JPH0496414A - Control emphasizing circuit - Google Patents

Abstract

PURPOSE:To improve picture quality by finding first and second difference between the signal of a main tap and the signal of a tap with large and small delay amounts and the absolute value of the difference, extracting a control signal by performing an operation with the use of the first and second absolute values, and controlling the gain of an output from a filter according to this control signal. CONSTITUTION:As an input signal, a luminance signal is supplied to an input terminal 11, inputted to a (-1) fold coefficient device 15 and inputted to a delay device 12, and the output of the delay device 12 is inputted to one input terminal of respective adders 16a and 17 and to a delay device 13. The output of the delay device 13 is inputted through a (-1)-fold coefficient device 14 to the other input terminal of the adder 16. The outputs of the adders 16 and 17 are respectively inputted through (-1/4)-fold coefficient devices 18 and 19 to an adder 20, and the high frequency component of the luminance signal is induced and inputted to a counter 21. On the other hand, the output of an adder 48 in a sample extraction part passes through a limiter 49 for limiting a numerical value and used as the gain control signal of the counter 21. Thus, the degree of contour emphasis can be freely set and the picture quality can be improved.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Field of Application) (7) The invention relates to an edge enhancement circuit used in a device that digitally processes baseband video signal processing.

(Prior Art) Generally, a digital television receiver is provided with an edge enhancement circuit that amplifies middle and high frequency components of a luminance signal or a color difference signal.

As a bandpass filter for extracting contour components, a symmetric coefficient FIR filter that does not cause phase distortion is used. Digital television receivers use 3 taps (tap coefficient -1/4 1/2 -1/4) to reduce hardware and prevent image quality deterioration due to ringing.
) FIR filters are often used.

FIG. 9 shows a conventional contour enhancement circuit.

A luminance signal is supplied to the input terminal 70 as an input signal. This luminance signal is input to a (-1/4) times coefficient multiplier 75 and is also input to a delay unit 71 . delay device 71
The output of is input to the (1/2) times coefficient multiplier 74 and also to the delay unit 72. The output of the delay device 72 is (
-1/4) times the coefficient unit 73 to the adder 76, and is added to the output of the previous coefficient unit 75. This adder 7
The output of 6 is input to an adder 77 and added to the output of the coefficient unit 74.

The high-frequency component of the luminance signal is extracted from the adder 77 and input to the nonlinear circuit 78 . The nonlinear circuit 78 has coring characteristics and removes minute level noise components included in the above-mentioned high frequency components. The output of the nonlinear circuit 78 is gain-adjusted by a gain adjuster 79 having a gain k set by the user, and is input to an adder 80 .

The adder 80 uses the output of the delay device 71 and the gain adjuster 7
9 is added to obtain an edge-enhanced luminance signal, which is output to an output terminal 81.

The sampling frequency of the luminance signal is 4 of the color subcarrier.
(14MHz), and the sampling period is 70n
5ee, the input signal shall take a value from 0 to 255.

When performing edge enhancement, it is effective to emphasize the signal components of the luminance signal at approximately 2 MHz or higher. Delay device 71.72
When the delay time is set to 210 n5ec, the center frequency of the bandpass filter section 82 becomes 2.4 MHz, and its characteristics are as shown in FIG.

When a signal with a waveform indicated by a dotted line 93 in FIG.
A signal with the waveform shown in 2 is obtained.

If the pattern is a sine wave, that is, if the pattern is uneven,
The brightness difference is expanded and the edges are emphasized. However, in step-like patterns, thick overshoots and preshoots may appear before and after edges, resulting in unnatural emphasis. In other words, depending on the content (frequency) of the picture, there are cases where the outline is effectively enhanced and cases where the enhancement is unnatural.

For this reason, in conventional circuits, when setting the degree of edge enhancement, the degree of edge enhancement is set to a level that does not make the edge look unnatural. However, this cannot be said to be an effective use of the contour enhancement circuit.

(Problem to be Solved by the Invention) According to the conventional contour enhancement circuit, the contour enhancement effect is effective when a mid-range frequency component of about 2 to 3 MHz is emphasized, but it is not effective for a step-like pattern without periodicity. Thick overshoots and preshoots appear before and after the edge, making it look unnatural, making it impossible to increase the degree of contour enhancement and making effective use of the contour enhancement circuit.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an edge enhancement circuit that can freely set the degree of edge enhancement and fully exhibit the effect of improving image quality.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides an edge enhancement circuit that extracts a signal component in a specific frequency band from a baseband video signal using a transversal filter and enhances the amplitude thereof. A plurality of delay lines are connected in series with a video signal as input, and the taps of each delay line are provided with a delay means for obtaining a plurality of baseband video signals with different delay times. Means for obtaining a first difference between a signal of a tap and a signal of a tap with a larger delay amount and its absolute value; means for obtaining a second difference with a signal of the tap with a delay amount and its absolute value, and controlling the gain of the output of the filter by calculating using the first and second absolute values. and means for extracting a control signal of the filter and controlling the gain of the output of the filter using the control signal.

