1. A method of image processing, the method comprising: obtaining blocks of an input image by dividing the input image into the blocks; obtaining orthogonal transform coefficients by performing an orthogonal transform on pixel values in the blocks; and generating a resulting image by normalizing the orthogonal transform coefficients within the blocks such that normalized orthogonal transform coefficients for an illuminated area, a penumbra area and an umbra area for a same block of the blocks are the same.