23 Replies Latest reply on May 24, 2016 1:47 PM by Rufus2015

    Setting Tone curve for correct CCP grey scale luminance values

    Rufus2015 Level 1

      Hi,

       

      Is there an easier way to set the tone curve for correct Colorchecker passport grey scale luminance values?

      I have only just discovered that this is the key to accurate colour reproduction when I am reproducing art work.

      It seems a bit pot luck trying to get all the grey patches to have the correct luminance, I am hoping there is a easier more accurate way to do this than fiddling with the slider until they are correct.

       

      Any assistance would be much appreciated.

        • 1. Re: Setting Tone curve for correct CCP grey scale luminance values
          Jao vdL Adobe Community Professional & MVP

          Have you tried creating a dng profile from a shot of your color checker using dng profile editor and using that in Lightroom?

           

          Instructions here: http://www.adobe.com/content/dam/Adobe/en/products/photoshop/pdfs/cs6/DNGProfile_EditorDoc umentation.pdf

           

          download here:

          Adobe - DNG Profile Editor : For Macintosh

          Adobe - DNG Profile Editor : For Windows

          • 2. Re: Setting Tone curve for correct CCP grey scale luminance values
            trshaner Adobe Community Professional & MVP

            Rufus2015 wrote:

            I have only just discovered that this is the key to accurate colour reproduction when I am reproducing art work.

             

            For "copy work" you'll want to use a camera profile that has lower contrast and color saturation (i.e. Faithful). If you're shooting with a Canon or Nikon DSLR use the 'Camera Faithful' profile or the equivalent "camera" profile for your camera. The Camera Faithful profile uses a Tone Curve and Color Saturation that provides very accurate rendering for copy work.

             

            You can also create a custom camera profile using your CCPP with the Adobe DNG Profile Editor as suggested by . Choose 'Camera Faithful' for the Base Profile, which will allow creating a "calibrated" CCPP profile more suitable for copy work. Here's a link to the documentation: http://www.adobe.com/content/dam/Adobe/en/products/photoshop/pdfs/cs6/DNGProfile_EditorDoc umentation.pdf

            • 3. Re: Setting Tone curve for correct CCP grey scale luminance values
              Rufus2015 Level 1

              Hi Jaovdl and trshanner,

               

              I have used th DNG profiler, but I was never satisfied with the colours, until I corrected the tone curve.

              I will follow the links and see if I can do better.

               

              thanks to both of you.

              • 4. Re: Setting Tone curve for correct CCP grey scale luminance values
                Rufus2015 Level 1

                Is 'Camera Neutral' the same as 'Camera Faithful' ?

                If not, where do I find a 'Camera Faithful' profile for my Nikon D7100?

                • 5. Re: Setting Tone curve for correct CCP grey scale luminance values
                  Jao vdL Adobe Community Professional & MVP

                  Camera Faithful is what's its called in Canons. Neutral is for Nikon. They are meant to mimic the shooting styles in the camera if you shoot jpegs. Unfortunately dng profile editor doesn't use the grey patches to calibrate the tone curve but you can calibrate the tone curve in profile editor in the tone curve tab. Click on the grey patches in the color checker and you should get new points on the tone curve that you can move up or down or use the numeric values. I believe the values are in a sRGB gamma corrected space but that is not very clear from the interface.

                  • 6. Re: Setting Tone curve for correct CCP grey scale luminance values
                    trshaner Adobe Community Professional & MVP

                    Rufus2015 wrote:

                     

                    Is 'Camera Neutral' the same as 'Camera Faithful' ?

                    If not, where do I find a 'Camera Faithful' profile for my Nikon D7100?

                    Sorry, the Nikon D7100 does not have a Camera Faithful profile. Camera Neutral has the same Tone Curve as Camera Faithful, but slightly higher color saturation (at least for the Canon profiles). It's still a better choice than the CCPP plugin profile or Adobe Standard for copy work. You can lower the Saturation sliders in DPE about -10, which appears equivalent to Camera Faithful.

                     

                    With the lower contrast Tone curve of Camera Neutral the grayscale patches should be close to correct. At least they are using the Canon Faithful or Neutral camera profiles.

