 signal. Fundamentals of Telecommunications, Second Edition, by Roger L. Freeman ISBN 0-471-71045-8 Copyright © 2005 by Roger L. Freeman TELEVISION TRANSMISSION 16.2 AN APPRECIATION OF VIDEO TRANSMISSION video transmission system must deal with four factors when transmitting images of moving objects: 1. Perception of the distribution of luminance or simply the distribution of light and shade 2. Perception of depth or a three-dimensional perspective 3. Perception of motion relating to the first two factors above 4. Perception of color (hues and tints) Monochrome TV deals with the first three factors. Color TV includes all four factors. A video transmission system must convert these three (or four) factors into electrical equivalents. The first three factors are integrated to an equivalent electric current or voltage whose amplitude is varied with time. Essentially, at any one moment it must integrate luminance from a scene in the three dimensions (i.e., width, height, and depth) as a function of time. And time itself is still another variable, for the scene is changing in time. The process of integration of visual intelligence is carried out by scanning. The hori- zontal detail of a scene is transmitted continuously and the vertical detail discontinuously. The vertical dimension is assigned discrete values that become the fundamental limiting factor in a video transmission system. The scanning process consists of taking a horizontal strip across the image on which discrete square elements called pels or pixels (picture elements) are scanned from left to right. When the right-hand end is reached, another, lower, horizontal strip is explored, and SO on, until the whole image has been scanned. Luminance values are translated on each scanning interval into voltage and current variations and are transmitted over the system. The concept of scanning by this means is illustrated in Figure 16.1. The National Television Systems Committee (US) (NTSC) practice divides an image into 525 horizontal scanning lines. 1 It is the n