JPH0738781A - Picture quality improving device - Google Patents

Abstract

PURPOSE:To provide a device in which a picture quality can be improved by sharpening especially the changing parts of a waveform, that is, the waveform edges, the picture quality can be improved in an natural form without making the viewer feel a sense of incompatibility, and the sharpness and resolution of a reproduced picture can be effectively improved, in a picture improving device suitable to each kind of video equipment or the like. CONSTITUTION:Three signal values in each fixed time interval are extracted from an input signal by delay circuits 1-1 and 1-2. Then, a constant item is obtained by synthesizing the extracted three signal values with a prescribed ratio by a synthesizer 1-3, so that a signal characteristic curve connecting the three signal values can approximate to the sum of a cosine term, sine term, and constant term and the coefficient values of the cosine term and the sine term are obtained by synthesizers 1-4 and 1-5. An amplitude value and a phase value are obtained by synthesizers 1-6 and 1-7 from the coefficient values of the cosine term and the sine term, the phase value is nonlinearly transformed, and an output signal obtained by sharpening the changing part of the waveform of the input signal is obtained by a synthesizer 1-8 from the phase value, and the coefficient value and the amplitude value of the cosine term.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to a television (TV).
The present invention relates to an image quality improving device suitable for various video devices such as a receiver and a video tape recorder (VTR), and various image processing devices for handling image data. The present invention improves the image quality by making the waveform change portion, that is, the waveform edge, sharp, but it is possible to improve the image quality in a natural manner without giving the viewer a feeling of discomfort. It is an object of the present invention to provide an image quality improving device capable of effectively improving the degree and resolution.

[0002]

2. Description of the Related Art Conventionally, in the contour correction used for improving the image quality, the contour correction component is obtained by quadratic differential processing,
This correction component is added to the original signal in an appropriate amount. In the contour correction by this method, the secondary differential waveform, which is the contour correction component, has a peak considerably outside the midpoint of the waveform change portion (edge portion) of the original signal.

[0003]

Therefore, in the conventional apparatus, when the secondary differential waveform is added to the original signal to perform edge emphasis, excessive preshoot or overshoot may occur, which is why Unnatural black-and-white edging was created at the edge of the reproduced image, and the effect expected for contour correction was not obtained.

According to the present invention, the waveform changing portion of the original signal, that is,
Edge enhancement is performed by adding a signal component for making the waveform steep with a smooth slope as much as possible at the almost midpoint position of the edge part to prevent unnatural contour correction due to excessive preshooting and overshooting. It is an object of the present invention to provide an image quality improving device that can improve sharpness and resolution in a natural manner without giving a feeling of strangeness.

[0005]

In order to solve the above problems, the present invention provides

An extraction circuit for extracting three signal values from the input signal at fixed time intervals;

In order to approximate the signal characteristic curve connecting the three extracted signal values by the sum of the cosine term, the sine term and the constant term, the three signal values are combined at a predetermined ratio to obtain the constant term. Together with a first combining circuit for obtaining coefficient values of the cosine term and the sine term,

An amplitude value and a phase value are obtained from the coefficient value of the cosine term and the coefficient value of the sine term, the phase value is nonlinearly converted, and the non-linearly converted phase value, the coefficient value of the cosine term, and the amplitude. (EN) An image quality improving apparatus characterized by comprising a second synthesis circuit for obtaining a new signal characteristic curve from a value and an output signal in which a waveform changing portion of an input signal is steepened.

[0009]

1 is a block diagram of a first embodiment of an image quality improving apparatus of the present invention. Further, FIG. 2 is a diagram showing a configuration example of an additional circuit (adjustment circuit) for making the first embodiment function more effectively, and FIGS. 3 to 11 are operation explanatory diagrams of the embodiment.

In the operation explanatory diagram, a simplified simulated expression method is also used for convenience. Further, even when a digital circuit is taken as an example for realizing the operation function, the signal waveform of the circuit is shown as an analog waveform in order to make the explanation of the operation easy to understand.

In FIG. 1, 1-1 is a first delay circuit,
1-2 is a second delay circuit, 1-3 is a constant term synthesizer, 1-
Reference numeral 4 is a cosine term coefficient value synthesizer, 1-5 is a sine term coefficient value synthesizer, 1-6 is an amplitude synthesizer, 1-7 is a phase synthesizer, and 1-8 is an output signal synthesizer. The first and second delay circuits 1-1 and 1-2 constitute an extraction circuit, and the constant term synthesizer 1
-3, the cosine term coefficient value synthesizer 1-4, the sine term coefficient value synthesizer 1-5 constitute a first synthesis circuit, and the amplitude synthesizer 1-6,
The phase combiner 1-7 and the output signal combiner 1-8 form a second combiner circuit.

For the sake of convenience of explanation, it is assumed that a signal delay due to the processing time of each circuit itself, and a delay circuit or the like normally used only for simply correcting the delay are omitted unless necessary for explanation. To do.

