JPH0530392A - Picture quality adjustment device - Google Patents

Abstract

PURPOSE:To obtain a video signal outputted from an adder circuit as an original video signal from which noise is subtracted by attenuating a high frequency component of the video signal at an input terminal and an output terminal of a delay circuit and making an output signal of a subtractor circuit zero when a changeover circuit is used to connect the output terminal of the delay circuit to the input terminal via a resistor. CONSTITUTION:A horizontal contour compensation circuit including a delay circuit 1, a subtractor circuit 2 and an adder circuit 4 is provided with a changeover circuit 5 used to connect an input terminal N of the horizontal contour compensation circuit and an output terminal of the delay circuit 1 electrically or to interrupt them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image quality adjusting device,
In particular, it relates to an image quality adjustment device having a noise reduction effect.

[0002]

2. Description of the Related Art A video device such as a video camera or a television receiver is a contour correction circuit for enhancing the sharpness of an image by emphasizing a portion having a relatively large luminance change such as a contour portion of a picture. including.

The contour correction circuit includes a horizontal contour compensation circuit for emphasizing a horizontal luminance change of the video screen and a vertical contour compensation circuit for emphasizing a vertical luminance change of the video screen.

FIG. 5 is a schematic block diagram showing the configuration of a conventional horizontal contour compensation circuit (generally called an H-APT compensation circuit).

The structure and operation of a conventional horizontal contour compensation circuit will be described below with reference to FIGS. 5, 6 and 8.

FIG. 8 is a diagram showing an example of an image to be contour-compensated. FIG. 6 is a diagram showing waveforms of signals appearing in respective portions of the horizontal contour compensation circuit when the video signal of the image shown in FIG. 8 is input to the horizontal contour compensation circuit of FIG.

Referring to FIG. 5, the horizontal contour compensation circuit includes a delay circuit 1, a buffer circuit 3, a subtraction circuit 2, an addition circuit 4 and a resistor R1. The video signal to be contour-compensated is input to the delay circuit 1 via the resistor R1.
The resistor R1 changes the input impedance to the delay circuit 1 to
It is provided to match the internal impedance of the delay circuit 1.

The delay circuit 1 delays the given video signal by a fixed time T _D. The video signal delayed by the delay circuit 1 is input to the addition circuit 4 via the buffer circuit 3 and also to the subtraction circuit 2.

The subtraction circuit 2 subtracts the video signal appearing at the input end of the delay circuit 1 from the video signal output from the delay circuit 1. The signal obtained as a result of this subtraction is a signal for horizontal contour compensation (hereinafter referred to as a horizontal aperture signal).
Is input to the adder circuit 4.

Since the resistor R1 for impedance matching is connected to the input end of the delay circuit 1, the input video signal to this horizontal contour compensation circuit is not reflected at the input end of the delay circuit 1. .. On the other hand, since such a resistor is not connected to the output terminal of the delay circuit 1, the internal impedance of the buffer circuit 3 and the output impedance of the delay circuit 1 do not match, so the input signal to the delay circuit 1 However, a phenomenon occurs in which the output is reflected at the output terminal of the delay circuit 1. As a result, at the input terminal of the delay circuit 1, the input signal to the delay circuit 1 is delayed by the delay time T of the delay circuit 1.
_D 2 times the (T _D × 2) delayed signals (reflected waves)
Is applied to the input terminal of the delay circuit 1.

For example, as shown in FIG. 8, when an image 100 in which a rectangle 100b having a uniform brightness brighter than the background 100a exists in a background 100a having a uniform brightness, an arbitrary portion passing through the rectangular portion 100b is taken. The video signal obtained from the horizontal scanning line HL becomes a square wave as shown in FIG.

When the signal shown in FIG. 6 (a) is input to this contour compensating circuit, the input terminal of the delay circuit 1 is connected to FIG.
A signal obtained by averaging the signal shown in (a) and the signal (FIG. 6C) delayed by a time (T _D × 2) that is twice the delay time T _D of the delay circuit 1 ( FIG. 6 (d) appears.

On the other hand, the output terminal of the delay circuit 1 is shown in FIG.
A signal (FIG. 6B) obtained by delaying the signal shown in FIG. 6A by the delay time T _D of the delay circuit 1 appears.

The subtraction circuit 2 subtracts the signal appearing at the input end of the delay circuit 1 from the signal appearing at the output end of the delay circuit 1 to derive a signal as shown in FIG. 6 (e).

As described above, the output signal of the subtraction circuit 2 includes the original video signal before being delayed, the video signal delayed by a minute time period T _D, and the delayed signal of a further minute time. It is a signal obtained by synthesizing a signal delayed by the period T _D , and corresponds to a signal obtained by differentiating the original video signal with respect to time.

