Question:Is Sunrise Light Normally Difficult to White Balance?

[Egg Born Son]

1. Yes, it will define green as white so it will reduce it's sensitivity to green. It will attempt to make the tree white although I'm not sure if the maximum parameters will let it will succeed. Everything else will turn the opposite of green which I think is purple but not 100% on that.

2. If the white card if reflecting blue-ish light then it will correct it to white, so knock out the corresponding amount of blue in everything else. This will have the effect of seemingly increasing green and red in everything else.

 

[Bruce Watson]

1. When I push the white balance button to do manual white balance does camera actually set R=G=B (to paraphrase Bruce's earlier post) based only on the color I am pointing at when I do this? In other words, to be extreme, if I pointed camera at green card and did white balance would camera "define" green as being white--when I then videotaped green trees would they appear white? I can try the experiment, but would like to understand the theory first.

Within limits. If the card is really green, the camera will probably only be able to take out part of it. But it will definitely take out some of the green. Then when you use that white balance on "normal" scene you'll get a magenta cast (magenta being opposite the color wheel to green).

2. To go back to my thread starter, my white card was reflecting bluish cast of lighting conditions. So, when I did white balance on that card with its bluish cast did camera "define" white as having a bluish cast and video I took would have a bluish cast?

That's not exactly how I read it. I think what it likely does is look at what you've shown it (say, R=G, but B>R or G) and it would build an internal lookup table (LUT) to so that every pixel gets B minus the difference between B and R or G. This is vastly simplified of course. The math is probably fairly complex. But the end result is to add orange to the image (orange being opposite of blue), so that R=G=B.

This technique is actually used quite a lot. An excellent and proven example is Warm Cards. Doug Jensen, founder of Vortex Media who makes the Warm Cards, is a forum member here.

 

[Denniscasey]

Thank you for clarification James and Bruce. Have had cloudy, dark days with occasional rain here recently (everything looks washed out color wise) limiting my experiments to see what happens when I apply theory to real world--or in other words test, test, test. As Bruce mentioned earlier, I would like to be able to maintain "that white wall behind the heroine that has that nice romantic orange glow" so it does not "become... just a dumb white wall that's lost all its character. "

I will look at the Warm Cards article (pictures showing what can happen to skin tones at least are quite impressive). I am also thinking Color Temp setting in HMC40 Scene File options may also be helpful (if I can figure out how to use it). Regards, Dennis