17 Replies Latest reply: May 28, 2009 2:59 PM by Chris Cox RSS

    discussing the definition of "gamut mapping"

    Christian Davideck Community Member

      This thread is solely intended to discuss the definition of "gamut mapping", and whether or not the conversion from the working color space to the monitor color space includes gamut mapping.

       

      So far we had different opinions here:

      Christian Davideck wrote:

       

      Photoshop talks to the OS to know what the active monitor profile is and then Photoshop does the following gamut mapping:

      [working color space => monitor color space].

       

      Chris Cox wrote:

       

      That's not a gamut mapping, just a profile conversion - in this case a color conversion correcting for the display.

      Gamut mapping is something much more essoteric, done when building a profile, or by hand when preparing a document for output.

        • 1. Re: discussing the definition of "gamut mapping"
          Christian Davideck Community Member

          “An ICC profile provides data for the LUT loader program, which is run at startup; it also provides information for the gamut mapping between the working color space and the monitor color space.”

          http://www.normankoren.com/makingfineprints1A.html

           

           

          Gamut mapping enables original colors to ‘fit’ inside differently shaped color gamuts”

          Ján Morovič in the book “Color Gamut Mapping” (2008), ISBN: 978-0-470-03032-5

           

           

          “Images in non-ICM aware programs are assumed to have the sRGB color space. No gamut mapping takes place when they are sent (through the LUT) to the monitor.“

          http://www.normankoren.com/color_management_2A.html

           

           

          “By default, ICC Version 4 profile operate exactly the same as the ICC V2 profile in regard to gamut mapping. A slight adjustment was made to the permitted tag contents, to allow things like Display profiles to contain the full range of AtoB and BtoA tables, so that they could also be gamut mapped.“
          http://www.argyllcms.com/doc/iccgamutmapping.html

           

          „The heart of color management is the translation or gamut mapping between devices with different color gamuts and files with different color spaces.”

          http://www.normankoren.com/color_management.html

           

           

          Gamut mapping: The transformation that takes place when an image is transferred between formats or devices, for example, from one color space to another.”

          http://www.normankoren.com/color_management.html

          • 2. Re: discussing the definition of "gamut mapping"
            Hudechrome-sd9sPI Community Member

            Gamut Mapping

            From ColorWiki

            "The redistribution of color values from an input device (e.g. color scanner or printer) to fit the smaller or larger gamut of the output device.

            If the input gamut is larger than the output gamut, gamut mapping is the same as Gamut Compression. If the input gamut is smaller than the output gamut, colors and contrast can be intensified through Gamut Expansion, or colors can be mapped to their exact equivalents, e.g. for digital proofing."

             

            I really don't have the expertise to argue this difference. However, imo, Chris has an edge here. That's not to say he gets everything perfectly, but any discussion about things like color theory and it's applications needs to be conducted in a forum which includes of knowledgeable people.

             

            I hope they join

            • 3. Re: discussing the definition of "gamut mapping"
              Christian Davideck Community Member

              D Fosse wrote:

               

              And you still insist on calling profile conversion "gamut mapping". It's not.

               

              Look, before Photoshop sends the pixels' RGB values to the graphics card, it does a gamut mapping from the working color space to the monitor color space, ironically for precisely the reaons you mentioned (for arguing it wouldn't happen, LOL ) :

               

              D Fosse wrote:

              Gamut mapping is fitting [...] colors into a smaller space that otherwise wouldn't accomodate them (resulting in clipping), or vice versa.

               

              Or do you want to suggest that working color space and monitor color space are exactly identical in volume and shape ?? Because this would mean, that you have chosen your monitor color space as your working color space, which is definitely NOT recommended!

              • 4. Re: discussing the definition of "gamut mapping"
                Chris Cox Adobe Employee

                No, Photoshop does a color conversion from the DOCUMENT space (not working space necessarily) to the display colorspace(s). In 90% of cases when going to the display there will be no gamut mapping - just a simple matrix-TRC conversion.

                 

                Gamut Mapping is something you do when building a more complex profile - like a printer/press profile, or a table based display profile with soft-proofing baked in, or a device link profile.   Gamut mapping is the math behind the scenes that defines the conversion parameters based on some constraint optimization system.  There are many, many different ways of doing gamut mapping.

                 

                A conversion uses the pre-defined parameters and just churns through the math.

