JPH11205634A - Contour emphasis circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a contour emphasis circuit in configuration simplified and reduced rather than conventional one. SOLUTION: This circuit has a filtering circuit 1 for cutting a frequency component higher than a prescribed cut-off frequency in a first signal as a video signal containing plural frequency components, amplifier circuit 2 for inputting a second signal outputted from the filtering circuit and amplifying the component of a prescribed frequency band in the second signal, and delay equivalent circuit 3 for inputting a third signal outputted from the amplifier circuit and compensating the group delay characteristics of the third signal. Thus, the component of the prescribed frequency band in the contour component of the video signal is amplified and the group delay characteristics can be made almost flat to the frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour emphasis circuit for emphasizing a contour component of a video signal photographed by an image pickup device, and more particularly to a contour emphasis circuit having a low-pass filter.

[0002]

2. Description of the Related Art An outline emphasizing circuit is used, for example, in a photographing device for photographing an object to be photographed by a CCD (Charge Coupled Device) image pickup device or the like, or an image display device for displaying a video signal photographed by such a photographing device. A built-in circuit that enhances the sharpness of the displayed image and enhances the sharpness of the image when the image signal is displayed on the image display device by enhancing the outline of the captured image signal. Circuit.

FIG. 6 is a diagram showing a configuration example of a conventional contour emphasizing circuit. In FIG. 6, an analog video signal from the image sensor is first input to a contour component emphasizing unit surrounded by a dotted line. The analog video signal input to the contour component enhancement unit is branched in two directions, and one video signal is input to the addition circuit 14 through the two differentiating circuits 11 and 12. The other video signal passes through a delay circuit (delay line) 13 and is input to an addition circuit 14 with a delay of the delay time of the differentiating circuits 11 and 12.

FIG. 7 is a diagram showing waveform characteristics, group delay characteristics, and amplitude characteristics of a video signal passing through each circuit shown in FIG. An input signal a having the waveform characteristic shown in FIG.
The signal is input to the differentiating circuit 11 and the delay circuit 13. The input signal a input to the differentiating circuit 11 is differentiated by the differentiating circuit 11 and a signal b having a waveform as shown in FIG.
Becomes The signal b is further input to the differentiating circuit 12.
The signal b input to the differentiating circuit 12 is further differentiated by the differentiating circuit 12 to become a signal c having a waveform as shown in FIG. This signal c is a signal obtained by extracting a contour component from a video signal.

On the other hand, as shown in FIG. 7D, the input signal a input to the delay circuit 13 is delayed by the delay time of the differential circuits 11 and 12 without changing its waveform characteristic. Output as d.

When the signal c and the signal d are input to the adder circuit 14, a signal e having a waveform in which the edge, that is, the contour component of the video signal is emphasized is obtained as shown in FIG. At this time, the signal c is inverted and added to the addition circuit 14.
Is input to

FIG. 7E shows a group delay characteristic and an amplitude characteristic of the signal e. According to FIG. 7E, the group delay characteristic of the signal e is flat. Further, according to the amplitude characteristic of the signal e, the amplitude characteristic of the high frequency component of the signal e is large.

Further, the signal e, which is an analog signal, is A
It is converted into a digital signal by a / D conversion circuit (not shown). At this time, when the signal e is input to the A / D conversion circuit, a frequency component equal to or more than の of the sampling frequency of the A / D conversion circuit among the frequency components of the signal e is cut off based on the sampling theorem. There is a need. If this cutoff is insufficient, various distortions such as so-called aliasing noise will occur in the video signal. Therefore, as shown in FIG. 5, the contour emphasizing circuit is provided with a low-pass filter 15 that blocks a frequency component of the signal e that is higher than a predetermined cutoff frequency.

FIG. 7F is a diagram showing a waveform, a group delay characteristic, and an amplitude characteristic of the signal f output from the low-pass filter 15. As shown in the amplitude characteristic diagram of FIG. 7F, of the frequency components of the signal f, the frequency components higher than the cutoff frequency are greatly attenuated and almost cut off. However, the group delay characteristic of the low-pass filter 15 is as shown in FIG.
Is not flat as shown in the group delay characteristic diagram of FIG. Specifically, the frequency component of the signal f near the cutoff frequency has a larger delay than the frequency component of the lower frequency band. Therefore, ringing occurs in the waveform of the signal f, as shown in the waveform characteristic diagram of FIG.

To compensate for the group delay characteristic of the low-pass filter 15, a delay equivalent circuit 17 is provided as shown in FIG. The delay equivalent circuit 17 is, for example,
It comprises a primary all-pass filter (primary APF) 17a and a secondary all-pass filter (secondary APF) 17b.

FIG. 7 (g) shows the waveform characteristics, group delay characteristics, and amplitude characteristics of the signal g passing through the delay equivalent circuit 17. As shown in the group delay characteristic diagram of FIG.
The delay of each frequency component of the signal f is adjusted by the delay equivalent circuit 17, and the group delay characteristic of the signal g output from the delay equivalent circuit 17 becomes substantially flat. Therefore, FIG.
As shown in the waveform characteristic diagram of (g), a signal g having no ringing is obtained. In addition, the low-pass filter 15
A buffer 16 for impedance matching is provided between the buffer 16 and the delay equivalent circuit 17.

[0012]

However, in such a conventional contour emphasizing circuit, the contour component emphasizing section shown by the dotted line in FIG.
The circuit has a large circuit size, and has a delay circuit 13 and an adder 14, which hinders downsizing of a photographing device or an image display device incorporating such a contour emphasizing circuit.

It is an object of the present invention to provide an outline emphasizing circuit having a simpler and smaller configuration than the conventional configuration.

[0014]

In order to achieve the above object, the configuration of the contour emphasizing circuit of the present invention comprises a frequency component higher than a predetermined cut-off frequency in a first signal which is a video signal containing a plurality of frequency components. A filter circuit that cuts off, a second signal output from the filter circuit is input, an amplifier circuit that amplifies a component of a predetermined frequency band of the second signal, and a second signal output from the amplifier circuit. And a delay equivalent circuit for receiving the three signals and compensating for the group delay characteristic of the third signal.

With this configuration, the components of the predetermined frequency band, which are the outline components, of the video signal are amplified, and
The group delay characteristic can be made almost flat with respect to the frequency.

The amplifier circuit has, for example, a configuration including an operational amplifier having a positive input terminal, a negative input terminal, and an output terminal, and a series circuit in which a first resistor, a coil, and a capacitor are connected in series. . In this case, one end of the series circuit is connected to the minus input terminal, the minus input terminal and the output terminal are connected via a second resistor, and the second signal is input to the plus input terminal. . With such a simple configuration, a predetermined frequency band component of the video signal can be amplified.

Further, it is preferable that the amplifying circuit has a buffer function of matching an output impedance of the filter circuit with an input impedance of the delay equivalent circuit.

This eliminates the need to separately provide a buffer for performing impedance matching between the filter circuit and the delay equivalent circuit, thereby contributing to a reduction in the number of components constituting the contour emphasizing circuit.

[0019]

Embodiments of the present invention will be described below. However, the technical scope of the present invention is not limited to this embodiment.

FIG. 1 is a block diagram of an outline emphasizing circuit according to an embodiment of the present invention. According to FIG. 1, the contour emphasizing circuit according to the embodiment of the present invention includes a low-pass filter 1, a peaking circuit 2, and a delay equivalent circuit 3. The delay equivalent circuit 3 is a primary all-pass filter (primary APF), like the delay equivalent circuit 17 in FIG.
3a and a secondary all-pass filter (secondary APF) 3b. The primary all-pass filter 3a and the secondary all-pass filter 3b have group delay characteristics as shown in FIG. 4, for example. The dotted line in FIG. 4 shows the group delay characteristic of the entire delay equivalent circuit 3 obtained by combining the group delay characteristics of the two all-pass filters 3a and 3b.

In this embodiment, the delay equivalent circuit 3 is composed of one primary APF 3a and one secondary APF 3b. However, the present invention is not limited to this. It may be composed of an APF and a plurality of secondary APFs.

Similarly to the low-pass filter 15 in FIG. 6, the low-pass filter 1 blocks the frequency components of the input signal that are higher than a predetermined cut-off frequency. The peaking circuit 2 is an arithmetic circuit that amplifies a frequency component in a predetermined band, as described later in detail.

FIG. 2 is a diagram showing a waveform characteristic, a group delay characteristic, and an amplitude characteristic of an analog video signal passing through each circuit in the contour emphasizing circuit according to the embodiment of the present invention. First, an analog video signal A having a waveform shown in FIG.

FIG. 2B is a diagram showing a waveform characteristic, a group delay characteristic, and an amplitude characteristic of the signal B output from the low-pass filter 1. As shown in the amplitude characteristic diagram of FIG. 2B, of the frequency components of the signal B, the frequency components higher than the cutoff frequency are greatly attenuated and almost cut off. However, the group delay characteristic of the low-pass filter 1 is not flat as shown in the group delay characteristic diagram of FIG. Specifically, a frequency component near the cutoff frequency in the signal B,
That is, the high-frequency component of the frequency components passing through the low-pass filter 1 has a larger delay than the low-frequency component. Accordingly, ringing occurs in the waveform of the signal B, as shown in the waveform characteristic diagram of FIG.

Next, the signal B is input to the peaking circuit 2. The peaking circuit 2 amplifies, of the frequency components passing through the low-pass filter 1, only a predetermined band component that is lower than the cutoff frequency and near the cutoff frequency. The peaking circuit 2 itself has a group delay characteristic (FIG. 5A) and an amplitude characteristic (FIG.
(B)).

Therefore, the amplitude characteristic of the signal C output from the peaking circuit 2 is such that the predetermined band component is amplified as shown in the amplitude characteristic diagram of FIG. Further, in the group delay characteristic of the signal C, as shown in the group delay characteristic diagram of FIG. 2C, the delay of the predetermined band component remains larger than the delay of the low frequency component having a lower frequency. Accordingly, as shown in the waveform characteristic diagram of FIG. 2C, the waveform of the signal C is a waveform in which a predetermined band component is amplified and ringing remains.

Then, the signal C is input to the delay equivalent circuit 3. FIG. 2D shows a signal D that has passed through the delay equivalent circuit 3.
FIG. 4 is a diagram showing a waveform characteristic, a group delay characteristic, and an amplitude characteristic of FIG.
When the signal C is input to the delay equivalent circuit 3, the group delay characteristic of the signal C (see FIG. 2C) and the group delay characteristic of the delay equivalent circuit 3 (see the dotted line in FIG. 4) are combined. Then, Figure 2
As shown in the group delay characteristic diagram of (d), the delay of each frequency component is adjusted, and the group delay characteristic of the signal D output from the delay equivalent circuit 3 becomes substantially flat. Accordingly, as shown in the waveform characteristic diagram of FIG. 2D, ringing is removed from the waveform of the signal D. Thus, a signal D in which the edge portion (contour component) of the video signal is emphasized is obtained.
Thereafter, the signal D is input to an A / D conversion circuit (not shown) and is converted into a digital signal.

FIG. 3 shows a specific example of the configuration of the peaking circuit 2. According to FIG. 3, the peaking circuit 2 has an operational amplifier 20. A signal (FIG. 1) is connected to the plus terminal of the operational amplifier 20 via a resistor 21 having a resistance value of R1.
Is input. The operational amplifier 20
The output terminal of the operational amplifier 20 is connected to the minus terminal, and the resistance R2 is connected between the minus terminal and the output terminal.
Is disposed. Further, one end of a series circuit (dotted line) in which the resistor 23, the coil 24, and the capacitor 25 are connected in series is connected to the minus terminal. The other end of the series circuit is grounded.

The amplification factor of the peaking circuit 2 is as follows.
Generally expressed by the following equation. That is, amplification factor G = 1 + R2 / Z (1) Here, Z is the impedance of the series circuit, and the absolute value | Z | of the impedance Z is generally represented by the following equation. That is, | Z | = √ (R3 ² + (2πfL−1 / 2πfC) ² ) (2) where R3 is the resistance value of the resistor 23, f is the frequency of the input signal, and L is the inductance of the coil 24. , C is the capacitance of the capacitor 25.

According to the equation (2), the frequency f is １ ／
When the frequency is much higher than π√LC (resonance frequency) and when the frequency f is much lower than √π√LC (resonance frequency), the impedance Z becomes a large value. That is, the amplification factor G in the above equation (1) decreases as the frequency f is higher than the resonance frequency and as the frequency f is lower than the resonance frequency. Therefore, by appropriately selecting the inductance L of the coil 24 and the capacitance C of the capacitor 25, the frequency component in the predetermined band can be amplified more as shown in FIG. 5B.

