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National Technical Systems (NTSC) : Info
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NTSC is the analog television system in use in Canada, Japan, Mexico, the Philippines, South Korea, Taiwan, the United States, and some other countries, mostly in the Americas (see map). It is named for the National Television System Committee, the U.S. standardization body that adopted it.

History The National Television System Committee was established in 1940 by the Federal Communications Commission (FCC), in the United States (US), to resolve the conflicts which had arisen between companies over the introduction of a nationwide analog television system in the United States. In March 1941 the committee issued a technical standard for Black and white (colours) television that built upon a 1936 recommendation made by the Radio Manufacturers Association (RMA). Technical advancements of the vestigial sideband technique allowed for the opportunity to increase the image resolution broadcast to consumer televisions. The NTSC compromised between RCA's desire to keep a 441-scan line standard (which was already being used by RCA's NBC TV network) and Philco's desire to increase the number of scan lines to between 605 and 800. The committee compromised and selected a 525-line transmission standard. Other technical standards in the final recommendation were a frame rate (image rate) of 30 frames per second consisting of 2 interlaced fields per frame (2:1 interlacing) at 262½ lines per field or 60 fields per second along with an Aspect ratio (image) of 4:3, and frequency modulation (FM) for the sound signal.

In January 1950 the Committee was reconstituted to standardize color television. In December 1953, it unanimously approved what is now called simply the NTSC color television standard (later defined as RS-170a). The updated standard retained full backwards compatibility ("compatible color") with older black-and-white television sets. Color information was added to the black-and-white image by adding a color subcarrier of 4.5 x 455/572 MHz (approximately 3.58 MHz) to the video signal. In order to minimise interference between the chrominance signal and FM sound carrier, the addition of the color subcarrier also required a slight reduction of the frame rate from 30 frames per second to 30/1.001 (very close to 29.97) frames per second, and changing the line frequency from 15,750Hz to 15,734.26Hz.The FCC had briefly approved a different color television standard, starting in October 1950, that was developed by CBS.A third "line sequential" system from Color Television Inc. (CTI) was also considered. The CBS and final NTSC systems were called "field sequential" and "dot sequential" systems, respectively. However, this standard was incompatible with black-and-white broadcasts. It used a rotating color wheel, reduced the number of scan lines from 525 to 405, and increased the field rate from 60 to 144 (but had an effective frame rate of only 24 frames a second). Legal action by rival RCA kept commercial use of the system off the air until June 1951, and regular broadcasts only lasted a few months before manufacture of all color television sets was banned by the Office of Defense Mobilization (ODM) in October, ostensibly due to the Korean War."Color TV Shelved As a Defense Step," New York Times, Oct 20, 1951, p. 1. "Action of Defense Mobilizer in Postponing Color TV Poses Many Question for the Industry," New York Times, Oct. 22, 1951, p. 23. "TV Research Curb on Color Avoided", New York Times, October 26, 1951. Ed Reitan, CBS Field Sequential Color System, 1997. A variant of the CBS system was later used by NASA to broadcast pictures of astronauts from space. Most of the existing devices were soon destroyed and only two receivers are known to exist today. CBS rescinded its system in March 1953,"CBS Says Confusion Now Bars Color TV," Washington Post, March 26, 1953, p. 39. and the FAA replaced it on December 17, 1953 with the NTSC color standard that was cooperatively developed by several companies (including RCA and Philco)."F.C.C. Rules Color TV Can Go on Air at Once," New York Times, Dec. 19, 1953, p. 1. The first publicly announced experimental TV broadcast of a program using the NTSC "compatible color" system was an episode of NBC's Kukla, Fran and Ollie on August 30, 1953."NBC Launches First Publicly-Announced Color Television Show," Wall Street Journal, Aug 31, 1953, p. 4.

The first color NTSC television camera was the RCA TK-40, used for experimental broadcasts in 1953; an improved version, the TK-40A, introduced in March 1954, was the first commercially available color TV camera. It was replaced later that year by an improved version, the TK-41, which became the standard camera used throughout much of the 1960s.

