a convulution of an image with a filter in the frequency domain can be performed via multiplication.
In the VisualApplets design "FFtandbandpass.va" this is done correctly. After the image is transformed via FFT to frequency space a multiplication with a filter image (buffered in operator CoefficientBuffer) is performed. The filter image ( e.g. bandpass filter) buffered in the operator Coefficient Buffer can be generated using external software.