title: Why does fundamental matrix have 7 degrees of freedom?
body: <p>There are 9 parameters in the fundamental matrix to relate the pixel co-ordinates of left and right images but only 7 degrees of freedom (DOF).</p>
  
  <p>The reasoning for this on several pages that I've searched says :</p>
  
  <ol>
  <li><p>Homogenous equations means we lose a degree of freedom </p></li>
  <li><p>The determinant of F = 0, therefore we lose another degree of freedom. </p></li>
  </ol>
  
  <p>I don't understand why those 2 reasons mean we lose 2 DOF - can someone explain it?</p>