JP3005527B1 - Infrared imaging device - Google Patents

Abstract

An infrared imaging apparatus capable of automatically removing an FPN variation due to a variation in an ambient temperature is provided. SOLUTION: In a state where uniform reference infrared light is incident, F
The PN data is stored in the FPN data memory 3. The imaging signal c is obtained by subtracting the FPN data d from the sensor image signal b by the subtraction circuit 2. The FPN detecting circuit 5 multiplies each pixel data between the output d of the FPN data reading circuit 4 and the imaging signal c, and outputs a residual FPN detecting signal e to the bias generating circuit 6.
The bias generation circuit 6 performs cumulative subtraction of the residual FPN detection signal e every time the signal is updated, and applies a current proportional to the result to the sensor 1 as a bias signal f. as a result,
The control is performed so that the FPN component included in the imaging signal c is minimized, and the deterioration of the image quality due to the FPN variation appearing on the screen is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared imaging apparatus, and more particularly to an infrared imaging apparatus using a resistance change type focal plane array infrared sensor.

[0002]

2. Description of the Related Art A resistance change type (for example, bolometer type) focal plane array infrared sensor has an intensity of incident power of infrared light incident on each of resistance change type sensor elements two-dimensionally arranged on a sensor substrate. For example, a temperature that changes according to the temperature is detected by a change in the resistance of a bolometer (a temperature sensor whose resistance changes according to the temperature).

This resistance change type (for example, bolometer type)
The focal plane array infrared sensor usually has an FPN (fixed pattern noise) generated for each pixel due to, for example, a variation in the resistance value of the bolometer. Even when uniform infrared light is input, the FPN appears in an image signal. In addition, the resistance change type infrared imaging apparatus needs to remove FPN included in the imaging signal.

As a method of removing the FPN, generally, an FPN unique to each sensor is used under a uniform infrared input condition.
By obtaining the data and storing it in the memory, and subtracting the stored FPN data from the input image data,
There is a method of obtaining image data from which FPN has been removed.

Conventionally, this type of non-uniformity (FPN) correction method for an infrared imaging apparatus has been disclosed in, for example, US Pat. No. 4,752,694. It is used for the purpose of correcting uniformity. FIG. 6 is a block diagram showing an example of this type of conventional non-uniformity correction method for an infrared imaging device. In the figure, infrared detecting elements 48 composed of bolometers are two-dimensionally arranged. The electronic switches 46 and 47 are switches composed of FETs for selecting a bolometer.

The switches 44 and 45 are, for example, mechanical switches, and are provided for driving the electronic switches 46 and 47, respectively. The correction voltage generator 43 includes a memory MEM, a D (digital) / A (analog) converter DAC, and a sample and hold circuit S & H, and generates a correction voltage VH. The sequencer 41 generates a timing pulse. The preamplifier 42 performs signal reading and amplification.

Next, the operation of the conventional example shown in FIG. 6 will be described. The bolometer 48 is made of a material whose resistance value changes due to a temperature change due to the incidence of infrared rays. A bias voltage Vbias is applied to the bolometer 48, and a current flowing out is read and amplified by the preamplifier 42. The bolometer is selected by the electronic switches 46 and 47. Although the electronic switch 47 is a mere electronic switch, the electronic switch 46 is a switch and also functions as a variable resistor, and compensates for variations in the bolometer resistance.

The resistance value of the electronic switch 46 is MEM, DA
By applying the correction voltage VH generated by the correction voltage generator 43 composed of C and S & H to each gate of the FET, the correction voltage can be freely selected within a certain range. Data for generating an optimum correction voltage for each bolometer is written in the MEM of the correction voltage generator 43. The sequencer 41 generates a timing pulse such that each unit operates at an appropriate timing.

[0009]

However, when a constant bias current is applied to a resistance change type (for example, bolometer type) infrared sensor as in the conventional infrared image pickup device shown in FIG. Is changed, FP
Since N fluctuates and the FPN fluctuation appears on the screen, there is a problem that the image quality is deteriorated. In order to prevent this problem, there is another problem that means for maintaining the substrate temperature of the sensor constant with high accuracy and a variable gain amplifier are required in order to prevent a change in sensitivity to infrared light. Furthermore, when there is no means for keeping the operating temperature of the sensor constant with high accuracy, there is a problem that it is necessary to reacquire the FPN data every time the operating temperature of the sensor changes.

It is an object of the present invention to provide an F
An object of the present invention is to provide an infrared imaging device capable of automatically removing a PN variation.

[0011]

According to the present invention, there is provided an infrared imaging apparatus having an infrared sensor, comprising: memory means for storing a fixed pattern noise of the infrared sensor in advance; Subtraction means for subtracting the pattern noise and outputting the same as an image signal; remaining fixed pattern noise detection means for detecting the remaining fixed pattern noise from the image signal; and controlling the bias of the infrared sensor based on the remaining fixed pattern noise. An infrared image pickup device characterized by including a control means is obtained.

The fixed pattern noise is a sensor image signal when the sensor is irradiated with uniform infrared light, and the residual fixed pattern noise detecting means is configured to detect the fixed pattern noise and the fixed pattern noise. The image signal is multiplied by each pixel data, and a total of the resultant one screen is obtained to output the residual fixed pattern noise.

The operation of the present invention is as follows. Although the resistance value of the sensor element corresponding to the pixel varies from pixel to pixel, the fact that the temperature coefficient of resistance is substantially uniform makes use of the fact that the FPN component contained in the output image signal is detected. The sensor bias is controlled so that the component is minimized. This eliminates the need for means for keeping the substrate temperature of the sensor constant at all times, prevents image quality deterioration due to the appearance of FPN fluctuations due to fluctuations in ambient temperature, etc., and suppresses fluctuations in sensitivity to infrared light. be able to.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of an infrared image capturing apparatus according to the present invention. In FIG. 1, an infrared imaging apparatus according to the present invention includes a resistance change type (for example, bolometer type) infrared sensor 1 for converting an input infrared image light a into light / electricity, an output sensor image signal b of the sensor 1 and an FPN data signal d. Is subtracted to output an imaging signal c.

Further, there is provided an FPN data memory 3 for storing FPN data corresponding to the sensor 1 obtained under uniform infrared input, and an FPN data read circuit 4 for reading out an FPN data signal d from the FPN data memory 3. Further, the residual FP is determined based on the imaging signal c and the FPN data signal d.
FPN detection device 5 for detecting N detection signal e, residual FPN
It has a bias generation circuit 6 for generating a bias signal f based on the detection signal e.

The operation of the embodiment of the present invention will be described with reference to FIGS. In FIG. 1, a sensor 1 is a resistance change type (for example, a bolometer type) focal plane array infrared sensor, and a sensor element (for example, a bolometer) is two-dimensionally arranged on a sensor substrate. For example, each element of the bolometer has a resistance value corresponding to the temperature due to a temperature change according to the intensity of the irradiated infrared light. Therefore,
By applying a bias signal f to each element of the bolometer of the sensor 1 in time series, a voltage corresponding to the resistance value of each bolometer element is output in time series as a sensor image signal b.

The temperature of the bolometer (element) changes depending on the intensity (power) of the incident infrared light, but is also affected by the substrate temperature of the sensor 1. Further, since the resistance values of the bolometer elements have variations, the FPN corresponding to the magnitude of the variation in the resistance values is included in the sensor image signal b. FIG. 2 shows an example of the sensor image signal b when the bias signal f has a constant value when uniform infrared light is incident on the sensor 1.

The period A of the sensor image signal b output in time series corresponds to a bolometer element having a low resistance value, the period B corresponds to a bolometer element having an intermediate resistance value, and the period C corresponds to a bolometer element having a high resistance value. Shows the output. Also, T
1 is a sensor image signal b, T at a certain sensor substrate temperature
2 is a sensor image signal b, T at a temperature higher than T1.
3 is a sensor image signal b when the sensor substrate temperature is lower than T1.

FIG. 3 shows an example of the sensor image signal b when the sensor substrate temperature is a constant value when uniform infrared light is incident on the sensor 1. In the sensor image signal b output in time series, the output corresponding to the bolometer element having a low resistance value during the period A, the bolometer element having the intermediate resistance value during the period B, and the bolometer element having the high resistance value during the period C is obtained. Show.

Further, I1 is a sensor image signal b at a certain bias signal f, and I2 is a bias signal f higher than I1.
Is the sensor image signal b when the bias signal f is lower than I1. The sensor image signal b is proportional to the resistance of the bolometer element and the magnitude of the current of the bias signal f, and the resistance of the bolometer element varies exponentially with the temperature of the sensor substrate. If so,
A change in the sensor image signal b due to a change in the sensor substrate temperature and a change in the sensor image signal b due to a change in the current of the bias signal f have a fixed relationship.

From the sensor image signal b, averaging is performed by frame integration (adding and averaging the sensor image signals b corresponding to the same bolometer element several times, respectively) in a state where uniform reference infrared light is previously incident. To obtain FPN data from which random fluctuations have been removed,
Is stored (recorded; stored). In the imaging signal c, the stored FPN data (signal) d is read out by the FPN data readout circuit 4 in synchronization with each pixel output of the sensor image signal b, and is subtracted from the sensor image signal b by the subtraction circuit 2. It is obtained by doing.

FIG. 4 shows an example of the FPN data signal d.
It is assumed that the FPN data in the FPN data memory 3 is stored in the FPN data memory 3 in a state of T1 in FIG.

