1. An image processing method for adjusting the luminance and contrast of an input image including a plurality of first pixels, comprising: performing local spatial luminance statistics on the first pixels of the input image to generate a luminance image including a plurality of second pixels; from a preset mapping curve group comprising a plurality of smooth mapping curves, selecting a corresponding smooth mapping curve for each of the second pixels according to an adjusting function; and adjusting the pixel values of the second pixels according to the corresponding smooth mapping curves to generate an adjusted image.