JPH0774985A - Picture quality improving device - Google Patents

Abstract

PURPOSE:To obtain a device appropriate for various video equipments or the like and capable of improving picture quality in a natural form without exerting a feeling of incompatibility upon an observer by sharpening a waveform edge and improving the sharpness and resolution of a reproduced picture. CONSTITUTION:A delay signal forming circuit 1-1 extracts a signal from an input signal in each time Tx interval and each time Ty interval. An edge emphasized signal forming circuit 1-2 approximates a signal characteristic curve for connecting the signal values of signals obtained in each Tx interval to a quadratic furaction equation and processes a coefficient value between a quadratic function term and a linear function term in the expression and a constant term to form a horizontal direction edge emphasized signal. Similarly an edge emphasized signal forming circuit 1-3 forms a vertical direction edge emphasized signal from the signal values of signals obtained in each Ty interval. Two edge emphasized signals are synthesized by addition through an adder 1-6, the synthesized edge emphasized signal is added to the input signal through an adder 1-7 to output an output signal obtained by two-dimensionally sharpening a waveform changing part.

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 preshoot and overshoot, and further 2 in playback image
It is an object of the present invention to provide an image quality improving device that can improve the sharpness and resolution in a natural manner by performing contour correction in a dimension and without giving a feeling of strangeness to a viewer.

[0005]

In order to solve the above problems, the present invention provides an extraction circuit for extracting a signal value from an input signal at every first time interval and every second time interval, and A horizontal direction edge enhancement signal forming circuit which is supplied with the signal value extracted every one time interval to obtain a horizontal edge enhancement signal; and a vertical direction which is supplied with the signal value extracted every second time interval. A vertical edge enhancement signal forming circuit for obtaining an edge enhancement signal, and two circuits for the horizontal and vertical directions
A combining circuit that combines two edge-enhanced signals to obtain a combined edge-enhanced signal; and an adder circuit that adds the combined edge-enhanced signal to the input signal and obtains an output signal in which the waveform changing portion of the input signal is steepened. The horizontal direction edge enhancement signal forming circuit and the vertical direction edge enhancement signal forming circuit each include at least three temporally adjacent signal values among the signal values for each time interval supplied from the extraction circuit. In order to approximate the signal characteristic curve connecting the two with a quadratic function consisting of the sum of a quadratic function term, a linear function term, and a constant term, a plurality of signal values including at least the three signal values are set at a predetermined ratio. While adding and synthesizing with, the constant term is obtained,
A first coefficient value for each of the quadratic function term and the linear function term from a plurality of signal values including at least the three signal values;
Of the quadratic function term and the linear function term, and an amplitude value is obtained from the coefficient value of the quadratic function term with respect to the amplitude value. The cosine value is non-linearly processed to obtain an amplitude limiting cosine value, a new coefficient value with edge enhancement of the quadratic function term is obtained from the amplitude limiting cosine value and the amplitude value, and the new coefficient value and the quadratic value are obtained. A second image synthesis processing circuit for obtaining an edge enhancement signal for each direction based on a difference from a coefficient value of a function term.

[0006]

1 is a block diagram showing an embodiment of an image quality improving apparatus according to the present invention, FIG. 2 is a diagram showing a detailed configuration of a delay signal forming circuit in FIG. 1, and FIG. FIG. 4 is a diagram showing a detailed configuration of a horizontal edge emphasis signal forming circuit, and FIG.
3 is a diagram showing a detailed configuration of a vertical edge enhancement signal forming circuit in FIG. 5 to 16 are operation explanatory diagrams.

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 delay signal forming circuit (extracting circuit for extracting a signal value), 1-2 is a horizontal edge enhancing signal forming circuit, 1-3 is a vertical edge enhancing signal forming circuit, 1 -4 is a first amplifier, 1-5 is a second amplifier, 1-6 is a first adder (these 1-4 to 1-6 form a combining circuit for obtaining a combined edge emphasis signal), and 1 -7
Is a second adder (adding circuit for obtaining an output signal).

For convenience of explanation, 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 will be 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
It is assumed that an NTSC broadcasting system signal in which frequency components exist up to the range (see FIG. 5E) (see FIG. 5E) is taken as an example.

The image quality improvement here is 2 for the reproduced image.
The purpose is to perform dimensional contour enhancement, and the signal handled in this embodiment is x in the horizontal direction as shown in FIG.
Five signal values (zx (n), n = -2, -1,
0,1,2) and five signal values (zy (m), m = -2, -1,0,1,2) arranged at intervals of yo in the vertical direction. xo and yo
Is the spatial distance, and in the actual signal, the time interval T is
It is a value corresponding to x (Equation 1 below) and time interval Ty (Equation 2 below).

