JPH07143361A - Ringing eliminating device - Google Patents

Abstract

PURPOSE:To provide the ringing eliminating device which can eliminate effectively ringing even if a cut-off frequency of an input image signal is unknown. CONSTITUTION:By a frequency characteristic analyzing circuit 1, a frequency characteristic of an input image signal Ei is analyzed and its signal band width BW is measured. A repeat period of ringing roughly coincides with a cut-off frequency of the input image signal, therefore, by adjusting the frequency characteristic of a filter circuit 2 in accordance with the measured band width BW, a ringing component R is extracted. By using the band width BW, a contour signal P for showing a contour part of the input image signal Ei is generated by a contour detecting circuit 3. Since ringing is conspicuous in a peripheral part of a contour, a correction amount CA in the peripheral part of the contour is generated, based on the contour signal P. By its correction amount CA, the ringing component R is corrected, and the correction ringing component CR is eliminated from the input image signal Ei delayed for the purpose of phase matching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal processing device for improving the image quality of an image, and more particularly to a ringing removing device for removing a ringing component contained in an image signal.

[0002]

2. Description of the Related Art As a technique for removing a ringing component already included in an image signal, there is a contour emphasis circuit disclosed in Japanese Patent Laid-Open No. 4-83477. Although this technique is originally related to the edge enhancement of the image signal, it also has the effect of removing the ringing component.

FIG. 10 is a schematic block diagram showing the circuit configuration disclosed in the above publication. In the figure, a contour extraction circuit 1001 extracts a contour portion from the input image signal Ei by a technique based on temporary difference. Upon inputting it, the gain control signal generation circuit 1002 classifies the image into a contour portion, a contour peripheral portion and other portions, and generates a gain control signal having a value according to this classification. Here, the gain control signal around the contour is set to a negative value.

On the other hand, the input image signal Ei is input to the contour emphasis component extraction circuit 1003, and the signal component near the cutoff frequency is extracted. The signal component and the gain control signal are multiplied by the multiplier 1.
004, and the result is added to the input image signal Ei by the adder 1005 to obtain the output image signal Eo.
Is obtained.

Since the gain control signal in the peripheral area is set to a negative value, the signal component in the vicinity of the cutoff frequency, which is ringing, is attenuated only in the peripheral area, and the output image signal Eo with the ringing component removed. Is obtained.

[0006]

However, in the above-mentioned conventional technique, since the contour emphasis component extraction circuit 1003 needs a filter function to pass a signal component near the cutoff frequency, the cutoff frequency of the input image signal Ei is reduced. In the unknown case, there was a problem that ringing could not be effectively removed. For example, when transmitting an image signal through a transmission line whose characteristics are unknown, effective ringing removal cannot be performed.

An object of the present invention is to provide a ringing removing device which can effectively remove ringing even if the cutoff frequency of an input image signal is unknown.

[0008]

A ringing removing apparatus according to the present invention extracts a ringing component from an input image signal by changing a frequency characteristic according to the bandwidth detecting means for detecting a bandwidth of the input image signal. Filter means to
A contour detection unit that detects a contour signal that represents the contour portion of the input image signal, a correction amount generation unit that generates a correction amount of the contour peripheral portion based on the contour signal, and a ringing component that is corrected by the correction amount of the contour peripheral portion. And a removing unit that removes the corrected ringing component from the input image signal.

[0009]

The bandwidth detecting means analyzes the frequency characteristic of the input image signal and measures the signal bandwidth. Since the repetition cycle of ringing almost coincides with the cutoff frequency of the input image signal, the ringing component can be extracted by the filter means whose frequency characteristic is adjusted according to the measured bandwidth. Since ringing tends to stand out in the peripheral portion of the contour, a correction amount of the peripheral portion is generated based on the contour signal, and the ringing component is corrected by the correction amount and removed from the input image signal.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of a ringing removing device according to the present invention. In the figure,
The input image signal Ei is input to the frequency characteristic analysis circuit 1, the filter circuit 2, and the contour detection circuit 3, respectively. The frequency characteristic analysis circuit 1 measures the signal bandwidth of the input image signal Ei, generates a bandwidth signal BW, and outputs it to the filter circuit 2 and the contour detection circuit 3.

