The thing which I am not getting is the role of scanning in generation of video signal by photoconductive way...the optical image is focused over the photoconductive material ...which decrease the resistance of the material according to the brightness of the scene being casted over the material... So exactly how does scanning cause a current to flow inside the material..?? The text says that " An electron beam is used to pick-up the picture information now available on the target plate in terms of varying resistance at each point. " what does pick up refer here??