Evolution of the mean DR value of short exposure images as a function of the root-mean-square of the piston error between interferometer arms. This was numerically obtained by a Monte Carlo statistical approach. Each point is evaluated over 10⁴ computed PSFs. This curve is computed using the actual test-bench characteristics (apodization coefficients, array configuration, working wavelength ...). The sole instrumental defect taken into account in this simulation is the piston error.