JPH04243381A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To obtain optimum picture quality without causing deterioration in the S/N and in the sharpness onto a picture even when the state is changed, e.g. from the state not implementing ghost elimination into the state implementing ghost elimination by a ghost elimination device. CONSTITUTION:A band pass filter 107 extracts a high frequency component from a luminance signal from a Y/C separator circuit 104 as a noise component and outputs the result. A full wave rectifier circuit 108 applies full wave rectification to the high frequency component from the band pass filter 107 and outputs the result. A smoothing circuit 109 smoothes an output signal from the full wave rectifier circuit 107 and outputs the result as a control signal. A picture quality correction circuit 105 receives the control signal from the picture quality correction circuit 105 and the luminance signal from the Y/C separator circuit 104 and amplifies or attenuates the high frequency component of the luminance signal in response to the control signal.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit used in a television receiver incorporating a ghost removal device or connected to a ghost removal device.

0002

2. Description of the Related Art In a television receiver, when a receiving antenna simultaneously receives direct waves from a broadcasting station and reflected waves from buildings, etc., ghost interference occurs, in which an unnecessary image appears on the screen. As a ghost removal device that removes such ghost interference, the broadcasting station uses
For example, a method that inserts a reference signal for ghost removal (GCR signal) and uses a transversal filter on the receiving side to perform ghost removal by comparing it with the GCR signal is disclosed in Japanese Patent Application Laid-Open No.
It is described in the publication No.-99378.

FIG. 5 shows a specific example of a general ghost removal device using such a transversal filter. In the figure, 401 is a video input terminal, 402 is an A/D conversion circuit, 403 is a delay compensation circuit, 404 is a subtraction circuit, 405 is a D/A conversion circuit, 406 is a video output circuit, 407a to 407c are delay elements, 408a-408
c is a multiplication circuit, 409 is an addition circuit, 410 is a transversal filter, 411 is a GCR signal extraction circuit, 4
12 is a comparison circuit, 413 is a reference signal generation circuit, and 414 is a tap gain control circuit.

Next, the principle of operation of this circuit will be explained. Radio waves (direct waves) sent from a broadcasting station include radio waves (reflected waves) from buildings and the like on the way, and arrive at a receiving antenna (not shown). The received radio waves (including ghost signals) pass through a tuner and a detection circuit (not shown) and are input to the video input terminal 401.

[0005] The input video signal is first converted from an analog signal to a digital signal in an A/D conversion circuit 402 . Here, the ghost removal reference signal (GCR signal) inserted at the broadcasting station side is also distorted due to the influence of the reflected waves (including the characteristics of the transmission path on the way). This distorted GCR signal is processed by a GCR signal extraction circuit 411.
, and is compared with the undistorted GCR signal generated from the reference waveform generation circuit 413 in the comparison circuit 412 .

The tap gain control circuit 414 uses the transversal filter 41 to minimize the error between the received GCR signal and the reference waveform based on the output of the comparison circuit 412.
The tap gains of the 0 multiplication circuits 408a to 408c are adjusted.

[0007] In this way, unnecessary reflected waves (ghost signal components) are extracted from the addition circuit 409, and the ghost is removed by subtracting the unnecessary reflected waves from the signal containing the reflected waves in the subtraction circuit 404. can do.

Furthermore, a digital signal is converted into an analog signal by a D/A conversion circuit 405, and a ghost-free video signal is obtained from an output terminal 406.

[0009]

[Problems to be Solved by the Invention] Now, let us consider the case where the propagation time difference between the direct wave and the reflected wave is very short (the case of a nearby ghost) as ghost interference.

FIG. 6A shows a case where a direct wave (solid line) and a reflected wave (dotted line) arrive with a propagation time difference Δt. The figure shows the noise component in the video signal and the 3.58MH luminance signal.
This is an enlarged representation of the z component.

When these two waves overlap as ghost interference, the noise component decreases, and the signal component of the luminance signal around 3.58 MHz also decreases, as shown in FIG. 6(b). do. If such a signal is input to a television receiver and ghost removal is not performed, the noise component will be reduced and the S/N will improve, but at the same time, the signal component of the luminance signal near 3.58 MHz will also be lost.
Sharpness deteriorates.

In such a case, in order to improve the sharpness, it is common practice to use an image quality correction circuit to amplify the high frequency components and compensate for the lost components.

However, when ghost removal is performed on the above-mentioned signal using a ghost removal device as shown in FIG.
Since the area around z is reproduced, if you perform the above-mentioned image quality correction in such a state, the high range will be further emphasized, causing "glare" in the image and also emphasizing noise components. Therefore, there was a problem that the S/N ratio deteriorated. Furthermore, depending on the phase of the ghost interference, there is a problem in that if the above-described image quality correction is performed with ghost removal performed, sharpness may be lost.

Regarding the problem in the former case, FIG.
This will be explained in more detail using FIG. FIG. 7 is a block diagram showing a conventional video signal processing circuit, and shows the flow of video signals when a ghost removal device is added to a television receiver.

