 above for options
   .resample   - [1] image resampling prior to homography estimation
   .sig        - [2] amount of Gaussian spatial smoothing to apply
   .epsilon    - [1e-3] stopping criteria (min change in error)
   .lambda     - [1e-6] regularization term favoring small transforms
   .outThr     - [inf] outlier threshold
   .minArea    - [4096] minimum image area in coarse to fine search
   .H0         - [eye(3)] optional initial homography estimate
   .show       - [0] optionally display res