JP2523532B2 - Television signal processing circuit - Google Patents

Description

The present invention relates to a signal processing circuit for a composite color television signal, and more particularly to a signal suitable for reducing noise contained in an NTSC composite color television signal. It relates to a processing circuit.

[Conventional technology]

JP-A-58-115995 discloses a Y / C separation circuit for separating a luminance signal and a chrominance signal of a composite color television signal in which a cyclic noise reduction circuit is provided by sharing a frame memory used for the separation. Some are listed. The noise reduction circuit in the present invention uses a chroma inverter and is configured to invert the polarities of the color difference signals of the signals separated by one frame and reduce the noise over the entire video signal band.

[Problems to be solved by the invention]

In the above-mentioned conventional example, the signal stored in the frame memory is a composite signal, and noise reduction processing is performed on the luminance signal and the color difference signals at the same time, so that optimum noise reduction is performed on each of the luminance signal and the color difference signal. There was a problem that I could not. For example, the noise reduction effect is small for a luminance signal that is likely to cause afterimage interference, and the noise reduction effect is large for a color difference signal that is less noticeable. It was impossible to perform noise reduction processing.

An object of the present invention is to solve the above problems and to provide a signal processing circuit capable of optimal noise reduction for each of luminance signal and color difference signals.

[Means for solving problems]

The above-mentioned object is based on the first memory circuit for storing the video signal, the second memory circuit for storing the color difference signal extracted from the video signal, and the magnitude of the difference between the input and output of the first memory circuit. And a second noise reduction circuit whose gain changes in accordance with the magnitude of the input / output difference of the second memory circuit. This can be achieved by making the gain of the second noise reduction circuit larger than the gain of the circuit.

[Action]

The first noise reduction circuit uses the difference between the input and output of the first memory circuit to determine whether the difference is due to noise or motion of the image, and when it is determined to be due to noise, the difference is determined. The noise is reduced by controlling the gain of and feeding back to the input signal. When it is determined that it is due to the movement of the image, zero is returned and noise reduction is not performed.

The second noise reduction circuit is similarly configured, but the gain of the second noise reduction circuit is set to a value larger than the gain of the first noise reduction circuit, and the difference between the input and output of the second memory circuit is caused by noise. When the determination is made, the gain of the difference is controlled and fed back to the input signal to reduce noise.

In this way, since the gains of the first and second noise reduction circuits can be controlled independently, optimum noise reduction can be performed for both the luminance signal and the color difference signal.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In the figure, 101 is an input terminal for a composite color television signal, 102 is a band-pass filter (hereinafter abbreviated as BPF), and 10
3 is an automatic color control circuit (hereinafter abbreviated as ACC), 104 is a color demodulation circuit, 105 to 107 are A / D converters, 108 is a selection circuit, 109 is a first noise reduction circuit, and 110 is The second noise reduction circuit, 111 is the first frame memory, and 112 is the second
, 113 is a luminance signal separation circuit, 114 is a color difference signal separation circuit, and 115 and 116 are luminance signal (Y) and color difference signal (C) output terminals.

The input composite color television signal is sent to the A / D converter 105.
The signal is digitized by the noise reduction circuit 109, noise is reduced by the noise reduction circuit 109, and the noise is supplied to the frame memory 111 and the luminance signal separation circuit 113. The luminance signal separation circuit 113 removes the color difference signal component using frame correlation or line correlation or both, and outputs a luminance signal.

On the other hand, in the color difference signal system, the input signal is band-limited by the BPF 102, and the color difference signal band component centered on fsc is extracted. The color difference signal band component thus taken out is kept at a constant level by the ACC 103, and is demodulated by the color demodulation circuit 104 into two types of color difference signals (for example, RY and BY). The demodulated two types of color difference signals are digitized by A / D converters 106 and 107, respectively, and multiplexed by time division by a selection circuit 108. After the noise is reduced by the noise reduction circuit 110, the multiplexed signal is supplied to the frame memory 112 and the color difference signal separation circuit 114. The color difference signal separation circuit 114 removes the luminance signal component contained in the band by using frame correlation, line correlation, or both, and outputs a color difference signal.

