1. An image processing apparatus comprising: a data processing unit for converting data consisting of pixel values at coordinates in an original image into a two-valued value to create data of a processed image consisting of resultant pixel values at coordinates as data of an initial alpha map; and a filtering unit for setting each of the coordinates in the processed image created by the data processing unit as an attention coordinate to be processed, defining a region containing plural coordinates including the attention coordinate as a filter window, and performing a weighted-average filtering operation on data of the filter window, thereby converting the pixel value at the attention coordinate; wherein the filtering unit comprises: a filter coefficient calculating unit for using a first pixel value at a first coordinate in the original image, which first coordinate corresponds to the attention coordinate in the filter window, and a second pixel value at a second coordinate in the original image, which second coordinate corresponds to a certain coordinate in the filter window, to calculate a filter coefficient at the certain coordinate on a coordinate to coordinate basis in the filter window; and a weighted-average filtering unit for using the filter coefficient of each coordinate in the filter window which is calculated by the filter coefficient calculating unit to apply the weighted-average filtering operation on the data of the filter window, and to create resultant data as data of a filtered alpha map.