JPH03179882A - Image pickup device picking up weak video image - Google Patents

Abstract

PURPOSE:To pick up a very weak video image while being separated from noise by picking up an image formed on a fluorescent screen of an image intensifier, binarizing it and adding significant parts of an output of a binarizing circuit. CONSTITUTION:An image formed on a fluorescent screen 1a of an image intensifier 1 is picked up by a television image pickup device 3, and the video signal included in the video signal of the television image pickup device 3 is extracted by a binarizing circuit 7 having a threshold level extracting as to be significant the center part of the signal waveform caused by a single electron generated from a photoelectric face to be valid. Thus, the video signal component caused by a noise component due to thermal noise is substantially eliminated. Then the signal component set to be correspondent to one photon is made incident in the photoelectric face of the image intensifier 1 of the photon from a measured photon source 0 with a control circuit 10, then a significant part of the output of the binarizing circuit 7 is added to a relevant address of frame memories 9a-9c for a prescribed period to form the picture.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is characterized in that the interval between the generation of photoelectrons excited by photons and emitted from the photocathode can be resolved into units of time corresponding to the pixels of a television imaging device. The present invention relates to an imaging device that captures weak images that are very weak.

(Problems to be solved by conventional technology and invention) S I
T (SILICON INTENSIFIED TA
The lower limit of the illuminance of an image that can be captured by an imaging device using R (JT) is about IQ-3jiux.

The following devices have been proposed as imaging devices for the above-mentioned weak images that cannot be captured by such high-sensitivity imaging devices.

Photons from the aforementioned weak image are made incident on the photocathode of the image intensifier.

Each photoelectron excited by a photon is doubled, causing a corresponding position on the fluorescent surface corresponding to the position where the photoelectron was generated to emit light.

Bright spots appear and disappear on the fluorescent surface in response to the generation of photoelectrons.

This image is captured on television at a framing speed such that individual images (bright spots) corresponding to one photoelectron do not overlap.

A two-dimensional image memory (frame memory) having an address corresponding to each position on the fluorescent surface is prepared, and 1 is added to the address corresponding to the bright spot at each frame period.

By capturing a large number of frames, each address in the frame memory stores the number of occurrences of bright spots on the fluorescent surface corresponding to that address.

By reading out the contents of this two-dimensional image memory and displaying it on the screen of a monitor, the two-dimensional weak image can be reproduced as a visible image.

However, when the image is weak, the following problems arise.

The output of an image intensifier having a photocathode and a microchannel plater fluorescent surface is considered to be the sum of the noise generated by the image intensifier, the photoelectrons excited by photons, and the signal output of the microchannel plate.

Thermionic electrons generated regardless of the photons incident on the photocathode, thermionic electrons generated by the microchannel plate, etc. are multiplied by the microchannel plate and output.

An object of the present invention is to provide an imaging device that can capture the above-mentioned extremely weak image, an image caused by a single photon, while separating it from noise.

(Explanation of configuration) In order to distantly relate to the above object, the present invention provides a feeble measure.

An imaging device that captures an image includes: an image intensifier having a photocathode, a microchannel plate, and a fluorescent surface; a television imaging device that captures an image formed on the fluorescent surface of the image intensifier; a binarization circuit having a threshold value for extracting a central portion of a signal waveform caused by a single electron generated by the photocathode as significant in the video signal included in the video signal of the television imaging device; a frame memory having a corresponding address, and the photons from the photon source to be measured are incident on the photocathode of the image intensifier for a certain period of time.
It is comprised of a control circuit that adds a significant portion of the output of the digitization circuit to a corresponding address in the frame memory, and an image reproduction device that outputs the addition result.

(Example) Hereinafter, the present invention will be described in more detail with reference to the drawings and the like.

FIG. 1 is a block diagram showing an embodiment of a two-dimensional weak image capturing apparatus according to the present invention.

The embodiment apparatus to be described in detail below performs weak video imaging in units of one photoelectron (hereinafter referred to as digital imaging mode).

The digital imaging mode includes the following steps. (Image imaging step) The image imaging step is to output the image intensifier in a state where the image intensifier 1 receives photons from the weak image that is the imaging target. This refers to the step of capturing and recording images for a certain period of time.

A photocathode 1a is provided on the inner surface of the vacuum container of the image intensifier 1.

Photons from the photon source O (image to be measured) are guided to the photocathode 1a by the imaging optics 21.

The imaging optical system 21 is provided so as to be adjustable so as to form an image of the photon source 0 on the fluorescent surface 1a.

Each electron (including thermoelectrons not caused by photons) generated by the photocathode 1a is brought to a corresponding position on the surface of the microchannel plate 1C by the electron lens 1b.

In this embodiment, three microchannel plates 1C are stacked in order to increase the multiplication factor.

One electron generated by the photocathode 1a is multiplied by the microchannel plate 1c, and a large number of electrons are made to collide with the fluorescent surface 1d of the image intensifier.

This image is formed via the optical system 2 on the photocathode of the vidicon 3, which has low afterimage characteristics.

The image intensifier 1 and the vidicon 3 are supplied with an operating voltage by a drive power supply circuit 4 and a drive power supply circuit 5, respectively.

An image of a bright spot on the fluorescent surface 1d of the image intensifier 1 formed on the photocathode of the vidicon 3 is taken out by television scanning.

Horizontal scanning frequency 15.75KHz, vertical scanning frequency 6
0Hz, interlace 2:1, and screen aspect ratio 3:4.

Here, a bright spot of the image intensifier 1 in the digital imaging mode and a video signal corresponding to the bright spot will be explained.

FIG. 2 shows a model of the brightness distribution on the fluorescent surface 1d caused by one electron generated on the photocathode 1a.

The magnitude of brightness is shown in the direction perpendicular to the fluorescent surface 1d.

The energy of this single brightness is not constant but has a statistical distribution.

Figure 3 shows the energy distribution.

FIG. 3 shows that the probability of occurrence of a bright spot with energy E2 is highest.

This curve is considered to be the bottom of the distribution n caused by thermoelectrons and the like and the distribution S caused by photoelectrons excited by photons.

In the present invention, a dark value corresponding to an intermediate value between energy E2 and energy E1 is set in the binarization circuit 7 to binarize the video signal. The level of this darkness value can be arbitrarily set while observing the video signal.

As a result, most of the distribution n caused by thermoelectrons is removed, and most of the distribution S caused by photons can be extracted.

The output of the binarization circuit 7 is connected to an arithmetic and storage circuit 9.

The calculation and storage circuit 9 includes a first frame memo I79.
a, a second frame memory 9b, a third frame memory 9c, and an arithmetic unit 9d. Each frame memory has a capacity of 512 x 512 x 16 bits, and
Each address defined by 12×512 is made to correspond to a pixel of television imaging.

The inventors have filed an application for a device for capturing weak images (Japanese Patent Laid-Open No. 102078/1983), and the contents thereof include the first and second frame memos IJ9a, 9b, the subtractor 9d, and the All of the frame memories 9c of 3 are used to perform calculations between the frame memories, but in the present invention, substantially only one of them (in this embodiment, the second frame memory) is used. This is intended for the most basic configurations.

In the image capturing step, the output of the binarization circuit 7 is connected to the second frame memory 9b for a certain period of time.

The subtracter 9d is a circuit that calculates the contents of the first and second frame memories 9a and 9b in accordance with addresses;
If no writing is performed to the first frame memory 9a and the contents are set to zero, the result of the above calculation is the second frame memory 9b.
The contents of are stored in the third frame memory 9C.

The contents of the third frame memory 9C are as follows:
Since the second frame memory 9b is connected to the television monitor 12 via the second frame memory 9b, the contents of the second frame memory 9b are substantially connected to the television monitor 12.

The control circuit 10 is a circuit that controls the order of operation of the various parts described above.

Next, the operation of the device will be explained in more detail.

Analog imaging mode is implemented before digital imaging mode.

The object that is the subject of digital imaging or its light emission, etc.
Usually cannot be observed with the naked eye.

With the output of the video amplification circuit 6 connected to the television monitor 12 by the switching circuit 8, the object to be digitally imaged is illuminated with another light source.

The operator can adjust the focus of the imaging lens 21 while observing the screen of the television monitor 12.

In the digital imaging mode, the switching circuit 8 connects the output of the video amplification circuit 6 to the binarization circuit 7.

Then, the control circuit 10 connects the output of the binarization circuit 7 to the second frame memory 9b.

Assuming that the bright spot appearing on the fluorescent surface of the image intensifier 1 coincides with the horizontal scanning line at the highest brightness as shown in FIG. This corresponds to 6 to 8 pixels included in the line and the scanning lines on both sides thereof.

Note that each pixel corresponds to one storage location in the frame memory.

FIG. 2 shows a virtual correspondence of a part of the row of the frame memory (9b) having address 512 corresponding to the scanning line.

Now, if the threshold value of the binarization circuit 7 is at the level indicated by Th in the figure, three 1's will be written to three addresses corresponding to the row of the frame memory 9b corresponding to the scanning line.

FIG. 4 is an explanatory diagram showing the principle of writing.

In the figure, (a) is the output of the video signal amplification circuit 6 corresponding to a specific scanning line, (mountain) is the output of the binarization circuit 7 corresponding to that output, and (C) is the output of the second video signal amplification circuit 6 corresponding to the scanning line. It shows the contents written in the row of frame memory 9b.

When the video signal shown in (a) appears on a specific scanning line on the screen during the first one-screen television scan F1, it is binarized by the binarization circuit 7 as shown in φ) of Fl. .

Frame memory 9 corresponding to the first output of the binarization circuit 7
1 is written to one address in the row of b, and 1 is written to each of the two addresses corresponding to the next output.

During the second television scan F2, when a video signal shown in F2(a)' appears on a scanning line located at the same position on the screen as the specific scanning line on the screen, the binarization circuit 7 converts F2(b
) is binarized as shown.

As a result, 1, 1 corresponding to the first signal and 1 corresponding to the next signal are written in the row of the frame memory 9b, as shown in F2(C).

In the third television scan F3, when the video signal shown in F3(a) appears on the scanning line at the same position on the tooth surface as the specific scanning line on the screen, the binarization circuit 7 converts F3(b )
The image is binarized as shown in .

As a result, 1, 1 corresponding to the first signal and 1 corresponding to the next signal are written in the row of the frame memory 9b as shown in F 3 (C).

Changes in the contents of the illustrated rows due to the scanning of the three frames are summarized below.

Fl 0100000000110 F2 0210001000110 F3 1310001010110 In this way, imaging is repeated a large number of times to accumulate data in the frame memory 9b.

For example, if 150 frames are captured in 5 seconds, 1 for each frame (if there is an area of the photocathode that emits electrons to II), the contents of the address corresponding to the photocathode in the frame memory 9b will be 150. It should be.

Although the specific row has been described above, similar recording is performed on other rows, and data related to the image is recorded based on the arrangement of all rows.

The addition result can be reproduced as a visible image by an image reproducing device including a television monitor 12 via a DA conversion circuit 11.

Various modifications can be made to the embodiments described in detail above within the scope of the present invention.

A solid-state image sensor can also be used instead of the vidicon.

(Effects of the Invention) As described above in detail, the imaging device according to the present invention that images a weak image captures an image formed on the fluorescent surface of the image intensifier with a television imaging device, and The video signal contained in the video signal of the photocathode is extracted by a binarization circuit having a threshold value for determining the central portion of the signal waveform caused by a single electron generated by the photocathode as significant.

This binarization circuit substantially eliminates video signal components caused by noise components caused by thermal noise.

The signal component determined to correspond to one photon is determined by the control circuit, and the photon from the photon source to be measured is allowed to enter the photocathode of the image intensifier for a certain period of time. An image can be formed by adding a significant portion of the digitization circuit output to a corresponding address in the frame memory.

The addition result is output by the image reproduction device.

This has made it possible to capture images in the weak light region, which was previously considered impossible.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an imaging device for capturing weak images according to the present invention. FIG. 3 is a graph showing the energy distribution of bright spots. FIG. 4 is a graph showing the relationship between signals extracted by horizontal scanning and storage. 1... Image intensifier 3... Vidicon 4,... Image intensifier power supply circuit 5.
...Visicon drive circuit 6...Video signal amplification circuit 7
...Binarization circuit 8...Switching circuit 9...
Memory and calculation circuit 9a...Fourth frame memory 9b...Second frame memory 9c...Third frame memory 9d...Subtraction circuit IO...Control circuit 11
...DA conversion circuit 12...television monitor

Claims (1)

[Scope of Claims] An image intensifier having a photocathode, a microchannel plate, and a fluorescent surface; a television imaging device that captures an image formed on the fluorescent surface of the image intensifier; and the television. a binarization circuit having a threshold value for extracting as significant a central portion of a signal waveform caused by a single electron generated by the photocathode in a video signal included in the video signal of the imaging device; and an address corresponding to a pixel of television imaging. a frame memory having a photon source to be measured;
An imaging device for capturing weak images, comprising: a control circuit that adds a significant portion of the output of the digitizing circuit to a corresponding address of the frame memory; and an image reproducing device that outputs the addition result.