As an example of the input signal handled by the image quality improving apparatus, a television luminance signal, a color signal, an RGB signal, etc. are assumed. Here, especially, the frequency band is 4MHz
The video signals of the NTSC broadcasting system up to here are treated as an example.

First, the input signal y coming from the line L1
A case where in is a cosine wave as shown in FIG. 4A will be described. This cosine wave is an example of a luminance signal with a frequency f = 2 MHz. The input signal yin is the first delay circuit 1
-1 is supplied. This is a delay circuit whose delay time T is given by the following equation.

[0015]

[Equation 1]

The value of T is a sampling period normally used when sampling an NTSC signal. The output of the delay circuit 1-1 is output on the line L2, and the second delay circuit 1 of the next stage is output.
-2. The delay time of the second delay circuit 1-2 is the same as the delay time T of the delay circuit 1-1.

FIG. 3A shows two delay circuits 1-1 and 1-.
2 shows the relationship between two input / output signals. Signal y at the center (t = 0)
Two signals, left and right, separated by time T with reference to 0, are y
_-1 and y1 (the signal value of each signal also uses the same sign as the signal). The signal y0 is the output signal of the first delay circuit, the signal y- ₁ is the output signal of the second delay circuit, and the signal y1 is the input signal of the first delay circuit. The waveform diagram used in the following explanation of operation is based on this signal y0 as a time reference.

A characteristic curve passing through the signal values of these three signals is approximated by the following equation.

[0019]

[Equation 2]

The first term on the right side of the equation of y is a cosine term, the second term is a sine term, and the third term is a constant term. In order to determine the coefficient values a, b, the constant term c, and the variable θ of this equation, the signal values y _-1 , y0, y1 are used. By substituting these three signal values into Equation 2, the following equation is obtained.

[0021]

[Equation 3]

The processing for obtaining the constants a, b, and c in this equation is performed by the following three blocks 1-3 to 1-5.

The constant synthesizer 1-3 has three signals y _-1 , y 3.
1, 1 and y0 are supplied, and the value c of the constant term added and synthesized with the mixing ratios k0 and k1 is output as in the following equation.

[0024]

[Equation 4]

The constant synthesizer 1-3 functions as an addition synthesizer. The output waveform diagram when the value of k1 is 1 / (2 + 2 ^1/2 ) is shown in FIG. 4 (b). How to determine the mixing ratio will be described later.

The following three signals y- ₁ , y1 and y0 are also supplied to the next cosine term coefficient value synthesizer 1-4, and the coefficient value a of the cosine term is output as in the following equation.

[0027]

[Equation 5]

The equation (5) is obtained by substituting the equation (4) into the second equation (3). Cosine term coefficient value synthesizer 1-4
The function of is an addition / subtraction combination function.

The signal y is sent to the next sine term coefficient value synthesizer 1-5.
_-1 , y1 and the constant values c and a already obtained are supplied, and the coefficient value b of the sine term is output as in the following equation.

[0030]

[Equation 6]

The condition of the mixing ratio in the proviso 6 is derived from the fact that the amplitude of the cosine wave cannot be larger than 1.
As an example that satisfies the condition of this mixing ratio, k1 = 1 / (2 + 2
^1/2 ) value is used to draw an example of operation waveform. At this time, θ 0 = 135 °.

This equation obtains the value of θ0 from the sum of the first and third equations of Equation 3 and c and a already obtained, and subtracts the first equation from the third equation of Equation 3, etc. Required by. The function of the sine term coefficient value synthesizer 1-5 can be realized by a digital circuit or the like using a table lookup type ROM or the like. The characteristic equation of the equation 2 is determined by the equations 4 to 6.

The next amplitude synthesizer 1-6 includes a block 1-4.
From the block 1-5 and the coefficient value b from blocks 1-5. As shown in FIG. 3B, since the coefficient value a is the coefficient value of the cosine term, the horizontal axis shows the coefficient value b, and the coefficient value b is the coefficient value of the sine term shows the right triangle drawn on the vertical axis. The amplitude value A is calculated by the following equation and output from the amplitude synthesizer 1-6.

[0034]

[Equation 7]

The output waveform diagram of the amplitude synthesizer 1-6 is shown in FIG.
It is (c). The function of the amplitude synthesizer 1-6 can also be realized by a digital circuit or the like using a table lookup type ROM or the like.

The phase synthesizer 1-7 is supplied with the coefficient value a from the block 1-4 and the coefficient value b from the block 1-5. From the ratio of the vertical axis to the horizontal axis of the right triangle in FIG. 3B, the phase value φ is calculated by the following equation and output from the phase combiner 1-7.

[0037]

[Equation 8]

The output waveform diagram of the phase synthesizer 1-7 is shown in FIG.
It is (d). In the figure, the value of π / 2 is normalized to 1 and displayed. The function of this block can also be realized by using a table lookup type ROM or the like by a digital circuit.

