JPH0865548A - Imaging device - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain an imaging device capable of controlling the edge enhancement characteristics of a video signal according to the aperture amount. [Structure] The diaphragm amount of the diaphragm 2 is detected by a potentiometer 12, and a control signal 96i corresponding to the detection is sent to the CPU 9
To the control signal 9i according to the control signal 96i.
5s is generated to control the characteristics of the contour emphasis circuit 6. [Effect] The contour emphasis characteristic of the video signal is automatically controlled according to the change of the spatial frequency characteristic of the image pickup system by adjusting the aperture amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device such as a video camera, and more particularly to an image pickup device having a contour enhancement circuit used for image processing.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing an image pickup apparatus having a conventional contour enhancement circuit for video signals, and FIG. 4 is a block diagram showing the contour enhancement circuit. Next, the characteristic setting will be described with reference to these drawings. In FIG. 3, reflected light from a subject passes through the lens 1 and the diaphragm 2 and enters the image sensor 3. A person operating the camera operates a diaphragm adjusting switch (not shown) to send a control signal 94i to the CPU 9. In response to this, the CPU 9 sends a control signal 94s to the diaphragm drive motor 10 to drive the diaphragm drive motor 10 and adjust the diaphragm 2 to a desired diaphragm amount.

The video signal output from the image pickup device 3 is subjected to adjustments such as white correction, black correction and gamma correction in the process circuit 4. The video signal output from the process circuit 4 is A /
After being A / D converted by the D converter 5, it is branched into two, one of which is input to the contour emphasis circuit 6. To set the contour emphasis circuit 6, a person who operates the camera operates an adjustment switch (not shown) to output control signals 91i, 92i, and 93i to the CPU.
By sending to 9. In response to this, the CPU 9 sends control signals 91s, 92s, 93s to the contour emphasizing circuit 6 to set each setting item to a desired characteristic.

In the contour emphasizing circuit 6, according to the characteristics determined by the control signals 91s, 92s and 93s from the CPU 9, FIG.
By the horizontal and vertical contour extraction units 610 and 609 shown in FIG.
Horizontal and vertical contour signals are extracted from the video signal.

FIG. 4 is a detailed block diagram of the contour enhancement circuit 6 of FIG. The structure of the contour emphasizing circuit 6 includes a threshold circuit 611, a vertical contour extracting unit 609, a horizontal contour extracting unit 610, and a crispening circuit 641. Here, the threshold, the horizontal contour signal gain, and the crispening are listed as the characteristic setting items of the contour emphasis circuit.

The digital video signal from the input terminal 601 is first subjected to a threshold operation having a nonlinear input / output characteristic as shown in FIG. According to the characteristic determined by the control signal 91s from the CPU 9 input to the input terminal 691,
The threshold circuit 61l performs non-linear conversion to compress a signal having a low signal level. By doing so, noise that stands out in the dark part of the image can be suppressed and the S / N feeling can be improved.

Next, in the vertical contour extraction unit 609, there are three types of video signals: one without a delay, one delayed by the delay element 621 for one scanning period, and one delayed by the delay element 622 by another scanning period. It is divided into two. These three video signals are respectively multiplied by −1, 2 and −1 by coefficient multipliers 623, 625 and 624, and then added by adder 628. The vertical contour signal thus extracted is used as a coefficient unit 6
The signal level is halved at 26, and a horizontal LPF (low pass filter) 627 further reduces high frequency components in the horizontal direction.

On the other hand, the delay element 6 of the vertical contour extraction unit 609
The video signal delayed by one scanning period at 21 is sent to the horizontal contour extraction unit 610. In the horizontal contour extraction unit 610,
The video signal is divided into three types: one having no delay, one delayed by one sampling period τ by the delay element 631, and one further delayed by one sampling period τ by the delay element 632. These video signals are calculated by the coefficient units 633, 635,
After being multiplied by -1 in 634, doubled, and multiplied by -1, respectively, they are added in the adder 629. In this way, an HPF (high pass filter) is constructed. The spatial frequency characteristic of this HPF is shown by the curve a in FIG. The signal level of the horizontal contour signal thus extracted is amplified K times by the coefficient unit 636 according to the amplification factor determined by the control signal 92s from the CPU input to the input terminal 692.

The horizontal and vertical contour signals thus obtained are added by the adder 630, and then the crispening circuit 641.
Then, the crispening operation having the input / output characteristics as shown in FIG. 6 is performed. CPU input to input terminal 693
The crispening circuit 641 removes the contour signal having a small signal level according to the characteristic determined by the control signal 93s from the signal line 9. By doing this, it is possible to prevent the noise of the video signal from being emphasized and to reduce the S / N when the contour signal is added.
Can be reduced.

The contour signal output from the output terminal 602 of the contour emphasizing circuit is added by the adder 10 to the original video signal whose phase is matched by the delay element 8 in FIG.
It is D / A converted by the A converter 7 and output from the output terminal 11. Since the contour of the video signal thus obtained is emphasized, it becomes a good video signal with a sense of resolution.

