How to Use a Gray Card for Photography

In photography, setting accurate exposure and white balance is crucial for creating professional and visually appealing images. One tool that many photographers use to assist in achieving this is the gray card. Often overlooked, the gray card is a simple yet powerful tool.

A gray card establishes a reference that is used to set exposure and white balance in the camera or in post-processing. It consists of a neutral gray surface that reflects an equal amount of light across the visible spectrum. We use a gray card to ensure proper exposure and natural color in our photographs.

In this article, we explore the benefits of using a gray card, why and how to use it, and provide an example along with step-by-step instructions on how to set up a camera with a gray card. This does not mean that the automatic settings for exposure and white balance don’t work. In many cases, they’re fine. In others, you may get better images – if only slightly – with the use of a gray card.

What is a Gray Card?

A gray card is just that but with a specific purpose. It is a reference point, 18 percent gray or a mid-range gray. That particular shade of gray sits exactly in the middle between black and white. So why not call them 50-percent gray cards? Because this shade of medium gray reflects 18 percent of the light falling on it.

A gray card tends to be small. The one I own is a 12-inch square with rounded corners. Usually, the card’s reverse is white, which is useful for setting the white balance to achieve accurate color representation. They’re inexpensive, lightweight, portable, and easy to stash in a backpack or camera bag.

They’re not very sexy. But if you want to set your camera’s exposure and white balance with precision, a gray card is an excellent tool.

Why Do Photographers Use a Gray Card?

Photographers encounter many different types of lighting. These light sources vary from bright sunshine to moonlight to the golden hours. Indoors, we encounter a broad spectrum of lighting, including fluorescent, incandescent, tungsten, etc. Using the gray card helps you resolve some of the issues that arise from this assortment of light sources by setting the camera’s custom white balance.

One important issue is how your camera measures light. A camera’s built-in light meter measures light reflected off your subject. And, in-camera meters attempt to set the exposure at 18 percent, which is very close in most situations.

However, dark objects reflect less than 18 percent, and bright objects are more than 18 percent. When you place a gray card in front of the subject and set the exposure, you get balanced exposure across the entire scene.

Dark or Light Areas May Fool the Light Meter

Photographing in snow is a good example of how light plays tricks on your camera’s meter. Snow, especially in bright sunlight, reflects more than 18 percent of the light. Still, the light meter sets the exposure at 18 percent. This results in an image that is underexposed by one or two stops and gives the photograph a gray or blueish tint.

The same is true when photographing a dark subject, except in reverse. With large dark areas in the picture frame, the camera’s light meter tries to set the exposure to 18 percent. As a result, the image is a half stop, or maybe one to two stops brighter than ideal.

In the image below, I exposed the top frame for the pear on the right, which left the blueberries on the left underexposed. In the bottom frame, I set the exposure for the dark blueberries, and the pear is overexposed.

I took a third photo below using a gray card to set exposure. It might not be perfect exposure, but it’s close enough that minor adjustments in post-processing are all that’s necessary.

Light Sources Can Alter Color Balancing

A gray card helps us set accurate white balance and capture colors with precision. You can use the gray or white side, but I recommend the white side. The white balance settings in digital cameras do a pretty good job most of the time. However, in some scenarios, such as indoors with mixed light sources, the correct white balance setting can be more complicated.

A room may have a combination of fluorescent and incandescent lighting with ambient natural sunlight through a window. That’s a cocktail of color temperatures.

In this case, the gray or white card establishes a reference color balancing point since its color tone is neutral. It has no hue. So, you get a custom white balance in the digital camera to faithfully recreate the colors in your image.

I shot the image below with auto white balance setting. As you can see, it has a slightly warm, yellowish color cast.

In a second shot of the same bouquet, I used the white side of a gray card to set a custom white balance. Other than that, the camera settings and the light source are identical.

The difference is slight, but the gray card shot established a true color temperature, and the various colors are more natural. As a result, the rose is a little redder, and the peony is whiter.

When to Use Gray Card for Photography?

I do most of my photography outdoors – sports and wildlife. In these scenarios, the light changes as I follow the action with the camera. Therefore, I would constantly be pulling out the gray card to set a new reference for just about every shot. And I would miss shots while I set a reference image with the gray card. So, for photographing action, I suggest you rely on the camera’s internal metering.

Street photography is another genre where you may want to trust the camera’s light meter. Changes in scenery from sunlight to shadow or from street lights to neon with car lights mixed in would require constant gray card meter readings. In this setting, exposure and white balance would require moment-to-moment meter recalibrating.

