In an image processing apparatus, four images are generated by shifting an original image before antialiasing by one pixel upward, downward, leftward, and rightward. Between the images obtained by shifting upward and downward, a difference in color information is taken for every pixel to generate a differential image. Similarly, also between the images obtained by shifting leftward and rightward, a difference in color information is taken to generate another differential image. Then, from these two differential images, a product of two difference values is calculated for every pixel for calculating a corner's degree for every pixel. Then, for every pixel, the original image and a blurred original image are blended according to the corner's degree, thereby generating an output image. Consequently, it is possible to obtain a clear image with only corners effectively blurred.