JPH079483Y2 - Noise reduction circuit - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial field of application) This invention relates to a signal-to-noise ratio in an image quality improving circuit used for a video enhancer or the like without deteriorating the rising and falling characteristics of a video signal. The present invention relates to a noise reduction circuit that prevents deterioration of the noise.

(Prior Art) Generally, a television receiver. In a video enhancer or the like, in order to clarify a contour of a video signal and reproduce a clear image, a correction is performed by adding preshoot and overshoot waveforms to a rising portion and a falling portion of the video signal, respectively.

FIG. 4 shows a basic configuration of a circuit for improving the image quality by adding the above-mentioned preshoot and overshoot waveforms. The input signal a is input to the delay circuit 1 and the secondary differentiating circuit 2 and is created by the secondary differentiating circuit 2. The quadratic differential waveform is inverted and amplified by the inverting amplifier 3, and the amplified inverted signal c is added to the signal b from the delay circuit 1 in the adder circuit 4 to obtain the output signal d with the contour emphasized. .

FIG. 5 shows the operation of the circuit of FIG. 4, where (a) is the input signal, (b) is the output waveform of the delay circuit 1, (c) is the second derivative waveform from the inverting amplifier 3, and (d) is This is the output waveform of the adder 4. In this way, the secondary differential waveform c is added to the rising portion and the falling portion of the input signal a, and the waveform characteristic of the output signal d is improved.

However, since the image quality improving circuit based on the above basic circuit increases the beam current in the white portion of the contour to emphasize the brightness difference, if excessive correction is performed, the beam spot diameter increases in the high-brightness portion and the beam spot diameter becomes appropriate. No correction can be made. Also,
When noise is mixed in the video signal, the noise is also corrected, and the signal-to-noise ratio (S / N) is deteriorated.

Conventionally, as a measure for removing noise from an image, for example, by changing the band characteristic of the video signal according to the electric field strength, the noise component is reduced or the gray level of a pixel is replaced with the average gray level in the vicinity of the pixel. The image is smoothed. However, the above-described measures for preventing the deterioration of the image quality with respect to the S / N have a drawback that the rising and falling of the video signal are deteriorated even if the noise can be reduced. Further, in the case of the smoothing processing, the image processing used by the microcomputer is performed, so that it is inevitable that the circuit becomes large in scale.

The circuit shown in FIG. 4 adds a shoot waveform for enhancing the contour of the image, but the circuit shown below makes the rising and falling portions of the video signal waveform steep. .

In FIG. 6, the delay circuits 12 and 13 are connected in series,
The input signal S0 is input to the delay circuit 12 at the front stage, and the delay circuit 12 outputs the signal S1 and the delay circuit 13 at the rear stage outputs the signal S2 as its delay output. The signal S1 is input to a contour correction circuit 18 using a secondary differentiation circuit as shown in FIG. 4, for example, and the contour correction circuit 18 becomes a signal S1 'to which preshoot and overshoot are added.

The output S1 'of the contour correction circuit 18 is input to each one input terminal of the first and second maximum level output circuits 14 and 15. The signals S0 and S2 are input to the other input terminals of the first and second maximum level output circuits 14 and 15, respectively, and
The signals are input to the third maximum level output circuit 16, respectively.
These maximum level output circuits 14, 15 and 16 selectively output the maximum level among the levels presented by a plurality of inputs. The outputs S3 to S5 of the first to third maximum level output circuits 14 to 16 are input to the minimum level output circuit 17, respectively. On the contrary, the minimum level output circuit 17 is a circuit for selecting the signal of the minimum level.

The maximum level output circuits 14, 15 and 16 and the minimum level output circuit 17 remove the preshoot and overshoot components from the signal S1 'to generate a waveform having steep rising and falling waveforms. Description will be made by referring to a shoot waveform removing circuit.

FIG. 7 is a waveform diagram showing the operation of the above-mentioned shoot waveform removing circuit. The delay circuits 12 and 13 generate signals S1 and S2 which are delayed by a predetermined time with respect to the input signal S0. To do. The contour correction circuit 18 outputs the contour correction circuit S1 '. The maximum level output circuit 14 compares the signals S0 and S1 'and selectively outputs the higher level signal, so that the obtained output has a waveform as shown in S3. Sx is the signal S0 (dotted line) and the signal S1 '(solid line) overlapped with each other, and the operation of the maximum level output circuit 14 can be easily understood. Since the maximum level output circuit 15 also operates in the same manner as the maximum level output circuit 14, the waveform of its output is as shown in S4. On the other hand, since the maximum level output circuit 16 outputs the higher one of the signals S0 and S2, its output is the signals S0, S1, S2 as shown at S5.
It becomes a waveform that includes. And the minimum level output circuit 17
Selects the signal at the lower level from among the signals S3, S4, S5, so as shown in S6, the output does not include preshoot and overshoot, and only the rising and falling signals are steep. be able to.

