JP2012058064A - Method for correcting data of infrared imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the conventional problem in which: output data outputted from an infrared imaging device drifts due to a change of the temperature of an infrared detector.SOLUTION: Data from four sides of infrared imaging devices 102 arrayed in two dimensions which are least susceptible to the heat fluctuation of a detection area is used as data for correction, and drift correction is performed by interframe difference data of the data for correction. When the correction is successful, the data from the infrared imaging device 200 is maintained of the same value as that just after the acquisition of calibration data. When the data fluctuates, it is determined to be correction abnormality and, by closing a shutter 101 and reacquiring the calibration data to perform calibration, data with corrected temperature drift can be acquired.

Description

  The present invention relates to a method for correcting data output from an infrared imaging device.

  As a method for correcting the temperature drift of image data from an infrared imaging device that does not require a cooling element such as a Peltier element, as shown in Non-Patent Document 1, from the first image data in a state in which the shutter is closed immediately after power-on. The drift component is extracted and correlated with the drift component from the second image data with the shutter opened, and the drift value included in the second image data is removed based on the correlation value.

JP 2000-131148 A

  The above method is effective because the component of the second image in the state where the shutter is opened is much larger due to drift than the component due to infrared input in the state of transient temperature change just after turning on the power, but stable. There is a problem that it is difficult to extract the drift component from the image data because the drift component due to the environmental temperature change at the time is much lower.

  In order to solve the above problems, the correction method of the present invention has a plurality of infrared detection elements 102 arranged two-dimensionally and a shutter 101 that periodically blocks external infrared input for calibration. After the signal is processed by the signal processing circuit 103, the A / D converter 104 performs A / D conversion, and the CPU 106 processes the time for the image data of the infrared imaging apparatus 200 that sequentially outputs two-dimensional digital image data in time series. The CPU 106 is provided with means for correcting the output drift due to the temperature change of the infrared detecting element 102 based on the difference between the different image data.

  According to the present invention, the Peltier element and the controller of the Peltier element are added to the infrared imaging apparatus by correcting the output drift due to the temperature change of the infrared detecting element based on the difference between the image data obtained from the infrared imaging apparatus at different times. An inexpensive infrared imaging device that does not have it can be used.

It is a block diagram which shows embodiment of the correction method of the infrared imaging device data which concerns on Example 1 of this invention. It is a flowchart which shows embodiment of the correction method of the infrared imaging device data which concerns on Example 1 of this invention.

Embodiments of the present invention will be described below.
Assume that the infrared imaging device 200 using a resistance change bolometer as the two-dimensionally arranged infrared detecting elements 102 is performing temperature measurement at a measurement frame interval of 5 times / second.

  For the sake of understanding, an example in which data is converted into temperature by the CPU 106 will be described based on the block diagram of FIG. 1 and the flowchart of FIG. 2, but the A / D 104 may process the data value after A / D conversion. First, the CPU 106 sends a command to close the shutter 101 (S301). After the incident infrared ray is cut off and the output from the infrared detection element is processed by the signal processing circuit 103, the data read by the CPU 106 after A / D conversion is performed by the infrared ray signal radiated from the shutter 101 surface and the FPN noise of the infrared detection element 102 Therefore, the read two-dimensional array data Tn (x, y) and the temperature TS read from the temperature output from the temperature sensor 107 attached in the vicinity of the shutter 101 are stored (S302). This is set to measurement frame n = 0. Next, a command to open the shutter 101 is sent (S303), the infrared signal from the detection area output from the infrared detection element 102 is processed by the signal processing circuit 103, A / D conversion is performed by the A / D 104, and FPN The subtraction of the noise Tn (x, y) is performed, the calibration and the temperature conversion process are performed at the shutter temperature TS, and the two-dimensional array temperature data Tn + 1 (x, y) is obtained and stored (S304). Further, the average temperature Tav0 of Tn + 1 (x, y) is calculated and stored. Since the measured temperature of the measured frame n + 1 is immediately after calibration, it can be measured with high accuracy.

Next, after 1/5 second, the CPU 106 similarly obtains the temperature converted data Tn + 2 (x, y) of the frame n + 2. (S305).
If there is an environmental temperature change within 1/5 second, Tn + 2 (x, y) is data including a temperature drift component due to the environmental temperature change. The infrared detecting element 102 receives infrared rays radiated from the object, and the temperature of the infrared detecting element 102 rises due to the infrared rays and changes its resistance.

  The temperature change of the infrared detection element 102 due to the incident infrared ray is very slight. For example, when the temperature change of the measurement object is 1 ° C., the temperature change of the infrared detection element 102 with the incident infrared ray is about 0.001 ° C. is there. At this time, the environmental temperature changes with a temperature gradient of 5 ° C./min, the temperature change is mitigated by the outer case of the infrared imaging device 200, and the temperature of the infrared detection element 102 changes at 0.3 ° C./min. Infrared detector output data Tn + 2 (x, y) after 1/5 second between measurements due to temperature change has a drift of temperature data equivalent to a change in the temperature of the object by about 1 ° C. per frame. Will occur. If the difference temperature changed between the measurements is almost regarded as a temperature drift due to the temperature change of the infrared detecting element 102, the CPU 106 subtracts the difference data 1 ° C. between the frames n + 1 and n + 2 from the temperature data of the frame n + 2. Drift due to environmental temperature changes can be corrected. The CPU 106 calculates difference data between the frames n + 2 and n + 1.

  However, if the above processing is performed on all the pixels, when a heat source enters the measurement area, there arises a problem that a measurement value variation due to the heat source is determined to be drift and corrected.

