Method and system for modeling handwriting using polynomials as a function of time

• US 5,764,797 A
• Filed: 04/25/1995
• Issued: 06/09/1998
• Est. Priority Date: 04/25/1995
• Status: Expired due to Term

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Adcock, James L.
• Primary Examiner(s): SHALWALA, BIPIN H
• Application Number:
  US08/428,412
• Time in Patent Office: 1,141 Days
• Field of Search: 382/181, 382/182, 382/184, 382/186-189, 382/241, 382/137, 382/195, 382/197, 382/198, 382/201, 382/203, 382/122, 382/123, 395/141, 345/441
• US Class Current: 382/187
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/186 by deriving mathematical or geometrical properties from the whole image
• CPC Class Codes: G06V 30/333 Preprocessing; Feature extraction
• CPC Class Codes: G06V 30/373 using a special pattern or subpattern alphabet

Abstract

A method and system for modeling handwriting using polynomials as a function of time. In a preferred embodiment, a user inputs handwriting by writing with an electronic pen on an electronic tablet. The tablet samples the location of the tip of the pen on the tablet from pen down until pen up at periodic intervals as each stroke in a character is written and inputs the (x,y) coordinates for each stroke in the character to a normalizer. The normalizer normalizes the (x,y) coordinates and inputs the normalized (x,y) coordinates to a featurizer. The featurizer generates a set of features that represent each stroke in the character. In the preferred embodiment, the features are coefficients of a Chebyshev. After the Chebyshev coefficients have been generated for each stroke in the character, the featurizer normalizes the set of Chebyshev coefficients. During training, the normalized Chebyshev coefficients are input to a prototype generator. After receiving all of the input samples for a given character and the corresponding set of Chebyshev coefficients for each sample, the prototype generator generates one or more prototypes of the given character and stores the prototype(s) in a database. During recognition, the normalized Chebyshev coefficients are input to a classifier. After receiving the set of Chebyshev coefficients for a character to be recognized, the classifier compares the set of Chebyshev coefficients to the prototypes stored in the database to find an acceptable match. If an acceptable match is found, the character corresponding to the matching prototype is output.

Claims

1. A method for recognizing handwriting in a computer system, the handwriting being written on an electronic tablet using an electronic pen, the handwriting comprising at least one character, each character comprising at least one stroke, the method comprising the computer-implemented steps of:

for each character in the handwriting,

for each stroke in the character,

obtaining a plurality of coordinates representing the location of a pen tip on a tablet from pen down until pen up at periodic intervals as the stroke is written,

normalizing the (x, y) coordinates;

generating coefficients of a Chebyshev polynomial to approximate the normalized (x,y) coordinates;

comparing the generated coefficients for all strokes in the character to a plurality of stored prototypes, each prototype comprising coefficients generated from an allowable character;

determining whether the generated coefficients match any of the stored prototypes; and

when there is a match, outputting the character corresponding to the stored prototype that matches the generated coefficients.

2. The method of claim 1, wherein the step of normalizing the (x,y) coordinates comprises the step of normalizing a time duration of each stroke in the character.

3. The method of claim 1, wherein the step of normalizing the (x,y) coordinates comprises the step of normalizing a position of the character.

4. The method of claim 1, wherein the step of normalizing the (x,y) coordinates comprises the step of normalizing the size of a character.

5. The method of claim 1, wherein the step of generating coefficients comprises the step of generating coefficients using the method of least squares applied to the normalized x coordinates versus time and to the normalized y coordinates versus time.

6. The method of claim 1, wherein the step of generating coefficients comprises the step of generating a predetermined number of coefficients based upon the number of strokes in the character.

7. The method of claim 6, wherein the number of coefficients generated for each character is approximately twenty.

8. The method of claim 1, further comprising the step of, for each character in the handwriting, normalizing the generated coefficients.

9. A computer system for recognizing handwriting, the handwriting being written on an electronic tablet using an electronic pen, the handwriting comprising at least one character, each character comprising at least one stroke, the system comprising;

a tablet for obtaining a plurality of (x,y) coordinates representing the location of a pen tip on a tablet from pen down until pen tip at periodic intervals as a stroke in a character is written;

a normalizer for normalizing the (x,y) coordinates;

a featurizer for generating coefficients of a Chebyshev polynomial to approximate the handwriting from the normalized (x y) coordinates;

a prototype generator for generating prototypes of allowable characters, each prototype comprising coefficients generated from an allowable character;

a database for storing the prototypes of the allowable characters;

a classifier for comparing the coefficients representing a character to be recognized to the stored prototypes and determining whether the coefficients match any of the stored prototypes; and

a display device for outputting the character corresponding to the stored prototype that matches the coefficients.

10. A computer-readable medium containing instructions for causing a computer system to recognize handwriting, the handwriting being written on an electronic tablet using an electronic pen, the handwriting comprising at least one character, each character comprising at least one stroke, by:

for each character in the handwriting,

for each stroke in the character,

obtaining a plurality of coordinates representing the location of a pen tip on a tablet from pen down until pen up at periodic intervals as the stroke is written;

normalizing the (x, y) coordinates;

generating coefficients of a Chebyshev polynomial to approximate the normalized (x, y) coordinates as a function of time;

comparing the generated coefficients for all strokes in the character to a plurality of stored prototypes, each prototype comprising coefficients generated from an allowable character;

determining whether the generated coefficients match any of the stored prototypes; and

when there is a match, outputting the character corresponding to the stored prototype that matches the generated coefficients.

11. The computer-readable medium of claim 10 wherein the normalizing of the (x, y) coordinates comprises normalizing a time duration of each stroke in the character.

12. The computer-readable medium of claim 10 wherein the normalizing of the (x, y) coordinates comprises normalizing a position of the character.

13. The computer-readable medium of claim 10 wherein the normalizing of the (x, y) coordinates comprises normalizing the size of a character.

14. The computer-readable medium of claim 10 wherein the generating of coefficients comprises generating coefficients using the method of least squares applied to the normalized x coordinates versus time and to the normalized y coordinates versus time.

15. The computer-readable medium of claim 10 wherein the generating of coefficients comprises generating a predetermined number of coefficients based upon the number of strokes in the character.