NTSC
NTSC is the television standard that was in effect from the 1940s onward in the USA, Canada, Japan, and parts of South America. It defined how an image is translated into an electrical signal and was the first standard to transmit color without rendering old black-and-white sets unusable.
In the past, a television picture had to be sent through the air as an electrical signal. For transmitter and receiver to understand each other, a shared rule is needed: How many picture lines are there? How often per second is a new image built up? Where in the signal is the color information located? These are exactly the rules that NTSC laid down. The abbreviation stands for National Television System Committee, a body in the USA that developed the standard starting in 1941. An NTSC picture consists of 525 lines, of which about 480 are visible, and is refreshed nearly 30 times per second.
Why color succeeded without breaking with the old
When the color version of NTSC was adopted in 1953, millions of living rooms had black-and-white sets. A new standard would have made these sets worthless overnight. The solution was a trick: the color information was additionally embedded into the existing signal, at a point that old sets simply ignored. A black-and-white television continued to show a clean grayscale image, while a color set read out the additional information. This principle is called backward compatibility, and NTSC was one of the first major examples of it.
This compromise came at a price. Color was transmitted as a sensitive additional signal and easily became garbled with poor reception. Faces turned greenish or reddish, depending on the signal path. That’s why American television sets had a dial labeled “Tint” for decades, with which viewers manually corrected the color. In Europe, people joked that NTSC stood for “Never The Same Color.”
The response to this were two competing standards: PAL in large parts of Europe and SECAM in France and Eastern Europe. PAL reversed the color information from line to line, thereby automatically compensating for errors. This split into three systems shaped the world market well into the 2000s. An American videocassette simply wouldn’t play on a German recorder.
Lines, fields, and the shift to 59.94 hertz
NTSC builds up a picture from individual lines that the electron beam of the picture tube scans from top to bottom. The entire image is not drawn all at once; instead, all the odd lines are drawn first, then all the even lines. These two fields merge for the eye into one complete picture. This process is called interlacing, and it halves the amount of data needed without the picture visibly flickering. Television worked this way until the end of the cathode-ray tube era.
The color is contained in an additional signal component, the color subcarrier. It oscillates at around 3.58 million cycles per second. The device reads the hue from its phase shift and the color saturation from its amplitude. This very phase shift is the weak point: if a long cable or a reflection delays the signal even slightly, the hue is no longer correct.
One curiosity is the frame rate. Originally, NTSC ran at exactly 60 fields per second, matching the American power grid frequency. For color, the rate had to be lowered slightly so that the color subcarrier and audio signal wouldn’t interfere with each other. Since then, NTSC has run at 59.94 instead of 60 hertz. This odd number continues to haunt video technology to this day, even in digital file formats.
What remains of NTSC today
As a broadcast standard, NTSC is history. The USA switched off analog over-the-air television in 2009, Japan in 2011, with other countries following suit. Digital methods took its place, in which the picture is transmitted as a data stream. Anyone streaming today has nothing to do with color subcarriers and fields.
Nevertheless, the term still comes up regularly. Old game consoles, VHS tapes, and camera archives exist in NTSC resolution, meaning 480 visible lines at 59.94 hertz. Anyone digitizing or emulating such material needs to know these values. That’s why video editing programs still have presets labeled NTSC to this day.
A common misconception: “NTSC” on a monitor spec sheet means something different. There, the term refers to the color space of the standard, i.e., the range of displayable colors. A specification like “72 percent NTSC” describes how much of that range the screen achieves. This has nothing to do with lines, frame rate, or television reception.