What is HDTV?
August 12, 2007
High Definition Television or HDTV is a term that can be better understood when we make a comparison between different digital television standards available today. In fact, HDTV is a relative term and is often analogous with higher resolution. When we date back to the days when TV was in its formative years, there were standards like NTSC, PAL, SECAM which measured the video quality of the TV in terms of scan lines and number of frames per second lines. It was in mid forties of last century , NTSC or National Television System Committee which universalized a video standard which had 4:3 aspect ratio and 525 scan lines refreshing at a rate of 30 interlaced frames, or 60 fields per second. A few nations like the UK, did not stick to this standard and made a change in refresh rate, thus UK followed TV standard based on 50 Hz instead of 60 HZ which was set as standard in countries like the US and Canada. However, PAL and SECAM which came as alternatives for NTSC had more scan lines (625 instead of 525 lines) to provide more detailed pictures on the screen. Although the pictures were better on PAL but the refresh rate tend to be slower resulting in flicker which used to annoy the viewers.
The real revolution took place in 1982, when ATSC or Advanced Television Systems Committee was formed to develop a new television technology that can altogether replace the analogue video formats like NTSC, PAL or SECAM. First began as technological advancement in analog television, ATSC soon started to develop digital TVs that include standard TV, enhanced TV and finally High-definition TV. All these DTVs promised better picture quality in terms of resolution, refresh rate, colour quality etc. Another advantage that DTVs holds over previous analog televisions was improved sound quality that comes with their impressive display.
All the Digital TVs that include LCD television or plasma TV differ depending up on how many pixels per inch make up the image (this is called resolution), number of scan lines over the screen (both vertically and horizontally) and the aspect ratio. The aspect ratio shows how wide is the screen in relation to its height. In early televisions (analog) and standard digital televisions the 4:3 is the aspect ratio is still followed which means the width will be slightly longer than the height of the screen. This aspect ratio is much closer to 16 mm or 35 mm movie, and was popular until the wider format of movies (70 mm) started to be used by most movie makers during the last two decades. The 16:9 or wider aspect ratio started to be followed by television makers to present movie like viewing experience and soon became the standard for the HDTVs.
Resolution is one of the major characteristics that help us to distinguish one TV from another. Compared with old analog televisions, present HDTVs can show ten times higher resolution or even twenty times! A high end HDTV LCD TV (which is 1980p resolution), can show more than 4 million pixels on its screen presenting imagers so sharper and more detailed. When resolution is taken into account, any digital TV that can show minimum resolution of 720p is HDTV. There are HDTV resolutions like 720p, 1080i, 1080p etc. While there is not much to compare between 720p and 1080i as they look more or less alike, however, 1080p images always look superior to any other HDTV resolution. Again, 720p and 1080p indicate the method of scanning is progressive scan which tends to present better image quality against the same resolution scanned by interlace method ( which is denoted by ‘i’ and which follows the resolution).
Digital TVs also come with improved audio quality as they adopt new audio systems like Dolby Digital which minimize the unwanted noises and also use much more audio data on their tracks. Dolby uses five channels to provide surround sound quality which is more or less similar to what one experiences in a cinema hall. However, most of the HDTVs usually feature only two channels and only a few can support 5.1 channel feature of full Dolby Digital.
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