3 Replies Latest reply on Dec 1, 2008 1:45 PM by MadManChan2000

    DNG Editor and absolute linear files

      For some time, I've wanted to be able to produce linear files using ACR that could be used as input to an HDR workflow. I'm able to do that using dcraw, but have never been able to get it right with ACR. I thought that setting the base profile to linear in DNG editor would do the trick, but even with that (and setting the ACR tone curve to linear, and all the adjustments to 0), the output files are not linear. I've been testing that by using a set of bracketted exposures, running them through the workflow and then comparing the resulting values (after correcting for the 2.2 gamma from storing the result in 16-bit AdobeRGB files). If they are linear, then there that brackets should be strictly scaled independent of the levels, but there is always some curves where it should be straight. It turns out that using the Adobe Standard profile gives something closer to linear than using DNG converter and setting a linear tone curve, but still not perfect. dcraw does give results that pass this scaling test.

      Anybody have any idea as to how to get linear data files from ACR?

      Brent
        • 1. Re: DNG Editor and absolute linear files
          MadManChan2000 Adobe Employee
          Use DNG PE to build a profile whose base curve is Linear (do not add any custom curve points to the curve pane). Export the profile.

          In Camera Raw, use the default settings, then set Blacks to 0 (instead of 5).

          The result is linear.

          (Your issue from your description is that you're setting Linear in DNG PE and then also setting linear in point curve in CR. That's not correct.)

          As you say, the final result saved/opened from CR will be gamma-encoded but that is easy to undo.
          • 2. Re: DNG Editor and absolute linear files
            Level 1
            OK, so you're saying that if you use a linear base curve in DNG PE, then selecting the "medium contrast" point contrast curve (the default) in ACR will result in a linear output file? So, the "medium contrast" is really passing through the unmodified base tone curve whereas "linear" is really lower contrast than the base curve?

            I just tried this and it does indeed seem to work correctly with some slight deviation near the extremes, but that may be due to how dcRaw vs. ACR does the demosaicing.

            Brent
            • 3. Re: DNG Editor and absolute linear files
              MadManChan2000 Adobe Employee
              Yes, Brent. CR/LR's controls are setup so that, at default values (with the exception of Blacks, mentioned above), they will give you exactly what the profile describes.