JPH05110954A - Image pickup device - Google Patents

Abstract

PURPOSE:To reduce a smear component with simple means under high-luminance irradiation for which smear is a problem. CONSTITUTION:Until photometric information from a photometry element (sensor) 7 exceeds a specified level corresponding to illuminance having the danger of generating the smear, normal image pickup is executed and when the information exceeds the specified level, on the other hand, an exposure control part 6 delays element shutter speed to a CCD 2 and extends signal charge storage time on a CCD photodetecting plane. Then, an image pickup gain in a camera process processor 4 is reduced, and the ratio of the smear component to a valid signal component is reduced.

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, and more particularly to an image pickup device having a reduced ratio of smear components to effective signal components under irradiation of high brightness light.

[0002]

2. Description of the Related Art It is widely known that when a high-luminance subject is imaged by an image pickup device using an image pickup device such as a CCD, an unpleasant smear occurs. This is a phenomenon that occurs when the CCD is irradiated with high-intensity light and the smear component leaks into the exposure charges vertically transferred under the CCD. The amount of smear generated is high when the CCD surface is irradiated. It is proportional to the illuminance of the luminosity light on the plate surface and the time taken for the signal charges to traverse the vertical transfer path under the irradiation of high-luminance light. If this is described as a screen image on a monitor, it becomes a shape in which a thin band is drawn in the vertical direction of a high-luminance round subject, which is very annoying.

[0003]

Therefore, in order to reduce such an unpleasant smear component, there has been proposed a technical means for reducing the smear component at the processing stage of the video signal after photoelectric conversion. Such means requires a complicated arithmetic processing, a memory, etc., and therefore the circuit scale becomes large.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above problems and to provide an image pickup apparatus capable of reducing the smear component by a simple means under the irradiation of high brightness light in which the smear phenomenon becomes a problem.

[0005]

In the image pickup apparatus of the present invention, the gain of the image pickup process system is reduced when the signal relating to the illuminance of the incident light on the image pickup element exceeds a level corresponding to the illuminance which may cause smear. In addition, it is characterized by comprising means for extending the signal charge accumulation time in the image pickup device.

[0006]

The present invention will be described below with reference to the illustrated embodiments. First, the basic concept of the present invention will be described prior to describing the embodiments of the present invention. First, when an image of a high-brightness subject is picked up by the CCD solid-state image pickup device, smear is generated, and the amount of the generated smear is the plate surface illuminance on the CCD light-receiving surface and the signal charge transferred in the vertical transfer path under the irradiation of the high-brightness light. It has been described in the above-mentioned conventional example that it depends on the transfer speed of the above. in this case,
Since the transfer speed in the vertical transfer path is constant, if the diaphragm is fixed, the smear component is proportional to the plate surface illuminance on the CCD light receiving surface, that is, the subject brightness.

By the way, in a CCD solid-state image pickup device using an element shutter, the light-receiving surface of the CCD is always irradiated with subject light. On the other hand, the element shutter open time is the CCD
This is the time from the discharge of the unnecessary charges of the photoelectric conversion unit to the reading of the effective signal charges from the photoelectric conversion unit to the vertical transfer path, and does not affect the smear component leaking to the vertical transfer path.

Therefore, the smear component in the output of the CCD solid state image pickup device depends on the shutter speed when the mechanical shutter is used, but does not depend on the electronic shutter speed when the device shutter is used. On the other hand, C
The effective signal component in the output of the CD solid-state imaging device is inversely proportional to the shutter speed in both the mechanical shutter and the device shutter.

Therefore, when a CCD solid-state image pickup device using an element shutter is used under irradiation of high brightness light, the electronic shutter speed is slowed down to increase the effective signal component, and
If the video signal gain of the CCD output is reduced by that amount, the effective signal component becomes the same. On the other hand, since the smear component is constant regardless of the shutter speed, it decreases corresponding to the reduction of the video signal gain. Therefore, the ratio of the smear component to the effective signal component can be reduced.