                    • 7. Re: Setting Tone curve for correct CCP grey scale luminance values
                      D Fosse Adobe Community Professional & MVP

                      Rufus2015 wrote:

                       

                      I have only just discovered that this is the key to accurate colour reproduction when I am reproducing art work.

                      This is a large part of my job description, and I quickly discovered that there is no such thing as "accurate" in this field. With some experience you can get "equivalent", and that's as good as it gets. It will be accepted as accurate by anyone.

                       

                      But you will never get a perfect colorimetric match. Even if you did, it would fall apart because it wouldn't be internally consistent, and thus not credible.

                       

                      Lighting plays a large part. If you use cross-polarizing, you'll end up with "wrong" contrast because diffused lighting reduces contrast by stray light. Which one is "real"? You don't know and there really is no answer.

                       

                      I use a color checker in all shots, and then I set 93% for the white patch, 48% for the #4 gray, and between 10 and 15% for the black. Actually the Lab value dictates 22%, but that always looks extremely washed out. You need to compensate for the paper/ink black point in printing.

                       

                      And then I start tweaking, to end up with a credible equivalent.

                      • 8. Re: Setting Tone curve for correct CCP grey scale luminance values
                        Rufus2015 Level 1

                        Hi D Fosse,

                         

                        When I said accurate I meant equivalent.

                        I appreciate that colour is a minefield of complexity.

                        I am trying to find the most efficient method, rather than re-inventing the wheel with every picture.

                        I need a good solid base to work from.

                        I had created a Lightroom preset, with the tone curve adjusted to align all the grey patches to their measured values.

                        This worked far better than I had hoped, but the prints looked slightly flat, although a good colour match.

                        The problem is that if I try to lift the image slightly a lot of the subtle colours get lost, and the image goes muddy.

                        I will try producing another preset with slightly darker black patch.

                         

                        I have also realized that my printer profile does not take into account the paper luminance on white areas, and will add grey if the white in the picture is the luminance of the paper, eg 95.

                        • 9. Re: Setting Tone curve for correct CCP grey scale luminance values
                          trshaner Adobe Community Professional & MVP

                          Rufus2015 wrote:

                           

                          I had created a Lightroom preset, with the tone curve adjusted to align all the grey patches to their measured values.

                          This worked far better than I had hoped, but the prints looked slightly flat, although a good colour match.

                          The problem is that if I try to lift the image slightly a lot of the subtle colours get lost, and the image goes muddy.

                          You'll get more consistent results by adjusting the tone curve in the camera profile. It is applied to the image before all of the other controls in the Develop module. Camera Faithful or Neutral will do that for you. If the image appears a little flat you can correct that with less impact to subtle colors using LR's Contrast, Blacks and Whites controls. It gives you a better starting point. I do transparency film capture using a DSLR camera and the Camera Faithful profile produces the most "accurate" and pleasing results. CCPP camera profiles created with the X-Rite plugin or software do not work well at all for copy work.

                          • 10. Re: Setting Tone curve for correct CCP grey scale luminance values
                            Rufus2015 Level 1

                            I spent all last night making camera profiles, but the tone curve didn't seem to be included in the profile.

                            I could not see how you are  supposed to check the changes you make to the profile, as the eye dropper tool only shows the values from the original DNG not the adjusted one.

                            Am I missing something?

                            • 11. Re: Setting Tone curve for correct CCP grey scale luminance values
                              trshaner Adobe Community Professional & MVP

                              Rufus2015 wrote:

                               

                              I spent all last night making camera profiles, but the tone curve didn't seem to be included in the profile.

                              You need to select Camera Neutral as the 'Base Profile.' When creating the DNG CCPP file to be used in DPE set the LR Camera Profile to Camera Neutral and correct the White Balance before Export. The DNG file will open in DPE with that profile and WB settings.

