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191NAB ENGINEERING HANDBOOKCopyright © 2007 Academic Press.

All rights of reproduction in any form reserved.

C H A P T E R

1.13

Worldwide Standards for Analog Television

D.H. PRITCHARD AND J.J. GIBSON

Updated for the 10th Edition by

ALDO CUGNINI AGC Systems LLC

Long Valley, New Jersey

INTRODUCTION

The performance of a film-based motion picture sys-tem in one location in the world is generally the sameas in any other location; thus, international exchangeof film programming is relatively straightforward.This is not the case, however, with analog broadcastcolor television systems. The lack of compatibility hasits origins in many factors, such as constraints in com-

munications channel allocations and techniques, dif-ferences in local power source characteristics, networkrequirements, pickup and display technology, andpolitical considerations relating to international tele-communications agreements.

The most outstanding effort—as well as the mostcontroversial effort—of the Eleventh Plenary Assem-

bly of the International Radio Consultative Committee(CCIR, now the ITU-R), held in Oslo in 1966, was anattempt at standardization of analog color televisionsystems by the participating countries of the world.The discussions pertaining to the possibility of a uni-versal analog system proved inconclusive; therefore,instead of issuing a unanimous recommendation for a

single CCIR analog system, the CCIR was forced toissue only a report describing the characteristics andrecommendations for a variety of proposed analogsystems. It was left to the controlling organizations ofthe individual countries to make their own choice asto which standard to adopt.

This outcome was not totally surprising becauseone of the primary requirements for any analog colortelevision system is compatibility with a coexistingmonochrome system. In many cases, the monochromestandards already existed and were dictated by such

factors as local powerline frequencies (relevant to fieldand frame rates) as well as radiofrequency channelallocations and pertinent telecommunications agree-ments. Thus, such technical factors as line number,field rate, video bandwidth, modulation technique,and sound carrier frequencies were predeterminedand varied in many regions of the world. The easewith which the international exchange of programmaterial may be accomplished is thereby hampered

and has been accommodated over the years by meansof standards conversion techniques, or transcoders,with varying degrees of loss in quality. While invari-ably introducing some compromises, standards con-version techniques now provide surprisingly goodservice with the use of satellite relays coupled withuse of digital signal processing in both the video andaudio domains.

MONOCHROME COMPATIBLE ANALOGCOLOR TV SYSTEMS

In order to achieve success in the introduction of an

analog color television system, it was viewed as essen-tial that the color system be fully compatible with theexisting black-and-white system. That is, monochromereceivers must be able to produce high-quality black-and-white images from a color broadcast, and colorreceivers must produce high-quality black-and-whiteimages from monochrome broadcasts. The first suchanalog color television system to be placed into com-mercial broadcast service was developed in the UnitedStates. On December 17, 1953, the Federal Communi-cations Commission (FCC) approved transmission



SECTION 1: BROADCAST ADMINISTRATION, STANDARDS, AND TECHNOLOGIES

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standards and authorized broadcasters, as of January23, 1954, to provide regular service to the public underthese standards. This decision was the culmination ofthe work of the National Television System Committee(NTSC), upon whose recommendation the FCC actionwas based [1]; subsequently, this system, commonlyreferred to as the NTSC system, was adopted by Can-ada, Japan, Mexico, and others. That these standards

are still providing, after more than 50 years, color tele-vision service of good quality testifies to the validityand applicability of the fundamental principles under-lying the choice of specific techniques and numericalstandards.

The previous existence of a monochrome televisionstandard was two edged, in that it provided a founda-tion upon which to build the necessary innovativetechniques while simultaneously imposing therequirement of compatibility. Within this framework,an underlying theme—that which the eye does not seedoes not need to be transmitted nor reproduced—setthe stage for a variety of fascinating developments inwhat has been characterized as an “economy of repre-sentation” [1].

The countries of Europe delayed the adoption of ananalog color television system, and in the years

between 1953 and 1967 a number of alternative sys-tems that were compatible with the 625 line, 50 fieldexisting monochrome systems were devised. Thedevelopment of these systems was to some extentinfluenced by the fact that the technology necessary toimplement some of the NTSC requirements was still inits infancy; thus, many of the differences betweenNTSC and the other analog systems are the result oftechnological rather than fundamental theoretical con-siderations.

Most of the basic techniques of NTSC are incorpo-rated into the other analog system approaches. For

example, the use of wideband luminance and rela-tively narrowband chrominance, following the teach-ings of the principle of mixed highs (discussed in thenext section of the chapter), can be found in all analogsystems. Similarly, the concept of providing horizontalinterlace to reduce the visibility of the color subcarriersis followed in all approaches. This feature is requiredto reduce the visibility of signals carrying color infor-mation that are contained within the same frequencyrange as the coexisting monochrome signal, thusmaintaining a high order of compatibility.

