Patent ID: 7431413

Claim:
An image forming apparatus, for forming an image by using distribution of two or more types of dots, each type of dots having a density per unit area different from a density per unit area of other type of dots, the image forming apparatus comprising: a first dot formation determining section, for making comparison between a pixel value of a target pixel in an input image and a value in a dither matrix stored in advance, and for determining, based on a result of the comparison, whether or not a dot, of a first type of dots having the highest density per unit area out of the two or more types of dots, should be formed at a position corresponding to the target pixel; a second dot formation determining section for determining whether or not a dot, of a second type of dots whose density per unit area is lower than that of the first type of dots, should be formed at the position where the first dot formation determining section has determined that the dot of the first type of dots should not be formed, wherein the second dot formation determining section makes a second comparison between the pixel value of the target pixel and a value obtained by subtracting from each value of the dither matrix a fixed value in response to the density per unit area of the second type of dots, and based on a result of the second comparison, the second dot formation determining section determines whether or not any one of the dots of the second type of dots should be formed at the position where the first dot formation determining section determined that a dot should not be formed; and a dot formation instructing section for instructing, based on results of determination by the first and second dot formation determining sections, whether or not a dot should be formed at the position corresponding to the target pixel; wherein the dither matrix comprises values, each of the values being equal to or greater than a predetermined value, which is greater than 0 and smaller than the maximum value taken by the pixel value of the input image.