1. An image processing apparatus for forming a color image on an image holding member based on image data, and transferring and fixing the color image onto a print medium, comprising: a first detector, arranged to detect an image characteristic of the image transferred and fixed onto the print medium; a second detector, arranged to detect an image characteristic of an image formed on the image holding member; a controller, arranged to form a first pattern to detect an image characteristic on the print medium by a sequence different from normal image formation, and control a condition for image formation on the image holding member based on the image characteristic of the first pattern, detected by said first detector; and a corrector, arranged to form a second pattern to detect an image characteristic on the image holding member after completion of control of the condition for image formation by said controller, hold the image characteristic of the second pattern detected by said second detector as reference information, and in the normal image formation, form the second pattern without an image formation area on the image holding member in the normal image formation, and correct the condition for image formation controlled by said controller, based on a difference between the image characteristic of the second pattern detected by said second detector and the reference information.