Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It only takes a minute to sign up.
Sign up to join this community
So I have some photos taken with a variable ND to create the flowing water effect, particularly with strong waves, and it looks white to the naked eye.
However, it seem that the filter does impart a tint.
Could I use the white water was a white-balance reference?
I'd say "Sure, try it". Worst case is that it may not be close enough, and then back it out and don't do that. But lacking better means, it can also be better. Many things that "look white" are very suitable for adjusting white balance. White porcelain dishes, white church steeples, a white envelope, white pizza signs, white polka dots on the kids pajamas, all can work quite well, if they are supposed to look white (not off-white).
Planning ahead with a white card will be more guaranteed, but anything already there that "should look white" can work quite well. More on that point at http://www.scantips.com/lights/whitebalance.html (including example of some white water).
Best if you use a white card. A gray card photo target (18%) gray on one side and white on the other is the tried and true target.
It depends. If the water is really white then yes, that will get you in the ballpark. But if the water is white in the photographs only because all three color channels are completely at max value you won't have much success.
You can actually create a WB correction after the fact assuming you still have the filter in question. Under similar lighting (including any tree cover or anything else that influences color) take some properly exposed shots of a gray card. Then put the filter on, use the same strength setting as you used for the original photos, and take a properly exposed shot of the gray card.
Import the raw files into your raw converter of choice, use the color temperature adjustment to get the unfiltered gray card shot properly balanced (you'll know it when the [R,G,B] values are all the same, like [115,115,115]). Next, apply the same color temperature setting to the filtered shot of the gray card. Then use your white balance correction function in whatever application you're using to adjust until the filtered image of the grey card is properly balanced. Record the differences in white balance correction to each image and you can then apply the same amount of correction to your original images.