However, even if the circuit of FIG. 6 is used, when noise is mixed in, the noise component is also corrected, and the same problem as that of the circuit of FIG. 4 remains.

(Problems to be Solved by the Invention) In the conventional contour correction technique, when noise is mixed in a video signal, the noise is also corrected, and thus the S / N is deteriorated. There was a problem. Further, the method of controlling the smoothing of the image and the high frequency characteristic according to the electric field strength has a drawback that the rising and falling of the video signal are deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a noise reduction circuit that improves S / N without deteriorating the rising / falling characteristics of a video signal.

[Structure of the Invention] (Means for Solving Problems) The present invention relates to a low-pass filter for limiting the band of an input signal and a signal from the low-pass filter,
Delay circuit means for outputting a first signal and second and third signals that are in time advance and delay relations with respect to the first signal, and first, second, and A maximum level selecting means and a minimum level selecting means for inputting a third signal and selecting and outputting a maximum level and a minimum level of the levels which each signal exhibits at the same time, and the signal using the first signal as an original signal. From a contour correction circuit for adding a preshoot and an overshoot waveform to the rising portion and the falling portion of the waveform and outputting a contour correction signal with a contour emphasized, a signal from the maximum level selecting means, and a minimum level selecting means Signal and the signal from the contour correction circuit are respectively supplied as inputs, the pre-shoot and the overshoot are removed from the contour correction circuit signal as an output, and the original Rising unit, comprising a chute waveform removing means for generating a signal waveform steeper characteristics falling portion, in which equally performs edge correction and noise removal with respect to No..

(Function) Since the maximum level output circuit and the minimum level output circuit input signals having respective delay relationships, the noise superimposed on the input signal is reduced to eliminate the shoot waveform regardless of the presence or absence of the low pass filter according to the present invention. Lead to the circuit. As a result, even if the noise component is increased when the rising portion and the falling portion are sharpened by the contour correction in the shoot waveform removing circuit, the noise component included in the output of the shoot waveform removing circuit has the maximum level output circuit and the minimum level. The level can be suppressed to the level of the output of the output circuit. However, according to this invention, the noise component contained in the output of the maximum level output circuit and the minimum level output circuit can be further reduced by passing it through the low pass filter before inputting it to the delay circuit. As a result, the noise component included in the output signal can be downgraded by several steps as compared with the conventional case.

(Example) Hereinafter, this invention is demonstrated about the Example shown in figure.

FIG. 1 is a circuit diagram showing an embodiment of an image quality improving circuit according to the present invention.

In FIG. 1, a predetermined high frequency component is removed from the input signal Vin by the band limiting low pass filter 11. The output S0 of the low-pass filter 11 is input to the delay circuit 12, the maximum level output circuit 19, and the minimum level output circuit 20, respectively, and the output S1 of the delay circuit 12 is input to the delay circuit 13, and the maximum level output circuit 19 and the minimum level output circuit 19 are also input. Input to the level output circuit 20,
The output of the delay circuit 13 is the maximum level output circuit 19 in S2.
And to the minimum level output circuit 20.

The output S MAX of the maximum level output circuit 19 and the output S MIN of the minimum level output circuit 20 are supplied to the shoot waveform removal circuit 21. This shoot waveform removal circuit 21
Is the same as the circuit described in FIG. 6, and is composed of maximum level output circuits 23, 24, 25 and minimum level output circuit 26, respectively. The maximum level output circuit 23 receives the signal S MAX.
And a signal S1 'are input, and a signal having a larger level among these inputs is selectively output. Maximum level output circuit 24
Inputs the signal S MIN and the signal S1 ′, outputs the signal exhibiting the larger level, and the maximum level output circuit 25
Input MAX and signal S MIN, and output the signal with the larger level. Then, the minimum level output circuit 26 inputs the outputs S13, S14, S15 of the maximum level output circuits 23, 24, 25, and selectively outputs the signal exhibiting the minimum level among these inputs. The signal thus obtained is the output signal S16 according to the present invention.

The contour correction circuit 18 uses the quadratic differential circuit described with reference to FIG.

Fig. 2 shows maximum level output circuit 19 and minimum level output circuit 2
It is a circuit diagram showing an example of a concrete circuit of 0 and 26. In FIG. 3, (a) shows the maximum level output circuit 19, and the collectors and emitters of the three transistors T1, T2, T3 are connected in common, the collector is connected to the voltage source terminal Vcc, and the emitter is connected to the resistor R1. It is connected to the reference potential point via. Each terminal X, Y, Z to which a signal is input is a transistor T
It is connected to the bases of 1, T2 and T3. The common emitter is connected to the output terminal P0. In such a circuit, since each of the transistors T1 to T3 operates by a differential input, only the transistor to which the signal of the highest level is input is turned on, and based on this, the signal appearing across the resistor R1 is output. Further, when the level difference between the inputs is less than the predetermined level, it operates as an adder. Therefore, for example, when signals of the same level are input to the three inputs, the operating current of the transistor becomes one-third. It outputs the same level of signal amplified by two transistors. Further, a noise component included in only one signal and smaller than a predetermined level is reduced to one-third level. That is, when three delay signals are input as in the embodiment, the noise position shifts, and the noise level in the output S MAX becomes one third.

Also, FIG. 2B shows an example of the minimum level output circuits 20 and 26. The three transistors T4, T5, T6 are PNP type transistors, each collector is connected to the reference potential point, and each emitter is connected to the voltage source terminal Vcc via the resistor R2. Input terminals X, Y and Z are transistors T4, T5 and T, respectively.
It is connected to the base of 6 and the common emitter is connected to the output terminal P0. In this circuit, among the signals guided to the input terminals X, Y, and Z, only the transistor to which the signal with the lowest input level is input turns on. When the level differences are less than a predetermined level or are the same, the circuit operates as an adder as in the circuit of FIG. 2a.

Next, the operation of the circuit having the above configuration will be described.

FIG. 3 is an operation waveform diagram of each part of the circuit of FIG. a is an input signal Vin, b is noise superimposed on the input signal Vin, c is an input signal on which noise is superimposed, S0 is an input signal of the delay circuit 12,
S1 is the output signal of the delay circuit 12, S2 is the output signal of the delay circuit 13, S MAX is the output waveform of the maximum level output circuit 19, S MIN is the output waveform of the minimum level output circuit 20, and S1 ′ is the contour correction circuit.
18 is the output waveform, S13 is the output waveform of the maximum level output circuit 23, S14 is the output waveform of the maximum level output circuit 24, S15 is the output waveform of the maximum level output circuit 25, and S16 is the output waveform of the minimum level output circuit 17. .

Now, when the noise as shown in b is superimposed on the input signal a, the frequency region of the noise is higher than the image trust, so a low-pass filter for inputting the waveform as shown in c
11 is a signal with the noise component amplitude reduced as an output
Output S0. As a result, the rising and falling edges of the waveform also become dull.

Next, the signal S0 passes through the delay circuits 12 and 13, and has a waveform as shown in S1 and S2. The signal S1 is a signal obtained by delaying S0 by the delay time of the delay circuit 12, and the signal S2 is two delay circuits.
This is a signal obtained by delaying S0 by the total delay time of 12,13.

The maximum level output circuit 19 inputs signals S0, S1 and S2, which are respectively the transistors T1, T2, and S2 in FIG.
Supplied to the base of T3. When signal S0 is input to the base of transistor T1, transistor T1 turns on and the output terminal
Output a high level signal to P0. And later on the signals S1, S
Even if 2 is added and each of the transistors T2 and T3 is turned on, the operating current is reduced to 1/3 because each transistor operates differentially, and the level of the output terminal P0 remains unchanged. Therefore, the output of the maximum level output circuit 19 becomes a signal S MAX whose rising edge matches the signal S0 and whose falling edge matches the signal S2. In this case, since the noise component is at a level at which each of the transistors T1 to T3 operates as an adder, the noise component N1 generated by this operation is 3 in the levels included in the signals S0, S1, and S2 in this embodiment. It becomes one-third.

