JPH0440090A - Line correlation noise canceling circuit - Google Patents

Abstract

PURPOSE:To improve the picture quality of an entire reproduced picture by de-emphasizing the noise components of a low frequency so as to be made smaller than the noise components of a high frequency in a de-emphasis circuit. CONSTITUTION:A de-emphasis circuit 10 is provided between a limiter 6 and a second subtracter 8. Then, among the noise components contained in the output of the limiter, the de-emphasis amounts corresponding to the noise components of the low frequency is made smaller than that corresponding to the noise components of the high frequency by the de-emphasis circuit 10. That is, the level of the noise components of the low frequency outputted to the second subtracter 8 is made larger than that of the noise components of the high frequency. Thus, it is possible to improve the picture quality of the entire reproduced picture because an influence of the noise components of the low frequency on the regenerated picture is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a line correlation noise canceling circuit included in video equipment such as a video tape recorder.

(Prior Art) Fig. 3 is a circuit diagram of a conventional line correlation noise canceling circuit, in which the main reproduced luminance signal Sl containing the noise component from the input terminal in is delayed by 1H along with the noise component in the 1H delay circuit 2. By doing so, the delayed reproduced luminance signal S2 is obtained, and the delayed reproduced luminance signal S2 and the main reproduced luminance signal S
l to the first subtractor 4. From this first subtractor 4, the main reproduced luminance signal S1 and the delayed reproduced luminance signal S2, which have line correlation, almost cancel each other out and are not substantially output, but the main reproduced luminance signal component has no or little line correlation. and a delayed reproduction luminance signal component,
and a noise component N having no line correlation are outputted and given to the limiter 6.

The limiter 6 substantially cancels the reproduced luminance signal component that has been output because there is no or little line correlation by limiting its amplitude.
For noise components N whose amplitude is below the limit, it is output. In this way, the noise component N output from the limiter 6 is provided to the second subtracter 8. In this second subtractor 8, the main reproduced luminance signal Sl is given to one input part, and the noise component N is given to the other input part. Almost canceled.

As a result, the main reproduced luminance signal St' with the noise component N canceled is output from the second subtracter 8 to the output terminal out.

Such noise canceling circuits are well known in home video.

(Problem to be Solved by the Invention) By the way, in the noise canceling circuit described above, in order to enhance the canceling effect of the noise component, the amplitude limit of the limiter 6 is relaxed to increase the amplitude level of the noise component output from the limiter 6. However, it is preferable to increase the cancellation between the second subtracter 8 and the noise component in the main reproduced luminance signal St. Therefore, in the second subtracter 8, the main reproduced luminance signal is subtracted by the reproduced luminance signal component from the limiter 6. As a result, waveform distortion or the like occurs in the main reproduction luminance signal, resulting in a deterioration in the image quality of the reproduction screen, which is inconvenient.

Therefore, if the amplitude limitation of the limiter 6 is made strict within a range where waveform distortion does not occur in such a main reproduced luminance signal, the effect of canceling the noise component will be reduced. In that case, since conventional noise canceling circuits cancel noise components uniformly from low frequencies to high frequencies, if the noise component canceling effect decreases and the noise component increases, the high frequency When the noise component increases, the noise does not become visually noticeable on the playback screen, but when the low frequency noise component increases, the noise becomes more noticeable on the playback screen. . In this case, it is well known that low-frequency noise components are more noticeable on the playback screen than high-frequency noise components, so a description thereof will be omitted.

Therefore, in the present invention, in order to prevent the original reproduced luminance signal from being damaged due to waveform distortion etc., the limiter's amplitude limit is made stricter, and even if the canceling effect of the noise component is sacrificed to some extent, it is possible to suppress the low frequency noise component. The purpose of this is to improve the overall image quality of the playback screen by increasing the cancellation effect relative to high-frequency noise components.

(Means for Solving the Problem) In order to achieve such an object, the noise canceling circuit of the present invention includes a 1H delay circuit, a first subtracter, a limiter, a de-emphasis circuit, and a second subtracter. The 1H delay circuit converts the main reproduction brightness signal into 1H.
(H is the horizontal scanning period) and outputs this as a delayed reproduction luminance signal. The limiter inputs the subtraction output, limits the amplitude of the subtraction output, and outputs the subtraction output, and the de-emphasis circuit de-emphasizes the limiter output. Of the noise components included in the limiter output, the second subtracter has a characteristic of making the de-emphasis amount for low-frequency noise components smaller than the de-emphasis amount for high-frequency noise components. It is characterized in that the main reproduction luminance signal and the de-emphasis circuit output are subtracted and output.

(Operations) The operations of the 1H delay circuit, the first subtracter, the limiter, and the second subtracter are the same as those of the conventional example, so a description of the operations will be omitted.

In the present invention, a de-emphasis circuit is provided between the limiter and the second subtracter, and the de-emphasis amount for the low-frequency noise component among the noise components included in the limiter output is reduced by the de-emphasis amount for the high-frequency noise component. In other words, the level of the low-frequency noise component output to the second subtractor is set to be higher than that of the high-frequency noise component, and as a result, the influence of the low-frequency noise component on the playback screen is reduced. are doing.

