JPH0380787A - Adaptive notch filter - Google Patents

Abstract

PURPOSE:To eliminate the crosstalk component of an edge part without lowering resolution by detecting an edge component included in an image from an input ted luminance signal, and increasing/decreasing the attenuation quantity of a bond blocking filter corresponding to the quantity of detected signal components. CONSTITUTION:Sampling values inputted to coefficient circuits 15-17 are shown as three points S1, S3, and S5 arranging in a vertical direction. Therefore, the output of the band blocking filter 3 goes to S3+(k/4) (S1-2S3+S5). It is pro vided with band blocking characteristic centering a vertical frequency 525/4(c/ph), and the attenuation quantity is increased as making a multiplication coefficient (k) approach to 1. Meanwhile, the correlation energy DYH and DYV of the image in horizontal and vertical directions are outputted from an edge detection circuit 4. A ROM table 34 decides the value of the multiplication coefficient (k) from the values DYV and DYH, and when the value DYV is small and the value DYH is large, the coefficient (k) is made approached to 1, and it is decreased when it is not. Therefore, the crosstalk component can be elimi nated as keeping the resolution of the luminance signal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an adaptive notch filter, and particularly to a notch filter circuit that attenuates crosstalk components of a chrominance signal in a luminance signal caused by incomplete YC separation. be.

[Conventional technology]

FIG. 6 is a block circuit diagram showing the configuration of a conventional notch filter that suppresses crosstalk components from an NTSC luminance signal sampled at four times the frequency fsc of the color subcarrier.

In the figure, l is an input terminal into which the digital data of the luminance signal is input, 303 to 312 are delay circuits that delay the luminance signal by two sampling periods 2T, and 313 to 323 are delay circuits that delay the luminance signal by two sampling periods 2T, respectively. This is a coefficient circuit that amplifies by a magnification, and the coefficient values are as shown in the figure. 324 is an adder circuit that adds the outputs of the coefficient circuits 313 to 323, and 2 is an output terminal that outputs digital data of a luminance signal from which crosstalk components have been removed.

Next, the operation will be explained.

The frequency characteristics (amplitude characteristics) of the filter shown in FIG. 6 are band rejection characteristics that are attenuated near the frequency f sc of the color subcarrier, as shown in FIG. 7. On the other hand, as shown in Figure 8, Y
If the characteristics of the C separation filter are such that it separates the area within the dotted line as a color signal and the area outside the dotted line as a luminance signal, the color signal will extend beyond the dotted line and leak into the luminance signal side at horizontal edges, etc., as shown by the diagonal lines in the figure. However, since this crosstalk component mainly exists near the horizontal frequency f fie, by passing the luminance signal through a filter with the characteristics shown in Fig. 4,
It is possible to fully remove it.

Although we have discussed conventional notch filters constructed with digital circuits, they may also be constructed with analog circuits as long as they have the frequency characteristics shown in Figure 4. Analog filters are currently more widely used. has been done.

[Problem to be solved by the invention]

Since the conventional notch filter is configured as described above, it attenuates not only the crosstalk component but also the high frequency component of the luminance signal, resulting in problems such as deterioration of the resolution of the reproduced image.

This invention was made to solve the above-mentioned problems, and aims to provide a notch filter that can attenuate only crosstalk components while maintaining resolution.

[Means to solve the problem]

The adaptive notch filter according to the present invention detects edge components included in an image from an input luminance signal, and detects a color signal in the same direction as the edge component in the input luminance signal according to the amount of the detected signal component. The amount of attenuation of a band rejection filter that removes crosstalk components is increased or decreased.

[Effect]

The variable attenuation band rejection filter in this invention is
Crosstalk components at the edge portions of an image where interference by crosstalk components is likely to be noticeable depending on the amount of edge components can be removed without reducing resolution.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In Figure 1, 1 is NT sampled at 4f0
3 is an input terminal into which the SC method luminance signal is input; 3 is a band rejection filter which inputs the luminance signal and suppresses crosstalk components;
4 is an edge detection circuit that detects horizontal edges from the luminance signal; 2 is an output terminal from which a luminance signal with suppressed crosstalk components is output.