An early analog system that received approval wasone proposed by Henri de France of the Compagniede Television of Paris. It was argued that if color could

be relatively band limited in the horizontal direction,it could also be band limited in the vertical direction;thus, the two pieces of coloring information (hue andsaturation) that must be added to the one piece ofmonochrome information (brightness) could be trans-mitted as subcarrier modulation that is sequentiallytransmitted on alternate lines—thereby avoiding thepossibility of unwanted crosstalk between color signalcomponents. At the receiver, a one-line memory, com-monly referred to as a 1-H delay element, must beemployed to store one line to then be concurrent with

the following line, then a linear matrix of the red and blue signal components (R and B) is used to producethe third green component (G). Of course, this necessi-tates the addition of a line-switching identificationtechnique. Such an approach, designated as SequentialCouleur Avec Memoire (SECAM; translates as“sequential color with memory”), was developed andofficially adopted by France and the former U.S.S.R.,

and broadcast service began in France in 1967.The implementation technique of a 1-H delay ele-ment led to the development, largely through theefforts of Walter Bruch of Telefunken Company, of thePhase Alternation Line (PAL) system. This approach wasaimed at overcoming an implementation problem ofNTSC that requires a high order of phase and ampli-tude integrity (skew symmetry) of the transmissionpath characteristics about the color subcarrier to pre-vent color quadrature distortion. The line-by-line alter-nation of the phase of one of the color signalcomponents averages any colorimetric distortions tothe observer’s eye to that of the correct value. The sys-tem in its simplest form (simple PAL), however, resultsin line flicker (Hanover bars). The use of a 1-H delay

device in the receiver greatly alleviates this problem(standard PAL). PAL systems also require a line identi-fication technique. The standard PAL system wasadopted by numerous countries in continental Europe,as well as in the United Kingdom. Public broadcasting

began in 1967 in Germany and the United Kingdomusing two slightly different variants of the PAL system.

NTSC, PAL, AND SECAM SYSTEMSOVERVIEW

To properly understand the similarities and differ-ences of the conventional analog television systems, a

familiarization with the basic principles of NTSC,PAL, and SECAM is required. As previously stated,

because many basic techniques of NTSC are involvedin PAL and SECAM, a thorough knowledge of NTSCis necessary in order to understand PAL and SECAM.

The same R, G, and B pickup devices and three pri-mary color display devices are used in all systems.The basic camera function is to analyze the spectraldistribution of the light from the scene in terms of itsred, green, and blue components on a point-by-point

basis as determined by the scanning rates. The threeresulting electrical signals must then be transmittedover a band-limited communications channel to con-trol the three-color display device to make the per-

ceived color at the receiver appear essentially the sameas the perceived color at the scene.It is useful to define color as a psycho-physical

property of light—specifically, as the combination ofthose characteristics of light that produce the sensa-tions of brightness, hue, and saturation. Brightnessrefers to the relative intensity; hue refers to thatattribute of color that allows separation into spectralgroups perceived as red, green, yellow, and so on (inscientific terms, the dominant wavelength); and satura-tion is the degree to which a color deviates from a



CHAPTER 1.13: WORLDWIDE STANDARDS FOR ANALOG TELEVISION

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neutral gray of the same brightness—the degree towhich it is “pure,” “pastel,” or “vivid.” These threecharacteristics represent the total information neces-sary to define or recreate a specific color stimulus.

This concept is useful to communication engineersin the development of encoding and decoding tech-niques to efficiently compress the required informa-tion within a given channel bandwidth and to

subsequently recombine the specific color signal val-ues in the proper proportions at the reproducer. TheNTSC color standards define the first commercially

broadcast process for achieving this result.A preferred signal arrangement was developed that

resulted in reciprocal compatibility with monochromepictures and was transmitted within the existingmonochrome channel, as shown in Figure 1.13-1. Onesignal (luminance) is chosen in all approaches tooccupy the wideband portion of the channel and toconvey the brightness as well as the detail informationcontent. A second signal (chrominance), representa-tive of the chromatic attributes of hue and saturation,is assigned less channel width in accordance with theprinciple that, in human vision, full three-color repro-

duction is not required over the entire range of resolu-tion (commonly referred to as the mixed-highs

principle).Another fundamental principle employed in all

systems involves arranging the chrominance andluminance signals within the same frequency bandwithout excessive mutual interference. Recognitionthat the scanning process, being equivalent to sam-pled-data techniques, produces signal componentslargely concentrated in uniformly spaced groupsacross the channel width led to introduction of theconcept of horizontal frequency interlace (dot interlace).The color subcarrier frequency is so chosen as to be anodd multiple of one-half the line rate (in the case of

NTSC) such that the phase of the subcarrier is exactlyopposite on successive scanning lines. This substan-tially reduces the subjective visibility of the color sig-nal dot pattern components.

The major differences among the three main analogsystems of NTSC, PAL, and SECAM are in the specificmodulating processes used for encoding and transmit-ting the chrominance information. The similarities and

differences are briefly summarized here:• All systems:

— Three primary additive colorimetric principles

— Similar camera pick-up and receiver displaytechnology

— Wideband luminance and narrowband color

• Compatibility with coexisting monochrome system:

— Introduces first-order differences:

• Line number

• Field/frame rates

• Bandwidth

• Frequency allocation

• Major differences in color techniques:

— NTSC—Phase and amplitude quadrature modu-lation of interlaced subcarrier

— PAL—Similar to NTSC but with line alternationof the “V” component

— SECAM—Frequency modulation of line sequen-tial color subcarriers

NTSC Color System

The importance of the colorimetric concepts of bright-ness, hue, and saturation comprising the three pieces

FIGURE 1.13-1 Preferred approach to compatible analog color TV systems.




