JPH0681269B2 - Video signal processor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing device that can be used in a video tape recorder [hereinafter referred to as "VTR"] and the like.

Configuration of Conventional Example and Problems Thereof In a consumer VTR which is widely used in recent years, a luminance signal is FM-modulated and recorded on a magnetic tape. This luminance signal is demodulated by the reproducing system, and the original luminance signal is reproduced. However, SN of tape head system
Since the ratio is not always sufficient, the reproduced luminance signal becomes a noisy signal. Therefore, a noise reduction device called a line noise canceller that uses the line correlation of the luminance signal is used.

The conventional line noise canceller will be described below. FIG. 1 is a circuit block diagram of a conventional line noise canceller. (1) is an input terminal of an FM modulated luminance signal reproduced from a VTR, (2) is a demodulator for demodulating the luminance signal, (3) Is a 1H glass delay line that delays the input FM-modulated luminance signal for one horizontal scanning period [1H], (4) is a demodulator that demodulates the signal delayed by the 1H glass delay line (3),
(5) is a subtractor that subtracts the output signal of the demodulator (4) from the output signal of the demodulator (2), (6) is an attenuator that attenuates the output signal of the subtractor (5) at a predetermined rate, (7) ) Is a limiter that limits the amplitude of the signal, (8) is a subtractor that subtracts the output signal of the limiter (7) from the output signal of the demodulator (2),
(9) is an output terminal from which a signal with reduced noise is obtained.

Next, the operation will be described. FM input from the input terminal (1)
The modulated luminance signal is demodulated by the demodulator (2) and then guided to the subtractor (5). On the other hand, the signal delayed by the 1H glass delay line (3) is demodulated by the demodulator (4) and subtracted by the subtractor (5).
Is input to. The subtractor (5) subtracts the luminance signal delayed by 1H from the demodulated luminance output, so that the output signal forms a C-shaped comb filter having the frequency characteristic shown in FIG. 2 with respect to the demodulated luminance signal. Will be
A noise component having no line correlation and a signal having no line correlation among the signal components are obtained. This signal is normally attenuated to 1/2 in amplitude by the attenuator (6) and input to the limiter (7). The limiter (7) is usually composed of a semiconductor nonlinear element such as a diode and has an input / output characteristic as shown in FIG. The function of the limiter (7) is to treat the input signal of the limiter (7) as noise when it is small and pass it through, and to treat it as a signal when it is large and suppress its amplitude. As a result, in the subtractor (8), the limiter (7) is calculated from the demodulated luminance signal.
When the signal input to the limiter (7) is noise of such small amplitude that it passes through the limiter (7) as it is, the output of the output terminal (9) is demodulated. The luminance signal has a Y-shaped comb filter characteristic as shown in FIG. 4, and noise having no line correlation can be reduced. However, 1/2 · f _H in the demodulated luminance signal
If there is a signal with a frequency component near an odd multiple of,
Since the limiter (7) limits the amplitude, the output of the output terminal (9) does not have the Y-shaped comb filter characteristic,
The luminance signal demodulated by the demodulator (2) is output almost as it is, and the vertical resolution of the image is not deteriorated. As described above, the line noise canceller basically takes measures to prevent unnecessary spectrum from being deteriorated by removing unnecessary spectrum by the Y-shaped comb filter by utilizing the line correlation of the luminance signal. .

However, the above conventional line noise canceller has some problems caused by using the 1H glass delay line (3) as the delay means. That is,
It is difficult to miniaturize the device, two demodulators (2) and (4) are required, and the comb filter characteristics due to the instability of the frequency characteristics of the 1H glass delay line (3) and the inaccuracy of the delay time Along with imperfections, there is a problem with the nonlinear characteristics of the limiter (7). As described above, since the nonlinear input / output characteristic of the limiter (7) is usually realized by using a semiconductor nonlinear element such as a diode, the input / output characteristic shown in FIG. 3 cannot be avoided. Therefore, even if the input signal amplitude of the limiter (7) is large and the level is such that it can be discriminated as a signal rather than noise, the output signal of the limiter (7) does not become 0 completely, and not a little in the vertical direction of the image. There was a problem that the resolution was deteriorated.

