Video and TV

At the present time most people who are watching TV have an analogue set and the majority of TV broadcasts are still transmitted in analogue. So what makes the new system of HDTV that much better?

HDTV has 2.1 million or more pixels and analog only has 210,000 pixels. That is a lot more picture information and that is what makes HDTV so crisp and detailed.

HDTV has an aspect ratio of 16:9 versus the 4:3 aspect ratio of analog. You get one-third more image area and ithis allows you to watch movies in their original format.

The 16:9 aspect ratio actually more closely matches the viewing angle of the human eye, making for a more immersive entertainment experience.

HDTV images are made up of from 720 to 1080 horizontal scan lines, whereas analog only has 480. Again, a lot more detail is possible with that much more visual information on the screen.

HDTV can provide 5.1 channel Dolby Digital sound, equal to what you hear in a movie theater. Plug in a home theater audio system and you can hear the distinctions between sound effects, dialogue and music. Analog can't offer anything close to that!

With so much more visual information (more pixels and more scan lines), HDTV provides amazing detail. In fact, many people are startled by the amount of detail they see And the multi-channel sound and wide screen format make the experience even more rewarding.

additional content

The video used in traditional television signals takes this particular form, but specific formats vary from country to country. There are three commonly used formats:

  • National Television Standards Committee (NTSC) format: Used in the United States, Canada, Japan and elsewhere
  • Phase Alternation by Line (PAL) format: Used in European countries and other parts of the world

On a PAL or SECAM system, the electron beam passes over the entire screen 50 times a second, which means the television presents a complete picture 25 times a second. This is pretty close to 24 frames per second, so if you make a direct conversion showing one complete film frame in every full video frame, the movie plays pretty well, just a tiny bit faster. The main thing you might notice is that all the sound has a slightly higher pitch.

NTSC format shows about 30 frames per second (60 fields), so it is a bit trickier. Mathematically, you can't easily spread 24 frames across 30 frames. But you can divide up 60 fields so that you show only 24 frames per second, if you use a block of five video fields to show two film frames. The math is pretty simple:

  • In one second of video, there are 60 fields.
  • So, you show five fields in 1/12th of a second (60/12 = 5).
  • In one second of film, there are 24 frames.
  • So, in 1/12th of a second, you show two frames.
  • If you record only two film frames for every five fields of video, you can create a video copy of a movie that plays at the correct speed.

Of course, you can't divide five by two evenly, so formatters have to stagger it. A video copy of a movie shows frame 1 for three fields, frame 2 for two fields, frame 3 for three fields and so on. This doesn't present motion exactly as it appeared when the movie was projected (pans aren't as fluid, for example), but the movie isn't sped up at all and the soundtrack isn't affected.

This process works a little bit differently with DVD movies. DVD's store movies in MPEG digital format, which compresses the movie file by using the same image information from frame to frame.