How to achieve invariance
Need both of the following:
1.Make sure your
detector is invariant
•Harris
is invariant to translation and rotation
•Scale
is trickier
–common
approach is to detect features at many scales using a Gaussian
pyramid (e.g., MOPS)
–More
sophisticated methods find “the best scale” to represent each
feature (e.g., SIFT)
2.
Design an invariant feature descriptor
•A
descriptor captures the information in a region around the detected
feature point
•The
simplest descriptor: a square window of
pixels
–What’s
this invariant to?
•Let’s
look at some better approaches…