Television fundamentals

For a reasonable understanding of colour television, it is essential that the fundamentals of television are known. As we shall see, all colour systems are firmly based on the original ‘electronic-image dissection’ idea which goes back to EMI in the 1930s, and is merely an extension (albeit an elaborate one) of that system. Although there are few black and white TVs or systems now left in use, the compatible colour TV system used today by all terrestrial transmitters grew out of the earlier monochrome formats. In the early days, it was essential that existing receivers showed a good black and white picture from the new colour transmissions, and the scanning standards, luminance signal and modulation system are the same. What follows is a brief recap of basic television as a building block of the colour TV system to be described in later chapters.

At the television studio, the scene to be transmitted is projected on a photosensitive plate located inside the TV camera. The scene is repeatedly scanned by a very fast electron beam which ensures that consecutive images differ only very slightly. At the receiving end, a display device such as a plasma or LCD panel or a cathode-ray tube (c.r.t.) is used to recreate the picture by an identical process of scanning a screen by an electron beam. The phenomenon of persistence of vision then gives the impression of a moving picture in the same way as a cine film does. In the UK television broadcasting system, known as PAL, 25 complete pictures are scanned every second whereas in the US, NTSC is used with 30 pictures per second. Both systems will now be considered.