JPH04294687A - Picture quality improving device - Google Patents

Abstract

PURPOSE:To obtain a device in which edge emphasis can be performed in a natural form without giving sense of incongruity to an appreciator and a circuit can be easily made into a digital circuit and fine adjustment can be applied to edge emaphasizing quantity by attaching a waveform step on the midpoint of the oblique part of an input signal precisely. CONSTITUTION:A control signal Sc can be obtained from the input signal S1, the output signal S2 of a delay circuit 1, and the output signal S3 of a delay circuit 2 by subtractors 3-5 and a control signal formation circuit 8. The output signal S7 of a mixer 6, the output signal S8 of a mixer 7, and the signal S2 are supplied to a signal selection circuit 9. The signal selection circuit 9 outputs selectively one of supplied three signals S7, S2, and S8 corresponding to the control signal Sc, and an output signal So to which edge emphasis is applied can be obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is applicable to television (TV).
) The present invention relates to an image quality improvement device suitable for various video devices such as television receivers, video tape recorders (VTRs), and printers, and various image processing devices that handle image data. and,
The purpose of this invention is to provide an image quality improvement device that can perform edge enhancement in a natural manner without causing any discomfort to viewers, improve the sharpness and resolution of reproduced images, and is suitable for digital circuits. There is.

0002

[Prior Art] Conventionally, in contour correction used to improve image quality, contour correction components are obtained by quadratic differential processing.
An appropriate amount of this correction component was added to the original signal. In this method, the second-order differential waveform, which is the contour correction component, has a peak far outside the midpoint of the waveform changing part (edge part) of the original signal. Therefore, if this second-order differential waveform is added to the original signal, preshoot or overshoot may occur, resulting in unnatural contour correction such as white and black borders on the edges of the reproduced image. was there.

0003

[Problems to be Solved by the Invention] The problem to be solved by the present invention is to prevent preshoot and overflow by adding a waveform step to the midpoint position of the waveform change part (edge part) of the original signal. In order to create an image quality improvement device that can prevent unnatural contour correction caused by shots, improve sharpness and resolution in a natural manner without giving viewers a sense of discomfort, and is suitable for digital circuitization. The point is what measures should be taken.

0004

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a second signal obtained by delaying a first signal as an input signal by a predetermined time, and a delay circuit that outputs a time-delayed third signal;
a fourth signal obtained by subtracting the second signal from the first signal;
a second subtracter that outputs a fifth signal obtained by subtracting the third signal from the second signal; and a second subtracter that outputs a fifth signal obtained by subtracting the third signal from the second signal; a third subtracter that outputs a sixth signal obtained by subtracting the fifth signal; and a third subtracter that outputs a sixth signal obtained by subtracting the fifth signal; and a third subtracter that outputs a sixth signal obtained by subtracting the fifth signal; a first mixer that outputs a signal No. 7; and a second mixer that outputs an eighth signal obtained by mixing the second signal and the fifth signal at a second predetermined ratio. and a ninth signal that is a control signal that is supplied with the fourth, fifth, and sixth signals and that changes depending on the combination of polarities of the fourth, fifth, and sixth signals. A control signal forming circuit that outputs the seventh, second, eighth, and ninth signals is supplied, and the seventh
, a signal selection circuit that selects and outputs one of the second and eighth signals, and the control signal forming circuit includes:
(b) Control in which the signal selection circuit selectively outputs the eighth signal when the values of the fourth, fifth, and sixth three signals are simultaneously positive or simultaneously negative values of the same polarity. (b) the values of the fourth and fifth signals are values of the same polarity that are simultaneously positive or negative at the same time, and the value of the sixth signal is the same as that of the fourth and fifth signals; (c) when the polarity of the signal value is different from the polarity of the signal value, the signal selection circuit outputs a control signal for selectively outputting the seventh signal; When the combination of signal values is a combination other than the above (a) and (b), the signal selection circuit outputs a control signal for selectively outputting the second signal, and the signal selection circuit outputs a control signal that selects and outputs the second signal. The present invention provides an image quality improvement device characterized by obtaining an output signal in which the edges of a first signal are emphasized.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an image quality improving apparatus according to the present invention. Further, FIG. 2 is a diagram showing a specific configuration example of a subtracter and a mixer, FIG. 3 is a diagram showing a specific configuration example of a control signal forming circuit and a signal selection circuit, and FIG. 4 is a diagram showing a specific configuration example of a control signal forming circuit and a signal selection circuit. FIG. 3 is an explanatory diagram of an example operation. In FIG. 4, the steps of the waveform slope are exaggerated to make the explanation easier to understand. Furthermore, even when using a digital circuit as a specific circuit example, in order to make the explanation of its operation easier to understand, FIG.
Assume that the signal waveform of the circuit is shown as an analog waveform. In FIG. 1, 1 and 2 are delay circuits having the same delay time, 3 to 5 are subtracters, 6 and 7 are mixers, 8 is a control signal forming circuit, and 9 is a signal selection circuit. For convenience of explanation, signal delays due to the processing time of each circuit itself, and delay circuits and the like that are normally used simply to correct the delays will be omitted. The input signals handled by this image quality improvement device include various video signals, brightness signals, RG
B signal etc. can be considered. First, a case will be described in which the input signal S1 coming from the line L1 is a signal with a bar pulse waveform as shown in FIG. 4(a). This signal is TV
This is an example of a waveform of a luminance signal of a video signal, and the frequency component is band-limited to an upper limit frequency of 4 MHz. Input signal S1 is supplied to delay circuit 1. Delay circuit 1
The delay time T of

