14 Replies Latest reply on Jul 1, 2017 2:10 AM by Samoreen

    Contrast slider vs. Tone Curve

    Samoreen Level 2

      Hi,

       

      I can adjust the contrast of an image either by using the contrast slider or by using the Tone Curve tool (or both). However, I never got clear explanations about how both tools interact. I can see that using the contrast slider doesn't modify the tone curve. So what data are referenced by the contrast slider when computing the contrast ? The original data or the data modified by the tone curve ? Reversely, does the tone curve tool act on the original data or on the data modified by the contrast slider ? Are these tools applied in a given order ? Always the same ?

       

      Thanks in advance.

        • 1. Re: Contrast slider vs. Tone Curve
          Samoreen Level 2

          Up.

           

          I have asked many experts and posted this question in various forums but nobody seems to be able to answer this (silly ?) question. Or am I unclear ?

          • 2. Re: Contrast slider vs. Tone Curve
            john beardsworth Adobe Community Professional & MVP

            Maybe you just haven't understood their answers?

             

            As far as I know there is no interaction between them - applying both has cumulative impact.

            • 3. Re: Contrast slider vs. Tone Curve
              Samoreen Level 2

              https://forums.adobe.com/people/john+beardsworth  wrote

               

              Maybe you just haven't understood their answers?

               

              Never got one. I have no problem understanding any explanation about how LR works, provided an explanation is given.

               

              By chance I eventually found an excerpt of Martin Evening's LR 5 book that says :

               

              "Basically, the two are interlinked. ... when you go to the Tone Curve panel [...], the adjustments you apply here are applied relative to the contrast adjustment that's already been applied in the Basic panel".

               

              So this would explain why adjusting the Contrast slider in the Basic panel has no effect on the tone curve itself although the base data used by the Tone Curve tool are changed : the Tone Curve tool doesn't use the original image data but the data already modified by the Contrast slider. It acts as a profile applied to the tone data resulting from the changes made in the Basic panel. I guess this is the same when using the Contrast slider after the Tone Curve tool.

               

              This seems to be logical. If someone at Adobe could confirm... In which case, it would be interesting to be able to display a curve showing the cumulative effect of both tools in order to see the actual "profile" applied to the original data (could be an option in the Tone Curve panel).

              • 4. Re: Contrast slider vs. Tone Curve
                john beardsworth Adobe Community Professional & MVP

                Martin might say "interlinked" and my word is "cumulative'. The Tone Curve and the Contrast slider both work on the base data. Think of the expression x times y times z - the sequence of y and z doesn't make any difference.

                • 5. Re: Contrast slider vs. Tone Curve
                  Conrad C Adobe Community Professional & MVP

                  Samoreen  wrote

                   

                  it would be interesting to be able to display a curve showing the cumulative effect of both tools in order to see the actual "profile" applied to the original data (could be an option in the Tone Curve panel).

                  Instead of looking for a curve that would show the effect of Contrast + Tone Curve (but not any other adjustments?), one way to see the effects right now would be to look at the histogram. Use the History panel to compare three history states: Before applying Contrast or Tone Curve, after applying one, and after applying both. Click each history state while you watch the histogram to see the effects of the edits on the tonal distribution of the image.

                  • 6. Re: Contrast slider vs. Tone Curve
                    Samoreen Level 2

                    https://forums.adobe.com/people/Conrad+C  wrote

                     

                    Instead of looking for a curve that would show the effect of Contrast + Tone Curve (but not any other adjustments?), one way to see the effects right now would be to look at the histogram.

                     

                    Thanks Conrad. However, this is not exactly the same thing. Looking at the histogram or at the image itself show me the result of applying the "profile" computed from the Tone Curve and Contrast slider settings. I'm interested in seeing the combining profile itself.

                    • 7. Re: Contrast slider vs. Tone Curve
                      Samoreen Level 2

                      https://forums.adobe.com/people/john+beardsworth  wrote

                       

                      Martin might say "interlinked" and my word is "cumulative'. The Tone Curve and the Contrast slider both work on the base data. Think of the expression x times y times z - the sequence of y and z doesn't make any difference.

                      Let's assume that the Tone Curve tool is set in such a way that for the input value of 80, the output value should be say, 85. That's an increase of 5. Now, let's assume that I move the Contrast slider to the right. A new output value will be computed for the input value of 80. Say, 83 (I don't know exactly how big the increase will be since, contrary to the Tone Curve tool, the Contrast slider doesn't give any indication about what it is doing. So we have an increase of 3.

                       

                      You tell me that both additions will apply to the base data. That is, the input value of 80 will become 88. What Martin Evening is saying is that the Tone Curve profile applies to the data already modified by the Contrast slider. So the addition made by the Tone Curve tool will not be the one computed for the input value of 80 but the one computed for the input value of 83, which will certainly be different.

                       

                      I'm not sure that I'll be able to setup a test in order to determine which algorithm is the correct one. Maybe using a calibration target. Is it worth it ? Not sure. I'm just curious about how LR contrast tools work. Obviously, opinions vary about that. Only the developer can tell...

