U.S. patent application number 10/863733 was filed with the patent office on 2005-12-08 for optically-augmented microwave imaging system and method.
Invention is credited to Baharav, Izhak, Rosner, S. Jeffrey, Taber, Robert C..
Application Number | 20050270223 10/863733 |
Document ID | / |
Family ID | 35229741 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050270223 |
Kind Code |
A1 |
Baharav, Izhak ; et
al. |
December 8, 2005 |
OPTICALLY-AUGMENTED MICROWAVE IMAGING SYSTEM AND METHOD
Abstract
An imaging system includes an optical (visible-light or near IR)
imaging system and a microwave imaging system. The optical imaging
system captures an optical image of the object, produces optical
image data representing the optical image and extracts optical
image information from the optical image data. The microwave
imaging system produces microwave image data representing a
microwave image of the object in response to the optical image
information.
Inventors: |
Baharav, Izhak; (Palo Alto,
CA) ; Taber, Robert C.; (Palo Alto, CA) ;
Rosner, S. Jeffrey; (Palo Alto, CA) |
Correspondence
Address: |
AGILENT TECHNOLOGIES, INC.
Legal Department, DL 429
Intellectual Property Administration
P.O. Box 7599
Loveland
CO
80537-0599
US
|
Family ID: |
35229741 |
Appl. No.: |
10/863733 |
Filed: |
June 8, 2004 |
Current U.S.
Class: |
342/52 ; 342/179;
342/22; 342/54 |
Current CPC
Class: |
G01S 13/89 20130101;
G01N 22/00 20130101; G01S 13/867 20130101 |
Class at
Publication: |
342/052 ;
342/054; 342/022; 342/179 |
International
Class: |
G01S 013/86 |
Claims
1. An imaging system, comprising: an optical imaging system
configured to capture an optical image of an object, to produce
optical image data representing the optical image and to extract
optical image information from the optical image data; and a
microwave imaging system operable to illuminate the object with
microwave radiation and to make microwave measurements in response
thereto, said microwave imaging system being configured to produce
microwave image data representing a microwave image of the object
in response to the optical image information and the microwave
measurements.
2. The imaging system of claim 1, wherein the microwave
measurements measure a characteristic of the response of the object
to the microwave radiation.
3. The imaging system of claim 1, wherein said microwave imaging
system is operable in response to the optical image information to
identify data points corresponding to spatial regions associated
with the object, said microwave imaging system being further
operable to solve for the identified data points using the
microwave measurements to produce the microwave image data.
4. The imaging system of claim 3, wherein said microwave imaging
system is operable to direct microwave radiation to the spatial
regions in response to the optical image information.
5. The imaging system of claim 3, wherein the spatial regions are
located at the perimeter of the object.
6. The imaging system of claim 3, wherein the spatial regions are
located within a boundary region including at least one side of the
object.
7. The imaging system of claim 3, wherein the spatial regions
enable said microwave imaging system to solve for the data points
in a volume occupied by the object.
8. The imaging system of claim 1, wherein said microwave imaging
system is operable to track motion of the object in response to the
optical image information.
9. The imaging system of claim 1, wherein said optical imaging
system comprises: a light source arranged to illuminate the object;
and a sensor for producing the optical image data in response to
light reflected by the object.
10. The imaging system of claim 1, wherein said microwave imaging
system comprises: a microwave node configured to direct microwave
radiation towards the object and receive reflected microwave
radiation from the object.
11-15. (canceled)
16. A method for imaging an object, the method comprising:
acquiring optical image data representing an optical image of an
object; extracting optical image information from the optical image
data; and producing microwave image data representing a microwave
image of the object in response to the optical image information
and microwave measurements taken responsive to illumination of the
object with microwave radiation.
17. The method of claim 16, wherein said producing further
comprises: using the optical image information to identify data
points corresponding to spatial regions associated with the object;
and solving for the identified data points using the microwave
measurements.
