7 Replies Latest reply on Jul 2, 2014 10:56 AM by areohbee

    Good resource for understanding custom camera profiles?

    alanterra Level 1

      Hi

       

      I thought I understood custom profiles, but it turns out that I don't understand them completely, and I'd love to know of a resource that discusses them in respect to Adobe's products (Lightroom + Photoshop). The best resource I've seen is the now old book "Photoshop Color Correction" by Michael Kieran which discusses how to apply incorrect (synthetic) color profiles to achieve remarkable results.

       

      My basic question is how do custom profiles interact with white balance? The two questions that lead to this are:

       

      1) I have been careful to try to create my custom profiles (using a ColorChecker Passport) in the light that I am using for a photo. Under forest canopy if I'm photographing under a forest canopy, with flashes if I'm photographing with flashes, etc. I then set the white balance using a gray patch in the ColorChecker image, and apply that white balance to all the photos taken in that light. What I don't understand is why I should have to set the white balance, because that should already be in the custom profile—I mean the profile should map a bunch of absolute colors to a bunch of numbers, and set up a robust transformation to achieve this. Why is the white balance left unresolved in this process? And what does it mean to use a different white balance—for instance to use a custom profile that I photographed in morning sun and then try to use it for a flash image? Does that give me any more accurate colors than the Adobe Standard profile?

       

      2) I, through a bunch of, in retrospect, stupid decisions, managed to create a completely inappropriate profile and apply it to some images. When I applied it, the color did seem to improve, and I thought I had made the photos more accurate. I later noticed that I had left these images with white balance "As Shot", and what was happening was that the white balance was correcting itself to an extreme value (6500° +50) in order to compensate for the inappropriate profile. If I locked down the white balance, then I could see that the color profile was inappropriate.

       

      So, my simple questions are: if changing the profile changes the "As Shot" white balance, then does using a custom color profile actually improve color accuracy compared to Adobe Standard + "As Shot" white balance? And, if I create a custom profile for a camera under light of say 4500° +5 (morning sun) and then I apply that profile to an image taken under a flash and set the white balance appropriately (using a patch of white in the slide) to, say, 6500° +10, will that give me more accurate color than just using the Adobe Standard profile?

       

      And, more generally, is there a good discussion somewhere of how camera profiles actually, in practice, combine with the white balance to achieve the color displayed?

        • 1. Re: Good resource for understanding custom camera profiles?
          thedigitaldog MVP & Adobe Community Professional

          WB and the camera profiles are completely separate and agnostic from each other. This might help:

           

           

          In this 30 minute video, we’ll look into the creation and use of DNG camera profiles in three raw converters. The video covers:

           

          What are DNG camera profiles, how do they differ from ICC camera profiles.

          Misconceptions about DNG camera profiles.

          Just when, and why do you need to build custom DNG camera profiles?

          How to build custom DNG camera profiles using the X-rite Passport software.

          The role of various illuminants on camera sensors and DNG camera profiles.

          Dual Illuminant DNG camera profiles.

          Examples of usage of DNG camera profiles in Lightroom, ACR, and Iridient Developer.

           

          Low Rez (YouTube):

          http://youtu.be/_fikTm8XIt4

           

          High Rez (download):

          http://www.digitaldog.net/files/DNG%20Camera%20profile%20video.mov

          • 2. Re: Good resource for understanding custom camera profiles?
            alanterra Level 1

            I tip my hat to you, Sir Andrew.

            • 3. Re: Good resource for understanding custom camera profiles?
              alanterra Level 1

              Hi Andrew. I did look at this video, but unfortunately it really doesn't explain how camera profiles work, but only demonstrates how to use them. (Please, this is not a criticism—it is a very good video about how to use camera profiles and other features about digital workflows).

               

              In particular, I noticed something that I wouldn't have if I hadn't had the experience I described above. When you show that changing the profile makes little or no change to an image (choosing among camera profiles taken at different times of day) you have Lightroom set up with White Balance "As Shot". As you choose among the various camera profiles, we can't see what is happening to the White Balance chosen by Lightroom.

               

              My experience is, like yours, that camera profiles made at different times of day usually have little or no effect on the colors. But what I found, that I didn't know before, is that camera profiles that are significantly "wrong" for the illuminant can also have little effect on the colors because Lightroom adjusts the white balance to try to keep whites white. How Lightroom does this is totally unclear to me. But to say that a camera profile has little or no effect without locking down the white balance can be misleading in some cases (perhaps not the cases you show, but I can't tell for sure).

