Phase Alternating Line

What Does Phase Alternating Line Mean?

Phase Alternating Line (PAL) is a color encoding system for analog television, and was created in 1961 in the United Kingdom. It features 624 horizontal lines per frame with a rate of 25 frames per second. PAL is used in broadcast television systems in many countries and is one of the three major broadcast standards, along with the NTSC and SECAM systems.


Techopedia Explains Phase Alternating Line

Similar to the NTSC system, Phase Alternating Line makes use of a quadrature amplitude modulated subcarrier which carries the chrominance data added to the video signal. The frequency for PAL is 4.43361875 MHz, while it is 3.579545 MHz for NTSC. PAL scans the cathode ray tube 625 times horizontally to form the video image. This is similar to the SECAM system. PAL makes use of a screen resolution of 720 × 576 pixels. PAL video can be converted to NTSC with the addition of extra frames. This can be done with techniques such as adaptive motion interpolation or inter-field interpolation.

Compared to NTSC, PAL has a more detailed picture due to the higher number of scan lines. Additionally, hues are more stable in PAL than with NTSC. Higher levels of contrast and better color reproduction are also present in PAL. Automated color correction is possible in the PAL system, unlike NTSC, which makes use of manual color correction. In fact, PAL is considered to have better picture quality than NTSC.

However, PAL has a slower frame rate, resulting in motion not being as smooth, and saturation varies at times between frames. The picture itself can appear to flicker at times. NTSC holds an edge over PAL when it comes to smoother pictures, especially with high-speed footage, due to its higher frame rate.


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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.