JPS6119198B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is directed to a carrier color signal in a color video signal.
The present invention relates to a carrier color signal processing circuit that improves the SN ratio and obtains good image quality. For example, in general home video tape recorders (hereinafter referred to as VTR), the recording density is extremely high, and the carrier color signal (hereinafter referred to as chroma signal) in the color video signal is converted to a low frequency band. Since chroma signals are recorded, it is extremely important to remove crosstalk components from chroma signals. In this case, taking advantage of the fact that the phase of the color subcarrier is inverted every 1H, the chroma signal is passed through a comb filter circuit 3 as shown in Figure 1 to remove crosstalk components. It's summery. The comb filter circuit 3 shown in FIG. 1 sends a reproduced video signal from the VTR, etc., supplied to the input terminal 1, to a 1H delay circuit 5 having a delay time of one horizontal period (hereinafter referred to as 1H). , an adder 4 subtracts a signal delayed by 1H from the original reproduced video signal and sends it to the output terminal 2. Therefore, the frequency characteristics of this comb filter circuit 3 are as follows:
As shown in Figure 2, the horizontal scanning frequency is f _H
When , the transmission gain at the frequency nf _H (n=1, 2, . . . ) is the minimum, and the transmission gain at the frequency (n+1/2) f _H is the maximum. This means that if the video signal has vertical correlation,
Since the signal components are concentrated near the frequency (n+1/2) f _H , by passing through the comb filter circuit 3, it is possible to obtain a video signal from which crosstalk components have been removed. Furthermore, in order to further improve the SN ratio, a feedback type comb filter circuit 6 as shown in FIG. 3 has been proposed. That is, this comb filter circuit 6 sends the reproduced video signal from the input terminal 1 to the output terminal 2 via the adder 7, and also sends a part of the output from the adder 7 to the 1H delay circuit 8.
This 1H delayed signal is sent to the adder 7 via the attenuator 9 and is subtracted from the original reproduced video signal. The frequency characteristics of such a feedback type comb filter circuit 6 are such that the transmission gain is small at frequency nf _H and large at frequency (n+1/2) f _H , as shown in FIG. Compared to the _frequency characteristics of
+1/2)f Since the frequency band of large gain near _H is narrow, the S/N ratio is further improved. However, in such a feedback type comb filter circuit 6, when the vertical correlation of the video signal shifts, the envelope of the original video signal in FIG. 5A changes as shown in FIG. 5B, The so-called sagging of information becomes large, and negative effects such as blurring of the outline of color parts on the screen occur. The present invention was made to eliminate these conventional drawbacks, and by using a configuration in which the transmission frequency characteristics automatically change according to the vertical correlation of the video signal, the SN ratio can be increased. It is an object of the present invention to provide a processing circuit for a carrier color signal (chroma signal) which not only improves the width but also reduces blurring of the outline of a color portion. That is, the feature of the carrier color signal processing circuit of the present invention is that the carrier color signal in the video signal from the input terminal and the signal mixed with this carrier color signal in a frequency interleaved relationship are processed horizontally by (2n-1). a comb filter configured to substantially subtract the output of the delay circuit from the carrier color signal, the mixed signal, and the output of the delay circuit; means for configuring a circuit; and means for extracting the mixed signal from the carrier color signal, the mixed signal, and the output of the delay circuit, and extracts the mixed signal according to the vertical correlation of the video signal. The output from the mixed signal extraction means is returned to the input terminal. Therefore, the filter characteristics change according to the vertical correlation of the video signal, and when the vertical correlation is large, crosstalk can be removed by the feedback comb filter characteristics, significantly improving the SN ratio. Furthermore, when the vertical correlation is small, bleeding and blurring of color contours can be prevented by the normal comb filter characteristics. Hereinafter, preferred embodiments of the present invention will be described.
