Multiple-object input to the recently introduced phase-extraction correlator may cause difficulties owing to interference effects. Similar effects have been observed previously in the nonlinear joint transform correlator. It is shown theoretically and by computer simulations that these effects are seldom observable in practice, and even then they can be substantially reduced by employing a proper space-variant threshold. The implementation of this scheme by a hybrid electro-optical architecture is also explained briefly and demonstrated. The results presented permit manipulation of information (spectral phase) that was previously believed to be contaminated beyond recovery.