JP2546457B2 - Image quality improvement device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present 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 sharpening the waveform change portion, that is, the waveform edge, but in a natural form without giving the viewer a feeling of discomfort.
An object of the present invention is to provide an image quality improving device capable of improving the sharpness and resolution of a reproduced image.

[0002]

2. Description of the Related Art Conventionally, in the contour correction used for improving the image quality, a contour correction component is obtained by a second derivative process.
An appropriate amount of this correction component was added to the original signal. 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. Therefore, if this second-order differential waveform is added to the original signal, preshoot or overshoot may occur, which does not have the expected image quality improvement effect, and black-and-white edging is possible at the edge portion of the reproduced image. This may result in unnatural contour correction.

[0003]

The problem to be solved by the present invention is to perform pre-processing by edge enhancement by smoothly adding a waveform step at the midpoint position of the waveform change portion (edge portion) of the original signal. It is possible to prevent unnatural contour correction due to shoots and overshoots, improve the sharpness and resolution in a natural form without giving a sense of discomfort to the viewer, and an image quality improving device suitable for IC integration. To do this, what kind of measures should be taken?

[0004]

In order to solve the above problems, the present invention provides a quadrature high-pass filter which is supplied with a first signal as an input signal and outputs a second signal, and An in-phase high-pass filter that is supplied with a first signal and outputs a third signal, and the second and third signals are supplied, and
An amplitude synthesizer that outputs a fourth signal having an amplitude value obtained by vector-synthesizing two signals, and the third and fourth signals are supplied to sharpen the waveform edge of the third signal. A waveform former for outputting the fifth signal,
A subtractor which is supplied with the fifth and third signals and outputs a sixth signal which is a waveform edge enhancement component obtained by subtracting the third signal from the fifth signal;
And an adder which receives the first and sixth signals and adds the sixth signal to the first signal to obtain an output signal in which a waveform edge of the first signal is emphasized. , The waveform former determines a product of the (α-1) th power of the fourth signal and the absolute value of the third signal, with the parameter α being a value of 1 or more, and further calculates the value of this product. (1 /
The image quality improving apparatus is characterized in that the fifth signal is obtained by applying the same polarity as the third signal to the value multiplied by α).

[0005]

FIG. 1 shows an embodiment of an image quality improving apparatus according to the present invention. 2 and 5 to 9 are operation explanatory diagrams of the embodiment, FIG. 3 is a diagram showing a concrete configuration example of the amplitude synthesizer, and FIG. 4 is a concrete configuration example of the waveform former. FIG. Note that, in the operation explanatory diagram, a simplified simulated expression method is also used for convenience. Further, even when a digital circuit is taken as a concrete circuit example, 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 quadrature high-pass filter, 1-2 is an in-phase high-pass filter, 1-3 is an amplitude synthesizer,
1-4 is a waveform shaper, 1-5 is a subtracter, and 1-6 is an adder. Note that, for convenience of explanation, a signal delay due to the processing time of each circuit itself, and a delay circuit or the like generally used only for simply correcting the delay are omitted. As input signals handled by this image quality improving apparatus, luminance signals, color signals, RGB signals of television signals, etc. are assumed.

First, the input signal S coming from the line L1
The case where a is a pulse signal as shown in FIG. 5A will be described. The signal Sa has an upper limit frequency f2 (about 4 MHz)
2 is an example of a luminance signal band-limited by 1., and is a waveform obtained by passing a pulse having an amplitude of 1 and a width of 2 μsec through a low-pass filter having a 100% roll-off characteristic at 0 to 4 MHz. The sloped portion of this waveform is a cosine wave of about 2 MHz. The input signal Sa is first obtained by the quadrature high-pass filter 1-1.
Is supplied to. The characteristics of this orthogonal high-pass filter are shown in FIG.
The characteristics are as shown in (a) and (c). Figure 2 (a)
In the frequency characteristic shown in, the imaginary part is expressed by the following equation,

[0007]

[Equation 1]

The real part becomes 0. The impulse response shown in FIG. 2 (c) is a characteristic of differential property and has a phase difference of 90 °, that is, orthogonal to the signal Sa. To realize the quadrature high-pass filter 1-1, for example, a transversal filter of an origin symmetric type, which is an analog circuit or a digital circuit, is used. The output waveform Sb of the quadrature high-pass filter 1-1 is as shown in FIG. On the other hand, the input signal Sa is also supplied to the in-phase high-pass filter 1-2. The characteristics of the in-phase high-pass filter are as shown in FIGS. 2 (b) and 2 (d). In the frequency characteristic shown in FIG. 2B, the real part is represented by the following equation,

