SIFT is a patented method that does both feature detection and description (US6711293 - http://www.google.com/patents/us6711293). The method consists of roughly of three points (please let me know if I am inaccurate):
- Detected features are local extrema of Difference of Gaussians in scale-space.
- Each detected feature are assigned (possibly) multiple dominant gradient orientations.
- For each detected feature and for all possible dominant orientations, a descriptor is computed in a rotationally invariant manner from several histograms of gradients.
Can I be sued...
if I design another method which:
- reimplements exactly claim (1) and claim (2), i.e., including all the associated technical details,
- but, for which, claim (3) is replaced by a strictly different nonpatented method, e.g., DAISY, FREAK...
- and will be used in a commercial application? (sold anywhere in the world)
Do I still have to replace claims (1) and (2) by strictly different methods?