The output signal synthesizer 1-8 has a constant value c obtained by the equation 4, a cosine term coefficient value a obtained by the equation 5, and an equation 7
The amplitude value A obtained by the above equation and the phase value φ obtained by the equation 8 are supplied, and an output signal zo represented by the following equation is synthesized using the non-linear parameter α and output from the line L3.

[0040]

[Equation 9]

As described above, the value obtained by normalizing the phase value in the range of 0 to 1 to the power of α is multiplied by π / 2, nonlinear phase conversion processing is performed to obtain a cosine term, and this is multiplied by A to obtain a coefficient value. The output signal zo is obtained by adding the constant value c to the value given the polarity of a. The function of the output signal combiner 1-8 can also be realized by a digital circuit, using a table lookup type ROM or the like.

Output waveform diagrams for the cases where the nonlinear parameter α is 2, 4, 8 and 16 are shown in FIGS. 5 (a), 5 (b), 5 (c),
Each is shown in (d). FIG. 4 is a waveform diagram of an input signal.
As compared with (a), it can be seen that the slope of each of the waveforms in FIG. 5 is steep. It is also clear that the steepness increases as the value of the nonlinear parameter α increases. Although there are some preshoots and overshoots, their magnitude is within about 10% of the signal value, so it is not an amount that poses a problem with respect to the large effect of sharpening the waveform.

The processing in the embodiment shown in FIG. 1 can be summarized by the following equation. That is, the approximate characteristic equation of the equation 1

[0044]

[Equation 10]

Then, the phase value φ is transformed into a new phase value φo by the non-linear conversion processing of the following equation.

[0046]

[Equation 11]

Then, the characteristic equation is converted into the following equation z,

[0048]

[Equation 12]

This is a process for obtaining z, that is, zo at the time of θ = 0 as in the equation 9, and outputting it instead of the signal y0.

FIG. 2 shows an adjusting circuit for optimizing the edge enhancement effect of the output signal zo in FIG. Subtractor 2
-1, a gain adjuster 2-2, and an adder 2-3. The subtractor 2-1 is supplied with the signal zo from the output signal synthesizer 1-8 via the line L3 and the output signal y0 of the first delay circuit 1-1 via the line L2, and from zo to y0. Is subtracted and the signal h is output.

[0051]

[Equation 13]

This signal h is the edge emphasis signal component formed by the processing of FIG. FIG. 6A shows a waveform diagram of the signal h when the nonlinear parameter α = 16.

The gain adjuster 2-2 at the next stage adjusts the amplitude of the signal h from the previous stage. The gain value given here is β (>
0), and the edge-enhanced signal whose amplitude has been adjusted is added to the above-mentioned input signal y0 by the adder 2-3 in the next stage. The resulting final output signal zoo is given by the equation below and is output via line L4.

[0054]

[Equation 14]

FIGS. 6B, 6C, and 6D are waveform diagrams of the output signal zoo when the values of β are 0.3, 0.5, and 0.7, respectively. The value of the gain β is set so that the optimum edge enhancement effect can be obtained by observing the image actually displayed on the display.

FIG. 7 is a diagram when the waveform edge enhancement effect in FIG. 1 is observed in the frequency domain. FIG. 7A shows FIG.
It is a spectrum figure of the input signal of (a). Certainly about 2M
A frequency component of Hz is observed. On the other hand, Fig. 7
FIG. 5B is a spectrum diagram of FIG. 5D, that is, the output signal zo of the embodiment when the nonlinear parameter α = 16. Figure 7
In addition to the same 2 MHz component as in (a), a harmonic component having an odd multiple is observed. These harmonic components are the spectrum newly added to emphasize the waveform edge. FIG. 7C shows an edge emphasis signal component h (see FIG.
It is a spectrum of (a) reference. This is this example
This is the newly formed harmonic component. FIG. 7D is a spectrum of the final output signal zoo (FIG. 6D) when the gain β = 0.7. The edge enhancement component of FIG. 7C is added to the input shown in FIG.

The above is the description of the basic operation of the embodiment shown in FIGS. 1 and 2 when a cosine wave having a frequency of 2 MHz is applied as an input signal. Let's take a look at how is working.

Pay attention to the right downward slope of the waveform of the signal of which the pulse signal having the amplitude of 1 and the width of 5 μsec is band-limited by the low-pass filter having the roll-off characteristic which is attenuated by the cosine characteristic in the range of 0 to 4 MHz. , I will observe the waveform.

FIGS. 8, 9, 10 and 11 correspond to FIGS. 4, 5, 6 and 7 in one-to-one correspondence with pulse signal inputs including parameter (α, β) settings. It is an output waveform diagram of each part. It can be seen that the waveform slope is steep as in the case of cosine wave input. As the value of the non-linear parameter α increases, preshoot and overshoot are still seen, but they are within 10% or less. This is a much smaller amount than in the case of adding the second derivative of the prior art, and if the preshoot and overshoot are appropriate, the image quality is improved. On the other hand, the steepening of the waveform is far superior to the conventional technique, and the effect of the steepening of the waveform is very large. In addition, FIG.
What can be seen by comparing (a) and (b) (comparing the spectrum of the input and the output) is that the sideband component related to the pulse edge is newly formed and added. The signal band, which was originally up to 4 MHz, has been expanded to 10 MHz.

