CA1171521A

CA1171521A - Method and apparatus for one line dropout compensation of color television signals

Info

Publication number: CA1171521A
Application number: CA000372310A
Authority: CA
Inventors: Bantval Y. Kamath
Original assignee: Ampex Corp
Current assignee: Ampex Corp
Priority date: 1980-03-24
Filing date: 1981-03-04
Publication date: 1984-07-24
Also published as: IT1144484B; JPS56149190A; FR2478924A1; GB2072457B; JPH0262997B2; NL8101437A; DE3111334C2; GB2072457A; IT8148079A0; DE3111334A1; HK26686A; FR2478924B1

Abstract

ABSTRACT OF THE DISCLOSURE

A method and apparatus for dropout compensation of composite color television signals is described in which both the, luminance and chrominance components forming a dropout compensation signal are derived from the same portion of the original color television information signal without dropouts immediately preceding the dropout. One horizontal line of the color television signal without dropouts is continuously stored in a memory. When a dropout occurs, the stored television signal line is circulated in the memory. The length of delay of the chrominance component of the stored television signal is con-trolled from line to line in response to the phase of the color burst synchronizing component. The length of delay of the luminance component of the stored television signal is controlled on consecutive lines in response to the horizontal line synchronizing component. The respectively delayed chromin-ance and luminance components of -the stored television signal are combined to form a composite dropout compensation signal which is inserted in the original color television signal in place of a detected dropout.

Description

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The present invention .relates -to a method and appara-tus for dropout compensa-tion of color televi~ion signals where both -the luminance and chrominance compon-ents forming the dropout compensation signal are delayed during consecutive horizontal line intervals for a time different from one horizontal line period by less than one eyele of the eolor subearrier eonponent which is suitable for utilization .in both. analog and digital signal systems.
; . 10 As it is well known in the art! television signal dropout eompensators are utilized to .replaee a missing or degraded portion of the television sic3nal whieh has "dropped out" due to an unpredietable instantaneous mal-funetion of th.e system. For examplef when the teIevision signal is reeorded and subsequently played bac~ from a recording medium, a dropout may oecur due to diminutive defeets of the reeording medium. When such dropouts in the television signal oeeur, they introduce subjective dis-tort-ion in the displayed televisi.on picture~ Dropout 'eompensators are utilized to eliminate the subjective dis-tortion of dropouts from the television pieture displayed to the viewer.
A eomprehensive survey of prior art teleyision dropout eompensators is contained in copending applieation serial no. 362,7S4 by B. Yeshwan-t Kamath, filed on October 20, 1980, which applieation is assigned to the assignee of this applieation, whieh deseribes a digital color television signal dropout compensatorO Generally, prior art dropout eompensators utilize an RF envelope level de-tec-tor that monitors the amplitude level of the modula-ted television signal carrier waveform to detec-t dropouts in -the television signal. A compensa-table dropout is manifested in a television pc~ 3 ~

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signal as a momentary substantial reduction in the amplitude or loss of the television signal. A delay line is utilized to continuously delay the original television signal. When a dropout ih the original signal is de-tected, the delayed signal is applied as a dropout compensation signal to replace the dropou-t portion of the television signal information. More specifically, a switch in the color television signal path is controlled to apply the incoming color tele-vision signal, or ~he delayed dropout compensation signal, respectively, in response to a control si~nal from the dropout detector. The color teleYision signal is delayed by one horizontal line period and the chrom-inance component is processed to have its phase sele~tively altered on consecutive television lines. For e~ample~
in NTSC television signal systems phase adjustment of the separated chrominance component of the dropout compensation signal is provided by delaying the chrominance component by two television line periods, or alternatively, the separated chrominance component is xeversed on consecutive television lines in various ways well known in the art.
~ However, there is a significant disadvantage characterizing the aforedescribed prior art techniques of dropout compensation. The original color television signal is separated into a luminance and chrominance component and each component is respec-tively delayed and processed in a separate signal pa-th. Then, the separately processed signal components are recor~ined for use as a dropout com-pensation signalO When two or more consecutive horizontal lines contain a dropout, the previously processed and re-combined composite signal is again separa-ted and processed, as above described.

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This re-separation and re-processing is repeated for each one of the consecutive lines containing a dropout. The re-separa-tion and re-processing causes line-to-line distortion and progressive degeneration of the dropout compensation signal results. Thus, when utilizing the above described prior art dropou-t compensation techniques, the obtained dropout compen-sation signal may become unacceptable whenever a few con-secutive lines of the color television signal contain dropouts.

SU~MARY OF THE INVENTION
Accordingly, it is an object of the present inven-tion to provide a method and apparatus for dropou-t compensation of composite color television signals, in which the above-mentioned disadvantages are eliminated.
It is a further object of the present invention to provide a method and apparatus for color television signal drop-out compensation in which consecutive lines of the dropout com-pensation signal are derived from the same portion of the original color television information signal without dropout immediately preceding the dropout.
It is another object of the invention to provide a dropout compensation method and apparatus in which -the same portion of the original composite color television signal is stored in a memory, from which signal portion consecutive lines of a dropout compensation signal are derived ahd which stored original signal remains unchanged while the dropout compen-sation takes place.
It is still another objec-t of the invention to provide a color television signal dropout compensation method and apparatus in which both the luminance and chrominance component of -the original signal are delayed during consecutive horizontal line intervals for a time differing Erom one tele-vision line interval by less than one cycle of the color sub-r ~:~7~5;2~
carrier component.
It is still a further object of the present invention to provide a method and apparatus for color television signal dropout compensation, suitable for use in both analog and digital color television signal systems.
Yet another object of the present invention is to provide a method and apparatus for dropout compensation of composite color television signals suitable for util- -ization, in known television signal systems, such as NTSC, PAL, PAL-M, etc.
It is still a further object of the present in-vention to provide a method and apparatus for dropout com-;~ pensation of composite color television signals suitable for use in embodiments in which the signal is sampled at a frequency equal to an integral multiple grea-ter than two of the color suocarrier signal frequency.
The foregoing and other objects are accomplished by the method of the present invention, according to which both the chrominance and luminance components of the com-posite color television signal are stored for a period of time equal to substantially one horizontal line period, and the stored information is circulated in response to a dropout signal. The actual length of delay of the chrom-inance component is controlled in accordance with the phase of the color burst component of the television signal line to be compensated for dropouts -to provide a delayed chrominance component, which is in phase with the color burst componen-t contained in the incoming composite color -television signal line to be compensated during consecu-tive horizontal line periods. The actual length of delay of the luminance component is controlled to provide a luminance Pg~ ~l - 6 -S,'2~

eomponent whieh is in synchronism with the ineoming horizontal line synchronizing componen-t of the composite eolor television signal during conseeutive horizontal line periods. The respec-tive]y delayed chrominance and luminance components are combined to form a eomposite dropout compensation signal, which, in turn is combined with the original eomposite eolor television signal to replace a dropout portion when it is detee-ted.
The eolor television signal dropout eompen-sator of the present invention has a eircula-ting storage means for delaying both the luminance and chrominance eomponents of an ineoming eomposite eolor television to be used in forming a dropout eompensation signal. A
first eontrol means, which is responsive to the color burst eomponent, is utilized to control the actual delay of the ehrominanee eomponent to provide a delayed ehrominance eomponent which is in phase with the eolor burst eompon-ent contained in the incoming composite eolor television signal during eonseeutive horizontal line periods. A
second eontrol means, which is responsive to ~he horizontal line synchronizing component of the ineoming eomposite eolor television signal is utilized to eontrol the aetual delay of the luminance component to provide a delayed luminance eomponent whieh is in synehronism with the hori-zontal line synehronizing eomponent of -the incoming com-posite color television signal. The delays of the stored luminance and chrominance components during consecutive horizontal line intervals differ from one horizontal line period by less -than one eyele of the color subcarrier componen-t of the color television signal. A signal com-bining means is utilized to eombine the respeetively delayed luminanee and ehrominance components to provide Pg/ ` ~ - 7 -~;

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a composite dropout compensation signal. A switching means responsive to the dropout control signal, selectively applies the incoming color -television signal or -the com-posite dropou-t compensation signal to an outpu-t of the dropout compensator.
Other objects, advantages and features of the present invention will become apparent from the following detailed description taken with reference to the accompany-ing drawings.
BRIEF DESCRIPTION OF T~E DRAWINGS
FIGURES la and lb lllustrate a preferred method of providing a dropout compensatlon signal in accordance with the invention.
FIGURE 2 is a functional block diagram of a preferred embodiment of the invention.
FIGURES 3a and 3b illustrate another preferred method in accordance with the invention.
FIGURE 4 illus-trates the operation of the apperatus of FIG. 2.
FIGURE 5 is a functional block diagram of - another preferred embodiment of -the inven-tion.
FIGURE 6 illustrates the operation of the apparatus of FIG. 5.
FIGURE 7 is a functional block diagram of a still further preferred embodiment of the invention.
FIGURES 8a to 8h are consecu-tive parts of a detailed electrical schematic diagram corresponding to the block diagram of FIG. 7.
_TAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An example of a preferred dropou-t compensation method of -the present invention will be described now with reference to Figs. la and lb. :[n the following description Pg/ ~ 8 -3 t- ~3 -1 "dropout compensation" is sometimes referred to as "DOC" and "dropout" as "DO". In Fig. la, a sine wave W1 is shown representing a color subcarrier signal waveform typically found in the chrominance component of a composite color television signal. Waveform Wl is in the form of consecutive samples lA, 2A! 3A, etc., at regularly spaced inter~als of the incominy color television signal, using any color television signal sampling techinque well known in the art. In this particular example, -the samples are obtained by sampling an NTSC composite color television signal at a frequency equal to three times the color subcarrier signal frequency, that is, at 3 x 3.58 ~Iz or 10.~4 ~z.
The obtained samples may be encoded into a digital form by an analog-to-digital encoder, utilizing, for example, pulse code modulation (PCM), where each individual code element represents a particular signal amplitude value.
; As an example, the subcarrier waveform Wl is indicated as occurring during a particular television line interval Al.
It is a well known feature of the NTSC television signal system that the subcarrier waveform W2 in a next sub-sequent television line interval Bl will have an opposite phase with respect -to subcarrier waveform Wl. Therefore, if a dropout occurs, for e~ample, after the original television line Al has been received and delayed by one television line period for subsequent utilization as a dropout compensation signal to replace a dropout occurring in line Bl, the delayed line Al would exhibit an undesired 180 phase shift with respect to Bl. The undesired 180 phase shift is reflected in -the samples lA, 2A, 3A, etc., of the delayed Wl signal being displaced by one and one-half sampling interva]s relative to the phase locations of the corresponding samples 2B, 3B, etc., of waveform W2.

