Computer and Video Issues

Video traces its history to early pioneers such as John Logie Baird, who managed to record a recognizable human face on video in 1925. The first microcomputer appeared in 1960, developed by Digital Equipment, priced at a mere $120,000 (it did include a keyboard and mouse). These two technologies existed very independently of each other for many years. All computer pixels are square in their native format. Professional video applications often use pixels that are nonsquare.

The National Television Standards Committee, known as the NTSC, has set the standard that television fits to the 4X3 aspect ratio. This is often interpreted by video boards as an image that is 648X486 pixels. Those countries that use the PAL format use boards that work with images that measure 768X576 square pixels. If designing for square systems, it is easy because no conversions are necessary.

Of course, if you offer a standard, it will be broken. In an effort to pack more pixels and increase resolution, the ITU-R BT 601 video standard was developed. It is often called "D1" (after the D1 format invented by Sony in 1986 that was the first component digital format available). In NTSC, the native "board" size of a D1 frame is 720X486 nonsquare pixels. The PAL format uses 720X576 nonsquare pixels.

This format has evolved into the Digital Video (DV) standard, which is employed in the consumer DV format as well as DVCAM and DVCPRO tape and DVD authoring. The native size for DV frames is 720X480 nonsquare pixels for NTSC (six less than the D1 format). The PAL DV format is identical to the standard PAL format and remains unchanged at 720 X 576 nonsquare pixels. These pixels are played back on analog televisions, which must display them as square pixels at the 4X3 aspect ratio.

Houston, we have a problem.

Discussing pixel aspect ratio is about as much fun as going to a great art museum and spending all your time discussing the doorknobs. Yes, they too are important, but hardly interesting. Please bear with me as I try to resolve this dilemma in a clear and orderly fashion. I will simplify as much as possible without neglecting essential intricacies.

Go Deeper into Video Pixels

Looking for a more sci-T^S) entific (and mathematical) version? The Quick Guide to Digital Video Resolution and Aspect Ratio Conversions takes a much deeper look at the issues. You can find it at http:// lipas.uwasa.fi/~f76998/video/ conversion/. Be warned though; while it may be quick, it's not easy.

Video Standards

^ NTSC: The National Television Standards Committee developed the North American broadcast standard in 1953. The group is jokingly referred to as "Never Twice the Same Color." PAL: Developed in the early 1960s, the Phase Alternate Line format is the standard for most of Europe. The group is sometimes called "Peace At Last."

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