In order to the monochromatic conversion of an image, in an image processing apparatus (1a), the color used within the image inputted from an image inputting section (2) is determined by a color analyzing section (3), the mixing-ratio of the color components of the image is defined based on the color by a mixing-ratio calculating section (4), the color components are mixed according to the mixing-ratio by an image converting section (5) thereby converting the input image to a monochromatic image, and it is outputted from an image outputting section (6). Further, in order to contract an composite image comprising a character, a line drawing, and a halftone dot, an image processing apparatus (21a) comprises an image inputting section (22), a character/line drawing region extracting section (23) for an input image, a pseudo-density region extracting section (24) for the input image, an image contracting section (25) for contracting the image using different methods respectively in the pseudo-density region, the character/line drawing region, and the other region, and an image outputting section (26) for outputting the image. Furthermore, in order to eliminate a ghost image, in an image processing apparatus (31a), front and back images are inputted from an image inputting section (32), an image reversing section (33a) reverses it, a positional relationship detecting section (34) detects the positional relationship, an image correcting section (35) corrects the image as to eliminate a ghost image, an image reversing section (33b) reverses it again, and an image outputting section (36). Further, in order to align the image position, in an image processing apparatus (50), the alignment of the images of the consecutive pages from among the images inputted page by page from the image inputting section (51) is carried out by a page contour detecting section (52), a page contents region extracting section (53), an inclination correcting section (54), and page information processing section (57), and it is outputted from the image outputting section (56).