In this network, each cell (k.sub.n) receives a current (I.sub.ph (k)) from a photodetector (12) and provides an output current (S.sub.n) representative of the local constrast in the zone in which this cell is situated. According to the invention, each cell comprises adjustable conductances determining an output current (I.sub.out (k)) depending in a monotonic increasing saturating manner of the ratio between photodetector current (I.sub.ph (k)) and a mean current (I.sub.mean (k)), said ratio representing the local contrast at the cell under consideration. The first of the conductances (P2) is regulated by the current (I.sub.ph (k)) flowing in the photodetector. Calculating means in each cell generate a mean current (I.sub.mean (k)) from the currents flowing in the photodetectors of the relevant cell and in at least some of the neighboring cells. This current is representative of the mean illumination to which the network is subjected. The conductances (P.sub.4a, P.sub.5a) are regulated by the mean current (I.sub.mean (k)). This network makes it possible to create image sensors which process illumination in a manner akin to that afforded by the biological retina of vertebrates.