When determining the constant term of the characteristic curve connecting the three signal values, three signals are added and synthesized at a predetermined ratio as shown in the equation (4). This is because the constant term is the low-frequency component of the signal. It is a process for obtaining the following, and has the function of improving the accuracy of the zero cross points of the sine term and cosine term which are AC components.
The addition synthesis ratio of the three signals when obtaining the constant term is
Since the settable range is clarified by the proviso of the equation and the equation 6, the value can be selected according to the purpose of use and the use conditions.

As described above, in the edge enhancement processing according to the embodiment, there is a perfect correlation with the input signal, and the edge enhancement component is smoothly added in a natural form. It is possible to give a feeling of improvement in sharpness and resolution in a natural manner without giving a feeling of strangeness to.

Next, the second and third embodiments are shown in FIGS. 12 (a) and 12 (b), respectively. FIG. 13 is a diagram showing a configuration example of an additional circuit (adjustment circuit) for making the embodiments shown in FIG. 12 function more effectively, and FIGS. 14 to 24 are operation explanatory diagrams.

In the description of the operation, a simplified simulated expression method is also used for convenience. Further, even when a digital circuit is taken as an example for realizing the operation function, the signal waveform of the circuit is shown as an analog waveform in order to make the explanation of the operation easy to understand.

In FIG. 12A, 1-1 is a first delay circuit, 1-2 is a second delay circuit, 1-3 is a constant term synthesizer, and 1-14 is a hyperbolic cosine function term coefficient value. Synthesizer, 1-15
Is a hyperbolic sine function term coefficient value synthesizer, 1-6 is an amplitude synthesizer,
1-7 is a phase synthesizer, and 1-8 is an output signal synthesizer. The first and second delay circuits 1-1 and 1-2 constitute an extraction circuit, and a constant term synthesizer 1-3, a hyperbolic cosine function term coefficient value synthesizer 1-14, a hyperbolic sine function term coefficient value Synthesizer 1-1
5 constitutes a first synthesizing circuit, and the amplitude synthesizing unit 1-6, the phase synthesizing unit 1-7 and the output signal synthesizing unit 1-8 constitute a second synthesizing circuit.

For the sake of convenience of explanation, it is assumed that a signal delay due to the processing time of each circuit itself and a delay circuit or the like which is usually used only for simply correcting the delay are omitted except where necessary for explanation. To do.

As an example of the input signal handled by the image quality improving apparatus, a television luminance signal, a color signal, an RGB signal, etc. are assumed. Here, especially, the frequency band is 4MHz
The video signals of the NTSC broadcasting system up to here are treated as an example.

First, the input signal y coming from the line L1
A case where in is a cosine wave as shown in FIG. 15A will be described. This cosine wave is an example of a luminance signal with a frequency f = 2 MHz. The input signal yin is the first delay circuit 1
-1 is supplied. This is a delay circuit whose delay time T is given by the following equation.

[0068]

[Equation 15]

The value of T is a sampling period normally used when sampling an NTSC signal. The output of this delay circuit is output on the line L2, and the second delay circuit 1-2
Is supplied to. The delay time of the second delay circuit 1-2 is the same as the delay time T of the delay circuit 1-1.

Two delay circuits 1-1 and 1 are shown in FIG.
2 shows the relationship of input / output signals of -2. Using the signal value y0 at the center (t = 0) as a reference, two left and right signals y- ₁ and y1 separated by a time T are used (the signal value of each signal also uses the same sign as the signal). The signal value y ₀ is the output signal of the first delay circuit, the signal y ₋₁ is the output signal of the second delay circuit,
y1 corresponds to the input signal of the first delay circuit. The waveform diagram used in the following explanation of operation is based on this signal y0 as a time reference.

The signal characteristic curve connecting the signal values of these three signals is approximated by the following equation.

[0072]

[Equation 16]

The first term on the right side of the equation of y is the hyperbolic cosine (hyperb
The second term is a hyperbolic sine function term consisting of a hyperbolic sine function, and the third term is a constant term. In order to determine the coefficient values a, b, the constant value c, and the variable x of this equation, the signal values y _-1 , y0, y1 are used. By substituting these three signal values into the equation 16, the following equation is obtained.

[0074]

[Equation 17]

It is the following three blocks 1-3, 1-14, and 1-15, which are the first synthesis circuit, that perform the processing for obtaining the constants a, b, and c of this equation.

The constant combiner 1-3 has three signals y _-1 , y 3.
1, 1 and y0 are supplied, and the value c of the constant term added and synthesized with the mixing ratios k0 and k1 is output as in the following equation.

[0077]

[Equation 18]

The constant synthesizer 1-3 functions as an addition synthesizer. The value of the mixing ratio is given by

[0079]

[Formula 19]

An output waveform diagram when the value of c is the average value of three signals is shown in FIG. 15 (b).

Next hyperbolic cosine function term coefficient value synthesizer 1-14
Is also supplied with three signals y-1, y1 and y0, and the coefficient value a is output as in the following equation.

[0082]

[Equation 20]

This equation is obtained by converting the equations (18) and (19) into the second equation (17).
It is calculated by substituting into the formula. The function of the combiner 1-14 is an addition / subtraction combination function.

Next hyperbolic sine function term coefficient value synthesizer 1-15
Are supplied with the signals y _-1 , y1 and the constant values c and a already obtained, and the coefficient value b is output as in the following equation.

[0085]

[Equation 21]

This equation is the sum of the first and third equations of Equation 17,
It can be obtained by obtaining the value of coshx0 from the already obtained c and a and subtracting the first equation from the third equation of the equation (17). The function of the synthesizer 1-15 can be realized by a digital circuit or the like using a table lookup type ROM or the like. The characteristic expression of the equation 16 is determined by the equations 18 to 21.

A block 1-1 is provided to the next amplitude synthesizer 1-6.
The coefficient value a from 4 and the coefficient value b from block 1-15 are supplied. The coefficient value a is a reference point (t = 0, that is, x
= 0) is a coefficient value of a hyperbolic cosine function term that is an even function, and a coefficient value b is a coefficient value of a hyperbolic sine function term that is an odd function with respect to a reference point. In general, since the even function and the odd function are orthogonal to each other, as shown in FIG. 14B, the amplitude value A is calculated as follows from the right triangle drawn with the coefficient value a on the horizontal axis and the coefficient value b on the vertical axis. It is calculated and output.

[0088]

[Equation 22]

The output waveform diagram of the amplitude synthesizer 1-6 is shown in FIG.
5 (c). The function of the amplitude synthesizer 1-6 can also be realized by a digital circuit or the like using a table lookup type ROM or the like.

The next phase synthesizer 1-7 has a block 1-1.
The coefficient value a from 4 and the coefficient value b from block 1-15 are supplied. Based on the ratio of the coefficient values on the horizontal axis and the vertical axis of the right triangle of FIG. 14B, the phase value φ is calculated by the following equation and output from the phase combiner 1-7.

[0091]

[Equation 23]

The output waveform diagram of the phase synthesizer 1-7 is shown in FIG.
5 (d). In the figure, the value of π / 2 is normalized to 1 and displayed. The function of this block can also be realized by a digital circuit using a table lookup type ROM or the like.

In the next output signal synthesizer 1-8, the constant value c obtained by the equation 18, the coefficient value a obtained by the equation 20, the amplitude value A obtained by the equation 22 and the equation 23 are obtained. The phase value φ thus obtained is supplied, and the output signal zo represented by the following equation is synthesized using the non-linear parameter α and output from the line L3.

[0094]

[Equation 24]

In this way, the output signal synthesizer 1-8 multiplies the value obtained by raising the value α obtained by normalizing the phase value in the range of 0 to 1 by π / 2, and performs the nonlinear phase conversion process to obtain the cosine term. .. is multiplied by A to give the polarity of the coefficient value a, and the constant value c is added to the output signal zo. Synthesizer 1
The function of -8 can also be realized by a digital circuit, such as a table lookup type ROM.

Output waveform diagrams for the cases where the nonlinear parameter α is 2, 4, 8 and 16 are shown in FIGS. 16 (a), 16 (b),
They are shown in (c) and (d), respectively. As compared with FIG. 15A which is an input signal waveform diagram, it can be seen that the slope portion of each waveform of FIG. 16 is sharpened. Non-linear parameter α
It is also clear that the steeper degree increases as the value of becomes larger.

The processing in the second embodiment shown in FIG. 12 (a) can be summarized by the following equation. That is, the approximate characteristic equation of the equation 15 is changed to the following equation.

[0098]

[Equation 25] Then, the phase value φ is transformed by the following non-linear conversion process,
New phase value φo

[0099]

[Equation 26]

Then, the characteristic equation is converted into the following equation z,

[0101]

[Equation 27]

In this processing, z at x = 0, that is, zo is obtained as in the equation 24 and is output instead of the signal y0.

FIG. 13 shows an adjusting circuit for optimizing the edge enhancement effect of the output signal zo in FIG. It is composed of three blocks: a subtractor 2-1, a gain adjuster 2-2, and an adder 2-3. The subtractor 2-1 outputs the signal zo from the output signal synthesizer 1-8 and the line L2 via the line L3.
The signal y0 from the first delay circuit 1-1 is supplied via the above, and y0 is subtracted from zo to output the signal h.

[0104]

[Equation 28]

This signal h is an edge emphasis signal component formed by the processing in the circuit shown in FIG. FIG. 17
A waveform diagram of the signal h when the nonlinear parameter α = 16 is shown in (a).

The gain adjuster 2-2 at the next stage adjusts the amplitude of the signal h from the previous stage. The amplification factor given here is β (>
0), and the edge-enhanced signal whose amplitude has been adjusted is added to the above-mentioned input signal y0 by the adder 2-3 in the next stage. The resulting final output signal zoo is given by the equation below and is output via line L4.

[0107]

[Equation 29]

17 (b), (c) and (d) are waveform diagrams of the output signal zoo when the values of β are 2, 3 and 5, respectively. The value of β is set so that the optimum edge enhancement effect can be obtained by observing the image actually displayed on the display.

FIG. 18 is a diagram when the waveform edge enhancement effect in the second embodiment of FIG. 12A is observed in the frequency domain. FIG. 18A is a spectrum diagram of the input signal of FIG. 15A. A frequency component of about 2 MHz is observed.
On the other hand, FIG. 18B is a spectrum diagram of FIG. 16D, that is, the output signal zo of the embodiment when the nonlinear parameter α = 16. In addition to the same 2 MHz component as in FIG. 18A, a harmonic component having a frequency that is an odd multiple thereof is observed. These harmonic components are the spectrum newly added to emphasize the waveform edge. FIG. 18C is a spectrum diagram of the edge emphasis signal component h (see FIG. 17A). This is the harmonic component newly formed in this embodiment. FIG. 18D is a spectrum diagram of the final output signal zoo (FIG. 17D) when the amplification factor β = 3. Figure 1
The edge emphasis component of FIG. 18C is tripled and added to the input shown in FIG. As described above, in the processing of the second embodiment, the edge emphasis component is added to be slightly smaller, so that the gain adjuster of FIG. 13 sets the value of the amplification factor β to a value larger than 1 to amplify it, and obtains the desired characteristic. Need to get

The above is the description of the basic operation of the embodiment shown in FIGS. 12 (a) and 13 when a cosine wave having a frequency of 2 MHz is added as an input signal. Let's see how it works. Paying attention to the downward sloping slope portion of the waveform in which the pulse signal having the amplitude of 1 and the width of 5 μsec is band-limited by the low-pass filter having the roll-off characteristic that attenuates with the cosine characteristic in the range of 0 to 4 MHz,
We will observe the waveform.

FIG. 19, FIG. 20, FIG. 21, and FIG. 22, including the parameter (α, β) settings, are shown in FIG. 15 and FIG. 1, respectively.
FIG. 19 is an output waveform diagram of each part with respect to a pulse signal input corresponding one-to-one to 6, FIG. 17, and FIG. It can be seen that the waveform slope is steep as in the case of cosine wave input. Also,
It can be seen by comparing FIGS. 22A and 22D that the sideband component related to the pulse edge is newly formed and added. The signal band that was originally up to 4MHz is 10MHz
It has been expanded to the above.

Next, the input signal is a pulse signal (s) having a flat spectrum component up to the frequency band 4 MHz as shown in the following equation.
Let's examine the response in the case of the (inc function).

[0113]

[Equation 30]

FIG. 23A is an input signal waveform diagram. FIG. 23B is a waveform diagram of the output signal zoo (zo) from the line L4 when α = 16 and β = 1. FIG. 23 (c)
23 is a waveform diagram of zoo when is α = 16 and β = 2, and FIG.
It is a waveform diagram of zoo when (d) is α = 16 and β = 3.
It can be seen that even for a complicated waveform with ringing, the steepening process is performed by accurately capturing the waveform changing portion.

FIG. 24 compares the difference between the input and output signals of this sinc function in the frequency domain. Figure 24 (a)
Is a sinc with the same frequency band of 4 MHz as in FIG.
(X) It is a waveform diagram of a pulse and is an input signal. Figure 24
(B) is the frequency spectrum. 24 (c) is the same as FIG. 23 (c). Output signal z when α = 16 and β = 2
It is a waveform diagram of oo. FIG. 24D shows the frequency spectrum. The spectral components added by this edge enhancement process appear to contain considerably more complex harmonics than the single cosine wave or pulse described above, but the basic principle is the same, and It is considered that such an apparently complex spectrum is obtained as a result of newly forming and combining the odd harmonics of.

Next, a third embodiment shown in FIG. 12B will be described. Looking at the equations 20, 20, and 18 for obtaining the coefficient values a and b and the constant value c derived in the description of the second embodiment shown in FIG. First-order difference value as

[0117]

[Equation 31]

Then, the quadratic difference value as

[0119]

[Equation 32]

It can be seen that it is included. A coefficient a is obtained by multiplying d1 by a coefficient k1, and a coefficient b is obtained by multiplying d0 by a value formed by the coefficient k1 and the like, and a constant c is obtained from the reference value y0 and the coefficients k1 and d1. Taking these features into consideration, the functions are exactly the same as those of the second embodiment shown in FIG. 12A, but the configuration is changed as shown in FIG.
It is a 3rd Example shown in (b).

Blocks b-1 and b-2 in FIG.
Are the same delay circuits as the blocks 1-1 and 1-2 of FIG. The block b-3 is a circuit for obtaining the first-order difference value d0 shown in Expression 31, and the block b-4 is a circuit for obtaining the second-order difference value d1 shown in Expression 32. In block b-5, the amplitude A of the equation 22 is replaced by the following equation to obtain A.

[0122]

[Expression 33]

In block b-6, the phase φ of equation 23 is obtained by replacing it with the following equation.

[0124]

[Equation 34]

In the next block b-7, the output zo of the equation 24 is obtained.
Is replaced by the following equation to obtain zo.

[0126]

[Equation 35]

It is considered that which construction method of FIGS. 12A and 12B is to be adopted depends on the way of thinking of the designer.

Here, as described above, when the constant term of the characteristic curve connecting the three signal values is determined, the three signals are added and synthesized at a predetermined ratio. This is a process for obtaining from the component, and it works to improve the accuracy of the zero crossing points of the hyperbolic cosine function term and the hyperbolic sine function term which are the AC components. Since the settable range is clarified by the proviso of Eq. 18 for the addition and synthesis ratio of the three signals when obtaining the constant term, a value can be selected according to the purpose of use and the conditions of use.

As described above, in the edge emphasizing process according to the embodiment, since there is a perfect correlation with the input signal and the edge emphasizing component is smoothly added in a natural form, this image quality improving apparatus is suitable for the viewer. It is possible to give a feeling of improvement in sharpness and resolution in a natural manner without giving a feeling of strangeness to.

Since each block of each of the above-described embodiments can be easily constructed by using a well-known circuit, a commercially available IC, etc., the entire apparatus can be realized at low cost.

In each of the above embodiments, a television luminance signal is used as an input signal example, but the image quality improving device of the present invention can be applied to a color signal, an RGB signal, and the like. Further, for digitalized image data, contour correction processing equivalent to the present invention, edge enhancement processing, similar processing for enlarged / reduced image data can be realized by software processing using a computer. It can be applied to image data processing by software. Furthermore, the present invention is applicable to NTSC to HDTV.
Various broadcasting systems up to and including V for recording and reproducing these signals
It is particularly effective for uniforming the image quality of reproduced images of low resolution to high resolution such as TR and various computer images.
Further, it is also effective for improving waveform deterioration of a general digital transmission communication system.

The present inventor has filed an application for the same purpose as the present invention. For example, Japanese Patent Application No. 3-313605
Image quality improving device (filed on October 31, 1991, reference number H03000870) and waveform correction device of Japanese Patent Application No. 3-360616 (filed on Dec. 27, 1991, reference number H0
However, in these prior applications, the combined amplitude and combined phase value of the quadrature and in-phase high-pass filters are obtained, and the edge emphasis component is obtained by nonlinear conversion of the combined phase value to improve the image quality. . On the other hand, the present invention is
The invention is more practical because it aims to obtain the same effect by simple means without using two high-pass filters.

[0133]

As described above, the image quality improving device of the present invention has the following effects.

(A) A characteristic curve connecting three adjacent signal values at every predetermined time (T) in the input signal is represented by a cosine term (or a hyperbolic cosine function term), a sine term (or a hyperbolic sine function term). ,
And the information of the waveform change portion (edge) of the input signal is obtained by approximating by the sum of the constant term. Then, the phase value obtained from the ratio of the coefficient values of the cosine term and the sine term (or the coefficient value of the hyperbolic cosine function term and the hyperbolic sine function term) is subjected to a non-linear conversion process to enhance the edge signal. And synthesize
The edge emphasis signal can be added to the input signal to make the substantially central portion of the slope portion of the input signal steep. As a result, a frequency component outside the frequency band of the input signal can be added to the input signal, and an edge-emphasized and contour-emphasized output signal can be obtained.

(B) When obtaining the constant term of the characteristic curve connecting the three signal values, the three signal values are added and synthesized at a predetermined ratio. This is because the constant term is obtained from the low frequency component of the signal. Processing, and functions to effectively operate the sine term and the cosine term (or the hyperbolic cosine function term and the hyperbolic sine function term). Furthermore, since the settable range of the ratio of the additive synthesis is clarified, the adjustment work becomes easy when adjusting the ratio according to the usage situation.

(C) For edge enhancement with preshoot and overshoot far exceeding the amplitude of the original signal, such as the conventional contour correction using the second derivative, the present invention can be applied within the amplitude of the original signal. This is edge enhancement processing that can suppress waveform changes as much as possible. Therefore, even if a device incorporating this image quality improving device is configured by a digital circuit, the overflow problem does not occur, and good image quality can be improved.

(D) The degree of waveform edge emphasis on the input signal depends on the contained frequency of the input signal, and the degree of the correlation is maintained including the amplitude information and the phase information. Further, the edge emphasis component smoothly makes the waveform change portion steep. Therefore, the image quality after processing can give the viewer a feeling of improvement in sharpness and resolution in a natural manner without giving a sense of discomfort to the viewer.

(E) When the function of separating the edge emphasis component and adjusting the amplitude thereof is added, the user can obtain the optimum image quality improvement state according to his preference while observing the actual reproduced image. You can Further, by taking advantage of the effects of preshoot and overshoot, it is possible to add a preshoot and overshoot that are thinner than in the past to enhance the edge.

(F) Since each component of the image quality improving device of the present invention can be realized with a simple circuit structure by using general-purpose parts such as commercially available ICs, the image quality improving device can be manufactured at a low cost. It's easy to manufacture, and
Since it has a wide range of uses, it is industrially effective and beneficial.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment.

FIG. 2 is a configuration diagram of an adjusting circuit added to the first embodiment.

FIG. 3 is an operation explanatory diagram of the first embodiment.

FIG. 4 is an operation explanatory diagram of the first embodiment.

FIG. 5 is an operation explanatory diagram of the first embodiment.

FIG. 6 is an operation explanatory diagram of the first embodiment.

FIG. 7 is an operation explanatory diagram of the first embodiment.

FIG. 8 is an operation explanatory diagram of the first embodiment.

FIG. 9 is an operation explanatory diagram of the first embodiment.

FIG. 10 is an operation explanatory diagram of the first embodiment.

FIG. 11 is an operation explanatory diagram of the first embodiment.

FIG. 12 is a block configuration diagram of second and third embodiments.

FIG. 13 is a configuration diagram of an adjusting circuit added to the second embodiment.

FIG. 14 is an operation explanatory diagram of the second embodiment.

FIG. 15 is an operation explanatory diagram of the second embodiment.

FIG. 16 is an operation explanatory diagram of the second embodiment.

FIG. 17 is an operation explanatory diagram of the second embodiment.

FIG. 18 is an operation explanatory diagram of the second embodiment.

FIG. 19 is an operation explanatory diagram of the second embodiment.

FIG. 20 is an operation explanatory diagram of the second embodiment.

FIG. 21 is an operation explanatory diagram of the second embodiment.

FIG. 22 is an operation explanatory diagram of the second embodiment.

FIG. 23 is an operation explanatory diagram of the second embodiment.

FIG. 24 is an operation explanatory diagram of the second embodiment.

[Explanation of symbols]

 1-1 First delay circuit 1-2 Second delay circuit 1-3 Constant term synthesizer 1-4 Cosine term coefficient value synthesizer 1-5 Sine term coefficient value synthesizer 1-6 Amplitude synthesizer 1-7 Phase synthesizer 1-8 Output signal synthesizer

Claims (4)

[Claims] 1. An extraction circuit for extracting three signal values from an input signal at fixed time intervals and a signal characteristic curve connecting the extracted three signal values are approximated by the sum of a cosine term, a sine term and a constant term. In order to do so, a first synthesizing circuit that finds the constant term by synthesizing the three signal values at a predetermined ratio and finds the coefficient values of the cosine term and the sine term, and the coefficient value of the cosine term and the The amplitude value and the phase value are obtained from the coefficient value of the sine term, the phase value is nonlinearly converted, and a new signal characteristic curve is obtained from the nonlinearly converted phase value, the coefficient value of the cosine term, and the amplitude value, An image quality improving device comprising a second synthesizing circuit for obtaining an output signal in which a waveform changing portion of an input signal is steepened. 2. The image quality improving apparatus according to claim 1, wherein an edge emphasis signal is obtained from a difference between an output signal of the second synthesizing circuit and the input signal, and the amplitude of the edge emphasis signal is adjusted to obtain the input signal. An image quality improving apparatus comprising an adjusting circuit for synthesizing an edge-emphasized signal whose amplitude is adjusted with a signal to obtain a new output signal. 3. An extraction circuit for extracting three signal values from an input signal at constant time intervals, and a signal characteristic curve connecting the extracted three signal values, a hyperbolic cosine function term and a hyperbolic sine function term. In order to approximate with a hyperbolic function composed of the sum of constant terms, the three signal values are combined at a predetermined ratio to obtain the constant term, and the coefficient values of the hyperbolic cosine function term and the hyperbolic sine function term are determined. A first synthesizing circuit, an amplitude value and a phase value are obtained from the coefficient value of the hyperbolic cosine function term and the coefficient value of the hyperbolic sine function term, the phase value is non-linearly converted, and the non-linearly converted phase value And a second synthesizing circuit for obtaining a new signal characteristic curve from the coefficient value of the hyperbolic cosine function term and the amplitude value and obtaining an output signal in which the waveform changing portion of the input signal is steepened. Image quality improvement device. 4. The image quality improving apparatus according to claim 3, wherein an edge emphasis signal is obtained from the difference between the output signal of the second synthesizing circuit and the input signal, and the amplitude of the edge emphasis signal is adjusted to obtain the input signal. An image quality improving apparatus comprising an adjusting circuit for synthesizing an edge-emphasized signal whose amplitude is adjusted with a signal to obtain a new output signal.