Direct positive silver halide photographic emulsions - with internal latent image silver halide grains and nucleating agent comprising bis:condensn. prod. of di:hydro:spiran with salicyl aldehyde

Direct positive silver halide emulsion comprises grains capable of forming an internal latent image and adsorbed on the surface of the grains, a cpd. (I) comprising the biscondensation prod. of a dihydrospiropyran with salicylic aldehyde or a substd. deriv. of this in an amt. sufficient to allow nucleation of the silver halide grains. Nucleating agent (I) pref. has the formula (I) in which X and Y (same or different) are S, Se or C(R1)(R2); R7 and R8 (same or different) are substd. alkyl gps. of the type normally found in cyanine sensitiser dyes; R3, R4, R5 and R6 are each H, lower hydroxyalkyl or lower alkoxy gps. with 1-5C; R1 and R2 are each 1-5C alkyl or together form a 4-5C alkylene gp.; Z1 and Z2 are the atoms necessary to complete a heterocyclic gp. of the type found in cyanines and opt. contg. substituents or condensed aromatic rings. The (I) have high stability and can be adsorbed onto the surface of the silver halide grains to give direct positive colour or black and white emulsions. LA PRESENTE INVENTION CONCERNE LES EMULSIONS PHOTOGRAPHIQUES POSITIVES-DIRECTES CONSTITUEES DE GRAINS D'HALOGENURES D'ARGENT A IMAGE INTERNE ET AUXQUELS EST ASSOCIE UN AGENT DE NUCLEATION DE FACON A PERMETTRE LE DEVELOPPEMENT EN POSITIF DE CES EMULSIONS DANS UN REVELATEUR SUPERFICIEL.L'AGENT DE NUCLEATION PRESENTE LA FORMULE:(CF DESSIN DANS BOPI)R ET R REPRESENTENT CHACUN INDEPENDAMMENT DES RADICAUX ALKYLE OU ARYLE SUBSTITUES;R, R ET R REPRESENTENT CHACUN UN ATOME D'HYDROGENE, UN RADICAL HYDROXY OU UN RADICAL ALKYLE INFERIEUR OU ALKOXY INFERIEUR;R ET R REPRESENTENT CHACUN UN RADICAL ALKYLE OU REPRESENTENT ENSEMBLE UN RADICAL ALKYLENE;X-Z ET Y-Z REPRESENTENT CHACUN LES ATOMES NECESSAIRES POUR COMPLETER UN RADICAL HETEROCYCLIQUE DU TYPE DE CEUX FIGURANT DANS LA FORMULE DES COLORANTS CYANINE.