these parameters as well as the pulse 39 s arrival time at the pixel error due to electronic noise and random fluctuations of the transmitting medium and variations in the outgoing waveform can be reduced by averaging data from many light pulses an alternative embodiment of the readout electronics permits the averaging to be done on the readout array 10 for many applications where a 3 d image of an object is required no knowledge of the position of the object is necessary by using the triggering circuit 21 function in fig4 the schmidt trigger automatically stops the counter and shift register when it senses a return pulse however if the object is semitransparent and it is desirable to obtain a 3 d image of both the outer and inner surfaces there may not be enough memory cells 17 to capture more than the return from the first surface under these circumstances the schmidt trigger 21 in fig4 can be held and the clock stopped after a programmed time this would allow two consecutive light pulses to capture information both from the transparent surface and the surface behind it in another embodiment critical parts of the readout unit cell circuitry.