In the figure, 601 is a receiving antenna;
02 is a tuner, 603 is a ghost removal device, 604 is a Y/C separation circuit, 605 is an image quality correction circuit, and 603 is a luminance signal output terminal.

First, consider a case where ghost removal is not performed in the ghost removal device 603. Radio waves containing ghosts are received by a receiving antenna 601, and tuned and detected by a tuner 602. Then, the composite video signal containing ghosts is sent to a ghost removal device 60.
3 to the Y/C separation circuit 604, where:
The composite video signal is separated into a luminance signal (Y) and a color signal (C). The separated luminance signal is sent to an image quality correction circuit 605.
After the high-frequency components are emphasized and the deterioration in sharpness due to ghosting is compensated for, the signal is output from the output terminal 606.

Here, the luminance signal whose high frequency components are emphasized by the image quality correction circuit 605 becomes as shown in FIG. 8(a).

Next, consider the case where ghost removal is performed in the ghost removal device 603. In this case, the ghost included in the composite video signal is removed by the ghost removal device 603, and as a result, the 3.58M
Since frequencies around Hz are reproduced, when the image quality correction circuit 605 emphasizes the high-frequency components of the luminance signal in the same manner as described above in such a state, noise components and 3. Components around 58 MHz are further emphasized, causing S/N deterioration and "glare" in the image.

That is, conventionally, when the ghost removal device 603 changes from a state where ghost removal is not performed to a state where ghost removal is performed, the operation of the image quality correction circuit 605 is uniform.
Deterioration of S/N ratio and deterioration of sharpness may occur in images.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to prevent the ghost removal device from changing from a state in which ghost removal is not being performed to a state in which ghost removal is being performed when the image quality correction circuit is performing image quality correction. , image S/N
An object of the present invention is to provide a video signal processing circuit that does not cause deterioration of image quality or sharpness.

[0021]

[Means for Solving the Problems] In order to achieve the above object, the present invention inputs a video signal from which a ghost has been removed by a ghost removal device, and detects the amplitude of a noise component contained in the video signal. a detection means for outputting the detection result as a control signal; and inputting the control signal from the detection means and the video signal from which the ghost has been removed by the ghost removal device, and correcting the image quality of the video signal. In order to achieve this, an image quality correction means is provided which amplifies or attenuates the high frequency component of the video signal according to the control signal and outputs the amplified or attenuated high frequency component.

[0022]

[Operation] The detection means extracts a change in the amplitude of the noise component of the video signal input to the image quality correction means, for example, a signal component around 4 MHz to 6 MHz using a band pass filter, and extracts the signal component in the vicinity of 4 MHz to 6 MHz, and outputs the output of the band pass filter. After full-wave rectification, the output obtained by smoothing is output as a control signal.

The image quality correction means controls a high frequency component of the video signal according to the control signal, and when the amplitude of the noise component increases, attenuates the high frequency component, and conversely, reduces the high frequency component of the noise component. If the amplitude of the signal decreases, the high frequency component is increased. Therefore, even if the ghost removal device changes from, for example, a state in which ghost removal is not performed to a state in which ghost removal is performed, there will be no deterioration in S/N or sharpness of the image, and the optimal state will be maintained. image quality can be obtained.

[0024]

[Embodiment] An embodiment of the present invention will be described below. FIG. 1 is a block diagram showing a video signal processing circuit as an embodiment of the present invention.

In the figure, 101 is an antenna, 102
is a tuner, 103 is a ghost removal device, 104 is Y/
C separation circuit, 105 is an image quality correction circuit, 106 is a luminance signal output terminal, 107 is a band pass filter, 108 is a full-wave rectifier circuit, and 109 is a smoothing circuit.

In this circuit, first, the Y/C separation circuit 10
Band pass filter 1 from the luminance signal (Y) separated by 4
07 to extract noise components and high frequency components, and then
The output of the bandpass filter 107 is full-wave rectified by a full-wave rectifier circuit 108, and then the output of the full-wave rectifier circuit 108 is converted to a DC level by a smoothing circuit 109 to obtain a control voltage proportional to the noise component. Then, the amount of correction of the image quality correction circuit 105 is controlled by this control voltage. As a result, the image quality correction circuit 105 emphasizes high-frequency components when there are few noise components, and does not emphasize them when there are many noise components.

Therefore, when the ghost removal device 103 changes from a state in which ghost removal is not performed to a state in which ghost removal is performed, for example, if the noise component increases, the high frequency emphasis is suppressed. Therefore, "glare" does not occur in the image, and since noise components are suppressed, the S/N ratio does not deteriorate. Conversely, when the sharpness deteriorates (when the noise component decreases), the high frequency range is emphasized, so that the sharpness can be improved.

FIG. 2 shows the image quality correction circuit 105 in FIG.
A specific example is shown below. In the figure, 201 is a luminance signal input terminal, 202 and 203 are delay lines, and 204a to 204
205 is a multiplication circuit, 205 is an addition circuit, 206 is a coring circuit, 207 is an addition circuit, and 208 is a control signal input terminal from the smoothing circuit 109.

This circuit has delay lines 202 and 203 of 7
By selecting 0 ns, a high frequency component centered around 3.58 MHz can be obtained from the adder circuit 205. Furthermore, by passing the signal through a coring circuit 206, the amount of noise removed can be varied.