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To replace a dropout in television line interval Bl with a dropout compensation slgnal derived from the immediately preceding television line interYal Al, sample lA has to be displaced with respect -to corres-ponding sample 2B, and similarly, sample 2A with respect to sample 3B, etc., by one and one-half sampling intervals in order to maintain the proper line-to-line chrominance phase relationship.
By the preferred method of the present inven-tion, the above-indicated phase shift oE the color subcarrier signal on consecutive lines is obtained by storing the color television signal and alternatively increasing or decreasing the storage deIay of the chrom-inance component of the television signal by a delay corresponding to one`and one-half sample periods. This latter feature i5 illustrated in Fig. la ! showing sample 3B of line sl as being obtained by delaying the chrominance component of sample 2A of the immediately~preceding original , television line Al by one horizontal line period~ increased by one and one-half sample periods. A dashed line CHl connecting corresponding samples 3B and 2A illustrates this feature. Fig. lb shows the subcarrier waveform W2 of line Bl, followed by waveEorm W3 of a next consecutive line A2. Fig. lb illus-trates an example where line sl is the last received original television signal line and line A2 is the first line containing a dropout requiring compen-sation. As Fig. lb reveals, sample lA of the subcarrier signal waveform W3 is obtained by delaying the chrominance component of sample 2B of waveform W2 by one horizontal line period decreased by a time interval corresponding to one and one-half sample periods. Dashed line CH2, connecting corresponding samples lA and 2B, indicates the latter feature.
.., Pg/,' , - 10 -5'~1 However, when the above-described dropout compensation method is utilized, the luminance component of the dropout compensation signal will introduce sub-jective distortions in the display of the compensated color television signal if it is also displaced by +
one and one-half sample periods with respect to its phase position in the original color te]evision signal line. A phase displacement of the chrominance component of + one and one-half sample periods is not objectionahle because chrominance informa-tion chan~es in a color tele-vision signal are ordinaxily at a low rate, whereas to obtain a high quality color si~nal for dropout compen-sation it is essential to maintain the line-to-line phase of the chrominance component as close to the required ;` phase as possible. On the other hand, such phase dis-placement of -the luminance component is quite objection-able because it introduces too large a line-to-line ~ horizontal displacement of samples in the television ; signal with respect to the samples of the original signal.; 20 To eliminate the above-discussed drawback, the preferred dropout compensation method of the inven-tion provides line-to-line adjustment of the luminance com-ponent displacement as follows.
When the chrominance component of the stored television signal is delayed one horizontal line plus one and one-half sample periods for dropout compensation, as depicted by Fig. la, the luminance component of the stored television slgnal is delayed by one horizontal line plus one-half sample period. When a horizontal line of a television line is dropout compensated with information from an immediately preceding horizontal line, the horizontal displacement of the luminance component ;, ~
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of the dropout compensation signal relative to -the luminance component of the -television signal being compensated is reduced from an objectionable one and one-half sample periods of an acceptable one-half sample period. The foregoing is illustrated in Fig. la b~ dashed line Ll connecting samples 3B and 3A.
Analogously, for obtaining the above reduc-tion in the luminance component displacement when the stored television signal is delayed one horizontal line less one and one-half sample periods, as depicted by Fig. lb, the luminance component of the stored television signal is delayed one horizontal line less one-half sample period. This is illustrated in Fib. lb by dashed line L2 connecting samples lA and lB. As will be appreciated I from the foregoing, the horizontal displacement of the luminance component of the dropout compensation signal relative to the television signal being compensated is reduced to an acceptable one-half sample period, which is one-third of a c~vcle of the color subcarrier in the example in all cases when a horizontal line of a tele-` vision signal is compensated for dropouts with a dropout compensation signal derived from the immediately pre-ceding horizontal line of the -televisi.on signal. In addition in both such cases the delay of the respective - chrominance components of the dropout compensation signal remains displaced by the desired one and one-half sample periods.
More specifically, the above features of the pre-ferred method of -the present invention can be conveniently realized through the practice of the method as follows.
One horizontal line of the incomin~ original composite color television sianal is con-tinuously stored in a memory.

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The memory is updated with a new horizontal line of the incoming -television signal each time a received horizontal line contains no dropouts. The length of delay of the stored composite signal is con-trolled in accordance with the line-to-line phase of the color burst componen-t of the original color television signal.
The exact delays of the chrominance component and luminance component are achieved by separating the composite signal into its luminance and chrominance components so that the length of delay of the lumin-ance component can be modulated about a length of one horizontal line a different amount rela-tive to that of the chrominance component. The difference is an integral number of sample periods. With respect to the above-described particular example illustrated in Figs.
la and lb, the s-tored chrominance component of the com-posite color television signal is delayed an interval equal to one horizontal line period modulated by + one and one-half sample periods on consecutive lines. Be-sides that, the length of delay of the stored luminance ; component is modulated line-to-line by + one-half sample period, in the same sense as the stored chrominance com-ponent, to reduce the line--to-line luminance component displacemen-t.
To illustrate the foregoing, a preferred embodiment of the apparatus of -the present invention will be described with reference to the func-tional block diagram of Fig. 2 of the attached drawings. A composite color television signal is received at inpu-t terminal 12 and is applied to firs-t input 20 of a first two-way switch 1. In this particular example, the television signal is received in digital form obtained , for example, Pg/ , ;~ - 13 -., , l5~
by encoding the color television signal in-to a well-~nown NRZ PCM code, as previously mentioned with referenct to Figs. la and lb. A control signal, DO, indicating presence of a dropout is received by a control terminal 23, for example, from a conventional dropout de-tector (not shownl~
A suitable dropou-t detector may be of a con-ventional carrler monitor type which provides a control signal when the RF envelope of the modulated television signal dropout is below a predetermined level, such as desired, for example, in AVR-2 Videotape Recorder, Theory of Operation, Catalog No. 1809179-01, published November, 1977, by Ampex Corporation, payes 5-31 to 5-33. The control terminal 23 is coupled to a control input 24 of first switch 1, and, also, to control input 29 of a second switch 2. Output 25 of switch l is coupled to an output terminal 13 of the dropout compensator circuit, as well as to first input 26 of switch 2. The output 27 of switch 2 ~ is coupled via a controlled delay line 3 and a compensating j 20 fixed delay line 4 to a second input 28 of switch 2.
Elements 2, 3 and 4 form together a circulating memory ` circuit 44, which will be described hereinafter in more ;::
detail. A control terminal 30 which receives a color burs-t synchronous control signal, CB, that controls the length of the controlled delay line 3 in the manner to be described in detail hereinafter, is coupled to a control input 31 of the controlled delay line 3. The output 32 of delay line 3 is coupled to an input 33 of a filter 5 and via a compensating fixed delay line 6 to a first input 35 of a differencing circuit 7. The compensating delay lines 4 and 6 are respectively utilized to compensate for circuit delays in the color television signal path, which will be described hereinaEter. An ou-tpu-t 34 of filter 5 is 1'7'1l,5'~,~
coupled to a second input 36 of differencing circuit 7, as well as to a first input 37 of a third two-way switch 10. The filter's output 34 is also coupled via a fixed delay line 9 to a second input 38 of switch 10. A control terminal 43, receiving a control signal HS/2, is coupled to a eontrol input 44 of ~hird switch 10. An output 39 of switeh 10 is coupled to a firs-t input 40 of a signal combining circuit 11. An output 45 of signal differencing eircuit 7 is coupled via a fixed delay line 8 to a seeond input 41 of eireuit 11. An output 42 of signal eombining cireuit 11 is eoupled to a seeond input 21 of the first two-way switeh 1.
It is to be realized that the above-described preferred embodiment of Fig. 2 as well as -the respeetive embodiments of Figs. 5 and 7 which will be described later, all represent respective digital dropout compensators in aeeordance with the present invention in which high speed digital data is processed. Consequently, the various elemen-ts shown in these respective functional block dia-grams may be constructed uslng conventional digital circuitsin which the high speed data is precisely clocked at the sampling frequency, equal to an integral number greater ; than two times the color subcarrier signal frequency, the various embodiments described herein being arranged to operate with a sampling frequency of the three times the NTSC color subcarrier signal frequency or 3 x 3.58 10.74 MHz, which elock signal is frequency and phase-locked to the color subearrier eomponent of the sampled television signal. In the further deseripti.on, the terms sampling frequeney and clock frequency will be used inter-changeably. For simplici-ty of representa-tion, the cloek signal pa-th is now shown in the above-indicated Fig~lres, pg/ ~ - 15 -, '7~5~