194

of information necessary to analyze or recreate a spe-cific color value becomes evident in the formation ofthe composite color television NTSC format. The lumi-nance, or monochrome, signal is formed by additionof specific proportions of the red, green, and blue sig-nals and occupies the total available video bandwidthof 0 to 4.2 MHz. The NTSC, PAL, and SECAM systemsall use the same luminance (Y) signal formation, dif-

fering only in the available bandwidths.The Y signal components have relative voltage val-ues representative of the brightness sensation in thehuman eye; therefore, the red, green, and blue voltagecomponents are tailored in proportion to the standardluminosity curve at the particular values of the domi-nant wavelengths of the three color primaries chosenfor color television. Thus, the luminance signalmakeup for all systems, as normalized to white, isdescribed by:

E′Y = 0.299E′R + 0.587E′G + 0.114E′B (1)

The signal of Eq. 1 would be exactly equal to the out-put of a linear monochrome sensor with ideal spectral

sensitivity if the red, green, and blue elements werealso linear devices with theoretically correct spectral-sensitivity curves. In actual practice, the red, green,and primary signals are deliberately made nonlinearto accomplish gamma correction (adjustment of theslope of the input/output transfer characteristic). Theprime mark (′ ) is used to denote a gamma-correctedsignal. Table 1.13-1 gives the equations for the chromi-nance signal components.1 Signals representative ofthe chromaticity information (hue and saturation) thatrelate to the differences between the luminance signaland the basic red, green, and blue signals are gener-ated in a linear matrix.

These new signals are termed color-difference signalsand are designated as R–Y, G–Y, and B–Y. These sig-

nals modulate a subcarrier that is combined with theluminance component and passed through a commoncommunications channel. At the receiver, the color dif-ference signals are detected, separated, and individu-ally added to the luminance signal in three separatepaths to recreate the original R, G, and B signalsaccording to the equations:

E′Y + E′(R–Y) = E′Y + E′R – E′Y = E′R (2a)

E′Y + E′(G–Y) = E′Y + E′G – E′Y = E′G (2b)

E′Y + E′(B–Y) = E′Y + E′B – E′Y = E′B (2c)

In the specific case of NTSC, two other color-differ-

ence signals, designated as I and Q, are formed at theencoder and are used to modulate the color subcarrier.Another reason for the choice of signal values in the

NTSC system is that the eye is more responsive to spa-tial and temporal variations in luminance than it is to

variations in chrominance; therefore, the visibility ofluminosity changes resulting from random noise andinterference effects may be reduced by properly pro-portioning the relative chrominance gain and encod-ing angle values with respect to the luminance values.For this reason, the principle of constant luminance isincorporated into the system standard [1,2].

The voltage outputs from the three camera sensorsare adjusted to be equal when a scene reference whiteor neutral gray object is being scanned for the colortemperature of the scene ambient. Under this condi-tion, the color subcarrier also automatically becomeszero. The colorimetric values have been formulated byassuming that the reproducer will be adjusted for illu-minant C, representing the color of average daylight.

Figure 1.13-2 is a CIE chromaticity diagram indicat-ing the primary color coordinates for NTSC, PAL, andSECAM. It is interesting to compare the available colorgamut relative to that of all color paint, pigment, film,and dye processes.

In the NTSC color standard, the chrominance infor-mation is carried as simultaneous amplitude andphase modulation of a subcarrier chosen to be in thehigh-frequency portion of the 0 to 4.2 MHz video

band and specifically related to the scanning rates asan odd multiple of one-half the horizontal line rate, asshown by the vector diagram in Figure 1.13-3. Thehue information is assigned to the instantaneousphase of the subcarrier. Saturation is determined bythe ratio of the instantaneous amplitude of the subcar-rier to that of the corresponding luminance signalamplitude value.

1Apparently, there is an error in the original 1953 calculations ofthese reduction factors. A luminance matrix coefficient of 0.115 wasused for blue instead of the correct 0.114. The reader is referred toSMPTE 170M [6], which also addresses calculation precision, han-dling of setup, revised chromaticity coordinates, and equiband colorencoding.

TABLE 1.13-1Electronic Color Signal Values for

NTSC, PAL, and SECAM

Luminance:

E′Y = 0.299 E′R + 0.587 E′G + 0.114 E′B

(Common for all systems)

Chrominance:NTSC

E′1 = –0.274 E′G + 0.596 E′R – 0.114 E′B

E′Q = –0.522 E′G + 0.211 E′R + 0.311 E′B

B-Y = 0.493 (E′B – E′Y)

R-Y = 0.877 (E′R – E′Y)

G-Y = 1.413 (E′G – E′Y)

PAL

E′U = 0.493 (E′B – E′Y)

±E′V = ±0.877 (E′R – E′Y)

SECAMD′R = –1.9 (E′R – E′Y)

D′B = 1.5 (E′B – E′Y)




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The choice of the I and Q color modulation compo-nents relates to the variation of color acuity character-istics of human color vision as a function of the field of

view and spatial dimensions of objects in the scene.The color acuity of the eye decreases as the size of theviewed object is decreased and thereby occupies asmall part of the field of view. Small objects, repre-sented by frequencies above about 1.5 to 2.0 MHz,produce no color sensation (mixed highs). Intermediatespatial dimensions (approximately in the 0.5 to 1.5MHz range) are viewed satisfactorily if reproducedalong a preferred orange–cyan axis. Large objects (0 to0.5 MHz) require full three-color reproduction for sub-

jectively pleasing results. The I and Q bandwidths arechosen accordingly, and the preferred colorimetricreproduction axis is obtained when only the I signalexists by rotating the subcarrier modulation vectors by

33°. In this way, the principles of mixed highs and I, Qcolor-acuity axis operation are exploited.At the encoder, the Q signal component is band lim-

ited to about 0.6 MHz and is representative of thegreen–purple color-axis information. The I signal com-ponent has a bandwidth of about 1.5 MHz and con-tains the orange–cyan color axis information. Thesetwo signals are then used to individually modulate thecolor subcarrier in two balanced modulators operatedin phase quadrature. The sum products are selected andadded to form the composite chromaticity subcarrier.

