following quick read… don’t get too tangled up with magenta things… as I recall Canon DSLRs will take an over exposed image of say a white sheet of paper as the custom W.B. reference image. Then when you shoot and check the multipliers, they are near perfect as I recall.
I found I had to “calibrate” by checking the clipping (using RT’s raw histogram) and comparing with the camera histogram. I decided I wanted the limit to be inside of the far right of the cam hist. So my cam jpeg settings are minimum contrast and saturation. Then clipping starts about half way through the rightmost of the 5 divisions in the cam hist for my 5D.
I’m not sure if I get all of those UniWB/ETTR concept right however I’ve abandoned the pursuit for the UniWB for the following reason:
I don’t want to clip highlights but my camera operates on JPGs not RAW (most digital cameras do). Thus exposure, histogram and highlight clipping alert are all derived from processed image not raw data.
My way of thinking is that I want as linear image as possible (Neutral, Natural, Mild… whatever your camera jpg style is) with reduced contrast, saturation, sharpness and so on (in my camera I have Natural image scene with all set to -5). Then I will want set WB. Having that I have, as I assume, approximation of RAW which will appear in Darktable. My tests confirms that more or less. The best approximation is with ColorChecker which mach exactly (highlights clipping). Other scenes are more then less accurate. Definitely not that I have 2EV headroom but rather 0.3. Worst case is when I need to adjust WB in Darktable. Then from initial correct image (no clippings) I go to clipped image.
My concern is that I have UniWB set on camera and set exposure accordingly then at least in Darktable I run into trouble. White Balance opens the pipeline and if I apply multiplies on channel values for right WB then I may go to far. Next in the pipeline is highlight recovery which will clip my channel(s). A few modules later exposure kicks in but it’s too late. Or it isn’t?
Is my way of thinking correct?
From this point on, it’s like a normal image development, and if you did ettr, you’ll will have to tame the highlights with more care, as you’ve described.
I see your point. Of course you’re correct. Thank you for illustrating the process.
My interest in UniWB came after reading Photographers: stop clipping your highlights post here. However my flow is that I rather set WB first (I carry ColorChecker Passport in my bag) and then try to avoid highlight clipping. During my experiments and tests it occurred to me that what I need is actually flat jpg lacking contrast and punch. I used to use portrait mode in my Lumix camera but it is heavily processed image and in the end RAW image was always underexposed. After switching to natural mode and decreasing every possible setting I’m quite fine and results are predictable. I also set zebra pattern (highlight warning in live view) to 105%.
Problems occur when:
a) I change WP in DT
b) I still did not figure out whether switch on/off vignette correction in camera. After applying lens correction I can still have some blown highlight (pana 20mm f/1.7 vignette is like 2EV when wide open). However I do like vignette and quite often I do not correct it.
Thus I assume that UniWB will be my last step in this journey. I need to solve other problems prior that.
