Method and apparatus for verifying identity using image correlation

A fingerprint verification method for verifying the identity of a person by comparing presently obtained fingerprint data with previously obtained fingerprint data, said method comprising the steps of:

• first enrolling one or more persons by the steps of forming a two-dimensional reference image of a fingerprint of each enrolling person, identifying a plurality of reference sections from each reference image by partitioning said reference image into a plurality of two-dimensional candidate reference sections from which said reference sections will be selected, performing an autocorrelation calculation for each candidate reference section to determine the degree of distinctiveness of said candidate reference section relative to a two-dimensional local region of reference section by comparing pixels of the two-dimensional image data of said candidate reference section to corresponding pixels of the two-dimensional image data of equal-sized areas throughout said local region, wherein said local region is larger than said candidate reference section and smaller than said reference image, and selecting said reference sections from the most distinctive of said candidate reference sections based on the results f the autocorrelation calculations, and saving the two-dimensional image and relative positioning data of each of said reference sections as fingerprint data for the enrolling person;
• and then
• verifying the identify of someone claiming to be an enrolled person by the steps of retrieving the two-dimensional image and relative positioning data of the reference sections of the enrolled person, forming a two-dimensional verify image of the fingerprint of the person claiming to be enrolled, wherein said verify image includes a plurality of two-dimensional verify regions each corresponding in position to one of said reference sections and each larger in extent than its corresponding reference section, determining a best-match location within each verify region at which the image data is most similar to the image data of its corresponding reference section, and verifying the identity of the person claiming to be enrolled according to the degree of similarity between the two-dimensional image data of said best-match locations and said corresponding reference sections and according to the degree of similarity between the relative positioning of said best-match locations and said corresponding reference sections.

A fingerprint verification method for verifying the identity of a person by comparing presently obtained fingerprint data with previously obtained fingerprint data, said method comprising the steps of:

• first enrolling one or more persons according to the steps of:
• forming a two-dimensional reference image of a fingerprint of a person seeking enrollment,
• partitioning said reference image into a plurality of two-dimensional candidate reference sections,
• determining the degree of distinctiveness of each candidate reference section within a two-dimensional local region surrounding said candidate reference section by comparing pixels of the two-dimensional image data of said candidate reference section to corresponding pixels of the two-dimensional image data of equal-sized areas throughout said local region, wherein said local region is larger than said candidate reference section and smaller than said reference image,
• determining the redetectability of each candidate reference section with respect to one or more subsequent images of the fingerprint of the person seeking enrollment by determining the degree of similarity between the image data of said candidate reference section and the image data of said one or more subsequent images,
• selecting a group of reference sections from said candidate reference sections according to the degree of distinctiveness and the degree of redetectability of said candidate reference sections, and
• saving the two-dimensional image and relative positioning data of each of the selected reference sections as fingerprint data for later use in verifying the identity of a person seeking verification;
• and later verifying the identity of a person seeking verification according to the steps of:
• obtaining an indication of which previously enrolled person that the person seeking verification claims to be,
• retrieving the two-dimensional image and relative positioning data of the reference sections of the previously enrolled person,
• forming a two-dimensional verify image of the fingerprint of the person seeking verification, wherein said verify image includes a plurality of two-dimensional verify regions each corresponding in relative position to and each larger in extend that a corresponding one of said reference sections,
• determining the best-match locations of said reference sections within their corresponding verify regions, wherein each best-match location is that location within a verify region at which the image data is most similar to the image data of the corresponding reference section,
• determining a displacement value for each of said reference sections, wherein each displacement value is a measure of the distance between the position of the best-match location and the expected position thereof,
• adjusting one or more of said displacement values to correct for misalignment of said verify image with respect to said reference image,
• classifying each reference section as tending to verify or not based on its corresponding correlation and displacement values, and
• verifying the identity of the person seeking verification if at least a predetermined number of said reference sections are classified as tending to verify.