This signal—in turn—is added to the luminance signalalong with the appropriate horizontal and verticalsynchronizing and blanking waveforms to include thecolor-synchronization burst. The result is the totalcomposite color video signal.

Quadrature synchronous detection is used at thereceiver to identify the individual color signal compo-nents. When individually recombined with the lumi-nance signal, the desired R, G, and B signals arerecreated. The receiver designer is free to demodulateeither at I or Q and matrix to form B–Y, R–Y, and G–Y,or, as in nearly all modern receivers, at B–Y and R–Y

and maintain 500 kHz equiband color signals.The chrominance information can be carried with-

out loss of identity provided that the proper phaserelationship is maintained between the encoding anddecoding processes. This is accomplished by transmit-ting a reference burst signal consisting of eight or ninecycles of the subcarrier frequency at a specific phase[–(B–Y)] following each horizontal synchronizingpulse, as shown in Figure 1.13-4.

The specific choice of color subcarrier frequency inNTSC was dictated by at least two major factors. First,the necessity of providing horizontal interlace toreduce the visibility of the subcarrier requires that thefrequency of the subcarrier be precisely an odd multi-

ple of one-half the horizontal line rate. Figure 1.13-5shows the energy spectrum of the composite NTSCsignal for a typical stationary scene. This interlaceprovides line-to-line phase reversal of the color sub-carrier, thereby reducing its visibility (and thusimproving compatibility with monochrome recep-tion). Second, it is advantageous to also provide inter-lace of the beat frequency (about 920 kHz) occurring

between the color subcarrier and the average value ofthe sound carrier. For total compatibility reasons, thesound carrier was left unchanged at 4.5 MHz and the

FIGURE 1.13-2 CIE chromaticity diagram.

FIGURE 1.13-3 NTSC color modulation phase dia-gram.




196

line number remained at 525; thus, the resulting line

scanning rate and field rate varied slightly from thosefor the monochrome values but stayed within the pre-viously existing tolerances. The difference is exactly 1part in 1000; specifically, the line rate is 15.734 kHz,the field rate is 59.94 Hz, and the color subcarrier is3.578545 MHz.

PAL Color System

Except for some minor details, the color encodingprinciples for PAL are the same as those for NTSC;however, the phase of the color signal, EV = R – Y, isreversed by 180° from line-to-line. This is done for thepurpose of averaging, or canceling, certain color errors

resulting from amplitude and phase distortion of thecolor modulation sidebands. Such distortions might

occur as a result of equipment or transmission pathproblems.

The NTSC chroma signal expression within the fre-quency band common to both I and Q is given by:

(3)

The PAL chroma signal expression is given by:

(4)

where U and ±V have been substituted for the B–Yand R–Y signal values, respectively.

The PAL format employs equal bandwidths for theU and V color-difference signal components that areabout the same as the NTSC I signal bandwidth (1.3MHz at 3 dB). There are slight differences in the U andV bandwidth in different PAL systems because of thedifferences in luminance bandwidth and sound carrierfrequencies. (See the applicable ITU-R documents forspecific details.)

The V component was chosen for the line-by-line

reversal process because it has a lower gain factor thanU and, therefore, is less susceptible to switching rate(½ f H) imbalance. Figure 1.13-6 provides a vector dia-gram for the PAL quadrature modulated and line-alternating color modulation approach.

The result of the switching of the V signal phase atthe line rate is that any phase errors produce comple-mentary errors from V into the U channel. In addi-tion, a corresponding switch of the decoder Vchannel results in a constant V component with com-plementary errors from the U channel. Any line-to-line averaging process at the decoder, such as reten-tivity of the eye (simple PAL) or an electronic averag-ing technique such as the use of a 1-H delay element

(standard PAL), produces cancellation of the phase(hue) error and provides the correct hue but with

FIGURE 1.13-4 NTSC color-burst synchronizing sig-nal.

CNTSCB Y–

2.03------------- ω SC t

R Y–

1.14-------------- ω SC tcos+sin=

CPA LU

2.03---------- ω SCtsin

V 1.14---------- ω SCtcos±=

FIGURE 1.13-5 Luminance/chrominance horizontal frequency interlace principle(energy spectrum of the composite NTSC signal for a typical stationary scene).




198

color signal components in an averaging technique,coupled with summation and subtraction functions.Hanover bars can also occur in this approach if animbalance of amplitude or phase occurs between thedelayed and direct paths.

In a PAL system, vertical resolution in chrominanceis reduced as a result of the line-averaging processes.The visibility of the reduced vertical color resolutionas well as the vertical time coincidence of luminanceand chrominance transitions differs depending uponwhether the total system, transmitter through receiver,includes one or more averaging (comb filter) pro-

cesses. PAL provides a system similar to NTSC andhas gained favor in many areas of the world, particu-larly for 625 line/50 field systems.

