The NTSC (National Television Standards Committee) was responsible for developing, in 1953, a set of standard protocol for television (TV) broadcast transmission and reception in the United States. Two other standards - Phase Alternation Line (PAL) and Sequential Couleur avec Memoire (SECAM) - are used in other parts of the world. The NTSC standards have not changed significantly since their inception, except for the addition of new parameters for color signals. NTSC signals are not directly compatible with computer systems.
An NTSC TV image has 525 horizontal lines per frame (complete screen image). These lines are scanned from left to right, and from top to bottom. Every other line is skipped. Thus it takes two screen scans to complete a frame: one scan for the odd-numbered horizontal lines, and another scan for the even-numbered lines. Each half-frame screen scan takes approximately 1/60 of a second; a complete frame is scanned every 1/30 second. This alternate-line scanning system is known as interlacing.
Adapters exist that can convert NTSC signals to digital video that a computer can "understand." Conversely, there are devices that can convert computer video to NTSC signals, allowing a TV receiver to be used as a computer display. But because a conventional TV receiver has lower resolution than a typical computer monitor, this does not work well for all computer applications, even if the TV screen is very large.
In recent years, there has been increasing pressure to adopt a new set of TV standards. One of the proposed protocols is known as high-definition television (HDTV). Ideally, the HDTV standard that is ultimately adopted will be directly compatible with computer systems. However, there are engineering problems associated with this. Some industry experts fear such compatibility could dramatically increase the cost of a conventional TV set.