Phase Alternating Line. The analog color coding system, which effectively compressed three TV frames of red, green and blue sent from the camera or scanner, into one whole color picture. It was widely used for television in Europe and in many countries around the world, always with the 625/50 (lines per picture/interlaced fields per second) system, except in Brazil (see PAL-M). The engineers designing PAL had the advantage of seeing the NTSC system, and managed to improve on it but by swinging the phase of the reference color ‘burst’ on alternate lines, hence Phase Alternating Line. NTSC had no way of automatically correcting the drift of its subcarrier that carried the color information. So, as the phase drifted, so did did the color’s hue. Hence the system’s other name ‘Never Twice the Same Color’! As PAL switched the subcarrier phase by 90-degrees line by line (+45 and -45 from the color axis), the phase and so the hue of the colors, could be averaged, so rendering the correct hue at the receiver. This required every decoder to have a one TV-line delay, which was expensive. However the price quickly dropped as sales took off in the mid 1960s.
Bandwidth for the PAL-I system (here ‘I’ indicates 625/50 line/field scanning) is typically 5.5 MHz luminance, and 1.3 MHz for each of the color difference signals, U and V which are coded with the luminance. Note that the PAL term is frequently used to describe any 625/50I analog format even if it is component, or in the 576/50I digital television system where PAL coding is not used.