1. A method of estimating an image orientation field, comprising: dividing an image into first partial regions; measuring gradients of pixels of the image; estimating representative orientations of the first partial regions; filtering the image using a double orientation filter to form an improved image; remeasuring the representative orientations of the first partial regions by remeasuring the gradients of the pixels of the improved image; dividing the first partial regions into second partial regions; and estimating representative orientations of the second partial regions with respect to curvature of the first partial regions in response to the remeasured representative orientations of the first partial regions and the remeasured gradients of the pixels.