U.S. patent application number 10/725542 was filed with the patent office on 2004-06-17 for system and method for capturing print information using a coordinate conversion method.
This patent application is currently assigned to Cross Match Technologies, Inc.. Invention is credited to Cannon, Greg L., Carver, John F., McClurg, George W..
Application Number | 20040114786 10/725542 |
Document ID | / |
Family ID | 32512324 |
Filed Date | 2004-06-17 |
United States Patent
Application |
20040114786 |
Kind Code |
A1 |
Cannon, Greg L. ; et
al. |
June 17, 2004 |
System and method for capturing print information using a
coordinate conversion method
Abstract
A system and method is provided for converting biometric image
data captured in a first coordinate system into biometric image
data in a second coordinate system (e.g., from polar to
rectangular). The system includes a receiving module for receiving
raw image data captured in a first coordinate system, a coordinate
conversion module, and a memory. The conversion system can be
implemented in a biometric imaging system or in a system external
to a biometric imaging system. After raw image data captured in a
first coordinate system has been received, for each pixel in a
defined output area, the coordinate conversion module retrieves an
entry in a conversion data array and one or more samples from the
captured raw image data. The coordinate conversion module then
interpolates the retrieved samples using weighting based on the
conversion data array entry to obtain the respective pixel value in
the second coordinate system.
Inventors: |
Cannon, Greg L.; (Boynton
Beach, FL) ; McClurg, George W.; (Jensen Beach,
FL) ; Carver, John F.; (Palm City, FL) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX PLLC
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
Cross Match Technologies,
Inc.
|
Family ID: |
32512324 |
Appl. No.: |
10/725542 |
Filed: |
December 3, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60431240 |
Dec 6, 2002 |
|
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|
60491537 |
Aug 1, 2003 |
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Current U.S.
Class: |
382/127 |
Current CPC
Class: |
G06V 40/13 20220101;
G06V 40/1324 20220101 |
Class at
Publication: |
382/127 |
International
Class: |
G06K 009/00 |
Claims
What is claimed is:
1. A system for processing image data representing biometric data,
comprising: a receiving module for receiving image data captured in
a first coordinate system; and a coordinate conversion module
coupled to the receiving module for converting the image data
captured in the first coordinate system to converted image data in
a second coordinate system.
2. The system of claim 1 further comprising a memory coupled to the
coordinate conversion module.
3. The system of claim 1 wherein the second coordinate system is a
rectangular coordinate system.
4. The system of claim 2 wherein the first coordinate system is a
polar coordinate system.
5. The system of claim 1 further comprising a scanning and
capturing system coupled to the receiving module wherein the
scanning and capturing system comprises: a non-planar prism; and a
scanning imaging system optically coupled to the non-planar prism
for capturing image data in a first coordinate system and for
communicating the image data to the receiving module.
6. The system of claim 4 wherein the scanning and capturing system
is coupled to the receiving module via a data network.
7. The system of claim 5 wherein the second coordinate system is a
rectangular coordinate system.
8. The system of claim 7 wherein the first coordinate system is a
polar coordinate system.
9. A system for processing image data representing biometric data,
comprising: a non-planar prism; a scanning imaging system optically
coupled to the non-planar prism for capturing the image data in a
first coordinate system; and an image conversion system coupled to
the scanning imaging system for converting the image data captured
in the first coordinate system to converted image data in a second
coordinate system.
10. The system of claim 9 wherein the image conversion system
includes: a receiving module for receiving image data captured in a
first coordinate system; and a coordinate conversion module coupled
to the receiving module for converting the image data captured in
the first coordinate system to converted image data in a second
coordinate system.
11. The system of claim 10 wherein the image conversion system
further comprises a memory coupled to the coordinate conversion
module.
12. The system of claim 11 wherein the second coordinate system is
a rectangular coordinate system.
13. The system of claim 12 wherein the first coordinate system is a
polar coordinate system.
14. The system of claim 11 wherein the non-planar prism is a
conical prism.
15. A system for processing image data representing biometric data,
comprising: a biometric imaging system comprising: a non-planar
prism, an scanning imaging system optically coupled to the
non-planar prism for capturing the image data in a first coordinate
system, and a first image conversion system coupled to the scanning
imaging system for generating and storing conversion data; and a
second image conversion system coupled to the biometric imaging
system for converting the image data captured in the first
coordinate system to converted image data in a second coordinate
system.
16. The system of claim 15 wherein the first image conversion
system includes: a receiving module for receiving image data
captured in a first coordinate system; and a coordinate conversion
module coupled to the receiving module for converting the image
data captured in the first coordinate system to converted image
data in a second coordinate system.
17. The system of claim 16 wherein the second image conversion
system includes: a receiving module for receiving image data
captured in a first coordinate system; and a coordinate conversion
module coupled to the receiving module for converting the image
data captured in the first coordinate system to converted image
data in a second coordinate system.
18. The system of claim 15 wherein the second coordinate system is
a rectangular coordinate system.
19. The system of claim 18 wherein the first coordinate system is a
polar coordinate system.
20. A system for processing image data representing biometric data,
comprising: means for converting image data captured in a first
coordinate system to converted image data in a second coordinate
system.
21. The system of claim 20 wherein the second coordinate system is
a rectangular coordinate system.
22. The system of claim 21 wherein the first coordinate system is a
polar coordinate system.
23. A method for processing image data representing biometric data
comprising: receiving the image data captured in a first coordinate
system and storing the captured image data; and converting the
captured image data in the first coordinate system to converted
image data in a second coordinate system.
24. The method of claim 23, wherein the converting comprises using
a rectangular coordinate system as the second coordinate
system.
25. The method of claim 24, wherein the first coordinate system is
a polar coordinate system.
26. The method of claim 23, further comprising: generating and
storing a conversion data array including coordinate and offset
data.
27. The method of claim 23, further comprising: prior to receiving
captured image data, receiving criteria associated with
specifications for processing the captured image data; and
generating and storing at least conversion data array corresponding
to the received criteria.
28. The method of claim 27 further comprising generating and
storing at least one conversion parameter corresponding to the
received criteria.
29. The method of claim 27 wherein one of the at least one
conversion parameter includes a parameter indicating the
interpolation method.
30. The method of claim 27 wherein each of the at least one
conversion data array is generated dynamically.
31. The method of claim 23, wherein said converting comprises: for
each pixel in an output rectangular area, the steps of: performing
a look up to obtain conversion data including the coordinate data
and the offset data associated with respective pixel coordinates;
retrieving at least one sample of stored captured image data; and
interpolating each retrieved sample with weighting based on the
looked up offset data to obtain a respective pixel value in the
second coordinate system.
32. A method for processing image data representing biometric data
in a system having a scanning and capturing system and an image
conversion system, comprising: generating and storing conversion
data in the image conversion system; capturing in the scanning and
capturing system the image data in a first coordinate system;
communicating the captured first coordinate system image data to
the image conversion system; and converting the captured first
coordinate system image data to converted image data in a second
coordinate system.
33. The method of claim 32, wherein the capturing comprises using a
polar coordinate system as the first coordinate system.
34. The method of claim 33, wherein the converting comprises using
a rectangular coordinate system as the second coordinate
system.
35. The method of claim 32, wherein said converting comprises: for
each pixel in an output rectangular area, the steps of: performing
a look up in a conversion data array to obtain conversion data
including the coordinate data and the offset data associated with
respective pixel coordinates; retrieving at least one sample of
stored captured image data; and interpolating each retrieved sample
with weighting based on the looked up offset data to obtain a
respective pixel value in the second coordinate system.
36. The method of claim 35 wherein the step of interpolating each
retrieved sample includes calculating the weighting.
37. The method of claim 35 wherein the step of interpolating each
retrieved sample includes performing a look up to determine the
weighting.
38. A method for processing image data representing biometric data
comprising: capturing the image data in a first coordinate system;
and converting the captured image data in the first coordinate
system to converted image data in a second coordinate system.
39. The method of claim 38, wherein the capturing comprises using a
polar coordinate system as the first coordinate system.
40. The method of claim 38, wherein the converting comprises using
a rectangular coordinate system as the second coordinate
system.
41. The method of claim 40, further comprising: generating and
storing conversion data including polar coordinate and polar offset
data.
42. The method of claim 41, wherein said converting comprises: for
each pixel in an output rectangular area, the steps of: performing
a look up to obtain conversion data including the polar coordinate
data and the offset data associated with respective pixel
coordinates; retrieving at least one sample of stored polar space
image data; and interpolating each retrieved sample with weighting
based on the looked up polar offset data to obtain a respective
pixel value in rectangular image space.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/431,240, filed Dec. 6, 2002 and U.S. Provisional
Application No. 60/491,537, filed Aug. 1, 2003, both of which are
incorporated herein by reference in their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention pertains to biometric imaging
technology, and in particular, to live scanning of prints.
[0004] 2. Background
[0005] Law enforcement, banking, voting, and other industries are
increasingly relying upon biometric data for security and identity
recognition. This increased reliance has created a demand for
highly reliable, efficient biometric imaging systems. In addition,
in order to perform further processing operations on captured
images, these groups require the captured image data to be in a
particular format. In post-processing applications, this format is
a rectangular coordinate system format.
[0006] Biometric imaging systems may include, but are not limited
to, print imaging systems. Such print imaging systems are also
referred to as scanners or live scanners. In conventional biometric
imaging systems, an object such as a hand or finger is placed on
the outer surface of a platen. The platen surface can be a surface
of a prism or another surface in optical contact with an outside
surface of a prism. For example, a platen surface can be a surface
of an optical protective layer (e.g., silicon pad) placed on a
prism. To produce raw image data representing the biometric print
data, an illumination source illuminates the underside of the
object. Raw image data representative of valleys, ridges, and other
minutiae of a print are then captured.
[0007] Conventional live scanners capture raw image data in a
rectangular coordinate system format. Thus, both conventional
capture and post-processing applications use the same rectangular
coordinate system format appropriate for the planar surfaces of a
conventional prism and camera.
BRIEF SUMMARY OF THE INVENTION
[0008] The present invention provides an image conversion system
that can process raw image data captured in a first coordinate
system format and convert the raw image data into a second
coordinate system format acceptable by downstream processing
systems. In an embodiment, the present invention can convert image
data captured in a scan of a non-planar platen surface such as a
curved conical prism surface to image data associated with an
approximately planar surface of a camera.
[0009] The inventors recognized that the use of a single
rectangular coordinate system for capture and in post-processing
applications limits implementation options for prisms and capturing
systems in the biometric imaging system. When a live scanner has a
prism that is non-planar, use of a single rectangular coordinate
system to capture the raw image data results in distorted or lost
information. As a result, the captured raw image becomes less
accurate and may introduce significant errors into post-processing
operations.
[0010] The present invention is directed to a system and method for
converting captured image data in a first coordinate system format
to a second coordinate system format. In accordance with
embodiments of the present invention, the image conversion system
includes a receiving module, a coordinate conversion module, and a
memory. The image conversion system can be implemented in a
biometric imaging system or as a system external to a biometric
imaging system.
[0011] In an embodiment of the invention, the coordinate conversion
module calibrates the image conversion system by generating a
conversion data array. The conversion data array maps each pixel in
a second coordinate system output area to a position in the first
coordinate system. After calibration, the receiving module of the
image conversion system receives captured image data in a first
coordinate system format from a biometric imaging system and stores
the captured image data in memory. For each pixel in the second
coordinate system output area, the coordinate conversion module
retrieves an entry in the conversion data array and one or more
samples from the captured raw image data. The coordinate conversion
module then interpolates the retrieved samples using weighting
based on the retrieved conversion data array entry to obtain the
respective pixel value in the second coordinate system.
[0012] Further embodiments, features, and advantages of the present
inventions, as well as the structure and operation of the various
embodiments of the present invention, are described in detail below
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0013] The accompanying drawings, which are incorporated herein and
form a part of the specification, illustrate the present invention
and, together with the description, further serve to explain the
principles of the invention and to enable a person skilled in the
pertinent art to make and use the invention.
[0014] FIG. 1 shows an image conversion system for converting image
data captured in a first coordinate system format to a second
coordinate system format in accordance with an embodiment of the
present invention.
[0015] FIG. 2 shows a system incorporating an image conversion
system in accordance with an embodiment of the present
invention.
[0016] FIG. 3 shows a view of a non-planar prism in accordance with
an embodiment of the present invention.
[0017] FIG. 4 shows a flowchart depicting a method for converting
captured image data in a first coordinate system to an image data
in a second coordinate system.
[0018] FIG. 4A illustrates how a subject places a hand on a
non-planar prism in accordance with various embodiments of the
present invention.
[0019] FIG. 4B shows a position for an illumination source in
accordance with various embodiments of the present invention.
[0020] FIG. 4C is a diagram that illustrates radial scan line
images captured along an arcuate scan path and stored in an
array.
[0021] FIG. 5 shows a flowchart depicting a calibration method.
[0022] FIGS. 5A-B are diagrams that illustrate a conversion data
array and the relationships between coordinates in polar and
rectangular coordinate systems.
[0023] FIG. 6 shows a flowchart depicting a method for converting
captured image data in a first coordinate system to an image data
in a second coordinate system using system calibration data.
[0024] FIGS. 7 and 8 illustrate the relationship between points on
a conical platen surface and corresponding points when the conical
platen surface is lifted and flattened to a rectangular coordinate
space.
[0025] FIG. 9 shows a system incorporating an image conversion
system in accordance with an alternate embodiment of the present
invention.
[0026] FIG. 10 shows a system incorporating an image conversion
system in accordance with an alternate embodiment of the present
invention.
[0027] The present invention will now be described with reference
to the accompanying drawings. In the drawings, like reference
numbers can indicate identical or functionally similar elements.
Additionally, the left-most digit(s) of a reference number may
identify the drawing in which the reference number first
appears.
DETAILED DESCRIPTION OF THE INVENTION
[0028] FIG. 1 is a block diagram of an image conversion system 150
for converting the raw image data captured in a first coordinate
system format into a second coordinate system format in accordance
with an embodiment of the present invention. In an embodiment,
image conversion system 150 is implemented in software. Persons
skilled in the relevant art(s) will appreciate that functions of
image conversion system 150 can be implemented in hardware,
firmware, or a combination of software and hardware/firmware.
[0029] Image conversion system 150 includes a receiving module 152,
a coordinate conversion module 154, and a memory 156. Receiving
module 152 is configured to receive captured image data in a first
coordinate system format from a live print scanner. The first
coordinate system used in capturing the raw image data depends upon
the geometry of a prism implemented in the live scanner. For
example, in a live scanner having a conical prism, the first
coordinate system is a polar coordinate system. The polar
coordinate system describes a point in terms of its angle, .theta.,
and distance (i.e., radius, r) from a fixed origin. Thus, the polar
coordinate system is ideal for describing non-planar surfaces such
as cones. In an embodiment, the polar coordinate system defines the
conical platen surface associated with a conical prism.
[0030] Coordinate conversion module 154 is coupled to the receiving
module 152 and to memory 156. Coordinate conversion module 154
contains logic to calibrate the image conversion system 150 and
logic to convert captured first coordinate system image data to a
second coordinate system format. The second coordinate system used
in converting the captured data depends upon the format required by
downstream processing systems. In an embodiment of the present
invention, the second coordinate system is a rectangular coordinate
system. In the case of a conical prism, coordinate conversion
module 154 converts image data captured in a polar coordinate
system format to a rectangular system format. This conversion is
described in further detail with respect to FIGS. 4-8.
[0031] FIG. 1 depicts a separate memory 156 coupled to coordinate
conversion module 154 and receiving module 152. In an alternative
embodiment, memory 156 could be integrated in coordinate conversion
module 154. However, the invention is not limited to these
configurations. Other configurations for memory 156 are possible as
would be appreciated by a person skilled in the relevant
art(s).
[0032] FIG. 2 shows a block diagram of a live scanner 200 having an
internal image conversion system 150 in accordance with an
embodiment of the present invention. Live scanner 200 includes a
non-planar prism 220 optically coupled between an illumination
source 215 and an electro-optical system 225 and an image
conversion system 150 coupled to the electro-optical system. In an
embodiment, live scanner 200 also includes a display processing
module 280 coupled to the image conversion system 150 and/or the
electro-optical system 225.
[0033] Live scanner 200 captures biometric data from objects
interacting with non-planar prism 220 and communicates the captured
raw image data to image conversion system 150. An exemplary
electro-optical system 225 is described in co-pending U.S. Patent
Application entitled, "Rotating Optical System Used in a System for
Obtaining Print and Other Hand Characteristic Information Having a
Non-Planar Prism," Serial No. (to be assigned), Attorney Docket No.
1823.0820004, by McClurg et al., filed concurrently herewith and
incorporated in its entirety herein by reference.
[0034] FIG. 3 depicts a cross-sectional view of an exemplary
non-planar prism 320 in accordance with an embodiment of the
present invention. Non-planar prism 320 has an opening 322 running
along an axis of symmetry 324. Opening 322 is defined within an
area 326 of non-planar prism 320 that has a non-planar first
section 328 and a substantially planar second section 332. A first
surface 336 of first section 328 is shaped so as to provide the
non-planar aspect to prism 320. The non-planar shape is preferably
approximately conical, but can also be curved, spherical, or the
like, so long as a second surface 334 provides total internal
reflection of incident beam.
[0035] Exemplary live scanners having non-planar prisms are
described in co-pending U.S. Patent Application entitled, "System
for Obtaining Print and Other Hand Characteristics Using A
Non-Planar Prism," Serial No. (to be assigned), Attorney Docket No.
1823.0820002, by McClurg et al., filed concurrently herewith and
incorporated herein by reference in its entirety, co-pending U.S.
Patent Application entitled, "Non-planar Prism Used in a System for
Obtaining Print and Other Hand Characteristic Information," Serial
No. (to be assigned), Attorney Docket No. 1823.0820003, by McClurg
et al., filed concurrently herewith and incorporated herein by
reference in its entirety, and co-pending U.S. Patent Application
entitled, "System Having A Rotating Optical System And A Non-Planar
Prism That Are Used To Obtain Print And Other Hand Characteristic
Information," Serial No. (to be assigned), Attorney Docket No.
1823.0820004, by McClurg et al., filed concurrently herewith and
incorporated herein by reference in its entirety.
[0036] Display processing module 280 is configured to communicate
information concerning the status of the image scanning and
capturing process to one or more output devices. For example,
display processing module 280 may generate a preview display of the
captured image data at or near real-time as radial scan lines are
being captured. Display processing module 280 may also activate
LEDs or audio devices in an output device to indicate a scan is in
process or other status information. An exemplary method of
generating a preview display is described in co-pending U.S. Patent
Application entitled, "Method of Generating a Preview Display in an
Hand Print Capturing System Using a Non-Planar Prism," Serial No.
(to be assigned), Attorney Docket No. 1823.082000A, by McClurg et
al., filed concurrently herewith and incorporated in its entirety
herein by reference
[0037] FIG. 4 depicts a flowchart of a method 400 for converting
image data captured in a first coordinate system format to a second
coordinate system format in accordance with the present invention.
The flowchart 400 will be described with continued reference to the
example image conversion system 150 described in reference to FIGS.
1 and 2, above. However, the invention is not limited to that
embodiment.
[0038] Method 400 includes a calibration (or pre-processing)
process 410 and a run-time process 420. Calibration process 410 can
be carried out anytime prior to run-time. Calibration process 410
involves the calibration of arrays, tables, and parameters used by
the image conversion system 150 for conversion processing (step
430). Step 430 is described in further detail below with respect to
FIG. 5.
[0039] Run-time process 420 is initiated when the image conversion
system 150 receives raw first coordinate system image data from a
live scanner (step 440). In step 445, the raw first coordinate
system image data are stored in memory 156.
[0040] Prior to the start of run-time process 420, a scan is
initiated in a live scanner (step 425). The scan can begin
automatically or manually (e.g., in response to a user selection at
a user interface to initiate a scan). During the scan, the
electro-optical system 225 captures image data from a platen
surface scanning area. The captured image data can include raw
image data representative of a print pattern from which biometric
data (such as finger minutiae, ridge data, and/or other finger and
hand characteristic information) can be extracted. This image data
is communicated to the image conversion system internally or via a
data network.
[0041] FIGS. 4A-C illustrate the scanning and capturing process in
a live scanner having an exemplary conical platen surface in
accordance with an embodiment of the present invention. FIG. 4A
illustrates the placement of a subject's hand on a conical platen
surface during the scan. FIG. 4B shows a cross-sectional view of a
portion of the live scanner performing the scan. In this
embodiment, illumination source 215 is positioned in opening 322 of
non-planar prism 320. Based on the reflection angle of a beam from
illumination source 215 off the second surface 334, the
electro-optical system 225 captures pixel images. Electro-optical
system 225 can rotate about axis 324 (e.g., axis of rotation) to
capture images from surface 336.
[0042] FIG. 4C illustrates a scan of a print pattern placed on the
conical platen surface depicted in FIGS. 4A and B. As shown in the
example diagram in FIG. 4C, a linear camera 227 having a length
between a radius r.sub.initial and r.sub.final moves from an
initial angular position .sigma..sub.initial along an arcuate path
y to a final angular position .sigma..sub.final. In this way, the
linear camera 227 sweeps out a path in polar space over an area
between angular positions .sigma..sub.initial and .sigma..sub.final
and radial positions r.sub.initial and r.sub.final.
[0043] As the linear camera scans, radial scan lines of image data
(referred to herein as polar space raw image data) are successively
captured and communicated to the receiving module 152 of the image
conversion system 150. The received polar coordinate system raw
image data are stored in memory 156 (step 445). The stored polar
system raw image data are shown schematically as an array of radial
scan line images 428 in FIG. 4C. In practice, because of the
conical platen surface, image data is captured and stored at a
higher resolution (e.g., a greater dpi) in the scanning area near
the top of the conical platen surface that is, closer to radial
position r.sub.initial, compared to the scanning area near the base
of the conical area, that is, closer to radial position
r.sub.final. The capture and storing of radial scan line image data
proceeds until the linear camera has swept a desired scanning
path.
[0044] The process of performing a scan in a live scanner having a
non-planar prism is described in co-pending U.S. Patent Application
entitled, "Methods For Obtaining Print And Other Hand
Characteristic Information Using A Non-Planar Prism," Serial No.
(to be assigned), Attorney Docket No. 1823.0820007, by McClurg et
al., filed concurrently herewith and incorporated in its entirety
herein by reference.
[0045] Returning to FIG. 4, in step 450, the coordinate conversion
module 154 converts the stored raw first coordinate image data to
second coordinate image data using the conversion data generated in
step 430. In an embodiment of the present invention, conversion
step 450 is not initiated until the scan is completed and all the
captured image data has been received by the image conversion
system 150. In an alternate embodiment, conversion step 450 begins
after sufficient captured image data to perform conversion has been
received. In this embodiment, the conversion step occurs in
parallel with the scan. Step 450 is described in further detail
below with respect to FIG. 6.
[0046] After the conversion process is completed, the conversion
coordinate module 154 stores the converted second coordinate system
image data in memory 156. Other optional image processing
operations such as filtering can be performed on the converted
second coordinate system image data prior to step 460 or after
storage. Second coordinate system image data can then be output for
display or further processing by downstream applications (step
470). Examples of further processing operations are extract and
match, store and forward, or other print processing or image
processing operations. Run-time process 420 is repeated for each
scan performed in an associated biometric imaging system.
[0047] In an embodiment of the present invention, after step 470,
the display processing module 280 generates a preview display of
the converted image. In this embodiment, the display processing
module 280 determines a representative pixel value for pixels in a
group of (x,y) coordinates using a decimation technique. For
example, the processing module may select every n.sup.th pixel as
the representative pixel value for that group. Alternatively, the
processing module may select a pixel at random. The representative
pixel values are then plotted at a corresponding output device and
displayed in a display window. In this way, a preview display can
be provided quickly. In an alternate embodiment, the representative
pixel values can be generated prior to step 470, during the
conversion process.
[0048] FIG. 5 depicts a flowchart of calibration (or
pre-processing) process 410. In step 512, the conversion coordinate
module 154 generates the conversion data. In an embodiment, the
coordinate conversion module 154 generates one or more conversion
data arrays in step 512. Each conversion data array contains data
necessary for converting captured first coordinate system image
data to a second coordinate system format. Generation step 512
includes creating an array entry for each pixel in the defined
output area of the second coordinate system. The conversion data
array maps each pixel to a position in the first coordinate system.
Each conversion data array entry includes second coordinate system
coordinates and second coordinate system offset values.
[0049] FIGS. 5A and B illustrate the generation of a conversion
data array in a system having a polar first coordinate system and a
rectangular second coordinate system. FIG. 5A shows an illustrative
graph 550 of a polar coordinate system. Graph 550 has multiple
radii 552 and angles 554. Point A.sub.RECT 556 represents the
mapping of a rectangular coordinate (x.sub.A, y.sub.A) into the
polar coordinate system.
[0050] FIG. 5B illustrates a conversion data array 570 associated
with the graph of FIG. 5A. Conversion data array 570 includes a
plurality of rectangular coordinate system (x,y) entries 572. Each
respective (x,y) entry has an associated polar coordinate (r,
.sigma.) 574 and associated polar offsets (r.sub.offset,
.sigma..sub.offset) 576 for example, point A.sub.RECT 556 having
coordinates (x.sub.A, y.sub.A) in (x,y) coordinate space has an
entry 578 that contains polar coordinates (r.sub.i, .sigma..sub.i)
and polar offsets (r.sub.offsetA, .sigma..sub.offsetA). As shown in
graph 550, polar coordinates (r.sub.i, .sigma..sub.i) point to a
point A.sub.POLAR in polar space, which is at or near point
A.sub.RECT. The polar offsets (r.sub.offsetA, .sigma..sub.offsetA)
identify displacements between point A.sub.POLAR in polar space and
point A.sub.RECT in rectangular coordinate space as shown in graph
550. The present invention is not intended to be limited to
conversion data array 570. Other types of data structures and/or
coordinate space conversions can be used, as would be apparent to a
person skilled in the art given this description.
[0051] FIG. 8 depicts a mapping 800 of a conical platen surface 890
onto a rectangular area 895. As can be seen in FIG. 8, portions of
the rectangular area 895 do not overlap with he conical platen
surface 890. For (x,y) coordinates located in these portions, no
data exists for conversion. Therefore, coordinate conversion is not
required for these (x,y) coordinates. To improve efficiency, during
generation of a conversion data array, the coordinate conversion
module 154 stores a flag or a data value in the entry for each
non-overlapped (x,y) coordinate. During run-time process 420, the
flag or value indicates to the coordinate conversion module 154
that no computation is necessary for this (x,y) coordinate. The
coordinate conversion module 154 then proceeds to the next (x,y)
coordinate to be processed. In this embodiment, when the image is
displayed, the display device will paint non-overlapped (x,y)
coordinates with a default value such as white.
[0052] Returning to FIG. 5, after the conversion data array is
generated, the conversion coordinate module 154 stores the
conversion data array in memory 156 (step 516). In addition to
generating and storing a conversion data array, other calibration
(e.g., camera calibration) or pre-processing operations can be
carried out as would be apparent to a person skilled in the art
given this description. Also, generating and storing a conversion
data array are described with respect to calibration and
pre-processing. In alternate embodiments of the invention, the
steps of generating and storing the conversion data array are
carried out in real-time during run-time processing.
[0053] FIG. 6 depicts a process loop 450 for converting first
coordinate space image data to second coordinate system image data
based on the stored conversion data. Process loop 450 is described
in reference to a first polar coordinate system and a second
rectangular coordinate system such as depicted in FIGS. 5A and 5B.
Persons skilled in the relevant art(s) will recognize that other
first and second coordinate systems can be used without departing
from the spirit or scope of the present invention.
[0054] Process loop 450 is performed for each pixel (x,y) in an
output rectangular area. An output rectangular area can correspond
to an area obtained when a conical platen surface is flattened as
shown in the mappings of FIGS. 7-8. In step 652, the coordinate
conversion module 154 retrieves conversion data associated with the
second coordinate system pixel being processed from the conversion
data array. In the example array 570, the retrieval for a given
pixel at coordinates (x,y) would obtain values for corresponding
polar coordinates (r, .sigma.) and polar offsets (r.sub.offset,
.sigma..sub.offset) This retrieved conversion data identifies a
region in polar space that corresponds to the particular pixel. For
example, as shown in graph 550, in the case of a look up for a
pixel at rectangular space coordinates (x.sub.A, y.sub.A), polar
coordinate values (r.sub.i, .sigma..sub.i) are retrieved which
correspond to a point in polar space near the pixel at point
(x.sub.A, y.sub.A).
[0055] In step 654, one or more samples of the captured image data
in first coordinate system format are retrieved from memory 156.
The samples are selected based on the retrieved conversion data
array entry. In particular, samples at or near polar coordinate
values (r, .sigma.) are selected. In step 656, the coordinate
conversion module 154 interpolates the retrieved samples to obtain
the pixel value for a respective pixel in rectangular image space.
The coordinate conversion module 154 uses a weighting in the
interpolation, which is based on the retrieved polar offsets
(r.sub.offset, .sigma..sub.offset).
[0056] Any conventional sampling and interpolation techniques can
be used in steps 654 and 656, including but not limited to,
bi-linear interpolation, and cubic spline interpolation (e.g., a
Catmull-Rom interpolation). In the example shown in graph 550,
sixteen samples denoted by an "X" may be retrieved from the
captured polar space image data at or near the looked up polar
coordinate values (r.sub.i, .sigma..sub.i). Weighting coefficients
for a Catmull-Rom interpolation are then determined based upon the
looked up polar offsets (r.sub.offset, .sigma..sub.offset). In this
way, a sampled and interpolated value is obtained from captured
polar space image data that corresponds to a pixel value in
rectangular image space. High resolution in the raw image data is
maintained.
[0057] Method 600 describes the coordinate conversion module 154
calculating the weighting coefficients during run-time process step
450. In an alternate embodiment, a weighting coefficient table for
each interpolation method supported could be generated and stored
during or prior to calibration. In this embodiment, in step 656,
the coordinate conversion module 154 accesses the appropriate
weighting coefficient table to determine the weighting used during
interpolation.