                • 5. Re: discussing the definition of "gamut mapping"
                  Chris Cox Adobe Employee

                  An analogy:   You buy a car and drive it - the parameters are already established.   You don't buy a car and then design and build it.  Yes, someone designed it and built it, but that was long before you got the car.

                  • 6. Re: discussing the definition of "gamut mapping"
                    Christian Davideck Community Member

                    Chris Cox wrote:

                     

                    ... from the DOCUMENT space (not working space necessarily) to the display colorspace(s).

                     

                    On that point you are right of course. Documents don't necessarily have to be in the working color space obviously.

                    • 7. Re: discussing the definition of "gamut mapping"
                      Christian Davideck Community Member

                      Chris Cox wrote:

                       

                      No, ...


                      Chris, so (apart from the distinction between working color space and document color space) you are basically saying that Norman Koren is wrong in his terminology ?

                       

                      “An ICC profile provides data for the LUT loader program, which is run at startup; it also provides information for the gamut mapping between the working color space and the monitor color space.”

                      http://www.normankoren.com/makingfineprints1A.html

                      • 8. Re: discussing the definition of "gamut mapping"
                        Chris Cox Adobe Employee

                        Technically, Norman has it close to right.   But it is misleading.   When applying a profile:  the gamut mapping has already been done, and is baked into the profile.  I would not have phrased it that way, because I can see how it would lead to misunderstandings.

                         

                        The analogy would be "I'm now driving John's well designed car" - you're using the defined parameters, but John did the creative design of those parameters.

                        • 9. Re: discussing the definition of "gamut mapping"
                          Christian Davideck Community Member

                          Chris Cox wrote:

                          Technically, Norman has it close to right.

                           

                          Good to hear that, because I did say the same as him.

                           

                           

                          I see the difference, that you are trying to point out. I just don't find the example a good one.

                           

                          Try this comparison: Chris Cox translates a book from English (=document color space) to Russian (=monitor color space). It doesn't matter that Chris Cox has not invented the Russian language. He is still translating into Russian.

                           

                          See ... examples are easy and can be conviently invented for both sides of the argument. So I'd find it more useful to talk about it in practical terms.

                          Getting therefore back to color spaces:

                           

                          You have a source color space A (i.e. the document color space). And you have a destination color space B (i.e. the monitor color space as defined by the monitor profile). Color space A has a certain color gamut. Color space B has a certain color gamut, too. Somehow you have to translate - i.e. you have to map - the colors in color gamut A to the color gamut B. Hence the term gamut mapping.

                          • 10. Re: discussing the definition of "gamut mapping"
                            Chris Cox Adobe Employee

                            No, you're still not getting it.

                             

                            There are many papers and books on gamut mapping - they all apply to building a profile.

                            When you use a profile to make a conversion, you are applying the gamut mapping that was done ahead of time - but you are not doing a gamut mapping at that time.

                             

                            In your analogy, the gamut mapping would have been done when Chris learned Russian, not when translating the book.

                             

                             

                            Boot Note - there have been attempts to produce a color management system that did the gamut mapping during the conversion, sometimes even data specific mappings. But to date they have been very clumsy, obtuse, and incredibly slow.  A few more limited attempts were also made (just black mapping), but met with limited market success.

                            • 11. Re: discussing the definition of "gamut mapping"
                              Christian Davideck Community Member

                              Chris Cox wrote:

                               

                              you are applying the gamut mapping that was done ahead of time - but you are not doing a gamut mapping at that time.

                               

                              Excuse-me, but if you say you APPLY gammut mapping but you don't DO it, that's really hairsplitting.

                               

                              Chris Cox wrote:

                               

                              ... attempts to produce a color management system that did the gamut mapping during the conversion         


                              What would be the advantage of that, if it can be done - like you said - ahead in time anyway ?

                              • 12. Re: discussing the definition of "gamut mapping"
                                Jeff Schewe Community Member

                                Christian Davideck wrote:

                                 

                                This thread is solely intended to discuss the definition of "gamut mapping"

                                 

                                LOL. . .no, this thread is an attempt to try to prove Chris wrong (which is actually a very foolish activity).

                                 

                                As Chris has tried to tell you, the gamut mapping is done when making the profile not when doing a color space transform. The only control you have over the gamut handling when doing a color space transform is the rendering intent and for simply RGB color space transforms you're locked into Relative Colorimetric when doing a documents space to display space profile (unless the profiles are ICC v4 profiles).

