A white balance card or gray card is the color of middle gray or 18% gray (click here for the technical jargon).
Why You Need a Gray Card
A gray card helps you achieve correct white balance.
Have you ever noticed color casts in your images? Often they are blue or red. This happens because your camera is reading the color temperature of the light incorrectly. Simply put, the white balance is off. White balance is very important to having professional-looking images.
Your eyes are pretty savvy at seeing colors correctly, no matter what the light source. On the other hand, your camera needs to be told what the color of the light is. A camera can determine the color temperature of the light by what is reflected off a gray card.
Using a gray card helps you nail your exposure.
Back in my high school days, when a digital camera was something like .3 megapixels and we scoffed at them as we produced our superior grainy black and white images from film (while inhaling dark room fumes), our only use for a gray card was to determine correct exposure.
Both hand-held and in-camera light meters work best using middle gray to measure the reflected light. Basically, taking a meter reading from a gray card will be more accurate than without one.
Now here’s the most useful part of this post:
How to USE a gray card:
1. With your lighting in place, have the gray card held in front of your subject (or where your subject will be).
2. Take a picture with the gray card in the frame. Note: Try to have the card fill the frame. You may need to switch to manual focus to do this. (Don’t forget to switch back to automatic focus afterward! If only I could count the times I’ve forgotten…).
3. Look at your histogram (see your user’s guide for your camera). You want to see a high peak in the middle – middle gray, get it?
- If the peak is to the left, then you need to adjust your exposure settings to let in more light.
- If it is to the right, then you need to let in less light.
Now you’ll have correct exposure. (Although some of my sources claim you need to then open up ½ stop because meters really measure 12-13% gray – but I’m just keeping it simple…).
4. Then, go to custom white balance (once again, see your camera’s user’s guide). Select the picture you took of the gray card. Make sure you also set your white balance choice to custom (user’s guide…).
Voilà! White balance should be correct!
5. Take a picture. Use your viewfinder to check for any glaring problems. Repeat the steps if necessary.
Go to B&H Photo and you’ll get lots of options from different manufacturers – mostly inexpensive.
You’ll also see alternatives to a traditional gray card such as a gray card target or a digital calibration target. In addition to middle gray, these have black and white. Then, when you look at your histogram, you can see if you’re clipping any blacks or blowing the whites.
I personally use a PhotoVision Calibration Target or an old gray card leftover from high school – whichever is most handy. I get good results from both, but I really do like being able to check whites and blacks in my histogram (which I can do with the calibration target).
There are a lot of pricey alternatives to a gray card – some people swear by them and some think they’re a waste of money when you could just use an inexpensive gray card. I’ll leave the choice to you and your pocketbook.