[0012]

[Equation 1]

[Equation 2]

FIG. 5 (b) is a waveform diagram showing the five signal values in the horizontal direction of FIG. 5 (a) so that the intervals and magnitudes thereof can be seen. FIG. 5C is a diagram in which the five signal values in the vertical direction in FIG. 5A are drawn in such a manner that the respective intervals and sizes can be known.

First, when the input signal Si coming from the line L1 shown in FIG. 1 is 2 as shown in FIGS. 6 (a) and 6 (b).
A case of a three-dimensional pulse (corresponding to an image in which a white rectangular pattern is displayed on a black background) will be described. Figure 6
The waveform diagram of (a) is a waveform diagram in which the horizontal direction is the horizontal direction and the vertical direction is the vertical direction, and the image is drawn in such a manner that the display image is viewed as shown in FIG. 5 (a). It is a figure for seeing a spread. Horizontal display range is -1 μsec
~ 1 μsec, vertical direction is -635 μsec ~ 635 μsec. Therefore, the number of scanning lines in the vertical direction is 21.
FIG. 6B is a perspective view in the vertical direction of FIG. 6A, and by overwriting the 21 scanning waveform diagrams in FIG. 6A, the details of the waveform that are difficult to understand in FIG. 6A are shown. You can see the changes. In the following explanation of the operation, such a waveform display method is adopted. (B) and (d) of each of FIGS. 6 to 16 show such a scanning waveform 2 in the vertical direction.
It is one overwriting waveform diagram.

The waveform of the input signal Si is a pulse waveform having an amplitude of 1 and a width of 1 μsec in the horizontal direction from 0 to 4M.
This is a waveform obtained by removing an out-of-band component of 4 MHz or more through a low-pass filter having a frequency characteristic that attenuates like a cosine wave up to Hz. In addition, the pulse is arranged in a total of nine scanning lines in the vertical direction, and a low-pass filter in the vertical direction is used to perform a light high-frequency reduction process to obtain a waveform.

As shown in FIG. 1, the input signal si is supplied to the delay signal forming circuit 1-1. FIG. 2 shows a specific configuration example of the delay signal forming circuit 1-1. In FIG. 2, blocks a-1 to a-4, which are delay circuits for time correction, delay an input signal by a time Ty (refer to the above-mentioned equation 2, equivalent to spatial distance yo) and output the delayed signal. Circuit a-5
To a-8 delay the input signal by the time Tx (refer to the above-mentioned formula 1 and correspond to the spatial distance xo) and output the delayed signal. The delay circuits a-9 to a-12 output the input signal at the time 2Tx.
Delay and output.

In terms of correspondence with FIG. 5A, the input signal S
It is zx (2) that i is output from the line Lx2 via the delay circuits a-1 and a-2, and zx (1) is output from the line Lx1 via a-5. And further a
It is zx (0) that is output from the line Lx0 via -6, zx (-1) is output from the line Lx-1 via a-7, and a- It is zx (-2) that is output from the line Lx-2 via 8. These outputs zx (n) (n = -2, -1,0,1,2) are used as signals for forming horizontal edge enhancement signals.

On the other hand, it is zy (2) that the input signal Si is outputted from the line Ly2 via the delay circuit a-9, and
It is zy (1) that is output from the line Ly1 via -1 and a-10, and is output from the line Ly0 via a-1, a-2, a-5, and a-6. Is zy (0),
It is zy (-1) that is output from the line Ly-1 via a-2 to a-3 and a-11, and a-3 to a-4,
It is z that is output from the line Ly-2 via a-12.
It is y (-2). These outputs zy (m) (m = -2, -1,0,1,2) are used to form vertical edge enhancement signals. The outputs zx (0) and zy (0) in FIG. 2 are the same signal, but they are the signals z (0) that are the center (reference) of the signal value sequences in the horizontal and vertical directions, respectively, and are processed as follows. Will be explained based on this z (0). Figure 6 (a)
And (b) are also waveform diagrams of this z (0).