FIG. 2 shows a configuration example of the noise reduction circuit 109 for the luminance signal. In the figure, 201 is an input terminal, 202 is a delay circuit, 20
3 is an adder, 204 is a non-linear conversion circuit, 205 is a low-pass filter (hereinafter abbreviated as LPF), 206 is a subtractor, 207 is an input terminal of a signal delayed by one frame, and 208 is an output terminal.

The input composite color television signal is subtracted from the signal delayed by one frame by the subtractor 206. This difference is LPF2
The band is limited by 05 to extract only the difference due to the low range of the luminance signal, and remove the influence of the difference due to the color difference signal. In the non-linear conversion circuit 204, for example, when this difference is small, it is determined that it is a difference due to noise, and when it is large, it is determined as a difference due to the motion of the image, and when it is determined to be a difference due to noise, the gain of this difference is controlled and output. When it is determined that the difference is due to movement, zero is output. In the adder 203, the input signal is delayed by the delay circuit 202, the subtractor 206, the LPF 205, and the nonlinear conversion circuit.
A signal delayed by the same amount as the delay amount by 204 and the output signal of the nonlinear conversion circuit 204 are added. Thereby, noise reduction can be realized.

The non-linear conversion circuit 204 is, for example, a read only memory (ROM).
And the input / output characteristics shown by the solid line in FIG. This characteristic defines a threshold value α for an input signal, and outputs a difference due to motion of zero when a signal exceeding α is input. For an input smaller than α, a signal obtained by multiplying the input signal by 0.3 to 0.5 is output.
If this gain is increased, the noise reduction effect is increased, but on the other hand, the interference due to the afterimage is increased.

FIG. 4 shows an example of the configuration of the noise reduction circuit 110 for color difference signals. 401 is an input terminal, 402 is a delay circuit, 403 is an adder, 404 is a non-linear conversion circuit, 405 is a subtractor, and 406 is 1
Reference numeral 407 denotes an input terminal for the frame-delayed signal and 407 an output terminal.

The input color difference signal band signal is output to the non-linear conversion circuit 404 by taking the difference with the signal delayed by one frame by the subtractor 405. The non-linear conversion circuit 404 is composed of a ROM having input / output characteristics as shown by the broken line in FIG. 3 similarly to the non-linear conversion circuit 204, and when it is determined that there is a difference due to noise, the input signal is input.
Output the signal multiplied by 0.5 to 0.8. In the adder 403, the input signal is delayed by the delay circuit 402, the subtractor 405, and the nonlinear conversion circuit 40.
A signal delayed by the same amount as the delay amount of 4 and the output signal of the non-linear conversion circuit 404 are added to reduce noise.

Here, the input / output characteristics of the non-linear conversion circuit 404 utilize the fact that the interference due to the afterimage of the color difference signal is less noticeable than that of the luminance signal, and thus the threshold value β and the gain are set to the non-linear conversion circuit.
If the value is larger than that of 204, a larger noise reduction effect can be obtained.

FIG. 5 shows a configuration example of the luminance signal separation circuit 113. This is a motion adaptive Y / C separation circuit that separates between frames when the image is stationary and within fields when the image is moving. In the figure, 501 is the current signal, that is, noise reduction circuit 109.
Of the output signal of the frame memory 111, that is, the input terminal of the output signal of the frame memory 111,
Is a 1H delay circuit, 504 is an adder, 505 and 510 are subtractors, 506 and 507 are coefficient multipliers, 508 is a BPF, 509 is a motion detection circuit, 511 is a mixer, and 512 is a luminance signal output. Indicates a terminal.

In-field processing is performed with the input signal in the subtractor 505.
Coefficient multiplier that takes the difference from the signal delayed by the H delay circuit 503
After halving by 506, the BPF 508 extracts the signal in the band centered on fsc and obtains the color difference signal. This color difference signal is subtracted from the subtractor 510
The luminance signal is subtracted from the input signal by the mixer 511
Supply to

In the inter-frame processing, the adder 504 adds the current signal and the signal one frame before to obtain a luminance signal, and the coefficient unit 50
It is halved by 7 and supplied to the mixer 511. The mixer 511 mixes and outputs the luminance signal obtained by the intra-field processing and the luminance signal obtained by the inter-frame processing at a mixing ratio according to the image motion information detected by the motion detection circuit 509.

