NL8101437A - METHOD AND APPARATUS FOR LOSS COMPENSATION FOR COLOR TELEVISION SIGNALS. - Google Patents

Description

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VO 1726

Method and device for drop-out compensation for color television signals.

The invention relates to a method and apparatus for drop-out compensation for color television signals, in which both the luminance and chrominance components are delayed by substantially one horizontal control period, which method and device are suitable for use in both analog and digital signal systems. As is known, television signal drop compensators are used to replace a missing portion of the information signal that has "failed" due to an unpredictable instantaneous system malfunction. When 10 e.g. the television signal is recorded and then reproduced from a recording medium, failure due to very small defects of the recording medium may occur. When such dropouts occur in the television signal, they disturb the picture visibly. Therefore, dropout compensators are used to eliminate the influence of dropouts on the observer.

An overview of known television drop-out compensators is found in U.S. Patent Application Serial No. 88719, which discloses a digital color television signal drop-out compensator. Generally, the known dropout compensators use an RF envelope level detector, which controls the amplitude level of the modulated television signal carrier to detect dropouts in the television signal. A delay line is used to continuously delay the incoming television signal. When a dropout is detected in the original signal, the delay signal is supplied as a dropout compensation signal to replace the missing portion of the television signal information. More specifically, a switch in the color television signal path is controlled such that the incoming color television signal resp. the delayed drop-out signal is applied in response to a control signal from the drop-out detector. The color television signal is delayed by one horizontal control period and the chrominance component is adjusted so that its phase is reversed with successive television lines. Them obtains e.g. phase adjusting the separated chrominance component of the dropout compensation signal by delaying the chrominance component by another television control period or inverting the separated chrominance component in successive television lines depending on the particular color television signal system, as known per se.

However, there is a major drawback with the above type of failure compensation, which will be explained below.

The original color television signal is split into a 15 luminance and a chrominance component and each component is resp. delayed and processed in a separate signal path. Thereafter, the separately processed signal components are combined together again to be used as a dropout compensation signal. When the dropout is longer than one horizontal line-20 period, the previously processed and recombined composite signal is re-split in the manner described above and processed with each subsequent dropout compensation line. Thus, line-to-line distortion and progressive degeneration of the dropout compensation signal occur. Therefore, when using the above-described known drop-out compensation method, the resulting drop-out compensation signal may become unacceptable after a few consecutive lines. ·

The object of the invention is therefore to provide a method and device for drop-out compensation of composite color television signals, wherein the above drawbacks do not arise.

A further object of the invention is to provide a color television signal drop compensation method and apparatus in which successive lines of the dropout compensation signal are obtained from the same portion of the original color television information signal, which is immediately supplied to the failure precedes.

Another object of the invention is to provide a drop-out 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 successive lines of a drop-out compensation signal are taken and which stored original signal remains unchanged. while the failure compensation takes place.

Yet another object of the invention is to provide a color television signal drop compensation method and apparatus, in which both the luminance and chrominance components of the original signal are delayed by substantially one television line interval.

The invention further contemplates providing a method and apparatus for color television signal drop compensation which is suitable for use in both analog and digital color television signal systems.

Another object of the invention is to provide a method and apparatus for drop-out compensation of composite color television signals suitable for use in known television signal systems, such as NTSC, PAL, PAL-M, etc.

A further object of the invention is to provide a method and apparatus for drop-out compensation of composite color television signals, which is suitable for use in embodiments in which the signal is sampled at a frequency equal to an integer, greater than 2, of the color subcarrier frequencies.

To this end, the invention provides a method in which both the chrominance and luminance components of the assembly store the color television signal for a period equal to one horizontal control period, and circulate the stored information in response to a dropout signal.

The actual delay length of the chrominance component is controlled by the phase of the color burst signal to provide a delayed chrominance component that is in phase with the color burst component during successive horizontal control periods. The actual delay length of the luminance component is controlled to provide a luminance component which is synchronous with the horizontal control synchronization component of the composite color television signal during successive horizontal control periods. The respective delayed chrominance and luminance components are combined to form a composite dropout compensation signal, which in turn is used to replace the composite color television signal when a dropout is found to be present.

The color television signal drop compensator of the invention includes circulation storage means to delay both the luminance and chrominance components of an incoming composite color television signal by substantially one horizontal control period in response to a dropout control signal. First controllers control in response to the color burst. component the actual delay of the chrominance component to provide a delayed chrominance component, which is in phase with the color burst component during successive horizontal control periods ;; Second controllers in response to the horizontal control synchronization component control the actual delay of the luminance component to provide a delayed luminance component, which is synchronous with the horizontal line synchronization component. Signal combiners serve to combine the respective delayed luminance and chrominance components to provide a composite dropout compensation signal. Switches selectively apply the incoming color television signal or composite dropout compensation signal to an output of the dropout compensator in response to the dropout control signal.

The invention will be explained in more detail below with reference to the drawing. In these drawings: Figures 1a and 1b show a preferred method for providing a dropout compensation signal according to the invention; 8101437-5 - Fig. 2 a functional block diagram of a preferred embodiment according to the invention; Figures 3a and 3b show another preferred method according to the invention; Fig. 4 shows the operation of the device according to Fig. 2; Figure 5 is a functional block diagram of another preferred embodiment of the invention; Fig. 6 shows the operation of the device according to Fig. 5; FIG. 7 is a functional block diagram of yet another preferred embodiment of the invention; and Figures 8a-8h show successive parts of a detailed diagram corresponding to the block diagram of Figure 7.

An example of a preferred drop-out compensation method according to the invention will now be described with reference to Figures 1a and 1b. In Fig. 1a, there is found a sine wave W1, which represents a color subcarrier signal waveform present in the chrominance component of a composite color television signal.

The waveform W1 includes successive samples 1A, 2A, 3A, etc. taken at equidistant sampling periods, which can be obtained by sampling the original color television signal. In this particular example, the above samples are obtained by sampling a composite NTSC color television signal at a frequency equal to three times the color subcarrier signal frequency, i.e.

25 at 3 x 3.58 MHz = 10.74 MHz. The samples obtained can be encoded in digital form by an analog-digital encoder using, e.g. pulse code modulation iPCM), each individual code or sample corresponding to a certain amplitude value of the original analog signal at a given sampling time. For example, the subcarrier waveform W1 is indicated as occurring during a given television control interval A1. It is known in an NTSC television signal system that a subcarrier W2 of a subsequent television control interval B1 has a phase opposite to that of W1, as shown in FIG.

35 la. Therefore, if a failure occurs e.g. after the original television line A1 has been received and delayed by one television line period 8101437 * * - 6 - for subsequent use as a dropout compensation signal replacing the "dropped out" line B1, the delayed line A1 would cause an unwanted phase shift of 180 ° Therefore, samples 1A, 2A, 5 3A etc. of the delayed W1 signal must be shifted over 1s sampling interval to obtain the same phase as that of the corresponding samples 2B, 3B, etc. of the waveform W2 , as shown in Fig. la. Therefore, for example, sample IA should be compared to the corresponding sample 2B and correspondingly, sample 2A to sample 3B, etc.

shifted with ls sample interval.

In the preferred method of the invention, the above-indicated phase shift of the color subwave signal on successive lines is obtained by alternately increasing or decreasing the delay of one horizontal line of the television signal with a delay corresponding to 1s sampling period. The latter is found in FIG. 1A, which indicates that the sample 3B of line B1 is obtained by delaying the sample 2A of the immediately preceding original television line 20 A1 by one horizontal control period, augmented by Is sampling period. A dotted line CH1, which connects corresponding samples 3B and 2A, illustrates this. Fig. 1b shows the subcarrier W2 of line B1 followed by the waveform W3 of a subsequent line A2. Fig. 1b illustrates an example, in which line B1 is the last received original television signal line and line A2 is the first drop-out compensation line. As can be seen from Fig. 1b, the sample IA of the subcarrier signal waveform W3 is obtained by delaying the sample 2B of the waveform W2 by one horizontal control period reduced by a time interval corresponding to Is sample period. Dashed line CH2, which connects corresponding samples IA and 2B, indicates this.

However, when the dropout compensation method described above is used, both the chrominance and luminance components of the dropout compensation signal are shifted by steek 8101437 i * - 7 sample period from the previous original color television signal line. As is known, such a phase shift of the chrominance component is no objection since it is essential to maintain the line-to-line phase of the chrominance component samples as close as possible to the required phase in order to obtain a good quality color signal for drop-out compensation. On the other hand, the displacement noted above is inconvenient for the luminance component, for which it is essential to maintain the smallest horizontal line-to-10 line displacement of samples on the television screen relative to the original signal.

In this respect, it is pointed out that in abbreviation "'failure compensation" "will hereinafter be referred to as" DOC "and" failure "with DO".

To eliminate the drawback discussed above, the preferred drop compensation method according to the invention provides the line-by-line adjustment of the luminance component displacement described below.

When the delay of one horizontal line of the original television signal with 1 sample period is increased, for a dropout compensation, as discussed above with reference to Fig. 1a, the luminance component delay is reduced by 1 sample period. And therefore, the horizontal displacement of the luminance component sample from a corresponding sample of a previous original television signal line from 15 sample period is reduced to half a sample period. This is indicated in Fig. 1a by the dotted line L1, which connects corresponding samples 3B and 3A. Dp becomes an analogous way to obtain the above reduction in the luminance component displacement, in the case where the delay of one horizontal line of the original television signal is decreased by 11 sample period, as described above with reference to Fig. 1B, increases the luminance component delay by one sampling period.

The latter is shown in Fig. 1b by the dotted line L2, which connects 8101437 * i - 8 - corresponding samples IA and 1B. It can be seen from Figure 1a that the luminance component of the sample 3B of the dropout compensation rule B1 is obtained by delaying the sample 3A of line A1 by one horizontal control period increased by only half a sample period, as shown by line L1. Similarly, in Figure 1B, it is indicated by the line L2 that the luminance component of the sample IA is obtained by delaying the sample 1B of line B1 by one horizontal control period less only half a sample period. In either case, however, the delay of the respective chrominance components remains unchanged, i.e., displaced by the sampling period, as desired and as already explained above.

More particularly, the above features of the preferred method of the invention are obtained as follows: One horizontal line of the original composite color television signal is continuously stored in a memory. The delay length of the stored composite signal is controlled in response to the line-before-control phase of the color burst component 20 of the original color television signal. The resulting delayed composite signal is split into its luminance and chrominance component, and the delay length of the luminance component is modulated in opposite direction to the delayed chrominance component by an integer number of sampling periods. With respect to the example described above in Figs. 1a and 1b, the composite color television signal is delayed by one horizontal control period, which delay is modulated with a sample sampling period, corresponding to half a color subcarrier signal period, on successive lines. . In addition, the delay length of the separated luminance component is modulated line by line with + 1 sample period, opposite to the modulation of the delayed composite color television signal, in order to reduce line-by-line luminance component displacement.

8101437 φ - 9 -

To illustrate the above, a preferred embodiment of a device according to the invention will now be described with reference to the block diagram shown in Figure 2. At the input terminal 12, a composite color TV-5 signal is received, which is applied to the first input 20 of a first two-way switch 1. In this particular example, the television signal is received in digital form, e.g. obtained by encoding the color television signal with a known NRZ code, as already mentioned with reference to Figs. 1a and 1b. A control signal indicating the presence of a failure is applied to a control terminal 23 e.g. received from a normal failure detector not shown.

A suitable dropout detector may be of the conventional carrier wave control type, which detector provides a control signal when the RF envelope of the modulated television signal dropout is below a predetermined level, such as e.g. is described in AVR-2 Videotape Recorder, Theory of Operation, Catalog No. 1809179-01, November 1977, Ampex Corporation, pp. 5-31 to 5-33.

The control terminal 23 is coupled to a control input 24 of the first switch 1 and further to the control input 29 of a second switch 2. The output 25 of the switch 1 is coupled to an output terminal 13 of the failure compensator circuit and to the first input 26 of the the switch 2. The output 27 of the switch 2 is coupled via a controlled delay line 3 and a compensating fixed delay line 4 to a second input 28 of the switch 2. The elements 2, 3 and 4 together form a circulation memory circuit 44, which will be explained in more detail later. A control terminal 30 is coupled to a control input 31 of the controlled delay line 3. The output 32 30 of the 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 differential circuit 7. The compensating delay lines 4 and 6 are resp. used to compensate for chain delays in the color television signal path, as will be described later. An output 34 of the filter 53 is coupled to a second input 36 of the differential circuit 7, as well as to a first input 37 of a third two-way switch 10, and also via a fixed delay line 9 to a second input 38 of the switch 10. A control terminal 43, which receives a control signal HS / 25, is coupled to a control input 44 of the third switch 10. An output 39 of the switch 10 is coupled to a first input 40 of a signal combination circuit 11. An output 45 of the signal difference circuit 7 is coupled to a second input 41 of the circuit 11 via a fixed delay line 8. An output 42 of the signal combination circuit 11 is coupled to a second input 21 of the first two-way switch 1.

It should be borne in mind that the above-described preferred embodiment of FIG. 2 as well as the respective embodiments of FIGS. 5 and 7 to be described later represent all of the respective digital dropout compensators of the invention in which digital information is processed at high speed. Therefore, the various elements depicted in these respective functional block diagrams can be designed as normal digital circuits, in which the high-speed information is accurately clocked at the sampling frequency, equal to three times the color subcarrier signal frequency ie at 3 x 3.58 sf 10, 74 MHz, while the clock signal in frequency and phase is locked to the color subcarrier component of the television signal from which samples are taken. Therefore, the sampling frequency and the clock frequency will always be discussed below. For the sake of simplicity, the clock signal path is not shown in the figures discussed above, but it is found in the detailed diagram of Figures 8a-8h, corresponding to the block diagram of Figures 7, which detailed diagram will be discussed later. wrote.

The operation of the preferred embodiment according to the invention shown in block diagram form in FIG. 2 will now be explained. A digital NTSC color television signal in the form of discrete information, which represents successive samples, is continuously received at the input terminal 12 and is fed to the first input 20 of the switch 1. When the system is operating normally, ie no failure of the incoming signal is detected, the switch 1 is in its first position, as shown, receiving the input signal at 20 and the signal at the output terminal 25 at the output terminal 13 of the failure compensator is applied and therefore the signal is also applied to the controlled delay line 3 via the input 26 and the output 27 of the switch 2. The delay line 3 has a delay length, equal to one horizontal control period, less chain delays in the color television signal path, as will be discussed later.

The delayed composite signal from the delay line 3 is applied to the filter 5, e.g. of the type described in the above-mentioned U.S. Patent Application 15 or which filter may be in the form of a known digital comb filter. The filter 5 separates the luminance component from the composite color television signal in a known manner. The separated luminance component occurring at the output 34 of the filter 5 is applied to the input 36 of the differential circuit 7. At the other input 35 of the circuit 7, the composite color television signal is output from the output 32 of the delay line 3 via the compensating fixed delay line 6 supplied. The difference circuit 7 supplies at its output 45 a difference signal of the two signals received at their respective inputs. The resulting difference signal represents the separated chrominance component of the color television signal. The delay line 6 compensates for the chain delay provided by the filter 5 in order to eliminate an undesired relative phase shift in the respective signal paths of the signals processed successively in the difference circuit 7.

In the known relationship of the color subcarrier signal frequency fgc and the horizontal control frequency f of NTSC signals f »227.5 f ^, in this particular embodiment according to the invention a non-integer number of samples becomes equal to 3 x 227 .5 * 682.5 clock periods obtained within one horizontal control period. For clarification and simplification of the explanation, the following description will not take into account a compensation of chain delays provided by the delay line 3, however these will be explained later. In this regard, the controlled delay line 3 will be considered a line with a fixed delay length, equal to one horizontal control period, represented by 682.5 clock periods. Feeding and discharging the samples to and from the delay line 3 is controlled by the control signal CB received on the terminal 30, which signal is synchronous with the color burst component of the color television signal during each horizontal line. The latter control signal is applied to the control input 31 of the delay line 3; the signal is derived in a known manner from the color burst synchronization component of the incoming television signal. As already mentioned, in this particular embodiment, one period of the color burst signal corresponds to three sampling periods, equal to three clock periods. Therefore, the relative line-by-line phase shift of 180 ° of the color burst component represents a delay of + 1 | sample periods 20 for i.e. + Ιέ clock periods. Therefore, the controlled delay line 3 provides alternating delays of the composite color television signal, equal to 882.5 + 1.5 = 684 clock periods and 682.5-1.5 681 clock periods on successive lines. The latter operation can be described as a modulation of the fixed delay length of the composite color television signal stored in the delay line 3 during successive television control periods by the phase of the color burst component. It is clear that the average signal delay during a number of consecutive lines approaches 682.5 clock periods, which is equal to the original period of one horizontal line.

