NTSC

Television encoding systems by nation; countries using the NTSC system are shown in green.

NTSC, named for the National Television System Committee, is the analog television system used in most of North America, most countries in South America, Burma, South Korea, Taiwan, Japan, Philippines, and some Pacific island nations and territories (see map). NTSC is also the name of the U.S. standardization body that developed the broadcast standard.^[1] The first NTSC standard was developed in 1941 and had no provision for color TV.

In 1953 a second modified version of the NTSC standard was adopted, which allowed color broadcasting compatible with the existing stock of black-and-white receivers. NTSC was the first widely adopted broadcast color system. After over a half-century of use, the vast majority of over-the-air NTSC transmissions in the United States were replaced with ATSC on June 12, 2009, and will be, by August 31, 2011, in Canada.

History

The National Television System Committee was established in 1940 by the United States Federal Communications Commission (FCC) to resolve the conflicts that arose 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 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. The NTSC selected 525 scan lines as a compromise between RCA's 441–scan line standard (already being used by RCA's NBC TV network) and Philco's and DuMont's desire to increase the number of scan lines to between 605 and 800. The standard recommended a frame rate of 30 frames (images) per second, consisting of two interlaced fields per frame at 262.5 lines per field and 60 fields per second. Other standards in the final recommendation were an aspect ratio of 4:3, and frequency modulation (FM) for the sound signal (which was quite new at the time).

In January 1950, the Committee was reconstituted to standardize color television. In December 1953, it unanimously approved what is now called the NTSC color television standard (later defined as RS-170a). The "compatible color" standard retained full backward compatibility with existing black-and-white television sets. Color information was added to the black-and-white image by adding a color subcarrier of 4.5 × 455/572 MHz (approximately 3.58 MHz) to the video signal. To reduce the visibility of interference between the chrominance signal and FM sound carrier required a slight reduction of the frame rate from 30 frames per second to approximately 29.97 frames per second, and changing the line frequency from 15,750 Hz to 15,734.26 Hz.

The FCC had briefly approved a different color television standard, starting in October 1950, which was developed by CBS.^[2] 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.^[3] CBS rescinded its system in March 1953,^[4] and the FCC replaced it on December 17, 1953 with the NTSC color standard, which was cooperatively developed by several companies (including RCA and Philco).^[5] The first publicly announced network 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, although it was viewable in color only at the network's headquarters.^[6] The first nationwide view of NTSC color came on the following January 1 with the coast-to-coast broadcast of the Tournament of Roses Parade, viewable on prototype color receivers at special presentations across the country.

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. Later that year, the improved TK-41 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. Most U.S. NTSC broadcasters were required by the FCC to shut down their analog transmitters in 2009. Low-power stations, Class A stations and translators are not immediately affected. An analog cut-off date for those stations has not been set.

Technical details

Lines and refresh rate

NTSC color encoding is used with the system M television signal, which consists of 29.97 interlaced frames of video per second, or the nearly identical system J in Japan. Each frame consists of a total of 525 scanlines, of which 486 make up the visible raster. The remainder (the vertical blanking interval) are used for synchronization and vertical retrace. This blanking interval was originally designed to simply blank the receiver's CRT to allow for the simple analog circuits and slow vertical retrace of early TV receivers. However, some of these lines now can contain other data such as closed captioning and vertical interval timecode (VITC). In the complete raster (ignoring half-lines), the even-numbered or 'lower" scanlines (Every other line that would be even if counted in the video signal, e.g. {2,4,6,...,524}) are drawn in the first field, and the odd-numbered or "upper" (Every other line that would be odd if counted in the video signal, e.g. {1,3,5,...,525}) are drawn in the second field, to yield a flicker-free image at the field refresh frequency of approximately 59.94 Hertz (actually 60 Hz/1.001). For comparison, 576i systems such as PAL-B/G and SECAM uses 625 lines (576 visible), and so have a higher vertical resolution, but a lower temporal resolution of 25 frames or 50 fields per second.

The NTSC field refresh frequency in the black-and-white system originally exactly matched the nominal 60 Hz frequency of alternating current power used in the United States. Matching the field refresh rate to the power source avoided intermodulation (also called beating), which produces rolling bars on the screen. When color was later added to the system, the refresh frequency was shifted slightly downward to 59.94 Hz to eliminate stationary dot patterns in the difference frequency between the sound and color carriers, as explained below in "Color encoding". Synchronization of the refresh rate to the power incidentally 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 to set the speed of the synchronous AC motor-drive camera. By the time the frame rate changed to 29.97 Hz for color, it was nearly as easy to trigger the camera shutter from the video signal itself.

