METHOD OF COMPRESSING DIGITAL INK

• US 20090046936A1
• Filed: 10/06/2008
• Published: 02/19/2009
• Est. Priority Date: 11/16/2001
• Status: Active Grant

• Current Assignee: Silverbrook Research Pty Limited
• Original Assignee: Silverbrook Research Pty Limited
• Inventors: Napper, Jonathon Leigh
• Granted Patent: US 7,650,033 B2
• Time in Patent Office: Days
• US Class Current: 382/238
• CPC Class Codes: G06V 30/1423 the instrument generating sequences of position coordinates corresponding to handwriting preprocessing or recognising digital ink G06V30/32
• CPC Class Codes: H03M 7/30 Compression speech analysis-synthesis for redundancy reduction G10L19/00; for image communication H04N; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
• CPC Class Codes: H03M 7/40 Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code

Abstract

A method of compressing a digital ink input including a sequence of strokes is provided in which each stroke is represented as a series of digital words representing x and y co-ordinates, at least one reference co-ordinate of each stroke is expressed in absolute terms, and a co-ordinate other than the at least one reference co-ordinate is expressed as an offset from a preceding co-ordinate. The co-ordinate other than the at least one reference co-ordinate is represented as a combination of an estimate determined from the previous m co-ordinates and a residual error value.

Claims

1. A method of compressing a digital ink input including a sequence of strokes, the method comprising the steps of:

representing each stroke as a series of digital words representing x and y co-ordinates;

expressing at least one reference co-ordinate of each stroke in absolute terms; and

expressing a co-ordinate other than the at least one reference co-ordinate as an offset from a preceding co-ordinate,

wherein the co-ordinate other than the at least one reference co-ordinate is represented as a combination of an estimate determined from the previous m co-ordinates and a residual error value.

2. The method of claim 1, further comprising the step of calculating the estimate using a linear prediction algorithm.

3. The method of claim 1, wherein the estimate is calculated from the previous m co-ordinates using the formula:

${\tilde{a}}_n=\underset{i=1}{\overset{m}{\sum <br><br>}}<br><br>c_i<br><br>{\mathrm{\alpha <br><br>}}_{n-i}$

where c_i are coefficients selected to model characteristics of the digital ink, and α

represents either an x or a y co-ordinate.

4. A method as claimed in claim 1 wherein m is 2, and a co-ordinate may be defined:

α

_n=C₁α

<sub>n−

1</sub>+C₂α

_n-2

5. A method as claimed in claim 4 wherein C₁>

0 and C₂<

0.

6. A method as claimed in claim 5 wherein:

1≦

C₁≦

3 and

−

2≦

C₂≦

1

7. A method as claimed in claim 6 wherein C₁=2 and C₂=−

1.

8. A method as claimed in any one of claims 3 to 7 wherein the coefficient values (C_i) for x co-ordinates are different to the coefficients for y co-ordinates.

9. A method as claimed in claim 8 wherein for x co-ordinates:

C₁=1.857

C₂=−

0.856, and

for y co-ordinates;

C₁=1.912

C₂=−

0.913

10. A method as claimed in claim 1 wherein m is 3, and a given co-ordinate may be defined:

{tilde over (α

)}_n=c₁α

_n-1+c₂α

_n-2+c₃α

_n-3

11. A method as claimed in claim 10 wherein C₁>

0 and C₂<

0 and C₃<

1.

12. A method as claimed in claim 10 or 11 wherein the coefficient values (C_i) for x co-ordinates are different to the coefficients for y co-ordinates.

13. A method as claimed in claim 12 wherein for x co-ordinates:

C₁=1.799

C₂=−

0.722

C₃=−

0.078, and

for y co-ordinates;

C₁=2.009

C₂=−

1.107

C₃=−

0.098

14. A method as claimed in claim 1, further comprising the steps of discarding the estimate, and storing the residual error.