JPH0927920A - Contour correction circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the contour correction circuit in which image quality deterioration due to overshoot or preshoot is reduced and waveform distortion is reduced in the case of correcting a high frequency signal. SOLUTION: A video signal received at an input terminal 11 is given to a contour correction detection circuit 12, in which a discrimination signal is obtained. The video signal given to the input terminal 11 is given further to an LPF 13, in which a low frequency component is extracted and given to a variable delay circuit 14. The variable delay circuit 14 uses the discrimination signal to vary a delay time thereby improving a transient signal of a contour part. A subtractor circuit 15 subtracts an output of the LPF 13 and the input video signal and outputs a high frequency component. The output is given to a coefficient circuit 16, in which a prescribed coefficient is multiplied with the output to change its signal level by a prescribed amount. An adder circuit 17 adds an output signal from the coefficient circuit 16 and an output signal of the variable delay circuit 14 and a final resulting output signal is obtained at an output terminal 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour correction circuit which corrects a blunting of a transient in a contour portion which occurs in the process of transmitting a video signal and improves image quality deterioration such as blurring and blurring.

[0002]

2. Description of the Related Art A conventional contour correction circuit will be described with reference to the circuit configuration diagram of FIG. The video signal a input to the input terminal 81 is input to the HPF 82 and the delay circuit 83, respectively. The HPF 82 obtains a contour correction signal b which is a high frequency component of the input video signal a. The contour correction signal b is added by the adder circuit 84 to the output signal of the delay circuit 83 to obtain an output video signal c, which is output from the output terminal 85. The delay circuit 83 adjusts the time of signal processing.

This will be described with reference to the waveform chart of FIG. FIG. 9A shows an input video signal a input to the delay circuit 83, and this video signal a is a waveform example of a square wave and a sine wave showing a high frequency component. Outline correction signal b (b)
The contour correction signal b and the video signal a are shown in FIG.
The output signal c obtained by adding 4 is shown in (c).

This correction method is simple, but in order to increase the degree of correction, it is necessary to increase the amplitude level of the contour correction signal b added by the adder circuit 84. As a result, the corrected output signal becomes a signal having a large overshoot / preshoot width and level. This signal is TV
When viewed on a receiver, unnatural emphasis is conspicuous in the image contour portion, and the image quality often deteriorates.

FIG. 10 is a circuit configuration diagram for explaining another conventional contour correction circuit. The video signal a input to the input terminal 101 is supplied to the contour correction section detection / determination circuit 10
2 to obtain the judgment signal b. The variable delay circuit 103 is controlled based on the determination signal b to obtain the contour correction signal c with the contour portion corrected and output from the output terminal 104.

A specific configuration example of the contour correction section detection / determination circuit 102 will be described with reference to FIG. A band-limited signal d of the input video signal a is output via the LPF 102a. Next, in the differentiating circuit 102b, primary differentiation is performed, the differential signal e is output, and the absolute value circuit 102c is temporarily output.
Takes the absolute value and again performs the second-order differentiation in the differentiating circuit 102d to output the differential signal f. The determination circuit 102e determines the signal f, which has been differentiated twice, with the reference value 102f of a predetermined level to obtain the determination signal b.

FIG. 12 shows an example of the circuit configuration of the variable delay circuit 103.
Shown in This is a case where a plurality of delay circuits are arranged in parallel. The input video signal a has N delay circuits 1031 to 1031 (a positive integer).
Delay at 103n. Delay circuit 1031 and delay circuit 10
The output signals of the 32nd to Nth delay circuits 103n are controlled by the selection circuit 103b based on the determination signal b, the delay time is selected, and the output signal c is obtained.

FIG. 13 shows the signal waveform of each part of FIG. That is, FIG. 13A shows the input video signal a, which is the same signal as the input video signal a of FIG.
(B) is the LPF 10 of the contour correction unit detection / determination circuit 102.
The output signals of 2a are (c) and (d), which are the primary differential signal e and the secondary differential signal f of the contour correction section detection / determination circuit 102. (E) shows the output signal c which controls the variable delay circuit 103 to which the input signal is input by the determination signal as a result of comparison and determination with the reference value 102f from the secondary differential signal f.

The square wave portion of the output signal c has no overshoot or preshoot and is well corrected, but the sine wave portion has a variable delay circuit 103 for the input signal.
Since the unit delay time is large, waveform distortion occurs. The output signals have different waveform phases.

In this case, the adverse effects of overshoot and preshoot are small even if the degree of correction is increased. However, if the input signal has only high-frequency components, the correction is non-linear, so that large waveform distortion occurs. Therefore, when viewed on the TV screen, the image quality is often different from that of the conventional example of FIG.

