1. An image processing apparatus generating pixel data inside a drawn area of a screen coordinate system to perform rendering with respect to a memory and generate an image drawn in said memory and, at that time, generating edge information and performing anti-aliasing, comprising an edge information extracting means for extracting said edge information based on predetermined pixel data drawn in said memory and an anti-aliasing means for determining the content of processing required for anti-aliasing based on the edge information obtained by said edge information extracting means and executing the determined processing.