Direct-positive photographic material

Abstract

Direct-positive photographic material having at least one layer which contains a silver halide emulsion surface-fogged by chemical means or by exposure and a tri-nuclear cyanine dye, which has the formula ##EQU1## in which A.sub.1 is .dbd.CH-- or .dbd.CH--CH.dbd.CH--, Z.sub.1 is a monocyclic or polycyclic heterocyclic radical which is linked by a double bond to the adjacent methine group, Z.sup..sym. is a positively charged radical which is mesomeric to Z.sub.1 and is linked by a single bond to the adjacent methine group, Z.sub.2 --is a nitrogen-heterocyclic radical which has its single positive charge on the nitrogen atom and Z.sub.3 .dbd. is a radical which has no charge on the nitrogen atom and is mesomeric to Z.sub.2, at least one of the radicals Z.sub.2 containing a betain-type structure and it being possible for the cyanine dyes of the formulae (4) and (5) to have a neutral or positive or negative charge, corresponding to the sum of the charges, the positively or negatively charged dyes containing a corresponding counter-ion, and X.crclbar. is a monovalent anion and Y.sup..crclbar..crclbar. is a divalent anion. If desired, the tri-nuclear cyanine dyes are used together with conventional cyanine dyes. The direct-positive material possesses excellent sensitivity in the longwave region of the visible spectrum.