For other meanings of "PAL" see PAL (disambiguation).
PAL, short for Phase Alternating Line, is the analogue video format used in television transmission in most of Europe (except France, Bulgaria, Russia, Yugoslavia, and some other countries in Eastern Europe, where SECAM is used), Australia and some Asian, African, and South American countries. PAL was developed in Germany by Walter Bruch, and first introduced in 1967.
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. NTSC receivers have a tint or hue control to perform the 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.
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. Like NTSC this is an interlaced format. Each frame consists of two fields (half-a-frame), each field has half of the lines of a frame (one has all the even lines, one has all the odd lines). Fields are transmitted and displayed successively. There are 50 fields per second. At the time of its design, the interlacing of fields was a compromise between flicker and bandwidth.
There are many variants of PAL. PAL-M is a hybrid of NTSC and PAL with 525 lines/60 Hz used in Brazil and PAL-N is a variant of PAL with narrow bandwidth which is used in Argentina, Paraguay, and Uruguay. (Both of these variants were designed to fit in the 6-MHz television channels used throughout South America.) PAL-I is the version used in the United Kingdom and Ireland. Other European countries use PAL-B/G. Some countries in Eastern Europe and the Middle East which formerly used SECAM-D or SECAM-K systems have switched to PAL color without changing other aspects of their video systems, giving rise to PAL-D/K. A variant named PAL60 uses, like NTSC, 59.94 fields per second. It is used mainly for displaying NTSC video or DVD on a PAL TV set. (Technically, the trailing letter(s) designate a precise video system in the ITU standard, which is theoretically independent of the color encoding. Systems A, E, and F were never used with color.)