import ij.plugin.FFT;
import ij.io.FileInfo;
import ij.ImagePlus;
String path = "C:\myfolder\images";
FileInfo[] info = ij.io.Opener.getFileInfo(path);
FFT fft = new FFT();
ImagePlus img = new ImagePlus();
for (int i = 0; i < info.length; i++) {
img = ij.io.Opener.openImage(info[i]);
fft.run(img);
ImagePlus fftImage = fft.getFFTImage();
img.setProcessor(fftImage.getProcessor().convertToFloat().mul(fftImage.getProcessor()));
fft.run(img);
ImagePlus mulFFTImage = fft.getFFTImage();
img.setProcessor(mulFFTImage.getProcessor().convertToFloat().mul(mulFFTImage.getProcessor()));
fft.inverseFFT();
img.show();
}