Gray card

A gray card, also known as a gray target or 18% gray card, is a flat object of a specific neutral gray color. It's primarily used in photography and videography to achieve consistent image exposure and color balance.

The card's reflectance value is typically calibrated to reflect 18% of incident light across the visible spectrum. This 18% reflectance approximates the average reflectance of a typical scene. Cameras use light meters to measure the amount of light in a scene and determine appropriate aperture, shutter speed, and ISO settings to achieve a proper exposure. However, meters can be fooled by scenes with predominantly very bright or very dark areas.

Using a gray card allows the photographer or videographer to take a reflected light reading from a known neutral source. By placing the gray card in the same lighting conditions as the subject and taking a meter reading from the card, the camera can calculate the correct exposure for a neutral tone, which can then be applied to the entire scene. This minimizes the influence of overly bright or dark elements.

In addition to exposure, a gray card is also used for color calibration. Digital cameras render color based on a white balance setting. Incorrect white balance can lead to unwanted color casts in the final image. By photographing the gray card under the same lighting conditions as the subject, the photographer can use image editing software to set the white balance based on the neutral gray of the card, ensuring more accurate and consistent color reproduction. This helps to correct for variations in lighting color temperature.

The use of a gray card provides a standard reference point for exposure and color accuracy, making it an invaluable tool for photographers and videographers seeking consistent and professional results. It is particularly useful in situations where lighting is complex or when consistent color is crucial, such as product photography or filmmaking.