SECAM Color System

The optimized SECAM system, known as SECAM III,is the system adopted by France and the formerU.S.S.R. in 1967. The SECAM method has several fea-tures in common with NTSC, such as the same E′Y sig-nal and the same E′B–E′Y and E′R–E′Y color-differencesignals; however, this approach differs considerablyfrom NTSC and PAL in the manner in which the colorinformation is modulated onto the subcarriers. First,

the R–Y and B–Y color difference signals are transmit-ted alternately in time sequence from one successiveline to the next, the luminance signal being common toevery line. Because there is an odd number of lines,any given line carries R–Y information on one fieldand B–Y information on the next field. Second, the R–Y and B–Y color information is conveyed by frequencymodulation of different subcarriers; thus, at thedecoder, a 1-H delay element, switched in time syn-chronization with the line switching process at theencoder, is required to obtain the simultaneous exis-

tence of the B–Y and R–Y signals in a linear matrix toform the G –Y component.

The R–Y signal is designated as D′R and the B–Ysignal as D′B. The undeviated frequency for the twosubcarriers, respectively, is determined by:

FOB = 272 f H = 4.250000 MHz;FOR = 282 f H = 4.406250 MHz (6)

These frequencies represent zero color differenceinformation (zero output from the FM discriminator),or a neutral gray object in the televised scene.

As shown in Figure 1.13-9, the accepted convention

for the direction of frequency change with respect tothe polarity of the color difference signal is oppositefor the DOB and DOR signals. A positive value of DOR

means a decrease in frequency, whereas a positivevalue of DOB indicates an increase in frequency. Thischoice relates to the idea of keeping the frequenciesrepresentative of the most critical color away from theupper edge of the available bandwidth to minimizethe instrumentation distortions.

The deviation for D′R is 280 kHz; for D′B, 230 kHz.The maximum allowable deviation, including preem-phasis, for D′R is –506 kHz and +350 kHz; the valuesfor D′B are –350 kHz and +506 kHz.

Two types of preemphasis are employed simulta-neously in SECAM. First, as shown in Figure 1.13-10, aconventional type of preemphasis of the low-fre-quency color difference signals is introduced. Thecharacteristic is specified to have a reference-level

break point at 85 kHz ( f 1) and a maximum emphasis of2.56 dB. The expression for the characteristic is givenas:

(7)

FIGURE 1.13-8 PAL meander burst blanking gate timing diagram for B, G, H, andI PAL.

A1 j f f 1 ⁄ ( )+

1 j f 3 f 1 ⁄ ( )+

-----------------------------=




199

A second form of preemphasis (Figure 1.13-10) isintroduced at the subcarrier level where the amplitudeof the subcarrier is changed as a function of the fre-quency deviation. The expression for this inverted bellshaped characteristic is given as:

(8)

where f c = 4.286 MHz and 2 M0 = 23% of the luminanceamplitude (100 IRE).

This type of preemphasis is intended to furtherreduce the visibility of the frequency-modulated sub-carriers in low-luminance-level color values and to

improve the signal-to-noise ratio (SNR) in high-lumi-

nance and highly saturated colors; thus, monochromecompatibility is better for pastel average picture levelobjects but sacrificed somewhat in favor of SNR in sat-urated color areas.

Of course, precise interlace of frequency modulatedsubcarriers for all values of color modulation cannotoccur; nevertheless, the visibility of the interferencerepresented by the existence of the subcarriers may bereduced somewhat by the use of two separate carriers,as is done in SECAM. Figure 1.13-11 illustrates theline-switching sequence in that at the undeviated“resting” frequency situation, the two-to-one verticalinterlace in relation to the continuous color differenceline-switching sequence produces adjacent line pairsof f OB and f OR signals. To further reduce the subcarrier

dot visibility, the phase of the subcarriers (phase car-ries no picture information in this case) is reversed180° on every third line and between each field. This,coupled with the bell preemphasis, produces a degreeof monochrome compatibility considered subjectivelyadequate.

As in PAL, the SECAM system must provide somemeans for identifying the line-switching sequence

between the encoding and decoding processes. This isaccomplished by introducing alternate DR and DBcolor identifying signals for nine lines during the ver-tical blanking interval following the equalizing pulsesafter vertical sync (see Figure 1.13-12). These bottle-shaped signals occupy a full line each and represent

the frequency deviation in each time sequence of DBand DR at zero luminance value. These signals can bethought of as a fictitious green color that is used at thedecoder to determine the line-switching sequence.

During horizontal blanking, the subcarriers are blanked and a burst of f OB/ f OR is inserted and used as agray-level reference for the FM discriminators toestablish their proper operation at the beginning ofeach line; thus, the SECAM system is a line sequentialcolor approach using frequency-modulated sub-carriers. A special identification signal is provided to

FIGURE 1.13-9 SECAM FM color modulation system.

FIGURE 1.13-10 SECAM color signal preemphasis.

G M0

1 j16 f f c---

f c f ---–⎝ ⎠

⎛ ⎞⋅+

1 j1.26 f f c---

f c f ---–⎝ ⎠

⎛ ⎞⋅+

---------------------------------------------=

FIGURE 1.13-11 Color versus line and field timingrelationships for SECAM.




