Patent US 4,337,514

The device comprises a variable-characteristic nonlinear four-terminal network having one input for receiving a video signal V.sub.e and eight inputs for controlling transfer parameters. Statistical analysis of the amplitude of the signal V.sub.e permits acquisition of the luminance distribution function of said signal. On the basis of this distribution function, computing means determine the values of the transfer parameters to be applied to the control inputs of the four-terminal network in order to deliver at the output of the network a video signal V.sub.s which extends over the entire luminance scale and has the desired distribution for satisfying optimum conditions of vision.