From the above description, it follows that the delay line 3 of FIG. 2 is controlled by a control signal CB synchronously with the color burst component, which signal is received at the terminal 30 to provide a delayed composite color television signal whose color subcarrier component is 81 01 4 37 - 13 - is in phase during each successive line with the color burst component * as detailed above with reference to Figs. 1a and 1b.

As also described with reference to Figures 1a and 1b, it is desirable that the luminance component samples of the dropout compensation signal of the invention be processed to minimize the horizontal displacement of respective sample positions on successive lines of the television screen. to bring. The line-by-line setting 10 of the luminance component delay provided by the device of Figure 2 to achieve the above will now be described. As explained above, in this preferred embodiment, the luminance component in the filter 5 is separated from the composite signal with a modulated delay. The delay length of the delayed separated luminance component is further modulated by a + +1 clock period in the opposite direction to the above-described modulation of the composite color television signal delay. To this end, the delayed separated chrominance component at the output 45 of the difference circuit 7 is delayed by one more clock period by the constant delay line 8. At the same time, the delayed separated luminance component at the output 34 of the filter 5 is delayed by another two clock periods during alternate television control periods by the fixed delay line 9. The separated delayed luminance component from the filter 5 is supplied directly to the first input 37 of the two-way switch 10, while the component is also supplied via the further delay line 9 to the second input -38 of the switch 10. The switch 10 is controlled by the control signal HS / 2, which is received on the terminal 43 and has a frequency equal to half the horizontal control frequency. The signal HS / 2 is taken from the horizontal line synchronization component of the incoming color television signal received at the input terminal 12. In the respective preferred embodiments of the invention described herein, the respective control signals 81014 3 7 - 14 -

HS / 2 in frequency and in phase with the horizontal control synchronization component of the incoming color television signal and also locked with the phase of the color burst component. During the dropout compensation, when the composite television signal is not received, the respective control signals CB, HS

or HS / 2 in synchronism with the respective synchronizing components of the missing television signal generated using a flywheel signal generator, not shown, the signal being locked in frequency and phase with the color television signal. From the above, it can be seen that the resulting delay of the luminance component is modulated with 1 clock period delay relative to the chrominance component delay. Because of this, the delay length of the luminance component of the dropout compensation signal on successive horizontal lines 15 is adjusted in response to the horizontal line synchronization component so as to adjust the. minimize horizontal line-by-line shift of samples during drop-out compensation.

The respective delayed luminance and chrominance components are combined in the adder 11 and the combined signals at the output 42 of the adder 11 represent the composite dropout compensation signal applied to the input 21 of the first switch 1. The latter signal is continuously present to be used for dropout compensation in response to a dropout compensation control signal DO received at control terminal 23, as explained above.

When a control signal DO is received at the terminal 23, which indicates that there is a failure in the television signal coming at 12, the switch 1 is influenced in such a way that it switches from input 20 to 21, while the switch 22 from 26 to 28 is switched. Therefore, the switch 1 will supply the output terminal 13 with the dropout compensation signal received at the input 21 of the switch 35, which signal is supplied by the circuit of FIG. 2, as described above 8101437-15. On the other hand, the switch 2 will close the circulation memory circuit 44 and thus circulate the last received line of the television signal information immediately prior to the failure, this signal being stored in delay lines 3 and 4. In this connection, the above-mentioned original color television signal line will circulate in memory 44 until the dropout is eliminated and the control signal DO is interrupted at 23. During the dropout compensation, the output signal at 32 from the memory IQ 44 is processed by the dropout compensator circuit of FIG. 2 in the manner previously described instead of the incoming color television signal.

As described above, the delay length of the controlled delay line 3 is decreased from the previously considered one horizontal line period to compensate for chain delay in the path in which the composite signal is processed. Therefore, if Δ is the delay provided by the filter 5 in the path of the separated luminance signal, and £ is the additional delay of one clock period, which is present in 2Q both the path of the separated luminance signal and the separated chrominance signal. , it appears from the block diagram of FIG. 2 that to obtain a total delay length equal to one horizontal control period of the composite DOC signal, the above-described modulation of the delay by the delay time is not taken into account. respective control signals, the delay of delay line 3 should be decreased by Δ + £. Similarly, from the above, to provide a memory 44 whose delay line equals exactly one horizontal control period, it is necessary to use the combined delay -Δ + £ in the form of a constant delay line 4, as indicated between the output 32 and the input 27 of the delay line 3.

As can be seen from the above, an important advantage of the invention is that successive lines of the dropout compensation signal are taken from the same portion of the original color television signal immediately prior to the dropout.

A further important advantage is that the composite signal is stored in the circulation memory in the original form of the signal and remains unchanged during the line-by-line processing of the signal components during the entire drop-out compensation. Therefore, no deterioration of the resulting dropout compensation signal occurs, as is the case with the prior art dropout compensators. At the same time, each sample of the dropout signal chrominance component is processed to have the same phase as that of a corresponding sample of the original television signal from which the dropout signal is formed, while the dropout signal luminance component is processed to minimize minimal horizontal displacement sampling of successive lines. Since the above-described example relating to the operation of the block diagram of FIG. 2 considers a sampling rate three times greater than the color subcarrier signal frequency, there is a line-by-line displacement of the dropout compensation signal sample, equal to 1.5 sampling periods for the chrominance component and just 0.5 sampling periods for the luminance component. From the above, it can be seen that the above-described respective line-to-line displacement of the samples achieves the previously described objectives associated with a good quality dropout compensation signal.

The above operation of the device of FIG. 2 is shown in FIG. 4, where the line-by-line displacement of the luminance and chrominance component samples is indicated at 30 consecutive lines of the DQC television signal. A last received original television signal line A1, immediately prior to the failure, includes successive samples 2A, 3A, 4A, 5A, etc. Fig. 4 shows that samples 2B, 3B, 4B, etc. of the first DOC line B1, as well as all subsequent odd DOC lines 35 B2, B3, etc., from the original line A1 are obtained in 81014 3 7-17 - a manner as described above with reference to Fig. 1a. For better comparison, corresponding samples in Figures 1a and 4 have the same references. However, it can be seen from FIG. 4 that the DOC chromance component samples 5 on the second DOO line A2 and all subsequent even DÜC lines A3, A4, etc., are obtained by matching the chrominance component samples of the original line A1 with exactly one horizontal line period. to slow down. Therefore, the respective chrominance components of the samples 3A, 4A, etc., on even DOC lines A2, 10 A3, etc., have moved in phase with that of the original line A1 but over 1.5 sampling periods relative to a immediately preceding odd DOC line. On the other hand, the luminance component samples of even DOC lines A2, A3, etc., have been shifted by one sampling period from the original line 15 A1 but shifted only by 0.5 sampling periods with respect to an immediately preceding odd DOC line . As a result of the failure compensation method described above in FIG. 4, a line-by-line displacement pattern of sample components is obtained, lines CH2, L2; CH3, L3j CH4, L4j etc., which connect, intersect corresponding chrominance and luminance component samples of adjacent DOC lines. This pattern provides the desired respective vertical line-by-line displacement of + 1.5 sampling periods of the chrominance component and + 0.5 sampling periods of the luminance component.

The above preferred method of the invention for providing a delayed luminance component of the composite dropout compensation signal in successive television lines is shown in Figures 3a and 3b. In FIG. 3a, a waveform M1 represents a portion of the luminance component of an original color television signal line A1 received at terminal 12 by the dropout compensation circuit of FIG. 2 immediately prior to a dropout. The samples 1A, 2A, 3A, etc., of the waveform M1 are obtained by taking samples of the color television signal at a frequency equal to three times the 8101437 -18 color subcarrier signal frequency, as already described above. Considering the above-described method, which serves to provide a dropout compensation signal luminance component by the apparatus of FIG. 2, the luminance component of the first dropout compensation signal line B1 following the original line A1 of the television display is shown in FIG.