The characteristics of this coring circuit 206 are shown in FIG. By controlling the control signal from the smoothing circuit 109, the characteristic shown by the solid line is selected when there is little noise, and the characteristics shown by the dotted line and dashed-dotted line are selected when there is a lot of noise. /N improves.

FIG. 4 is a block diagram showing a video signal processing circuit as another embodiment of the present invention. In this example, S/
When the S/N deteriorates, the control voltage of the color synchronization circuit (APC circuit) is disturbed, which is used to detect the deterioration of the S/N.

This circuit has a burst gate circuit 801, a phase comparator circuit 802, and a 3.58M
A Hz reference signal generation circuit 803, a color demodulation circuit 804, and an integration circuit 805 are newly added.

The operation of this circuit will be explained below. A burst signal is extracted from the color signal (C) separated by the Y/C separation circuit 104 by a burst gate circuit 801, and its phase is compared with the output of a reference signal generation circuit 803 in a phase comparison circuit 802, and the phase difference is determined by an integration circuit 805. It is converted into a voltage value and output as a control voltage. This control voltage controls the oscillation frequency of the reference signal generation circuit 803 so that the phase difference is eliminated. When a signal with a degraded S/N ratio enters this control system, there is a discontinuous part in the phase of the burst signal, so the control voltage output from the integrating circuit 805 is proportional to the S/N. It becomes what it is.

Therefore, the image quality correction circuit 105 may be controlled using a voltage corresponding to this control voltage. That is, the image quality correction circuit 105 emphasizes the high frequency component when the S/N is not degraded, and does not emphasize it when the S/N is degraded.

Therefore, when the ghost removal device 103 changes from a state where ghost removal is not performed to a state where ghost removal is performed, for example, if the S/N deteriorates, the high frequency emphasis is This suppresses "glare" in the image and suppresses noise components, thereby suppressing S/N deterioration. Conversely, if the sharpness deteriorates (if the S/N does not deteriorate),
Since high frequencies are emphasized, sharpness can be improved.

[0036]

According to the present invention, the amplitude of the noise component contained in the video signal from which the ghost has been removed is detected by the ghost removal device, and the image quality correction in the image quality correction means is controlled according to the detection result. (i.e., amplifies or attenuates the high frequency components of the video signal).
For example, even if the ghost removal device changes from a state where ghost removal is not performed to a state where ghost removal is performed, there is no deterioration in S/N or sharpness of the image, and optimal image quality is maintained. Obtainable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a specific example of the image quality correction circuit in FIG. 1;

FIG. 3 is a characteristic diagram showing the characteristics of the coring circuit in FIG. 2;

FIG. 4 is a block diagram showing another embodiment of the present invention.

FIG. 5 is a block diagram showing a specific example of a general ghost removal device.

FIG. 6 is a waveform diagram showing a waveform of a video signal including a ghost.

FIG. 7 is a block diagram showing a conventional video signal processing circuit.

8 is a waveform diagram showing a luminance signal with high frequency components emphasized by the image quality correction circuit in FIG. 7; FIG.

[Explanation of symbols]

101... Antenna, 102... Tuner, 103... Ghost removal device, 104... Y/C separation circuit, 105... Image quality correction circuit, 107... Band pass filter, 108... Full wave rectifier circuit, 109... Smoothing circuit.

Claims (3)

[Claims] 1. In a video signal processing circuit used in a television receiver incorporating a ghost removal device or connected to a ghost removal device, a video signal from which ghosts have been removed by the ghost removal device is input, and the video signal is a detection means for detecting the amplitude of a noise component included in a signal and outputting the detection result as a control signal; and a detection means for detecting the amplitude of a noise component contained in a signal and outputting the detection result as a control signal, and the control signal from the detection means and the video signal from which ghosts have been removed by the ghost removal device. and an image quality correction means for amplifying or attenuating high frequency components of the video signal according to the control signal and outputting the high-frequency components of the video signal in order to correct the image quality of the video signal. circuit. 2. The video signal processing circuit according to claim 1, wherein the detection means includes a bandpass filter that extracts a predetermined high frequency component from the input video signal as the noise component and outputs the extracted high frequency component; It is characterized by comprising a full-wave rectifier circuit that full-wave rectifies the high frequency component from the band-pass filter and outputs it, and a smoothing circuit that smoothes the output signal from the full-wave rectifier circuit and outputs it as the control signal. video signal processing circuit. 3. The video signal processing circuit according to claim 1, wherein the detection means is a color burst signal extraction circuit that extracts and outputs a color burst signal included in the input video signal from the input video signal. a reference burst signal generation circuit that generates and outputs a reference burst signal and controls the frequency of the generated reference burst signal according to an input frequency control signal; a phase comparison circuit that detects a phase difference between the color burst signal and the reference burst signal from the reference burst signal generation circuit and outputs a voltage according to the phase difference; A video signal processing circuit comprising: an integrating circuit that outputs a frequency control signal and outputs a signal corresponding to the frequency control signal as the control signal.