[0006]

[Math 1]

[0007] The value of this delay time T is a value set based on the sampling frequency fs (fs = 4fsc) that is normally used when quantizing a TV video signal and processing the signal in a digital system. It corresponds to the period of change. If the frequency component of the TV video signal is band-limited up to 4MHz, the impulse response obtained from the ideal characteristics is as follows:

[0008]

[Math 2]

From the half width (approximately 150.8 ns) of

0010

[Math 3]

That is, the object of the present invention can be achieved by setting the value to be less than 1/2 of the half width. In delay circuit 1,
The output signal S2 delayed by time T is shown in FIG. 4(b). The next-stage delay circuit 2 has the same function as the delay circuit 1, and outputs a signal S3 (see FIG. 4(c)) obtained by further delaying the supplied signal S2 by a time T. The subtracter 3 subtracts the output signal S2 of the delay circuit 1 from the input signal S1 and outputs a signal S4 expressed by the following equation. Waveform of signal S4 (Figure 4 (
d) is a differential waveform.

0012

[Math 4]

The subtracter 4 has the same function as the subtracter 3, and subtracts the output signal S3 of the delay circuit 2 from the output signal S2 of the delay circuit 1, and outputs a signal S5 shown in the following equation.

[0014]

[Math 5]

The subtracter 5 also has the same function as the subtracter 3, and converts the output signal S5 of the subtracter 4 from the output signal S4 of the subtracter 3.
is subtracted, and a signal S6 shown in the following equation is output. The waveform of the signal S6 (see FIG. 4(f)) is a second-order differential waveform, that is, a second-order differential waveform.

[0016]

[Math 6]

Specific configuration examples of the subtracters 3 to 5 based on equations (4) to (6) are shown in FIGS. 2(a) to 2(c), respectively. Returning to FIG. 1, the mixer 6 receives the output signal S of the subtracter 3.
4 and the output signal S2 of the delay circuit 1 are supplied. The output signal S7 of the mixer 6 when the mixing ratio is k is shown in the following equation.

[0018]

[Math 7]

By substituting equation (4) into equation (7) above, the following equation (8) is obtained.

