Television Systems

Television is the system for transmitting moving images together with sound over a distance. The picture is broken down into a sequence of horizontal lines by a process called scanning, and each frame is sent rapidly enough that the eye perceives continuous motion. At the receiver the lines are reassembled into a complete image. Early systems used analogue transmission, while modern broadcasting is largely digital, encoding the picture and sound as compressed data that makes more efficient use of the available bandwidth.

Several analogue colour standards were developed regionally, the best known being PAL, used widely in Europe and many other countries, along with NTSC and SECAM. These standards differ in the number of scan lines, the frame rate and the way colour information is encoded. The transition to digital television introduced high-definition formats with greater resolution and the ability to carry many channels and additional data within the same broadcast spectrum, improving picture quality and flexibility.

Television display technology has changed dramatically. The cathode-ray tube (CRT) dominated for decades, scanning an electron beam across a phosphor screen, but it was bulky and heavy. Flat-panel technologies replaced it: liquid-crystal displays (LCDs) modulate a backlight through liquid-crystal cells, while plasma displays excite small cells of gas to emit light. Projection systems form a large image by projecting light onto a screen. Each display technology offers a different balance of size, brightness, contrast and cost.

Frequently asked questions

What is scanning in television?

It is the process of breaking a picture into a series of horizontal lines for transmission and reassembling them into a full image at the receiver.

What is PAL?

PAL is an analogue colour television standard used widely in Europe and elsewhere, differing from NTSC and SECAM in scan lines, frame rate and colour encoding.

How does an LCD television differ from a CRT?

An LCD modulates a backlight through liquid-crystal cells in a thin flat panel, whereas a CRT scans an electron beam across a phosphor screen in a bulky tube.