On the other hand, unless the high-intensity light is irradiated, the smear generation amount itself is a negligible small, so that no problem occurs even if an image is taken at a normal electronic shutter speed. Then, the above switching is performed depending on whether or not the photometric information exceeds a certain level.

The above will be described with reference to FIGS. 2 (A) to 2 (F) with specific numerical values. In FIG. 2, (A) and (D) represent the signal component ratios during CCD output, that is, during video signal input,
(B) and (E) show the video signal gain, and (C) and (F) show the respective signal component ratios during the video signal output. And in the case of (A), (B), (C),
In each of (D), (E), and (F), the light from the same subject is supposed to be applied to the CCD.

First, as shown in FIG. 2A, the CCD when the element shutter speed is set to 1/2000 seconds
In the output 11, the smear component 11b is 1 out of all CCD outputs.
It is assumed that 0% is included, that is, the effective signal component 11a is the remaining 90%. Assuming that the video signal gain at this time is 0 dB (× 1 times) as shown in FIG. 2B, the component ratio between the effective signal component 12a and the smear component 12b in the video signal output 12 is shown in FIG. As shown in C), the ratio is exactly the same as in the case of (A).

Next, when the same subject is imaged by setting the element shutter speed to a slower speed, for example, 1/1000 second, the CCD output 21 is doubled as shown in FIG. 2 (D).
00% is obtained. In this case, since the smear component 21b is not related to the electronic shutter speed, it remains the same 10% as in FIG. 2 (A). Therefore, the effective signal component 21a becomes the remaining 190%.

When this CCD output is passed through an amplifier having a video signal gain of -6 dB (× 1/2 times) shown in FIG. 2 (E), an effective signal component 22a and a smear component 2 in the video signal output 22 are obtained.
As for the signal ratio with 2b, the smear component is halved to a ratio of 5% as shown in FIG. 2 (F).

In other words, the electronic shutter speed is set to 1 /
Doubled from 2000 seconds to 1/1000 seconds and the video signal gain was halved from 0 dB to -6 dB, so there is no change in the total video signal output, but the ratio of smear component during output to effective signal component is halved. It was done. However, for simplification, gamma processing and the like in the camera process processing unit 4 are omitted at all.

The above is the basic concept of the present invention. Next, examples will be described. FIG. 1 is a block configuration diagram of a main part of an image pickup apparatus showing a first embodiment of the present invention, and here, a fixed diaphragm type image pickup optical system is assumed.

That is, this image pickup apparatus has an image pickup lens 1 which transmits a subject light, a CCD 2 as an image pickup element which photoelectrically converts the transmitted light into an electric signal, and a signal signal which is obtained by subjecting the electric signal to necessary signal processing. Camera process processing unit 4 as an imaging process system for outputting the image from the video signal output terminal 5
And a photometric element 7 that measures the subject brightness and outputs photometric information as a signal related to the illuminance of light incident on the image sensor, and an exposure condition of this image capturing apparatus based on the photometric information from the element 7 according to a predetermined program diagram. An electronic shutter control signal for controlling the device shutter speed of the CCD 2 via the CCD drive circuit 3 and a video signal for setting the signal gain of the camera process processing unit 4 to an appropriate value. And an exposure control section 6 which sends out the gain control signals respectively.

In the first embodiment thus constructed, if the photometric information output from the photometric element 7 is below the level (hereinafter referred to as a specific level) corresponding to the illuminance at which smear may occur, The electronic shutter control signal output from the exposure control unit 6 is, for example, 1 / shown in FIG.
In 2000 seconds, the gain control signal of the video signal is set to 0 dB shown in FIG. 2B, that is, the normal state. In this case, the ratio of the smear component in the video signal output from the camera process processing unit 4 to the effective signal component is
Although it is the same as that for video signal input, there is no problem because the smear component is originally a negligible small.

