JPS60154780A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To improve S/N of a video signal and sharpness of a picture by functioning a circuit as an S/N improving circuit with respect to a signal of a picture part which has either no upper/lower contour of the picture or a weak signal and as a picture sharpness improving circuit with respect to a signal whose picture has a strong contour. CONSTITUTION:The level of a limiter circuit 5 is set to the level equivalent to the noise level of a signal inputted into a circuit 5 from a comb-shaped filter 4 for extracting contour signals. An input signal of the circuit 5 fails to reach a limiter level at a part where no contour in an upper/lower direction is on the picture and passes through the circuit 5 as it is, thereby functioning as an S/N improving circuit. At the part where the upper/lower direction contour is on the picture, an amplitude of the input signal of the circuit 5 is large enough to exceed the limiter level, blocks the passage of the circuit 5, and functions as a sharpness improving circuit, thereby accomplishing sharpness improvement less in blur or less in S/N deterioration.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a video signal processing circuit, and in particular, to a video signal processing circuit suitable for improving the S/N of a video signal and improving the sharpness of an image using vertical correlation of an image. Related to signal processing circuits.

[Background of the invention]

There is a so-called comb filter that utilizes the line correlation of image parts as a means for improving the S/N of a video signal and improving the sharpness of an image. Figure 1 shows a comb filter that adds and outputs the signals before and after a 1-line delay line that delays the signal by 1 horizontal scanning time, and signals with line correlation are doubled,
Random noise is multiplied by , so the S/N ratio becomes 6 times (
3dB) is an improved S/N improvement circuit. However, since this circuit adds the signal of one line before, it naturally has the disadvantage that the vertical interval of the image becomes blurred. A comb filter that adds an appropriate amount of the difference between signals before and after a line to the original signal improves image sharpness by emphasizing signals that have no line correlation (signals from parts of the image that are spaced in the vertical direction) However, this circuit has the drawback of emphasizing random noise in a flat image portion with no annular spacing in the vertical direction, thereby worsening the S/N ratio.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-described drawbacks of the prior art and to provide an S/N improvement circuit with less blurring of image intervals and an image sharpness improvement circuit with less deterioration of S/N.

[Summary of the invention]

In order to achieve the above object, the first aspect of the present invention is to obtain an output signal of a comb filter for extracting a ring interval signal, which extracts an upper and lower ring interval of an image by subtracting signals before and after a line delay line, and a comb filter for extracting a ring interval signal. By adding or subtracting an appropriate amount of the output signal from the original signal with the signal obtained through a limiter circuit or a base clip circuit that blocks the passage of small amplitude signals, it is possible to eliminate the image parts with no or weak upper and lower distances. The circuit functions as an S/N improvement circuit for signals, and functions as an image sharpness improvement circuit for signals in image portions with strong ring intervals.

The second point is to make the limiter level or clip level of the limiter circuit or base clip circuit variable, and to adjust the limiter level or clip level of the limiter circuit or base clip circuit, and to adjust the limiter level or clip level of the limiter circuit or base clip circuit, and to adjust the limiter level or clip level of the limiter circuit or base clip circuit, and to adjust the limiter level or clip level of the limiter circuit or base clip circuit, and to adjust the limiter level or clip level of the above-mentioned limiter circuit or base clip circuit. This can be automatically controlled so that it is large when the gain is high and small when the gain is low, or it can be controlled by the output in of a circuit that detects the amount of noise in the video signal to be processed.

The third point is that the mixing ratio at which the output signal of the comb filter and the signal obtained through the limiter circuit or the base clip circuit are mixed into the original signal is controlled in conjunction with the AGC or in the signal to be processed. It is controlled by the output signal of a circuit that detects the amount of noise.

[Embodiments of the invention]

The present invention will be explained in detail below. Figure 3 shows the first embodiment of the present invention.
1 is an input terminal for a video signal to be processed, 2 is an output terminal, 4 is a ring interval signal extraction type (diamond-shaped filter) for extracting the upper and lower ring intervals of an image, and 5 is a limiter circuit or a small amplitude signal 6 and 7 are coefficient circuits that determine the mixing ratio of No. 1 h, and 8 is a mixing circuit.A specific circuit of the ring-shaped filter is shown in Figure 4. In the case of the circuit shown, the operation will be explained in the case of a limiter circuit 5 having the characteristics shown in FIG.
(+) The noise level shall be set approximately equal to or slightly higher than the noise level in the signal input to the miter circuit. The input signal is S, the signal after one line delay is Sd, the output signal is S
Display as O. The input signal of the limiter circuit 5 is (S-8
d), and in the part where there is no vertical ring interval in the image, (
Since S - Sd') does not reach the limiter level and passes through the limiter circuit as it is, the output signal So at this time is expressed by the following equation.

It will be done.

So= (1+ (α→−β)Is−(α+β) Sd
(1) Here, if we set the condition that the coefficients of S and Sd are equal, that is, α + β = −1/2 (2), this means that the signals before and after the 1-line delay line are added without equivalence, It functions as an S/N improving circuit equivalent to the circuit shown in FIG. 1.

Next, in the part where the image has a vertical ring interval, (S-8
Since the amplitude of the limiter circuit input signal represented by d) is large enough to exceed the limiter level, passage through the limiter circuit is blocked, and the output signal So is represented by the following equation.

5o=S+a (S-3d) (3)(S-8d)
Since the signal represented by is a signal representing the ring distance in the vertical direction of the screen, by setting α to a positive value, the output signal S
o is a ring-spacing emphasized signal to which the ring-spacing signal is added, and this circuit functions as an acuity improvement circuit. Specific example numerical values for α and β are α=+ and β=−1.

As a result, an image signal can be obtained in which the S/N ratio is improved in a portion of the image where there is no upper or lower ring gap, and the sharpness is improved in a portion where there is a ring gap. Also, as a special example of α and β, α−0, β
There are = -1/2 combinations. In this case, the portion without the ring gap acts as an S/N improvement circuit, and the portion with the ring gap allows the signal to pass through. As a result, an S/N improving circuit with less sharpness deterioration can be obtained. As yet another example of a combination of α and β, there is a method of setting the values within the range defined by the formula (4).

In this case, the S/N improvement effect of the part without an annular interval is the above-mentioned (
Although it is lower than when setting the conditions of formula 2), the deterioration of minute changes (details) within the flat portion of the image is reduced accordingly.

Next, the circuit block indicated by 5 in FIG.
The operation of the base clip circuit having the characteristics shown in the figure will be explained. The clip level of the base clip circuit is set to be approximately equal to or slightly higher than the noise level in the signal input to the base clip circuit.

In areas where there is no vertical ring gap in the image, the input signal (S - Sd) of the base clipping circuit does not reach the clipping level and is blocked from passing through the base clipping circuit, so the output signal So at this time is expressed by the following formula: It is expressed as

5o=(1+a) S−a Sd (51where, S
The condition that makes the coefficients of and Sd equal, that is, α= −”
When set to (6), the signals before and after the one-line delay line are added without equivalence, and the circuit shown in FIG. 1 acts as an equivalent S/N improvement circuit.

Next, in the part where the image has a vertical ring interval, (S-8
Since the amplitude of the base clip circuit input signal represented by d) exceeds the clip level and passes through the base clip circuit, the output signal So is expressed by the following equation.

So = S + (α+β) (S - Sd) (
The signal represented by 71 (S-8d) is a signal representing the ring distance in the vertical direction of the screen, so it satisfies equation (8).
β) > O(8) When α and β are determined in 5, the output signal So becomes an enhanced signal by adding the intercircular signal, and this circuit acts as a sharpness improvement circuit. Examples of specific numerical settings for α and β are:
α=−±, β=1. This combination performs a circuit operation completely equivalent to the circuit operation obtained by the combination of .alpha.=fragrance and .beta.=-1 in the case of using the limiter circuit described above. This is because limiter circuits and base clip circuits have a complementary relationship in which the characteristics obtained by subtracting the output signal of one circuit from the input signal are equivalent to the characteristics of the other circuit. Of course.

Therefore, as in the above description, an S/N improvement effect can be obtained in a portion without an image ring interval, and an acuity improvement effect can be obtained in a portion with an image ring gap.

Next, a second embodiment of the present invention will be explained using FIG. 7. In this embodiment, the image interval signal extraction comb filter 4 consists of two line delay lines. The input signal is applied to terminal 1, but the correspondence with the first embodiment is noted (for easier understanding, terminal 1' is considered to be a virtual input terminal, and the signal at that point is expressed as S). Then, it is assumed that the signal Ig, which is one line time ahead of the signal at terminal 1', is generated at terminal 1, and this is denoted by Sa.

Therefore, the output signal of the ring interval signal extraction type comb filter 4 in this embodiment is S'2 (Sa + sr+
). This is an annular signal that occurs oddly symmetrically in the annular region in the vertical direction. Distal signal is limiter 17 times ¥65
Doesn't reach Mita level ii! For the jl image ah, the output signal So is expressed by the following equation.

5o==(1+((X+β)) S −4−(a +
/S' ) (Sa+5d) (9) Here, S and (Sa
If the coefficient ratio of 10Sd) is set to 2-1, that is, (α+β) = -4(10), then SO = +S + + (Sa 10sa) (9i(4
), and since it is a signal that is a mixture of a signal that is one line ahead of time and a signal that is delayed, the random noise is
f'÷] i' = 0.61 times (= -4,3dB) in V for the original signal
reduced to

Next, in a portion of the image where there is an annular interval in the vertical direction, the amplitude of the annular interval signal exceeds the limiter level of the +) miter circuit and passage through the limiter circuit is blocked, so the output signal So is expressed by the following equation.

So = S + α [S , 2 (Sa + Sd
) l ("S(S 2 (Sa + Sa) Since the signal represented by the month is a ring interval signal, by setting α to a positive value, a video signal with emphasis on the ring interval can be obtained. If the embodiment is compared to the first embodiment, the S/N reshaping effect is large and the ring gap is emphasized with odd symmetry (print and overshoot). In this embodiment as well, the circuit block 5 is replaced with a base τ buffer circuit, and the equation (10) is replaced with the equation (4).
) can be changed as in the case of the first embodiment.

Next, a third embodiment of the present invention will be described using FIG. 8. Image interval extraction type comb 2 filter 4 in this embodiment
is a feedback 31<L3 filter that feeds back to the input with the feedback rate being the difference between (@+i) before and after the line delay line.Then, the transfer function Gk of this feedback comb filter is
is expressed by the following formula.

Here, T is the delay time of one line delay line.

The frequency function of the absolute value IGkl of Gk is illustrated in FIG. 9(A), taking as an example the case where I=1. In the figure, fH is the horizontal scanning repetition frequency and is equal to the reciprocal of the delay time (T) of one line delay line. Gk has a response of zero at frequencies that are integral multiples of fH. This means that the video signal passed through this (diamond-shaped filter) contains only the interval signal components in the vertical direction of the image. In the part where the th image has no vertical annular interval, the amplitude of the output signal of the image annular interval extracting comb filter is small, and the IJ of the limiter circuit 5
Since it passes through this without reaching the terminating level, is this between the transmission from terminal 1 to terminal 2? Gp is expressed by the following formula.

Here, by setting (α+β) = K (14), (
13) The formula becomes. Moreover, if (α+β)=is set to 10+(15), then the following is obtained. The absolute frequency function of Gp is 1m1Gpl = 1
An example is shown in FIG. 9 (b). It has a peak at a frequency that is an integral multiple of fn, and reaches a minimum at a frequency that is shifted by yfn from the integral multiple frequency. Since the frequency spectrum of the video signal in the vertically discontinuous part of the image concentrates around an integer multiple of fH, there is little image deterioration caused by passing it through this circuit, and noise in the frequency domain shifted by 4 fH is minimized. Only the oppressed.

S/N is improved. Note that the values of K and (α+β) are not limited to the conditions of formulas (141 and (151), but can take any value in the vicinity thereof.

Next, in a part where the image has a vertical ring gap, the output signal of the image ring gap extraction comb filter has a large amplitude and is blocked from passing through the limiter circuit, so Gp at this time is calculated by the following equation. Is displayed.

holds true, and at this time Gp is − as shown in FIG. 9(C)K.
The frequency region shifted by jfH exhibits a peaked characteristic, and this circuit acts as an image interval enhancement circuit.

As described above, in this embodiment, a circuit is obtained which functions as an S/N improvement circuit in areas where there is no upper and lower ring spacing in the image, and functions as an acuity improvement circuit in areas where there is a ring gap. The feature of this embodiment is that there is a degree of freedom in setting the maximum value of the S/N improvement effect by setting the feedback rate, and a greater effect than the previous embodiments can be obtained.

In addition, in this example as well, the above-mentioned 8I! As in the case of the first embodiment, it is possible to configure the circuit block 5 by using a base clip circuit instead of the limiter circuit, but detailed explanation will be omitted.

Next, a fourth embodiment of the present invention will be described using FIG. 10. FIG. 10 is a circuit diagram of an image interval extraction type comb filter used in this embodiment.

The difference from that used in the third embodiment (FIG. 8) is the injection point of the feedback signal.

The transfer function from terminals 41 to 42 of this circuit is expressed by the following equation.

1-4-j scream Gk=-”] -ni' g-j” (js) (1B)
Comparing the equation with equation (12) of the transfer function of the comb filter of the third embodiment, when K=T (191) is set, the transfer function of the comb filter of the third embodiment is It can be seen that a transfer function equivalent to (1+K) times (=7 times) is obtained.The frequency function of 1Gkl is
The case of =+ is shown in FIG. 11 as an example. In this way, by the circuit of FIG. 10, K/K in the case of the third embodiment
'You will get twice as much intercircular signal.

In this embodiment using this, by setting α and β in the third embodiment to α and β which are multiplied by , the operation and effect are completely the same as in the third embodiment. can get.

Next, a fifth embodiment of the present invention will be described using FIG. 12. In this embodiment, 9 is a variable gain circuit, 10 is a control circuit for controlling the gain of the variable gain circuit, and the others are the same as in the first embodiment, but 5 is a variable gain circuit with a variable limiter level or clip level. The feature of 6.7 is that it is a limiter circuit or a base clip circuit, and that the coefficients of α and β are variable under the control of the control circuit 100. The variable gain circuit 9 is normally an AGC (Automatic).
3ain Contro! ), which serves to increase the gain and maintain an appropriate output signal level when the input signal size is insufficient. However, when the input signal decreases, the S/N usually deteriorates, and in such a case, it is recommended to strengthen the S/N improvement effect of the present invention and weaken the sharpness improvement effect. Effective. In this embodiment, first, the limiter level (or clip level) of the limiter circuit (or base clip circuit) is increased in conjunction with the gain increase of the variable gain circuit 9. Since it acts as an S/N improvement circuit in the part where the interdiaphragm signal does not reach the limiter level (or clip level), increasing the limiter level expands the range in which it acts as an S/N improvement circuit, increasing the S/N improvement effect. do. Second, α
and the coefficient of β in conjunction with the increase in gain of the variable gain circuit.
Control is performed to strengthen N improvement and weaken sharpness improvement. In the circuit format of the first embodiment using a limiter circuit,
1α1 is decreased and β is controlled to approach −1.

According to the implementation of Book 5, the degree of S/N improvement and sharpness improvement can be optimally controlled depending on when the S/N of the input signal is good and bad. Mutually contradictory side effects can be suppressed to a minimum, and a good image body without deterioration in image quality can be obtained.

Next, a sixth embodiment of the present invention will be described using FIG. 13. In this embodiment, 10 is the limiter level (or clip level) of the limiter circuit (or base clip circuit)
and a control circuit for controlling coefficients α and β of the coefficient circuit, 11
is a noise amount detection circuit that detects the amount of noise in an input signal.

The rest is the same as the first embodiment. Detects the amount of noise in the input signal, and adjusts the level (crimp level) and α, β according to the detected signal.
control. When the amount of noise is large, the limiter level and α and β are controlled in the same way as when the variable gain circuit in the fifth embodiment has a large original gain, and an appropriate amount of S/
N improvement and sharpness improvement are performed. Noise detection circuit 11
One example is to extract the flat part of the horizontal blanking or vertical blanking of the input video signal through a gate circuit, amplify the amount of noise contained therein, and then detect it. This is the way to obtain.Also,
Another example is when the present invention is implemented in a television camera, there is a method of extracting a no-signal part of a signal waveform called an optical blank, which is usually used as a reference for clamping, and detecting the amount of noise superimposed thereon. be. According to this embodiment, even when the system in which the present invention is implemented does not include an AGC circuit as in the fifth embodiment, the S/
The effects of N improvement and sharpness improvement can be automatically set to optimal amounts.

Therefore, the reception signal of TV broadcasting and the reproduction of VTR 4
It is effective even when applied to signals such as No. g where the amount of noise depends heavily on the signal generator side.

〔Effect of the invention〕

As explained above, according to the present invention, the circuit functions as an S/N improvement circuit in areas where there is no image annular interval, and stops the S/N improvement operation or acts as an acuity improvement circuit in areas where there is an image interval. As a result, S/N improvement with less blurring of the ring interval and improvement in sharpness with less S/N deterioration can be achieved. Also,
The above effects are further enhanced because the transition point and improvement amount of the above two effects are controlled in conjunction with the AGC of the system or in response to the negative noise in the input signal.

[Brief explanation of drawings]

FIG. 1 shows an example of a conventional S/N improvement circuit. FIG. 2 is a block diagram showing an example of a conventional sharpness improvement circuit, FIG. 3 is a block diagram showing a first embodiment of the present invention, and FIG. 4 is a block diagram showing a circuit used in this embodiment. Block diagram showing an example of an interval extraction comb filter, Nos. 5 and 6
The figure shows a limiter circuit. Characteristic diagrams showing examples of characteristics of base clip circuits,
FIG. 7 is a block diagram showing a second embodiment of the invention, FIG. 8 is a block diagram showing a third embodiment of the invention, and FIG. 9 is a block diagram showing a third embodiment of the invention.
The figure is a characteristic diagram for explaining the operation of the third embodiment.
The figures are block diagrams showing a fourth embodiment of the present invention, and an eleventh embodiment.
The figure is a characteristic diagram for explaining the operation of the fourth embodiment.
The figures are block diagrams showing the fifth embodiment of the present invention, and the thirteenth embodiment.
The figure is a block diagram showing a sixth embodiment of the present invention. 1 - Input terminal 2... Output terminal 3... 1 line delay line 4... Image interval extraction type comb filter 5 - Limiter circuit or base clip circuit 6.7 - Coefficient circuit 8 - Mixing circuit 9, - Variable Gain circuit 10.10'...control circuit 11
・・Noise amount detection circuit Kasusha λ・2 figure 3 items, t g 4 off (! l Fang 3 figure Fang 10 figure O + 2 figure O Fang 13 figure, II

Claims (1)

[Claims] 1. A comb-shaped filter for extracting the upper and lower intervals of an image by using a video signal as an input signal and extracting the upper and lower intervals of the image by subtracting signals before and after a line delay line; A limiter circuit with a variable limiter level or a base clip circuit with a variable clip level that uses the output signal of the input signal as an input signal;
A video signal processing circuit characterized by comprising a mixing circuit that adds or subtracts an appropriate amount of the output signal of the interval extraction type comb filter and the output signal of the limiter circuit or base clip circuit to the original video signal and mixes the output signal. 2. The limiter circuit whose limiter level is variable or the base clip circuit whose clip level is variable is characterized in that its limiter level or clip level is controlled in conjunction with an AGC circuit of a system including the video signal processing circuit. A video signal processing circuit according to claim 1. 3. The limiter circuit with a variable limiter level or the base clip circuit with a variable clip level has a limiter level or clip level that is horizontal blanking in a video signal to be processed. 2. The video signal processing circuit according to claim 1, wherein the video signal processing circuit is controlled by a control signal obtained by detecting noise superimposed on a waveform portion of at least one of vertical blanking and optical black. 4. Percentage In the video signal processing circuit according to any one of claims 1 to 3, the mixing ratio of the mixing circuit is determined by horizontal blanking, vertical blanking, or optical black in the video signal to be processed. A video signal processing circuit characterized in that it is controlled by a control signal obtained by detecting noise superimposed on at least one waveform portion of the circuit. 5. In the video signal processing circuit according to any one of claims 1 to 3, the mixing ratio of the mixing circuit is controlled in conjunction with an AGC circuit of a system including the video signal processing circuit. Video signal processing circuit 0