JPH07250271A - Image pickup device and its operating method - Google Patents

Abstract

PURPOSE:To photograph a picture over a wide dynamic range by providing a means for stepwise and monotonously increasing the impressed voltage of a target electrode at a target power source part. CONSTITUTION:This device is provided with an image pickup tube 1, target electrode 2 and light transmissive glass substrate 3, and an electrode pin 4 is connected through the substrate 3 to the target electrode 2 inside the image pickup tube 1. Further, the device is provided with a photoconductive film 5, deflection converging part 6, scanning electronic beam 7, cathode 8, load resistor 9, pre-amplifier 10, A/D and D/A converting device 11, frame memory device 12, arithmetic processor 13, target power source part 14, synchronizing signal generator 15, electronic beam control circuit 16 and television monitor 17. Then, the target power source part 14 is provided with the means for stepwise and monotonously increasing the impressed voltage of the target electrode synchronously with a field term so that stored signal charged can be divided and read by plural times of electronic beam scanning.

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 using an image pickup tube having a wide dynamic range and a method of operating the same.

[0002]

2. Description of the Related Art Generally, an image pickup device converts image information such as ultraviolet rays, X-rays, visible light and infrared rays into electric video signals,
Or a device for recording this. 2. Description of the Related Art Conventionally, an image pickup tube, particularly a photoconductive type image pickup tube having excellent resolution sensitivity characteristics, has been widely used for the image receiving unit.

The above photoconductive type image pickup tube converts the incident light (ultraviolet rays, X-rays, visible light, infrared rays, etc.) into a charge pattern and stores the charge pattern, and the accumulated charge pattern as a signal. And a scanning electron beam unit for reading as a current. Further, the target portion basically includes a target electrode and a photoconductive film which are sequentially formed on a transparent substrate. The scanning electron beam unit includes a cathode for emitting an electron beam and a deflection focusing unit for scanning the electron beam.

The image pickup tube is usually used by constantly applying a constant positive voltage of several V to several hundred V to the cathode to the target electrode. At this time, the surface of the photoconductive film on the electron beam scanning side is sequentially scanned by the electron beam for each field period (a period in which the surface of the photoconductive film on the scanning side is scanned once) to be attached with electrons. Immediately after scanning, the potential of the cathode is almost equilibrium, and surplus electrons during scanning return to the cathode side. When light is incident, signal charges corresponding to the amount of incident light are generated in the photoconductive film, and are accumulated as a positive signal charge pattern on the film surface. As a result, the surface of the photoconductive film rises above the cathode by a voltage obtained by dividing the amount of charge generated in one field period by the capacitance of the photoconductive film. The above-mentioned voltage increase amount is about several V to ten and several V at most in normal operation. During the next electron beam scanning, this signal charge pattern is read out as a signal output, and the surface potential of the film returns to almost the cathode potential immediately after scanning. Further, in recent years, an avalanche multiplication type image pickup tube has been known in which a high voltage is applied to a target electrode to cause avalanche multiplication of charges in a photoconductive film to realize high sensitivity. Regarding the above-mentioned image pickup tube, for example, Ninomiya et al .: Image pickup optics, Corona Publishing Co., Ltd. (1975), pp. 109-116, IEE Electron Device Letters,
EDL-8, Number 9 (1987) 39
Pages 2 to 394 (IEEE Electron Device Letters, EDL
-8, No. 9 (1987) pp392-394).

Since an image pickup tube has excellent resolution and sensitivity characteristics, it is generally used for television cameras, image pickup devices such as optical microscopes and electron microscope images, X-ray nondestructive inspections and X-ray diagnostics. Widely used in imaging devices and the like. Regarding these, for example, Ninomiya et al .: Imaging Engineering, pages 323 to 326 of Corona Publishing Co., Ltd. (1975), or Hitachi Review, Vol. 41 (1992) No. 4, pages 187 to 192 (Hitachi Review, Vol. 41). (1992), No. 4).