[0020]

[Math. 8]

From equation (8), when the mixing ratio k=0, the signal S2 becomes the output signal S7, when k=1, the signal S1 becomes the output signal S7, and when k=0.5, the signal S2 becomes the output signal S7, and when k=0.5, the signal S2 becomes the output signal S7.
2)/2 becomes the output signal S7. The waveform of the signal S7 when k=0.5 is shown in FIG. 4(g). Compared to the original signal S1, the rising and falling slopes of the signal S7 (k=0.5) are slightly gentler. Formula (7)
A specific circuit example of the mixer 6 based on the above is shown in FIG. 2(d). Block 6-1 is an amplifier that sets the mixing ratio k. In an analog circuit, the amplifier 6-1 can be realized by an amplifier with gain control, and in a digital circuit, it can be realized by a ROM
This can be realized using a table lookup circuit using, for example. Block 6-2 is an adder. Similarly, the expression (
A specific circuit example of the mixer 6 based on 8) is shown in FIG. 2(f). Blocks 6-3 and 6-4 are amplifiers that set the same mixing ratio as the amplifier 6-1, and block 6-5
is an adder. Returning to FIG. 1, the output signal S5 of the subtracter 4 and the output signal S2 of the delay circuit 1 are supplied to the mixer 7. The output signal S8 of the mixer 7 when the mixing ratio is k is shown in the following equation.

[0022]

[Math. 9]

By substituting equation (5) into equation (9) above, the following equation (10) is obtained.

[0024]

[Math. 10]

From equation (10), when the mixing ratio k=0, the signal S2 becomes the output signal S8, and when k=1, the signal S3 becomes the output signal S8.
becomes the output signal S8, and when k=0.5, (S2+
S3)/2 becomes the output signal S8. The waveform of the signal S8 when k=0.5 is shown in FIG. 4(h). Compared to the original signal S1, the rising and falling slopes of the signal S8 (k=0.5) are slightly gentler. Formula (9)
A specific circuit example of the mixer 7 based on equation (10) is shown in FIG. 2(e), and FIG. 2(g) shows a specific circuit example of the mixer 7 based on equation (10).
) are shown respectively. Each block 7-1 to 7-5 is a circuit similar to each block of mixer 6. Returning to FIG. 1 again, the next stage control signal forming circuit 8 includes subtracters 3, 4,
5 output signals S4, S5, S6 are provided. The control signal forming circuit 8 forms the control signal Sc according to the combination of polarities of the signals S4, S5, and S6. The control signal Sc is composed of three signals Sc7 and S shown in the following equation (11).
It is a low active (negative logic) logic signal consisting of c2 and Sc8. Waveform diagrams of the signals Sc7, Sc2, and Sc8 are shown in FIGS. 4(j), (k), and (i).

[0026]

[Math. 11]

As described above, when the values of the signals S4, S5, and S6 are both positive or both negative and have the same polarity, the signal Sc8 becomes 0 (Low), and the values of the signals S4, S5 are both positive or both negative. When the signal S6 is negative and has the same polarity and has a different polarity from the signals S4 and S5, the signal Sc7 becomes 0 (
When the combination of values of signals S4, S5, and S6 is other than the above (when both Sc8 and Sc7 are 1 (High)), signal Sc2 becomes 0 (Low).
becomes.

An example of a circuit implementing the control signal forming circuit 8 is shown in FIG. 3(a). In FIG. 3(a), converters 3-1 to
3-3 converts the signals S4 to S6 (8-bit signals in two's complement representation) to 1 when positive, 0 when zero, and -1 when negative, and converts them into two's complement representation. Output as a 2-bit signal. The conversion table of each converter is shown in Table 1, and the 2-bit signals of the signals S4 to S6 expressed in two's complement are shown in the following equation (12).

[0029]

[Table 1]

[0030]

[Math. 12]

The converters 3-1 to 3-3 can be realized using a table lookup method using TTL-IC, ROM, etc., and can also be realized using PLA (Programmable L
It can also be realized using Logic Array). The three converter outputs are AND circuits 3-4 to 3-8 and OR circuit 3-9.
, 3-10, NAND circuit 3-11, 3-12, 3-1
3, control signals Sc7, Sc2, Sc8 shown in the following equations
becomes.

