JPH04268881A - Picture quality improvement device - Google Patents

Abstract

PURPOSE:To supply a picture quality improvement device having resistance for noise performance which is suitable for a video unit, which can add an edge emphasis component to the inclination part of an input signal in a natural form without giving the sense of incongruity to a person who appreciates the video unit and which is easily made into a digital circuit. CONSTITUTION:A signal Sd obtained by an orthogonal high pass filter 1, an in-phase high pass filter 2 and an amplitude synthesizer 3, and a signal Sc obtained by the in-phase high pass filter 2 are supplied to a waveform forming unit 4 so as to obtain the edge emphasis component Se. The signal Se is set to the edge emphasis component Sf where a noise component is suppressed through a noise restriction unit 5. The signal Sf is added to the edge part of the input signal Sa in an adder 6 and an output signal Sg which is appropriately edge-emphasized is obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is applicable to television (TV).
) This invention relates to an image quality improvement device suitable for various video equipment such as television receivers, video tape recorders (VTRs), and printers. In addition, the present invention can add an edge emphasis component to the sloped portion of the input signal in a natural manner without giving the viewer a sense of discomfort, improve the sharpness and resolution of the reproduced image, and improve the noise resistance. The purpose is to provide an excellent image quality improvement device.

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. 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 also has excellent noise resistance. The question is what measures should be taken.

0004

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an in-phase high-pass filter which is supplied with a first signal as an input signal and outputs a second signal; a quadrature high-pass filter that is supplied with a first signal and outputs a third signal; and an amplitude value that is supplied with the second and third signals and obtained by vector-combining the two signals; an amplitude synthesizer that outputs a fourth signal having a polarity of the second signal; and an amplitude synthesizer that outputs a fourth signal having a a waveform former that outputs a fifth signal which is an edge emphasis component obtained by subtracting the fifth signal; a noise limiter outputting a sixth signal; and the first and sixth signals are supplied, and by adding the sixth signal to the first signal, edges of the first signal are emphasized. The present invention provides an image quality improvement device characterized by comprising an adder that obtains an output signal.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an image quality improving apparatus according to the present invention. Also, FIG. 2 is a diagram showing the characteristics of a quadrature high-pass filter and an in-phase high-pass filter, FIG. 3 is a diagram showing a specific configuration example of an amplitude synthesizer, and FIG. 4 is a diagram showing a specific configuration example of a waveform former. , a characteristic diagram of the noise limiter, and FIGS. 5 and 6 are explanatory diagrams of the operation of the embodiment shown in FIG. 1. In FIGS. 5 and 6, the steps of the waveform slope are exaggerated to make the explanation easier to understand. Further, even when a digital circuit is cited as a specific circuit example, the signal waveform of the circuit is shown as an analog waveform in FIGS. 5 and 6 in order to make the explanation of its operation easier to understand. In FIG. 1, 1 is a quadrature high-pass filter, 2 is an in-phase high-pass filter, 3 is an amplitude synthesizer, and 4 is a quadrature high-pass filter.
is a waveform former, 5 is a noise limiter, and 6 is an adder. For convenience of explanation, signal delays due to the processing time of each circuit, and delay circuits and the like that are normally used to correct the delays will be omitted. First, a case will be described in which the input signal Sa coming from the line L1 is a signal with a pulse waveform as shown in FIG. 5(a). The input signal Sa is supplied to a quadrature high-pass filter 1. The characteristics of the orthogonal high-pass filter 1 are those shown in FIG. 2(b), and the imaginary part of the frequency characteristic is

[0006]

[Math 1]

The real part is 0. The impulse response of the orthogonal high-pass filter 1 is shown in FIG. 2(c). The illustrated impulse response waveform is a waveform obtained for a signal band-limited with an upper limit frequency of 4 MHz, such as a TV video signal. The orthogonal high-pass filter 1 having such characteristics can be constituted 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. With the orthogonal high-pass filter 1, Fig. 5 (
A signal Sb shown in b) is obtained. On the other hand, the input signal Sa
is also supplied to the in-phase high-pass filter 2. The characteristics of the in-phase high-pass filter 2 are those shown in FIG. 2(e), and the real part of the frequency characteristic is

[0008]

[Math 2]

##EQU1## This is a characteristic in which the imaginary part is 0. The impulse response of the in-phase high-pass filter 2 is shown in Fig. 2(f) (
Impulse response waveform obtained for a band-limited signal with an upper limit frequency of 4 MHz). The in-phase high-pass filter 2 having such characteristics can be constituted by a transversal filter or the like having coefficient values symmetrical about the axis of time reference t=0, which is made of an analog circuit or a digital circuit. Quadrature high-pass filter 1 and in-phase high-pass filter 2 have the same amplitude characteristic G(f).

