Television system dissect the image and transmit the pixel information serially. The image is divided into a stack of horizontal stripes (“lines”) which are scanned left to right, producing a sequence of pixel (picture element) brightness values. The lines are scanned in order, one after the other, from top to bottom. Brightness values for each pixel are transmitted to the receiver(s). The image is reconstructed by a display device, whose pixels are illuminated according to the received brightness values. This chapter presents television technology in historical order: (1) the electromechanical system that Nipkov patented in 1884 but which was not demonstrated until 1923; (2) all-electronic television, made possible by the development of cathode ray picture tubes and camera tubes; and (3) digital television, which uses data storage and processing in the receiver, allowing the station to update the changing parts of the image, rather than retransmit the entire image for every frame. With the lowered data rate, the bandwidth needed previously to transmit one analog television program can now hold multiple programs.

The Nipkov system

Electronic image dissection and reconstruction were first proposed in the Nipkov disk system, patented in 1884, which used a pair of rotating disks, as shown in Figure 19.1. The camera disk dissected the image while the receiver disk reconstructed it. The receiver screen, a rectangular aperture mask, was covered by an opaque curtain containing a pin hole, illuminated from behind by an intensity-modulated gas discharge lamp.