[0032]

[Math. 13]

Note that in FIG. 3(a), each signal name Sc7
, Sc2, and Sc8 are listed as mere names, but in the above equation (13), in order to clarify the purpose of use and operation of the signals, they are expressed as low active (negative logic) logical expressions (i.e., the bar is ), each signal is shown. In order to improve the performance of the control signal forming circuit 8 against noise components, the converters 3-1 to 3-3 are provided with a patent application filed by the present inventor (filed on March 18, 1991, reference number H0300).
The converters 3-1 to 3-3 (converters having a slicing function) of the control signal forming circuit 6 described in 0095) may be used. In this case, the control signal formed by the control signal forming circuit 8 of this embodiment is the same as the control signal described in the previous patent application. Returning to FIG. 1, the next stage signal selection circuit 9 has a control signal Sc (signals Sc7, Sc2).
, Sc8) and signals S7, S2, and S8 are supplied. The signal selection circuit 9 selects the signals S7, S7, and S7 according to the control signal Sc.
One of the signals S2 and S8 is selectively output. The output So of the signal selection circuit 9 is expressed by the following equation (14).

[0034]

[Math. 14]

That is, the signal selection circuit 9 selects the control signal Sc7.
When is 0 (Low), the signal S7 is selectively output, when the control signal Sc2 is 0 (Low), the signal S2 is selectively output, and when the control signal Sc8 is 0 (Low), the signal S8 is selectively output. .

An example of a circuit for realizing the signal selection circuit 9 is shown in FIG.
Shown in c). Blocks 3-14, 3-15, and 3-16 are switch circuits. Each switch circuit 3-14 to 3-1
6 are supplied with signals S7, S2, and S8, respectively, and one of the control signals Sc7, Sc2, and Sc8 is 0 (Low).
), the switch circuit to which the control signal is supplied is turned on, and one of the signals S7, S2, and S8 is output from the common output terminal. Each of the switch circuits 3-14 to 3-16 has the same configuration. FIG. 3B shows the switch circuit 3-14 as a representative example of the switch circuits 3-14 to 3-16. The signals S7 and So are assumed to be 8-bit, two's complement representation. Blocks 3-20 to 3-27 are buffer circuits with control terminals, and the common control terminals have a control signal Sc.
7 is supplied. This control signal Sc7 is 0 (Low)
), the input signal S7, that is, S70 (LSB) ~
S77 (MSB) is the output So (i.e. S00
(LSB) to S07 (MSB)). When the control signal Sc7 is 1 (High), the output is in a tristate or high impedance state. The output signal So of the signal selection circuit 9 (output of this image quality improvement device) obtained in this way has a waveform shown in FIG. 4(l).

Comparing this output waveform So with the input waveform S1, the output waveform So has a waveform step added at approximately the midpoint of the waveform changing part (edge part) of the input waveform S1, and the slope of the waveform slope part is steep. It can be seen that the waveform has properly edge-emphasized edges. By reproducing the output signal So, a contour-corrected image can be obtained. In addition, as can be seen from the output waveform So shown in FIG. 4(l), the edge enhancement processing of this image quality improvement device is effective against edges that exceed the amplitude of the original signal, such as preshoot and overshoot, as in conventional contour correction. This is not an enhancement process, but an edge enhancement process within the amplitude of the original signal. Therefore, even if a device incorporating this image quality improvement device is configured with a digital circuit, the problem of overflow will not occur, and the device can improve the image quality. The output waveform So shown in FIG.
This is a waveform when both mixing ratios k are set to k=0.5. FIG. 4(m) shows the output waveform So when the mixing ratios k of the mixers 6 and 7 are both set to 1, which is the maximum value that can be set. This is a state in which the maximum waveform step is added (a state in which the amount of edge enhancement is maximum). The output waveform So when the mixing ratio k is set to 0, which is the minimum settable value, is the same waveform as the original signal S1 to which no waveform step is added. In this way, in this embodiment, the amount of edge enhancement can be adjusted, so the viewer can adjust the amount of edge enhancement that suits his or her preference, that is, the image quality that suits his or her preference, while viewing the reproduced image or signal waveform. Can be set. Furthermore, in this embodiment, two mixers are provided as described above. The output signal S8 of one of the mixers 7 is a portion to the left of the midpoint of the waveform changing portion (edge portion) of the output waveform So. The output signal S7 of the other mixer 6 is on the right side of the midpoint of the waveform changing section. Therefore, by setting the mixing ratios of the mixers 6 and 7 to different values, the waveform can be changed independently on both sides of the midpoint of the waveform changing section. Therefore, in this embodiment, the amount of edge enhancement can be adjusted more finely, and the various demands regarding image quality from viewers can be fully met. In this way, the signal So output from the line L2 has new sideband components formed as a result of edge emphasis, and becomes a signal to which a spectrum beyond the original band of the input signal S1 has been newly added. . The addition of this new spectrum equivalently gives the viewer the impression that the resolution of the original signal has been improved, and serves to improve the sharpness of the image.

Here, the steepness of the edge portion of the signal So (degree of edge emphasis) depends on the frequency characteristics of the edge portion of the original signal S1 before edge emphasis, regardless of the value of the mixing ratio k. ing. If the rising and falling parts (edge parts) of the original signal have steeper slopes as shown in Figure 4(n), a strong degree of edge enhancement as shown in Figure 4(o) can be performed. be exposed. On the other hand, for a gentle slope as shown in FIG. 12(p), a weak degree of edge emphasis as shown in FIG. 2(q) is performed. In this way, the degree of edge enhancement processing depends on the frequency of the input signal and has a perfect correlation with the input signal, so this image quality improvement device can produce a natural shape without causing any discomfort to the viewer. With this, sharpness and resolution can be improved.

Another embodiment will be explained. In this embodiment, the mixer 6 mixes the signal S1 and the signal S2 to generate the signal S.
This embodiment is different from the embodiment shown in FIG. 1 in that the signal S2 and the signal S3 are mixed in the mixer 7 to obtain the signal S8. The other configurations and circuit operations are the same as the embodiment shown in FIG. A specific example of the configuration of the mixers 6 and 7 is shown in FIG.
f) and (g). In addition to having the same effect as the embodiment shown in FIG. 1, this embodiment can obtain the signals S7 and S8 that become the output signal So without using a subtracter, so that the small amplitude signal for the output signal So can be obtained. It has the unique effect of reducing the risk of noise intrusion in the subtracter used.

In each of the above embodiments, the input signal is a luminance signal band-limited to an upper limit frequency of 4 MHz, but the image quality improvement device of the present invention can input all baseband video signals and images such as RGB signals. Can handle signals. This image quality improvement device is also suitable for image processing devices that handle CG (computer graphics) images and natural images. In particular, for digitized image data, contour correction processing and edge enhancement processing equivalent to the present invention can also be realized by software processing using a computer. can also be applied. Furthermore, the present invention
It is also effective in improving eye pattern deterioration caused by waveform distortion in digital transmission systems.

[0041]

As described above, the image quality improving device of the present invention has the following effects. (b) Edge enhancement is performed by properly adding a waveform step to the midpoint of the slope part of the input signal, and as a result, an output signal with frequency components outside the frequency band of the input signal is obtained. , contour correction of the reproduced image can be performed. (b) This process does not emphasize edges exceeding the amplitude of the original signal, such as preshoot and overshoot, as in conventional contour correction, but emphasizes edges within the amplitude of the original signal. Therefore,
Even when a device incorporating this image quality improvement device is configured with a digital circuit, the problem of overflow does not occur, and the device can improve image quality satisfactorily. (c) The degree of edge enhancement for the input signal depends on the frequency of the input signal and has a perfect correlation with the input signal, so this image quality improvement device can produce a natural image without causing any discomfort to the viewer. sharpness and resolution can be improved. (d) Since two mixers are provided, by setting the mixing ratios of the two mixers to different values, the waveform can be changed independently on both sides of the midpoint of the waveform changing section. Therefore, this image quality improvement device can more finely adjust the amount of edge enhancement, and can satisfactorily meet various demands regarding image quality from viewers. (E) Each component of the present invention can be configured by combining conventional circuits, so the image quality improvement device of the present invention can be easily manufactured and has a wide range of uses.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment.

FIG. 2 is a diagram showing a specific configuration example of a subtracter and a mixer.

FIG. 3 is a diagram showing a specific configuration example of a control signal forming circuit and a signal selection circuit.

FIG. 4 is an explanatory diagram of the operation of the embodiment shown in FIG. 1;

[Explanation of symbols]

1, 2 Delay circuit 3, 4, 5 subtractor 6,7 Mixer 8 Control signal formation circuit 9 Signal selection circuit

Claims (2)

[Claims] 1. A delay circuit that outputs a second signal obtained by delaying a first signal that is an input signal by a predetermined time, and a third signal obtained by delaying the second signal by the predetermined time; 1st
a first subtracter that outputs a fourth signal obtained by subtracting the second signal from the second signal;
a second subtractor that outputs a fifth signal obtained by subtracting the fifth signal from the fourth signal; and a third subtractor that outputs a sixth signal obtained by subtracting the fifth signal from the fourth signal. a first mixer that outputs a seventh signal obtained by mixing the second signal and the fourth signal at a first predetermined ratio; a second mixer that outputs an eighth signal obtained by mixing the fourth, fifth, and sixth signals at a second predetermined ratio; , a control signal forming circuit that outputs a ninth signal that is a control signal that changes according to a combination of polarities of the seventh, second, eighth, and ninth signals; A signal is supplied, and the seventh, second,
and a signal selection circuit that selects and outputs one of the and eighth signals, and the control signal forming circuit is configured to: (a) select the values of the fourth, fifth, and sixth signals; are values of the same polarity that are simultaneously positive or negative at the same time, the signal selection circuit outputs a control signal for selectively outputting the eighth signal, and (b) the values of the fourth and fifth signals are When the values of the sixth signal are of the same polarity, which are simultaneously positive or negative at the same time, and the value of the sixth signal is a value of a polarity different from the polarity of the values of the fourth and fifth signals, the signal selection circuit outputting a control signal for selectively outputting the seventh signal; (c) the combination of the values of the fourth, fifth, and sixth signals is determined by
, (b), the signal selection circuit outputs a control signal for selectively outputting the second signal, and the signal selection circuit emphasizes the edge of the first signal, which is the input signal. An image quality improvement device characterized in that it obtains an output signal that is 2. A delay circuit that outputs a second signal obtained by delaying a first signal that is an input signal by a predetermined time, and a third signal obtained by delaying the second signal by the predetermined time; 1st
a first subtracter that outputs a fourth signal obtained by subtracting the second signal from the second signal;
a second subtractor that outputs a fifth signal obtained by subtracting the fifth signal from the fourth signal; and a third subtractor that outputs a sixth signal obtained by subtracting the fifth signal from the fourth signal. a first mixer that outputs a seventh signal obtained by mixing the first signal and the second signal at a first predetermined ratio; a second mixer that outputs an eighth signal obtained by mixing the No. 3 signal at a second predetermined ratio, and the fourth, fifth, and sixth signals are supplied; , a control signal forming circuit that outputs a ninth signal that is a control signal that changes according to a combination of polarities of the seventh, second, eighth, and ninth signals; A signal is supplied, and the seventh, second,
and a signal selection circuit that selects and outputs one of the and eighth signals, and the control signal forming circuit is configured to: (a) select the values of the fourth, fifth, and sixth signals; are values of the same polarity that are simultaneously positive or negative at the same time, the signal selection circuit outputs a control signal for selectively outputting the eighth signal, and (b) the values of the fourth and fifth signals are When the values of the sixth signal are of the same polarity, which are simultaneously positive or negative at the same time, and the value of the sixth signal is a value of a polarity different from the polarity of the values of the fourth and fifth signals, the signal selection circuit outputting a control signal for selectively outputting the seventh signal; (c) the combination of the values of the fourth, fifth, and sixth signals is determined by
, (b), the signal selection circuit outputs a control signal for selectively outputting the second signal, and the signal selection circuit emphasizes the edge of the first signal, which is the input signal. An image quality improvement device characterized in that it obtains an output signal that is