Phase Alternating Line (PAL) is a colour encoding system for analog television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 frames) per second, and associated with CCIR analogue broadcast television systems B, D, G, H, I or K. The articles on analog broadcast television systems further describe frame rates, image resolution, and audio modulation.

PAL video is composite video because luminance (luma, monochrome image) and chrominance (chroma, colour applied to the monochrome image) are transmitted together as one signal.

A latter evolution of the standard, PALplus, added support for widescreen broadcasts with no loss of vertical image resolution, while retaining compatibility with existing sets. Almost all of the countries using PAL are currently in the process of conversion, or have already converted transmission standards to DVB, ISDB or DTMB.

Geographic reach

PAL was adopted by most European countries, by several African countries, by Argentina, Brazil, Paraguay, Uruguay, and by most of Asia Pacific (including the Middle East).^[1] Countries in those regions that did not adopt PAL were France,^[2] Francophone Africa,^[2] several ex-Soviet states,^[2] Japan,^[3] South Korea, Liberia, Myanmar, the Philippines,^[3] and Taiwan.^[3]

PAL region

With the introduction of home video releases and later digital sources (e.g. DVD-Video), the name "PAL" might be used to refer to digital formats, even though they use completely different colour encoding systems. For example, 576i (576 interlaced lines) digital video with colour encoded as YCbCr, intended to be backward compatible and easily displayed on legacy PAL devices, is usually mentioned as "PAL" (eg: "PAL DVD"). Likewise, video game consoles outputting a 50 Hz signal might be labeled as "PAL", as opposed to 60 Hz on NTSC machines. These designations should not be confused with the analog colour system itself.

History

In the 1950s, the Western European countries began plans to introduce colour television, and were faced with the problem that the NTSC standard demonstrated several weaknesses, including colour tone shifting under poor transmission conditions, which became a major issue considering Europe's geographical and weather-related particularities. To overcome NTSC's shortcomings, alternative standards were devised, resulting in the development of the PAL and SECAM standards. The goal was to provide a colour TV standard for the European picture frequency of 50 fields per second (50 hertz), and finding a way to eliminate the problems with NTSC.

PAL was developed by Walter Bruch at Telefunken in Hanover, West Germany, with important input from Gerhard Mahler [de].^[4] The format was patented by Telefunken in December 1962, citing Bruch as inventor,^[5][6] and unveiled to members of the European Broadcasting Union (EBU) on 3 January 1963.^[6] When asked why the system was named "PAL" and not "Bruch" the inventor answered that a "Bruch system" would probably not have sold very well ("Bruch" is the German word for "breakage"^[7]).

The first broadcasts began in the United Kingdom in July 1967, followed by West Germany at the Berlin IFA on August 25.^[6][8] The BBC channel initially using the broadcast standard was BBC2, which had been the first UK TV service to introduce "625-lines" during 1964. The Netherlands and Switzerland started PAL broadcasts by 1968, with Austria following the next year.^[6]

Telefunken PALcolour 708T^[9] was the first PAL commercial TV set. It was followed by Loewe-Farbfernseher S 920 and F 900.^[10]

Telefunken was later bought by the French electronics manufacturer Thomson. Thomson also bought the Compagnie Générale de Télévision where Henri de France developed SECAM, the first European Standard for colour television. Thomson, now called Technicolour SA, also owns the RCA brand and licences it to other companies; Radio Corporation of America, the originator of that brand, created the NTSC colour TV standard before Thomson became involved.

The Soviets developed two further systems, mixing concepts from PAL and SECAM, known as TRIPAL and NIIR, that never went beyond tests.^[6]

In 1993,^[11] an evolution of PAL aimed to improve and enhance format by allowing 16:9 aspect ratio broadcasts, while remaining compatible with existing television receivers,^[12] was introduced. Named PALplus, it was defined by ITU recommendation BT.1197-1. It was developed at the University of Dortmund in Germany, in cooperation with German terrestrial broadcasters and European and Japanese manufacturers. Adoption was limited to European countries.

With the introduction of digital broadcasts and signal sources (ex: DVDs, game consoles), the term PAL was used imprecisely to refer to the 625-line/50 Hz television system in general, to differentiate from the 525-line/60 Hz system generally used with NTSC. For example, DVDs were labelled as PAL or NTSC (referring to the line count and frame rate)^[13] even though technically the discs carry neither PAL nor NTSC encoded signal. These devices would still have analog outputs (ex; composite video output), and would convert the digital signals (576i or 480i) to the analog standards to assure compatibility. CCIR 625/50 and EIA 525/60 are the proper names for these (line count and field rate) standards; PAL and NTSC on the other hand are methods of encoding colour information in the signal.

Color decoding methods

"PAL-D", "PAL-N", "PAL-H" and "PAL-K" designations on this section describe PAL decoding methods and are unrelated to broadcast systems with similar names.^[6]

The Telefunken licence covered any decoding method that relied on the alternating subcarrier phase to reduce phase errors, described as "PAL-D" for "delay", and "PAL-N" for "new" or "Chrominance Lock".^[6]

This excluded very basic PAL decoders that relied on the human eye to average out the odd/even line phase errors, and in the early 1970s some Japanese set manufacturers developed basic decoding systems to avoid paying royalties to Telefunken. These variations are known as "PAL-S" (for "simple" or "Volks-PAL"),^[14] operating without a delay line and suffering from the “Hannover bars” effect. An example of this solution is the Kuba Porta Color CK211P set.^[6] Another solution was to use a 1H analogue delay line to allow decoding of only the odd or even lines. For example, the chrominance on odd lines would be switched directly through to the decoder and also be stored in the delay line. Then, on even lines, the stored odd line would be decoded again. This method (known as 'gated NTSC') was adopted by Sony on their 1970s Trinitron sets (KV-1300UB to KV-1330UB), and came in two versions: "PAL-H" and "PAL-K" (averaging over multiple lines).^[6][14] It effectively treated PAL as NTSC, suffering from hue errors and other problems inherent in NTSC and required the addition of a manual hue control.