On the other hand, when the photometric information exceeds the specific level, means for reducing the gain of the camera process processing unit 4 as the image pickup process system and extending the signal charge storage time in the image pickup device are taken. .. That is, the electronic shutter control signal is, for example, 1 / shown in FIG.
The gain control signal of the video signal is set to 1000 seconds and set to -6 dB shown in FIG. As a result, the ratio of the smear component to the effective signal component in the video signal output from the camera process processing unit 4 can be calculated as shown in FIG.
As shown in (F), it can be reduced compared to that during the input of the video signal. Therefore, good image information with reduced smear can be obtained.

When determining whether or not the photometric information from the photometric element 7 in the above embodiment exceeds the specific level, an average photometric method for detecting the average photometric level of the entire area of the image pickup surface, or Any of these may be applied by a spot metering method in which a partial area such as a central portion of the image pickup surface is metered.

FIG. 3 is a block diagram of the essential parts of an image pickup apparatus showing a second embodiment of the present invention. The difference of the second embodiment from the first embodiment is that it is independent in obtaining photometric information. Since the exposure control video signal from the camera process processing unit 4 is used instead of the photometric element 7 in FIG. 1, that is, the imager photometry is used, except for this point, there is no difference from the first embodiment. The same components are designated by the same reference numerals and the description thereof will be omitted.

According to the second embodiment, the exposure control video signal as the photometric information exceeds the above-mentioned specific level, so that the normal electronic shutter control signal from the exposure control section 6 exceeds the predetermined shutter speed. On the other hand, in image pickup, when the shutter speed exceeds a predetermined value, the gain of the image pickup process system is reduced, and the image pickup is switched to the image pickup according to the present invention under irradiation of high-intensity light which extends the accumulation time of signal charges in the image pickup device. Therefore, the point that the ratio of the smear component to the effective signal component under the irradiation of high brightness light is reduced to obtain good image information is the same as the first embodiment,
No separate photometric element is required.

In each of the above-described embodiments, the description has been made on the premise of the image pickup apparatus having a fixed aperture, but the present invention is not limited to this. For example, a general auto iris camera is manually operated to a predetermined aperture value. The present invention can also be applied to a camera in which the aperture is controlled or the aperture is controlled automatically.

That is, even in the case of the above auto iris control, when the photometric information exceeds a specific level, the gain of the image pickup process system is reduced and the smear is reduced by extending the accumulation time of the signal charge in the image pickup element. And good image information can be obtained.

By the way, the smear component can be reduced also by narrowing down with the auto iris mechanism. Therefore, if this narrowing down is used in combination with the present invention, a larger smear reduction effect can be obtained. Further, in comparison with the method of reducing the smear component at the stage of processing the video signal after photoelectric conversion, the smear component can be reduced very easily in each of the above-mentioned embodiments and without increasing the circuit scale. ..

[0026]

As described above, according to the present invention, the gain of the image pickup process system is reduced when the signal relating to the illuminance of the incident light on the image pickup element exceeds the level corresponding to the illuminance which may cause smear. At the same time, since the signal charge storage time in the image pickup device is extended, a remarkable effect that the smear component can be reduced by a simple means even under irradiation of high-luminance light in which the smear phenomenon is a problem is exhibited.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a main part of an image pickup apparatus showing a first embodiment of the present invention.

FIG. 2 is a diagram illustrating the basic concept of the present invention.

FIG. 3 is a block configuration diagram of a main part of an image pickup apparatus showing a second embodiment of the present invention.

[Explanation of symbols]

2 ... CCD (imaging device) 4 ... Camera process processing unit (imaging process system) 6 ... Exposure control unit (means for reducing the gain of the imaging process system and extending the signal charge accumulation time in the imaging device)

Claims (1)

[Claims] 1. When the signal related to the illuminance of incident light on the image pickup device exceeds a level corresponding to the illuminance that may cause smear, the gain of the image pickup process system is reduced and the signal charge accumulation time in the image pickup device is extended. An image pickup apparatus comprising means for performing.