[0011]

In the conventional HPF of the contour correction circuit described above, when a large enhancement or correction is performed, the image quality is often deteriorated due to overshoot or preshoot. Further, in the case where the variable delay circuit is used, it is not effective for high signal components, and the image quality may be deteriorated due to signal processing accompanied by waveform distortion. The present invention provides a contour correction circuit which reduces image quality deterioration due to overshoot or preshoot and reduces waveform distortion when correcting a high frequency signal.

[0012]

In order to solve the above-mentioned problems, in the contour correction circuit of the present invention, the contour portion detecting means for detecting the contour portion of the input video signal and the contour portion detecting means detect the contour portion. Determination means for obtaining the determination signal obtained by determining the determined contour portion detection signal at a predetermined level, and variable delay means for delaying the low-frequency component of the input video signal and allowing the delay time to be varied. Generating means for controlling the variable delay means by the judgment signal of the judging means to generate a contour correction video signal of a low frequency component; and a high frequency component of the input video signal or a predetermined coefficient for the high frequency component. And adding means for adding the signals multiplied by.

[0013]

With the above-described means, the contour correction using the variable delay circuit is performed on the low-frequency component of the input video signal. Therefore, even if the contour correction amount is emphasized, the overshoot or preshoot does not reach a large level. Further, since the high frequency component is stored and added to the main signal output from the variable delay circuit, the high frequency component can be faithfully reproduced. Further, since the high frequency component in the input signal is separately extracted and added to the signal after the contour correction, the detail of the image can be sufficiently improved, and the contour correction in which the image quality deterioration is unlikely to occur can be performed.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 is a circuit configuration diagram for explaining a first embodiment of the present invention. In FIG. 1, the contour correction unit detection circuit 121 obtains a determination signal for the video signal input to the input terminal 111. The specific configuration of the contour correction section detection circuit 121 is the same as that shown in FIG. The video signal input to the input terminal 111 is further input to the LPF 131, where low frequency components are extracted and input to the variable delay circuit 141. The variable delay circuit 141 varies the delay time according to the determination signal to improve the signal transient at the contour portion. Further, the output of the LPF 131 and the input video signal are subtracted by the subtraction circuit 151, and the high frequency component is taken out as the output of the subtraction circuit 151. The coefficient circuit 161 multiplies this output by a predetermined coefficient to change the signal level to a predetermined amount. The adder circuit 171 adds the output signal of the coefficient circuit 161 and the output signal of the variable delay circuit 141 to obtain a final output signal at the output terminal 181.

The coefficient circuit 161 may be omitted and a high frequency component with a coefficient of 1 may be input to the adder circuit 171. Also,
The HPF configured by the subtraction circuit 151 and the LPF 131 may bring another HPF circuit.

The operation of FIG. 1 will be described with reference to FIG. 2 showing the signal waveform of each part of FIG. 2A shows a video signal input to the input terminal 111, and FIG.
1 shows an output signal of the first embodiment. (C) and (d) show the output signals of the primary differential and secondary differential circuits inside the contour correction section detection circuit 121 of FIG. 11, and (e) shows the output signal of the subtraction circuit 151. (F) shows the output signal of the variable delay circuit 141 as (g)
Indicates the final output signal.

As is apparent from FIG. 2, since the square wave signal is contour-corrected using the variable delay circuit 141, the adverse effects of overshoot and preshoot are greatly reduced.
Further, in the sine wave signal indicating the high frequency component, the waveform distortion accompanying the phase fluctuation does not occur. Therefore, this output waveform is
It can be seen that the image quality is improved even when viewed on the V screen, and the image quality degradation due to excessive overshoot and preshoot and the image quality degradation due to waveform distortion are significantly reduced.

FIG. 3 is a circuit configuration diagram for explaining the second embodiment of the present invention. The same parts as those of this embodiment and the embodiment of FIG. In this embodiment, an adder 171 that adds the outputs of the variable delay circuit 141 and the coefficient circuit 161 is used.
1 is different from the configuration shown in FIG.

That is, the HPF 311 extracts a high frequency component from the video signal input to the input terminal 111, the coefficient circuit 321 multiplies it by a predetermined coefficient, and the adder circuit 171 outputs the output signal of the variable delay circuit 141 and the coefficient circuit 161. Output signal is added together, and the final output signal is obtained from the output terminal 181.

In this embodiment, as compared with the embodiment of FIG.
HPF 311 and coefficient circuit 32 for correcting high frequency components
The correction of the high region can be further increased by the addition of 1.

In each of the above-described embodiments, the contour correction of one input video signal has been described, but in each of the embodiments described below, an example in which a plurality of input signals are input will be described. To do. As a matter of course, there is no problem even in the case of plural inputs other than 3.

FIG. 4 is a circuit configuration diagram for explaining the third embodiment of the present invention. In this embodiment, three circuit blocks 41 to 43 having the same structure as the embodiment of FIG. 1 are systematically connected.

That is, the circuit block 41 has the same structure as in FIG. The circuit block 42 is a contour correction detection circuit 122.
The configuration from the input terminal 112 to the output terminal 182 is the same as that of the contour correction block 41, except that the video signal input to the input terminal 111 is input. Further, the circuit block 43 supplies the contour correction detection circuit 123 with the input terminal 1
The configuration from the input terminal 113 to the output terminal 183 is the same as that of the circuit block 41 except the configuration in which the video signal input to 11 is input.

In this way, when a plurality of circuit blocks are systematically constructed, one signal is selected from a plurality of types of input signals, and the contour correction section detection circuits 121 to 123 detect the contour correction section signals. And a determination signal is obtained. The circuit characteristics of the contour correction unit detection circuits 121 to 123 may be different or the same. Each input signal 111-113
Is input to the LPFs 131 to 133 for each signal and is input to the variable delay circuits 141 to 143. The variable delay circuits 141 to 143 are controlled by the determination signals which are the output signals of the contour correction section detection circuits 121 to 123. The output signals of the variable delay circuits 141 to 143 are added to the input video signal and the LP signal by the addition circuits 171 to 173, respectively.
After subtracting F131 to 133 by the subtractors 151 to 153, the outputs of the coefficient circuits 161 to 163 are added, and output signals are obtained from the output terminals 181 to 183.

In this embodiment, among the plurality of input video signals, the contour correction section detection circuits 121 to 123 obtain the determination signal only from the signal input to the input terminal 111, so that the plurality of input signal delay times are different. Even if the timing of the transient part is different, the contour correction part information is detected from one signal and the variable delay circuit corresponding to each signal is controlled, so the position of the contour part of the corrected signal becomes constant and As a matter of course, the above correction positions also coincide. Problems associated with contour correction of multiple signals can be cleared.

FIG. 5 shows a fourth embodiment of the present invention in the case where the second embodiment of FIG. 3 of the present invention is formed into a plurality of circuit blocks like the third embodiment of FIG. It is a circuit block diagram for explaining.

In this embodiment, the circuit blocks 41 to 41 shown in FIG.
43 input terminals 111-113 and adders 171-173
Between HPF 311 to 313 and coefficient circuit 3
21. A series circuit of 21 to 323 is added and the circuit blocks are set to 51 to 53, respectively, which is different from the embodiment of FIG.

Also in this embodiment, as in the circuit configuration of FIG. 4, since the contour correction positions are made to coincide with each other in response to a plurality of signal inputs, it is assumed that a plurality of input signal delay times are different and the timing of the transient portion is different. Also, since the information of the contour correction section is detected from one signal and the variable delay circuit corresponding to each signal is controlled, the position of the contour section of the corrected signal can be made constant.

FIG. 6 is a circuit configuration diagram for explaining a fifth embodiment of the present invention, which is a simplified version of the embodiment of FIG.
6, the circuit block 61 has the same configuration as the circuit block 41 of FIG. 4 up to the input terminal 111 and the output terminal 181. The circuit block 62 inputs the video signal input to the input terminal 112 to the variable delay circuit 142, and the variable delay circuit based on the determination signal obtained from the video signal input to the input terminal 111 via the contour correction unit detection circuit 122. The delay amount of 142 is changed and output from the output terminal 182. Further, the circuit block 63 inputs the video signal input to the input terminal 113 to the variable delay circuit 143, and changes the video signal input to the input terminal 111 according to a determination signal obtained via the contour correction unit detection circuit 123. Delay circuit 1
The delay amount of 43 is varied and output from the output terminal 183.

Of a plurality of input video signals, the input terminal 11
The low frequency component of the video signal input to 1 is taken out by the LPF 131 and input to the variable delay circuit 141. The contour correction portion detection circuit 121 detects the contour portion of the video signal to obtain a contour portion detection signal, and controls the variable delay circuit 141 by the determination signal obtained by determining the detection signal at a predetermined level. To generate the low frequency component of the contour corrected video signal. The high frequency component of the input video signal is subtracted from the output of the LPF 131 by the subtractor 15.
It is obtained by subtraction using 1. This high frequency component is converted to the coefficient circuit 16
Input 1 to obtain the signal multiplied by the coefficient. The output of the variable delay circuit 141 and the output of the coefficient circuit 161 are added by the adder 171, and the output signal is output to the output terminal 181.