That is, the output signal of the subtraction circuit 2 is as shown in FIG.
As shown in (e), the original video signal (Fig. 6 (a))
Pulses of positive polarity and negative polarity appear in each portion corresponding to the luminance change portion (rising portion and falling portion) of the signal (FIG. 6 (b)) delayed by the delay circuit 1 by the time T _D.

As described above, the subtraction circuit 2 extracts the brightness change portion of the signal at the output end of the delay circuit 1. Finally, the adder circuit 4 superimposes the output signal of the subtraction circuit 2 (FIG. 6E) on the signal at the output end of the delay circuit 1 (FIG. 6B) given through the buffer circuit 3. As a result, as shown in FIG. 6 (f), the voltage level of the portion immediately before the rising and the trailing edge of the original video signal is lowered and the voltage level of the portion immediately after the rising is raised from the adder circuit 4. Signal is output. In other words, the video signal of each horizontal scanning line HL is emphasized in its luminance change by this contour compensation circuit.

Specifically, referring to FIG. 8, the brightness of the left side 200 and the right side 300 of the rectangular portion 100b is slightly increased, and the left side 200 and the right side 300 of the periphery 100a of the rectangle 100b are respectively increased. The brightness of the contact portion is slightly lowered. As a result, the boundaries 200, 30 between the rectangular portion 100b and its surrounding 100a are
Since the change in brightness at 0 is emphasized, the boundaries 200 and 300 between the rectangular portion 100b and the periphery 100a become clear in the image displayed by the video signal that has passed through the horizontal contour compensation circuit, and the rectangle 100b becomes sharp. Looks like.

As described above, according to the contour correction circuit, the contour of the pattern is clarified and the sharpness of the image is improved by slightly increasing the difference in brightness between the pattern and the surroundings.

[0020]

As described above, the conventional horizontal contour compensation circuit, which is one of the image processing circuits for adjusting the image quality, has a horizontal aperture signal created based on the input image signal. Is superimposed on the original video signal. Therefore, when the original video signal contains many noise components, the noise components are more emphasized in the video signal output from the horizontal contour compensation circuit, and as a result, the image quality may deteriorate.

Therefore, when a video signal containing a lot of noise components is input to the horizontal contour compensation circuit, the gain of the horizontal aperture signal superimposed on the original video signal is reduced, or the horizontal aperture signal is superimposed on the original video signal. Methods such as not doing so have been proposed. However, according to such a method, the noise component is not so emphasized by the horizontal contour compensation circuit, but the noise component is not extinguished. Therefore, the image displayed by the output signal of the horizontal contour compensation circuit still contains much noise. In general, a large amount of a video signal containing a lot of noise components is obtained when a subject having a low illuminance is imaged. Therefore, according to the conventional method, it is difficult to image a subject having low illuminance and display a high quality image.

Next, referring to FIG. 7, a problem that occurs when a video signal containing a lot of noise components is input to the conventional horizontal contour compensation circuit shown in FIG. 5 will be described. Figure 7
FIG. 6 is a diagram showing waveforms of signals appearing at various parts in the horizontal contour compensation circuit when a video signal containing many noise components is input to the horizontal contour compensation circuit of FIG. 5.

Consider, for example, a case where a video signal corresponding to the rectangular portion 100b contains a lot of noise because a subject as shown in FIG. 8 is imaged with low illuminance.

A video signal of an arbitrary horizontal scanning line HL passing through the rectangular portion 100b is, for example, as shown in FIG. 7A, the delay time T of the delay circuit 1 in the horizontal contour compensation circuit.
_When noise on a pulse having a period twice as long as _D (2 × T _D ) is included, the output terminal of the delay circuit 1 has a waveform shown in FIG.
Signal appears at the input end of the delay circuit 1 and the signal (FIG. 7C) in which the signal at the output end of the delay circuit 1 is further delayed by the delay time T _D of the delay circuit 1 and the original image. The signal (FIG. 7 (a)) is averaged and the signal shown in FIG. 7 (d) appears.

Therefore, the output signal of the subtraction circuit 2 is obtained by amplifying the noise of the original video signal as shown in FIG. 7 (e).

The adder circuit 4 outputs this amplified noise (FIG. 7 (e)) to the signal at the output end of the delay circuit 1 (FIG. 7 (e)).
(B)). Since the signal at the output end of the delay circuit 1 and the output signal of the subtraction circuit 2 have the same phase, the output signal of the addition circuit 4 is the noise of the original video signal as shown in FIG. 7 (f). Is greatly amplified.

As can be seen from the above, the closer the cycle of noise included in the video signal to the time (2 × T _D ) which is twice the delay time T _D of the delay circuit 1 in the horizontal contour compensation circuit, Since this noise component is greatly amplified in the horizontal contour compensation circuit, the image quality is further deteriorated.

Therefore, an object of the present invention is to solve the above problems and adjust a video signal containing a lot of noise components to a video signal capable of displaying a high quality image. An object is to provide an image quality adjustment device.

[0029]

In order to achieve the above-mentioned object, an image quality adjusting apparatus according to the present invention comprises a delay means for delaying a video signal, and an output end and an input end of the delay means. Switch means for electrically connecting and disconnecting, subtracting means for subtracting the signal at the input end of the delay means from the signal at the output end of the delay means, and the subtraction output of this subtracting means,
Adding means for adding to the signal at the output end of the delay means.

[0030]

Since the image quality adjusting apparatus according to the present invention is configured as described above, when the output end and the input end of the delay means are electrically coupled by the switch means, the input end of the delay means is A signal obtained by averaging the video signal before being delayed by the delay means and the video signal after being delayed by the delay means appears, and when the output end and the input end of the delay means are electrically cut off, Since the video signal is reflected by the output end of the delay means, the input end of the delay means receives the video signal before being delayed by the delay means and the delay signal by the delay means.
The delayed signal and the averaged signal appear. On the other hand, at the output end of the delay means, the video signal before being delayed by the delay means and the delay means by the delay means, regardless of whether the output end and the input end of the delay means are cut off or connected. A signal obtained by averaging the delayed video signal appears.

Therefore, when the switch means cuts off the output end and the input end of the delay means, the subtraction means outputs an AC signal indicating the change in the luminance of the video signal, so that the output signal of the addition means. Indicates that the luminance change portion of the original video signal is emphasized. On the other hand, when the switch means connects the input end and the output end of the delay means, the output of the subtraction means becomes 0, so that the signal from the output end of the delay means, that is, before being delayed by the delay means from the addition means. The video signal and the video signal delayed by the delay means are signals averaged with each other.

[0032]

1 is a schematic block diagram showing the structure of an image quality adjusting apparatus according to an embodiment of the present invention.

Referring to FIG. 1, this image quality adjusting apparatus is provided with a switching circuit 5 and a resistor between an input terminal and an output terminal of the delay circuit 1 in the conventional horizontal contour compensating circuit shown in FIG. R2 and R2 are connected in series with each other. Further, an operation switch 6 is provided to control the switching circuit 5.

The switching circuit 5 connects the resistor R2 to the input terminal (node N) of the image quality adjusting device, or
It works so as not to be electrically connected to either.

The operation switch 6 is operated by a user, for example, and a signal for controlling the switching circuit 5 so that the switching circuit 5 connects the resistor R2 to the node N or the switching circuit 5 switches the resistor R2 to either one. A signal for controlling the switching circuit 5 so as not to be connected is also given to the switching circuit 5. Hereinafter, the signal supplied from the operation switch 6 to the switching circuit 5 will be referred to as an image quality switching control signal.

When the switching circuit 5 does not connect the resistor R2 to the node N, the signal at the output end of the delay circuit 1 is given only to the subtraction circuit 2 and the buffer circuit 3, so that this image quality adjusting apparatus is arranged horizontally in FIG. Performs exactly the same operation as the contour compensation circuit.

That is, a video signal (FIG. 6) obtained from an arbitrary horizontal scanning line HL passing through the rectangular portion 100b of FIG.
When (a)) is input to this image quality adjusting device, the input terminal of the delay circuit 1, the output terminal of the delay circuit 1, the output terminal of the subtraction circuit 2, and the output terminal of the adder circuit 4 are respectively output as shown in FIG. ),
The signal waveforms shown in (b), (e) and (f) appear.

Next, the switching circuit 5 connects the resistor R2 to the node N.
The operation of this image quality adjusting device when connected to the camera will be described with reference to FIGS.

FIG. 2 is a diagram showing waveforms of signals appearing in respective parts in the image quality adjusting apparatus when a square wave-shaped video signal containing no noise is input to the image quality adjusting apparatus.

FIG. 3 is a diagram showing waveforms of signals appearing in respective parts in the image quality adjusting apparatus when a video signal containing noise on a pulse is input to the image quality adjusting apparatus.

When the resistor R2 is connected to the node N, the video signal input to the image quality adjusting device is input to the delay circuit 1 via the resistor R1 and at the same time, is input to the delay circuit via the resistor R2. 1 is transmitted to the output terminal. Resistor R2
Are provided to match the internal impedance of the source (not shown) of the video signal input to the image quality adjusting device with the internal impedance of the delay circuit 1.

Therefore, the signal transmitted from node N to output terminal of delay circuit 1 via switching circuit 5 and resistor R2 passes through delay circuit 1 and appears at the input terminal of delay circuit 1. Therefore, at both the input terminal and the output terminal of the delay circuit 1, a signal obtained by averaging the original video signal and a signal obtained by delaying this video signal by the delay time T _D of the delay circuit 1 appears.

On the other hand, since the subtraction circuit 2 subtracts the signal appearing at the input end of the delay circuit 1 from the signal appearing at the output end of the delay circuit 1, the output signal of the subtraction circuit 2 becomes zero. Therefore, the adder circuit 4 outputs the signal at the output end of the delay circuit 1 provided via the buffer circuit 3 as it is.

For example, from the horizontal scanning line HL in FIG.
It is assumed that a square wave with no noise is obtained as shown in (a). When this square wave is input to the image quality adjusting apparatus, the square wave (FIG. 2 (a) is input to the input terminal and the output terminal of the delay circuit 1 as shown in FIGS. 2 (d) and 2 (c), respectively. )) And this square wave are delayed by the delay circuit 1 for a time T _D (FIG. 2 (b)) are averaged to obtain a signal having a stepwise rising portion and a falling portion. ..

Since the output signal of the subtraction circuit 2 is 0 as shown in FIG. 2 (e), the output signal of the addition circuit 4 is as shown in FIG. 2 (f). 2 shows the same waveform as the signal (FIG. 2B).

As is clear from a comparison between FIG. 2A and FIG. 2F, the output signal of this image quality adjusting device moderates the voltage change at the rising and falling portions of the original video signal. It will be what you did. Therefore, in the image (see FIG. 8) displayed by the output signal of the image quality adjusting device, the change in luminance at the boundary portions 200 and 300 between the rectangular portion 100b and the surrounding 100a becomes gentle.
That is, the contours 200 and 300 of the rectangular portion 100b are relaxed.

Therefore, when the picture is too sharp in the reproduced image, such as when the difference between the picture brightness and the surrounding brightness is too large, the user uses the operation switch 6 to
If an image quality switching control signal for controlling the switching circuit 5 so that the resistor R2 is connected to the node N is given to the switching circuit 5, an image with appropriate sharpness and easy to see can be obtained.

Next, consider a case where a video signal containing a lot of noise is input to the image quality adjusting apparatus.

For example, the image signal obtained from the horizontal scanning line HL because the image of the subject in FIG.
As shown in FIG. 3A, consider a case where a portion corresponding to the rectangular portion 100b contains a lot of noise. Further, in the following description, in order to simplify the description, it is assumed that this noise has a pulse shape having a period (2 × T _D ) twice the delay time T _D of the delay circuit 1 as one cycle. To do.

Such a pulse signal is applied to the delay circuit 1
Signal obtained by delaying the delay time T _{D of}
(B)) is a signal that interpolates a portion where no pulse appears in the original signal (FIG. 3A).

Therefore, when a signal as shown in FIG. 3 (a) is input to this image quality adjusting apparatus, the input terminal and the output terminal of the delay circuit 1 are changed to those shown in FIGS. 3 (d) and 3 (c), respectively. As shown, in the period from the first rise of the original video signal to the last fall of the signal obtained by delaying the original video signal by the time T _D (FIG. 3B), A square wave appears with a voltage level corresponding to half the noise amplitude of the video signal.

Of course, in this case as well, the output signal of the subtraction circuit 2 is 0 as shown in FIG. 3 (e), so the output signal of the addition circuit 4 is as shown in FIG. 3 (f). It will be the same square wave that appears at the output of the delay circuit.

Therefore, in the image projected by the output of this image quality adjusting device (see FIG. 8), the rectangular portion 100b is projected relatively sharply without any noise.

In this way, the switching circuit 5 turns on the resistor R2.
Video that is input when it is controlled to connect
Of the noise components included in the signal, when the delay circuit 1 delays
Interval T _DTwice the time (2 × T_D) Has a period equivalent to
Component at the input and output ends of the delay circuit 1
Since it is completely canceled, the original image is displayed at the output end of the adder circuit 4.
A signal with an improved signal-to-noise ratio appears.

Therefore, when the displayed image contains a lot of noise, the user operates the operation switch 6 to
The switching circuit 5 supplies an image quality switching control signal for controlling the switching circuit 5 so that the resistor R2 is connected to the node N.
, It is possible to obtain an easy-to-see image with reduced noise.

As described above, when the switching circuit 5 does not connect the resistor R2 to the input terminal, the image quality adjusting device operates so as to emphasize the high frequency component of the input video signal, and the switching circuit 5 operates. When the resistor R2 is connected to the input end, it operates so as to attenuate the high frequency component of the input video signal.

FIG. 4 is a graph showing the frequency characteristic of this image quality adjusting apparatus. In FIG. 4, the horizontal axis represents the frequency of the input signal to this image quality adjusting device, and the vertical axis represents the gain of the output signal of this image quality adjusting device.

Referring to FIGS. 1 and 4, if resistor R2 is not connected to node N, subtraction circuit 2 has a delay time T _D of delay circuit 1 which is included in the original video signal and is twice the delay time T _D. Frequency (1 / (2 × T _D ) with time (2 × T _D ) as one cycle
Since the T _D )) component is extracted, the gain of the output signal of the adder circuit 4 is as shown in the curve B of FIG. 4 when the frequency of the input video signal is this frequency (1 / (2 × T _D )). ), The higher the value.

On the contrary, if the resistor R2 is not connected to the node N, the output voltage of the subtraction circuit 2 becomes 0, while the original video signal and this video signal are delayed at the output end of the addition circuit 4. A signal obtained by averaging the signal delayed by the time T _D by the circuit 1 appears, so that the gain of the output signal of the adding circuit 4 is equal to the frequency of the original video signal as shown by the curve A in FIG. The frequency (1 / (2 ×
It decreases as it approaches T _D )). That is, by switching the internal connection state of the switching circuit 5, the frequency characteristic of this image quality adjusting device changes greatly.

The user uses the operation switch 6 to change the frequency characteristic of the image quality adjusting apparatus to the curve A or B in FIG.
Can be selectively set to the one shown in. Actually, the user switches the internal connection state of the switching circuit 5 using the operation switch 6 while watching the image displayed by the output of the video equipment in which the image quality adjustment device is incorporated, and a more preferable image quality is obtained. The internal connection state of the switching circuit 5 may be set to the person who obtains it.

The delay time T _D of the delay circuit 1 is effective for increasing the sharpness of the pattern in the reproduced image,
In addition, it is set to an appropriate value corresponding to the frequency of noise that is likely to be included in the video signal. As a result, the image quality adjusting device can adjust the sharpness of the pattern in the reproduced image in a wide range, and can also sufficiently reduce the noise in the reproduced image.

[0062]

As described above, according to the present invention, a video signal which does not contain much noise is subjected to an effective process for adjusting the sharpness of a pattern in a reproduced image, and the noise is reduced. It is possible to obtain an image quality adjustment device capable of performing an effective process for reducing this noise on a video signal containing a lot of noise. As a result, the image quality of the reproduced image can be effectively improved.

For example, if the image quality adjusting apparatus according to the present invention is applied to a video camera, a camera-integrated VTR (video tape recorder), etc., a reproduced image with less noise can be obtained even when shooting under low illuminance. It will be possible.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing the configuration of an image quality adjusting apparatus according to an embodiment of the present invention.

[Fig. 2] When a video signal with less noise is input,
FIG. 3 is a waveform diagram for explaining the operation of the image quality adjustment device in FIG. 1.

FIG. 3 is a waveform diagram for explaining the operation of the image quality adjustment device in FIG. 1 when a video signal containing a lot of noise is input.

FIG. 4 is a graph showing frequency characteristics of the image quality adjustment device of FIG.

FIG. 5 is a block diagram showing a configuration of a conventional horizontal contour compensation device.

FIG. 6 shows a case where a video signal with less noise is input,
FIG. 6 is a waveform diagram for explaining the operation of the horizontal contour compensation device in FIG. 5.

7 is a waveform diagram for explaining the operation of the horizontal contour compensating apparatus in FIG. 5 when a video signal containing a lot of noise is input.

FIG. 8 is a diagram showing an example of a subject.

[Explanation of symbols]

 1 delay circuit 2 subtraction circuit 3 buffer circuit 4 addition circuit 5 switching circuit 6 operation switch

Claims (1)

Claim: What is claimed is: 1. A unit having an input end and an output end for delaying a video signal, and for electrically connecting and disconnecting the output end and the input end of the delay unit. Switch means, means for subtracting the signal at the input end of the delay means from the signal at the output end of the delay means, and addition of the subtracted output of the subtraction means to the signal at the output end of the delay means And an image quality adjusting device.