JP2739959B2 - Video signal noise reduction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a video signal noise reduction device.

(Prior Art) A circuit for reducing noise included in a television video signal by digital processing has been developed. This noise reduction circuit detects noise using the correlation between video signals between fields or between frames and the decorrelation due to the presence of noise, and subtracts a signal corresponding to a noise component from the original signal. To reduce noise.

FIG. 7 is a block diagram showing a conventional noise reduction device. The video signal from the input terminal 1 is guided to a luminance / color separation circuit (hereinafter referred to as a Y / C separation circuit) 2 for separating a luminance signal and a chrominance signal. The luminance signal Y separated by the Y / C separation circuit 2 is supplied to an analog / digital (A / D) converter 3 and converted into a digital luminance signal. The color signal C separated by the Y / C separation circuit 2 is input to the color decoder 4 and
The signal is decoded into a color difference signal, that is, a (RY) signal and a (BY) signal. The (RY) signal and the (BY) signal are:
The signal is input to the color multiplexer 5, alternately selected and converted into a time-series color signal, and then input to the A / D converter 6.

The Y / C multiplexer 7 converts the digital luminance signal from the A / D converter 3 and the digital color signal from the A / D converter 6 into M
Select and multiplex at a sample to N sample ratio. M
Is, for example, 10 samples, N is 1 sample, and the (RY) and (BY) components are alternately selected. As a result, a multiplexed signal is obtained from the Y / C multiplexer 7,
It is supplied to the next stage noise elimination circuit.

The noise elimination circuit is composed of a subtractor 8, a field memory 9, and a subtractor.
10, a nonlinear characteristic circuit 11 is provided. When a subtraction process between the output of the field memory 9 and the multiplexed signal is performed, a difference signal indicating the degree of correlation between the fields is obtained from the subtractor 10. When the correlation is strong, the level of the difference signal is low, and when the correlation is weak, the level of the difference signal is high. The non-linear characteristic circuit 11 is constituted by a ROM, for example, and multiplies the difference signal by a coefficient K (0 <K <1) and outputs the result. The noise-removed signal obtained in this way is attenuated and added with the noise signal included in the original multiplexed signal in the subtractor 8 at the field period, and a noise signal having no correlation between fields is attenuated. On the other hand, the still image signal is not attenuated because the correlation between the fields is large, and the S / N of the output is eventually improved. The improvement effect is as follows: S / N improvement degree = 10 log {(1 + K) / (1-K)} (dB). In the characteristics of the nonlinear characteristic circuit 11, when the difference signal is larger than a certain range, the output is zero.This is because when the motion image is input and the inter-field correlation is low, the output becomes zero. This is because the effect of the afterimage is eliminated without performing the addition.

The multiplexed signal whose S / N is improved as described above is input to the Y / C demultiplexer 12, where it is sampled again and separated into a digital luminance signal Y and a chrominance signal C. The digital luminance signal Y is supplied to a digital / analog (hereinafter, referred to as D / A) converter 13 and converted into an analog luminance signal. The digital chrominance signal C is input to a color demultiplexer 14, where it is separated into a (RY) signal and a (BY) signal, each of which is supplied to D / A converters 15, 16 and converted into an analog signal. You. Then, the analog (RY) signal and the (BY) signal are input to the color encoder 17 and become a chroma signal. The chroma signal is mixed in the Y / C mixer 18 with the analog luminance signal. As a result, a color video signal subjected to noise reduction processing can be obtained from the output terminal 19.

The above-described conventional noise reduction apparatus has an advantage in that the noise reduction circuit processes the luminance signal and the chrominance signal as one system signal. If each of the luminance signal and the chrominance signal is performed by using a separate noise reduction circuit, the scale of hardware is large and the cost is high.

However, it has the following disadvantages. Since the noise reduction circuits for the luminance signal and the chrominance signal are shared, the optimum level of noise reduction for each signal cannot be obtained, and the noise reduction characteristics must be compromised. Further, the combination of the noise reduction levels of the luminance signal and the chrominance signal cannot be changed due to the characteristics of the input signal.

(Problems to be Solved by the Invention) As described above, the conventional noise reduction circuit cannot set the noise reduction level of the luminance signal and the chrominance signal to an optimum level suitable for each signal or independently change and set. . For this reason, the noise reduction characteristics are determined by comparing the luminance signal and the color signal.
It can only be improved to a level that can be compromised by looking at S / N.

Therefore, according to the present invention, the noise reduction level of the luminance signal and the chrominance signal can be set to the optimum level for each signal with a small number of additional circuits, and can be set or changed independently for each signal. It is an object of the present invention to provide a video signal noise reduction device.

[Means for Solving the Problems] The present invention uses a digital luminance signal and a digital chrominance signal separated from a video signal to convert a digital chrominance signal into N samples with respect to M digital luminance signals. Means for multiplexing at a ratio of 1 to obtain a multiplexed signal of one system, a multiplexed signal is supplied, a noise reduction unit for reducing noise of the multiplexed signal, and an output multiplexed signal of the noise reduction unit is Means for sampling at a ratio to separate into two signals of a digital luminance signal and a digital chrominance signal, wherein the noise reduction unit performs a first subtraction in which the input multiplexed signal is supplied to one input unit. , A field or frame memory to which the output of the first subtractor is supplied, a second subtractor for obtaining a difference signal between the output of the memory and the input multiplexed signal, and the second subtractor Out of A differential signal circuit that is supplied with a differential signal and is capable of obtaining a plurality of nonlinear characteristic outputs having different nonlinear characteristics according to the differential signal. In response to the timing of input to the subtractor of
A predetermined nonlinear characteristic output predetermined among the plurality of nonlinear characteristic outputs is selected and supplied to the other input section of the first subtractor to adaptively reduce noise according to the content of the input multiplexed signal. And means for performing the above.

(Operation) By the above means, a noise reduction level suitable for each of the luminance signal and the chrominance signal can be given in a time-division manner, and the optimum noise reduction level for each signal can be set independently according to the input characteristics. can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The difference from the conventional noise reduction device shown in FIG. 6 is that the noise reduction circuit to which the multiplexed signal obtained from the Y / C mixer 7 is supplied is a nonlinear circuit to which the difference signal output of the subtracter 10 is supplied. The point is that at least two characteristic circuits are provided, and one of the outputs of the plurality of nonlinear characteristic circuits is selected by a switch and supplied to the subtractor 8. The other parts are the same as those of the apparatus shown in FIG.
The same reference numerals as those in the drawing are attached.

That is, the multiplexed signal from the Y / C mixer 7 is supplied to one input of the subtractor 8 and one input of the subtracter 10. The output of the subtractor 8 is input to the field memory 9. The output of the field memory 9 is supplied to the other input of the subtractor 10. Accordingly, a difference signal of a signal corresponding to each field is obtained from the subtractor 10. The difference signal will indicate the degree of correlation between the fields.
The difference signal is supplied to the nonlinear characteristic circuits 111 and 112. The non-linear characteristic circuit 111 is prepared for, for example, a luminance signal, and the non-linear circuit 112 is prepared for a chrominance signal. The input and output characteristics are optimal for reducing the luminance signal noise and the chrominance signal noise, respectively. It is set to the best characteristics. The difference signal is multiplied by an appropriate coefficient different in each of the nonlinear circuits 111 and 112, and the respective arithmetic outputs are output from the switch 11
3 are supplied to terminals a and b.

Here, the switch 113 is controlled by a switching signal from the timing generator 114. When a luminance signal is input to the subtractor 8, the output of the nonlinear circuit 111 is selected and input to the subtracter 8, and When a color signal is input, the output of the nonlinear circuit 112 is selected and controlled so as to be input to the subtractor 8. The timing generator 114 is synchronized with the multiplexed timing signal in the Y / C mixer 7 and generates a switching signal using, for example, a decoded value of a shift register or a counter output.

FIG. 2 shows an example of a time-series component of the multiplexed signal (FIG. 2A), and a positional relationship between a switching signal (FIG. 2B) and an output of the switch 113 (FIG. 2C). ing. This example
An example is shown in which the sixth sample position of the luminance signal is replaced with sample data of the color signal, and the (RY) and (BY) components are alternately multiplexed at the sample timing for the color signal. I have.

In the above embodiment, there are two types of non-linear circuits 111 and 112. However, different types of non-linear circuits may be prepared so that an appropriate non-linear characteristic can be freely selected. In addition to the above, the non-linear characteristic circuit may be, for example, one having a limiter characteristic.

 FIG. 3 shows a characteristic example of the nonlinear characteristic circuit.

When the input is at a low level, the output OUT = KI (0 <K <1). When the input is at a high level, the output OUT = 0.
Here, when the value of K in the small level range is switched, the degree of improvement in S / N described above changes. The above-described nonlinear characteristic circuits 111 and 112 are set so that the degree of improvement is optimal for each luminance signal and color signal.

As described above, a plurality of non-linear characteristic circuits whose characteristics are set in advance may be prepared.
The data of the ROM may be prepared so that various characteristics can be obtained from M.

In other words, to change or switch the degree of improvement of S / N, there is a method of preparing several ROMs and arbitrarily selecting them. However, if there are many types of switching, the number of bits of the ROM increases. Therefore, a non-linear characteristic circuit which can freely produce a plurality of characteristics by means as shown in FIG. 4 may be used.

In FIG. 4, reference numeral 200 denotes a ROM from which output data having nonlinear characteristics can be read. The type of the nonlinear characteristic may be one type, and may be less than the type switched by the switching signal.

The output of the ROM 200 is supplied to the multiplier 201. Multiplier 201
A plurality of types of multipliers are prepared. In the illustrated example, LY (for a luminance signal) (0 ≦ LY ≦ 1) and Lc (for a color signal) (0 ≦ Lc ≦ 1). According to such a nonlinear characteristic circuit, the overall input / output characteristics can be changed by switching the multiplier. The multiplier LY is selected at the timing when the luminance signal is input to the subtractor 8, and the multiplier Lc is selected when the chrominance signal is input to the subtracter 8, so that an optimal noise removal signal can be adaptively given to each signal. it can. In this case, it is natural that the values of the multipliers LY and Lc are selected so as to make the adverse effect such as the afterimage unnoticeable while utilizing the S / N improvement effect.

For example, adopt it for S-VHS type VTR or VHS type VTR
The multiplier can be selected depending on whether the VTR is adopted, or the multiplier can be switched depending on whether the VTR is in the normal reproduction mode or the double-speed reproduction mode.
For example, in the normal playback mode of an S-VHS VTR, LY = 0, Lc = 0.7 at the noise reduction level 1, LY = 0.7, Lc = 0.85 at the noise reduction level 2, and LY = 0.9, Lc at the noise reduction level 3. A combination of coefficients may be set in advance, such as = 0.95, and may be selected according to conditions. In this way, the fifth
Various characteristics can be obtained as shown in the figure.

In the multiplexed signal, the luminance signals (Y1, Y2.
Bits, color signals CR1, CR2 ...) and (CB1, CB2 ...)
In the case of bits, the subtractor 8 processes the input data of the color signal as if two bits of "0" were added to the lower order (see FIG. 6). Then, the amplitude ratios of the luminance signal and the chrominance signal, which are symmetric with respect to the non-linear processing, become the same with respect to the entire dynamic range, and good processing can be obtained. At this time, if information is obtained in the lower digit of the color signal, the output may be truncated.

However, if the bit capacity of the frame memory is configured corresponding to the number of bits of the luminance signal, the lower two bits of the chrominance signal storage part are left inside the memory, and this part may be used effectively. For example, even if the input is 6 bits, if the arithmetic unit and the memory unit handle it with 8 bits, the error of the value of K at the time of small amplitude limited by the resolution of 6 bits can be equivalently reduced. It is possible to eliminate a phenomenon in which the noise reduction is excessively applied and an afterimage remains for a long time, or the noise reduction cannot be obtained.

[Effects of the Invention] As described above, according to the present invention, the noise reduction level of the luminance signal and the chrominance signal can be optimized for each signal by a small number of additional circuits, and It can be set or changed independently for the signal, and the S / N of the output video signal can be further improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a timing chart for explaining an operation example of the circuit of FIG. 1, FIG. 3 is an explanatory diagram of nonlinear characteristics, and FIG. Is a diagram showing another example of the nonlinear characteristic circuit, FIG. 5 is an explanatory diagram of the nonlinear characteristic obtained by the circuit of FIG. 4, and FIG. 6 is shown for explaining an example of data bits in the noise reduction circuit. FIG. 7 is an explanatory view of the configuration of a conventional noise reduction device. 2 ... Y / C separation circuit, 3, 6 ... A / D converter, 4 ... Color decoder, 5 ... Color multiplexer, 7 ... Y / C
Mixer, 8,10 ... Subtractor, 9 ... Field memory, 12
…… Y / C demultiplexer, 13, 15, 16 …… D / A converter,
17 …… Color encoder, 18 …… Y / C mixer, 111,112…
... Non-linear characteristic circuit, 113 ... Switch, 114 ... Timing generator.

Continued on the front page (72) Inventor Seiichi Tanaka 1-9-2 Hara-cho, Fukaya-shi, Saitama Pref. Inside the Toshiba Fukaya Plant (72) Inventor Hisayuki Mihara 1-9-1-2 Harara-cho, Fukaya-shi, Saitama East Shiba Audio Video Engineering Co., Ltd. (72) Inventor Koichi Kurihara 1-9-2 Haracho, Fukaya City, Saitama Prefecture Higashi Shiba Audio Video Engineering Co., Ltd. (56) References JP-A 61-61 158274 (JP, A) JP-A-55-10228 (JP, A) JP-A-63-157574 (JP, A) JP-A-63-90968 (JP, A)

Claims (1)

(57) [Claims] A digital chrominance signal is multiplexed at a ratio of N samples to M samples of a digital luminance signal using a digital luminance signal and a digital chrominance signal separated from a video signal, and a multiplexed signal of one system is formed. Means for obtaining, the multiplexed signal is supplied, a noise reduction unit for reducing noise of the multiplexed signal, and a digital luminance signal and a digital chrominance signal obtained by sampling the output multiplexed signal of the noise reduction unit at the ratio. Means for demultiplexing into two systems of signals, wherein the noise reduction unit is provided with a first subtractor whose input multiplexed signal is supplied to one input unit, and an output of the first subtractor. A field or frame memory to be provided, a second subtractor for obtaining a difference signal between the output of the memory and the input multiplexed signal, and an output difference signal of the second subtractor. Thigh A non-linear characteristic circuit capable of obtaining a plurality of non-linear characteristic outputs having different non-linear characteristics, and a digital luminance signal and a chrominance signal included in the input multiplexed signal are responsive to timings input to the first subtractor. A predetermined non-linear characteristic output selected from the plurality of non-linear characteristic outputs is selected and supplied to the other input of the first subtracter to adaptively generate noise according to the content of the input multiplexed signal. A video signal noise reduction device comprising: means for reducing noise.