The other video signals input to the input terminals 112 and 113 are directly variable delay circuits 142 and 143.
To the variable delay circuits 142 and 143,
Output signals controlled based on the determination signals obtained by the contour correction unit detection circuits 122 and 123 are output to the respective output terminals 18
2, 183.

In this embodiment, since the contour correction positions are made to correspond to each other in response to a plurality of signal inputs as in the previous embodiments, not only can the position of the contour portion of the corrected signal be constant. The circuit can be simplified.

A circuit configuration diagram of FIG. 7 shows a sixth embodiment of the present invention in which the circuit of the embodiment of FIG. 5 is simplified in a different way. The circuit block 71 from the input terminal 111 to the output terminal 181 has the circuit configuration shown in FIG. 3, and the circuit block 72, 73 from the input terminals 112 and 113 to the output terminals 182, 183 has the circuit configuration shown in FIG. It has become.

Also in this embodiment, the contour correction section detection circuit 12
Since Nos. 1 to 123 are detected from the video signal input to the input terminal 111, the output signals output to the output terminals 181 to 183 are signals whose contour correction positions match.

Although the circuit configurations for handling a plurality of types of input signals have been described in the embodiments of FIGS. 4 to 7, the input terminal 1 is actually used.
An example of signals input to 11 to 113 will be described. The plurality of input signals are signals forming a transmission image signal, but first, they may be a luminance signal / color signal. The color signal is a signal obtained by modulating two types of color difference signals by quadrature modulation with a color subcarrier. A luminance signal is used as a signal for detecting the contour correction unit.
The variable delay circuit for inputting the color signal is controlled by the determination signal detected from the luminance signal.

The same can be applied to the case of two types of luminance signal and color difference signal. Color difference signal is RY
It may be a / BY signal. Further, it may be a signal decoded on another phase axis. In general, the color signal has a narrower signal band than the luminance signal, and therefore a simplified circuit configuration as shown in FIGS. 6 and 7 can be used. That is, when the input signal 2 is a color signal, it may be input to the variable delay circuit without using the LPF. Even when the color difference signals are input to the inputs 2 and 3, it is not necessary to extract only the low frequency component of each color difference signal by the LPF.

Next, there are cases of R, G, B signals. R ・
In the case of the G and B signals, the most abundant component among the luminance signal components is the G signal, and therefore, the G signal is generally used as the input signal 1 to detect the contour correction portion from the G signal. This principle can also be applied to the present invention, and it is recommended to use the G signal as the input to the contour correction unit detection circuit. However,
The R, G, B signals are generally wideband. Therefore, it is preferable to use the contour correction circuit corresponding to FIGS. 4 and 5 as the circuit configuration.

[0038]

As described above, according to the contour correction circuit of the present invention, the low-frequency component of the video signal is corrected by the variable delay circuit, which enables contour correction with less overshoot and preshoot. Not only can low-frequency components be emphasized reasonably, but details can also be corrected by performing coefficient processing on high-frequency components. In addition, since a correction signal is created from one main signal for a plurality of video signal inputs, the positions of contour correction for luminance and color signals or R, G, B signals match, which is a factor of image quality deterioration due to contour correction. Can be eliminated.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram for explaining a first embodiment of the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of FIG.

FIG. 3 is a circuit configuration diagram for explaining a second embodiment of the present invention.

FIG. 4 is a circuit configuration diagram for explaining a third embodiment of the present invention.

FIG. 5 is a circuit configuration diagram for explaining a fourth embodiment of the present invention.

FIG. 6 is a circuit configuration diagram for explaining a fifth embodiment of the present invention.

FIG. 7 is a circuit configuration diagram for explaining a sixth embodiment of the present invention.

FIG. 8 is a circuit configuration diagram for explaining a conventional contour correction circuit.

9 is a signal waveform diagram of each part for explaining the operation of FIG.

FIG. 10 is a circuit configuration diagram for explaining another conventional contour correction circuit.

11 is a circuit configuration diagram for explaining a configuration example of the contour correction unit detection / determination circuit shown in FIG.

12 is a circuit configuration diagram for explaining a configuration example of the variable delay circuit shown in FIG.

13 is a signal waveform diagram of each part for explaining the operation of FIG.

[Explanation of symbols]

111-113 ... Input terminal, 121-123 ... Contour correction part detection circuit, 131-133 ... LPF, 141-143
... Variable delay circuit, 151-153 ... Subtraction circuit, 161-
163, 321 to 323 ... Coefficient circuit, 171 to 173 ...
Adder circuits, 181-183 ... Output terminals, 311-313
... HPF, 41-43, 51-53, 61-63, 71
~ 73 ... Circuit block.

Claims (9)

[Claims] 1. A contour portion detecting means for detecting a contour portion of an input video signal, and a judging means for obtaining a judging signal by judging the contour portion detecting signal detected by the contour portion detecting means at a predetermined level. A variable delay means for delaying and allowing the low-frequency component of the input video signal to pass therethrough, and controlling the variable delay means by the judgment signal of the judging means to perform contour correction. A contour correction circuit comprising: a generation unit that generates a low-frequency component of a video signal; and an addition unit that adds a high-frequency component of the input video signal or a signal obtained by multiplying the high-frequency component by a coefficient. 2. A contour portion detecting means for detecting a contour portion of an input video signal, and a judging means for obtaining a judgment signal by judging the contour portion detecting signal detected by the contour portion detecting means at a predetermined level. And a variable delay means capable of delaying and passing the low-frequency component of the input video signal and varying the delay time, and controlling the variable delay means by the judgment signal of the judgment means to control the contour correction video signal. Generating means for generating a low frequency component, and a new contour correction for adding a high frequency component of the input video signal or a signal obtained by multiplying the high frequency component by a coefficient, and extracting a high frequency component of the input video signal A contour correction circuit comprising: an addition unit that adds signals to obtain a main signal. 3. A generation means for inputting a low-frequency component of an input video signal to a variable delay circuit and controlling the variable delay circuit with a determination signal to generate a low-frequency component of a contour correction video signal; Adding means for adding a high-frequency component of the signal or a signal obtained by multiplying the high-frequency component by a coefficient, and adding a new contour correction signal obtained by extracting the high-frequency component of the input video signal as a main signal. The determination signal is provided for each of a plurality of input video signals, and the determination signal detects a contour portion of a specific video signal of the plurality of input video signals to obtain a contour detection signal, and determines the detection signal at a predetermined level. And a plurality of the variable delay circuits are controlled by the determination signal. 4. A generation means for inputting a low-frequency component of an input video signal to a variable delay circuit and controlling the variable delay circuit with a determination signal to generate a low-frequency component of a contour correction video signal; A high-frequency component of the signal or an adder circuit for adding a signal obtained by multiplying the high-frequency component by a coefficient is provided for each of a plurality of input video signals, and the determination signal is a specific video among the plurality of input video signals. A contour characterized by detecting a contour portion of a signal to obtain a contour detection signal, judging and generating the detection signal at a predetermined level, and controlling the plurality of variable delay circuits by the judgment signal. Correction circuit. 5. At least one of a plurality of input video signals
Input the low frequency components of one input video signal to the variable delay circuit,
The contour portion of the video signal is detected to obtain a contour portion detection signal, and the variable delay circuit is controlled by the determination signal obtained by determining the detection signal at a predetermined level, so that the low band of the contour correction video signal is controlled. A component is generated and an output signal is obtained by adding a high frequency component of the video signal or a signal obtained by multiplying the high frequency component by a coefficient, and other input video signals are directly input to each variable delay circuit. Then, an output signal controlled based on the determination signal is obtained from the variable delay circuit, or a new high frequency component of the input video signal is extracted by using the output signal of the variable delay circuit as a main signal. A contour correction circuit, wherein an outline correction signal is added to the main signal to obtain an output signal. 6. At least one of a plurality of input video signals
Input the low frequency components of one input video signal to the variable delay circuit,
A contour detection signal is obtained by detecting a contour portion of the video signal, and the variable delay circuit is controlled by a determination signal obtained by determining the detection signal at a predetermined level, and the contour correction video signal low frequency component is controlled. A high-frequency component of the video signal or a signal obtained by multiplying the high-frequency component by a predetermined coefficient to form a main signal, and a new contour correction signal obtained by extracting the high-frequency component of the input video signal, The output signal is obtained by adding it to the main signal, and the other input video signals are directly input to the respective variable delay circuits, and the variable delay circuits are respectively controlled by the judgment signals to obtain the output signals. A contour which is characterized in that an output signal is obtained by adding a new contour correction signal obtained by extracting a high frequency component of the input video signal to the one using the output signal of the variable delay circuit as a main signal and the main signal. Correction circuit. 7. The plurality of input video signals are a luminance signal and a color signal or two color difference signals, and the contour portion is detected from the luminance signal. Contour correction circuit. 8. The contour correction circuit according to claim 5, wherein the signal input to the variable delay circuit is a color signal or two color difference signals. 9. The contour correction circuit according to claim 3, wherein the plurality of input video signals are an R signal, a G signal, and a B signal, and the contour portion is detected from the G signal.