An image processing apparatus comprises a characteristic value generator for receiving image data, analyzing neighboring pixels of a to-be-processed pixel and calculating characteristic values comprising average illumination, illumination variability and histogram of illumination of a local image; a weighting generator for generating first and second weightings according to the characteristic values, wherein the first weighting is inversely proportional to the average illumination and directly proportional to the illumination variability, and the second weighting is relative to the histogram of illumination and illumination of the to-be-processed pixel; a first/second modulated illumination generator for generating first/second modulated illumination according to the illumination of the to-be-processed pixel; and a computation unit for generating first and second weighting illumination according to the first and second weightings and the first and second modulated illumination, and synthesizing the first and second weighting illumination together to output an image value.