1. An image processing apparatus capable of dividing a document image into block images, each including a predetermined number of pixels, and determining whether an attribute of each of the divided block images is a character, the image processing apparatus comprising: a smoothing unit configured to smooth a block image to generate a smoothed block image; a color distribution acquiring unit configured to acquire a color distribution characteristic amount of the smoothed block image; an edge acquiring unit configured to acquire an edge characteristic amount of the block image; a color distribution determination unit configured to determine whether an attribute of the block image is a character based on the color distribution characteristic amount acquired by the color distribution acquiring unit; an edge determination unit configured to determine whether the attribute of the block image is a character based on the edge characteristic amount acquired by the edge acquiring unit; and a determination unit configured, in a case where the color distribution determination unit determines with high reliability that the attribute of the block image is a character, to determine the attribute of the block image is a character, and in a case where the color distribution determination unit determines with not high reliability that the attribute of the block image is a character, to determine the attribute of the block image based on a determination result by the edge determination unit.