Abstract: An image processing system wherein for an inputted composite image composed of a line image and a dither image, both a line image processing and a dither image processing are carried out in parallel, and one of the processed results is selected in accordance with the image region discrimination result. The dither image processing is carried out through data conversion for calculating multivalued gray scale image from the inputted image data, grey scale data conversion for adjusting the gray scale image data so as to match an output device and obtaining such adjusted gray scale image data, and re-binarization for re-binarizing the gray scale image data after subjected to the grey scale conversion. The image region discrimination for discriminating if an image region is of a line image or a dither image is carried out based on a ratio of the number of black or white pixels within the region to the contour line length within the range.