The filter circuit 2 extracts a signal component near the frequency indicated by the bandwidth signal BW from the input image signal Ei and outputs it as a ringing component R. Further, the contour detection circuit 3 receives the input image signal Ei based on the bandwidth signal BW.
The first-order difference is calculated and is output to the correction amount generation circuit 4 as the contour signal P.

The correction amount generating circuit 4 receives the bandwidth signal BW and the contour signal P, and generates a correction amplitude signal CA whose value increases in the peripheral portion of the contour based on the contour signal P. The multiplier 5 multiplies the ringing component R from the filter circuit 2 and the correction amplitude signal CA from the correction amount generating circuit 4 to generate a correction ringing component CR.

On the other hand, the input image signal Ei is given a necessary delay by the delay circuit 6, and this delay time corresponds to the elapsed time until the corrected ringing component CR is generated from the input image signal Ei by the above processing. ing.

The subtractor 7 subtracts the corrected ringing component CR from the image signal delayed by the delay circuit 6 and outputs the output image signal Eo from which the ringing component has been removed.

Next, a detailed configuration example of each of the above circuits will be shown.

FIG. 2 is a block diagram showing an example of the configuration of the frequency characteristic analysis circuit 1 in this embodiment. The frequency characteristic analysis circuit 1 includes a conversion circuit 101 that performs frequency conversion,
An integrating circuit 102 that performs accumulation for each frequency component; a maximum frequency detecting circuit 103 that detects a maximum frequency among components having an accumulated value of a predetermined value or more and outputs a bandwidth signal BW;
Composed of.

The input image signal Ei is frequency-converted by the conversion circuit 101 by, for example, Fourier transform, and sent to the integration circuit 102. In the integrator circuit 102, for example, each frequency component for one screen is accumulated and sent to the maximum frequency detection circuit 103. The maximum frequency detection circuit 103 outputs, as the bandwidth signal BW, the maximum frequency among frequency components having a cumulative value equal to or higher than a predetermined value.

FIG. 3 shows a filter circuit 2 according to this embodiment.
3 is a block diagram showing an example of the configuration of FIG. Filter circuit 2
Is a filter for extracting a signal component near the frequency indicated by the bandwidth signal BW from the input image signal Ei, which can be realized by a known technique. Here, a 7-tap symmetrical FIR filter will be described as an example.

In the figure, the input image signal Ei is sequentially input to the six delay circuits 201 to 206 connected in series,
Each delay circuit delays by one clock (here, one pixel). The signals respectively output from the delay circuits 201 to 206 are z-1, z-2, z-3, z-4, z-5 and z-6.

In the case of the 7-tap symmetric FIR filter, the same filter coefficient is multiplied by the front-back contrast around the signal delayed by three pixels, that is, the output signal z-3 from the delay circuit 203. Therefore, to reduce the number of multiplications,
The signal value multiplied by the same filter coefficient is previously added by the adder 20.
7 to 209, and the multipliers 210 to 212 are added.
The addition results are respectively multiplied by the filter coefficients α1 to α3. The signal z-3 of the central delay circuit 203 is multiplied by the filter coefficient α0 in the multiplier 213. The signals multiplied by the respective filter coefficients are added by the adder 214, and the result is output as the ringing component R. That is, the ringing component R is expressed by the following equation.

R = α0z-3 + α1 (z-2 + z-4) + α2
(Z-1 + z-5) + α3 (1 + z-6).

The filter coefficients α0 to α3 are the coefficient selection circuit 21.
It is output from 5. The coefficient selection circuit 215 has, for example, a plurality of sets of coefficient values in advance, of which the bandwidth signal B is selected.
Select a set of coefficient values according to the value of W, and
Output as 0 to α3.

FIG. 4 shows the contour detection circuit 3 in this embodiment.
3 is a block diagram showing an example of the configuration of FIG. Contour detection circuit 3
Calculates the first-order difference of the input image signal Ei based on the bandwidth signal BW and outputs it as the contour signal P.

In the figure, an input image signal Ei is sequentially input to a plurality of delay circuits 301 to 303 connected in series,
Each delay circuit is given a delay of one pixel, and all the delay outputs of these delay circuits are input to the selection circuit 304.

Based on the bandwidth signal BW, the selection circuit 304 selects one signal from the delay output signals of the delay circuits 301 to 303 on the basis of the selection criterion of selecting a delay output with a smaller delay amount as the bandwidth becomes narrower. Select and output to the difference circuit 305. Note that selection accuracy can be improved by performing oversampling in advance when selecting the delay amount.

In the difference circuit 305, the delayed output signal selected by the selection circuit 304 is subtracted from the input image signal Ei, and a first-order difference signal corresponding to the bandwidth signal BW is obtained.
Since the delay amount of this primary difference signal differs depending on the bandwidth signal BW, the delay difference is adjusted in the delay adjustment circuit 306, and finally the absolute value circuit 307 performs absolute value processing to obtain the contour signal P ( (See (a) and (b) of FIG. 6).

FIG. 5 is a block diagram showing an example of the configuration of the correction amount generating circuit 4 in this embodiment. The correction amount generation circuit 4 includes a variable low-pass filter circuit (hereinafter simply referred to as LPF) 401 that can change the cutoff frequency according to the bandwidth signal BW, a clip circuit 402 for extracting only a contour portion, and a contour. It is composed of a subtractor 403 for taking out the peripheral portion and a clipping circuit 404, and generates a corrected amplitude signal CA whose value becomes large in the peripheral portion of the contour based on the contour signal P.

In the figure, the contour signal P is the LPF 401.
And to the clip circuit 402. The LPF 401 changes the cutoff frequency according to the bandwidth signal BW, and outputs the filter output LP to the subtractor 403. The clipping circuit 402 subtracts a predetermined value from the contour signal P and clips the negative value to zero, thereby subtracting the clip output CLP from the subtractor 40.
Output to 3. Filter output LP in subtractor 403
Is subtracted from the clip output CLP, and when the result is negative, it is clipped to zero in the clip circuit 404 and output as the corrected amplitude signal CA. Note that the clipping circuit 404 may not only clip a negative value to zero but also provide a positive upper limit value.

FIG. 6 is a signal waveform diagram for explaining a specific operation of the correction amount generating circuit 4. It is assumed that the input image signal Ei including ringing as shown in FIG. 9A is input and the contour detection circuit 3 generates the contour signal P (FIG. 9B). When the contour signal P is input to the LPF 401, the filter output LP as shown in FIG. 7C is obtained with the cutoff frequency according to the bandwidth signal BW. At the same time, the contour signal P is input to the clipping circuit 402, a predetermined value is subtracted, and a negative value is zero-clipped, so that FIG.
A clip output CLP as shown in is obtained. And
Subtract clip output CLP from filter output LP,
By zero-clipping the negative value, the corrected amplitude signal CA in the peripheral portion of the contour as shown in FIG.

The corrected amplitude signal CA thus obtained is multiplied by the ringing component R by the multiplier 5 to form the corrected ringing component CR, as shown in FIG. The corrected ringing component CR has the corrected amplitude signal CA increased in the peripheral portion of the contour as shown in FIG.
The waveform is similar to the ringing component included in i. This corrected ringing component CR is subtracted by the subtractor 7 from the input image signal Ei delayed by the delay circuit 6.

By the above processing, the ringing component generated in the peripheral portion of the contour is effectively removed from the input image signal Ei, and the high-quality output image signal Eo without ringing is obtained.
Can be obtained.

The present invention is not limited to the first embodiment shown in FIG. 1, but can be implemented by other configurations shown below.

FIG. 7 is a block diagram showing a second embodiment of the ringing removing device according to the present invention. In this embodiment, the frequency characteristic analysis circuit 1, the filter circuit 2, and the correction amount generation circuit 4 are the same circuits as in the first embodiment shown in FIG.

The ringing component R output from the filter circuit 2 is input to the contour circuit 701 and the delay circuit 702. The contour circuit 701 extracts the zero-cross point of the ringing component R as a contour signal P1 and outputs it to the correction amount generation circuit 4. The correction amount generation circuit 4 receives the bandwidth signal BW and the contour signal P1 and inputs the correction amplitude signal C as in the first embodiment.
Generate A1.