[0009]

[Equation 2]

The imaginary part becomes zero. The impulse response shown in FIG. 2D has a high-pass filtering characteristic and is in phase with the signal Sa. To realize the in-phase high-pass filter 1-2, time =
A transversal filter having a coefficient value symmetrical with respect to the 0 axis is used. The output waveform Sc of the in-phase high-pass filter 1-2 is as shown in FIG. Orthogonal high-pass filter 1-1
And the in-phase high-pass filter 1-2 have the same amplitude characteristic G (f),

[0011]

(Equation 3)

And the characteristics that they are mutually orthogonal and have a phase difference of π / 2. Since the characteristic shown in FIG. 2A is the characteristic of a high-pass filter having a value in the imaginary part, the one having the characteristic is called an orthogonal high-pass filter. Further, the characteristic shown in FIG. 2B is the characteristic of the high-pass filter having a value in the real part, so that the one having the characteristic is called an in-phase high-pass filter. The characteristics shown in FIGS. 2A and 2B are set to be linear in the range of f = 0 to f1 (1.25 MHz) and set to be a constant value in the range of f = f1 to f2 (4 MHz). Is the VSB of the television signal
This is because the (residual sideband) characteristics are taken into consideration, but as a result, this setting was suitable for this embodiment. here
Then, FIG. 10A shows a configuration example of the orthogonal high-pass filter 1-1 by a general origin symmetric type transversal filter. The quadrature high-pass filter 1-1 includes 2N delay circuits p1 to p2N having a delay time T connected in series and 2N + 1 amplifiers q-N to weight input / output signals of the delay circuits.
qN (N is a natural number or 0) and a combiner r1 for adding and combining the weighted signals. When the delay circuits p1 to p2N perform digital signal processing, the delay time T
Is the sampling period. The weighting values of the amplifiers q-N to qN are A-N to AN. The signal coming from the line La is given a predetermined delay time, weighted (multiplied by a predetermined value), added and synthesized, and output from the line Lb. In order to obtain the characteristic of the equation (1), at least the weighting values A0 = 0, An = -A-n
The condition (n = -N to N) is required. An impulse response waveform diagram of the illustrated quadrature high-pass filter 1-1 is shown in FIG.
Shown in The impulse response waveform is symmetrical with respect to the origin and represents the weighted state of this filter as it is. Next, the in-phase high-pass filter 1-2 by a general transversal filter having a symmetrical coefficient on the axis of time = 0
11A shows an example of the configuration of the above. In-phase high-pass filter 1-2
Are 2N delay circuits u1 connected in series with a delay time T
.About.u2N, 2N + 1 amplifiers v-N to vN for weighting the input / output signals of each delay circuit, and a combiner w1 for adding and combining the weighted signals. When the delay circuits u1 to u2N perform digital signal processing, the delay time T is a sampling cycle. The weighting values of the amplifiers v-N to vN are B-N to BN. The signal input from the line Lc is given a predetermined delay time, weighted (multiplied by a predetermined value), added and combined, and output from the line Ld. In order to obtain the characteristic of the equation (2), at least the weighting values B0 = 0, Bn = B-n
The condition (n = -N to N) is required. FIG. 11B is an impulse response waveform diagram of the illustrated in-phase high-pass filter 1-2.
Shown in The impulse response waveform is symmetrical with respect to the axis of time = 0 (time reference position), and represents the weighted state of this filter as it is. The output signals Sb and Sc of the quadrature high-pass filter 1-1 and the in-phase high-pass filter 1-2 are supplied to the amplitude synthesizer 1-3. Here, by vector composition of the quadrature component and the in-phase component shown in the following equation,

[0013]

[Equation 4]

Square root S of sum of squares of two signals Sb and Sc
d is required. FIG. 5D is a waveform diagram of the signal Sd. It goes without saying that the signal Sd is a signal that does not take a negative value. Two concrete configuration examples of the amplitude synthesizer 1-3 are shown in FIG. The first example shown in FIG. 3A is
It is functionally composed of four blocks (3-1 to 3-4). In block 3-1, the phase angles θ from the input signals Sb and Sc are expressed by the following equation,

[0015]

(Equation 5)

Then, in block 3-2, the input signal S
From b and the phase angle θ, the contribution of the orthogonal component as shown in the following equation

[0017]

(Equation 6)

In block 3-3, the input signal S
From c and the phase angle θ, the contribution of the in-phase component as shown in the following equation,

[0019]

(Equation 7)

Find Finally, the combiner of the block 3-4 combines the output signals of the blocks 3-2 and 3-3 according to the following equation to obtain the output signal Sd of the amplitude combiner 1-3.