               

              I think I understand how profiling works for output devices, and I have read descriptions about how an image, which only consists of RGB triplets, is mapped to real-world colors, and the trade-offs in the various ways of mapping these colors.

               

              What I don't understand is how white balance and a camera profile work together to map RGB triplets to color, and why you can't create an "absolute" camera profile, which would specify that each triplet of RGB values always maps to a specific color (just as an image profile does). While camera profiles are absolutely magical in how they take into account white balance, I want to understand how this magic works.

               

              For what it is worth, my workflow when I can completely control the lighting is as follows:

               

              a) Create a camera profile for that situation

              b) Decide on a white balance for that situation. I usually pull it off a gray patch on the Colorchecker Passport, but sometimes I go for a different white balance.

              c) Process all the images with that profile and white balance

               

              I'm pretty sure that this works, so my questions above are more for insight than to improve my workflow.

               

              Thanks for any insight you can give.

               

              Alan

              • 4. Re: Good resource for understanding custom camera profiles?
                thedigitaldog MVP & Adobe Community Professional

                Each custom profile will create a different WB value for As Shot. So the numbers reported for temp/tint As Shot depends on the contents of the profile. If the profile changes, so will the reported numbers. The numbers don't change if you choose one of the WB presets such as Daylight, Shade, etc because those presets are setting a specific Temp and Tint value (e.g., 5500/10 for Daylight), and then using the profile to translate those temp/tint numbers into the actual WB color changes to the image.  The resulting numbers seen depend on what is selected as well as the profile.

                • 5. Re: Good resource for understanding custom camera profiles?
                  alanterra Level 1

                  Hi Andrew.

                   

                  To be honest, this is why I am looking for an in-depth discussion of this issue. I am confused what you mean by "each custom profile will create a different value for 'As Shot'". So, if I take a profile that is taken at high noon, it is presumably somewhere around 5500° +10. Then if I apply it to a scene taken under incandescent, say 3600° +0, then some magic happens that maps the colors. But what I also find is that if I set Lightroom to White Balance 'As Shot', then the values chosen for 'As Shot' will vary according to the camera profile used. So, while it might show 5500° +10 for one profile, it can show a different value for another profile, for the 'As Shot' color temperature. This is a different sort of magic, which I didn't expect at all. It has the effect of keeping grays neutral, so minimizing the effect of the color profile (which may be the most intelligent thing it can do).

                   

                  In any event, there are at least three sorts of magic going on here: 1) mapping colors taken under one lighting to another lighting (ie, white balance, per se, independent of camera profile), 2) mapping reference colors taken under one lighting to reference colors taken under a different lighting (applying a camera profile to a different illumination), and 3) mapping the auto white balance when the camera profile is changed (which Lightroom does, but I don't know if it is a common feature of other programs).

                   

                  FWIW, your video does a nice job of addressing how to take into account the magic in (2) above. You state (simplifying greatly) that if the color is 'not too different', for instance taken at a different time of day, then you can use the a profile made under a different illumination, but if the color is 'quite different', eg, taken under fluorescent lights, then you do need to set a new camera profile. I don't think you are addressing metamerism here, but are saying simply that color profiles have a space of utility that encompasses some but not all lighting situations, and then give some rules of thumb about when to make a new profile. What you don't address is why this is true or how it is implemented.

                   

                  Thanks for the discussion.

                  • 6. Re: Good resource for understanding custom camera profiles?
                    thedigitaldog MVP & Adobe Community Professional

                    If we both build a custom DNG profile for our two cameras and shoot the same scene, the 'as shot' values may be different as the profiles are different. No matter, you have full control over using that value or another or by altering tint/temp. Produce the WB appearance you desire.

                    • 7. Re: Good resource for understanding custom camera profiles?
                      areohbee Level 5

                      alanterra,

                       

                      Custom camera profiles may define temperature/tint biases.

                       

                      In other words, you can define a camera profile with a warm bias, but temperature will still be settable in Lightroom, granted it won't go as cool as (and will go warmer than) a profile without a warm bias.

                       

                      Likewise, you can define a camera profile with a red bias - tint will still be settable in Lightroom, but it won't go as green as a profile with a non-red bias (and will go redder).

                       

                      etc.