Package: ImageFFT Filed on [Indigo]Documentation>ImageFFTDoc.tioga Maintainer: Plass Date: July 3, 1984 3:35:15 pm PDT DF file: [Indigo]Top>ImageFFT.df Purpose: Client package for 2 dimensional Fast Fourier Transforms (forword and reverse), intended for image-processing applications. A simple commandTool user interface is also provided. Public interface: ImageFFT Executive commands: ClipAIS output _ input clips a sampled image to the specified dimensions. There are probably more user-friendly ways to do this. "output" and "input" are AIS file names (including extensions). FFTFilter output _ input filter1 filter2 . . . Applies the specified filters (see below) to the input AIS file to obtain the output AIS file. FFTShow input filter1 filter2 . . . Displays the log intensity of the FFT of the input AIS file on the color display (ignoring Viewers!), after the specified filters are applied. Filters: The following spectral filters may be used with the commands above: SquareLowPass a square-shaped low-pass filter Spot scales fuzzy spot around [x, y] by the factor m BandBoost scales annulus centered on the origin by m All the filters are applied symmetically in the four quadrants. The values in the frequency domain are in units such that half of the sampling frequency corresponds to a value of 1.0. Examples: ClipAIS y.ais _ [pixel]bighumber.ais 150 1060 256 256 FFTFilter yy.ais _ y.ais 0.5 0.5 0.05 0.05 Spot .9 20 .1 0 BandBoost .95 20 .1 0 BandBoost Limitations: The FFT program works on square images whose size (height & width) is a power of two. Images that do not conform to this are automatically padded out to the next larger legal size; note that this may result in a lot of wasted space. The largest size tested was 512 square, which takes several minutes. On a machine with four megawords of real memory it might be possible to go to 1024 square, but it would take awhile. It is advisable to experiment with a small patch of the image (say 128 square) to find the appropriate filter before doing the whole thing.