Wide-area image restoration using a new iterative registration method

Over a wide field of view (e.g., 100 arcsec in optical astronomy) the point spread function due to atmospheric effects is found to be far form position invariant, and appears as a combination of local warping and local blurring. Recently, we discussed a method in which the first step in restoration is to register all points in every frame of a movie sequence to the corresponding points in a prototype image. After registration, each frame is de- warped and summed to form an average, motion-blur corrected result. Previously, we applied a hierarchical, windowed cross correlation process to obtain local x and y registration information, similar to common methods in stereo cartography. We discuss a new approach to image registration for this purpose. Suppose two images to be registered differ mainly in varying random, but spatially coherent warping (such as occurs as one effect of a slowly varying wavefront tip-tilt over a wide field of vies). Imagine that one image, the reference image, is represented by a solid surface corresponding to its intensity distribution. Imagine that the second image is also represented by a surface, but in the form of a flexible, rubber mold. If the two images are identical, then the mold fits the solid like a glove. If one image includes local warping relative to the other, then the mold or glove must be forced to fit though local distortions.