1. An image processing method for removing noise contained in an image, comprising: inputting an original image constituted with a plurality of pixels; extracting a first high-frequency component through first high-pass filter processing executed on the original image; extracting a second high-frequency component through second high-pass filter processing executed on the extracted first high-frequency component; extracting a noise component by separating the noise component through nonlinear conversion processing executed on the extracted second high-frequency component; and removing noise in the original image based upon the extracted noise component, wherein the nonlinear conversion processing is attenuation processing whereby a non-noise component contained in the second high-frequency component is attenuated by multiplying the second high-frequency component by a weighted Gaussian coefficient having an argument of a value resulting from a comparison of the second high-frequency component with a predetermined threshold value.