200

identify the line-switch sequence and is especiallyadapted to the 625 line/50 field wideband systemsavailable in France and the former U.S.S.R. It should

be noted that SECAM, as practiced, employs ampli-tude modulation of the sound carrier as opposed tothe FM sound modulation in other systems.

ADDITIONAL SYSTEMS OFHISTORICAL INTEREST

Of the numerous analog system variations proposedover the intervening years since development of theNTSC system, at least two others, in addition to PALand SECAM, should be mentioned briefly. The firstof these is additional reference transmission (ART),which involved the transmission of a continuous ref-erence pilot carrier in conjunction with a conven-tional NTSC color subcarrier quadrature modulationsignal. A modification of this scheme involved a mul-tiburst approach that utilized three color bursts—oneat black level, one at intermediate gray level, and oneat white level—to be used for correcting differentialphase distortion.

Another system, perhaps better known, wasreferred to as NIR or SECAM IV. Developed by theU.S.S.R. Nauchni Issledovatelskaia Rabota (NIR;

translates as “scientific discriminating work”), thissystem consists of alternating lines of (1) an NTSC-likesignal using an amplitude- and phase-modulated sub-carrier and (2) a reference signal having U phase todemodulate the NTSC-like signal. In the linear ver-sion, the reference is unmodulated; in the nonlinearversion, the amplitude of the reference signal is modu-lated with chrominance information.

Since the early 1990s, a number of enhanced-defini-tion television (EDTV) systems were proposed foranalog terrestrial service, offering a combination of

widescreen picture and increased resolution. Thesesystems include PALplus and Enhanced SECAM [7].Although various EDTV systems based on NTSC werealso proposed, that work eventually gave way to thedevelopment of analog-incompatible terrestrial digitaltelevision systems.

Of the various EDTV systems proposed, PALplushas seen the most widespread use. The system deliv-

ers a 16:9 picture with 574 active lines to a PALplusreceiver. Appearing on a conventional television as a16:9 letterboxed image with 430 active lines, the addi-tional vertical luminance information is carried by a“helper” signal within the letterbox black bars. Atransmission in this mode is indicated by the specialWide Screen Signaling (WSS) data carried on line 23.The specification for PALplus was standardized by theEuropean Broadcasting Union (EBU) in 1997 [8], andthe signal has been transmitted by various broadcast-ers since 1994.

SUMMARY AND COMPARISONS OF

ANALOG SYSTEMSHistory has shown that it is exceedingly difficult toobtain total international agreement on “universal”television broadcasting standards. Even with the firstscheduled broadcasting of monochrome television in1936 in England, the actual telecasting started usingtwo different systems on alternate days from the sametransmitter. The Baird system was 250 lines (noninter-laced) with a 50 Hz frame rate, while the Electric andMusical Industries (EMI) system was 405 lines (inter-laced) with a 25 Hz frame rate.

These efforts were followed in 1939 in the UnitedStates with the broadcast of a 441 line interlaced sys-tem at 60 fields per second (the Radio Manufacturers

Association [RMA] system). In 1941, the NTSC initi-ated the current basic monochrome standards in theUnited States of 525 lines (interlaced) at 60 fields persecond, designated as system M by the CCIR. Inthose early days, the differences in powerline fre-quency were considered as important factors andwere largely responsible for the proliferation of dif-ferent line rates versus field rates, as well as the widevariety of video bandwidths. However, the existenceand extensive use of monochrome standards over aperiod of years soon made it a top-priority matter toassume the reciprocal compatibility of any develop-ing analog color system.

In 1998, the successor to the CCIR, the International

Telecommunications Union, RadiocommunicationSector (ITU-R), formalized the definition of all world-wide analog television systems then in use in a Rec-ommendation [9], which was subsequently amended[10]. The ITU-R documents define recommended stan-dards for worldwide analog color television systemsin terms of the three basic color approaches—NTSC,PAL, and SECAM [4]. The variations—at least 13 ofthem—are given alphabetical letter designations;some represent major differences, while others signifyonly very minor frequency-allocation differences in

FIGURE 1.13-12 SECAM line identification signal.




201

channel spacings or differences between the VHF andUHF bands. The key to understanding the CCIR/ITUdesignations lies in recognizing that the letters referprimarily to local monochrome standards for line andfield rates, video channel bandwidth, and audio car-rier relative frequency. Further classification in termsof the particular color system then adds to NTSC,PAL, or SECAM as appropriate.

As an example, the letter “M” designates a 525line/60 field, 4.2 MHz bandwidth, 4.5 MHz sound car-rier monochrome system; thus, M(NTSC) describes acolor system employing the NTSC technique for intro-ducing the chrominance information within the con-straints of the basic monochrome signal values.Likewise, M(PAL) would indicate the same line andfield rates and bandwidths but use the PAL color sub-carrier modulation approach. In another example, theletters “I” and “G” relate to specific 625 line/50 field,5.0 or 5.5 MHz bandwidth, 5.5 or 6.0 MHz sound car-rier monochrome standards; thus, G(PAL) woulddescribe a 625 line/50 field, 5.5 MHz bandwidth, colorsystem utilizing the PAL color subcarrier modulationapproach. The letter “L” refers to a 625 line/50 field,

6.0 MHz bandwidth system to which the SECAMcolor modulation method has been added (oftenreferred to as SECAM III). System E is an 819 line/50field, 10 MHz bandwidth, monochrome system. Thischannel was used in France for early SECAM tests andfor system E transmissions.