The NTSC standard has been adopted by other countries, including most of the Americas and Japan. With the advent of digital television, analog broadcasts are being phased out. NTSC broadcasts are mandated by the FCC to end in the United States on February 17, 2009.

Technical details Lines and refresh rate The NTSC format is used with the M format (see broadcast television systems), which consists of 29.97 interlaced frames of video per second. Each frame consists of 486 visible scanlines out of a total of 525 (the rest are used for sync, vertical retrace, and other data such as captioning). PAL uses 625 lines, and so has a higher picture resolution. The NTSC system interlaces its scanlines, with visible scanlines 21-263 drawn in the first field, and visible scanlines 283-525 drawn in the second field, yielding a nearly Flicker fusion threshold image at its approximately 59.94 hertz (nominally 60 Hz/100.1%) refresh frequency. The refresh compares favorably to the 50 Hz refresh rate of the PAL and SECAM video formats used in Europe, where 50 Hz alternating current is the standard; flicker was more likely to be noticed when using these standards until modern PAL TV sets began using 100 Hz refresh rate to eliminate flicker. This produces a far more stable picture than native NTSC and PAL had, effectively displaying each frame twice. This did, at first, cause some motion problems, so it was not universally adopted until a few years ago. Interlacing the picture does complicate editing video, but this is true of all interlaced video formats, including PAL and SECAM.

The NTSC refresh frequency was originally exactly 60 Hz in the black and white system, chosen because it matched the nominal 60 Hz frequency of alternating current power used in the United States. Matching the screen refresh rate to the power source avoided wave interference that produces rolling bars on the screen. Synchronization of the refresh rate to the power cycle also helped kinescope cameras record early live television broadcasts, as it was very simple to synchronize a film camera to capture one frame of video on each film frame by using the alternating current frequency as a shutter trigger.

The figure of 525 lines was chosen as a consequence of the limitations of the vacuum-tube-based technologies of the day. In early TV systems, a master voltage-controlled oscillator was run at twice the horizontal line frequency, and this frequency was divided down by the number of lines used (in this case 525) to give the field frequency (60 Hz in this case). This frequency was then compared with the 60 Hz power-line frequency and any discrepancy corrected by adjusting the frequency of the master oscillator.

The only practical method of frequency division available at the time was the use of multivibrators, which could only divide by small numbers. For interlaced scanning an odd number of lines per frame was required, and so a chain of multivibrators was needed, each of which had to divide by a small, odd number. (Note that an odd number is never divisible by any even number). The closest practical sequence to 500 was 3 × 5 × 5 × 7 = 525. Similarly, the British 405-line system used 3 × 3 × 3 × 3 × 5. Although other values were theoretically possible, all of them involved division by unacceptably large numbers like 13 or 17, which produced reliability problems. Modern systems derive all their frequencies from the color subcarrier frequency (see below).

In the color system the refresh frequency was shifted slightly downward to 59.94 Hz to eliminate stationary dot patterns in the color carrier, as explained below in "#Color encoding".

Color encoding

There are 3 main standards in use around the world, PAL (Phase Alternating Line), NTSC (National Television System Committee) and SECAM (Séquentiel Couleur à Mémoire — Sequential Color with Memory).

The system used in North America is NTSC. Western Europe, Australia and Eastern South America use PAL. Eastern Europe and France use SECAM. Generally, a device (such as a television) can only read or display video encoded to a standard that the device is designed to support; otherwise, the source must be converted (such as when European programs are broadcast in mainland North America or vice versa).

This table illustrates the differences:{]-chrominance encoding system invented in 1938 by Georges Valensi. Luminance (derived mathematically from the composite color signal) takes the place of the original monochrome signal. Chrominance carries color information. This allows black and white receivers to display NTSC signals simply by ignoring the chrominance. In NTSC, chrominance is encoded using two 3.579545 MHz signals that are 90 degrees out of phase, known as I (in-phase) and Q (quadrature) QAM. Mathematically, the combination of two sine waves 90 degrees out of phase with each other, with varying respective amplitudes, can be viewed as a single sine wave with varying phase relative to a reference, and varying amplitude. In essence, the phase represents the instantaneous color hue captured by a TV camera and the amplitude represents the color saturation.

For a TV or a display to recover hue information from the I/Q phase as just described, it must know the reference for it (i.e. what phase is zero). It also needs a reference against which to compare the amplitude to make saturation sense out of it. So the NTSC signal includes a short sample of this reference signal, known as the color burst, located on the 'back porch' of each horizontal line (the time between the end of the horizontal synchronization pulse and of the blanking pulse on each line). The color burst consists of a minimum of eight cycles of the unmodulated (fixed phase and amplitude) color subcarrier. By comparing the reference signal derived from color burst to the chrominance signal's amplitude and phase at a particular point in the scan, the device determines what chrominance to assign to the pixel then being displayed. Combining that with the amplitude of the luminance signal, the receiver calculates exactly what color to make the pixel.

When a transmitter broadcasts an NTSC signal, it amplitude-modulates a radio-frequency carrier with the NTSC signal just described, while it frequency-modulates a carrier 4.5 MHz higher with the audio signal. If non-linear distortion happens to the broadcast signal, the 3.58 MHz color carrier may beat with the sound carrier to produce a dot pattern on the screen. To make the resulting pattern less noticeable, designers adjusted the original 60 Hz field rate down by a factor of 1000/1001, to approximately 59.94 fields per second.

The 59.94 rate is derived from the following calculations. Designers chose to make the chrominance subcarrier frequency an n + 0.5 multiple of the line frequency to minimize interference between the luminance signal and the chrominance signal. They then chose to make the audio subcarrier frequency an integer multiple of the line frequency to minimize interference between the audio signal and the chrominance signal. The original black and white standard, with its 15750 Hz line frequency and 4.5 MHz audio subcarrier, does not meet these requirements, so designers had either to raise the audio subcarrier frequency or lower the line frequency. Raising the audio subcarrier frequency would prevent existing receivers from properly tuning in the audio signal. Lowering the line frequency is comparatively innocuous, because the horizontal and vertical synchronization information in the NTSC signal allows a receiver to tolerate a substantial amount of slop in the line frequency. So that is the route the color standard took. In the black and white standard, the ratio of audio subcarrier frequency to line frequency is 4.5 MHz / 15750 = 285.71. In the color standard, this becomes rounded to the integer 286, which means the color standard's line rate is 4.5 MHz / 286 ~ 15734 lines per second. Dividing by 262.5 lines per field, this gives approximately 59.94 fields per second.

Transmission modulation scheme An NTSC television channel as transmitted occupies a total bandwidth of 6 MHz. A guard band, which does not carry any signals, occupies the lowest 250 kHz of the channel to avoid interference between the video signal of one channel and the audio signals of the next channel down. The actual video signal, which is amplitude modulation, is transmitted between 500 kHz and 5.45 MHz above the lower bound of the channel. The video carrier frequency is 1.25 MHz above the lower bound of the channel. Like most AM signals, the video carrier generates two sidebands, one above the carrier and one below. The sidebands are each 4.2 MHz wide. The entire upper sideband is transmitted, but only 750 kHz of the lower sideband, known as a vestigial sideband, is transmitted. The color subcarrier, as noted above, is 3.579545 MHz above the video carrier, and is quadrature amplitude modulation with suppressed carrier. The highest 25 kHz of each channel contains the audio signal, which is frequency modulation, making it compatible with the audio signals broadcast by FM radio stations in the 88-108 MHz band. The main audio carrier is 4.5 MHz above the video carrier. Sometimes a channel may contain an Multichannel television sound signal, which is simply more than one audio signal. This is normally the case when stereophonic sound and/or second audio program signals are used.

