How is white ballance calculated on auto setting?

[kipp]

Hi everybody my question is as above "How does the camera (canon 7d) work out what to set the white ballance as on the auto setting?"
Do the metering modes affect this? And will low light affect it's ability to do this correctly?
I took some photo's at a mates wedding this weekend and it seemed to get it wrong (in my opinion). They were saved in raw so i can change them, i'm just trying to learn for next time.
thanks kipp

[ricktas]

I am not sure how the camera auto-determines white balance, but as long as you shoot RAW it is easily correctable. Certainly the camera can be readily tricked to produce a white balance on auto that is anything but the correct one. Try taking a shot under mixed indoor lighting, with fluorescents and incandescent light together

[kipp]

Yeah thanks rick that was exactly what i was doing (CFL's, halogen downlights, candles, standard fluros and to top it off party lights).
And i wondered if changing the metering setting would affect it? Or does it simply deal with the exposure side of things?

[arthurking83]

I don't think that the metering mode itself affects the WB chosen by the camera.

I think most cameras use the matrix(or evaluative) metering system and measure an average colour component, or something else to this effect.

As Rick said.. this is possibly one of the major advantages of shooting raw, in that the actual WB setting is an insignificant factor when shooting and always best set in your raw processing software anyhow.
(unless the camera got it right that is!)

SO, if you shoot raw, then no matter what WB setting you choose .... lets say 10000K when shooting under incandescent lighting, which is typically set to about 3000K on most cameras, if you make such a gaff shooting in jpg mode, the image is irrevocably set with massive orange cast and no amount of post processing will help the image to recover to what you can achieve with a raw file.

[kipp]

thanks arthurking i've just recently started to only shoot in raw, so thats not a problem. thought it might just be that i had the wrong setting in camera, but if everybody just changes it in post processing, then i suppose i'll just keep doing it that way.

[ricktas]

thanks arthurking i've just recently started to only shoot in raw, so thats not a problem. thought it might just be that i had the wrong setting in camera, but if everybody just changes it in post processing, then i suppose i'll just keep doing it that way.

A good way to understand WB is to go out one evening at sunset and take a series of shots. Set your camera up, and between each shot, change one thing, the white balance setting. Then go home and have a look at them on the computer, noting the WB setting used. This will give you a good understanding of what happens, and also how to create specific results by choosing a WB to give your photo a specific look.

[reaction]

AWB is guessed using the camera's CPU.
just like matrix metering, it looks thru a database of images, takes into account contrast etc and does some guessing magic. that's why some cameras AWB well, some do not. also, intelligent flashes with coded gels can affect the magic inside.
metering mode doesn't affect it.

it's said that your screen generally needs a neutral color in it for AWB to be accurate.