Standards
Standards
Recorded video signals are rather complex and tightly structured. The standard unit of video is a frame. Similar to film, motion video is created by displaying progressive frames at a rate fast enough for the human eye and brain to perceive continuous motion. The basic means by which video images are recorded and displayed is a scanning process. When a video image is recorded by most cameras, a beam of electrons sweeps across the recording surface in a progressive series of lines. This basic technology is simple enough, widely understood, and, after a certain point, easily manufactured. The concept can be applied and the effect of a video image can be achieved, however, in various ways, with varying rates of electronic activity. Line frequencies and scanning rates are flexible, determined in part by a level of user (producer and viewer) satisfaction and in part by concerns of equipment manufacturers and broadcasters. Consequently, not all video or television systems are alike. The variations among them are defined in terms of "standards."
Bio
In the United States, industry-wide agreement on engineering standards for television did not come until 1941, when the Federal Communications Commission (FCC) decided to adopt a black-and-white standard (postponing the issue of color). The FCC accepted the National Television System Committee (also referred to as the National Television Standards Committee [NTSC]) recommendations and set line frequency at 525 per frame scanned at a rate of approximately 30 frames per second (29.97 to be exact). In 1953, corporate interests (the Columbia Broadcasting System [CBS] and the Radio Corporation of America [RCA]/National Broadcasting Company [NBC]) agreed to another proposal that allowed the NTSC to establish color television standards; these standards were compatible with those already set for black-and white transmission.
These standards are not, however, uniformly accepted elsewhere. There are presently three world standards for transmitting a color video signal. The NTSC recommendations accepted by the FCC as a national standard for the United States in 1953 are used in several other countries, including Canada, Chile, Costa Rica, Cuba, El Salvador, Guatemala, Honduras, Japan, Mexico, Panama, the Philippines, Puerto Rico, South Korea, and Taiwan.
PAL (phase alternating line) and SECAM (sequential couleur a memoire) are the two other major world wide television standards. PAL is a modified form of NTSC and specifies a different means of encoding and transmitting color video designed to eliminate some NTSC problems, specifically a shift in chroma phase (hue). PAL uses 625 lines per frame (versus NTSC's 525) scanned at a rate of 25 frames per second (versus NTSC's 29.97) and operates at a 50-Hertz frequency (versus NTSC's 60-Hertz frequency). The PAL system is standard in more countries than NTSC or SECAM, including Argentina, Australia, Belgium, Brazil, China, Denmark, Finland, Great Britain, India, Indonesia, Ireland, Italy, Norway, New Zealand, the Netherlands, Portugal, Spain, Sweden, Switzerland, and Turkey.
SECAM is a video color system developed by the French; though it differs from PAL, it too uses 625 lines per frame, scanned at a rate of 25 frames per second, and operates at a 50-Hertz frequency. SECAM is used in France as well as several other countries, including Egypt, Germany, Greece, Haiti, Iran, Iraq, North Korea, Poland, and parts of the former Soviet Union.
There are enough differences between these three standards so that a videotape recorded using PAL will not play on a VCR set up for NTSC or SECAM and vice versa. NTSC, PAL, and SECAM are thus incompatible with each other. Standards converters can convert video from one standard to another, but the resultant image is often poor. Digital standards converters can provide better-quality converted video. Productions intended to be broadcast or released in different video standards are often shot on film, which can be converted to any video standard with reasonably good quality.
Recent developments in high-definition television (HDTV) have closed the gap between the technical quality of broadcast television and motion pictures. HDTV doubles the current broadcast NTSC number of scanning lines per frame-from 525 to 1,050 or 1,125, depending on the specific system-with a fourfold improvement in resolution (and a change to a wide screen format).