title: OpenCV Error: Unsupported format or combination of formats (Unsupported combination of input and output formats) in getRectSubPix
body: <p>Running <code>cv2.getRectSubPix(img, (5,5), (0,0))</code> throws the error:</p>
  <pre><code>OpenCV Error: Unsupported format or combination of formats (Unsupported combination of input and output formats) in getRectSubPix.
  </code></pre>
  <p>The <code>dtype</code> of <code>img</code> is <em>float64</em>, which was determined with <code>img.dtype</code>.</p>