EM-5: Confused by Auto White-Balance results

Started Feb 12, 2013 | Discussions thread
micksh6
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Re: EM-5: Confused by Auto White-Balance results
In reply to Timur Born, Feb 12, 2013

Timur Born wrote:

micksh6 wrote:

There can't be pure daylight indoors, unless all objects inside completely lack colors. Part of the light is always reflected.

Of course, what I meant to say is that there was only one light-source, which was non artificial and thus full spectrum.

My point was that light reflected from colorful walls, drapery, etc. may affect WB significantly in some cases. Don't underestimate the impact of the reflected light.


Now, you were saying that your halogen lights are rated at 2900-3000K. It's important to realize that this may not be the case after the lights were mounted in your particular room. As I tried to explain in my previous post the light spectrum will change after it's reflected from walls, ceiling, clothes and other objects that aren't neutral. The light mix will change after you change camera position resulting different WB value. This should explain inconsistency in Auto WB results.

Yes, but the whole circumstances with all the reflections and imperfections don't change too much from one shot to the other, so I would expect WB measurements to come up with results that are closer to each other instead of being worlds apart. The first example is somewhat close, but the second example really is worlds apart. It's the same skin, the same purple bathtub and the same walls reflecting the light. What changed was the additional of TTL fill-flash bounced towards the same ceiling that the halogen light came from (even at -1 EV flash power).

So I am really still baffled at the difference of 2400K vs. 5100K even while knowing that mixed light is difficult. And my X10 examples show that "usable" Auto WB is still possible even in the most wild mixed light situations.

It looks to me that the light was totally different between those two bathtub shots and, probably more important, these were two different starting points for AutoWB algorithm. I'm not surprised that AutoWB values vary that much.

It's easier for camera to find right WB with direct flash. It's possible that with bounced flash camera tends to choose WB closer to flash WB. This works well only if your ceiling has neutral white or white-grey color (no color, actually).

Once you start bouncing flash from colored ceiling, or if your walls are brightly colored, you are likely to have problems with WB. You are saying that Fuji X10 did better with AWB, but, as I read, you only used direct flash with X10. Try bounced flash on it, I guess it will have WB problems too.

I used that for my comparison of how different raw converters handle "as shot", auto and WB picker, which can be seen in the table I posted earlier.

Could you give a link to the thread where you originally posted your WB table? I'd like to read it.

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