JPH0226437B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an S/N improvement device for a reproduced video signal in a VTR having a variable speed reproduction function.

Leave the tape on the rotating head drum and set the tape speed to 2 to 20, for example during normal playback.
VTRs with a so-called variable speed playback function are known, in which the playback screen corresponding to the tape speed can be viewed on a television receiver by fast-forwarding or rewinding the tape speed at twice the speed. ing.

A processing system for a reproduced video signal when performing normal playback and variable speed playback in this type of conventional device in a VTR equipped with the variable speed playback function described above will be outlined with reference to FIG.

The signals recorded on the tape 1 are picked up from the tape 1 by two video heads A and B, and the pickup output is amplified by a reproduction amplifier 2. A switching pulse is supplied to the reproduction amplifier 2 from the terminal _T1 , and the pickup outputs from the two video heads A and B are alternately switched to form one continuous signal.
Although not shown, the output from the reproduction amplifier 2 described above is separated into a color signal system and a luminance signal system by an LPF and an HPF, and the color signal that has passed through the LPF is mixed after passing through a color signal processing process 5. It is supplied to the container 6. The luminance signal that has passed through the HPF is supplied to the mixer 6 via the limiter 3 and the demodulation circuit 4, where it is mixed with the color signal and taken out as a video output from the terminal _T2 . In the signal processing system of the conventional apparatus described above, no processing is performed on the luminance signal even when variable speed reproduction is performed.

That is, in the above-mentioned conventional device, the output of the reproducing amplifier 2 is passed through the limiter 3 and the demodulation circuit 4, and is directly output as a video output. FIG. 4 is a diagram for explaining the state during fast-forward playback, and FIG. 5 is a diagram for explaining the state during rewind playback, and numeral 1 indicates the relationship between the tape pattern and the video head. The illustrated arrow X indicates the tape running direction during normal playback, the arrow _Y1 indicates the tape running direction during fast forward playback, and the arrow _Y2 indicates the tape running direction during rewind playback. Further, arrow Z indicates the direction of rotation of the video head. And A _T is the trace trajectory by A head, B _T is B
ABAB... shown at the bottom of the tape pattern is the trace trajectory by the head, and ABAB... is the memory track corresponding to the A head, and B
B tracks, which are storage tracks corresponding to the heads, are shown. 2 shows the state of the reproduction output from both heads A and B, but what is shown here does not show the reproduction output itself from the tape pattern shown in 1. 3 shows the state of the playback screen on the television receiver, and this is shown in correspondence with the playback output from the heads shown in 2 above. In this case, the playback output from both heads A and B is Since the portions that become zero, that is, the portions that appear as noise, overlap, they appear as two bar noises as shown in the figure.

Therefore, when fast-forwarding or rewinding is performed at a tape speed 20 times faster than normal playback, both the A and B heads trace the recorded tracks every 20 tracks. At this time,
Since both tracks are recorded with azimuth angles of ±α, both heads A and B can obtain output only from recording tracks with the same azimuth angle. Therefore, the playback output from the head in the above case is a composite output from the 10 tracks.
Furthermore, the reproduction output from both heads A and B is determined by the trace angle of the head (see Fig. 4 1 and Fig. 5 1).
Since the output becomes significantly different from that during normal playback, it becomes a diamond shape as shown in 2 in Figures 4 and 5, and the output becomes zero at the joints of each track.
On the playback screen of a television receiver, this appears as noise as shown in 3 in FIGS. 4 and 5.

In other words, parts where the playback output from the head is zero appear as noise on the playback screen, and parts where the playback output level is low have poor S/N, making it difficult to perform variable speed playback during fast forward playback or rewind playback. The reproduced screen in this case had noticeable noise and areas with poor S/N, and was visually very unsightly.