The delay circuit 702 delays the ringing component R and outputs the corrected amplitude signal CA which is the other input of the multiplier 5.
Phase adjustment with 1. The multiplier 5 multiplies the ringing component R and the correction amplitude signal CA1 to generate the correction ringing component CR1.

On the other hand, the input image signal Ei is delayed by the delay circuit 703.
The required delay is given by
It corresponds to the elapsed time until the corrected ringing component CR1 is generated from the input image signal Ei by the above processing. The subtractor 7 subtracts the correction ringing component CR1 from the input image signal Ei delayed by the delay circuit 703, and outputs the output image signal Eo from which the ringing component is effectively removed as in the first embodiment.

FIG. 8 is a block diagram showing a third embodiment of the ringing removing device according to the present invention. This embodiment is equivalent to the first embodiment shown in FIG. 1, and only the circuit configuration is changed. That is, in this embodiment, the frequency characteristic analysis circuit 1, the filter circuit 2, and the contour detection circuit 3 are the same as those in the first embodiment, and the correction amount generation circuit 4 of the first embodiment is changed to the attenuation amount generation circuit 801. The difference is that the attenuation amount signal ATT is used instead of the correction amplitude signal CA.

The attenuation amount generation circuit 801 receives the contour signal P and the bandwidth signal BW and generates the attenuation amount signal ATT. The attenuation amount signal ATT and the correction amplitude signal CA of the first embodiment are used.
Has a relationship of ATT = 1-CA. Therefore, the attenuation signal ATT is as shown in FIG.
Contrary to the waveform of (e), the peripheral portion of the contour has a small value.

The attenuation amount signal ATT and the ringing component R are multiplied in the multiplier 5 and become one input of the adder 804. The delay circuit 802 delays the input image signal Ei by a time corresponding to the delay amount in the filter circuit 2,
The ringing component R is subtracted from the input image signal Ei delayed by the subtractor 803, and the result is the other input of the adder 804. Thus, the output from the adder 804 becomes the output image signal Eo from which the ringing component is effectively removed, as in the first embodiment.

The frequency characteristic analysis circuit 1 in each of the above embodiments may have the configuration shown in FIG. The frequency characteristic analysis circuit 1 has a plurality of analysis circuits 104 to 106 having different frequency bands, operates the switch 107 and the selection circuit 108 based on a selection signal from the outside, and selects an appropriate analysis circuit. The basic configuration of the analysis circuits 104 to 106 may be the same as that shown in FIG.

As described above, the plurality of analysis circuits 104 to 106 are provided.
By providing image signals from a plurality of signal sources subjected to different frequency band restrictions, each bandwidth signal BW is provided.
Can be generated, and effective ringing removal can be performed for each input image signal.

In each of the above embodiments, the ringing removal in the horizontal direction of the image has been described, but the present invention can be similarly applied in the vertical direction.

[0044]

As described in detail above, the ringing removal apparatus according to the present invention performs frequency analysis of an input image signal, extracts a ringing component and a contour signal based on the analysis result, and based on them. Since the ringing around the contour is removed by the ringing, the ringing can be effectively removed even when the cutoff frequency of the input image signal is unknown.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a ringing removing device according to the present invention.

FIG. 2 is a block diagram showing an example of a configuration of a frequency characteristic analysis circuit 1 in this embodiment.

FIG. 3 is a block diagram showing an example of a configuration of a filter circuit 2 in this embodiment.

FIG. 4 is a block diagram showing an example of a configuration of a contour detection circuit 3 in this embodiment.

FIG. 5 is a block diagram showing an example of a configuration of a correction amount generation circuit 4 in this embodiment.

FIG. 6 is a signal waveform diagram for explaining a specific operation of the correction amount generation circuit 4.

FIG. 7 is a block diagram showing a second embodiment of the ringing removing device according to the present invention.

FIG. 8 is a block diagram showing a third embodiment of a ringing removing device according to the present invention.

FIG. 9 is a block diagram showing another configuration example of the frequency characteristic analysis circuit 1.

FIG. 10 is a schematic block diagram showing an example of a conventional ringing removal device.

