Method for signature verification
First Claim
1. A method for controlling access to a system, the method comprising an initializing step wherein at least one authorized signature is recorded and a recognition step wherein an entrant signature is compared to the authorized signature, wherein:
- the initializing step comprises the steps of;
a) digitally recording a multiplicity of authorized sample signature received from digitizing means;
b) calculating a speed function corresponding to each sample signature, performing pairwise comparisons of the speed functions by applying dynamic time warping (to be referred to as "DTW"), and selecting that signature, to be referred to as a "representative signature," which is most typical according to the DTW calculations;
c) segmenting the representative signature into individual word features, to be referred to as "letters", based on relatively small local values of the speed function;
d) segmenting each of the remaining sample signatures into letters by mapping thereupon the segmentation of the representative signature by DTW, such that there is a correspondence between the letters of each pair of segmented sample signatures; and
e) constructing a reference signature by averaging each set of corresponding letters from the sample signatures; and
the recognition step comprises the steps of;
f) digitally recording an entrant signature received from digitizing means;
g) calculating a speed function for the entrant signature, and segmenting the entrant signature into letters by mapping thereupon the segmentation of the representative signature by DTW such that there is a correspondence between the letters of the entrant signature and the letters of the reference signature;
h) calculating a dynamic mismatch between the entrant signature and the representative signature by DTW;
i) calculating a shape mismatch, totalled over all the relevant letters, between the entrant signature and the reference signature;
j) comparing the dynamic and shape mismatch values to a predetermined acceptance criterion; and
k) if the acceptance criterion is satisfied, activating an electric circuit such that access to the system is made available.
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Accused Products
Abstract
A method and apparatus are described for verifying handwritten, human signatures, and for permitting access to a system if such a signature is accepted. In an initializing stage, an authorized entrant submits a sample of multiple signatures. A first reference signature is selected from the sample, and a second reference signature is constructed by averaging over the sample. When a subsequent, prospective entrant submits a signature, a dynamic mismatch is calculated with respect to the first reference signature, and a shape mismatch is calculated with respect to the second reference signature. The signature is accepted if it satifies a predetermined criterion that refers to the dynamic and shape mismatch values.
86 Citations
6 Claims
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1. A method for controlling access to a system, the method comprising an initializing step wherein at least one authorized signature is recorded and a recognition step wherein an entrant signature is compared to the authorized signature, wherein:
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the initializing step comprises the steps of; a) digitally recording a multiplicity of authorized sample signature received from digitizing means; b) calculating a speed function corresponding to each sample signature, performing pairwise comparisons of the speed functions by applying dynamic time warping (to be referred to as "DTW"), and selecting that signature, to be referred to as a "representative signature," which is most typical according to the DTW calculations; c) segmenting the representative signature into individual word features, to be referred to as "letters", based on relatively small local values of the speed function; d) segmenting each of the remaining sample signatures into letters by mapping thereupon the segmentation of the representative signature by DTW, such that there is a correspondence between the letters of each pair of segmented sample signatures; and e) constructing a reference signature by averaging each set of corresponding letters from the sample signatures; and the recognition step comprises the steps of; f) digitally recording an entrant signature received from digitizing means; g) calculating a speed function for the entrant signature, and segmenting the entrant signature into letters by mapping thereupon the segmentation of the representative signature by DTW such that there is a correspondence between the letters of the entrant signature and the letters of the reference signature; h) calculating a dynamic mismatch between the entrant signature and the representative signature by DTW; i) calculating a shape mismatch, totalled over all the relevant letters, between the entrant signature and the reference signature; j) comparing the dynamic and shape mismatch values to a predetermined acceptance criterion; and k) if the acceptance criterion is satisfied, activating an electric circuit such that access to the system is made available. - View Dependent Claims (2)
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3. A method for controlling access to a system which comprises verifying that an entrant signature is an authorized signature, the method comprising:
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a) digitally recording a sample set of n sample signatures made by an authorized entrant, n a positive integer at least equal to 2, each sample signature being received from digitizing means, each sample signature being described as a time-dependent vector function (x(t), y(t)), and the recording step resulting in a digitally stored record of the time-dependent functions x(t) and y(t), where x and y refer to mutually orthogonal positions on a planar surface, and t refers to time; b) for each sample signature, calculating a time-dependent speed function v(t) from the stored record; c) comparing the speed function of each sample signature with the speed function of each of the other sample signatures using dynamic time warping, resulting in the selection of a most typical sample signature with respect to the function signal, the selected signature to be referred to as the "first reference signature"; d) segmenting the first reference signature into individual features to be referred to as "letters", the breaks between letters being associated with relatively small local values of v(t); e) mapping the first reference