The Spatial Fast Fourier Transforms subsystem in DigImage provides access to spatial FFTs in one dimension at full resolution or in two dimensions at a reduced resolution of 256x128. The reduced resolution in two dimensions is necessary due to the limited available memory within MS-DOS.
This option scales etc. enables a full resolution FFT of lines or columns (not both simultaneously) to be calculated. The FFT may be of a window or the whole screen. If the number of pixels in the required direction in the window is not equal to 2^n, then the data is padded in an appropriate manner.
Two-dimensional FFTs may be evaluated only at a reduced resolution due to limitations in the amount of memory available under MS-DOS. As for [1 One-dimensional FFT], the main purpose of this option is for the evaluation of length scales etc.
DigImage User Documentation