however, it is shown in the detailed electrical schematic diagram of Figs. 8a to 8h, corresponding to -the block diagram of Fig. 7, which detailed diagram will be described hereinafter.
Now the opera-tion of the preferred embodiment of the invention shown in the block diagram of Fig. 2 will be described. A digital NTSC color television signal in the form of discrete data representing consecutive samples is continuously received at input terminal 12 and fed to 10 first input 20 of switch 1. When the dropout compensator system is in normal operation, that is, no dropout in the incoming signal is detected, swi-tch 1 is in its first position as shown, receiving the input signal a-t 20 and simultaneously applying it via output 25 to output terminal 13 of the dropout compensator and via input 26 and output 27 of switch 2 -to the controlled delay line 3. Delay line 3 has a length that is controllable + one and one-half sample periods abou-t a nominal delay equal to one horizontal line period less circuit delays in the color television signal 20 path, as will be disclosed hereinafter.
The delayed composite signal from delay line 3 is fed -to filter 5 which may be, for example, of the type, disclosed in the above-indicated copending patent application SN 362,754, or alternatively, it may be a well known digital comb filter. Filter 5 separates the luminance component from the stored composite color television signal, in a manner well known in the art. The separated luminance component ob-tained at the output 34 of filter 5 is applied to input 36 of differencing circuit 7. The composite color 30 television signal from output 32 of delay line 3 is applied via compensating fixed delay line 6 to the other input 35 of circuit 7. Differencing circui-t 7 provides at its mg/ - - 16 -output 45 a difference signal of the two signals received at its respective inputs. The resulting difference signal represents the separated chrominance component of the stored color television signal. Delay line 6 compensates for the circuit delay provided by filter 5, in a manner well known in the art, to eliminate undesirable relative phase shifts in the respective signal paths of the signals subsequently processed in differencing circuit 7.
In the particular embodiment of the invention illustrated in Fig. 2 a non-integral number of samples equal to 3 ~ 227.5 = 682.5 clock cycles is obtained within one horizontal line period, the color subcarrier frequency being equal to 227.5 times the horizontal line frequency in NTSC color television signals. The con-trolled delay line 3 has a length of delay equal to one horizontal line period represented by 682.5 clock cycles, less one clock cycle plus the following circuit delay, which is alterable by - one and one-half sample periods. Loading an~ unloading of the samples into and from delay line 3, respec-tively, is controlled by the control signal CB received a-t terminal 30, which signal is derived from the color burst component of the incoming color television signal duriny each horizontal line in a manner well known in -the art so that it is synchronous with such color burst component. The CB
con-trol signal is applied to control inpu-t 31 of delay line 3. As men-tioned earlier, in this particular embodiment one cycle of the color burst corresponds -to three sample periods defined by three clock cycles. Consequently, the relative line-to-line phase shift by 180 oE the color burst component represents a delay of plus or minus 12 sample periods, that is plus or minus 1 12 clock cycles. As will become apparent from the following description, the controlled delay line 3 is operated to provide alterna-tive delays of the , . ~
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composite color television signal equal to 682 1 + 1 2 = 684 clock cycles and 682 1 - 1 12 = 681 clock cycles on consecutive lines, less the aforementioned one clock cycle and circuit compensation delays. The latter operation may be described as modulating the fixed length of delay of the composite color television sisnal stored in delay line 3 during consecutive television line periods by the phase of the color burst component. It will be understood that the average signal delay during several consecu-tive lines approaches 682 2 clock cycles, which is e~ual to the original one horizontal line period.
From the foregoing description it follows that delay line 3 of Fig. 2 is controlled hy a control signal CB
synchronous with the color burst component, which signal is received at terminal 30 to provide a delayed composite color television signal of one horizontal line whose color subcarrier component is in phase with the color burst component of a following horizontal line, as previously described in detail wi-th respect to Figs. la and lb.
As previously disclosed with reference to Figs.
la and lb, it is desirable that the luminance component samples of the dropout compensation signal be processed to minimize the horizontal displacement of respective sample positions on consecutive lines of the displayed television signal. Now, the line-to-line adjustment of the luminance component delay provided by the apparatus of Fig. 2 to achieve the foregoing will be described. As above described, in this preferred embodiment the luminance component is separated in fil-ter 5 from the composite signal having a modulated delay. The length of delay of -the delayed separated luminance componen-t is further modulated by -1 clock cycle in -the opposi-te sense with respec-t to the chrominance component that is to be combined with the ,mg/ ~ - 18 -5'~L
luminance component to form the dropout compensation composite color television signal. To this effec-t, the delayed separated chrominance component at the output 45 of differencing circuit 7 is delayed by additional one clock cycle by fixed delay line 8. At the same time, the delayed separated luminance component from filter 5 is directly applied to the first input 37 of two-way switch lO while it is also applied via additional delay line 9 of -two clock cycles to the second input 33 of switch lO. Switch lO is controlled by the control signal HS/2 received at terminal 43, having a frequency equal to one-half horizontal line frequency. The switch lO is responsive to the HS/2 signal to connect first and second inputs 37 and 38 to the output 39 on alternate horizontal lines, thereby alternating the delay of the luminance component between zero and two clock cycles on alternate horizontal lines. Signal HS/2 is derived from the horizontal line synchronizin~ component contained in the incoming color -television signal received at input terminal 12. In the respective preferred embodiments of the invention described herein, -the control signal XS/2 is frequency and phase-locked to the horizontal line synchronizing component and the color burst component of the incoming color television signal. During dropout compensation, when the composite television signal is not received, the respective control signals cs, HS or HS/2 are generated synchronously with the respective synchronizing componen-ts of the missing television signal, utilizing a flywheel signal generator (not shown) frequency and phase-locked to the color television signal, in a manner well known in the art. As will be understood Erom the foregoing description, the resulting delay of the luminance component is modulated by - one clock cycle delay relative to the chrominance component delay. By this latter feature the - mg/`~ - l9 -L5'~1 length of delay of the luminance component oE the dropout compensation signal is adjusted on consecutive horizontal lines in response to the horizontal line synchronizing component to minimize line-to-line horizontal displacement of samples inserted in the outpu-t color television signal for dropout compensation.
The respectively delayed luminance and chrominance components are combined in adder 11 and the combined signals at the output 42 of adder 11 represent the composite dropout compensation signal applied to input 21 of first switch 1. The dropout compensation signal is continuously available to be utilized for dropout compensation in response to a dropout compensation control signal DO received at control terminal 23, as has been described previously.
Upon receiving a control signal DO at terminal 23, indicating that a dropout has occurred in the incoming television signal a-t terminal 12, switch 1 is controlled to switch from input 20 to 21, and switch 2 to switch from input 26 to 28. Consequently, switch 1 will apply to output terminal 13, the dropout compensation signal received at its input 21, which is provided by the circuit of Fig. 2 as above disclosed. On the other hand, switch 2 will close the circulating memory circuit 44, and, thus, effect circulation of the last received line of the television signal information from a previous horizontal line or set of previous horizontal lines without dropouts immediately preceding the dropout, which signal has been stored in delay lines 3 and 4. Consequently, the above-indicated original color television signal line will circulate in circulating memory 44 until the dropout is eliminated and the con-trol signal DO at terminal 23 is discontined. During the dropout compensation, the output signal at outpu-t 32 from the circulating memory 44 is processed by the dropout compensator mg/ - 20 -L5'~L
circuit of Fig. 2 in the previously disclosed manner, instead of the incoming color television signal.
As above mentioned, the leng-th of delay of controlled delay line 3 is decreased from the previously considered one horizontal line period to compensate for circuit delays in the processed composite signal path. Thus, if the delay provided by filter 5 in the separated luminance signal path is designated ~ and the additional one cloc~ cycle delay provided in both the separated luminance and chrominance signal paths is designated ~, then it will become apparent from the block diagram of Fig. 2 that to obtain an overall length of delay equal to one horizontal line period of the composite DOC signal, while not considering the above-described modulation of the delay by the respective control signals, delay line 3 must have its delay decreased by a + ~.
Similarly, it will become apparent from the above disclosure that to provide a circulating memory 44 which has a length of delay equal -to exactly one horizontal line period, it is necessary to re-insert the combined delays ~ + ~ in form of a fixed delay line 4 as shown between the output 32 and input 27 of delay line 3.
As it is seen from the foregoing description, it is a significant advantage of the inven-tion that consecutive lines of the dropout compensation signal are derived from the same portion of the original color television signal without a dropout immediately preceding the dropout.
It is a further important advantage, that the composite signal is stored in the circula-ting memory ln its original form, and remains unchanged by -the line-to-line processing of the signal components throughout the dropout compensation. Consequently, no deterioration of the resulting dropout compensation signal occurs, as takes place in the known prior art dropout compensators. At the mg/J - 21 -5'~

same -time, each sample of the dropout compensation signal chrominance component is processed to have the same phase as that of a corresponding sample of the incoming television signal, for which the dropout signal is formed, while -the dropout compensation signal luminance component is processed to introduce a minimum horizontal displacement of samples on consecutive lines of the dropout compensa-ted composite color television signal. Since in the above described example related to the operation of the block diagram of Fig. 2, a sampling rate of three times the color subcarrier signal frequency is considered, there is a line-to-line displacement of the dropout compensation signal sample equal to 1 12 sample periods for the chrominance component and just 1 sample period for the luminance component. It is understood from the foregoing description that by the above-indicated respective line-to-line displacement of samples, the previously described objectives related to a high quality dropout compensation signal are achieved.
The operation of the apparatus of Fig. 2 for dropout compensation of a series of consecutive horizontal lines containing dropouts is illustrated in Figs. 3 and 4.
These figures illustrate the line-to-line displacement of the luminance and chrominance components combined to form a series of dropout compensation signals from one stored horizontal line of a composite television signal without a dropout for use in consecutive lines of the DOC television siynal~ As seen in Fig. 4 a last received original television signal line Al, immediately preceding the series of dropouts, comprises consecutive samples 2A, 3A, 4A, 5A, etc. It is seen from Fig. 4 that the apparatus of Fig. 2 operates to delay the chrominance component forming each of the samples 2B, 3B, 4B, etc., of -the first DOC line Bl, mg/ - 22 -s~
as well of all subsequent odd DOC lines B2, B3, etc., relative to the phase position of such each chrominance component in the original line by an amount equal to an odd multiple of the interval of one horizontal line plus one and one-half sample periods. However, it is seen from Fig. 4 that the apparatus of Fig. 2 operates to delay such chrominance component again after circulation in circulating memory 44 on the second DOC line ~2 and all subsequent even DOC lines A3, A4, etc., by an amount equal to the interval of one horizontal line less one and one-half sample periods.
AS a result of the operation of the circulating memory 44, each chrominance component forming each sample of the dropout compensation signal for even DOC line A2, A3, etc., is delayed even multiples of the interval of one horizontal line. Consequently, the chrominance components of samples 3A, 4A, etc., on even DOC lines A2, A3, etc., are in phase with those of original line Al, however, displaced by 1 12 sample periods with respect to an immediately preceding odd DOC line. On the other hand, the operation of the apparatus results in the displacement of the luminance component forming each sample of even DOC lines A2, A3, etc., by one sample period with respect -to the oriyinal line Al, but each is displaced only by 1 sample period with respect to the luminance component of the same sample appearing in an immediately preceding odd DOC line. During the first odd DOC line Bl, the apparatus operates to delay -the luminance component forming each sample of the dropout compensation signal by an amount equal to the interval of one hori~ontal line plus one-half sample period. The opera-tion of the circula-ting memory in cooperation with the operation of -the third -two-way swi-tch 10 in alternately inserting a two clock cycle delay and no delay in the luminance component path on consecutive horizontal lines " .
ir ~ mg/ ~ - 23 -S;~

results in delaying the circulated luminance component of each sample forming the dropout compensation signal for even DOC lines A2, A3, etc., relative to the phase position of such luminance component in the original line ~y an amount equal the lnterval of one horizontal line less one-half sample period, whereby such luminance component is positioned in phase within one-half sample period of its phase position in the original line Al. ~s a result of the above-described dropout compensation method shown in Fig. 4, a line-to-line displacement pattern of sample components is formed in the display of the compensated color television signal in which the displacements of chrominance and luminance components forming a dropout compensated sample point, represented by lines CH2, L2; CH3; CH4, L4; etc., connecting corresponding chrominance and luminance component samples of adjacent DOC
lines, are in opposite directions horizontally from line to line. By this pattern, the desired respective line-to-line horizontal displacement of - 1 12 sample periods of the chrominance component and of ~ 12 sample period of the luminance component is achieved.
The foregoing preferred me-thod of the invention with respect to providing a delayed luminance component of the composite dropou-t compensation signal on consecutive television lines is illustrated in Figs. 3a and 3b. In Fig. 3a a waveform Ml represents a portion of -the luminance component of an incoming original color television signal line Al received at terminal 12 by the dropout compensation circui-t of Fig. 2, immediately preceding a line containing a dropout. Samples lA, 2A, 3A, etc., of waveform Ml are obtained by sampling the color television signal a-t a frequency equal to three times the color subcarrier signal frequency, as described previously. When considering the above~described method of providing a dropout compensation ., ~ ~ mg~ - 24 -S~21 luminance component employing the apparatus of Fig. 2, the luminance component of the first dropout compensation signal line Bl, following the original television signal line without a dropout, is represented by M2 in Fig. 3A, which illustrates the dropout compensation signal lines as it appears in a raster display of the television signal.
It is seen that waveform M2 is a replica of the original waveform Ml with the exception of samples lB, 2B, 3B, etc., of M2 being displaced by only one-half sample period in one direction, for example, to the right with respect to samples lA, 2A, 3A, etc., of waveform Ml. However, waveform M3 of the next consecutive line A2 which waveform is a replica of the original waveform Ml, is displaced from M2 of line Bl by one-half sample period, but it is displaced from the original waveform Ml of line lA by one sample period, as illustrated by Figs. 3a and 3b by the location of samples 2A, 3A, 4A, etc., on M3 with respect to the samples of the previous lines Bl and Al, respectively.
The lat-ter effect is not objectionable to the viewer, since only a one-half sample period displacement in the horizontal direction of the luminance component of a given DOC sample occurs from line-to-line in the displayed dropout compensated color television signal when a single horizontal line is used to compensate a series of consecutive horizontal lines containing dropouts. The above me-thod allows forming a composite dropout compensation signal having its composite samples composed of chrominance component sample portions horizontally displaced in one direction and luminance component sample portions horizontally displaced in the opposite direction with respect to the composite samples of the previous color television signa] line. This pattern alternates on consecutive dropout compensa-tion lines by changing the above directions -to achieve an overall mg/ ~ - 25 -~.~ll7~.S~l compensating effect, as has been described above with respect to Fig. 4.
Fig. 3b depicts the luminance component of an incoming oriyinal color television line Bl immediately preceding a dropout. Waveform Nl comprising samples lB, 2B, 3s, e-tc., is identical to waveform Ml pertaining to line Al of Fig. 3a, with the exception of having its samples lB, 2B, etc., displaced by 1 sample period with respect to waveform Ml. It will be seen from Fig. 3b, that N2 depicts respective waveforms of all the "odd" DOC lines A2, A3,...AN following the original line Bl. Similarly, N3 depicts all the even DOC lines s2, B3,...BN following the original line Bl. There is a difference between forming DOC luminance components on consecutive television lines, as shown in Figs. 3a and 3b in that the luminance components of the samples forming the dropout compensation signal for the "odd" lines are~displaced with respect to the phase locations in the original line by one-half sample period and those forming the dropout compensation signal for the "even" lines are displaced wi-th respect to the phase locations in the original line by one whole sample period in respectively opposite directions. The reason for the difference in the direction of the displacement of the samples forming the dropout compensation signal resides in the arbitrary nature of the control of the delay lines exercised by the control signals CB and HS/2. Should the incoming color television signal start with the control signals causing the delay line 3 to increase the delay by one and one-half sample periods while the third two-way switch 10 is conditioned to connect its output 39 to its input 37, the displacement of the samples follows the pattern depicted in Fig. 3a. However, should the dropout compensa-tion sequence start with the control signals causing mg/ - 26 -1~7~S~
the delay line 3 to decrease the delay by one and one half sample periods while the third two-way switch 10 is conditioned to connect its output 39 to its input 37, the displacement of the samples follows the pa-ttern depicted in Fig~ 3b.
Ano-ther preferred embodiment of the dropout compensator in accordance with the present invention is shown in Fig. 5. In Fig. 5, circuit elements similar to those previously described with respect to Fig. 2 are designated by like reference numerals. Description of these elements wi-th respect to Fig. 5 will be omitted to avoid undue repetition. In the dropout compensation circuit of Fig. 5, filter 5, which separates the luminance component from the composite color television signal, is coupled to the output 25 of the first two-way switch 1. The separated luminance component at the output 34 of filter 5 is fed to input 36 of differencing circuit 7, whose other input 35 is coupled to receive the color television signal from output 25 of switch 1, via compensa-ting fixed delay line 6.
The resulting separated chrominance component at the output 45 of differencing circuit 7 is coupled to a first input 47 of a second two-way switch 14. The output 50 of switch 14 is coupled via a first controlled chrominance delay line 16, which has its output coupled to a second input 49 of switch 14. The delay line 16 and switch 14 thus represent a first circulating memory circuit 81 for the separated chrominance component. The delay line 16 is controlled by the previously described control signal indicated CB received at control terminal 30 and applied to the control input 84 of the delay line. The separated luminance component at the outpu-t 34 of filter 5 is further coupled to a first input 46 of a third two-way switch 15, and it is coupled by output 51 of switch 15 via a second controlled luminance mg/ ~ - 27 -delay line 17 to a second input 48 of swi-tch 15. It is seen that delay line 17 and switch 15 form a second circulating memory circuit 84 for the separated luminance component. The delay line 17 is controlled by a control signal indicated HS received at control terminal 43 and applied to the control input ~4 of the delay line. A
dropout control signal DO received at control terminal 23 is coupled to respective control inputs 24, 85 and 86 of switches 1, 15 and 14, respectively.
In operation, a dropout control signal DO, which indicates the presence of dropout in the incoming composite color television signal received at 12, activates all three switches 1, 14 and 15, respec-tively. In response to the receipt of a dropout control signal DO switch 1 is conditioned to couple a dropout compensation signal from its input 21 to its outpu-t 25, which signal is provided by the circuit of Fig. 5. The above-indicated dropou-t compensation signal is formed as follows. During times when no dropout is de-tected, filter 5 continuously receives the digital color television signal present at input terminal 12 composed of samples of an analog television signal taken at a frequency equal to three times the color subcarrier signal frequency.
The separated l~ninance component at the output 34 of filter 5 is fed via switch 15 to the luminance delay line 17.
Delay line 17 has a nominal length of delay equal to one horizontal line period and stores one horizontal line of the separated luminance component ob-tained from a horizon-tal line preceding the horizontal line of the color television signal then being received at terminal 12. The loading and unloading of the signal stored in delay line 17 is controlled by the control signal HS received a-t terminal 43.
Signal HS is derived from the horizontal synchronizing component of the received color television signal and is mg/~. - 28 -~7~L5~
synehronous therewi-th. Wi-th respect to the ahove feature, a separated luminance component is obtained whieh is delayed by one horizontal line period and, at the same time, which is coherent with the horizontal line synehronizing eomponent during eonseeutive television lines.
Similarly, the ehrominance delay line 16, whieh also has a length equal to one horizontal line period, eontinuously reeeives the separated chrominance component from differencing circuit 7, via switch 14. Thus, one horizontal line of the separated chrominance component will be stored in the chrominance delay line 16, which chrominance component is obtained from the same portion of the color television signal as the separated luminance component stored simultaneously in the luminance delay line 17.
Loading and unloading of the chrominance component stored in delay line 16 is controlled by the control signal CB
received at terminal 30, which signal is derived from the color burst synchronizing component of the color television signal received at terminal 12. sy controlling the chrominance delay line 16 by the control signal CB, a separated chrominance component is obtained which is delayed by one horizontal line period, and at the same time, which is in phase wi-th the color burst component during consecutive television lines.
As it is shown in Fig. 5, the respectively delayed separated luminance and chrominance components are combined in the signal combining circuit 11 and the combined signal at the output 42 of circui-t 11 is fed to the second input 21 of first switch 1. The signal at inpu-t 21 represents the dropout compensation signal which is utilized by the apparatus of Fig. 5 when a dropout control signal DO is received.