Returning to FIG. 1, the delay signal forming circuit 1-1
Zx (n) (n = -2, -1,0,1,2) of the signals output from the above is supplied to the next horizontal edge enhancement signal forming circuit 1-2, and zy (m) (m = -2, -1,0,1,2) is supplied to the next vertical edge enhancement signal forming circuit 1-3. 3 shows a detailed configuration example of the horizontal edge enhancement signal forming circuit 1-2, and FIG. 4 shows a detailed configuration example of the vertical edge enhancement signal forming circuit 1-3. The two edge enhancement signal forming circuits shown in FIGS. 3 and 4 have the same configuration and the same function, and the difference is the value of the parameter to be used. The line Lxn (n = -2, -1,0,
1,2) from each of the five signals zx (n) (n = -2, -1,0,1,
2) is input. These signals are temporally and spatially arranged as shown in FIG. First, in the edge enhancement signal forming circuit 1-2, a signal characteristic curve connecting three signal values zx (-1), zx (0), and zx (1) temporally adjacent to each other among the five signal values is calculated as follows. It is approximated by a quadratic functional expression of.

[0020]

[Equation 3]

The first term on the right side of the expression of zx is a quadratic function term consisting of a quadratic function, the second term is a linear function term consisting of a linear function, and the third term is a constant term. The signal value zx (n) (n = -2,
-1,0,1,2), the constant values ax, bx, cx and the variable x are obtained, and the horizontal edge emphasis signal hx is obtained by giving a parameter for waveform steepening. −
It has two functions.

The vertical edge emphasis signal forming circuit 1-3 has five signals zy (m) (m = -2, -1) from the line Lym (m = -2, -1,0,1,2). , 0,1,2) is input. These signals are temporally and spatially arranged as shown in FIG. Three of these signal values zy (-
1), a signal characteristic curve connecting zy (0) and zy (1) is approximated by the following quadratic function formula.

[0023]

[Equation 4]

The first term on the right side of the expression of zy is a quadratic function term consisting of a quadratic function, the second term is a linear function term consisting of a linear function, and the third term is a constant term. The signal value zy (m) (m = -2,
-1,0,1,2), constant values ay, by, cy, and a variable y are obtained, and a vertical edge emphasis signal hy is obtained by giving a waveform steepening parameter. −
3 functions.

Two horizontal and vertical edge enhancement signals hx,
hy is calculated with respect to the reference position (t = 0, x = y = 0). The values of the reference position in the above equations 3 and 4 are the same value and are represented by the following equation.

[0026]

[Equation 5]

The edge enhancement signals hx and hy in the horizontal and vertical directions are calculated with respect to the value of z (0), and hx is multiplied by βx (amplification factor) by the first amplifier 1-4, and hy is obtained. Is multiplied by βy (amplification factor) in the second amplifier 1-5. In the next first adder 1-6, the two edge emphasis signals are added and combined to obtain a combined edge emphasis signal e, and in the second adder 1-7, the reference position of the reference position shown in Formula 5 is calculated. The value z (0) is combined with the combined edge emphasizing signal e, and the input signal is subjected to edge emphasizing processing to output a signal zo (see the following equation) from the line L2.
The above is the description of the schematic operation of FIG.

[0028]

[Equation 6]

Next, the two edge emphasis signal forming circuits 1-2 and 1-3 in FIG. 1 will be described in detail. First, the operation of the horizontal edge enhancement signal forming circuit 1-2 shown in FIG. 3 will be described. As shown in FIG.
The edge emphasis signal forming circuit 1-2 is composed of eight functional blocks. B-1 is a constant term synthesizer, b-2 is a quadratic function term coefficient value synthesizer, and b-3 is a linear function term. Numerical synthesizer, b-4 is amplitude synthesizer, b-5 is cosine synthesizer, b-
6 is an amplitude limiting amplifier, b-7 is a multiplier, and b-8 is a subtractor. The blocks b-1 to b-3 form a first combination processing circuit, and the blocks b-4 to b-8 form a second combination processing circuit.

Under the condition that the curve expressed by the equation 3 is a curve connecting three signal values zx (-1), zx (0) and zx (1), these three signal values zx Substituting (-1), zx (0), and zx (1) into Equation 3, the following equation is obtained.

[0031]

[Equation 7]

The processing for obtaining the constants ax, bx, and cx of this equation is performed by the following three blocks b-1 to b-3. The constant term synthesizer b-1 includes a delay signal forming circuit 1-1.
Is supplied with five signals zx (n) (n = -2, -1,0,1,2), and the value cx of the constant term added and synthesized with the mixing ratio kn as shown in the following equation.
Is output.

[0033]

[Equation 8]

As a result, the constant term synthesizer b-1 functions as a low pass filter. The value of the mixing ratio kn is given by

[0035]

[Equation 9]

Output waveform diagrams when the value of cx is the average value of five signals are shown in FIGS. 7 (a) and 7 (b). The characteristic of the constant term synthesizer b-1 in this case is a low-pass filter characteristic having a frequency characteristic as shown in FIG. This characteristic will be used in the description of the operation of the device below. The characteristics of the low-pass filter for averaging with such equal mixing ratio vary depending on the number of signal values used. As the number of signal values is reduced, the cutoff frequency of the low pass filter becomes higher. On the contrary, as the number of signal values is increased, the cutoff frequency of the low-pass filter moves to the lower side.

As a low-pass filter for obtaining the value of the constant term cx, in addition to the method using the average value as described above, depending on how the coefficient kn is given, under various conditions, various low characteristics can be obtained. A bandpass filter can be realized.

The following quadratic function term coefficient value synthesizer b-2:
Two signals of zx (0) via the line Lx0 and the value cx of the constant term from the constant term synthesizer b-1 are supplied, and the processing of the following equation is performed to determine the relation of the quadratic function term. The numerical value ax is output.

[0039]

[Equation 10]

This equation is obtained by substituting equations 8 and 9 into the second equation of equation 7. The function of the quadratic function term coefficient value synthesizer is a subtractor. 8 (a) and 8 (b) show waveform diagrams of the coefficient value ax. Clearly the input signal (Fig. 6 (a),
It is a horizontal high frequency signal component of (b)). The signals zx (-1), zx (0), zx are sent to the next-order linear function term coefficient value synthesizer b-3.
(1) and the coefficient value ax of the quadratic function term that has already been obtained
Is supplied, and xo is first obtained by the following equation,

[0041]

[Equation 11]

Subsequently, the coefficient value bx of the linear function term is obtained by the following equation.

[0043]

[Equation 12]

[Mathematical formula-see original document] This equation 12 obtains the sum of the first and third equations of equation 7 and the value of xo (equation 11) already obtained from cx and ax. It can be obtained by subtracting the expression. The function of the linear function term coefficient value synthesizer b-3 can be realized by a digital circuit or the like using a ROM of a table lookup system or the like. FIGS. 9A and 9B are waveform diagrams of bx.

The amplitude synthesizer b-4 at the next stage has the coefficient value ax from the quadratic function term coefficient value synthesizer b-2 and the coefficient value bx from the linear function term coefficient value synthesizer b-3. Is being supplied.
The coefficient value ax is a coefficient value of a quadratic function term that is an even function with respect to the reference point (t = 0, that is, x = 0), and the coefficient value bx is a linear function term that is an odd function with respect to the reference point. Is a coefficient value of.
In general, considering that the even function and the odd function are in an orthogonal relationship, the coefficient value ax is plotted on the horizontal axis and the coefficient value bx is plotted on the vertical axis. It is calculated by the following formula and output.

[0046]

[Equation 13]

Waveform diagrams of the output Ax of the amplitude synthesizer b-4 are shown in FIGS. 10 (a) and 10 (b). The function of the amplitude synthesizer can also be realized by a digital circuit using a table lookup type ROM or the like.

The next cosine value synthesizer b-5 has a coefficient value ax from the quadratic function term coefficient value synthesizer b-2 and an amplitude synthesizer b-4.
From the relationship between the hypotenuse Ax of the right-angled triangle in FIG. 5D and the coefficient value ax on the horizontal axis,
The cosine value COS φx is calculated by the following equation and output.

[0049]

[Equation 14]

The cosine value synthesizer b-functions to normalize the coefficient value ax by the amplitude value Ax obtained from the synthesis of the two coefficient values ax and bx to obtain a waveform of amplitude 1.
5 functions. The function of the cosine synthesizer can also be realized by a digital circuit using a table lookup type ROM or the like. The value of the phase value φx in the equation 14 can be calculated by the following equation also from the ratio of the value bx on the vertical axis and the value ax on the horizontal axis in FIG. 5 (d).

[0051]

[Equation 15]

From this phase value φx, the cosine value (COS φx) shown in Expression 14 can be obtained. The following amplitude limiting amplifier b-6 is a circuit commonly called a limiter, and an example of its input / output characteristics is shown in FIG. 5 (f). The relation of the output gx (qx) with respect to the input qx is expressed as follows.

[0053]

[Equation 16]

When the input signal level is relatively lower than the value of the amplitude limiting parameter αx, the input signal is amplified by αx times and output, while the input signal level is relatively higher than αx. When the input signal is large, the input signal is limited in amplitude, and a signal of amplitude 1 is output. As a result, the slope of the signal waveform of the small amplitude portion of the cosine value input from the previous stage is made steep, and the other signal portions are output as the signal waveform of the amplitude value 1.

The next block b-7 is a multiplier, and the amplitude value Ax from the amplitude synthesizer b-4 and the amplitude limiting amplifier b-6 are used.
The product ex with the output gx from is obtained.

[0056]

[Equation 17]

The output ex of this block is obtained as a result of the quadratic function term coefficient value ax being transformed by the amplitude limiting amplifier b-6. Therefore, the amplitude limiting parameter α
When x = 1, ex has exactly the same waveform as ax.
Therefore, as in the following equation,

[0058]

[Equation 18]

When added and combined with the constant term cx,
A signal zox in which the value zx (0) of the expression is edge-enhanced in the horizontal direction is obtained. However, since the purpose of the present invention is to perform the two-dimensional contour enhancement including the vertical direction as well, the addition like the equation 18 is not performed at this stage.

The next subtracter b-8 has a signal ax from the quadratic function term coefficient value synthesizer b-2 and a signal e from the multiplier b-7.
x is supplied, a horizontal edge enhancement signal hx as shown in the following equation is obtained, and is output via the line Lhx.

[0061]

[Formula 19]

The amplitude limiting parameter in Equation 16 is αx
11 is a waveform chart of hx processed as = 0.25.
Shown in (a) and (b). It can be seen that a clear enhancement component is formed at the transient of the input pulse waveform on each scanning line. The above is the function of FIG.

Next, the operation of the vertical direction edge enhancement signal forming circuit 1-3 whose internal structure is shown in FIG. 4 will be described. As described above, the circuit configuration itself is the same as that of the horizontal edge enhancement signal forming circuit 1-2. In FIG. 4, c-1 is a constant term synthesizer, c-2 is a quadratic function term coefficient value synthesizer, c-3.
Is a linear function term coefficient value synthesizer, c-4 is an amplitude synthesizer, c-
Reference numeral 5 is a cosine synthesizer, c-6 is an amplitude limiting amplifier, c-7 is a multiplier, and c-8 is a subtractor. Blocks c-1 to c-
Reference numeral 8 corresponds to the blocks b-1 to b-8 shown in FIG.

In the vertical edge emphasis signal forming circuit 1-3, the curve expressed by the above-mentioned equation 4 has three signal values zy (-
1), zy (0), and zy (1) are the conditions to be connected, so these three signal values zy (-1), zy (0), and zy (1) are substituted into equation 4. Then, the following equation is obtained.

[0065]

[Equation 20]

The processing for obtaining the constants ay, by and cy in this equation is performed in the following three blocks c-1 to c-3. The constant term synthesizer c-1 has five signals zy (m) (m = -2,-
1,0,1,2) is supplied from the delay signal forming circuit 1-1,
The value c of the constant term added and synthesized with the mixing ratio kn as shown in the following equation.
y is output.

[0067]

[Equation 21]

As a result, the constant term synthesizer c-1 functions as a low pass filter. The value of the mixing ratio kn is given by

[0069]

[Equation 22]

Output waveform diagrams when the value of cy is the average value of five signals are shown in FIGS. 7 (c) and 7 (d). The characteristic of the constant term synthesizer b-1 in this case is a low-pass filtering characteristic having a frequency characteristic as shown in FIG. This characteristic will be used in the description of the operation of the device below. The characteristics of the low-pass filter for averaging with such equal mixing ratio vary depending on the number of signal values used. As the number of signal values is reduced, the cutoff frequency of the low pass filter becomes higher. On the contrary, as the number of signal values is increased, the cutoff frequency of the low-pass filter moves to the lower side.

As a low-pass filter for obtaining the value of the constant term cy, in addition to the method based on the average value as described above, depending on how the coefficient kn is given, under various conditions, various low characteristics can be obtained. A bandpass filter can be realized.

The following quadratic function term coefficient value synthesizer c-2:
Two signals of zy (0) and the value cy of the constant term from the constant term synthesizer c-1 are supplied via the line Ly0, and the processing of the following equation is performed to determine the relation of the quadratic function term. The numerical value ay is output.

[0073]

[Equation 23]

This equation is obtained by using Equation 21 and Equation 22 as the second equation of Equation 20.
It is obtained by substituting it in the expression. The function of the quadratic function term coefficient value synthesizer is a subtractor. 8C and 8D show waveform diagrams of the coefficient value ay. Clearly the input signal (Fig. 6 (a))
And (b) are vertical high frequency signal components.

The following linear function term coefficient value synthesizer c-3 outputs the signals zy (-1), zy (0), zy (1), and the coefficient value ay of the quadratic function term that has already been obtained. Is supplied, and yo is first obtained by the following equation,

[0076]

[Equation 24]

Subsequently, the coefficient value by of the linear function term is obtained by the following equation.

[0078]

[Equation 25]

This formula 25 obtains the sum of the first and third formulas of formula 20 and the value of yo (formula 24) obtained from cy and ay, and the first formula from formula 3 of formula 20 It can be obtained by subtracting the expression. Linear function term coefficient value synthesizer c-3
The function of can be realized by a digital circuit using a table lookup type ROM or the like. 9 (c) and 9 (d) are waveform diagrams of the coefficient value by.

The amplitude synthesizer c-4 at the next stage has the coefficient value ay from the quadratic function term coefficient value synthesizer c-2 and the coefficient value by from the linear function term coefficient value synthesizer c-3. Is being supplied.
The coefficient value ay is a coefficient value of a quadratic function term that is an even function with respect to the reference point (t = 0, that is, y = 0), and the coefficient value by is a linear function term that is an odd function with respect to the reference point. Is a coefficient value of.
In general, considering that the even function and the odd function are orthogonal to each other, the coefficient value ay is plotted on the horizontal axis and the coefficient value by is plotted on the vertical axis. It is calculated by the following formula and output.

[0081]

[Equation 26]

Waveform diagrams of the output Ay of the amplitude synthesizer c-4 are shown in FIGS. 10 (c) and 10 (d). The function of the amplitude synthesizer can also be realized by a digital circuit using a table lookup type ROM or the like.

The next cosine value synthesizer c-5 has a coefficient value ay from the quadratic function term coefficient value synthesizer c-2 and an amplitude synthesizer c-4.
From the relationship between the hypotenuse Ay of the right triangle and the coefficient value ay on the horizontal axis in FIG. 5 (d),
The cosine value COS φy is calculated by the following equation and output.

[0084]

[Equation 27]

The function of the cosine value synthesizer is to normalize the coefficient value ay by the amplitude value Ay obtained from the synthesis of the two coefficient values ay and by to obtain a waveform of amplitude 1. The function of this cosine synthesizer can also be realized by a digital circuit using a ROM of a table lookup system or the like.

The value of the phase value φy of the equation 27 can be calculated by the following equation from the ratio of the value by of the vertical axis to the value ay of the horizontal axis in FIG. 5 (d).

[0087]

[Equation 28]

From this phase value φy, the cosine value (COS φy) shown in Expression 27 can be obtained. The next amplitude limiting amplifier c-6 is a circuit generally called a limiter, and an example of its input / output characteristics is shown in FIG. The relation between the output qy (qy) and the input qy is expressed by the following equation.

[0089]

[Equation 29]

When the input signal level is relatively lower than the value of the amplitude limiting parameter αy, the input signal is amplified by αy times and output, while the input signal level is relatively higher than αy. When the input signal is large, the input signal is limited in amplitude, and a signal of amplitude 1 is output. As a result, the slope of the signal waveform of the small amplitude portion of the cosine value input from the previous stage is made steep, and the other signal portions are output as the signal waveform of the amplitude value 1.

The next block c-7 is a multiplier, and the amplitude value Ay from the amplitude synthesizer c-4 and the amplitude limiting amplifier c-6 are used.
The product ey with the output gy from

[0092]

[Equation 30]

The output ey of this block is obtained as a result of the quadratic function term coefficient value ay being transformed by the amplitude limiting amplifier c-6. Therefore, the amplitude limiting parameter α
When y = 1, ey has exactly the same waveform as ay.
Therefore, as in the following equation,

[0094]

[Equation 31]

When added and combined with the constant term cy, the signal zoy in which the value zy (0) of the second expression of the equation 20 is edge-enhanced in the vertical direction
Will be required. However, the purpose of the present invention is to perform two-dimensional contour enhancement including the horizontal direction as well.
The addition like the equation 31 is not performed at this stage.

The next subtracter c-8 has a signal ay from the quadratic function term coefficient value synthesizer c-2 and a signal e from the multiplier c-7.
y is supplied, a vertical edge enhancement signal hy is calculated as in the following equation, and is output via the line Lhy. The above is the function of FIG.

[0097]

[Equation 32]

Let αy be the amplitude limiting parameter in Equation 29.
11 is a waveform diagram of hy processed as = 0.25.
Shown in (c) and (d). It can be seen that a clear emphasis component is formed at the transient of the input pulse waveform on each scan line.

Returning to FIG. 1, the horizontal edge enhancement signal hx output via the line Lhx is amplified (βx times) by the first amplifier 1-4 to become ex = βx hx,
It is added to the first adder 1-6 at the next stage. On the other hand, the vertical edge enhancement signal hy output through the line Lhy
Is amplified (βy times) by the second amplifier 1-5 and ey =
βy hy, which is added to the first adder 1-6 at the next stage.

In the first adder 1-6, as shown in the following equation, the signal ex from the amplifier 1-4 and the signal ey from the amplifier 1-5 are added and combined to obtain the edge emphasizing signal e. .

[0101]

[Expression 33]

12A and 12B, the amplitude limiting parameter is α x = α y = 0.25 and the amplification factor of the amplifier is β.
It is a wave form diagram of the edge emphasis signal e when x = βy = 0.5. In the next second adder 1-7, the additive synthesis of the reference point signal z (0) from the delay signal forming circuit 1-1 and the edge emphasis signal e from the adder 1-6 is performed as shown in the following equation. Done,
The final output signal zo is determined.

[0103]

[Equation 34]

12C and 12D, the amplitude limiting parameter is αx = αy = 0.25, and the amplification factor of the amplifier is βx.
It is a waveform diagram of zo when = βy = 0.5. 12
Comparing (c) and (d) with FIG. 6 (a) and (b) which are the input signals, it can be seen that the slope around the two-dimensional pulse is sharpened more than twice.

FIGS. 13A to 13D are shown in FIGS.
It is a waveform diagram of each part corresponding to (d), but here, the amplitude limiting parameter is αx = αy = 0.25 and the amplification factor of the amplifier is βx = βy = 0.75. Compared to this, the amplification rate is slightly larger. Comparing the waveform diagram of zo with the input signal, the edge enhancement effect is clear. In comparison with FIGS. 12A to 12D, there is a difference in the value of the amplification factor.

FIGS. 14A and 14B show an example of the input signal having a slightly rhombic white pattern, whereas the rectangular white pattern shown in FIGS. 6A and 6B. .
Output waveform diagrams of the respective parts for this are shown in FIGS. 15 and 16 (a) to (d). This is shown in FIGS.
FIG. 6 is a waveform chart of each part corresponding to the above. In both cases, the effect of sharpening the waveform sloping portion is clear, but in the comparison using parameters of the same value, the preshoot and overshoot are larger than in the case of a simple rectangular white pattern. However, in comparison with the case of edge enhancement by the second derivative of the conventional method, the preshoot and overshoot are so small as not to be a problem. As described above, it can be seen that this embodiment functions sufficiently effectively even for a diagonal pattern such as a diamond.

As a characteristic of the low-pass filter (constant term synthesizer b-1, c-1) used in the edge enhancement processing, the average value by the equal mixing ratio as shown in equation 9 and equation 22 is used. There are several methods other than the method used, for example, a method using a mixing ratio as shown in the following formula.

[0108]

[Equation 35]

[Equation 36]

Equation 35 is an example of the low-pass filter in the horizontal direction, and Equation 36 is an example of the low-pass filter in the vertical direction. The mixing ratios shown in the equations (35) and (36) are different from the characteristics used in the above description of the operation regarding the characteristics of the details, but essentially the same functions.

Further, when the linear function coefficient value bx or by is obtained, a peak pulse may occur mainly due to a calculation error when the signal has a waveform with a complicated change. Since the frequency component of such a peak pulse is mainly a component outside the contained frequency band of the input signal, b
This peak pulse can be removed by applying a low-pass filter for band limiting to x or by.
FIG. 5 (e) shows the characteristic of the low-pass filter with respect to bx, and is an example in which fa = 4.5 MHz.

Furthermore, the degree of edge enhancement can be adjusted more finely by providing a low-pass filter that limits the horizontal edge enhancement signal hx to a band that is several times the input signal band. FIG. 5E shows an example of the characteristics of the low-pass filter (when fb = 5fm).

If the gains of the amplifiers 1-4 and 1-5 with respect to the edge emphasis signals are adjusted while observing the actual image, the image quality improving effect in an optimum state according to the taste can be obtained. Further, by taking advantage of the effects of preshoot and overshoot, it is possible to attach a preshoot and overshoot that are narrower than those in the past to enhance the edge.

As described above, in the edge emphasizing process according to the present embodiment, the optimum edge emphasizing signal which has a perfect correlation with the input signal and which has a perfect correlation with the reproduced image is reproduced in a natural manner.
Since the image quality improving device is added dimensionally, the image quality improving device can give the viewer a feeling of improvement in sharpness and resolution in a natural manner without giving a feeling of strangeness.

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

Although the television luminance signal is used as an example of the input signal in the embodiment, the image quality improving apparatus of the present invention can be applied to a color signal and an RGB signal. 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 particularly effective for uniforming the image quality of reproduced images of low resolution to high resolution such as various broadcasting systems from NTSC to HDTV, VTRs for recording and reproducing these signals, and various computer images. . Further, it is also effective for improving waveform deterioration of a general digital transmission communication system.

[0116]

As described above, the image quality improving device of the present invention has the following effects. (B) In order to obtain the information of the waveform changing portion (edge) in each of the horizontal and vertical directions of the input signal, every predetermined time (time Tx corresponding to the horizontal direction or time Ty corresponding to the vertical direction) in the input signal A characteristic curve connecting at least three adjacent signal values is approximated by the sum of a quadratic function term, a linear function term, and a constant term. Next, the coefficient values of the quadratic function term and the linear function term and the constant term are processed to form an emphasis signal for sharpening edges in the horizontal and vertical directions. Then, the two edge-enhanced signals are combined and added to the input signal, so that the substantially central portion of the inclined portion of the input signal can be made steep. As a result, the frequency components outside the frequency band of the input signal can be recombined and added to the input signal, the edges of the input signal are two-dimensionally emphasized, and an output signal that is a reproduced image with emphasized contours is obtained. be able to.

(B) When determining the constant term of the characteristic curve connecting the three signal values in the horizontal and vertical directions, a plurality of adjacent signals are added and synthesized at a predetermined ratio. A process for obtaining a constant term from the low-frequency component of the signal,
It functions to effectively operate the quadratic function term and the linear function term. Furthermore, the settable range of the ratio of the additive combination is quite wide, and various settings can be made 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 applies the amplitude 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) Each component of the image quality improving device of the present invention can be realized with a simple circuit configuration by using general-purpose parts such as commercially available ICs. 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 an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a delay signal forming circuit in the embodiment.

FIG. 3 is a diagram showing a configuration example of a horizontal edge enhancement signal forming circuit in the embodiment.

FIG. 4 is a diagram showing a configuration example of a vertical direction edge enhancement signal forming circuit in the embodiment.

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

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

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

FIG. 8 is a diagram illustrating the operation of the embodiment.

FIG. 9 is a diagram illustrating the operation of the embodiment.

FIG. 10 is a diagram illustrating the operation of the embodiment.

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

FIG. 12 is an explanatory diagram of the operation of the embodiment.

FIG. 13 is a diagram illustrating the operation of the embodiment.

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

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

FIG. 16 is a diagram illustrating the operation of the embodiment.

[Explanation of symbols]

1-1 Delay signal forming circuit (extracting circuit for extracting signal value) 1-2 Horizontal direction edge emphasizing signal forming circuit 1-3 Vertical direction edge emphasizing signal forming circuit 1-4 First amplifier 1-5 Second amplifier 1-6 First adder 1-7 Second adder (adding circuit for obtaining output signal)

Claims (1)

[Claims] 1. An extraction circuit for extracting a signal value from an input signal at every first time interval and every second time interval; and a horizontal direction to which the signal value extracted at each first time interval is supplied. A horizontal edge enhancement signal forming circuit for obtaining an edge enhancement signal; a vertical edge enhancement signal forming circuit for obtaining a vertical edge enhancement signal supplied with the signal values extracted at the second time intervals; And a combining circuit for obtaining two combined edge emphasis signals in the vertical direction to obtain a combined edge emphasis signal, and an output signal obtained by adding the combined edge emphasis signal to the input signal and sharpening the waveform changing portion of the input signal. And a horizontal direction edge emphasis signal forming circuit, and the vertical direction edge emphasis signal forming circuit, respectively, among the signal values for each time interval supplied from the extraction circuit, In order to approximate a signal characteristic curve connecting at least three signal values adjacent to each other with a quadratic function consisting of a quadratic function term, a linear function term, and a constant term, the three signal values are The constant term is obtained by adding and synthesizing at least a plurality of signal values at a predetermined ratio, and the coefficient values of the quadratic function term and the linear function term are calculated from the plurality of signal values including at least the three signal values. And a cosine value from the ratio of the coefficient value of the quadratic function term to the amplitude value, the amplitude value is calculated from the two coefficient values of the quadratic function term and the linear function term. Is obtained by non-linearly processing the cosine value to obtain an amplitude limiting cosine value, and a new coefficient value with edge enhancement of the quadratic function term is obtained from the amplitude limiting cosine value and the amplitude value, and the new coefficient value is obtained. From the difference between the coefficient value of the quadratic function term and Tsu and a second synthetic processing circuit for obtaining a di-emphasized signal, the image quality improving device characterized in that.