WO1991016792A1

WO1991016792A1 - Video recorder with improved colour rendering

Info

Publication number: WO1991016792A1
Application number: PCT/EP1990/002205
Authority: WO
Inventors: Hans-Jürgen Kluth
Original assignee: Deutsche Thomson-Brandt Gmbh
Priority date: 1990-04-24
Filing date: 1990-12-17
Publication date: 1991-10-31
Also published as: AU6914791A; CN1056210A

Abstract

The bandwidth of the brightness signal in S-VHS video recorders is increased by some 5.15 MHz. However, the bandwidth of the recorded colour signal is still only ± 0.5 MHz. The aim is to obtain colour recording with an increased bandwidth and hence sharper colour reproduction with a greater signal-to-noise ratio. The modulated colour carrier (F) is recorded with second heads (K2) with wider gaps in a deeper-lying layer of the magnetic tape (T). Especially for S-VHS video recorders.

Description

VCR with improved color recording

The invention is based on a video recorder according to the preamble of claim 1. Such a video recorder is a VHS or S-VHS video recorder. known.

In a video recorder, the luminance signal is recorded by frequency modulation of an image carrier, which e.g. occupies a frequency range of 1.3 - 6 MHz. The modulated color carrier is converted into a frequency carrier with a reduced frequency, modified color carrier with a frequency of approximately 627 kHz and recorded in the free frequency range below the frequency spectrum of the modulated image carrier. Since this free frequency range is approximately 1 MHz, a maximum bandwidth of approximately 0.5 MHz results for the recorded color signals in the case of double-sided band quadrature modulation.

An improved VHS system is known (Super VHS or S-VHS) in which an increased frequency modulation range of 5.4-7.0 MHz and a larger overall bandwidth of the Spectrum are achieved. With this system, the bandwidth of the recorded luminance signal Y of about 3 MHz is recorded 5 MHz, thereby increasing the sharpness and the signal-to-noise ratio.

However, the bandwidth of the recorded color signals remains unchanged because, for reasons of compatibility, only the free frequency range from approximately 0 to 1: 2 MHz below the frequency spectrum of the frequency-modulated image carrier is still available for recording the color carrier. This has the disadvantage that the sharpness and signal-to-noise ratio leave something to be desired for the color signals, that is to say for the reproduction of colored image parts.

The object of the invention is to improve the bandwidth of the recorded color signals and thus the quality of the color reproduction in such a recorder without the available frequency range below the frequency spectrum of the modulated image carrier having to be enlarged.

This object is achieved by the invention specified in claim 1. Advantageous developments of the invention are specified in the subclaims.

The invention is based on the following consideration. The recording with heads with a larger gap width in a lower lying magnetic layer has a correspondingly smaller bandwidth due to the larger gap width. It would not be possible to record the modulated image carrier over a frequency range of 1 to 10 MHz. For the recording of the color signals, which have a smaller bandwidth compared to the luminance signal, it is possible in the lower magnetic layer with the reduced bandwidth. Rather, the bandwidth is sufficient to record the PAL color carrier with its entire bandwidth in accordance with the PAL standard. The possibility of recording a second signal of lower bandwidth in a lower one The magnetic layer of the tape is therefore used for a new type of application. Density signal by recording Leucht¬ and color carrier in superimposed layers of the tape Magnet¬ ^• several advantages. The color carrier can be recorded in the deeper layer in traces with a space, a so-called lawn. The crosstalk between adjacent tracks is kept low by this lawn. This has the advantage that comb filters used up to now with the delay of two lines for eliminating the crosstalk as well as the annoying averaging over several lines which is thereby caused are eliminated. The crosstalk between the luminance signal and the color signals is, however, reduced by the recording in different magnetic layers compared to the known recording in frequency multiplexing in a magnetic layer. The invention can in principle be used in all color television standards, that is to say in PAL, SECAM, NTSC. There is compatibility with the previous recording of a frequency carrier with a reduced frequency below the frequency spectrum of the luminance signal, since this known type of recording can also be used independently of the invention. The bandwidth in the deeper magnetic layer is sufficient to record the color carrier with the full color bandwidth and two additional frequency-modulated sound carriers. The magnetic heads with a larger gap width, which are already present in known devices, for recording sound carriers can advantageously also be used for recording the color carrier. During playback, the recorder can deliver the luminance signal on the one hand and the color carrier on the other hand each with a full bandwidth at separate outputs with little crosstalk. This type of signal processing, also called YC playback, is particularly advantageous for high-quality playback, such as with S-VHS or ADTV. The invention is explained below with the aid of an exemplary embodiment. 1 shows the frequency spectra of the recorded signals, FIG. 2 shows a block diagram for the recording, FIG. 3 shows a block diagram for the reproduction in each case for a PAL color television signal, FIG. 4, 5 shows a variant in the recording of the

Color carrier, Fig. 6 curves to show the achievable

S / N ratio and Fig. 7 curves to explain a further development.

The symbols used in the figures have the following meaning and values:

fH = line frequency of 15.625 kHz fl = 4.43361875 MHz frequency of the PAL color carrier F f2 = 0.62695313 MHz frequency of Fm f3 = fl + 40 fH + 1/8 fH = 5.0605718 MHz mixed frequency f4 = 490.25 * fH = 7.66015625 MHz mixed frequency f5 = 3.2265375 MHz = frequency of Ft

Tl = FM sound carrier for L with 1.4 MHz ± 170 kHz

T2 = FM sound carrier for R with 1.8 MHz ± 170 kHz

Ft = ink carrier recorded in the lower layer with

3.2265375 MHz Fm = recorded below the frequency spectrum of the image carrier, the frequency reduced

Color carrier F = modulated PAL color carrier

Here f4 - fl = f5 f3 - f1 = f2 applies In Fig. 1, the luminance signal Y is recorded in the form of a frequency-modulated image carrier B with magnetic heads Kl with a gap width of 0.2 μ in an upper magnetic layer SI of the magnetic tape T. The image carrier B has a static modulation shift of 5.4 MHz to 7.0 MHz and a bandwidth of approximately 1.2 to 10 MHz. The ink carrier Ft is, however, recorded with magnetic heads K2 with a larger gap width of 0.4 to 0.45 μm in the deeper magnetic layer S2 of the magnetic tape T. This recording takes place with an intermediate space, a so-called lawn, between the tracks and an azimuth angle between the two heads K2 of ± 30 °. The color carrier Ft is obtained from the PAL color carrier with a mixed carrier with the frequency f4.

With the second heads K2, the two sound carriers T1, T2 for stereo sound are additionally recorded in the lower lying magnetic layer S2. When recording, the signals T1, T2, Ft are first written with the heads K2 in the lower magnetic layer S2. Shortly thereafter, with a slight spatial offset, the image carrier B is recorded with the heads K1 in the layer SI, the recording already made by K2 in the layer SI being deleted again.

In the layer Ξl, below the frequency spectrum of the image carrier B, the frequency carrier Fm, which is reduced in frequency, can additionally be recorded in a known manner in order to ensure compatibility with previous devices. The color signals would then be recorded twice. The color carrier Fm can be inserted as a replacement signal in the event of a fault in Ft. Fm can also be used in the search run to enable color reproduction. Such a search with color reproduction would be the carrier Farb¬ Ft from the deeper layer S2 not readily available, a he _b basically also possible. Instead of the frequency modulated sound carrier T1, T2, another sound signal, for example a digital sound signal in the form of a NICAM carrier, can also be recorded. If the additional recording of Fm is dispensed with, the luminance signal can be extended into the lower frequency range from 0 to 1 MHz and the recording bandwidth of Y can thus be increased. The color carrier Ft extends from about 2.5 to 4.5 MHz and has the full color bandwidth of about +1.3 MHz. A correspondingly recorded SECAM color carrier would have a frequency range of 2.41 MHz - 4 in the second layer S2. Take 28 MHz.

In Fig. 2, the CVBS signal is separated with the isolating stage 1 into the luminance signal Y and the color carrier F. Y reached via the pre-emphasis stage 2, the FM modulator 3 and the amplifier 4 to the adder stage 5, the output of which is connected in parallel to the two heads Kl. The color carrier F passes through the bandpass filter 6 with a passband of 4.43 MHz +0.6 MHz -0.8 MHz to the frequency converter 7, which causes a frequency conversion from fl to f2. The color carrier Fm thus obtained passes through the low-pass filter 8 to the adder stage 5. In the synchronous separator stage 9, the line synchronizing pulses are separated with the frequency fH and converted in the converter 10 to a mixed carrier with the frequency f3, which passes through the high-pass filter 11 to the other Entrance of the converter 7 arrives. This type of recording, also known as "color under", is known.

The color carrier F is fed to the converter 13 via the bandpass filter 12 with a pass band of 4.43 MHz +0.6 MHz -1.2 MHz, which on the other hand is supplied from the synchronous isolating stage 9 via the converter 14 and the high-pass filter 15 with a mixer carrier is fed with the frequency f4. At the output of the converter 13, the color carrier Ft is formed, which passes through the bandpass filter 16 with a pass band of 3.22 MHz +1.2 MHz -0.6 MHz reaches the adder stage 17. In the adding stage 17, the two sound carriers Tl, T2 are added. The sum signal with the frequency spectrum according to FIG. 1b reaches the two magnetic heads K2 via the amplifier 18 with a gap width of approx. 0.4 to 0.45 μm larger than the Kl.

With the heads K 1 having a narrow gap width of 0.2 μm, the image carrier B modulated with Y and the color carrier F m are recorded in the upper layer SI of the magnetic tape T. With the heads K2, however, the color carrier Ft and the sound carrier T1, T2 are recorded in the deeper magnetic layer S2.

Fig. 3 shows the playback circuit. The image carrier B scanned with the heads Kl from the tape T arrives at the terminal 26 via the switch 19, the delay stage 50, the deemphasis stage 21, the FM demodulator 22, the low pass 23 and the deemphasis stage 24 and the switch 25 which the demodulated luminance signal Y is available. The color carrier Fm passes through the low-pass filter 27, the converter 28, the bandpass filter 29, the delay line 30 for two lines and the changeover switch 31 to the terminal 32, at which the original PAL carrier F is again located. The adder 33 supplies the CVBS signal formed from Y and F. The line synchronizing pulses are separated in the synchronizing pulse separating stage 34 and converted in the converter 35 to a mixed carrier with the frequency f3. This passes through the high pass 36 to the converter 28. This playback circuit for "color under" operation is known.

The heads K2 initially deliver the ink carrier Ft according to FIG. 1b via the changeover switch 37. This is evaluated with the bandpass filter 38 with a passband of 3.22 MHz +1.2 MHz -0.6 MHz and fed to the converter 39, which is also provided by the synchronizing pulse separation stage 34 via the converter 41 and the high-pass filter 42 is supplied with a mixed carrier with the frequency f4. The color carrier F at the output of the converter 39 reaches the bandpass 40 with a passband of 4.43 MHz +0.6 MHz -1.2 MHz and the transit time stage 46 to the second input of the switch 31. When recording of the color carrier Ft in the deeper layer S2 according to FIG. 1b, a switching voltage 43 is generated from the signal at the terminal 44. This actuates the changeover switch 31, so that instead of the ink carrier Fm from the heads Kl the broadband ink carrier Ft is now supplied from the heads K2 to the terminal 32. The switching voltage 43 at the terminal 44 also actuates the changeover switch 25. This switches on the runtime stage 45, which effects a runtime adaptation of the signal Y to the now broadband ink carrier F. The switching voltage 43 can be derived from an additional modulation of the likewise recorded sound carriers T1, T2. For example, a modulation of 22 kHz in T1 indicates that the color carrier Ft is recorded in the deeper layer S2 and that the switch 31 must therefore be actuated for the broadband color reproduction. A modulation of 22 kHz in the sound carrier T2, however, indicates the recording of a broadband SECAM color carrier in layer S2. Level 46 is used to adjust the run times.

The sound carriers Tl, T2 recorded in addition to Ft according to FIG. 1b are evaluated with the band filter 47 and are available at terminal 48 for the sound channel. Instead of the frequency-modulated sound carriers T1, T2, other sound signals, e.g. a digitally modulated NICAM sound carrier can be recorded.