0010

[Math 3]

##EQU1## and have characteristics that the phases are different by π/2 and are orthogonal to each other. The characteristic shown in FIG. 2(b) has a value in the imaginary part, so a device having this characteristic is called a quadrature high-pass filter, and the characteristic shown in FIG. 2(e) has a value in the real part, so We decided to call a device with this characteristic a common-mode high-pass filter. The output signal Sc of the in-phase high-pass filter 2 is
The waveform is shown in FIG. 5(c). The amplitude synthesizer 3 receives each output signal Sb of the orthogonal high-pass filter 1 and the in-phase high-pass filter 2.
, Sc are supplied. In the amplitude synthesizer 3, the following equation (4)
By vector composition of the orthogonal component and the in-phase component shown in

[
0012

[Math 4]

An output Sd is obtained. Examples of circuits implementing the amplitude synthesizer 3 are shown in FIGS. 3(a) and 3(b). Figure 3(a)
In the circuit example shown in , the angle θ is calculated from two input signals Sb and Sc when the horizontal axis is the signal Sc and the vertical axis is the signal Sb.

[0014]

[Math 5]

##EQU1## is determined in block 3-1. Next, in block 3-2, the product of the signal Sb and sin θ,

[0016]

[Math 6]

Then, in block 3-3, the signals Sc and c
Product with osθ,

[0018]

[Math 7]

Find . Then, in the adder 3-4, the formula (6
) and (7), the output shown by the above-mentioned vector composition equation (4) can be obtained. Block 3-1
3-3 can be realized by a table lookup method using a ROM or the like. In the circuit example of the amplitude synthesizer 3 shown in FIG. 3(b), the multipliers 3-5 and 3-6 produce square values Sb2 and Sc2 of the input signals Sb and Sc, respectively.
and add these in adder 3-7, block 3-8
Find the square root of it. Block 3-8 is a ROM
This can be achieved using a table lookup method such as The output Sd of the amplitude synthesizer 3 shown in FIGS. 3(a) and 3(b)
has the waveform shown in FIG. 5(d). In-phase high-pass filter 2
The output signal Sc of the amplitude synthesizer 3 and the output signal Sd of the amplitude synthesizer 3 are supplied to the waveform former 4. In the waveform former 4, the following equation is used.

[0020]

[Math. 8]

[0021] That is,

[0022]

[Math. 9]

Based on the above, a signal Se (see FIG. 5(e)), which is an edge emphasis component, is obtained from the difference between the signal Sc and a signal obtained by changing the polarity of the signal Sd according to the polarity of the signal Sc. An example of realizing this waveform generator 4 with a digital circuit (
(using a commercially available TTL-IC) is shown in FIG. 4(a). Here, the data (signals Sc, Sd, Se) are 8-bit, two's complement representation. Blocks 4-1 to 4 shown in the figure
-8 is a two-input EOR circuit (exclusive OR circuit), blocks 4-10 to 4-17 are inverter circuits, and blocks 4-9 and 4-18 are full adders. A signal Sd, that is, Sd0 (LSB) to Sd7 (MSB) is supplied to one input terminal of the EOR circuits 4-1 to 4-8.
A signal Sc7, which is the MSB of the signal Sc, is commonly supplied to the other input terminal. Each output of the EOR circuits 4-1 to 4-8 is sent to a full adder 4-9.
is supplied to one of the input terminals A1 to A8. full adder 4
The other input terminals B1 to B8 of -9 are connected to GND. The carry input C0 of the full adder 4-9 has
A signal Sc7 is supplied. The addition outputs Σ1 (LSB) to Σ8 (MSB) obtained thereby are one input terminal B1 (LSB) to B8 (M
SB). The processing up to this point is the first half of the right-hand side of equation (8).