The minimum level output circuit 20 has a low output level because all the transistors T4, T5 and T6 are turned on when no signal is applied. Then, the level of the output terminal P0 is the same low level even if the signal S0 is added and the signal S1 is further added, and when the signal S2 is added, the level of the output terminal P0 is that all the transistors T4, T5, T6 are turned off. Will be at a high level. When the signal S0 falls, the transistor
Since T4 is turned on, the level of the terminal P0 returns to the initial low level. The signal S MIN is thus formed. Since this minimum level output circuit 20 also operates as an adder, the noise component contained therein is smaller than the signals S0, S1, S2.

On the other hand, the contour correction circuit 18 adds the second-order differential waveform using the signal S1 as the original signal, so that the shoot waveform is added to the rising portion and the falling portion of the signal S1 and the characteristics thereof are sharpened. At this time, the amplitude of the noise component also increases (see N3).

Next, as the maximum level output circuit 23, a circuit having two transistors in FIG. 2a can be used, and the maximum level signal is selected by turning on the transistor which always inputs a signal of a larger level than one. Signal whose rising edge coincides with S0 and whose falling edge coincides with signal S2
Form S13. This signal S13 contains noise N3 whose amplitude is increased by contour correction. Maximum level output circuit
The same applies to 24, and the signal S MIN and the signal S1 'cause the rising and falling to coincide with the signal S1', and a signal S14 having a shoot waveform is output. This signal S14 also contains noise N3. In addition, the maximum level output circuit 25 controls the signals S MAX and S MIN.
To output a signal S15 that matches the signal S MAX, so that the signal S15 does not contain noise increased by contour correction.

In the minimum level output circuit 26, since the signal S14 whose rising edge coincides with the signal S1 'rises latest in time and falls early, the rising edge and falling edge of the output coincide with the rising edge and falling edge of S1', and Signal S16 with the shoot waveform cut
Is output.

Since the rising edge and the falling edge of the signal S16 are sharpened and the maximum level is regulated by the signal S15,
It does not include the noise component increased by the contour correction.

Thus, in this embodiment, the maximum level output circuit 19 is provided by providing the low-pass filter 11 in the preceding stage of the delay circuits 12 and 13.
Also, since the noise level included in each of these outputs S MAX, S MIN is reduced to a level above the level reduced by the minimum level output circuit 20, the rising portion and the falling portion are included in the steepened signal S16. The noise component generated becomes a signal in which the noise level is reduced by several steps as compared with the case where the low-pass filter 11 is not provided, and the image quality can be improved.

The above embodiment is an example, and for example, the noise reduction effect is enhanced as the number of signals input to the maximum level output circuit 19 and the minimum level output circuit 20 is not limited to three.
Further, the shoot waveform removing circuit 21 may be configured by a circuit in which the maximum level output circuit and the minimum level output circuit are reversed.

[Effect of the Invention] As described above, according to the present invention, noise does not increase even when the rising and falling edges are made steep.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a noise reduction circuit according to the present invention, FIG. 2 is a circuit diagram showing an example of a maximum level output circuit and a minimum level output circuit used in the present invention, and FIG. 1 is an operation waveform diagram of each part for explaining the operation of the embodiment of FIG. 1, FIG. 4 is a circuit diagram for explaining the basic configuration of the contour correction circuit, FIG. 5 is a waveform diagram showing the operation of FIG. 5, and FIG. Is a circuit diagram showing an example of a conventional image quality improving circuit, and FIG. 7 is an operation waveform diagram of each part showing the operation of FIG. 12, 13 ... Delay circuit, 19 ... Maximum level output circuit, 20 ... Minimum level output circuit, 18 ... Contour correction circuit, 21 ... Shoot waveform removal circuit.

Claims (1)

[Scope of utility model registration request] 1. A low-pass filter for limiting a band of an input signal, and a signal from the low-pass filter, which is inputted to the first signal and which has a time advance and delay relation with respect to the first signal. Delay circuit means for outputting the second and third signals, and inputting the first, second and third signals from the delay circuit means,
Maximum level selecting means and minimum level selecting means for selectively outputting the maximum level and the minimum level of the levels that each signal exhibits at the same time, and the rising portion and the falling edge of the signal waveform with the first signal as the original signal. A contour correction circuit for adding a preshoot and an overshoot waveform to a portion and outputting a contour correction signal with a contour emphasized, a signal from the maximum level selection means, a signal from the minimum level selection means, and the contour correction circuit Signal from which the preshoot and overshoot are removed from the contour correction signal as an output, and the waveform of which has a sharp rise and fall characteristic with respect to the original signal. A noise reducing circuit comprising: