JPS5823795B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging device in a still image search system.

In recent years, still image retrieval systems using microfilm and hologram memory have been attracting attention.

In particular, document files that handle documents are
In fields such as drawing management, literature search, and management of office documents, etc.
It is attracting attention as a measure to save labor and improve efficiency.

One of the important points in the configuration of such a system is how to capture and display searched images.

Generally, for still image files, pulsed imaging is often performed in order to shorten the time the file occupies the terminal.

In other words, imaging is done instantaneously, and the video signal obtained at this time is stored in a frame memory.

The contents of the frame memory are supplied and displayed on the terminal monitor as a continuous image.

The image pickup tube that has taken the image performs afterimage erasure (empty readout) after the image is taken to prepare for the next image pickup.

Here, the afterimage characteristic of the image pickup tube is important, and the next image cannot be captured until the previously captured image cannot be erased.

The afterimage characteristics of an image pickup tube vary depending on the type of photoconductive film of the image pickup tube, the area of the target surface, load resistance, beam characteristics, etc., but in general, large diameter ones for high resolution are
It is larger than the small diameter ones used in V, for example, vidicon (Sb2S3) is said to be considerably larger than plumbicon (PbO), carnicon (SdSe), etc.

Several methods have been proposed to improve the afterimage characteristics.

For example, there is a method of improving the afterimage characteristics by increasing the amount of beam during erasing than the amount of beam during reading and causing a large amount of charging current to flow.

If this method is not sufficient to erase the image, the afterimage characteristics can be greatly improved by uniformly illuminating the target surface from the outside to eliminate the influence of the previous image, and then increasing the beam intensity as described above to erase the image. You can do good luck.

However, the latter method only erases the previously captured image and does not take into account the influence of afterimages caused by externally applied bias light later.

If the bias light is used at a sufficiently long imaging interval so that afterimages do not become a problem, it can be considered that the bias light has no effect on the signal current, but if the imaging interval is set short and randomly, An afterimage remains due to the bias light, and the bias of the signal current changes due to the accumulation of this afterimage component.

The afterimage caused by this bias light also differs depending on the image pickup tube used, but for example, with a vidicon, the image retention rate increases by 10 to 20% in 2 to 3 seconds.
There is a measurement result that shows that there is a certain amount of water remaining.

Therefore, even when the same image is captured, for example, the brightness changes depending on the length of the imaging interval, resulting in an image that is very difficult to see.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above drawbacks and provide an imaging device that can automatically correct changes in signal brightness caused by changes in imaging intervals and obtain good images.

FIG. 1 shows an equivalent circuit of a commonly used image pickup tube.

In the figure, C' is the capacitance of the photoconductive surface, R' is the resistance that shows the change in the conductivity of the photocathode depending on the intensity of light, SW' is the switch that shows image switching by electron beam scanning, and Rb is the electronic The beam resistance of the beam, R1 is a load resistance, and EBB is a bias source.

Now, when light hits the target surface, the resistance R' becomes smaller and the potential across the capacitor C' drops.

Next, when the switch SW' is closed by electron beam scanning, a charging current flows into the capacitor C' via the resistor Rb.

This charging current is taken out from terminals P and Q as a signal output.

At this time, an afterimage occurs because the charging current to the capacitor C' is not sufficient.

In other words, the afterimage t is the time that the switch SW' is closed,
R" is the charging resistance of the circuit.

When the target is uniformly illuminated and the capacitor C' is sufficiently discharged at the same time as the image capturing is completed, the components of the previous image become extremely small and become uniform over the entire imaging surface.

Then, switch SW' is closed and the voltage is proportional to .

Furthermore, even if uniform illumination is not sufficient, the afterimage component due to the previous image will rapidly become smaller due to the influence of the bias light.

Next, a case where the imaging interval becomes random will be explained using FIG. 2.

For simplicity, FIG. 2 shows a case in which only bias light from uniform illumination is applied.

A signal current waveform is shown when bias light is incident at random intervals from time t1 to t4.

The solid line indicates the case where the bias light is small, and the broken line indicates the case where the bias light is sufficiently large.

Further, the signal current at the time point ~t'3 represents the signal current caused by the bias light during imaging.

In this way, the signal current during imaging is close to O when the imaging interval is long, but increases as the interval becomes shorter.

In reality, the signal current caused by the bias light shown in FIG. 2 (bias portion) is superimposed on the signal current caused by the image, so that when displayed on a monitor, it appears as a change in brightness.

This bias amount is the afterimage due to uniform illumination light, or the capacitance C
′ is not sufficiently charged, so
By subtracting this bias amount from the signal current, a constant bias level can always be obtained regardless of the imaging interval.

Therefore, in the present invention, a current (voltage) corresponding to the uncharged portion of the capacitor C' is generated by a charging/discharging circuit with a time constant of approximately equal constraints provided separately from the target, and this current (voltage) is By holding a sample and holding the video circuit and controlling the clamp potential of the video circuit with this sample and hold value, the pedicle level is changed and bias changes are automatically corrected.

FIG. 3 shows an embodiment of the present invention.

This imaging device has 1024 scanning lines and 992 effective scanning lines.
The horizontal scanning speed is 63.5 μs (same as the standard television system), and the interlace 1:1 frame frequency is 15.
The frequency was 3 Hz, and a 2" vidicon camera tube was used.

In Fig. 3, 1 is an image pickup tube, 2 is a deflection coil, 3 is a face plate, 4 is a lens, 5 is a lamp for eliminating afterimages,
6 is a flange for holding the lamp 5, 7 is a lamp drive circuit, 8 is a charge/discharge circuit, 9 is a sample hold circuit,
10 is a clamp circuit, and 11 is a control circuit. The charging/discharging circuit 8 has a time constant almost equivalent to that of the image pickup tube 1.

A charging pulse is supplied to this charging/discharging circuit 8 at the same time that the lamp 5 is turned on.

Then, before reading out the stored image from the image pickup tube 9, the discharge voltage is held in the sample and hold circuit 9 at this time.

The output signal of the sample and hold circuit 9 is supplied as a pedicle control signal to a clamp circuit 10 to control the pedicle level of the video signal from the image pickup tube 1.

A timing chart of this embodiment is shown in FIG.

A waveform 100 represents a vertical synchronizing signal of this imaging device, and the interval between two consecutive vertical synchronizing signals corresponds to one frame period.

A waveform 101 is an image read command (request) signal.

As shown in the figure, request signal 1 is sent during the first frame period.
When 01 is supplied, 1 starts from the next falling edge of signal 100.
During the frame period (i.e., the second frame period), the beam current of the image pickup tube 1 is cut off as shown by a waveform 103.
At the same time, a light irradiation signal is output as shown by a waveform 102.

The light irradiation signal causes the image pickup tube 1 provided on the front surface of the lens 4 (not shown in FIG. let

The request signal 101 also causes the control circuit 11 to output a sample pulse at the beginning of the second frame as shown by waveform 108.

This sample pulse 108 causes the sample hold circuit 9 to hold the discharge voltage of the charge/discharge circuit 8 .

The output signal of the sample and hold circuit 9 fixes the clamp level of the clamp circuit 10.

In the next third frame period, the light irradiation signal 102 is turned off and the beam current is turned on.

Thus, the image stored on the target surface of the image pickup tube 1 is read out and a video signal is supplied to the clamp circuit 10.

Waveform 105 represents the period during which this video signal is obtained.

This video signal is adjusted to the pedestal level by the output of the sample and hold circuit 9.

After the file is controlled, it is output as a video output.

When the reading of the stored image is completed, the beam current 103 is cut off (fourth frame period).

Further, during this fourth frame period, a lamp lighting pulse shown by a waveform 106 is supplied to the lamp drive circuit 7, and the afterimage erasing lamp 5 is turned on.

At the same time, the charging/discharging circuit 3 is charged by a charging pulse shown by a waveform 107.

The purpose of turning off the beam current 103 here is to increase the illumination efficiency of the lamp 5, and it is not necessarily necessary to turn it off.

Furthermore, at the beginning of the fourth frame period, the request disallowance signal shown by the waveform 104 goes to H level, informing the outside that erasing is in progress.

