1、 1 Scope This guideline is intended to provide supplemental and background information for SMPTE 170M . The guideline also provides information on the development of the National Television System Committee 1953 Recommendations for Transmission Standards for Color Television. Use of this guideline w
2、ill aid in the understanding and implementation of modern NTSC television signals, equipment, and practices. 2 NTSC chroma levels 2.1 Saturated colors The video from a live camera viewing a saturated color scene can have an upper chroma excursion of 131 IRE units. Full-level color bars are represent
3、ative of such a saturated color scene. When full-amplitude G, B, and R video signals in the form of a full-field color bar signal are present at the NTSC encoder input, the encoder composite video (N), with the two color components (I and Q or B-Y and R-Y), will be a 100% level, 7.5% setup color bar
4、 signal (see figure 1). Full-level color bars, with setup, have the video and chroma levels listed in table 1. Each individual value in table 1 is rounded to 0.1 IRE. Note that following rounding, chroma maximum minus chroma minimum does not necessarily exactly equal the rounded value for the chroma
5、 level. The largest discrepancy is 0.1 IRE. For more precise values, see annex A of SMPTE 170M. NOTE Although burst is the phase reference in the NTSC signal, the subcarrier phase reference used in the encoded signal formulas and in table 1 is the phase of the color burst +180. 2.2 Clipping In video
6、 equipment where the luminance and chrominance signals are separated for processing, white and black level clipping on the luminance (Y) portion of the signal may be employed. Other equipment may clip the composite signal. Note that any such clipping can result in a change in chrominance saturation.
7、 3 Color bar signals 3.1 Color bar signal amplitudes As noted in 2.1, video from a live camera viewing a saturated color scene can have an upper chroma excursion of 131 IRE units, as represented by full-level color bars. Page 1 of 14 pages EG 27-2004 Revision of EG 27-1994 Copyright 2004 by THE SOCI
8、ETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartsdale Ave., White Plains, NY 10607 (914) 761-1100 Approved November 8, 2004 SMPTE ENGINEERING GUIDELINE Supplemental Information for SMPTE 170M and Background on the Development of NTSC Color Standards EG 27-2004 Page 2 of 14 pages Properly a
9、djusted television transmitters do not pass chroma information with an amplitude greater than 120 IRE units. Therefore, reduced amplitude color bar signals are used for transmitter testing. NOTE The NTSC 1953 standard assumed the use of 75% color bar signals for transmitter testing (see NTSC 1953, a
10、ppendix A, clause III.D.6, reproduced in annex B of this document). Many present-day encoders and test generators implement the SMPTE color bar test signal (SMPTE EG 1), which is a reduced amplitude (75%) signal (see table 2). Some equipment also implements full-amplitude color bars (see tables 3 an
11、d 4). Figure 1 Composite video signal amplitudes with two color components (full field, full amplitude color bar signal input) Table 1 Video and chroma levels Bar Luminance (IRE) Chroma level (IRE) Minimum chroma excursion (IRE) Maximum chroma excursion (IRE) Phase (degrees) White 100.0 0.0 Yellow 8
12、9.5 82.8 48.1 130.8 167.1 Cyan 72.3 117.0 13.9 130.8 283.5 Green 61.8 109.2 7.2 116.4 240.7 Magenta 45.7 109.2 8.9 100.3 60.7 Red 35.2 117.0 23.3 93.6 103.5 Blue 18.0 82.8 23.3 59.4 347.1 Black 7.5 0.0 Burst 0.0 40.0 20.0 20.0 180.0 EG 27-2004 Page 3 of 14 pages Table 2 SMPTE color bar test signal w
13、ith setup (100/7.5/75/7.5) Chroma excursions (IRE) Bar Video level nominal (IRE) Chroma level nominal (IRE) Lower nominal Upper nominal White flag 100.0 0.0 Gray 76.9 0.0 Yellow 69.0 62.1 37.9 100.0 Cyan 56.1 87.7 12.3 100.0 Green 48.2 81.9 7.3 89.2 Magenta 36.2 81.9 4.8 77.1 Red 28.2 87.7 15.6 72.1
14、 Blue 15.4 62.1 15.6 46.4 Black 7.5 0.0 NOTE When using the SMPTE color bar test signal, the upper excursion of the yellow and cyan bar chroma signals is exactly 100 IRE units. Table 3 Full-amplitude color bars without setup (100/0/100/0) Chroma excursions (IRE) Bar Video level nominal (IRE) Chroma
15、level nominal (IRE) Lower nominal Upper nominal White 100.0 0.0 Yellow 88.6 89.5 43.9 133.3 Cyan 70.1 126.5 6.9 133.3 Green 58.7 118.1 0.3 117.7 Magenta 41.3 118.1 17.7 100.3 Red 29.9 126.5 33.3 93.2 Blue 11.4 89.5 33.3 56.1 Black 0.0 0.0 NOTE When using a full amplitude color bar signal (with or wi
16、thout setup), the upper excursion of the magenta bar chroma is approximately 100 IRE units. Table 4 Full-amplitude color bars with setup (100/7.5/100/7.5) Chroma excursions (IRE) Bar Video level nominal (IRE) Chroma level nominal (IRE) Lower nominal Upper nominal White 100.0 0.0 Yellow 89.5 82.8 48.
