JPH01288075A - Video signal recording method - Google Patents

Abstract

PURPOSE:To devise a method where almost no vertical smear takes place even at mutual reproduction by retarding an inputted video signal, attenuating it to a prescribed level and applying negative feedback so as to subtract the signal from the original input signal. CONSTITUTION:The amplification factor of an amplifier A12 is set to (1+KP), where KP is the attenuation of attenuators A11, A13. A transfer function G(jomega) of the input/output of a signal of a level not passing through a limiter 7 is expressed in equation I, where K=1/KP. Since the factor KP is set in general to be 0<=KP<1, then the relation of K>1 exists. Although the S/N improving effect is expected largely as the KP approaches 1, the most expected effect is caused at KP=0.33. The method is applied similarly even in the video signal having the correlation of n-line and a 1H delay line 4 is replaced into an nH delay line in this case, Thus, no vertical smear takes place even in any mutual reproduction and the screen is made sharp.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video signal recording method for a video tape recorder or the like.

2. Description of the Related Art A video tape recorder (hereinafter abbreviated as VTR) generally performs FM modulation on a video signal and records it on a magnetic medium. At this time, in order to reduce triangular noise during playback, the video signal is emphasized during recording and then FM modulated, and during playback, de-emphasis is applied to obtain the original waveform.

On the other hand, in home VTRs, in order to further improve the S/N ratio, it is possible to use vertical emphasis, which uses the line correlation of the video signal to extend the assist in the vertical direction of the screen. be.

For example, in a VH3 type VTR, it has been standardized as one of the high picture quality techniques (HQ) to apply vertical emphasis in the signal processing system for each of the intensity signal and the two color signals.

FIG. 4 is a block diagram showing an example of vertical emphasis standardized in the luminance signal system of a conventional VH8 system VTR. In the figure, a luminance signal input from input terminal 1 is input to adder 2.8 and subtracter 10, respectively. The signal output from adder 2 is 1H (H: horizontal period)
After passing through the delay line 4, the level is attenuated by an attenuator B3 and returned to the adder 2, thereby applying positive feedback due to line correlation and emphasizing the luminance line correlation component.

The level of the signal output from the 1H delay line 4 with enhanced correlation components is attenuated in level by an attenuator C5, and input to the subtracter 1o, where it is subtracted from the original input luminance signal. Therefore, the signal output from the subtracter 10 is only a signal of the weak part of the luminance line correlation of the original luminance signal, and this signal is attenuated in level by the attenuator D6, passed through the limiter 7, and then added. The signal is inputted to a device 8, added to the original input signal, and outputted to an output terminal 9.

In the figure, when the attenuation factor of attenuator B3 is Kp, the attenuation factor of attenuator C6 is set to (1-Kp). Further, when the attenuation factor of the attenuator D6 is x, and the IJ limit level of the limiter 7 is L, the HQ technology of VH3 type VTRs is standardized as KP≦0.6, X≦0.66, L≦6%.

FIG. 5 is a signal waveform diagram showing the input/output response of the circuit in FIG. 4, and shows a small level signal that completely passes through the limiter 7. In Fig. 4, for the input signal &, which has a step response in the vertical direction, the output signal has a stepwise response every 1H, greatly emphasizing the weak vertical correlation part of the input signal a, and then eliminating the vertical smear. It becomes a convergent response. The degree of emphasis of this portion without vertical correlation is determined by the value of X, and the degree of convergence of the vertical smear is determined by the value of KP. Generally the VH3
In the circuit used in this type of VTR, it takes 3 to 4 hours for the vertical smear to converge.

On the other hand, vertical de-emphasis has completely opposite characteristics to the above-mentioned vertical emphasis, and in FIG. It can be configured by changing

Problems to be Solved by the Invention Although the vertical emphasis and de-emphasis described above are configured to work only on low-level signals by the limiter 7, vertical smear occurs significantly, so vertical emphasis is not applied during recording. It is configured to apply vertical de-emphasis during playback.

However, when a medium recorded with vertical emphasis is played back on a device that does not use vertical de-emphasis, or when a medium recorded without vertical emphasis is played back on a device that uses vertical de-emphasis, the Vertical smear was occurring.

Also, if large jitter occurs in the playback signal, such as during compatible playback or repeated dubbing,
Unless the horizontal period is one regular horizontal period, the line correlation will be broken, and the part that was vertically emphasized during recording cannot be reliably vertically de-emphasized, and a large vertical smear will occur at this time as well. There was a problem.

In view of this point, the present invention provides a video signal recording method using vertical emphasis in which almost no vertical smear occurs even during the above-mentioned compatible playback.

Means for Solving the Problems In order to solve this problem, the video signal recording method of the present invention delays an input video signal by n horizontal periods, attenuates it to a predetermined level, and converts the signal back to its original state. Transfer function obtained by applying negative feedback to subtract from the input signal (ω: angular frequency, T: 1 horizontal period, n: positive integer, K:
This is a method of recording a signal output from a vertical emphasis having a response expressed by a positive integer K>1).

Function: In the present invention, negative feedback is applied to subtract the signal delayed by n horizontal periods by the above method from the input signal, so that the polarity of the vertical smear is reversed for each line and the vibration is attenuated. Vertical smear becomes visually smaller.

EXAMPLE A specific example of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a vertical emphasis circuit used in the video signal recording method of the present invention. 3 in Figure 1
The same components as in the conventional example shown in the figure are given the same numbers. In FIG. 1, a luminance signal input from an input terminal 1 is input to a subtracter 1o and a 14° adder 8. The signal output from the subtracter 14 passes through the 1H delay line 4, has its level attenuated by the attenuator A11, and is then subtracted from the original input signal by the subtracter 14, thereby applying negative feedback due to line correlation. . As a result, the signal outputted from the 1H delay line 4 becomes a signal having vibration damping characteristics whose amplitude varies from line to line. This signal is amplified in level by an amplifier AI2, and is input to a subtracter 1o, thereby subtracting it from the original input luminance signal. The signal output from the subtracter 1o is attenuated in level by an attenuator AI3 having the same characteristics as the attenuator A11, and then input to an adder 8 through a limiter 7, where it is added to the original input signal and sent to an output terminal 9. Output to.

When the attenuation factors of the attenuators A11 and 13 are Kp, the amplification factor of the amplifier AI2 is set to (1+Kp).

Furthermore, when K = 1 /K p, the input/output transfer function G(i
ω) is expressed as.

Since K is generally set to 0≦KP<1, K>1. As Kp becomes Kp→1, a greater S/N improvement effect can be expected, but the vertical smear also increases accordingly, and the effect of the present invention can be expected the most when Kp = 0, 33, and Ni = 3. It's time.

FIG. 2 is a signal waveform diagram showing the input/output response when Kp = 0 and 33 in FIG. There is. In FIG. 2, with respect to the input signal a having a step response in the vertical direction, the output signal C becomes a response with vibration damping characteristics every 1H.

Therefore, the apparent convergence of vertical smear is greatly improved, and only 1H vertical smear can be detected on the monitor screen. This is almost the same as a signal that emphasizes vertical details.

It goes without saying that the medium recorded by the recording method of the present invention will have the greatest effect when played back by a playback device equipped with vertical de-emphasis based on the idea of the present invention. Even if the image is played back using a playback device that does not have the same function, there is no loss in image quality at all, and the effect is that vertical details can be emphasized to some extent.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 3 shows an embodiment of a vertical emphasis and vertical emphasis circuit constructed based on the present invention. In the figure, when the switch 19 is connected to the E side, it becomes a vertical emphasis circuit, and conversely, when it is connected to the D side, it becomes a vertical de-emphasis circuit. For vertical emphasis circuit,
The luminance signal input from input terminal 1 is input to adder 18 . The signal output from the adder 18 is input to the subtracter 17, the subtracter 16, and the 1H delay line 4. The signal output from the 1H delay line 4 is input to a subtracter 16, and is subtracted from the signal before entering the 1H delay line. The level of the signal output from the subtracter 16 is attenuated by an attenuator D16, and then fed back to the adder 18 through a limiter 7 and a switch 19. Thus the subtractor 17
The input signal is output to the output terminal 9 as it is.

On the other hand, in the case of the vertical de-emphasis circuit, the luminance signal inputted from the input terminal 1 passes through the adder 18 as it is, and is inputted to the subtracter 17 and 15 and the 1H delay line 4. The signal output from the 1H delay line 4 is input to a subtracter 16. The signal output from the subtracter 15 is sent to an attenuator D16.
．． The signal is input to the subtracter 17 via the limiter 7° switch 19. The signal output from the subtracter 17 is output to the output terminal 9.

In the figure, when the attenuation factor of the attenuator D16 is KP', it is set as xp'=, . That is, when =3, Kp' =0, 25.

Furthermore, the input/output transfer function of a signal at a level that does not pass through the limiter 7 is G(jω)E at the time of vertical emphasis.

At the time of vertical de-emphasis, G(iω)D is +tj (TG(iω)D=+1).In other words, the vertical emphasis shown in FIG. There is.

Further, the vertical emphasis and vertical de-emphasis shown in FIG. 5 have completely opposite characteristics. From this, the vertical emphasis used in the video signal recording method according to the present invention is
It can be restored to its original state by vertical de-emphasis constructed from an acyclic circuit that does not apply feedback. Therefore, even if large jitter occurs in the reproduced signal during compatible reproduction, vertical de-emphasis can be applied between lines without circulating the signal, so vertical smear will not occur.

Further, as shown in FIG. 3, the present invention can be constructed with a very simple circuit.

In the above explanation, the input video signal was a luminance signal with a one-line correlation, but the present invention can also be applied even if the input video signal is a video signal with an n-line correlation, and in that case, In this case, the 1H delay line 4 is replaced with an nH delay line.

As described in detail, the video signal recording method of the present invention causes almost no vertical smearing even in any compatible playback, resulting in a very clear screen. Moreover, it can be carried out in a simple manner, and its practical effects are very large.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a vertical emphasis circuit used in the video signal recording method of the present invention, FIG. 2 is a signal waveform diagram of an input/output response showing characteristics of the embodiment of FIG. 1, and FIG. is a vertical emphasis system constructed based on the present invention.
Block diagram of another embodiment of the de-emphasis circuit, No. 4
6 is a block diagram of a conventional vertical emphasis circuit, and FIG. 6 is a signal waveform diagram of an input/output response showing characteristics of the conventional example shown in FIG. 1... Input terminal, 2, 8.18... Adder, 3゜5.6, 11.16... Attenuator, 4
...1H delay line, 7...Limiter, 9
...Output terminal, 10,14°15.17...
...Subtractor, 12...Amplifier. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4 Figure 5

Claims (2)

[Claims] (1) After delaying the input video signal by n horizontal periods,
A transfer function obtained by attenuating to a predetermined level and applying negative feedback to subtract that signal from the original input signal ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ Output from vertical emphasis with a response expressed as ▼ A video signal recording method characterized by recording a signal obtained by (ω: angular frequency, T: 1 horizontal period, n: positive integer, K:
positive integer K>1) (2) Claim 1 characterized in that n=1 and K=3.
The described video signal recording method.