[0021]

(Equation 8)

Such a configuration is suitable for a digital circuit, and the blocks 3-1 to 3-3 are realized by a table lookup method in which precalculated data is written in a ROM or the like and an output is obtained by referring to the data. it can. The other configuration example shown in FIG. 3B is also functionally composed of four blocks. Blocks 3-5 and 3-
Reference numeral 6 denotes a multiplier, which is 2 of the input signals Sb and Sc, respectively.
Multipliers Sb ² and Sc ² are obtained. The squared values Sb ² and Sc ² are combined by the adder in block 3-7, and block 3-
The square root is obtained at 8 and the output signal Sd is obtained.
Such a configuration can be realized by both digital and analog circuits. Block 3-8 for digital circuits
For ROM, ROM is used.

Returning now to FIG. 1, the waveform former 1-4.
Is a function of obtaining an output signal Se in which a waveform changing portion (that is, a waveform edge) of the signal Sc is sharpened from the signal Sd from the amplitude synthesizer 1-3 and the signal Sc from the in-phase high-pass filter 1-2. It is a block to do. The function of the waveform former 1-4 is expressed by the following equation.

[0024]

[Equation 9]

That is, a signal whose polarity is the same as that of the signal Sc and whose amplitude is the same as that of the signal Sd is obtained, and the ratio of the ratio of the signal Sc to the absolute value of the signal Sc to the 1 / α power is obtained, and the product is obtained. The output Se is required. When α is 1, the signal Se
Becomes the same value as the signal Sc, and as α becomes larger than 1, the influence of the term of 1 / α power increases, and the edge of the waveform becomes steep. This formula is summarized as follows.

[0026]

[Equation 10]

The above modification eliminates the division operation.
In the case of a digital circuit, it is important not to use a division operation that requires a long processing time. As a result, the polarity is made the same as that of the signal Sc and (α-1) of the signal Sd.
The output Se is obtained by taking the product of the power and the absolute value of the signal Sc, and then multiplying the product by (1 / α)
Is required. FIG. 5E shows the signal Se when α = 4.
It is a waveform diagram of. It can be clearly seen that the edge of the waveform is steep as compared with the signal Sc in FIG. 5C. The parameter α is a real number of 1 or more.

FIG. 4 shows a concrete configuration example of the waveform former 1-4. This example is composed of 6 functional blocks. The block 4-1 which receives the signal Sd inputs the signal Sd
Has a function of calculating the (α-1) th power of
The block 4-2 which receives as an input functions to obtain the absolute value of the signal Sc. Similarly, the block 4-3, which receives the signal Sc, functions to obtain the polarity of the signal Sc and output the values of 1, 0 and -1 to the next stage corresponding to the positive, zero and negative polarities, respectively. ing. A block 4-4 is a multiplier for obtaining the product of the signals from the blocks 4-1 and 4-2, and a block 4-5 obtains the (1 / α) th power of the output of the block 4-4. Amplitude value from block 4-5 and block 4-3
The signal representing the polarity from is multiplied by the multiplier of block 4-6 to obtain the desired signal Se. In the case of a digital circuit, a table look-up method using a ROM is used for the blocks 4-1, 4-2, 4-5, etc., and the other blocks are configured by using a general-purpose circuit. Figure 1 again
Returning to the block 1-, to which the signals Se and Sc are supplied
Reference numeral 5 is a subtracter that functions to subtract the signal Sc from the signal Se, and outputs a signal Sf of the following equation.

[0029]

[Equation 11]

This signal Sf is an edge enhancement component, and its waveform is shown in FIG. 5 (f). As can be seen from the above-mentioned formula 11, this signal Sf is obtained from the difference between the signal Se and the signal Sc, and these signals Sf are processed in order to replace the signal Sc with the edge-enhanced signal Se. You are looking for the difference between the signals. The last block 1-6 in FIG. 1 is an adder, which calculates the output signal Sg by adding and synthesizing the edge enhancement component Sf to the input signal Sa as in the following equation.

[0031]

(Equation 12)

FIG. 5 (g) is a waveform diagram of the signal Sg. In the signal Sg, the rising and falling portions of the pulse are steepened and the edges of the signal Sg are emphasized as compared with the input signal Sa shown in FIG. 5A. In addition, the degree of emphasis is smooth in a natural form without adding unnatural preshoot or overshoot, and the sharpening of this smooth edge (that is, the waveform changing portion) is a characteristic of this device. is there.

