Gray Card

A gray card is a flat card with a neutral gray surface that reflects 18% of the light hitting it. Photographers place it in a scene and photograph it as a reference. That frame gives the camera or editing software a known standard for setting exposure and white balance, because the card's tone matches what camera meters expect and its color is fully neutral.

Camera meters are calibrated to assume the average scene reflects about 18% of the light falling on it, a tone called middle gray. A card that reflects the same amount matches the meter's assumption exactly. Reading off the card gives a correct exposure even when the real subject is much brighter or darker than average, like snow or a black coat.

Place the card in the scene, photograph it under the same light as the subject, and use that frame as a reference. In camera, the custom white balance function reads the card and removes the color cast. In editing software, clicking the card with the white balance eyedropper does the same, and the setting can be copied to every photo from the session.

Meters get fooled by scenes that are mostly bright or mostly dark, like a snowfield or a black stage curtain. Metering off a gray card ignores the subject and reads a known 18% tone instead. Setting exposure from that reading keeps whites white and blacks black instead of dragging everything toward gray.

Both are neutral, so either can set white balance. Only the gray card matches the 18% reflectance meters are calibrated for, which makes it the right target for exposure readings. A white card reflects far more light and would push the meter several stops toward underexposure. Some products print a white side and a gray side on the same card.

In the same light as the subject, facing the camera, and close to where the subject stands. Light a few steps away can differ in both brightness and color, especially indoors under mixed lighting. If the subject moves to new light, take a new reference photo of the card before continuing.

Yes. The 18% standard predates digital photography, and light meters in film cameras and handheld meters are calibrated the same way. Metering off the card works exactly as it does on a digital body. For color film, a frame of the card at the start of a roll also helps the lab or the scanning software correct color.

Some everyday surfaces sit close to middle gray, and photographers meter off them in a pinch: green grass, weathered concrete, or even a Weimaraner's coat. These approximations vary from one surface to the next, though. A real card is cheap, pocket-sized, and consistent, which is why it remains the standard reference.

Raw files allow white balance changes in editing without quality loss, so the card matters less than it does with JPEG. It still saves time. A reference frame gives one-click color accuracy instead of eyeballing, and it keeps color consistent across a whole session. The exposure benefits are unchanged, since metering happens before the file is saved.

A gray card is a single neutral tone used for exposure and white balance. A color checker adds rows of patches with known color values, so editing software can build a full color profile of the light. Checkers cost more and matter most for product and reproduction work. For everyday color accuracy, a gray card covers most needs.