Gray cards



Gray cards are used, together with reflective light meters, as a way to produce consistent images in film and photography.

A gray card is a flat object of a neutral gray color that derives from a flat reflectance spectrum. A typical example is the Kodak R-27 set, which contains 2 8x10" cards and one 4x5" card which have 18% reflectance across the visible spectrum, and a white reverse side which has 90% reflectance. Note that flat spectral reflectance is a stronger condition than appearing neutral; this flatness ensures that the card appears neutral under any illuminant.