Has anyone used a totally over-exposed shot as a custom white balance in this camera, please?
Until today I’d not heard of UniWB, I saw it in the Diagonal Interpolation thread. I plan to try it, as it apparently makes exposing to the right, ETTR, easier. I wondered if anyone had experience of doing this, especially with a 6D (“mark one”), and in particular, whether the “total over exposure” method gives white balance factors close to 1.
Good references to UniWB:
@RawConvert I mention this all of the time: if you aren’t aware of Magic Lantern, check it out. It has a bunch of tools that can assist you with ETTR, and other powerful features. It may not support the latest Canon DSLRs but it supports your 6D.
Hey Andrew thought I’d contribute my 2 nickels. I first heard of UniWB through Luijk and for a couple or so years I “tested” it and thus all that came out my D700 (nikon) were very very sick still images. I don’t remotely have the knowledge to intelligently argument on my findings… but I’ll mention a couple interesting “side-effects”.
First thing is that I regained a bit the post’s magic. Images were always green so I just checked for composition and histogram/meter/blown/cold symptoms; avoiding to get caught in the colour zone {spooky black}. Was later on the computer that the darkroom like feelings of anticipation and surprise broke free as green metamorphosed into myriad hues.
A shock at the beginning is incredible how fast one gets used to… well, almost anything, like these horns. The fact that the images were more homogeneous and had less information helped the culling in particular and the dreaming in general.
There was also a bit of fun when showing the pictures to someone, OMG is all green, what happened?!!! to which I’d respond OMG!! is true we’re totally doomed. Clients’ faces were a priceless treat.
Now, for the question you’re probably after does it make a difference? my answer is yes… and no. In my experience it does make a difference regarding metering/accuracy >> ETTR. So I would say that if slightly but certainly impacted IQ. Why did you stop using it then? could be a follow-up {wouldn’t you agree? =)} because (suddenly I turned into an old 500-pound rheumatic gorilla that thinks the zoo is the world) in the long run & grand scheme of things the improvements I got from using UniWB were almost negligible compared to context-specific needs, mix media (video) incompatibilities, post facilities and speed delivery (some jobs were on_da_spot jpeg only!) and that sort of contraints and conditions, the same that would later make me dump nikon FF for µFT.
There I said it, now a cat, well an UniWB papperdigits’ kitten to be precise. Cheers 
After your post, I shot a white screen of my desktop (overexposed, out of focus) and used the corresponding raw file to set the CustomWB on my 6D. Although the camera warned me about not getting my colors right with this setting, it allowed me to set it up. Now I am also getting all green JPG’s out of my camera. Yay!
However, I am unable to run dcraw on my win10 64. I am uploading the custom white balance raw file and a raw file shot with this custom white balance. If anyone can check the multipliers, I will be much obliged!!
First the custom RAW
IMG_3134.CR2 (14.0 MB)
And now Dendrobium Jury Red orchids shot with this WB:
IMG_3156.CR2 (26.4 MB)
hi @shreedhar, I’m also on green screens!
I’ve put your img 3156 thru’ DCRAW -
dcraw -v -w -q 3 -T -4 IMG_3156-shreedhar.CR2
Loading Canon EOS 6D image from IMG_3156-shreedhar.CR2 …
Scaling with darkness 2048, saturation 15490, and
multipliers 1.000000 1.000000 1.000000 1.000000
AHD interpolation…
Converting to sRGB colorspace…
Writing data to IMG_3156-shreedhar.tiff …
I also put a CR2 of mine taken with my custom white balance raw and that gave virtually identical output -
dcraw -v -w -q 3 -T -4 IMG_7644.CR2
Loading Canon EOS 6D image from IMG_7644.CR2 …
Scaling with darkness 2047, saturation 15490, and
multipliers 1.000000 1.000000 1.000000 1.000000
AHD interpolation…
Converting to sRGB colorspace…
Writing data to IMG_7644.tiff …
So perfect multipliers I believe. Is this too good to be true? From the little I’ve read I thought they’d just be approx. unity.
And thanks @chroma_ghost, interesting comments and the wider perspective on things. I do feel a bit awkward sometimes pouring over processing and tech details when I could be out and about seeking good photos.
And also thanks for the info @afre. I’m aware of magic lantern but have so far put it to one side, partly because I’m a bit scared of messing with the camera, but more because it’s yet another layer of tech to have to get into.
Thanks Andrew! Now, we have one more toy to play around when we get bored with the usual!!!
It is really great to see the colours emerging out of the green cocoon as @chroma_ghost said.
Cheers.
PS: Do we have to keep this raw file in the camera to use it again? Or does the camera has it in its default memory.
You could delete it and see what happens!
Of course! as I had guessed, the camera has stored the data for Custom WB separately. So it does not matter if the original is present or not.