Radiant energy – Infrared-to-visible imaging
Reexamination Certificate
2001-08-29
2004-08-03
Gagliardi, Albert (Department: 2878)
Radiant energy
Infrared-to-visible imaging
C250S332000, C250S341500, C250S252100
Reexamination Certificate
active
06770880
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
In general, the present invention relates to an infrared imaging apparatus and, more particularly, relates to correction of shading included in data of a picture taken by infrared imaging apparatus.
2. Description of the Related Art
Each substance radiates substance-temperature-dependent electromagnetic waves caused by motions of atoms or molecules on the surface of the substance unless the temperature of the substance is equal to the absolute zero. The maximum wavelength of electromagnetic waves radiated by many substances on the earth has a value in an infrared range. An infrared imaging apparatus is an apparatus for carrying out image processing by detection of infrared rays. In many cases, an infrared imaging apparatus is used in light reception equipment. One of most outstanding features of an infrared imaging apparatus is a characteristic that allows such equipment to be designed into small and light one. In general, such light-receiving equipment is referred to as a passive system. On the other hand, a system comprising a set of a transmission apparatus and a reception apparatus is known as an active system. Since an infrared passive system does not radiate an electromagnetic wave by using a transmission apparatus as a radar does, such a system has a characteristic of high concealability. For this reason, such a system has been developed for military purposes and has become the base of development of infrared technologies. At the present time, a number of application products centered at an image processing apparatus are available in the market as consumer products. The reception apparatus of the infrared system comprises a camera head for detecting infrared rays and converting the infrared rays into electrical signals, an A/D converter for converting an analog signal into digital data and an image-processing unit for processing the digital data representing an image in accordance with an application.
FIG. 32
is a diagram showing the general configuration of the camera head. As shown in the figure, the camera head
2
comprises an optical system
4
and an infrared detector
6
. The optical system
4
comprises a lens
8
and a lens housing
10
. The lens
8
condenses infrared rays. The lens housing
10
plays roles of supporting the lens
8
and preventing reflection of infrared rays by absorption of the infrared rays introduced to the inside of the lens housing
10
. Such reflection is a cause of noise. The infrared detector
6
comprises a window
12
, a cold shield
14
, an infrared sensor
16
, an inner shell
18
and an outer shell
20
. The window
12
is a window for passing through infrared rays. The cold shield
14
plays a role of reducing the quantity of an unnecessary infrared ray hitting the infrared sensor
16
. The infrared sensor
16
plays a role of outputting electrical signals with a level proportional to the intensity of incident infrared energy. The inner shell
18
and the outer shell
20
play a role of accommodating the infrared sensor
16
.
FIG. 33
is a diagram showing a typical configuration of the camera head
2
. The lens
8
shown in the figure comprises a plurality of lenses
8
a
to
8
d
. The lens
8
a
is made of Si while the lens
8
b
is made of ZnSe. On the other hand, the lens
8
c
is made of Ge while the lens
8
d
is made of Si. The window
12
is made of Ge and the cold shield
14
is a metallic plate. The infrared sensor
16
is made of semiconductor such as Hg
1−x
Cd
x
, Te or Pb
1−x
Sn
x
Te. The inner shell
18
and the outer shell
20
are each made of a metal such as kovar.
FIG. 34
is a diagram showing a typical implementation of the infrared detector
6
shown in FIG.
32
. The infrared detector
6
is a vacuum thermal-insulating container having a dual structure comprising the inner shell
18
and the outer shell
20
. On a portion of the outer shell
20
, the window
12
is provided. On the inner shell
18
facing the window
12
, the infrared sensor
16
is mounted. The inner shell
18
of the vacuum thermal-insulating container accommodates refrigerant such as liquid nitrogen. As an alternative, a cryostat
28
adopting a Joule-Thompson law operates at a predetermined temperature. The cold shield
14
is provided so as to enclose the infrared sensor
16
. The cold shield
14
reduces the quantity of an unnecessary infrared ray entering the infrared sensor
16
. Electrodes of the infrared sensor
16
and their conductor patterns are connected to each other by bonding wires
22
adopting a bonding technique. Infrared rays detected by the infrared sensor
16
is output to an external device as analog electrical signals appearing on lead pins
26
which are connected to semiconductor patterns by bonding wires
24
. The analog electrical signals output from the lead pins
26
are each converted by the AD converter into digital data consisting of a predetermined number of bits. The digital data is supplied to the image-processing unit such as an apparatus for keeping track of an observation target or implementing medical treatment. In the image-processing unit, the digital data is subjected to various kinds of image processing.
FIG. 35
is an explanatory diagram used for describing a role played by the cold shield
14
. As described above, the cold shield
14
is provided so as to enclose the infrared sensor
16
. The inner surface of the cold shield
14
is coated with a black coating material. Baffles
30
are provided on the walls of the inner surface. The baffles
30
each reduce the quantity of an unnecessary infrared ray entering the infrared sensor
16
. The cold shield
14
is designed so that infrared rays in a range denoted by reference numeral
32
are condensed by the lens
8
at a position A on the surface of the infrared sensor
16
. In general, about a photographed picture output by the camera head
2
infrared rays are incident on the surface of the infrared sensor
16
not in a uniform irradiance distribution even if the picture is taken as a result of photographing a scene or an image-taking object having a uniform distribution of radiation intensities. Instead, a signal output by the infrared sensor
16
shows a quadratic-function distribution with respect to the position of a field of view. This quadratic-function distribution is a phenomenon known as shading. If the shading phenomenon becomes too excessive, an accurate picture of the scene or the objects of image-taking cannot be taken, and the objective of the image-taking cannot be achieved in some cases. In order to reproduce accurate picture information of a scene or another image-taking object by using an image-taking unit, it is necessary to adopt a shading correction method capable of effectively removing only shading components from a signal generated by the infrared sensor
16
.
FIG. 36
is an explanatory diagram used for describing the aforementioned shading phenomenon. The shading phenomenon occurring in an infrared imaging apparatus includes two components, namely, a shading component caused by an optical system and a shading component caused by a housing comprising the lens housing
10
, the inner shell
18
and the outer shell
20
. The shading component caused by the optical system is a shading component due to irradiance distribution which is developed on the surface of the infrared sensor
16
when an image is created by scene components
40
passing through an effective aperture of the optical system. On the other hand, the shading component caused by the housing parts containing the lens housing
10
, the inner shell
18
and the outer shell
20
is a housing components
42
incident to the infrared sensor
16
. The infrared rays are radiated by the lens housing
10
, the inner shell
18
and the outer shell
20
themselves, which constitute the housing as described above. The shading component caused by the housing parts is peculiar to an infrared imaging apparatus and does not exist in a visible image-taking apparatus. The most important problem raised in the shad
Kamata Masaki
Nakamura Osamu
Shimomae Hiroki
Fujitsu Limited
Gagliardi Albert
Katten Muchin Zavis & Rosenman
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