U.S. patent number RE41,839 [Application Number 11/854,855] was granted by the patent office on 2010-10-19 for image distortion compensation technique and apparatus.
Invention is credited to Laurence Hamid.
United States Patent |
RE41,839 |
Hamid |
October 19, 2010 |
Image distortion compensation technique and apparatus
Abstract
A method of compensating for distortion within a composite image
is disclosed. A biometric surface is sensed with a swipe imager.
The images so provided are assembled into a composite image of the
biometric surface. The composite image is then adjusted by
insertion or deletion of rows therein to result in an image with a
different number of rows.
Inventors: |
Hamid; Laurence (Ottawa,
Ontario, CA) |
Family
ID: |
23185325 |
Appl.
No.: |
11/854,855 |
Filed: |
September 13, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60306448 |
Jul 20, 2001 |
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Reissue of: |
10189443 |
Jul 8, 2002 |
06944321 |
Sep 13, 2005 |
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Current U.S.
Class: |
382/124; 382/275;
382/284 |
Current CPC
Class: |
G06K
9/00026 (20130101) |
Current International
Class: |
G06K
9/00 (20060101); G06K 9/40 (20060101); G06K
9/36 (20060101) |
Field of
Search: |
;382/124,232,254,275,298,284 ;359/17,30 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 813 164 |
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Dec 1997 |
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EP |
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WO 99/63476 |
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Dec 1999 |
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WO |
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WO 99/63476 |
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Dec 1999 |
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WO |
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WO 00/36548 |
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Jun 2000 |
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WO |
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WO 00/36548 |
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Jun 2000 |
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WO |
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Other References
Harvey, Mike. "Why veins could replace fingerprints and retinas as
most secure form of ID." Times Online Nov. 11, 2008, 2 pages
<http://technology.timesonline.co.uk/tol/news/tech_and_web/articles512-
9384.ece>. cited by other.
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Primary Examiner: Patel; Kanji
Attorney, Agent or Firm: Perkins Coie LLP
Parent Case Text
This application claims priority from the U.S. Provisional
Application No. 60/306,448 filed Jul. 20, 2001.
Claims
What is claimed is:
1. A method of compensating for distortion within a composite image
comprising.[.the steps of.]. : .[.sensing a biometric surface with
a swipe imager to provide sensed data;.]. forming a composite image
.Iadd.from sensed data .Iaddend.of .[.the.]. .Iadd.a
.Iaddend.biometric surface.[.from the sensed data.]. ; and,
adjusting the composite image along a dimension thereof to .[.one
of.]. expand or decrease the composite image size along said
dimension by .[.one of.]. removing composite image elements along a
line perpendicular to said dimension within the composite image
.[.and.]. .Iadd.or .Iaddend.adding .[.additional.]. image elements
along a line perpendicular to said dimension within the composite
image to result in a second composite image with a different number
of parallel lines of composite image elements perpendicular to the
dimension.[.therein.]. .
2. A method according to claim 1 wherein .[.the step of.].
adjusting the composite image includes .[.the step of.]. adding
rows interspersed at row intervals within the image.
3. A method according to claim 2 wherein the additional rows are
added to compensate for compression of the biometric surface during
imaging.[.thereof.]. .
4. A method according to claim 3 wherein the surface is a fingertip
and wherein the compression results from a downward swipe direction
of the fingertip.
5. A method according to claim 4 wherein a row is added to the
composite image for every N rows within the composite image.
6. A method according to claim 5 wherein the rows are added at
consistent row intervals.
7. A method according to claim 6 wherein the row interval is 4.
8. A method according to claim 6 including .[.the step of.].
determining a row interval based on an amount of compression within
the composite image.
9. A method according to claim 2 wherein a row is added to the
composite image for every N rows within the composite image.
10. A method according to claim 9 wherein the rows are added at
consistent row intervals.
11. A method according to claim 1 further comprising.[.the steps
of.]. : determining an amount of compression within the composite
image; adding lines of image elements within the composite image
based on the determined .Iadd.amount of .Iaddend.compression; and
compensating for image distortion along .Iadd.an .Iaddend.axis
orthogonal to the dimension.
12. A method according to claim 11 wherein .[.the step of.].
compensating is performed in dependence upon the determined amount
of compression.
13. A method according to claim 11 comprising .[.the step of.].
determining a distribution of the compression within the composite
image.
14. A method according to claim 13 wherein .[.the step of.]. adding
is performed in dependence upon the determined distribution of the
compression within the composite image and .[.the step of.].
compensating is performed in dependence upon the determined amount
of the compression within the composite image.
15. A method according to claim 1 further comprising .[.the step
of.]. determining a distribution of compression within the
composite image.
16. A method according to claim 15 wherein .[.the step of.].
adjusting includes .[.a step of.]. inserting additional lines of
elements within the composite image in dependence upon the
determined distribution of the compression within the composite
image, the lines perpendicular to the dimension.
17. A method according to claim 1 wherein .[.the step of.].
adjusting the composite image includes .[.the step of.]. removing
rows interspersed at row intervals within the composite image.
