High-Definition Television (HDTV)

HDTV is an abbreviation used for High Definition Television. It is a digital broadcasting standard where the audio and video quality are better in comparison to that of Standard Television. Basically, HDTV is designed in a way that the images displayed by it appear clearer and colourful than the ancient ones.

HDTV is broadcasted by cable or satellite and the offered resolution is as high as 1920*1080 pixels which are quite higher than SDTV.

Content: HDTV

  1. Introduction
  2. What is HDTV?
  3. Working
  4. HDTV Displays


Today’s world has shown rapid growth towards High-Definition Television. This has significantly improved the quality of the image as well as the colour fidelity. Roughly, one can say that the resolution provided by the HDTV is around 5 times more in comparison to traditional, Analog Televisions.

An HDTV is different from a Standard TV mainly in terms of the number of pixels involved in forming the image on a single screen.

The basic question that may emerge in anyone’s mind is that – how can we define any television asadvanced’?

Advanced Television is another name given to Digital Television by US Federal Communications Commission. Digital Television allows the audio and video to get digitally transmitted for broadcasting and one to one services. The services which advanced television offered is beyond traditional, linear TV delivery sets.

What is HDTV?

For HDTV, it is generally said that it provides around 5 times higher resolution and image quality than the standard televisions i.e., the one used in ancient times. There are three major factors that define the HDTV broadcast systems, these are Frame Size, Scanning System, and Frame Rate.

Comparison of images of standard TV and HDTV

The frame size of an image defines the number of horizontal pixels times the vertical pixels such as 1920 * 1080. Generally, the horizontal pixels in the configuration are not represented thus, sometimes different systems are contextually given only vertically such as 1080.

In a scanning system, there are two types of scanning schemes namely, interlaced (represented as i) and progressive (represented as p).

Interlaced scanning is done in a way that here the overall frame is divided into two parts and each one is called field. While scanning the top left corner is considered to begin the process and meanwhile sweeping the complete way the bottom right corner is reached. However, each alternate row in the sequence is skipped during the scanning. This leads to a reduction in bandwidth by 2 thereby providing higher refresh rates.

Sometimes, an issue called motion artifacts is noticed in the interlaced video as in the case of fast-moving videos there will be chances of repetitive capturing of a part at different positions. Another drawback of this scanning technique is interline twitter where the fine vertical details of the object under shot get mixed with the horizontal details of the video format. In order to overcome these drawbacks progressive scanning is used.

In the Progressive type of scanning the complete image is considered a single frame and thus here scanning is performed line by line in a downward pattern. Thus, this avoids the chances of flickering.

Another important factor to be defined over here is the frame rate. Basically, the frame rate is given as the overall image frames per second (fps). If interlaced scanning is performed then it is equivalent to the field rate and so the number is twice as we consider two fields over here.

For high-definition television, it is said that it offers a widescreen aspect ratio of about 16:9. Along with this, it offers a horizontal resolution of 1920 pixels under progressive scanning. Hence resultantly according to 1920*1080 pixels format, a frame resolution of 2,073,600 is achieved.

How Satellite HD Works?

Satellite HD service works similar to that of satellite communication involved in standard television. We are aware of the basic functioning of a satellite-based system that a satellite orbiting in space acts as both a transmitter as well as a receiver for the signal under transmission.

For the signal coming from the earth-based station, the satellite acts as a receiver while for the receiving end of the actually transmitted signal, the satellite acts as a transmitter as it retransmits the received signal. Sometimes the satellite performs necessary modifications in the received signal while sometimes it simply retransmits the original signal. This depends on the type of satellite under action and the necessary operation that is taking place.

Various sources provide programming to satellite service providers then a compressed digital channel is beamed towards the GEO orbit via satellite dish. It is necessary that the satellite should present in Geostationary orbit for satellite television to take place. The reason behind the same is that there must be proper alienation so that correct aiming towards the satellite overhead must be maintained.

The signal from the satellite service provider is received by satellite orbiting in space and then it retransmits back towards the Earth in the form of a beam. The dish at the customer’s location is the earth-based receiving antenna. The signal received by the dish is sent to the set-top box (STB).

HDTV Displays

The cathode ray tube that is used as a display unit for analogue TV is not used for HDTV. There is a Rear projection CRT (RPTV) used for HDTV as these are comparatively of low costs, however, with the advent of technologies, other display options are also considered. Some of the promising display units that are used in HDTV are LCD, plasma displays, digital light processing (DLP) displays, etc.

In Plasma display, there are multiple small cells that are coated with red, green, and blue phosphors. The width of these display units is around 3 to 5 inches and are around 60 inches large. The video signal which is to be displayed that is coming from the satellite orbiting in space reaches the display unit through the dish and when the video signal incident on these cells then gas is stimulated. This resultantly triggers the phosphorus within the cells and this leads to the glowing up of the cell.

In an LCD display, there is a thin sheet of liquid crystal material on which light is passed. This material forms the viewing screen of the system. The video signal which is to be incident on the screen is obtained from a thin film transistor array. This transistor array is responsible for producing different degrees of polarization of the liquid crystal according to different colours depending on the wavelength. The screen sizes can be up to 50 inches and are quite thin and flat panel displays.

Furthermore, the Digital Light Processing displays make use of the Digital Micrometre Device (DMD) which was invented by Texas Instruments. There are about 1.3 million micro-mirrors present in the device and each mirror is used for the representation of one pixel. These mirrors are mechanically rotated in a similar fashion as that of the hinge and the rotational count is around 5000 times per second. The rotation of the mirrors is dependent on the video signal. Basically, according to the signal level, the degree of rotation shows variation.

There exists a ‘colour wheel’ having red, blue and green filters and this exhibit a rotational speed of around 120 revolutions per second. This wheel captures the light which is reflected by the DMD and accordingly, the image is projected on the screen. DLP is a rear projection display device, and its width is around 12 to 14 inches.

A light source is necessarily required in the case of Liquid Crystal and Digital Light Processing Displays. Only CRT is the one that cannot operate on digital signals, other than that LCD and DLP can perform an operation on digital signals thus digital to analog conversion is not required.

For HDTV, it is generally said that it provides a great level of sound quality along with excellent image clarity.

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