                      • 8. Re: Contrast slider vs. Tone Curve
                        john beardsworth Adobe Community Professional & MVP

                        Don't you think you're reading too much into Martin's use of "relative"? One can equally say when you go to the Basic panel [...], the adjustments you apply here are applied relative to the contrast adjustment that's already been applied in the Tone Curve panel .

                        • 9. Re: Contrast slider vs. Tone Curve
                          Samoreen Level 2

                          https://forums.adobe.com/people/john+beardsworth  wrote

                           

                          Don't you think you're reading too much into Martin's use of "relative"? One can equally say when you go to the Basic panel [...], the adjustments you apply here are applied relative to the contrast adjustment that's already been applied in the Tone Curve panel .

                          Only the Adobe development team knows. However, I always thought that the displayed preview was the result of applying the current settings to the base data always in the same order (this is why using the various development settings in a given order is not that important - although the suggested top-down order is rather logical). In that case, Martin's statement makes more sense.

                          • 10. Re: Contrast slider vs. Tone Curve
                            Samoreen Level 2

                            I got in touch with Martin and here is his answer :

                             

                            The way to look at this is that the Basic panel adjustments are applied first in the Camera Raw pipeline. Therefore, it makes most sense to do all the 'heavy lifting' in the Basic panel, where you can use the Contrast slider to add or reduce the global contrast. I have always been told that happens in the Tone Curve is further along in the Camera Raw pipeline and contrast adjustments applied here are cumulative to those applied in Basic. There is essentially an interlinked relationship between Basic and Tone Curve, but the order does matter.

                             

                            Because you can use either to have a cumulative contrast adjustment effect. It is best however to start with the main Contrast slider in Basic to apply first. That way you gain more precision to make refined Tone Curve adjustments using the Tone Curve panel. Doing it in reverse can work, but it is a bit like using the tail to wag the dog.

                            • 11. Re: Contrast slider vs. Tone Curve
                              joefry99 Adobe Community Professional

                              "I always thought that the displayed preview was the result of applying the current settings to the base data always in the same order (this is why using the various development settings in a given order is not that important - although the suggested top-down order is rather logical)."

                               

                              " but the order does matter."

                               

                              That can't be right. Consider that if that were true, one could create two different appearances from identical images with same settings but different based solely on applied slider order!

                               

                              I think the key here is to understand that Adobe has placed the slider/workflow in the order that best leads you to good settings quickly/easily. That is, the earlier sliders do more heavy lifting to get you in the ballpark correctly and things "narrow" as you go. Often after setting tone curve I return to basic settings to "tidy up" and find that if I move anything a hair, it's worse. Props to Adobe there.

                               

                              Having said all that... I'm one who's struggled to get the contrast I want in the shadows or highlights, wishing for blinking guiding lights to help me balance the best combination of two different sliders...

                               

                               

                              • 12. Re: Contrast slider vs. Tone Curve
                                Samoreen Level 2

                                joefry99  wrote

                                 

                                " but the order does matter."

                                 

                                That can't be right. Consider that if that were true, one could create two different appearances from identical images with same settings but different based solely on applied slider order!

                                 

                                Misunderstanding. This is not what Martin means. The LR engine always handles settings in the same order but the result would be different if the Tone Curve tool settings were applied before the Contrast slider setting. Of course, the order in which the user sets these settings has no impact on the result.

                                • 13. Re: Contrast slider vs. Tone Curve
                                  richardplondon Level 4

                                  You can find out for yourself, what the logical order (dependency) of the various kinds of adjustments is.

                                   

                                  Analogy: say that one operator will double, and another will halve, a two-digit number - but that any figure that would calculate above 99, gets "clipped" down to that limit; all these numbers must be two-digit (highlight clipping).

                                   

                                  So feeding in two starting values 58 and 60 - if your doubling adjustment comes first, these both now become 99. When your second adjustment halves those numbers, they both become 50... and whatever other factor you may apply, still cannot reveal again which one was originally the larger - that damage is done, unless you can reduce the power of that front-end adjustment. 

                                   

                                  OTOH if your halving adjustment comes first, then 58 becomes 29 and 60 becomes 30, for now. Then your doubling adjustment puts them back to 58 and 60 respectively, without incident. So different results are possible, purely due to the innate order of operations - BTW things work somewhat the same but in reverse, for low values (shadow crushing).

                                   

                                  Start with neutral adjustments for both Basic and Tone Curve. Use Tone Curve to brighten the image so completely, that parts of the image become featureless white. Then try to negate that using the Basic panel, and see how well LR recovers the original detail in these brighter areas. The same settings applied in some different working sequence, will still deliver the identical result of course.

                                   

                                  Then begin again and try things the other way around: this time use Basic adjustments to brighten the image excessively, then try to negate that with a darkening Tone Curve.

                                   

                                  This experiment leads to the clear conclusion, that Tone Curve has to work with whatever is the result of Basic adjustments.

                                   

                                  However this does not mean that Basic adjustments are always first. Trying the above approach with Basic vs Local adjustments, it becomes clear that Locals happen first, and then Basic adjustments get to work on whatever is the result of having used those.

                                  • 14. Re: Contrast slider vs. Tone Curve
                                    Samoreen Level 2

                                    Thanks Richard for taking the time to make this interesting test.