[0006]

In the above-mentioned prior art image pickup device using the image pickup tube, since the scanning electron beam current of the image pickup tube is at most several microamperes, the maximum accumulated charge that the photoconductive film of the image pickup tube has. From the incident light amount corresponding to the amount,
You can only follow much lower levels. That is,
The above-described image pickup device according to the conventional technique can handle only a light amount level corresponding to at most several to ten and several% of the limit accumulated charge amount of the photoconductive film, and the video signal is not provided for incident light having a light amount higher than that. There was a drawback that it was saturated. Therefore, for a bright subject, the amount of incident light must be reduced by a neutral filter or a lens diaphragm, and the amount of incident light on the image pickup tube cannot be increased to further increase the S / N ratio of the image signal. In order to improve the above-mentioned drawback, even if the scanning electron beam current is increased by taking measures against the cathode, the focus of the scanning electron beam is deteriorated and the resolution characteristics are deteriorated, and secondary electrons and scattered electrons generated in the image pickup tube are also generated. However, there is a problem that the image quality is deteriorated.

On the other hand, in the subject region where the incident light is weak, the amplifier noise of the image pickup device becomes conspicuous, so that the SN ratio of the reproduced image is inevitably deteriorated. Therefore, when capturing and recording an image with a wide dynamic range that is mixed over a wide range from a dark subject portion to a bright subject portion, the high illuminance portion will be saturated if the SN ratio of the low illuminance portion is increased by opening the lens diaphragm. On the contrary, when trying to obtain the image information of the high illuminance portion by narrowing down the lens diaphragm, the SN ratio of the low illuminance portion decreases, so that it is impossible to faithfully reproduce an image having a wide dynamic range. Even if the sensitivity of the image pickup tube is improved as described above, the SN ratio can be surely increased for a dark subject, but conversely there is no margin for a bright subject part, so that the dynamic range is widened. Did not become.

Further, in the case of picking up an image of a bright object as a whole, in order to reduce the amount of light incident on the image pickup tube by narrowing down the lens as described above, the amount of light of the object is generally used to reduce the SN ratio. I could not raise it further.

An object of the present invention is to provide an image pickup apparatus and an operating method thereof for suppressing the above various problems and realizing an image having a wide dynamic range.

[0010]

The above object is to provide a target electrode, a photoconductive film for converting incident light into a signal charge and storing the same, and a cathode for emitting an electron beam for reading the stored signal charge. An image pickup tube having a deflection focusing unit for scanning the electron beam, and a target power supply unit for applying a positive charge to the cathode to the target electrode, and the target power supply unit is In order to read the accumulated signal charges by dividing the accumulated signal charges by a plurality of electron beam scans, a means for monotonically increasing the voltage applied to the target electrode stepwise in synchronization with a field period is achieved. .

Furthermore, a voltage that causes an avalanche multiplication phenomenon of electric charges in the photoconductive film of the image pickup tube in the image pickup device is applied to the target electrode and is used, and step 1 for resetting the image pickup device is input. Step 2 for accumulating signal charges due to light in the photoconductive film of the image pickup tube
And a predetermined voltage V1 is applied to the target electrode in the state where the incident light is OFF and the scanning electron beam is ON in step 1, and the operation is performed in three stages including step 3 for reading the accumulated signal charge by dividing it into plural times. In step 2, the incident light is turned on, the scanning electron beam is turned off, the target electrode voltage is set to V1, and in step 3, the incident light is turned off.
While the F-scanning electron beam is ON, the target electrode voltage is synchronized with each reading period, and V1-V2 (V1 ≧ V
This is achieved by operating in such a manner as to monotonically increase in steps from 2) to V1.

[0012]

The inventors examined the case where the amount of incident light is increased to increase the amount of accumulated signal charges, and the accumulated signal charges are read out by dividing the accumulated signal charges into a plurality of times by electron beam scanning. It was confirmed that even with the reading, there were problems such as remarkable image distortion and generation of false signals. As a result of investigating these causes, it was clarified that the scanning electron beam causes a landing abnormality due to a large potential rise on the surface of the photoconductive film which changes according to the amount of accumulated signal charges. Further, when the amount of light is increased and a large amount of charges accumulated in the photoconductive film according to the intensity of light is read out by the scanning electron beam, the scanning electron beam rushes into the photoconductive film at a higher speed, so that secondary electrons of It was clarified that the generation of electrons became active, and as a result, the effective beam current of scanning electrons decreased, and the efficiency of reading accumulated charge was significantly reduced. Therefore, it has been found that even if the accumulated signal charges are simply divided into a plurality of times and read out, not only the number of times of reading increases significantly but also image distortion and spurious signals cannot be removed. Various means have been studied to avoid these problems, and the target electrode voltage is synchronized with the field period when reading the accumulated signal charge in multiple steps, and the voltage is restored monotonically to the voltage during signal charge accumulation in steps. However, it has been found that the accumulated signal charge may be divided into a plurality of times and read.

