JPS6347031B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a video signal recording and reproducing device. Since video signals generally have line correlation, the S/N ratio can be improved using a comb filter. The Y-shaped comb filter shown in FIG. 1a or the C-shaped comb filter shown in FIG. 1b has a theoretical S/N improvement effect of 3 dB. In the figure, 1 uses CCD or ultrasound
1H delay line, 2 is an adder, and 3 is a subtracter. By passing the carrier color signal through a C-shaped comb filter, random cross colors caused by high-frequency components of the luminance signal can be removed, and the visual S/N improvement effect is very large. In order to further enhance the S/N improvement effect of such a comb filter, a feedback type comb filter was devised to obtain a sharp amplitude frequency characteristic by feeding back part of the output of a conventional comb filter to the input side. has been done. The block diagram and frequency characteristics of this feedback type C-comb filter are shown in FIGS. 2a and 2b, respectively. In the figure, 4 is an attenuator for feeding back the output signal. Also, the delay time of 1H delay line 1 is t
shall be. The feedback comb filter has a feedback rate K
By changing the sharpness of the amplitude frequency characteristic, the amount of S/N improvement can be set freely, and a significant S/N improvement effect can be expected. This return rate K
FIG. 3 shows the relationship between this and the theoretical S/N improvement effect. S/N at this time

[Formula] becomes. When K=0, it is equivalent to a general C-shaped comb filter. When using these comb filters, the S/
It has an N improvement effect. However, it has the drawback that the vertical resolution of the image deteriorates in situations where there is no line correlation of the video signals. Particularly in the feedback comb filter, there is a problem in that the vertical resolution of the image is significantly degraded in proportion to the increase in the feedback rate K. for example,
When the signal changes stepwise when K=0.5,
The response time requires approximately 5H period. The present invention prevents the S/N improvement effect of the feedback comb filter from being impaired when attempting to improve the S/N of a reproduced color signal using the feedback comb filter during recording and reproduction by a video tape recorder or the like. The aim is to minimize the deterioration of the vertical resolution of the image. Most of the noise contained in the reproduced color signal of a video tape recorder is noise generated in the tape head system and head amplifier.
S/ of the reproduced color signal using a comb filter
In order to improve N, there is no effect unless a comb filter is introduced into the regeneration circuit. When a comb filter is introduced into the recording circuit, it is only effective in removing random cross colors. When a video signal is passed through a comb filter, the vertical resolution is degraded because there are parts of the video signal that have no line correlation. Therefore, when recording a video signal, a signal for correcting the inferior vertical resolution may be inserted into the portion where there is no line correlation by some method. Generally, when recording, if the color signal is passed through an inverse conversion circuit of a comb filter, the deterioration in vertical resolution can be completely corrected. The inverse conversion circuit of the feedback type C-shaped comb filter (Figure 2a) and its amplitude frequency characteristics are shown in Figures 4a and b.
are shown respectively. In the figure, 5 is a 1H delay line,
6 is a subtracter, and 7 and 8 are adders. In the recording/reproducing system, the color signal is used as the fourth color signal during recording.
The reproduced color signal is completely restored to the original signal because it passes through the feedback type C-comb filter inverse conversion circuit shown in FIG. 2A and then passes through the feedback type C-comb filter shown in FIG. On the other hand, most of the noise components are generated in the tape head system and head amplifier during the playback process after recording, and these are generated by passing through the feedback C-shaped comb filter during playback shown in Figure 2a. , significantly reduced. Therefore, it can be expected that the S/N ratio will be significantly improved without any deterioration in vertical resolution. However, the feedback type C-comb filter inverse conversion circuit has an amplitude frequency characteristic of n/τ (τ:
Since it has an infinite gain at the frequency of one horizontal scanning period (63.56 μs), if the color signal contains a frequency component of n/τ, that is, a signal with no vertical correlation, oscillation will occur. This oscillation is caused by even a slight disturbance noise.
Since this may occur, stable operation cannot be expected. Therefore, it is very difficult to put into practical use the feedback type C-comb filter inverse conversion circuit shown in FIG. 4a. Therefore, the circuit shown in FIG. 5a is proposed as a circuit for correcting the deterioration of the vertical resolution of color signals during recording. In the figure, 9 is a 1H delay line, 10 is an amplifier,
11 and 12 are adders. The circuit shown in Figure 5a passes the input color signal through a Y-shaped comb filter, extracts the color signal with no vertical correlation, amplifies that signal to a predetermined level, and then adds it to the original input color signal. It is. In other words, portions of color signals that have no vertical correlation are emphasized during recording. In this circuit, the signal in the part without vertical correlation is amplified by K/1-K times (K: feedback type, feedback rate of C-shaped comb filter, 0≦K<1) and added to the original input color signal. It was found that the vertical resolution deterioration during playback was the least when recorded in the same manner. The reason for this will be explained using a transfer function. In the C-shaped comb filter shown in Figure 1b, 1H
Since the delay line 1 delays the signal transmission time by τ, its transfer function G(jw) _D can be expressed as G(jw) _D = ε ^jw = coswτ + jsinwτ (1). Therefore, the transfer function G(jw) _C of the C-shaped comb filter in FIG. 1b can be expressed as G(jw) _C =1-ε ^jw =1-coswτ-jsinwτ (2) On the other hand, the transfer function G(jw) _CR of the feedback type C-comb filter shown in Fig. 2a is G(jw) _CR =1−ε ^jw 〓/1+Kε ^jw 〓 =1−coswτ−jsinwτ/1+Kcoswτ+jKsinwτ…(3
) can be expressed as In general, the transfer function G of a feedback comb filter including a Y-shaped comb filter
(jω) _R can be expressed as G(jω) _R = 1〓ε ^jw 〓/1±Kε ^jw 〓 (3a). The signs - and + in the numerator and + and - in the denominator in the same formula indicate polarity in the case of C type and Y type, respectively. In addition, the _transfer function G(jw) _CA of the vertical resolution deterioration correction circuit ^{in FIG} . It can be expressed as =1/1-K(1+Kcosωτ+jKsinωτ) (4). Therefore, the color signal is shown in Figure 5a.
If it is suitable for both the vertical resolution deterioration correction circuit shown in Figure 2a and the feedback type C-comb filter shown in Figure 2a, its transfer function is the product of Equations 3 and 4, so G(jw) _CR ×G(jw ) _CA = 1−coswτ−jsinwτ/1+Kcoswτ+jKsinwτ×1/1−K(1+Kcoswτ+jKsinwτ) =1/1−K(1−coswτ−jsinwτ) (5). This equation (5) is equivalent to equation (2) multiplied by 1/1-K. Therefore, if the color signal is passed through the vertical resolution deterioration correction circuit shown in Figure 5a and the feedback type C-comb filter shown in Figure 2a, it is equivalent to passing it through the C-shaped comb filter shown in Figure 1b. Therefore, the deterioration in vertical resolution can be corrected to the extent that it passes through one comb filter. In addition, in the vertical resolution deterioration correction circuit shown in FIG. Become.
Furthermore, when the signal is amplified to a level higher than K/1-K and added, the vertical resolution deterioration is corrected too much and the vertical edge portions of the image are emphasized. In addition, the vertical resolution deterioration correction circuit _{in Fig. 5a has the same effect if its transfer function G(jw) CA ′} =1+Kε ^jw 〓 =1+Kcoswτ+jsinwτ …(6) It can be seen that a circuit as shown in Figure 6 may be used. In the figure, 13 is a 1H delay line, 14 is an attenuator,
15 is an adder. Generally, the transfer function G(jω) of such a vertical resolution deterioration correction circuit is G(jω) _A = _L (1±Mε ^j 〓〓) = 1±Kε ^j 〓〓(L=1, M=K) = 1/1-K(1±Kε ^j 〓〓)(L=1/1-K, M
= K) ...(6a) The signs + and - in the equation correspond to the signs in equation 3a. Next, a case where the vertical resolution deterioration correction circuit is introduced into a color signal recording circuit of an actual video tape recorder will be explained with reference to FIG. FIG. 7a shows a recording circuit of a video tape recorder to which the present invention is applied. In the figure, the video signal input to the input terminal is passed through a low-pass filter 16 to obtain a luminance signal, and an automatic gain adjuster 17 adjusts the amplitude to a constant level. The luminance signal adjusted to an appropriate amplitude is sent to the emphasis circuit 1.
8 to emphasize the high range, and the clip circuit 19 to suppress the peak level of the signal to a constant value,
The signal is frequency-modulated by a frequency modulator 20, and after attenuating low-frequency sidebands by a high-pass filter 21, it is sent to an adder 22. On the other hand, the color signal is separated from the luminance signal by a bandpass filter 23, and the automatic color gain adjuster 2
After adjusting the amplitude to a certain level by 4,
The signal enters a vertical resolution deterioration correction circuit composed of a 1H delay line 9, adders 11 and 12, and a slice amplifier 10. In this vertical resolution deterioration correction circuit, a color signal in a portion with no vertical correlation is extracted through a Y-shaped comb filter constituted by a 1H delay line 9 and an adder 11, and the signal is amplified by K/1-K times. When doing so, by using the slice amplifier 10, signals below a certain amplitude are cut off. This is to prevent unnecessary components and noise of the output signal of the 1H delay line 9 from being greatly amplified and causing malfunctions. In the color signal that has passed through this vertical resolution deterioration correction circuit, the color signal in the part with no vertical correlation is emphasized, but this means that the peak value is up to 2/1-K times higher than the original signal level. Sometimes. Therefore, if this signal is recorded as is, the color signal will be saturated in that part, causing distortion during playback, or
There will be more cross-modulation. Therefore, the peak value of the signal that has passed through the vertical resolution deterioration correction circuit must be compressed by the peak compression circuit 25 so that the peak value is about 3 to 6 dB with respect to the original signal level. This does not cut large signal levels, but compresses only peak values so that the original signal level can be restored during playback. The color signal whose peak value has been compressed by the peak compression circuit 25 is converted into a carrier wave by a frequency conversion circuit 26 and a low-pass filter 27 to a low frequency.
After being added to the frequency-modulated luminance signal by an adder 22, it is sent to a video head 29 through a recording amplifier 28 and recorded on a magnetic medium. On the other hand, the reproducing circuit has a configuration as shown in FIG. 7b. The video signal reproduced from the video head 29 is amplified by a head amplifier 30, and then separated by a high-pass filter 31 and a low-pass filter 38 into a frequency-modulated luminance signal and a chrominance signal whose carrier wave is low-frequency converted. After amplitude fluctuations are removed from the frequency-modulated luminance signal by a limiter 32, the frequency demodulation circuit 33 and low-pass filter 34 demodulate the frequency. Since the peak level of the demodulated luminance signal is kept at a constant value by passing it through the clipping circuit 19 during recording, the original waveform is restored by passing it through the peak expansion circuit 35. Thereafter, the de-emphasis circuit 36 reduces high-frequency noise to improve the S/N ratio, and the signal is sent to the adder 37. Further, the color signal whose carrier wave has been low frequency converted is adjusted to have a fixed level amplitude by the automatic color gain adjuster 39, and then the carrier wave is converted to the original frequency by the frequency conversion circuit 40 and band pass filter 41. . By passing the signal through the peak expansion circuit 42, the peak level of the signal, which had been suppressed to a constant value by the peak compression circuit 35 during recording, is expanded to the original level and the original signal waveform is restored.
After that, the S/N of the reproduced color signal is improved through a feedback C-shaped comb filter composed of a 1H delay line 1, an adder 2, a subtracter 3, and an attenuator 4.
The adder 37 mixes the signal with the reproduced luminance signal and outputs it to the output terminal as a reproduced video signal. Comparing the above circuit configurations for the luminance signal system and the color signal system, it can be seen that the two are very similar. In other words, in the luminance signal system, during recording, the signal is separated by a filter, the gain is adjusted, and then the high-frequency signal level is emphasized by emphasis, thereby compressing the increased peak level of the signal to a certain level ( Similarly, in the color signal system, the signal is separated by a filter during recording, the gain is adjusted, and then a vertical resolution deterioration correction circuit is used to eliminate vertical correlation. The color signal of the part is emphasized, the increased peak level of the signal is compressed to a certain level, and the signal is frequency-converted. During playback, the signals are similarly separated by a filter, the amplitude fluctuations of the playback signal are removed by a limiter or gain adjuster, the playback signal is demodulated by a demodulator, etc., and the signal is converted into a signal by an expansion circuit. The peak level of the signal is restored to the original level, and then S/N is improved using de-emphasis or a feedback C-comb filter. In this way, in this system, the chrominance signal system has almost the same circuit configuration as the luminance signal system, resulting in a very rational circuit configuration. The present invention can be applied to various video signal recording and reproducing apparatuses, regardless of magnetic recording and reproducing apparatuses.