More specifically, the output waveform Sg is compared with the input waveform S
Compared with a, the output waveform Sg has a smooth waveform step at the almost midpoint of the waveform changing portion (edge portion) of the input waveform Sa, and the slope of the waveform sloping portion is steep. You can see that it has a different waveform. By reproducing the output signal Sg, a contour-corrected image can be obtained.
In addition, the edge enhancement processing of this image quality improving device is not the edge enhancement processing that exceeds the amplitude of the original signal such as preshoot and overshoot as in the conventional contour correction, but is the edge enhancement processing within the amplitude of the original signal. is there. Therefore, even if a device incorporating this image quality improving device is configured with a digital circuit, the overflow problem does not occur, and the device can perform good image quality improvement.

In this way, the signal Sg output from the line L2 is subjected to edge enhancement, and as a result, a new sideband component is formed, and a spectrum beyond the band originally possessed by the input signal Sa is newly added. Become a signal. The addition of this new spectrum equivalently gives the viewer an impression that the resolution of the original signal has been improved, and serves to improve the sharpness of the image.

The steepness of the edge portion of the signal Sg (the degree of edge enhancement) is the frequency of the edge portion of the original signal before edge enhancement if the parameter α of the waveform former 1-4 is a fixed value. It depends on the characteristics. If the rising portion and the falling portion (edge portion) of the original signal have a steeper slope, a strong degree of edge enhancement is performed. on the other hand,
For mild slopes, a weaker degree of edge enhancement is applied. As described above, the edge enhancement component Sf added to the input signal depends on the frequency of the input signal and has a perfect correlation with the input signal. Therefore, the image quality improving device gives the viewer a feeling of strangeness. In a natural manner, sharpness and resolution can be improved.

As described above, the waveform former 1 for converting the signal Sc, which is the in-phase component, into the edge-enhanced signal Se.
In the processing of -4, α is used as a parameter that determines the degree of edge enhancement. The parameter α can determine the degree of edge enhancement independently of the degree of edge enhancement (the degree of edge enhancement depending on the frequency characteristic of the edge portion in the original signal before edge enhancement). FIGS. 6 and 7 show changes in the effect of edge enhancement by changing the value of α. FIG. 6 is an enlarged waveform diagram of the falling portion of the pulse waveform used in FIG. 5, and FIG. 7 is an example of an input signal of a sine wave with a frequency of 2 MHz. (A) in both figures
Is α = 1, that is, the output signal S when the edge enhancement processing is not performed
It is a waveform diagram of g, similarly (b) is α = 2, (c) is α
= 4, (d) is a waveform diagram of the output signal Sg when α = 8. In this way, if α is increased in the range of 1 or more,
It can be seen that the waveform edge of the output signal Sg is gradually sharpened. Therefore, by providing a variable circuit for changing the value of the parameter α in the waveform former and adjusting the variable circuit, this image quality improving device can optimize the degree of edge enhancement according to the taste of the viewer. You can

The degree of edge enhancement can be adjusted by changing the signal level of the signal Sf.
It is also possible to change the signal levels of the outputs Sb and Sc of the two high-pass filters 1-1 and 1-2 at the same time.
As another method, it is also possible to make the value of the parameter p that determines the amplitude characteristics of the quadrature and in-phase high-pass filters 1-1 and 1-2 shown in FIGS. 9A and 9B variable. is there. The signal levels of the outputs Sb and Sc and the parameter p are adjusted by the quadrature and in-phase high-pass filters 1-1 and 1-.
2 is provided with a variable circuit that makes each value variable. In addition, as shown in FIG. 8 and the following equation,

[0038]

(Equation 13)

It is also possible to optimize the edge emphasis degree by changing the frequency characteristics of the edge emphasis component by switching and using several kinds of high-pass filters having different characteristics. The high pass filters (1) to (4) shown in FIG.
4 illustrates four example combinations of quadrature and in-phase high pass filters.

As described above, the edge enhancement processing according to the present invention has a perfect correlation with the input signal, and the edge enhancement component is smoothly added in a natural form. On the other hand, it is possible to give a feeling of improvement in sharpness and resolution in a natural form without giving a feeling of strangeness.

Further, since each block itself of the illustrated embodiment can be easily constructed by using a well-known circuit such as a commercially available IC, the whole apparatus can be realized at a low cost.

In the above embodiment, the luminance signal of the television is used as an example of the input signal, but the image quality improving apparatus of the present invention can be applied to the color signal and the RGB signal. Further, even for digitized image data, contour correction processing and edge enhancement processing equivalent to those of the present invention can be realized by software processing using a computer, and the present invention can be applied to processing of image data by software. It can be applied. Furthermore, the present invention is also effective in improving waveform deterioration of a portable digital transmission communication system.

[0043]

As described above, the image quality improving apparatus of the present invention has the following effects. (B) Edge enhancement is performed by appropriately adding a smooth waveform step to the midpoint of the slope of the input signal, and as a result, an output signal with a frequency component outside the frequency band of the input signal is obtained. The contour is emphasized. (B) Edge emphasis processing within the amplitude of the original signal, instead of edge emphasis exceeding the amplitude of the original signal such as preshoot and overshoot as in conventional contour correction. Therefore,
Even when a device incorporating this image quality improvement device is configured by a digital circuit, the problem of overflow does not occur, and the device can perform good image quality improvement. (C) The degree of waveform edge enhancement for an input signal depends on the contained frequency of the input signal and has a perfect correlation with the input signal. Further, since this edge enhancement processing smoothly sharpens the waveform changing portion, This image quality improving device can give the viewer a feeling of improvement in sharpness and resolution in a natural form without giving a sense of discomfort. (D) The image quality improving device in which the parameters of the waveform shaper, the quadrature high-pass filter, and the in-phase high-pass filter are variable, adjusts the degree of edge enhancement independently of the degree of edge enhancement in (c) above. it can. Therefore, the viewer can obtain various image quality by adjusting the degree of edge enhancement according to his / her preference, and can set the optimum image quality among them. (E) Since the waveform former can obtain a target signal without performing division processing, the processing time can be shortened when it is configured by a digital circuit. (F) 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 a commercially available IC. Therefore, this image quality improving device can be easily manufactured at low cost and has a wide range of applications, so it is industrially effective,
Be beneficial.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment.

FIG. 2 is a diagram showing characteristics of a quadrature high-pass filter and an in-phase high-pass filter.

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

FIG. 4 is a specific configuration example of a waveform former.

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

FIG. 6 is a diagram showing changes in the degree of edge enhancement when the value of a parameter α is changed.

FIG. 7 is a diagram showing changes in the degree of edge enhancement when the value of a parameter α is changed.

FIG. 8 is a diagram showing characteristics of a quadrature high-pass filter and an in-phase high-pass filter.

FIG. 9 is a diagram showing characteristics of a quadrature high-pass filter and an in-phase high-pass filter.

FIG. 10 is a diagram for explaining an orthogonal high-pass filter.

FIG. 11 is a diagram for explaining an in-phase high-pass filter.

[Explanation of symbols]

 1-1 Quadrature high-pass filter 1-2 In-phase high-pass filter 1-3 Amplitude synthesizer 1-4 Waveform former 1-5 Subtractor 1-6 Adder

Claims (3)

(57) [Claims] 1. A first signal, which is an input signal, is supplied,
The imaginary part is I (f) = jf / f ₀ (where f ₀ is the first signal
Band limiting frequency that determines the upper limit of the number) and the real part is 0
A quadrature high-pass filter that outputs a second signal obtained by processing the first signal in accordance with a frequency characteristic that is: R (f) = | f /
f ₀ | and the imaginary part becomes 0
A common-mode high-pass filter that outputs a third signal obtained by processing the first signal, and an amplitude value obtained by vector-synthesizing the two signals supplied with the second and third signals An amplitude synthesizer that outputs a fourth signal, and the third and fourth signals are supplied and the parameter α is 1
As the above value, the fourth signal to the power of (α-1)
The product of the absolute value of the third signal and the value of this product
To the power of (1 / α), and the same polarity as the third signal
To make the waveform edge of the third signal steep
A waveform former for obtaining a signal of No. 5, and a sixth, which is a waveform edge enhancement component, obtained by subtracting the third signal from the fifth signal supplied with the fifth and third signals. A subtractor for outputting the first signal and the sixth and sixth signals, and an output in which the waveform edge of the first signal is emphasized by adding the sixth signal to the first signal. An image quality improving device comprising an adder for obtaining a signal . 2. The waveform forming device is provided with a variable circuit for varying the value of the parameter α, and the variable circuit adjusts the degree of waveform edge enhancement. Image quality improvement device. 3. The quadrature high-pass filter and the in-phase high-pass filter are provided with variable circuits for varying amplitude characteristics or for varying the values of the second and third signals which are output signals. The image quality improving apparatus according to claim 1 or 2, wherein the variable circuit is provided to adjust the degree of waveform edge enhancement.