                              I suggest creating a CCPP profile with DPE using the Camera Neutral Base Profile and only the 'Chart' automatic color patch corrections. Do not use the eyedropper tool on the grayscale patches since there is no way to adjust the Exposure Bias to determine correct values. The Tone Curve should be used to "correct" the grayscale tracking. You can create dual-illuminant profiles as well. What type of lighting do you use for your art work reproduction? Did you download and read the DPE PDF?

                               

                              Here's an article that should be helpful: http://petapixel.com/2014/10/01/colorchecker-how-to-get-perfect-skin-colors-with-every-cam era/

                              • 12. Re: Setting Tone curve for correct CCP grey scale luminance values
                                Jao vdL Adobe Community Professional & MVP

                                You're not missing anything. It just doesn't work very well and the

                                interface is not very friendly. First what you do is do the chart tab and

                                create the chart patches. Then in the first tab, you select a neutral base

                                profile (something like camera neutral) and then you edit the tone curve.

                                In the tone curve panel click on the grey patches to create new handles.

                                Move those up and down (or type them). You'll need to do some math to

                                relate the values of the patches relative to each other instead of to the

                                absolute values of the chart except when you happen to have exposed it

                                perfectly. Then export the profile.

                                • 13. Re: Setting Tone curve for correct CCP grey scale luminance values
                                  Rufus2015 Level 1

                                  I use 2 speed lights at the moment, but I have tried various other lights, I decided the 'full spectrum' of flash should work better.

                                  I am in the process of building a 'light box' with a single studio flash that splits the light into 2 low angle 'beams' to eliminate variance when using 2 speed lights.

                                   

                                  The profiles I created using DPE seemed too red in comparison to that created by the X-rite plug-in.

                                  I will read the article you suggest and have another go.

                                  • 14. Re: Setting Tone curve for correct CCP grey scale luminance values
                                    trshaner Adobe Community Professional & MVP

                                    Rufus2015 wrote:

                                    I use 2 speed lights at the moment, but I have tried various other lights, I decided the 'full spectrum' of flash should work better.

                                    A single illuminant (6500K) profile should work fine.

                                     

                                    Rufus2015 wrote:

                                     

                                    The profiles I created using DPE seemed too red in comparison to that created by the X-rite plug-in.

                                    I will read the article you suggest and have another go.

                                    Are you selecting the Base Profile Camera Neutral, moving to the DPE Chart tab, selecting 6500K Only, and then positioning the four color dots to the appropriate color patches?

                                    Here's a CCPP Plugin created profile versus a DPE Profile with Camera Faithful or Neutral Base profile:

                                     

                                    CCPP Plugin vs DPE Camera Faithful Base Profile.jpg

                                    • 15. Re: Setting Tone curve for correct CCP grey scale luminance values
                                      Rufus2015 Level 1

                                      Ah, I probably select both rather than just 6500K.

                                      • 16. Re: Setting Tone curve for correct CCP grey scale luminance values
                                        Rufus2015 Level 1

                                        I case you are interested I have attached 3 screen shots.

                                         

                                        Using CCPP generated Camera Neutral my tone adjustment...no other adjustment...

                                        DNG Tone curve.jpg

                                        Then DNG generated camera neutral with quick tone adjustment...DNG.jpg

                                        Then the same tone adjustment but with CCPP camera neutral as in first image...CCPP.jpg

                                        See how in the DNG camera neutral  image the 'art' paper is red compared to the yellow in the CCPP.

                                        • 17. Re: Setting Tone curve for correct CCP grey scale luminance values
                                          Rufus2015 Level 1

                                          Ooops.

                                           

                                          You will notice that the DNG image is for camera standard, here is the same with camera neutral...DNG Neutral.jpg

                                          • 18. Re: Setting Tone curve for correct CCP grey scale luminance values
                                            trshaner Adobe Community Professional & MVP

                                            Rufus2015 wrote:

                                             

                                            Then the same tone adjustment but with CCPP camera neutral as in first image...CCPP.jpg

                                            See how in the DNG camera neutral image the 'art' paper is red compared to the yellow in the CCPP.

