PAL, short for phase-alternating line, phase alternation by line or for phase alternation line,
is a colour encoding used in broadcast television systems, used throughout the world except in most of the Americas, some East Asian countries (which use NTSC), parts of the Middle East and Eastern Europe, and France (which use SECAM, though most of them are in the process of adopting PAL). PAL was developed in Germany by Walter Bruch, working at Telefunken, and first introduced in 1967.

Note that French Thomson, where Henri de France developed SECAM, later bought Telefunken. Thomson is also behind the RCA brand for consumer electronics products, and RCA created the NTSC color TV standard (before Thomson became involved).

Technical details

The basics of PAL are quite similar to the NTSC system; the SECAM system, on the other hand, is quite different from both of the others. The name "Phase Alternating Line" describes the way that part of the colour information on the video signal is reversed in phase with each line, which automatically corrects phase errors in the transmission of the signal by canceling them out.
(Lines where the color phase is reversed compared to NTSC are often called PAL or
phase-alternation lines, which justifies one of the expansions of the acronym,
while the other lines are called NTSC lines.)
Early PAL receivers relied on the imperfections of the human eye to do that canceling, however this resulted in a comb-like effect on stronger phase errors. Thus, most receivers use a delay line which stores the received color information on each line of display; an average of the color information of the current line and that of the previous line is then used to drive the picture tube. This reduces vertical color resolution compared to the NTSC system, however since the human retina also has a color resolution that is much lower than its brightness resolution, this effect is not visible.

NTSC receivers have a tint control to perform that correction manually. Some engineers jokingly expand NTSC to "Never Twice the Same Colour" while referring to PAL as "Perfect At Last" or "Peace At Last"! However, the alternation of colour information - Hanover bars - can lead to picture grain on pictures with extreme phase errors even in PAL systems.

The PAL colour system is usually used with a video format that has 625 lines per frame and a refresh rate of 25 frames per second, interlaced, such as systems B, G, H, I, and N (see broadcast television systems for the technical details of each format). Some countries in Eastern Europe which formerly used SECAM with systems D and K have switched to PAL while leaving other aspects of their video system the same. (However, some other countries changed completely from SECAM-D/K to PAL-B/G.) In Brazil, PAL is used in conjunction with the 525 line, 29.97 frame/s system M, using (very nearly) the NTSC color subcarrier frequency. Almost all other countries using system M use NTSC. In Argentina, Paraguay and Uruguay, PAL is used with the standard 625 line system, but again with (very nearly) the NTSC color subcarrier frequency; these variants are called PAL-N and PAL-CN.
Recently-manufactured PAL television receivers can typically decode all of these systems, except in some cases PAL-M and PAL-N. Many of them can also receive Eastern European and Middle Eastern SECAM, though usually not French SECAM, unless they are made in France. Many of them can also accept baseband NTSC-M, such as from a VCR or game console, though not usually broadcast NTSC.

When video is transmitted baseband, most of the differences between the "one-letter" systems are no longer significant, other than vertical resolution and frame rate, and in that context, unqualified PAL invariably means 625 lines at 25 frames per second, interlaced, with PAL color. In digital video applications, such as DVDs and digital broadcasting, even the color encoding is no longer significant; in that context, PAL means only 625 lines at 25 frames per second interlaced, and there is no longer any difference to SECAM.

Cinema films are typically recorded at 24 frames per second; when played back at PAL's standard of 25 frames per second, films therefore typically run 4% faster[1]. Unlike NTSC's telecine system, this is usually un-noticeable in practice, although as a consequence films shown on video equipment in PAL countries run for 4% less time than their NTSC brothers, despite being otherwise identical.

Countries and territories which use PAL B/G or PAL D/K

Europe

Asia

The Americas

Africa

Australia and Oceania

Countries and territories which use PAL-I

Europe

United Kingdom and Ireland

Asia

Hong Kong and Macao,

Countries and territories which use PAL-M

Latin America

Brazil (NTSC & PAL-M)

Asia

Laos (SECAM & PAL-M).

Countries which use PAL-N or PAL-CN

Latin America

Argentina, Paraguay and Uruguay.

Reference

• The standard that defines the PAL system was published by the International Telecommunications Union in 1998 and has the title Recommendation ITU-R BT.470-6, Conventional Television Systems.
  

  See also

• PALplus
• Broadcast television systems

  External links

• More information about TV standards