Television standards

The accepted criteria for a television system, including the image aspect ratio, number of lines per frame, type of scanning, original video signal bandwidth, transmission format and bandwidth, reception, demodulation, decoding, and sound system. The implementation of high-definition television (HDTV), where the image resolution and audio fidelity are significantly higher than for conventional television, has required new standards. See also Television.

In the early 1950s, the National Television Systems Committee (NTSC) was formed to set standards for a color television signal (in the United States) that would be fully compatible with the existing monochrome signal. Any color can be formed as a linear combination, that is, a weighted sum, of red (R), green (G), and blue (B). The NTSC standard started with three image signals—R, G, and B—and matrixed these three primary color image signals as linear combinations into one luminance signal (the conventional black-and-white video signal, often called the Y-signal) and two chrominance signals that control hue and saturation. The chrominance signals are termed the in-phase (I) signal and the quadrature (Q) signal. Although the luminance signal retained the original 4.2-MHz bandwidth, the characteristics of human color perception allowed the I-signal to be limited to 1.5 MHz and the Q-signal to only 0.5 MHz.

While NTSC color television standards are used in North America, South America, and Japan, the European International Radio Consultative Committee (CCIR) system is used in England, Germany, Italy, and Spain. The color system employed with CCIR television is called Phase Alternate Line (PAL). A modified CCIR television standard is used in France and Russia, where the color system is called SECAM (Sequential Couleur à Mémoire).

The next generation of television, HDTV, is not compatible with the previous television systems. HDTV relies on digital technology, making it more amenable with computer displays, while taking full advantage of the power and efficiency of digital signal processing (DSP). The desired characteristics of the HDTV system that would replace the NTSC system was expected to have a resolution that would approach the quality of a 35-mm film, that is, approximately twice the horizontal and twice the vertical resolution of conventional television, with a widescreen aspect ratio of 16:9. The target HDTV system standard was required to avoid interlace scanning artifacts, as well as chrominance artifacts and deliver digital multichannel audio. The end result was a 1996 FCC digital television (DTV) standard, and HDTV broadcasting commenced in the United States in 1998.

In Europe, a different transmission standard has been adopted. The European system is referred to as the Digital Video Broadcasting (DVB) standard.

The FCC expects everyone to be using new HDTV receivers by the year 2011, at which time NTSC broadcasting will cease, and all NTSC color television receivers will need to be replaced or modified with some type of converter to be able to decode and display HDTV images.