An image processing apparatus includes a decimating unit configured to decimate pixels in a target image to obtain a decimated image containing a smaller number of pixels than the target image; an extracting unit configured to extract similar pixels at each of which a similarity to a pixel of interest is a threshold or more, from a region containing the pixel of interest among pixels of the decimated image; a first calculating unit configured to calculate a correction candidate value based on pixel values of the similar pixels; a second calculating unit configured to calculate a correction candidate value for each decimated pixel, based on the correction candidate value calculated for each pixel of the decimated image; and a correcting unit configured to correct a target pixel value of a target pixel in the target image, based on the correction candidate value calculated by the first or second calculating unit.