A very-high-contrast direct-positive image was obtained when a prefogged AgBr photographic emulsion containing certain bipyridinium salts, such as 1-n-butyl-4-(4′-pyridyl)pyridinium bromide hydrochloride (Compound 1), was processed with a developer that contains Metol and ascorbic acid as developing agents. Results of photographic and electrochemical studies suggested that Compound 1 has two functions, as an electron acceptor and as a precursor of a nucleator. A theory was developed that, during exposure, Compound 1 acts as an electron acceptor, which produces a direct-image,and that Compound 1 is neutralized during development to form 1-n-butyl-4-(4′-pyridyl)pyridinium bromide (Compound 2), which acts as a nucleator during development and produces very-high-contrast images.