1. An image quality evaluation method comprising, based on an alternating-current component differential value, which is a difference between a statistical quantity of alternating-current components within a pixel group in a first image and a statistical quantity of alternating-current components within a pixel group in a second image at the same position as a position of said pixel group in said first image, evaluating image quality of said second image, wherein said statistical quantity of alternating-current components within the pixel group is an average of absolute differences within an image group, each of said differences being an absolute difference between an average of pixel values within said pixel group and each pixel value within said pixel group, wherein the method comprises applying weighting processing to said alternating-current component differential value based on the statistical quantity of alternating-current components for said second image, wherein said weighting processing comprises comparing a statistical quantity of alternating-current components for said second image with a predetermined threshold, and in a case that the statistical quantity of alternating-current components for said second image is greater than said predetermined threshold, multiplying said alternating-current component differential value by a predetermined constant smaller than one.