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PAL

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Phase Alternating Line, or PAL, is a major color encoding system for analog television.

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It was designed to transmit color information reliably through broadcast signals. While there were other major standards like NTSC and SECAM, PAL became one of the most widely used systems in the world. It matters because it solved specific technical problems that made earlier color television difficult to watch. By managing how color data is sent, PAL ensures that the colors on your screen look accurate even if the signal is not perfect.

Pal channel
Pal channel

To understand the mechanism, we must look at how the signal handles color. PAL uses a variant of the Y′UV color space. This system separates the monochrome luma signal, which is the brightness, from the chrominance, which is the color.

PAL picture
PAL picture

The chrominance is added to the luma signal using a quadrature amplitude modulated subcarrier. In the PAL system, the frequency of this subcarrier is 4.43361875 MHz. The defining feature of PAL is that the phase of this color information reverses with every single line of the video. This means the timing of the color waves flips back and forth between odd and even lines. This constant switching allows the system to automatically correct phase errors during transmission.

PAL signal frame (20ms) and line (64µs) decoding
PAL signal frame (20ms) and line (64µs) decoding

Because the phase reverses every line, receivers need a way to process this information. Many receivers use a chrominance analogue delay line. This component stores the color information from the previous line so it can be compared to the current line. By averaging the color information from both lines, the receiver can cancel out errors. If errors are not corrected this way, they can cause the colors to shift in hue. In the PAL system, these errors usually result in changes to saturation instead. While this makes the vertical color resolution slightly lower than NTSC, the human eye does not notice the difference.

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History shows that PAL was born from a need for better stability. In the 1950s, Western European countries began planning for color television. They noticed that the NTSC standard had weaknesses, such as color tone shifting during poor transmission. This was a major issue due to Europe's specific geography and weather. To fix this, Walter Bruch developed PAL while working at Telefunken in Hanover, West Germany. He patented the format in December 1962 and unveiled it to the European Broadcasting Union in January 1963. Interestingly, Bruch did not name the system after himself. He joked that a "Bruch system" would not sell well because "Bruch" is the German word for "breakage."

PAL multi lines
PAL multi lines

The rollout of PAL happened in stages across different nations. The first broadcasts began in the United Kingdom in July 1967. West Germany followed shortly after at the Berlin IFA on August 25 of that same year. The Netherlands and Switzerland began their PAL broadcasts by 1968, and Austria followed in 1969. In Italy, a different system called ISA was proposed, but it was abandoned in 1975 in favor of PAL. Even the Soviet Union tested its own versions, known as TRIPAL and NIIR, though these never went beyond the testing phase.

PAL has a massive geographic reach. It was adopted by most European countries and many African nations, such as South Africa. It is also used in Argentina, Brazil, Paraguay, and Uruguay. Much of the Asia Pacific region, including the Middle East and South Asia, uses PAL as well. However, some regions did not adopt it. France and Francophone Africa used SECAM instead. Japan, South Korea, Taiwan, and several ex-Soviet states also used different standards. The technical specifications for PAL were officially last published by the International Telecommunication Union in 1998 as Recommendation ITU-R BT.470.

Today, the term "PAL" is often used in a way that relates to modern digital technology. Even though we no longer use analog signals for most things, the name persists. For example, a "PAL DVD" refers to a digital format that uses 576 interlaced lines. This is intended to be backward compatible with older PAL devices. Similarly, video game consoles that output a 50 Hz signal are often labeled as "PAL" to distinguish them from 60 Hz NTSC machines. This usage is technically imprecise because digital signals use different encoding, like YCbCr, rather than the original analog PAL method. However, it helps users understand how the device connects to their television systems.

PAL-I
PAL-I
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🖼️ Images & Media (10)
File:Mousepad_in.jpg
Mousepad_in.jpg
File:Mousepad_out.jpg
Mousepad_out.jpg
File:Pal channel.svg
Pal channel.svg
File:PAL-I.png
PAL-I.png
File:PAL picture.png
PAL picture.png
File:PAL multi lines.png
PAL multi lines.png
File:PAL 2 lines.png
PAL 2 lines.png
File:An interlaced PAL frame with 20ms duration.jpg
An interlaced PAL frame with 20ms duration.jpg
File:PAL signal frame (20ms) and line (64µs) decoding.jpg
PAL signal frame (20ms) and line (64µs)...
File:Composite Video.svg
Composite Video.svg
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