                                 

                                Norm is a pretty smart guy but I would put my money on Chris in a debate such as this...really, it's foolish to try to prove Chris wrong unless you enjoy self-flagellation...

                                 

                                :~)

                                 

                                P.S. On the other hand, I've sometimes been able to prove him wrong about photographic type things :~)

                                • 13. Re: discussing the definition of "gamut mapping"
                                  Chris Cox Adobe Employee

                                  "Excuse-me, but if you say you APPLY gammut mapping but you don't DO it, that's really hairsplitting"

                                   

                                  No.  Just as driving a car versus designing and building a car are very different activities.  One produces a car to use, the other uses a premade car.  But both involve the same car.

                                   

                                   

                                  "What would be the advantage of that, if it can be done - like you said - ahead in time anyway ?"

                                   

                                  There is some limited benefit to doing image/data specific mappings - this has been shown in published research.  There may be some benefit to choosing different mappings as you go - but that's a user interface issue, and just complicates the process.  But even experimenting with the concepts has been painfully slow.  (the best gamut mapping algorithms take on the order of several minutes to run)

                                  • 14. Re: discussing the definition of "gamut mapping"
                                    Chris Cox Adobe Employee

                                    "P.S. On the other hand, I've sometimes been able to prove him wrong about photographic type things :~)"

                                     

                                    True, that.

                                    • 15. Re: discussing the definition of "gamut mapping"
                                      Christian Davideck Community Member

                                      Jeff Schewe wrote:

                                      LOL. . .no, this thread is an attempt to try to prove Chris wrong (which is actually a very foolish activity).

                                       

                                      Foolish ... LOL, yes ... but I'm trying my best

                                       

                                      Jeff Schewe wrote:

                                      As Chris has tried to tell you, the gamut mapping is done when making the profile not when doing a color space transform.

                                       

                                      That's easy to say, now that Chris had said it already, don't you think ?

                                      Besides, you are wrong. Chris said a gamut mapping is applied when doing the color space conversion. (see above)

                                       

                                      Jeff Schewe wrote:

                                       

                                      The only control you have over the gamut handling when doing a color space transform is the rendering intent and for simply RGB color space transforms you're locked into Relative Colorimetric when doing a documents space to display space profile (unless the profiles are ICC v4 profiles).

                                       

                                      Okay, then let's say I have ICC v4 profiles. How can I choose the rendering intent for the conversion "documents space to display space profile" ?

                                       

                                       

                                       

                                      Norm is a pretty smart guy but I would put my money on Chris

                                       

                                      See. Both are certainly smart guys. If they disagree, it's certainly not a shame to settle for either one definition ... untill I find additional information which might change my opnion about it.

                                       

                                       

                                      ...really, it's foolish to try to prove Chris wrong unless you enjoy self-flagellation... :~)

                                       

                                       

                                      I'm not afraid of loosing, LOL It won't do any harm to my self-confidence

                                       

                                      P.S. On the other hand, I've sometimes been able to prove him wrong about photographic type things :~)

                                       

                                      see

                                      • 16. Re: discussing the definition of "gamut mapping"
                                        Christian Davideck Community Member

                                        Chris Cox wrote:

                                         

                                        "Excuse-me, but if you say you APPLY gammut mapping but you don't DO it, that's really hairsplitting" No.

                                         

                                        So you are arguing there is a difference between APPLY and DO, right ? See, we aren't even talking about gamut mapping here anymore!

                                         

                                        By the way, I actually don't mind if I'm supposed to call it "apply gamut mapping" or "do gammut mapping". My point is, that gamut mapping takes place. That's the only thing I ever argued. I never said, that the parameters of the algorithms would be established in real-time or whatsoever ...

                                         

                                        Chris Cox wrote:

                                         

                                        There is some limited benefit to doing image/data specific mappings - this has been shown in published research.  There may be some benefit to choosing different mappings as you go - but that's a user interface issue, and just complicates the process.  But even experimenting with the concepts has been painfully slow.  (the best gamut mapping algorithms take on the order of several minutes to run)

                                        thanks for the insight.

                                        • 17. Re: discussing the definition of "gamut mapping"
                                          Chris Cox Adobe Employee

                                          "Besides, you are wrong. Chris said a gamut mapping is applied when doing the color space conversion. (see above)"

                                           

                                          You are claiming that you design the car by driving the car.  I'm trying to explain to you that the design comes first, before you even buy the car.   When you drive the car you are using the design, not performing the design.