A method to extract the visibility of celestial objects in real time using a parallel-shear interferometer is described. Such an instrument produces fringes of constant visibility but with random atmospheric-induced phases. The fringes are modulated internally, and synchronuous detection with many parallel channels recovers their contrast. First, we perform parallel sine and cosine phase-locked accumulation for the short period in which the atmosphere is presumed frozen. The visibility amplitude is then calculated allowing for Poisson noise. We find that a 7.8mstar can be resolved by a single detector to the diffraction limit of the telescope; with twenty such detectors, the limit is 10m.