                                            The Basic panel settings -100 Contrast and +100 Blacks may be causing the color shift.  You also may need to set the White Balance in the CCPP for each new profile used. You are using the Basic Tone controls incorrectly. Please see PV2012 control  instructions I posted here for a better understanding on how they should be set: Re: camera calibration profiles: standard vs neutral

                                             

                                            Can you post the above raw file to Dropbox for download?

                                            • 19. Re: Setting Tone curve for correct CCP grey scale luminance values
                                              Rufus2015 Level 1

                                              Here is the same DNG Camera neutral profile but with the tone curve, should have done this first.DNG Tone curve.jpg

                                              here is a link to the raw in One drive:https://onedrive.live.com/redir?resid=6225C942011B0CEB!495&authkey=!AIu_QOUP6KD2o20&ithint =folder%2cdng

                                              • 20. Re: Setting Tone curve for correct CCP grey scale luminance values
                                                trshaner Adobe Community Professional & MVP

                                                I downloaded the DNG file and don't see any issues when using normal Basic panel settings. What I do see is a loss in detail, contrast, and and color saturation when using ANY camera profile. The Nikon 50mm F1.4 is not the best lens for copy work and perhaps something with your lighting may be the cause. I would also suggest using a neutral background whenever possible to prevent reflected light from causing color shifts. The green board is not a good choice for this reason. The color values with my 5D MKII are much closer than your Test 2 DNG to X-Rite's published values using DPE with Camera Neutral Base Profile. Myabe as to what's going on.

                                                 

                                                In the below images only WB and Exposure (+.31 and -.31 EV) were adjusted to get the grayscale patches close to the published values.

                                                (click on image to see full-size)

                                                Nikon 7100 vs Canon 5D MKII - CCPP DPE Camera Faithful Bse Profile.jpg

                                                • 21. Re: Setting Tone curve for correct CCP grey scale luminance values
                                                  Rufus2015 Level 1

                                                  Ok, thanks for your input.

                                                  I shall change the background, maybe a dark neutral grey.

                                                  Any suggestions as to a better lens?

                                                   

                                                  I don't want to sound stupid, but could you explain the +0.31 and -0.31 EV.

                                                  • 22. Re: Setting Tone curve for correct CCP grey scale luminance values
                                                    trshaner Adobe Community Professional & MVP

                                                    Rufus2015 wrote:

                                                     

                                                    Any suggestions as to a better lens?

                                                     

                                                    It depends on the size of the artwork. If photographing smaller art work that requires close focusing a macro lens is a better choice. A focal length of 85mm or more for your APS-C sensor camera (135mm full-frame cameras) will work best. See this PDF for details: http://www.betterlight.com/downloads/conference07_notes/finley_artCopy.pdf

                                                     

                                                    Rufus2015 wrote:

                                                    I don't want to sound stupid, but could you explain the +0.31 and -0.31 EV.

                                                    With your Test 2 DNG I needed to use Exposure +.31 to get the grayscale patches close to the target values (see X-Rite link I provided). My Canon 5D MKII CCPP image file required Exposure -.31 to obtain those values. For "faithful" color rendering both the grayscale Luminance level (L) and Hue (ab) must be correct. You can set LR to display Lab values in the Develop module by right-clicking on the Histogram:

                                                    At the X-Rite link you'll see the Lab values listed, which is what you want to use for measuring the CCPP values. If you aren't familiar with Lab color space values: Lab color space - Wikipedia, the free encyclopedia

                                                     

                                                    Here are the CCPP Lab values to one decimal place as you see them inside LR:

                                                    • 23. Re: Setting Tone curve for correct CCP grey scale luminance values
                                                      Rufus2015 Level 1

                                                      I didn't want to sound stupid, but I was then.

                                                      I use a 105mm macro for the small stuff, the 50mm is used for pictures up to A2, I don't have a huge amount of space for the copying of bigger pictures, hence the 50mm.

                                                      Most of the smaller pictures I copy don't need to be colour matched to the same extent as the bigger pictures, as they are mainly used for Vistaprint postcards, but the larger ones I print for the artists to sell.

                                                       

                                                      I use the Lab colours in Lightroom.

                                                      I have just started to look at Photoshop to if it could assist, and working in Lab colour space looks promising.