1. An image processing apparatus, comprising: image reducing means, for generating a reduced image by reducing an original image in at least one of a main direction and a sub direction; noise image extracting means, for generating a linear noise image by extracting linear noise components from the reduced image generated by the image reducing means; image enlarging means, for enlarging the linear noise image generated by the noise image extracting means to the image size of the original image; and image correcting means, for removing the linear noise components from the original image, employing the linear noise image which has been enlarged by the image enlarging means.