White Balance and Gray Cards

I've read in several places that people sometimes use gray cards to set white balance. I'm trying to figure out why. Can anyone help?

Using a custom white balance helps the camera record colors that require the least amount of correction during editing. Custom white balance needs to be reestablished frequently during the dive, however, because of changing depths and light quality.

Setting custom white balance without a reference requires having something you can aim toward that is relatively neutral in color. That's a hit or miss thing but you can do it.

Gray cards work because "white balance" does not actually require white. It only requires a neutral shade. Lighter grays will work better, but anything that is neutral and not close to black will work. I've used a card in the past but now use a gray glove (no sequins).

The point with custom white balance is not to achieve absolute accuracy. Your goal is to help the camera out by telling it what a reasonable neutral tone is. If you get it 90% right you will be far ahead of the game. Video cameras discard vast amounts of the video data they collect so it's important that they record the stuff you want to keep. With the low light performance of today's cameras, good white balance settings can help you achieve good color over a broad range of depths.

Thanks Craig,

I thought "white" balance meant "white". I've been using sand as a white balance reference for a lot of my uw video and it seems to work fine. If a gray card or a "gray glove" is a better reference, I can do that. If I use a gray card, will the camera set gray as white and somehow overexpose anything that is lighter than the gray card? Or is it JUST color that is of concern?

No, it only cares about the hue. Exposure won't be effected.

Dark grays don't work as well because there is less resolution to play with. The camera has a harder time getting it right and small errors are magnified.

I've used sand or dead patches plenty and find it works pretty well. Frequently I have to try more than once, though.

Craig,

Thank you for your advice. I've learned something.

White balance is a function which gives the camera a reference to "true white". In effect, you are telling the camera what the color white looks like, so the camera will record it correctly. Since white light is the sum of all other colors, the camera will then display all colors correctly.

A reference card for white balance needs to be white. Grey cards will not register your white balance properly. They are used for metering. Even though you can use a 18% gray card for

white balancing I believe it’s not recommenced or as reliable form of balancing. Read your documentation that came with you camcorder.

If you expect to get accurate and consistent colors in your video, your camera must be told what "color" of light is illuminating the subject you're shooting. This is called "white balancing". And that's basically all white balancing is - showing the camera something that should look white and using that as a reference point so that all the other colors in the scene will be reproduced naturally.

That’s my opinion,

Marc

Have you tried it with a gray card rather than a white one, Marc?

The difference between white and gray is a matter of brightness, not color. Brightness is controlled by exposure. White balance doesn't concern itself with exposure.

White balance could just as easily be called neutral balance or color balance, but that wouldn't as clear to people. Just because the name says "white" doesn't mean it has to be a pure white. If you set exposure to it, then maybe so. Of course, gray cards are used for exposure but that's another story.

When you activate your white balance calibration, the camera will be pointing at something. The camera won't explode if its not white. Try it in a variety of ways and see if the results are good. I find that sand is good, but not ideal. I have no problem using my camera that way with no reference card at all. Your camera may work different.

Ran out this morning and took three exposers using a gray card, white card, and auto white balance. I used my Fuji S2 Pro for the comparison pictures.

I stand corrected, to my surprise all the images were slightly different in color but not enough to make my point.

I’d like to give the gray card a chance underwater next time I white balance.

So it’s not true, you can teach an old dog new tricks.

Thanks,

Marc

A white diver's slate works fine for video, too. Maybe a little shiney. I've had on a retractable cord on my BC in the past.

Hi Graig,

I’m quite familiar with using a white card. Here’s the housing I made for my Fuji S2 Pro.

As you can see it has a white card mounted under the housing. I swing it up when I want to white balance, and it stows nicely under the housing after.

Marc

I remember seeing that. Very clever.

Nice system Marc. I've got a question. How do you do white balance (or grey balance) with lights? Isn't the card too close to the lense to get any lights from your video lights on it? The same question for Craig. If you use a glove, can you reach far enough so the video light reaches your glove?

My lights (Watervisions) are extremely wide so I have no problem with that. Generally when I shoot close with lights I try to find something white to calibrate on rather than use the glove. I tend to shoot a lot in sandy areas.

Amphibico's white balance slate is actually slightly green...

I too would like to know how one white balances with a white slate just a few inches in front of the port if you have lights.

Actually kind of simple. Turn the light down until it hits your slate. Also, if you cup the housing in your right arm, hold the button while white balancing across your chest (vs out in front) you can get more distance from the lens. takes a couple of tries to get this. another option is to drop you slate and back up and balance off it.

Sorry to add another headache to the WB equation, but....

The horizontal distance to subject (the water column itself) affects the amount of absorbed red light, also.

For Example... If one were to balance off a slate at arm's length, to then turn to shoot a subject 20+ metres away, wouldn't the subject appear too blue?

I know that there is no easy way around this but isn't it a point that should be considered for a new-comer to manual WBing?

Sand seems like a good option in this instance as one could - theoretically - aim the camera at a patch of sand some distance away and balance off that...... (Maybe after a few attempts.)

The most important factor with balancing seems to be that the device that we choose to balance off (whether it be white slate, grey glove, ungloved hand etc.......) should always be in the same light as the subject that one then wants to go on to capture.

Chris

Crhis,

Good points. Frequetly WB off the surface light achieves good results. Also, using a blueish slate at arms lengths tends to warm the immage and compensate for the increased distance and less red in your subject that is of greater distance away.. Point is, every condition requires variance in WB technique. First step is to just start figuring out how to get is close. then experimenting will get it great.

shawn

And if all else fails....colour correction on the good old puter

And if all else fails....colour correction on the good old puter

<{POST_SNAPBACK}>

Well unless you edit in uncompressed, color correction is destructive on pixels. Plus to really get it right, you almost have to paint it in.

Boy this is an old thread.

I've attached my Warm Card 1 onto my slate which is attached to a regular light arm. When not in use I just fold it over my monitor so that it is out of the way and does not interfere with or create unnecessary off trim. It is easy to access when I need to wb again.

Steve B)