OBJECT OF THE INVENTION The present invention solves the above-mentioned conventional drawbacks by eliminating a glass delay line having many drawbacks and removing noise without deteriorating the vertical resolution of an image.
It is another object of the present invention to provide a video signal processing device capable of suppressing noise and improving vertical resolution of an image.

To achieve the above object, a video signal processing device of the present invention is a digital memory that delays an input luminance signal obtained by digitizing a luminance signal for one horizontal scanning period, an input luminance signal and an output signal of the digital memory. And a non-linear processing means for obtaining a specific output according to the output signal of the first computing means, and the input luminance signal and the output signal of the non-linear processing means are mixed. A second arithmetic means, wherein the non-linear processing means, in the range where the input signal amplitude is smaller than the first threshold value, is 1 / 2.fH (fH is horizontal scanning) of the output signal of the second arithmetic means. Frequency component in the vicinity of an odd multiple of (frequency) is suppressed, and in the range in which the input signal amplitude is larger than the second threshold value larger than the first threshold value, 1/2. Frequencies near odd multiples of fH The configuration has a non-linear characteristic that emphasizes the component.

According to this configuration, the glass delay line having many defects can be removed, noise can be removed without deteriorating the vertical resolution of the image, and further, the noise can be suppressed and the vertical resolution of the image can be improved. be able to.

Description of Embodiments An embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 is a circuit block diagram of a video signal processing device according to an embodiment of the present invention, in which (10) demodulates a FR-modulated luminance signal reproduced from a VTR and then inputs a digitized luminance signal. Input terminal, (11) is a digital memory that delays the input luminance signal for one horizontal scanning period [1H],
(12) is a subtractor that subtracts the signal delayed by the digital memory (11) from the input luminance signal, and (13) is an attenuator that attenuates the output signal of the subtractor (12) to 1/2. 13) can be realized by shifting the signal data downward by 1 bit. (14) is a non-linear processing circuit that outputs a specific output according to the amplitude of the output signal of the attenuator (13), (1
5) is a subtracter that subtracts the output of the non-linear processing circuit (14) from the input signal, and (16) is an output terminal from which an output with reduced noise can be obtained. The non-linear processing circuit (14) has a sixth
As shown in the figure, it is composed of a ROM (17) in which a non-linear input / output characteristic table in which the input (a) to the non-linear processing circuit (14) is an address and the output (b) is data is stored in advance.

The operation of the video signal processing apparatus according to the present embodiment configured as described above is basically the same as that of the conventional example shown in FIG. 1, and the input terminal (10) changes to the input of the nonlinear processing circuit (14). The frequency characteristics up to this point are the C-shaped comb filter characteristics as shown in Fig. 2. Depending on the input signal amplitude of the nonlinear processing circuit (14), the input terminal (10) to the output terminal (16)
The frequency characteristics of the circuit up to are changed.

Here, the input / output characteristics of the nonlinear processing circuit (14) and the frequency characteristics of the circuit from the input terminal (10) to the output terminal (16) will be briefly described. If the input / output characteristic of the nonlinear processing circuit (14) is always 0 as shown by the solid line (c) in FIG. 7 (a), the input signal is output to the output terminal (16) in FIG. Is output as it is, and at that time, the frequency characteristic of the circuit from the input terminal (10) to the output terminal (16) is as shown by the solid line (h) in FIG. 7b). If the input / output characteristic of the non-linear processing circuit (14) is as shown by the solid line (a), the frequency characteristic of the circuit is a Y-shaped comb filter characteristic as shown by the solid line (f) of FIG. 7 (b). . On the other hand, if the input / output characteristic of the nonlinear processing circuit (14) is as shown by the solid line (e) in FIG. 7 (a), the corresponding frequency characteristic is as shown by the solid line (nu) in FIG. 7 (b). , 1/2 ・ f
_This has the characteristic of emphasizing the frequency band near an odd multiple of _H. Similarly, if the input / output characteristics of the nonlinear processing circuit (14) are as shown by the solid line (b) and (d) in FIG. 7 (a), the input terminal (10) to the output terminal (16) in FIG. The frequency characteristics of the circuits up to are as shown by the solid lines (g) and (d) in FIG. 7 (b).