One odd thing about NTSC is the Cvbs (Composite vertical blanking signal) is something called "setup." This is a voltage offset between the "black" and "blanking" levels. Cvbs is unique to NTSC.
Cvbs has one defect: it makes NTSC more easily separated from its primary sync signals, but Cvbs has a smaller dynamic range when compared with PAL or SECAM.

Framerate conversion There is a large difference in framerate between film, which runs at 24.0 frames per second, and the NTSC standard, which runs at approximately 29.97 frames per second.

Unlike the two other video formats, PAL and SECAM, this difference cannot be overcome by a simple PAL#PAL speed-up.

A complex process called "Telecine#3:2 pulldown" is needed, which duplicates parts of frames. This induces noticeable jitter/"stutter" during slow pans of the camera.

For viewing native PAL or SECAM material (such as European television series and some European movies) on NTSC equipment, a standards conversion has to take place. There are basically two ways to accomplish this.

The framerate can be slowed from 25 to 23.976 frames per second (a slowdown of about 4%) to subsequently apply Telecine#3:2 pulldown.
Interpolate of the contents of adjacent frame (film) in order to produce new intermediate frames; this introduces artifact (observational), and even the most modestly trained of eyes can quickly spot video that has been converted between formats. (See also stutter frame)

Modulation for TVRO transmission NTSC when it is transmitted for TVRO viewing is transmitted substantially differently from terrestrial transmission.

Full transponder mode (eg: 36 MHz)

Luma signal is FM modulated, but with a 60Hz dithering signal to spread out energy over the transponder
Chroma is phase modulated
FM subcarrier at 6.8 MHz is added for mono sound
Other FM subcarriers are added for discrete stereo service, or stereo multiplex, often 5.8 and/or 6.2 MHz
Data subcarrers may be added as well

Half transponder mode (eg: 18 MHz)

all of the above is done, but signal is bandwidth limited to 18 MHz
the bandwidth limiting does not affect audio subcarriers

Use with Progressive Sources When NTSC is used to transmit content which was originally composed of 29.97 progressive full frames per second, the even field of the frame is transmitted first. This is opposite to PAL, and opposite to what would be expected ('Even first' means the frame starts being drawn on the second line). Systems which recover progressive frames or transcode video should ensure that this 'Field Order' is obeyed, otherwise the recovered frame will consist of a field from one frame and a field from an adjacent frame, resulting in 'comb' interlacing artifacts.

Comparative quality Video professionals and television engineers jokingly referred to NTSC as "Never The Same Color" or "Never Twice the Same Color".Jain, Anil K., Fundamentals of Digital Image Processing, Upper Saddle River NJ: Prentice Hall, 1989, p. 82. Reception problems can degrade an NTSC picture by changing the Phase (waves) of the color signal, so the color balance of the picture will be altered unless a compensation is made in the receiver. This necessitates the inclusion of a tint control on NTSC sets, which is not necessary on PAL or SECAM systems. NTSC also uses a different set of RGB primary color than later systems. This actually translates into a bigger YIQ color space, namely in the green part of the spectrum, but also introduces color distortions, when viewed on uncorrected sRGB monitors. http://www.jentronics.com/color.html

However, the mismatch between NTSC's 30 frames per second and film's 24 frames is well overcome by an ingenious process that capitalizes on the field rate of the interlaced NTSC signal, thus avoiding the film playback speedup that is used for PAL and SECAM at 25 frames per second (which results in audio distortion). See #Framerate conversion above.

There is no question the NTSC system reflects the technology of its originating era, but its compatibility and flexibility has been the key to its longevity over seven decades. The coming of digital television and high-definition television may end the need for analog television systems.

Variants of NTSC NTSC-M Unlike PAL, with its many varied underlying broadcast television systems in use throughout the world, NTSC color encoding is invariably used with broadcast system M, giving NTSC-M.

NTSC-J Only Japan's variant "NTSC-J" is slightly different: in Japan, black level and blanking level of the signal are identical (at 0 IRE (unit)), as they are in PAL, while in American NTSC, black level is slightly higher (7.5 IRE (unit)) than blanking level. Since the difference is quite small, a slight turn of the brightness knob is all that is required to enjoy the "other" variant of NTSC on any set as it is supposed to be; most watchers might not even notice the difference in the first place.

