1. An image processing method comprising: comparing by an ε filter a difference between a pixel value of a target pixel to be processed and a pixel value of a surrounding pixel neighboring the target pixel in each pixel block of an input image with at least a first predetermined threshold and a second predetermined threshold that is larger than the first predetermined threshold; performing replacement of the pixel value of the surrounding pixel on a basis of the comparison, wherein when the difference is less than the first threshold, the ε filter leaves the pixel value of the surrounding pixel without the replacement, when the difference exceeds the first threshold and is less than the second threshold, the ε filter replaces the pixel value of the surrounding pixel with an average of pixel values of the target pixel and the surrounding pixel, and when the difference exceeds the second threshold, the ε filter replaces the pixel value of the surrounding pixel with the pixel value of the target pixel.