Abstract: A platemaking system uses an intermediate imaging mask made of a film of photochromic material, preferably bacteriorhodopsin. The film is normally transparent, but it is temporary made opaque by exposure to light of a certain wavelength. An image is formed on the mask using light of the appropriate wavelength, which renders portions of the mask opaque. The mask is then interposed between a photosensitive printing plate and a light source which produces light to which the plate is sensitive, exposing the printing plate and thereby transferring the desired image onto the plate. The described method is preferably implemented using a transparent rotating drum that is coated with a bR film. As the drum rotates past a green or yellow laser, a desired image is written onto the film by the laser's beam. The drum rotates the image until it is opposite a photosensitive printing plate, and a light source inside the drum exposes the plate through the mask to transfer the image.