NTSC
NTSC was the first American standard for analog television, published and adopted in 1941. It was one of three major color formats for analog television; the others were PAL and SECAM. NTSC color was usually associated with System M, and this combination was sometimes called NTSC II. A second NTSC standard was adopted in 1953, which allowed color television compatible with the existing stock of black-and-white sets. The EIA defined NTSC performance standards in EIS-170 in 1957.
The term "NTSC" has referred to digital formats with 480–487 active lines and a 30 or 29.97 FPS frame rate since the introduction of digital sources such as DVDs, and is a digital shorthand for System M. The NTSC-Film standard has a digital resolution of pixels for DVD-Videos, pixels for Super Video CDs and pixels for Video CDs. The digital video -camcorder format equivalent of NTSC is pixels. The digital television equivalent is pixels.
History
The NTSC was established in 1940 by the United States Federal Communications Commission to resolve conflicts between companies about the introduction of a nationwide analog television system. In March 1941, the committee issued a technical standard for black-and-white television based on a 1936 recommendation by the Radio Manufacturers Association. Technical advancements of the vestigial sideband technique provided an opportunity to increase image resolution. The NTSC selected 525 scan lines as a compromise between RCA's 441-scan line standard and Philco and DuMont's desire to increase the number of scan lines to between 605 and 800. The standard recommended a frame rate of 30 FPS, 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 of the sound signal.In January 1950, the committee was reconstituted to standardize color television. The FCC had briefly approved a 405-line field-sequential color TV standard, developed by CBS, in October 1950. The CBS system was incompatible with existing black-and-white sets. 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 with an effective frame rate of 24 fps. 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 the manufacture of all color sets was banned by the Office of Defense Mobilization in October. A variant of the CBS system was later used by NASA to broadcast pictures of astronauts in space. CBS rescinded its system in March 1953, and the FCC replaced it on December 17 of that year with an NTSC color standard developed by several companies.
In December 1953, the FCC unanimously approved what became the NTSC color-television standard. The standard retained backward compatibility with existing black-and-white sets. Color information was added to the black-and-white image by introducing a color subcarrier of MHz. This frequency was chosen so horizontal line-rate modulation components of the chrominance signal fall between the horizontal line-rate modulation components of the luminance signal; the chrominance signal could be easily filtered out of the luminance signal on new sets, and would be minimally visible on existing sets. Due to limitations of frequency divider circuits when the color standard was promulgated, the color subcarrier frequency was constructed as a composite frequency assembled from small integersin this case, 5 × 7 × 9 MHz divided by 8 × 11. The horizontal line rate was reduced to 15,734 lines per second from 15,750 lps, and the frame rate was reduced to 30/1.001 ≈ 29.970 fps from 30 fps. The changes amounted to 0.1 percent, and were tolerated by existing TV sets.
The first publicly-announced network television broadcast of a program using the NTSC "compatible color" system was an episode of NBC's Kukla, Fran and Ollie on August 30, 1953, viewable in color only at NBC headquarters. The first nationwide viewing of NTSC color was 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 nationwide. The first color NTSC television camera was the RCA TK-40, used for experimental broadcasts in 1953; an improved version, the TK-40A, was the first commercially-available color-television camera. Later that year, an improved TK-41 became the standard camera and was used through much of the 1960s. The NTSC standard was adopted by other countries, including Japan and several in the Americas.
Digital conversion
With the advent of digital television, analog broadcasts were largely phased out. NTSC broadcasters in the U.S. were required by the FCC to shut down their analog transmitters by February 17, 2009; the shutdown was later moved to June 12 of that year. Low-power and Class A stations and translators were required to shut down by 2015, although an FCC extension allowed some stations operating on Channel 6 to operate until July 13, 2021. Canadian analog TV transmitters in markets not subject to the mandatory 2011 transition were to be shut down by January 14, 2022, under a 2017 schedule from Innovation, Science and Economic Development Canada.Most countries using the NTSC standard and those using other analog television standards have switched to newer digital television standards; at least four different standards are in use worldwide. North America, parts of Central America, and South Korea are adopting the ATSC standards; other countries, such as Japan, are adopting standards other than ATSC. Most over-the-air NTSC transmissions in the United States ended on June 12, 2009, and by August 31, 2011, in Canada and most other NTSC markets.
Technical details
Colorimetry
refers to the colorimetric characteristics of the system and its components, including the primary colors used, the camera, and the display. NTSC color had two distinctly-defined colorimetries, shown on the chromaticity diagram as NTSC 1953 and SMPTE C. Manufacturers introduced a number of variations for technical, economic, marketing, and other reasons.''Note: displayed colors are approximate and require a wide gamut display for faithful reproduction.''
