1. An image processing apparatus comprising: a block attribute determination unit which determines, for each block including a predetermined number of pixels of a document image, a block attribute based on the number of edge pixels included in the block, the number of connected edges formed from the edge pixels, and the number of edge pixels included in a connected area formed from the edge pixels, wherein the block attribute determination unit determines the block attribute as a background block, which is formed with background pixels, when the number of edge pixels included in the block is not more than a first threshold, and wherein the block attribute determination unit determines the block attribute as a character block on background area, which is formed with background pixels and character pixels, when the number of edge pixels included in the block is more than the first threshold and the number of connected edges is less than a second threshold, and wherein the block attribute determination unit determines the block attribute as a halftone dot block, which is formed from halftone dot pixels, when the number of edge pixels included in the block is more than the first threshold, the number of connected edges is not less than the second threshold, and there is no connected edge whose number of edge pixels included in the connected area is not less than the third threshold, and wherein the block attribute determination unit determines the block attribute as a character block on halftone dot area, which is formed from halftone dot pixels and character pixels, when the number of edge pixels included in the block is more than the first threshold, the number of connected edges is not less than the second threshold, and there is a connected edge whose number of edge pixels included in the connected area is not less than the third threshold; a block color quantization unit which quantizes color information of each pixel of the block including the predetermined number of pixels of the document image; a block connected area extraction unit which extracts, based on the color information of each pixel quantized by the block color quantization unit, connected areas each included in the block and including connected pixels of the same color; a block background/foreground determination unit which determines whether each connected area is a foreground or a background, based on the block attribute determined by the block attribute determination unit, the color information quantized by the block color quantization unit, and the connected areas acquired by the block connected area extraction unit; a block background/foreground attribute determination unit which determines, based on the block attribute determined by the block attribute determination unit, an attribute of a connected area determined by the block background/foreground determination unit to be the foreground of the block and an attribute of a connected area determined to be the background of the block; and a block background/foreground attribute information recording unit which records and holds information of the attribute of the block determined by the block attribute determination unit and the attribute of each connected area determined by the block background/foreground attribute determination unit.