EM-5: Confused by Auto White-Balance results

Started Feb 12, 2013 | Discussions thread
Barrie Davis
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Scene colour data are crucial..
In reply to Timur Born, Feb 13, 2013

Timur Born wrote:

Detail Man wrote:

Since the Auto WB mode is clearly vastly inconsistent and essentially worthless to you for the purpose of setting RAW processor WB Temp and Tint "starting points", why not just use a fixed WB mode - say, "Daylight" for outdoor, and a set (3,000-4,000 degrees K, or something) Color Temperature for indoor scenes - then just manually tweak the WB Temp (and then fine-tune with WB Tint) in the RAW processing ? Have you yet actually tried this approach ?

I may go there, but remember my WB table for different RAW processors? Setting a "fixed WB" leads to different results in different RAW converters, and the consistently of what a given RAW converters presents "as shot" even differs with the value chosen for WB. This is one reason why I did that comparison/table, in order to get an idea what values and software to trust most.

Nothing like using a fixed Temperature reference for consistency. I find that "Daylight" works quite well just fine over a wide range of outdoor lighting spectrums (with my LX3 RW2s). My GH2 is UniWB - so in that case I "wing it" entirely in RAW processing. The eyes know what they like.

Yes, consistency likely is the best starting point. I just hoped that I could get away with more "Auto" snapshotting instead of having to work on every single image, especially for the myriad of family (snap)shots. We are more likely to put those into an album at the end of each year rather than taking single ones out for larger prints, so some work vs. outcome balance has to be kept.

If you want consistency, do NOT use Auto White Balance.

Auto white balance estimation is done on a shot to shot basis, and, since the colours in frame are the only data available for the system to work with, the actual proportions (in area) of the colours AVAILABLE are deeply significant.

If there are very FEW colours to work with, instead of a whole rainbow's worth, (like your shots that are mostly flesh tones and nothing else... no green and blue, say)...

....then the AWB has very little to work with, meaning that small variations in composition, shot to shot, will make significant variations in the proportions of colour data available, shot to shot, leading to relatively wide variations in colour balance...(shot to shot.)

So your camera is behaving normally.

Added to this is the fact that all AWB systems currently seem to default to a very yellow (warm) rendition of tungsten incandescent lighting. I don't know the technical reason why this should be so, but feel it may be a policy decision more than anything else.... possibly because that is how normal daylight colour film used to behave.... (compared with daylight, tungsten incandescent lamps, also the CFLs that simulate them, ARE very yellow, of course!)

If you want consistent colour, shot to shot, either use a preset, and stick with it until the colour of the light changes...

... or use a Custom White Balance, and stick with it until the colour of the light changes.

Conclusion: As you have discovered AWB is a route to inconsistency. When it doesn't have a wide range of subject colours in frame to work with, (with approximately equal proportions of all of them) it does not cancel out minor differences in WB from one frame to the next... it magnifies them.

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Regards,
Baz
"Ahh... But the thing is, these guys were no ORDINARY time travellers!"

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