ABSTRACT
The visual scene is explored by examining the small areas of detail that are contained in it, a process known as scanning. When we read the page of a book, our eyes scan it line by line to extract the total visual information. Electronic scanning carries out a similar line-by-line scan process, the detail encountered being translated into voltage variations that can be used to modulate a radio transmitter. At the receiver, the received signals are demodulated and used to vary the beam current(s) of a display tube, the beam of which is sweeping in synchronism with the transmitter scanning beam. A constraint of the electronic scanning system is the need to
put a frame round the field of view to be transmitted. In the human seeing process, the eye is quite unrestricted in its movements, and it roams freely over a very wide angular range which, with head and body movements, provides an unlimited field of view. In the electronic process, a finite limitation must
be imposed by means of a frame, within which the picture can be analysed line by line.