NTSC 1953
The original 1953 color NTSC specification, still part of the United States Code of Federal Regulations, defined the colorimetric values of the system as shown in the table. Early color-television receivers, such as the RCA CT-100, were faithful to this specification which had a larger gamut than most present-day monitors. Their low-efficiency phosphors were weak and persistent, leaving trails after moving objects. Beginning in the late 1950s, picture-tube phosphors sacrificed saturation for increased brightness; this deviation from the standard at receiver and broadcaster was the source of considerable color variation.SMPTE C
To ensure more uniform color reproduction, some manufacturers incorporated color-correction circuits into sets which converted the received signal—encoded for colorimetric values—and adjusted the monitor's phosphor characteristics. Since color cannot be accurately corrected on the nonlinear transmitted gamma corrected signals, the adjustment can only be approximated.At the broadcaster stage, in 1968–69 the Conrac Corporation defined a set of controlled phosphors for use in broadcast color video monitors. This specification survives as the SMPTE C phosphor specification. As with home receivers, it was recommended that studio monitors incorporate similar color-correction circuits so 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 Committee on Television Technology Working Group on Studio Monitor Colorimetry adopted the SMPTE C phosphors for general use in Recommended Practice 145; this prompted many manufacturers to modify their camera designs to encode for SMPTE C colorimetry without color correction as approved in SMPTE standard 170M, "Composite Analog Video Signal – NTSC for Studio Applications". 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.
The Japanese NTSC never changed primaries and white point to SMPTE C, continuing to use the 1953 NTSC primaries and white point. The PAL and SECAM systems used the original 1953 NTSC colorimetry until 1970; unlike NTSC, the European Broadcasting Union rejected color correction in receivers and studio monitors and called for all equipment to encode signals for EBU colorimetric values.
Color compatibility issues
In the gamuts on the CIE chromaticity diagram, variations among colorimetries can result in visual differences. Proper viewing requires gamut mapping via LUTs or additional color grading. SMPTE Recommended Practice RP 167-1995 refers to such an automatic correction as an "NTSC corrective display matrix." Material prepared for 1953 NTSC may look de-saturated when displayed on SMPTE C or ATSC/BT.709 displays, and may have noticeable hue shifts. SMPTE C materials may appear slightly more saturated on BT.709/sRGB displays, or significantly more saturated on P3 displays, if appropriate gamut mapping is not done.Color encoding
NTSC uses a luminance-chrominance encoding system. Using a separate luminance signal maintained backward compatibility with contemporary black-and-white television sets; only color sets would recognize the chroma signal.The red, green, and blue primary color signals are weighted and summed into a single luma signal, designated , which replaces the original monochrome signal. The color-difference information is encoded into the chrominance signal, which carries only the color information. This allows black-and-white receivers to display NTSC color signals by ignoring the chrominance signal. Some black-and-white TVs sold in the U.S. after the introduction of color broadcasting in 1953 were designed to filter chroma out, but early sets did not do this and chrominance could be seen as a crawling dot pattern in areas of the picture with saturated colors.
To derive separate signals with only color information, the difference is determined between each color primary and the summed luma; the red difference signal is, and the blue difference signal is. These difference signals are used to derive two new color signals, known as and , in a process known as QAM. The color space is rotated relative to the difference-signal color space; orange-blue color information is transmitted on the signal at 1.3 MHz bandwidth, and the signal encodes purple-green color information at 0.4 MHz bandwidth. This allows the chrominance signal to use less overall bandwidth without noticeable color degradation. The two signals each amplitude modulate 3.58 MHz carriers, which are 90 degrees out of phase with each other, and the result is the sum with the carriers suppressed. The result can be viewed as a single sine wave, with varying phase relative to a reference carrier and with varying amplitude. The varying phase represents the instantaneous color hue captured by a TV camera, and the amplitude represents the color saturation. The MHz subcarrier is added to the luminance to form the composite color signal, which modulates the video-signal carrier.
For a color TV to recover hue information from the color subcarrier, it must have a zero-phase reference to replace the previously-suppressed carrier. The NTSC signal includes a short sample of this reference signal, known as the colorburst, located on the back of each horizontal synchronization pulse. The colorburst consists of at least eight cycles of the unmodulated color subcarrier. The TV receiver has a local oscillator, which is synchronized with these color bursts to create a reference signal. Combining the reference phase signal with the chrominance signal allows the recovery of the and signals, which is reconstructed to the individual signals which are sent to the CRT to form the image.
In CRT televisions, the NTSC signal is turned into three color signals: red, green, and blue; each controls an electron beam designed to excite only the corresponding red, green, or blue phosphors. TV sets with digital circuitry use sampling techniques to process the signals, with identical results. For analog and digital sets processing an analog NTSC signal, the original three color signals are transmitted with three discrete signals, recovered as three separate colors, and presented as a color image.
When a transmitter broadcasts an NTSC signal, it amplitude-modulates a radio-frequency carrier with the NTSC signal and frequency-modulates a carrier 4.5 MHz higher with the audio signal. With non-linear distortion of the broadcast signal, the MHz color carrier may beat with the sound carrier to produce a dot pattern on the screen.