JP2670879B2 - Ghost removal device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ghost removing apparatus adapted to remove a ghost by using a ghost removing reference signal, and particularly effective even if a large ghost occurs. It can be removed.

2. Description of the Related Art In order to remove a ghost signal from a ghost-containing video signal, a ghost removal device that uses a ghost removal reference signal has been developed.

FIG. 2 shows an example of a ghost removal reference signal (GCR signal) inserted in a video signal to remove a ghost.

This GCR signal is a signal of an eight-field sequence (period) and is inserted in a vertical blanking period of the video signal as shown in the figure.

In the first, third, sixth and eighth fields, a GCR waveform having a characteristic of sinX / X on the rising edge and a characteristic of 2T on the rising edge is inserted. In the second, fourth, fifth and seventh fields,
Zero pedestal waveforms, each having the same setup as the GCR waveform, are inserted.

The two GCR signals (the GCR waveform and the 0 pedestal waveform) form an eight-field sequence that is repeatedly transmitted with eight fields as shown in FIG.

FIG. 4 shows a ghost removing device for removing a ghost by using this GCR signal.

The video signal input from the terminal 1 is converted into a digital signal by the A / D converter 12, which is supplied to the delay circuit 13 and the front ghost transversal filter 14, and the respective outputs are added by the adder 15 in the subsequent stage. It

The output of the adder 15 is added to the output signal of the post-ghost transversal filter 17 input to the next adder 16. The output video signal of the adder 16 is used as a video signal after ghost removal. The output video signal is converted to an analog signal by the D / A converter 18 and is then output to an output terminal 19.

The initial coefficients of the transversal filters 14 and 17 are both 0.

The video signal is further supplied to the sync separation circuit 2 to separate the horizontal sync signal and the vertical sync signal, which is supplied to the GCR gate signal generation circuit 3 to generate a gate signal for the GCR signal (G
A CR gate pulse) is formed, and this is supplied to the reference signal generating circuit 7 and the GCR signal gate circuit 4.

The GCR signal passed through the gate circuit 4 is output to the GCR signal detection circuit 5
And the following eight-field sequence arithmetic processing is performed.

That is, in the 8-field sequence of FIG. 2, the fields of the GCR waveform, that is, the first, third, sixth and eighth fields are added, and the fields of the zero pedestal waveform are added.
Therefore, the second, fourth, fifth, and seventh fields are subjected to subtraction processing.

By this arithmetic processing, signals existing before and after the GCR signal (synchronization signal, burst signal, signal of previous line, etc.) are removed and only the GCR waveform as shown in FIG. 3A is output. This GCR waveform is differentiated by the differentiation circuit 6 (FIG. 3B), and this differentiation signal is input to the subtractor 8.

On the other hand, in accordance with the timing when the differential signal from the differentiating circuit 6 is sent to the subtractor 8 by the GCR gate pulse, the reference signal generating circuit 7 causes the sinX / X pulse reference signal (internal reference signal) as shown in FIG. 3C. Generate. The subtractor 8 forms a difference signal between the differential signal and the internal reference signal, and supplies this to the filter coefficient setting circuit 9.

The filter coefficient setting circuit 9 calculates and sets the coefficients of the front ghost transversal filter 14 and the rear ghost transversal filter 17 based on the difference signal, and removes the ghost.

The ghost removal range, that is, the setting range of the filter coefficient is up to about 44.7 μsec before the 2T pulse in FIG. 3B.

[Problem to be Solved by the Invention] In a conventional device, a synchronization signal is separated from an input video signal, and a gate signal of a GCR signal is formed by the synchronization signal. Therefore, when an excessive ghost signal is superimposed on the input video signal, the synchronization signal cannot be completely separated.

As a result, it becomes difficult to reliably extract and separate the GCR signal. Therefore, since it is necessary to keep waiting until a correct GCR signal is captured, the ghost may not be removed for a long time.

In particular, even if the GCR signal can be extracted correctly at one time, if a large ghost occurs after that, the GCR signal may not be separated again at that point, so the ghost removal process becomes unstable and a high-quality video signal is always generated. Cannot be output.

Therefore, the present invention solves such a problem and proposes a ghost removing device capable of accurately extracting and separating a GCR signal even if an excessive ghost is mixed.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a transversal filter for removing a ghost signal from an input video signal and a ghost removal reference signal inserted in the input video signal are provided. A gate circuit to gate, a ghost removal reference signal detection circuit that detects the ghost removal reference signal by calculating the reference signal in eight fields, a differentiation circuit that differentiates the reference signal, and an internal reference that matches the timing of the differentiation signal. A reference signal generation circuit that generates a signal, a subtraction circuit that calculates the error between the differential signal and the internal reference signal, a filter coefficient calculation circuit that calculates the error signal and calculates the filter coefficient, and sets it in the filter. A first sync separation circuit for extracting a sync signal from the first and a second sync separation circuit for extracting a sync signal from the output video signal A switching circuit for switching and selecting one of these two synchronization signals based on the output of the ghost removal reference signal detection circuit, and a gate signal for gated the ghost removal reference signal from the selected synchronization signal. And a gate signal generating circuit for generating the gate signal, wherein the switching circuit, in an initial state, selects the synchronization signal from the first synchronization separation circuit and keeps the state at least until the ghost elimination reference signal is first detected. If the ghost elimination reference signal is no longer detected after the ghost elimination reference signal is detected once,
It is characterized in that the synchronizing signal from the second synchronizing separation circuit is selected.

"Operation" The first sync separation circuit 2 extracts the input sync signal from the input video signal. Further, the second sync separation circuit 22 extracts the output sync signal from the output video signal.

Since the switching circuit 23 is designed so that the input synchronizing signal is first selected, if an excessive ghost is mixed in the input video signal, the GCR signal cannot be correctly separated as in the conventional case. However, if the input synchronization signal is correctly synchronized and separated even once, the GCR signal is accurately separated by the gate signal created based on the input synchronization signal at that time.

Then, the coefficient of the filter is set, and a signal with reduced ghost is output from the output terminal 19.

After that, when the ghost becomes large again, the input sync signal cannot be accurately synchronized and separated.

In such a case, the switching circuit 23 is controlled by the switching signal obtained from the detection circuit 5 to switch from the input synchronization signal to the output synchronization signal.

Since the output video signal is a signal in which the ghost is reduced, it can be accurately separated in synchronization, so that the ghost removal processing is performed without any problem.

This ensures that the ghost is not removed for a long time.

[Example] Next, regarding the ghost removing device according to the present invention,
This will be described in detail with reference to FIG.

Although the description of the same components as those in FIG. 4 is omitted, the present invention provides an input sync separation circuit 2 for separating a sync signal from an input video signal mixed with a ghost, and an output from which a ghost is removed. An output sync separation circuit 22 for separating the sync signal from the video signal is provided.

Then, the respective synchronization signals are supplied to the synchronization switching circuit 23 and any one of them is selected. It is assumed that the input synchronizing signal is controlled so as to be selected in the initial state where the power of the device is turned on.

The selected synchronizing signal is supplied to the GCR gate signal generating circuit 3 to form a gate signal. The gate circuit 4 is controlled by this gate signal, and the GCR signal is gated from the input video signal. The gated GCR signal is supplied to the detection circuit 5 and the GCR signal is detected by the 8-field arithmetic processing as described above.

The detection circuit 5 has a built-in means for determining whether or not the input signal is the GCR signal.
If the signal is a GCR signal, the fact that the GCR signal has been detected is stored, and the switching signal supplied to the synchronization switching circuit 23 remains unchanged.

However, if it is determined that it is not a GCR signal, the GCR signal
If no signal is detected, the switching signal remains unchanged, and if a GCR signal is detected, the level switching signal (hereinafter referred to as an inverted switching signal) controls the synchronous switching circuit 23. At this time, The output synchronization signal is selected instead of the input synchronization signal.

At this time, the output synchronization signal is extracted and separated from the output video signal from the D / A converter 18 from which the ghost has been removed, so that the synchronization separation processing is stable. Then, even if an excessive ghost is mixed in the input video signal, the ghost is significantly reduced and output,
The output sync signal is stably extracted and separated.

Therefore, even if an excessive amount of ghost is mixed and the separation of the input synchronization signal is disturbed, the input synchronization signal is accurately separated at a slight timing, and if the ghost is reduced, a stable output synchronization signal can be obtained. After that, when the input synchronizing signal is disturbed, the inverted switching signal is obtained and the output synchronizing signal is selected.

As a result, once switched to the output synchronization signal, in most cases thereafter, the GCR signal is gated by the output synchronization signal until the input video signal is interrupted.

Therefore, when an excessive ghost is mixed in again, even if the sync separation process of the input sync signal is disturbed again, it has no effect on the GCR signal gate process. This is because the input sync signal is no longer used for GCR signal gating. Therefore, even in the case of an input video signal having a poor D / U ratio, the ghost removal processing is stable.

For this reason, stable ghost removal processing is performed unless the synchronous switching circuit 23 returns to the initial switching state, such as when the power is turned on.

[Advantage of the Invention] As described above, according to the present invention, the GCR signal gate signal is formed by performing the synchronous separation from both the input signal and the output signal, and using the more suitable one of them. Therefore, the GCR signal can be accurately extracted and separated as compared with the conventional device.

Therefore, stable ghost removal processing can be performed even for an input video signal having a poor D / U ratio in which a large ghost is mixed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a ghost eliminating device according to the present invention, FIG. 2 is an explanatory diagram of a GCR signal of an 8-field sequence, FIG. 3 is various waveform diagrams of the ghost eliminating device, and FIG.
FIG. 1 is a block diagram showing a conventional example of a ghost removing device. 2 ... Input synchronization separation circuit 3 ... GCR signal gate signal generation circuit 4 ... GCR signal gate circuit 5 ... GCR signal detection circuit 6 ... Differentiation circuit 7 ... Reference signal generation circuit 9 ... Coefficient setting circuit 12 …… A / D converter 14,17 …… Transversal filter 18 …… D / A converter 22 …… Output sync separation circuit 23 …… Sync switching circuit

Claims (1)

(57) [Claims] 1. A transversal filter for removing a ghost signal from an input video signal, a gate circuit for gated a ghost removal reference signal inserted in the input video signal, and a ghost removal by operating the reference signal for 8 fields. A ghost elimination reference signal detection circuit that detects the reference signal, a differentiation circuit that differentiates the reference signal, a reference signal generation circuit that generates an internal reference signal at the timing of the differentiation signal, and a differentiation signal and an internal reference signal A subtraction circuit that obtains the error, a filter coefficient calculation circuit that calculates the error signal to calculate the filter coefficient and sets it in the filter, a first synchronization separation circuit that extracts a synchronization signal from the input video signal, and an output video signal A second sync separation circuit for extracting a sync signal, and one of these two sync signals is used as the ghost elimination reference. A switching circuit for switching and selecting based on the output of the signal detection circuit, and a gate signal generating circuit for generating a gate signal for gating the ghost removal reference signal from the selected synchronization signal, wherein the switching circuit is in an initial state. Then, the synchronizing signal from the first synchronizing separation circuit is selected, and the state is maintained at least until the ghost elimination reference signal is first detected, and after the ghost elimination reference signal is once detected, the ghost elimination reference signal is detected. The ghost elimination device characterized by selecting the sync signal from the second sync separation circuit when no longer detected.