By first finding out why a fixed-point method is not feasible for the original CDD model, we then proposed a modified CDD model for which a fixed-point method is feasible and developed a nonlinear MG for the modified model. A local Fourier analysis shows that the global smoother is faster than the local smoother. Numerical results confirmed that the modified model retains the desirable property of the original model in reconnecting the level lines across large distances, and our multigrid method is very efficient.