When one scans document pages from a bound book, shading artifacts are commonly occurred in the book spine area. In this letter, we propose a general-purpose method for image shading correction based on an assumption that the reflectance function of the page surface is piecewise constant and the illumination function is smooth. The proposed method is able to completely correct more general types of shading artifacts which are nonuniformly distributed along the book spine. Comparison experiments on a synthetic and a variety of real scanned book images demonstrate the feasibility and effectiveness of the proposed method.