1. An image processing method for projection transforming of an original image into a transformed image, the transformed image correcting distortion of the original image, the method comprising: partitioning a whole area of the transformed image to be obtained by a projection transformation of the original image into a plurality of regions, wherein none of the plurality of regions is intersected by either a vertical axis or a horizontal axis, the vertical and horizontal axes extending in a plane containing the transformed image and passing through an origin at a center of the whole area; determining, for each region of the plurality of regions defined in the whole area of the transformed image, a corresponding region in the original image that corresponds to each of the plurality of regions defined in the whole area of the transformed image; and performing the projection transformation for each of the corresponding regions defined in the original image to obtain the transformed image, wherein the partitioning step includes: a first partitioning step carrying out the partitioning at a predetermined size so that the whole area of the transformed image is partitioned into a plurality of first regions; and a second partitioning step changing a size of each of the plurality of first regions partitioned in the first partitioning step, into second regions, so that none of the second regions is intersected by any of the axes, and the determining step determines, based on the second regions, the corresponding regions in the original image.