The actual 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. For interlaced scanning, an odd number of lines per frame was required in order to make the vertical retrace distance identical for the odd and even fields, which meant the master oscillator frequency had to be divided down by an odd number. At the time, the only practical method of frequency division was the use of a use of a chain of vacuum tube multivibrators, the overall division ratio being the mathematical product of the division ratios of the chain. Since all the factors of an odd number also have to be odd numbers, it follows that all the dividers in the chain also had to divide by odd numbers, and these had to be relatively small due the problems of thermal drift with vacuum tube devices. The closest practical sequence to 500 that meets these criteria was 3 × 5 × 5 × 7 = 525. (For the same reason, 625-line PAL-B/G and SECAM uses 5 × 5 × 5 × 5, the old British 405-line system used 3 × 3 × 3 × 3 × 5, the French 819-line system used 3 × 3 × 7 × 13 etc).

Colorimetry

The original 1953 color NTSC specification, still part of the United States Code of Federal Regulations, defined the colorimetric values of the system as follows:^[7]

Early color television receivers, such as the RCA CT-100, were faithful to this specification, having a larger gamut than most of today's monitors. Their low-efficient phosphors however were dark and long-persistent, leaving trails after moving objects. Starting in the late 1950s, picture tube phosphors would sacrifice saturation for increased brightness; this deviation from the standard both at the receiver and broadcaster ends was the source of considerable color variation.^[8]

Color correction in studio monitors and home receivers

To ensure more uniform color reproduction, receivers started to incorporate color correction circuits that converted the received signal --- encoded for the colorimetric values listed above --- into signals encoded for the phosphors actually used within the receiver.^[8] Since such color correction can not be performed accurately on the nonlinear (gamma-corrected) signals transmitted, the adjustment can only be approximated,^[9] introducing both hue and luminance errors for highly-saturated colors.

Similarly at the broadcaster stage, in 1968-69 the Conrac Corp., working with RCA, defined a set of controlled phosphors for use in broadcast color picture monitors.^[8] This specification survives today as the SMPTE "C" phosphor specification:

As with home receivers, it was further recommended^[10] that studio monitors incorporate similar color correction circuits so that broadcasters would transmit pictures encoded for the original 1953 colorimetric values, in accordance with FCC standards.

In 1987, the Society of Motion Picture and Television Engineers (SMPTE) Committee on Television Technology, Working Group on Studio Monitor Colorimetry, adopted the SMPTE C (Conrac) phosphors for general use in Recommended Practice 145^[11], prompting many manufacturers to modify their camera designs to directly encode for SMPTE "C" colorimetry without color correction.^[12], as approved in SMPTE standard 170M, "Composite Analog Video Signal --- NTSC for Studio Applications" (1994). As a consequence, the ATSC digital television standard states that for 480i signals, SMPTE "C" colorimetry should be assumed unless colorimetric data is included in the transport stream.^[13]

Variations

Japanese NTSC uses the same colorimetric values for red, blue and green, but employs a different white point of CIE Illuminant D93 (x=0.285, y=0.293).^[10] Both the PAL and SECAM systems until 1970 used the original 1953 NTSC colorimetry as well;^[10] unlike NTSC however, the European Broadcasting Union (EBU) in 1970 eschewed color correction in receivers and studio monitors and instead explicitly called for all equipment to directly encode signals for the "EBU" colorimetric values,^[14] further improving the color fidelity of those systems.

Color encoding

For backward compatibility with black-and-white television, NTSC uses a luminance-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. These two signals are each amplitude modulated and then added together. The carrier is suppressed. Mathematically, the result can be viewed as a single sine wave with varying phase relative to a reference and varying amplitude. The phase represents the instantaneous color hue captured by a TV camera, and the amplitude represents the instantaneous color saturation.

For a TV to recover hue information from the I/Q phase, it must have a zero phase reference to replace the suppressed carrier. It also needs a reference for amplitude to recover the saturation information. 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 the end of the blanking pulse.) The color burst consists of a minimum of eight cycles of the unmodulated (fixed phase and amplitude) color subcarrier. The TV receiver has a "local oscillator", which it synchronizes to the color bursts and then uses as a reference for decoding the chrominance. By comparing the reference signal derived from color burst to the chrominance signal's amplitude and phase at a particular point in the raster scan, the device determines what chrominance to display at that point. Combining that with the amplitude of the luminance signal, the receiver calculates what color to make the point, i.e. the point at the instantaneous position of the continuously scanning beam. Note that analog TV is discrete in the vertical dimension (there are distinct lines) but continuous in the horizontal dimension (every point blends into the next with no boundaries), hence there are no pixels in analog TV. (Digital TV sets receiving analog signals convert the continuous horizontal scan lines into discrete pixels before displaying them. This process of discretization necessarily degrades the picture information somewhat, though with small enough pixels the effect may be imperceptible. Digital sets include all sets with a matrix of discrete pixels built into the display device, such as LCD, plasma, and DLP screens, but not conventional CRTs.

