Heat development using acids

A method of forming an image comprising (A) imagewise exposing a light-sensitive material having on a support at least (1) a light-sensitive silver halide, (2) a binder, and (3) a compound which is chemically involved in the reduction of the light-sensitive silver halide to silver under high temperature thereby causing the production or the release of a mobile dye, (B) heating the light-sensitive material in a substantially water-free condition to form the mobile dye with an imagewise distribution subsequently to or simultaneously with the imagewise exposure and then, (C) transferring the mobile dye formed into a dye-fixing layer under high temperature and fixing it thereto;

• wherein an acidic component participates chemically in the reaction system for forming said mobile dye after the conclusion of the mobile dye-forming reaction, wherein said high temperature is not less than 80.degree. C., wherein said acidic component is present in an amount sufficient to adjust the pH value to in the range of below 8.5, further wherein step (C) is conducted in the presence of a hydrophilic thermal solvent.