JP2760255B2 - Image quality correction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image quality correcting apparatus used for improving a horizontal frequency characteristic of a video signal in a television image in a horizontal direction.

[0002]

2. Description of the Related Art As a conventional image quality correction device for improving a horizontal frequency characteristic of a video signal such as a luminance signal in a television image, for example, a horizontal enhancer using analog signal processing or digital signal processing is used. Have been. FIG. 11 is a block diagram showing a configuration of an example of a conventional image quality correction device, that is, an example of an enhancer. As shown in FIG. 11, the enhancer includes delay circuits 1 and 2, adders 3 and 6, subtracters 4, multipliers 5, and a limiter circuit 7. In FIG. 11, FIG.
The luminance signal shown in (a) is input to the delay circuit 1 and the adder 3. The luminance signal input to the delay circuit 1 is delayed by a predetermined amount, and its output is input to the subtractor 4, the delay circuit 2, and the adder 6. The delay circuit 2 delays the output of the delay circuit 1 by a predetermined amount and inputs the output to the adder 3. The adder 3 adds the input luminance signal shown in FIG. 12A and the output of the delay circuit 2, multiplies it by ２, and inputs the result to the subtractor 4.

The subtracter 4 subtracts the output of the adder 3 from the output of the delay circuit 1 and multiplies the output by １ ／ to obtain a signal shown in FIG. Can be Note that the delay circuits 1 and 2, the adder 3, and the subtractor 4 operate as a band-pass filter. The signal shown in FIG. 12B output from the subtractor 4 is input to the multiplier 5. The multiplier 5 multiplies the output of the subtractor 4 by the set gain and inputs the result to the adder 6. The adder 6 adds the output of the delay circuit 1 and the output of the multiplier 5 to obtain a luminance signal as shown in FIG. The luminance signal shown in FIG. 12C output from the adder 6 is output after limiting the number of bits (for example, 8 bits) or more set by the limiter circuit 7. As a result, undershoot and overshoot occur at the edge of the luminance signal shown in FIG. 12A, and the high-frequency component is reinforced.

[0004]

The conventional image quality correcting apparatus reinforces the high-frequency component of the video signal by using the enhancement method as described above, but as shown in FIG. Undershoots and overshoots occur at the edges of the signal, which often results in an unnatural image. Therefore, there is a need for a means for reinforcing a high-frequency component of a video signal without undershoot or overshoot. SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and an object of the present invention is to provide an image quality correction device for improving a high-frequency characteristic in which a natural image free of undershoot and overshoot is obtained.

[0005]

According to the present invention, there is provided an image quality correcting apparatus for improving the high frequency characteristics of a television signal to solve the above-mentioned problems of the prior art. A delay device for delaying a signal, a first derivative operation device for obtaining a first derivative signal from the television signal output from the delay device, and a second derivative signal for obtaining a second derivative signal from the television signal output from the delay device2 A second derivative calculating device for generating left and right interpolation pixel data of the correction target pixel data from the television signal output from the delay device, and generating the left and right interpolation pixel data based on the first and second differential signals. The present invention provides an image quality correction device characterized by comprising a pixel interpolation calculation device for selecting and outputting one of them.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image quality correcting apparatus according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of an image quality correction device according to the present invention, FIG. 2 is a block diagram showing a specific configuration of a delay device 10 and a primary differential operation device 20 in FIG. 1, and FIG. FIG. 4 is a block diagram showing a specific configuration of the pixel interpolation calculation device 40, and FIG. 5 is a block diagram showing a specific configuration of the pixel interpolation calculation device 40. Coring circuit 2
FIG. 6 is a graph showing characteristics of the first and second differential operation devices 20 and 33.
And limiter circuits 23 and 34 in the second order differential operation device 30
FIG. 7 is a diagram showing the characteristics of the low-pass filter 32 in the second-order differential operation device 30 and its effect. FIG. 8 is a diagram showing the characteristics of the limiter circuit 42 in the pixel interpolation operation device 40. Is a waveform diagram for explaining the image quality correcting device of the present invention, and FIG. 10 is a diagram for explaining the principle of the image quality correcting device of the present invention.