This will be explained with reference to the drawings. FIG. 6 shows a chroma signal processing circuit 10 as a first embodiment of the present invention, and an input terminal 11 is supplied with a reproduced video signal from, for example, a VTR (video tape recorder). The phase of the chroma signal in this reproduced video signal is inverted every 1H due to frequency interleaving in the NTSC system, and crosstalk components of the chroma signal from adjacent tracks on the video tape are It is mixed into the chroma signal of the playback track in a frequency interleaved relationship. This reproduced video signal is sent to the adder 13, and the output signal from the adder 13 is sent to the output terminal 12 via the adder 14. A part of the output signal of the adder 13 is
It is sent as a subtraction input to the adder 14 via the 1H delay circuit 16. Further, the output signal of the adder 13 and the output signal of the 1H delay circuit 16 are added by the adder 15, and a difference component is taken for the chroma signal. It is sent to adder 13 as a subtraction input. Here, the 1H delay circuit 16 delays the video signal by one horizontal period, and by substantially subtracting this 1H delayed signal from the original signal,
It has the comb filter characteristics mentioned above. Note that the delay time of the delay circuit 16 is generally (2n-1) times the horizontal period H (however, n=1, 2...
), a comb filter characteristic can be obtained. Next, the adder 15 detects the correlation (vertical correlation) between the original signal and the 1H delayed signal, and when the vertical correlation deviates, a large signal is output, and the limiter 17 operates to transmit it. gain is almost 0
It becomes close to. When the vertical correlation is good, the transmission gain of the limiter 17 is approximately 1. Next, the operation will be explained. The input signal of input terminal 11 is E ₁ , the output signal of adder 13 is E ₂ , adder 14
Let E ₃ be the output signal sent from the output terminal 12 to the output terminal 12. Here, the transfer function of the 1H delay circuit 16 is expressed as e ^- 〓
^s , the transfer function of the limiter 17 is k, and the attenuation rate of the attenuator 18 is l, then E ₂ = E ₁ − kl (E ₂ + E ₂ e ^- 〓 ^s ) ………(1) E ₃ = E ₂ −E ₂ e ⁻ 〓 ^s ………(2) Therefore, when calculating E ₃ /E ₂ which is the transfer function of the chroma signal processing circuit 10, E ₃ /E ₁ =1−e ⁻ 〓 ^s /1+kl (1+e ⁻ 〓
^s )......(3). In this equation (3), when the vertical correlation of the video signal deviates, k≒0, so E ₃ /E ₁ ≒1−e ^- 〓 ^s ......(4), and the curve shown in Figure 7 is obtained. This results in a frequency characteristic curve that shows the characteristics of a normal comb filter. Next, when the vertical correlation is good, k≒1
Therefore, E ₃ /E ₁ ≒1−e〓 ^s /1+l(1−e ⁻ 〓 ^s )
......(5) As shown in the curve of FIG. 7, a characteristic close to the frequency characteristic of a feedback comb filter can be obtained. Therefore, the transfer function changes depending on the vertical correlation of the video signal, and when the vertical correlation deviates, it becomes a normal comb filter characteristic as shown in the curve in Figure 7, whereas when the vertical correlation is good, , when the chroma signal components are strongly concentrated near the frequency (n+1/2) f _H , the frequency characteristics become as shown in FIG. 7, in which feedback type characteristics are superimposed, and the S/N ratio is greatly improved.
Therefore, the signal-to-noise ratio is improved, and phenomena such as color bleeding in colored portions can be effectively prevented. Next, a second embodiment of the present invention will be described with reference to FIGS. 8 and 9. In the chroma signal processing circuit 20 shown in FIG. 8, an input terminal 21 is supplied with a chroma signal in a reproduced video signal, and an input terminal 22 is supplied with a normal color video signal, that is, a Y signal (luminance signal) and a C signal. (chroma signal) is supplied. The chroma signal from the input terminal 21 is sent to one switching terminal a of the mode switching switch 24 via the adder 23, and the Y+C signal from the input terminal 22 is sent to the other switching terminal b of the switching switch 24. being sent. The output signal from the fixed terminal c of this changeover switch 24 is sent to the 1H delay circuit 25.
and delayed by one horizontal period. This 1H delayed signal is added to the original signal, ie, the output signal from the changeover switch 24, in an adder 26, and the vertical difference component of the chroma signal is extracted. Further, the 1H delayed signal is subtracted from the original signal in an adder 27 to form a comb filter circuit.
The output signal from 7 is the output terminal 2 of the reproduced chroma signal.
