PURPOSE:To form a positive image having satisfactory photographic performance in a short time by imagewise exposing a photographic material having an internal latent image type silver halide emulsion layer and by developing the exposed material with an alkaline soln. of a developer in the presence of specified zwitter ion (N-ylide). CONSTITUTION:A compound represented by general formula I (where Y is acyl or cyano: X- is an anion; and the 3-, 4- and 5-positions of the pyridium ring and the acyl may be substituted), e.g., the compound of formula II or III (beta-ketopyridinium salt which gives N-ylide under alkali conditions) is blended into a photosensitive material having an internal latent image type silver halide emulsion layer in an amount of about 1X10-4-6X10-3mol per mol of silver halide. The above-mentioned compounds forms N-ylide represented by formula IV under alkaline conditions of development.
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