KR19980054418A - A method of removing ghost in a vehicle-mounted image receiver - Google Patents

Abstract

The present invention relates to a ghost canceling technique for a video signal receiver mounted on a vehicle. In the conventional ghost canceling system for a vehicle, there is a defect that the gain of the input video signal can not be maintained in a stable state, Distortion can not be compensated, the system performance is degraded due to the distorted IIR filter coefficient, and the signal-to-noise ratio after the ghost removal is greatly reduced.

Therefore, in order to solve this problem, in the initial state, the filter coefficient of the FIR filter is set and loaded, the correlation value is loaded, and then the gain compensation value of the image input signal is calculated to determine whether the gain is valid or not. When the validity of the result gain is established, the filter coefficient of the FIR filter is modified according to the gain change of the input video signal so that distortion compensation by equalization is performed, and the filter coefficient of the IIR filter is calculated based on the calculated correlation value Respectively.

Description

A method of removing ghost in a vehicle-mounted image receiver

Figure 1 is a block diagram of a ghost removal of a typical vehicle mounted video receiver.

FIG. 2 is a block diagram of a vehicle image receiver to which the ghost removing method of the present invention is applied.

FIG. 3 is a signal flow diagram of a method for removing ghost in a video receiver of the present invention.

Description of the Related Art [0002]

21: A / D converter 22: FIR filter

23: IIR filter 24: D / A converter

25: sync separator 26: timing generator

27: correlation value computing unit 28: first-in first-

29:

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a ghost canceling technique for a video signal receiver mounted on a vehicle, and more particularly, And more particularly, to a ghost removal method for a vehicle-mounted image receiver, which improves the stability of the ghost removal without affecting the ghost image.

FIG. 1 is a ghost removal block diagram of a general on-board video receiver. As shown in FIG. 1, the A / D converter 11 converts an analog input video signal CVBS _in to a digital signal. An IIR filter 12 for receiving an output video signal of the A / D converter 11 and performing an IIR (Infinite Impulse Response) filtering on a filter coefficient loaded from the control unit 18; A D / A converter 13 for converting the ghost-removed digital image signal output from the IIR filter 12 into an analog image signal; A synchronization separator 14 for separating a sync signal from a digital video signal output from the A / D converter 11; A timing generator 15 for generating a timing signal required by each system section from the synchronization signal output from the synchronization separator 14; The correlation value between the ghost canceling reference signal (GCR) including the ghost signal inputted through the A / D converter 11 and the original ghost cancel reference signal GCR is calculated in hardware and inputted A correlation value calculator (16) for storing the result in the selector (17); And a control unit (for example, a DSP) 18 for appropriately modifying the correlation value stored in the first-in first-out selector 17 and loading the correlation value into the IIR filter 12. The operation will be described below.

The analog input video signal CVBS _in is converted into a digital signal by the A / D converter 11 and then subjected to IIR filtering by the IIR filter 12 and the filter coefficients loaded from the control unit 18, And then converted into an analog signal through the D / A converter 13 and output as an output video signal CVBS _out .

The first difference is that the vehicle ghost controller requires a fast (more than 10 times per second) coefficient update while maintaining some ghost removal performance compared to a conventional ghost remover.

Therefore, in contrast to the filter coefficient calculation using a Least Mean Square (LMS) algorithm in software in a general ghost eliminator, in the vehicle ghost canceler, a correlation value calculator 16 is provided to calculate a ghost elimination standard The correlation value between the signal GCR and the original ghost canceling reference signal GCR given in advance is calculated in hardware and stored in the first-in first-out selector 17. In the controller 18, And the filter coefficients are generated and then loaded into the IIR filter 12.

At this time, in the case of using the Korean ghost canceling reference signal (GCR) in particular, since the original GCR signal is composed of only a combination of three values of -1, 0 and 1 (length: 366) So that it can be implemented simply.

It can be seen in FIG. 1 that, unlike a normal ghost remover, the IIR filter 12 is not combined with an FIR filter but is solely removed from the ghost because the FIR filter coefficient and the IIR filter coefficient are both computed It is difficult and even if it is possible to operate it, because it takes a long time, it is not suitable for vehicles.

Therefore, if the correlation value is judged to be suitable for ghost removal, the controller 18 modifies the correlation value appropriately and loads the filter coefficient of the IIR filter 12 to perform the continuous ghost removal operation.

However, in the conventional on-vehicle ghost removing system, there are several defects as follows.

First, there is a defect that can not compensate when the gain of the applied input video signal is not stable. This is because the IIR filter can not compensate for the gain of the input signal due to its structural characteristics, even if the RF detector is well designed for the vehicle.

Second, the IIR filter can not compensate the gain and group delay on the frequency spectrum of the high frequency detector, especially the linear distortion other than the ghost. Further, since the correlation value itself is distorted, the distorted IIR filter coefficient is obtained, There was a defect that deteriorated the performance.

Third, it is almost impossible to remove the noise included in the input image signal while maintaining the ghost canceling function in the structure of the IIR filter. Therefore, a defect in which the signal to noise ratio (S / N ratio) there was.

For reference, the Korean Patent Application No. 95-58740 filed by the same applicant uses the above-mentioned defects to some extent. However, the most important processing speed in the on-board type ghost remover, as well as stability and ghost removal performance, remain an unsolved problem.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a ghost of a vehicle-mounted image receiver that obtains correlation between an input signal passed through an FIR filter and a self-stored Korean ghost canceling reference signal, and generates an FIR filter and an IIR filter coefficient Removal method.

According to an aspect of the present invention, there is provided a ghost removing method comprising: a first step of setting and loading a filter coefficient of an FIR filter in an initial state and loading a correlation value; A second step (S3, S4) of determining whether the gain is valid by calculating a gain compensation value of the video input signal; When the validity of the gain is established, the FIR filter coefficient is modified according to the gain change of the input video signal so that distortion compensation by equalization is performed, and the filter coefficient of the IIR filter is calculated based on the calculated correlation value, And a third step (S5, S6).

FIG. 3 is a block diagram of a vehicle-mounted image receiver to which the ghost removing method of the present invention is applied. As shown in FIG. 3, an FIR filter (for example, 22; An IIR filter 23 for performing IIR filtering on the filter coefficients loaded from the control unit 29; A D / A converter 24 for converting the ghost-removed digital image signal output from the IIR filter 23 into an analog image signal; The correlation value between the ghost cancel reference signal GCR including the ghost signal input through the FIR filter 22 and the original ghost cancel reference signal GCR is calculated and stored in the first selector 28 A value computing unit 27; After the initial filter coefficient is loaded into the FIR filter 22, the filter coefficient is modified according to the gain change, and the correlation value stored in the first-in first-outrunner 28 is appropriately corrected and loaded into the IIR filter 23 And a control unit 29. The operation and effect of the present invention constructed as described above will be described in detail with reference to FIGS. 4 and 5.

The input video signal CVBS _in is converted into a digital signal through the A / D converter 21 and then supplied to the FIR filter 22 and subjected to FIR filtering with the filter coefficient calculated by the control unit (e.g., DSP) 29, The signal is supplied to the IIR filter 23 and subjected to IIR filtering with the filter coefficient calculated by the controller 29 and then converted into an analog signal through the D / A converter 24 so that a ghost signal is supplied to the video signal output terminal CVBS _out The removed video signal is supplied.

The FIR filter 22 is not merely used to perform a ghost removing function such as an FIR filter of a general ghost eliminator but is used to compensate for fatal defects when only the IIR filter 23 is used in a vehicle. Therefore, it requires only a much shorter filter tap than a general ghost remover, so that it does not cause any significant cost increase. In addition, even if this FIR filter 22 is added, there is no need to change other blocks in the previous system in hardware.

The main role that the FIR filter 22 performs is as follows.

First, a stable signal is output by compensating for the fluctuation of the gain caused by the high frequency detector at the front end of the ghost eliminator.

Second, the output signal of the high frequency detector appears to be distorted in some magnitude and group delay in the spectrum even though it is not a ghost. The ghost canceller compensates them, or at least it hinders the filter tap operation of the ghost canceller It is necessary not to receive the data. If the distortion is not compensated, an error due to distortion occurs in the output signal itself of the correlation value calculating unit 27, and the filter coefficient can not be normally obtained. Accordingly, the FIR filter 22 equalizes the input image signal, removes the distortion, and outputs the result to the IIR filter 23 and the correlation value operation unit 27. The distortion is compensated for, and an error in the IIR filter coefficient operation The substrate is removed. In addition, since the FIR filter 22 is designed as a low-pass filter, noise in a high frequency band is reduced.

However, the distortion in the spectrum except the ghost of the high frequency detector has a characteristic that it hardly changes with time. Therefore, when the controller 29 initially loads the FIR filter coefficient (LPF type) for channel equalization in software in the FIR filter 22 and then performs the real ghost removal in real time, It does not require any extra time to remove the ghost because it only needs to be reflected in the count.

FIG. 3 shows a control signal flow for removing the ghost of the control unit 29, and a main process of ghost removal will be described in detail with reference to FIG.

The controller 29 sets and loads the filter coefficient of the FIR filter 22 in the initial state (S1). At this time, the correlation value calculator 16 compares the ghost removal reference signal GCR included in the input signal The correlation value of the given original ghost removal reference signal GCR is calculated and the calculated correlation value is loaded into the first-in first-out selector 28 under the control of the control unit 29. (S2)

Then, the control unit 29 calculates a gain compensation value G of the input video signal and compares the gain compensation value G with a predetermined reference value to determine whether the gain is valid (S3, S4)

As a result, if the condition is established, that is, if the gain is valid, the FIR filter coefficient is corrected by reflecting the gain change according to the time in the FIR filter coefficient, and the result is loaded into the FIR filter 22. (S5)

Thereafter, the controller 29 calculates an IIR filter coefficient based on the correlation value stored in the first-in first-out selector 28, and loads the resultant value into the IIR filter 23. (S6)

As described in detail above, the present invention provides a simple algorithm for adding an FIR filter and calculating its filter coefficient, thereby improving the ghost removal performance while maintaining a stable state without causing any delay in processing speed, There is an effect that it can be reduced.

Claims (2)

A first step of setting and loading filter coefficients of an FIR filter in an initial state, and loading a correlation value; A second step of determining whether the gain is valid by calculating a gain compensation value of an image input signal; When the validity of the gain is established, the filter coefficient of the FIR filter is modified according to the gain change of the input video signal to perform distortion compensation by equalization, and the filter coefficient of the IIR filter is calculated based on the calculated correlation value, And a third step of removing the ghosts of the on-board type image receiver. The method of claim 1, wherein an FIR filter having a low-pass filter is used to reduce noise in a high frequency band.