Why do we white balance?

[PerroneFord]

So here is a question to some of you more advanced shooters.

Why do we insist on white balance? What purpose does it serve?

As closely as I can tell, the main purpose of white balancing a video camera is to prevent the camera from over saturating and clipping any particular color channel. Since we are most likely to lose reds first when underwater, that is NOT the channel we'd be most likely to clip. Likely it would be blue. And in rare cases, maybe green.

So, knowing this, if we could somehow shift our cameras so that the blue sensors somehow were less sensitive, or registered colors less prominently, we might be able to get away with not white balancing the camera at all. This is NOT to say the image would be "accurate" when we got back to the edit bay, but we'd have preserved all information in each color channel even if it was not in the correct proportion.

My camera, like many others, has a chroma phase which does this very thing. I am able to shift my camera from under saturating reds, to under saturating blue. In general, I set my camera to under saturate all colors. I purposely try to get a nearly pastel soft image out of my camera. This tends to keep my blacks more noise free, even in lower light, it tends to keep me from clipping whites, and I have a very "flat" image that I can manipulate in many ways. Shifting color in camera seems a natural extension of this idea.

Have any of you tried this underwater? Or would any of you be WILLING to give it a shot to see what you come back with? I am somewhat limited in that my camera for underwater shooting does not have these adjustments. Only my topside camera does. I am really curious as to how this might work.

-P

 

[Papa_Bear]

Okay, digital cameras measure color from 0-255 on three channels giving each channel RGB a value based on white as the starting point to give each color a value between 0 and 255. 255cubed is 16581375 color combination in a three chip or RGB comos or CCD. So take a piece of white paper and hold it in the light! If it is sun light the temp will be 5000k now move it to different lighting positions like shade or into a room! The paper didn't change color it is still white! But look at it it is not the same color to your eye or the camera! So you take a white slate with you and follow the cameras directions and shoot the slate under the light conditions you will be working in and all the color will be shifted to reproduce the colors based on white at that light source!

 

[PerroneFord]

Well, I think I understand what you said, but you told me HOW to white balance, rather than why. Certainly, if the color of the light shifts, so will the color of what we capture on film or on the sensors. But so what? Why do we care in the field what happens as long as we are not clipping values?

As you said, that shift of color happens in real life simply by walking from direct sunlight to shade. Or by shooting at 9am versus 4pm. So if we are ok with those color shifts happening naturally, why do we care about it so much underwater?

Similarly, do most of you white balance at night? Without sunlight changing colors, your unchanging lights are the only thing in the mix. Do you continually white balance for them? And yes I realize subject distance plays a role, but CERTAINLY you can't always be that accurate.

So again, why bother to white balance?

 

[Papa_Bear]

White balance for each shot or segment at a given depth! It does help with red and all the colors for better saturation! It helps remove the blue or reduce "Over blue"! Night does not provide enough light for most HD cameras! So you have to use Light as close to the 5500k range as possible for reproduction of sun light! Then with the lights on you would set it! Why is to fool the spectrum and adjust the 0-255 to a reference point that is known! You can take some great pictures with a digital at 60ft with no light if you use the White balance!

 

[PerroneFord]

White balance for each shot or segment at a given depth!

So, suppose I don't? Why does it matter? I am going to do the same thing after the fact, that I am asking the camera to do.

It does help with red and all the colors for better saturation! It helps remove the blue or reduce "Over blue"!

So suppose I am not getting overblue because I adjusted my camera before the dive to make sure I don't.

Night does not provide enough light for most HD cameras! So you have to use Light as close to the 5500k range as possible for reproduction of sun light! Then with the lights on you would set it!

So, since I am using the same light color for the entire dive at night, I never need to reset the white balance right? So I can set the balance on the boat, and not have to adjust again? Right?

You can take some great pictures with a digital at 60ft with no light if you use the White balance!

Why would my picture change just because I don't white balance. All that SHOULD happen is that they appear more blue before being corrected. Are you saying that you don't color correct your footage after you shoot? Even with a white balance?

 

[Papa_Bear]

I encourage people to try it! I use auto at night because the lights are matched and 5500k so it is right on! Thats why night shots look so good! It only matters so that you start with the best you end with it as well! Think of it as calibrating for white! Your setting Values for the best picture! Try it and walk around with a white slate and set different WB until you get what you want, its a good exercise in understanding the finished result!

 

[under water]

P -
I think the simple answer is that our eyes and brain actually compensates for ambient light on an ongoing basis. When we walk into a room with flourescent lights or tungsten lights, we compensate for that color difference in our minds. Similarly, we compensate for the red tint that happens at sunset to a degree.
White balance is particularly useful with film because I believe that film does not have a uniform exposure over all ambient colors.
Basically we want our pictures to look as much like what we call 'the real colors' and one way to do that is to shift the exposure by forcing the image to center on "daylight' aka white balance.

Underwater images of course lose red light as we get deeper. White balancing in that case probably turns up the red sensitivity to compensate in digital and with filters in film, still with the goal of balancing to a "daylight" color balance.

 

[Gombessa]

OK, I know there may be variations in how certain cameras work, but I was under the impression that WB 1) does not affect your exposure (so ISO, aperture, shutter are not affected), and 2) WB works by BOOSTING color channel sensitivity rather than muting it. So if you're shooting on an incandescent setting, blue output (and thus any noise in the blue channel) will be boosted to compensate for the reddish/yellowish hue of the light, and it's the same reason why everything will have a blue cast if you use that setting outdoors. My guess is that chroma shift features take the same easy way out by boosting output after the capture.

If you're trying to prevent a certain color channel from clipping prematurely, then filters are your only bet. In daylight shooting, a mild magenta filter does this by cutting down the green channel, which is double the capture area of red or blue in a bayer pattern sensor. So a magenta filter gets you unamplified, "equalized" data between channels that you have the most latitude in post-processing. Some tests I remember seeing from a few years ago showed that doing this results in slightly noticeable improvements in noise and low-light fidelity.

It sounds like in theory it would translate even underwater, though what you'd need to do is to use a filter that shows the sensor equalized light input while underwater. I assume serious underwater shooters are using such filters, although it seems equally likely that most filters are designed simply to mimic traditional sensor response under plain daylight, which would call for an additional magenta shift to boost red/blue to compensate for excess green.

I'm sure I'll be corrected rather quickly if this is totally off-base.

 

[Papa_Bear]

We don't use a filter for underwater unless you are using ambient light! Otherwise it would make everything red! It doesn't increase saturation at all or reduce noise or effect it! It just calibrates like the color bars on the TV so the cameraman can calibrate the camera or screen settings! It simple tells the camera what white is under the ambient light! Nothing more or less! it is simple and straight forward!

 

[drbill]

I don't white balance. Why? Because I want the resulting unlit image to more closely look like what a diver's eye will see. All those beautiful, white balanced videos give divers an unrealistic idea of what things will look like when they go down. OK, so why don't I white balance really? Because my housing doesn't allow me to. Sniff.