DE3244942A1 - Method for recording and reproducing television signals - Google Patents

Abstract

A method for recording and reproducing colour television signals in analog form. The luminance information Y is transmitted during the forward linescan and the chrominance information (R-Y) (B-Y) is transmitted sequentially time-compressed during the blanking interval. Together with the information items, a carrier-frequency carrier, the frequency of which is switched at half-line rate, is coupled in for generating the synchronisation pulses, which carrier is transformed with the aid of a discriminator to form line synchronisation pulses during the reproduction.

Description

Method for recording and reproducing television signals.

PRIOR ART The invention is based on a method for Recording and reproduction of television signals in analog form, the luminance information while the line period is running and the color information is time-compressed sequentially during the remainder of the line period within the blanking time is recorded.

One such method is entitled: "Timeplex" - a serial Color coding method for home video recorders in the magazine "Fernseh und Kinotechnik" 34 year no. 12/1980 page 451-458 as well as in DE-AS 2-6 29 706 described.

This practice has been used with color television signals traveling over channels are to be transmitted with limited quality, e.g. with video recorders, well proven. Here, the luminance signal and the color difference signals become line frequencies transmitted or recorded serially. This is done in such a way that the luminance signal is recorded during the line trace while the two color difference signals recorded alternately by a factor of 5 time-compressed during the blanking time or transferred.

The line sync pulse and a must also be inserted in the blanking interval Clamp level must be keyed in. Since the time, however, for the keying in of these signals is very limited by the presence of the color difference signals, it has been suggested that alternately key in the line sync pulse and the clamping pulse from line to line. Therefore, a line pulse with a duration of 1.6 / u sec.

and within the following return line an equally long one Clamping pulse keyed in. However, it has been shown that such a short Impulse leads to synchronization problems, especially if it is only every second line is present, especially when recording and playing back images with video recorders for home use.

Task The invention is therefore based on the task of this To correct the deficiency, so that a reliable line synchronization is guaranteed. This object is achieved by the measures specified in the claims.

Description The following describes the essentials of an exemplary embodiment the invention will be explained with the help of the drawing.

Figure 1 shows a voltage-time diagram in the Timeplex method generated signal.

Figure 2 and Figure 3 show block diagrams for performing the notified procedure.

Figure 4 shows the frequency response of the FM transmission range of the magnetic head signal with the carrier frequencies of the additional pulse signal.

In Figure 1 is the composite signal generated by the Timeplex method recorded. You can see that the greater part of the line period during the time Luminance signal Y occupying TH and those recorded in the blanking intervals TA1 and TA2 time-compressed color difference signals (R-Y), (B-Y), with inside the one Blanking TA1 a clamping pulse K and during the next blanking interval TA2 Synchronous pulse S is transmitted.

The essentials are shown below in a block diagram in FIGS. 2 and 3 the invention explained. These are based on the well-known Timeplex method related circuit assemblies are drawn above the dashed line, while below this line those required for the process according to the invention Assemblies are recorded.

First of all, the Timeplex method should be briefly discussed.

In Figure 2, the recording of a video signal on a magnetic tape described. The Y signal arrives at a switch via a color carrier trap 1 2, which is controlled by a clock 3 in such a way that the Y signal during of the line feed to the recording channel 4, which from the FM modulator of the pre-emphasis and the recording amplifier is connected. During the return time TA is alternately line frequency through the fH / 2 clock that processed by the PAL decoder 5 R-Y signal or B-Y signal switched to recording channel 4 after she in a memory 6 with the aid of a read-in clock generated by the clock generator 3 of e.g. 2 MHZ read in and read out again with the help of a readout cycle of 10 MHZ which results in time compression by a factor of 5.

According to the invention, a generated with the aid of an oscillator 7 is now Synchronization signal placed on the recording head of the magnetic tape recorder 8, so that together recorded with the time-compressed color difference signals R-Y, and the Y signal will. The carrier frequency of the synchronization signal is preferably in the upper transmission range of the magnetic head signal. The amplitude of this signal is chosen so that an impairment the Y and chroma signals are avoided. The identifier required for the PAL standard can be generated with the help of a switched carrier frequency for the synchronous signal will. For this purpose, the oscillator 7 is taken from the clock generator 3 by a device half-line frequency control clock via a stage 9 symmetrically in frequency a center frequency switched by the half-line frequency control clock over the switch 9a - shown here as a mechanical switch for the sake of simplicity -keyed switch 9b. As a result, a capacitor 23 is alternately connected to the oscillator switched. The effect of the control cycle H is achieved through vertical frequency switching of the 2 contact 9b with the aid of a control clock taken from the clock generator 3 V switched off. This measure enables recovery on the playback side of the vertical sync pulse as will be explained later.