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a basic configuration of an image pickup apparatus according to the present invention. Reference numeral 1 is an image pickup tube, 2 is a target electrode, 3 is a translucent glass substrate, 4 is an electrode pin which penetrates the substrate 3 and is connected to the target electrode 2 inside the image pickup tube 1. 5 is a photoconductive film, 6 is a deflection focusing unit, 7 is a scanning electron beam, 8 is a cathode, 9 is a load resistor, 10 is a preamplifier, and 11 is A.
/ D, D / A converter, 12 is a frame memory device,
Reference numeral 13 is an arithmetic processing unit, 14 is a target power supply unit, 15 is a synchronizing signal generator, 16 is an electron beam control circuit, and 17 is a television monitor. The operation of the apparatus of the present invention will be described below.

FIG. 2 is a diagram showing an example of a basic embodiment relating to the operation of the image pickup apparatus. The imaging device of the present invention basically comprises step 1 for resetting the device, step 2 for accumulating signal charges, and step 3 for reading signal charges. In step 1 above, the incident light OF
The device is reset at F, scanning electron beam ON, and target voltage V1 to equilibrate the surface potential of the photoconductive film 5 to the cathode potential. In step 2, the scanning electron beam is OF
In the state of F, the incident light is turned on and the signal charges are accumulated on the surface of the photoconductive film 5. At this time, the surface potential rises according to the incident light, and the maximum potential can rise to the target voltage during storage. In step 3, the incident light is turned off, the target voltage is lowered by V2, and the electron beam is turned on. Next, in synchronization with the scanning electron beam, a step-like target voltage that monotonically increases to the target voltage at the time of storage is applied for each field period to read out the signal charges. Since the scanning electron beam is turned on and off in synchronization with the field period, it is performed by the electron beam control circuit 16 capable of external synchronization.

The signals read in time series for each field are output to the preamplifier 10 via the load resistor 9, amplified, and shaped. The A / D and D / A conversion device 11 and the frame memory device 12 convert the preamplifier output signal into a digital signal for each pixel and store the digital signal. The arithmetic processing unit 13 is the frame memory unit 12 described above.
The video signal stored in 1 is sequentially calculated for each pixel, transferred to the frame memory device 12 again, and integrated with the video signal of the next field. In this way, the video signals for three fields are synthesized by the time-sequential integration. When one cycle of step 1, step 2 and step 3 is completed, the combined video signal is A / D, D / A conversion device 11
Is converted into an analog signal and output to the television monitor 17. Here, the synchronizing signal generator 15 is for supplying the target power supply unit 14, the A / D, D / A converter 11, and the electron beam control circuit 16 with synchronizing signals for matching the field period and the timing.

The outline of the operation of the image pickup apparatus is as described above, and a more detailed description will be given with reference to FIG. FIG. 3 is a diagram showing the state of the surface potential distribution of the photoconductive film 5 caused by the incident light and the state of the output signal current obtained for each field. As shown in the figure, the surface potential increased to near the target voltage (V1) at the time of charge accumulation is as a signal current in the A part in the first field, the B part in the second field, and the C part in the third field. Read. The signals divided and read as described above are finally combined in the arithmetic processing unit 13 and demodulated to the original signal. The important thing is the first field, the second field,
It is to read while applying a third field and a target voltage that monotonically increases in each field. As a result, the potential difference between the cathode and the surface of the photoconductive film can be reduced in each field, so that it is possible to prevent the image abnormal phenomenon due to the abnormal landing of the scanning electron beam as described above. Even with respect to, faithful image reproduction is possible.

In the above description, the case where the signal charges are read by dividing into 3 fields has been described, but the number of fields to be divided may be determined according to the incident light amount, that is, according to the accumulated charge amount. Further, the scanning electron beam in the above step 3 does not have to be always ON, and may be OFF at the transition of the field. Furthermore,
The stepped target voltage does not necessarily have to be constant in each field. What is required, unlike a normal television camera, is to increase the target voltage stepwise by turning off the scanning electron beam when accumulating signal charges and turning off the incident light when reading signal charges. As the image pickup tube of the present image pickup device, various types such as a photoconductive type and a shock conductive type image pickup tube (SIT: Silicon-Intensifier-Tube) can be used in principle, but a small dark current is preferable. For such a purpose, a photoconductive type image pickup tube using an amorphous Se-based semiconductor is suitable. Further, the Se-based photoconductive type image pickup tube can be used by increasing the target power supply voltage so that the avalanche multiplication of electric charges occurs, and therefore, it is particularly suitable for weak light imaging. Furthermore, step 1
By repeating the cycle from Step 3 to Step 3, it is possible in principle to shoot a wide range of images from still images to moving images.

As described above, since the image pickup apparatus of the present invention is operated by applying the stepwise target power supply voltage that monotonically increases for each field, there is no image distortion due to the scanning electron beam landing abnormality or superimposition of a false signal. Moreover, an image with a wide dynamic range can be obtained.

[0019]

Embodiments of the present invention will now be described with reference to the drawings. 4 is a diagram showing a first embodiment of the image pickup device according to the present invention, FIG. 5 is a diagram showing a second embodiment of the image pickup device according to the present invention, and FIG. 6 is a diagram showing a third embodiment of the image pickup device according to the present invention. Is.

First Embodiment FIG. 4 showing a first embodiment of the present invention is a diagram showing an embodiment in which the image pickup apparatus of the present invention is used in a general television camera. Reference numeral 1 is an image pickup tube, 2 is a target electrode, 3 is a translucent glass substrate, 4 is an electrode pin, which penetrates the substrate 3 and is connected to the target electrode 2 inside the image pickup tube 1.
Reference numeral 5 is a photoconductive film, 6 is a deflection focusing unit, 7 is a scanning electron beam,
8 is a cathode, 9 is a load resistance, 10 is a preamplifier, 11
Is an A / D and D / A conversion device, 12 is a frame memory device, 13 is an arithmetic processing device, 14 is a target power supply unit, 1
5 is a synchronizing signal generator, 16 is an electron beam control circuit, 17
Is a television monitor, 18 is a first switch circuit, 1
Reference numeral 9 is a second switch circuit, 20 is a shutter, and 21 is a shutter control circuit. The shutter 20 is turned on and off by the shutter control circuit 21 operated by a trigger generated by the synchronization signal generator 15 for the incident light on the image pickup tube 1. Further, the target power supply unit 14 is a battery E
1, E2, E3, and the first switch circuit 18, the second
Of the switch circuit 19 and outputs a step-shaped target voltage when the synchronizing signal generator 15 is triggered. In this embodiment, the battery E1 is 100 V, and the battery E is
A battery of 50 V was used for 2 and a battery of 50 V was used for battery E3. Further, the first switch circuit 18 is provided with a double switch for connecting the battery E2 directly or through, and the second switch circuit 19 is provided with a resistor for dividing the voltage of the battery E3 into five to generate a voltage of 10V step. Five switches were used as possible. By configuring the target power supply unit 14 as described above, from 100V to 150V, 10
A target voltage increasing in V steps was obtained. Next,
The operation of the image pickup apparatus will be described step by step. In step 1, the shutter 20 is turned off and the scanning electron beam is turned on. Further, the battery E2 is directly connected by the first switch circuit 18, and the battery E3 is connected by the second switch circuit 19.
Of the target voltage (target voltage = E1 + E2 + E3 = 100V + 50V + 0V = 150
V) is applied to the image pickup tube 1 to reset the image pickup device. In step 2, the shutter 20 is turned on and the scanning electron beam is turned on.
The signal charges are accumulated while the FF and the target voltage are kept at 150V. In step 3, the shutter 20 is turned off.
F, the scanning electron beam is turned on, and the signal charge under each target voltage is read. In the first field, the first switch circuit 18 allows the battery E2 to pass through,
The output of the battery E3 is set to 0 V by the second switch circuit 19, and the target voltage of the first field is 100 V (E1
+ E2 + E3 = 100V + 0V + 0V = 100V) is applied. Further, the signal charge of the first field read by the scanning electron beam passes through the preamplifier 10 and is converted into a digital signal by the A / D and D / A converter 11 and the frame memory device 12 and stored. After the second field, the second switch circuit 19
10V divided into 5 by the battery E3 is added to the target voltage of the previous field for each field and applied. Therefore, the target voltage of each field is 110V in the second field, 120V in the third field, 130V in the fourth field, 140V in the fifth field, and 150V in the sixth field.
The signal charges read under each target voltage are stored in the frame memory device 12 in the same path as the signal charges in the first field, and are sequentially processed by the arithmetic processing device 13 in high-speed digital manner for each pixel. Accumulated. Therefore, when the reading and integration of the signal of the sixth field is completed, the signals of the first field to the sixth field are combined. The combined signal is converted into an analog signal by the A / D and D / A conversion device 11 and output to the television monitor 17.