By the way, in the present embodiment, since the non-linear processing is performed in the form of a digital signal, unlike the limiter which has been inevitably the characteristic peculiar to the conventional semiconductor non-linear element or the like,
It is possible to realize arbitrary characteristics, and in particular, since non-linear processing is performed using ROM, any input / output characteristics can be easily realized. Here, the input / output characteristics stored in the ROM are as shown in FIG. 8 (a), for example. As a result, when the input amplitude of the nonlinear processing circuit (14) is small and can be regarded as noise, the frequency characteristic of the circuit becomes as shown by the solid line (f) in Fig. 7 (b), which is an odd multiple of 1/2 · f _H. Noise having a frequency component in the vicinity is suppressed. Also, when the input amplitude is large and can be regarded as a signal, the frequency characteristic of the circuit is that the input signal is output as it is as shown by the solid line (h) in FIG. 7B, which deteriorates the vertical resolution of the image. There is no. Here, comparing the characteristic of FIG. 8 (a) with the characteristic of the conventional limiter shown in FIG. 3, the output amplitude is 0 when the input amplitude is larger than a predetermined level. Therefore, in the conventional limiter, even if the input amplitude is an amplitude that can be regarded as a signal in distinction from noise, the vertical resolution deteriorates to a considerable extent, whereas the characteristic of FIG. 8 (a) does not deteriorate the resolution at all. However, since this characteristic is discontinuous in the threshold portion, unnatural flicker may occur in this discontinuous portion depending on the magnitude of the threshold value.
Therefore, as shown in FIG. 8 (b), it is possible to improve by making the characteristics without discontinuity. However, when the amplitude is large and can be regarded as a signal, the input signal is output as it is, as indicated by the solid line (h) in FIG. 7B, and the vertical resolution of the image cannot be increased. Therefore, the input / output characteristic is set as shown in FIG. In this case, when the input signal amplitude of the non-linear processing circuit (14) is small, the effect is exactly the same as in FIG. 8 (b), and when the amplitude is large, the frequency characteristic of the circuit is shown in FIG. The solid line (b) in (b) is obtained, and the signal can be emphasized. That is, the noise can be reduced and the vertical resolution of the image can be increased.

As described above, according to the present embodiment, since the digital memory (11) is used to delay by 1H, it is possible to reduce the size and cost by using a semiconductor as compared with the case of using the conventional glass delay line. In addition to the effect that only one system is required and the complete comb-shaped characteristic can be obtained, any non-linear input / output characteristic can be realized because the non-linear processing is performed in the form of digital signal. Especially, the non-linear processing circuit (14) Since it is configured using ROM, any input / output characteristics can be easily realized. As a result, it is possible to remove only noise without deteriorating the vertical resolution as compared with the related art, and it is possible to suppress noise and improve the vertical resolution of the signal. Although the attenuator (13) for halving the signal is provided in this embodiment, the attenuator (13) is omitted and the input / output characteristics of the non-linear processing circuit (14) show an output 1 / th that of the case of FIG. Of course, if you double it, the effect is the same.

Further, in the present embodiment, the non-linear processing circuit (14) is realized by the ROM storing one input / output characteristic table, but it is constituted by the ROM storing a plurality of input / output characteristic tables, and the input / output characteristic table It is also possible to adopt a configuration in which one of them is selected. FIG. 9 is an explanatory diagram showing the concept of the ROM in this case. (18) is a signal input terminal, a part of the ROM address, and (19) is a control terminal for selecting the input / output characteristics. It is part of the address. (20) is a signal output terminal,
ROM data output terminal. The switches (21) and (22) are controlled by a signal from the control terminal (19) to switch the input / output characteristics (23a) to (23n). By using such a ROM, it is possible to appropriately adjust the noise reduction amount and the vertical resolution enhancement amount by appropriately selecting the input / output characteristics according to the image type and the noise amount.

FIGS. 10 (A) to 10 (C) are circuit block diagrams of the video signal processing device in the second to fourth embodiments of the present invention, respectively. The same components as those of the embodiment shown in FIG. The same reference numerals are given and the description thereof is omitted.

The second embodiment shown in FIG. 10A is different from the first embodiment shown in FIG. 5 in that the subtractor (25) has a digital memory (1
The input signal is subtracted from the signal delayed by 1), and an adder (26) for adding the input signal and the signal of the nonlinear processing circuit (14) is provided instead of the subtractor (15). And two points. However, the second embodiment operates exactly the same as the first embodiment shown in FIG. 5, and the effect is the same.