To be effective, the gray card and your subject need to be reflecting the same light.

In the photo below, the egret was at some distance from the camera, so I used auto exposure (shutter priority) and auto white balance. And in this setting, I trust the camera.

However, in situations where you have controlled lighting, a gray card is very useful. In a photography studio shooting portraits, in product photography, and in real estate photography, you can use a gray card to help get good exposure, along with saturated colors and no color cast.

I shot the photo below about five years ago. This was before I had an “official” gray card. I used a white sheet of paper to set the color balance. The colors are nicely saturated and appear natural.

How to Use a Gray Card?

Setting up your camera meter by using a gray card varies with brand and model, so check your camera’s manual. However, the steps to follow are similar. First of all, set the camera to manual mode and spot metering mode.

Capture an image of the gray card. This reference shot will be used to determine exposure and white balance. Review the image and examine the histogram.

Ensure that the tonal values of the grey card peak in the middle of the histogram, indicating a balanced exposure. If the histogram is skewed to the left, the image is underexposed. If it’s skewed to the right, it’s overexposed. Adjust the shutter speed, aperture, or ISO accordingly and retake the shot until the histogram is well-balanced. The exposure is set.

Set the White Balance

Navigate to the custom white balance settings in your camera menu and select the image of the grey card you just captured. Select this image as the reference white balance. This calibrates your camera’s custom white balance based on the neutral reference color of the gray card.

You have now successfully set up your camera with accurate exposure and white balance using a gray card. Stay in manual mode. You are ready to photograph the subject.

How to Set White Balance in Lightroom

As a post processing option, the gray card can set a custom white balance in Lightroom or Photoshop. If you choose to adjust white balance in post processing, make sure you shoot in RAW format.

Capture an image of the card prior to shooting each new scene. This also helps to organize your photos by having a new gray card image each time the lighting or the scene changes.

If you’re photographing a product or food, simply place the card in the frame in front of the subject and capture a single image. Continue with the shoot. With any change in the lighting or scene, repeat the process.

I use Lightroom for post processing. In the Develop module, Basic panel, click WB: a window with nine options appears (left panel in image below). You can leave it As Shot and fine-tune the color temperature with the Temp slider. You may select Auto and leave the white balance setting to Lightroom. Or you can select any of six light temperature settings: Daylight, Cloudy, Shade, Tungsten, Fluorescent, or Flash.

As a final option, you could select Custom. In this case, bring up the gray or white card image in the Develop module. Select the eyedropper tool and click on the card. This gives you a color temperature number (white block in the right panel below). Copy that number, return to the image you are editing, and paste it into the Temp block under Custom. You may want to tweak the Temp slider to get the desired look.

Where to Get a Gray Card

Gray cards are available from almost any photography store, brick-and-mortar or online. I got mine from Adorama. You’ll also find them at B&H Photo, Amazon, and other online retailers. Prices start at under $10.

Another tool that some professional photographers use is the color checker. It contains a variety of colors that help you get the exact color balance in photos. It is most useful for food or product photographers who are contracted to photograph a subject on a white background.

Clients will want the colors to be highly accurate. However, most of us will do fine with gray cards.

How to Print Your Own

I recommend this only if you know your printer is accurate; however, you can print a gray card. First, open a blank image in Photoshop. Then, open the Color Picker (Foreground Color). Set Hue (H) and Saturation (S) to zero. Set Brightness (B) to 82. Red, Green, and Blue (RGB) will all be 209. That’s an 18-percent gray. Send it to the printer and you have a homemade gray card.

Final Thoughts

When it comes to cost-effective options for photography, a gray card is hard to beat. It’s simple to use and offers precise control of two of the basic parameters in photography: exposure and white balance. Very often, a gray card exposure reading is more accurate than the in-camera meter reading.

My own use of gray cards is limited since most of my photography is outdoors. However, if I’m working indoors, I like the exposure and white balance accuracy that gray cards are designed to deliver. Also, I prefer setting it in-camera as opposed to making the adjustments in post processing. It takes just a few minutes, and the results are well worth the effort.

I hope this article introduces you to a useful technique that advances your photography skills. If you have experience using gray cards, any comments or questions, please submit them in the space below.

Take Away

A gray, or grey, card establishes a reference that can be used to set precise exposure and color balance in the camera or post-processing. It consists of a neutral gray surface that reflects an equal amount of light across the visible spectrum. With careful use of a gray card, we ensure proper exposure and true white balance in our photographs.