Auto White Balance vs. Custom

[Roxie2401]

Been taking some outdoor band concert pictures - concerts start at twilight and end after dark - band has several "flood" lights and when using "Auto" white balance, I tend to get overly warm colors.  Tried Tungsten and also manually setting Kelvin to around 3400 and got better results.

Questions:

1.  How does the Canon EOS (specifically 40D) measure white balance for the "Auto" mode?  Is it via a spot meter reading even if the camera is not in spot meter mode?  Or is there a better way to understand what the "Auto" is trying to accomplish?

2.  Does any one have experience with the "through the lens" white balance products like the ExpoImaging ExpoCap?  Do they work and do they work better than the white/gray cards?  If I can't get "on stage" to measure the actual light with a card, would the ExpoCap do a good job?

3.  Currently my lenses are 77mm, 67mm and 58mm.  If I get a 77mm ExpoCap can I hand hold it in front of the 67 & 58mm lenses or should I get step up rings for each of those; or, do I need to get a white balance ExpoCap for each lens?

Any other thoughts on White Balance would be appreciated.  Bob, if you have written any general articles on this subject (other than the camera body specific reviews), please mention them.

(I know, shooting RAW lets me "fix" later, but I hate to rely on post-processing if I don't need to.)

Thanks to all.

[jodaco]

Don't know the specifics of the auto white balance technology but I do know that it does not handle mixed lighting well. Since it is somehow taking an average temperature reading, in mixed lighting it is a compromise at best. My guess is that concert lighting, with all the colored gels and different types of lights, is among the most difficult for the auto setting.

The "through the lens" white balance products all utilize some kind of strong diffuser. The effect of this is to blend all the light which makes it easier for the camera to make an accurate average reading. This may not actually help in extreme settings since the average is still wrong.

You can hold large ones in front of small lenses, although this can be a pain in the field.

Even though you want to avoid post processing, you may have no choice. The bottom line is that the white balance in your shots may not be the same throughout the frame. The only way to get results without compromise may be to use masks in post in order to effectively apply different white balance to different parts of the image.

-Josh

[marcfs]

Try shooting a neutral reference point and then create a custom wb or adjust in raw.

Also there is an interesting short article on understanding WB at:  http://www.cambridgeincolour.com/tutorials/white-balance.htm

 “Multiple illuminants with different color temperatures can further complicate performing a white balance.  Some lighting situations may not even have a truly "correct" white balance, and will depend upon where color accuracy is most important.
Under mixed lighting, auto white balance usually calculates an average color temperature for the entire scene, and then uses this as the white balance.  This approach is usually acceptable; however auto white balance tends to exaggerate the difference in color temperature for each light source, as compared with what we perceive with our eyes.
Exaggerated differences in color temperature are often most apparent with mixed indoor and natural lighting.  Critical images may even require a different white balance for each lighting region.  On the other hand, some may prefer to leave the color temperatures as is.
Note how the building to the left is quite warm, whereas the sky is somewhat cool.  This is because the white balance was set based on the moonlight-- bringing out the warm color temperature of the artificial lighting below.  White balancing based on the natural light often yields a more realistic photograph.  Choose "stone" as the white balance reference and see how the sky becomes unrealistically blue.” 

Source:  Cambridge in Color

[onurrus]

Thank you guys I learned a lot from this topic.and article was simply great!

[Roxie2401]

Thanks for the information.

Does anyone know how the Canon EOS (40D) Auto White Balance takes its measurement?  And, does the "Custom" take the measurement the same way?

Also, additional experiences with the ExpoCap (or similar products) and step-up rings would be appreciated.

[KeithB]

I believe that it just looks at the raw RGB data, tries to figure out which colors are likely to be neutral, and biases the colors based on that.

If you want real control, just shoot RAW and adjust it yourself later.

Here are some articles about getting accurate color:
http://theonlinephotographer.typepad.com/the_online_photographer/2008/12/white-balance-p.html
http://www.kenrockwell.com/tech/expodisc.htm

[Roxie2401]

KeithB,

Thanks for the information.  That really helped.  I was thinking you used the Expodisc from your shooting position, similar to what the Canon manual describes as taking a reference image of something white (I think they say to "fill the spot meter completely") and set the custom from that image.  That made me think you did the same with the ExpoDisc - but in reading further, it appears that you still need to use the disk from the subject location (similar to a gray card).

Then, I found something called "ColorRight" that you apparently use from shooting position and not the subject position.   Now, I'm really confused.

More to research!