First, the principle of the image quality correcting apparatus of the present invention will be described with reference to FIG. In FIG. 10, circles are data points. As an example, FIG.
The input signal (luminance signal) shown in FIG. FIG. 10 (b)
Is a signal obtained by first-order differentiating the input signal shown in FIG. 10A, and positive and negative values are generated at the rising and falling slopes, respectively.
FIG. 10 (c) is a signal obtained by secondarily differentiating the input signal shown in FIG. 10 (a). Negative and positive values occur at the rising and falling slopes of the primary differential signal shown in FIG. 10 (b), respectively. . In addition,
Here, the signs of the primary differential signal and the secondary differential signal change depending on the subtraction direction. Here, the secondary differential signal is different from the primary differential signal. The waveform is such that a signal obtained by differentiating the primary differential signal is inverted. FIG. 10D summarizes the results for each region. In order to improve the high frequency characteristics regardless of the conventional enhancement method, the input signal shown in FIG. Therefore, when the sign of the first derivative is +, the data is shifted from left to right when the sign of the second derivative is-, and when the sign of the first derivative is +, the sign is + from the right. In the same manner, when the sign of the first derivative is-, the sign of the second derivative is +, the data is shifted from left to right, and the sign of the first derivative is-, and the sign of the second derivative is-. Place the data from right to left.

That is, as a means for determining the sign of the first derivative and the sign of the second derivative, for example, an EXOR (exclusive OR) circuit is used, and an exclusive OR of them is obtained as shown in FIG. In addition, a control signal is obtained such that data of 1 is interpolated from the left of the pixel to be corrected and data of 0 is interpolated from the right of the pixel to be corrected. When data is interpolated by this control signal, a signal as shown in FIG. 10E is obtained, and the slope is raised to improve the high frequency characteristics. Also, the place where the value of the first derivative shown in FIG. 10 (b) is 0 is a flat part, so it may be left as it is. Therefore, the part for detecting the zero value of the first derivative may be used as a control signal that outputs the data without correction. It should be noted that, even if the correction is performed in all the parts, there is no significant effect on the image quality, so that the main effects of the present invention can be obtained without the detection of the zero value and the control thereof.

Next, the configuration and operation of the image quality correcting apparatus of the present invention based on the above principle will be described. As shown in FIG. 1, the image quality correction device of the present invention includes a delay device 10,
It comprises a first-order differential operation device 20, a second-order differential operation device 30, and a pixel interpolation operation device 40. Delay device 10
Is composed of four delay circuits 11 to 14 as described later with reference to FIG.
Next differentiating circuit 21, Coring circuit 22, Limiter circuit 2
3, an OR circuit 24, a secondary differential operation device 30
Is a second-order differentiator 31, a low-pass filter (LPF) 3
2, a coring circuit 33, and a limiter circuit 34. The pixel interpolation operation device 40 includes an interpolation filter 41, a limiter circuit 42, a delay circuit 43, a determination circuit 44, and a switch 4.
5 and 46. In FIG. 1, the signal lines from the delay device 10 to the primary differential operation device 20, the secondary differential operation device 30, and the pixel interpolation operation device 40 are simplified and drawn. In the present embodiment described below, the input signal is a luminance signal, for example, a waveform shown in FIG.

As shown in FIG. 2, the delay device 10 is composed of four delay circuits 11 to 14 having a delay time P, and the delay circuit 11 receives the input 8-bit pixel data D.
(-2) is delayed to output D (-1), and the delay circuit 12
Delays D (-1) and outputs D (0), and delay circuit 1
3 delays D (0) and outputs D (1), and delay circuit 1
4 delays D (1) and outputs D (2). For example, if the sampling of the delay circuits 11 to 14 is four times the subcarrier, the delay circuit for one pixel is set to about 70 ns. Now, assuming that the central pixel of the operation is D (0), the first derivative is obtained by {D (-1) -D (1)}. Therefore, D (-1) and D (1) output from the delay circuits 11 and 13 in the delay device 10 are input to a primary differential circuit (subtraction circuit) 21 in a primary differential operation device 20,
The primary differentiating circuit 21 subtracts D (1) from D (-1) to obtain 1
The next differential signal (corresponding to FIG. 10B) is output.

The primary differential value (8 bits) is used to adjust the detection sensitivity and to avoid the influence of noise.
As shown in FIG. 5, the input is ± a
In the range, the output is cored so that the output becomes 0 and output. Here, as an example, the coring circuit 22
Is a straight line, but it may be a curve, and it is more preferable that the curve shape and a can be arbitrarily set. The output (9 bits) of the coring circuit 22 from which the minute level signal of ± a or less has been removed is input to the limiter circuit 23. The reason why the input of the coring circuit 22 is 8 bits and the output is 9 bits is that the carry or the borrow is added to the 8 bits to make the operation 9 bits.

The characteristics of the limiter circuit 23 are as shown in FIG. 6. For example, the input of 9 bits is limited to 4 bits. Here, the coring circuit 22 and the limiter circuit 23 are configured by different blocks, but may have both characteristics of the coring and the limiter. One bit of the most significant bit (MSB) of the four bits output from the limiter circuit 23 is a polarity detection signal (FIG. 1).
0 (d), and all four bits of the output of the limiter circuit 23 are input to an OR circuit 24 to perform a logical OR operation, and a 0 detection signal representing a flat portion (0 value) is obtained. I do. Therefore, the OR circuit 24 operates as a 0 detection signal output unit. In this embodiment, the limiter circuit 2
Although 3 is provided, polarity detection and 0 detection are possible without a limiter circuit. Here, the handling of signed data is exemplified by two's complement.

On the other hand, D from the delay device 10 shown in FIG.
Output data A, B, (-2), D (0), D (2)
C is input to the second derivative operation device 30. As shown in FIG. 3, the second differentiating circuit 31 in the second differentiating operation device 30 is composed of an adder 311 and a subtractor 312.
The F32 includes delay circuits 321 and 322 and adders 323 and 324, as shown in FIG. Now, since the central pixel of the operation is data B which is D (0), the second derivative is ΔD (0) −0.5 × (D (−2)
+ D (2))}. Therefore, as shown in FIG. 3, the adder 311 adds the data A (D (−2)) and the data C (D (2)), multiplies them by 、, and subtracts them.
Subtracts the output of the adder 311 from the data B (D (0)), multiplies it by 倍, and outputs a second derivative signal (corresponding to FIG. 10C).

The second derivative (8 bits) is input to the LPF 32 and processed in order to remove the vicinity of 3.58 MHz where the adverse effect of the phase shift occurs from being corrected. That is, the second derivative output from the subtractor 312 is sequentially delayed by the delay circuits 321 and 322 having the delay time Q.
23 adds the secondary differential value output from the subtractor 312 and the output of the delay circuit 322 and multiplies by 微分, and the adder 324 adds the output of the adder 323 and the output of the delay circuit 321 to 1 /
Output twice. The frequency characteristic of the secondary differential signal from the secondary differential circuit 31 is as shown in FIG.
(B) is a frequency characteristic of the LPF 32 described above. Therefore, the resulting detection area (image quality improvement area) is shown in FIG.
An area indicated by oblique lines in FIG. Note that the delay circuit 321
And 322 are about 140 ns with a delay of 2 pixels if sampling is, for example, four times the subcarrier.

The output (8 bits) of the LPF 32 is input to a coring circuit 33 in order to adjust the detection sensitivity and avoid the influence of noise, and as shown in FIG.
When the input is in the range of ± a, the output is cored so that the output becomes 0. Here, as an example, the characteristic of the coring circuit 33 is a straight line, but may be a curve.
It is even better if the curve shape and a can be arbitrarily set. The output (9 bits) of the coring circuit 33 from which the minute level signal of ± a or less has been removed is input to the limiter circuit 34. The reason why the input of the coring circuit 33 is 8 bits and the output is 9 bits is that the carry or the borrow is added to the 8 bits and the operation becomes 9 bits as described above.