3a represented by M2. It turns out that the waveform M2 is a replica of the original waveform M1 with the exception of the samples 1B, 2B, 3B etc. of M2, which over half-test period in one direction e.g. have shifted to the right with respect to samples IA, 2A, 3A, etc. of waveform M1.

However, the waveform M3 of the next line A2, which waveform is a replica of the original waveform M1, has been shifted by half of the sample B1 over M2 from the line B1 but with respect to the original waveform M1 of the line 1A by shifted one sample period, as shown by the location of samples 2A, 3A, 4A, etc. of M3 relative to the samples of previous lines B1 resp. A1. The latter effect does not object to the observer since only a displacement of half a sampling period in horizontal direction between respective samples is seen on successive lines. The above method allows to form a composite dropout compensation signal whose chrominance component samples are shifted horizontally in one direction, while the luminance component samples thereof are shifted horizontally in a direction opposite to that of an on-screen color television signal line. This pattern changes with successive dropout compensation rules by changing the above directions, resulting in a total compensation effect for the observer, as already explained above with reference to Fig. 4.

Therefore, the dropout compensation CDOC) line A2 is followed by the DOC line B2, which is formed by moving the luminance component samples of the original line A1 by half a sample period in the same direction as for the line B1 and therefore in phase therewith . The above-described method is repeated in this way for all "odd" DQC lines B1, B2 ... »BN, the samples of which are horizontal in one direction over half of the original A1 in one direction. sampling period have been shifted and alternated for all 5 "even" DOC lines A2, A3, ..... AN of which the samples have shifted horizontally in one sampling period from the original line A2 in the same direction, as indicated in It is clear that the overall influence of the horizontal line-by-line displacement of the DOC signal luminance component for the observer is + 0.5 sampling periods. Therefore, in the above-described method of the invention, the influence of a horizontal displacement of the DOC signal luminance component is minimized.

Fig. 3b shows the luminance component of an original color television rule B1 immediately prior to a cutout.

The waveform N1, which includes samples 1B, 2B, 3B, etc., is identical to the waveform 1Ί1 associated with line A1 of FIG. 3a except that samples IB, 2B, etc. thereof are 0.5. sampling periods have shifted relative to waveform M1. Figure 3b shows that N1 indicates respective waveforms of all "odd" DOC lines A2, A3, ..... AN after the original line B1. Similarly, N3 represents all even DOC lines B2, B3, ... BN after the original line B1.

There is a difference in forming DQC luminance component on 25 consecutive television lines, as shown in Figures 3a and 3b, in that the samples of the "odd" lines are moved from the original line by half a sample and the samples of the "even" lines relative to the original line are moved across an entire sample in 30 or opposite directions, respectively.

From the foregoing, it follows that the method of the present invention for line-by-line modulation of both the chrominance and luminance component delay, synchronous with the color burst phase, and line-by-line modulation of the luminance component delay, synchronously with the horizontal line synchronization 8101437 · * - 20 component to reduce the line-by-line delay thereof, is obtained in a relatively simple manner by a control signal related to the color burst component and a control signal related to the horizontal line synchronization component to the to apply respective delay lines. Since the two control signals CB and HS / 2 are locked in frequency and in phase with the incoming television signal, and are also locked together, the above-described method can be realized by assigning the sample displacement direction or phase 10 in any desired way. point each dropout compensation line to the right or left, viewed on the television screen, with respect to the original signal. Once assigned, this direction or phase is maintained with alternating DOC rules in response to the HS / 2 signal, the frequency of which is equal to half the horizontal control frequency. The HS / 2 signal is also used to modulate the luminance signal delay, as described above. As a result of the above-described method, a drop-out compensation pattern is obtained, as shown in Fig. 4.

In Fig. 5 there is found another preferred embodiment of a failure compensator according to the invention, which will now be described. In FIG. 5, circuit elements corresponding to those described with reference to FIG. 2 are provided with the same references. An explanation of these elements with respect to FIG. 5 will not be made to avoid unnecessary repetition. In the dropout compensation circuit of FIG. 5, the 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 the filter 5 is applied to the input 36 of the differential circuit 7 to the other input 35, the color television signal of which is supplied from the output 25 of the switch 1 via a compensating fixed delay line 6. The the resulting separated chrominance component at the output 45 of the differential circuit 7 is applied to a first input 47 of a second 81 01 437-21 two-way switch 14. The output 50 of the switch 14 is coupled to a first control chrominance delay line 16 whose output is coupled to a second input 49 of the switch 14. Delay line 16 and switch 14 therefore represent a first circulation memory circuit 81 for the separated chrominance component. The delay line 16 is controlled by the previously described control signal, indicated by CB, which is received on the control terminal 30. The separated luminance component on the output 34 of the filter 5 is further supplied to a first input 46 of a third two-way switch 15 and is supplied from the output 51 of the switch 15 via a second controlled luminance delay line 17 to a second input 48 of the switch 15. It appears that the delay line 17 and the switch 15 form a second circulation memory circuit 82 for the separated luminance component. The delay line 17 is controlled by a control signal, indicated by HS, which is received on the control terminal 43. A dropout control signal DO received at control terminal 23. is applied to respective control inputs 24, 85 and 86 of respective switches 1, 15 and 14.

During operation, a failure control signal DO, indicating the presence of a failure in the incoming composite color television signal received at 12, activates the three switches 1, 14 and 10, respectively. 15. Therefore, a dropout compensation signal will be applied to the output 25 of the first switch 1 from the input 21 thereof, which signal is supplied by the circuit of FIG. The aforementioned dropout compensation signal is formed as follows: During normal operation of the circuit, when no dropout is present, the filter 5 continuously receives the digital color television signal at 12, which signal has a frequency equal to three times the color subcarrier signal. frequency. The separated luminance component at the output 34 of the filter 5 is supplied to the luminance delay line 17 via the switch 15. The delay line 17 has a delay line.

35 length which is equal to one horizontal control period. Therefore, at some point during normal circuit operation, in the delay line 17, one horizontal line of the separated luminance component will be obtained from an immediately preceding portion of the color television signal, which is output at the terminal 12; 5 received are stored. The input and output of the signal stored in the delay line 17 is controlled by the control signal HS received at the terminal 43. The signal HS is taken from the horizontal synchronizing component of the received color television signal and is synchronous therewith. Regarding the above, a separated luninance component is obtained, which is delayed by one horizontal control period and at the same time is coherent with the horizontal control synchronization component during subsequent television vision rules.

Similarly, the chrominance delay line 16, which also has a length equal to one horizontal control period *, continuously receives the separated chrominance component from the difference circuit 7 through the switch 14. Therefore, at some point in the normal operation of the circuit, one horizontal line of the separated chrominance component is stored in the chrominance delay line 16, this portion of the chrominance component corresponding to that of the separated luminance component, which is simultaneously stored in the luminance delay line 17. The input and output of the chrominance component stored in the delay line 16 is controlled by the control signal CB received on the terminal 30, which signal is derived from the color burst synchronization component of the color television signal received on the terminal 12. Through the chrominance delay line 16 through the. to control the control signal CB, a separated chrominance component is obtained, which is delayed by one horizontal control period and is in phase v with the color burst component simultaneously during successive television vision rules.

As shown in Figure 5, the respective delayed separated luminance and chrominance components in the signal combination circuit 11 are combined and the combined signal 35 at the output 42 of the circuit 11 is applied to the second input 8101437-23-21 of the first switch. 1 as described above. The signal at 21 represents the dropout compensation signal used by the device of FIG. 5 when a dropout control signal DO is received.

When a failure is present, the switches 14 and 15 controlled by the signal DO close the respective circulation memory circuits 81, 82. Thus, the separated luminance and chrominance components both circulate in their respective circulation memory circuits, synchronously, under control of the previously mentioned clock signal at a frequency equal to three times the color subcarrier signal frequency.

From the above it follows that the preferred embodiment of the circuit of FIG. 5 over the circuit of FIG. 2 has the advantage that no additional modulation of the delayed separated luminance component is required relative to the delayed separated chrominance component. to reduce the horizontal line-to-line displacement of the luminance component samples. Instead, in the embodiment of flg.

5 two separate circulation delay lines are present, one delay line for the separated luminance component and another delay line for the separated chrominance component. Each delay line 16, 17 is controlled by a separate control signal CB resp. HS for providing a signal component which is in synchronism therewith.

To illustrate the above, the operation of the embodiment of FIG. 5 is shown in FIG. 6, showing the respective horizontal displacements between the luminance and chrominance component samples in successive dropout compensation lines. To simplify comparison with the previously described diagram of FIG. 4, which is related to the circuit of FIG. 2, the last original color television signal lines received prior to dropout are the successive dropout compensation (DOC) lines as well as successive samples of this respective rule in the both diagrams of FIGS. 4 and 6 provide the same references. The diagram of 81014 37 - 24 - Fig. B shows that the luminance component of each DOC sample 2B, 3B, 4B etc, on odd DOC lines B1, B2, etc. is obtained by the luminance component of a corresponding sample 2A, 3A, 4A etc. of the original line A1 to be delayed by 5 one horizontal line period, increased by half a sample period, At the same time, the chrominance component of each DOC sample 3B, 4B, etc. indicated above becomes, on odd DOC lines obtained by delaying the chrominance component of a corresponding sample 2A, 3A of the original line A1 by one horizontal line period plus Ιέ sample period. On the other hand, the luminance component of each DOC sample becomes 3A; 4A, etc., on even DOC lines A2, A3, etc., obtained by delaying both the luminance and chrominance components of the corresponding samples 3A, 4A, etc., of the original color television-15 signal by one horizontal control period. Therefore, in the operation of the preferred embodiment of the invention shown in FIG. 5, the relative vertical line-by-line displacement of the DDC signal samples is + 0.5 sample periods for the luminance component and + 1.5 sample periods for 20 the chrominance component, Compared to the method of FIG.

4, the preferred method of the invention shown in FIG. 6 has the advantage, however, that each alternating DOC line is in phase with the original television signal line with respect to both luminance and chrominance components, and no horizontal displacement of samples at this time. rules take place with regard to both the luminance and the chrominance components.

It will be apparent from the explanation of FIG. 5 that in this particular embodiment of the invention, it is not necessary for the color television signal to be sampled at a frequency equal to an integer multiple of the color subcarrier signal frequency as is the case. in the embodiment form according to fig. 2. In the embodiment of FIG. 5, use may be made of a sampling frequency which is equal to a rational number multiple of the lower carrier frequency.

8101437 - 25 -

For a more complete description of the device and method according to the invention, a further embodiment according to the invention is shown in block diagram in Fig. 7. A correspondingly detailed electrical diagram is shown in the following Figures 8a-8h. The embodiment of FIGS. 7 and 8a-8h is for a particular DOC device that requires a delay of two horizontal lines from the original color television signal. First, the block diagram of FIG. 7 will be described, followed by a description of the corresponding detailed diagram. In the embodiment according to fig.

7, a color television signal is received at an input terminal 9Q in the form of successive digital samples having a frequency equal to three times the color subcarrier signal frequency as described above. The received signal is applied to the input 91 of a two-way switch 52 and through its output 93 to a first controlled delay line 54, which produces a delay of one horizontal line minus chain delays, denoted by ^. The delayed color television signal V from the output 115 of the delay line 54 is supplied through a second compensating fixed delay line 56, which provides a delay, equal to a second input 92 of the switch 52. Therefore, the elements 52, 54 and 56 formed a circulation memory circuit 94 corresponding to that described above with reference to FIGS. 2 and 5. A control signal CB is applied to a control input 125 of the delay line 54, which is received on the control terminal 124. The latter signal corresponds to the signal previously described with reference to FIG. 5 has been described. The color television signal V from the delay line 54 is also applied to a first input 101 of a signal difference circuit 64 via a third compensating fixed delay line 113 with a delay, designated V, as a delayed signal V. The signal V from the output of the delay line 54 is also applied to the input 104 of a digital filter 60. The filter 60 is designed as the digital comb filter, as described in the aforementioned US 81014 3 7-26. patent application. The filter 60 separates the luminance component from the color television signal in a manner as described in said United States Patent Application. The separated luminance component L ', obtained at the output 105 of the filter 60, is supplied to a first input 107 of a second two-way switch 62 and also via a second delay line 67 with a double clock period to a second input 106 of the switch 62. An output 109 of switch 62 is connected to a first input 98 of a signal combination circuit 66. Therefore, through the switch 62, the delayed separated luminance component L is fed from the filter 60 to the signal combination circuit 66 either directly or delayed by two clock periods, indicated by 2 6.

The switch 62 is controlled at its control input 112 by a control signal, denoted HS / 2, which is received on a control terminal 111. An inverted separated luminance signal component L ', obtained at an inverting output 106 of the filter 60, is applied to a second input 102 of the signal difference circuit 64. The circuit 64 supplies at output 20 103 a difference signal C', which is the separated chrominance component. nent obtained as a difference between the delayed composite color television signal V 'and the delayed separated luminance component, respectively. applied to the first and second inputs of the chain. In this preferred embodiment, the difference circuit 64 is configured as a signal adder and the separated chrominance component C 'is obtained by adding together the delayed composite signal V' and the inverted separated luminance component L7 '.

The separated chrominance component C 'on the output 103 30 of the difference circuit 64 is applied via a delay line 6Θ with one clock period to one input 99 of the signal adder 66. As already mentioned, the other input 98 of the signal adder 66 is the separated luminance component L is supplied from the second switch 62. The signal adder 35 66 combines the received chrominance and luminance components 8101437-27 into a composite color television signal at the output 100 of the device, which signal represents the color television dropout compensation signal. The latter signal is added to a first input 95 of a third two-way switch 58. To a second input 9B of the switch 56, the composite color vision signal received at the input terminal 90 is supplied through the first switch 52, the first control delay line 54, and via the second compensating delay line 56. A drop-out compensation control signal DO is applied to a control input 97 of the switch 58 via a delay line 53 providing a delay of one horizontal line. The latter control signal is received at the input terminal 110 when a failure in the incoming color television signal at the terminal 90 is detected, e.g. by a normal failure failure detector not shown, as described above. The dropout control signal at 110 is also applied to a control input 114 of the first switch 52. An output 127 of the switch 58 is coupled through a further controlled delay line 126 to an output terminal 70 of the dropout compensation circuit of FIG. 7. The delay line 126 provides a delay of one horizontal line and is controlled by the signal CB, which is applied to the control input 128 of the line, simultaneously and in the same manner as described above for the controlled delay line 54.

The operation of the dropout compensation chain according to FIG. 7 will now be described. When a dropout in the composite color television signal is detected, e.g. by normal failure detector not shown, a failure control signal DO received at terminal 110 is supplied to switch 52 and through delay line 53, which provides a delay of one horizontal line * to switch 58. The switch 52 closes the circulation memory circuit 94 and, therefore, the last horizontal line of the color television signal received immediately prior to the failure stored in delay lines 54 and 56 will pass through the input 92 and the output 93 of the switch. 52 circulate with a clock signal frequency equal to 8101437 - 28 - 3 x 3.58 MHz to 10.74 MHz. The clock signal used to clock the respective circuit elements of FIG. 7 is not shown in the block diagram for clarity, but it is shown in the diagram of FIGS. 8a-8h, which will be described later. The filter 60 receives the composite signal V, delayed by substantially two horizontal control periods, from the memory 94 and secretes its luminance component L 'in a manner as described in the above-mentioned U.S. Patent Application. The separated luminance component is supplied via the switch 1062 to the signal combination circuit 66, which in the preferred embodiment is configured as a signal adder.

In response to the control signal HS / 2, the switch 62 supplies the separated luminance component L 'alternately delayed directly or over two further clock periods in the delay line 67, via the switch 62 to the signal combination circuit 66. The control signal HS / 2 has a frequency of half the horizontal control frequency. The signal is derived from the horizontal synchronization component of the color television signal received on terminal 90. The phase of the signal HS / 2 is controlled by the signal CB1. that is received at terminal 124, to ensure that the same phase relationship between these two control signals will be maintained throughout operation. Therefore, the switch 62 is controlled by the signal HS / 2 to alternate the signal L ", delayed and, respectively, during successive horizontal lines. with 2 clock periods 2 ƒ delayed to the input 98 of the adder 66. On the other hand, as already described, the signal adder 64 receives both the delayed composite signal V 'and the inverted luminance component TT and delivers a separated chrominance component C' to output 103 thereof. To compensate for the chain delay T30, which starts with the processing of the separated luminance component in the filter 60, the signal V in the third fixed compensation delay line 113 is delayed by Γ. The separated chrominance component C 'is delayed in the delay line 68 by one clock period é and the delayed chrominance component C is combined with the above-described luminance component L in the signal adder 66.

From the above, it follows that when the separated luminance component L 'is delayed by two more clock periods during 5 alternating horizontal control periods, and the separated chrominance component is delayed by one more clock period during successive horizontal control periods, in the adder 66 with each other are combined, they represent a composite dropout compensation signal whose luminance component delay is modulated by 10 + 1 clock period relative to the chrominance component delay during successive horizontal control periods. Therefore, the aforementioned feature of the invention, relating to decreasing the luminance component delay relative to the chrominance component delay, of the resulting dropout compensation signal in the preferred embodiment of FIG. 7 is obtained by the above-described combination of chain elements.

From the above description of the block diagram of FIG. 7, it further appears that the delay T compensates for the delay in the filter chain 60 and the delay compensates for the combined delays Γ sn the delay <f, provided by the delay line 68. therefore ^ * = Γ + when it is assumed that the chains 64 and 66 have no chain delays.

Furthermore, it is apparent from Figure 7 that in this particular preferred embodiment, the controlled delay line 54 is included in the main lane of the composite color television signal. Therefore, when no dropout compensation takes place, the incoming composite signal, received at 124, is continuously delayed in delay lines 54 and 56 by one television control period, which delay is controlled synchronously with the color burst component.

Therefore, the original composite signal at output 127 of switch 58 exhibits an undesired fps shift of + 180 degrees with alternating lines. In order to compensate for this effect, an additional delay line 126 is included in the main trajectory of the color television signals, which provides a delay of one horizontal line. The supply and removal of the delay line 126 is controlled by the above-described control signal CB, which is received on the control terminal 124, and is applied to the control input 128 of the delay line 126. Since the color television signal received by delay line 126 is first delayed in delay lines 54 and 56 by one horizontal control period and both delay lines 54 and 126, respectively. are controlled by the same signal CB, the respective output signals of these controlled delay lines 54 and 126 occur in opposite phases of phase shifts of + 180 °. Therefore, these opposite phase shifts cancel each other out and no phase shift is present in the output signal at the output 70 of the dropout compensation circuit of FIG. 7.

From the above explanation, it follows that in the block diagram 15 of FIG. 7, the dropout compensation signal at the output terminal 70 is delayed by three horizontal control periods to meet certain requirements of the particular apparatus in which this particular embodiment of the invention is applied. However, it is apparent from the above that it. actual dropout compensation signal obtained at output 127 of switch 58 is still formed from the last received original television signal line at input 124 substantially in the same manner as previously with reference to FIGS. 2 and 5 was discussed.

However, it is to be noted that in the respective embodiment of Figures 2 and 5 previously described, their respective controlled delay lines are not included in the main lane of the composite color television signal and therefore do not exhibit an undesired phase shift as in the embodiment. according to FIG. 7 occurs during normal operation of the system when no failure omission takes place.

The detailed diagram shown in FIGS. 8a - 8h essentially corresponds to the simplified block diagram of FIG. 7 described above. For comparison purposes, individual chains in the detailed scheme, corresponding to elements of the block scheme, are indicated by dotted lines and have the same references. Likewise, connecting lines between the circuits of the detail scheme are indicated by references, corresponding to input / output designations of corresponding rectangles in Figure 7. For a complete description 5, the integrated circuit components shown in the preferred embodiment of FIGS. 8a-6h are designated by respective component numberers as commonly used by manufacturers.

More specifically, the filter circuit 60, which is used to separate the luminance component of the composite color television signal and which circuit is shown in FIGS. 8d and 8e, is similar to that described in the above-mentioned U.S. Patent Application. . It is clear, however, that a known digital comb filter can be used instead. As can be seen from the detail diagram of FIGS. 8a-8h, an advantage of the digital dropout compensation circuit according to the invention is that the entire signal processing takes place in a timely manner using a normalized TTL circuit. The circuit of the above figures is for dropout compensation in a color television signal recording and reproduction system, wherein an NTSC color television signal is encoded in digital form by sampling at a frequency equal to three times the color carrier frequency of the television signal ie, that PstgQkpj.Qgf “3 x 3 * 58 MHz 10.74 MHz. The sample 25 signal is locked in phase with the color burst component of the subcarrier signal. The sampling frequency is equal to the clock frequency, as already mentioned above in the description of Fig. 2.

Generally, for the operation of the dropout capacitor of the present invention, the sampling frequency used to encode the composite analog signal, e.g. the color television signal, not to be the same as the clock-frequency, which is used to synchronize the various elements of the dropout compensation chain. In the latter case, samples can be received and stored e.g.

81 014 37 - 32 - at the sampling frequency and then recovered at the clock frequency, the latter frequency being used for chain synchronization.

The preferred embodiment according to the invention shown in Figs. Ba - 8h will now be described. In Fig. 8a, subsequent samples S1, S2, S3, etc. of the digital color television signal at the input 90 of the dropout compensator are received as 8-bit parallel information through a first set of inputs 91 of two information selectors / multiplexers A24 and A34 of the two-way switch 52. These multiplexers also receive information at the second input 92 from the output 116 of the delay line 56, as shown in FIG. A dropout control signal DO is received at the input 110 by the multiplexers at 114 via the flip-flop A16 from a normal non-illustrated RF envelope level dropout detector circuit as noted above. The flip-flop A16 is used to accurately clock the dropout control signal DO. In normal operation, the multiplexers supply the input information 90 to the output 93 via the flip-flop A23. In general, flip-flops corresponding to A23 are used throughout the chain to delay the processed information by one clock period to ensure accurate information clocking. When the DO control signal is received at 110, the multiplexers switch from input 91 to input 92. The information from 93 is applied to the output 70 of the failure compensator circuit through the first controlled delay line 54 of FIG. BB, the second compensation delay line 56 of FIG. BC, the switch 58 of FIG. 8g and a further controlled delay line 126 of FIG. 8g, as will be explained below.

The delay line 54 of FIG. BB includes eight equal 4 x 256 bit freely accessible memories, six of which are designated B1, Bil, B31, B51, B61, and B81. Two groups of four memories each are used to receive resp. bits of high and low order. The controlled delay line 35 54 has a delay length equal to one horizontal control period of the color television signal reduced by the compensation delay ƒ **, which is provided by the fixed delay line 56 of FIG. 8c, which is in the delayed color television. signal path is included. The delay line 56 is composed of 5 eight shift registers, four registers A51, A61, A52 and A82 are shown. The flip-flop B41 at the output of delay delay 54 is used to ensure proper timing of the output information to obtain the above delay. The delayed composite signal on output 115 is applied to input 96 of switch 58 of FIG. 8g via the fixed compensation delay line 56.

As indicated in Fig. 8d, the information S1, S2, S3 etc. from the output 115 of the delay line 54, which represents the signal V, is also applied to one set of inputs 104 of the filter 60. As in the above-mentioned US patent application As described, the filter 60 always provides an average value of three consecutive samples S1, S2, S3. As shown in Fig. 8c, a sample S1 is obtained, which is fed through part of the delay line 56, at the output 117 since -20 from which line the sample is delayed by one clock signal period to ensure its proper timing in order to be added to a sample S2 which is received one clock signal later. The latter delayed sample is applied to the second set of inputs 104 of the filter 60. The 25 samples S1 and S2 are added in two binary adders A33, A43 of four bits according to Fig. 8d and the sum thereof is S1 + 52 in the flip-flop A53 is delayed by one clock signal to be ready to be added to the subsequently received sample 53 from the output 115 of 54. The latter summation takes place in two binary adders A54, A44 of four bits and one output thereof. the sum signal S = S1 + S2 + S3 for.

_. The signal S is passed over the flip-flop A55 to ensure proper timing for further processing. In this particular embodiment of the invention, an average sample value is obtained by dividing the signal S by three. Dividing i 81 01 437 - 34 - by three is done with an accuracy of 0.13% by an approximation algorithm:

S S S_ S

3 “4 + 16 + 256 5 For the particular application of sampling averaging in the preferred embodiment just described, the approximation algorithm is realized in two steps as follows: PS = - + - 4 16 - rr Ps + £ §.

10 3 16

These two steps take place in the remaining parts of the diagram of the filter 60, shown in Fig. Be, which will be described later.

The two binary adders A64, A65 of four bits 15 according to Fig. 8e receive the signal S at two sets of inputs, shift the signal S to become equal to S / 4 at one of the sets of inputs, and provide the sum (S + S / 4). The output of the latter adders is shifted further to obtain an output corresponding to CS + S / 4) / 2. The latter output signal represents twice the partial sum PS defined above. The signal 2PS is applied to the flip-flop A75, which supplies the signal 2PS to two sets of inputs of two binary adders A66 and A67 of four bits. The latter adders shift

2PS

25 / of the signal 2PS to obtain -rs · for one set of inputs and

. u-o 2PS

provide an output signal corresponding to (2PS + —yg-3/2. This output signal sets the approximation algorithm shown above

^ S

before me. The resulting signal g-L corresponds to the mean value output signal supplied by the filter 60 in accordance with what is described in the above-mentioned United States patent application. The output signal of the adders A66, A76 therefore represents the color television signal without chrominance signal, i.e., the separated luminance component, as explained above with reference to FIG. 7. It

S

35 signal -g is applied to flip-flops A67 and A77, both eeh 81014 3 7 - 35 -

S

output signal -g-, denoted L 'at output 105, at output 107 of switch 62 in FIG. 8f and an inverted S-output signal i — denoted L', at output 106 and supplied to a first set of inputs 102 of the adder 5 64 of FIG. Bf.

The adder 64 is composed of two four-bit binary adders A36, A46.

In this preferred embodiment, the compensating fixed delay line 113 depicted in the block diagram of FIG. 7 and providing a delay Τ 'is formed by a portion of the fixed compensating delay line 56 at its output 130, as shown in FIG. . The thus delayed composite color television signal from the output 130 of the delay line 56, denoted by V ', is applied to a second-pair input 101 of two binary adders A36, A46 of the adder 64 in FIG. SF. . The adder 64 supplies at the output 103 an output signal, denoted by C ', which represents the separated chrominance component, as explained above with reference to Fig. 7. The signal C '20 is applied via the flip-flop A56 siA5, which represents the compensating fixed delay line 68, to a first set of inputs 99 of two binary adders A84, AB5 of the adder 66 in FIG. 8g. The separated set of inputs 9B of these adders is fed with the separated delayed luminance component L from the outputs 109 of the multiplexers A87, A86 representing the switch 62 in FIG. 8f. As described above, one set of inputs 107 of the multiplexers A87, A86 is supplied with the separated luminance component L 'from the output 105 of the filter 60 in Fig. Be. To the . Other sets of inputs 108 of these multiplexers representing the switch 62 in FIG. 8 are supplied with the luminance component L "delayed by the delay line 67 formed by the flip-flops A68, A78 shown in FIG. 8f. The multiplexers A87, A86 of FIG. 8f are controlled at input 112 by the 7.8 kHz control signal HS / 2 received at 111, 8101437-36, which signal is described with reference to FIG. As previously explained with reference to the block diagram of Fig. 7, the switch 62 at the input 98 of the signal adder 66 outputs the separated luminance component L directly from the output 105 of the filter 60 or alternatively via the delay line 67 with two clock periods on successive horizontal lines in response to the control signal HS / 2. The adder 66 of FIG. 8g combines the respective luminance and chrominance components received at the respective inputs 98, 99 thereof into a composite color television signal representing the dropout compensation signal. The latter signal is applied to a first set of inputs 95 of the switch 58 in FIG. 5g formed by the multiplexing devices A73, A74 through the flip-flop A89, which is used for proper timing of the information. At the other set of inputs 96 of the multiplexing devices A73, A74, an output signal from the delay line 56 of FIG. 8c is received. The output at 127 from the switch 58 is applied to the delay line 126, which is shown as a rectangle. The latter delay line is used in the particular embodiment of Figures 8a-8h to eliminate the unwanted 180 ° phase shift, as already explained with reference to Figure 7. The delay line 126 provides a delay of one horizontal line and is controlled by the control signal CB, simultaneously and in the same manner as the controlled delay line 54. The delay line 126 may be designed using freely accessible memories corresponding to those of the delay line 54 in FIG. 8b. The output of delay line 126 therefore represents the previously described output of the dropout compensation circuit of FIGS. 8a-8h present on output terminal 70.

The switch 58 of FIG. 8g is controlled by the dropout control signal DO, which is received at the input terminal 110 in FIG. 8a and is applied to the input 97 through the output 112 and the output 55 of the delay line 53 of FIG. 8a. control of switch 58.

8101437 - 37 -

Fig. 8h shows a memory address generator circuit 150, which supplies output signals on memory address lines Ag - A, which lines serve to rasp the information stream via a memory line AB through the respective delay lines 53, 54. in Figs. Ba and 8b are indicated -5. In Figure 8h, counters A2, A12, A22, B2, B12 and B22 are used to count the respective clock periods, corresponding to the actual delay provided by these delay lines. The schematic of FIG. 8a shows the memory address generator 150 in sufficient detail and therefore no further explanation is considered necessary.

To provide a complete description of the detailed circuit, respective clock signals, indicated at 10.7 MHz, and inverted clock signals, indicated at 10.7 MHz, which signals are used to drive different circuit elements, are detailed diagram of fig. 8a - 8h. As is known, the sample signals are taken at this clock signal frequency, e.g. it is also explained in the above-mentioned United States patent application.

In the above, the preferred embodiments of the invention have been illustrated for a digital dropout compensation circuit, in which samples are taken from a composite NTSC color television signal at a frequency equal to three times the color subcarrier signal frequency, ^ g ^ gg ^ ppf ^ 3 x 3 .58 MHz = 10.74 MHz * It is clear that the respective block diagrams of FIGS. 2, 5 and 7 can also be used for other digital as well as for analog color television signal systems, such as NTSC, PAL, PAL-M, etc. If eg the drop-out compensation device according to the invention is used in an analog color television signal system, it may be preferable to use the 30 sent delay lines e.g. the delay line 3 of FIG. 2, realized by normal charge coupled devices CCCD). As is known, the latter devices such as the delay lines for delaying signals can be analogized, while the information to be delayed can be clocked in response to a control signal in and out of the delay line, in a manner as described above for the other embodiments. At the same time, the delay lines, such as 8 and 9 in Figure 2, can be realized by conventional analog delay lines. In the latter case, the delay line 8 provides a desired amount of the analog sig-5 sew, substantially corresponding to the line-by-line shift of the color subcarrier signal, and the delay line 9 preferably provides substantially twice that delay to obtain a desired luminance component delay modulation relative to the chrominance component delay, such as-1Q as explained above.

In general, the invention may be used with reference to FIG. 2 in any digital color television signal system in which the sampling frequency is equal to an integer multiple of the color subcarrier signal frequency. If 15 e.g. Sampling of an NTSC color television signal at a frequency equal to four times the subcarrier wave signal frequency serves to obtain a desired dropout compensation signal with an appropriate line-for-control phase of the chrominance component, e.g. by the embodiment of FIG. 2, the original signal chrominance component samples are shifted by successive television lines by + 2 sampling periods. Therefore, to reduce the luminance component displacement in successive lines, the delay line 9 of FIG. 2 should provide a delay of four clock periods, 4 i, while the delay line 8 should provide a delay of two periods, 2 i. .provide.

The above-described invention also applies to PAL or PAL-M signal systems since the respective control signals, such as respective signals CB, HS and HS / 2 in FIGS. 2, 5 or 7, 30 in frequency and phase with the incoming color television signal are locked. It is clear that the so-called quarter-period shift, corresponding to the 90 ° phase shift, which occurs during successive television lines in the PAL subcarrier component, in the dropout compensator according to the invention can be compensated for by the above 81 01437-39 - supply control signals to the respective controlled delay lines of the above-described embodiments, which will be loaded and unloaded in successive lines synchronously with the control signals of the particular signal system used.

It is further understood that other embodiments corresponding to the detailed scheme of FIGS. 8a-8g as well as other circuit elements may be used in these embodiments to achieve the desired performance of the failure compensator of the invention. For example, the differential chain 64 e.g. are designed as a subtractor to which signals L ', V * of the same polarity are applied. Similarly, known other circuit elements in the summing circuit 66 can be used to obtain a combination of the chrominance and luminance components. As an alternative, other means for obtaining the delay in the delay lines 54 may be used, such as shift registers instead of freely accessible memories. In order to obtain division by three of the samples in the filter circuit 60, read-only memories may be used instead of the described circuit elements for realizing the approximation algorithm.

The individual circuit elements of all the above-described embodiments according to the invention can be realized by normal, standardized integrated devices.

81 01 437

Claims (7)

1, A method of compensating for color television signals for dropouts, wherein a dropout interval occurring in an input color television signal is replaced by a dropout compensation signal derived from a previously occurring corresponding interval of the input color television signal, which luminance and chrominance components which define successive horizontal lines of the color television information, characterized in that intervals of each horizontal line of the input color television signal are stored without dropouts, intervals of an immediately following horizontal line of the input color television signal without dropouts instead of corresponding stored intervals of said each horizontal line are stored, corresponding stored intervals of each said horizontal line instead of intervals of the immediately following horizontal line of the corridor color Levels signal are kept stored when dropouts occur in the immediately following horizontal line, the luminance and chrominance components of the stored color television signal are separated, the storage time of the stored chrominance component of successive horizontal line intervals is set between a first time, which greater then, and a second time less than an interval, corresponding to one horizontal line, in order to phase synchronize the stored chrominance component with the corresponding component contained in the input color television signal, is the beat time of the stored luminance component of consecutive horizontal line intervals is set between a third time greater than and a fourth time less than an interval corresponding to one horizontal line so as to adjust the phase difference between the stored luminance component and the corresponding component present in the input color television signal, the set chrominance and luminance components are combined to form the dropout compensation signal, and the dropout compensation signal in place of the input Color TV signal is introduced when in This input Color TV signal fails. Method according to claim 1, characterized in that the input Color TV signal consists of a digital signal obtained by taking samples from the analog form of the color TV signal, a sample signal having a frequency equal to a integer multiple of at least 10 times the frequency of the unmodulated color subcarrier frequency of the color television signal, said first time being greater than, and said second time being less than, the interval corresponding to one horizontal line of a first amount less than one period of the non-15 modulated color subcarrier frequency, and the third time greater than, and the fourth time less than, the interval corresponding to one horizontal line, with a second amount less is then one period of the unmodulated color subcarrier frequency. Method according to claim 1, characterized in that samples of the color television signal are taken at a frequency which is three times the frequency of the unmodulated color subcarrier frequency, the intervals of a first and alternating subsequent horizontal lines of the input color television. vision signal are stored during a first interval, corresponding to one horizontal line plus one half period of the sample signal before the chrominance and luminance components are separated, the intervals of a second and alternating horizontal lines of the input Color TV signal are stored during a second interval, corresponding to one horizontal line less 2 | period of the sample signal before the chrominance and luminance components are separated, the separated chrominance component of each horizontal line is stored for a third interval, equal to one period of the sample signal, storing 81014 37 - 42 - of the chrominance components of successive horizontal lines is set by the first resp. second times, and the separated luminance component of the second and alternating horizontal lines is stored for a fourth interval, which is equal to two periods of the sample signal, the luminance components of consecutive horizontal lines being stored by the third resp. fourth time. Method according to claim 1, characterized in that samples of the color television signal are taken at a frequency which is three times the unmodulated color subcarrier frequency, the input color television signal being first converted into chromium and luminance components. separated, the separated chrominance component of a first and alternating next horizontal line is stored during a first interval, which corresponds to one horizontal line plus 1 period of the sample signal, the separated chrominance component of a second and alternating next horizontal line is stored during a second interval, corresponding to one horizontal line less 1h period of the sample signal, wherein the storing of the chrominance components of successive horizontal lines is set by the first and second times, respectively, the separated luminance component of the first and alternate and the following horizontal control intervals are stored for a third interval plus half a period of the sample signal, and the separated luminance component of the second and alternate subsequent horizontal control intervals becomes. stored for a fourth interval, corresponding to one horizontal line interval less a half period of the sample signal, wherein the storing of the luminance components 30 of successive horizontal lines is set by resp. the third and fourth times. 5. Color television signal failure compensator, comprising luminance and chrominance components, which determine successive horizontal lines of the color television information, in which a failure detection signal is generated upon the occurrence of a 81 01 4 3 7 - 43 failure interval in the input color television signal in order to replace it. of the dropout interval by controlling a corresponding interval previously encountered in the color television signal, characterized by memory means having an input for receiving the color television signal, said memory means having sufficient storage capacity to accommodate at least one horizontal line of the color television signal storing memory controllers, which cooperate with the memory members to receive a storage of intervals of each horizontal line received at the input 10 of the memory members, instead of corresponding intervals of immediately preceding horizontal lines, which are received on the input of the memory means, to effect first switching means to supply the input color television signal to the input of the memory means, which first switching means 15 interrupt the supply of the input color television signal to said input of the memory means in response to the drop-out detection signal. , means for separating the luminance and chrominance components of the stored color television signal, means for setting the storage time of the stored chrominance component 20 of successive horizontal control intervals, where the storage time of the chrominance component is adjustable between a first time, which is greater then, and a second time less than an interval, corresponding to one horizontal line, in order to synchronize the stored chrominance component in phase with the corresponding component, which is present in the input color television signal, means to to set the storage time of the stored luminance component of consecutive horizontal line intervals, the storage time of the luminance component being adjustable between a third time greater than 30 and a fourth time less than an interval corresponding to one horizontal line , in order to reduce the phase difference between the stored luminance component and the corresponding component present in the input color television signal, means for combining the set chrominance and luminance 35 components to form a composite color television dropout compensation signal, and second switches 81 01 437 - 44 - to selectively apply the input color television signal and drop-out compensation signal to an output, the second switching means supplying the off-compensation signal to the output in response to the drop-out detection signal and the second switching means supplying the input color TVs apply signal to the output in the absence of the failure detection signal. Drop-out compensator according to claim 5, characterized in that the input color television signal is a digital signal obtained by taking samples of the analog form 10 of the color television signal with a sample signal whose frequency is equal to three times the unmodulated sub-signal. carrier frequency of the color television signal, the memory means are provided with a first memory, the input of which is coupled to the first switching means, a second memory with a input which serves to receive the separated chrominance component, and a third memory with an input serving to receive the separated luminance component, wherein the second memory provides a first delay of less than one period of a sample signal and the second memory 20 provides a second delay which is two periods of the sample signal , with the first memory in response to the memory controllers store a first and alternately following horizontal line of the output color television signal before it is applied to the luminance and chrominance separators 25 during a first interval corresponding to one horizontal line plus half a period of the sample signal, and a second and alternately stores the next horizontal line of the input color television signal before it is applied to the luminance and chrominance separators, during a second interval, corresponding to one horizontal line less 2k period of the sample signal, with third switches having one input with the output of the third memory is coupled and a second input is for receiving the separated luminance component from the 35 luminance and chrominance separators, these third 8101437 - 45 switches in response to the memory b controllers supply the luminance component, which is received from the luminance and chrominance separators, to the combiners during the first and alternately subsequent horizontal lines and to the 5 combiners the luminance component, which is received from the third memory, during the second and alternate subsequent horizontal lines supply lines. Drop-out compensator according to claim 5, characterized in that the input color television signal is first applied to the luminance and chrominance separators, and the memory members are provided with a first memory and a second memory, each having a storage capacity of at least one horizontal line, wherein the first memory serves to receive the separated chrominance component and the second memory serves to receive the separated luminance component, the first memory in response to memory controllers providing the first and second storage times for the chrominance component and the second memory in response to the memory controllers provide the third and fourth storage times. ! 8101437