AfterDawn: Glossary

PAL

The PAL (Phase Alternating Line) TV standard was introduced in the early 1960's in Europe. It has better Resolution than NTSC, having 576 lines in the Active Area of the Frame. The Framerate, however, is slightly lower at 25fps.

The term PAL may also be used to describe any video, including digital video, formatted for playback on a PAL TV. This generally includes any Standard Definition (SD) video with a vertical Resolution of up to 576 Pixels and a horizontal resolution no greater than 720, which also has a Framerate of 25fps. PAL may also be called 625/50, in reference to the total number of lines (including lines not in the Active Area) and fieldrate.

Geography
PAL is used in most of the western European countries (except France), Australia, some countries of Africa, some countries of South America and in some Asian countries. Because the PAL signal is very close to the SECAM format used in France and some eastern European countries, SECAM viewers generally use PAL equipment (like DVD players) modified to convert the output to use SECAM's unique color encoding.

Flavors of PAL
There are various versions of PAL, most commonly used method is called PAL B/G, but others include PAL I (used in the UK and in Ireland) and PAL M (a hybrid standard, which has the same resolution as NTSC has, but uses PAL transmission and color coding technology). All of these standards normally work nicely together, but audio frequencies might vary and therefore you should check that your appliances work in the country you're planning to use them (older PAL B/G TVs can't Decode UK's PAL I audio transmissions even that the picture works nicely).

Capture Resolution
According to the ITU-R BT.601 (Rec.601) standard for capturing analog video, the correct resolution is 720x576, with the Active Area (the area containing the actual picture) represented by the center 702 horizontal Pixels. Some Capture cards will use 720 pixels for the active area instead. The two lines below show the slight difference between using the full 720 pixels versus only using the center 702.


Standard Digital PAL Formats
Various consumer digital video formats have standards designed to work with PAL TVs. These include VCD, SVCD, DVD, and DV. Below is a table showing the standard resolutions for each format. In the case of DV, the Full Frame represents the Active Area of the Frame, meaning you may need to resize and add borders to the sides when converting to other formats like MPEG-2 for DVD. DVD players may also implement the digital to analog conversion improperly, resulting in the Full Frame being squeezed into the analog video's Active Area.

FormatPAL Resolution
DVD720x576
704x576
352x576
352x288
DV720x576
SVCD480x576
VCD352x288


Minimum Horizontal Capture Resolution
Since actual analog PAL video always contains 576 lines, it's best to always capture to a frame with a vertical resolution of 576. If you don't necessarily care about capturing to the Rec.601 frame size you should at least make sure you're capturing at more than twice the Bandwidth (range of frequencies) of the analog source. The table below gives the frequencies for some common analog PAL video sources, along with the minimum number of horizontal samples required to meet the Nyquist-Shannon sampling requirements and the lowest DVD-Video resolution that meets this requirement.
FormatBandwidthMin Horiz SamplesMinimum DVD Capture Size
PAL B/G5MHz521704x576
PAL I5.5MHz573704x576
VHS3MHz313352x576
S-VHS5MHz521704x576
Video83.3MHz345352x576
Hi 85.5MHz573704x576
Laserdisc5.8MHz605704x576



Related Guides
Digital Video Fundamentals - Resolution and Aspect Ratio





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