Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site brand.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!lll-crg!dual!qantel!hplabs!sdcrdcf!oberon!brand!shankar From: shankar@brand.UUCP (Shankar Chatterjee) Newsgroups: net.graphics Subject: Re: FFT of image in sections ? Message-ID: <159@brand.UUCP> Date: Fri, 9-Aug-85 13:42:10 EDT Article-I.D.: brand.159 Posted: Fri Aug 9 13:42:10 1985 Date-Received: Wed, 14-Aug-85 22:11:23 EDT References: <360@ur-laser.uucp> Reply-To: shankar@brand.UUCP (Shankar Chatterjee) Distribution: net.graphics Organization: U. of So. Calif., Los Angeles Lines: 14 Keywords: Images, matrix transpositions, FFT In most cases, when a 2-D FFT of an image is required, 1-D FFT is performed on one row at a time if the image is too large to fit into the core. After this the image in the disk is 'transposed' using some block allocation strategy. The block size can be fixed or can be determined (alongwith the no. of passes over the image) from the available core. [Note here that the transpostion has to be done block by block to speed up processing. One could refer to J.O. Eklundh (IEEE Tr. on Computers, vol. C-21, 1972) or a more generalized version of it in H.K. Ramapriyan (IEEE Tr. on Comp., Dec. 1972). I had implemented a modified version of the latter in software on a PE-3220 machine.] After this another 1-D FFT is performed on the rows. However some smart addressing scheme is needed (butterfly ?) to center the d.c. term. Shankar Chatterjee USC Signal & Image Processing Institute shankar!brand%oberon%usc-cse@csnet-relay