17、1 130.8 Cyan 72.3 117.0 13.9 130.8 Green 61.8 109.2 7.2 116.4 Magenta 45.7 109.2 8.9 100.3 Red 35.2 117.0 23.3 93.6 Blue 18.0 82.8 23.3 59.4 Black 7.5 0.0 NOTE When using a full amplitude color bar signal (with or without setup), the upper excursion of the magenta bar chroma is approximately 100 IRE
18、 units. EG 27-2004 Page 4 of 14 pages 3.2 Different color bar signals Although the NTSC 1953 recommendation clearly called for the use of setup on all signals (see NTSC 1953, appendix A, clause III.C.2, reproduced in annex B of this document), some equipment manufacturers implement full-amplitude co
19、lor bars with setup and others without setup (see tables 3 and 4). Some manufacturers implement full-amplitude color bar signals as full-field signals, while others use split fields with both the color bars and the reference white bar (sometimes called white flag) at full amplitude. As a result, the
20、re are different color bar signals that have been in common use over the years. NOTE The different color bar signals are described by four amplitudes separated by slashes. The amplitudes are all expressed in percent. The first number is the reference white bar amplitude. The second number is the ref
21、erence black bar amplitude. The third number is the white amplitude from which the color bars are derived. The fourth number is the black amplitude from which the color bars are derived. For example, 100/0/75/7.5 bars would be 75% bars with 7.5% setup in which the white bar has been set to 100% and
22、the black bar is set to 0%. 4 Comparison of NTSC (1953) and equal-bandwidth NTSC encoders 4.1 NTSC (1953) encoder The 1953 National Television System Committee (NTSC) specifications called for the use of two matrices (see figure 2). The first matrix encoded the gamma-corrected green (G), blue (B), a
23、nd red (R) video signals into Y, R-Y, and B-Y. The second matrix encoded R-Y and B-Y into I and Q. The NTSC 1953 standard also called for the I and Q signals to be bandwidth limited as follows: I signal less than 2 dB down at 1.3 MHz at least 20 dB down at 3.6 MHz Q signal at 0.4 MHz less than 2 dB
24、down at 0.5 MHz less than 6 dB down at 0.6 MHz at least 6 dB down Figure 2 Original NTSC two-matrix encoder EG 27-2004 Page 5 of 14 pages 4.2 Standard practice NTSC encoder Most equipment manufacturers implement the NTSC signal using a single matrix to encode the gamma-corrected green (G), blue (B),
25、 and red (R) video signals directly into the color-difference signals (see figure 3). The low-pass filters (LPF) in the I and Q color-difference paths cause signal delay. The Q signal 0.5 MHz LPF causes more delay than the I signal 1.3 MHz LPF. This requires the use of a delay line (DL) in the I col
26、or-difference signal and a longer delay line in the luminance (Y) signal. (Any filtering of the color-difference signals requires a delay line in the luminance Y signal.) When this signal is transmitted, a low-pass filter in the transmitter bandwidth limits the luminance (Y) signal and the upper sid
27、eband of the I signal to 4.2 MHz. Some equipment manufacturers include a low-pass filter in their encoders to bandwidth limit the luminance (Y) signal and the upper sidebands of the color-difference signals (either B-Y and R-Y or I and Q) to 4.2 MHz. Figure 3 Standard practice NTSC single-matrix enc
28、oder 4.3 Equal-bandwidth NTSC encoder The NTSC encoder described in SMPTE 170M uses equal-bandwidth color-difference signals (either B-Y and R-Y or I and Q). This removes the need for a delay line in the color-difference signal. A shorter delay line than required for NTSC 1953 is used in the luminan
29、ce (Y) signal (see figure 4). When this signal is transmitted, a low-pass filter in the transmitter bandwidth limits the luminance (Y) signal and the upper sidebands of the color-difference signals (either B-Y and R-Y or I and Q) to 4.2 MHz. Transmission of equal-bandwidth color-difference signals t
30、o the receiver has the effect of limiting the recoverable chroma bandwidth to 0.6 MHz as a result of the truncation of the upper sidebands of the chroma modulation in the transmitters 4.2 MHz filter. This is considered acceptable since there are no modern receivers that utilize the theoretically pos
31、sible wideband I demodulation made possible by maintaining narrow-band Q. If it is desired to transmit equal-bandwidth encoded NTSC signals and permit recovery of the wide-band I, it is necessary to decode and re-encode with the appropriate narrow-band Q channel filter prior to transmission. EG 27-2
32、004 Page 6 of 14 pages Figure 4 Equal-bandwidth NTSC encoder 5 Background on NTSC, EIA, and SMPTE committees 5.1 Black-and-white TV and NTSC-1 The first National Television System Committee (NTSC-1), started by the Radio Manufacturers Association (RMA), met during 1940 and 1941. The groups work resu
33、lted in the submission of “Transmission Standards for Commercial Television Broadcasting“ to the Federal Communications Commission (FCC) at a hearing on March 20, 1941. The FCC adopted the NTSC-1 recommendations as the standards for “Monochrome Transmission Systems“ in May 1941. Commercial televisio
34、n broadcasting began in the United States on July 1, 1941. The chairman of the first NTSC was Dr. W.R.G. Baker. The editor of papers was Donald G. Fink. Dr. Alfred N. Goldsmith, co-founder of the Institute of Radio Engineers (IRE), headed the research on physiological and psychological factors. Pete
35、r Goldmark of CBS headed the TV systems group. 5.2 Color TV In 1950, after eight months of hearings and about 10,000 pages of testimony, the FCC selected the incompatible field-sequential system for color television broadcasting. The Commissions decision was challenged in the courts, with the United
36、 States Supreme Court upholding the validity of the FCC decision on May 28, 1951. The challenges to the field-sequential color system, both at the Commission and in the courts, were based primarily on the fact that the field-sequential color system was incompatible with the already existing black-an
37、d-white television sets. The Commission apparently felt that the talk about compatible color systems was just a way of delaying Commission action on any color television system. On June 11, 1951, the FCC, in Public Notice 656008, stated that color television broadcasting would use the field-sequenti
38、al color system until someone could come up with a better (but not necessarily compatible) system. EG 27-2004 Page 7 of 14 pages 5.3 NTSC-2 The second National Television System Committee (NTSC-2) was started during 1950 by the Radio-Television Manufacturers Association (RTMA) in hopes that the comm
39、ittee would be as effective as was the committee of 1940-1941. This group (which is often referred to as the RTMA group) made comments to the FCC during the 1949-1950 color hearings, suggesting a series of tests for color television systems. The NTSC/RTMA committee also set up an ad hoc group to stu
40、dy the contemporary state-of-the-art. This ad hoc group had access to the engineering community through publication in the IRE “Proceedings“ (Dr. A. Goldsmith, editor). From the work of the ad hoc group came the broad ideas of using the 1941 black-and-white standard for the brightness information an
41、d adding color information using subcarriers. With the release of the FCC notice on June 11, 1951, the chairman of the committee recommended that NTSC-2 be reorganized as a group to achieve the “optimum standard for commercial color television.“ This reorganized NTSC-2 met 26 times between June 18,
42、1951 and September 1, 1953. The chairman of the second NTSC was, again, Dr. W.R.G. Baker. NTSC-2 had a main committee of about 40 members with 10 panels or working groups. The panels and chairpersons were: Panel 11 Subjective Aspects of Color, Dr. A. N. Goldsmith Panel 11-A Color Transcription, Dr.
43、A. N. Goldsmith Panel 12 Color System Analysis, Donald G. Fink Panel 13 Color Video Standard, A. V. Loughren Panel 14 Color Synchronizing Standard, D. E. Harnett Panel 15 Receiver Compatibility, Rinaldo DeCola Panel 16 Field Testing, Knox McIlwain Panel 17 Broadcast System, R. E. Shelby Panel 18 Co-
44、ordination, D. R. Smith Panel 19 Definitions, Dr. R. M. Browie The writing of the NTSC color TV system came from the work of Panels 13 and 14, with Panel 13 doing the video and Panel 14 providing the synchronizing pulses. 5.4 Petition to the FCC On February 2, 1953, NTSC-2 had approved for publicati
45、on a recommendation for transmission standards for color television. Like many committees, the second NTSC had difficulties finishing its work in a timely manner. Impatient with the delays, RCA and NBC let it be known that they would file a Petition for Rule Making with the FCC if the NTSC did not a
46、ct. At the meeting on June 24, 1953, the committee was aware that RCA was planning to file a Petition for Rule Making. Still, the NTSC did not act. The next day, June 25, 1953, RCA and NBC filed a Petition for Rule Making (known as the RCA Red Book). The RCANBC color television system was to become,
47、 in fact, the NTSC-2 approved recommendation. On July 8, 1953, Rosel H. Hyde, chairman of the FCC, wrote to Dr. Baker of NTSC advising that RCA and NBC had filed a petition and asking for the results of the NTSC field testing. Chairman Hyde ended his letter with the following: “Your prompt reply adv
48、ising the Commission of your organizations plans would be greatly appreciated.“ At the full NTSC meeting of July 21, 1953, a motion was passed sending to the FCC a petition “for the adoption of transmission standards for color television.“ The motion was made by D. B. Smith (Philco) and seconded by Dr. Pet
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