Further, in the third embodiment shown in FIG. 10 (B),
The subtracter (25) is the same as that of the second embodiment shown in FIG. 10 (A) and the same subtractor (1) as that of the first embodiment shown in FIG.
5) is used. Further, in the fourth embodiment of FIG. 10 (C), the subtractor (12) has the same configuration as that of the first embodiment, but it is the same as that of the second embodiment shown in FIG. 10 (A). This is a configuration using an adder (26). In these third and fourth embodiments, the input / output characteristics of the nonlinear processing circuit (27),
The relationship with the frequency characteristic of the circuit from the input terminal (10) to the output terminal (16) is different from that of the first embodiment, and the input / output characteristic of the nonlinear processing circuit (27) is the solid line of FIG. I)~
When it is like (e), the frequency characteristic of the circuit corresponding to it becomes like (nu)-(f) of FIG. 7 (b), respectively. Therefore, by setting the input / output characteristics as shown in FIG. 11 corresponding to the input / output characteristics of the nonlinear processing circuit (14) in the first embodiment shown in FIG.
Also, in the fourth embodiment, the same effect as in the first embodiment can be obtained.

As described above, according to the present invention, since the digital memory is used to delay 1H, many drawbacks of the conventional glass delay line are overcome, and the device is miniaturized and the cost is reduced by using the semiconductor. Down can be realized, a single demodulator is sufficient, and further complete comb characteristics can be obtained. Further, since the non-linear processing is performed in the form of a digital signal, any non-linear characteristic can be realized, and in particular, by configuring the non-linear processing circuit using a ROM, any input / output characteristic can be easily realized. Therefore, the drawbacks of the conventional limiter can be overcome. That is, the noise can be removed without deteriorating the vertical resolution, and the noise can be suppressed and the vertical resolution of the image can be improved at the same time. Further, by using a ROM storing a plurality of input / output characteristic tables as a non-linear processing means, it is possible to optimally adjust the noise reduction amount and the vertical resolution by appropriately selecting the input / output characteristics according to the image type and the noise amount. it can.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a conventional line noise canceller, FIG. 2 is an explanatory diagram of frequency characteristics of a C-shaped comb filter, and FIG. 3 is an explanatory diagram of input / output characteristics of a limiter in a conventional line noise canceller. FIG. 4 is an explanatory diagram of frequency characteristics of the Y-shaped comb filter, FIG. 5 is a circuit block diagram of the video signal processing device in the first embodiment of the present invention, and FIG. 6 is a non-linear processing circuit in the video signal processing device. FIG. 7, FIG. 7 is an explanatory diagram of input / output characteristics of the video signal processing device, FIG. 8 is an explanatory diagram of input / output characteristics of a non-linear processing circuit in the video signal processing device, and FIG. Explanatory view of the concept of ROM storing characteristic table, FIGS. 10 (A) to (C)
Is a circuit block diagram of the video signal processing device in each of the second to fourth embodiments of the present invention, and FIG. 11 is an explanatory diagram of the input / output characteristics of the non-linear processing circuit in the third and fourth embodiments of the present invention. is there. (11) …… Digital memory, (12) (25) …… Subtractor,
(13) …… Attenuator, (14) (27) …… Nonlinear processing circuit,
(15) …… Subtractor, (26) …… Adder.

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Claims (1)

[Claims] 1. A digital memory for delaying an input luminance signal obtained by digitizing a luminance signal for one horizontal scanning period, a first arithmetic means for taking out a difference between the input luminance signal and an output signal of the digital memory, and The non-linear processing means includes a non-linear processing means for obtaining a specific output in accordance with the output signal of the first calculation means, and a second calculation means for mixing the input luminance signal and the output signal of the non-linear processing means. , In the range where the input signal amplitude is smaller than the first threshold value, the frequency component in the vicinity of an odd multiple of 1 / 2fH (fH is a horizontal scanning frequency) of the output signal of the second computing means is suppressed and input. In the range where the signal amplitude is larger than the first threshold value and larger than the second threshold value, 1/2 · f of the output signal of the second computing means
A video signal processing device having a non-linear characteristic that emphasizes a frequency component near an odd multiple of H.