JPH04273775A - Picture quality improving device - Google Patents

Abstract

PURPOSE:To provide a device in which edge emphasis is naturally performed without giving the sense of incongruity to an appreciator and a digital circuit is easy by being a picture quality improving device optimum to video equipment and each kind of image processors and adding suitably the waveform level difference to the midpoint of the inclination portion of an input signal. CONSTITUTION:An input signal S1, an output signal S2 of a delaying circuit 1 and an output signal S3 of a delaying circuit 2 are supplied to a signal selecting circuit 6. From the signal S2, a control signal Sc is obtained by a differential circuit 3, a differential circuit 4 and a control signal forming circuit 5. A signal selecting circuit 6 selects and outputs one of three signals S1, S2 and S3 to be supplied in accordance with the control signal Sc and an edge emphasized output signal S0 is 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;
The second signal is supplied with a fourth signal, which is a first-order differential signal.
a differential circuit that outputs a signal of a control signal forming circuit that outputs a sixth signal that is a control signal that changes; the first, second, third, and sixth signals are supplied; Then, the first
, a signal selection circuit that selects and outputs one of the second and third signals, and when the fourth and fifth signals have the same polarity, The third signal is output, and when the fourth and fifth signals have different polarities, the first signal is output, and the value of at least one of the fourth and fifth signals is The present invention provides an image quality improvement device characterized in that when the input signal is zero, the second signal is outputted to obtain an output signal in which the edges of the first signal, which is the input 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. In addition, FIG. 2 is a diagram showing the characteristics of the differentiating circuit, FIG. 3 is a diagram showing specific configuration examples of the control signal forming circuit and the signal selection circuit, and FIGS. 4, 5, and 6 are diagrams showing the implementation shown in FIG. FIG. 6 is an explanatory diagram of an example operation. In FIGS. 4 to 6, the steps of the waveform slope are exaggerated to make the explanation easier to understand. Furthermore, even when a digital circuit is cited as a specific example of a circuit, the signal waveforms of the circuit are shown as analog waveforms in FIGS. 4 to 6 in order to make the explanation of its operation easier to understand. In FIG. 1, 1 and 2 are delay circuits having the same delay time, 3 and 4 are differentiating circuits having the same characteristics, 5 is a control signal forming circuit, and 6 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. As input signals handled by this image quality improvement device, various video signals, luminance signals, RGB signals, 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 an example of a waveform of a luminance signal of a TV 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. The delay time T of the delay circuit 1 is

00
06]

[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 output signal S2 of the delay circuit 1 is also supplied to the differentiating circuit 3. Differential circuit 3
The characteristic is the characteristic shown in FIG. 2(a), and the imaginary part of the frequency characteristic is

0012

[Math 4]

The real part is 0. Differential circuit 3
The impulse response of is shown in FIG. 2(b). The illustrated impulse response waveform has an upper limit frequency of 4M, like a TV video signal.
This is a waveform obtained for a signal band-limited at Hz. The differentiating circuit 3 having such characteristics can be configured by an analog circuit or a digital circuit, for example, a transversal filter symmetrical to the origin with respect to the time reference t=0. The differentiating circuit 3 generates the signal S4(1) shown in FIG. 4(d).
(order differential signal) is obtained. The output signal S4 of the delay circuit 3 is supplied to a differentiating circuit 4 having the same characteristics as the differentiating circuit 3. The output signal S5 (secondary differential signal) of the differentiating circuit 4 is shown in FIG.
The waveform is shown in e). The output signals S4 and S5 of the differentiating circuit 3 and the differentiating circuit 4 are supplied to the control signal forming circuit 5 at the next stage. Then, the control signal forming circuit 5 generates a signal S4
, S5, the control signal Sc is formed according to the combination of polarities of the signals. The control signal Sc is a low active (negative logic) logic signal consisting of three signals Sc1, Sc2, and Sc3 shown in the following equation (5). Signals Sc1, Sc2, S
Each waveform diagram of c3 is shown in FIGS. 4(g), (h), and (f).

[0014]

[Math 5]

As described above, when the values of the signals S4 and S5 have different polarities between positive and negative or negative and positive, the signal Sc1 becomes 0.
(Low), and when at least one of the values of the signals S4 and S5 is 0, the signal Sc2 becomes 0 (Low),
When the values of the signals S4 and S5 are both positive or negative and have the same polarity, the signal Sc3 becomes 0 (Low). An example of a circuit implementing the control signal forming circuit 5 is shown in FIG. 3(a). The illustrated control signal forming circuit 5 can be realized by a table lookup method using a TTL-IC, ROM, or the like. Signal S
4, S5 is a digital signal expressed in two's complement. The multiplier 3-1 multiplies the signal S4 and the signal S5, and supplies the output S45 to the comparators 3-2 to 3-4. Comparator 3-
2 compares the signal S45 with 0 (GND) and outputs the signal S4.
When 5 is smaller than GND (S45<0), the output S
c1 is set to 0 (Low), and when the signal S45 has a value equal to or higher than GND (0≦S45), the output Sc1 is set to 1 (High). The comparator 3-3 compares the signal S45 with 0 (GND), and when the signal S45 has a value equal to GND (S45
= 0), the output Sc2 is set to 0 (Low), and when the signal S45 is any other value (S45≠0), the output Sc2 is set to 1 (
High). The comparator 3-4 also sets the signal S45 to 0 (
GND), when the signal S45 has a value larger than GND (0<S45), the output Sc3 is set to 0 (Low), and when the signal S45 has a value other than that (S45≦0), the output Sc3 is set to 1. (High). In this way, the control signal forming circuit 5 generates the control signal Sc (signals Sc1, Sc2, S
c3) is formed and output. Since the aforementioned signals S4 and S5 are output signals of a high-pass filter, there is a risk that they generally contain a large amount of high-frequency noise components. In order to improve the performance of the control signal forming circuit 5 against such noise components, the comparison reference values in the comparators 3-2 to 3-4 are set to 0(
GND) but a small positive value β (a value approximately equal to the level of high-frequency noise components). Comparator 3-2 receives signal S45
is compared with β, and when the signal S45 is a value smaller than -β (S45<-β), the output Sc1 is set to 0 (Low), and when the signal S45 is a value greater than or equal to -β (-β≦S45), the output Sc1 is set to 0 (Low). The output Sc1 is set to 1 (High). The comparator 3-3 compares the signal S45 with β, and sets the output Sc2 to 0 (Low) when the absolute value of the signal S45 is less than or equal to β (|S45|≦β), and sets the output Sc2 to 0 (Low) when the signal S45 has other values. When (β<|S45|
) sets the output Sc2 to 1 (High). Comparator 3-4
Also, the signal S45 is compared with β, and when the signal S45 is larger than β (β<S45), the output Sc3 is set to 0 (Low).
), and when the signal S45 is less than or equal to β (S45≦β)
sets the output Sc3 to 1 (High). By setting the comparison reference value β, the noise resistance performance of the control signal forming circuit 5 is improved. Returning to FIG. 1, control signal Sc (signal Sc
1, Sc2, Sc3), and the signals S1, S2, S3 are
The signal is supplied to the next stage signal selection circuit 6. The signal selection circuit 6 selectively outputs one of the signals S1, S2, and S3 according to the control signal Sc. Output So of signal selection circuit 6
is shown in the following equation (6).

[0016]

[Math 6]

That is, the signal selection circuit 6 selects the control signal Sc1.
When is 0 (Low), the signal S1 is selectively output, when the control signal Sc2 is 0 (Low), the signal S2 is selectively output, and when the control signal Sc3 is 0 (Low), the signal S3 is selectively output. .

An example of a circuit for realizing the signal selection circuit 6 is shown in FIG.
Shown in c). Blocks 3-5, 3-6, and 3-7 are switch circuits. Signals S1 to S3 are supplied to each switch circuit 3-5 to 3-7, respectively, and control signals Sc1 to S
When one of c3 is 0 (Low), the switch circuit to which that control signal is supplied is turned on, and the signals S1 to
Any one of S3 is output from the shared output terminal. Each of the switch circuits 3-5 to 3-7 has the same configuration. In FIG. 3(b), switch circuits 3-5 to 3
As a specific circuit example of -7, a switch circuit 3-5 is shown as a representative. The signals S1 and So are assumed to be 8-bit, two's complement representation. Blocks 3-10 to 3-17 are buffer circuits with control terminals, and the common control terminals include
A control signal Sc1 is supplied. This control signal Sc1
is 0 (Low), the input signal S1, that is, S10
(LSB) to S17 (MSB) are output as they are So(
That is, it is output as S00 (LSB) to S07 (MSB)). When the control signal Sc1 is 1 (High), the output is in a tristate or high impedance state. The output signal S of the signal selection circuit 6 obtained in this way
o (output of this image quality improvement device) has a waveform shown in FIG. 4(i).

