1. An apparatus for estimating edge areas of a digital image comprising: a luminance difference average calculation unit calculating, for each one of pixels in an input image, a luminance difference average, representing an average in absolute values of luminance differences between the one of pixels and each of neighboring pixels around the one pixel; a histogram difference average histogram calculation unit generating a histogram for the calculated luminance difference average of the input image; a luminance difference average cumulative distribution calculation unit calculating a cumulative distribution of the luminance difference average from the calculated histogram for the luminance difference average; and a binary mask generation unit setting a luminance difference average having a frequency distribution of the histogram preset in a cumulative distribution of the luminance difference average to be a reference value, and generating a binary mask used for distinguishing a pixel having a luminance difference average lower than the reference value from a pixel having a luminance difference average higher than the reference value, wherein the binary mask generation unit determines that the pixel with the luminance difference average higher than the reference value is in an edge area of the input image.