GB1412833A - Process of producing direct-positive photographic images - Google Patents

Abstract

1412833 Direct positive photographic silver containing image production AGFA-GEVAERT AG 15 Jan 1973 [15 Jan 1972] 1985/73 Heading G2C Direct positive photographic images are produced by imagewise exposing a photographic material comprising at least one uniformly fogged direct positive silver salt emulsion layer with imagewise elimination of the developable fog followed by development, the fogged and developable direct-positive silver salt emulsion layer having a degree of fogging and a silver salt concentration such that when the unexposed layer is developed with the developer used for developing the exposed layer, maximum densities of between 0.02 and 0.8 are obtained, and treatment of the developed material with a peroxide compound (i.e. a compound which contains the peroxo grouping) which is decomposed at the positive silver image, the positive silver image then being intensified either physically by development of a vesicular image superimposed on the positive silver image (see Exs. 1 and 2) or chemically by an oxidation reaction with colour producing reactants, e.g. colour couplers, to produce a dye image superimposed on the positive silver image (see Exs. 3-5). The fogged and developable direct-positive silver halide emulsion layer may have (i) a degree of fogging of up to 70% and a silver halide concentration of 1-6g silver in the form of silver halide per m<SP>2</SP>, or (ii) a degree of fogging of 70-100% and a silver concentration of 0.02-0.5g per m<SP>2</SP> in the form of silver halide. These emulsions are extremely sensitive to light, but have such a low concentration of fogged silver halide grains that normal processing would only result in direct positive images with insufficient image densities.