Colour encoding

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Most PAL systems encode the colour information using a variant of the Y'UV colour space. ${\displaystyle Y'}$comprises the monochrome luma signal, with the three RGB colour channels mixed down onto two, ${\displaystyle U}$ and ${\displaystyle V}$.

Like NTSC, PAL uses a quadrature amplitude modulated subcarrier carrying the chrominance information added to the luma video signal to form a composite video baseband signal. The frequency of this subcarrier is 4.43361875 MHz for PAL 4.43, compared to 3.579545 MHz for NTSC 3.58. The SECAM system, on the other hand, uses a frequency modulation scheme on its two line alternate colour subcarriers 4.25000 and 4.40625 MHz.

The name "Phase Alternating Line" describes the way that the phase of part of the colour information on the video signal is reversed with each line, which automatically corrects phase errors in the transmission of the signal by cancelling them out, at the expense of vertical frame colour resolution. Lines where the colour 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 human eye to do that cancelling; however, this resulted in a comb-like effect known as Hanover bars on larger phase errors. Thus, most receivers now use a chrominance analogue delay line, which stores the received colour information on each line of display; an average of the colour information from the previous line and the current line is then used to drive the picture tube. The effect is that phase errors result in saturation changes, which are less objectionable than the equivalent hue changes of NTSC. A minor drawback is that the vertical colour resolution is poorer than the NTSC system's, but since the human eye also has a colour resolution that is much lower than its brightness resolution, this effect is not visible. In any case, NTSC, PAL, and SECAM all have chrominance bandwidth (horizontal colour detail) reduced greatly compared to the luma signal.

The 4.43361875 MHz frequency of the colour carrier is a result of 283.75 colour clock cycles per line plus a 25 Hz offset to avoid interferences. Since the line frequency (number of lines per second) is 15625 Hz (625 lines × 50 Hz ÷ 2), the colour carrier frequency calculates as follows: 4.43361875 MHz = 283.75 × 15625 Hz + 25 Hz. The frequency 50 Hz is the optional refresh frequency of the monitor to be able to create an illusion of motion, while 625 lines means the vertical lines or resolution that the PAL system supports. The original colour carrier is required by the colour decoder to recreate the colour difference signals. Since the carrier is not transmitted with the video information it has to be generated locally in the receiver. In order that the phase of this locally generated signal can match the transmitted information, a 10 cycle burst of colour subcarrier is added to the video signal shortly after the line sync pulse, but before the picture information, during the so-called back porch. This colour burst is not actually in phase with the original colour subcarrier, but leads it by 45 degrees on the odd lines and lags it by 45 degrees on the even lines. This swinging burst enables the colour decoder circuitry to distinguish the phase of the ${\displaystyle R-Y'}$vector which reverses every line.

PAL signal details

For PAL-B/G the signal has these characteristics.

(Total horizontal sync time 12.05 µs)

After 0.9 µs a 2.25±0.23 μs colourburst of 10±1 cycles is sent. Most rise/fall times are in 250±50 ns range. Amplitude is 100% for white level, 30% for black, and 0% for sync.^[16] The CVBS electrical amplitude is Vpp 1.0 V and impedance of 75 Ω.^[18]

The vertical timings are:

(Total vertical sync time 1.6 ms)

As PAL is interlaced, every two fields are summed to make a complete picture frame.

Colorimetry

PAL colorimetry, as defined by the ITU on REC-BT.470, and based on CIE 1931 x,y coordinates:^[20]

The assumed display gamma is defined as 2.8.^[20] The PAL-M system uses color primary and gamma values similar to NTSC.^[21] Color is encoded using the YUV color space.

Luma (${\displaystyle E'{\scriptstyle {\text{Y}}}}$) is derived from red, green, and blue (${\displaystyle E'{\scriptstyle {\text{R}}},E'{\scriptstyle {\text{G}}},E'{\scriptstyle {\text{B}}}}$) gamma pre-corrected (${\displaystyle E'}$) primary signals:^[17]

• ${\displaystyle E'{\scriptstyle {\text{Y}}}=0.299E'{\scriptstyle {\text{R}}}+0.587E'{\scriptstyle {\text{G}}}+0.114E'{\scriptstyle {\text{B}}}}$

${\displaystyle E'{\scriptstyle {\text{U}}}}$ and ${\displaystyle E'{\scriptstyle {\text{V}}}}$ are used to transmit chrominance. Each has a typical bandwidth of 1.3 MHz.

• ${\displaystyle E'{\scriptstyle {\text{U}}}=0.492(E'{\scriptstyle {\text{B}}}-E'{\scriptstyle {\text{Y}}})}$
• ${\displaystyle E'{\scriptstyle {\text{V}}}=0.877(E'{\scriptstyle {\text{R}}}-E'{\scriptstyle {\text{Y}}})}$

Composite PAL signal ${\displaystyle =E'{\scriptstyle {\text{Y}}}+E'{\scriptstyle {\text{U}}}\sin(\omega t)+E'{\scriptstyle {\text{V}}}\cos(\omega t)+}$timing^[17] where ${\displaystyle \mathrm{\omega <!--\; \omega \; -->}=2\mathrm{\pi <!--\; \pi \; -->}{F}_{SC}}$Zdroj:https://en.wikipedia.org?pojem=PAL_region
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