JPH09149314A - Video camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend a dynamic range of a video signal by combining a video signal resulting from the extinguished image of an object with a video signal resulting from the extinguished image of the object. SOLUTION: An object image via a lens 12 and an iris 14 of this camera is dispersed by a prism 16. One dispersed image of the object is given to a CCD 18, the other dispersed image of the object is attenuated for its luminous quantity by an extinction filter 20 and the resulting image is fed to a CCD 22. Then a video signal from the CCD 18 is combined with a video signal from the CCD 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera,
In particular, the present invention relates to a video camera that captures an optical image of a subject having a large amount of light.

[0002]

2. Description of the Related Art Usually, CCD (Charge Coupled Device)
Has a photoelectric conversion characteristic of γ = 1, and an image signal that is directly proportional to the amount of incident light can be taken out, but the charge that can be stored in the CCD is limited. I will end up. That is, the dynamic range of the video signal has a limit, and is actually considerably narrower than human vision. Therefore, when an image of a subject is taken under the sunlight, a bright part is blown out in white and a dark part such as a shadow is crushed in black. Further, even in the case of an indoor image, if an outside landscape is captured through a window in a part of the image, the landscape will fly white as in the above case.

In consideration of such a point, Japanese Patent Application Laid-Open No. 1-204579 filed on August 17, 1989, discloses:
The optical image irradiated on the solid-state image sensor is captured using a high-speed shutter and a low-speed shutter, and two video signals are added to obtain 1
Are making two video signals. As a result, the bright and dark parts of the subject can be imaged with appropriate sensitivity, and the dynamic range of the video signal can be expanded.

[0004]

However, in such a conventional technique, since a high-speed shutter is used to capture an image of a bright portion of a subject, flicker becomes severe with respect to the subject image under a fluorescent lamp. The problem arises. When the subject is moving at high speed, the unblurred subject image captured by the high-speed shutter and the blurred subject captured by the low-speed shutter are added to output the image using only the low-speed shutter. There is also a problem in that the quality is lower than that of the output image obtained. Further, the use of the high-speed shutter causes a problem that smear becomes conspicuous.

Therefore, a main object of the present invention is to provide a video camera capable of expanding the dynamic range of a video signal and outputting a clear video.

[0006]

According to the present invention, there is provided a spectroscopic means for dispersing an optical image of an object through a lens and a diaphragm, a first image pickup device for receiving one of the spectrally separated optical images and outputting a first video signal, Attenuator for attenuating the light amount of the other spectrally separated light image, a second image sensor for receiving the attenuated light image output from the light reducer and outputting a second video signal, and a first predetermined level of the first video signal. The video camera is provided with a combination means for combining the following and a second predetermined level or more of the second video signal.

[0007]

The optical image of the subject that has passed through the lens and the diaphragm is split by a prism as a spectral means. One of the separated light images is given to the first image sensor, and the first image signal is output from the first image sensor. The light amount of the other spectrally separated light image is attenuated by, for example, a light attenuating filter as a light attenuating means, and the attenuated light image is applied to the second image sensor. Then, the second image signal is output from the second image sensor. The first video signal and the second video signal are provided to the combining means, and thereby the first video signal having a first predetermined level or lower and the second video signal having a second predetermined level or higher are combined.

The first video signal is clipped at a first predetermined level or higher by, for example, the first clipping means. The second video signal is clipped to a second predetermined level or lower by, for example, the second clipping unit, and clamped to the first predetermined level by, for example, the clamping unit. Then, for example, the clipped first video signal and the clamped second video signal are added by the adding means.

If only the first image pickup device is activated according to the light quantity of the light image of the object, the first video signal clipped above the first predetermined level is output.

[0010]

According to the present invention, the first video signal of the first
Since the predetermined level or lower and the second predetermined level or higher of the second video signal are combined, the dynamic range of the output video signal can be widened. Further, since the shutter speeds of the first image sensor and the second image sensor can be arbitrarily set, it is possible to avoid the problem of image quality deterioration as in the prior art, and it is possible to output a clear image.

If only the first image pickup device is activated in accordance with the light quantity of the light image of the object, it is possible to suppress the deterioration of the contrast due to the addition of the second image signal, and to obtain a clearer image. Can be output. The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a video camera 10 of this embodiment includes a lens 12. The optical image of the subject is this lens 1
2 and the iris 14 to the prism 16,
It is split into two by the prism 16. One of the separated light images is applied to the CCD 18, and the other light image is applied to the CCD 22 after the light amount is attenuated to 1/4 by the neutral density filter 20. The CCDs 18 and 22 have the same photoelectric conversion characteristic and the same saturation level, and the characteristic straight lines of the output video signal with respect to the light amount of the subject image irradiated on the lens 12 are represented by straight lines α and β in FIG. That is, C
Since both the CDs 18 and 22 are saturated at the level A, and the CCD 22 is irradiated with the attenuated light image in which the light amount is attenuated to 1/4, the CCD 22 receives the light amount F which is four times the light amount E at which the CCD 18 is saturated. When it gets saturated. When the lens 12 is illuminated with a subject image having a light intensity of B, the CCD
A video signal of level C is output from 18 and the CCD 22
Outputs a video signal of level D, which is ¼ of level C.

Referring to FIG. 2, a video signal output from the CCD 18 is subjected to correlation double sampling by a CDS (Correlation Double Sampling) circuit 24 and then clamped at a black level by a clamp circuit 26. The clamped video signal is then clipped by the highlight clip circuit 34 to a level H or higher shown in FIG. The video signal clamped by the clamp circuit 26 is also supplied to the iris control circuit 28, the comparison circuit 30, and the video switch 32.

The video signal output from the CCD 22 is C
Similar to the video signal from the CD 18, the CDS circuit 38 and the clamp circuit 40 respectively perform correlated double sampling and clamping at the black level, and then the dark clip circuit 42 clips the level I and below shown in FIG. It should be noted that the levels H and I are output levels of the CCDs 18 and 22 corresponding to a light amount G smaller than the light amount at which the CCD 18 is saturated. The dark clipped video signal is clamped to the level H by the clamp circuit 44, and then added by the adder 36 with the video signal from the CCD 18.

Accordingly, the characteristic curve of the added video signal is represented by K. The video signal output from the adder 36 is supplied to the video switch 32, and the video switch 3
2 selects the video signal from the adder 36 or the video signal from the clamp circuit 26 according to the switching signal from the comparison circuit 30. Then, the output from the video switch 32 is controlled in gain by an AGC (Automatic Gain Control) circuit 46 and is used for signal processing.

The structures of the comparison circuit 30 and the video switch 32 are shown in FIG. The video signal output from the clamp circuit 26 is input to the base of the transistor Q1 forming the differential amplifier 48. By adjusting the variable resistor VR1, the differential amplifier 48 outputs a voltage signal of level H or higher in FIG. 5, which is inverted and amplified by the transistor Q2. The inverted and amplified voltage signal is transmitted from the transistor Q3.
Q5, after being clamped by a clamp circuit 50 including a capacitor C1 and a diode D1, resistors R1 and R2
Is detected by the diode D2 and the capacitor C2. The detected level is given to the + input terminal of the comparator 50 and compared with the predetermined level adjusted by the variable resistor VR2. When the detection level is higher than the predetermined level, the comparator 50 outputs the high level signal as a switching signal, and when the detection level is lower than the predetermined level, the comparator 50 outputs the low level signal as the switching signal. When the switching signal is at a high level, the video switch 32 turns on the analog switch SW1 to output the video signal from the adder 36,
When the switching signal is at the low level, the analog switch SW2 is turned on and the video signal from the clamp circuit 26 is output.

By configuring the video camera 10 as described above, when the lens 12 is irradiated with a subject image having a brightness level as shown in FIG.
6B, a video signal of a subject image in which the level A or higher is missing is output as shown in FIG. 6B, and the level H or higher of the video signal is highlighted and clipped, and is output from the highlight clip circuit 34. The luminance level of the subject image corresponding to the generated video signal is as shown in FIG. 6 (C). On the other hand, from the CCD 22 as shown in FIG.
As shown in, the video signal of the subject image whose brightness level is compressed to 1/4 is output, and the video signal dark clip is applied, so that the brightness level of the subject image corresponding to the dark clipped video signal is 6 (E). On the other hand, the video signal of the subject image shown in FIG. 6B is input to the comparison circuit 30. Then, the detection level based on the voltage signal of level H or higher is
If it is larger than the predetermined level adjusted by 2, the video switch 32 selects the video signal output from the adding circuit 36. Therefore, the video signal corresponding to the luminance level shown in FIG. 6F is output from the video switch 32.

