1. An image processing apparatus, comprising: a determination unit configured to determine whether or not a size of a region which is specified based on a comparison between pixel values of adjacent pixels in an input image is larger than a predetermined threshold; a smoothing unit configured to perform smoothing processing on the input image according to a result of the determination by the determination unit such that a region having a larger size than the predetermined threshold is smoothed stronger than a region having a smaller size than the predetermined threshold; and an image transformation unit configured to perform image transformation processing on the image on which smoothing processing was performed by the smoothing unit.