0 Replies Latest reply on Apr 28, 2012 5:51 PM by Alan in LA

    DNG Profile Editor can't read ColorChecker shot on slide film

    Alan in LA

      I use my DSLR (Olympus E-5, 50mm macro) to digitize old Kodachrome and Ektachrome slides.  As it happens, I have reference shots of a Macbeth Color Checker I shot back then.  I thought I would be able to create custom DNG profiles to get accurate digital conversions of the slides.  But when I shoot the slide of the color checker, convert to DNG and try to build a profile in the DNG Profile Editor, I get an error when I hit the Create Color Table button, specifically, "Non-neutral grey patches.  The gray patch in row 4, column3, has a significant color cast.  Please reshoot the chart carefully to avoid color casts and try again."  I've had the same problem with Kodachrome 64, and Ektachrome 200.

      If I shoot a ColorChecker directly using the same illumination (I've tried both strobe and incandescent for the slides, neither works) the profile is generated OK.

       

      BTW, the RGB values for neutral color checker patches on the short of  the slide (strobe illumination) when I open it in the profile editor are

      White  123, 127, 92

      LLG  91, 94, 78

      LG  61,60,60

      DG  27,26,31

      DDG  7, 6, 9

      Black 0, 0 ,0

       

      I tried reshooting the slide gelling the strobe with 30Y, so I got 89,89,88 for what I think is row 4 column 3, but I got the same error message.

       

      So you can see that there is not a consistent color shift across the brightness range (skews from -B at the light end to +B at the dark end, while R and B are relatively constant)

       

      OTOH, the values for the Color Checker shot straight with the camera are consistent in the color shift across the brightness range:

       

      White 104, 104, 107

      LLG  71, 70, 75

      LG  46, 45, 48

      DG  24, 23, 26

      DDG  10, 10, 11

      Black 2, 2, 2

       

       

      Any way to get around this or am I just screwed. 

       

      Thanks