camera to compensate for the illuminant color in a scene. Gray cards can be used for in-camera white balance or post-processing white balance. Many digital cameras have a custom white balance feature. A photo of the gray card is taken and used to set white balance for a sequence of photos. For post-processing white balance, a photo of the gray card in the scene is taken, and the image processing software uses the data from the pixels in the gray card area of the photo to set the white balance point for the whole image. Gray cards are made of a variety of materials including fabric, plastic, paper, and foam. Limitations A gray card is useful for setting or correcting the balance of neutral colors, as well as for exposure. Other charts, such as various color charts, provide standard reference patterns with calibrated reflectance spectrum and color coordinates, for use in adjusting color rendering in a larger range of situations. References Photography equipment Shades of gray Photometry