JPH0730777A - Ringing suppression circuit - Google Patents

Abstract

PURPOSE:To suppress the generation of ringing based on a level change generated at the border part of a video signal and a reproduced synchronizing signal. CONSTITUTION:Digital data containing the video signal and the reproduced synchronizing signal are branched and supplied to a frequency analyzer 11 and a low-pass filter circuit 12. The frequency analyzer 11 performs the Fourier transform of digital data and compares the signal level of a high frequency component with a previously stored reference signal level. The low-pass filter circuit 12 outputs either the inputted digital data or filtered digital data based on the compared result of the frequency analyzer 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ringing suppression circuit.

[0002]

2. Description of the Related Art In video transmission technology, in order to improve coding efficiency (to reduce the amount of data to be transmitted), video data signals are subjected to high-efficiency coding and then transmitted. Here, a vertical synchronizing signal and a horizontal synchronizing signal are added to the video data signal in addition to the video signal, but the high efficiency encoded video data signal does not include these signals. Therefore, the receiving device needs to reproduce these synchronization signals in order to reproduce the image.

A method of reproducing a synchronizing signal in a conventional receiver will be described with reference to FIG. First, the high-efficiency-coded signal input to the input terminal 41 is branched into two and input to the selector 42 and the sync separator 43. The sync separator 43 establishes synchronism with the input signal and outputs a timing signal. This timing signal is input to the selector 42 and the synchronization signal generator 44.

The synchronizing signal generator 44 generates a digital pattern representing the synchronizing signal according to the timing signal from the synchronizing separator and outputs it to the selector 42. The selector 42 stores the input signal from the input terminal 41 and the digital synchronization signal from the synchronization signal generator 44 in a buffer, respectively, and selectively selects one of the input signal and the digital synchronization signal at a predetermined speed according to the timing signal. Then, the digital data which is read out in step S1 and the synchronizing signal is inserted in the video signal is output to the output terminal 45.

After that, the digital data output to the output terminal 45 is digital-to-analog converted and input to a low pass filter to extract only the base band signal.

[0006]

In the conventional sync signal reproducing method, a large level change may occur at the boundary between the video signal and the sync signal. When such a large level change exists in the digital data, ringing occurs when the signal is digital-to-analog converted and then passed through a low pass filter. This ringing has a problem of deteriorating the image quality of reproduced video.

Similarly, there is a problem that ringing occurs even when there is a sharp level change in the video signal itself, and the image of the reproduced video is deteriorated.

An object of the present invention is to suppress the occurrence of ringing caused by a level change included in digital data.

[0009]

According to the present invention, a branching means for branching an input signal into two to form a first and a second input signal, and a frequency of the first input signal are analyzed to obtain a reference frequency from a reference frequency. A frequency analysis unit that outputs a detection signal when a high frequency is detected, and a low-pass filter unit that performs a filtering process on the second input signal when the detection signal is input. A ringing suppression circuit that operates is obtained.

Further, according to the present invention, synchronization is established with the input digital signal sequence to reproduce the digital synchronization signal, the digital synchronization signal is inserted into the input digital signal sequence, and then converted into an analog signal for filtering processing. In a ringing suppression method applied to a receiving device that reproduces an image, a frequency analysis is performed before converting the input digital signal sequence in which the digital synchronization signal is inserted into the analog signal, and the frequency is higher than a reference frequency. A ringing suppression method characterized in that a filtering process is performed on a signal having a high frequency can be obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Here, the same parts as those in the related art are designated by the same reference numerals and the description thereof is omitted.

The ringing suppression circuit of this embodiment comprises a frequency analyzer 11 for analyzing the frequency of the digital data output from the selector 42, and a low pass filter for filtering the digital data output from the selector 42. And a circuit 12.

The frequency analyzer 11 is constructed, for example, as shown in FIG. That is, the frequency analyzer 11 includes an FFT calculator 21 for performing a fast Fourier transform on the input digital data, and a ROM 22 in which a reference signal is written in advance.
And a comparator 23 that compares the output of the FFT calculator 21 and the output of the ROM 22 and outputs a control signal indicating the comparison result to the low-pass filter circuit 12.