Further, this peaking circuit 2 corresponds to FIG.
The buffer 16 is disposed between the low-pass filter 1 and the delay equivalent circuit 3 and functions as a buffer for performing impedance matching between them. Conversely,
According to the embodiment of the present invention, the buffer 16 having the outline component enhancing function of the dotted line portion in FIG. 6 is provided by the peaking circuit 2 having the simple circuit configuration as described above.

Further, the group delay in the peaking circuit 2 is compensated by the delay equivalent circuit 3 together with the group delay of the low-pass filter 1 as described above. Therefore, it is not necessary to provide the delay circuit 13 shown in FIG. 6, and the number of components can be reduced.

As described above, the contour emphasizing circuit according to the embodiment of the present invention achieves the simplification and downsizing of the circuit configuration as compared with the conventional one while maintaining the same function as the conventional one. Can be.

Note that the video signal output from the image sensor may be displayed on a predetermined image display means as an analog signal without being converted into a digital signal. In this case, the contour enhancement circuit does not need to have a low-pass filter for A / D conversion. That is, the contour emphasizing circuit includes the peaking circuit 2 and the delay equivalent circuit 3. The delay equivalent circuit 3 in this case is the peaking circuit 2 shown in FIG.
Is designed so as to have a group delay characteristic that compensates for the group delay characteristic.

[0035]

As described above, according to the present invention, the contour component emphasizing section in the contour emphasizing circuit is constituted by an amplifier circuit (peaking circuit) for amplifying a predetermined frequency band component. An outline emphasizing circuit can be provided.

The group delay of the amplifier circuit is compensated for by the delay equivalent circuit together with the group delay of the low-pass filter. Therefore, there is no need to provide a delay circuit conventionally provided in the contour component emphasizing section, and the number of components can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a contour emphasizing circuit according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a signal waveform characteristic, a group delay characteristic, and an amplitude characteristic of each unit of the contour emphasizing circuit according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating a specific configuration example of a peaking circuit 2;

FIG. 4 is a diagram illustrating an example of group delay characteristics of a primary all-pass filter 3a and a secondary all-pass filter 3b.

FIG. 5 is a diagram illustrating an example of a group delay characteristic and an amplitude characteristic of the peaking circuit 2.

FIG. 6 is a block diagram of a conventional edge enhancement circuit.

7 is a diagram illustrating signal waveform characteristics, group delay characteristics, and amplitude characteristics of each unit of the contour emphasizing circuit in FIG. 6;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 low-pass filter 2 peaking circuit 3 delay equivalent circuit 20 operational amplifier 21 resistor 22 resistor 23 resistor 24 coil 25 capacitor

Claims (5)

[Claims] 1. A filter circuit for cutting off a frequency component higher than a predetermined cutoff frequency of a first signal which is a video signal containing a plurality of frequency components, and a second signal output from the filter circuit is input. ,
An amplifier circuit for amplifying a component of a predetermined frequency band of the second signal; a delay equivalent circuit for receiving a third signal output from the amplifier circuit and for compensating a group delay characteristic of the third signal And a contour emphasizing circuit. 2. The amplifier circuit according to claim 1, wherein the amplifier circuit has an operational amplifier having a plus input terminal, a minus input terminal, and an output terminal, and a series circuit in which a first resistor, a coil, and a capacitor are connected in series. One end of the series circuit is connected to the minus input terminal, the minus input terminal and the output terminal are connected via a second resistor, and the second signal is input to the plus input terminal. Contour emphasis circuit to feature. 3. The contour emphasis circuit according to claim 1, wherein the amplification circuit has a buffer function of matching an output impedance of the filter circuit with an input impedance of the delay equivalent circuit. 4. An amplifying circuit for amplifying a frequency component of a predetermined band in a first signal which is a video signal including a plurality of frequency components, a second signal output from the amplifying circuit being input, and A delay equivalent circuit for compensating a group delay characteristic of the two signals. 5. The amplifier circuit according to claim 4, wherein the amplifier circuit has an operational amplifier having a positive input terminal, a negative input terminal, and an output terminal, and a series circuit in which a first resistor, a coil, and a capacitor are connected in series. One end of the series circuit is connected to the minus input terminal, the minus input terminal and the output terminal are connected via a second resistor, and the first signal is input to the plus input terminal. Contour emphasis circuit to feature.