Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83 SMI; site ur-laser.uucp Path: utzoo!linus!philabs!cmcl2!seismo!rochester!ur-laser!nitin From: nitin@ur-laser.uucp (Nitin Sampat) Newsgroups: net.graphics Subject: FFT of image in sections ? Message-ID: <360@ur-laser.uucp> Date: Tue, 6-Aug-85 13:16:53 EDT Article-I.D.: ur-laser.360 Posted: Tue Aug 6 13:16:53 1985 Date-Received: Thu, 8-Aug-85 00:23:02 EDT Organization: Lab for Laser Energetics, Univ. of Rochester Lines: 25 FFT's as we know exhibit a nonlinear increase in computation time as the size of the image increases. Also, the hardware determines the CPU time you get from the computer. If your record size is too large for the core the computer starts paging, copying to and fro from disk, therby increasing the processing time. One solution to this could be to process the image in sub-sections. Each sub-section of the image could be so chosen that the record size is large enough to fit in core memory at one time. This would eliminate any paging. Can this be done and if so how does one go about chosing the sub-sections ? After all, theory defines that the image is a function f(x,y) with a period N(=no. of points). If we divide the image into sections, we are in effect defying the basis of linear system theory. I was told that the trick is to overlap one section onto the other is some fashion, after the FFT operation. Does anybody have any experience with this ? I guess the question I am asking is this : We know that processing small images takes less time. Well, how does one go about breaking up a large image and process it in sections, and then most importantly, how does one put all these sections back to get the FFT of the original image ? nitin {seismo,allegra}!rochester!ur-laser!nitin.uucp