September 21, 2014, 04:35:22 PM

Author Topic: What is white balance and what's the correct way to use it?  (Read 18867 times)

TrumpetPower!

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Re: What is white balance and what's the correct way to use it?
« Reply #60 on: January 18, 2013, 04:35:18 PM »
There's no way to actually understand white balance without also understanding linear raw, which also gets into exposure and profiling and dynamic range (of both the scene and the camera) and lots more.

In uniform illumination, it's possible to get truly perfect exposure and white balance (and near-perfect color reproduction and contrast and all the rest) by knowing what to do with a quality profiling chart and all sorts of arcane software. In less tightly controlled situations, you can use similar techniques with a ColorChecker to get as close as the actual lighting in the scene permits.

If you're truly insane, Elle Stone outlines a procedure here:

http://www.freelists.org/post/argyllcms/Profile-input-white-not-mapping-to-output-white,68

that does that. I have a follow-up post in that thread with refinements and simplifications...but, alas, only the images and not my actual text made it to the archives. But Elle's process works, is logically equivalent to what I do, and the inspiration for what I do.

If, for whatever reason, shooting a color chart isn't an option, I have two suggestions, both of which work better than anything else I've seen discussed in this thread. (Both assume you're shooting RAW and setting white balance in post-processing.)

First, forget all the expensive white balance targets. None of them is as good as a styrofoam coffee cup.

Styrofoam is the right level of reflectance to get a noise-free sample without clipping, and it's spectrally flat. Indeed, with only two notable exceptions, nothing is better than styrofoam as a white balance target.

The first exception is Tyvek, which is 98% - 99% reflective and even more spectrally flat than styrofoam (which is 80% reflective or so). Your local office supply store sells Tyvek envelopes. Tyvek tends to be on the glossy side and prone to glare...which is good for knowing if you've got glare in the scene, but not so good for setting white balance. The other exception is Spectralon, which is ludicrously-refined PTFE (Teflon) with a glare-free surface. Expect to pay as much for a Spectralon target as for an L lens.

But back to the coffee cup. You can put it in your scene and get an even sampling of the illumination from every direction; you can then eyedropper from any part of the cup to get a white balance from light in that direction. Or, you can put it over your lens and get an average of all the color in the space where you're shooting, perfect for an in-camera custom white balance.

There are, of course, times when it isn't even practical to put a coffee cup in the scene. In such cases, it's still easy to get an excellent white balance. All you have to do is crank the saturation to maximum, fiddle with the white balance knobs until the colors in the scene look the least weird you can make them, and then return the saturation back to wherever you want it.

So, there're my two recommendations for white balance for the not-insane.

I'd also especially recommend avoiding using anything other than styrofoam (or Tyvek or Spectralon) for white balance, and especially avoiding "white" paper. With the exception of a small number of expensive fine art papers, paper is actually light yellow and has fluorescent blue dyes added to trick the eyes into thinking that the paper is whiter than white. It's a similar story with white clothing, with the added bonus that you usually get a non-trivial amount of skin showing through the fabric. Very few walls painted white are actually free of colorants, even though the base paints are generally themselves pretty good potential targets. Even those walls painted with truly white paint...well, it doesn't take long for them to take on colors from the environment.

I could go on, but this is already more information than is healthy....

Cheers,

b&

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Re: What is white balance and what's the correct way to use it?
« Reply #60 on: January 18, 2013, 04:35:18 PM »

mirekti

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Re: What is white balance and what's the correct way to use it?
« Reply #61 on: January 18, 2013, 04:37:26 PM »
In camera metering is generally about the luminance (brightness) of light, more usually that reflected from the subject, white balance is more about the colour of the source light.

Both systems cans be easily confused, metering by light or dark subjects, by lights behind the subject etc, white balance can be confused by the colour of the subject.

Despite the 'it's subjective' crew this is why I think its impoetant to understand how the camera is working, and where it can get things wrong, as this helps you get things right.

I'm sorry, but I believe you didn't understand my question. My point is to understand the way camera works and that's why I asked the question:
Is white balance metering related to light metering or not?
So let's say that before I recompose my image, the frame is filled with some light color (e.g. 2600K) that doesn't appear in the frame once I do the recomposition (e.g. 3000K), but I locked the metering at the first frame. Will AWB change to 3000K or it will remain at 2600K even though the metering is locked? 
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paul13walnut5

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Re: What is white balance and what's the correct way to use it?
« Reply #62 on: January 18, 2013, 05:05:47 PM »


I'm sorry, but I believe you didn't understand my question. My point is to understand the way camera works and that's why I asked the question:
Is white balance metering related to light metering or not?
So let's say that before I recompose my image, the frame is filled with some light color (e.g. 2600K) that doesn't appear in the frame once I do the recomposition (e.g. 3000K), but I locked the metering at the first frame. Will AWB change to 3000K or it will remain at 2600K even though the metering is locked?

AWB is an adaptive system, I don't know how rapidly it adapts,  or how accurately, ehich is why I tend to avoid using it.

paul13walnut5

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Re: What is white balance and what's the correct way to use it?
« Reply #63 on: January 18, 2013, 05:17:08 PM »
@hjulenissen

I'm never going to win this one, and life's just too short.

If you are happy with your results then I'm happy for you.

You got your way, I've got mine.

I think it's important to understand at least a little about whats happening, and that was I believe the spirit of the OP's question.

Anyway, cheers.

paul13walnut5

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Re: What is white balance and what's the correct way to use it?
« Reply #64 on: January 18, 2013, 05:25:17 PM »
@TrumpetPower

Good stuff, in defense of the humble bit of 'white' paper, its something that fits in the kit bag quite easily, and is less imperfect than awb etc.  paper will at least get you close enough that fixes in post are minor.

I'll try the styrofoam cup sometime.

I have the qpcards & a calumet grey white black card in my kit bag, but accept that even this is s bit cumbersome for many, especially given canons old fashion manusl wbbprocedure.
With live view it should take one button.

I look forward to working my way through your link, everyday is a school day and all that.

Cheers

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Re: What is white balance and what's the correct way to use it?
« Reply #64 on: January 18, 2013, 05:25:17 PM »