With the help of the figure. 3 below is the preparation of the synchronization serving impulse are explained. The signal emitted by the recording device 8 is in a playback channel 10, which consists of a playback amplifier, a dropout compensator, a limiter, an FM demodulator and a deemphasis, amplifies and the brightness signal Y arrives from there via one controlled by the clock generator 3 Switch 11 to an adder 12 during the line trace time. In a secondary branch is with the help of a controlled by the clock 3 memory 13a / 13b and a PAL encoder 14 decompresses the color signal again via the adder circuit 12 to a complete one Converted composite signal, which is reproduced by a television receiver. the Decompression happens in the Heise that the memory 13 with a clock of 10 MHZ is read in and read out again at a rate of 2 MHZ. That for synchronization The synchronizing signal necessary for the television receiver is recovered in the following manner and also applied to the addition stage 12. The one recorded during recording The carrier signal is transmitted via a device that limits and amplifies the signal 15 connected to a phase discriminator 16. The phase discriminator 16 is on a frequency matched between the carrier frequencies of the sync signal lies. Through the phase discriminator 16 or an equivalent circuit, signals alternating polarity generated. The generated square wave signal with half the line frequency serves as the reference frequency of a phase-locked-loop circuit (PLL), consisting of the voltage-controlled (VCO) oscillator 19 oscillating at line frequency, the the divider 20 halving the oscillator frequency, the phase comparator 17 and the low-pass filter 18. The way of working a dar-like circuit can be known as are assumed. A monostable multivibrator connected to the oscillator 19 21 generates horizontal-frequency synchronizing pulses dio via the clock gunerator with the likewise regenerated vertical synchronization pulse to the adder circuit 12 reach. The vertical sync pulses are monostable with the help of another Flip-flop 22 is generated, which receives trigger pulses from the phase comparator 17, which by the previously described H suspension of the half-line frequency pulses 2 during of the image rewind at the output of the phase comparator 17.

The FM transmission range of the head signal is plotted in FIG and the frequency position of the carrier of the keyed synhronic pulse, which is at the upper The end of the transmission range.

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Claims (8)

Claims method for recording and reproducing color television signals in analog form, with the luminance information during the run of the line period and the color information is time-compressed sequentially for the remainder of the time of the line period in the blanking time is transmitted or recorded, with the Compression and for decompression the digitized color signals with the help of Clock pulses generated by a clock are written into and read out from the memory be, d u r c h e -k e n n n z e i c h n e t that one for synchronization Serving carrier is coupled. 2. The method according to claim 1, d a d u r c h g e -k e n n z e i c h n e t that the carrier frequency of the ynchrontrg, ers in the upper transmission range of the Magnetic head signal of the recording device lies. 3. The method according to claims 1 to 2, d a d r c h g e k e n n z E i C h'n e t that the carrier frequency of the synchronizing signal is half-line frequency symmetrical is switched to a center frequency. 4. The method of claim 3, d a d u r c h g e -k e n n z e i c h n e t that the switching of the carrier frequency by a vertical frequency control clock V is interrupted while the picture is being reversed. 5. The method according to claims 1 to 3, d a d u r c h g e k e n n z e i c h n e t that during playback the coupled sync signal after a gain is connected to a discriminator, which is dependent on the carrier frequency delivers signals of different polarity. 6. The method according to claim 4, d a d u r c h g e -k e n n z e i c h n e t that the center frequency of the discriminator between the two carrier frequencies the impulse lies. 7. Ver-driving according to claim 4 and flj, d a d u r c h g e -k e n n z e i c h e t, dar3 the signal generated by the discriminator with an oscillator phase-locked in a control loop. 8. The method according to claim 7, d a d u r c h g e -k e n n z e i c h n e t that the clocks for the horizontal pulses II, vertical pulses V and the clock with half the line frequency, derived from the PLL loop and via the clock generator (3) can be added as a combined sync signal to the demodulated color signal