Some general comparison statements can be madeabout the underlying monochrome systems and exist-ing analog color standards:

• There are three different scanning standards:525 lines/60 fields, 625 lines/50 fields, and 819lines/50 fields.

• There are six different spacings of video-to-soundcarriers: 3.5, 4.5, 5.5, 6.0, 6.5, and 11.15 MHz.

• Some systems use FM and others use AM for thesound modulation.

• Various schemes were developed in the 1980s tocarry stereophonic audio and additional audio pro-grams within an analog television transmission.The reader is referred to Chapter 6.3, “MultichannelTelevision Sound,” of this handbook for furtherdetails.

• A number of countries using PAL transmissionhave approved the use of a two-sound-carrier FMsystem [11]. The second carrier is placed at a fre-quency f H × 15.5 = 242.1875 kHz above the first (tra-ditional) carrier, at a power level 20 dB below peak

visual power, and employing the same modulationas the first sound carrier. The second carrier cancarry a second audio program or the right channelof a stereo program (wherein the first carrier carriesthe (L + R)/2 signal).

• A number of European countries using PAL orSECAM transmission have approved the use of anadditional digital carrier for stereophonic or multi-channel sound transmission [12]. Based on theNICAM-728 system introduced in 1987, a high-fre-quency subcarrier is digitally modulated with a

728 kb/s data stream consisting of 728-bit packets.Using a sampling rate of 32 kHz, the 14-bit samplesare digitally companded to 10-bit words.

• Some systems use positive polarity (luminance pro-portional to voltage) modulation of the video car-rier, but others, such as the U.S. (M)NTSC system,use negative modulation.

• There are differences in the techniques of color sub-carrier encoding represented by NTSC, PAL, andSECAM, and in each case many differences can befound in the details of various pulse widths, timing,and tolerance standards.

• Various countries have developed their ownschemes for using the vertical interval for someform of data. Although each analog standard canaccommodate data in various ways, it is up to theindividual permitting authority as to what data isallowed. The reader is referred to Chapter 5.24,“Closed Captioning Systems,” and Chapter 5.25,“Data Broadcast Systems for Television,” of thishandbook for details on Teletext and other data sys-tems in use over analog television systems.

It is evident that one must refer to the ITU docu-ments for accurate information on the combined ana-log monochrome/color standards. Figure 1.13-13presents a comparison of the relative bandwidths,color subcarrier frequencies, and sound carrier spac-ing for the major analog color systems used in theworld today.

The signal in the M(NTSC) system occupies theleast total channel width, which when the vestigial

FIGURE 1.13-13 Bandwidth comparison betweenNTSC, PAL, and SECAM.




202

sideband plus guard bands are included, requires aminimum radiofrequency channel spacing of 6 MHz.The L(III) SECAM system signal occupies the greatestchannel space with a full 6 MHz luminance band-width. Signals from the two versions of PAL lie in

between and vary in vestigial sideband width as wellas color and luminance bandwidths. NTSC is the onlysystem to incorporate the I , Q color acuity bandwidthvariation. PAL minimizes the color quadrature phasedistortion effects by line-to-line averaging, andSECAM avoids this problem by only transmitting thecolor components sequentially at a line-by-line rate.

Figures 1.13-14 to 1.13-16 summarize, in organiza-tion chart form, the ITU-R designations for NTSC,PAL, and SECAM basic system identifications andcharacteristics. In Figure 1.13-14, M(NTSC) identifiesthe system used in the United States, Canada, Japan,Mexico, the Philippines, and several other Central

American and Caribbean area countries. The N systemmay be implemented in color either in the NTSC orthe PAL format [3]. An N version of PAL has been inuse in Argentina. Figure 1.13-15 provides a summaryof the PAL systems. PAL systems in one or another of

the 625 line formats are predominately used in Conti-nental Europe, the United Kingdom, some Africancountries, Australia, and various Asian countries,including India and China. An M (525 line) version ofPAL has been in use in Brazil.

Figure 1.13-16 summarizes the SECAM III system,which is in use primarily in France and the formerU.S.S.R. It should be noted that, as the SECAM systemuses frequency modulation for the color subcarrier,the video signal cannot be directly switched or editedin this format; it typically originates in PAL and istranscoded prior to transmission. The proposedSECAM IV system almost gained favor in 1966 as auniversal European approach but was never imple-mented [1]. The E system, mentioned in connectionwith early SECAM tests in France, was limited tomonochrome broadcasts.

Table 1.13-2 provides a summary of the major ana-

log color television system general characteristics.Table 1.13-3 characterizes the fundamental featuresrelating to the differences between NTSC, PAL, andSECAM in the critical areas of color encoding tech-niques. Similarly, Table 1.13-4 illustrates the color

FIGURE 1.13-14 ITU-R designation for NTSC system (summary).

FIGURE 1.13-15 ITU-R designation for PAL system (summary).




203

FIGURE 1.13-16 ITU-R designation for SECAM (summary).

