Digital Television standards

January 3, 2016
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Part II

The World Moves to DTV

y 2014, the majority of countries in the world had switched from analog to digital broadcasting.

Digital TV has numerous advantages. For one thing, it uses a more efficient transmission technology allowing for improved picture and sound quality.

In addition, digital signals provide more programming options through the use of multiple digital subchannels (channels of information within the basic broadcast signal).

Compared to analog signals, digital broadcast signals react differently to interference.

Common problems with over-the-air analog television include ghosting of images (seeing multiple faint images at the same time; note photo), noise or "snow" because of a weak signal, etc.

Changes in analog signal reception result from factors such as a poor or misdirected antenna and changing weather conditions.

But even under these conditions an analog signal may still be viewable and you may still hear the sound.

Digital television transmissions are more demanding. The nature of digital TV results in a perfect picture initially, until the receiving equipment starts picking up interference or the signal is too weak to decode.

With poor reception some digital receivers will show a "blocky" video or a garbled picture with significant damage, other receivers may go directly from a perfect picture to no picture at all. This phenomenon is known as the digital cliff effect.

The first country to make a complete switch to digital over-the-air (terrestrial) broadcasting was Luxembourg, in 2006. Shortly thereafter, the Netherlands made the switch. Finland, Andorra, Sweden and Switzerland followed in 2007.

In June 2009, major broadcast stations in the United States switched to DTV. We say "major" because some lower power TV stations were allowed to stay with the NTSC analog standard for a period of time.

Some countries don't plan a complete analog-to-digital transition until around 2020.

As shown in the illustration below there are four basic international standards for digital broadcasting..

You will note that the United States and Canada use the ATSC (Advanced Television Systems Committee) standard.

Even though the differences between the four systems gets quite technical and is beyond the scope of this discussion, the fact that these incompatibilities exist is important to keep in mind with dealing in international programming.*

One of the major differences between analog and digital TV is the number of horizontal scanning lines that make up the picture. The greater number of lines the more picture detail is possible. The table below summarizes these.

Standards

SDTV (Analog)

HDTV (Digital)

Total Lines 525 1125 Active Lines 480-486 (maximum visible on the screen) 1080 (maximum visible on the screen) Sound Two channels (stereo) 5.1 channels (surround sound) Max Resolution 720 X 486 1920 X 1080

As you can see, the ATSC standard is capable of 16:9 images up to 1920 by 1080 pixels in size and resolution. This is more than six times the display resolution of the analog standard.

In addition, many different image sizes and line standards can be supported. These include:

  • Standard definition - 480i (interlaced) that are compatible with existing NTSC sets
  • Enhanced definition - 480p, (progressive), about the same quality as current DVDs
  • High-definition - 720p
  • High-definition - 1080i (the highest definition currently being broadcast)
  • High-definition - 1080p (Blu-ray equipment and a few cable operators)

It was thought that the move to digital TV and the "sudden" loss of all major NTSC television stations in the U.S. would be met with widespread viewer consternation.

In fact, TV stations braced themselves for an avalanche of unhappy viewers demanding to know what happened to their regular TV stations - the ones they had been viewing for decades.

This did not happen for four reasons.

First, TV stations had launched a major educational campaign about the switch that had lasted for months, second, most viewers were receiving the stations by cable or by satellite, which were not affected, third, for some time new TV sets had been equipped to handle ATSC signals, and, finally, the government went so far as to issue vouchers to help pay for set-top boxes to enable existing over-the-air NTSC receivers to convert to over-the-air ATSC signals.

Differences in Detail

Compare the screen enlargements shown here that represent HDTV (on the left) and the standard NTSC systems (on the right).

When projected on a 16 x 9-foot screen and observed from normal viewing distance the picture detail in good (1, 080p) HDTV systems appears to equal or better that attained by projected 35mm motion picture film.

The enlarged illustrations on the left above show the relative pixel detail of SDTV and HDTV. (The illustrations assume a 40-inch TV screen.)

SDTV produces an image with about 200, 000 pixel (picture) points. HDTV increases that by a factor of about 10 to two million pixels.

Ultra High-Definition

There are now two additional levels of sharpness beyond HDTV.

In 2013, Ultra high-definition sets and monitors started appearing.

These are divided into two levels: 2K with 2048 pixel lines and 4K with 4096 pixel lines. (Pixel stands for pixel element.)

However, it's been shown that average TV viewers can't discern the difference between them and HDTV at normal TV set viewing distances.

Source: cybercollege.com
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