As an image forming apparatus such as a copying apparatus, a printer and the like using a digital photographic process or an inkjet technique, a full-color copying apparatus, a complex machine and the like which reproduces high quality color images has been manufactured according to development of digital image processing techniques.
In these image forming apparatuses, in order to obtain a successful reproductive image of a document image, it is required to perform an image processing suitable for each type of the document image. For this reason, in the image forming apparatus, a segmentation process is performed to separate an input image data to be processed into multiple regions.
For example, Patent Document 1 discloses that each pixel of an input image data is separated into a halftone region, a text region, a photographic paper region, a page-background region, and an indefinite region to which pixels, which cannot be classified in any regions above, belong. The page-background region is a background section where brightness of the image is more than a certain degree. Therefore, pixels belonging to the page-background region are separated based on the brightness.
Moreover, Patent Document 2 discloses a page-background density is removed by an automatic exposure process with respect to a region separated into the page-background region. The automatic exposure process is a method to obtain a high quality image by determining a document type and selecting a color correction property according to the document type.
With the conventional configurations, the page-background removal process is performed, so that a text can be vividly reproduced in an image having the text. Furthermore, as a series of processes, a black generation process, an under color removal process (UCR), and a filter process (edge emphasizing process) are performed, so that the text on the page-background is reproduced in such a manner that the page-background around the text does not become white.    Patent Document 1: Japanese Unexamined Patent Publication, Tokukai, No. 2004-272557 (published on Sep. 30, 2004)    Patent Document 2: Japanese Unexamined Patent Publication, Tokukai, No. 2001-285635 (published on Oct. 12, 2001)
As described above, in ordinary printings except a newspaper, the page-background removal process is just performed, so that a visual sharpness of the text can be improved in an image printed by the image forming apparatus. This is because in ordinary printings except for a newspaper, a density change of a text edge section is clear.
However, unfortunately, in the case where an image to be processed is printed on a newspaper, when the page-background removal process is performed, a visual sharpness of the text becomes rather lower. This is because a quality of recycled papers used for newspapers and the like is rough. Therefore, the text printed thereon has a wide density change region at the edge section and the edge section is blurred. Accordingly, when a gray page-background is removed, the edge section of the text is rather more blurred.