It has been sent to 8. The output signal from the adder 26 is sent to an output terminal 29 for the recording Y signal. The output signal from the adder 26 is sent as a subtraction signal to the adder 23 on the chroma signal input terminal 21 side via a switch 30 and a weighting circuit 31 for transfer function k. Therefore, when the switch 30 is turned on, the difference component of the chroma signal from the adder 26 is fed back to the input terminal 21 side. Next, adder 2
The output terminal of 7 is sent to a recording chroma signal output terminal 33 via an adder 32.
2, the output signal from the switch 30 is sent as an addition signal. Next, the switch 30 is turned on and off by a signal that detects the vertical correlation of the luminance signal (Y signal), and the switch 30 is controlled to turn on and off by the signal that detects the vertical correlation of the luminance signal (Y signal).
The Y-Y _D signal obtained by taking the difference from the delayed Y _D signal is supplied to the input terminal 34, and is passed through the double-wave rectifier circuit 35.
It is sent to the OR circuit 36. Furthermore, in the burst signal section, it is necessary to cancel the feedback, and the burst flub signal is sent to the OR circuit 36 via the input terminal 37. This OR circuit 36
The output from the switch becomes "H" when the vertical correlation deviates or during a burst signal section, and the output is sent to one switching terminal a of the switching switch 38 and to the other switching terminal b via the inverter 39. It's on. The switch 30 is turned on and off by the output signal from the fixed terminal c of the changeover switch 38.
Control. Here, the changeover switches 24 and 38 are
It is connected to the switching terminal a during reproduction and to the switching terminal b during recording. In the chroma signal processing circuit 20 having the above configuration, during recording, the changeover switches 24 and 38 are both connected to the changeover terminal b side,
The input terminal 22 is supplied with the Y+C signal. When the luminance signal has no vertical correlation, the switch 30 is turned on, and the output signal from the adder 26 and
The output signal from the adder 27 is added by the adder 32 and sent to the recording chroma signal output terminal 33. Therefore, the transfer function is (1-e ^{- 〓s} )+(1+e ^{- 〓s} )=2 (6), and a frequency characteristic curve as shown in FIG. 9 is obtained. When the luminance signal has vertical correlation, the switch 30 is turned off and the output signal from the adder 27 is only sent to the output terminal 33 via the adder 32, so the transfer function is 1-e ^- 〓 ^s (7), and the comb filter characteristics as shown in FIG. 9 are obtained. Next, during playback, selector switches 24 and 3
8 are both connected to the switching terminal a side, and a reproduced chroma signal is supplied to the input terminal 21. When the luminance signal has no vertical correlation, the switch 30
is off, and the subtraction output from the adder 27 is sent to the reproduced chroma signal output terminal 28. Therefore, the transfer function of the chroma signal processing circuit 20 is 1-e ^{- s} (8), and a normal comb filter characteristic as shown in FIG. 9 is obtained. When the luminance signal has vertical correlation, the switch 30 is turned on and the adder 2
The difference component signal of the chroma signal from 6 is fed back via the weighting circuit 31 to the adder 23 on the input terminal 21 side as a subtraction signal. Therefore, the transfer function is 1-e ^{- 〓s} /1+k(1+e ^{- 〓s} ) (9), and the frequency characteristic becomes a feedback-type comb filter characteristic as shown in FIG. Therefore, during recording, when there is no vertical correlation of luminance signals, all frequency components are output to the output terminal 33 as a flat frequency characteristic as shown by the curve in FIG.
When there is a vertical correlation, the chroma signal component near the frequency (n+1/2) f _H is sent to the output terminal 33 to improve the S/N ratio due to the comb filter characteristics as shown in the curve in Figure 9. ing. Also, during playback, since the crosstalk component increases, even when there is no vertical correlation, the chroma signal component near the frequency (n+1/2) f _H is output to the output terminal 28 due to the comb filter characteristics of the curve in FIG. I am sending it to Furthermore, when there is a vertical correlation during playback, the chroma signal components are concentrated near the frequency (n+1/2) f _H , so as shown in the curve in Figure 9, the passband near the frequency (n+1/2) f _H The comb-shaped filter characteristics, which are narrowed down and close to those of a feedback type, significantly improve the signal-to-noise ratio. It should be noted that when there is no vertical correlation, the normal comb filter characteristics are used, so-called sagging of information is reduced, and blurring of the outline of the color portion is effectively prevented. Next, regarding the third example of the present invention, the tenth example
This will be explained with reference to the drawings. In FIG. 10, the same parts as in FIG. 8 are given the same reference numerals and their explanations will be omitted. In the chroma signal processing circuit 40 as the third embodiment shown in FIG.
