Video (NTSC/PAL)

Resolution of Picture

Nearly everyone owns a VHS VCR, right? Well, lets talk about DVD video by first looking back at what is VHS video.

We live in Australia, and a long time ago, someone decided we would use the PAL video system for video signal transmission. This video system provides around 520 lines of horizonal resolution and 720 vertical rows of resolution. Follow so far?

Aha! I found the numbers! (this is for NTSC I think) * Standard VHS resolution - 210 horizontal lines * Laser disc - 425 horizontal line * DVD - 540 horizontal line. OK, your VHS video stores roughly 387-odd horizontal lines of resolution, which is acceptable and what we have come to know as VHS-quality video (Beta video actually stored more resolution but was defeated in a merketing bungle, but this is not the place to discuss such things).

Now, DVD is capable of storing all 525 lines of resolution on a DVD disc and then outputting them to your TV. This results is what we interpret to be a far superior picture than we have seen before. A good quality DVD blows away everything you have ever seen on your TV before.

However, DVD does not store the image on the disc is analogue format like a VHS tape. The amount of video that can be stored on a disc is not a fixed quantity. While the statistics commonly used are "up to 2 hours on a single side, sing layer disc", this is at best, a guess. DVD uses a digital compression algorithm called MPEG-2 to encode and store the video information.

Things start to get complicated now, because MPEG-2 is a variable rate compression algorithm, which means you can get from 1:1 compression (which is no comression at all) all the way up to 10:1 compression where the data fits in just 10% of the original videos required space.

So, now you know how the picture is stored on the disc. The PAL image, as above, uses around 525 lines of resolution versus NTSC's 425 lines. This means that PAL requires extra space on the disc to store the additional lines of information. So, in rough terms, this means a PAL disc will look superior to an NTSC disc.

Frame Rates

The remainig variable we will talk about between PAL and NTSC is the frame rate which the image is decoded at. Again, the PAL format differs from the NTSC format. PAL uses 25 frames per second (fps) and NTSC uses 30 frames per second. This results in the Television being used requiring the capability to display both formats.

Now, DVD player manufacturers recognised this and implemented a video standard called PAL-60 for use when playing NTSC discs. PAL-60 outputs the NTSC signal using PAL colour codes at 30 fps. Most televisions no older than 8 or 10 years are capable of displaying PAL-60 even though they cannot display NTSC.

The New Wave...

Recently, Samsung have introduced a DVD player which completely converts NTSC into PAL, requiring no additional compatibility from the television being used. The newer DVD-ROM player software also has this ability.

If you are planning of buying a DVD player and importing or purchasing discs in NTSC (mostly USA-sourced material is NTSC), then you need to consider this when buying a DVD player.

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