In the band rejection filter 3, 7 to 10 are human luminance signals of 908T, 2T, 2T, and 908T, respectively (T=1
Delay circuits 15 to 17 delay the outputs of delay circuits 7 to 9 by W+
/z, % multiplication coefficient circuit, 24 is coefficient circuit 15-1
7 is an adder circuit that adds a sign to the output, 11 is a delay circuit that delays the output of adder circuit 24 by 2T, and 30 is R.
A multiplication circuit 25 multiplies the output of the OM table 33 and the output of the delay circuit 11;
This is a sign addition/addition circuit that subtracts the output of .

Next, the edge detection circuit 4 includes a horizontal correlation detection circuit 5 for detecting correlation in the horizontal direction and a vertical correlation detection circuit 6 for detecting correlation in the vertical direction. In the horizontal correlation detection circuit 5, 18
19.20 is a coefficient circuit that multiplies the input luminance signal by A, 19.20 is a coefficient circuit that multiplies the outputs of delay circuits 8 and 10 by A+'74, 26 is an addition circuit that adds the outputs of coefficient circuits 18 to 20, and 12 is an addition circuit. A delay circuit that delays the output of the circuit 26 by 4T, 27 a sign addition/addition circuit that subtracts the output of the delay circuit 12 from the output of the addition circuit 26, and 31 a sign addition/addition circuit 2.
This is an absolute value circuit that takes the absolute value (ABS) of the output of 7.

In the vertical correlation detection circuit 6, 28 is a sign addition/addition circuit that calculates the difference between the human luminance signal and the output of the delay circuit 1O, 13.14 is a delay circuit that delays the output of the sign addition/addition circuit 28 by 2T, and 21 is a Coefficient circuits 22 and 23 multiply the output of the adder circuit 28 by x, and 23 and 23 respectively represent the outputs of the delay circuits 13 and 14 as A.

29 is an adder circuit that adds the outputs of the coefficient circuits 21 to 23; and 32 is an absolute value circuit that takes the absolute value (ABS) of the output of the adder circuit 29.

Next, the operation will be explained. The delay circuits 7 to 10 obtain pixel sampling values 31 to S shown in FIG. 3. Here, the band rejection filter 3 has a sampling value S,
(Sz 233 + Ss) is obtained as the output of the adder circuit 24 using S,,S,. This results in a bandpass filter centered at f me. The frequency characteristics are shown in FIG. Next, this output is sent to the multiplier circuit 30
Therefore, it is multiplied by k (0≦≦1) and subtracted from the original signal S by the adder circuit 25. Therefore, the output of the adder circuit 25 is S, + (St -232+34
). This is a bandstop filter centered at fsc. The frequency characteristics are shown in FIG. The amount of attenuation of this filter changes depending on the multiplication coefficient k, and the larger k is, the greater the amount of attenuation is.

The horizontal correlation detection circuit 5 includes delay circuits 7 to 10. Coefficient circuit 1
8-20. The adder circuit 26 has a characteristic that the low voltage in the vertical direction is O. If Y,, Y, are the vertical low frequency components of St, S4 obtained by this low-pass filter, the output of the sign adder 27 is Y, -Y.

becomes. This is a bandpass filter whose gain is O at DC component and fsc, and its characteristics are shown in FIG. When the image does not change horizontally, Y2 and Y4
The values of are equal, Yz Y4=0, but otherwise O, in Figure 9 are generally
Frequency components other than f and c are extracted, so that Y, -Y4≠O. Therefore, by the absolute value circuit 31, DvH=Y
Find t Ya and use it as the correlation energy in the horizontal direction. It can be said that the smaller the value of D7H, the stronger the correlation between images in the horizontal direction.

On the other hand, in the vertical correlation detection circuit 6, the output of the sign adder 28 is a vertical band-pass filter centered at /8 (c/ph), where 525/8 (C/ph) is the vertical color. This corresponds to half of the subcarrier frequency 525/4 (c/ph). Next, delay circuits 13 and 14, coefficient circuits 21 to 23
, the adder circuit 29 constitutes a horizontal low-pass filter. As shown in FIG. 11, this filter has a characteristic in which the gain is O at fo. Therefore, the output of the adder circuit 29 can be written as I Ys. Here, Y, , Y are horizontal low frequency components in St and Ss. When the image does not change in the vertical direction, the values of Yt and Y are equal, and Y t Ys
= 0, but otherwise, Yt Ys≠O. Therefore, the output Dvv of the absolute value circuit 32 = Y
t Ys gives the correlation energy of the image in the vertical direction.

