JPS5917588B2 - infrared imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an infrared imaging device that has an infrared optical system and a scanner and obtains a video signal with an infrared detector cooled to a low temperature.

FIG. 1 is a block diagram of a conventional infrared imaging device.

The signal infrared light 1 is collected by a light receiving optical system 2, scanned by a scanner 3, and incident on an infrared detector 4. The video signal generated from the infrared detector 4 is processed by the video signal amplifier 5.
After being processed and amplified, it is supplied to an image display 6. The synchronization signal control circuit T controls the movement of the scanner 3 and the display on the image display 6. FIG. 2 is a diagram showing the optical path of infrared light in an infrared imaging device having a refractive light receiving optical system.

Germanium is often used as a lens material for infrared imaging devices that target infrared light with a wavelength of around 10 μm due to its cost and durability. Surface reflection is extremely large.
Therefore, it is usually used with an anti-reflection coating applied to the surface.
With current technology, it is difficult to create a durable anti-reflection film that has a sufficient anti-reflection effect over the wide wavelength range targeted by infrared imaging devices, and it is difficult to create an anti-reflection film that is durable enough to have sufficient anti-reflection effects over the wide wavelength range targeted by infrared imaging devices. At present, the reflection is much larger than in the case of visible light optical systems. Therefore, the infrared light 8 emitted from inside the device is also reflected by the receiving optical system lens surface 9 and enters the infrared detector 4. This is the sum of the infrared light 8 emitted from the inside, and the greater the reflection on the receiving optical system lens surface 9, the more components of the infrared light 8 emitted from the inside of the device. The intensity of the infrared light 8 emitted from inside the device depends on the temperature distribution in the i0 part of the device, but most of the inside of the device usually has a uniform temperature distribution at room temperature. However, the infrared detector 4 is often cooled to an extremely low temperature, and the intensity of the infrared light emitted from it is very small compared to that from other parts. When the scanner 3 is oriented at such an angle that the infrared detector 4 sees itself on the receiving optical system lens surface 9, most of the infrared light incident on the infrared detector 4 is the signal infrared light 1. component, which is smaller than when the scanner is facing other angles. Figure 3 is an example of an image obtained with a conventional infrared imaging device.The image near the center of the image is displayed at a lower brightness level than other parts because the scanner is oriented at an angle where the infrared detector looks at itself. , it looks like a scotoma with a certain area.

This is called Narcissus Spot 10. The above explanation has been about an infrared imaging device with a refractive receiving optical system, but infrared imaging devices with a reflective receiving optical system such as the Cassegrain type can also be detected by infrared light emitted from inside the device through a scanner. If the structure is such that the light enters the device, Narcissus spots will occur, similar to devices with refractive optical systems.

This Narcissus spot has been a major drawback of conventional infrared imaging devices because it destroys information near the center of the image. In order to eliminate this drawback, the present invention adds a Narcissus spot removal circuit to the conventional video signal amplifier to remove Narcissus spots from the displayed image, and will be described in detail below with reference to the drawings.

FIG. 4 shows an embodiment of the present invention, in which the signal obtained from the infrared detector 4 is amplified and processed by the video signal amplification circuit 5, and then
The voltage waveforms for canceling the Narcissus spot are superimposed in the Narcissus removal circuit 11, and the superimposed voltage waveforms are supplied to the image display 6 to display an image.

FIG. 5 is a diagram showing the correspondence between the video waveform 12 of the Narcissus spot and the voltage waveform 13 necessary to cancel the Narcissus spot. It is obtained by measuring the signal waveform of the output of an infrared detector when capturing an image of a landscape. The voltage waveform 13 required to cancel the Narcissus spot must be equal in alternating current to the video waveform 12 of the Narcissus spot, but opposite in sign. FIG. 6 is an example of a circuit that approximately generates the voltage waveform necessary to cancel the Narcissus spot.

