1. An image processing apparatus for performing region segmentation of an image, comprising: a memory; and a processor in communication with the memory that, upon execution of codes stored in the memory, functions as: a generation unit configured to generate a plurality of block images by dividing an input image into blocks each of which has a predetermined size; and a segmentation unit configured to perform clustering of pixels contained in the plurality of block images based on a representative point associated with each of those block images so as to apply the region segmentation to those block images, wherein the representative point is a part of a plurality of representative points disposed in the input image, wherein the clustering in a target block image of the region segmentation is performed by referring to a representative point in the target block image, a representative point of a processed block image on which the region segmentation has been performed, and a representative point of an unprocessed block image on which the region segmentation has not been performed yet, and wherein the processed block image and the unprocessed block image are adjacent to the target block image.