1. An image processing apparatus comprising: a selection unit selecting an RGB color component having minimum average values of each RGB color component among RGB color components of a read image having reflection of a light source that occurs when a document is read; a calculation unit calculating the amount of change of luminance values of pixels of the read image derived from the reflection, from the values of pixels of the color components selected in the read image; and a correction unit correcting the reflection of the light source in the read image by correcting the luminance values of pixels of the read image using the calculated amount of change of the luminance values of the pixels.