(Function) With the above means, the gain of high-frequency components is automatically controlled and the degree of edge emphasis is controlled according to the content of the picture. For example, for a step-like picture, thick edges are There is no preshoot or overshoot, and appropriate contour enhancement is performed for sinusoidal patterns.

Furthermore, since the content of the calculation can be changed, it is possible to obtain contour enhancement characteristics that exhibit characteristics depending on the content.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. A luminance signal is supplied to the input terminal 11 as an input signal.

This luminance signal is input to a (-1) times coefficient multiplier 15 and also input to a delay unit 12 . The output of the delay device 12 is connected to one input terminal of each of the adders 16 and 17 and the delay device 13.
is input. The output of the delay device 13 is input to the other input terminal of the adder 16 via the (-1) times coefficient multiplier 14 . Further, the other input terminal of the adder 17 is connected to a counter 15.
The output of is input. The outputs of adders 16 and 17 are
Each is input to the adder 20 via (-1/4) times coefficient multipliers 18 and 19.

A high-frequency component of the luminance signal is derived from this adder 20, and a block 24 surrounded by a broken line constitutes a bandpass filter.

The high-frequency component is input to the counter 21, and the gain is adaptively adjusted according to the picture pattern by a gain control signal to be described later, and the adder 2
It is input to one input terminal of 2.

The output (luminance signal) from the delay device 12 is input to the other input terminal of the adder 22 . As a result, adder 2
2, a contour-enhanced luminance signal is obtained and is delivered to an output terminal 23.

The above-described configuration of the band-pass filter 24 is configured so that a sample can be easily taken out when examining changes in the components extracted by this filter, and the characteristics are as shown in FIG. 10 above, for example. This is a characteristic.

The sample extractors are output terminals of adders 16 and 17, which are connected to absolute value circuits 41 and 42, respectively. The output of the absolute value circuit 41 is the maximum value circuit 4.
3 and is also input to the minimum value circuit 44. Further, the output of the absolute value circuit 42 is also input to the maximum value circuit 43 and also to the minimum value circuit 44.

The maximum value circuit 43 detects the larger absolute value and derives it as the signal X, and the minimum value circuit 44 detects the smaller absolute value and derives it as the signal Y. The signal X serves as an index that indicates the magnitude of the signal change and the magnitude of the edge, and the signal Y serves as an index that indicates whether the signal change is sinusoidal or step-like. This means that the adder 16 creates a difference component between the center tap signal and a signal that is ahead in time, and the adder 17 creates a difference component between the center tap signal and a signal that is delayed in time. This is because

As shown in Figure 2, when the minimum value signal Y is much smaller than the maximum value signal X like yl, the input waveform is close to a step waveform, and when it is large like y4 The input waveform is close to a sine wave. Therefore,
In order to obtain such a waveform determination signal, the signals X and Y are
Each is input to RAM45.46 and the function f (X)
and f (y). Now, if we assume that the characteristics of the bandpass filter are as shown in FIG. /4) t (y) -1nt (y/2) However, int (a) is set to a function indicating the integer part of a.

The functions f (X) and f (y) obtained in this way are added in an adder 48 (f (X) + f (y)
), when y is large, the value becomes large, and when y is small, the value becomes small. In other words, when the input waveform is close to a step waveform, the adder 48
The output of the adder 48 has a small value, and when the human waveform is close to a sine wave, the output of the adder 48 has a large value, thereby obtaining a picture identification signal.

Since functions for the RAM 45 and 46 can be written by the microcomputer (CPU) 47, it is also possible to change the identification characteristics of the picture identification itself.

The output of the adder 48 is sent to a limiter 49 that limits the numerical value.
It is used as a gain control signal for the counter 21 via the .

FIG. 3 shows the input signal 31 of the above-mentioned edge enhancement circuit, the output signal 30 output after edge enhancement, and the gain control signal 32 for the counter 21.

FIG. 4 shows an example of the input signal 34, output signal 33, and gain control signal 35 when the characteristics of the limiter 49 of the circuit described above are changed to set the lower limit of the numerical limit to 2. If this is done, some preshoot and overshoot will be added compared to the signal shown in FIG.

According to this contour enhancement circuit as described above, it is possible to adaptively enhance the contour of the picture to be emphasized, but by adjusting the characteristics of the limiter, the range of the picture subject to the contour enhancement can also be expanded. It can also be reduced.

In the above embodiment, the characteristics of the bandpass filter 24 are 2.
The characteristic was 4MHz.

The bandpass characteristic of the bandpass filter 24 is 3.58M)
If lz is to be a characteristic, delay device 12.13
The delay time may be set to 140 n5ec. FIG. 8 shows the bandpass characteristics in this case. FIG. 6 shows an input signal 95 and an output signal 94 when the 3.58 MHz component is emphasized in a conventional circuit.

Here, by applying the circuit of the present invention, functions f (X), f
(y) as f (X) = 1nt((x-4)/2))f
When contour enhancement is performed using (y) = jnt ((y-25)c), the result is as shown in FIG. Signal 9 in Figure 7
4 is the output of the conventional circuit, and signal 36 is the output signal of the circuit of the present invention. As you can see from this comparison,
For sine waves, the same contour enhancement (amplitude difference) as before is expanded,
It can be seen that contour enhancement is not performed for small amplitude signals such as noise. It can also be seen that in the case of a step-like edge, the width of preshoot and overshoot is shortened, and in the case of a large-amplitude impulse, the amplitude is expanded without causing preshoot or overshoot.

By doing so, it is possible to selectively switch the emphasis component.

Further, this edge enhancement circuit can also be realized using a digital signal processor, and is not limited to the circuit configuration shown.

As described above, according to the present invention, it is possible to accurately correct a portion whose outline is to be emphasized depending on the content of the picture. Furthermore, the degree of freedom in edge enhancement can be expanded by changing the function, adjusting the limiter characteristics, and adjusting the delay amount of the delay device in combination, depending on the component to be emphasized and preference.

Note that various embodiments are possible as an example of the configuration of the bandpass filter 24. FIG. 8 shows yet another example. A luminance signal is supplied to the input terminal 241 and the delay device 24
2 and the input luminance signal (-1/4
) is led to a multiplication counter 244. The output of the delay device 242 is input to the delay device 243 and also to the counter 245 which multiplies it by (1/4). Further, the output of the delay device 243 is input to a coefficient multiplier 246 which multiplies it by (-1/4).

The outputs of coefficient units 244 and 245 are added in adder 247, and the outputs of coefficient units 244 and 246 are added in adder 247.
8 is added. The outputs of adders 247 and 248 are then added together in adder 249. As a result, the high frequency component of the luminance signal is derived from the adder 249. Here, the signal for pattern determination shown in FIG.
The outputs of 47 and 248 are utilized, and as described above, according to the edge enhancement circuit of the present invention, the degree of edge enhancement can be freely set, and the image quality improvement effect can be fully exhibited.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a signal waveform diagram shown to explain the operation of the circuit of this invention, and Figs. 3 and 4 are processed by the circuit of this invention. 5 is a diagram showing the characteristics of the filter section in another embodiment of the present invention, FIG. 6 is a diagram showing the waveform of the signal processed by the conventional circuit, and FIG. 7 is a diagram showing the waveform of the signal processed by the conventional circuit. A diagram showing a signal waveform processed by a conventional circuit and a signal waveform processed by this inventive circuit, FIG. 8 is a diagram showing another example of the bandpass filter in this invention, and FIG. 9 is a diagram showing a conventional contour enhancement circuit. 10 is a diagram showing the characteristics of the filter section of the circuit of FIG. 9, and FIG. 11 is a diagram showing a signal waveform processed by the circuit of FIG. 9. 12.13...Delay device, 14.15.21...Counter, 16.17.20.22...Adder, 24...
Bandpass filter, 41.42... Absolute value circuit, 4
3... Maximum value circuit, 44... Minimum value circuit, 45.4
6...RAM, 47...CPU, 48...adder, 49...limiter. Applicant's agent Patent attorney Takehiko Suzue "N Sode 11

Claims (5)

[Claims] (1) In an edge enhancement circuit that extracts a signal component in a specific frequency band from a baseband video signal using a bandpass filter and enhances the amplitude by adding the extracted signal component to the original signal, the baseband A plurality of delay devices are connected in series with a video signal as input, and the taps of each delay device have delay means for obtaining a plurality of baseband video signals with different delay times. means for obtaining a first difference between a signal of a tap and a signal of a tap with a larger delay amount and its absolute value; means for obtaining a second difference from a tap signal with a delay amount and its absolute value; generating a function signal corresponding to the first and second absolute values and calculating the function signal; control signal generating means for extracting a control signal for controlling the gain of the output of the filter; and supplying the output control signal of the control signal generating means as a gain control signal to a coefficient multiplier for controlling the gain of the output of the filter. An outline enhancement circuit characterized by comprising means. (2) The control signal generating means is configured to generate the first difference and the second difference.
a maximum value circuit and a minimum value circuit to which the absolute value output of the difference is supplied; a memory that generates each function signal according to the maximum value detection output and the minimum value detection output from the maximum value circuit and the minimum value circuit; 2. The contour emphasizing circuit according to claim 1, further comprising an adder for adding the function signals obtained from the memory. (3) The contour emphasizing circuit according to claim 2, wherein the control signal generating means includes means for rewriting data for generating a function to be stored in the memory. (4) The contour emphasizing circuit according to claim 2, wherein the control signal generating means includes a limiter for controlling the value of the output of the adder. (5) The contour emphasizing circuit according to claim 1, wherein the control signal generating means further includes switching means for switching the delay amount of the delay device of the delay means.