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 3.579545 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 approximately 1.001 (0.1%), to approximately 59.94 fields per second. This adjustment ensures that the sums and differences of the sound carrier and the color subcarrier and their multiples (i.e., the intermodulation products of the two carriers) are not exact multiples of the frame rate, which is the necessary condition for the dots to remain stationary on the screen, making them most noticeable.

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. (Another way this is often stated is that the color subcarrier frequency is an odd multiple of half the line frequency.) They then chose to make the audio subcarrier frequency an integer multiple of the line frequency to minimize visible (intermodulation) 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 (black and white) 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 variation in the line frequency. So the engineers chose the line frequency to be changed for the color standard. In the black-and-white standard, the ratio of audio subcarrier frequency to line frequency is 4.5 MHz / 15,750 = 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 = approximately 15,734 lines per second. Maintaining the same number of scan lines per field (and frame), the lower line rate must yield a lower field rate. Dividing (4,500,000 / 286) lines per second by 262.5 lines per field gives approximately 59.94 fields per second.

Transmission modulation scheme

Spectrum of a System M television channel with NTSC color.

An NTSC television channel as transmitted occupies a total bandwidth of 6 MHz. The actual video signal, which is amplitude-modulated, is transmitted between 500 kHz and 5.45 MHz above the lower bound of the channel. The video carrier 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 1.25 MHz 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-modulated with a suppressed carrier. The audio signal is frequency-modulated, like the audio signals broadcast by FM radio stations in the 88–108 MHz band, but with a +/- 25 kHz maximum frequency swing, as opposed to 75 kHz as is used on the FM band. The main audio carrier is 4.5 MHz above the video carrier, making it 250 kHz below the top of the channel. Sometimes a channel may contain an MTS signal, which offers more than one audio signal by adding one or two subcarriers on the audio signal, each synchronized to a multiple of the line frequency. This is normally the case when stereo audio and/or second audio program signals are used. The same extensions are used in ATSC, where the ATSC digital carrier is broadcast at 1.31 MHz above the lower bound of the channel.

The Cvbs (Composite vertical blanking signal) (sometimes called "setup") is a voltage offset between the "black" and "blanking" levels. Cvbs is unique to NTSC. Cvbs has the advantage of making NTSC video more easily separated from its primary sync signals.

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 576i video formats this difference cannot be overcome by a simple speed-up.

A complex process called "3:2 pulldown" is used. One film frame is transmitted for three video fields (1½ video frame times), and the next frame is transmitted for two video fields (one video frame time). Two 24 frame/s film frames are therefore transmitted in five 60 Hz video fields, for an average of 2½ video fields per film frame. The average frame rate is thus 60 / 2.5 = 24 frame/s, so the average film speed is exactly what it should be. There are drawbacks, however. Still-framing on playback can display a video frame with fields from two different film frames, so any motion between the frames will appear as a rapid back-and-forth flicker. There can also be noticeable jitter/"stutter" during slow camera pans (telecine judder).

To avoid 3:2 pulldown, film shot specifically for NTSC television is often taken at 30 frame/s.

For viewing native 576i 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 3:2 pulldown.
• Interpolation of the contents of adjacent frames in order to produce new intermediate frames; unless highly sophisticated motion-sensing computer algorithms are applied, this introduces artifacts, and even the most modestly trained of eyes can quickly spot video that has been converted between formats.

Modulation for analog satellite transmission

Because satellite power is severely limited, analog video transmission through satellites differs from terrestrial TV transmission. AM is a linear modulation method, so a given demodulated signal-to-noise ratio (SNR) requires an equally high received RF SNR. The SNR of studio quality video is over 50 dB, so AM would require prohibitively high powers and/or large antennas.

Wideband FM is used instead to trade RF bandwidth for reduced power. Increasing the channel bandwidth from 6 to 36 MHz allows a RF SNR of only 10 dB or less. The wider noise bandwidth reduces this 40 dB power saving by 36 MHz / 6 MHz = 8 dB for a substantial net reduction of 32 dB.

Sound is on a FM subcarrier as in terrestrial transmission, but frequencies above 4.5 MHz are used to reduce aural/visual interference. 6.8, 5.8 and 6.2 MHz are commonly used. Stereo can be multiplex or discrete, and unrelated audio and data signals may be placed on additional subcarriers.

