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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.
Did
I miss something? Let me know via email.
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