[0058] In an alternate embodiment of the present invention, method
600 also includes the ability for a user to configure various
aspects related to the scan, conversion, and/or display. In this
embodiment, a user may input criteria to be used during conversion
and/or display processing. For example, a user may input a desired
output resolution (e.g., 600 dpi, 1200 dpi, etc.), a desired output
size, and/or a desired output location. If the coordinate
conversion module supports input criteria, the coordinate
conversion module 154 may generate multiple data arrays. For
example, the coordinate conversion module may generate one array
for use if 600 dpi is selected, a second array for use if 800 dpi
is selected, a third array if 1200 dpi is selected, and so on.
These multiple data arrays may be generated dynamically upon input
by the user or may be generated during or prior to calibration.
[0059] In this embodiment, a user may also input goal criteria such
as reducing aliasing, improving focus, and/or improving contrast.
Based on these criteria, the coordinate conversion module 154
selects the appropriate parameters for meeting these goals. For
example, the coordinate conversion module 154 may select the best
interpolation method to be used during conversion to meet the user
input criteria. In an alternate embodiment of the invention, the
live scanner may automatically generate the criteria to be used for
the scan.
[0060] In an alternate embodiment, the orientation of a print being
displayed can also be adjusted. During conversion processing, the
image conversion system 150 determines the center of the scanned
image (e.g., the center of the handprint or the center of the
fingerprint). For example, the image center can be represented by a
coordinate point or by horizontal and/or vertical lines. The system
150 then assigns the image center as the root for display and
conversion processing. By identifying the center, the coordinate
conversion module 154 can rotate the orientation of the print image
during conversion processing. In this way, the print image can be
displayed in the correct orientation without requiring additional
processing to correct the orientation. In an alternate embodiment,
the orientation can be adjusted after conversion by the coordinate
conversion module 154 or by the display processing module 280.
[0061] FIGS. 7 and 8 illustrate point-by-point how mapping between
a polar coordinate system and a rectangular coordinate system can
be performed for a conical prism using the above described methods
and systems. FIG. 7 illustrates where polar coordinates and
rectangular coordinates approximately overlap before conversion.
FIG. 8 illustrates how a few polar coordinate system points on the
conical platen surface correlate to rectangular coordinate system
points.
[0062] FIGS. 9-10 depict alternative embodiments of the image
conversion system described above. FIG. 9 depicts a system 900
having a live scanner 910 coupled to an external image conversion
system 950 via a data network 960. In an alternate embodiment, two
or more live scanners are coupled to the external image conversion
system 950 via data network 960. Live scanner 910 and image
conversion system 950 may also be coupled to a display processing
module 980. Electro-optical system 225 captures raw image data and
communicates the raw data to external image conversion system 950
via data network 960. Network 960 can be any type of network or
combination of networks known in the art, such as a local area
network (LAN), a wide area network (WAN), an intranet, or an
Internet. In an embodiment of the present invention, network 960 is
a data link between the live scanner 910 and the external image
conversion system 950.
[0063] FIG. 10 depicts a system 1000 incorporating a distributed
architecture in accordance with an alternate embodiment of the
present invention. System 1000 includes a live scanner 1010 having
an internal image conversion system 1050A coupled to an external
image conversion system 1050B via a data network 1060. Image
conversion processing is distributed between image conversion
systems 1050A and 1050B. For example, internal image conversion
system 1050A may include the calibration logic and external image
conversion system 1050B may include the conversion logic. As will
be appreciated by persons skilled in the relevant art(s), other
architectures for distributing image conversion processing among
multiple image conversion systems can be used without departing
from the spirit or scope of the invention.
[0064] The terms "biometric imaging system," "scanner," "live
scanner," "live print scanner," "fingerprint scanner," and "print
scanner" are used interchangeably, and refer to any type of system
which can obtain an image of all or part of one or more fingers,
palms, toes, foot, hand, etc. in a live scan.
CONCLUSION
[0065] While various embodiments of the present invention have been
described above, it should be understood that they have been
presented by way of example only, and not limitation. It will be
apparent to persons skilled in the relevant art that various
changes in form and detail can be made therein without departing
from the spirit and scope of the invention. Thus, the breadth and
scope of the present invention should not be limited by any of the
above-described exemplary embodiments, but should be defined only
in accordance with the following claims and their equivalents.
* * * * *