1. An image processing apparatus for extracting a halftone dot region in inputted image data, the image processing apparatus comprising: an isolated point detecting section for detecting an isolated point in inputted image data and a size of the isolated point; a temporary halftone dot region determining section for determining a temporary halftone dot region based on presence of isolated points detected by the isolated point detecting section; an isolated point magnifying section for determining a magnified isolated point region that is equivalent to magnification of an isolated point detected by the isolated point detecting section up to at least a size of the isolated point detected by the isolated point detecting section; and a halftone dot region restricting section for determining a halftone dot processing region that is equivalent to restriction of a temporary halftone dot region with reference to a magnified isolated point region based on a temporary halftone dot region determined by the temporary halftone dot region determining section and a magnified isolated point region determined by the isolated point magnifying section.