18. The method of claim 17, further comprising: directing the
microwave radiation to the spatial regions using the optical image
information.
19. The method of claim 16, wherein said producing further
comprises: tracking motion of the object in response to the optical
image information to produce the microwave image data.
20. The method of claim 16, wherein said acquiring further
comprises: illuminating the object with light; receiving light
reflected from the object; and producing the optical image data in
response to the reflected light.
21. The method of claim 16, wherein said producing further
comprises: illuminating the object with microwave radiation; and
receiving microwave radiation reflected by the object.
Description
BACKGROUND OF THE INVENTION
[0001] A typical microwave imaging system operates in the frequency
range of 1 GHz to 100 GHz, corresponding to wavelengths in
free-space of 30 cm to 0.33 cm. By comparison, optical or visible
light imaging systems operate in the frequency range of 750 THz to
430 THz, corresponding to wavelengths of 0.4 .mu.m to 0.7 .mu.m.
Though both are electromagnetic waves in nature, the different
wavelengths produce different imaging characteristics. For example,
microwave radiation is capable of penetrating objects that are
opaque to visible light. As a result, microwave imaging systems are
able to obtain measurements of the object beyond the external
layer.
[0002] Traditional microwave imaging systems rely on measuring the
microwave radiation from an object, and constructing an image of
the object based on the radiation measurements. The radiation
measurement is obtained using an antenna and adjacent receiver
circuitry. The antenna can be a single element antenna, or one that
is composed of an array of smaller sub-antenna elements. In
addition, the antenna and the receiver circuitry can operate in a
transmitting mode, a receiving mode or a combination of
transmitting and receiving modes.
[0003] The measured microwave radiation includes either one or both
of the amplitude and the phase of the wavefront scattered from the
object. The amplitude and/or phase measurements are processed to
construct an image of the object. For example, the sampled
wavefront can be constructed using a Fourier-based computer image
construction algorithm. An example of a Fourier-based computer
image construction algorithm is described in Fourier Array Imaging
by Mehrdad Soumekh (1994). However, the construction process is
often computationally intensive. In addition, in many instances,
the resulting constructed image suffers from poor resolution or
processing artifacts, such as speckles. Therefore, what is needed
is a microwave imaging system for constructing a high quality image
with reduced computational complexity.
SUMMARY OF THE INVENTION
[0004] Embodiments of the present invention provide an imaging
system including an optical (visible light or near IR) imaging
system and a microwave imaging system. The optical imaging system
is configured to capture an optical image of the object, produce
optical image data representing the optical image and extract
optical image information from the optical image data. The
microwave imaging system is operable to illuminate the object with
microwave radiation and to make microwave measurements in response
thereto. The microwave imaging system is configured to produce
microwave image data representing a microwave image of the object
in response to the optical image information and the microwave
measurements.
[0005] In one embodiment, the microwave imaging system is operable
to identify data points corresponding to spatial regions associated
with the object in response to the optical image information, and
solve for the identified data points using the microwave
measurements. In a further embodiment, the microwave imaging system
is operable to direct microwave illumination to the spatial regions
associated with the object. The spatial regions are identified
using the optical image information. In another embodiment, the
microwave imaging system is operable to track motion of the object
in response to the optical image information.
[0006] The optical imaging system uses a fast and simple algorithms
to extract the optical image information. The optical image
information can reduce the computational complexity of constructing
the microwave image and limit the microwave illumination to the
regions of interest on the object, thereby enabling improved
resolution and a reduction in artifacts of the microwave image.
Furthermore, the invention provides embodiments with other features
and advantages in addition to or in lieu of those discussed above.