mg/` - 29 -117~5'~
~ hen a dropout is deteeted, switches 14 and 15, controlled by signal DO, elose the respective circulating memory eircuits 81, 82. Consequently, the separated luminanee and ehrominance components circulate in their respective circulating memory circuits, synchronously, eontrolled by a elock signal at a frequeney equal to three times the color subcarrier signal frequency in the manner deseribed hereinbefore with reference to the dropout eompensation embodiment illustrated in Fig. 2.
It follows from the above description, that the cireuit of the preferred embodiment of Fig. S has an advantage with respect to the cireuit of Fig. 2 in that it does not require addi-tional modulation of the delayed separated luminance component with respect to the delayed separated chrominance component to reduee the line-to-line horizon-tal displaeement o-f the luminance component samples.
Ins-tead, in the embodiment of Fig. 5, two separate eireulating delay lines are provided, one delay line for the separated luminanee eomponent and another one for the separated chrominanee eomponent, respectively. Each delay line 16, 17 is controlled by a separate control signal cs or HS, respeetively, to provide a signal component in synchronization therewith.
The operation of the embodiment of Fig. 5 is illustrated in Fig. 6, where the respective horizontal displacements between the luminanee and ehrominanee component samples on consecutive dropout compensation lines is shown.
To facilitate comparison with the previously described diagram of Fig. 4 and the rela-ted circuit of Fig. 2, the last received original color television si.gnal line without a dropou-t, -the eonseeutive dropout compensation IDOC) lines, as well as conseeutive samples of these respeetive lines are designated by like reference charaeters in the diagrams . mg/' - 30 -lS~
of Figs. 4 and 6. It is seen in the diagram of Fig. 6 that the luminance component of each DOC sample 2B, 3B, 4B, etc., on odd DOC lines Bl, B2, etc., is obtained by delaying the luminance component of a corresponding sample 2A, 3A, 4A, etc., of the original line Al by one horizontal line period increased by one-half sample period. At the same time, the chrominance component of each above-indicated DOC sample 3B, 4B, etc., on odd DOC lines is obtained by delaying the chrominance component of a corresponding sample 2A, 3A of -the original line Al by one horizontal line period increased by one and one-half sample period. On the other hand, the luminance component of each DOC sample 3A, 4A, etc., on even DOC lines A2, A3, etc., is obtained by delaying the luminance component by an interval equal to one horizontal line period less one sample period and the chrominance component of the corresponding samples by an interval equal to one horizontal line period less one and one-half sample periods. Thus, in the operation of the preferred embodiment of the invention of Fig. 5, the relative line-to-line horizontal displacement of the DOC
signal samples is ~ 12 sample period for the luminance component and - 1 12 sample periods for the chrominance component. However, it i5 an advantage of the preferred method of the invention depicted by Fig. 6 when comparing it to the method depicted by Fig. 4 -that, when a sequence of consecutive horizontal lines are compensated for dropouts from a single horizontal line provided by the dropout compensa-tor, every other DOC line is in phase wi-th the original television signal line wi-th respect to both the luminance and chrominance components, and no horizontal displacement of samples takes place on these lines with respect to both luminance and chrominance components.

'' ; mg/ - 31 -1~7~S~
In the embodiment of the inven-tion illus-trated in Fig. 5 it is not necessary to have the color television signal sampled at a frequency equal to an in-tegral multiple of the color subcarrier signal frequency, as is the case in the embodiment of Fig. 2. In the embodiment of Fig. 5, a sampling frequency equal to a rational number multiple of the subcarrier frequency may be utilized.
For the purpose of a more complete disclosure of the apparatus and method of the present invention, a further embodiment of the present invention is shown in the block diagram of Fig. 7. A corresponding detailed electrical schematic diagram is shown in consecutive Figs.8a to ~h. The embodiment of Figs. 7 and 8a to 8h has been designed for a specific DOC apparatus in which a two horizontal line delay of the original color -television signal is required. First, the block diagram of Fig. 7 will be described, followed by the description of the corresponding detailed circuit diagram illustrated in Figs. 8a to 8h. In the embodiment of Fig. 7, a color television signal is received at an input terminal 90, in the form of consecutive digital samples at a frequency equal to three times the color subcarrier signal frequency.
The received signal is applied to input 91 of a two-way switch 52 and via the switch's output 93 to a first controlled delay line 54, providing one horizontal line delay less circuit delays designated ~ . The delayed color television signal V from output 115 of delay line 54 is applied via a second compensa-ting fixed delay line 56 providing a delay equal to ~ to a second input 92 of switch 52. Thus, a circulating memory circui-t 94 is formed by elements 52, 54 and 56, similarly as previously descrihed with respect to the embodiments of Figs. 2 and 5, respectively.

mg/` - 32 -s~
A control signal CB is applied to a control input 125 of the delay line 54, which is received at control terminal 124.
The CB control signal is similar to that described previously with respect to Figs. 2 and 5, respectively. The color television signal V from delay line 54 is also applied via a third compensating fixed delay line 113 having a delay designated T to a first input 101 of a signal differencing circuit 64, as a delayed signal V'. Signal V from the output of delay line 54 is also applied to input 104 of a digital filter 60. The digital comb filter described in the above-mentioned copending patent application SN 362,754 may be employed as filter 60. Fil-ter 60 separa-tes the luminance component from the color television signal, in a manner described in the copending application. The separated luminance component L' obtained at the output 105 of filter 60 is applied to a first input 107 of a second two-way switch 62 and it is also applied via a fixed two-clock cycle delay line 67 to a second input 108 of switch 62. An output 109 of switch 62 is connected to a first inpu-t 98 of a signal combining circuit 66. Thus, the delayed separated luminance component L is applied by switch 62 to signal combining circuit 66 either directly or delayed by additional two clock cycles indicated 2 ~. Switch 62 is controlled at its con-trol input 112 by a control signal designated HS/2 received at a control terminal 111. An inverted separated luminance signal component L' obtained at an inverting output 106 of filter 60 is applied to a second input 102 of the signal differencing circuit 64. Circuit 64 provides at output 103 a difference signal C' representing the separa-ted chrominance component obtained as a difference between the delayed composite color television signal V' and the delayed separated luminance component L', respectively applied to the first and second inputs of the signal .g/ ~ - 33 -1~7~S~
differencing circuit 64. In this preferred embodiment, -the differencing circuit 64 is implemented as a signal adder and the separated chrominance componen-t C' is obtained by adding the delayed composite signal V' and inverted separated luminance component L'.
The separated chrominance component Cl provided at output 103 of differencing circuit 64 is applied via a one-clock-cycle delay line 68 to one input 99 of signal adder 66. As previously mentioned, the other input 98 of signal adder 66 receives the separated luminance component L from the second swith 62. Signal adder 66 combines the received chrominance and luminance components into a composite color television signal at its output 100, which signal represents the color television dropout compensation signal. The dropout compensation signal is applied to a first input 95 of a third two-way switch 58. A second input 96 of switch 56 is coupled to receive the composite color television signal present at input terminal 90 via first switch 52, first controlled delay line 54 and second compénsating delay line 56. A control input 97 of switch 58 is coupled to receive a dropout compensation control signal DO via a delay line 53 providing a one horizontal line delay. The latter control signal is received at input terminal 110 when a dropout in the incoming color television signal at terminal 90 is detected, for example, by a conventional dropout detector (not shown) of the kind previously described. The dropout control signal at 110 is also applied directly to a control input 114 of the first switch 52. An ou-tput 127 of switch 58 is coupled via a further controlled delay line 126 -to an output terminal 70 of the dropout compensation circuit of Fig. 7.
Delay line 126 provides a one horizontal line delay and is controlled by signal CB applied to i-ts control input 128, mg/ - 34 -:~.7~

simultaneously with and in the same manner as previously described with respec-t to controlled delay line 54.
Now the operation of -the dropou-t compensa-tion circuit of Fig. 7 will be described. When a dropout in the composite color television signal is detected, for example, by a conventional dropout detector (not shown), a dropout control signal DO received at terminal 110 is applied to switch 52 and to switch 58 via delay line 53 providing a one horizontal line delay. Switch 52 closes the circulating memory circuit 94 and, consequently, the last received horizontal line of the color television signal immediately preceding the dropout, which has been stored in delay lines 54 and 56, circulates in the memory circuit 94 via input 92 and ouput 93 of switch 52 at a clock signal frequency equal to 3 x 3.58 MHz~10.74 ~Iz. The clock sianal which is utilized for clocking the respective circuit elements of Fig~ 7 is not shown in the block diagram for better clarity of representation, but it is shown in the correspond-ing detailed schematic diagram of Figs. 8a to 8h, which will be described hereinafter. Fil-ter 60 receives the composite signal V, delayed by one horizontal line period less circuit delay compensation, from the circulating memory 94 and separates the luminance component L' -therefrom in a manner described in the above referenced copending patent application SN 362,754. The separated luminance component is applied via switch 62 to signal combining circuit 66 which is implemented in the preferred embodiment as a signal adder. Switch 62, in response to -the control signal HS/2, alternatively applies the separated luminance component L', directly or delayed by two additional clock cycles in delay line 67, to signal combining circuit 66.

