static ImageSurface showFrequencyImage(final File audioFile) {
  if (audioFile == null) null;
  ImageSurface is = showZoomedBWImage(audioFile.getName(), audioFileToFrequencyImage(audioFile));
  addButtonsToWindow(is, "Play", rThread { playAudioFile(audioFile) });
  packInNorthEastCorner(is);
  ret is;
}