Image-formation methods and photosensitive materials used in such methods are disclosed that form very high-resolution patterns. The photosensitive materials comprise an ingredient that is triggered by a radical to undergo a latent-image-forming reaction. The radicals are produced by photons from an illumination light. Alternatively, the ingredient is triggered by a reactive-intermediate compound that is activated by the exposure-produced radical. The photosensitive materials possess a non-linear sensitivity characteristic in which the latent-image reaction density increases according to the mth power (m>1) of the incident light intensity. The photosensitive material can be applied to a sensitive substrate for exposure. Multiple exposures of the sensitive substrate are performed using a projected mask pattern in the presence of a radical deactivator. The multiple exposures can be performed while: (a) changing the exposure intensity distribution on the photosensitive material, or (b) shifting the projected mask pattern and the sensitive substrate relative to each other by a specified amount, or (c) using a different projected mask pattern for each exposure.