Second Embodiment FIG. 5 showing a second embodiment is a diagram showing a case where the image pickup apparatus of the present invention is used in an X-ray diagnostic apparatus. 22 is an X-ray source, 23
Is an object, 24 is an X-ray image intensifier (X
Line I. The X-ray image incident in I) is image-amplified and converted into a visible light image. 25 is a tandem lens. The X-rays emitted from the X-ray source 22 in a pulsed manner pass through the subject 23 and the X-ray I.D. You will be led to I24. With the X-ray diagnostic apparatus, images having various strengths and weaknesses are recorded by X-ray I.D. Since I is amplified several hundred times or more by I, the contrast of the image becomes very large. The image thus amplified is output to the tandem lens 25 and optically converged. On the other hand, as the image pickup tube 1, a photoconductive type image pickup tube using a Se-based amorphous semiconductor for the photoconductive film 5 is used, and the image pickup tube is coupled with the tandem lens 25 so that the image pickup tube 1 receives X-rays. A video signal of the transmission image was obtained. In this embodiment, the operating voltage of the image pickup tube used is 5
Since it is about 0V, a step voltage can be generated in the target power supply unit 14 by the trigger of the synchronization signal generator 15.
A C power supply was used. The step voltage width obtained from the DC power supply was set to 5 V, and the X-ray image was taken by operating step 1, step 2 and step 3 as in the first embodiment.

The X-ray diagnostic image obtained as described above is
It has a very wide dynamic range, improved by two orders of magnitude, and high resolution and high S / N images were obtained.

Third Embodiment FIG. 6 showing a third embodiment is a diagram showing an example in which the image pickup apparatus of the present invention is used to photograph an electron beam diffraction image by a transmission electron microscope (hereinafter referred to as TEM). In the figure, 26 is an electron beam, 27 is a TEM body, 28 is a scintillator, 29 is a quartz plate, 30 is an optical lens, 31 is a cathode power supply, 32 is a high voltage DC power supply, and the same reference numerals as those of the other embodiments described above are attached. What has been done has the same function as the above-mentioned embodiment. The electron beam 26 transmitted through the sample of the TEM 27 is converted into visible light by the scintillator 28, and the quartz glass plate 29
Through the optical lens 30 to the image pickup tube 1. In this embodiment, since the avalanche multiplication type image pickup tube whose target voltage during operation is 800V is used as the image pickup tube 1,
It is not preferable to configure the target power supply unit 14 with the battery as described in the first embodiment because of the danger of high voltage discharge. Further, in the method as described in the second embodiment, high-voltage switching noise is mixed and the S /
N is deteriorated, which is not preferable. Therefore, in the present embodiment, the target power supply unit 14 is provided with the high-voltage DC power supply 32 that constantly outputs a voltage of 800 V and the cathode power supply 31 that is connected in series with this and has a reverse polarity. By doing so, the cathode power supply 31 can be switched at a relatively low voltage, and the mixing of switching noise can be prevented. As the cathode power supply 31, a high withstand voltage DC power supply that generates a step voltage by a trigger of the synchronization signal generator 15 was used. The step voltage width is set to 5 V because the incident image is an image in which weak light and high-intensity light are mixed and it is desired to capture a weak light image clearly, and the number of steps, that is, the number of fields required for reading accumulated charge is set. Was set to 20. 700 by the above method
A switching noiseless target voltage that monotonically increases in 5 V steps from V to 800 V can be applied to the image pickup tube 1. With the above-described structure, the electron beam diffraction image was observed by operating the steps 1, 2, and 3 as in the first and second examples. As a result, the picked-up electron beam diffraction pattern was an image with a very wide dynamic range, which was improved by three digits compared to the conventional one.

