Feature distance
How to define the difference between two features f1, f2?
•Better approach:  ratio distance = SSD(f1, f2) / SSD(f1, f2’)
–f2         is best SSD match to f1 in I2
–f2’        is  2nd  best SSD match to f1 in I2
–gives small values for ambiguous matches
http://www.canyonstatevinyl.com/images/Picket%20Fence.jpg http://www.canyonstatevinyl.com/images/Picket%20Fence.jpg
I1
I2
f1
f2
f2'