[Explanation of symbols]

 1 frequency characteristic analysis circuit 2 filter circuit 3 contour detection circuit 4 correction amount generation circuit 5 multiplier 6 delay circuit 7 subtractor 101 frequency conversion circuit 102 integration circuit 103 maximum frequency detection circuit 201-206 delay circuit 207-209 adder 210- 213 multiplier 214 adder 215 coefficient selection circuit 301 to 303 delay circuit 304 selection circuit 305 difference circuit 306 delay adjustment circuit 307 absolute value circuit 401 low-pass filter circuit 402 clip circuit 403 subtractor 404 clip circuit 701 contour circuit 702 delay Circuit 703 Delay circuit 801 Attenuation amount generation circuit

Claims (11)

[Claims] 1. A ringing removal apparatus for removing ringing from an input image signal, wherein the bandwidth detection means detects a bandwidth of the input image signal, and the input image signal is changed in frequency characteristic according to the bandwidth. Filter means for extracting a ringing component from the contour image, contour detecting means for detecting a contour signal representing a contour portion of the input image signal, and correction amount generating means for generating a correction amount for the peripheral portion of the contour based on the contour signal. And a removing means for removing the corrected ringing component from the input image signal by correcting the ringing component based on the correction amount of the contour peripheral portion, and a ringing removing device. 2. The bandwidth detecting means, a frequency conversion circuit for converting the input image signal into a plurality of frequency components, an accumulation circuit for accumulating each of the frequency components for a predetermined period, and a predetermined value of the frequency component or more 2. A ringing removal apparatus according to claim 1, further comprising: a maximum frequency detection circuit that detects a maximum frequency as the bandwidth among frequencies having a cumulative value of 1. 3. The bandwidth detection means includes a plurality of bandwidth detection circuits having different detection bands, and a selection means for selecting one of the plurality of bandwidth detection circuits according to a signal source of the input image signal. The ringing removing device according to claim 1, wherein the ringing removing device comprises: 4. Each of the plurality of bandwidth detection circuits includes a frequency conversion circuit that converts the input image signal into a plurality of frequency components, an accumulation circuit that accumulates each of the frequency components for a predetermined period, and the frequency components. 4. The ringing removing device according to claim 3, further comprising: a maximum frequency detecting circuit that detects a maximum frequency among the frequencies having a cumulative value equal to or more than the predetermined value as the bandwidth. 5. The ringing removal according to claim 1, wherein the filter means is a digital filter and has a coefficient selection circuit that selects a set of filter coefficients according to the bandwidth. apparatus. 6. The contour detecting means includes a plurality of serially connected delay circuits that delay the input image signal pixel by pixel, and one output of the delay outputs of the plurality of delay circuits according to the bandwidth. 6. A ringing removal device according to claim 1, further comprising: a selection circuit that selects a difference between the input image signal and the selected delay output. apparatus. 7. The contour detecting means inputs the ringing component from the filter means, extracts a zero-cross point thereof, and generates the contour signal. The ringing removal device according to claim 1. 8. A variable low-pass filter capable of changing a cutoff frequency according to the bandwidth and extracting a low-frequency component from the contour signal, the correction amount generating means, and only a contour portion from the contour signal. And a correction amount generation circuit that removes the contour portion from the filter output of the variable low-pass filter to generate a correction amount in the peripheral portion of the contour. The ringing removal device according to any one of claims 1 to 7. 9. The removing unit multiplies the ringing component by a correction amount of the contour peripheral portion to generate the correction ringing component, and a subtraction circuit for subtracting the correction ringing component from the input video signal. The ringing removal device according to any one of claims 1 to 8, which comprises: 10. The ringing removal device according to claim 9, wherein the input video signal subtracted by the subtraction circuit is delayed in order to match the phase with the corrected ringing component. 11. A ringing removal device for removing ringing from an input image signal, wherein the bandwidth detection means detects a bandwidth of the input image signal, and the input image signal is changed in frequency characteristic according to the bandwidth. Filter means for extracting a ringing component from the contour image, contour detecting means for detecting a contour signal representing a contour portion of the input image signal, and attenuation amount generating means for generating an attenuation amount in the peripheral portion of the contour based on the contour signal. A multiplying unit that multiplies the ringing component and the attenuation amount of the contour peripheral portion to generate a corrected ringing component; and an addition that adds the result of subtracting the ringing component from the input image signal and the corrected ringing component. A ringing removing device comprising: