JP2737411B2 - Chroma signal separation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chroma signal separation circuit, and more particularly, to NTSC in video equipment such as TV and VTR.
The present invention relates to a chroma signal separation circuit for separating a chroma signal from a composite video signal.

[0002]

2. Description of the Related Art As one method of a conventional chroma signal separation circuit, there is a method of switching the characteristics of a separation filter according to the magnitude relation of the chroma difference between the current line and the preceding and succeeding lines. Hereinafter, description will be made using a specific block diagram.

FIG. 3 is a block diagram of an example of the related art.
First, the input signal 126 passes through the one-line delay circuit 55 and is then input to the one-line delay circuit 56. Input signal 12
The outputs of the 6 and 1 line delay circuits 55, 56 are connected to bandpass filters 57, 58, 59, respectively.
The band-pass filters 57, 58, and 59 are filters having the same band characteristics centered on the color subcarrier frequency (3.58 MHz), and remove signals in a frequency band where no chroma signal exists. The outputs of the band-pass filters 57, 58, and 59 are hereinafter referred to as a rear signal 127, a main signal 128, and a front signal 129, respectively. These signals are also referred to as frequency-separated chroma signals, and are obtained by mixing a luminance component near 3.58 MHz into a chroma signal component.

After the polarity of the post signal 128 is inverted by the coefficient unit 63, the post signal 128 is added to the main signal 128 by the adder 65, and output as a post comb signal 132. Similarly, the polarity of the previous signal 129 is inverted by the coefficient unit 62, then added to the main signal 128 by the adder 64, and output as the previous comb signal 134. Further, the post-comb signal 132 and the pre-comb signal 134 are averaged by the adder 66 and the coefficient unit 67 and output as a 3-line comb signal 133. After comb signal 13
The second and third line comb signals 133 and the previous comb signal 134 have attenuated luminance components and can be regarded as chroma signals. However, which of the post-comb signal 132, the 3-line comb signal 133, and the pre-comb signal 134 is the optimum signal changes depending on the vertical correlation of the video. Therefore, the selectors 74 and 75 select one of these signals 132, 133 and 134 and outputs it as a chroma signal 134. Hereinafter, the selector 74,
The 75 control signal generation part will be described.

The post signal 127 and the main signal 128 are added to the adder 60.
After obtaining the differential signal 130, the absolute value conversion circuit 6
Enter 8 Similarly, the previous signal 129 and the main signal 128 are added by the adder 61 to obtain a previous difference signal 131, which is then input to the absolute value conversion circuit 69. Here, the difference between the outputs of the adders 60 and 61 is due to the property that the polarity of the chroma signal is inverted by one line delay. The output of the absolute value conversion circuit 68 is connected to one input of a comparator 73 and is also connected to one input of a comparator 72 through a coefficient unit 70. Similarly, the output of the absolute value conversion circuit 69 is connected to one input of a comparator 72 and is also connected to one input of a comparator 73 through a coefficient unit 71. As values (K) of the coefficient units 70 and 71, values between 1.0 and 1.5 are usually used. The output of the comparator 72 is connected to the control input of the selector 74, and the output of the comparator 73 is connected to the selector 75.
Is connected to the control input.

Next, the operation will be described. Comparator 70
Operates so that the absolute value of the front differential signal 131 is compared with the value obtained by multiplying the absolute value of the rear differential signal 130 by K, and the selector 74 selects the rear comb signal 132 when the front differential is larger. Similarly, the comparator 73 compares the absolute value of the post-difference signal 130 with the absolute value of the post-difference signal 130 multiplied by K times the absolute value of the pre-differential signal 131. Works to pick.

The above operation is qualitatively described. Basically, a comb signal having a smaller chroma difference between lines is selected, and if the difference signals before and after are at the same level, a 3-line comb signal is selected. I will say. Since the chroma difference between the lines can be regarded as a luminance component, the above description may be re-read as the magnitude comparison of the luminance components.

Next, another example of the prior art will be described with reference to FIG. In response to the input signal 138, the rear comb signal 154, the three-line comb signal 155, and the front comb signal 156
Means for obtaining the difference signal 151 and the difference signal 152 before and after are exactly the same as those in FIG. Hereinafter, selectors 92 and 93
The configuration of the part that obtains the control signal described above will be described.

In an adder 85, a signal obtained by inverting the polarity of the rear signal 139 by the coefficient unit 82 and the front signal 141 are added to obtain a front-back difference signal 153. The rear difference signal 151 and the front and rear difference signal 153 are connected to the same sign detection circuit 90, and the output of the same sign detection circuit 90 is connected to the control input of the selector 92. Further, the front difference signal 152 and the front-back difference signal 153
Is connected to a different code detection circuit 91,
Is connected to the control input of the selector 93.

The operation will be described below. If the sign (+,-polarity) of the rear difference signal 151 and the front and rear difference signal 153 are the same, the same sign detection circuit 90 outputs the rear comb signal 154.
The selector 92 is controlled so as to select. The different sign detection circuit 91 controls the selector 93 to select the previous comb signal 156 when the sign of the difference signal 152 before and after the difference signal 153 is different.

Next, the operation of the two conventional examples described above will be supplementarily described based on the magnitude relationship between the rear signal, the main signal, and the front signal. FIG. 5 shows the correspondence between the magnitude relationship and the type of comb signal selected as the chroma signal. In the circuit of FIG. 3, a comb is taken from the line near the main signal 128, and if both lines have the same difference, a 3-line comb is taken. Further, in the circuit of FIG. 4, if the signal change between the three lines is pulse-shaped (peak-shaped or valley-shaped), the line near the main signal 140 is combed, and if the signal is step-shaped (up-hill, down-hill). I am taking three line combs.

[0012]

In the above-described conventional chroma signal separation circuit, if the signal change between the three lines is step-like, there is a difference between the signal level of the three-line comb and the signal level of the preceding or subsequent comb. This difference increases as the signal levels of the front difference and the rear difference are closer. For this reason, if the coefficient K is close to 1 in the circuit of FIG. 3 described above, the level of the output chroma signal fluctuates due to the fluttering of the switching of the comb signal. As a result, there is a problem that the picture of the finally displayed image becomes unnatural. More specifically,
There is a drawback in that unevenness occurs in the way of cross color and dot disturbance, and the image quality deteriorates more conspicuously than when there is no unevenness. When the coefficient K is selected to be sufficiently larger than 1, the signal change between the three lines is pulse-like. There is a disadvantage that level fluctuation sometimes occurs.

On the other hand, in the circuit shown in FIG. 4, when the step is performed, three lines are always selected, so that there is no problem of switching flutter. However, there is a drawback that dot interference is likely to occur because three lines are selected even when the phase of the video is either the front signal or the rear signal.

[0014]

According to a first aspect of the present invention, there is provided a chroma signal separating circuit for separating a chroma signal from a composite video signal, comprising: a post signal corresponding to an input signal (1); A first adding circuit for adding a main signal corresponding to the input signal (2) obtained by delaying (1) by one line and outputting a post-difference signal;
An input signal (3) obtained by delaying the input signal (2) by one line
And a second addition circuit for adding a previous signal corresponding to the second signal to output a previous difference signal, and a first addition circuit for converting the rear difference signal into an absolute value.
A second absolute value converting circuit for converting the previous differential signal into an absolute value.
, An output signal of the first absolute value circuit, a first coefficient circuit for multiplying the output signal by a coefficient K1 or K2, and an output signal of the second absolute value circuit, K1
Or a second coefficient circuit for multiplying and outputting K2, a different sign detection circuit for detecting whether the sign of the rear difference signal and the sign of the front difference signal are positive or negative, and outputting a different sign discrimination signal; A first comparing circuit for comparing the level of an output signal of the first coefficient circuit with an output signal of the second absolute value circuit; an output signal of the first absolute value circuit; A third comparing circuit for comparing the level of the level with the output signal of the second coefficient circuit, and K1 or K2 as a coefficient in the first and second coefficient circuits controlled by the different sign discrimination signal. A first selection circuit for selecting any one of them, and a second selection circuit for selecting and outputting any one of a predetermined three-line comb signal and a previous comb signal under the control of an output signal of the second comparison circuit. , Controlled by the output signal of the first comparison circuit, Select one of the second output signal and a predetermined after comb signal of the selection circuit configured to include a third selection circuit for outputting as a chroma signal.

According to a second aspect of the present invention, there is provided a chroma signal separating circuit for separating a chroma signal from a composite video signal, the post signal corresponding to the input signal (1) and the input signal (1) being one line. A first addition circuit that adds the main signal corresponding to the delayed input signal (2) and outputs a post-difference signal; an input signal (1) obtained by delaying the main signal and the input signal (2) by one line; A second addition circuit that adds the previous signal corresponding to 3) and outputs a front difference signal, a first absolute value circuit that converts the post difference signal to an absolute value, A second absolute value conversion circuit for converting a value, a sign difference detection circuit for detecting whether the sign of the post-difference signal and the sign of the pre-difference signal are positive or negative, and outputting a sign identification signal; Inverts the polarity of the output signal of the absolute value A first coefficient circuit, the output signal of said first absolute value circuit and a third adding circuit for adding and outputting an output signal of said first coefficient circuit, the third
A positive sign detection circuit for detecting a positive sign of the output signal of the adder circuit and outputting a positive sign discrimination signal; and an output of the first and second absolute value conversion circuits controlled by the positive sign detection signal. A first selection circuit for selecting and outputting any of the signals;
A third absolute value circuit for converting an output signal of the third adder circuit into an absolute value, a second coefficient circuit for multiplying an output signal of the first selection circuit by a coefficient K1, and outputting the result; A third coefficient circuit which multiplies the output signal of the absolute value conversion circuit by a coefficient K2 and outputs the result, and an output signal of the second coefficient circuit and the first selection circuit which are controlled by the different sign discrimination signal. A second selection circuit for selecting and outputting any of the output signals of the circuit; and an output signal of the third absolute value conversion circuit and an output of the third coefficient circuit controlled by the different sign determination signal. A third selection circuit that selects and outputs one of the signals, a comparison circuit that compares the magnitudes of the output signals of the second and third selection circuits, and a predetermined signal controlled by the positive sign determination signal. A fourth selection circuit for selecting and outputting any of the post-comb signal and the pre-comb signal; A fifth selection circuit controlled by an output signal of the comparison circuit to select one of a predetermined three-line comb signal and an output signal of the fourth selection circuit and to output the selected signal as a chroma signal. Be composed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a first embodiment of the present invention.
The rear difference signal 105 and the front difference signal 106 are input to the different sign detection circuit 11, and the output of the different sign detection circuit 11 is connected to the control inputs of the selectors 21 and 22. Post differential signal 10
5 is connected to one input of coefficient units 17 and 18 and a comparator 24 through the absolute value conversion circuit 10. Previous difference signal 1
Reference numeral 06 passes through the absolute value conversion circuit 12 and is connected to one input of coefficient units 19 and 20 and a comparator 23. Coefficient unit 1
After one of the outputs 7 and 18 is selected by the selector 21, the output is input to the comparator 23. After one of the outputs of the coefficient units 19 and 20 is selected by the selector 22, the output of the comparator
Is input to The output of the comparator 23 is connected to the control input of the selector 26, and the output of the comparator 24 is connected to the control input of the selector 25.

Next, the operation will be described. When the signs of the rear difference signal 105 and the front difference signal 106 match,
The output of the different sign detection circuit 11 becomes L, and the selector 21,
Reference numeral 22 selects the L side. Therefore, the comparator 23 outputs the signal obtained by converting the front difference signal 106 into an absolute value and the rear difference signal 10
5 is converted to an absolute value, and a magnitude comparison with a signal multiplied by K1 is performed.
Similarly, the comparator 24 compares the magnitude of the signal obtained by converting the differential signal 105 into an absolute value and the signal obtained by converting the differential signal 106 into an absolute value and multiplied by K1. On the other hand, when the signs of the subsequent difference signal 106 do not match, the output of the different sign detection circuit 11 becomes H, and the selectors 21 and 22 select the H side. As a result, the value of K1 times is changed to K2 times, and the magnitude is compared.

As a result of the comparison by the comparator 23, the post-selection signal 1
07 is output, but if it is smaller by K1 times or K2 times, the selector 26 is set to the H side to select the post-comb signal 109. Similarly, as a result of the comparison by the comparator 24, the preselection signal 1
08 is output. If the value obtained by multiplying K1 or K2 is smaller, the selector 25 is set to the H side to select the previous comb signal 112. If the next comb signal 109 and the previous comb signal 112 are not selected, the three-line comb signal 110 is selected. Thus, the desired chroma signal 113 is output from the selector 26.

Although a value close to 1 is selected as a specific value of K1, a value suitable for a binary number (5/4, 8
9/17/16), the coefficient units 17,1
9 requires less hardware. As a value of K2, a value larger than 1 is selected, but a power of 2 (2,
4, 8,...), The coefficient units 18 and 20 are bit-shifted, and hardware is substantially unnecessary.

FIG. 2 is a block diagram of a second embodiment of the present invention. Hereinafter, portions different from those in FIG. 1 will be described.
The output of the absolute value conversion circuit 37 is connected to the L-side input of the selector 45 and one input of the adder 42. The output of the absolute value conversion circuit 38 is connected to the H-side input of the selector 45 and to the other input of the adder 42 via the coefficient unit 43. The output of the adder 42 is connected to a positive sign detection circuit 44 and an absolute value conversion circuit 47. The output of the positive sign detection circuit 44 is connected to control inputs of selectors 45 and 46. The output of the absolute value conversion circuit 47 is connected to the L side input of the selector 52 and also connected to the H side of the selector 52 via the coefficient unit 49. The output of the selector 45 is connected to the H-side input of the selector 51, and
It is also connected to the L side of the selector 51 via the coefficient unit 48. The outputs of the selectors 51 and 52 are compared in magnitude by a comparator 53, and the output of the comparator 53 is connected to a control input of a selector 54. The output of the selector 46 is connected to the L side of the selector 54, and the three-line comb signal 124 is input to the H side. The rear comb signal 120 is input to the L side of the selector 46, and the front comb signal 121 is input to the H side.

Next, the operation will be described. Signals having absolute values of the rear difference signal 118 and the front difference signal 119 are compared in magnitude by a coefficient unit 43, an adder 42, and a positive sign detection circuit 44, and the smaller one is selected by a selector 45. at the same time,
If the previous difference is small, the selector 46 also outputs the previous comb signal 121,
If the error is small, control is performed so that the post-comb signal 120 is selected. On the other hand, the rear difference signal 118 and the front difference signal 119
Is detected by the different sign detection circuit 36 as to whether the sign is different, and if the sign is the same, the selectors 51 and 52 are selected on the L side, and if the sign is different, the selectors are selected to the H side. As a result, the rear signal 115,
When the changes of the main signal 116 and the front signal 117 are pulse-like, the smaller of the absolute values of the rear difference signal 118 and the front difference signal 119 is multiplied by K1 and the rear difference signal 118
The comparator 53 compares the magnitude of the previous difference signal 119 with a signal obtained by further subtracting the difference. Also, the rear signal 11
5, when the changes of the main signal 116 and the previous signal 117 are stepwise, the smaller of the absolute values of the rear difference signal 118 and the front difference signal 119, the rear difference signal 118 and the front difference signal 11
From 9, a signal obtained by further multiplying the difference by K2 is compared in magnitude by the comparator 53. When the difference between the rear difference signal 118 and the front difference signal 119 is smaller, that is, when the rear difference signal 118 and the front difference signal 119 have substantially the same value, the comparator 53 sets the selector 54 to the H side and sets the three-line comb signal 124 Choose The desired chroma signal 125 is output from the selector 54 in the same manner as in the first embodiment.

In the second embodiment, the coefficients K1 and K2 are set to 2
Can be selected to be a power of one, so that the hardware of the coefficient units 48 and 49 can be made substantially unnecessary. Further, the number of comparators is reduced by one as compared with the first embodiment, so that hardware costs can be reduced.

The first and second embodiments differ in how to select coefficients. When K1 in the second embodiment is selected to be 1/8 or 1/16, the values corresponding to K1 in the first embodiment are 1.12 and 1.06, respectively. Similarly, when K2 of the second embodiment is 1/2, the values corresponding to K2 of the first embodiment are 2 and 3, respectively.

[0024]

As described above, according to the present invention, the coefficient for comparing the difference signals is switched by detecting whether the signal change between the three lines is pulse-like or step-like.
As a result, even if the switching of the comb signal is fluctuated, it is possible to select a coefficient capable of suppressing the level fluctuation, and it is possible to obtain an effect that the picture of the video finally displayed can be made more natural. Specifically, in "scenes where grass and green grass undulates due to strong winds" and "scenes where dense small golden wheat ears are swaying," etc., even if cross color or dot interference occurs, unnaturalness This has the effect of making it less noticeable.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional example.

FIG. 4 is a block diagram showing another embodiment.

FIG. 5 is a diagram showing a correspondence between magnitudes of a rear signal, a main signal, and a front signal in a conventional example, and types of comb signals selected as chroma signals.

[Explanation of symbols]

1, 2, 27, 28, 55, 56, 76, 77 1-line delay circuit 3-5, 29-31, 57-59, 78-80 Bandpass filter 6,7,13-15,32,33,39 ~ 41, 42,
60,61,64-66,83-88 Adder 8,9,16-20,34,35,43,48-50,
62, 63, 67, 70, 71, 81, 82, 89
Coefficient unit, 10, 12, 37, 38, 47, 68, 69 Absolute value conversion circuit 11, 36, 90, 91 Different sign detection circuit 21, 22, 25, 26, 45, 46, 51, 52, 5
4, 75, 92, 93 selector 23, 24, 53, 72, 73 comparator 44 positive sign detection circuit

Claims (2)

(57) [Claims] A chroma signal separating circuit for separating a chroma signal from a composite video signal.
And a main signal corresponding to the input signal (2) obtained by delaying the input signal (1) by one line,
A first adding circuit that outputs a post-difference signal; adding the main signal and a pre-signal corresponding to the input signal (3) obtained by delaying the input signal (2) by one line to output a pre-differential signal A second adder circuit, a first absolute value circuit that converts the post-difference signal into an absolute value, a second absolute value circuit that converts the pre-differential signal into an absolute value, and the first absolute value. A first coefficient circuit for multiplying the output signal of the conversion circuit by a coefficient K1 or K2, and a second coefficient circuit for multiplying the output signal of the second absolute value circuit by a coefficient K1 or K2 and outputting the result. When,
Positive / negative coincidence of signs of the rear differential signal and the front differential signal
A different sign detection circuit for detecting a mismatch and outputting a different sign discrimination signal; an output signal of the first coefficient circuit;
A first comparison circuit for comparing the magnitude of the level with the output signal of the absolute value circuit, and the magnitude of the level of the output signal of the first absolute value circuit and the output signal of the second coefficient circuit. A second comparison circuit for performing comparison, a first selection circuit controlled by the different sign determination signal, and selecting either K1 or K2 as a coefficient in the first and second coefficient circuits; A second selection circuit that selects and outputs one of a predetermined three-line comb signal and a previous comb signal under the control of an output signal of the second comparison circuit; and a control circuit that controls the output signal of the first comparison circuit. A third selection circuit for selecting one of the output signal of the second selection circuit and the predetermined post-comb signal and outputting the selected signal as a chroma signal. 2. A chroma signal separating circuit for separating a chroma signal from a composite video signal.
And a main signal corresponding to the input signal (2) obtained by delaying the input signal (1) by one line,
A first adding circuit that outputs a post-difference signal; adding the main signal and a pre-signal corresponding to the input signal (3) obtained by delaying the input signal (2) by one line to output a pre-differential signal A second adder circuit, a first absolute value circuit for converting the post-difference signal into an absolute value, a second absolute value circuit for converting the pre-differential signal to an absolute value, A different sign detection circuit that detects whether the sign of the preceding difference signal is positive or negative and outputs a different sign discrimination signal, and a first output circuit that inverts the polarity of the output signal of the second absolute value conversion circuit and outputs the inverted signal. Coefficient circuit, a third addition circuit that adds an output signal of the first absolute value conversion circuit and an output signal of the first coefficient circuit, and outputs an output signal of the third addition circuit. A positive sign detection circuit that detects a positive sign of
Controlled by the positive sign detection signal, the first and second
A first selection circuit for selecting and outputting any of the output signals of the absolute value conversion circuit, a third absolute value conversion circuit for converting the output signal of the third addition circuit to an absolute value, A second coefficient circuit for multiplying the output signal of the selection circuit by the coefficient K1 and outputting the result, and a coefficient K2 for the output signal of the third absolute value conversion circuit.
And a third coefficient circuit, which is output by multiplying the output signal, and one of an output signal of the second coefficient circuit and an output signal of the first selection circuit, which is controlled by the different sign determination signal, and outputs the selected signal. A second selection circuit and the output signal of the third absolute value conversion circuit and the third
And selecting and outputting one of the output signals of the coefficient circuit
Selection circuit, a comparison circuit that compares the magnitudes of the output signals of the second and third selection circuits, and selects one of a predetermined post-comb signal and a pre-comb signal under the control of the positive code discrimination signal. A fourth selection circuit which outputs a predetermined three-line comb signal and an output signal of the fourth selection circuit, which are controlled by an output signal of the comparison circuit;
A fifth selection circuit that outputs a chroma signal.