TABLE 1.13-2General Analog System Technical Summary

NTSC PAL SECAM

TV system M B/G/H/I D/K/L

Field rate ( f V) (Hz) 50 50

TV lines 525 625 625

Line rate ( f H ) (Hz) 15,734.265… 15,625 15,625

Luma BW (MHz) 4.2 5.0, 5.5 6.0

Sound subcarrier (MHz) 4.5 (F3) 5.5, 6.0 (F3) 6.5 (A3)

Gamma 2.2 2.8 2.8

White point C D65 D65

TABLE 1.13-3Chrominance Encoding Systems Comparison

NTSC PAL SECAM

Color subcarrier (Hz) 5,000,000 × = 3,579,545.45… 4,433,618.75 f OB = 4,250,000

f OR = 4,406,250

Color subcarrier relationshipto line rate

f OB

= 272 f H

f OR = 282 f H

Chroma encodingPhase and amplitude quadrature

modulation

Phase and amplitudequadrature modulation

(line alternation)

Frequency modulation(line sequential)

Color difference signalsI , Q

(1.3 MHz) (0.6 MHz)U, ±V

(1.3 MHz) (1.3 MHz)

DR ( f OR) (>1.0 MHz)

DB ( f OB) (>1.0 MHz)

6010001001------------× 59.94=

6388------

SC 4552--------- f H= f SC 11354

------------ 1625---------+⎝ ⎠⎛ ⎞ f H=




204

encoding line-by-line color sequence operation for the

three systems. The information conveyed in thesetables highlights the technical equalities and differ-ences among the systems and attempts to show somekind of order as an aid to understanding the world-wide situation. It serves as well to point out the diffi-culties of achieving a “universal” analog system [5].

ACKNOWLEDGMENT

The original version of this article was first publishedin the SMPTE Journal and has been reprinted with per-mission of the Society of Motion Picture and Televi-sion Engineers.

References

[1] Herbstreit, J. W. and Pouliquen, J., International standards forcolor television, IEEE Spectrum, March 1967.

[2] Fink, D. G. (Ed.), Color Television Standards, McGraw-Hill, NewYork, 1955.

[3] Pritchard, D. H., U.S. color television fundamentals: A review,SMPTE J., 86, 819–828, 1977.

[4] CCIR Characteristics of Systems for Monochrome and Colour Televi-sion: Recommendations and Reports, Recommendation 470-1

(1974–1978) of the Fourteenth Plenary Assembly of CCIR,

Kyoto, Japan, 1978.[5] Roizen, J., Universal color television: An electronic fantasia,

IEEE Spectrum, March 1967.[6] SMPTE Standard for Television, Composite Analog Video Signal:

NTSC for Studio Applications, SMPTE 170M-1999, revision ofANSI/SMPTE 170M-1994, Society of Motion Picture and Tele-vision Engineers, White Plains, NY, 1999.

[7] Recommendation ITU-R BT.1117-2, Studio Format Parameters forEnhanced 16:9 Aspect Ratio 625-Line Television Systems (D- andD2-MAC, PALplus, Enhanced SECAM), International Telecom-munication Union, Geneva, Switzerland, 1994, 1995, 1997.

[8] European Telecommunication Standard ETS 300 731, TelevisionSystems; Enhanced 625-Line Phased Alternate Line (PAL) Televi-sion; PALplus, European Telecommunications Standards Insti-tute (ETSI), Sophia Antipolis, France, 1997.

[9] Recommendation ITU-R BT.470-6, Conventional Television Sys-tems, International Telecommunication Union, Geneva, Swit-zerland, 1970, 1974, 1986, 1994, 1995, 1997, 1998.

[10] Recommendation ITU-R BT.1700, Characteristics of CompositeVideo Signals for Conventional Analogue Television Systems, Inter-national Telecommunication Union, Geneva, Switzerland,2005.

[11] Recommendation ITU-R BS.707-5, Transmission of Multi-Soundin Terrestrial Television Systems PAL B, B1, D1, G, H, and I, andSECAM D, K, K1, and L, International TelecommunicationUnion, Geneva, Switzerland, 1990, 1994, 1995, 1998, 2005.

[12] Report ITU-R BT.2043, Analogue television systems currently inuse throughout the world, International TelecommunicationUnion, Geneva, Switzerland, 2004.

Color burst phase –(B–Y) U and ±V f OR and f OB 180° phaseswitch every third line

and every field

Color switch identification Not required Swinging burst ±45° Nine lines of DR and DB during vertical interval

Additional signals None Meander gate f H/2 f H/2, f H/4, f V, f V/2

TABLE 1.13-4Line-to-Line Chroma Signal Sequence Comparison

Line (N) Line (N + 1) Line (N+ 2) Line (N+ 3)

NTSC Chroma: I, Q I, Q I, Q I, QBurst phase: –(B-Y) –(B-Y) –(B-Y) –(B-Y)

PAL Chroma: U1 + V U1 – V U1 + V U1 – VBurst phase: –U + V = +135° –U – V = +225° –U + V = +135° –U – V = +225°

SECAM(FM)

Chroma: DR ± 280 kHz DB ± 230 kHz DR ± 280 kHz DB ± 230 kHz

Burst phase: DR Deviation = +350 kHz–500 kHz

DB Deviation = +500 kHz–350 kHz

Chroma Switch Ident. Lines During Vertical Interval

Line #: 7 8 9 10 11 12 13 14 15320 321 322 323 324 325 326 327 328

Ident Signals: DR DB DR DB DR DB DR DB DR

Note: Phase reversed 180° every third line and every field.

TABLE 1.13-3 (continued)Chrominance Encoding Systems Comparison

NTSC PAL SECAM

nab_1_13 worldwide standards for analog television

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