JP2987454B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus, and more particularly to an image pickup apparatus in which the ratio of a smear component to an effective signal component under high-luminance light irradiation is reduced.

[0002]

2. Description of the Related Art It is widely known that an unsightly smear occurs when a high-luminance subject is imaged by an imaging device using an imaging element such as a CCD. This is a phenomenon that occurs when the CCD is irradiated with high-intensity light, and the smear component leaks into the exposure charge that is vertically transferred below the CCD. It is proportional to the illuminance of the surface of the luminance light and the time for which the signal charge crosses the vertical transfer path under the irradiation of the 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 object, which is very obtrusive.

[0003]

In order to reduce such an unsightly smear component, there have been proposed technical means for reducing the smear component at the stage of processing the video signal after photoelectric conversion. Such means requires complicated arithmetic processing, a memory, and the like, thus increasing the circuit scale.

It is an object of the present invention to solve the above-mentioned problems and to provide an image pickup apparatus capable of reducing the smear component by simple means under irradiation of high-intensity light in which the smear phenomenon becomes a problem.

[0005]

The image pickup apparatus according to the present invention reduces the gain of the image pickup process system when the signal relating to the illuminance of the light incident on the image pickup element exceeds the level corresponding to the illuminance at which smear may occur. And means for extending the signal charge accumulation time in the image sensor.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments. First, a basic concept of the present invention will be described before describing embodiments of the present invention. First, when a high-brightness subject is imaged by the CCD solid-state imaging device, smear occurs. The transfer speed depends on the transfer speed described above. in this case,
Since the transfer speed in the vertical transfer path is constant, if the aperture is fixed, the smear component is proportional to the illuminance of the plate surface on the CCD light receiving surface, that is, the luminance of the subject.

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

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

Therefore, when a CCD solid-state imaging device using an element shutter is used under high-luminance light irradiation, the electronic shutter speed is reduced to increase the effective signal component, and
If the video signal gain of the CCD output is reduced accordingly, the effective signal component becomes the same. On the other hand, since the smear component is constant irrespective of the shutter speed, the smear component decreases in accordance with the reduction in the video signal gain. Therefore, the ratio of the smear component to the effective signal component can be reduced.

[0010] On the other hand, if the image is not irradiated with high-intensity light, the amount of smear generation itself is negligible small, so that no problem occurs even if imaging is performed at a normal electronic shutter speed. Then, the above switching is performed based on whether or not the photometric information exceeds a specific level.

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

First, as shown in FIG. 2A, the CCD when the element shutter speed is set to 1/2000 sec.
In the output 11, the smear component 11b is 1 in all the 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) as shown in FIG. 2B, the component ratio between the effective signal component 12 a and the smear component 12 b in the video signal output 12 is as shown in FIG. As shown in (C), the ratio is exactly the same as in (A) above.

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

When this CCD output is passed through an amplifier having a video signal gain of −6 dB (× １ ／) shown in FIG. 2E, an effective signal component 22 a and a smear component 2 in the video signal output 22 are output.
As shown in FIG. 2 (F), the signal ratio with respect to 2b is reduced to 5% by reducing the smear component by half.

In other words, the electronic shutter speed is reduced to 1 /
Since the video signal gain has been doubled from 2000 seconds to 1/1000 second and the video signal gain has been halved from 0 dB to -6 dB, there is no change in the total video signal output, but the ratio of the smear component in the output to the effective signal component has been halved. You can do it. However, for simplicity, gamma processing and the like in the camera process processing section 4 are omitted at all.

The above is the basic concept of the present invention. Next, an embodiment will be described. FIG. 1 is a block diagram of a main part of an image pickup apparatus according to a first embodiment of the present invention. Here, a fixed stop type image pickup optical system is assumed.

That is, the image pickup apparatus includes an image pickup lens 1 that transmits object light, a CCD 2 serving as an image pickup element that photoelectrically converts the transmitted light into an electric signal, and performs a required signal processing on the electric signal to generate a video signal. Process processing unit 4 as an imaging process system that outputs video from video signal output terminal 5
And a photometric element 7 for measuring the luminance of the subject and outputting photometric information as a signal relating to the illuminance of incident light to the image sensor, and a predetermined program chart for exposing conditions of the image pickup apparatus based on the photometric information from the element 7. And an electronic shutter control signal for determining the element shutter speed of the CCD 2 via the CCD drive circuit 3 and a video signal for setting the signal gain of the processing unit 4 to an appropriate value to the camera process processing unit 4. , And an exposure control unit 6 for sending out the respective gain control signals.

In the first embodiment configured as described above, if the photometric information output from the photometric element 7 is equal to or lower than 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 / A shown in FIG.
At 2000 seconds, the gain control signal of the video signal is set to 0 dB shown in FIG. 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 not different from that in the video signal input, there is no problem since the smear component is originally a small small.

On the other hand, when the photometric information exceeds the specific level, measures are taken to reduce the gain of the camera processing unit 4 as an imaging process system and extend the signal charge accumulation time in the imaging device. . 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 -6 dB shown in FIG. As a result, the ratio of the smear component in the video signal output from the camera process processing unit 4 to the effective signal component is calculated as shown in FIG.
As shown in (F), it can be reduced compared to that during input of a 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 imaging surface, or Any method may be used according to a spot metering method for emphasizing metering of a partial area such as a central portion of the imaging surface.

FIG. 3 is a block diagram of a main part of an image pickup apparatus according to a second embodiment of the present invention. The difference between the second embodiment and the first embodiment is that the second embodiment is independent of obtaining photometric information. Instead of the photometric element 7 described above, the exposure control video signal from the camera process processing unit 4 was used, that is, the imager photometry was used. Except for this point, there is no difference from the first embodiment. The same components are denoted by the same reference numerals, and description thereof is omitted.

According to the second embodiment, the exposure control video signal as the photometric information exceeds the above-mentioned specific level, so that the electronic shutter control signal from the exposure control section 6 exceeds the predetermined shutter speed. On the other hand, when the imaging exceeds a predetermined shutter speed, the imaging is switched to the imaging according to the present invention under the irradiation of high-brightness light, which reduces the gain of the imaging process system and extends the accumulation time of the signal charges in the imaging device. Therefore, the point that the ratio of the smear component to the effective signal component under high-luminance light irradiation is reduced to obtain good image information is the same as in the first embodiment,
The need for an independent photometric element is eliminated.

Although the above embodiments have been described on the assumption that the image pickup apparatus has a fixed aperture, the present invention is not limited to this. For example, a general auto iris camera is manually set to a predetermined aperture value. The present invention is also applicable to a camera that performs aperture control or controls the aperture by an automatic operation.

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

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

[0026]

As described above, according to the present invention, when the signal relating to the illuminance of light incident on the image sensor exceeds the level corresponding to the illuminance at which smear may occur, the gain of the imaging process system is reduced. At the same time, the signal charge accumulation time in the image pickup device is extended, so that a remarkable effect that smear components can be reduced by a simple means even under irradiation of high-intensity light, in which a smear phenomenon is a problem, is exhibited.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of an imaging apparatus according to a first embodiment of the present invention.

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

FIG. 3 is a block diagram of a main part of an imaging apparatus according to 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)

(57) [Claims] When a signal relating to the illuminance of light incident on an image sensor exceeds a level corresponding to the illuminance at which smear may occur, the gain of an imaging process system is reduced and the signal charge accumulation time in the image sensor is extended. An imaging apparatus comprising: