e
 running on anything bigger.

 USAGE
  [Vx,Vy,reliab] = optFlowCorr( I1, I2, patchR, searchR,
                                 [sigma], [thr], [show] )

 INPUTS
  I1, I2      - input images to calculate flow between
  patchR      - determines correlation patch size around each pixel
  searchR     - search radius for corresponding patch
  sigma       - [1] amount to smooth by (may be 0)
  thr         - [.001] RELATIVE reliability threshold
  show        - [0] figure to use for display (no disp