[0011]

In a video camera or the like, the spatial frequency characteristic (Modulation Transfer Fu
nction: hereinafter referred to as MTF) is quantitatively determined by the product of the MTFs of the optical elements such as the lens, the diaphragm, the image pickup element, and the crystal LPF. Among these, the F value of the diaphragm mechanism changes depending on the degree of opening / closing, and accordingly, the MTF of the diaphragm changes in the ideal case as shown in FIG. Therefore, it can be seen that the higher the F value, the lower the degree of modulation in the high range of the video signal captured by the camera.

By the way, in recent years, HDTV (High Definition TV) cameras have been used to obtain high-definition images, but such cameras handle signals having a higher spatial frequency than conventional ones. As a result, the decrease in modulation in the high frequency range due to the diaphragm has become difficult to ignore. However, since the conventional contour enhancement circuit as described above independently performs the contour enhancement regardless of the change of the aperture F value, when the characteristic enhancement of the contour enhancement is performed in consideration of the change of the MTF, There is a problem that the person who operates the device has to manually make the setting.

In view of the above problems, the present invention provides an image pickup apparatus capable of automatically setting the characteristics of contour enhancement associated with a change in MTF of an image pickup system without bothering a person who operates the camera. The purpose is to get.

[0014]

According to the present invention, in an image pickup apparatus having an edge enhancing circuit for enhancing the edge of a video signal, an aperture amount adjusting means for adjusting the aperture amount of an aperture mechanism, an aperture amount detecting means, and A control means for controlling the characteristics of the contour emphasis circuit according to the detected aperture amount is provided.

[0015]

According to the image pickup apparatus of the present invention, the diaphragm amount by the diaphragm mechanism is detected, and the detected diaphragm amount is sent to the control means, and the control means determines the M of the imaging system from the sent diaphragm amount.
Since the TF is calculated and the optimum contour enhancement characteristic is calculated based on the TF, the setting of the contour enhancement circuit is controlled, so that the person who operates the camera pays attention to the contour enhancement characteristic setting associated with the change of the MTF of the imaging system. You can operate the camera without having to. Further, even after the automatic setting, it is possible to match the arbitrary characteristics of the person who operates the camera.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an image pickup apparatus, and FIG. 2 is a block diagram showing a contour enhancement circuit for a video signal according to the present invention. In FIGS. 1 and 2, parts corresponding to those in FIGS. 3 and 4 are designated by the same reference numerals, and description thereof will be omitted.

In FIG. 1, a potentiometer 12 as diaphragm amount detection means installed in the diaphragm 2 detects the current diaphragm position (diaphragm amount) of the diaphragm 2 and sends a control signal 96i corresponding to the detection to the CPU 9. The CPU 9 sends the control signal 96
The MTF of the diaphragm 2 is obtained based on i, and each setting item is optimized based on the setting method described later. Then, by sending control signals 91 s, 92 s, 93 s, and 95 s for each setting item to the contour emphasizing circuit 6, each setting item is set to a characteristic in consideration of the change in MTF of the diaphragm 2. In the contour emphasizing circuit 6, the control signals 91s, 92s, 9 from the CPU 9
According to the characteristics determined by 3s and 95s, the horizontal shown in FIG.
Vertical contour extracting units 610 and 609 extract horizontal and vertical contour signals from the video signal.

Next, an example of a method of changing the MTF of the diaphragm 2 and optimizing each setting item of the contour emphasizing circuit 6 will be described. Here, as the characteristic setting items, the threshold, the first and second horizontal contour signal gains, and the crispening are mentioned. In a state where the diaphragm 2 is close to full aperture (small F number), the high range is slightly reduced by the diaphragm 2 as shown in FIG. 8, so the MTF of the imaging system extends to the high range. Considering this state as a reference, the correspondence when the aperture is narrowed down (F value becomes large) is considered. When the diaphragm 2 is narrowed down, the limiting resolution frequency of the image pickup system gradually decreases. Therefore, the peak frequency of the HPF that extracts the high frequency component also decreases accordingly. By doing so, the contour signal can be extracted within the frequency band in which the signal exists.

However, due to the lowering of the critical resolution frequency,
Images gradually lose their resolution. Therefore, the gain of the contour signal is amplified accordingly. However, since the amplification of the gain is accompanied by an increase in noise, the S / N feeling particularly in the dark portion of the image is noticeably deteriorated. Therefore, the black compression level of the threshold circuit 611 is shifted to a high level. In addition, the crispening circuit 6
The low amplitude removal level of 51 is shifted to a high level to strengthen the removal of noise extracted as the contour signal so that the S / N of the entire image does not change due to the increase in gain.
The correspondence between them is shown in Table 1.

[0020]

[Table 1]

Next, the configuration of the contour emphasizing circuit 6 shown in FIG. 2 includes a threshold circuit 611, a vertical contour extracting section 609, and a first contour
Horizontal contour extraction unit 610, second horizontal contour extraction unit 64
0, a crispening circuit 651. Input terminal 60
The digital video signal from No. 1 is processed by the vertical extraction unit 609 and the first horizontal contour unit 610 as in the conventional example of FIG.

On the other hand, the delay element 6 of the vertical contour extraction unit 609
The video signal delayed by one scanning period in 21 is also sent to the second horizontal contour extraction unit 640. Second horizontal contour extraction unit 6
At 40, the video signal is divided into three types: one without delay, one delayed by the delay element 641 for two sampling periods, and one delayed by the delay element 642 for another two sampling periods. These video signals are processed by the coefficient unit 64
The values are multiplied by -1, 3, and -1 by 3, 644, and 645, respectively, and then added by the adder 647. The spatial frequency characteristic of the HPF thus configured is shown by the curve b in FIG. In this case, the first peak frequency of the HPF is half that of the first HPF of the curve a. The signal level of the second horizontal contour signal thus extracted is amplified by the coefficient unit 646 in accordance with the amplification factor determined by the control signal 95s from the CPU 9 input to the input terminal 694.

First and second horizontal contour extraction units 610 and 6
By adding the first and second horizontal contour signals from 40 in the proper ratio, the peak frequency of the contour signal moves continuously from curve a to curve b. By utilizing this fact, it is possible to control the gain of the contour signal and the peak frequency position at the same time.

After the first and second horizontal and vertical contour signals thus obtained are added by the adder 648, a crispening operation having an input / output characteristic as shown in FIG. 6 is performed. That is, according to the characteristic determined by the control signal 93s from the CPU 9 input to the input terminal 693, the crispening circuit 6
41 removes the contour signal having a low signal level. By doing so, it is possible to prevent the noise of the video signal from being emphasized and reduce the S / N deterioration when the contour signal is added.

The contour signal output from the contour emphasizing circuit 6 is added to the original video signal whose phase is matched by the delay element 8 in FIG. 1 by the adder 10 and D / A converter 7 by D / A converter 7. It is A-converted and output from the output terminal 11. In the image signal thus obtained, the characteristic setting of the contour enhancement according to the change of the MTF of the imaging system is automatically performed without the trouble of the person who operates the camera.
A good image signal with a feeling of resolution with enhanced edges can be obtained without paying attention to the change of.

Even if a person who operates the camera operates the aperture adjusting switch (not shown) to send the control signals 91i, 92i, 93i, and 95i to the CPU, as in the prior art, the meaning of the present invention. There is nothing wrong with it. In this case, it is possible to provide a selection switch capable of selecting automatic or manual characteristic setting, or to relatively manually perform characteristic adjustment using the characteristic after automatic setting as an initial value.

[0027]

As described above, according to the present invention, in an image pickup apparatus having a contour enhancement circuit for enhancing the contour of a video signal, the aperture amount is detected, and the characteristic of the contour enhancement circuit is controlled according to the detection. With such a configuration, it is possible to automatically set the characteristic of the edge enhancement according to the change of the MTF of the imaging system without the trouble of the person who operates the camera, and thus the person who operates the camera. Automatically obtains the optimum contour enhancement characteristic, and also has the effect that it can be manually adjusted based on the setting.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing details of a contour emphasis circuit in FIG.

FIG. 3 is a block diagram showing a conventional imaging device.

FIG. 4 is a block diagram showing details of a contour emphasis circuit in FIG.

5 is a graph showing input / output characteristics of the threshold circuit in FIGS. 1 and 3. FIG.

FIG. 6 is a graph showing input / output characteristics of the crispening circuit shown in FIGS. 1 and 3.

FIG. 7 is a graph showing the spatial frequency characteristics of the horizontal contour extraction unit in FIGS. 1 and 3.

FIG. 8 is a graph showing changes in MTF with changes in F-number of the diaphragm in an ideal state.

[Explanation of symbols]

 1 Lens 2 Aperture 3 Image Sensor 6 Contour Enhancement Circuit 9 CPU 12 Potentiometer 609 Vertical Contour Extractor 610 First Horizontal Contour Extractor 640 Second Horizontal Contour Extractor

Claims (2)

[Claims] 1. A lens for condensing reflected light from a subject, a diaphragm mechanism for limiting the amount of light condensed by the lens, an image sensor for receiving the light and converting it into a video signal, and the video image. A contour enhancement circuit for enhancing the contour of the signal, an aperture amount adjusting means for adjusting the aperture amount of the aperture mechanism, an aperture amount detecting means for detecting the aperture amount of the aperture mechanism, and an aperture amount detecting means. An image pickup apparatus provided with a control unit that controls the characteristics of the contour enhancement circuit based on the aperture amount. 2. The contour emphasis circuit comprises: a vertical contour extraction unit for generating a vertical contour signal; a first horizontal contour extraction unit for generating a first horizontal contour signal having a high-pass filter characteristic; 2. A second horizontal contour extracting section having a high-pass filter characteristic controlled according to the aperture amount detected by the detecting means and generating a second horizontal contour signal. The imaging device described.