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!watmath!clyde!bonnie!akgua!whuxlm!harpo!decvax!genrad!panda!talcott!harvard!seismo!rochester!ur-laser!nitin From: nitin@ur-laser.uucp (Nitin Sampat) Newsgroups: net.graphics Subject: FFT of image in sections.. Message-ID: <298@ur-laser.uucp> Date: Mon, 19-Aug-85 11:18:51 EDT Article-I.D.: ur-laser.298 Posted: Mon Aug 19 11:18:51 1985 Date-Received: Sat, 24-Aug-85 15:15:46 EDT Organization: Lab for Laser Energetics, Univ. of Rochester Lines: 27 From what I have reading regarding this article since I posted it, it seems to me that I may not have communicated my question clearly enough. Carl Lowenstein and Shep Seigel mention that taking an FFT does involve doing it in "sections" or representing a two dimensional string of numbers as a one dimensional string etc..All that is fine but my question did not refer to the FFT algorithm itself or how it manifests itself(although that would be an interesting discussion in itself) in "sections". I am saying that once we have a certain FFT algorithm that we start using, we may be limited by the core memory depending on the computer we are using. If we have a megabyte image and we try an FFT on it, most computers will start paging, copying to and fro from disk since they can't fit the entire image in core at one time. However, they can process a smaller image almost instantaneously(that is an image small enough to get complete processing in core without any significant paging). Once we determine what the physical limitof our computer is, we will know the smallest image we can process FAST. Given this information, my question is, can we now process the megabyte image in such sections and get any increase in speed. Also, does linear system theory allow such a process.. because an FFT of a part is NOT the FFT of the whole image. I dont think we can take a 64 X 64 image ( say ) , break it up into 16 X 16 sub-images, FFT them and put these FFT'd sub-images together to say that this is the FFT of the original 64 X 64 image, or can we ? nitin {allegra,seismo}!rochester!ur-laser.uucp