signature onto each of the other n-1 sample signatures with the use of dynamic time warping such that each break between letters of the first reference signature is associated with a corresponding break point on each of the other sample signatures; f) segmenting each of the other n-1 sample signatures according to the corresponding break points, leading to a sample set of size n for each letter; g) applying affine invariant averaging to each letter sample set such that a reference letter corresponding to that set is created, all of the reference letters together constituting a second reference signature; h) digitally recording x(t) and y(t) of the entrant signature, and calculating a corresponding time-dependent speed function v(t); i) comparing v(t) of the entrant signature with v(t) of the first reference signature using dynamic time warping, such that a dynamic mismatch value is calculated; j) segmenting the entrant signature by mapping the first reference signature onto it using dynamic time warping and breaking it into entrant letters at the points corresponding to the break points of the first reference signature; k) comparing each entrant letter with the corresponding reference letter, the comparison performed using affine invariant averaging and resulting in a shape mismatch value for the entrant signature; l) comparing the shape mismatch value and the dynamic mismatch value with a predetermined selection criterion such that for certain shape and dynamic mismatch values, the entrant signature is accepted as an authorized signature, and for certain other shape and dynamic mismatch values, the entrant signature is rejected; and m) if the entrant signature is accepted, activating an electric circuit such that access to the system is made available. - View Dependent Claims (4)
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5. An access-controlled system which comprises:
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a) means for digitizing a multiplicity of handwritten, human signatures, such that for each signature, a digital signal is produced that represents the signature as a time-dependent vector function (x(t), y(t)), the multiplicity of signatures to include at least two sample signatures from an authorized person and an entrant signature; b) means for digitally storing the time-dependent vector functions; c) means for digitally processing at least some of the stored time-dependent vector functions, said means comprising;
means for calculating a time-dependent speed function v(t) from each stored function;
means for comparing each pair of speed functions by dynamic time warping such that a dynamic mismatch is calculated;
means for selecting a most typical speed function;
means for segmenting the signature (to be referred to as the "first reference signature") that corresponds to the most typical speed function, such segmentation to be carried out with reference to relatively small local values of v(t), each of the resulting segments to be referred to as a "letter";
means for mapping the first reference signature, by dynamic time warping, onto each of the other signatures whose corresponding stored functions are being processed, such that each break between letters of the first reference signature is associated with a corresponding break point on each of the other signatures; and
means for segmenting each of the other signatures according to the corresponding break points;d) digital processing means for applying affine invariant averaging to a multiplicity of corresponding letters, such that the processing of each pair of letters results in the calculation of a shape mismatch, and the letter-by-letter processing of the sample signatures results in the construction of a second reference signature; e) digital processing means for comparing a predetermined selection criterion to the dynamic mismatch between the entrant signature and the first reference signature, and to the shape mismatch, totalled over all corresponding letters, between the entrant signature and the second reference signature; and f) means, responsive to the comparison means, for permitting access to the system if the selection criterion is satisfied.
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6. An access-controlled system which comprises:
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a) means for digitizing a multiplicity of handwritten, human signatures, such that for each signature, a digital signal is produced that represents the signature as a time-dependent vector function (x(t), y(t)), the multiplicity of signatures to include at least two sample signatures from an authorized person and an entrant signature; b) means for digitally storing the time-dependent vector functions; c) means for digitally processing at least some of the stored time-dependent vector functions, said means comprising;
means for calculating a time-dependent speed function v(t) from each stored function;
means for comparing each pair of speed functions by dynamic time warping such that a dynamic mismatch is calculated;
means for selecting a most typical speed function;
means for segmenting the signature (to be referred to as the "first reference signature") that corresponds to the most typical speed function, such segmentation to be carried out with reference to relatively small local values of v(t), each of the resulting segments to be referred to as a "letter";
means for mapping the first reference signature, by dynamic time warping, onto each of the other signatures whose corresponding stored functions are being processed, such that each break between letters of the first reference signature is associated with a corresponding break point on each of the other signatures; and
means for segmenting each of the other signatures according to the corresponding break points;d) digital processing means for averaging each set of corresponding letters from the sample signatures, the letter-by-letter processing of the sample signatures resulting in the construction of a second reference signature; e) means for calculating a shape mismatch, totalled over all the relevant letters, between the entrant signature and the second reference signature; f) digital processing means for comparing a predetermined selection criterion to the dynamic mismatch between the entrant signature and the first reference signature, and to the shape mismatch between the entrant signature and the second reference signature; and g) means, responsive to the comparison means, for permitting access to the system if the selection criterion is satisfied.
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Specification