A grey scale is something like of piece of card or film that has greys of known values (typically expressed as density, or percentage reflectance or transmittance). The scale can then be photograged, or enlarged, or scanned, or whatever, in order to calibrate elements of the photographic process.(posted 9030 days ago)For example, it might be photographed, and the densities of the resulting negative is measured. A graph can then be drawn, showing the response of the film to different levels of light.