In other words, by tightening the amplitude limit of the limiter, when waveform distortion etc. of the main reproduced luminance signal output from the second subtracter is eliminated, the level of the noise component is lowered due to the amplitude limit. In this case, a de-emphasis circuit is installed to prevent the low-frequency noise components from adversely affecting the image quality of the playback screen, which was a problem when the level of noise components uniformly decreased from low to high frequencies as in the past. Therefore, the level of the low frequency noise component can be made higher than that of the high frequency noise component, and as a result of the subtraction in the second subtracter, the level of the low frequency noise component included in the main reproduced luminance signal can be decreased.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a noise canceling circuit according to an embodiment of the present invention. The same parts as in FIG. 3 according to the conventional example are given the same reference numerals, and the same parts will be described in detail here. is omitted.

The feature of this embodiment is that a non-linear de-emphasis circuit 0 is provided between the limiter 6 and the second subtracter 8.

The nonlinear de-emphasis circuit IO is a differential amplifier A.
Equipped with MP. The output of the limiter 6 is given to one input section (+) of the differential amplifier AMP, and the output is fed back to the other input section (mc-) via a parallel circuit of a resistor R1 and a capacitor CI. ing. Further, a resistor R2 is connected between the other input section (=) of the differential amplifier AMP and the ground. The resistor R2 is connected to a capacitor C2 and two diodes D1. A circuit formed by connecting the reverse polarity parallel circuit of D2 in series is connected in parallel.

This non-linear de-emphasis circuit IO performs non-linear de-emphasis on the noise component N from the limiter 6. In this case, for the noise component N with a small level, the level is reduced according to the characteristic (■) in Fig. 2. The noise component N is non-linearly de-emphasized and output to the second subtracter 8 using the characteristic (■) for a moderate noise component N, and the characteristic (■) for a noise component N with a large level. do.

That is, when a noise component N with a small level is input from the limiter 6 to one input section (→-) of the differential amplifier AMP, the resistance across the diode DID2 increases, and the resistance between both ends of the diode DID2 increases. resistance is resistance R2
The output of the differential amplifier AMP will be as shown in Figure 2, with the noise component N having a medium level.
When input is input, it becomes like ■ in the same figure, and when a high-level noise component N is input, conversely, the differential amplifier AMP output increases and becomes like ■ in the same figure. Become. Also, depending on the capacitance of capacitors C1 and C2,
The frequency characteristics from the low frequency region (2) to the high frequency region H have shoulder characteristics as shown in (1) to (2) in the same figure for the noise component N having each level.

Therefore, even if the amplitude limit of limiter 6 is made stricter,
Since the amount of non-linear de-emphasis is made smaller for the low-frequency noise component N than for the high-frequency one, the level of the low-frequency noise component output from the non-linear de-emphasis circuit IO to the second subtractor 8 is large. Therefore, in the second subtracter 8, low frequency noise components are canceled to a greater extent than high frequency noise components. This reduces the influence of low-frequency noise components on the playback screen.

Note that in this embodiment, the nonlinear de-emphasis circuit I
However, the diodes D I and D 2 may be omitted and a simple de-emphasis circuit may be used to reduce the influence of low frequency noise components on the reproduced screen in the same manner as described above.

(Effects of the Invention) As is clear from the above explanation, according to the present invention,
If the reproduced luminance signal component included in the output of the first subtracter is sufficiently removed by limiting the amplitude of the limiter, the level of the noise component will also decrease due to the amplitude limiting, and
The effect of canceling the noise component in the subtracter decreases, but in the de-emphasis circuit, the low-frequency noise component is made smaller than the high-frequency noise component. The second subtracter subtracts the noise component from the main reproduction luminance signal by increasing the noise component, so the amplitude limitation of the limiter eliminates waveform distortion of the main reproduction luminance signal, and it also eliminates waveform distortion caused by low frequency noise components. As a result, it is possible to reduce the negative influence on the playback screen, and as a result, it is possible to obtain a noise canceling circuit that improves the image quality of the entire playback screen.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a noise canceling circuit according to an embodiment of the present invention, and FIG. 2 is a diagram showing frequency characteristics of the differential amplifier output in the nonlinear de-emphasis circuit of FIG. 1. FIG. 3 is a circuit diagram of a conventional noise canceling circuit. 2...1H delay circuit, 4...first subtracter, 6...
Limiter, 8...second subtracter, lO...nonlinear de-emphasis circuit.

Claims (1)

[Claims] (1) 1H delay circuit (2), first subtracter (4), limiter (6), de-emphasis circuit (10), and second
It has a subtracter (8), and a 1H delay circuit (2) converts the main reproduction luminance signal into 1H (H
is delayed by a period (horizontal scanning period) and outputs this as a delayed reproduced luminance signal.The first subtracter (4) inputs the main reproduced luminance signal and the delayed reproduced luminance signal, and also The limiter (6) inputs the subtracted output, limits the amplitude of the subtracted output, and outputs the subtracted output, and the de-emphasis circuit (10) outputs the subtracted output from the limiter (6). ) A characteristic that de-emphasizes the output, and makes the amount of de-emphasis for low-frequency noise components smaller than the amount of de-emphasis for high-frequency noise components among the noise components included in the output of the limiter (6). A line correlation noise canceling circuit comprising: a second subtracter (8) for subtracting and outputting the main reproduction luminance signal and the output of the de-emphasis circuit (10).