A triangular 60 Hz energy dispersal waveform is added to the composite baseband signal (video plus audio and data subcarriers) before modulation. This limits the satellite downlink power spectral density in case the video signal is lost. Otherwise the satellite might transmit all of its power on a single frequency, interfering with terrestrial microwave links in the same frequency band.

In half transponder mode, the frequency deviation of the composite baseband signal is reduced to 18 MHz to allow another signal in the other half of the 36 MHz transponder. This reduces the FM benefit somewhat, and the recovered SNRs are further reduced because the combined signal power must be "backed off" to avoid intermodulation distortion in the satellite transponder. A single FM signal is constant amplitude, so it can saturate a transponder without distortion.

Field order

^[15] An NTSC 'frame' consists of an 'even' field followed by an 'odd' field. As far as the reception of an analog signal is concerned, this is purely a matter of convention and, it makes no difference. It's rather like the broken lines running down the middle of a road, it doesn't matter whether it is a line/space pair or a space/line pair, the effect to a driver is exactly the same.

The introduction of digital television formats has changed things somewhat. Most digital TV formats, including the popular DVD format, record NTSC originated video with the even field first in the recorded frame (The development of DVD took place in regions that traditionally utilize NTSC). However this frame sequence has migrated through to the so-called PAL format (actually a technically incorrect description) of digital video with the result that the even field is often recorded first in the frame (The European 625 line system is specified as odd frame first). This is no longer a matter of convention because a frame of digital video is a distinct entity on the recorded medium. This means that when reproducing many non NTSC based digital formats (including DVD) it is necessary to reverse the field order otherwise an unacceptable shuddering 'comb' effect occurs on moving objects as they are shown ahead in one field and then jump back in the next.

This has also become a hazard where non NTSC progressive video is transcoded to interlaced and vice versa. Systems that recover progressive frames or transcode video should ensure that the '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. This can often be observed in PC based video playing utilities if an inappropriate choice of de-interlacing algorithm is made.

Comparative quality

The SMPTE color bars, an example of a test card.

Reception problems can degrade an NTSC picture by changing the phase of the color signal (actually differential phase distortion), 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. When compared to PAL in particular, NTSC color accuracy and consistency is considerably inferior, leading to video professionals and television engineers jokingly referring to NTSC as Never The Same Color, Never Twice the Same Color or No True Skin Colors,^[16] while for the more expensive PAL system it was necessary to Pay for Additional Luxury. This color phase, "tint", or "hue" control allows for anyone skilled in the art to easily calibrate a monitor with SMPTE color bars, even with a set that has drifted in its color representation, allowing the proper colors to be displayed.

The use of NTSC coded color in S-Video systems completely eliminates the phase distortions. As a consequence, the use of NTSC color encoding gives the highest resolution picture quality (on the horizontal axis & frame rate) of the three color systems when used with this scheme. (The NTSC resolution on the vertical axis is lower than the European standards, 525 lines against 625)

The mismatch between NTSC's 30 frames per second and film's 24 frames is overcome by a process that capitalizes on the field rate of the interlaced NTSC signal, thus avoiding the film playback speedup used for 576i systems at 25 frames per second (which causes the accompanying audio to increase in pitch slightly, sometimes rectified with the use of a pitch shifter) at the price of some jerkiness in the video. See Framerate conversion above.

Variants

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), as they are in PAL, while in American NTSC, black level is slightly higher (7.5 IRE) than blanking level. Since the difference is quite small, a slight turn of the brightness knob is all that is required to correctly show 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

PAL-M system uses the same broadcast bandwidth, frame rate, and number of lines as NTSC, but using PAL color encoding. It is therefore partially NTSC-compatible. NTSC-M tv sets can receive terrestrial PAL-M broadcasts, NTSC VCRs can play videotapes recorded in PAL-M and vice versa, but only in black & white because the color information cannot be decoded.

PAL-N

This is used in Paraguay and Uruguay. This is very similar to PAL-M (used in Brazil). It is also closely related to PAL-Nc (used in Argentina).

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

As it is shown, aside from the number of lines and frames per second, 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), though some newer sets come with baseband NTSC 3.58 support (NTSC 3.58 being the frequency for color modulation in NTSC: 3.58 MHz).

NTSC 4.43

In what can be considered an opposite of PAL-60, NTSC 4.43 is a pseudo color system that transmits NTSC encoding (525/29.97) with 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 sources in PAL, SECAM, and NTSC video formats. The heterodyne 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 629 kHz subcarrier while U-Matic & Betamax use a 688 kHz 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 from PAL's 50 Hz field rate to NTSC's 59.94 Hz field rate, and faster linear tape speed.

