Abstract: A method of photographic trichromatic printing comprises the steps ofA. applying to the substrate a photosensitive emulsion comprising(a) a binder;(b) three types of grains of semiconductor oxides dispersed in the binder, each adapted to desorb OH.sup.- ions under the action of a primary color radiation; and either(c) a diazo system comprising a diazonium salt and three couplers each being adsorbed onto, or dispersed in the immediate vicinity of, one of said three types of grain; or(d) a diazo system comprising a coupler and three diazonium salts each being adsorbed onto, or dispersed in the immediate vicinity of, one of said three types of grain;B. exposure,C. development by heating; andD. decomposition of unreacted diazonium salts by exposure to UV light, to fix the image.An emulsion so produced and substrates carrying such an emulsion are also produced.