JPH0491571A - Ghost removing device - Google Patents

Abstract

PURPOSE:To improve pictures in stability and picture quality fluctuation by detecting a ghost in such a way that a phase is detected by adding GCR signals inserted into ADD-converted video signals to each other and the GCR signals added to a selected reference GCR signal is subtracted. CONSTITUTION:GCR signals 1 containing a ghost are fetched by means of GCR gate signals outputted from a timing generation circuit and added to each other by means of a synchronous adding section 2 for making SIN improvement, etc., after the signals 1 are subjected to a field sequence process. After addition, the phase of the GCR signals 1 is detected by means of a phase detecting section 5. A subtracting section 3 generates a ghost detecting signal 4 by subtracting a reference GCR signal selected output GCR signals 6, 7, and 8 by means of a switch 9 from the output data of the section 2. When such a constitution is used, pictures can be improved in stability and picture quality fluctuation, because the error signal detected as a ghost signal due to the phase lag of the fetched GCR signals can be made smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a ghost removal device that performs ghost removal using a ghost reference signal (GCR signal) inserted into a video signal.

2. Description of the Related Art In recent years, television receivers have tended to become larger, and with the start of Clear Vision broadcasting, there has been a demand for higher image quality.

Among them, ghost removal is attracting a lot of attention, and G
CR signaling was proposed and introduced. Regarding GCR signals, see [Television Society Technical Report ROFT89-4,
Reported in pp 19-24J.

An example of a ghost removal device will be described below with reference to the drawings.

FIG. 3(a) is a block diagram showing the configuration of a conventional ghost removal device. In FIG. 3(a), 31 is an A/D converter that digitizes the video signal, and 32 is a transversal filter 33 for removing ghosts, which is a D/A converter that returns the ghost-free video signal to an analog signal. vessel,
35 is a memory for taking in the GCR signal inserted into the video signal, 34 is a switch for taking in data into the memory 35, 36 is a CPU, 38 is a timing generation circuit, and 37 is a ROM. The CPU 36 is connected to provide tap coefficients to the transversal filter 32. The timing generation circuit 38 receives f, (vertical synchronization signal)
, f.

(horizontal synchronization signal), GCR for extracting the GCR signal inserted into the video signal from the 2fN timing signal.
It generates a gate signal and notifies the CPU 36 of the timing of the GCR gate.

In the GCR signal, as shown in FIG. 4(a), the WRB signal and the 0 pedestal signal are as follows: WRB signal → 0 pedestal signal → WRB signal → O pedestal signal → 0 pedestal signal →
The signal is transmitted in the same horizontal period in a sequence of 8 fields: WRB signal → 0 pedestal signal → WRB signal. By performing the calculation shown in the first equation below on the signals of these 8 fields, the GCR shown in FIG. 4(b) is obtained.
I can get a signal. However, Fn (n=1 to 8
) represents the nth field signal.

F= 1/4 ((Fl-F5) + (F6-F2)
+ (PIF7) + (F8-F4) )...
(1) If the difference of one clock is taken from the GCR signal in FIG. 4(b), a waveform as shown in the lower part of the figure is obtained. When this waveform is enlarged, it becomes a 5INC waveform (S
IN(x)/x), about 4.2M as shown in Figure 4(d)
Waveforms with up to 7 flat frequency components can be obtained.

However, the waveforms shown in FIGS. 4(C) and (6) represent ideal GCR signals, and the GCR signal extracted from the video signal processed by the television receiver is
As already mentioned, the waveform is not ideal because it is subject to considerable distortion due to the effects of the radio wave transmission system, the tuner's bandpass filter, etc.

A ghost removal device is a device that detects and removes ghosts using GCR signals, and uses a ghost removal method (
Various methods such as the MSE method and the ZF method have been proposed as algorithms), but in any of the methods, the GCR signal waveform in the input video signal is basically the ideal GC
It is controlled to have the same waveform as the R signal waveform.

- As an example, the process of determining the tap coefficients of the transversal filter 32 will be explained using the ZF (Zero Forcing) method.

In Figure 3(a), the output signal of the transversal filter is (Ykl, the reference signal is (Rkl), and the difference signal between the output signal of the 4-transversal filter and the reference signal is fEk.
1, the n-th tap coefficient C(ill-1) of the transversal filter is modified based on the second equation in the ZF method. However, α is a coefficient for determining the amount of one modification.

(Ci l ””' = (Ci l ”' - α
・Ei・・・・・・(2) The CPU 36 in FIG. 3(a) performs the synchronous addition shown in the first equation,
After performing the Felton-Kens processing, the second equation is calculated and the tap coefficients are repeatedly corrected until the amount of residual ghost becomes sufficiently small. Here, the reference GCR
The signal is written in ROM37.

The original GCR signal is taken in by the GCR gate signal generated by the switch 34 timing generation circuit 38, and the output of the transversal filter 32 is taken into the memory 35 by turning it to the ■ side. As a result, the GCR signal waveform inserted into the video signal input to the A/D converter 31 becomes almost equal to the waveform of the reference GCR signal, and the ghost interference caused by the television signal on the transmission path and the antenna This improves the frequency and phase characteristics of the tuner and video detection stage.

In the process of ghost removal described above, ghost detection is performed in the third stage.
This is done as shown in Figure (b). Figures 3 and 3) are Pronk diagrams showing an example of a conventional ghost detection method. In the figure, 41 is a GCR signal including a ghost and is taken in by the GCR gate signal. Reference numeral 42 indicates a synchronous addition section that performs Felton-Kens processing to improve S/N, etc., 46 indicates a GCR signal serving as a reference, 43 indicates a subtraction section, and synchronous addition section 42
A reference GCR signal 46 is subtracted from the output data of the ghost detection signal 44 to produce a ghost detection signal 44 .

This operation will be explained using FIG. 5. FIG. 5 shows the state of the waveform in the ghost detection method shown in FIG. 3, etc. In FIG. 5, a waveform 51 is a GCR signal waveform including a ghost after synchronous addition. Since the waveform is sampled, only the points indicated by circles on the waveform are observed. This corresponds to the waveform after synchronous addition of 42 in FIG. 3(b). Waveform 52 is a reference GCR signal, which is stored in ROM 37 that can be accessed from CPU 36 during boat fishing.

The waveform 53 is a ghost signal detected by subtracting the reference GCR signal of the waveform 52 from the GCR signal waveform including the ghost of the waveform 51. In order to correctly detect a ghost, the amplitude and phase of waveforms 51 and 52 must match before subtraction.

Problems to be Solved by the Invention However, in the configuration as shown in FIG. 3 0)), if the phase of the GCR signal after synchronous addition is shifted, a ghost will be erroneously detected.

In FIG. 6, similarly to FIG. 5, a waveform 61 is a GCR signal waveform including a ghost after synchronous addition, and a waveform 62 is a reference GCR signal. Waveform 63 is a GCR that includes the ghost of waveform 61.
This is a ghost signal detected by subtracting the reference GCR signal of waveform 62 from the signal waveform. Waveform 61 is waveform 5 in Figure 5.
The phase is advanced by π/8 (approximately 17.5 ns) when 1 is converted into a subcarrier. In this state, when the peaks are aligned with the reference GCR signal of waveform 62 and subtraction is performed, as shown in waveform 63, base 1! An error signal appears near the GCR signal and is detected as a ghost.In this way, even if there is no ghost, if the phase is shifted, the alignment cannot be corrected, and even areas without ghosts are detected as ghost components. become. Of course, even if a ghost is detected, the waveform is basically equalized by the ghost removal operation, so it does not immediately become a problem.
Ghosts detected due to phase shifts result in relatively large errors due to slight phase shifts, as shown in the example in Figure 6.
Even if the waveform is equalized, it is not preferable because the stability of the image decreases and the image quality fluctuates.

In view of the above-mentioned problems, the present invention aims to provide a ghost removal device that can extremely effectively reduce a ghost signal even if a phase shift occurs between a GCR signal containing a ghost and a base $GCR signal. It is something.

Means for Solving the Problems In order to solve the above problems, the ghost removal device of the present invention adds a GCR signal inserted into an A/D converted video signal along with the GCR signal transmission contents of an 8-field sequence. means for detecting the phase of the added GCR signals; means for generating one or more reference GCR signals; and means for selecting the reference GCR signal based on the output of the GCR signal phase detection means. , selected criterion G
The apparatus includes means for detecting a ghost by subtracting the CR signal and the added GCR signal.

Effect of the present invention With the above configuration, the phase of the GCR signal inserted into the A/D converted video signal is determined by the factors of the transmitter of the broadcasting station, the propagation path of radio waves, the filter circuit of the receiver side, and the sampling clock. Even if a ghost signal detected due to a phase shift is detected, a reference GCR signal can be selected according to the phase state of the detected GCR signal, so ghost signals detected due to phase shift can be It can be made smaller, improving image stability and reducing fluctuations in image quality.

Embodiment Hereinafter, a ghost removal device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a bronch diagram of a ghost detection section of a ghost removal device according to an embodiment of the present invention. The configuration of the ghost removal device is the same as that shown in FIG. 3(a) described in the conventional example described above, so a description thereof will be omitted.

In FIG. 1, 1 is a GCR signal including a ghost and is taken in by a GCR gate signal output from a timing generation circuit. Reference numeral 2 denotes a synchronous adder that performs field sequence processing and improves the S/N, etc., and reference numerals 6, 7.8 denote GCR signals that are different in phase from each other. 5 is a phase detection unit that detects the phase of the GCR signal added by the synchronous addition unit 2; 9 is a switch that selects one of the reference GCR signals based on the phase detected by the phase detection unit 5; 3 is a subtraction unit Then, the reference GCR signal selected by the switch 9 is subtracted from the output data of the synchronous adder 2 to generate the ghost detection signal 4.

Figure 2(a) shows the phase detection of the captured GCR signal.

Explain using (b). Figure 2 (a) shows the central part of the GCR signal waveform.
g+, then divide the difference between g-+ and g+ by g.
Assuming ψ, there is a relationship as shown in FIG. 2(b) with the phase ψagφ of the GCR signal. In this graph, GCR
The phase ψ of the signal is expressed in terms of subcarriers of the video signal, and π/16 corresponds to approximately 8.7 ns. As shown in the graph, there is a nearly linear relationship between gψ and ψ. A table like Table 1 is created using this relationship.

The following is a margin (normalized to a maximum amplitude of 1000) Table 1 is a table in which a range of gψ representing the phase of the captured GCR signal is defined, and the reference GCR signal used within that range is defined as a table. Reference GCR signal 6 in Figure 1
, 7...8 correspond to each of the table holes in Table 1. When the sampling frequency of the video signal is four times that of the subcarrier, if the phase of the GC'R signal is set in the table from -π/4 to π/4 as shown in Table 1, all possible phases of the GCR signal can be covered. I can express it. In order to improve accuracy, gψ may be divided into smaller sections.

Effects of the Invention As described above, the present invention converts a GCR signal inserted into an A/D converted video signal into an 8-field sequence GCR.
Means for adding according to signal transmission contents and added GCR
means for detecting the phase of the signal and one or more reference Gs;
means for generating a CR signal, means for selecting the reference GCR signal based on the output of the phase detection means for the GCR signal, and ghost detection by subtracting the selected reference GCR signal and the added GCR signal. Ghost removal bag with means! With this configuration, it is possible to reduce the error signal detected as a ghost signal due to the phase shift of the captured GCR signal, and it is possible to improve image stability and reduce image quality fluctuations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a ghost detection section of a ghost removal device according to an embodiment of the present invention, and FIG. 2(a). (b) is a waveform diagram and a characteristic diagram showing the phase detection process in the ghost detection section of FIG. 1, FIG. 3(a) is a block diagram of the ghost removal device, and FIG. 3(b) is a conventional ghost detection device. Figure 4 (a) is a block diagram of the main part of the 8-field sequence waveform of the GCR signal, Figure 4 (b) is
GCR signal waveform after field sequence processing and part 1
Clock difference waveform diagram, Figure 4 (C) is 1 in Figure 4 (b)
An enlarged diagram of the clock difference waveform, Figure 4 (6) is its frequency characteristic diagram, Figure 5 is a diagram showing the ghost detection state when the GCR signal is in phase, and Figure 6 is a diagram showing the ghost detection state when the GCR signal is out of phase. FIG. 4 is a diagram showing a state of ghost detection when the screen is not being used. l...Imported GCR signal, 2...
Synchronous adder that adds GCR signals along the field sequence, 3... Subtractor, 4... Ghost detector, 5... Adds the phase of the GCR signal that has been synchronously added. Phase detection unit to detect, 6... One of the reference GCR signals (NCLO), 7... One of the reference GCR signals (N[11), 8...
・One of the reference GCR signals (Ncin), 9...
...Switch for selecting the reference GCR signal. Name of agent: Patent attorney Shigetaka Awano (1 figure) Diagram

Claims (1)

[Claims] The GCR signal inserted into the A/D converted video signal is
means for adding according to the GCR signal transmission contents of the field sequence; means for detecting the phase of the added GCR signal; means for generating one or more reference GCR signals; and means for detecting the phase of the GCR signal. means for selecting said reference GCR signal by an output; and means for selecting said reference GCR signal;
A ghost removal device comprising means for detecting a ghost by subtracting the R signal and the added GCR signal.