When a subject image having a brightness level shown in FIG. 7A is irradiated on the lens 12, the brightness level does not exceed the saturation level A as shown in FIG.
A video signal corresponding to the subject image is output from the CD 18, and is clipped by the highlight clip circuit 34 as shown in FIG. 7C. Also, from the CCD 22 as shown in FIG.
The video signal of the luminance level shown in is output, and this is clipped by the dark clip circuit 42 as shown in FIG. The video signal having the brightness level shown in FIG. 7B is applied to the comparison circuit 30, and the detection level based on the voltage signal of level H or higher is compared with the predetermined level adjusted by the variable resistor VR2, and as a result, the detection level is obtained. Is smaller than a predetermined level, the video switch 32 causes the clamp circuit 26 to
Select the video signal output from. Therefore, the video switch 32 outputs the video signal having the luminance level shown in FIG.

According to this embodiment, C having the same characteristics
Since the CDs 18 and 22 are provided and the attenuation filter 20 is provided in front of the CCD 22 so that the video signals output from the CCDs 18 and 22 are combined, the characteristic curve of the video signal with respect to the light amount of the subject image is shown as K in FIG. Therefore, the dynamic range of the video signal can be expanded. In addition, CCDs 18 and 22 having the same characteristics
Since the above is provided, it is possible to suppress the occurrence of flicker and smear and the deterioration of image quality as in the conventional technique.

Further, since the video switch 32 is controlled in accordance with the level of the video signal output from the CCD 18, the video signal clamped by the clamp circuit 26 is selected for the subject image to the extent that the CCD 18 is not saturated. . Therefore, it is possible to prevent such a decrease in the contrast of the video signal below the saturation level. That is, referring to FIG. 7, if the video signal added by the adder 36 is used even when a subject image below the saturation level is irradiated, the contrast of the video signal above the level H is lowered. In the embodiment, since the video signal clamped by the clamp circuit 26 is selected in such a case, it is possible to prevent the contrast from being lowered.

In this embodiment, the attenuating filter 20 is used to obtain the attenuating light image, but the prism 1
An attenuated light image may be obtained by providing a half mirror at 6. Although the highlight clip level is set to H in this embodiment, the highlight clip level can be raised to about 90% of the CCD saturation level. Further, in this embodiment, a CCD is used as an image sensor.
However, it goes without saying that a MOS type image pickup device may be used instead of the CCD. Furthermore, an electronic shutter may be provided on the image pickup device, and the shutter speed may be switched within a range in which flicker and smear that occur in the related art are not noticeable.

[Brief description of the drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention;

FIG. 2 is a block diagram showing another part of the embodiment shown in FIG.

FIG. 3 is a circuit diagram showing a part of the embodiment shown in FIG. 2;

FIG. 4 is a graph showing characteristics of a video signal output from a CCD.

FIG. 5 is a graph showing characteristics obtained by adding video signals.

FIG. 6 is an illustrative view showing one portion of an operation of the embodiment in FIG. 1;

FIG. 7 is an illustrative view showing a part of the operation of the embodiment in FIG.

[Explanation of symbols]

 10 ... Video camera 16 ... Prism 18, 22 ... CCD 20 Dark filter 32 ... Video switch 34 ... Highlight clip circuit 42 ... Dark clip circuit

Claims (3)

[Claims] 1. A spectroscopic unit that disperses a light image of a subject through a lens and a diaphragm, a first image pickup device that receives one of the separated light images and outputs a first video signal, and the other of the separated lights. A darkening means for attenuating the light quantity of the image, a second image pickup element for receiving a attenuated light image output from the darkening means and outputting a second video signal, and a first predetermined level or less of the first video signal and the first video signal A video camera comprising a combining means for combining two or more second predetermined levels of video signals. 2. The combination means includes first clipping means for clipping the first video signal above the first predetermined level, and second clipping means for clipping below the second predetermined level of the second video signal. 2. A clamp means for clamping the clipped second video signal to the first predetermined level, and an adding means for adding the clipped first video signal and the clamped second video signal.
The described video camera. 3. The activating means for activating only the first image pickup device according to the light quantity of the light image.
Or the video camera described in 2.