JPH0810951B2 - Television signal noise reduction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a television signal (hereinafter referred to as a TV signal).
Which is effective in improving the S / N ratio of TV signals,
In particular, the present invention relates to a noise elimination circuit that can obtain a great effect when applied to a TV signal processing circuit in a magnetic recording device.

[Conventional technology]

FIG. 4 is a block diagram showing a conventional noise elimination circuit disclosed in, for example, Japanese Patent Publication No. 59-2228.

In the figure, 1 is a TV signal input terminal, 2 is a delay circuit for delaying the TV signal input to the input terminal for a period corresponding to one horizontal scanning, and 3 is a TV signal input from the input terminal 1 and one horizontal scanning. Reference numeral 4 is a first subtraction circuit for extracting a difference component from the TV signal delayed for a period, and 4 is an amplitude limiting circuit for the difference component signal. When the input signal level is very small, the amplitude limiting circuit 4 makes a linear response in the input / output relationship and operates as a clipping circuit for an input / output signal having an amplitude of a certain value or more. Reference numeral 5 is a second subtraction circuit for subtracting the signal component obtained from the amplitude control circuit 4 from the TV signal input from the terminal 1, and the signal introduced to the output terminal 6 by the second subtraction circuit 5 is , Two signals (signal of one horizontal scanning period × 2) which are consecutive with one horizontal scanning period obtained by the delay circuit 2 and the first subtraction circuit 3 as a unit are compared with each other, and the difference is obtained. A signal with a small amplitude is almost completely canceled, and a signal with a certain amplitude (amplitude is large) is a signal with a constant amplitude canceled. That is, the above-mentioned noise components having a low level included in the TV signal are almost completely canceled, but those of the edge portion of the TV signal having a small vertical correlation, which are larger than the noise level, are canceled by the limiter so as to cancel them. Never be done. Therefore, there is no substantial reduction in resolution.

FIG. 5 is intended to explain the device shown in FIG. 4 from the viewpoint of frequency characteristics, and FIG. 5 (a), (b), (c)
The horizontal axis represents the frequency and the vertical axis represents the signal gain at each frequency. That is, assuming that the function for the frequency of the signal at the input terminal 1 of the circuit block diagram shown in FIG. 4 is as shown in FIG. 5 (a), the function at the output of the first subtraction circuit 3 is shown in FIG. The so-called comb filter shown in (b) is constructed. Here, fa ₁ , fa ₂ , ..., Fa _n shown in the figure are frequencies indicated by n / T _D , respectively. However, n is a positive integer and T _D is the delay time of the delay circuit 2 shown in FIG.

Due to the characteristics shown in FIG. 5 (b), the input terminal 1
Signals included in the input TV signal that differ in phase from each other at one horizontal scanning interval, particularly signals that differ by 180 °, are most efficiently extracted.

The transfer characteristic shown in FIG. 5C has an output terminal 6 when the signal level is a minute level in view of the operation of the amplitude limiting circuit 4, that is, a level at which the amplitude limiting circuit does not limit the amplitude. 3 shows the transfer characteristic of the input terminal 1 of FIG. In Fig. 5C, fb ₁ , f
_{b 2, fb 3, ...,} fb n becomes a frequency represented by each (2n-1) / (2T D), constituting the comb filter for the luminance signal in the so-called TV signal. Note that n is a positive integer,
T _D is the delay time of the delay circuit 2.

As described above, if the filter is configured to operate as a comb filter only in a portion where the signal amplitude level is low, noise having a random component with respect to a practical TV signal is usually peak-to-peak (hereinafter referred to as P- Since it is 1/10 or less (noise level is 10% or less) in terms of the ratio of the P value), the limiting level of the amplitude limiting circuit 4 can be set to 1/10 or less with respect to the signal PP value. There is almost no deterioration in the resolution in the vertical direction, and the noise reduction effect is almost the same as that of the existing comb filter.

[Problems to be Solved by the Invention]

Since the conventional noise elimination circuit is configured as above, even in the case of a luminance signal that is uncorrelated in the vertical direction on the screen, about 1/10 of the vertical difference of the signal passes through the amplitude limiting circuit and the original signal is passed. Therefore, there is a problem that a so-called Y sag phenomenon occurs in which the luminance signal is vertically sloped.

The present invention has been made in order to solve the above problems, and an object of the present invention is to obtain a noise elimination circuit for a television signal, which is free from Y droop and has almost no deterioration in vertical resolution.

[Means to resolve issues]

A television signal noise elimination circuit according to the present invention,
Detects the correlation in the horizontal and vertical directions of the TV signal and adaptively switches the filter that detects the strong correlation component, and outputs the signal obtained by delaying the input by one line through the amplitude limit circuit for the output signal. It is designed to be subtracted.

[Action]

In the television signal noise elimination circuit according to the present invention, the signal obtained by adaptively switching the filters according to the correlation of the signals passes through the filters other than the vertical direction when the correlation in the vertical direction is small, It is input to the width limiting circuit.

〔Example〕

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

FIG. 1 is a schematic block diagram showing a noise elimination circuit for a television signal according to an embodiment of the present invention. In FIG. 1, 11 is an input terminal to which a composite color television signal of NTSC system is given, and 12 is an input. An A / D converter for converting an analog composite color television signal input via the terminal 11 into a digital signal, 13 is a first one-line delay circuit for inputting an output signal of the A / D converter 12, 14 Reference numerals 15 and 15 are second 1-line delay circuits and compensation delay circuits for inputting the output signal of the first 1-line delay circuit 13, and 16, 17, 18 are output signals 101 of the A / D converter 12 and the first 1-line delay circuit. A vertical direction color signal extraction filter, a horizontal and vertical direction color signal extraction filter, and an image correlation determination circuit for inputting the output signal 102 of the line delay circuit 13 and the output signal 103 of the second 1-line delay circuit 14, respectively, 19 are first Horizontal for inputting the output signal 102 of the 1-line delay circuit 13 A color signal extraction filter, 20 is a compensation delay circuit that outputs the output signal 104 of the vertical color signal extraction filter 16, 21 is a compensation delay circuit that inputs the output signal 108 of the horizontal vertical color signal extraction filter 17, and 22 is a horizontal Output signal of directional color signal extraction filter 19
Compensation delay circuit for inputting 106, 23 for image correlation judging circuit 18
Output signal 110 of the compensation delay circuit 20,21,22 output signal 1
A switch circuit for selecting any one of 05, 107, and 109, 24 is an output terminal of the switch circuit 23, and 25 is an output signal 113 by subtracting the output signal 112 of the compensation delay circuit 15 and the output signal 114 of the amplitude limit circuit 27. The subtraction circuit, 26 is an output terminal of the subtraction circuit 25.

Further, 27 is a swing limit circuit for inputting the output signal 111 of the switch circuit 23.

FIG. 6 shows the internal structure of the image correlation judgment circuit 18 shown in FIG. In the figure, 27 is a horizontal color signal decorrelation energy extraction circuit, 28 is a horizontal luminance signal decorrelation energy extraction circuit, 29 is a vertical color signal decorrelation energy extraction circuit, and 30 is a vertical luminance signal decorrelation energy extraction circuit. , 31 to 38, 43, and 44 are multiplication circuits, 45 and 46 are comparison circuits, and 47 is a determination circuit.

Next, the operation of the above embodiment will be described. When the composite color television signal of the NTSC system is given through the input terminal 11, the A / D converter 12 samples this composite color television signal at the sampling frequency f _s = 4f _sc .

The sampled composite color television signal is given to the first 1-line delay circuit 13 and further passed through the second 1-line delay circuit 14 to obtain a sample value at a certain sample point of interest and the sample point of interest. On the screen, 1 line, 1
Sample values at three sample points below the line are simultaneously extracted.

That is, when the composite color television signal (sample value) S (m, n) at the position of coordinates (m, n) appears at the output of the first 1-line delay circuit 13, the second 1-line delay circuit
At the output of 14, the signal S (m, n-1) appears and the A / D converter
The signal S (m, n + 1) appears at the output of 12 (see FIG. 2). A luminance signal / color signal separation filter is constructed based on the sample values of the sample points over these three lines on the screen.

The sample values extracted by the first and second one-line delay circuits 13 and 14 are the vertical color signal extraction filter 16, the horizontal direction signal extraction filter 19, the horizontal and vertical direction color signal extraction filter 17, and the image correlation determination circuit. Given to 18:

That is, the vertical color signal extraction filter 16, the horizontal vertical color signal extraction filter 17, and the image correlation determination circuit 18 are input to the output signal 101 of the A / D converter 12 and the output of the first 1-line delay circuit 13. The signal 102 and the output signal 103 of the second 1-line delay circuit 14 are provided respectively. Further, the output signal 102 of the first 1-line delay circuit 13 is given to the horizontal color signal extraction filter 19.

At this time, for example, the vertical direction color signal extraction filter 16 is expressed as C _v (z) = (− 1/4) (1-Z ^−L ) ² when expressed by using a transfer function, and also in the horizontal direction. The color signal extraction filter 19 is expressed as C _h (z) = (− 1/4) (1-Z ⁻² ) ² and the horizontal / vertical color extraction filter 17 is expressed as C _hv (z) = ( -1/4) (1-Z ^-2 ) ² · (-1/4) (1-Z
^-L ) ² is a filter.

The output signal 104 of the vertical color signal extraction filter 16 is the output signal 105 of the compensation delay circuit 20, and the output signal 106 of the horizontal color signal extraction filter 19 is the output signal 1 of the compensation delay circuit 22.
As 07, the output signal 108 of the horizontal / vertical direction color signal extraction filter 17 is given to the switch circuit 23 as the output signal 109 of the compensation delay circuit 21.

Here, the operation of determining which of the color output signals of the vertical color signal extraction filter 16, the horizontal color signal extraction filter 19 and the horizontal and vertical color signal extraction filter 17 is selected will be described.

With respect to the sample point of interest, the correlation between the vertical and horizontal images is detected, and when the correlation is particularly strong in the vertical direction, the output signal 105 of the compensation delay circuit 20 based on the output signal 104 of the vertical color signal extraction filter 16 is selected. When the correlation is particularly strong in the horizontal direction, the output signal 107 of the compensation delay circuit 22 based on the output signal 106 of the horizontal color signal extraction filter 19 is selected, and in other cases, the output signal of the horizontal and vertical direction color signal extraction filter 17 is selected. The switch circuit 23 is switched so as to select the output signal 109 of the compensation delay circuit 21 based on 108.

The image correlation determination circuit 18 detects the image correlation and controls the switch circuit 23. In this image correlation determination circuit 18, the switch circuit is controlled by the following operations.

Let DCH (z) be the horizontal color signal decorrelation energy,
Let DYH (z) be the horizontal luminance signal decorrelation energy,
Let the vertical color signal decorrelation energy be DCV (z) and the vertical luminance signal decorrelation energy be DYV (z).

DCH (Z) = | 1−Z ⁻⁴ | DYH (Z) = max (| (1/4) ・ (1 + Z ^−L ) ²・ (1-
Z) ^-2 |, ｜ (1/4) ・ (1 + Z ^-L ) ²・ (Z ^-2 -Z) |) DCV (Z) = | (1-Z ^-2 ) ²・ (1 + Z ^-2L ) | DYV (Z) = max (| (1/4) ・ (1 + Z ^-2 ) ²・ (1-
Z- ^L ) | | (1/4) ・ (1 + Z ^-2 ) ²・ (Z- ^L- Z) |) At this time, the first horizontal correlation energy is DH1 and the second horizontal correlation energy is DH2, the first vertical decorrelation energy is DV1, and the second vertical decorrelation energy is DV2.

DH1 = max (K1 · DCH, K2 · DYH) DH2 = max (K9 · DCH, K10 · DYH) DV1 = max (K3 · DCV, K4 · DYV) DV2 = max (K7 · DCV, K8 · DYV) At this time When DV1 ≧ K5 · DH2, the comparison circuit 46 of the image correlation determination circuit 18 determines that there is a correlation in the horizontal direction and no correlation in the vertical direction, and sends a signal “1” to the determination circuit 47. When DV1 <K5 · DH2, it is determined that there is no correlation in the horizontal direction, and a signal “0” is sent to the determination circuit 47.

On the other hand, when DH1 ≧ K6 · DV2, the comparison circuit 45 of the image correlation determination circuit 18 determines that there is a correlation in the vertical direction and no correlation in the horizontal direction, and sends a signal “1” to the determination circuit 47. When DH1 <K6 · DV2, it is determined that there is no correlation in the vertical direction, and a signal “0” is sent to the determination circuit 47.

The determination circuit 47 controls the switch circuit 23 as follows according to the result of the above correlation detection. That is, the determination circuit 47
Table 1 shows the relationship between the input and output.

At this time, the switch circuit 23 outputs a first output signal (which is output from a first AND circuit (not shown) in the determination circuit 47) and a second output signal (this is a second output signal (not shown) in the determination circuit 47). Output from the AND circuit) is "0", the output signal 107 of the compensation delay circuit 22 is allowed to flow.

When the first output signal is "1" and the second output signal is "0", the output signal 105 of the compensation delay circuit 20 is allowed to flow.

When the first output signal is "0" and the second output signal is "1", the output signal 109 of the compensation delay circuit 21 is made to flow.

Therefore, in the embodiment of FIG. 1, the filter characteristic C (z) for color signal extraction is switched as follows depending on the presence or absence of correlation.

With horizontal correlation, C (z) = C _h (z) Without horizontal correlation, with vertical correlation C (z) = C _v (z) Without horizontal correlation, vertical correlation, C (z) = C _hv (z) From the above description of operation, it is understood that the color signal is separated from the TV signal, and the leakage of the luminance signal and the color signal into the mutual channels can be reduced. In this circuit, if a luminance signal is input to the input terminal 11, the output signal 111 of the switch circuit 23 becomes a noise component in the chrominance signal band, and a compensation delay is applied to this signal 111 by limiting the amplitude so that only the noise component passes. Circuit 15
The noise of the luminance signal can be reduced by subtracting the luminance signal from the output signal 112. Moreover, when a signal having no correlation in the vertical direction of the screen, for example, a screen in which the upper half of the screen is white and the lower half is black is input, the horizontal color signal extraction filter 19 is selected. Therefore, the noise removal operation is performed, and no signal dripping in the vertical direction occurs.

Further, in this embodiment, since the vertical filter 16 selected when a signal having a strong correlation in the vertical direction constitutes a comb filter (see FIG. 3) of signals for three lines, 1/2 of the luminance signal is included. The crosstalk component of the color signal can be greatly suppressed even when the color signal component serving as the offset frequency leaks.

Further, the circuit of this embodiment is a color VTR using a so-called low-frequency conversion carrier color signal system as a color signal processing system called home or industrial, and is standardized by, for example, the Electronic Opportunity Industry Association and referred to as a unified I type. VTR color T
A VTR using a V signal processing method, that is, a method in which a luminance signal is FM-modulated, a carrier color signal is converted to a low frequency, and both are added and recorded, or a signal processing method that is substantially equivalent to the following points. It is possible to obtain a remarkable noise improving effect by applying

That is, the frequency fs of the carrier color signal converted into the low frequency band in the unified type I is about 767 KHz, which is 1/4 offset with respect to the horizontal scanning frequency of the TV signal, that is, fs = (2n
_{-1) f H / 4 (f} H is the horizontal scanning frequency, n represents are chosen positive integer). An intermodulation signal of a signal generated by an odd-order distortion of the transmission system by transmitting a transmission system composed of a VTR magnetic tape and an electromagnetic conversion system between the carrier color signal and the FM modulated luminance signal. Ingredient is FM
The main component is fm ± 2fs with respect to the carrier frequency fm. fm ± 2fs is demodulated as a signal having a frequency of 2fs by an FM signal demodulation circuit. Here, since 2fs is 1/4 offset with respect to f _H , the frequency of 1/2 offset, that is, 2fs =
(2n-1) f _H / 2, and 2fs included in this luminance signal
Since the intermodulation component having the frequency of 1/2 has a 1/2 offset, it can be easily removed by the circuit of this embodiment.

Further, in a recording method using means for FM-modulating and recording a TV signal on a recording medium, as a means for improving the recording density, the FM modulation frequency is (2n-1) f between adjacent signal tracks on the recording medium. _The recording is performed with a shift of _H / 2 (f _H : horizontal scanning frequency, n: positive integer), so that the signals leaked from the adjacent tracks at the time of reproduction and reproduced are inverted in phase between adjacent horizontal sections. A method for visually reducing the leaked component on the TV screen by seeing, that is, JP-A-51-29111 or JP-A-52
If the signal processing method of the present embodiment is used in the reproduction system signal processing circuit of the recording / reproducing apparatus using the method described in Japanese Patent Laid-Open No. 105729, the so-called FM carrier interleave method, the effect of the method can be further enhanced. . That is, as described above, the leakage components from the adjacent tracks have their phases inverted from each other between the adjacent horizontal sections. That is, since the offset is 1/2, it can be effectively removed by the circuit of this embodiment.

〔The invention's effect〕

As described above, the television signal noise elimination circuit according to the present invention detects the correlation of the TV signal, adaptively switches the filter, and limits the output of the filter so that the output is subtracted from the original signal. With this configuration, it is possible to reduce noise without causing vertical sag of the luminance signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a noise elimination circuit for television signals according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing an array of sampled signals, and FIG. 3 is 3 lines. Frequency characteristic diagram of the comb filter, FIGS. 4 and 5 are circuit block diagrams of the conventional example and a frequency characteristic diagram for explaining the operation thereof, and FIG. 6 is an internal configuration of the image correlation determination circuit of FIG. FIG. In the figure, 12 is an A / D converter, 13 and 14 are 1-line delay circuits, 16 is a vertical color signal extraction filter, 17 is a horizontal vertical color signal extraction filter, 18 is an image correlation determination circuit, and 19 is a horizontal direction. Color signal extraction filters, 15, 20, 21, and 22 are compensation delay circuits, 23 is a switch circuit, 25 is a subtraction circuit, and 27 is a limiter circuit. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A target sampling point for separating a luminance signal and a chrominance signal by delaying a television signal sampled at a predetermined frequency synchronized with a horizontal scanning frequency, and a target sampling point on the screen around the target sampling point. A plurality of one-line delay means for simultaneously obtaining sample values of a plurality of reference sample points; and at least a sample value of the sample point of interest is input to extract a frequency component corresponding to a component of a horizontal color subcarrier. A horizontal color signal extraction filter that obtains one color signal, and sample values of the sample point of interest and a predetermined reference sample point are input, and at least a frequency component corresponding to a component of a color subcarrier in the vertical direction is extracted to obtain a first color signal. A vertical color signal extraction filter for obtaining a second color signal, and a horizontal and vertical direction color signal extraction for obtaining a third color signal by extracting a frequency component corresponding to a color subcarrier component in both the vertical and horizontal directions. Filter, and the sample values of the sample point of interest and a predetermined reference sample point as input, detect the horizontal and vertical decorrelation energies, and determine the first, second, third according to the magnitude of the decorrelation energy. An image correlation judging circuit for outputting a signal for switching the filter, a means for switching and outputting the output sample values of the first, second, and third filters to limit the amplitude of the sample value. And a means for removing or reducing a noise component contained in the input television signal by the method.