The output signal from the adder 26 is sent to the recording/reproducing chroma signal output terminal 42 via the adder 41, and the output signal from the adder 26 is sent to one switching terminal a of the switching switch 43. Further, the output signal from the switch 30 is sent to the other switching terminal b of the changeover switch 43, and the output signal from the fixed terminal c of the changeover switch 43 is sent to the adder 41 through an attenuator 44 that attenuates it to 1/2. It is sent as a subtraction signal to Further, the circuit section for controlling ON/OFF of the switch 30 is almost the same as that of the second embodiment, but it does not include the changeover switch 38 and the inverter 39 shown in FIG. The switch 30 is directly controlled ON/OFF by the output from the switch 30. In the operation of the third embodiment, the transfer function changes depending on whether there is vertical correlation or not during recording and reproduction, and these relationships are shown in Table 1.

[Table] The frequency characteristic curve based on the transfer function in Table 1 is similar to that shown in FIG. 9 described above, and the third embodiment also provides the same effects as the second embodiment. Next, FIG. 11 shows a chroma signal processing circuit 50 as a fourth embodiment of the present invention, in which the output signal from the changeover switch 24 is sent via an adder 51 to a chroma signal output terminal 52 for recording and reproduction. At the same time, the output signal of the switch 30 is also supplied to the adder 51 as a subtraction signal via an attenuator 53 with 1/2 attenuation. The other configurations are the same as those of the second embodiment shown in FIG. 8 and the third embodiment shown in FIG. do. In this fourth embodiment as well, the transfer function changes depending on the vertical correlation of the luminance signals during recording and reproduction. Changes in the transfer function in each of these cases are as shown in Table 2.

[Table] In this fourth embodiment, when there is no vertical correlation during reproduction, the transfer function is set to a constant 1, and the input signal is sent as it is to the output terminal 52 due to the flat frequency characteristic, and the color due to information sag is Completely prevents blurring and blurring of outlines. Other effects are the second above,
This is similar to the third embodiment. In addition, also in these second, third and fourth embodiments, the 1H delay circuit 25 is (2n-1)
A delay circuit having a delay time of a horizontal period can be used.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the principle of a comb filter circuit, Figure 2 is a graph showing the frequency characteristics of the circuit in Figure 1, Figure 3 is a circuit diagram showing the principle of a feedback type comb filter circuit, and Figure 4 is a circuit diagram showing the principle of a comb filter circuit. The figure is a graph showing the frequency characteristics of the circuit in Figure 3, and Figures 5A and B show the original signal A and output signal B when the vertical correlation of the video signal is shifted when using the circuit in Figure 3. FIG. 6 and 7 show a first embodiment of the present invention, FIG. 6 is a circuit diagram, and FIG. 7 is a graph showing frequency characteristics. Figures 8 and 9
The figures show a second embodiment of the present invention, with FIG. 8 being a circuit diagram and FIG. 9 being a graph showing frequency characteristics.
FIG. 10 is a circuit diagram showing a third embodiment of the present invention. FIG. 11 is a circuit diagram showing a fourth embodiment of the present invention. 10, 20, 40, 50...Chroma signal processing circuit, 13, 14, 15, 23, 26, 27, 3
2,41,51...Adder, 16,25...1H
Delay circuit, 17... limiter, 30... switch.

Claims (1)

[Claims] 1 The carrier color signal in the video signal from the input terminal and the signal mixed with this carrier color signal in a frequency interleaved relationship are transmitted over (2n-1) horizontal periods (where n = 1, 2, ......) means for configuring a comb filter circuit to substantially subtract the output of the delay circuit from the carrier color signal and the mixed signal; means for extracting the mixed signal from the mixed signal and the output of the delay circuit, and returns the output from the mixed signal extracting means to the input terminal according to the vertical correlation of the video signal. A carrier color signal processing circuit designed to