work as I did without colour management. I would first "convert" the picture to the profile "no corrections". This would mean that "the numbers" in the picture are the same as the gray values the final user should see. And then I would account for dot gain by either applying a gradation curve or by saving as EPS with a transfer curve.

                       

                      However if I want to use colour management, then I "convert" the picture to the the printer's ICC profile. Without a specialized program, I cannot create such a profile myself, even if I know the transfer curve. So either I find a suitable profile somewhere or the print shop must provide me that profile.

                       

                      So far I think I understand. But now the questions.

                       

                      Concerning missing profiles: Can I just take the gray channel of a suitable CMYK profile (e.g. ISO Coated v2) or would this contain some sort of black generation information which would spoil a grayscale picture?

                       

                      I assume that it's possible to embed the black and white point into the profile, so that I don't have to worry about them anymore but can assign the full range of gray values from 0% to 100%. With the colour sync tool, I looked into the grayscale profiles that come with Photoshop, and as far as I can tell, none of them does set the black and white point. So I assume that despite using colour management, I have to do this by hand in the picture itself by assigning appropriate grayscale values?

                       

                      If I find a profile which does set the black and white point, then I assume that this is done lossless when I set the intent to "photographic", but when I set the intent to "colorimetrc", then the shadows and lights are just clipped (which jeopardizes the idea)?

                       

                      I see that the profiles contain a intent. I assume that this embedded intent will be overridden by the colour setting in photoshop?

                       

                      What does the option "blackpoint compensation" (or similiar, I use the German photoshop) do with grayscale images? Does it alter the black point, so I should turn the potion off off when I set it by hand? Is there some documentation what this option *exactly* does?

                       

                      The colour settings in Photoshop offers "dot gain xx%" settings, but I didn't find such profiles. Do I assume correctly that those are "internal" profiles of photohop? Are they documented somewhere?

                       

                      Thanks.

                      • 8. Re: Working space settings for Grayscale?
                        rmphoto Community Member

                        But when it comes to pictures for print, some questions remain.

                         

                        John Smith,

                         

                        I may have missed it, but have you mentioned what sort of printing you are doing?

                        Inkjet?

                        4/C offset?

                        1/C offset?

                        Lightjet?

                        Etc?

                         

                        It would definitely (and helpfully) narrow the scope of the discussion if we knew. (And, I apologize if you already stated it.)

                         

                        Rick

                        • 9. Re: Working space settings for Grayscale?
                          John Smith for example Community Member

                          Reasonable question, Rick. The pictures will be imported into a magazine which will be printed on an offset press and at the same time will be published on a homepage.

                           

                          My background: I was up to date in professional prepress some 15 years ago. I left that business, and now I have to fill that knowledge gap of 15 years in a couple of weeks. Which means that until 2 months ago, all I knew about colour management and ICC profiles was their names. But I did some reading since.

                           

                          My first project will be to deliver grayscale pictures for the abovementioned magazine. Everything is pretty low-end, layouter and print shop included. But as low-end as the whole project is, I want to – and will! – prepare the pictures on a high quality level. So, as ridiculous as it is, I won't be able to ask somebody but rather will be the "guru" myself. So I not only want to but must thoroughly update myself.

                          • 10. Re: Working space settings for Grayscale?
                            c.pfaffenbichler Community Member

                            As regards Black Point Compensation:

                            http://www.color.org/AdobeBPC.pdf

                            But at least for grayscale-to-grayscale-conversions I don’t think it matters.

                            Edit: I haven’t read that document by the way, I just happened upon it some time ago …

                             

                            Other than that I quite frankly don’t fully follow what You are on about – what are You trying to use CMYK-profiles for?

                             

                            Do You work on RGB-files that You then convert to grayscale (as is often advantageous) or are You worried about  grayscale-to-grayscale-conversions?

                            • 11. Re: Working space settings for Grayscale?
                              Mike Ornellas Community Member

                              BPC affects grayscale to grayscale conversions.  You can always load a CMYK profile into the grayscale working space setting. Only the black will be used.

