An image processing method for adjusting the luminance and contrast of an input image comprises the following steps. First, local spatial luminance statistics is performed on the first pixels of the input image to generate a luminance image including a plurality of second pixels. Then, from a preset mapping curve group comprising a plurality of smooth mapping curves, a corresponding smooth mapping curve is selected for each of the second pixels according to an adjusting function. Next, the pixel values of the second pixels are adjusted according to the corresponding smooth mapping curves to generate an adjusted image.