  We present a new formulation of a family of proximity operators that
generalize the projector step for phase retrieval. These proximity operators
for noisy intensity measurements can replace the classical "noise free"
projection in any projection-based algorithm. They are derived from a maximum
likelihood formulation and admit closed form solutions for both the Gaussian
and the Poisson cases. In addition, we extend these proximity operators to
undersampled intensity measurements. To assess their performance, these
operators are exploited in a classical Gerchberg Saxton algorithm. We present
numerical experiments showing that the reconstructed complex amplitudes with
these proximity operators perform always better than using the classical
intensity projector while their computational overhead is moderate.