                              • 12. Re: Working space settings for Grayscale?
                                John Smith for example Community Member

                                c.pfaffenbichler wrote:

                                 

                                As regards Black Point Compensation:

                                 

                                Thanks. Finally a paper which explains what Adobe's black point compensation does.

                                c.pfaffenbichler wrote:

                                 

                                Other than that I quite frankly don’t fully follow what You are on about

                                 

                                I'm on about understanding. Why can't you just answer my questions, they are clear enough.

                                • 13. Re: Working space settings for Grayscale?
                                  p_d_f Community Member

                                  "I assume that it's possible to embed the black and white point into the profile, so that I don't have to worry about them anymore but can assign the full range of gray values from 0% to 100%. With the colour sync tool, I looked into the grayscale profiles that come with Photoshop, and as far as I can tell, none of them does set the black and white point. So I assume that despite using colour management, I have to do this by hand in the picture itself by assigning appropriate grayscale values?"

                                   

                                  The profiles neither embed nor set black point or white point information. If you use a profile for conversion from one color space to another, they will map the pixel value from one space to a visually equivalent pixel value of another - even from one grayscale space to another. For instance, an eighty-seven percent black in one grayscale might map to a ninety-two on a different device, and still give a very similar visual appearance. Yes, you still need to set the endpoints where you want them.

                                   

                                  "If I find a profile which does set the black and white point, then I assume that this is done lossless when I set the intent to "photographic", but when I set the intent to "colorimetrc", then the shadows and lights are just clipped (which jeopardizes the idea)?"

                                   

                                  Not quite sure what you're referring to as "lossless". Whenever you convert from one space to another, even different grayscale spaces, there are bound to be changes in pixel value. Don't know about "photographic" rendering intent, but if you're referring to Perceptual, which is often mistakenly taken to be meant for photographic images only, I can't think of a reason you would want to use that for grayscale, as there is no gamut compression that is needed in such a conversion. A relative colorimetric conversion between two grayscale profiles should not clip any tones, light or dark. If you're seeing that then there is something else going on.

                                   

                                  "I see that the profiles contain a intent. I assume that this embedded intent will be overridden by the colour setting in photoshop?"

                                   

                                  Yes, the default always seems to be Perceptual, but it really doesn't mean anything as you're virtually always going to override that and pick whatever is the best for your image - usually Relative Colorimetric and for some very colorful images, Perceptual.

                                   

                                  "What does the option "blackpoint compensation" (or similiar, I use the German photoshop) do with grayscale images? Does it alter the black point, so I should turn the potion off off when I set it by hand? Is there some documentation what this option *exactly* does?"

                                   

                                  BPC maps the darkest printable area of the source profile to the darkest printable equivalent of the destination. It can alter the black point, and you *might* want to override that manually at times, depending on the image and how it's being printed. This ICC stuff works pretty well most of the time, but you still have to watch and see what it does and intervene when necessary.

                                   

                                  "The colour settings in Photoshop offers "dot gain xx%" settings, but I didn't find such profiles. Do I assume correctly that those are "internal" profiles of photohop? Are they documented somewhere?"

                                   

                                  Those setting are sort of a profile on the fly. You can always set your color settings to different dot gain amounts and then save that setting as a grayscale profile. Those dot gain grayscale profiles are fine for many applications, but they just assume a single midtone dot gain with the dot gain in the rest of the tonal range adhering to the same basic curve. A grayscale profile derived from actual measured data will be far more accurate across the entire tonal range, taking into account any inconsistencies in tonal response. For instance, if you are printing grayscale to a magazine printed to SWOP standards in the U.S. you'll be better off using a GS profile derived from the SWOPv2 CMYK profile, both for viewing and for actual printing.

                                  • 14. Re: Working space settings for Grayscale?
                                    c.pfaffenbichler Community Member

                                    I stand corrected.

                                    • 15. Re: Working space settings for Grayscale?
                                      John Smith for example Community Member

                                      Thank you very much, PDF.

                                       

                                      I think I've understood enough now to be able to set up a reasonable and reliable environment which fits my needs. I guess that if I want to dig even deeper, I'll have to read the full technical specifications of the ICC profiles as a starter, but I guess I'll postpone this to 2010.