GB1587496A - Method of recording and/or transmitting colour television signals - Google Patents

Description

(54) A METHOD OF RECORDING AND/OR TRANSMITTING COLOUR TELEVISION SIGNALS (71) We, ROBERT BOSCH GMBH, of Robert-Bosch-Strasse 7, 6100 Darmstadt, Federal Republic of Germany, a German Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of recording and/or transmitting colour television signals.

A method for the recording of colour television signals has already been disclosed (German AS 2 056 684) wherein the colour information is compressed and recorded during the back porch of the television signal. In this method, however, the flyback time is extended, with the result that the useful duration of the lines is curtailed. In.

this known system the compression factor for the colour information is approximately 5.

It has also been proposed (German OS 26 29 706) to transmit the colour informa- tion during almost 'the whole of the duration of the horizontal frequency blanking interval, this being achieved by transmitting, in line alternating sequence, colour component signals and colour difference signals.

According to the present invention there is provided a method for recording or transmitting a colour television signal wherein successive lines of colour information are recorded or transmitted in compressed form, within successive horizontal frequency blanking intervals of the luminance information, alternately as the sum and the difference of a pair of colour difference signals.

The method of the invention has the advantage that PAL colour television signals may be converted with a relatively low capital expenditure on equipment into signals for recording or transmission, although the invention is not limited in application to PAL signals. In the reproduction of PAL signals recorded or transmitted by the invention it is a particular advantage that it is possible, without carrying out a full reconversion into a standard PAL colour television signal, to employ a commercially available PAL colour television receiver without any mcdifications. For this reason it is not only possible to save capital expenditure on the recording or transmitting apparatus, but it is also possible when reproducing or receiving the signals to dispense with the necessity for performing integration of the colour information over a line of the picture in addition to the integration already afforded in the standard PAL receiver.

Furthermore, in the transmission of television signals phase errors are liable to occur. The method of the present invention is less prone to these errors than is the line-sequential method of transmission of amplitude modulated colour difference signals having a phase difference of 900.

Embodiments of the invention will now be described with reference to the accompanying drawings, wherein: FIG. 1 is the voltage-time diagram of a typical signal recorded or transmitted by the invention, FIG. 2 shows a circuit arrangement for recording a PAL colour television signal in accordance with one embodiment of the invention, FIG. 3 shows a circuit arrangement for reproducing the PAL signal recorded by the arrangement of FIG. 2, FIG. 4 shows a further circuit arrangement for reproducing the recorded PAL signal, FIG. 4a shows a modification of part of the circuit arrangement of FIG. 4, FIG. 5 shows a circuit arrangement for recording a S.E.C.A.M. signal in accord ance with a further embodiment of the invention, and FIG. 6 shows a circuit arrangement for the reproduction of the signal recorded by the arrangement of FIG 5.

In the drawings equivalent components are provided with similar reference characters.

FIG. 1 is the voltage-time diagram of a typical colour television signal recorded or transmitted according to the invention. The selected example represents a colour bar test picture. The time intervals between to and to and between t, and to correspond approximately to the horizontal blanking intervals of a conventional television signal.

As is the case in conventional television techniques, each line of the luminance signal is recorded or transmitted without compression during the period to to t,. This ensures that, in the application of the invention, the luminance signal can be transmitted or recorded without incurring the expense of subsequent luminance coding and decoding operations which might impair the quality of the signal.

As will be seen from FIG. 1, each line of colour information is transmitted during by far the greater portion of a respective blanking interval of the luminance signal; the period between to and t2 representing the portion allocated for the sum U + V of the reduced colour difference signals U and V, and that between t4 and to being allocated for withe difference U - V of the reduced colour difference signals. These sum and difference of the colour difference signals alternate line-by-line in the blanking intervals.

