  Incoming optical interferometers will allow spectro-imaging at high angular
resolution. Non-homothetic Fizeau concept combines good sensitivity and high
spectral resolution capabilities. However, one critical issue is the design of
the beam recombination scheme, at the heart of the instrument. We tackle the
possibility of reducing the number of pixels that are coding the fringes by
compressing the pupil plane. Shrinking the number of pixels -- which
drastically increases with the number of recombined telescopes -- is indeed a
key issue that enables to reach higher limiting magnitude, but also allows to
lower the required spectral resolution and fasten the fringes reading process.
By means of numerical simulations, we study the performances of existing
estimators of the visibility with respect to the compression process. We show
that, not only the model based estimator lead to better signal to noise ratio
(SNR) performances than the Fourier ones, but above all it is the only one
which prevent from introducing baseline mixing biases in the visibilities as
the pupil plane compression rate increases. Furthermore, we show that moderate
compression allows to keep the visibilities SNR unaffected. In the light of
these conclusions, we propose an optimized pupil arrangements for 6 and 8 beam
recombiners.