The present invention has been made to eliminate the above-mentioned drawbacks of conventional devices equipped with a variable speed playback function.
By lowering the frequency characteristics and amplitude of only the deteriorated parts of the video signal, the S/N ratio can be visually improved and a playback screen that is easy to see even during variable speed playback can be obtained. The purpose of the present invention is to provide an S/N improvement device for the following.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the device according to the present invention, and the same parts as in FIG. 1 are given the same reference numerals. Among the outputs of the reproduction amplifier 2, the color signals are supplied to the mixer 6 via the color signal processing process 5 as described above. On the other hand, the luminance signal (reproduced video signal) is supplied to the mixer 6 via the limiter 3 → demodulation circuit 4 and noise reduction circuit 7. The above-mentioned noise reduction circuit 7 receives the reproduced video signal that has passed through the demodulation circuit 4 and the reproduced video signal from the reproduction amplifier 2, which are obtained through the envelope detection circuit 8 → pulse generation circuit 9 → H blanking insertion circuit 10. is supplied, and from its output, a video output is obtained in which the frequency characteristics and amplitude of only the noise part and the degraded S/N part in the reproduced video signal are lowered, and the above-mentioned mixer 6 processes the color signal processing process 5. mixed with the color signal via the . The above-mentioned H blanking insertion circuit 10 is supplied with a signal obtained from the above-mentioned reproduced video output, which is the output of the noise reduction circuit 7, via the synchronization separation circuit 11 and then the H blanking pulse generation circuit 12.

In the above circuit configuration, when fast-forward playback or rewind playback is performed, the output of the playback amplifier 2 is the playback output from the head shown in FIGS. 4 and 5, as described above. Figures 4 and 5
The number of peaks in the reproduced output from the head shown in FIG. 2 varies depending on the tape speed at the time of reproduction, but for convenience of explanation it is assumed that the reproduction is performed in the form shown. Note that the outputs of the A and B heads normally overlap, but are alternately switched by a switching pulse and reproduced as a continuous wave as shown in the figure.

Next, the operation of the device having the circuit configuration shown in FIG. 2 will be explained with reference to the waveform diagram shown in FIG. 6. Note that the numbers in parentheses in FIG. 2 correspond to 1 to 10 in FIG. 6.

The output of the reproduction amplifier 2 includes A shown in FIG.
Reproduction output from both B heads can be obtained. This continuous wave is formed as a continuous wave by the switching pulses supplied to the terminal _T1 whose phase differs by 180 degrees for each field as shown in FIG. 6, as described above. The signal from the reproduction amplifier 2 is sent to the limiter 3.
→It is demodulated by the demodulation circuit 4. At the output of the demodulation circuit 4, a reproduced video signal shown in FIG. 6 is obtained. In FIG. 6, VD represents a vertical synchronizing signal, N represents a noise portion, and S represents a portion with poor S/N. Comparing this reproduced video signal with FIG. 61, it can be seen that noise occurs where the reproduced output of the head is zero, and the S/N becomes worse in areas where the reproduced output level is low. FIG. 6 4 shows the output of the reproduction amplifier 2, that is, FIG. 6 1
This is an envelope detection waveform of the reproduced output obtained by detecting the reproduced output of both heads A and B shown in FIG. The envelope detection waveform of the reproduced output obtained by the envelope detection circuit 8 (see FIG. 6, 4) is supplied to the pulse generation circuit 9, and the output of the pulse generation circuit 9 is as shown in FIG. A pulse, that is, a pulse corresponding to a portion S with poor S/N as shown in FIG. 6 is obtained. Note that the pulses generated by the pulse generating circuit 9 are formed by processing the envelope of the output of the reproducing amplifier 2 as described above, but if the rise and fall are made gentler, the change in S/N will be reduced. This results in a more gradual transition and a better visual appearance on the playback screen.

FIG. 6 shows an enlarged time axis of the reproduced video signal waveform shown in FIG. 6 and a portion with a poor S/N ratio. Note that HD in FIG. 6 above indicates a horizontal synchronizing signal, and CB indicates a color burst signal. The processing up to this point is performed by the envelope detection circuit 8 and the pulse generation circuit 9.

Subsequently, the video output, which is the output of the noise reduction circuit 7, which will be described later, is supplied to the sync separation circuit 11, and the sync separation circuit 11 extracts only the sync signal, which is supplied to the H blanking pulse generation circuit 12. The H blanking pulse shown in FIG. 6 is generated from the output, which may include a horizontal synchronization signal as well as a color burst signal. FIG. 6 8 shows the pulses obtained from the pulse generation circuit 9 shown in FIG. 6 5 enlarged on the same time axis as the reproduced video signal shown in FIG. circuit 9
(see FIG. 6, 8) and the output from the H blanking pulse generation circuit 12 (see FIG. 6, 7), the H blanking insertion circuit 10 suppresses the H blanking portion shown in FIG. 6, 9. A pulse is formed. The pulse generated by the H blanking insertion circuit 10 and suppressing the H blanking portion (see FIG. 6 and 9) is supplied to the noise reduction circuit 7.

The above noise reduction circuit 7 is configured as shown in FIG. 3, for example. Thus, the pulse shown in FIG. 6 from the above-mentioned H blanking insertion circuit 10 is
When applied to the base of the transistor Q (indicated by terminal _T4 ) constituting the noise reduction circuit 7, the video signal excluding the H blanking period is connected to the capacitor C.
As a result, the frequency characteristics are lowered, and the noise component of the input video signal (the signal shown in FIG. 6, which is applied from the demodulator circuit 4 to the terminal _T3 ) is reduced, and the S/N is improved as shown in FIG. 6, 10. The reproduced video signal is obtained from terminal _T5 . Note that the same effect as described above can be obtained even when the level is lowered by a resistor R instead of the capacitor C described above.

Here, the reason why noise is not suppressed during the H blanking period as described above will be explained.

When the synchronization signal part is also suppressed, the value of capacitor C of the noise reduction circuit 7 shown in FIG. 3 becomes small,
If the frequency characteristics of the video signal are not changed significantly, the S/N of the synchronization signal of the reproduced video signal will improve a little, but if the value of the capacitor C mentioned above is increased to increase the degree of S/N improvement. teeth,
This is because the synchronization signal portion of the reproduced video signal becomes small, causing synchronization disturbances on the reproduction screen in the television receiver. Furthermore, if the color burst signal portion is also suppressed, synchronization disturbances will occur on the playback screen in the same way as described above.

In the output of the above-mentioned noise reduction circuit 7, noise in a portion other than the H blanking period shown in FIG. 6 is suppressed, and a reproduced video signal with improved S/N is obtained. Incidentally, FIG. 7 shows a comparison between a conventional apparatus and the above-described apparatus according to the present invention, as viewed from the reproduction screen of a television receiver. "O"
These are examples of fast-forward and rewind playback of a tape on which characters are recorded. 1 is a playback screen during variable speed playback with a conventional device, and 2 is a playback screen during variable speed playback with a device according to the present invention. The S/N ratio has been improved compared to the past, making the screen visually easier to view.

In the circuit configuration showing one embodiment described above,
The color signal that has passed through the color signal processing process 5 is
Although the color signals are mixed at the output side of the noise reduction circuit 7, even if the above color signal is input to the input side of the noise reduction circuit 7 and noise components are suppressed together with the color signal, the color burst signal remains. The color in the noise-containing part simply disappears, and no problem occurs.

FIG. 8 explains the deviation of the reproduced horizontal synchronization signal from the reference horizontal synchronization signal that inevitably occurs when a tape recorded by azimuth recording is reproduced at variable speed (the case of fast-forward reproduction is shown). That is, in the case of the figure, the shift on the time axis due to the azimuth angle during fast-forward playback is explained. 1 to 3 in the figure represent the relationship 1 between the tape pattern and the trace locus A _T of the head when the A track is traced with the A head, the playback output from the A head 2, and the lead/lag relative to the reference horizontal synchronization phase. State 3 is shown. Also 4
- 6 are the relationship between the tape pattern and the head trace locus B _T when the B track is traced by the B head, 4, the playback output from the B head, 5,
A state 6 of lead/lag with respect to the reference horizontal synchronization phase is shown.