PAL-M The Brazilian PAL-M system uses the same broadcast bandwidth, frame rate, and number of lines as NTSC, but using PAL encoding. It is therefore NTSC-compatible in sources such as video cassettes and DVDs, but its color picture cannot be received on a standard NTSC television set.

NTSC-N This is used in Paraguay, and Bolivia (though Paraguay has recently switched to NTSC-M from PAL-M). This is very similar to PAL-M (television) (used in Brazil). It is also closely related to PAL-Nc (used in Argentina) and PAL-N (used in Uruguay).

The similarities of NTSC-M and NTSC-N can be seen on the broadcast television systems#ITU identification scheme table, which is reproduced here:

{] and Caribbean, Philippines, South Korea, Republic of China (all NTSC-M) and Brazil (PAL-M).], Paraguay, Uruguay (all PAL-N). Economises bandwidth use at the expense of picture quality.], the systems are identical. NTSC-N/PAL-N/PAL-Nc are compatible with sources such as game consoles, VHS/Betamax VCRs, and DVD players. However, they are not compatible with baseband broadcasts (which are received over an Antenna (radio)), though some newer sets come with baseband NTSC 3.58 support (NTSC 3.58 being the frequency for colour modulation in NTSC: 3.58 MHz).

NTSC 4.43 In what can be considered an opposite of PAL, NTSC 4.43 is a pseudo color system that transmits NTSC encoding (525/29.97) in a color subcarrier of 4.43 MHz instead of 3.58 MHz. The resulting output is only viewable by TVs that support the resulting pseudo-system (usually multi-standard TVs). Using a native NTSC TV to decode the signal yields no color, while using a PAL TV to decode the system yields erratic colors (observed to be lacking red and flickering randomly). The format is apparently limited to few early laserdisc players and some game consoles sold in markets where the PAL system is used.

The NTSC 4.43 system while not a broadcast format appears most often as a playback function of PAL cassette format VCRs, Beginning with the Sony 3/4" U-Matic format and then following onto Betamax and VHS format machines. As Hollywood has the claim of providing the most cassette software (movies and television series) for VCRs for the world's viewers, and as not all cassette releases were made available in PAL formats, a means of playing NTSC format cassettes was highly desired.

Multi-standard video monitors were already in use in Europe to accommodate broadcast and professional needs regarding PAL, SECAM and NTSC video formats from sources dedicated to just one of those formats. The Heterodyne#Heterodyning in analog videotape recording color-under process of U-Matic, Betamax & VHS lent itself to minor modification of VCR players to accommodate NTSC format cassettes. The color-under format of VHS uses a 629khz subcarrier while U-Matic & Betamax use a 688KHz subcarrier to carry an amplitude modulated chroma signal for both NTSC and PAL formats. Since the VCR was ready to play the color portion of the NTSC recording using PAL color mode, the PAL scanner and capstan speeds had to be adjusted upwards from PAL's slower 50Hz field rate to match NTSC's 59.94Hz field rate, and faster linear tape speed.

Although easier to do than explain, the changes to the PAL VCR are very minor thanks to the existing VCR recording formats. The output of the VCR when playing an NTSC cassette in NTSC 4.43 mode is 525 lines/29.97 frames per second with PAL compatible heterodyned color. The multi-standard receiver is already set to support the NTSC H & V frequencies; it just needs to do so while receiving PAL color.

The existence of those multi-standard receivers was probably part of the need for region coding of DVDs. As the color signals are component on disc for all display formats almost no changes would be required for PAL DVD players to play NTSC (525/29.97) discs as long as the display was frame-rate compatible.

NTSC-film NTSC with a frame rate of 23.976 fps is described in the NTSC-film standard.

Evolution of the NTSC standard NTSC I NTSC I is the original monochromatic 525/60 signal standard that first became standard in the U.S. in 1941 and later in Canada.

