title: Interpret numpy.fft.fft2 output
body: <p>My goal is to obtain a plot with the spatial frequencies of an image - kind of like doing a fourier transformation on it. I don't care about the position on the image of features with the frequency f (for instance); I'd just like to have a graphic which tells me how much of every frequency I have (the amplitude for a frequency band could be represented by the sum of contrasts with that frequency).</p>
  
  <p>I am trying to do this via the <a href="http://docs.scipy.org/doc/numpy/reference/generated/numpy.fft.fft2.html" rel="noreferrer"><code>numpy.fft.fft2</code></a> function.</p>
  
  <p>Here is a link to a <a href="http://nbviewer.ipython.org/urls/gist.github.com/TheChymera/8606917/raw/2a93b8b1c3b15e8467cca21b5924c20533787fc5/imFreq?create=1" rel="noreferrer">minimal example</a> portraying my use case.</p>
  
  <p>As it turns out I only get distinctly larger values for <code>frequencies[:30,:30]</code>, and of these the absolute highest value is <code>frequencies[0,0]</code>. How can I interpret this? </p>
  
  <ul>
  <li>What exactly does the amplitude of each value stand for?</li>
  <li>What does it mean that my highest value is in <code>frequency[0,0]</code> What is a <code>0 Hz</code> frequency?</li>
  <li>Can I bin the values somehow so that my frequency spectrum is orientation agnostic?</li>
  </ul>