Next, the output signal Sc of the in-phase high-pass filter 2
That is, Sc0 (LSB) to Sc7 (MSB) are inverted by inverter circuits 4-10 to 4-17 and supplied to the other input terminals A1 to A8 of full adder 4-18. The carry input C0 of the full adder 4-18 is connected to the power supply Vc.
c (5V). Inverter circuit 4-1
Since there are 0 to 4-17, the full adder 4-18 performs subtraction processing. Outputs Σ1 to Σ of full adder 4-18
8 is the signal Se, that is, Se0(LSB) to Se7(
MSB), and the processing up to this point completes the processing of equation (8), that is, equation (9). Here, returning to FIG. 1, the output Se of the waveform former 4 is supplied to the noise limiter 5, and the noise limiter 5 outputs the signal Sf. An example of the characteristics of the noise limiter 5 is shown in FIG. 4(b). This characteristic is expressed by the following formula,

[0025]

[Math. 10]

As shown in [0026] When the amplitude value of the input signal Se is less than β, the input signal Se is not output, and when the value of the signal Se is greater than β, the signal Se is outputted from β.
This characteristic is to output a signal with a value obtained by subtracting .beta., and when the value of the signal Se is smaller than -.beta., a signal with a value obtained by adding .beta. to the signal Se is output. Processing based on this characteristic (a type of nonlinear characteristic) is generally performed using a threshold (threshold).
hold) processing. By the above threshold processing, it is possible to remove the noise component whose amplitude value is below β in the small level portion of the signal Se where the amplitude value is below β. FIG. 5(f) shows the waveform of the output signal Sf of the noise limiter 5. The actual value of β is very small, and is within several percent of the dynamic range (fluctuation range) of the input signal Sa to this image quality improvement device. The broken line shown in FIG. 4(b) indicates the unprocessed characteristic without noise restriction processing,

[0027]

[Math. 11]

This is shown for comparison with threshold processing. Although noise removal using nonlinear characteristics itself is a well-known technique, there has been no example of its application to such an image quality improvement device. Noise limiter 5 with nonlinear characteristics
is provided after the waveform former 4, and the edge emphasis component Se
Removing the noise produces excellent effects as described below. It is possible to remove the noise component superimposed on the small amplitude part of the edge emphasis component Se whose original value should be 0 (that is, the signal part added to the part of the input signal Sa that does not require edge emphasis), and the original accuracy can be removed. This method is extremely effective in improving image quality. Edge emphasis component S
The noise suppressing operation of the noise limiter 5 is not very effective in the large amplitude part of e, that is, the part added to the waveform slope part of the input signal Sa as an edge emphasis component, but in the large amplitude part, small amplitude noise The component is masked, and even if a small-amplitude noise component remains in this part, it will hardly affect the edge enhancement operation. Another example of the characteristics of the noise limiter 5 is shown in FIG. 4(c). This characteristic is expressed by the following formula,

[0029]

[Math. 12]

As shown in FIG. 4(
Similar to the characteristic shown in b), the aim is to suppress small amplitude noise components. This characteristic has less influence on the signal Sf (effect on waveform change) due to noise removal than the characteristic shown in FIG. 4(b). The noise limiter 5 can be implemented using a table lookup method using a ROM or the like.

The output signal Sf of the noise limiter 5 is supplied to an adder 6 and added to the signal Sa which is the input signal of this image quality improvement device. The waveform obtained by the adder 6 is
The waveform Sg (output signal waveform of this image quality improvement device) is shown in FIG. 5(g). This output waveform Sg is converted into input waveform Sa
In comparison, the output waveform Sg has a waveform step approximately at the midpoint of the waveform changing part (edge part) of the input waveform Sa, and the slope of the waveform slope part is steep, and it is different from a properly edge-emphasized waveform. You can see that it is happening. Output signal S
If g is reproduced, a contour-corrected image is obtained. Furthermore, the edge enhancement processing of this image quality improvement device is shown in Fig. 5(g).
As can be seen from the output waveform Sg shown in the figure, this method does not emphasize edges that exceed the amplitude of the original signal, such as preshoot or overshoot, as in conventional contour correction, but rather emphasizes edges 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 Sg output from the line L2 has new sideband components formed as a result of edge emphasis, and becomes a signal with a new spectrum beyond the original band of the input signal Sa. . 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.

Note that the steepness of the edge portion of the signal Sg (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 5 (h
), if the slope is steeper, as shown in (i) of the same figure.
A strong degree of edge enhancement is performed as shown in . on the other hand,
For gentle slopes as shown in figure (j),
A weak degree of edge enhancement is performed as shown in k). In this way, the edge emphasis component added to the input signal is
Since it depends on the frequency of the input signal and has a perfect correlation with the input signal, this image quality improvement device can improve sharpness and resolution in a natural manner without giving any discomfort to the viewer. can.

FIG. 6 shows the output waveform of each block when an AM modulated wave of modulation frequency f2 (=4 MHz) is input as the input signal Sa, corresponding to FIG. The frequency of 4 MHz is the upper limit frequency for NTSC TV video signals. The envelope (the waveform indicated by the broken line) in FIGS. 6(a) to (c) is the waveform Sd shown in FIG. 6(d), and the edge emphasis component obtained from the waveform generator 4 is the waveform Sd shown in FIG. 6(e). The finally obtained output signal is the signal Sg shown in FIG. 6(g). As can be seen from this signal Sg, the carrier wave is converted into a rectangular wave and the edges are emphasized.

Note that FIG. 2 shows the characteristics of the orthogonal high-pass filter 1.
The characteristics shown in FIG. 2(b) and the characteristics shown in FIG. 2(e) were used as the characteristics of the in-phase high-pass filter 2, but the characteristics shown in FIG. 2(a) were used as the characteristics of the orthogonal high-pass filter 1. In-phase high-pass filter 2
The characteristics shown in FIG. 2(d) may be used as the characteristics. The characteristic shown in FIG. 2(a) is the characteristic shown in the following equation (13), and the characteristic shown in FIG. 2(d) is the characteristic shown in the following equation (14).

[0035]

[Math. 13]

[0036]

[Math. 14]

[0037] Also, FIGS. 2(a), (b), (d), (e
) 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. In the embodiment shown in FIG. 1, the noise limiter is provided only after the waveform former 4, but before and after the waveform former 4, that is, between the waveform former 4 and the in-phase high-pass filter 2. Another similar noise limiter may be provided. If the noise limiter provided between the waveform shaper 4 and the in-phase high-pass filter 2 suppresses the noise in the signal Sc, the accuracy of the polarity judgment of the signal Sc in the waveform shaper 4 will improve, making it more accurate. An edge emphasis component Se is obtained.

[0038]

As described above, the image quality improving device of the present invention has the following effects. (a) Since the edge emphasis component can be appropriately added to the midpoint of the slope portion of the input signal, an output signal to which a frequency component outside the frequency band of the input signal is added can be obtained, and the contour of the reproduced image can be corrected. (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) By providing the noise limiter 5 after the waveform former 4, it is possible to suppress the noise of the edge emphasis component Se, obtain the original accurate edge emphasis component, and improve noise resistance performance. Image quality can be improved. (d) The edge enhancement component added to 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 does not give a sense of discomfort to the viewer. Sharpness and resolution can be improved in a natural way. (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 quadrature high-pass filter and an in-phase high-pass filter.

FIG. 3 is a diagram showing a specific example of the configuration of an amplitude synthesizer.

FIG. 4 is a diagram showing a specific configuration example of a waveform former, and a characteristic diagram of a noise limiter.

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 Quadrature high-pass filter 2 In-phase high-pass filter 3 Amplitude synthesizer 4 Waveform former 5 Noise limiter 6 Adder

Claims (1)

[Claims] Claim 1: A first signal, which is an input signal, is supplied;
an in-phase high-pass filter that outputs a second signal; a quadrature high-pass filter that is supplied with the first signal and outputs a third signal; and a quadrature high-pass filter that is supplied with the second and third signals; an amplitude synthesizer that outputs a fourth signal having an amplitude value obtained by vector-combining the two signals, and the second and fourth signals are supplied, and the fourth signal is combined with the second signal. a waveform former that outputs a fifth signal that is an edge emphasis component obtained by subtracting the second signal from a signal that has been given the polarity of the signal, and the fifth signal is supplied; a noise limiter that outputs a sixth signal obtained by suppressing a small amplitude signal portion of the signal; and a noise limiter that outputs a sixth signal obtained by suppressing the small amplitude signal portion of the signal; An image quality improvement device comprising: an adder that obtains an output signal in which edges of the first signal are emphasized by adding .