Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2001-07-12
2004-03-02
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
Reexamination Certificate
active
06700124
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a technique of performing a temperature calibration in an infrared imaging device, and a technique of displaying an infrared image in a more legible manner.
BACKGROUND ART
An infrared imaging device is capable of remotely measuring the temperature of an object, and is used as a surveillance camera, or the like, for detecting a human or detecting a car.
FIG. 9
is a diagram illustrating an exemplary configuration of a conventional infrared imaging device (described in Japanese Laid-Open Patent Publication No. 5-302855). The configuration of
FIG. 8
is used for the purpose of calibrating the relationship between the output signal and the temperature.
In
FIG. 8
, the characteristics of an infrared detector
1010
(object temperature versus brightness table) as illustrated in
FIG. 9
are pre-stored in temperature characteristic correction means
1050
. Each of graph curves
1210
,
1220
,
1230
and
1240
of
FIG. 9
represents a relationship between an object temperature T and an output voltage Ei of the infrared detector
1010
, with temperatures T
1
, T
2
, T
3
and T
4
in the vicinity of the infrared detector
1010
being used as parameters.
Temperature measurement means
1080
measures a temperature Tx in the vicinity of the infrared detector
1010
. Temperature characteristic correction means
1050
uses the temperature Tx and the characteristics of
FIG. 9
to obtain the object temperature T from the output voltage Ei of the infrared detector
1010
. Assuming that T
2
<Tx<T
3
, the temperature characteristic correction means
1050
creates a characteristic curve
1250
by interpolating the graph curves
1220
and
1230
, respectively corresponding to the temperatures T
2
and T
3
, and converts the output voltage Ei of the infrared detector
1010
into the object temperature T by using the characteristic curve
1250
.
FIG. 10
is a diagram illustrating another exemplary configuration of a conventional infrared imaging device (described in Japanese Laid-Open Patent Publication No. 10-111172).
In
FIG. 10
, optical systems
1310
and
1320
cause the infrared image of an object
1330
to form an image on an infrared detector
1340
. Each of a reference heat source A
1350
and a reference heat source B
1360
is a heat source using a Peltier element, and the temperature thereof is variable and controlled by controllers
1440
and
1450
, respectively.
The infrared imaging device illustrated in
FIG. 10
images the target object during an effective scanning period, while it images the reference heat source A
1350
and the reference heat source B
1360
during an ineffective scanning period. Average value calculation means
1370
calculates the average value of the output of the infrared detector
1340
during the effective scanning period. Reference heat source A output calculation means
1380
calculates the average value of the output of the infrared detector
1340
while imaging the reference heat source A
1350
during the Ineffective scanning period, whereas the reference heat source output calculation means
1390
calculates the average value of the output of the infrared detector
1340
while Imaging the reference heat source B
1360
during the ineffective scanning period, and median value output means
1400
outputs the median value of these calculation results. A subtractor
1410
subtracts the output of the median value output means
1400
from the output of the average value calculation means
1370
, and an adder
1420
adds a predetermined temperature difference &Dgr;T to the subtraction result and provides the obtained value to the reference heat source A controller
1440
, whereas a subtractor
1430
subtracts the temperature difference &Dgr;T from the subtraction result and provides the obtained value to the reference heat source B controller
1450
. The controllers
1440
and
1450
perform a feedback control so that the subtraction result of the subtractor
1410
is zero, i.e., the output of the average value calculation means
1370
and the output of the median value output means
1400
are equal to each other.
With such a control, even if the scene being imaged changes, the temperatures of the reference heat source A
1350
and the reference heat source B
1360
change according to the average value of the temperature of the obtained image, and are always controlled within a predetermined temperature range (average value &Dgr;t). Correction means
1460
obtains a correction coefficient used for correcting output variations, based on the output of the infrared detector
1340
while imaging the reference heat source A
1350
and the reference heat source B
1360
during the ineffective scanning period. In this way, a temperature calibration suitable for the temperature range to be measured is realized.
FIG. 11
is a diagram illustrating another exemplary configuration of a conventional infrared imaging device (described in Japanese Laid-Open Patent Publication No. 10-142065). The configuration of
FIG. 11
is used for the purpose of eliminating two-dimensional output variations.
In
FIG. 11
, first shutting means
1510
is provided for shading correction, and second shutting means
1530
is provided for inter-pixel output variation correction. During an imaging operation, the first and second shutting means
1510
and
1530
are open, whereby an infrared radiation coming through an optical system
1520
forms an image on an infrared detector
1540
.
The first shutting means
1510
is closed by a control means
1560
once in every 30 seconds so as to shut off the infrared radiation. In this state, inter-pixel output variation correction means
1550
determines a shading correction value based on the output of the infrared detector
1540
. On the other hand, the second shutting means
1530
is also closed by the control means
1560
once in every 30 seconds so as to shut off the infrared radiation. In this state, the inter-pixel output variation correction means
1550
determines a sensitivity correction value based on the output of the infrared detector
1540
.
PROBLEMS TO BE SOLVED BY THE INVENTION
In order to obtain, with a good precision, the temperature information of the object by using an infrared imaging device, it is necessary to perform two types of image correction. One is a so-called “temperature calibration”, i.e., a calibration of the relationship between the output signal (brightness signal) and the temperature, and the other is a correction of two-dimensional output variations in the image.
Possible factors necessitating the temperature calibration include changes in characteristics due to changes in the temperature of the infrared detector itself, fluctuations in the amount of infrared radiation from an optical system such as a lens or a lens barrel due to changes in temperature, etc. For example, when an infrared imaging device is used outdoors, there are violent temperature changes, whereby even immediately after a temperature calibration, the correspondence between the temperature and the brightness shifts from the actual values, thereby reducing the, legibility of the image. Moreover, when it rains, the brightness level substantially decreases for the same object being imaged due to a temperature decrease.
There are two factors for two-dimensional output variations. One is sensitivity variations among various pixels of an infrared detector, and non-uniformities are introduced to the surface of an infrared image by such sensitivity variations. The other is what is called “lens shading”, which is a phenomenon wherein the amount of light received by a central portion of the infrared detector is uniformly higher than that received by a peripheral portion thereof, due to the nature of the optical system.
In the conventional example of
FIG. 8
, the temperature in the vicinity of the infrared detector
1010
is measured, and an object temperature versus brightness table is referenced based on the vicinity temperature. However, in the case of imaging with an infrared imaging device bein
Imagawa Taro
Mekata Tsuyoshi
Morikawa Koji
Hannaher Constantine
Harness & Dickey & Pierce P.L.C.
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