The low-pass filter circuit 12 is, for example,
It is configured as shown in FIG. That is, the low-pass filter circuit 12 delays the input digital data for a predetermined time, the digital low-pass filter 32 for filtering the input digital data, and the control signal from the frequency analyzer 11 according to the control signal. It has a selector 33 that selectively outputs one of the output of the delay device 31 and the output of the digital filter 32.

Next, the operation of this embodiment will be described with reference to FIGS. 1, 2 and 3. First, the digital data output from the selector 42 is branched into two, one is input to the frequency analyzer 11 and the other is input to the low-pass filter circuit 12.

The digital data input to the frequency analyzer 11 is fast Fourier transformed by the FFT calculator 21. The Fourier-transformed digital data is the comparator 23.
Is supplied to one of the inputs. From the ROM 22,
The previously input reference signal is supplied to the other input of the comparator 23. The comparator 23 receives the input FFT calculator 2
The output of 1 and the output of the ROM 22 are compared. In the comparison here, the signal level of the high frequency component exceeding the predetermined frequency in the output from the FFT calculator 21 is compared with the reference signal level written in the ROM 22. The comparator 23 outputs the comparison result as a control signal to the control terminal of the low-pass filter circuit 12.

On the other hand, the digital data input to the low pass filter circuit 12 is branched into two and input to the delay unit 31 and the digital low pass filter 32. The digital low-pass filter 32 removes a high frequency component of the input digital data and outputs it to one input terminal of the selector 33. In addition, the delay device 31 includes the digital low-pass filter 3
The input digital data is delayed by the filtering processing time in 2 and output to the other input terminal of the selector 33. The selector 33 selectively outputs one of the outputs of the delay unit 31 and the digital low-pass filter 32 to the output terminal 45 according to the control signal from the frequency analyzer 11 input to the control terminal.

After this, the digital data is digital /
Analog conversion is performed and filtering processing by a low-pass filter is performed.

As described above, in this embodiment, the frequency analysis of the digital data is performed, and the filtering process by the digital low-pass filter is performed on the portion including the high frequency component. Therefore, the filtering process performed after the conversion to the analog signal is performed. It is possible to prevent ringing that occurs in the.

[0020]

According to the present invention, the frequency of the digital input signal is analyzed, and the filtering process for removing the high frequency component is performed only for the portion including the high frequency component. It is possible to suppress the ringing that occurs in the filtering process performed after the conversion into.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing details of a frequency analyzer 11 shown in FIG.

3 is a block diagram showing details of a low-pass filter circuit 12 shown in FIG.

FIG. 4 is a block diagram of a synchronization signal reproducing circuit of a receiver to which the present invention is applied.

[Explanation of symbols]

 11 frequency analyzer 12 low-pass filter circuit 21 FFT calculator 22 ROM 23 comparator 31 delay device 32 digital low-pass filter 33 selector 41 input terminal 42 selector 43 sync separator 44 sync signal generator 45 output terminal

Claims (4)

[Claims] 1. Branching means for branching a digital input signal into two first and second input signals, frequency analysis means for analyzing the frequency of the first input signal and outputting an analysis result, and the analysis result. And a digital low-pass filter means for filtering the second input signal in accordance with the above. 2. The frequency analysis means, an FFT calculator for fast Fourier transforming the first input signal, a ROM for storing a reference level, an output of the FFT calculator and the reference level read from the ROM. 2. The ringing suppression circuit according to claim 1, further comprising a comparator that compares the result of the comparison and the comparison result and outputs the comparison result as the analysis result. 3. The low-pass filter means divides the second input signal into two to form third and fourth input signals, a delay device for delaying the third input signal, and A low-pass filter for filtering the fourth input signal, and a selector for outputting one of the output of the low-pass filter and the output of the delay device according to the analysis result. 1 or 2 ringing suppression circuit. 4. An image is reproduced by establishing synchronization with an input digital signal sequence, reproducing the digital synchronization signal, inserting the digital synchronization signal into the input digital signal sequence, converting it into an analog signal and performing filtering processing. In the ringing suppression method applied to a receiving device, frequency conversion is performed before converting the input digital signal sequence in which the digital synchronization signal is inserted into the analog signal, and for a signal having a frequency higher than a reference frequency. A ringing suppression method characterized by performing filtering processing by means of a method.