1. A method of extracting image regions from an image including different types of image regions, comprising: using a processor to perform the steps of: generating an edge-emphasized image by applying an edge-emphasis process to an input image; setting an inner edge signal of a pixel of the edge-emphasized image to an affirmative value when a value of the pixel is greater than a first threshold value, and setting an outer edge signal of a pixel of the edge-emphasized image to an affirmative value when a value of the pixel is less than a second threshold value, wherein the first threshold value is positive and the second threshold value is negative; determining whether an OR signal of each pixel is set to an affirmative value or not based on the inner and outer edge signals of each pixel; counting a first number of pixels having the affirmative OR signal in an area which includes a pixel of interest and has a first pixel size so as to compare the counted first number with a third threshold value; counting a second number of pixels having the affirmative OR signal in an area which includes the pixel of interest and has a second pixel size larger than the first pixel size so as to compare the counted second number with a fourth threshold value; and determining whether or not the pixel of interest belongs to a halftone dot region based on the comparison results in the first and second counting steps.