1. An image processing apparatus comprising: a first image processing unit configured to have a fixed image processing function to perform image processing of image data; a second image processing unit configured to have a fixed image processing function to perform image processing of image area data; a reconfigurable image processing unit configured to be capable of having selectively, by reconfiguration of an architecture of the reconfigurable image processing unit, one of least a first image processing function for image processing of image data and a second image processing function for image processing of image area data; and a control unit configured to reconfigure the architecture of the reconfigurable image processing unit to have one of at least the first image processing function for image processing of the image data and a second image processing function for image processing of the image area data on a basis of whether the image processing apparatus processes a color image or a monochrome image, and to control the first image processing unit, the second image processing unit, and the reconfigurable image processing unit, wherein the control unit is further configured: if the image processing apparatus processes a color image, to reconfigure the architecture of the reconfigurable image processing unit to have the first image processing function, to control both the first image processing unit and the reconfigurable image processing unit to perform image processing of image data of the color image, and to control the second image processing unit to perform image processing of image area data of the color image, and if the image processing apparatus processes a monochrome image, to reconfigure the architecture of the reconfigurable image processing unit to have the second image processing function to control the first image processing unit to perform image processing of image data of the monochrome image, and to control both the second image processing unite and the reconfigurable image processing unit to perform image processing of image area data of the monochrome image.