I found a paragraph in the book about SSD, can't get one thing:
Most commonly, the distance measure is the sum of squared differences. For two images f(x, y) and g (x, y) it is defined as
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where the summation extends over the region of size (2n1 + 1) X (2n2 + 1)
I can not get, why does i changes from -n1 to n1, but not from 0 to n1. The similar about j. And why does summation goes over the (2n1 + 1) X (2n2 + 1) but not over the (n1)x(n2)