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(i), 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. 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 before edge emphasis. The rising and falling parts (edge parts) of the original signal are shown in Figure 4 (j
), if the slope is steeper, as shown in (k) in the same figure.
A strong degree of edge enhancement is performed as shown in . On the other hand, for a gentle slope as shown in figure (l),
Edge enhancement is performed to a weak degree as shown in FIG. 4(m). 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.

Moreover, the illustrated embodiment does not use an expensive quadrature high-pass filter or in-phase high-pass filter with a complicated circuit configuration, but uses a low-cost differentiation circuit with a simpler circuit configuration than those filters. The control signal Sc can be formed, and a signal whose edges are properly emphasized is obtained. Therefore, the earlier patent application filed by the present inventor (filing date: February 27, 1991, reference number: H
03000046), the cost of the entire device can be reduced.

FIGS. 5(a) to 5(i) show operating waveforms of various parts when a pulse signal having a narrower pulse width than the input signal of FIG. 4(a) enters the image quality improvement device of the above embodiment. are shown in correspondence with FIGS. 4(a) to (i). Figure 5
It can be seen that the edge enhancement effect appears in the signal So shown in (i). In FIGS. 6(a) to (i), the frequency is approximately 2 MH
Figure 4 (
These are shown in correspondence with a) to (i). Figure 6(i
It can be seen that the edge enhancement effect also appears in the signal So shown in ).

Note that the characteristics of the differentiating circuits 3 and 4 are shown in FIG.
Although the characteristics shown in a) are used, the characteristics shown in FIG. 2(c) may be used as the characteristics of the differentiating circuits 3 and 4. Figure 2(c)
The characteristic shown in is the characteristic shown in the following equation (7).

[0024]

[Math 7]

Furthermore, each of the characteristics shown in FIGS. 2(a) and 2(c) may be subjected to band limitation to cut signals outside the frequency range in which the input signal exists. This leads to improved noise resistance performance. Note that if the differentiating circuits 3 and 4 are implemented using the above-mentioned transversal filters, a signal delay will inevitably occur. Therefore, in order to operate the embodiment shown in FIG. 1 as described above, a delay circuit is required to correct the delay time caused by the transversal filter. However, in the explanation of this embodiment, the delay time caused by the transversal filter is not related to the essence of the present invention, and if a delay circuit to correct it is included in the explanation, the explanation will be complicated and difficult to understand. Therefore, the delay time of the differentiating circuits 3 and 4 is assumed to be 0 in the explanation.

In the above embodiment, 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 image signals such as RGB signals. can be handled. 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 are
This can also be realized by software processing using a computer, and the present invention can also be applied to processing of image data by software. Furthermore, the present invention is also effective in improving eye pattern deterioration caused by waveform distortion in a digital transmission system.

[0027]

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 is an edge enhancement process within the amplitude of the original signal, rather than an edge enhancement that exceeds the amplitude of the original signal such as preshoot or overshoot as in conventional contour correction. 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 the control signal Sc can be formed by a low-cost differential circuit with a simple circuit configuration without using a filter with a complicated circuit configuration, the cost of the entire device can be reduced. (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 the drawing]

FIG. 1 is a block diagram of an embodiment.

FIG. 2 is a diagram showing the characteristics of a differentiating circuit.

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;

FIG. 5 is an explanatory diagram of the operation of the embodiment shown in FIG. 1;

FIG. 6 is an explanatory diagram of the operation of the embodiment shown in FIG. 1;

[Explanation of symbols]

1, 2 Delay circuit 3,4 Differential circuit 5 Control signal formation circuit 6 Signal selection circuit

Claims (1)

[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; Second
a differentiation circuit that is supplied with the signal and outputs a fourth signal that is a first-order differential signal and a fifth signal that is a second-order differential signal; a control signal forming circuit that outputs a sixth signal that is a control signal that changes depending on a combination of polarities of the fourth and fifth signals, and the first, second, third, and sixth signals; is supplied, and the first, second,
and a signal selection circuit that selects and outputs one of the third signals, and the signal selection circuit selects one of the third signals when the polarities of the fourth and fifth signals are the same. outputting a signal, when the fourth and fifth signals have different polarities, outputting the first signal, and when the value of at least one of the fourth and fifth signals is zero; An image quality improvement device characterized by outputting the second signal to obtain an output signal in which edges of the first signal, which is the input signal, are emphasized.