A fingerprint verification method for verifying the identity of a person by comparing presently obtained fingerprint data with previously obtained fingerprint data, said method comprising the steps of:

• first enrolling one or more persons according to the steps of:
• forming a two-dimensional reference image of a fingerprint of a person seeking enrollment, wherein said reference image consists of grey pixels having a plurality of brightness values on a grey scale ranging between black and white,
• partitioning said reference image into a plurality of two-dimensional candidate reference sections from which a set of reference sections will be selected,
• rejecting certain candidate reference sections based on the grey scale values of the pixels within said candidate reference sections,
• performing an autocorrelation calculation for each remaining candidate reference section to determine the degree of distinctiveness of said candidate reference section within a local region surrounding said candidate reference section, wherein said autocorrelation calculation includes the steps of computing a plurality of correlation values throughout said local region, wherein each correlation values throughout said local region, wherein each correlation value is a measure of the similarity between the image data of said candidate reference section with the image data of an equal-sized area of said local region, and computing an autocorrelation score based on the highest correlation value computed within said local region but outside of a region near the location of said candidate reference section, wherein a high autocorrelation score indicates a locally non-distinct candidate reference section,
• selecting a number of the most distinctive of said candidate reference sections based on the results of the autocorrelation calculations,
• measuring the redetectability of each of the remaining candidate reference sections with respect to one or more subsequent two-dimensional images of the fingerprint of the person seeking enrollment by determining the degree of similarity between the image data of said remaining candidate reference sections and the image data of said one or more subsequent images,
• selecting a template of reference sections from the set of remaining candidate reference sections according to said redetectability of said remaining candidate reference sections with respect to said one or more subsequent images, and
• saving the two-dimensional image and relative positioning data of each of the selected reference sections as fingerprint data for later use in verifying the identity of a person seeking verification;
• and later verifying the identity of a person seeking verification according to the steps of:
• obtaining from the person seeking verification an indication of which previously enrolled person that the person seeking verification claims to be,
• retrieving the two-dimensional image and relative positioning data of the reference sections of the previously enrolled person,
• forming a two-dimensional verify image of the fingerprint of the person seeking verification, wherein said verify image includes a plurality of two-dimensional verify regions each corresponding in relative position to and each larger in extent than a corresponding one of said reference sections,
• determining the best-match locations of said reference sections within corresponding verify regions of said verify image, wherein each best-match location is that location within a verify region at which the image data is most similar to the image data of the corresponding reference section, wherein said best-match location is determined by the steps of computing correlation values throughout said verify region, wherein each correlation value is a measure of the similarity between the image data of said corresponding reference section and the image data of an equal-sized area of said verify region, and specifying the best-match location as that location within said verify region where the correlation value is highest,
• determining a displacement value for each of said reference sections, wherein each displacement value is a measure of the distance between the position of the best-match location and the expected position thereof,
• adjusting one or more of said displacement values to correct for misalignment of said verify image with respect to said reference image,
• classifying each reference section as tending to verify or not based on its corresponding correlation and displacement values, and
• verifying the identity of the person seeking verification if at least a predetermined number of said reference sections are classified as tending to verify.

A fingerprint verification method for verifying the identity of a person by comparing presently obtained fingerprint data with previously obtained fingerprint data, said method comprising the steps of:

• first enrolling one or more persons according to the steps of:
• forming a reference image of the ridges and valleys of a fingerprint of a person seeking enrollment, wherein said reference image consists of grey pixels having a plurality of brightness values on a grey scale ranging between black and white, and wherein said fingerprint ridges and valleys are represented by brightness values tending toward black or white,
• partitioning said reference image into a plurality of candidate reference sections from which a set of reference sections will be selected,
• rejecting certain candidate reference sections based on the grey scale values of the pixels within said candidate reference sections,
• performing an autocorrelation calculation for each remaining candidate reference section to determine the degree of distinctiveness of said candidate reference section within a local region surrounding said candidate reference section, wherein said autocorrelation calculation includes the steps of converting the grey pixels of said local region into binary pixels having brightness values of black or white, converting the grey scale pixels of said candidate reference section into trinary pixels having brightness values of black, grey, or white, computing a plurality of correlation values throughout said local region, wherein each correlation value is a measure of the similarity between the black and white trinary pixels of said candidate reference section with the black and white binary pixels of an equal-sized area of said local region, and computing an autocorrelation score based on the highest correlation value computed within said local region but outside of a region near the location of said candidate reference section, wherein a high autocorrelation score indicates a locally non-distinct candidate reference section;
• selecting a number of the most distinctive of said candidate reference sections based on the results of the autocorrelation calculations,
• measuring the redetectability of each of the remaining candidate reference sections with respect to one or more subsequent images of the finger print of the person seeking enrollment by determining the degree of similarity between the image data of said remaining candidate reference sections and the image data of said one or more subsequent images,
• selecting a template of reference sections from the set of remaining candidate reference sections according to said redetectability of said remaining candidate reference sections with respect to said one or more subsequent images, wherein the image data contained in each of said reference sections is locally unique, and
• saving the image and relative positioning data of each of the selected reference sections as fingerprint data for later use in verifying the identity of a person seeking verification;
• and later verifying the identity of a person seeking verification according to the steps of:
• obtaining from the person seeking verification an indication of which previously enrolled person that the person seeking verification claims to be,
• retrieving the image and relative positioning data of the reference sections of the previously enrolled person,
• forming a verify image of the ridges and valleys of the fingerprint of the person seeking verification, wherein said verify image includes binary pixels having brightness values of black or white to indicate said ridges and valleys, and wherein said verify image includes a plurality of verify regions each corresponding in relative position to and each larger in extent than a corresponding one of said reference sections,
• determining a first best-match location of one of said reference sections within a first verify region of said verify image, wherein each best-match location is that location within a verify region at which the image data is most similar to the image data of the corresponding reference section, wherein each best-match location is determined by the steps of computing correlation values throughout the verify region and specifying the first best-match location as that location within the verify region where the correlation value is highest, wherein each correlation value is a measure of the similarity between the black and white pixels of the reference section and the black and white pixels of an equal-sized area of the corresponding verify region, and then
• locating the rest of said verify regions relative to said first best-match location, and then
• determining the best-match locations of the rest of said reference sections with respect to said verify image by searching within the rest of said verify regions for best-match locations,
• determining a displacement value for each of said reference sections, wherein each displacement value is a measure of the distance between the position of the best-match location and the expected position thereof,
• adjusting one or more of said displacement values to correct for rotational misalignment of said verify image with respect to said reference image,
• classifying each reference section as tending to verify or not depending on its corresponding correlation and displacement values, and
• verifying the identity of the person seeking verification if at least a predetermined number of said reference sections are classified as tending to verify.

An apparatus for verifying the identify of a person by comparing a two-dimensional image of that person's fingerprint to reference data derived from a two-dimensional fingerprint image obtained during a prior enrollment procedure, said apparatus comprising:

• means for forming a two-dimensional image of a fingerprint during both enrollment and verification procedures,
• means for generating reference data from a fingerprint image obtained from a fingerprint during an enrollment procedure, wherein said reference data includes the two-dimensional image data and relative positioning of a plurality of reference sections of the fingerprint image, and wherein the image data contained in each of said reference sections is distinct relative to the image data adjacent to and surrounding said reference section and is redetectable by virtue of its similarity with the image data of one or more subsequent images of the fingerprint;
• means for saving said reference data for later use during the verification procedure;
• means for retrieving the reference data associated with an enrolled person when a person claiming to be that enrolled person seeks to be verified;
• means for defining a plurality of two-dimensional verify regions in the fingerprint image of the person seeking verification, wherein each verify region corresponds in position to one of said reference sections, and wherein each verify region is larger in extent than its corresponding reference section;
• means for determining a best-match location within each verify region at which the image data is most similar to the image data of its corresponding reference section;
• and
• means for verifying the identity of the person claiming to be enrolled according to the degree of similarity between the image data of said best-match locations and said corresponding reference sections, and according to the degree of similarity between the relative positioning of said best-match locations and said corresponding reference sections.