cally-conductive substance, and a photoresistive coating. The light of an image passes through the transparent conductor, strikes the photoresistive coating, and thereby produces a charge that varies in proportion to the light that strikes it. An electron beam behind the target measures the fluctuating charges and translates them into a series of voltages that are proportional to the changing light intensity. Heating of a cathode creates the electron beam that does the measuring. It is focused using principles of static electricity. Electromagnetic deflection coils that are placed around the neck of the vidicon tube move the beam vertically and horizontally. Starting second field Horizontal retrace Vertical retrace End of first scanned field Figure 5-8. TV Raster Scan (Michel Bayard). The optic nerve is a huge number of separate fibers that each carries a minuscule part of the image to the brain. All operate in parallel, and the brain receives a single image that consists of many parts. Video transmission networks do not operate like the optic nerve; they could never cost-justify parallel communications. Processing images with human vision techniques would require hundreds of thousands of channels. Each would have synchronized with all others. Parallel communication is not feasible over distance; it is too complex and costly to have separate paths for each information bit. Color cameras separate light waves into RGB components using prisms, color filters, or dichroic mirrors. After separating RGB signals, older systems used multiple Video Communications: The Whole Picture camera tubes to apply these principles. Today's cameras utilize solid state chips known as charge-coupled devices (CCDs) to store the electrical charges that make up the light's intensity. The charges are transferred to another layer called a frame buffer where they are formatted. Next, a formatted electrical signal, with amplitude directly proportional to the amplitude of the light, is sent across a transmission medium or network for a viewer's