FIG. 6 shows a configuration example of the color difference signal separation circuit 114. This is also a motion adaptive type separation circuit like the luminance signal separation circuit 113, and in the figure, 601 is the current signal, that is, the noise reduction circuit 1.
The input terminal of the output signal of 10 and the input terminal of the output signal of the frame memory 112, that is, the input signal of the signal one frame before, 602,
Reference numeral 03 is a 1H delay circuit, 604 and 605 are adders, 606 and 607 are coefficient units, 608 is a motion detection circuit, 609 is a mixer, and 610 is a color difference signal output terminal.

In-field processing is performed with the input signal in the adder 605.
The color difference signal is extracted by adding it to the signal delayed by the H delay circuit 603, and is multiplied by 1/2 by the coefficient unit 606 to be a mixer.
Supply to 609.

In the inter-frame processing, the adder 604 adds the current signal and the signal one frame before to obtain the color difference signal, and the coefficient unit 60
7 times 1/2 and supply to mixer 609. The mixer 609 mixes and outputs the color difference signal obtained by the intra-field processing and the color difference signal obtained by the inter-frame processing at a mixing ratio according to the motion information of the image detected by the motion detection circuit 608.

The luminance signal separation circuit 113 and the color difference signal separation circuit 114 are circuits for optimally separating the luminance signal and the color difference signal,
The configuration is not limited to those shown in FIGS. 5 and 6.

As described above, according to the embodiment of FIG. 1, the noise reduction effect on the luminance signal and the noise reduction effect on the color difference signal can be controlled independently, so that optimum noise reduction can be performed for each of the luminance signal and the color difference signal. It can be carried out.
Also, by setting the noise reduction circuit for color difference signals to have a greater reduction effect than the noise reduction circuit for luminance signals, a larger noise reduction effect as a whole can be achieved without making interference due to afterimages noticeable. Can be obtained.

FIG. 7 shows another embodiment of the present invention. This is a non-recursive configuration in which a frame memory dedicated to noise reduction is provided in contrast to the cyclic configuration in the first embodiment. In the figure, 701 and 703 are noise reduction circuits for luminance signals and color difference signals, 702, 704, 706 and 708 are frame memories, 705 is a luminance signal separation circuit, 707 is a color difference signal separation circuit and 709 and 710 are luminance signals and color difference signals. Indicates the output terminal. Others are the same as those in FIG.

The noise of the composite color television signal digitized by the A / D converter 105 is reduced by the noise reduction circuit 701, the color difference signal component is removed by the luminance signal separation circuit 705, and the luminance signal is output.

On the other hand, the noise reduction circuit 703 reduces noise in the color difference signal band component of the base band which is time-division multiplexed by the selection circuit 108, the luminance signal component is removed by the color difference signal separation circuit 707, and the color difference signal is output.

The noise reduction circuit 701 can be realized by the same configuration as that of FIG. 2, and removes the difference due to the color difference signal from the difference between the current signal and the signal one frame before, and then controls the gain and adds it to the input signal. Is.

The noise reduction circuit 703 can also be realized by the same configuration as that of FIG. 4, and the gain of the difference between the current signal and the signal one frame before is controlled and added to the input signal.

The noise reduction circuits 701 and 703 are noise reduction circuits 1 in FIG.
The difference from 09,110 is that in FIG. 1 it has a cyclic structure in which the noise-reduced signal is delayed by one frame and the operation with the current signal is performed, whereas in FIG. This is a point of non-recursive configuration in which the previous signal is delayed by one frame and the operation with the current signal is performed. When the non-recursive type is used, the frame memory cannot be shared with the Y / C separation circuit, however, the disturbance due to the afterimage does not appear over several frames unlike the cyclic type. Also,
Noise reduction circuit for color difference signals even in non-recursive type
A larger reduction effect can be obtained by making the gain of 703 larger than that of the luminance signal.

The luminance signal separation circuit 705 and the color difference signal separation circuit 707 are also the fifth
This can be realized with the same configuration as that shown in FIGS.

As described above, also in the embodiment of FIG. 7, as in the embodiment of FIG. 1, the noise reduction effect on the luminance signal and the noise reduction effect on the color difference signal can be set independently, so that the luminance signal and the color difference signal are respectively set. On the other hand, optimum noise reduction can be performed.