  Therefore, the area for obtaining the difference data between frames is set as image data on the upper and lower sides, the left and right sides of the measurement area that is least affected by the measurement area, or the vicinity thereof. For example, in the case of the infrared detection elements 102 arranged in a two-dimensional manner of 64 × 64, if the average of the inter-frame differences of the data from the 252 infrared detection elements 102 with four sides on the upper and lower sides and the left and right sides is defined as drift data, in most cases the measurement area There is no problem with the effect of the heat source inside.

The CPU 106 obtains differential temperatures of four sides of Tn + 2 (x, y) and Tn + 1 (x, y) (S306). In this case, the four sides are used, but the data near the four sides may be used.
When a heat source enters from outside the measurement area, it always crosses any part of these four sides, so the data of this crossing part cannot be used as correction data. Therefore, it is confirmed whether there is any pixel whose absolute value of the difference temperature is equal to or higher than the set temperature t1 (S307). If the data from the four sides of the infrared detection element where the difference between frames is t1 = 2 ° C. or higher is not used as correction data, this problem can be avoided and correction can be performed if the temperature drift between frames is less than 2 ° C. can do. When there is no pixel exceeding the set temperature t1, the average difference temperature av on the four sides is calculated and stored (S309).
If the ingress heat source is large and the amount of pixel data that is not used as correction data increases, the accuracy of the correction data in the remaining pixels is reduced. The CPU 106 sends a calibration command for the shutter to the shutter controller 105, closes the shutter, and acquires calibration data (S308). If there is a pixel whose absolute value of the difference temperature exceeds t1 and the number of pixels does not exceed the set number, the average av of the difference temperature obtained by removing the data of the pixels exceeding the difference temperature data on the four sides is calculated and stored ( S310).

The average temperature av of the difference temperature data is subtracted from all the two-dimensional array data Tn + 2 (x, y) stored after temperature conversion and stored as corrected data. Further, the average Tav1 of all the pixels of the corrected data is obtained and stored.
If there is a heat source with an absolute value of temperature change less than the set temperature t1 = 2 ° C in these four areas with no environmental temperature change or temperature drift, the size of this heat source will affect the correction error, When a heat source for 20 pixels enters with a temperature difference of 1.9 ° C, a correction error of (1.9 * 20) /252≈0.15°C occurs, and the temperature of the entire measurement area where the temperature does not fluctuate It affects the value and drops by 0.15 ° C. When a heat source for 40 pixels enters, the temperature of the entire 0.3 ° C. measurement area is lowered, greatly affecting the temperature measurement accuracy. Therefore, when a correction that causes the temperature of the entire measurement range to fluctuate by a predetermined threshold temperature t2 or more is entered as a result of the drift correction, or a measurement temperature fluctuation of the threshold temperature t2 or more occurs as the measurement frame n advances. If | Tav1-Tav0 |> t2 (S312), the CPU 106 sends a command to close the shutter to the shutter controller 105 as a correction error (S301), obtains calibration data, and resets the frame count n (S302). . The shutter is opened (S303). Repeat measurement and correction operations. These set threshold temperatures t1 and t2 are determined by the accuracy and tolerance of the target measurement temperature. If t2 = 0.3 ° C. is set, the correction error between frames and the correction error integrated while the frame proceeds do not exceed 0.3 ° C. Further, when the temperature of the entire measurement area changes, if there is a temperature change of 0.3 ° C. or more from the measured temperature immediately after the acquisition of calibration data (S 202), the shutter is closed and the calibration data is acquired and calibrated to perform calibration. Temperature measurement can always be performed with an error within.
If the correction is successful, the CPU 106 outputs the corrected temperature data to the outside (S313).
The CPU 106 increments the frame count n (process 314).
If n does not exceed a preset value, the next frame data is acquired, the difference data is obtained, corrected, and output is repeated.
When n exceeds the set value, the shutter is closed, the calibration data is acquired, the frame count n is reset, and the measurement and correction are repeated. The set value of n is set according to the measurement environment.

  In the case of an infrared imaging device that periodically calibrates with the shutter closed, if the temperature of the infrared detection element is not kept constant with Peltier etc., the measured value drifts from the time of calibration due to fluctuations in the environmental temperature between calibrations. Therefore, it is necessary to make the calibration interval at the shutter very short. However, the present invention can prevent data temperature drift even in an infrared imaging device having no cooling device such as a Peltier element. Can be set long, and an infrared imaging device that is inexpensive and does not consume power can be used.

101 Shutter 102 Infrared Detector 103 Signal Processing Circuit 104 A / D Converter 106 CPU
107 Temperature sensor, infrared imaging device 200

Claims (5)

  Two-dimensionally arranged infrared detection elements and a shutter that periodically blocks external infrared input for calibration, processes the signals from the infrared detection elements, performs A / D conversion, and sequentially in time series A correction method for correcting an output drift due to a temperature change of an infrared detection element based on a difference between image data obtained at different times in data processing from an infrared imaging device that outputs two-dimensional digital image data.   The correction method according to claim 1, wherein the image data for obtaining the drift correction difference data is image data of upper and lower sides, left and right sides on the outermost side from the center of the two-dimensional image data, or image data in the vicinity thereof.   The correction method according to claim 1, wherein pixel data having an absolute value of inter-frame difference data of a correction pixel that is greater than or equal to a set value is not used as correction data.   2. The correction method according to claim 1, wherein when there are more than a set number of pixels whose absolute value of the inter-frame difference data of the correction pixels exceeds the set value, the shutter is closed, calibration data is acquired, and a calibration command is output. .   2. The correction method according to claim 1, wherein when a change in a measured value that has been corrected after calibration by the shutter exceeds a set value, the shutter is immediately closed, calibration data is acquired, and a command to perform calibration is output.

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