The mixed carriers used in the recording and in the reproduction for converting the frequencies of the color carrier are coupled to the line frequency. A so-called half-line offset is preferably used for this, in which the frequency of the mixed carrier is a full line multiple of half the line frequency. This coupling is particularly advantageous if a comb filter is also used in the path of the signals in order to separate luminance signal Y and color carrier F from one another or to additionally suppress residual components of the other signal in one of the signal paths. The first heads K 1 and the second heads K 2 are preferably formed by so-called combination heads. The column of heads K1 and the column of heads K2 are inevitably geometrically offset from one another. This means that the signals supplied by these heads are also staggered in time. The geometric arrangement of the heads and their gaps is preferably such that there is deliberately a time shift between the signals of the first heads K1 and the signals of the second heads K2 by a whole number of line periods, for example two lines. By means of a corresponding geometric arrangement of the heads, a temporal offset between the signals of the first heads and the second heads which is desired in the reproduction can thus be achieved.

4, 5, the color carrier Ft recorded with the second magnetic heads K2 in the lower-lying magnetic layer S2 is converted to a frequency range of 0.9-2.9 MHz with a carrier frequency of 1.57 MHz. This is the frequency range in which the signal-to-noise ratio has its maximum during recording. The sound carrier T2 is recorded at 0.45 MHz. The sound carrier T1 is, however, recorded with the first magnetic heads K1 in the upper magnetic layer SI according to FIG. 4a at a frequency of 0.85 MHz. This solution has the advantage that a sound carrier that can be used in the search run can be removed both from the first magnetic heads K1 and from the second magnetic heads K2, which was previously not possible with the VHS and _S- VHS system, since the search run only one track at a time can be read correctly, either the image track or the sound track. However, since the search image was necessary, the search tone was previously switched off. It is sufficient for the search run if only T1 or only T2 is reproduced.

It is also possible to record the two sound carriers Tl, T2 above the frequency range of Ft in the range of approximately 3-4 MHz, as indicated by dashed lines. Then the sound carrier Tl can be omitted in the upper magnetic layer. In this solution, the frequency range of the modulated image carrier B according to FIG. 4a can be extended to lower frequencies, as indicated by the dashed curve 51 in FIG. 4a. This expansion of the frequency range can further improve the image sharpness and signal-to-noise ratio.

FIG. 6 shows recorded measurement curves which represent the signal-to-noise ratio when recording the color carrier Ft as a function of the frequency. Curve 52 shows the noise signal from the heads during playback and curve 53 shows the useful signal. It can be seen that a sufficient signal-to-noise ratio of approximately 30 db can be achieved within the frequency range occupied by the ink carrier Ft, represented by line 54. The somewhat lower signal-to-noise ratio in the range of 3 - 4 MHz is, however, sufficient for the recording of additional FM sound carriers.

7 shows a variant with which the signal-to-noise ratio can be further improved. According to FIG. 7a, the synchronization pulses S have an amplitude of 0.3 V and the BA signal an amplitude of 0.7 V for a standardized video signal. For the recording, the amplitude of the synchronization pulses S is now 0.1 V decreased and the amplitude of the BA signal increased accordingly to 0.9 V. With the same modulation, this results in an increase in the BA amplitude from 0.7 V to 0.9 V. As a result, the frequency swing which can be used for the BA signal can be increased from 1.6 to 2 MHz, which means an increase of 28% in the frequency swing for the BA signal and a corresponding increase in the signal-to-noise ratio. During the reproduction, the amplitude of the synchronizing pulses S is raised again to the standardized value of 0.3 V or 30% of the maximum amplitude between the synchronous roof and peak white.

A so-called azimuth offset from track to track is additionally used for the recording of B in the layer sowiel and the recording of Tl, T2, Ft in the layer S2. This is preferably ± 6 ° for SI and ± 30 ° for S2. This azimuth offset serves to reduce crosstalk between two adjacent tracks. Both the recording of B in layer SI and the recording of T1, T2, Ft in layer S2 can be carried out with or without an intermediate space, a so-called turf, between adjacent tracks.

Claims

.Patent claims

1. Video recorder with improved color recording, in which an image carrier modulated with the luminance signal is recorded with first heads of narrow gap width in an upper magnetic layer (SI) of the tape (T), characterized in that the modulated color carrier (Ft ) is recorded with second heads (K2) of larger gap width in a lower lying magnetic layer (S2) of the tape (T).

2. Recorder according to claim 1, characterized in that the frequency of the color carrier (F) is implemented with a mixed carrier whose frequency is coupled to the line frequency (fH) during recording and / or playback.

3. Recorder according to claim 2, characterized in that the color carrier (Ft) is coupled to the line frequency in half-line offset.

4. Recorder according to claim 2, characterized in that the mixed carrier is obtained by frequency multiplication from the line synchronizing pulses.

5. Recorder according to claim 1, characterized in that a comb filter for suppressing one of the two signals is arranged in the playback of the luminance signal (Y) and / or the modulated color carrier (F).

6. Recorder according to claim 1, characterized in that the recording of the color carrier (Ft) with anyway existing heads (K2) for the recording of FM sound carriers (Tl, T2).

7. Recorder according to claim 1, characterized in that the color carrier (Ft) is recorded in frequency division multiplexing together with FM sound carriers (Tl, T2).

8. Recorder according to claim 1, characterized in that the playback circuit for the second heads (K2) contains a detector which recognizes the ink carrier (Ft) recorded in the lower magnetic layer (S2) and detects the recorder automatically on the Evaluation of this color carrier switches.

9. Recorder according to claim 8, characterized in that the detection is carried out by an identification signal with which an additionally recorded FM sound carrier is modulated.

10. Recorder according to claim 1, characterized in that in the frequency range below the modulated image carrier (B) additionally the frequency-reduced color carrier (Fm) is recorded.

11. Recorder according to claim 1, characterized in that a modulated sound carrier is recorded in the frequency range below the modulated image carrier (B) instead of a color carrier reduced in frequency.

12. Recorder according to claim 11, characterized in that the color carrier (Fm) is omitted and the bandwidth of the image carrier in the freed frequency range is extended to low frequencies.

13. Recorder according to claim 11, characterized in that during playback during a disturbance of the color carrier (Ft) scanned by the deeper magnetic layer (S2), the color carrier (Fm) from the upper layer (SI) is used for signal reproduction.

14. Recorder according to claim 1, characterized in that the tracks are written by the second heads (K2) in the deeper magnetic layer (S2) with a space, so-called lawn.

15. Recorder according to claim 1, characterized in that the first heads (Kl) and the second heads (K2) are each formed by combi heads.

16. Recorder according to claim 1, characterized in that the first heads (Kl) and the second heads (K2) are arranged geometrically to one another such that the signals supplied by the two heads are offset in time by a whole number of line periods .

17. Recorder according to claim 16, characterized in that the time offset is equal to the duration of two lines.

18. Recorder according to claim 1, characterized in that the modulated color carrier (Ft) is in a frequency range (1-3 MHz), in which the signal-to-noise ratio of the second heads (K2) is at a maximum (Fig. 5, 6).

19. Recorder according to claim 18, characterized in that below the frequency range occupied by the color carrier (Ft) a modulated FM sound carrier (T2) is recorded (Fig. 5).

20. Recorder according to claim 18, characterized in that a modulated FM sound carrier (Tl, T2) with the second magnetic heads (K2) is recorded above the frequency range of the modulated color carrier (Ft) (Fig. 5).

21. Recorder according to claim 1, characterized in that the recording with the first and second Magnetköp¬ fen (Kl, K2) with different azimuth angles (6 °, 30 °).

22. Recorder according to claim 1, characterized in that a first FM sound carrier (Tl) with the first Magnetköp¬ fen (Kl) and a second FM sound carrier (T2) with the second th magnetic heads (K2) is recorded (Fig 4, 5).

23. Recorder according to claim 1, characterized in that the amplitude of the synchronizing pulse (S) in the recorded signal is reduced from the standardized value (0.3 V) to a lower value (0.1 V) and during playback ¬ be increased again to the standardized value (Fig. 7).