In optics, a raster-type screen is a grating for the structural transformation of a directed beam of light rays. A distinction is made between transparent screens in the form of alternating transparent and opaque elements and reflecting screens with elements that specularly reflect and absorb (or scatter) the light. The geometric structures of raster gratings exhibit great variety; both regular designs and irregular or random designs are used. When the elements of a screen do not alter the path of the rays that are incident on them, the screen is known as a mechanical or slit-type screen. Screens that focus the rays are called optical screens; they may be of specular or lenticular types. Tiny lenses are the transparent elements in lenticular screens. Raster-type screens are the basic components of raster optical systems. Raster optics studies the optical images formed by such systems.