pctechguide.com

Digital Video Fundimentals

Understanding what digital video is first requires an understanding of its ancestor – broadcast television or analogue video. The invention of radio demonstrated that sound waves can be converted into electromagnetic waves and transmitted over great distances to radio receivers. Likewise, a television camera converts the colour and brightness information of individual optical images into electrical signals to be transmitted through the air or recorded onto video tape. Similar to a movie, television signals are converted into frames of information and projected at a rate fast enough to fool the human eye into perceiving continuous motion. When viewed by an oscilloscope, the unprojected analogue signal looks like a brain wave scan – a continuous landscape of jagged hills and valleys, analogous to the ever-changing brightness and colour information.

There are three forms of TV signal encoding:

  • most of Europe uses the PAL system
  • France, Russia and some Eastern European countries use SECAM, which only differs from the PAL system only in detail, although sufficient to make it incompatible
  • the USA and Japan use a system called NTSC.

With PAL (Phase-Alternation-Line) each complete frame is drawn line-by-line, from top to bottom. Europe uses an AC electric current that alternates 50 times per second (50Hz), and the PAL system ties in with this to perform 50 passes (fields) each second. It takes two passes to draw a complete frame, so the picture rate is 25 fps. The odd lines are drawn on the first pass, the even lines on the second. This is known as interlaced, as opposed to an image on a computer monitor which is drawn in one pass, known as non-interlaced. Interlaced signals, particularly at 50Hz, are prone to unsteadiness and flicker, and are not good for displaying text or thin horizontal lines.

PCs, by contrast, deal with information in digits – ones and zeros, to be precise. To store visual information digitally, the hills and valleys of the analogue video signal have to be translated into the digital equivalent – ones and zeros – by a sophisticated computer-on-a-chip, called an analogue-to-digital converter (ADC). The conversion process is known as sampling, or video capture. Since computers have the capability to deal with digital graphics information, no other special processing of this data is needed to display digital video on a computer monitor. However, to view digital video on a traditional television set, the process has to be reversed. A digital-to-analogue converter (DAC) is required to decode the binary information back into the analogue signal.

Filed Under: Digital Video

Latest Articles

Ethernet Networks

To adapt the technology for the consumer market, Ethernet home network vendors have designed networking kits - consisting of low-cost network adapters, an inexpensive non-managed hub and simple configuration software - to make the technology easier to … [Read More...]

Hard Drive Upgrade Reasons

There are an number of reasons why you may wish to install a second hard drive: you simply need more hard disk space you want to use it for backup purposes you want to create a dual-boot system. A variation on the backup reason is a scenario in which you're going to have to do a clean … [Read More...]

Color Laser Printers

Laser printers are usually monochrome devices, but as with most mono technologies, laser printing can be adapted to colour. It does this by using cyan, magenta and yellow in combination to produce the different printable colours. Four … [Read More...]

Guides

Recent Posts

IEEE 802.11n

Demand for wireless LAN hardware experienced phenomenal growth in the years following the ratification of the IEEE 802.11a standard in the … [Read More...]