1. An image processing apparatus performing a compression process on an input image, the image processing apparatus comprising: a background layer generation section generating a background layer by extracting a text region from the input image and removing at least the text region from the input image; a background region extraction section extracting, from the background layer, a background region corresponding to a color characteristic, the background region extraction section including: a background color estimation section estimating, from the background layer, a background color that is a uniform local background color determined to belong in a same color, according to the color characteristic, or a uniform page background color determined to belong in a same color, according to the color characteristic; and a background image extraction section extracting, from the background layer, the background region having the background color estimated; a coordinate recording section recording coordinate values indicative of a rectangle region including the background region extracted by the background region extraction section; and a data storage section storing the background region in a form in accordance with the color characteristic of the background region extracted by the background region extraction section, the background image extraction section including: a background shape determination section determining a shape of the background region extracted; and a mask image generation section generating a mask image showing the shape of the background region, wherein, in a case where the background shape determination section determines that the shape of the background region is a rectangle, the data storage section stores a local background and a page background as information including: the background color estimated by the background color estimation section; and the coordinate values indicative of the rectangle region recorded in the coordinate recording section, the local background and the page background being included in the background layer, and in contrast, in a case where the background shape determination section determines that the shape of the background region is not a rectangle, the data storage section stores the local background and the page background as information including: the background color estimated by the background color estimation section; and data obtained by subjecting, to lossless compression, the mask image generated by the mask image generation section, the local background and the page background being included in the background layer.