JPH0683463B2 - Image quality improvement circuit - Google Patents

Description

The present invention relates to color signal processing of color television signals,
In particular, it relates to an image quality improving circuit using two contour signals respectively generated from a luminance signal and a color signal.

[Prior Art] A luminance contour signal and a color contour signal representing a contour are respectively created from a luminance signal and a color signal separated from a composite color television signal, and these are used to prevent occurrence of color blur in a contour portion of a reproduced image. US patent as an image quality improvement circuit
There is one shown in No. 4,504,853.

The main part of this conventional circuit is shown in FIG. Color signal input terminal
The color signal A'arriving at 11 becomes a signal B'which is equalized by the group delay characteristic by the bandpass filter 12 including the color signal phase equalizer. Next, this signal B'is added by the first adder 18 to the signal D'which is delayed by the time corresponding to 1/2 carrier period in the color sub, and becomes a signal E '. This signal processing corresponds to the differentiation of color signals. On the other hand, the baseband luminance signal F is fed from the luminance signal input terminal 13 to the low pass filter.
A band-limited signal G is input to 24, and this signal G becomes a signal H differentiated by a differentiating circuit 26. The signal H has opposite polarities at the rising edge and the falling edge of the luminance signal F, but full-wave rectification is performed by the full-wave rectifying circuit 23 in order to make them the same polarity. The full-wave rectified signal J is differentiated again by the differentiating circuit 30, and the differentiated signal K is given to the limiter 32 to be the signal L whose amplitude is limited. Next, the signal L is waveform-shaped by the waveform shaping circuit 34 to obtain the signal M.

Here, the signals M and E are generated from the color signal A ′ and the luminance signal F which have the same edge on the screen. The signals M and E'need to be timed as shown in FIG. The signal N obtained as a result of the multiplication is the delay circuit 14
The second adder 22 adds the color signal C ′ whose timing has been adjusted by the second adder 22 to form an output signal O.

In this way, the correlation between the chrominance signal and the luminance signal is used for a chrominance signal in which the band of the chrominance signal is narrowed and the transient time of the chrominance edge is deteriorated, such as the reproduction signal of a VTR that uses the low band conversion recording method. By doing so, contour correction is performed.

[Problems to be Solved by the Invention] Next, the problems in the operation of the conventional image quality improving circuit will be described.
This will be described with reference to FIGS. 22 and 23. In the figure,
The respective luminance signal waveforms, carrier color signal waveforms and their timings are shown. In addition, Fig. 22 assumes a pattern in which the luminance and color signals have a correlation, and Fig. 23 assumes a pattern in which the luminance and color signals are uncorrelated and in which a change in the color signal occurs near the change in the luminance signal. It is a waveform. When a waveform as shown in FIG. 22 is input, the conventional circuit of FIG. 20 operates as shown in US Pat. No. 4,504,853, and the circuit output waveform becomes a signal with color fringing corrected.

However, when the waveform as shown in Fig. 23 enters the conventional circuit, the timing of the differential waveform becomes as shown in and in the figure, and the edge information of the chrominance signal is modulated by the edge information of the luminance signal which is originally irrelevant. It This modulated signal is combined with the input signal to generate a pseudo contour of the color signal as shown in. Therefore, the conventional circuit had to set a small amount of contour enhancement.

As described above, in the conventional circuit, since the luminance signal is used as the multiplication signal for correcting the color contour, the above problem occurs when the color signal and the luminance signal have no correlation.
In order to prevent this, it is also possible to perform contour correction with the color signal itself, in which case pseudo contour does not occur, but because the high frequency signal S / N ratio of the color signal with degraded band characteristics is poor. The contour correction causes a problem that the S / N ratio of the color signal is deteriorated.

Therefore, according to the present invention, the pseudo contour of the color signal does not occur.
An object of the present invention is to provide an image quality improving circuit with less deterioration of the S / N ratio of a color signal due to contour correction.

[Means for Solving the Problem] In the present invention, in order to solve the above-mentioned conventional problems and achieve the above-mentioned object, a contour signal made from a luminance signal and a contour signal made from a color signal are compared, and both are correlated. The non-correlated portion is detected. When there is no correlation, the non-correlated component of the contour signal created from the luminance signal is attenuated, and the signal obtained by attenuating the non-correlated portion of the contour signal created from the luminance signal is multiplied. The contour correction is performed by multiplying the color signal by differentiating the color signal.
Since the present invention detects non-correlation, it is possible to suppress the generation of color pseudo contours, and in order to use a luminance signal with a good S / N ratio, deterioration of the S / N ratio of the color signal due to contour correction. It has the characteristic that there is little.

That is, according to the present invention, first means for differentiating the color signals separated from or constituting the composite color television signal to produce a signal for displaying the contour in the image, and the first means separated from the composite color television signal. Or a signal for displaying the contour in the image from the luminance signal constituting the second
An image quality improving circuit comprising means, means for multiplying the output signals from the first means and second means, and means for adding the color signal to the output signal of the multiplying means, the output of the first means A third means for detecting and then differentiating the signal is provided, and in response to the signal from the second means and the signal from the third means, the signal from the second means is output when both signals have the same polarity. On the other hand, when the polarities of the two signals are not the same, a fourth means for outputting a signal having an amplitude smaller than the amplitude of the signal from the second means is provided between the second means and the multiplying means. There is provided an image quality improving circuit characterized in that the output signal of the means is supplied to the multiplying means and is multiplied by the output signal from the first means.

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

FIG. 1 is a block diagram showing an embodiment of an image quality improving circuit of the present invention, and FIGS. 2 and 3 are waveform charts showing the operation thereof. The luminance signal Y given to the luminance signal (Y) input terminal 13 is passed through a low pass filter (LPF) 24 to a differentiating circuit 26.
Is applied to the second differentiating circuit 30 via the double-wave rectifying circuit 28, and the output signal is applied to the limiter.
It is given to the logic circuit 40 via 32. On the other hand, the color signal applied to the color signal (C) input terminal 11 is applied to the differential circuit 17 and the delay circuit 14 after being band-limited by the BPF 12.
The output signal of the differentiating circuit 17 is given to one input of the multiplier 20 via the other delay circuit 19, and is given to the logic circuit 40 via the AM detecting circuit 36 and the differentiating circuit 38.

The numbers in the waveforms of FIGS. 2 and 3 correspond to those of FIG. 1, and FIG. 2 shows the case where the luminance signal Y and the color signal C are correlated, and FIG. In each case, there is no correlation. It should be noted that in FIGS. 1 to 3, ′ and ′ are signals different from those in FIG.

The logic circuit 40 includes a phase comparator 42, a voltage comparator 44, a delay circuit 46, and a selection switch 48. The phase comparator 42 and the selection switch 48 may have the circuit configurations shown in FIGS. 4 and 5, respectively. FIG. 6 shows a truth table of the logic circuit 40. When the output signal of the limiter 32 is A and the output of the differentiating circuit 38 is B, when each is a positive value (a, b), it is 0. , The content of the output signal C ″ obtained when the value is negative (−a, −b).

In the waveform diagrams of FIGS. 2 and 3, the output signal of the limiter 32 is a contour signal formed from the luminance signal and is called a luminance contour signal. An output signal 'of the differentiating circuit 38 is a contour signal formed from the color signal, which is obtained by AM-detecting the differentiated carrier color signal to form a baseband signal and differentiated, and is called a color contour signal.

In this embodiment, these two contour signals, ', are input to the phase comparator 42 as shown in FIG. 1 to detect the non-correlated portion. As the phase comparator 42, for example, the one having the configuration shown in FIG. 4 can be used. The phase comparator 42 outputs a positive voltage with respect to the operating point when the two input signals have the same polarity, and outputs a negative voltage with respect to the operating point when the two inputs have different polarities. . The waveforms in FIGS. 2 and 3 represent the output of the phase comparator 42. As shown in the figure, the output of the phase comparator 42 has a positive value when the luminance and color contours have a correlation, and a negative value when there is no correlation. Next, the output of the phase comparator 42 is sliced by the voltage comparator 44 and becomes a pulse signal which becomes H level only when there is no correlation.

Further, the contour signal generated from the luminance signal is supplied to the selection switch 48 after passing through the delay circuit 46 having a delay time similar to the delay of the decorrelation detection circuit. Here, the selection switch 48 mutes the output while the non-correlation pulse is at the H level, and outputs the contour signal generated from the luminance signal during the correlation. As the selection switch circuit 48, for example, the one having the configuration shown in FIG. 5 can be used. At the output of the selection switch circuit 48, as shown in FIGS. 2 and 3, a luminance contour signal in which the portions of the luminance contour signal and the color contour signal 'having different polarities are attenuated is obtained.

As described above, the pseudo contour of the color has an originally irrelevant luminance contour near the color contour, and the irrelevant luminance contour signal and color differentiation signal are input to the multiplier 20 at the same time. Occurs when there is a period. In such a case, there is a position (time) shift between the color contour and the luminance contour, so that there is always a shift in the position of the zero-cross point of the two contour signals (and ′ in FIGS. 2 and 3). Therefore, there always exists a period when the two have different polarities. If the luminance contour signal in this period is input to the multiplier 20 as it is, the color fringing that should originally be canceled is modulated to the opposite polarity and emphasized as described in the conventional circuit, and a pseudo contour is generated. . In the present invention, when the two contour signals, ′, have different polarities, a signal having a smaller amplitude than the luminance contour signal is sent to the multiplier 20, so contour correction can be performed while preventing false contours, and the conventional problem is solved. Is done.

As is clear from the truth table of FIG. 6, the logic circuit 40 has 2
The configuration is such that the value a, -a or 0 of the input signal A is output as the output C "in accordance with the values of the two input signals A and B (corresponding to ???, respectively).
Instead of this, other configurations are possible.

FIG. 7 is a block diagram showing the configuration of a logic circuit 50 which can be used in place of the logic circuit 40 of FIG. 1, and the circuit configuration using this logic circuit 50 constitutes the second embodiment of the present invention. To do. In FIG. 7, 51 is a coefficient unit constituted by an amplifier, 52 and 54 are maximum value selection circuits (MAX), 56 and 58 are minimum value selection circuits (MIN), and 60 is an adder. The maximum value selection circuits 52 and 54 are circuits for selecting and outputting the larger one of the two inputs, and for example, the circuit configuration shown in FIG. 8 can be used. Also, the minimum value selection circuit 56,
Reference numeral 58 is a circuit for selecting and outputting the smaller one of the two inputs, and for example, the circuit having the circuit configuration shown in FIG. 9 can be used.

When the two inputs A and B have the same polarity,
It is used to amplify the B input to the same extent as the A input in order to preferentially output the A input.

FIG. 10 is a truth table of the logic circuit 50. In this MIN
(A, b) and MAX (-a, -b) mean that the smaller or larger of the signals in parentheses is output. This embodiment is similar to the embodiment of FIG.
2. Since it does not require the voltage comparator 44 and the like, it has a feature that stable operation can be obtained with relatively few circuit components.

FIG. 11 is a block diagram showing a third embodiment of the present invention,
It is a modification of the second embodiment of FIG. That is, the difference from FIG. 7 is that the A input is given to the maximum value selection circuit 52 and the minimum selection circuit 56 via the inverter 53, and the output of the adder 60 and another adder for adding the A input. 62 is provided. Figure 12 shows the logic circuit of Figure 11.
It is a truth table of 64.

FIG. 13 is a block diagram showing a fourth embodiment of the present invention.
In this embodiment, the logic circuit 82 that responds to the two inputs A and B has two
It is composed of two coefficient units 84 and 88 and an adder 86. The coefficient units 84 and 88 are amplifiers whose amplification is set to match a predetermined coefficient, and the coefficient of the coefficient unit 84 is set to a value that amplifies the B input until the amplitude of the B input becomes almost equal to the amplitude of the A input. Is set. The output B'of the coefficient unit 84 is applied to the adder 86 and added to the A input, and the sum signal S is applied to the multiplier 20 via the coefficient unit 88 as the output C ". Since the A input, that is, the luminance contour signal and the B input, that is, the portion where the polarities of the color contour signal ′ have different polarities, that is, when there is no correlation, the amplitude of the output signal S of the adder 88 becomes almost zero and the pseudo contour is prevented. On the other hand, when there is a correlation between the two, a signal B ′ obtained by multiplying the A input and the B input by a predetermined coefficient is added to each other, and the amplitude of the signal S is the original A input,
It becomes larger than B input, and contour correction is performed.

FIG. 14 and FIG. 15 are diagrams showing signal waveforms of respective parts of the embodiment of FIG. 13 at the time of correlation and at the time of non-correlation. As described above, the present embodiment can effectively prevent the generation of the pseudo contour with a very simple circuit configuration.

FIG. 16 is a block diagram showing a fifth embodiment of the present invention.
As the logic circuit 66, any of the logic circuits 40, 50, 62 and 82 shown in FIGS. 1, 7, 11, and 13 may be used. In this embodiment, the input B and the output C ″ of the logic circuit 66 are output to the multiplier 20 via the absolute value maximum value selection circuit 70 which outputs the signal with the larger amplitude. In the embodiment, the contour correction is not performed in the non-correlated portion of the luminance contour and the color contour, but in the present embodiment, by adding the absolute value maximum value selection circuit 70, the correction signal of the non-correlated portion is obtained. The color signal is used, and the luminance contour signal is used at the time of correlation, so that the correction at the time of non-correlation can be performed.

The B input is inputted to the absolute maximum value selecting circuit 70 through the noise removing circuit 68. The noise removing circuit 68 is necessary when handling a color signal having a poor S / N ratio. It is not necessary for color signals whose / N ratio is not so bad. As the noise removing circuit 68, the one having the configuration shown in FIG. 17 can be used.

FIG. 18 is a block diagram showing an example of a specific configuration of the absolute maximum value selecting circuit 70. 71 is a coefficient unit, 72 and 74 are maximum value selection circuits (MAX), 76 and 78 are minimum value selection circuits (MIN), and 80 is an adder. FIG. 19 is a signal waveform diagram when the A input and the B input are uncorrelated.

Here, the signal E is the other input of the multiplier 20, that is, the output signal of the delay circuit 19 in FIG.

In each of the above-described embodiments, each signal waveform is slightly delayed by the processing circuit, and therefore it is necessary to actually compensate for this, but in the above description, such delay and its compensation are omitted. The color signal C may be a baseband signal or a carrier color signal. In the above embodiment, the configuration in which the carrier color signal is input as the color signal has been described, but when the baseband signal is input, the AM detection circuit 36 in FIG. 1 may be replaced with a double wave rectification circuit.

[Effect] As is clear from the above description, by using the image quality improving circuit of the present invention, a pseudo contour is generated even in the case of a picture image having no correlation between the luminance signal and the color signal. Never. Therefore, there is a feature that the amount of edge enhancement can be increased more than in the past and the image quality can be improved by more appropriate edge correction.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an image quality improving circuit of the present invention, FIG. 2 and FIG. 3 are waveform diagrams explaining the operation of the circuit of FIG. 1, FIG. 4 and FIG. FIG. 6 is a diagram showing a configuration example of the phase comparator and the selection switch circuit of FIG. 1, FIG. 6 is a diagram showing a truth table of the logic circuit in FIG. 1, and FIG. 7 is a diagram of a second embodiment of the present invention. Block diagrams showing essential parts, FIGS. 8 and 9 are diagrams showing the configurations of the maximum value selection circuit and the minimum value selection circuit in FIG. 7, respectively, and FIG. 10 is a truth table of the logic circuit of FIG. FIG. 11, FIG. 11 is a block diagram showing an essential part of a third embodiment of the present invention, FIG. 12 is a diagram showing a truth table of the logic circuit of FIG. 11, and FIG. 13 is a fourth diagram of the present invention. FIG. 14 is a block diagram showing an essential part of the embodiment, FIG. 14 is a waveform diagram explaining the operation of the embodiment of FIG. 13, FIG. 16 is a block diagram showing an essential part of the fifth embodiment, and FIG. Figure, Figure 18 16 is a diagram showing a configuration example of the noise removal circuit and the absolute maximum value selection circuit in FIG. 16, FIG. 19 is a waveform diagram for explaining the operation of the embodiment of FIG. 16, and FIG. 20 is a conventional image quality improvement circuit. Block diagram showing Figure 21, Figure 22, Figure 22,
FIG. 23 is a waveform diagram for explaining the operation of the conventional circuit of FIG. 12 …… Band filter, 14,19,46 …… Delay circuit 17,26,30,38 …… Differentiation circuit, 20 …… Multiplier 22,60,62,80,86 …… Adder, 24 …… Low Band filter 28 …… Both-wave rectifier circuit, 32 …… Limiter 36 …… AM detection circuit, 40,50,64,66,82 …… Logic circuit 42 …… Phase comparator, 44 …… Voltage comparator 48 …… Selection switch, 51, 71, 84, 88 …… Coefficient multiplier 52, 54, 72, 74 …… Maximum value selection circuit 53 …… Inverter 56, 58, 76, 78 …… Minimum value selection circuit 68 …… Noise elimination circuit 70 ... Absolute maximum value selection circuit

Claims (3)

[Claims] 1. A first means for differentiating a color signal separated from or constituting a composite color television signal to generate a signal for displaying a contour in an image, and a first means separated from the composite color television signal. Alternatively, second means for producing a signal for displaying the contour in the image from the luminance signal constituting the same, means for multiplying the output signals from the first means and second means, and the output signal of the means for multiplying In an image quality improving circuit including means for adding color signals, third means for detecting and then differentiating the output signal of the first means is provided, and responding to the signal from the second means and the signal from the third means. When the polarities of both signals are the same, the signal from the second means is output. On the other hand, when the polarities of the two signals are not the same, a signal having an amplitude smaller than the amplitude of the signal from the second means is output. 4 means Provided between said means for multiplying the unit, said fourth means quality improving circuit, characterized in that the output signal and configured to multiply the output signal from said first means to supply to said means for multiplying the. 2. A first means for differentiating a color signal separated from or constituting the composite color television signal to generate a signal for displaying an outline in an image, and a first means separated from the composite color television signal. Alternatively, second means for producing a signal for displaying the contour in the image from the luminance signal constituting the same, means for multiplying the output signals from the first means and second means, and the output signal of the means for multiplying In an image quality improving circuit including means for adding color signals, third means for detecting and then differentiating the output signal of the first means is provided, and responding to the signal from the second means and the signal from the third means. When the polarities of both signals are the same, the signal from the second means is output. On the other hand, when the polarities of the two signals are not the same, a signal having an amplitude smaller than the amplitude of the signal from the second means is output. 4 means are provided, A fifth means for responding to the output signal of the third means and the output signal of the fourth means for selecting and outputting the signal having the larger amplitude of the both signals is provided, and the output signal of the fifth means is An image quality improving circuit, characterized in that the image quality improving circuit is configured to be supplied to a multiplying unit and multiply the output signal of the first unit. 3. A first means for differentiating a color signal separated from or constituting the composite color television signal to produce a signal for displaying a contour in an image; and a first means separated from the composite color television signal. Alternatively, second means for producing a signal for displaying the contour in the image from the luminance signal constituting the same, means for multiplying the output signals from the first means and second means, and the output signal of the means for multiplying In an image quality improving circuit including means for adding color signals, third means for detecting and then differentiating the output signal of the first means, and the third means.
A coefficient unit for amplifying the signal from the means by a predetermined amplification degree and an adder for adding the output signal of the coefficient unit to the signal from the second means are provided, and the output signal of the adder is multiplied by the means. An image quality improving circuit, which is configured to be supplied and multiplied by an output signal from the first means.