Many of these features and advantages are apparent from the
description below with reference to the following drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The disclosed invention will be described with reference to
the accompanying drawings, which show important sample embodiments
of the invention and which are incorporated in the specification
hereof by reference, wherein:
[0008] FIG. 1 is a simplified representation of an exemplary
imaging system incorporating an optical (visible-light) imaging
system with a microwave imaging system, in accordance with
embodiments of the present invention;
[0009] FIG. 2 is a simplified representation of an exemplary
optical imaging system, in accordance with embodiments of the
present invention;
[0010] FIG. 3 is a simplified representation of an exemplary
microwave imaging system, in accordance with embodiments of the
present invention;
[0011] FIG. 4 is a block diagram of an image processing system for
augmenting a microwave imaging system with an optical imaging
system, in accordance with embodiments of the present
invention;
[0012] FIG. 5A illustrates a simplified prior art image
construction of a volume of an object;
[0013] FIG. 5B illustrates a simplified image construction of a
volume of an object, in accordance with one embodiment of the
present invention;
[0014] FIG. 6 illustrates a simplified construction of a perimeter
of an object, in accordance with another embodiment of the present
invention;
[0015] FIG. 7A illustrates a simplified prior art image
construction of a portion of a perimeter of an object;
[0016] FIG. 7B illustrates a simplified image construction of a
portion of a perimeter of an object, in accordance with another
embodiment of the present invention;
[0017] FIG. 8 is a flow chart illustrating an exemplary process for
determining a microwave image by augmenting a microwave imaging
system with an optical imaging system, in accordance with
embodiments of the present invention;
[0018] FIG. 9 is a flow chart illustrating an exemplary process for
constructing a microwave image using optical image information
provided by the optical imaging system, in accordance with one
embodiment of the present invention;
[0019] FIG. 10 is a flow chart illustrating an exemplary process
for directing microwave illumination to regions of interest on an
object using optical image information provided by the optical
imaging system, in accordance with another embodiment of the
present invention; and
[0020] FIG. 11 is a flow chart illustrating an exemplary process
for tracking motion of the object using optical image information
provided by the optical imaging system to construct a microwave
image of the object.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0021] FIG. 1 is a simplified representation of an exemplary
imaging system 10 in which a microwave imaging system 200 is
augmented with an optical imaging system 100. As used herein, the
term "microwave imaging system" refers to an imaging system
operating the microwave frequency range, and the resulting images
obtained by the microwave imaging system are referred to as
"microwave images." In addition, as used herein, the term "optical
imaging system" refers to an imaging system operating in the
visible light or near IR frequency range, and the resulting images
obtained by the optical imaging system are referred to as "optical
images" in order to differentiate these images from microwave
images obtained by the microwave imaging system.
[0022] The imaging system 10 can be used, for example, in airport
security systems for inspecting luggage or passengers, or any other
microwave imaging application. The optical imaging system 100
includes a light source 110 for illuminating an object 20 with
light 120 and a camera 140 for receiving reflected light 130 from
the object to capture an optical image of the object 20. The camera
140 includes one or more cameras 140 for capturing the optical
image. The microwave imaging system 200 includes microwave nodes
210 and 230 configured to emit microwave radiation 220 for
illuminating the object 20. Microwave nodes 210 and 230 are further
configured to receive reflected microwave radiation 225 from the
object to capture a microwave image of the object 20.
[0023] The optical imaging system 100 is shown in more detail in
FIG. 2. As described above, the light source 110 illuminates the
object 20 with light 120. The light source 110 can be any suitable
source of visible or near IR light. For example, the light source
110 can include one or more light emitting elements, such as one or
more point light sources, one or more collimated or structured
light sources, one or more arrays of light sources, or any other
combination of light sources suitable for use in the optical
imaging system 100. Reflected light 130 from the object 20 is
received by the camera 140. It should be understood that the camera
140 includes one or more cameras optimally positioned in the
optical imaging system 100. For each camera 140, the reflected
light 130 is directed by a lens 145 to a sensor 150 within the
camera 140. The sensor 140 includes a plurality of pixels 155 for
capturing the optical image of the object 20 and producing optical
image data 165 representing the optical image.