FIG. 8 shows still another embodiment of the present invention. In the figure, 801 is a BPF, 802 is an ACC, 803 is a color demodulation circuit, and 804
Indicates a selection circuit. Others are the same as those in FIG. In contrast to the configuration shown in FIG. 1 in which a color difference signal is obtained from a composite color television signal by an analog circuit, the BPF801, ACC802, and color demodulation circuit 803 are realized by digital circuits, and the A / D converter 105 performs digital conversion. The color difference signal is obtained from the converted composite color television signal.

From the composite color television signal digitized by the A / D converter 105, the color difference signal band component centering on fsc is extracted by the BPF 801 and the level is adjusted by the ACC 802, and then demodulated into two types of color difference signals by the color demodulation circuit 803. To do. Others function similarly to those in FIG.

As described above, the same effect as that of the embodiment of FIG. 1 can be obtained by the embodiment of FIG. Further, such a configuration has an advantage that the number of A / D converters can be reduced.

In addition, in FIG. 1, after the BPF 102, or the ACC 103
Similar effects can be obtained even if an A / C converter is provided in the subsequent stage.

The noise reduction circuits 109, 701 and 110, 7 are shown in FIGS.
Another configuration example of 03 is shown. This is shown in Figs. 2 and 4, respectively.
2 and 4 have the same transfer function as the one shown in the figure, and the gains of the differences between the frames are controlled by adding the gains of the differences between the frames to the current signal. The configuration is such that it is controlled and added to the signal delayed by one frame.

FIG. 9 shows a noise reduction circuit for luminance signals.
1 is an input terminal, 902 is a subtractor, 903 is an LPF, 904 is a non-linear conversion circuit, 905 is an adder, 906 is a delay circuit, 90
Reference numeral 7 denotes an input terminal for a signal delayed by one frame, and 908 denotes an output terminal.

The subtracter 902 calculates the difference between the frames, and the LPF 903 extracts only the difference due to the low range of the luminance signal and removes the difference due to the color difference signal. The non-linear conversion circuit 904 controls the gain when it is determined that the difference is due to noise, and outputs the gain as it is when it is determined that the difference is due to the motion of the image. In the adder 905, noise is reduced by adding the output of the non-linear conversion circuit 904 and the 1-frame delay signal whose delay amount has been adjusted by the delay circuit 906.

Figure 10 shows a noise reduction circuit for color difference signals.
01 is an input terminal, 1002 is a subtractor, 1003 is a non-linear conversion circuit, 1004 is an adder, 1005 is a delay circuit, 1006 is an input terminal of a signal delayed by one frame, and 1007 is an output terminal.

The subtracter 1002 calculates the difference between the frames, the non-linear conversion circuit 1003 controls the gain, and supplies it to the adder 1004. The non-linear conversion circuit 1003 controls the gain when it is determined that the difference is due to noise, and outputs the gain as it is when it is determined that the difference is due to the motion of the image. In the adder 1004, noise is reduced by adding the output of the non-linear conversion circuit 1003 and the one-frame delay signal whose delay amount has been adjusted by the delay circuit 1005.

When the configurations shown in FIGS. 9 and 10 are used, the input / output characteristics of the non-linear conversion circuits 904 and 1003 are as shown in FIG. In FIG. 11, the characteristic of the non-linear conversion circuit 904 for the luminance signal is shown by a solid line, and the characteristic of the non-linear conversion circuit 1003 for the color difference signal is shown by a broken line. Also in this case, by setting the threshold value β for the color difference signal to be a value equal to or larger than the threshold value α for the luminance signal, it is possible to obtain a larger noise reduction effect as a whole as in FIG. Also, looking at the gain,
The value for the luminance signal is larger than that for the color difference signal, but it is clear that the smaller the gain, the greater the noise reduction effect in the case of the configuration shown in FIGS. 9 and 10. is there.

The input / output characteristic of the non-linear conversion circuit is shown as an ideal curve in FIGS. 3 and 11, but when it is configured by a digital circuit such as a ROM, in addition to such a characteristic, for example,
The characteristics shown in Figs. 12 and 13 may be used. In both figures, the video signal is digitized with a resolution of 8 bits and concrete numerical values are set as decimal numbers from 0 to 255. The solid line shows the luminance signal and the broken line shows the color difference signal. Figure 12 shows the ideal curve digitized with α = 9 and β = 14. FIG. 13 shows a steep gain near the threshold value, where α = 7 and β = 13.
Further, in FIG. 12, the gain for the color difference signal is always higher than the gain for the luminance signal, but as shown in FIG. 13, the gain of the luminance signal becomes a larger value in a small part. The present invention is also applicable.

〔The invention's effect〕

According to the present invention, the gain of the noise reduction circuit for the luminance signal and the gain of the noise reduction circuit for the color difference signal are set independently, and the gain of the noise reduction circuit for the color difference signal is set to the gain of the noise reduction circuit for the luminance signal. Since it can be made larger than the gain, optimum noise reduction can be performed for both the luminance signal and the color difference signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment of a signal processing circuit of the present invention, FIG. 2 is a block diagram of a noise reduction circuit of FIG. 1, FIG. 3 is FIG. 2 and FIG. FIG. 4 is a characteristic diagram showing input / output characteristics of the nonlinear conversion circuit shown in FIG. 4, FIG. 4 is a block diagram of the noise reduction circuit of FIG. 1, FIG. 5 is a block diagram of the luminance signal separation circuit of FIG. 1, and FIG. FIG. 1 is a block diagram of the color difference signal separation circuit, FIG. 7 is a block diagram showing another embodiment of the present invention, FIG. 8 is a block diagram showing still another embodiment of the present invention, FIGS. 9 and 10. FIG. 11 is a block diagram showing another configuration example of the noise reduction circuit, FIG. 11 is a characteristic diagram showing input / output characteristics of the non-linear conversion circuits of FIGS. 9 and 10, and FIGS. 12 and 13 are non-linear conversion circuits. 6 is a characteristic diagram showing another input / output characteristic of FIG. 109.110,701,703 …… Noise reduction circuit 111,112,702,704,706,708 …… Frame memory 203,403,905,1004 …… Adder 204,404,904,1003 …… Nonlinear conversion circuit 205,903 …… LPF 206,405,902,1002 …… Subtractor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shigeru Hirahata 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Hitachi, Ltd. Home Appliances Research Laboratory (72) Masato Sugiyama 292 Yoshida-cho, Totsuka-ku, Yokohama, Hitachi, Ltd. Inside the laboratory (72) Kenji Katsumata Inventor Kenji Katsumata 292 Yoshida-cho, Totsuka-ku, Yokohama Inside the Home Appliances Laboratory, Hitachi, Ltd. (56) Reference JP 61-147697 (JP, A) Takahiko Fukiguki "Digital Signal Processing of Images" (Sho 56-5-25) Nikkan Kogyo Shimbun p. 114-119

Claims (4)

(57) [Claims] 1. A television signal processing circuit for reducing noise by utilizing the correlation of video signals, wherein a first memory circuit delays an input video signal by about 1 frame, and the first video signal is input to the first memory circuit. A first noise reduction circuit that reduces noise by changing the gain of the difference and mixing it with the input video signal depending on the magnitude of the difference from the video signal delayed by the memory circuit of FIG. A second memory circuit that delays the color difference signal by about one frame, and an input color difference by changing the gain of the difference depending on the magnitude of the difference between the color difference signal and the color difference signal delayed by the second memory circuit. A second noise reduction circuit that performs noise reduction by mixing with the signal, and the difference of the mixed difference of the second noise reduction circuit is within a certain range of the difference. There the television signal processing circuit characterized by having a portion to be a value larger than the gain of the difference to be mixed in the first noise reduction circuit for the differential value of the same size. 2. The television signal processing circuit according to claim 1, wherein the first noise reduction circuit has a low-pass filter circuit for removing a color difference signal in the difference signal, A television signal processing circuit having a noise reduction effect only in a low frequency range. 3. The television signal processing circuit according to claim 1 or 2, wherein the first noise reduction circuit is an image delayed by the input video signal and the first memory circuit. The second noise reduction circuit has a first threshold value that is determined to be a difference due to noise when the difference from the signal is smaller than a predetermined value, and the second noise reduction circuit delays the color difference signal and the second memory circuit. When the difference between the color difference signal and the color difference signal is smaller than a predetermined value, the second threshold value is determined to be the difference due to noise, and the second threshold value is equal to or more than the first threshold value. And a television signal processing circuit. 4. The television signal processing circuit according to claim 1, further comprising a digital color demodulation circuit,
The demodulated color difference signal is transferred to the second memory circuit and the second memory circuit.
And a noise reduction circuit of the television signal processing circuit.