image registration
- limitations in scope
  - object is near by
  - object is given
- alternate techniques
  - coarse-fine
  - alpha-beta pruning
  - limited search space
derivative estimate
- begin with average
- use the second derivative for weighted average
alternative estimate
- no div by zero problems
- more general
- can add weighting from the original
convergence
- for sinusoids it will converge if h < half period
- lowpass filtering helps convergence
- coarse-fine can be used
derivative estimation
- f' = f(x + dx) - f(x) / dx
- fancier techniques are pretty much LPF then differentiate
generalizations
- affine transforms
- solve simultaneously