Azimuth angle on tape pattern ±α゜,
If the recording track width is W, and if the deviation from the reference is zero at the point where the reproduction output from both heads A and B is maximum (see Figure 8, 2, 3, 5, and 6), then head A and head B At the head, the lead and lag are reversed. In addition,
During rewind playback, the advance and lag of both heads A and B are reversed. This lead/lag P-P value (△
Hmax) is W x tanα, and since the outputs of the A head and B head overlap on the playback screen, and the outputs of the A head and B head are in opposite directions, 2W・tanα・(1H time)/(1H worth of tape) Even if there is a time lag (length) and the H of adjacent trads are lined up consecutively on the tape pattern,
Only the value shown in the above formula is displayed on the playback screen as the 9th
It appears in the form shown in FIG. Furthermore, when the H's of adjacent treads are not lined up, the playback screen takes the form shown in FIG. 9, although it varies depending on the amount of H deviation. Note that FIG. 9 shows the original form on the playback screen during normal playback. In addition, in FIGS. 1 and 2, only the beginning of the signal is bent because the AFC of the television receiver is applied.

The device according to the invention described above may work in all playback modes; during normal playback, since the playback output is large, no noise suppression operation is performed. Furthermore, in areas where the playback level is low, such as still image playback, the playback screen will be easier to see if noise suppression is performed. Furthermore, even when playing back compatible tapes, it is better for this device to work in areas where the playback level is low.

In the above explanation, the case of the azimuth recording method was explained, but even in the method with a guard band, the s/n in the low playback level part is
The present invention is effective for improving.
In the conventional device, a dropout compensation circuit detects the envelope of the reproduced output to form a dropout pulse, and the dropout pulse is used to generate a video signal using a circuit configuration similar to that of the device according to the present invention described above. Some have performed mean value clamping of the dropout portion of the signal, but this is essentially different from the device according to the invention described above.

As described above, according to the present invention, pulses formed from the waveform obtained by envelope detection of the playback output of the video head, and the horizontal synchronization signal and color burst formed by separating the synchronization signal from the playback video signal. A noise suppression pulse is formed with the H blanking pulse that may contain a signal, and the noise suppression pulse improves the noise and S/N in the S/N degraded portion of the reproduced video signal. It is possible to provide an S/N improvement device for a reproduced video signal in a VTR having a variable speed reproduction function that can provide a visually easy-to-read reproduction screen even in a VTR.

[Brief explanation of drawings]

Fig. 1 is a schematic circuit diagram of a conventional device, Fig. 2 is a schematic circuit diagram of a device according to the present invention, and Fig. 3 is a schematic circuit diagram of a conventional device.
The figure is a circuit diagram showing one embodiment of the noise reduction circuit. Figures 4 and 5 are the relationship between the tape pattern and the video head trace locus during fast-forward playback and rewind playback, the output waveform of the playback amplifier, and the playback screen. FIG. 6 is a waveform diagram for explaining the operation of the device according to the present invention, and FIG. 7 is a diagram showing the above configuration.
Figure 8 is a diagram comparing the conventional device and the device according to the present invention on the playback screen, Figure 8 is a diagram for explaining the deviation on the time axis due to the azimuth angle during fast forward playback, and Figure 9 is a diagram for explaining the time axis deviation during fast forward playback and the winding. FIG. 6 is a diagram showing a playback screen during backward playback. 3: Limiter, 4: Demodulation circuit, 7: Noise reduction circuit, 9: Pulse generation circuit, 8: Envelope detection circuit, 10: H blanking insertion circuit, 11:
Synchronous separation circuit, 12: H blanking pulse generation circuit.

Claims (1)

[Claims] 1 In a VTR equipped with a variable speed playback function, pulses are formed from the waveform obtained by envelope detection of the playback output of the video head, and a horizontal synchronization signal and color are formed by separating the synchronization signal from the playback video signal. Forming a noise suppression pulse with an H blanking pulse containing a burst signal,
Variable speed, characterized in that the noise suppression pulse improves the S/N in the noise and S/N degraded portions of the reproduced video signal, except for the portions including the horizontal synchronization signal and the color burst signal. An S/N improvement device for a playback video signal in a VTR equipped with a playback function.