Because a large portion of the blanking interval is used for transmitting the colour difference signals only a small period of time remains for accommodating the synchronizing pulse and the blanking level. It has already been proposed in the above mentioned German OS 26 29 706 to transmit during alternate line periods the synchronizing pulse and in the intervening line periods the blanking level. This technique is used in the present example, and accordingly in FIG. 1 there is shown between to and t1 a synchronizing pulse S', the amplitude of which lies outside the amplitude range of the picture content of the signal, so that the synchronizing pulse can be separated by well-known circuitry (amplitude filter). The blanking level A is transmitted in the next following line period from t, to t4. Because the colour difference signals, and consequently also their sum and difference, can assume positive as well as negative values, it is advantageous to select for the blanking level about 50% of the total amplitude range provided for the picture content.

In the arrangement shown in FIG. Z, an incoming PAL colour television signal (PAL-FBAS) is separated into its chrominance and luminance signals by means of the band pass element 2 and the low pass element 14. Moreover the input signal is also delivered to a pulse generator 10 which generates in accordance with known principles the timing pulses necessary for the operation of the circuit arrangement.

The carrier frequency chrominance signal admitted by the band pass element 2 is delayed by exactly one line duration in the delay line 3, and the undelayed and the delayed chrominance signals are subtracted in the subtraction circuit 4. By this operation a comb filter effect is achieved such that the spectral lines of the luminance signal which are allowed through in the frequency range admitted by the band filter 2 are suppressed. This serves to prevent so-called cross-colour disturbances.

Secondly the result is obtained that, at the output of the subtraction circuit 4, the sum and the difference of the colour difference signals U and V.are alternately produced line by line. This result is derived in the following manner.

The carrier frequency chrominance signal in the standard PAL technique is composed of the signals U and V alternating line by line in the following form: F = U + jV; F* = U - jV Taking into account the delay of 64 ys there will then appear at the output of the subtraction circuit 4 in alternate line sequence: F1 = F - jF* = (U + jV) - (U - jV) = (I - j) (U - V) and F2 = F* - jF = (U - jV) - (U + jV) = (I - j) (U + V) Thus, at the output of the comb filter there will appear in alternating line sequence the signals U + V and U - V, with the phase position rotated through - 450 as compared with the reference phase (that of the U signal).

Without the use of any additional circuitry these signals can be demodulated by means of a synchronous demodulator 5, to which there is delivered a colour carrier F rotated through - 450. The colour carrier F is regenerated in a colour carrier regenerator (not shown) from the colour synchronising signal derived from the carrier frequency chrominance signal. The demodulated signals are subsequently amplified in an amplifier 6 and time compressed in a compression circuit 7, so that by means of an electronic switch 8 they can be interposed in the horizontal frequency blanking intervals of the luminance signal.

The amplification in the amplifier 6 can be different (Kl and K2 respectively) in respect of alternate lines, in order to match the amplitudes of the signals U + V and U - V to the dynamic range of the compression circuit 7. For this purpose the amplifier 6 may include, for example, a voltage divider, at the base point of which a switch is interposed, which is controlled at one half the line frequency.

The signal from the switch 8 can be recorded in a simple manner by means of a magnetic tape device 9 of the kind designed exclusively for monochrome television signals. The line compression circuit comprises essentially an adequate number of stores into which the signals are read at a slow clock pulse frequency and are read out at a higher clock pulse frequency. These clock pulses are generated in the pulse generator 10. A detailed description of a line compression circuit is disclosed in the above mentioned German OS 26 29 706.

Between the compression circuit 7 and the switch 8 there is provided an addition circuit 11, by means of which a suitable direct voltage value U as well as a synchronism identification signal S' can be added to the compressed signals.

FIG. 3 shows a circuit arrangement for reproducing the signal recorded as described above into standard PAL colour television form, the necessary components and circuitry such as magnetic heads, reproducing amplifiers and demodulators conventionally used. in television signal recording practice being already sufficiently well known and therefore not being described in detail.

In the circuit of FIG. 3 the synchronising signal S' (FIG. 1) is separated from the recorded signal derived from the magnetic tape device, for which purpose an amplitude filter 21 is used. The signal S' controls a pulse generator 22, which generates the clock pulses necessary for driving the circuit of FIG. 3. By means of one of these pulses a switch 23 is controlled in such a manner that the colour information signals U + V and U - V, which appear alternately during consecutive horizontal frequency blanking intervals, are applied to a decompression circuit 24. In the circuit 24 the colour information signals are decompressed to the duration of the luminance signal.

In an amplifier 25 having an amplification factor of 1/K, and 1/K2 in respect of alternate lines the direct voltage value is restored, and in a following addition circuit 26 a K pulse is inroduced which occurs during the period provided for the colour synchronising signal.

The signals then arrive at an amplitude modulator 27 with suppressed carrier, which modulator carries out a suitable modulation of a colour carrier F which is also generated by the pulse generator 22. The phase position of the colour carrier is rotated by the element 28 through - 450 but, by means of a switch 29 controlled by K and P pulses and a delay member 30, is additionally rotated through 900 in each second line period during the period provided for the colour synchronising signal. The P pulses are the so-called PAL switching identification signals which occur at half the line frequency and identify the switching phase of the V signal in the PAL system. By this means, together with the addition of the K pulse by the addition circuit 26, the result is obtained that, in the output signals of the modulator 27, a line alternating colour synchronizing signal is present. The output signals of the modulator 27 are delayed by one line period in a delay circuit 31 and added in an adding circuit 32 to the undelayed signals. By the addition of the undelayed and the delayed signals there is produced a carrier frequency chrominance signal corresponding to the PAL standard. A detailed derivation of this may be dispensed with as it is the reverse of the mathematical derivation described with reference to FIG. 2. However, since the amplitude of the chrominance signal is too large by the factor of 2, suitable means for the reduction thereof are provided in the form of a voltage division circuit 33.

Finally the carrier frequency chrominance signal is added to the luminance signal in a further addition circuit 34, to which there is also added a true to standard synchronising signal mixture S from the pulse generator 22. Furthermore there is provided a delay member 35 in the luminance channel for compensating the delay times inherent in the chrominance channel. At the output 36 there is then available a colour television signal corresponding to the PAL standard.

In the circuit arrangement of FIG. 4 a full reconversion of the recorded signal into a standard PAL colour television signal is dispensed with. Surprisingly, we have shown that such signals can be processed by commercially available PAL colour television receivers without making any modifications in the receivers. The preparation of the signals taken from the magnetic tape device 20 up to the stage including the modulation in the modulator 27 takes place in much the same manner as in the arrangement of FIG. 3. The only difference lies in the line by line inversion of the phase position of the colour synchronising signal as compared with the arrangement of FIG. 3, for which purpose the pulses (the inverse of the pulses P) and K are delivered to the switch 29. The output signals of the modulator 27 are delivered without further processing to the addition circuit 34, so that the colour television signal available at the output 36 includes carrier frequency chrominance signals in line alternating sequence U + V and U - V with the same phase position.

Of a conventional PAL colour television receiver there is only shown here the portion of the chrominance channel comprising the delay line 38, the addition circuit 39, and the subtraction circuit 40. The receiver is shown notionally connected to receive the signal from 27, although in practice it will act on the equivalent portion of the signal from 36. On the basis of an assumed delay period of 283.5 colour carrier periods, the following signals appear at the outputs of the signal separation circuit: A: (I - j) (U + V + U - V) = (1 - j) 2U and B: (I - j) (U + V - U + V) = (1 - 2V 2V alternating line by line with: B': (l-j)(U-V-U-V)=(l-1)(-2V) In each case the component used by the corresponding synchronous demodulator of the receiver is shown underlined. A comparison with the conventional PAL signals shows that the same values are produced for the colour difference signals U and V: A : U + jV + U - jV = 2U B : U + jV - U + jV = j2V B': U - jV - U - jV = -j2V The only difference is that the switching phase of the V component is transposed as compared with the conventional PAL signals, but this can be compensated in the circuit arrangement of FIG. 4 by suitable control of the switch 29.

