JPH0730783A - Ghost removing circuit - Google Patents

Abstract

PURPOSE:To stably perform processing in a linear state and to enable exact ghost removal by optimumly controlling an amplification factor and a clamp level corresponding to the state of an inputted video signal. CONSTITUTION:A reference signal GCR signal for ghost cancel fetched from a synchronous adding circuit 1-9 is inputted to comparing circuits 2-2 and 2-5. At the circuit 2-2, a minimum value is detected and stored in a minimum value storage circuit 2-3. Corresponding to this minimum value, optimum control data are selected from a previously decided clamp table 2-4 and corresponding to these data, the clamp level of a clamp circuit 1-3 is controlled to be optimum. At the circuit 2-5, a maximum value is detected and this is stored in a maximum value storage circuit 2-6. Corresponding to this maximum value, optimum control data are selected from a previously decided gain table 2-7 and corresponding to these data, the amplification factor of an amplifying circuit 1-2 is controlled. Thus, since the intensity of the input video signal is controlled in the optimum state, the ghost removing operation can be always performed in the linear state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ghost removing apparatus for removing ghosts or waveform distortions, which is used in various video equipment such as a television (TV) receiver that handles TV video signals. The present invention particularly relates to a ghost removing apparatus that enables correct ghost removing processing in a linear state at all times for video signals in various states, and a transversal filter according to the noise level of the video signal. It is an object of the present invention to provide a ghost removing device capable of accurately removing the ghost without being affected by the noise of the video signal, by updating the coefficient of (4) in a timely manner.

[0002]

2. Description of the Related Art In recent years, in order to improve the image quality of TV broadcasting, a TV video signal in which a reference signal (GCR signal) for ghost cancellation is inserted is broadcast. On the receiver side,
The reference signal for canceling the ghost is taken out, and the ghost is removed based on the signal. Since this GCR signal is described in detail in Japanese Patent Application No. 1-69179, detailed description thereof will be omitted here.

FIG. 9 shows a conventional example of a well-known ghost removing device based on the above-mentioned principle.

The analog video signal input from the input signal line of L1-1 is input to the timing generation circuit of block 1-1, and the timing generation circuit 1-1 outputs necessary timing signals such as waveform sampling pulses. Occur.

Further, the input video signal is amplified by the amplifier circuit 1-2 to a sufficient level, and its output is clamped to a predetermined level by the clamp circuit 1-3. The output of the clamp circuit 1-3 is A / D converted in the A / D conversion circuit 1-4. Actually, the sampling frequency is 4 fsc (however, fsc
Are sampled at the color subcarrier frequency, fsc = 3.58 MHz).

The video signal converted into a digital signal passes through the transversal filter 1-5, and is extracted by the waveform capturing circuit 1-7 for a predetermined fixed period (for example, one scanning line) including the GCR signal.

FIG. 10 shows an example in which the GCR signal in the input video signal causes waveform distortion due to the influence of ghost.
FIG. 10A shows an original signal of a reference GCR signal, and the rising location and frequency characteristics are known. FIG. 10B shows the waveform of the GCR signal having waveform distortion due to the influence of ghost.

The output of the waveform capturing circuit 1-7 is subjected to waveform conversion (for example, differentiation) according to the reference waveform in the waveform check circuit 1-8 in the arithmetic processing circuit 1a. The converted waveforms are synchronously added by the synchronous adder circuit 1-9 to improve the SN. Next, the waveform comparison circuit 1-10 compares the original reference signal waveform calculated in advance in the ideal reference waveform generation circuit 1-15 with the output of the synchronous addition circuit 1-9. Figure 10
FIG. 10C shows an output waveform of the ideal reference waveform generation circuit 1-15 (waveform after conversion of the reference signal waveform calculated in advance).
The output waveform of the synchronous adder circuit 1-9 is shown in (d) (the waveform that has been distorted due to ghost effects).

Based on the error signal sequence obtained as the result of the comparison (in this case, the subtraction result), a certain magnification is set in the evaluation function calculation circuit 1-11, the cumulative addition circuit 1-12, and the magnification setting circuit 1-13, The tap gain setting circuit 1-14 determines the tap gain (coefficient) of the transversal filter 1-5. Blocks 1-8 to 1-15 form the arithmetic processing circuit 1a.

