ElectronTrail

Television systems

NTSC, PAL, SECAM, and digital television

The three analog colour systems differ mainly in how they carry colour. Below: a parameter comparison, how each encodes colour, and how analog differs from digital TV.

Picture parameters

NTSC

525 / 59.94
Lines525
Fields/s60
Line frequency: 15.734 kHz
Colour subcarrier: 3.579545 MHz

North America, parts of South America, Japan, others

PAL

625 / 50
Lines625
Fields/s50
Line frequency: 15.625 kHz
Colour subcarrier: 4.43361875 MHz

Much of Europe, Asia, Africa, Oceania

SECAM

625 / 50
Lines625
Fields/s50
Line frequency: 15.625 kHz
Colour subcarrier: ,

France, parts of Eastern Europe, parts of Africa & the Middle East

Monochrome (B&W)

525 / 59.94
Lines525
Fields/s60
Line frequency: 15.734 kHz
Colour subcarrier: ,

Historical / any system without colour

How colour is carried

NTSC

Subcarrier phase carries hue, amplitude carries saturation. A phase error shifts hue (hence the "tint" control).

PAL

Like NTSC, but the phase alternates each line; averaging two lines cancels hue error.

SECAM

Colour-difference signals are frequency-modulated (FM) and sent on alternate lines; a delay line reconstructs both.

Analog vs digital television

Digital TV (DVB-T/T2 in Europe, ATSC in North America, ISDB-T in Japan) replaced analog broadcasting. Here are the key conceptual differences.

Analog (CRT)
Digital (DVB/ATSC)
Representation
Continuous voltage (brightness, colour, sound)
Sampled bitstream (MPEG-2/H.264/HEVC)
Degradation
Gradual: snow, ghosting, noise
Abrupt: blocking and freezing, then nothing (the "digital cliff")
Error handling
None, noise is shown directly
Forward error correction hides errors up to a threshold
Channel use
One programme per RF channel
Many programmes (a multiplex) in one RF channel
Picture
Interlaced, 525/625 lines
SD/HD/UHD, interlaced or progressive
Aspect ratio
Usually 4:3
Usually 16:9, with extra services (EPG, subtitles, surround)
Display
CRT scanned by a beam
Usually LCD/OLED panels, pixel-addressed

This is a conceptual comparison. Details (codecs, COFDM/8VSB modulation, profiles) depend on region and standard.

Sources:International Telecommunication Union (ITU-R)Analog DevicesWikipedia contributors
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