18. A method according to claim 17 wherein the rows are removed to
compensate for stretching of the biometric surface during
imaging.[.thereof.]. .
19. A method according to claim 18 wherein the surface is a
fingertip and wherein the stretching results from an upward swipe
direction of the fingertip.
20. A method according to claim 19 wherein a row is removed from
the composite image for every N rows within the composite
image.
21. A method according to claim 20 wherein the rows are removed at
consistent row intervals.
22. A method according to claim 21 including .[.the step of.].
determining a row interval based on an amount of stretching within
the composite image.
23. A method according to claim 17 wherein a row is removed from
the composite image for every N rows within the composite
image.
24. A method according to claim 23 wherein the rows are removed at
consistent row intervals.
25. A method according to claim 1 further comprising.[.the steps
of.]. : determining an amount of stretching; removing lines of
image elements from the composite image based on the determined
.Iadd.amount of .Iaddend.stretching; and compensating for image
distortion along an axis orthogonal to the dimension.
26. A method according to claim 25 wherein .[.the step of.].
compensating is performed in dependence upon the determined amount
of stretching.
27. A method according to claim 25 comprising .[.the step of.].
determining a distribution of the stretching within the composite
image.
28. A method according to claim 27 wherein .[.the step of.].
removing is performed in dependence upon the determined
distribution of the stretching within the composite image and
.[.the step of.]. compensating is performed in dependence upon the
determined amount of the stretching within the composite image.
29. A method according to claim 16 comprising .[.the step of.].
determining a distribution of stretching within the composite
image.
30. A method according to claim 29 wherein .[.the step of.].
adjusting includes .[.a step of.]. removing lines of composite
image elements in dependence upon the determined distribution of
the stretching within the composite image, the lines perpendicular
to the dimension.
31. A method according to claim 1 wherein .[.the step of.].
adjusting comprises.[.the steps of.]. : determining whether the
composite image is stretched or compressed along the dimension;
when the composite image is compressed, adjusting the composite
image along the dimension to expand the composite image size along
said dimension by adding .[.additional.]. image elements along a
line perpendicular to said .[.a.]. dimension within the composite
image to result in the second composite image with a different
number of parallel lines of image elements perpendicular to said
dimension; and, when the composite image is stretched, adjusting
the composite image along the dimension to decrease the composite
image size along said dimension by removing image elements along a
line perpendicular to said .[.a.]. dimension within the composite
image to result in the second composite image with a different
number of parallel lines of image elements perpendicular to said
.[.at least one.]. dimension.[.therein.]. .
32. A method according to claim 1 further comprising .[.a step
of.]. determining an amount of .[.one of.]. compression .[.and.].
.Iadd.or .Iaddend.stretching along the dimension of the composite
image and wherein .[.the step of.]. adjusting .Iadd.of .Iaddend.the
composite image is performed in order to compensate for a
determined amount of the .[.one of.]. compression .[.and.].
.Iadd.or .Iaddend.stretching along said dimension.
33. A method according to claim 1 further comprising .[.a step
of.]. determining an amount and distribution of .[.one of.].
compression .[.and.]. .Iadd.or .Iaddend.stretching along the
dimension of the composite image and wherein .[.the step of.].
adjusting .Iadd.of .Iaddend.the composite image is performed in
order to compensate for a determined amount and distribution of the
.[.one of.]. compression .[.and.]. .Iadd.or .Iaddend.stretching
along said dimension.
34. A swipe contact imager comprising: a platen across which a
biometric surface is to be passed for imaging thereof; an imaging
circuit for sensing a biometric surface passing across the platen
and for providing image data relating to portions thereof; and a
processor .[.for forming.]. .Iadd.that forms .Iaddend.a composite
image from the image data and .[.for adjusting.]. .Iadd.adjusts
.Iaddend.the composite image along a dimension thereof to .[.one
of.]. expand or decrease the composite image size along said
dimension by .[.one of.]. removing composite image elements along a
line perpendicular to said dimension within the composite image
.[.and.]. .Iadd.or .Iaddend.adding .[.additional.]. image elements
along a line perpendicular to said dimension within the composite
image to result in a second composite image with a different number
of parallel lines of composite image elements perpendicular to the
dimension.[.therein.]. .
35. A storage medium .[.having stored therein data, the data
indicative of instructions for performing the steps of.].
.Iadd.whose contents cause a computing system to perform a method,
comprising.Iaddend.: .[.sensing a biometric surface with a swipe
imager to provide sensed data;.]. forming a composite image .[.of
the.]. .Iadd.from sensed data of a .Iaddend.biometric
surface.[.from the sensed data.]. ; and.[.,.]. adjusting the
composite image along a dimension thereof to .[.one of.]. expand or
decrease the composite image size along .[.said.]. .Iadd.the
.Iaddend.dimension by .[.one of.]. removing composite image
elements along a line perpendicular to .[.said.]. .Iadd.the
.Iaddend.dimension within the composite image .[.and.]. .Iadd.or
.Iaddend.adding .[.additional.]. image elements along a line
perpendicular to .[.said.]. .Iadd.the .Iaddend.dimension within the
composite image to result in a second composite image with a
different number of parallel lines of composite image elements
perpendicular to the dimension.[.therein.]. .
36. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 35 wherein .[.the data relating to the step
of.]. adjusting the composite image includes .[.data relating to a
step of.]. adding rows interspersed at row intervals within the
image.
37. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 36.[.wherein the instructions relate to.].
.Iadd., the method further comprising .Iaddend.adding a row to the
composite image for every N rows within the composite image.
38. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 37.[.wherein the instructions relate to.].
.Iadd., the method further comprising .Iaddend.adding the rows at
consistent row intervals.
39. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 38 wherein the row interval is 4.
40. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 38.[.wherein the data relates to
instructions for performing the step of.]. .Iadd., the method
further comprising .Iaddend.determining a row interval based on an
amount of compression within the composite image.
41. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 35.[.wherein the data relates to
instructions for performing the comprising the step of.]. .Iadd.,
the method further comprising.Iaddend.: determining an amount of
compression within the composite image; adding lines of image
elements within the composite image based on the determined
compression; and compensating for image distortion along .Iadd.an
.Iaddend.axis orthogonal to the dimension in dependence upon the
determined amount of compression.
42. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 41.[.wherein the data relates to
instructions for performing the step of.]. .Iadd., the method
further comprising .Iaddend.determining a distribution of the
compression within the composite image.
43. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 42 wherein .[.the data relating to
instructions for performing the step of.]. adding includes .[.data
relating to instructions for performing the step of.]. adding in
dependence upon the determined distribution of the compression
within the composite image.
44. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 35.[.wherein the data relates to
instructions for performing the step of.]. .Iadd., the method
further comprising .Iaddend.determining a distribution of
compression within the composite image.
45. .[.A.]. .Iadd.The .Iaddend.storage medium according to claim 44
wherein .[.the data relating to instructions for performing the
step of.]. adjusting the composite image includes .[.data relating
to instructions for performing the step of.]. inserting additional
lines of elements within the composite image in dependence upon the
determined distribution of the compression within the composite
image, the lines .Iadd.being .Iaddend.perpendicular to the
dimension.
46. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 35 wherein .[.the data relating to
instructions for performing the step of.]. adjusting the composite
image includes .[.data relating to instructions for performing the
step of.]. removing rows interspersed at row intervals within the
composite image.
47. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 46.[.wherein the data relates to
instructions for performing the step of.]. .Iadd., the method
further comprising .Iaddend.determining a row interval based on an
amount of stretching within the composite image.
48. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 35.[.wherein the data relates to
instructions for performing the steps of.]. .Iadd., the method
further comprising.Iaddend.: determining an amount of stretching;
removing lines of image elements from the composite image based on
the determined .Iadd.amount of .Iaddend.stretching; and
compensating for image distortion along an axis orthogonal to the
dimension in dependence upon the determined amount of
stretching.
49. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 48 .[.wherein the data relates to
instructions for performing the step of.]. .Iadd., the method
further comprising .Iaddend.determining a distribution of the
stretching within the composite image.
50. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 49 wherein .[.the data relates to
instructions for performing the step of.]. removing in dependence
upon the determined distribution of the stretching within the
composite image and .[.the step of.]. compensating is performed in
dependence upon the determined amount of the stretching within the
composite image.
51. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 45 .[.wherein the data relates to
instructions for performing the step of.]. .Iadd., the method
further comprising .Iaddend.determining a distribution of
stretching within the composite image.
52. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 51 wherein .[.the data relating to
instructions for performing the step of.]. adjusting includes
.[.data relating to performing a step of.]. removing lines of
composite image elements in dependence upon the determined
distribution of the stretching within the composite image, the
lines .Iadd.being .Iaddend.perpendicular to the dimension.
53. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 35 wherein .[.the data relating to
instructions for performing the step of.]. adjusting .[.include
instructions relating to performing the steps of.]. .Iadd.further
comprises.Iaddend.: determining whether the composite image is
stretched or compressed along the dimension; when the composite
image is compressed, adjusting the composite image along the
dimension to expand the composite image size along .[.said.].
.Iadd.the .Iaddend.dimension by adding additional image elements
along a line perpendicular to .[.said.]. .Iadd.the .Iaddend.a
dimension within the composite image to result in the second
composite image with a different number of parallel lines of image
elements perpendicular to .[.said.]. .Iadd.the .Iaddend.dimension;
and, when the composite image is stretched, adjusting the composite
image along the dimension to decrease the composite image size
along .[.said.]. .Iadd.the .Iaddend.dimension by removing image
elements along a line perpendicular to .[.said.]. .Iadd.the
.Iaddend.a dimension within the composite image to result in the
second composite image with a different number of parallel lines of
image elements perpendicular to .[.said.]. .Iadd.the .Iaddend.at
least one dimension therein.
54. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 35 wherein .[.the data relates to
instructions for performing the step of.]. determining an amount of
.[.one of.]. compression .[.and.]. .Iadd.or .Iaddend.stretching
along the dimension of the composite image and .[.wherein the
instructions relate to.]. adjusting the composite image .[.is
performed in order to.]. .[.compensate.]. .Iadd.compensates
.Iaddend.for a determined amount of .[.the one of.]. compression
.[.and.]. .Iadd.or .Iaddend.stretching along .[.said.]. .Iadd.or
.Iaddend.dimension.
55. .[.A.]. .Iadd.The .Iaddend.storage medium .[.according to.].
.Iadd.of .Iaddend.claim 35 wherein .[.the data relates to
instructions for performing the step of.]. determining an amount
and distribution of .[.one of.]. compression .[.and.]. .Iadd.or
.Iaddend.stretching along the dimension of the composite image and
.[.wherein the instructions relate to.]. adjusting the composite
image .[.in order to compensate.]. .Iadd.compensates .Iaddend.for a
determined amount .[.and distribution of the one.]. of .Iadd.the
.Iaddend.compression .[.and.]. .Iadd.or .Iaddend.stretching along
.[.said.]. .Iadd.or .Iaddend.dimension.
.Iadd.56. A swipe contact imager comprising: means for sensing a
biometric surface and for providing image data relating to portions
thereof; and means for forming a composite image from the image
data and adjusting the composite image along a dimension thereof to
expand or decrease the composite image size along said dimension by
removing composite image elements along a line perpendicular to
said dimension within the composite image or adding image elements
along a line perpendicular to said dimension within the composite
image to result in a second composite image with a different number
of parallel lines of composite image elements perpendicular to the
dimension..Iaddend.
.Iadd.57. The swipe contact imager of claim 34, further comprising
a force measurer configured to measure an amount of force applied
to the platen when the biometric surface passes the
platen..Iaddend.
.Iadd.58. The swipe contact imager of claim 57 wherein the
processor is configured to adjust the composite image based on the
measured amount of force..Iaddend.
.Iadd.59. The swipe contact imager of claim 57 wherein the force
measurer is configured to measure an amount of force applied to the
platen in at least two regions, and wherein the processor is
configured to adjust the composite image according to the amount of
force applied in the at least two regions..Iaddend.
Description
FIELD OF THE INVENTION
The invention relates generally to contact imagers and more
particularly to swipe contact imagers.
BACKGROUND OF THE INVENTION
Biometric techniques for determining the identity of individuals
are being used increasingly in authentication, recognition, and/or
access systems. These techniques use biometric identifiers or human
characteristics to verify or identify an individual. The fact that
most human characteristics are unique to each individual, are
difficult to reproduce by others, and are easily converted to
electronic data, is particularly advantageous in biometric
identification applications.
Historically, fingerprints have been the most widely used biometric
identifiers, as is evident from law enforcement's extensive use of
fingerprinting. The recent trends in biometric identification have
been toward automating the above-mentioned authentication,
recognition, and/or access systems. Most current techniques rely
upon correlation methods that use automated detection systems
connected to a computer database, for comparing detected biometric
data to biometric data stored in the database, to confirm or
determine the identity of an individual. Such automated systems
have been used to identify individuals before granting access to
cars, computers, home or business offices, hotel rooms, and in
general, any sensitive or restricted area.
Various optical devices are known which employ prisms upon which a
finger whose print is to be identified is placed. For example, the
prism has a first surface upon which a finger is placed, a second
surface disposed at an acute angle to the first surface through
which the fingerprint is viewed and a third illumination surface
through which light is directed into the prism. In some cases, the
illumination surface is at an acute angle to the first surface, as
seen for example, in U.S. Pat. Nos. 5,187,482 and 5,187,748. In
other cases, the illumination surface is parallel to the first
surface, as seen for example, in U.S. Pat. Nos. 5,109,427 and
5,233,404.
An alternative type of contact imaging device is disclosed in U.S.
Pat. No. 4,353,056 in the name of Tsikos issued Oct. 5, 1982,
herein incorporated by reference. The imaging device that is
described by Tsikos uses a capacitive sensing approach. To this
end, the imaging device comprises a two dimensional, row and
column, array of capacitors, each comprising a pair of spaced apart
electrodes, carried in a sensing member and covered by an
insulating film. The sensors rely upon deformation to the sensing
member caused by a finger being placed thereon so as to vary
locally the spacing between capacitor electrodes, according to the
ridge/trough pattern of the fingerprint, and hence, the capacitance
of the capacitors.
A further contact imaging device is described in U.S. Pat. No.
5,325,442 in the name of Knapp, issued Jun. 28, 1994, herein
incorporated by reference. Knapp discloses a capacitance measuring
contact imaging device in the form of a single large active matrix
array, formed by the deposition and definition by photolithographic
processes of a number of layers on a single large insulating
substrate. Electrodes and sets of address conductors formed of
metal and field effect transistors are formed as amorphous silicon
or polycrystalline silicon thin film transistors (TFTs) using an
appropriate substrate of, for example, glass or quartz.
