High definition television
High definition television (HDTV) is arguably the most important innovation in television since the introduction of colour. Commercial HDTV services have become a reality and HD broadcasts are now commonplace.
HDTV is not new and HDTV broadcasts have been going on in the USA and Japan for a number of years. However, what was lacking was an inter- nationally agreed standard. Europe did not enter the HDTV market till recently and that delay was utilised to reach an agreement on a unified standard. The first step was to agree to a common interface format (CIF) for HDTV. HDTV is invariably associated with digital television, and altho- ugh this is not necessarily the only way it can be delivered, without the processing capabilities of digital technology, HDTV would be impractical.
Why HDTV?
The two most prominent television systems, PAL and NTSC produce a moving picture with a quality referred to as standard definition (SD). While picture quality using SDTV is very good and has served television users very well over decades, it does suffer from noticeable degradation in quality in large size displays. To keep up with customer expectations and maintain picture quality, higher picture definition, i.e. high resolution must be used. The following summarises the advantages of HDTV:
● HDTV offers a step change in picture quality, delivering a home view- ing experience similar to that offered in cinemas.
● Viewers will see greater depth and tone of colours and textures. The improved clarity of HDTV broadcasts will bring an even greater sense of excitement and drama to a wide range of programme genres.
● HDTV can provide more than four times more data on a display screen than a SD broadcast. This is because of the increased picture resolution that HD broadcasts deliver and HD display devices will be able to receive.
● Availability of multi-channel audio and surround sound.
● Widescreen as standard.
HDTV common interface format
An ITU-R BT.709 standard provides three different specifications for HDTV: 720/50p, 1080/50i and 1080/50p. For North America 1080/60i and 720/60p are available. In each case the number of lines (720 or 1080) is the
active lines for the display. These were chosen in order to have a CIF with the SMPTE standards used in North America and Japan. For Japan and Korea it is 1080/60i and for China and Australia 1080/50i (Table 5.1).
HDTV is widescreen television with an aspect ratio of 16:9 (1.78:1). This is the same ratio as the pixel ratios: 1920 X 1080 for the 1080i and 1280 X 720 for the 720p formats. This means that for HDTV, the pixels are ‘square’ in the same way as computer-based graphics making integration between the two easier.