[0024]

As described above, according to the image pickup device and the method of operating the same of the present invention, the target electrode, the photoconductive film for converting incident light into signal charges and storing them, and reading the accumulated signal charges. An imaging tube having a cathode for emitting an electron beam, a deflection focusing unit for scanning the electron beam, and a target power supply unit for applying a positive charge to the cathode to the target electrode, And means for monotonically increasing the voltage applied to the target electrode stepwise in synchronization with a field period so that the target power supply unit divides and reads the accumulated signal charges by electron beam scanning a plurality of times. Since it is possible to capture an image with a very wide dynamic range, it is possible to provide an image pickup apparatus according to the present invention and an operating method thereof. Normal television cameras, of course, be applied to a transmission electron microscope and X-ray diagnostic apparatus,
It enables faithful image reproduction even for images with extremely high contrast. In addition, since the contrast can be compared faithfully with the input image, it is possible to provide more accurate medical diagnosis and new physical property evaluation. Furthermore, since it is possible to suppress the landing abnormality of the scanning electron beam that occurs due to the surface potential of the photoconductive film on the scanning side significantly increasing, it is possible to obtain a faithful reproduced image in which image distortion and spurious signals are not superimposed. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of an image pickup apparatus according to the present invention.

FIG. 2 is a diagram illustrating an operation of the image pickup apparatus according to the present invention.

FIG. 3 is a diagram for explaining the operation of the image pickup apparatus according to the present invention in more detail.

FIG. 4 is a diagram showing a first embodiment of an image pickup apparatus according to the present invention.

FIG. 5 is a diagram showing a second embodiment of the image pickup apparatus according to the present invention.

FIG. 6 is a diagram showing a third embodiment of the image pickup apparatus according to the present invention.

[Explanation of symbols]

 1 Imaging Tube 2 Target Electrode 5 Photoconductive Film 6 Deflection Focusing Unit 7 Scanning Electron Beam 8 Cathode 11 A / D, D / A Converter 12 Frame Memory Device 13 Arithmetic Processing Device 14 Target Power Supply Unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Oshima 1-280, Higashi Koikeku, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Inventor Tadaaki Hirai 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Laboratory (72) Inventor Yoshiro Takiguchi 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the Japan Broadcasting Corporation Broadcasting Technology Laboratory (72) Inventor Junichi Yamazaki 1-10-11 Kinuta, Setagaya-ku, Tokyo Broadcasting Technology Institute

Claims (6)

[Claims] 1. A target electrode, a photoconductive film for converting incident light into a signal charge and storing the signal charge, a cathode for emitting an electron beam for reading the stored signal charge, and for scanning the electron beam. And a target power supply unit for applying a positive charge to the cathode to the target electrode, and the target power supply unit, the target power supply unit, the accumulated signal charge. An imaging apparatus having means for monotonically increasing the voltage applied to the target electrode stepwise in synchronization with a field period in order to read the data in a divided manner by scanning the electron beam a plurality of times. 2. The image pickup device includes an A / D and D / A and a frame memory device for converting each of the divided and read signal outputs into a digital signal for each pixel and recording the digital signal. The image pickup apparatus according to claim 1. 3. The image pickup device according to claim 1, wherein the image pickup device includes a calculation processing device for calculating a digital signal corresponding to each pixel. 4. The image pickup device according to claim 1, wherein the photoconductive film of the image pickup tube is made of an amorphous material mainly containing selenium. 5. A target electrode, a photoconductive film for converting incident light into a signal charge and storing the signal charge, a cathode for emitting an electron beam for reading the stored signal charge, and for scanning the electron beam. And a target power supply unit for applying a positive charge to the cathode to the target electrode, and the target power supply unit, the target power supply unit, the accumulated signal charge. In a method of operating an image pickup apparatus having means for monotonically increasing a voltage applied to the target electrode stepwise in synchronization with a field period in order to divide and read by a plurality of electron beam scans, the photoconductivity of the image pickup tube is increased. A method of operating an imaging device, wherein a voltage that causes an avalanche multiplication phenomenon of charges in a film is applied to the target electrode and used. 6. A means for monotonically increasing the voltage applied to the target electrode stepwise for resetting the image pickup device and for accumulating signal charges due to incident light in a photoconductive film of an image pickup tube. The target electrode is operated in three stages including step 2 and step 3 for reading the accumulated signal charge by dividing it into a plurality of times, and in step 1 with the incident light OFF and the scanning electron beam ON. When a predetermined voltage V1 is supplied, the target electrode voltage is set to V1 in the state where the incident light is ON and the scanning electron beam is OFF in the step 2, and the incident light is OFF and the scanning electron beam is in the state in the step 3 described above. The target voltage is synchronized with each reading period, and V1-V2
6. The method of operating an image pickup apparatus according to claim 5, wherein the operation amount is monotonically increased stepwise from (V1 ≧ V2) to V1.