Photo

Setting White Balance with a Gray Card (2008)

tvalleau

This is for the more serious photographers and videographers on the list, and there’s no doubt that some of you (certainly the pros) already know this… but some may not.

White Balance.

The human eye is very adaptive: take a sheet of typing paper outdoors, and it looks white. Take it indoors and it looks white. But that’s just our brains at work. Photograph it out doors and it looks slightly blue; shoot it indoors and it looks significantly orange. That’s because it’s not the paper – it’s the light.

In the film days, this was compensated for by using indoor or outdoor film, but in the digital age, it’s done in your camera. Every digital camera offers “automatic white balance” and often a range of cute little icons for outdoors (sunny) outdoors (cloudy) indoors (incandescent bulbs) indoors (florescents) and so on.

And better cameras will also have “custom white balance” as well.

Now: if you go to the trouble to set your white balance for a given lighting situation, there _will_ be a visible improvement in the color accuracy of your print.

The process involves choosing “custom white balance” in your camera’s menu, and then shooting something “white” filling the frame. That setting is then saved, and used as long as you don’t change the lighting in the current environment. (If you do change it; go outdoors; whatever, you have to go thru the process again.)

Except that my description above is incorrect. The bit about “shooting something white” is where it fails… because (unless you’ve paid for it specifically) “white” isn’t white. White typing paper, for example, has optical brighteners in it which reflect more blue, making it appear whiter to the human eye.

“White” as far as the digital camera (or digital video camera) is concerned is (here’s the key) -equal- amounts of 100% red, 100% green and 100% blue. On a scale of 0-255, for example, that would be R255, G255, B255. White light is an equal mixture of all the primary colors.

Your white typing paper is probably something more like R240, G248, B255. And those are not fixed numbers for typing paper… what I’m saying is that your white typing paper is really R?, G?, B?.

What you’re tying to achieve in white balancing your camera is, not surprisingly, “balance.” You want to photograph something under the “custom white balance” setting in your camera that is EQUAL amounts of R, G, and B.

And fortunately, that’s easy and inexpensive: take a trip to your local photo store, and buy an “18% gray card”… because gray IS, by definition, equal amounts of red, green and blue.

Take your white balance setting off of gray card, and you’ll see your color accuracy jump _way_ up.

“Balance” achieved.

Finally, as many of you know, if you also include the gray card in one of the photos in a given lighting situation, you can use that later on in Photoshop to help adjust the photo colors was well.

hth

Tracy

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