The image processing method for determining an inside or outside of the rectangular region (window) on the basis of counted values of the first and second raster scanning counters, comprises a step of dividing the entire screen by a region which is encircled by an outer peripheral and straight lines extended from each sides of a rectangular region separated in the sub scanning direction, a step of performing a state transition corresponding to the present scanning position, a step of determining a state to be changed by the counted value of the second counter when both ends in the main scanning direction coincides with both ends of the screen, a step of determining a state to be changed by the counted value of the first counter when an end portion in the main scanning direction does not coincide with an end of the screen, and a step of determining a state to be changed by the counted value of the second counter when an end portion in the main scanning direction does not coincide with an end of the screen and when a starting end does not coincide with an end of the screen, thereby providing a method and system for an image processing capable of determining any of image of inside or outside in the rectangular region with a small circuit scale.