The control signal ~S/2 has a frequency of one-half of the horizontal line frequency. It is derived from the mg/ - 35 -5'~
horizontal synchronizing component of the color television signal coupled to terminal 90. The phase of signal HS/2 is con-trolled by signal CB received at terminal 124 to assure that the same phase-relationship of these two control signals will be maintained during the entire operation.
Thus, switch 62 is controlled by the signal HS/2 to alternatively apply, during consecutive horizontal lines, the luminance component signal L', undelayed and delayed by two clock cycles 2 ~, respectively, to input 98 of adder 66. On the other hand, as previously described, signal adder 64 receives both the delayed composite signal V' and the inverted luminance component L' and provides a separated chrominance component C' at its output 103. To compensate for the circuit delay ~ effected by processing -the separated luminance component in filter 60, signal V' is delayed by ~ in the third fixed compensating delay line 113. The separated chrominance component C' is delayed by one clock cycle ~ in delay line 68 and the delayed chrominance component C is combined with the above-described luminance component L in signal adder 66.
As will be appreciated from the foregoing description with respect to Figs. 3 and 4, alternately delaying and not delaying the separated luminance component L' by additional two clock cycles on the occurrence of alternate horizontal line periods, and delaying -the separated chrominance component by an additional one clock cycle during consecutive horizontal line periods, and combining such components in adder 66, results in the genera-tion of a composite dropout compensation signal, whose luminance component delay is modulated by - 1 clock cycle with respect to the chrominance component delay during consecutive horizontal line periods.
Thus, the previously mentioned feature of the invention related to decreasing the luminance component delay with ~,~
~f mg/~ - 36 -1~7~S~
respect -to the chrominance component delay of the resulting dropout compensation signal is achieved in the preferred embodiment of Fig. 7 by the above-described combination of circuit elements.
It will become apparent from -the above-description of -the block diagram of Fig. 7, that delay I compensates for the delay in the filter circuit 60 and -that delay for the combined delays ~ and delay ~ provided by delay line 68; thus, ~ = T + ~, when considering that circuits 64 and 66 have no significant circuit delays.
It will also become apparent with respect to Fig. 7 that in this particular preferred embodiment the controlled delay line 54 is coupled in the main composite color television signal path. Therefore, when no dropout compensation takes place, the incoming composite signal received at 90 is continuously delayed in delay lines 54 and 56 by one television line period, which delay is controlled by a clock signal that is synchronous with the color burst component contained in the incoming television signal. Thus, the original composite signal at the output 127 of switch 58 exhibits an undesired - 180 phase shift on alternative lines relative to the reference timing associated with the main composite color television signal path. To compensate for this effect, an additional delay line 126 providing a one horizontal line delay is coupled in the main color television signal path at the output 127 of switch 58. The loading and unloading of delay line 126 is controlled by the above~described con-trol signal CB
received at control terminal 124 and applied to control input 128 of delay line 126. Since the color television signal received by delay line 126 has been previously delayed by one horizontal line period in delay lines 54 and 56, and both delay lines 54 and 126, respectively are c ~ mg/ - 37 -~17~5~
controlled by the same signal CB, respective phase shifts of - 180 in opposite sense are effected on respective output signals of these controlled delay lines 54 and 126.
Consequently, these opposite phase shifts cancel, and no adverse phase shift is present in the output signal at output 70 of the dropout compensation circuit of Fig. 7.
In -the dropout compensator embodiment of Fig. 7, the dropout compensation signal at the output terminal 70 is delayed by three horizon-tal line perlods from the line it appeared at input terminal 90 to the time it appears at the output terminal 70 as the dropout compensation signal. This delay consists of the one horizontal line period delay resulting from the ini-tial passage through the memory circuit 9~ before the dropout being compensated is detected. After -the dropou-t is detected, the horizontal line is again circulated through the memory circuit 94 before the s~itch 58 receives and responds to the delayed control ~signal DO to couple the dropout compensation signal formed from the recirculated horizontal line to the output 127.
This adds a second one horizontal line period delay to the dropout compensation signal. The third one horizontal line period delay results form the presence of the delay line 126.
The three horizontal line delay is needed to satisfy the-specific requirements of a particular appara-tus in which this par-ticular embodiment of the invention is u-tilized.
However, the actual dropout compensation signal obtained at output 127 of siwtch 58 is still formed from -the last received original television signal line at input 90, substantially in the same manner as that previously described with respect to Figs. 2 and 5.
It is noted, however, tha-t the previously described respective embodiments of Figs. 2 and 5 do not have their respective controlled delay lines coupled in the main mg/ - 38 -5~
composite color television path and, -therefore, they do not exhibit an undesired phase shift such as provided by the embodiment of Fig. 7 during normal system operation when no dropout compensation is provided.
The detailed circuit diagram shown in consecutive Figs. 8a to 8h essentially corresponds to the previously described simplified block diagram of Fig. 7. To facilitate comparison, individual circuits in the detailed diagram corresponding to elements of the b]ock diagram are delineated by dashed lines and designa-ted by like reference numerals.
Similarly, connecting lines between -the circuits of the detailed diagram are designated by reference numerals corresponding to input/output designations of corresponding blocks of Fig. 7. For the purpose of complete disclosure, the integrated circui-t components shown in the preferred embodiment of Figs. 8a to 8h are designated by respective part numbers commonly used by manufacturers.
Specifically, the filter circuit 60, which is utilized to separate the luminance component from the composite color television signal and which is shown in consecutive Figs. 8d and 8e is similar to that disclosed in the above-indicated copending application SN 362,754.
It is understood, however, that a well known digi-tal comb filter may be utilized instead. As it will be seen ~rom the detailed circuit diagram of Figs. 8a to 8h, it is an advantage of the digital dropout compensation circuit of the present invention that all signal processing is provided in real time utilizing standard TTL (transistor~to-transistor logic) circuitry. The circuit of the above-indicated Figures is designed for dropout compensation in a color television signal recording and reproducing system where an NTSC color television signal is encoded in digi-tal form by sampling at a frequency equal to three times -the color ` mg/` - 39 -subcarrier frequency of the television signal, -that is, fsampl = 3 x 3.58 ~Iz ~ 10.74 ~z. The sampling signal is phase locked to the color burst component of -the subcarrier signal in a manner well known in the art. The sampling frequency is equal to the clock frequency as previously mentioned with respect to the description of Fig. 2.
Generally, for operation of the dropout compensator of the invention, the sampling frequency utilized to encode the composite analog color television signal, does not have to be -the same as the clock signal frequency utilized to synchronize the various elements of the dropout compensation circuit. The samples may be received and stored, for example, at the sampling frequency, and subsequently recovered at the clock frequency, while the latter frequency is utilized for synchronization of the circuit.
Now the preferred embodiment of the invention shown in the detailed circuit diagram of Figs. 8a to 8h will be described. In Fig. 8a, consecutive samples Sl, S2, S3, etc., of the digital color television signal are received at input 90 of the dropout compensator as 8-bit parallel data by a first set of inputs 91 of two data selector/multiplexers A24 and A34 of two-way switch 52.
These multiplexers also receive data at second input 92 from output 116 of delay line 56, shown in Fig. 8c. A
dropout control signal DO from a conventional RF envelope level dropout detector circuit (no-t shown) is received by the multiplexers at 114 via input 110 and flip-flop A16.
Flip-flop A16 is utilized for the common purpose to precisely clock the dropout con-trol signal. In normal operation, the multiplexers apply the input data 90 via flip-flop A23 to output 93. Generally, flip-flops similar to A23 are utilized throughout the entire circuit -to delay the mg/~ - 40 -s~
processed data by one clock cycle to assure precise data clocking. When the DO control signal at 110 is received, the output of multiplexers is switched from input 91 to input 92. The data from output 93 is fed to output 70 of the dropout compensator circuit via first controlled delay line 54 of Fig. 8b; second compensating delay line 56 of Fig. 8c; switch 58 of Fig. 8g; and a fur-ther controlled delay line 126 of Fig. 8g.
Delay line 54 of Fig. 8b comprises eight identical 4 x 256 bit random access memories of which six memories designated Bl, Bll, B31, B51, B61 and B81 are shown. Two groups of four memories each are utilized for receiving higher and lower order bits, respectively. The controlled delay line 54 has a length of delay equal to one horizontal line period of the color television signal less the compensating delay ~ provided by fixed delay line 56 of Fig. 8c coupled in the delayed color television signal path.
Delay line 56 is implemented by eight shift registers, of which four registers A51, A61, A52 and A82 are shown.
Flip-Flop ~41 at the output of delay line 54 is utilized to assure proper timing of the output data to achieve the desired delay. The delayed composite signal at output 115 is applied via fixed compensating delay line 56 to input 96 of switch 58 of Fig. 8g.
As shown in Fig. 8d, the data S1, S2, S3, etc., from output 115 of delay line 54, representing signal V, is also applied to one set of inputs 104 of filter 60.
As described in -the above-iden-tified copending application, filter 60 continuously provides an average value of three consecutive samples Sl, S2, S3. As shown in Fig. 8c, a sample Sl, applied via a portion of delay line 56, is obtained at output 117 thereof, where it has been delayed by one clock signal period to assure its proper timing for mg~ - 41 -~7~C~
addition with a sample S2 received one clock signal later.
The delayed sample, S2, is applied to a second se-t of inputs 104 of filter 60. Samples Sl and S2 are added in two 4-bit binary adders A33, A43 of Fig. 8d and -their sum Sl + S2 is delayed in flip-flop A53 by one clock signal in preparation for addition with the subsequently received sam~le S3 from output 115 of 54. The lat-ter summation is performed by two 4-bit binary adders A54, A44 and an output signal therefrom represents the sum S=Sl+S2~S3.
Signal S is fed through flip-flop A55 to assure proper timing for further processing. In this particular embodiment of the invention, an average sample value is obtained by dividing signal S by 3. The division by 3 is performed with a 0.13% accuracy by an approximation algorithm:

S ~ S + S + S

For the particular application of averaging the samples in the presently described preferred embodiment, the approximation algorithm is implemented in two steps as follows:

PS = 4 + 16 3 ~ PS ~ P16 These two steps are performed in the remaining portions of the circuit diagram of filter 60 shown in Fig. 8e as described below.
Two 4-bit binary adders A64, A65 of Fig. 8e receive the signal S at two se-ts of inputs, they shift the signal S
in the well known manner to effect a division and generate 4 at one of the sets of inputs and they provide a sum of mg~ - 42 -~ 7~S~
(S + 4). The output signal from the lat-ter adders is further shifted to obtain a divided ou-tput signal corresponding to (S + S4)/2. The latter output signal represents twice the partial sum PS defined above. The signal 2PS is applied to flip-flop A75 which supplies signal 2PS to two sets of inpu-ts of two 4-bi.-t binary adders A66 and A76. The latter adders shift the signal 2PS to obtain 2P6S at one set of inputs and they provide an output signal corresponding to (2PS + 216S)/2. This output signal represents S3 of the approximation algorithm indicated above. The obtained signal 3 corresponds to the average value output signal provided by filter 60 in accordance with the disclosure of the above-referenced copending application. The output signal of adders A66, A76 thus represents the chrominance-less color television signal, that is, the separated luminance component described hereinbefore with reference to Fig. 7. Signal S3 is applied to flip-flops A67 and A77, which provide both an output S/3, indicated L' at output 105, to input 107 of switch 62 in Fig. 8f and an inverted output signal (-S/3), indica-ted -L' at output 106 and applied to a first set of inputs 102 of adder 64 of Fig. 8f~ Adder 64 is implemented by -two 4-bit binary adders, A36, A46.
In this preferred embodiment, the compensating fixed delay line 113 shown in the block diagram of Fig. 7, is implemented by a portion of the fixed compensating delay line 56 at ou-tput 130 thereof, as i-t is shown in Fig. 8c. The thusly delayed composite color television signal from output 130 of delay line 56, indicated V', is applied to a second set of inputs 101 of two 4-bit binary adders A36, A46 of adder 64 in Fig. 8f. Adder 64 provides at output 103 an output signal indica-ted C', which represents the separated chrominance component, as it has been described , ---i~
.? mg/'. _ 43 _ ~.7~5~
before with reference to Fig. 7. Signal C' is applied via flip-flop A56 and A5 representing the compensating fixed delay line 68 to a first set of inputs 99 of two 4-bit binary adders A84, A85 of adder 66 in Fig. 8g. The separated delayed luminance component L is applied from the outputs 109 of multiplexers A87, A86, representing switch 62 in Fig. 8f, to the other set of inpu-ts 98 of adder 66. As described above, the separated luminance component L' from output 105 of filter 60 in Fig. 8 is applied to one set of inputs 107 of multiplexers A87, A86. The luminance component L', which has been delayed by delay line 67, implemented by flip-flops A68, A78 shown in Fig. 8f, is applied to the other set of inputs 108 of the multiplexers representing switch 62. Multiplexers A87, A86 of Fig. 8f are controlled at input 112 by the control signal HS/2 of 7.8 kHz, received at 111, which signal has been described with reference to Fig. 7. As it has been previously disclosed with respect to block diagrams of ; Fig. 7, in response to control signal HS/2, switch 62 applies to input 98 of signal adder 66 the separated luminance component L directly from output 105 of filter 60, or via the two-clock-cycle delay line 67, alternatively, on consecutive horizontal lines. Adder 66 of Fig. 8g combines the respective luminance and chrominance components received at its respective inputs 98, 99 into a composite color television signal, representing the dropout compensa-tion signal. Tha-t signal is applied, via re-timing flip-flop A89, to a first set of inputs 95 of switch 58 in Fig. 8g, which is implemented by multiplexers A73, A74.
- 30 On the other set of inputs 96 of mul-tiplexers A73, A74, an output signal from delay line 56 of Fig. 8c is received.
The outpu-t signal at 127 from swi-tch 58 is applied to delay line 126 which is shown as a bloc]c. This delay line is mg/J~ - 44 -~ ~ 7~S'2~

utilized in the specific embodiment o Figs. 8a -to 8h to eliminate the undesired 180 phase shift as previously explained with reference to Fig. 7. Delay line 126 provides a one horizontal line delay and is controlled by the control signal CB, simultaneously with and ln the same manner as the controlled delay line 54. Delay line 126 may be constructed utilizing random access memories similar to those of delay line 54 in Fig. 8b. The output signal of delay line 126 thus represents the output signal of the dropout compensation circuit of Figs. 8a to 8h provided at output terminal 70.
Switch 58 of Fig. 8g is controlled by the dropout control signal DO received at input terminal 110 in Fig. 8a and applied via output 55 of delay line 53 of Fig. 8a to control input 97 of switch 58.
Fig. 8h shows a memory address generator circuit 150 providing output signals at memory address lines Ao to A7 of a memory address bus AB, coupled to control the data flow through the respective delay lines 53, 54 shown in Figs. 8a and 8b, respec-tively. In Fig. 8h counters A2, A12, A22, B2, B12 and B22 are utilized to count the respective clock cycles corresponding to the actual delay provided by these delay lines. The diagram of Fig. 8h reveals the memory address generator 150 in sufficient detail, consequently, no further disclosure is necessary.
To provide a complete disclosure of -the detailed circuit, respective clock signals indicated 10.7 MHz and inverted clock signals indicated 10.7MHz utilized for clocking various circuit elements are shown in the detailed circuit diagram of Figs. 8a to 8h. These signals are derived in a well known manner, as described, for example, in the above-indlcated copending applica-tion.

mg~ ~ - 45 -In the foregoing specification, the preferred embodiments of the invention have been described with respect to a digital dropout compensation circuit, in which an NTSC composite color television signal is sampled at a frequency equal to three times the color subcarrier signal frequency, fsampl ~ 3 x 3.58 MHz = 10.74 MHz. As it will become apparent to those skilled in the art, the respective block diagram of Figs. 2, 5 and 7 could also be utilized for other digital as well as analog color -television signal systems, such as NTSC, PAL, PAL-M, etc. For example, if the dropout compensation apparatus of the invention is utilized in an analog color television signal system, it may be preferable to implement the controlled delay lines, for example, delay line 3 of Fig. 2, by conventional charge-coupled devices (CCD). As it is known in the art, such devices could be utilized as delay lines for delaying signals in analog form, while the information to be delayed may be clocked in and out of the delay line in response to a control signal, similarly, as it has been disclosed with respect to the above-described embodiments. At the same time, delay lines, such as 8 and 9 of Fig. 2, may be implemented by conventional analog delay lines. In the later case, delay line 8 would provide a desired amount of the analog signal delay substantially corresponding to the line-to-line offset of the color subcarrier signal, and advantageously delay line 9 would provide substantially twice that amount of delay to achieve a desired luminance component delay modulation with respect to the chrominance component delay, àS described above.
Generally, the invention wi-th respect to Fig. 2 may be utilized ln any digital color -television signal system where the sampling frequency is equal to an integral multiple of the color subcarrier signal frequency. For mg/` - ~6 -5i~
example, if an NTSC color television signal is sampled at a frequency equal to four -times the suhcarrier signal frequency, then, to achieve a desired dropout compensation signal, having a proper line-to-line phase of the chrominance component, for example, by the embodiment of Fig. 2, the original signal chrominance component samples would have to be displaced on consecutive television lines by plus or minus two sampling periods. Consequent]y, to reduce the luminance component displacement on consecutive lines, the delay line 9 of Fig. 2 would have to provide a four clock cycle delay 4 ~, while the delay line 8 would have to provide a two cycle delay 2 ~.
The above-disclosed invention is applicable also to PAL or PAL-M signal systems, since the respective con-trol signals, such as signal CB, HS and HS/2, respectively, in Figs. 2, 5 or 7 are frequency and phase locked to the incoming color television signal. It will be apprecia-ted by those skilled in the art that the so-called one-quarter cycle offset corresponding to the 90 degree phase shift occurring in the PAL subcarrier component during consecutive television lines may be compensated for in the dropout compensator of the present invention by applying the above control signals to the respective controlled delay lines of the above-indicated embodiments, whlch will be loaded and unloaded on consecu-tive lines synchronously with the control signals of the particular signal system utilized.
As it will become apparent to those skilled in the art, alternative e~bodiments similar to the disclosed detailed circuit diagrams of Figs. 8a to 8g, as well as alternative circuit elements in these embodiments, may be utilized to obtain the disclosed opera-tion oE the dropout compensator in accordance with the method of the present invention. For example, the differencing circuit 64 may be mg/~. - 47 -~7~
implemented as a subtracting circuit to which respective signals L', V' of the same polarity are applied. Similarly, known alternative circuit elements in -the summing circuit 66 may be utilized to obtain -the desired combination of the chrominance and luminance components. As an alternative, different means of obtaining the delay in delay lines ~4 may be utilized, such as shift registers, instead of the random access memories. Likewise, to obtaln division by 3 of the samples in filter circuit 60, read only memories may be utilized instead of the disclosed circuit elements implementing the approximation algorithm.
The individual circuit elements of all the above disclosed embodiments of the invention may be implemented by conventional, standard integrated devices.
While the invention has been shown and described with particular reference to preferred and alternative embodiments thereof, it will be understood -that variations and modifications in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

~ mg/ c - 48 -

Claims

I CLAIM:
1. A method of compensating color television signals for dropouts wherein a dropout interval occuring in an input color television signal is replaced by a dropout compensation signal derived from a previously occuring corresponding interval of the input color television signal including luminance and chrominance components defining consecutive horizontal lines of color television information; the steps comprising:
storing intervals of each horizontal line of the input color television signal without dropouts;
storing intervals of an immediately succeeding horizontal line of the input color television signal without dropouts in place of corresponding stored intervals of said each horizontal line, retaining in storage corresponding stored intervals of said each horizontal line in place of intervals of said immediately succeeding horizontal line of the input color television signal when dropouts occur in said immediately succeeding horizontal line;
separating the luminance and chrominance components of the stored color television signal;
adjusting the time of storage of the stored chrominance component of successive horizontal line intervals between a first time greater than and a second time less than an interval corresponding to one horizontal line to phase synchronize the stored chrominance component with the corresponding component included in the input color television signal;

adjusting the time of storage of the stored luminance component of successive horizontal line intervals

