EM-5: Confused by Auto White-Balance results

Started Feb 12, 2013 | Discussions thread
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Timur Born
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EM-5: Confused by Auto White-Balance results
Feb 12, 2013

Hey everyone!

I mostly do family snapshots, which means no controlled light and no white-cards around. Since I am shooting RAW I am not really depending on Auto White-Balance, but that doesn't mean I want to manually edit every shot.

And this is where the E-M5 (and other cameras) still leave me confused by their range of white-points being too broad and especially skin-tones being all over the place. Not to mention that the camera and each RAW software give different WB numbers to the same image file even when all are set to "as shot".

Here an examples of where I struggle to understand the differences. Both images were taken within minutes of each other, same target, same light (daylight through a window from the right image side), no indoor lights, no flash.

Reported "as shot" WB by LR4: 3600K

Reported "as shot" WB by LR4: 4150K

I've got several versions (shot within seconds) of both 3600K and the 4100K images in this series. Two possible explanations come to my mind:

1) Maybe some clouds may have hidden/revealed the sun within those 4 minutes time difference?

2) The 3600K images were shot at F1.8 and ISO 1600-2000, the 4100K images were shot at F6.3 and ISO 12800. This shouldn't matter for WB, but maybe it did.

Here another example, where I know the difference, but still struggle to accept that the outcome is so vastly different. Both shots were done within minutes, indoor, with no window/daylight, halogen lights (2900-3000K) coming straight from above, white/grey/black walls, white ceiling.

No flash, reported "as shot" WB by LR4: 2400K (shadow from my arm blocking the ceiling lights)

FL-600R pointed toward ceiling (-1 EV flash comp), reported "as shot" WB by LR4: 5150K

Again there is an ISO difference, ISO 2000 for the non-flash version, ISO 200 for the flash version. But again I wouldn't expect that to make much of a difference, at least not such a big one as seen here.

While I know that the second image is "mixed" light in that it mixes the flash with the halogen ceiling light my understanding of "Auto" WB is that it should get roughly the same results when presented with the same color targets. Obviously the skin and everything else looks vastly different here.

Since I had to push exposure by 2 stops in LR4 for the second shot I can only speculate that the flash was too weak while the camera expected it to fill in stronger versus the halogen light. Still I would expect "Auto" WB to measure the light, not just turn to 5000K once a flash is fired. Especially since there is a dedicated "Flash" WB setting, too.

Any hints and explanations welcome!

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