An excellent picture is produced with precise exposure. If the light in the scene is excessively bright or dark, exposure deviation might be produced.
Gray card can balance all mixed lights to be 18% neutral gray. With a photometer, you’ll get a precise exposure value by means of recording the light that was reflected from the grey card. (it can measure the exposure value through the exposure photometer, the TTL SLR camera, the digital camera, etc.)
An 18% grey card not only has the use of measuring the camera exposure value but is also able to adjust color balance and revert the color truly and perfectly by controlling the gray balance in digital photography.