[0024] The optical imaging system 100 further includes a processor
160 for receiving the optical image data 165 representing the image
of the object 20 and processing the optical image data 165 to
extract optical image information 175 associated with the optical
image. The processor 160 can be a microprocessor, microcontroller,
programmable logic device or other type of processing device
capable of performing the functions described herein. In addition,
the processor 160 can include multiple processors or be a single
general-purpose processor capable of executing a number of
algorithms.
[0025] The optical image information 175 is used by the microwave
imaging system 200 (shown in FIG. 1) to produce microwave image
data representing the microwave image of the object 20. For
example, in one embodiment, the optical image information 175
identifies data points corresponding to spatial regions of interest
associated with the object 20. The identified data points
corresponding to the spatial regions of interest can be used to
direct microwave radiation to the spatial regions of interest or to
construct the microwave image using the microwave measurements
corresponding to the identified data points. In another embodiment,
the optical image information 175 is used to track motion of the
object 20 by correlating the microwave measurements with a position
of the object 20.
[0026] The optical image information 175 can be stored in a
computer-readable medium 170 for later processing by the microwave
imaging system and/or output directly to display 180. The
computer-readable medium 170 can be a memory device, such as random
access memory (RAM), read-only memory (ROM), flash memory, EEPROM,
disk drive, compact disk, floppy disk or tape drive, or any other
type of storage device. Additional processing information (not
shown) can also be stored on the computer-readable medium 170 and
accessed by the processor 160. For example, such processing
information can include various processing parameters, such as
algorithms that can be used to process the image data 165 and
extract the optical image information 175 from the image data
165.
[0027] The microwave imaging system 200 is shown in more detail in
FIG. 3. As described above in connection with FIG. 1, the microwave
nodes 210 and 230 illuminate the object 20 with microwave radiation
220 and receive reflected microwave radiation 225 from the object
20 to capture a microwave image of the object 20. Microwave nodes
210 and 220 each include a respective antenna array 215 and 235
having multiple antenna elements 216 and 235, respectively. Antenna
elements 216 and 236 direct microwave radiation 220 towards the
object 20 and receive reflected microwave radiation 225 from the
object 20.
[0028] It should be understood that one or more microwave nodes 210
and 220 can be used, depending on the type of microwave node 210
and 220 and the application. It should further be understood that
microwave nodes 210 and 220 can include any type of microwave
antenna, including point source antennas, unidirectional antennas
that receive microwave radiation from the object and bi-directional
antennas that both transmit microwave radiation 220 towards the
object 20 and receive reflected microwave radiation 225 from the
object 20. For example, the microwave nodes 210 and 230 can include
separate transmit and receive antennas, separate transmit and
receive antenna elements within the same antenna array, separate
transmit and receive antenna arrays or one or more antennas or
antenna elements capable of both transmitting and receiving
microwave radiation.
[0029] Antenna elements 216 and 236 are controlled by respective
transceivers 218 and 238. For example, transceivers 218 and 238
control the antenna elements 216 and 236, respectively, to direct
the microwave radiation 220 to regions of interest associated with
the object 20 (e.g., on or around the object). Transceivers 218 and
238 further monitor the received reflected microwave radiation 225,
measure the intensity and/or the phase of the reflected microwave
radiation 225 as a function of the direction of the received
microwave radiation 225 and record microwave measurements 245
corresponding to a characteristic of the response of the object 20
to the microwave radiation 220.
[0030] In one embodiment, the microwave measurements 245 include
amplitude and phase measurements of the wavefront scattered from
the object 20. The measurements 245 are transmitted to processor
240 which operates to construct a microwave image of the object 20
in response to the measurements 245. For example, the processor 240
can construct the microwave image using a Fourier-based
construction algorithm. The processor 240 can be a microprocessor,
microcontroller, programmable logic device or other type of
processing device capable of performing the functions described
herein. In addition, the processor 240 can include multiple
processors or be a single general-purpose processor capable of
executing a number of algorithms.
[0031] The measurements 245 are used by the processor 240 to
produce microwave image data 255 representing the microwave image
of the object 20. The microwave image data 255 can be stored in a
computer-readable medium 250 for later processing by the microwave
imaging system 200 and/or output directly to display 180. The
computer-readable medium 250 can be a memory device, such as random
access memory (RAM), read-only memory (ROM), flash memory, EEPROM,
disk drive, compact disk, floppy disk or tape drive, or any other
type of storage device. Additional processing information (not
shown) can also be stored on the computer-readable medium 250 and
accessed by the processor 240. For example, such processing
information can include various processing parameters, such as
algorithms that can be used to process the measurements 245 and
produce the microwave image data 255.
[0032] The processor 240 further receives the optical image
information 175 from the computer-readable medium 170 that stored
the optical image information 175 for the optical imaging system
100 (shown in FIG. 2). The computer-readable medium 170 can be the
same computer-readable medium 250 used by the microwave imaging
system 200 or a separate computer-readable medium. The processor
240 uses the optical image information 175 in producing the
microwave image data 255. For example, as discussed above, in one
embodiment, the optical image information 175 identifies data
points corresponding to spatial regions of interest associated with
the object 20. The processor 240 uses the optical image information
175 to control transceivers 218 and 238 to direct the microwave
radiation 220 to the spatial regions of interest or to construct
the microwave image using the measurements 245 corresponding to the
identified data points. In another embodiment, the processor 240
uses the optical image information 175 to track motion of the
object 20 by correlating the received microwave measurements 245
with a position of the object 20, as identified by the optical
image information 175.
[0033] FIG. 4 is a block diagram of an image processing system 400
in which a microwave imaging system is augmented with an optical
imaging system, in accordance with embodiments of the present
invention. The image processing system 400 includes optical image
processor 160 and microwave image processor 240. The optical image
processor 160 includes image processor 420 and extraction processor
430. In one embodiment, image processor 420 and extraction
processor 430 are ASICs or FPGA circuits configured to perform the
functions described below. In another embodiment, image processor
420 and extraction processor 430 are combined in a general-purpose
processor that executes algorithms to perform the functions
described below.
[0034] The optical image processor 160 receives from sensor 150
image data 165 representing an optical image. It should be
understood that if there are multiple cameras, each camera provides
a separate optical image to the optical image processor 160. In
addition, depending on the light source used, the optical image
processor 160 may further need to obtain information concerning the
illumination pattern of the light source.
[0035] The image data 165 is converted from analog to digital by
A/D converter 410 and passed to image processor 420 that processes
the digital image data 165. For example, if the sensor 150 is a
color sensor incorporating a color filter array, the image
processor 420 can demosaic the image. Demosaicing is a process by
which missing color values for each pixel location are interpolated
from neighboring pixels. There are a number of demosaicing methods
known in the art today. By way of example, but not limitation,
various demosaicing methods include pixel replication, bilinear
interpolation and median interpolation. Other types of processing
that the image processor 240 can perform include noise filtering
and image enhancement.
[0036] Extraction processor 430 is connected to receive the
processed image data from image processor 420, and operates to
extract the optical image information 175 from the processed image
data. There are a number of fast and simple known algorithms that
can be used to extract the optical image information 175 from the
image data 165. For example, in one embodiment, extraction
processor 430 extracts the 3D surface of an object using an image
construction algorithm for three-dimensional images. An example of
an image construction process for three-dimensional images is
described in co-pending and commonly assigned U.S. application for
patent, Ser. No. 10/392,758, in which an illumination gradient is
used to spatially vary the intensity and/or spectral
characteristics of the reflected illumination from the object in
order to determine surface gradients at spatial locations on the
surface of the object. The surface gradients are then used to
construct a three-dimensional image of the object. Other
three-dimensional image construction processes include laser
triangulation, stereoscopic imaging, structured light and
photometric stereo. For example, various three-dimensional image
construction processes are described in Horn et al., "Toward
Optimal Structured Light Patterns," IEEE Proceedings International
Conference on Recent Advances in 3-D Digital Imaging and Modeling,
Ottowa, Ontario, Canada, May 12-15, 1997, pp. 28-35 and Beraldin et
al., "Optimized Position Sensors for Flying-Spot Active
Triangulation System," IEEE Proceedings International Conference on
Recent Advances in 3-D Digital Imaging and Modeling, Banff,
Albertta, Canada, Oct. 6-10, 2003, pp. 29-36.
[0037] In another embodiment, extraction processor 430 extracts
features of the object 20 that are of interest. It should be
understood that as used herein, the phrase "features of the object"
includes measurements of the object 20, components on a surface of
or within the object 20 or other indicia of the object 20. In
further embodiments, extraction processor 430 extracts any other
information from the image data 165 that is desired.
[0038] The optical image information 175 is output by the
extraction processor 430 to the microwave processor 240 for use in
constructing the microwave image. The optical image information 175
is also transmitted from the extraction processor 430 to the
display 180.
[0039] Microwave processor 240 includes transceiver logic 440, A/D
converter 450 and image construction processor 460. In one
embodiment, transceiver logic 440 and image construction processor
460 are ASICs or FPGA circuits configured to perform the functions
described below. In another embodiment, transceiver logic 440 and
image construction processor 460 are combined in a general-purpose
processor that executes algorithms to perform the functions
described below.
[0040] The transceiver logic 440 receives microwave measurements
245 including amplitude and phase measurements of the scattered
wavefront from a receive microwave node (e.g., node 210). It should
be understood that the receive microwave node 210 can include a
single antenna, an entire antenna array or one or more antenna
elements within one or more antenna arrays. The microwave
measurements 165 are converted from analog to digital by A/D
converter 450 and passed to image construction processor 460 to
construct a microwave image of the object. The image construction
processor 460 produces microwave image data 255 representing the
microwave image of the object and transmits the microwave image
data 255 to the display 180.
[0041] The optical image information 175 output by the extraction
processor 430 is received at either one or both of the transceiver
logic 440 and the image construction processor 460. In one
embodiment, the optical image information 175 identifies data
points corresponding to spatial regions of interest associated with
the object 20. In one implementation embodiment, the transceiver
logic 440 uses the optical image information 175 to provide
transmit instructions 470 to the transmit microwave node (e.g.,
microwave node 230) to direct the microwave radiation 220 to the
spatial regions (or regions) of interest. It should be understood
that the transmit microwave node 230 can include a single antenna,
an entire antenna array or one or more antenna elements within one
or more antenna arrays. In another implementation embodiment, the
image construction processor 460 uses the optical image information
175 to construct the microwave image using the measurements 245
corresponding to the identified data points.
[0042] For example, a conventional microwave image construction
process is described in David M. Sheen et al., "Three-dimensional
Millimeter-Wave Imaging for Concealed Weapon Detection," IEEE Tran.
On Microwave Theory and Techniques (MTT), Vol. 49 (9): 1581-1592,
September 2001 (hereinafter "Sheen"). In the Sheen paper, the whole
volume (x,y,z) is discretely sampled in the solution. A 3D inverse
Fourier transform is done on the whole volume, which introduces a
significant computational load and possible inaccuracies that can
manifest themselves as noise. With the optical image information
175, the actual volume occupied by the object being interrogated
can be identified to determine what data points in the volume
really need to be solved for. Thus, in the discrete-sampling of the
space, only relevant data points need to be addressed. Depending on
the maximum allowed volume to analyze, and the minimum that can be
encountered, the computational load can be significantly
reduced.
[0043] As an example, if the object is 1 m (width).times.2 m
(long).times.1 m (deep), the volume of the object is
1.times.1.times.2=2 m.sup.3. However, since the orientation is
typically not known, a volume of 1.4.times.1.4.times.2=4 m.sup.3
may need to be solved for in a conventional microwave image
construction.
[0044] By using the optical image information 175 to determine the
actual volume occupied by the object, the image construction
processor 460 only needs to solve for the actual volume, which
represents a large saving in computation time. This saving in
complexity can be translated into one or more of: (1) faster
computation, (2) fewer measurements by the system (e.g., fewer
frequencies used or fewer antennas/receivers), and (3) better
accuracy or rejection of aliasing "images" of the object that fall
outside of the properly-defined region of interest. Additionally,
the optical image information 175 can provide knowledge about the
shadows induced by the object 20. Determining which data points are
shadowed will produce a "cleaner" solution with reduced artifacts
in the microwave image and/or a faster solution.
[0045] In another embodiment, the optical image information 175
includes 3D object position information that is used by the image
construction processor 240 to determine the location of the object
in three dimensions while in motion by correlating the received
microwave measurements 245 with the optical image information 175.
The optical processor 160 can correlate every point at a given time
with the corresponding point at a previous time through the use of
conventional visible-light tracking algorithms. This enables the
microwave processor 240 to solve for the microwave image data 255,
even when the object has moved. Examples of tracking algorithms are
described in Shirai, "Estimation of 3-D Pose and Shape from a
Monocular Image Sequence and Real-Time Human Tracking," IEEE
Proceedings International Conference on Recent Advances in 3-D
Digital Imaging and Modeling, Ottowa, Ontario, Canada, May 12-15,
1997, pp. 130-139, and Mecke et al., "3-D Motion and Shape from
Multiple Image Sequences," IEEE Proceedings International
Conference on Recent Advances in 3-D Digital Imaging and Modeling,
Banff, Alberta, Canada, Oct. 6-10, 2003, pp. 155-162.
[0046] FIGS. 5A and 5B illustrate a simplified image construction
of a volume of an object 20. FIG. 5A represents a conventional
image construction, while FIG. 5B represents an image construction
in accordance with one embodiment of the present invention. FIGS.
5A and 5B both illustrate a two-dimensional example that can be
readily applied to three dimensions.
[0047] In FIG. 5A, a grid 500 made up of multiple data points 550
is used to solve for the whole area. Since the orientation/location
of the object 20 in space is unknown, the grid must accommodate all
variations. Therefore, in FIG. 5A, each of the data points 550 in
the grid 500 is solved for. By contrast, as shown in FIG. 5B, when
the location of the object 20 is known (at least approximately),
only a subset 560 of the data points 550a needs to be solved
for.
[0048] FIG. 6 illustrates a simplified construction of the
perimeter of an object 20, in accordance with another embodiment of
the present invention. FIG. 6 also illustrates a two-dimensional
example that can be readily applied to three dimensions. FIG. 6
uses the same grid 500 shown in FIG. 5A. However, in FIG. 6, only
the data points 550b corresponding to a perimeter 600 of the object
20 are solved for. The perimeter 600 is identified from the optical
image information. With certain kinds of objects (e.g., people with
loose clothing), the perimeter 600 can include data points within a
"deep" shell around the object perimeter, as shown in FIG. 6. In a
further embodiment, rather than solving for the whole perimeter,
techniques similar to beam-forming can be used to direct microwave
radiation to only specific data points in question. The specific
data points are identified using the optical image information.
[0049] FIGS. 7A and 7B illustrate a simplified image construction
of a portion of a perimeter of an object 20. FIG. 7A represents a
conventional image construction, while FIG. 7B represents an image
construction in accordance with another embodiment of the present
invention. The advantages of the above perimeter method are
amplified by the fact the human body is a very good reflector in
the microwave frequency range. Thus, for example, in FIGS. 7A and
7B, the ellipse represents a cross section of a human body (object
20), and the triangles represent the imaging system 10.
Traditionally, the whole volume would be solved for, even though
due to the reflectivity of the body, only the portion of the body
facing imaging system 10 is imaged. In accordance with embodiments
of the present invention, using the microwave imaging system
augmented with an optical imaging system, a boundary region 700
including data points 550c corresponding to a portion of a
perimeter of the human body is identified using the optical image
information. The microwave imaging system then directs microwave
radiation to and solves only for the data points 550c in the
boundary region 700.
[0050] FIG. 8 is a flow chart illustrating an exemplary process 800
for producing microwave image data representing a microwave image
using an optically-augmented microwave imaging system, in
accordance with embodiments of the present invention. The process
begins at block 810. At block 820, an optical image of the object
is acquired by the optical imaging system. At block 830, optical
image information is extracted from the optical image data
representing the optical image, and at block 840, the optical image
information is provided to the microwave imaging system. At block
850, the microwave imaging system produces microwave image data
representing the microwave image in response to the optical image
information and microwave measurements made by the microwave
imaging system. The process ends at block 860.
[0051] FIG. 9 is a flow chart illustrating an exemplary process 900
for constructing a microwave image in response to optical image
information provided by the optical imaging system, in accordance
with one embodiment of the present invention. The process begins at
block 910. At block 920, an optical image of the object is captured
by the optical imaging system. At block 930, optical image data
representing the optical image is processed to extract optical
image information. At block 940, microwave measurements
corresponding to various characteristics of the response of the
object to microwave radiation are acquired by the microwave imaging
system. At block 950, the microwave imaging system produces
microwave image data representing the microwave image of the object
in response to the optical image information and the microwave
measurements. The process ends at block 960.
[0052] FIG. 10 is a flow chart illustrating an exemplary process
1000 for directing microwave illumination to regions of interest on
an object in response to optical image information provided by the
optical imaging system, in accordance with another embodiment of
the present invention. The process begins at block 1010. At block
1020, an optical image of the object is captured by the optical
imaging system. At block 1030, optical image data representing the
optical image is processed to extract optical image information. At
block 1040, spatial regions (e.g., regions of interest) associated
with the object are identified using the optical image information.
At block 1050, the identified spatial regions or regions of
interest are illuminated with microwave radiation, and at block
1060, microwave measurements corresponding to various
characteristics of the response of the object to the microwave
radiation are acquired by the microwave imaging system. At block
1070, the microwave imaging system constructs the microwave image
of the object from the microwave measurements by producing
microwave image data representing the microwave image. The process
ends at block 1080.
[0053] FIG. 11 is a flow chart illustrating an exemplary process
1100 for tracking motion of the object using optical image
information provided by the optical imaging system to construct a
microwave image of the object. The process begins at block 1110. At
block 1120, the microwave imaging system begins to acquire
microwave measurements corresponding to various characteristics of
the response of the object to microwave radiation. At block 1130,
an optical image of the object is captured by the optical imaging
system. At block 1140, optical image data representing the optical
image is processed to extract optical image information. At block
1150, the optical image information is used to determine the
location of the object and the spatial regions on the object that
were illuminated by microwave radiation. At block 1160, a
determination is made whether the microwave measurement acquisition
process is complete. If not, an additional optical image of the
object is captured at block 1130 and is processed in blocks
1140-1150 to determine a new location of the object that is
correlated with the microwave measurements. If the microwave
acquisition process is complete, at block 1170, the microwave
imaging system constructs the microwave image of the object in
response to the optical image information and the microwave
measurements. The process ends at block 1180.
[0054] The innovative concepts described in the present application
can be modified and varied over a wide rage of applications.
Accordingly, the scope of patents subject matter should not be
limited to any of the specific exemplary teachings discussed, but
is instead defined by the following claims.
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