1. An image processing apparatus, comprising: an isolated dot discriminating portion judging, for each of a plurality of pixels included in an image, whether the pixel corresponds to a center pixel of an isolated dot; a size detector detecting an isolated dot size; a dot region discriminating portion judging whether a target pixel is included in a dot region based on a position of said pixel judged as being the center pixel of the isolated dot; and a dot region determining portion determining a dot region based on a position of said target pixel judged as being included in the dot region and said isolated dot size detected.