Details
FVDIF computes the Nth order vertical differentiation of a potential field. The filter is applied in frequency domain after transforming the image using 2D FFT.
FVDIF does not require the entire image to be loaded into memory. There is, therefore, no limit on the size of input image. If necessary, a disk buffer file is used. FVDIF automatically creates a buffer file if there is no suitable one given by FILB. The file name is recorded in FILB for efficiently reusing the buffer in another run.
For maximum efficiency, x-size and y-size values must be in power of 2.