FIG. 5 shows an example of the image signal c. The result of subtraction of the FPN data signal d from the sensor image signal b by the subtraction circuit 2 is indicated by an arrow. T2 is an imaging signal c when the sensor substrate temperature becomes higher than T1 before the bias signal f starts control, and T3 is the bias signal f.
Is an imaging signal c when the sensor substrate temperature before the control is started becomes lower than T1. The sensor image signal b in each case is the same as that in the state of T2 and T3 in FIG.

The FPN detecting circuit 5 multiplies each pixel data between the output d of the FPN data reading circuit 4 and the image pickup signal c, obtains the total of the resultant one screen, and generates a bias generating circuit (integrating circuit). 6) Residual FPN detection signal e
Is output. Since this calculation result is averaged in one screen, it indicates how much the FPN component is included in the imaging signal c, and appears in the imaging signal c by the infrared image input a. Even if the image signal is included, it does not affect the residual FPN detection signal e. This residual FPN detection signal e is a signal that is updated every screen.

The bias generation circuit 6 performs cumulative subtraction of the residual FPN detection signal e every time the signal is updated, and applies a current proportional to the result to the sensor 1 as a bias signal f. When the sensor substrate temperature of the sensor 1 rises from T1 to T2, the resistance value of the bolometer (element) rises, and FIG.
As shown by 2, the generation of a positive FPN component in the imaging signal c causes the residual FPN detection signal e of the FPN detection circuit 5 to output a positive value.

Residual FPN detection signal e of FPN detection circuit 5
Is a positive value, the bias generation circuit 6 supplies the bias signal f
The FPN included in the sensor image signal b is reduced by lowering the current value of the sensor image signal b, and the bias signal f is continuously reduced until the residual FPN detection signal e is minimized.
It is controlled to approach 1. Conversely, when the sensor substrate temperature of the sensor 1 decreases from T1 to T3, the resistance value of the bolometer (element) decreases, and a negative FPN component occurs in the imaging signal c as shown by T3 in FIG. By doing so, the residual FPN detection signal e of the FPN detection circuit 5 outputs a negative value.

The residual FPN detection signal e of the FPN detection circuit 5
Is a negative value, the bias generation circuit 6 outputs the bias signal f
By increasing the current value of T, the FPN included in the sensor image signal b is increased, and the bias signal f is continuously increased until the residual FPN detection signal e is minimized.
It is controlled to approach 1. As a result, control is performed so that the FPN component included in the imaging signal c is minimized, and deterioration of the image quality due to the appearance of the FPN fluctuation on the screen is prevented. At the same time, since the product of the bolometer (element) resistance value and the bias current is controlled so as to be kept constant even when the sensor temperature fluctuates, the fluctuation of the sensitivity to infrared light is prevented.

[0028]

As described above, according to the present invention, an FPN component contained in an image pickup signal is detected and the FP is detected.
By controlling the bias of the sensor so that the N component is minimized, it is possible to prevent the deterioration of the image quality due to the variation of the FPN appearing on the screen without requiring a means for keeping the sensor substrate temperature constant at all times. This has the effect of preventing fluctuations in sensitivity to light. Further, the present invention has an effect not only on the sensor temperature fluctuation but also on the circuit temperature fluctuation. Further, a similar effect can be obtained when the bias signal is controlled by voltage.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a sensor image signal when uniform infrared light is incident and a constant bias is applied.

FIG. 3 is an explanatory diagram of a sensor image signal when uniform infrared light is incident and a constant sensor substrate temperature is applied.

FIG. 4 is an explanatory diagram of an FPN data signal.

FIG. 5 is an explanatory diagram of control of an imaging signal.

FIG. 6 is a block diagram of an example of a conventional infrared imaging apparatus.

[Explanation of symbols]

 Reference Signs List 1 sensor 2 subtraction circuit 3 FPN data memory 4 FPN data read circuit 5 FPN detection circuit 6 bias generation circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01J 1/02 G01J 1/42-1/44

Claims (6)

(57) [Claims] 1. An infrared image capturing apparatus having an infrared sensor, wherein a memory means in which a fixed pattern noise of the infrared sensor is stored in advance, and the fixed pattern noise is subtracted from an image signal of the sensor to output as an image signal. Subtracting means for detecting the residual fixed pattern noise from the imaging signal, and control means for controlling a bias of the infrared sensor based on the residual fixed pattern noise. Infrared imaging device. 2. The infrared imaging apparatus according to claim 1, wherein the fixed pattern noise is a sensor image signal when the sensor is irradiated with uniform infrared light. 3. The residual fixed pattern noise detecting means,
For each pixel, the fixed pattern noise and the imaging signal
3. The infrared image pickup apparatus according to claim 1, wherein the residual fixed pattern noise is output by multiplying the remaining fixed pattern noise. 4. The infrared image pickup device according to claim 1, wherein said infrared sensor is a two-dimensional array infrared sensor. 5. An infrared imaging apparatus according to claim 4, wherein said infrared sensor is a resistance change type infrared sensor. 6. An infrared imaging apparatus according to claim 5, wherein said infrared sensor is a bolometer-type infrared sensor.