1. An image processing apparatus for performing an image quality improving processing of an image, comprising: a domain block extracting section for extracting a domain block image from an original image in the unit of a first block unit; a range block extracting section for extracting a range block image from the original image in the unit of a second block unit which is larger than the first block unit with respect to the domain block image; a reduced range block forming section for reducing the extracted range block image to the size of the first block unit; and an improved domain block forming section for performing a pixel value conversion with respect to the reduced range block image formed by the reduced range block forming section, and for outputting the pixel-value-converted reduced range block image as an improved domain block image.