A further possibility of synthesising the colour synchronising signal is shown in FIG. 4a. FIG. 4a shows only those portions which are changed as compared with FIG. 4. Thus, following the modulator 27 a further addition circuit 41 is inserted in the path of the chrominance signal. The colour carrier F is delivered to the modulator 27 always with a phase rotated through - 450. However, during each second line, the colour synchronising signal, which is already present in the output signal of the modulator but not yet alternating at line frequency, has superimposed upon it in the adding circuit 41 a 900 rotated colour carrier oscillation train of suitable amplitude, for which purpose the switch 42 is actuated by the pulses K and P through a gate 43.

The circuit arrangement of FIG. 5 serves for the recording of S.E.C.A.M. colour television signals by a method according to the invention. The S.E.C.A.M. colour tele- vision signal delivered at the terminal 51 is divided into the luminance and chrominance signals by means of the low pass element 52 and a de-emphasis network 53. For purposes of synchronisation the input signals are also delivered to a pulse generator 10, which, as in the circuit arrangements already described, generates the timing pulses necessary for the functioning of the present circuit. The distinguishing features as compared with the circuit for PAL colour television signals are, firstly, that the chrominance signal is in a frequency modulated form and, secondly, only a colour difference signal U or V appears in alternate line sequence. Accordingly the amplitude of the chrominance signal, which is admitted by the de-emphasis network 53, is limited in a limiter 54, and the higher frequencies produced in the limiter 54 are suppressed in a band pass element 55. The chrominance signals are then delayed in a delay line 56. The delayed and the undelayed signals are demodulated in respective demodulators 57 and 58. To conform with the condition that the line alternating carrier frequency chrominance signals exhibit different steady state frequencies and polarities, undulating volt ages of one half the line frequency are delivered to the demodulators. A suitable demodulator for this purpose is described in German OS 24 13 917.

The delayed and the undelayed colour difference signals are added together in an addition circuit 59, and by means of the subtraction circuit 60 the delayed signals are subracted from the undelayed colour difference signals. At the two inputs of a selector switch 61, which is likewise driven at half the line frequency, there are thus applied in line alternating sequence the signals U + V and U - V. The application of a correct switching phase to the switch 61 ensures that these signals arrive in succession at the compression circuit 62, at which point they are compressed in accordance with the action of the circuits previously described, and are subsequently interposed by means of the selector switch 63 into the blanking intervals of the luminance signal.

For this purpose the luminance signal is again delayed by means of a delay circuit 64.

The signals indicated in FIG. 1 are then available for recording at the output 65 of the circuit arrangement of FIG. 5.

It is alternatively possible to carry out the demodulation prior to the delay action.

In such a case only one demodulator is required. The delay line must then however be suitable for video frequency signals.

A circuit arrangement for reproducing the recorded S.E.C.A.M. signal is shown in FIG. 6. The signals arriving at the point 70 are conveyed, during the horizontal frequency blanking gaps, by a selector switch 71 through a decompression circuit 76 to the input of a delay circuit 72. The output of the delay circuit 72 is connected to respective inputs of an addition circuit 73 and a subtraction circuit 74. To each of the other inputs of these circuits there are delivered the undelayed input signals of the delay circuit 72. The outputs of the circuits 73 and 74 are connected to respective inputs of another selector switch 75, which, like the circuit arrangement of FIG. 5, is driven at one half the line frequency. In this way the line sequential signals U + V and U - V are reconverted into line sequential signals U and V. After undergoing a frequency modulation according to the S.E.C.A.M. technique in the modulator 77, these signals are added in the addition circuit 78 to the luminance signal, and a S.E.C.A.M. signal is then available at the output 79 in standard form. Again a delay circuit 80 is provided for taking into account the different delay times in the chrominance and luminance channels. The generation of the clock pulses is effected in a similar manner to that in the circuit arrangements of FIGS. 3 and 4 by means of an amplitude filter 81 and a clock generator 82.