NTSC II NTSC II is the color system with some, but not all, aspects of the signal rigorously defined. NTSC II has a minor change in its temporal structure, becoming a 525/59.94 system. From this point 525/60 becomes a separate production standard that interoperates with NTSC via a 1/100.1 drop frame solution.

NTSC III NTSC III came about due to digital television routing during the late 1980s*; all aspects of NTSC III are rigidly mathematically defined.

The current state of NTSC III The North American analog transmission chain is strictly NTSC III now. Many NTSC II devices feed into existing transmission chains, with NTSC III compatibility being achieved by signal processing in the digital domain.

Typical terrestrial TV transmitters or cable company distribution units send out NTSC III signals, especially if the originating signal comes from a TVRO or ATSC Standards source. All free-to-air analog satcom transmissions are NTSC III. Video scrambling systems such as VideoCipher cannot achieve full NTSC III compatibility due to end-to-end analog processing issues.

There are no known compatibility problems between NTSC II and NTSC III. Older NTSC II sets should handle NTSC III signals without any problems, even with respect to minor frequency variances of the color sync subcarrier that exist in NTSC II.

Vertical Interval Reference The standard NTSC video image contains some lines (lines 1–21 of each field) which are not visible; all are beyond the edge of the viewable image, but only lines 1–9 are used for the vertical-sync and equalizing pulses. The remaining lines were deliberately blanked in the original NTSC specification to provide time for the electron beam in CRT-based screens to return to the top of the display.

VIR (or Vertical interval reference), widely adopted in the 1980s, attempts to correct some of the color problems with NTSC video by adding studio-inserted reference data for luminance and chrominance levels on line 19. Suitably-equipped television sets could then employ these data in order to adjust the display to a closer match of the original studio image. The actual VIR signal contains three sections, the first having 70 percent luminance and the same chrominance as the color burst signal, and the other two having 50 percent and 7.5 percent luminance respectively.

A less-used successor to VIR, ghost-canceling reference, also added ghost (multipath interference) removal capabilities.

The remaining vertical blanking interval lines are typically used for datacasting or ancillary data such as video editing timestamps (vertical interval timecodes or SMPTE timecodes on lines 12–14 ), Vertical Interval Test Signal on lines 17–18, a network source code on line 20 and closed captioning, XDS and V-chip data on EIA-608. Early teletext applications also used vertical blanking interval lines 14–18 and 20, but teletext over NTSC was never widely adopted by viewers .

Many PBS stations transmit TV Guide On Screen (TVGOS) data for an electronic programme guide on VBI line 17.

Countries and territories that use NTSC North America

, NTSC broadcast to be abandoned by 2011, simulcast in ATSC
, NTSC broadcast to be abandoned in 2009, simulcast in ATSC

Central America and the Caribbean

Leeward Islands

(U.S.)
U.S. Virgin Islands

South America

(until 2006 Paraguay used PAL)

Asia

Republic of China (Taiwan)
Union of Myanmar (Burma)

(Propaganda station aimed at South Korea; domestic broadcasts use PAL)
(Historic; Cambodia now uses PAL)
(Historic; all of Vietnam now uses PAL)
(Historic; Thailand now uses PAL)

The Pacific US Territories

Northern Mariana Islands
Midway Atoll (a US military base)

Other Pacific island nations

(in Compact of Free Association with US; US aid funded NTSC adoption)
Federated States of Micronesia (in Compact of Free Association with US)
(in Compact of Free Association with US; adopted NTSC before independence)
(closely tied to American Samoa; US aid funded NTSC adoption)
(US aid funded NTSC adoption)

Historic (used NTSC experimentally before adopting PAL)

(Historic; used before 1989, Fiji has used PAL since 1990)
(Historic; Australia now uses PAL)

Indian Ocean

Diego Garcia

Middle East

(Historic; all of Yemen now uses PAL)

Europe

(Experimented with a 405-line variant of NTSC in the 1950s and 1960s; dropped in favor of PAL)