A method is provided for processing image data read from a book document placed on a platen of an image reading apparatus. The method includes determining a background pixel of the image data based on a luminance difference or a color difference between neighboring pixel arrays, identifying a shadow region based on a luminance change between the neighboring background pixel arrays, discriminatively detecting a shadow of a binding portion and a shadow of a front edge in a document region with reference to a changing direction of shadow luminance, and performing a luminance correction on the shadow region according to characteristics of the shadows.