This request disallowance signal remains high until the 15th frame period.
held at the level.

That is, in this embodiment, the minimum interval between request signals is set to 15 frame periods, and request signals generated at shorter intervals are not accepted.

During this period, that is, the 10 frame period from the 5th frame to the 15th frame is the erasing period, and the beam current is 10
Erasing operation is performed by increasing the amount of 3 and defocusing.

Details of this erasing operation are described in Japanese Patent Application No. 52-96170.

Thereafter, when the request signal 101 is supplied after the 16th frame period, similar operations are repeated.

Note that at the beginning of the fourth frame period, the sample pulse 108
becomes L level, and the sample hold circuit 9 becomes in a state where it can sample the discharge voltage of the charge/discharge circuit 8.

A specific configuration of the above embodiment is shown in FIG.

The charging/discharging circuit 8 is composed of a CR circuit, and its time constant is adjusted to be the same as the time constant of the image pickup tube 1 by making the resistor R variable.

Here, the CR circuit 8 generates a negative voltage, and its amplitude can be optimized by adjusting the resistors R1 and R2.

Next, a video output correction method will be explained with reference to FIG.

Signal 110 is representative of lamp lighting pulse 106 and charging pulse 107 shown in FIG.

The signal 111 indicates the bias light signal of the image pickup tube 1. Since the lamp 5 emits light only while the signal 110 is at the H level, the bias light signal increases, and when the signal 110 goes to the L level, the bias light signal of the image pickup tube 1 increases. It decays according to the time constant.

On the other hand, while the signal 111 is at the H level, the CR circuit 8 is charged, and when the signal 111 goes to the L level, it is discharged according to the time constant.

The output signal waveform of such a CR circuit 8 is shown at 112.

Since the time constant of the CR circuit 8 is matched to the time constant of the image pickup tube 1, the attenuation waveform of the bias optical signal and the discharge waveform of the CR circuit 8 are drawn almost symmetrically.

In the figure, arrow t. , tl. t2 represents the time at which each image is captured.

As mentioned above, the period (to-1l) and (11-12)
Since the lengths are different between the two, the residual bias optical signals at times t1 and t2 are different, and this makes the image difficult to see.

That is, as indicated by reference numeral 113, the video signal (before correction) is superimposed on this residual bias optical signal.

Then, at time t1. A corrected video output 115 is obtained by taking out the discharge voltage at t2 as a correction voltage 114 and subtracting this correction voltage 114 from the video signal (before correction) 113.

In FIG. 5, this correction voltage is held in a sample and hold circuit 9 that holds the output of the CR circuit 8.

By using this correction voltage as a pedicle control signal of the clamp circuit 10, the clamp circuit 10
A corrected video output 115 is obtained.

As described above, according to the present invention, even if the imaging interval is random, it is possible to output a video signal that always has a constant bed scale level, and it is possible to obtain a stable image signal.

Although the above embodiments have been described using pulsed imaging as an example, it is clear that the present invention is not limited to this.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an equivalent circuit of an image pickup tube, Fig. 2 is a diagram showing a signal current due to an afterimage of bias light, Fig. 3 is a diagram showing an embodiment of the present invention, and Fig. 4 is a diagram showing an embodiment of the invention. FIG. 5 is a diagram showing a specific configuration of an embodiment of the present invention, and FIG. 6 is a diagram for explaining the operation of an embodiment of the present invention. 1... Image pickup tube, 5... Afterimage erasing lamp, 7... Lamp drive circuit, 8... Charge/discharge circuit, 9...・Sample hold circuit, 10
... Clamp circuit, 11 ... Control circuit.

Claims (1)

[Claims] 1. An image pickup tube that captures a still image, a light source that illuminates the target surface of the image pickup tube almost uniformly in order to erase afterimages of the image pickup tube, and discharges at a time constant that is approximately the same as that of the image pickup tube. A charging/discharging circuit, a one-sample field circuit for holding the discharge voltage of the charging/discharging circuit, and means for correcting the video signal representing the stationary surface according to the discharge voltage held by the sample and hold circuit. An imaging device comprising: