White balance was set to unity to make the live histogram useful
OK you lost me here, would you please explain?
Mirrorless cameras (Fuji X series) provide the option to view a histogram for the scene live before the photo is taken. This can be a big assist in fine-tuning the exposure. The problem with all such live histograms is that they are drawn from the data generated by the camera JPEG processor and so do not accurately reflect the sensor exposure.
These are two different exposures:
1. Sensor exposure = raw file.
2. Camera generated JPEG.
Or to phrase that differently; an ideal exposure for one will not be ideal for the other.
Depending on the engineering of the specific camera the difference between the two is slight to as much as a full stop or slightly more. The camera's on-board meter is adjusted to produce #2. above.
WARNING: Definitely heading into nerd territory here where it's legitimate to ask the question; really? Does it matter? I'm retired and have nothing better to do with my time than to refine my exposure to hair-splitting tolerances -- arguably a waste of time and more so with every passing year as camera sensors get better and cover over any need for increased precision.
So I have this option with my camera to check a live histogram before clicking the shutter and so determine if I'm clipping highlights -- nice feature, but that info is for the camera generated JPEG and not accurate for the raw file which is all I care about. How can the histogram be made more accurate for the raw file? Unity WB. Here's a good reference:
What is UniWB? | byThom | Thom Hogan
So when I unboxed my X-T2 four weeks ago the first thing I did was set it to save raw only. The next thing I did was turn off pattern/matrix/evaluative metering. And the next thing I did was start testing the metering system and working to nail down exposure. For me exposure means only one thing: a full sensor exposure for the raw file. My only exposure goal is to place diffuse highlights as close to the sensor threshold as possible. That goal makes the live histogram that much more attractive and so I set my custom WB to unity so the live histogram would be giving me better info.
This is not a methodology for anyone shooting "in business" or anyone who so much as glances at the camera JPEGs expecting to get an idea of what their photo looks like. My camera generated JPEGs are all green and overexposed -- see above, but the raw file that JPEG represents is a perfect exposure.
Joe