PAL

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.

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 control to perform the correction manually). This is
why some engineers jokingly expand NTSC to "Never Twice the Same Colour"
while referring to PAL as "Peace At Last"! However, the alternation of
colour information -- Hanover bars -- can lead to picture grain on pictures
with extreme phase errors. PAL was developed in Germany by Walter Bruch, and
first introduced in 1967.

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 used in
Brazil and PAL-N is a variant of PAL with narrow bandwidth which is used in
Argentina, Paraguay, and Uruguay. PAL-I is the version used in the United
Kingdom. Other European countries use PAL-B/G. 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.

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