The above tap gain is given to the filter 1-5,
By optimizing the characteristics of filter 1-5 for ghost removal, the video signal from which ghost has been removed is filtered.
Obtained from 1-5. The output signal of filter 1-5 is D / A
Converted to an analog signal by the conversion circuit 1-6 and output signal line L
It is output to 1-2.

By repeating the above operation, the filter 1-5
The ghosts are quickly removed by successively updating the tap gains (coefficients) of the input signals according to the ghost situation of the input signal.

[0012]

(A) The ghost elimination processing is premised on being linearly processed, and in order to perform the linear processing, a signal generator is conventionally used,
The gain of amplifier circuit 1-2 and the clamp level of clamp circuit 1-3 were adjusted. However, in the natural world, since there are various ghost conditions, it is impossible to make adjustments that can deal with all ghost conditions, and nonlinear processing rarely occurs. When non-linear processing occurs, good ghost removal processing cannot be performed, and malfunctions and divergence occur. For example, assuming that there is a large level of ghost, if the gain of the amplifier circuit is narrowed down by pre-adjustment so that non-linearity does not occur, or if there is almost no ghost interference, then the S / If N is deteriorated and conversely the setting is made to increase the S / N of the output video signal, if there is a large ghost interference, it is caught in the frontage of the A / D conversion, and nonlinear processing occurs.

A first object of the present invention is to enable correct ghost removal processing in a linear state for video signals in various states, and also to perform ghost removal while maintaining a good S / N ratio. It is to provide a ghost removing device.

(B) In the conventional ghost removing apparatus, as a measure for preventing erroneous setting of the tap gain coefficient of the transversal filter due to noise included in the video signal, noise reduction is performed by performing synchronous addition on the extracted GCR signal. Was taking.

However, if noise is dealt with by simply increasing the number of times of synchronous addition, the number of times of capturing the GCR waveform increases in proportion, and the broadcasting station transmits the GCR signal which is transmitted once at a predetermined vertical synchronizing signal interval. Processing becomes slower in proportion to the interval. If the number of synchronous additions is reduced to improve the processing speed, the tap gain coefficient may be erroneously set due to noise.

Further, when the method of gradually increasing the number of synchronous additions by the number of times of successive update of the tap gain coefficient is used, the noise level is sufficiently suppressed by the synchronous addition immediately after the start of the ghost removal where the number of synchronous additions is small. Since there is no noise, the noise is mistaken as a ghost, and a low level distortion is generated by calculating a tap gain coefficient at a minute level.

A second object of the present invention is to update the coefficient of the transversal filter in a timely manner in accordance with the noise level of the video signal to accurately remove the ghost without being affected by the noise of the video signal. An object of the present invention is to provide a ghost removing device that can be used.

[0018]

In order to solve the above problems, the present invention provides

A ghost removing device for removing a ghost by using a reference signal (GCR signal) for ghost cancellation inserted in a video signal,

An A / D converter circuit for converting an incoming video signal into digital data after passing through an amplifier circuit and a clamp circuit;

A transversal filter for removing the ghost from the video signal converted into digital data by the A / D conversion circuit and outputting the weighted signal by performing weighting for canceling the calculated ghost,

A D / A conversion circuit for converting the ghost-removed digital data output from the transversal filter into analog data,

A waveform acquisition circuit for extracting and storing a predetermined fixed period including the GCR signal from the output of the transversal filter;

The output of the waveform capturing circuit is supplied,
Using the error signal obtained by detecting the reference timing and performing the calculation between the signal obtained by performing synchronous addition and waveform conversion based on this timing and the preset ideal reference waveform signal A ghost elimination device comprising an arithmetic processing circuit that arithmetically processes the coefficient for the transversal filter and writes the coefficient to the transversal filter at any time,

Using the circuit for detecting the maximum value of the GCR signal captured by the waveform capturing circuit, the circuit for detecting the minimum value of the captured GCR signal, and the detection result of the maximum value and the minimum value, Provided is a ghost eliminating device comprising a control circuit including a circuit for outputting clamp level control data of the clamp circuit and a circuit for outputting data for controlling the gain of the amplifier circuit. Along with

A ghost removing device for removing a ghost by using a reference signal (GCR signal) for ghost cancellation inserted in a video signal,

An A / D conversion circuit for converting an incoming video signal into digital data,

A transversal filter for removing the ghost from the video signal converted into digital data by the A / D conversion circuit and outputting the weighted signal by performing weighting for canceling the calculated ghost,

A D / A conversion circuit for converting the ghost-free digital data output from the transversal filter into analog data,

A waveform acquisition circuit for extracting and storing a predetermined fixed period including the GCR signal from the output of the transversal filter;

The output of the waveform acquisition circuit is supplied,
Using the error signal obtained by detecting the reference timing and performing the calculation between the signal obtained by performing synchronous addition and waveform conversion based on this timing and the preset ideal reference waveform signal A ghost elimination device comprising an arithmetic processing circuit that arithmetically processes the coefficient for the transversal filter and writes the coefficient to the transversal filter at any time,

An S / N detection circuit for detecting the random noise level of the incoming video signal,

A control circuit for controlling a calculation process for obtaining the coefficient to be written in the transversal filter in accordance with a detection signal from the S / N detection circuit;

The present invention provides a ghost removing device characterized by comprising an unnecessary component removing circuit for removing an unnecessary component of the coefficient written in the transversal filter.

[0035]

FIG. 1 shows a first embodiment of the present invention. The same parts as those in the conventional example are designated by the same reference numerals, and a detailed description of those parts will be omitted. This embodiment is intended to solve the above-mentioned problem (a), and the maximum of the GCR waveform that has been acquired so that the GCR waveform can be acquired in a state where the S / N is as good as possible without causing non-linearity. Automatic control circuit that detects the value and minimum value and uses the results to control the amplification level and clamp level of the input signal to the optimum values.
1 is provided to enable accurate ghost removal processing.

In FIG. 1, the output of the synchronous adder circuit 1-9 is also input to the newly provided automatic control circuit 2-1 and the output of the automatic control circuit 2-1 causes amplification circuit 1-2 and clamp Controls circuit 1-3.

FIG. 2 shows the structure of the automatic control circuit 2-1 and its operation will be described. The signal (acquired GCR signal) sent from the synchronous addition circuit 1-9 is compared with the comparison circuit (m
in) 2-2 and the comparison circuit (max) 2-5. Comparison circuit 2
At -2, the minimum value is detected and the result is stored in the minimum value storage circuit 2-3. Optimal control data is selected from a predetermined clamp table 2-4 according to the detected minimum value, and the clamp level of the clamp circuit 1-3 is controlled to the optimum value by the control data.

In the other comparison circuit 2-5, the maximum value of the captured GCR signal is detected, and the result is stored in the maximum value storage circuit 2-6. Optimal control data is selected from a predetermined gain table 2-7 according to the detected maximum value, and the amplification degree of the amplifier circuit 1-2 is controlled by the control data.

In this way, the automatic control circuit 2-1
Since the size of the input video signal is controlled to the optimum state,
This ghost removing device can always perform a ghost removing operation in a linear state.

Next, a second embodiment is shown in FIG. 4 to 8
FIG. 8 is a diagram for explaining the operation of the second embodiment. The same parts as those in the conventional example are designated by the same reference numerals, and a detailed description of those parts will be omitted. This embodiment is to solve the above-mentioned problem (b), and controls the arithmetic processing for obtaining the coefficient of the transversal filter in accordance with the magnitude of the noise level of the video signal so as to suppress the influence of the noise of the video signal. The ghost can be removed accurately without being affected by it.

The noise component contained in the video signal received on the viewer side varies depending on the state of the antenna, the radio wave transmission distance from the transmitting station, and the like. FIG. 10A shows the original signal of the GCR waveform transmitted at the transmitting station. FIG. 4A is an example of a GCR waveform including noise received by the viewer.

Here, the noise level is measured using the S / N measurement section shown in FIGS. 4 (a) and 4 (b). This S / N measurement section is set at a location behind the GCR signal and less susceptible to ghost influence. This is because ghosts appear to have a lower level as they are farther away, and have higher levels as they are closer to the ghost.

In the ideal state, the GCR signal has a uniform value at substantially the same level in the sampled data as shown in FIG. 4 (c) when the measurement section is enlarged.
However, if the received signal contains a noise component,
The sampled data is, as shown in FIG.
The values will be scattered evenly on the same level. The noise level can be measured by detecting this variation. Although there are many possible methods of detecting the variation, for example, a method of taking the sum of squares of data in the measurement section and a method of taking the sum of absolute values can be given. It can be easily inferred that the variation can be similarly detected before or after the waveform conversion by the waveform check circuit 1-8. In this embodiment, as shown in FIG. 3, the noise level is detected by the S / N detection circuit 3-7 before the waveform conversion.

A control signal according to the noise level output from the S / N detection circuit 3-7 is supplied to a control circuit (not shown) in the synchronous addition circuit 3-9, and a synchronization signal for removing noise is supplied. It is used to control the number of additions. FIG. 5A is an example of a graph showing the relationship between the number of synchronous additions and the noise level. However, when the noise level is low, the control circuit reduces the number of initial additions and increases the number of processings. The degree is also relatively small. On the other hand, when the noise level is high, the number of times of addition for the first time is increased, the degree of increase in the number of times of processing is set to a large value, and processing according to the noise level is performed. In the graph, the noise level is high, medium, and low, but the noise level may be detected in multiple stages.

The control signal corresponding to the noise level output from the S / N detection circuit 3-7 is supplied to the control circuit (not shown) in the waveform comparison circuit 3-10. The control signal is used to determine an error recognition threshold value that distinguishes an error due to a ghost from an error due to a noise component when comparing the ideal reference waveform with the captured GCR waveform. FIG. 5B is an example of a graph for determining the threshold value, but the threshold value is gradually decreased as the number of times of processing is increased to separate the minute level ghost and the noise component.
The reason why the threshold value is gradually lowered is to correspond to the fact that the original noise component is gradually reduced due to the progress of the above-mentioned synchronous addition. By this threshold value control, large ghosts that the viewer is interested in are detected and removed in order. In the graph, the noise level is high, medium, and low, but the noise level may be detected in multiple stages. .

The control signal corresponding to the noise level output from the S / N detection circuit 3-7 is further supplied to the magnification setting circuit 3-13.
It is supplied to a control circuit (not shown) therein. The control signal is used to control the magnification output to the tap gain setting circuit according to the noise level. The control here aims to gradually change the magnification according to the number of times of processing in order to avoid erroneous setting of the tap gain coefficient due to noise components, and to perform high-speed processing when there are few noise components. . FIG. 6 is an example of a graph of magnification setting. In the proximity ghost portion where the influence of the noise level is great, the magnification setting starts from a large setting, and the magnification setting is gradually set smaller as the number of processing times increases. The normal ghost portion and the long ghost portion, which are less affected by the noise level, are set in reverse from the smaller magnification setting to the larger magnification setting. In the graph, the case where the noise level is high, the case where the noise level is medium, and the case where the noise level is small are shown separately, but it can be easily inferred to make the noise level detection stage multistage.

The control signal corresponding to the noise level output from the S / N detection circuit 3-7 is also the unnecessary component removal circuit 3-
It is supplied to the control circuit (not shown) in 6. Then, the control signal is used for the unnecessary component cut level control.
In the ideal state, the tap gain coefficient set in the transversal filter is not affected by noise as shown in FIG. 7A, and only the inverse coefficient for the ghost is set. However, when the noise component is included,
As shown in FIG. 7B, it is often the case that the noise component is erroneously determined to be a ghost component and the tap gain coefficient of a minute level is calculated. If a large number of minute level coefficients are set, low-frequency distortion will occur, giving the viewer a strange feeling. Simply removing the minute level tap gain coefficient at a constant level leaves a ghost component to be removed.
Therefore, as shown in the graph of FIG. 8, the cut level of the unnecessary component shown in FIG. 7B is gradually decreased according to the number of times of processing, so that ghost removal can be performed without causing low-frequency distortion. It will be possible. In the graph, the noise level is high, medium, and low, but the noise level may be detected in multiple stages.

By the above control operation, the ghost removing device can remove the ghost accurately and at high speed without being affected by the noise level of the input video signal.

[0049]

As described above, the ghost elimination device according to the first aspect can control the amplification degree and the clamp level to the optimum states according to the state of the input video signal, so that it is an essential condition for the ghost elimination process. It is possible to always perform stable processing in a linear state, and it is possible to achieve both good S / N and accurate ghost removal.

According to the ghost removing apparatus of the present invention, the arithmetic processing for obtaining the coefficient of the transversal filter can be controlled according to the noise level of the input video signal. High-speed ghost removal can be performed with.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment.

FIG. 2 is a diagram showing a configuration of an automatic control circuit in the first embodiment.

FIG. 3 is a diagram showing a second embodiment.

FIG. 4 is a diagram for explaining the operation of the second embodiment.

FIG. 5 is a diagram for explaining the operation of the second embodiment.

FIG. 6 is a diagram for explaining the operation of the second embodiment.

FIG. 7 is a diagram for explaining the operation of the second embodiment.

FIG. 8 is a diagram for explaining the operation of the second embodiment.

FIG. 9 is a diagram showing a conventional example.

FIG. 10 is a diagram for explaining distortion due to a GCR reference signal and a ghost.

[Explanation of symbols]

 1-2 Amplification circuit 1-3 Clamp circuit 1-4 A / D conversion circuit 1-5 Transversal filter 1-6 D / A conversion circuit 1-7 Waveform acquisition circuit 1a, 1b Arithmetic processing circuit 2-1 Automatic control circuit 3-6 Unwanted component removal circuit 3-7 S / N detection circuit

Claims (2)

[Claims] 1. A ghost removing device for removing a ghost by using a ghost canceling reference signal (GCR signal) inserted in a video signal, which is provided after an incoming video signal is passed through an amplifier circuit and a clamp circuit. An A / D conversion circuit for converting into digital data, and a transformer for removing the ghost from the video signal converted into digital data by the A / D conversion circuit and outputting the weighted signal by canceling the calculated ghost. A Versal filter, a D / A conversion circuit for converting the ghost-removed digital data output from the transversal filter into analog data, and the GCR output from the output of the transversal filter.
A waveform capture circuit that extracts and stores a predetermined fixed period including a signal, and the output of the waveform capture circuit are supplied, the reference timing is detected, and synchronous addition and waveform conversion are performed based on this timing. Error signal obtained by performing an arithmetic operation between the generated signal and a preset ideal reference waveform signal, arithmetic processing is performed on the coefficient for the transversal filter, and the coefficient is written in the transversal filter at any time. A ghost removing device comprising an arithmetic processing circuit, a circuit for detecting a maximum value of the GCR signal captured by the waveform capturing circuit, a circuit for detecting a minimum value of the captured GCR signal, and the maximum and minimum values. A circuit for outputting the control data of the clamp level of the clamp circuit by using the detection result of Ghost canceling apparatus characterized by a control circuit provided with a circuit for outputting data for controlling the gain of the amplifier circuit. 2. A ghost removing device for removing a ghost by using a reference signal (GCR signal) for ghost cancellation inserted in a video signal, and an A / D conversion circuit for converting an incoming video signal into digital data. A transversal filter for removing the ghost from the video signal converted into digital data by the A / D conversion circuit and outputting the weighted signal by canceling the calculated ghost; and outputting from the transversal filter. A D / A conversion circuit for converting the ghost-removed digital data into analog data, and the GCR from the output of the transversal filter.
A waveform capture circuit that extracts and stores a predetermined fixed period including a signal, and the output of the waveform capture circuit are supplied, the reference timing is detected, and synchronous addition and waveform conversion are performed based on this timing. Signal and the ideal reference waveform signal set in advance are used to calculate the coefficient for the transversal filter and write the coefficient to the transversal filter at any time. In a ghost removing device including an arithmetic processing circuit, an S / N detection circuit for detecting a random noise level of the incoming video signal, and a transversal filter according to a detection signal from the S / N detection circuit. A control circuit for controlling a calculation process for obtaining the coefficient to be written, and writing to the transversal filter A ghost removing device, comprising: an unnecessary component removing circuit for removing an unnecessary component of the coefficient.