A process for reducing the size of halftone dot images obtained by exposing and developing a metal image-forming material comprising a support, a thin metallic layer composed mainly of aluminum on the support and a photosensitive resin (or photoresist) layer on the thin metallic layer uniformly by first applying a solution capable of swelling the photosensitive resin layer to those parts which are to be subjected to dot size reduction, and then applying a reducer solution to the parts so treated.