This circuit receives as input a sawtooth sweep signal used to sweep a bright spot in the horizontal direction (X direction) and vertical direction (Y direction) on an image display. For example, the X-direction sweep signal 14 is subjected to a DC level adjustment using a subtracter 15 so that the voltage becomes 0 at the center of the Narcissus spot, and then a squarer 16 that outputs a voltage proportional to the square of the input voltage. The Y-direction sweep signal 17 and the similarly processed Y-direction sweep signal 17 are added by an adder 18. The instantaneous voltage values of the sweep signal in the X direction and the Y direction are respectively expressed by adjusting the DC level so that the voltage becomes O at the center of the Narcissus spot. If y, the output voltage Z of the adder 18 will be.

Here A. b is a constant determined by the squarer 16 and the adder 18. As is clear from equation (1), the output of the adder 18 changes in a parabolic shape centered on the center of the Narcissus spot. From the output of the adder 18, a clipper 19 extracts only the signal above a certain level, and after amplifying it with an amplifier 20,
By adding the original waveform with the output adder 21, the Narcissus cancellation signal 22 is obtained. The Narcissus removal circuit includes the voltage generating circuit shown in FIG. 6, and removes the Narcissus spot component from the video signal by adding the Narcissus elimination signal 22 and the video signal. FIG. 7 shows waveforms of various parts of the circuit shown in FIG. 6 when only the X-direction sweep signal is input.

From the top of the figure, the X-direction sweep signal 14, the DC level-adjusted X-direction sweep signal 23, and the adder output 24
, clipper output 25, and Narcissus erase signal 21.
FIG. 8 is an example of an image obtained by the infrared imaging device according to the present invention.

There are no narcissus spots seen in the image obtained with the conventional infrared imaging device shown in FIG. 3, and the image quality is improved. The shape of the Narcissus spot and the video waveform of the Narcissus spot may vary depending on the structure of the infrared imaging device, and the voltage waveform required to cancel the Narcissus spot can be approximated by the circuit shown in Figure 6. There may be cases where this is not possible, but in that case, you can make the clipper in the circuit shown in Figure 6 multi-stage, change the squarer to another power generator or an exponential function generator, or use a combination of these. It is easily possible to improve the approximation accuracy using the following method.

Although the above description has been made regarding the case of removing Narcissus spots from an infrared imaging device, the present invention is not limited thereto, and can be applied to the removal of shading when it occurs in a visible light imaging device. As described above, in the infrared imaging device according to the present invention, due to the function of the Narcissus removal circuit configured in an analog manner, the characteristics of the antireflection film of the light receiving lens are not improved, and the circuit configuration is relatively simple. An infrared image without Narcissus spots can be obtained. Furthermore, since the generation of the Narcissus removal signal uses a sweep signal used in an image display, even if the scanner direction and the sweep signal correspond accurately, even if the scanner performs non-linear scanning in time. A Narcissus-removed signal with no errors can be obtained even if the Although the generation of the Narcissus removal signal has been described above using a function generator that receives a sweep signal as input, it is also easy to configure a function generator that receives a scan synchronization signal as input.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional infrared imaging device, Fig. 2 is a diagram showing the optical path of infrared light in the infrared imaging device, Fig. 3 is a diagram showing an example of an image obtained by a conventional infrared imaging device, Figure 4 is a diagram showing an embodiment of the present invention, Figure 5 is a diagram showing the correspondence between the video waveform of the Narcissus spot and the voltage waveform required to cancel the Narcissus spot, and Figure 6 is a diagram showing the correspondence between the video waveform of the Narcissus spot and the voltage waveform required to cancel the Narcissus spot. A diagram showing an example of a circuit that approximately generates a necessary voltage waveform, FIG. 7 is a waveform diagram of each part of the circuit shown in FIG. 6, and FIG. 8 is an example of an image obtained by an infrared imaging device according to the present invention. FIG.

Claims (1)

[Claims] 1. In an infrared imaging device that has an infrared optical system, a scanner, and an infrared detector cooled to a low temperature and obtains a video signal, a function that approximates the video signal of the Narcissus spot is calculated using horizontal and vertical sweep signals as input. An infrared imaging device comprising a Narcissus spot removal circuit comprising an analog function generator and an adder that inverts the sign of an approximate function generated from the function generator and adds it to a video signal. Device.