15 Replies Latest reply on Apr 12, 2014 2:16 AM by D Fosse

    why don't color values change when using proof colors?

    juandent@mac.com Level 1

      Hi,

       

      i am very interested in obtaining exact replicas of the image in screen (in ProPhoto) and the image printed (using a suitable printer profile). However when I select Proof Colors from the view menu, the appearance changes but the RGBV or Lab colors remain the same. This is counter intuitive and goes against the well known recomendation to do color correcting using numbers instead of your eyes.

       

       

      What's happening? Is there a way to accomplish what I want?

       

       

      Thanks,

      Juan

        • 1. Re: why don't color values change when using proof colors?
          G.Hoffmann Level 3

          Short answer:

          RGB-->CMYK soft proofing does not change RGB-numbers, but appearance.

          Lab -->CMYK soft proofing does not change Lab-numbers, but appearance.

          CMYK-numbers are newly generated.

           

          Long answer:
          In soft proofing we have always a Source Profile (SP) and a Destination Profile (DP).

           

          1) SP and DP belong to the same class, for instance both RGB or both CMYK.

          a) Preserve Numbers: this is equivalent to Assign Profile. Appearance changes.

          b) Don't Preserve Numbers: this is equivalent to Convert to Profile.

               Appearance changes if SP colors are out-of-gamut in DP.

           

          2) SP and DP belong to different classes, for instance SP=RGB, DP=CMYK.

          This is equivalent to Convert to Profile. 

          Preserve Numbers is not explicitly available.

          SP numbers are preserved, DP numbers are newly generated.

          a) Absolute Colorimetric:

              Appearance changes if SP colors are out-of-gamut in DP. These are clipped.

          b) Relative Colorimetric:

              Appearance changes if SP colors are out-of-gamut in DP.

              Appearance changes for RGB-->CMYK a little with Black-point-compensation (BPC).

              Appearance changes for RGB-->CMYK a little, because RGB-white appears as paper

              white in CMYK.

          c) Perceptual:

              Appearance changes globally if any SP color is out-of-gamut in DP.

              Appearance changes for RGB-->CMYK generally, because BPC is applied implicitly.

              Appearance changes for RGB-->CMYK a little, because RGB-white appears as paper

              white in CMYK.

           

          Your work flow may be 2b): Offset printing RGB-->CMYK with RelCol and BPC.

          Dark black becomes brighter, RGB-white becomes paper white and out-of-gamut colors

          are mapped to printable colors at the CMYK gamut boundary.

           

          Best regards --Gernot Hoffmann

          • 2. Re: why don't color values change when using proof colors?
            juandent@mac.com Level 1

            Hi Gernot,

             

            Yes, thanks for this detailed explanation of how proofing works. However I believe my main question has not been answered, I may have expressed myself in an unclear manner.

             

            Let me try to be very exact:

             

            I have a i1Pro spectrocolorimeter. Say I have a pixel in my image whose coordinates are in ProPhoto RGB, (45, 20, 60). I then print to my 7900 EPSON printer. I take my i1Pro and measure the Lab values of the given pixel, and the corresponding RGB values. The printer pixel now has different RGB values as well as Lab. Say RGB(55,10,34). I now need to change the pixel values in the source image so that the values of the printed pixel will coincide with the original pixel values in photoshop. The printer profile knows (must know) what value conversion it is going to make, and if I had a way to find this value then I could be very precise in adjusting the source pixel values and obtain printed values in complete accordance with the original.

             

            Is this clear?

             

            Thanks,

            Juan

            • 3. Re: why don't color values change when using proof colors?
              D Fosse Adobe Community Professional & MVP

              Not quite sure what you want, but the info panel can be set up to read out proof values.

              • 4. Re: why don't color values change when using proof colors?
                juandent@mac.com Level 1

                I think this might get there. Will try and let you know!

                 

                Thank you so much!!

                 

                Juan

                • 5. Re: why don't color values change when using proof colors?
                  G.Hoffmann Level 3

                  Juan,

                   

                  are you treating your Epson printer as an RGB device (instead of CMYK)? In this case you'll

                  have two different RGB values, which can be shown by Info Panel: Actual Color and Proof Color.

                  I can simulate this only for the case of two different work spaces, like sRGB-->ProPhoto, with

                  Preserve Numbers unchecked (disabled).

                   

                  Proofing requires a source profile and a destination profile. If your simulated colors (proof colors)

                  are generally very wrong, then your destination profile is wrong. A further explanation of your

                  work flow might help us here.

                   

                  Best regards --Gernot Hoffmann

                  • 6. Re: why don't color values change when using proof colors?
                    juandent@mac.com Level 1

                    Ok, I will explain my workflow. I start in Lightroom and edit in Photoshop. There I Choose View->Proof Setup and select the profile for my printer and also select BPC, Simulate Paper Color, Relative Colorimetric. Then I select one particular point (with shift+eye droper tool), and use RGB for the first Info colors and Lab for the second. Now, first question: is Lab maintained as I move from one RGB space to another (from ProPhoto to EPSON 7900 printer with luster paper)?

                    I believe it is maintained. However, the Actual colors are not the same as the Proof colors. I can understand this because the primaries of the EPSON printer are different than ProPhoto (is this correct?). However, Lab remaining constant across RGB colorspaces seems very unintuitive because the color produce at the selected point as printed is often slightly different than the color in monitor .... therefore I would presume that Lab values would change accordingly (since a Lab value is associated with EXACTLY one color - right??).

                     

                    What am I looking for? I look for a numerical value in the destination profile so I can compare with the numeric value in the source profile and from here have a numerical way of making the two colors match --- in other words doing proofing but numerically, not with my eyes only...

                     

                    Am I clear?

                     


                    Thanks again,

                    Juan

                    • 7. Re: why don't color values change when using proof colors?
                      juandent@mac.com Level 1

                      Also, I forgot, I use my spectrocolorimeter to meaure the selected point in the printed image, from which I get a Lab value. This Lab value is usually different from the photoshop's value for the same point. This numerical values are what I would like to use as an objetive way to produce as identical as possible a print from an image.

                       

                      Is there a way in Photoshop to obtain this final Lab value? I mean, Proof values are available for RGB but not for Lab values (as if the printed color would remain the same as the original color)...

                       

                      Again thanks,

                      Juan

                      • 8. Re: why don't color values change when using proof colors?
                        D Fosse Adobe Community Professional & MVP

                        I believe you are chasing a couple of red herrings and making this more complicated than it has to be.

                         

                        First of all, "simulate paper color" is something you should deal with in calibration, not by using this very coarse tool. You calibrate your display to a white point that is a visual match to paper white, both in luminance and temperature. Then you don't need to simulate, and have more direct control. Your calibration targets should be determined by what gives you a screen to print match.

                         

                        The same goes for black point/contrast. You can calibrate to a contrast range that matches the paper. And if your calibrator / display supports it, you can have several calibration targets for different papers.

                         

                        Lab values are constant, as far as it goes. The whole basis of color management is the "profile connection space", which is either Lab or CIE XYZ. This is the reference upon which all conversions are based.

                         

                        But when you get near the gamut boundaries, Lab is no longer constant because the color itself is changed by clipping in the target space. A Lab readout will stop at the gamut bondary in the target space, but still continue in the source space. So they'll be different.

                         

                        All in all I get the feeling that your calibration isn't optimal, not giving you the match from screen to print that you need. I would start there.

                        1 person found this helpful
                        • 9. Re: why don't color values change when using proof colors?
                          juandent@mac.com Level 1

                          Hi,

                           

                          How can I "calibrate" my monitor fora each paper? Id this something done by making a profile? I have i1Profiler and i1Pro. How can I use these to calibrate?

                           

                          What targets should I use?

                           

                           

                          thank you!!

                           

                          Juan

                          • 10. Re: why don't color values change when using proof colors?
                            D Fosse Adobe Community Professional & MVP

                            I have i1 Profiler but it's not installed at the moment (using another calibrator) - but in any case it has the normal options for white point luminance and temperature. Depending on your viewing environment and ambient lighting, you need to find the values that give you the visual equivalent of paper white on screen.

                             

                            Normal defaults are 120 cd/m² luminance, and 6500K temperature. But these may not work for you, so you have to experiment a little. My settings happen to be 110 and 6300K.

                             

                            IIRC i1 profiler also lets you specify a contrast range. Few good papers exceed 300:1, some are closer to 200:1. Some experimenting is necessary here as well. But it is usually not necessary to calibrate to that low contrast; you can often compromise at, say, 400:1.

                            • 11. Re: why don't color values change when using proof colors?
                              G.Hoffmann Level 3

                              Juan,

                               

                              please let me tell you my opinion, based on working with i1Pro, ProfileMaker and a couple

                              of printers and monitors:

                               

                              a) one doesn't calibrate a monitor for a better match of monitor view and print result.

                              The monitor has to be calibrated for preferred settings, here for 100cd/m² and 6500K.

                              In my case, calibrated in an almost dark room in order to avoid any flare, the minimal

                              luminance is about 0.3cd/m², which results in a contrast of about 300. With some ambient

                              light the actual contrast is probably not as large.

                               

                              b) one doesnt calibrate a printer with respect to a monitor. The printer is calibrated by

                              printing a target and measuring this, followed by profile generation. As a result, a printer

                              can print color patches with certain Lab values with a measurable accuracy, without any

                              reference to a monitor. By the way: calibration takes the paper color into account, there-

                              for one needs for each paper a new profile (as well for different printing modes or diffferent

                              black inks and so on).

                               

                              What is to do?

                               

                              You have already i1 Profiler. Each version can profile monitors, but you need a version

                              which can profile printers as well. In this German doc means Drucker=printer:

                               

                              http://www.pdfmarkt.de/index_de,marktcm,15,528,,49.php

                               

                              It looks as you have a version which can calibrate printers in RGB mode (perhaps i1 Basic Pro2 ).

                               

                              Then follow the procedures in these docs, mainly the third:

                               

                              http://www.northlight-images.co.uk/reviews/profiling/i1_profiler_overview.html

                              http://www.northlight-images.co.uk/reviews/profiling/i1_profiler_monitor.html

                              http://www.northlight-images.co.uk/reviews/profiling/i1_profiler_rgb_print.html

                               

                              What means RGB mode? Epson printers, for instance my model 7890, can be calibrated in

                              RGB mode or in CMYK mode. Of course. the printer prints finally by CMYK inks, but the

                              targets are defined either by RGB values or by CMYK values.

                               

                              RGB mode is preferred by photographers (RGB images), CMYK mode accepts as well CMYK

                              data as generated in PostScript workflows and is used for proofing offset-print-ready PDFs.

                               

                              An example: technical graphics may contain one or two inks in order to avoid registration

                              errors. Sending these data to an 'RGB-printer' would result in printing by all inks.

                               

                              I'm calibrating in CMYK mode. The profile interpretation by Profile Inspector shows CMYK

                              as device space. Available profiles by others (for common papers) show RGB as device space.

                              Profile connection space is in either case CIELab.

                               

                              How are the viewing conditions?

                              Probably not by viewing monitor and print side by side. The monitor has 6500K, prints are

                              to be inspected under 5000K. Thus, a simultaneous adaptation is impossible.

                              Also, it would be wrong, because the rendering is mostly not Absolute Colorimetric.

                               

                              For the critical inspection of prints the illuminance should be very bright, 2000lx (lux),

                              according to ISO.  100cd/m² is roughly equivalent to 300lx (3-hundred).

                              As a result, one cannot expect a match, but an impression: looks right on the monitor, looks

                              right on the print. And an offset printing press can be adjusted by matching a proof print.

                               

                              Best regards --Gernot Hoffmann

                              • 12. Re: why don't color values change when using proof colors?
                                D Fosse Adobe Community Professional & MVP

                                G.Hoffmann wrote:

                                 

                                one doesn't calibrate a monitor for a better match of monitor view and print result.

