formula for cardinality

[jeyalakshmi]

hi friends,
i want to know formula for findinding cardinality of two pixel f(x,y) &
g(x,y) of two image f & g respectively


Cij=Card{ (f(x,y),g(x,y)) / f(x,y)=i,g(x,y)=j}

i want expression for above formula(how to evaluate

 

[jeyapreetha]

Cardinality is nothin but the no of elements in one set.