1. An image processing apparatus for adding a blur to an image in use of depth information corresponding to the image, comprising: a conversion unit configured to convert the depth information into blur size information; a division unit configured to divide the image into a plurality image areas having a same blur size; an image generation unit configured to perform blur processing on each of the plurality of image areas with the blur size to generate blurred images; and a synthesizing unit configured to synthesize the plurality of blurred images generated by the image generation unit.