                                Maybe I'm misinterpreting what you're saying here, but most people would disagree with that. I certainly would. I don't print much, I work mostly for offset print. But it's essential that what I see on screen is a predictable preview of what the finished result will be, so I would say, yes, you set your calibration targets to match printed output. If 6200K gives a better match than 6500K, then that's what you use.

                                 

                                http://www.luminous-landscape.com/tutorials/why_are_my_prints_too_dark.shtml

                                • 13. Re: why don't color values change when using proof colors?
                                  D Fosse Adobe Community Professional & MVP

                                  Just to clarify a bit. I think it’s important to take a pragmatical approach to this. Setting calibration targets, and particularly the white point, is the part of the bigger color matching picture that is and has to be subjective, simply because lighting and viewing conditions can not be standardized. Or rather  - you could standardize it but nobody would see your work in that standardized lighting anyway. So it wouldn’t have any practical relevance.

                                   

                                  Again it’s important to separate calibration from the monitor profile. The color management chain itself is objective and neutral. 255/255/255 in the file remaps to 255/255/255 in the monitor profile. The question here is determining what that white is. In a way, setting the white point is about defining the environment for color management to work in.

                                   

                                  Comparing a print next to your display is probably futile. You’ll never see an exact match between an emissive screen and a reflective print. So you have to rely on your “visual memory”. But that can be pretty reliable.

                                   

                                  Everybody has a visual perception of paper white, and the difference between a white paper with optical brighteners, and a yellowish uncoated one. And everybody has a visual perception of neutral light. That doesn’t have to be 5000K – direct sunlight is 5000K and that has always appeared warm and yellowish to me. In my head neutral light is a lightly overcast day, probably closer to 7000K or 8000K. So somewhere between 6000 and 6500 will get you in the neighborhood of “paper white”. The same principles apply to luminance target. You need to rely on your visual memory to be able to “see” paper white on screen. There’s no way to standardize luminance because your perception is so heavily influenced by the ambient light.

                                   

                                  The next consideration is contrast. The native black point in most modern displays will give you a contrast range (a white:black luminance ratio) of up to 1000:1. But a finished print is almost never above 300:1 with good glossy papers, usually around 250:1 and for matte papers often down to 150:1 or lower. So what you see on screen is misleading, unless you compensate by calibrating to a higher than native black point. Then, again, document black remaps to monitor black and you get a match, as far as it goes.

                                   

                                  But from here on in, the display profile handles the rest and what you see on screen is the reference. Neutral colors are neutral relative to the wite point (have the same chromaticity).

                                  • 14. Re: why don't color values change when using proof colors?
                                    G.Hoffmann Level 3

                                    Twenty_one,

                                     

                                    I don't think that we disagree generally. Also we know both how to handle this stuff.

                                     

                                    But I wanted to give Juan some guidelines, instead of the principle 'anything goes'.

                                    For instance, in my opinion one needs a light box for a repeatable comparison of

                                    print results (instead of waiting for the right weather). We have some ISO standards

                                    and following them isn't bad.

                                     

                                    As well I had given some advice how to use i1-profiler.

                                     

                                    The only phrase I would like to change is this one:

                                    Not

                                    one doesn't calibrate a monitor for a better match of monitor view and print result

                                    but

                                    one doesn't calibrate a monitor with respect to printed images

                                     

                                    For Juan: devices are calibrated with respect to a profile connection space, which

                                    is Lab for printers and large monitor profiles and CIE XYZ for small monitor profiles.

                                     

                                    For a calibrated device, numbers in the device space have a physical meaning in

                                    the profile connection space.

                                     

                                    Best regards --Gernot Hoffmann

                                     


                                    • 15. Re: why don't color values change when using proof colors?
                                      D Fosse Adobe Community Professional & MVP

                                      G.Hoffmann wrote:

                                       

                                      I don't think that we disagree generally.


                                      No, I didn't think so either

                                       

                                      This tends to change a bit depending on what viewpoint you choose to look at it from. I just felt there was the possibility of some misunderstanding.