Let $A$ and $B$ be $C^*$-algebras with cenerscenters $Z_A$ and $Z_B$. Suppose $\rho:A\rightarrow B$ is a surjective $*$- homomorphism. It is easy to check $\rho(Z_A)\subset Z(B)$.
I wonder how to assure that $\rho(Z_A) \neq Z(B)$?
If $rho$ is not surjective, what is the relationship between $\rho(Z_A)$ and $Z_B$?