I think that a DNG file is not loading properly when I use a certain lens (Summicron 35mm). The colour of the image always has a magenta cast. The embedded jpg, however, does not have this colour interference. Attached is an example, in the screenshot I think I have the magenta cast in the histogram squiggled in yellow. How do I get rid of the yellow magenta cast? I tried it with the module “colour zones”, but without success. I use the latest Linux git version of darktable.
There are some sites on the Web where people complain about
magenta casts in some Leica lenses… and the reply seems to boil
down to “It is a coded lens and the camera menu is set to Automatic
lens detection”. Hopefully you will know more about this than I do…
I opened your image and saw the same histogram that you saw. Then I created a duplicate and started from scratch. I see that your white balance is set to 6502 K - I just used the “as shot” value of 4637 K. Then, I increased the overall saturation slightly (in the color_zones module with a single point, moved up by about 20%) and adjusted the tone_curve as can be seen in the screen capture. The result has much warmer colors in the grass. L1002878_01.DNG.xmp (8.8 KB)
The histogram looks fine to me esp with just wb as shot and not adding any modules which of course moves it around …also in the vectorscope I didn’t see a major issue…but we all see these things differently… personally I like a warmer version which is what you get if you just take a wb on the whole image… I realize its biased by all the blue but I like the result and out of the gate I don’t see any issues wrt yellow magenta… but again could be me
Nothing to hate just a cooler version… when I see the blue of the sky bleeding into the white clouds as it often can I find warming things up will take then to white and then a bit further can often add some character… in this case that is sort of where a full image spot wb led me to go and so I did. I liked the outcome but I am sure its nails on the chalkboard for someone
Upon opening the image I saw no major problem. I opened the image with legacy WB set to as shot. There was a hint of magenta (maybe?) so I went to rgb curves and increased the green curve a little to tweak the color.
Does your camera give a RAW file option rather than DNG? Was the DNG produced by the camera? What brand of camera is it? Not sure if any of these answers will prove helpful, but maybe.
Thank you all to solve finally the riddle of the magenta cast with the Summicron 35mm. The trick is to change the WB to “as shot” as you described and, as a result of that, the image looks really different. As soon as I change a value in the legacy WB I get an error in module color calibration. The best result I can get is when I change the “adaption” to none (bypass) and the error disappears. At the end this is editing to personal taste. L1002878.DNG.xmp (13.8 KB)
Basically each of these actions with the autopickers in the 4 way tab will pick from the default mask or the mask as you edit it in the mask tab a hue that is 180 degrees in the selected tonal range so for example in highlights it will determine that hue and add enough chroma/sat to cancel that… Often I find just doing highlights can help to deal with subtle image casts… you can also select a roi on the image as the area to sample for highlights… Then you can go further and you have the same operations for shadows and midtones should you wish to experiment… You can use them in the reverse way as well and use them to enhance a particular color in those zones. To do that select a region and add 180 to the hue that is determined and then dial in the chroma slider and you will get enhancement rather than a correction…
At the end this is editing to personal taste.