Page 261 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

250 CHAPTER 10 Video
10.1 History
Motion pictures are, in their most simplistic form, still pictures arranged sequentially and displayed in succession in order for our brains to create a sense of movement. The first “movie” was a stack of pictures shuffled rapidly in sequence so as to create for the viewer a sense of fluid motion. If the pictures are shuffled quickly enough, the brain loses the sense that the picture was changing incre- mentally and the motion perceptually appears even. The rate at which individual pictures were dis- played was (and still is) measured in frames per second (quantified in the metric hertz or cycles per second).
In the nineteenth and early twentieth centuries, studies were made on human subjects to deter- mine the threshold of perception for sensing frame change (termed “intermittent light stimuli”) between pictures such that the perceived flicker perceptually disappears. The objective for these studies was to determine the frame rate at which the brain loses the sense of frame change and per- ceives the changing picture as even motion. The concept itself is termed “flicker fusion threshold,” and in several landmark studies, the average human perception threshold was measured.
Flicker is the sinusoidal variance of light intensity over time measured in both frequency and intensity. The flicker frequency threshold at which humans can perceive motion averages in the 16 Hz range. In practice, movies today are generally displayed at 24 frames per second (fps), and video is shown at between 25 and 30 fps (depending upon the standard employed). However, human light intensity flicker perception is above the frequency of human perception of motion, thus requiring video to run in the 50
60 fps range in order to avoid viewer objection.
The major breakthrough from simple film motion pictures to television came about when elec- tronic capture sensors (through the photoelectric effect) and circuits were discovered that could sense light and transfer it into radio frequency (RF) signals for transmission. The system was com- plete when the cathode ray tube (CRT) was invented to convert the RF signals back to a display compatible with human perception.
Early television transmission systems were electromechanical devices projecting light upon pho- toelectric plates exhibiting low image quality. The first truly functional television system with elec- tronic scanning of both the pickup and the display devices is credited to Philo Farnsworth in the United States in 1928. The 1936 Berlin Olympics were broadcast in monochrome (black and white) via television bringing the first large-scale viewing of television to a world audience.
During the development of this new communication medium, it became obvious that the manu- facturers of commercial and consumer television equipment required standards so that all devices could be made to a common communications protocol. In the United States, the National Television Systems Committee (NTSC) was formed within the US Federal Communications Commission (FCC) to issue standards for transmission of television signals in the United States. The original monochrome analog standards were issued in 1941 and were later updated in 1953 to add the analog color transmission standards. The NTSC standard set the frame rate, screen aspect ratio, and line count so that the electronics industry could design equipment compatible with the standard.
In Europe and other parts of the world, other standards (including PAL or “Phased Alternation Line” and SECAM or “Sequentiel Couleur Avec Memoire”) evolved for various reasons including improved resolution over NTSC, synchronization of frame rate to standard electrical (alternating current) grid frequency, resolution preferences, and (periodically) nationalistic fervor.