Sum of Squared Differences

The Sum of Squared Differences (SSD) is a way of determining the correlation between two image regions. It is usually involved when motion compensation needs to be done. SSD is defined as followed:

There are some variations of SSD. Like the Zero-mean Sum of Squared Differences (ZSSD):

Shi-Thomasi is a corner detection algorithm improved from Harris' corner detector. The improvement is the way how a certain region within the image is scored (and thus treated as corner or not). Where the Harris-corner detector determines the score  with the eigenvalues  and  of two regions (the second region is a shifted version of the first one and used to compare to the first one to see if the difference between the two is big enough to say if there is a corner or not) in the following way: