•3D to 2D “Invariance” isn’t captured by mathematical definition of invariance because 3D to 2D transformations don’t form a group.
–You can’t compose or invert them.
•Definition:
Let f be a function on images. We say f is an invariant iff for every Object O, if I1 and I2 are images of O, f(I1)=f(I2).
•This means we can define f(O) as f(I) for I any image of O. O
and I match only if f(O)=f(I).
•f is a non-trivial invariant if there exist two image I1 and I2 such that f(I1)~=f(I2).
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