Now, at horizontal edges where cross-luminance interference is more noticeable, the correlation in the horizontal direction is strong and the correlation in the vertical direction is weak.The ROM table 33 determines the value of the multiplication coefficient from the value of DYH+I)yv, It works to bring k closer to 1 when Dvv is large, and to make k smaller when it is not.

Note that the delay circuit 11 is for adjusting the difference in signal delay amount between the band rejection filter and the phase amount detection circuit.

In the above embodiment, the band rejection filter 3 is configured with a horizontal filter, and the attenuation amount is increased at the horizontal edge. However, the band rejection filter 3 is configured with a vertical filter, and the attenuation amount is increased at the vertical edge. You may also do so.

In FIG. 2, which shows another embodiment of the present invention, the same components as those in FIG. 1 are denoted by the same reference numerals. In the same figure, the sampling values input to the coefficient circuits 15 to 17 are at three points St aligned in the vertical direction in FIG.
,S! , Ss.

Therefore, the output of the band rejection filter 3 is S3 +
(s+233+3%), which has a band rejection characteristic centered at the vertical frequency 525/4 (C/ph), and its attenuation increases as k approaches 1, as in the case of Figure 1. Become.

On the other hand, in the edge detection circuit 4, the edge detection circuit 4 in FIG.
It is configured in exactly the same manner as described above, and the correlation energy of the horizontal image and the correlation energy of the vertical image, DvH-I Yt Y41 Dvv=YI Ys, are output.

At vertical edges where cross-over interference is more noticeable, the correlation in the vertical direction is strong and the correlation in the horizontal direction is weak. R
The OM table 34 is D VV, D? The value of the multiplication coefficient is determined from the values of , and when DVv is small and DVH is large, k is brought close to 1, and otherwise, k is made small.

Note that the delay circuit 11 is for adjusting the difference in signal delay amount between the band rejection filter and the correlation detection circuit.

Further, in the embodiments shown in FIGS. 1 and 2, all the circuits are constructed from digital circuits, but they may also be constructed from analog circuits using glass delay lines or the like.

Further, in the above embodiment, the input is a luminance signal of the NTSC system, but the input is not limited to this, and an input signal other than the NTSC system may be used as long as the amount of delay is adapted.

Furthermore, the sampling frequency is not limited to 4f-, and neighboring pixels can be obtained above, below, and to the left and right of the pixel of interest. Regardless of the sampling frequency, the chrominance signal component is strongly attenuated only at the edge parts where nonce is noticeable, so the notch filter can effectively remove crosstalk components while maintaining the resolution of the luminance signal. There are benefits to be gained.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of a notch filter according to one embodiment of the invention, FIG. 2 is a block circuit diagram of another embodiment of the invention, and FIG. 3 is a diagram showing the positions of sampling points in this embodiment. Figures 4, 5, 9, 10, 11, and 12 are diagrams showing the filter characteristics of this embodiment, Figure 6 is a configuration diagram showing a conventional notch filter, and Figure 7 is a diagram showing the filter characteristics of this embodiment. , FIG. 8 is an explanatory diagram showing the operation of a conventional notch filter. 3...band rejection filter, 4...edge detection circuit,
5...Horizontal correlation detection circuit, 6...Vertical correlation detection circuit, 7-14...Delay circuit, 15-23...Coefficient circuit, 24-29...Addition circuit, 30...Multiplication circuit, 3
1.32... Absolute value circuit, 33.34... ROM table. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) An edge detection means for detecting horizontal or vertical edge components included in an image from a luminance signal separated from a color television signal, and a color signal in the same direction as the edge detected by this edge detection means. and a variable-attenuation band rejection filter that attenuates the frequency components of the luminance signal, and the edge detection means detects that among the frequency components of the luminance signal, there are low-frequency components in the direction perpendicular to the edge to be detected, and horizontal The first step extracts a frequency component corresponding to one half of the color subcarrier frequency in the direction, and calculates its absolute value to detect the correlation energy of the image in the horizontal direction with the edge to be detected. Correlation energy detection means; Of the frequency components of the luminance signal, the horizontal direction to be detected is a low frequency component, and the vertical direction is a frequency component corresponding to one half of the color subcarrier frequency. a second correlation energy detection means for extracting a component and finding its absolute value to detect the correlation energy of the image in a direction perpendicular to the edge to be detected; the first correlation energy detection means; 2. An adaptive notch filter characterized in that the attenuation amount of the band rejection filter is increased or decreased depending on the output of the correlation energy detection means 2.