The characteristics of the limiter circuit 34 are as shown in FIG. 6. For example, the input of 9 bits is limited to 4 bits. Here, the coring circuit 33 and the limiter circuit 34 are configured by different blocks, but may have both characteristics of the coring and the limiter. One of the most significant bit (MSB) of the four bits output from the limiter circuit 34 is used as a polarity detection signal (FIG. 1).
0 (d)). In this embodiment, the limiter circuit 34 is provided, but the polarity can be detected without the limiter circuit. Here, the handling of signed data is exemplified by two's complement.

The primary and secondary differential signs shown in FIG. 10D correspond to the primary differential circuit (subtraction circuit) 21 in the primary differential operation device 20 shown in FIG. 2 and the secondary differential circuit shown in FIG. The sign changes when the direction of subtraction of the subtraction circuit 312 of the secondary differentiation circuit 31 in the differentiation operation device 30 is changed. In the above-described embodiment, the sign is set so that the determination circuit 44 in the pixel interpolation calculation device 40 described later will be easily configured.

Next, the pixel interpolation operation device 40 will be described. As described in the principle of the present invention, since the correction target pixel data obtains the left and right values before the correction as the correction value,
First, a method of directly converting left and right data can be considered. In this case, since the effect may be remarkable, it is preferable to interpolate values between adjacent pixels and derive the result. In addition, this configuration has a feature that the effect of correction can be adjusted within the range of one pixel. As shown in FIG. 4, the interpolation filter 41 in the pixel interpolation operation device 40 is configured by multipliers 411 to 414 to which data D to G are input and an adder 415 for adding outputs of the multipliers 411 to 414. ing. D (−) from the delay device 10 shown in FIG.
Output data D, E, F, and G, which are 2), D (-1), D (0), and D (1), are input to the interpolation filter 41 in the pixel interpolation operation device 40.

The pixel data to be interpolated is in data F which is D (0), and its left and right components are between E and F, respectively.
It is between G. The function of the pixel interpolation arithmetic unit 40 is to create the data between EF and FG by four-point interpolation. First, to generate interpolation data between E and F by the interpolation filter 41, all the data D, E, F, and G are used. The coefficients of multipliers 411 and 414 are β, and the coefficients of multipliers 412 and 413 are α. These coefficients α and β are, for example, the following two types. α = 5/8, β = −1 / 8 (1) α = 1/2, β = 0 (2) If the coefficients α and β of the multipliers 411 to 414 are set to (1), this interpolation is performed. The filter 41 has good high-frequency reproducibility. If the condition (2) is satisfied, the interpolation filter 41 does not have good high-frequency reproducibility, but has a noise suppression effect of about 3 dB.

The output of the interpolation filter 41 is input to a limiter circuit 42 having characteristics as shown in FIG. 8, and is output with its amplitude limited to 8 bits. Thereby, interpolation data (interpolated value) between EF is generated. Since the interpolated data (interpolated value) between FG is delayed from the interpolated data (interpolated value) between EF by one pixel time, the limiter circuit 4
2 is input to the delay circuit 43 having a delay time P, and is delayed by a time corresponding to one pixel. Then, an interpolation value between FG, that is, an interpolation value on the right side of the interpolation target pixel data in FIG. 9 or FIG. 10A is obtained at one terminal 45a of the switch 45, and the other terminal 45b is obtained at the other terminal 45b. An interpolation value between E and F, that is, an interpolation value on the left side of the interpolation target pixel data in FIG. 9 or FIG. 10A is obtained. The polarity detection signal obtained from the primary differential operation device 20 and the polarity detection signal obtained from the secondary differential operation device 30 are input to the determination circuit 44 which is an EXOR circuit.
By taking the OR, a determination signal is output as to which interpolation value should be selected.

The switch 45 is switched by a 1 or 0 decision signal output from the decision circuit 44. That is, when the judgment signal is 1, the output of the delay circuit 43 is selected to shift the data from left to right, and when the judgment signal is 0, the output of the limiter circuit 42 is shifted to shift the data from right to left. Select Further, the data F is input to one terminal 46a of the switch 46,
The output of the switch 45 is input to the other terminal 46b. As described above, the place where the value of the first derivative is 0 is a flat place, and it is not necessary to perform correction on the data.
The switch 46 is switched by the 0 detection signal obtained from the primary differential operation device 20. That is, the 0 detection signal output from the OR circuit 24 in the primary differential operation device 20 is 0
In this case, the switch 46 is connected to the terminal 46a, and when the 0 detection signal is 1, the switch 46 is connected to the terminal 46b. If the image quality correction is not performed, the switch 46 may be forcibly connected to the terminal 46a.

In this manner, the switch 46 is turned off as shown in FIG.
A luminance signal whose image quality has been corrected as shown in (c) is output. By comparing the input luminance signal shown in FIG. 9A and the output luminance signal shown in FIG. 9C, it can be seen that the slope portion is sharpened and the high frequency component is reinforced. FIG. 9 (b)
Shows a luminance signal after image quality correction by a conventional image quality correction device (enhancer) for comparison. This FIG. 9 (b)
9 (c) and FIG. 9 (c), according to the image quality correcting apparatus of the present invention, the high frequency characteristic is improved without undershoot and overshoot, and a natural image can be obtained. Further, since the image quality correction device of the present invention includes the interpolation filter 41 in the image quality interpolation operation device 40, it also has a high-frequency noise attenuation effect.

In the image quality correcting apparatus according to the present embodiment described above, a luminance signal has been described as an example of an input signal, but an R, G, B signal or a demodulated color difference signal may be used as an input signal. Good. Further, in the image quality correction device of the present embodiment, the delay time of the four delay circuits 11 to 14 constituting the delay device 10 is set to the delay time for one pixel, and the high frequency component is corrected. Applying the image quality correction device of the present invention, if the input signal contains many low-frequency components, a longer pixel delay time and interpolation from distant pixels can obtain a lower-frequency enhancement effect. Is also possible. At this time, the target band is also detected in the primary differential operation device 20 and the secondary differential operation device 30. Also, at this time, the band limiting characteristic of the LPF 32 in the secondary differential operation device 30 is changed in accordance with it.

[0024]

As described in detail above, the image quality correcting apparatus according to the present invention comprises a primary differential operation device for obtaining a primary differential signal of a television signal and a secondary differential operation device for obtaining a secondary differential signal. And a pixel interpolation arithmetic unit that generates left and right interpolation pixel data of the pixel data to be corrected and selects one of the left and right interpolation pixel data from the primary differential signal and the secondary differential signal. The slope portion of the John signal can be made steeper, so that there is no undershoot or overshoot at the edge portion of the signal unlike a conventional enhancer, and a natural image can be obtained. Further, if the interpolation pixel data is set between the pixel data to be corrected and the adjacent left and right pixel data, the effect of the image quality correction can be adjusted within the range of one pixel, and the primary differential operation device and the secondary If a coring circuit is provided in the differential operation device, the sensitivity can be adjusted and the influence of noise can be avoided. Further, since the pixel interpolation operation device includes the interpolation filter for generating the interpolation pixel data, it has a secondary effect that it also has an attenuation effect on high-frequency noise.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of an image quality correction apparatus according to the present invention.

FIG. 2 shows a delay device 10 and a first-order differential operation device 2 in FIG.
FIG. 3 is a block diagram showing a specific configuration of a 0.

FIG. 3 is a block diagram showing a specific configuration of a secondary differential operation device 30 in FIG.

FIG. 4 is a block diagram showing a specific configuration of the pixel interpolation operation device 40.

FIG. 5 shows a primary differential operation device 20 and a secondary differential operation device 3
FIG. 4 is a diagram illustrating characteristics of the coring circuits 22 and 33 within 0.

FIG. 6 shows a primary differential operation device 20 and a secondary differential operation device 3
FIG. 4 is a diagram illustrating characteristics of limiter circuits 23 and 34 in 0.

FIG. 7 shows a low-pass filter 3 in the second-order differential operation device 30;
FIG. 4 is a diagram showing characteristics of No. 2 and its effects.

8 is a diagram showing characteristics of a limiter circuit 42 in the pixel interpolation operation device 40. FIG.

FIG. 9 is a waveform chart for explaining the image quality correction device of the present invention.

FIG. 10 is a diagram for explaining the principle of the image quality correction device of the present invention.

FIG. 11 is a block diagram illustrating an example of a conventional image quality correction device.

FIG. 12 is a waveform chart for explaining a conventional image quality correction device.

[Description of Signs] 10 Delay device 11 to 14, 43 Delay circuit 20 Primary differential operation device 21 Primary differential circuit 22, 33 Coring circuit 23, 34, 42 Limiter circuit 24 OR circuit (detection signal output means) 30 2 Secondary differentiation operation device 31 Secondary differentiation circuit 32 Low-pass filter 40 Pixel interpolation operation device 41 Interpolation filter 44 Judgment circuit (EXOR circuit) 45, 46 Switch

Claims (6)

(57) [Claims] An image quality correction device for improving a high frequency characteristic of a television signal, comprising: a delay device for delaying an input television signal; A first differential operation device for obtaining a second differential signal; a second differential operation device for obtaining a second differential signal from the television signal output from the delay device; and a pixel to be corrected based on the television signal output from the delay device A pixel interpolation arithmetic unit that generates left and right interpolation pixel data of the data and selects and outputs one of the left and right interpolation pixel data from the primary differential signal and the secondary differential signal. An image quality correction device characterized by the above-mentioned. 2. The delay device includes first to fourth delay circuits for sequentially delaying the input television signal, and the primary differential operation device includes left and right adjacent to the correction target pixel data. A first differentiating circuit for obtaining a first derivative signal from the pixel data, a first coring circuit for coring below a minute level of the first derivative signal for sensitivity adjustment, and a positive / negative sign of the first derivative signal. Means for obtaining a first polarity detection signal for determining the polarity, wherein the secondary differential operation device obtains a secondary differential signal from left and right pixel data separated by two pixels from the correction target pixel data. A second-order differentiating circuit, a low-pass filter for limiting a band of the second-order differential signal, a second coring circuit for coring below a minute level of an output of the low-pass filter for sensitivity adjustment, and the second-order differential signal of Means for obtaining a second polarity detection signal for determining a negative polarity, wherein the pixel interpolation operation device calculates a second polarity detection signal from a television signal output from the first to fourth delay circuits of the delay device. An interpolation filter that generates left and right interpolation pixel data between the correction target pixel data and adjacent left and right pixel data,
2. The apparatus according to claim 1, further comprising a first switch for selecting the left and right interpolation pixel data, and a determination circuit for controlling the first switch based on the first polarity detection signal and the second polarity detection signal. 2. The image quality correction device according to 1. 3. A detection signal output means for detecting a flat portion of the inputted television signal and outputting a detection signal to said first derivative operation device, and said pixel interpolation operation device includes: A second switch for selecting pixel data and the interpolated pixel data output from the first switch; and controlling the second switch by a detection signal output from the detection signal output unit. 3. The image quality correction apparatus according to claim 2, wherein the correction target pixel data is output as it is in a flat portion of the input television signal. 4. The method according to claim 1, wherein the first polarity detection signal and the second polarity detection signal are the most significant bits of the primary differential signal and the secondary differential signal, respectively, or a signal obtained by limiting the bits. The image quality correction device according to claim 2. 5. The detection signal output means according to claim 1, wherein the first differential signal or a signal obtained by bit-limiting the first differential signal is ORed.
The image quality correction device according to claim 3, wherein the image quality correction device is an R circuit. 6. An EXOR circuit for calculating an exclusive OR of the first polarity detection signal and the second polarity detection signal.
6. The image quality correction device according to claim 2, wherein the image quality correction device is a circuit.