Although the embodiments of the invention have been described with reference to the recording and reproduction of colour television signals, nevertheless there will frequently occur in-the transmissions and reception of television signals problems similar to those in the recording of signals (for example unsatisfactory signal-to-noise ratios or fluctuations in delay time) which means that the invention can be used with advantage both for the recording and reproduction as well as for the transmission and reception of colour television signals.

From the foregoing it will be clear that it is possible by the aid of the invention to perform television recordings and transmissions in which the recorded or transmitted signals are independent of the television standard originally employed. Thus magnetic tape cassettes which have been recorded upon in accordance with the method of the invention can, according to the choice of the reproduction apparatus, be reproduced in accordance with either one or the other television standard, irrespective of the original standard of the signal prior to recording. As will be evident from the drawings, a large proportion of the components used in the arrangements of FIGS. 2 to 6 are independent of the particular television standard, so that the invention makes it possible to produce multiple standard apparatus without excessive capital expenditure.

WHAT WE CLAIM IS: 1. A method for recording or transmitting a colour television signal wherein successive lines of colour information are recorded or transmitted in compressed form, within successive horizontal frequency blanking intervals of the luminance information, alternately as the sum and the difference of a pair of colour difference signals.

2. A method as claimed in claim 1, wherein the colour television signal is a PAL signal, and wherein the carrier frequency chrominance signal is separated from the PAL signal and delayed by one line, the undelayed and the delayed carrier frequency chrominance signals are subtracted from each other3 and the result of the subtraction is demodulated, time-compressed, and keyed into the horizontal frequency blanking intervals of the luminance signal.

3. A method as claimed in claim 2, wherein the result of the subtraction is synchronously demodulated by deriving the colour synchronizing signal from the carrier

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. ages of one half the line frequency are delivered to the demodulators. A suitable demodulator for this purpose is described in German OS 24 13 917. The delayed and the undelayed colour difference signals are added together in an addition circuit 59, and by means of the subtraction circuit 60 the delayed signals are subracted from the undelayed colour difference signals. At the two inputs of a selector switch 61, which is likewise driven at half the line frequency, there are thus applied in line alternating sequence the signals U + V and U - V. The application of a correct switching phase to the switch 61 ensures that these signals arrive in succession at the compression circuit 62, at which point they are compressed in accordance with the action of the circuits previously described, and are subsequently interposed by means of the selector switch 63 into the blanking intervals of the luminance signal. For this purpose the luminance signal is again delayed by means of a delay circuit 64. The signals indicated in FIG. 1 are then available for recording at the output 65 of the circuit arrangement of FIG. 5. It is alternatively possible to carry out the demodulation prior to the delay action. In such a case only one demodulator is required. The delay line must then however be suitable for video frequency signals. A circuit arrangement for reproducing the recorded S.E.C.A.M. signal is shown in FIG. 6. The signals arriving at the point 70 are conveyed, during the horizontal frequency blanking gaps, by a selector switch 71 through a decompression circuit 76 to the input of a delay circuit 72. The output of the delay circuit 72 is connected to respective inputs of an addition circuit 73 and a subtraction circuit 74. To each of the other inputs of these circuits there are delivered the undelayed input signals of the delay circuit 72. The outputs of the circuits 73 and 74 are connected to respective inputs of another selector switch 75, which, like the circuit arrangement of FIG. 5, is driven at one half the line frequency. In this way the line sequential signals U + V and U - V are reconverted into line sequential signals U and V. After undergoing a frequency modulation according to the S.E.C.A.M. technique in the modulator 77, these signals are added in the addition circuit 78 to the luminance signal, and a S.E.C.A.M. signal is then available at the output 79 in standard form. Again a delay circuit 80 is provided for taking into account the different delay times in the chrominance and luminance channels. The generation of the clock pulses is effected in a similar manner to that in the circuit arrangements of FIGS. 3 and 4 by means of an amplitude filter 81 and a clock generator 82. Although the embodiments of the invention have been described with reference to the recording and reproduction of colour television signals, nevertheless there will frequently occur in-the transmissions and reception of television signals problems similar to those in the recording of signals (for example unsatisfactory signal-to-noise ratios or fluctuations in delay time) which means that the invention can be used with advantage both for the recording and reproduction as well as for the transmission and reception of colour television signals. From the foregoing it will be clear that it is possible by the aid of the invention to perform television recordings and transmissions in which the recorded or transmitted signals are independent of the television standard originally employed. Thus magnetic tape cassettes which have been recorded upon in accordance with the method of the invention can, according to the choice of the reproduction apparatus, be reproduced in accordance with either one or the other television standard, irrespective of the original standard of the signal prior to recording. As will be evident from the drawings, a large proportion of the components used in the arrangements of FIGS. 2 to 6 are independent of the particular television standard, so that the invention makes it possible to produce multiple standard apparatus without excessive capital expenditure. WHAT WE CLAIM IS:

1. A method for recording or transmitting a colour television signal wherein successive lines of colour information are recorded or transmitted in compressed form, within successive horizontal frequency blanking intervals of the luminance information, alternately as the sum and the difference of a pair of colour difference signals.

2. A method as claimed in claim 1, wherein the colour television signal is a PAL signal, and wherein the carrier frequency chrominance signal is separated from the PAL signal and delayed by one line, the undelayed and the delayed carrier frequency chrominance signals are subtracted from each other3 and the result of the subtraction is demodulated, time-compressed, and keyed into the horizontal frequency blanking intervals of the luminance signal.

3. A method as claimed in claim 2, wherein the result of the subtraction is synchronously demodulated by deriving the colour synchronizing signal from the carrier

frequency chrominance signal and delivering it to a colour carrier regenerator, and the regenerated colour carrier is phase shifted by - 450 with respect to the reference phase of the carrier frequency chrominance signal and is delivered to a synchronous demodulator.

4. A method as claimed in claim 1, wherein the colour television signal is a S.E.C.A.M. signal, and wherein the carrier frequency colour difference signals are separated from the S.E.C.A.M. signal and delayed by one line, the undelayed and the delayed signals are separately added and subtracted, and the individual results of the addition and the subtraction in demodulated form are time compressed and keyed alternately line-by-line into the horizontal frequency blanking intervals of the luminance signal.

5. A method of reproducing or receiving a signal recorded or transmitted by the method of any preceding claim, wherein the colour information signals present during the horizontal frequency blanking intervals of the recorded or transmitted signals are decompressed and a colour carrier is amplitude modulated by the decompressed signals.

6. A method as claimed in claim 5, wherein the output signal of the modulator is added to the luminance signal.

7. A method according to claim 5, wherein the output signal of the modulator is delayed by one line period, the undelayed and the delayed signal are added together and the result of the addition is added to the luminance signal.

8. A method as claimed in claim 5, 6 or 7, wherein the colour carrier being modulated has a phase position of - 450 relative to the reference phase, the colour carrier being additionally rotated through - 900 in alternate lines during the period provided for the colour synchronising signal, and wherein a pulse is keyed into the decompressed signals prior to modulation during the period provided for the colour synchronising signal.

9. A method of reproducing or receiving a signal recorded or transmitted by the method of any one of claims 1 to 4, wherein the colour information signals present during the horizontal frequency blanking intervals of the recorded or transmitted signals are decompressed and delayed by one line period the undelayed and the delayed signals are separately added and subtracted, and the individual results of the addition and the subtraction, in frequency modulated form, are added alternately line-by-line to the luminance signal.

10. A method as claimed in any preceding claim, wherein the sum and the difference of the colour difference signals are amplified with different amplification factors.

11. A method substantially as described with reference to any one of FIGS. 2 to 6 of the accompanying drawings.

12. A circuit arrangement which is adapted to operate in accordance with the method of any preceding claim.