1. An image processing system for processing a digital binary image, comprising: image memory means for temporarily storing first binary image data; determining means for determining, on the basis of the first binary image data stored in said image memory means, one of a line image area and a pseudo gray scale image area to which a point to be processed of the image belongs; means for scanning, when it is determined by said determining means that said point to be processed belongs to the pseudo gray scale image area, said first binary image data in said image memory means with a first scan window of m1.times.n1 pixel where is m1.times.n1 is greater than 1, on an arbitrary coordinate system; means for converting said first binary image data of m1.times.n1 pixels scanned with said first scan window into multivalued gray scale image data; means for scanning, when it is determined by said determining means that said point to be processed belongs to the line image area, said first binary image data in said image memory means with a second scan window of m2.times.n2 pixel where m2.times.n2 is greater than 1, on a arbitrary coordinate system; and means for converting said first binary image data of m2.times.n2 pixels scanned with said second scan window into second binary image data.