The changes to the PAL VCR are 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 drive 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 frame/s is described in the NTSC-film standard.

Canada/U.S. Video Game Region

Sometimes NTSC-US or NTSC-U/C is used to describe the video gaming region of North America (the U/C refers to U.S. + Canada), as regional lockout usually restricts games released within a region to that region.

Vertical Interval Reference

The standard NTSC video image contains some lines (lines 1–21 of each field) that are not visible (this is known as the Vertical Blanking Interval, or VBI); 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.^[17] 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.^[18]

A less-used successor to VIR, GCR, 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^[19][20]), test data on lines 17–18, a network source code on line 20 and closed captioning, XDS, and V-chip data on line 21. Early teletext applications also used vertical blanking interval lines 14–18 and 20, but teletext over NTSC was never widely adopted by viewers.^[21]

Many stations transmit TV Guide On Screen (TVGOS) data for an electronic program guide on VBI lines. The primary station in a market will broadcast 4 lines of data, and backup stations will broadcast 1 line. In most markets the PBS station is the primary host. TVGOS data can occupy any line from 10-25, but in practice its limited to 11-18, 20 and line 22. Line 22 is only used for 2 broadcast, DirecTV and CFPL-TV.

TiVo data is also transmitted on some commercials and program advertisements so customers can autorecord the program being advertised, and is also used in weekly half-hour paid programs on Ion Television and the Discovery Channel which highlight TiVo promotions and advertisers.

Countries and territories using NTSC

North America

•  Canada, Over-the-air NTSC broadcasting in major cities only scheduled to be abandoned by August 2011, simulcast in ATSC^[22]
•  Mexico, Over-the-air NTSC broadcasting scheduled to be abandoned by December 31, 2021 simulcast in ATSC^[23]
•  United States, High-power over-the-air NTSC broadcasting was switched off on June 12, 2009^[24][25] in favor of ATSC. Low-power stations, Class A stations and translators are not immediately affected, nor are remaining analog cable television systems. NTSC also remains in use as an interconnect standard for A/V devices such as televisions and DVD players.

Central America and the Caribbean

South America

Asia

Pacific

U.S. Territories

•  American Samoa
•  Guam
• Northern Mariana Islands
• Midway Atoll (a U.S. military base)

Chilean Territories

•  Easter Island, NTSC broadcast to be abandoned by December 31, 2017, simulcasting ISDB-T/b

Other Pacific island nations

•  Marshall Islands (in Compact of Free Association with U.S.; U.S. aid funded NTSC adoption)
• Micronesia (in Compact of Free Association with U.S.)
•  Palau (in Compact of Free Association with U.S.; adopted NTSC before independence)
•  Samoa (closely tied to American Samoa; U.S. aid funded NTSC adoption)
•  Tonga (U.S. aid funded NTSC adoption)

Historic (used NTSC experimentally before adopting PAL)

•  Fiji (Historic; used before 1989, Fiji has used PAL since 1990)
•  Australia (Historic; All of Australia uses PAL)

Indian Ocean

• Diego Garcia

Middle East

•  South Yemen (Historic; all of Yemen now uses PAL)

Europe

•  United Kingdom (UK TV was 405-line 50Hz system until 625/50Hz and the introduction of PAL Colour in late 1960s.)

See also

• Broadcast television systems
  • ATSC Standards
  • BTSC
  • NTSC-J
  • NTSC-C
  • PAL
  • RCA
  • SECAM
• List of video connectors
• Moving image formats
• Oldest television station
• Television channel frequencies
  • Very high frequency
  • Ultra high frequency
  • Knife-edge effect
  • Channel 1 (NTSC-M)
  • Channel 37
  • North American broadcast television frequencies
  • North American cable television frequencies
  • Australasian TV frequencies
• Broadcast safe
• DTV transition in the United States

Notes

References

• A standard defining the NTSC system was published by the International Telecommunication Union in 1998 under the title "Recommendation ITU-R BT.470-7, Conventional Analog Television Systems". It isn't publicly available on the Internet, but it can be purchased from the ITU.
• Ed Reitan (1997). CBS Field Sequential Color System.

External links

• U.S. cable television channel frequencies
• TVTower.com - Commercial Television Frequencies
• Representation of the NTSC refresh rate on a television and on a DVD
• Understanding & Measuring Video TV-RF Signals by Glen Kropuenske, CET, Sencore Application Engineer