Additionally, a fingerprint sensing device and recognition system
that includes an array of closely spaced apart sensing elements,
each comprising a sensing electrode and an amplifier circuit, is
described in U.S. Pat. No. 5,778,089 in the name of Borza, issued
Jul. 7, 1998, herein incorporated by reference.
"Swipe imagers" are also known, wherein an individual places a
fingertip into contact with a surface of a contact imaging device
and then draws, or "swipes", the fingertip across a sensing portion
of the surface. Images from adjacent portions of the fingertip are
captured and combined in order to construct a composite image of
the fingertip having an area that is greater than the area of a
single captured image. In this way, an area of the fingertip that
is substantially larger than the sensing portion is imaged. Such an
arrangement allows a smaller capacitive fingerprint scanner to be
used, which is advantageous due to lower manufacturing costs,
improved robustness, and so forth. Also, the small area required is
highly advantageous for embedded applications such as with a cell
phone, a telephone, a computer (laptop) and so forth.
Unfortunately, images acquired with conventional swipe imagers are
typically distorted relative to images captured with static imaging
techniques.
It is an object of the invention to image a biometric surface using
a swipe contact imager and to provide a composite image having less
distortion than the raw composite image formed through mere image
concatenation.
SUMMARY OF THE INVENTION
In accordance with the invention there is provided a method of
compensating for distortion within a composite image comprising the
steps of: sensing a biometric surface with a swipe imager to
provide sensed data; forming a composite image of the biometric
surface from the sensed data; and, adjusting the composite image
along a dimension thereof to one of expand or decrease the
composite image size along said dimension by one of removing
composite image elements along a line perpendicular to said
dimension within the composite image and adding additional image
elements along a line perpendicular to said dimension within the
composite image to result in a second composite image with a
different number of parallel lines of composite image elements
perpendicular to the dimension therein.
In accordance with another aspect of the invention there is
provided a swipe contact imager comprising: a platen across which a
biometric surface is to be passed for imaging thereof; an imaging
circuit for sensing a biometric surface passing across the platen
and for providing image data relating to portions thereof; and a
processor for forming a composite image from the image data and for
adjusting the composite image along a dimension thereof to one of
expand or decrease the composite image size along said dimension by
one of removing composite image elements along a line perpendicular
to said dimension within the composite image and adding additional
image elements along a line perpendicular to said dimension within
the composite image to result in a second composite image with a
different number of parallel lines of composite image elements
perpendicular to the dimension therein.
In accordance with yet another aspect of the invention there is
provided a storage medium having stored therein data, the data
indicative of instructions for performing the steps of: sensing a
biometric surface with a swipe imager to provide sensed data;
forming a composite image of the biometric surface from the sensed
data; and, adjusting the composite image along a dimension thereof
to one of expand or decrease the composite image size along said
dimension by one of removing composite image elements along a line
perpendicular to said dimension within the composite image and
adding additional image elements along a line perpendicular to said
dimension within the composite image to result in a second
composite image with a different number of parallel lines of
composite image elements perpendicular to the dimension
therein.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to the attached
drawings in which:
FIG. 1 is a computer generated diagram of a plurality of images of
a same fingerprint each acquired with different parameters;
FIG. 1a is a fingerprint as imaged by a flat contact imager of a
non-swipe configuration;
FIG. 1b is same fingerprint as FIG. 1a with heavy pressure applied
in an upward swipe direction;
FIG. 1c is the same fingerprint as FIG. 1a with medium pressure
applied in an upward swipe direction;
FIG. 1d is the same fingerprint as FIG. 1a with light pressure
applied in an upward swipe direction;
FIG. 1e is the same fingerprint as FIG. 1a with heavy pressure
applied in an downward swipe direction;
FIG. 1f is the same fingerprint as FIG. 1a with medium pressure
applied in an downward swipe direction;
FIG. 1g is the same fingerprint as FIG. 1a with light pressure
applied in an downward swipe direction;
FIG. 2 is a simplified flow diagram of a method of reducing
compression related distortion within some of the images of FIG. 1
according to the invention;
FIG. 3 is a simplified flow diagram of a generalized method of
reducing compression related distortion within some of the images
of FIG. 1 according to the invention;
FIG. 4 is a simplified flow diagram of a method of reducing
compression related distortion within some of the images of FIG. 1
according to the invention;
FIG. 5 is a simplified flow diagram of a method of reducing
compression related distortion along both the direction of swiping
and along a direction orthogonal thereto;
FIG. 6 is a simplified flow diagram of a method of reducing
stretching related distortion within some of the images of FIG. 1
according to the invention;
FIG. 7 is a simplified flow diagram of a generalized method of
reducing stretching related distortion within some of the images of
FIG. 1 according to the invention;
FIG. 8 is a simplified flow diagram of a method of reducing
stretching related distortion within some of the images of FIG. 1
according to the invention;
FIG. 9 is a simplified flow diagram of a method of reducing
stretching related distortion along both the direction of swiping
and along a direction orthogonal thereto;
FIG. 10 is a simplified flow diagram of a method of reducing both
compression and stretching related distortion along a direction of
swiping as well as distortion along a direction orthogonal thereto;
and,
FIG. 11 is a simplified block diagram of an apparatus for
performing the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
Referring to FIG. 1, a set of computer generated images of a
fingerprint are shown. Each is presented upside down as that is how
they are stored electronically and, as such, a top of each image is
shown at a bottom of each image within the figure. FIG. 1(a) shows
the fingerprint as imaged by a flat contact imager of a non-swipe
configuration. Such an imager maintains an approximately
distortionless relation between features and is used in the
description that follows as a reference fingerprint image.
In FIG. 1(b) the same fingerprint is shown reconstructed. The
fingertip was swiped in a generally upward direction along the
swipe contact imager and during swiping thereof, a heavy pressure
was applied by the individual. Thus, the distortion is significant
therein causing a stretching of the fingerprint as is noted by the
increased distance between the features f1 and f2.
In FIG. 1(c), a same fingerprint is again shown reconstructed. The
fingertip was swiped in a generally upward direction along the
swipe contact imager and during swiping thereof, a medium pressure
was applied by the individual. Thus, the distortion is significant
therein causing a stretching of the fingerprint as is noted by the
increased distance between the features f1 and f2.
In FIG. 1(d), a same fingerprint is again shown reconstructed. The
fingertip was swiped in a generally upward direction along the
swipe contact imager and during swiping thereof, a light pressure
was applied by the individual. Thus, the distortion is less
significant than in either of the two previous images though a
stretching of the fingerprint is evident as is noted by the
increased distance between the features f1 and f2.
In FIG. 1(e) the same fingerprint is again shown reconstructed. The
fingertip was swiped in a generally downward direction along the
swipe contact imager and during swiping thereof, a heavy pressure
was applied by the individual. Thus, the distortion is significant
therein causing a compressing of the fingerprint as is noted by the
decreased distance between the features f1 and f2.
In FIG. 1(f), a same fingerprint is again shown reconstructed. The
fingertip was swiped in a generally downward direction along the
swipe contact imager and during swiping thereof, a medium pressure
was applied by the individual. Thus, the distortion is significant
therein causing a compressing of the fingerprint as is noted by the
decreased distance between the features f1 and f2.
In FIG. 1(g), a same fingerprint is again shown reconstructed. The
fingertip was swiped in a generally downward direction along the
swipe contact imager and during swiping thereof, a light pressure
was applied by the individual. Thus, the distortion is less
significant than in either of the two previous images though a
compressing of the fingerprint is evident as is noted by the
decreased distance between the features f1 and f2.
Of course, for a swipe contact fingerprint imager to be a drop in
replacement to existing platen based contact imaging devices, the
resulting fingerprint image is preferably as similar as possible to
those captured by a non-swipe contact imager. As such, it would be
advantageous to transform the image to reduce effects of stretching
and compressing visible in reconstructed swipe images.
Table 1 below sets out the effects of distortion. It is observed
that swiping a finger upwards causes stretching while swiping a
finger downwards causes compression. Further, the compression in a
downward swiped fingertip is more acute near a top of the
fingerprint .[.that.]. .Iadd.than .Iaddend.elsewhere. There is also
some horizontal distortion, more so in the upward swipe direction
.[.that.]. .Iadd.than .Iaddend.in the downward swiped
fingerprints.
TABLE-US-00001 TABLE 1 Distortion Effects Summary Type Dir/Press
Abs (f.sub.1x-f.sub.2x) Abs (f.sub.1y-f.sub.2) abs
(f.sub.1-f.sub.2) Error.sub.x Error.sub.y Error Flat n/a 129 153
200 n/a n/a n/a Swipe Up/Heavy 147 172 226 14.0% 12.4% 13.0% Swipe
Up/Medium 151 188 241 17.0% 22.9% 20.5% Swipe Up/Light 150 182 236
16.3% 19.0% 18.0% Swipe Down/Heavy 151 110 187 17.0% -28.1% -6.5%
Swipe Down/Medium 134 112 175 3.9% -26.8% -12.5% Swipe Down/Light
140 113 180 8.5% -26.1% -10.0%
Referring to FIG. 2, a simplified flow diagram of a method for
correcting vertical distortion in a swipe image captured with a
fingertip moving downward across a swipe contact imager is shown. A
biometric surface is passed across a swipe contact imager and a
plurality of image portions are captured at 21. The image portions
are assembled into a composite image at 22.
Once the composite image is constructed, one row is inserted within
the image for every N image rows at 23. For example, N=4. Thus, the
image is increased in vertical direction. By doing so, the feature
spacing along the vertical direction--the y axis--is increased to
compensate for compressing of the image occurring during image
capture. Finally, the corrected composite image is provided at
24.
Of course, the use of a single fixed row insertion rate is not
equally beneficial to each of the images 1(e), (f), and (g) since
the compression ratio for each is different. That said, it was
found to sufficiently improve the imaging results in general as
shown in Table 2 and to therefore be advantageous.
TABLE-US-00002 TABLE 2 Distortion Correction Summary Type Dir/Press
Abs (f.sub.1x-f.sub.2x) Abs (f.sub.1y-f.sub.2) abs
(f.sub.1-f.sub.2) Error.sub.x Error.sub.y Error Flat n/a 129 153
200 n/a n/a n/a Swipe Down/Heavy 151 158 218 17.0% 3.3% 8.5% Swipe
Down/Medium 134 140 194 3.9% -8.5% -3.2% Swipe Down/Light 140 141
199 8.5% -7.8% -0.7%
Referring to FIG. 3, a simplified flow diagram of a more
complicated but generalized method is shown. Here a plurality of
image portions is sensed during a downward swipe of a fingertip
across an imager. A biometric surface is passed across a swipe
contact imager and a plurality of image portions are captured at
31. The image portions are assembled into a composite image at
32.
Once the composite image is constructed, an analysis of the image
is performed to determine an amount of compression therein at 33.
The determined amount of compression is used to estimate N. At step
34, one row is inserted within the image for every N image rows.
Thus, the image is increased in vertical direction. By doing so,
the feature spacing along the vertical direction--the y axis--is
increased to compensate for compressing of the image occurring
during image capture. Finally, the corrected composite image is
provided at 35.
Referring to FIG. 4, a simplified flow diagram of a more
complicated but generalized method is shown. Here a plurality of
image portions is sensed during a downward swipe of a fingertip
across an imager. A biometric surface is passed across a swipe
contact imager and a plurality of image portions are captured at
41. The image portions are assembled into a composite image at
42.
Once the composite image is constructed, an amount of compression
therein is determined. For example, an analysis of the image
compared to a known image of the same biometric surface is
performed to determine an amount of compression therein.
Alternatively, the compression is determined based on a measured
force applied during sensing of the image of the biometric surface.
The amount of compression is then used with further image analysis
to determine a distribution of compression within the image at 43.
The distribution may be constant such as 1 in every 4 rows or may
be a segmented distribution such as 1 in 3 for the top third and 1
in 5 for the remaining portion of the image. Alternatively, the
distribution may be mathematical in nature following a linear or
non linear relation with a location within the image.
The determined amount of compression is used to estimate where to
insert additional rows within the image. At step 44, one row is
inserted within the image for each estimated location wherein a row
is to be inserted. Thus, the image is increased in vertical
direction. By doing so, the feature spacing along the vertical
direction--the y axis--is increased to compensate for compressing
of the image occurring during image capture. Finally, the corrected
composite image is provided at 45.
Referring to FIG. 5, a simplified flow diagram of a more
complicated method for correcting vertical and horizontal
distortion is shown. As is evidenced from the tables 1 and 2, there
is a correlation between vertical and horizontal distortion for a
sensed downward swiped fingertip. Here a plurality of image
portions is sensed during a downward swipe of a fingertip across an
imager. A biometric surface is passed across a swipe contact imager
and a plurality of image portions are captured at 51. The image
portions are assembled into a composite image at 52.
Once the composite image is constructed, an amount of compression
therein is determined. For example, an analysis of the image
compared to a known image of the same biometric surface is
performed to determine an amount of compression therein.
Alternatively, the compression is determined based on a measured
force applied during sensing of the image of the biometric surface.
The amount of compression is then used with further image analysis
to determine a distribution of vertical compression within the
image and horizontal distortion within the image at 53.
The determined amount of compression is used to estimate where to
insert additional rows within the image. At step 54, one row is
inserted within the image for each estimated location wherein a row
is to be inserted and horizontal distortion compensation is
performed. Thus, the image is increased in vertical direction. By
doing so, the feature spacing along the vertical direction--the y
axis--is increased to compensate for compressing of the image
occurring during image capture and distortion along the horizontal
axis is compensated for in dependence upon the amount of
compression. Finally, the corrected composite image is provided at
55.
Referring to FIG. 6, a simplified flow diagram of a method for
correcting vertical distortion in a swipe image captured with a
fingertip moving upward across a swipe contact imager is shown. A
biometric surface is passed across a swipe contact imager and a
plurality of image portions are captured at 61. The image portions
are assembled into a composite image at 62.
Once the composite image is constructed, one row is removed within
the image for every N image rows at 63. For example, N=4. Thus, the
image is decreased in vertical direction. By doing so, the feature
spacing along the vertical direction--the y axis--is decreased to
compensate for stretching of the image occurring during image
capture. Finally, the corrected composite image is provided at
64.
Referring to FIG. 7, a simplified flow diagram of a more
complicated but generalized method is shown. Here a plurality of
image portions is sensed during an upward swipe of a fingertip
across an imager. A biometric surface is passed across a swipe
contact imager and a plurality of image portions are captured at
71. The image portions are assembled into a composite image at
72.
Once the composite image is constructed, an amount of stretching
therein is determined. For example, an analysis of the image
compared to a known image of the same biometric surface is
performed to determine an amount of stretching therein.
Alternatively, the stretching is determined based on a measured
force applied during sensing of the image of the biometric surface.
The determined amount of stretching is used to estimate N. At step
74, one row is removed from within the image for every N image
rows. Thus, the image is decreased in vertical direction. By doing
so, the feature spacing along the vertical direction--the y
axis--is decreased to compensate for stretching of the image
occurring during image capture. Finally, the corrected composite
image is provided at 75.
Referring to FIG. 8, a simplified flow diagram of a more
complicated but generalized method is shown. Here a plurality of
image portions is sensed during an upward swipe of a fingertip
across an imager. A biometric surface is passed across a swipe
contact imager and a plurality of image portions are captured at
81. The image portions are assembled into a composite image at
82.
Once the composite image is constructed, an amount of stretching
therein is determined. For example, an analysis of the image
compared to a known image of the same biometric surface is
performed to determine an amount of stretching therein.
Alternatively, the stretching is determined based on a measured
force applied during sensing of the image of the biometric surface.
The amount of stretching is then used with further image analysis
to determine a distribution of stretching within the image at 83.
The distribution may be constant such as 1 in every 4 rows or may
be a segmented distribution such as 1 in 3 for the top third and 1
in 5 for the remaining portion of the image. Alternatively, the
distribution may be mathematical in nature following a linear or
non linear relation with a location within the image.
The determined amount of stretching is used to estimate where to
remove extra rows within the image. At step 84, one row is removed
from within the image for each estimated location wherein a row is
to be removed. Thus, the image is decreased in vertical direction.
By doing so, the feature spacing along the vertical direction--the
y axis--is decreased to compensate for stretching of the image
occurring during image capture. Finally, the corrected composite
image is provided at 85.
Referring to FIG. 9, a simplified flow diagram of a more
complicated method for correcting vertical and horizontal
distortion is shown. Here a plurality of image portions is sensed
during an upward swipe of a fingertip across an imager. A biometric
surface is passed across a swipe contact imager and a plurality of
image portions are captured at 91. The image portions are assembled
into a composite image at 92.
Once the composite image is constructed, an amount of stretching
therein is determined. For example, an analysis of the image
compared to a known image of the same biometric surface is
performed to determine an amount of stretching therein.
Alternatively, the stretching is determined based on a measured
force applied during sensing of the image of the biometric surface.
The amount of stretching is then used with further image analysis
to determine a distribution of vertical stretching within the image
and horizontal distortion within the image at 93.
The determined amount of stretching is used to estimate where to
remove rows from within the image. At step 94, one row is removed
from within the image for each estimated location wherein a row is
to be removed and horizontal distortion compensation is performed.
Thus, the image is decreased in vertical direction. By doing so,
the feature spacing along the vertical direction--the y axis--is
decreased to compensate for stretching of the image occurring
during image capture and distortion along the horizontal axis is
compensated for in dependence upon the amount of stretching.
Finally, the corrected composite image is provided at 95.
Referring to FIG. 10, a simplified flow diagram of a more
complicated method for correcting vertical and horizontal
distortion is shown. Here a plurality of image portions is sensed
during a swipe of a fingertip across an imager. A biometric surface
is passed across a swipe contact imager and a plurality of image
portions are captured at 101. The image portions are assembled into
a composite image at 102.
Once the composite image is constructed, an amount of vertical
distortion therein is determined. For example, an analysis of the
image compared to a known image of the same biometric surface is
performed to determine an amount of vertical distortion therein.
Alternatively, the vertical distortion is determined based on a
measured force applied during sensing of the image of the biometric
surface. The amount of stretching or compression is then used with
further image analysis to determine a distribution of vertical
stretching or compression within the image and horizontal
distortion within the image at 103.
The determined amount of vertical distortion is used to estimate
whether to add or remove rows and where within the image to do so.
At step 104a, one row is removed from within the image for each
estimated location wherein a row is to be removed when vertical
stretching is detected. Alternatively at step 104b, one row is
added within the image for each estimated location wherein a row is
to be inserted when vertical compression is detected. At 105,
horizontal distortion compensation is performed. Thus, the image is
adjusted in vertical direction. By doing so, the feature spacing
along the vertical direction--the y axis--is adjusted to compensate
for detected vertical distortion of the image occurring during
image capture and distortion along the horizontal axis is
compensated for in dependence upon the amount of vertical
distortion. Finally, the corrected composite image is provided at
106.
Referring to FIG. 11, a block diagram of an apparatus for
performing the invention is shown. The apparatus includes a swipe
imager 110 and a processor 111.
Of course, other forms of detectable distortion are compensatable
according to the invention as are other forms of distortion highly
correlated to detectable forms of distortion. The improvement in
the composite image quality for a particular purpose is a function
of the biometric surface imaged, the quality of image
reconstruction, and the particular purpose.
Numerous other embodiments may be envisaged without departing from
the spirit or scope of the invention.
* * * * *
References