Signature verification data compression for storage on an identification card

• US 5,054,088 A
• Filed: 09/20/1989
• Issued: 10/01/1991
• Est. Priority Date: 09/20/1989
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gunderson, Steven C., Wadia, Aspi B.
• Primary Examiner(s): Moore, David K.
• Assistant Examiner(s): Mancuso, Joseph
• Application Number:
  US07/409,906
• Time in Patent Office: 741 Days
• Field of Search: 382/3, 382/56, 382/13, 364/419, 364/724.1, 358/426, 358/428, 358/431, 340/825.3, 340/825.34
• US Class Current: 382/120
• CPC Class Codes: G06V 40/30 Writer recognition; Reading and verifying signatures
• CPC Class Codes: G07C 9/247 electronically, e.g. by comparing signal of hand-writing with a reference signal from the pass

Abstract

Apparatus and methods are described which take advantage of the peculiar characteristics of dynamic signature data while segmenting and compressing such data for storage on a limited capacity device. Compression is accomplished by digital oversampling, segmenting, filtering, decimating and later interpolating reference signature data, thereby allowing storage in compressed form without significant matching degradation. The pen down and pen up information which define signature segments is separated from the pressure waveform and stored in a separate array for each reference signature. The acceleration and pressure data are then filtered, decimated and stored for each reference signature. Later, during identity verification, the stored acceleration and pressure data are restored to an oversampled rate by interpolation. To verify the identity of a person supplying a trial signature, each segment of the trial signature is compared with corresponding segments of one or more of the stored reference signatures.

Claims

1. The method of enrolling signature information of an authorized user onto an identification card comprising the steps of:

(a) acquiring a first signal and a second signal representative of a signature of said user;

(b) sampling said first signal at a rate of at least n times a highest frequency component of said first signal which is to be preserved, where n is an integer greater than three;

(c) sampling said second signal at a rate of at least m times a highest frequency component of said second signal which is to be preserved, where m is an integer greater than three;

(d) locating portions of said first signal representative of periods of time when said pen was in contact with a writing surface;

(e) storing on said card, an array of the starting and ending times identifying when said pen was in contact with said writing surface;

(f) digitally filtering said samples representing said first signal to remove substantially all energy at frequencies above said highest frequency component of said first signal to be preserved;

(g) digitally filtering said samples representing said second signal to remove substantially all energy at frequencies above said highest frequency component of said second signal to be preserved;

(h) discarding (n/2) - 1 of said filtered first samples out of each n/2 of said filtered first samples;

(i) discarding (m/2) - 1 of said filtered second samples out of each m/2 of said filtered second samples;

(j) storing the remaining of said filtered first samples on said card;

(k) storing the remaining of said filtered second samples on said card.

2. The method of claim 1, wherein said first signal is a change of pressure signal and said second signal is an acceleration signal.

3. The method of claim 2, further comprising the steps of:

repeating steps (a) through (i) at least five times to acquire at least five signatures;

matching the respective samples of each signature with the corresponding samples of each other signature to obtain a segmentation measure, correlation measure and a coherence measure for each pair of signatures;

selecting as primary reference signatures, a pair of said signatures;

repeating steps (j) and (k) to store said primary reference signatures.

4. The method of claim 3, further comprising the step of:

again performing steps j) and k) to store a secondary reference signature.

5. The method of verifying the identity of a holder of an identification card having signature information of an authorized user stored thereon, comprising the steps of:

acquiring a first signal and a second signal representative of a trial signature of said holder;

sampling said first signal at a rate of at least n times a highest frequency component of said first signal which is to be preserved, where n is an integer greater than three;

sampling said second signal at a rate of at least m times a highest frequency component of said second signal which is to be preserved, where m is an integer greater than three;

locating portions of said first signal representative of periods of time when a trial signature pen was in contact with a writing surface;

digitally filtering said samples representing said first signal to remove substantially all energy at frequencies above said highest frequency component of said first signal to be preserved;

digitally filtering said samples representing said second signal to remove substantially all energy at frequencies above said highest frequency component of said second signal to be preserved;

reading from said identification card, third samples representing a third signal and fourth samples representing a fourth signal,

reading from said identification card, an array of starting and ending times identifying when a reference signature pen was in contact with a writing surface while writing a reference signature represented by said third and said fourth samples;

interpolating between each of said third samples to recover (m/2)-1 samples representative of samples of said third signal which had been discarded prior to storing said third samples on said card, m being an integer greater than three;

interpolating between each of said fourth samples to recover (n/2)-1 samples representative of samples of said fourth signal which had been discarded prior to storing said fourth samples on said card, n being an integer greater than three;

identifying those third samples and recovered samples of said third signal which represent said third signal while said reference signature pen was in contact with writing surface;

identifying those fourth samples and recovered samples of said fourth signal which represent said fourth signal while said reference signature pen was in contact with said writing surface;

matching said first samples representing said first signal when said trial pen was in contact with said writing surface with said identified third samples and recovered samples of said third signal which represent said third signal while said reference signature pen was in contact with writing surface and matching said second samples representing said second signal when said trial pen was in contact with said writing surface with said identified fourth samples and recovered samples of said fourth signal which represent said fourth signal while said reference signature pen was in contact with writing surface to obtain a similarity measure;

accepting said holder of said identification card as said authorized user of said identification card if said similarity measure is greater than a threshold.

6. The method of claim 5, further comprising the steps of:

tentatively rejecting said holder of said identification card as said authorized user of said identification card if said similarity measure is less than said threshold;

reading from said identification card, fifth samples representing a fifth signal and sixth samples representing a sixth signal,

reading from said identification card, an array of starting and ending times identifying when a reference signature pen was in contact with a writing surface while writing a reference signature represented by said fifth and said sixth samples;

interpolating between each of said fifth samples to recover (n/2)-1 samples representative of samples of said fifth signal which had been discarded prior to storing said fifth samples on said card, n being an integer greater than three.

interpolating between each of said sixth samples to recover (m/2)-1 samples representative of samples of said sixth signal which had been discarded prior to storing said sixth samples on said card, m being an integer greater than three.

identifying those fifth samples and recovered samples of said fifth signal which represent said fifth signal while said reference signature pen was in contact with writing surface;

identifying those sixth samples and recovered samples of said sixth signal which represent said sixth signal while said reference signature pen was in contact with said writing surface;

matching said first samples representing said first signal when said trial pen was in contact with said writing surface with said identified fifth samples and recovered samples of said fifth signal which represent said fifth signal while said reference signature pen was in contact with a writing surface and matching said second samples representing said second signal when said trial pen was in contact with said writing surface with said identified sixth samples and recovered samples of said sixth signal which represent said sixth signal while said reference signature pen was in contact with a writing surface to obtain a second score;

accepting said holder of said identification card as said authorized user of said identification card if said second similarity measure is greater than said threshold.

7. The method of reducing for storage, a number of digital samples needed to represent a signal and recovering representative samples for correlation with another signal, comprising the steps of:

sampling said signal at a rate exceeding n times a highest frequency component of said signal which is to be preserved, where n is an integer greater than three;

digitally filtering said samples representing said signal to remove substantially all energy at frequencies above said highest frequency component of said signal to be preserved;

discarding (n/2) - 1 of said samples out of each n/2 of said samples;

storing the remaining of said samples;

interpolating between each of said stored samples to recover (n/2) -1 samples representative of said samples which have been discarded.

8. The method of claim 7, wherein said step of interpolating further comprises the steps of:

inserting (n/2 -

     1) zero valued samples between each of said stored samples to restore an original number of samples.

digitally filtering said restored samples to remove substantially all energy at frequencies above said highest frequency component of said signal to be preserved;

multiplying each filtered sample by n/2 to restore said filtered samples to an amplitude representative of said signal.

9. The method of reducing for storage, a number of digital samples needed to represent information in a signal to permit recovery of representative samples for correlation with another signal, comprising the steps of:

sampling said signal at a rate exceeding n times a highest frequency component of said signal which is to be preserved, where n is an integer greater than three;

segmenting said signal and storing a starting sample number and number of samples for each segment;

digitally filtering said samples representing said signal to remove substantially all energy at frequencies above said highest frequency component of said signal to be preserved;

discarding (n/2) - 1 of said samples out of each n/2 of said samples;

storing the remaining of said samples.

10. The method of claim 9 further comprises the steps of:

interpolating between each of said stored samples to recover (n/2) - 1 samples representative of said samples which have been discarded.

11. The method of compressing signature information signals for storage comprising the steps of:

sampling said signals at a rate exceeding n times a highest frequency component of said signal which is to be preserved, where n is an integer greater than three;

segmenting one of said signals and storing a starting sample number and number of samples for each segment;

digitally filtering said samples representing each of said signals to remove substantially all energy at frequencies above said highest frequency component of said signal to be preserved;

discarding (n/2) -1 of said samples out of each n/2 of said samples;

storing the remaining of said samples of each of said signals.

12. The method of claim 11, wherein said one of said signals is a change of pressure signal and where another of said signals is and acceleration signal.

13. The method of restoring a segment of said change of pressure signal of claim 12 comprising the steps of:

inserting (n/2 -

     1) zero valued samples between each of said stored samples to restore an original number of samples.

digitally filtering said restored samples to remove substantially all energy at frequencies above said highest frequency component of said signal to be preserved;

multiplying each filtered sample by n/2 to restore said filtered samples to an amplitude representative of said signal.

14. A computer program for enrolling a signature of an authorized user onto an identification card comprising:

means for receiving a first signal representative of changes in pressure between a pen and a writing surface during signing of said signature by said user, said first signal having been sampled at a rate of at least n times a highest frequency component of said first signal which is to be preserved, where n is an integer greater than three;

means for receiving a second signal representative of acceleration of said pen during signing of said signature by said user, said second signal having been sampled at a rate of at least m times a highest frequency component of said first signal which is to be preserved, where m is an integer greater than three;

means for locating portions of said first signal representative of periods of time when said pen was in contact with a writing surface;

means for storing on said card, an array of the starting and ending samples identifying when said pen was in contact with said writing surface;

means for digitally filtering said samples representing said first signal to remove substantially all energy at frequencies above said highest frequency component of said first signal to be preserved;

means for digitally filtering said samples representing said second signal to remove substantially all energy at frequencies above said highest frequency component of said second signal to be preserved;

means for discarding (n/2) -1 of said filtered first samples out of each n/2 of said filtered first samples;

means for discarding (m/2) - 1 of said filtered second samples out of each m/2 of said filtered second samples;

means for storing the remaining of said filtered first samples on said card;

means for storing the remaining of said filtered second samples on said card.

15. The computer program of claim 14, further comprising:

means for repeatedly operating said means for receiving, means for locating, means for filtering, and means for discarding of claim 14 to acquire at least five signatures;

means for matching the respective samples of each signature with the corresponding samples of each other signature to obtain a segmentation measure, correlation measure and a coherence measure for each pair of signatures;

means for selecting as primary reference signatures, a pair of said signatures;

means for storing said primary reference signatures on said card.

16. A computer program for verifying the identity of a holder of an identification card having signature information of an authorized user stored thereon comprising:

means for receiving a first signal representative of a trial signature of said holder, said first signal having been sampled at a rate of at least n times a highest frequency component of said first signal which is to be preserved, where n is an integer greater than three;

means for receiving a second signal representative of said trial signature of said holder, said second signal having been sampled at a rate of at least m times a highest frequency component of said second signal which is to be preserved, where m is an integer greater than three;

means for locating portions of said first signal representative of periods of time when said trial signature pen was in contact with a writing surface;

means for digitally filtering said samples representing said first signal to remove substantially all energy at frequencies above said highest frequency component of said first signal to be preserved;

means for digitally filtering said samples representing said second signal to remove substantially all energy at frequencies above said highest frequency component of said second signal to be preserved;

means for receiving from said identification card, third samples representing a third signal and fourth samples representing a fourth signal,

means for receiving from said identification card, an array of starting and ending times identifying when a reference signature pen was in contact with a writing surface while writing a reference signature represented by said third and said fourth samples;

means for interpolating between each of said third samples to recover (m/2)-1 samples representative of samples of said third signal which had been discarded prior to storing said third samples on said card, m being an integer greater than three.

means for interpolating between each of said fourth samples to recover (n/2)-1 samples representative of samples of said fourth signal which had been discarded prior to storing said fourth samples on said card, n being an integer greater than three.

means for identifying those third samples and recovered samples of said third signal which represent said third signal while said reference signature pen was in contact with writing surface;

means for identifying those fourth samples and recovered samples of said fourth signal which represent said fourth signal while said reference signature pen was in contact with said writing surface;

means for matching said first samples representing said first signal when said trial pen was in contact with said writing surface with said identified third samples and recovered samples of said third signal which represent said third signal while said reference signature pen was in contact with writing surface and matching said second samples representing said second signal when said trial pen was in contact with said writing surface with said identified fourth samples and recovered samples of said fourth signal which represent said fourth signal while said reference signature pen was in contact with writing surface to obtain a similarity measure;

means for accepting said holder of said identification card as said authorized user of said identification card if said similarity measure is greater than a threshold.

17. A program for reducing a number of digital samples needed to represent a handwriting signal sampled at a rate exceeding n times a highest frequency component of said signal which is to be preserved, where n is an integer greater than three and recovering representative samples for correlation with another signal, comprising:

means for locating portions of said signal representative of periods of time when a signature pen was in contact with a writing surface;

means for filtering said samples representing said signal to remove substantially all energy at frequencies above said highest frequency component of said signal to be preserved;

means for discarding (n.2) - 1 of said samples out of each n/2 of said samples;

means for interpolating between each of said stored samples to recover (n/2) - 1 samples representative of said samples which have been discarded.

18. The program of claim 17, wherein said means for interpolating further comprises:

means for inserting (n/2 -

     1) zero valued samples between each of said stored samples to restore an original number of samples.

means for digitally filtering said restored samples to remove substantially all energy at frequencies above said highest frequency component of said signal to be preserved;

means for multiplying each filtered sample by n/2 to restore said filtered samples to an amplitude representative of said signal.

19. A system for reducing for storage, a number of digital samples needed to represent information in a signal to permit recovery of representative samples for correlation with another signal, comprising:

means for sampling said signal at a rate exceeding n times a highest frequency component of said signal which is to be preserved, where n is an integer greater than three;

means for segmenting said signal and storing a starting sample number and number of samples for each segment;

means for digitally filtering said samples representing said signal to remove substantially all energy at frequencies above said highest frequency component of said signal to be preserved;

means for discarding (n/2) - 1 of said samples out of each n/2 of said samples;

means for storing the remaining of said samples.

20. The system of claim 19, further comprising:

means for interpolating between each of said stored samples to recover (n/2) -1 samples representative of said samples which have been discarded.

21. The apparatus for compressing signature information signals for storage, comprising:

means for sampling said signals at a rate exceeding n times a highest frequency component of said signal which is to be preserved, where n is an integer greater than three;

means for segmenting one of said signals and storing a starting sample number and number of samples for each segment;

means for digitally filtering said samples representing each of said signals to remove substantially all energy at frequencies above said highest frequency component of said signal to be preserved;

means for discarding (n/2) - 1 of said samples out of each n/2 of said samples;

means for storing the remaining of said samples of each of said signals.

22. The apparatus of claim 21 wherein said one of said signals is a change of pressure signal and where another of said signals is an acceleration signal.

23. The apparatus for restoring a segment of said change of pressure signal of claim 22, comprising:

means for inserting (n/2-1) zero values samples between each of said stored samples to restore an original number of samples.

means for digitally filtering said restored samples to remove substantially all energy at frequencies above said highest frequency component of said signal to be preserved.