An image processing method applied in an image processor for processing an image including first pixels each having a pixel value, a first reference pixel value representing a mean value of the pixel values of the first pixels, the pixel values of the first pixels being distributed within a first distribution range bounded between a second reference pixel value and a third reference pixel value. Second pixels are selected from the first pixels. The pixel values of the second pixels are distributed within a second distribution range. The second distribution range of the second pixels is smaller than the first distribution range of the first pixels. A local characteristic of the image is obtained according to the second pixels. A parameter of the image is adjusted according to the local characteristic.