High-definition television (HDTV) is an arbitrary term that applies to any television production, transmission, or reception technology with a scanning rate that exceeds the 525 lines of the present U.S. NTSC standard or the 625 lines of the PAL or SECAM standards. Most global HDTV systems have at least 1,000 scanning lines, and multi-channel audio capability. When viewed on a large television tube or projected on a screen, HDTV images are demonstrably brighter and sharper than those of present video systems.

The first viable HDTV system known as Hi-Vision/MUSE (the former is a production standard, the latter is a compatible transmission companion) was perfected in the 1970s in the laboratories of NHK, the Japan Broadcasting Company. Distinctive characteristics of analog Hi-Vision technology include a wide-screen 16:9 aspect ratio (compared with a conventional 4:3 ratio), and 1,125 scanning lines. After abortive Japanese attempts to have Hi-Vision/MUSE adopted as a de facto world television standard in 1986, a European consortium developed an alternative incompatible standard with 1,250 scanning lines.

The following year the Federal Communications Commission created an Advisory Committee on Advanced Television Service (ACATS) to conduct a testing program to select an American advanced television standard. After eight years of development and testing, the FCC is expected to adopt a digital transmission scheme that will permit American broadcasters to simultaneously transmit a number of channels with variable resolution levels. One true HDTV channel can be broadcast, or up to five lower-quality standard-definition (SDTV) digital channels. The U.S. HDTV digital standard will also include a wide-screen 16:9 aspect ratio and six-channel "surround" audio. Digital data such as stock market quotes or weather information can also be transmitted within the HDTV spectrum allocation.

The FCC plans for U.S. broadcasters to simulcast digital HDTV signals in conjunction with conventional NTSC transmissions until the year 2010, at which time the old system will be turned off and the spectrum will revert to the Commission for reallocation. Japanese and European television manufacturers are expected to develop advanced digital television production and transmission systems which are transcodable with the American format.

HDTV and SDTV are variable-resolution examples of advanced television technology. By shifting from an analog to a digital transmission scheme, electronic engineers have merged the previously incompatible worlds of television and computers. Advanced television sets will have the capability to be linked into the same digital networks as personal computers for accession of global services such as the Internet.

- Peter B. Seel