Claim 1 continued between a third time greater than and a fourth time less than an interval corresponding to one horizontal line to reduce the phase difference between the stored luminance component and the corresponding component included in the input color television signal;
combining the adjusted chrominance and luminance components to form the dropout compensation signal; and inserting the dropout compensation signal in place of the input color television signal when a dropout occurs in said input color television signal.
2. The method of Claim 1 wherein said input color television signal is a digital signal obtained by sampling the analog form of the color television signal with a sampling signal having a rate equal to an integral multiple of at least three times the frequency of the unmodulated color subcarrier frequency of the color television signal, said first time is greater than and said second time is less than said interval corresponding to one horizontal line by a first amount less than one cycle of said unmodulated color subcarrier frequency, and said third time is greater than and said fourth time is less than said interval corresponding to one horizontal line by a second amount less than one cycle of said unmodulated color subcarrier frequency.
3. The method of Claim 1 wherein the color television signal is sampled at rate of three times the frequency of the unmodulated color subcarrier frequency;
the intervals of a first and alternate subsequent horizontal lines of the input color television signal are stored for a first interval corresponding to one horizontal line plus one half cycle of the sampling signal prior to separating the chrominance and luminance components; the intervals of a second and alternate horizontal lines of the input color television signal are stored for a second interval corresponding to one horizontal line less two and one half cycles of the sampling signal prior to separating the chrominance and luminance components; the separated chrominance component of each horizontal line is stored for a third interval equal to one cycle of the sampling signal whereby the storage of the chrominance components of consecutive horizontal lines are adjusted by said first and second times respectively; and the separated luminance component of said second and alternate horizontal lines is stored for a fourth interval equal to two cycles of the sampling signal whereby the storage of the luminance components of consecutive horizontal lines are adjusted by said third and fourth times, respectively.
4. The method of Claim 1 wherein the color television is sampled at a rate of three times the frequency of the unmodulated color subcarrier frequency; the input color television signal is first separated into chrominance and luminance components; the separated chrominance component of a first and alternate subsequent horizontal lines are stored for a first interval corresponding to one horizontal line plus one and one half cycles of the sampling signal; the separated chrominance component of a second and alternate subsequent horizontal lines are stored for a second interval corresponding to one horizontal line less one and one half cycles of the sampling signal whereby the storage of the chrominance components of consecutive horizontal lines are adjusted by said first and second times, respectiviely the separated luminance component of the first and alternate subsequent horizontal line intervals are stored for a third interval plus one half cycle of the sampling signal and the separated luminance component of the second and alternate subsequent horizontal line intervals are stored for a fourth interval corresponding to one horizontal line interval less one half cycle of the sampling signal whereby the storage of the luminance components of consecutive horizontal lines are adjusted by said third and fourth times, respectively.

5. A dropout compensator for color television signals including luminance and chrominance components defining consecutive horizontal lines of color television information in which a dropout detection signal is generated upon the occurrence of a dropout interval in an input color television signal for controlling the replacement of said dropout interval with a corresponding interval that previously occurred in the color television signal; comprising:
memory means having an input for receiving said color television signal, said memory means having a storage capacity sufficient to store at least one horizontal line of said color television signal;
memory control means operatively associated with the memory means for effecting storage of intervals of each horizontal line received at the input of said memory means in place of corresponding intervals of an immediately preceeding horizontal line received at said input of said memory means;
first switch means for coupling the input color television signal to the input of the memory means, said first switch means responsive to said dropout detection signal to decouple said input color television signal from said input of said memory means;
means for separating the luminance and chrominance components of the stored color television signal;
means for adjusting the time of storage of the stored chrominance component of successive horizontal line intervals, said time of storage of the chrominance component adjustable between a first time greater than and a second time less than an interval corresponding
Claim 5 continued to one horizontal line to phase synchronize the stored chrominance with the corresponding component included in the input color television signal;
means for adjusting the time of storage of the stored luminance component of successive horizontal line intervals, said time of storage of the luminance component adjustable between a third time greater than and a fourth time less than an interval corresponding to one horizontal line to reduce the phase difference between the stored luminance component and the corresponding component included in the input color television signal;
means for combining the adjusted chrominance and luminance components to form a composite color television dropout compensation signal; and a second switch means for selectively coupling the input color television signal and the dropout compensation signal to an output, said second switch means responsive to the dropout detection signal to couple the dropout compensation to said output, and said second switch means coupling the input color television signal to the output in the absence of the dropout detection signal.

6. The dropout compensator of Claim 5 wherein said input color television signal is a digital signal obtained by sampling the analog form of the color television signal with a sampling signal having a rate equal to three times the frequency of the unmodulated subcarrier frequency of the color television signal; the memory means includes a first memory having said input coupled to said first switch means, a second memory having an input coupled to receive the separated chrominance component and a third memory having an input coupled to receive the separated luminance component, said second memory providing a first delay of less than one cycle of the sampling signal and said second memory providing a second delay two cycles of the sampling signal, said first memory responsive to the memory control means for storing a first and alternate subsequent horizontal lines of the input color television signal prior to coupling to the luminance and chrominance separating means for a first interval corresponding to one horizontal line plus one half cycle of the sampling signal and for storing a second and alternate subsequent horizontal lines of the input color television signal prior to coupling to the luminance and chrominance separating means for a second interval corresponding to one horizontal line less two and one half cycles of the sampling signals;
and further comprising a third switch means having one input coupled to the output of the third memory and second input coupled to receive the separated luminance component from the luminance and chrominance separating means, said third switch means responsive to the memory control means to couple to the combining means the luminance component
Claim 6 continued received from the luminance and chrominance separating means during said first and alternate subsequent horizontal lines and to couple to the combining means the luminance component received from the third memory during said second and alternate subsequent horizontal lines.
7. The dropout compensator of Claim 5 wherein the input color television signal is first coupled to the luminance and chrominance separating means; and said memory means includes a first memory and a second memory each having a storage capacity of at least one horizontal line, said first memory coupled to receive the separated chrominance component and said second memory coupled to receive said separated luminance component, said first memory responsive to the memory control means to provide said first and second times of storage for the chrominance component, said second memory responsive to the memory control means to provide said third and fourth times of storage.
8. A method of compensating an input color tele-vision signal for dropouts by replacing said dropouts with previously occurring portions of the input color.
television signal not containing dropouts, the input color television signal having consecutive horizontal lines of video information including luminance and chrominance components, each horizontal line of a selected horizontal line interval, the chrominance component modulated on a carrier signal of known fre-quency; the steps comprising:
transmitting the luminance and chrominance com-ponents of the input color television signal not contain-ing dropouts of each horizontal line of said input color television signal through a delay to provide a first inter-val of delay for the luminance component and a second interval of delay for the chrominance component, adjusting -the first interval of delay for different horizontal lines of the input color television signal to times greater than and lesser than the horizontal line interval to maintain any phase difference between the delayed luminance component and the luminance component included in the input color television signal less than one half cycle of the carrier signal;
adjusting the second interval of delay for different horizontal lines of the input color television signal to times greater than and lesser than the horizontal line interval to maintain phase coherence between the delayed chrominance component and the chrominance component included in the input color television signal and inserting the delayed luminance and chrominance components in the input color television signal in place of a dropout occurring therein.
9. The method of claim 8 wherein the luminance and chrominance components included in the input color tele-vision signal are combined to define a composite video information signal, and further comprising the steps of:
separating the luminance and chrominance com-ponents before transmitting them through a delay, said separated luminance and chrominance components trans-mitted through separate delays; and combining the separated and delayed luminance component and the separated and delayed chrominance com-ponent to form a delayed composite video information signal, the delayed composite video information signal inserted in the input color television signal.
10. The method of claim 8 wherein the luminance and chrominance components included in the input color television signal are combined to define a composite video information signal, the transmitting step includes transmitting the luminance component through a first delay and a following second delay and transmitting the chrom-inance component through the first delay and a following third delay, the luminance and components are combined during their transmission through said first delay, and the adjusting steps include adjusting the first and second delays with the third delay remaining fixed; and further comprising the steps of:
separating the luminance and chrominance compon-ents after transmission through said first delay, said separated luminance component transmitted through the second delay, and said separated chrominance component transmitted through the third delay; and combining the separated luminance component and separated chrominance component after transmission through the second and third delays, respectively, to form a delayed composite video information signal, the delayed composite video information signal inserted in the input color television signal.
11. The method of claim 10 wherein the input color television signal in a digital signal obtained by sampling an analog color television signal at times determined by a sampling signal having a rate equal to three times the frequency of the carrier signal, the first delay is alternately adjusted on alternate horizontal lines of the input color television signal between a first selected time delay plus one and one-half cycle of the carrier signal and the first selected time delay minus one and one-half cycles of the carrier signal, the second delay is alternately adjusted on alternate horizontal lines of the input color television signal between a second selected time delay and the second selected time delay plus two cycles of the carrier signal, and the third delay has a time delay equal to the second selected time delay plus one cycle of the carrier signal.
12. The method of claim 11 wherein consecutive hori-zontal lines of the input color television signal contain dropouts, and the first selected time delay is adjusted by an additional time delay equal to one cycle of the carrier signal.
13. The method of claim 8 wherein consecutive hori-zontal lines of the input color television signal contain dropouts, and each of the first and second intervals of delay are adjusted a further interval of delay equal to one cycle of the carrier signal for each of said con-secutive horizontal lines of the input color television signal containing a dropout.