1. An image processing apparatus for carrying out an image processing on image data composed of a plurality of color components, comprising: a document type discrimination section for discriminating a type of a document which is read to obtain the image data; an image processing section for carrying out enhancement and error diffusion processes on the image data; a black generation amount calculation section for calculating a black generation amount for each pixel based on the image data; and an under color removal process section for performing an under color removal process in which the under color removal process section calculates an under color removal amount for each pixel based on the image data so as to determine image data of a plurality of color components, which image data is to be obtained by the under color removal process, if the document type discrimination section discriminates the document as a printed photo document or a text/printed photo document that includes black halftones, then the image processing section carrying out the enhancement and the error diffusion processes on the image data, and the black generation amount calculation section and the under color removal process section executing a non-uniform image suppressing operation mode in which no black generation and under color removal process is carried out on a pixel in which a minimum value of the image data composed of the plurality of color components is at least equal to or less than a predetermined threshold.