Furthermore, as is clear from the relationship of transfer functions, the present invention applies not only to feedback type C-comb filters but also to feedback type Y-type comb filters.
The same effect can be obtained by applying the same method to a comb filter. As explained above, in the color signal system of a video tape recorder, the present invention provides a method for improving the S/N by introducing a feedback C-shaped comb filter on the playback circuit side. The simple and rational configuration of emphasizing the areas without a comb filter does not impair the significant S/N improvement effect of the feedback comb filter, and eliminates the deterioration of vertical resolution, which is a drawback of the feedback comb filter. This has the effect of minimizing the

[Brief explanation of the drawing]

Figure 1 a is a system diagram of a general Y-shaped comb filter, b is a system diagram of a C-shaped comb filter, and Figure 2 a
is a system diagram of a general feedback type C-shaped comb filter, b
is its frequency characteristic diagram, Figure 3 is a diagram showing the relationship between the feedback rate and S/N improvement ratio of a general feedback type comb filter, and Figure 4a is the inverse transformation of a general feedback type C-type comb filter. A system diagram of the circuit, b is its frequency characteristic diagram, FIG. 5 a is a system diagram showing an example of the vertical resolution deterioration correction circuit of the present invention, b is its frequency characteristic diagram, and FIG. 6 is the vertical resolution deterioration correction circuit of the present invention. A system diagram of another example of the circuit, FIG. 7 is a system diagram when the present invention is applied to an actual video tape recorder. 1, 5, 9, 13...1H delay line, 2, 7, 8,
11, 12, 15, 22, 37...adder, 3...
...Subtractor, 4, 6...Attenuator, 10...Amplifier (slice amplifier), 18...Emphasis circuit,
19... Clip circuit, 25... Peak compression circuit, 35, 42... Peak expansion circuit, 36... De-emphasis circuit.

Claims (1)

[Claims] 1. A first video signal to be recorded and a second video signal including at least a signal obtained by delaying the first video signal by n horizontal periods are mixed at a predetermined level ratio. The transfer function G(jω) obtained by _A = L
A signal expressed as (1±Mε ^j 〓〓) is recorded on a recording medium, and during playback, the reproduced signal is converted into a transfer function G(jω) _R =
A video signal recording and reproducing method characterized by passing the video signal through a feedback comb filter expressed as 1〓ε ^j 〓〓〓/1±Kε ^j 〓〓. (ω: angular frequency, τ: delay time, LMK: constant 0≦KLM<1) 2 The second video signal is obtained by passing the first video signal through an n horizontal period delay device. A video signal recording and reproducing method according to claim 1. 3. The video signal recording and reproducing method according to claim 1, characterized in that L=1 and M=K (however, 0≦K<1). 4 A second video signal is obtained by mixing the first video signal at the same level with a signal obtained by passing the first video signal through an n horizontal period delay device. Featured Claim No. 1
The video signal recording and reproducing method described in . 5. The video signal recording and reproducing method according to claim 4, wherein the second video signal is brought to a predetermined level and then mixed with the first video signal through a slice circuit. 6 The first video signal and the second video signal are 1:
6. The video signal recording and reproducing method according to claim 4 or 5, wherein the video signal recording and reproducing method is performed by mixing at a level ratio of K/1-K (0≦K<1). 7 A first video signal to be recorded and a second video signal containing at least a signal obtained by delaying this first video signal by n horizontal periods are mixed at a predetermined level ratio, and the mixed video signal is The maximum level is level-compressed to a predetermined value and recorded on a recording medium, and during playback, the maximum level of the reproduced signal is level-expanded to the maximum level ratio before the level compression and is passed through a feedback comb filter. Video signal recording and playback method.