Method of imaging a coding pattern with data elements encoding by pulse-position modulation

• US 7,913,923 B2
• Filed: 02/05/2008
• Issued: 03/29/2011
• Est. Priority Date: 02/08/2007
• Status: Expired due to Fees

• Current Assignee: Silverbrook Research Pty Limited
• Original Assignee: Silverbrook Research Pty Limited
• Inventors: Silverbrook, Kia, Lapstun, Paul
• Primary Examiner(s): Le; Thien M.
• Assistant Examiner(s): TAYLOR, APRIL ALICIA
• Application Number:
  US12/025,756
• Publication Number:
  US 20080191016A1
• Time in Patent Office: 1,148 Days
• Field of Search: 235/375, 235/487, 235/494, 235/454
• US Class Current: 235/494
• CPC Class Codes: G06F 2203/0337 Status LEDs integrated in the mouse to provide visual feedback to the user about the status of the input device, the PC, or the user
• CPC Class Codes: G06F 2203/0384 Wireless input, i.e. hardware and software details of wireless interface arrangements for pointing devices
• CPC Class Codes: G06F 3/0321 by optically sensing the absolute position with respect to a regularly patterned surface forming a passive digitiser, e.g. pen optically detecting position indicative tags printed on a paper sheet constructional details of pen-shaped pointing devices G06F3/03545, G06F3/03542, G06F3/037
• CPC Class Codes: G06F 3/03545 Pens or stylus
• CPC Class Codes: G06K 19/06 characterised by the kind of the digital marking, e.g. shape, nature, code
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06T 7/32 using correlation-based methods

Abstract

A method of imaging a coding pattern disposed on a surface of a substrate. The method includes the steps of: (a) capturing an image of a portion of the coding pattern; and (b) low-pass filtering the captured image so as to obscure data elements in the image and preserve target elements in the image. The data elements encode data values by pulse position modulation, which facilitates the low-pass filtering.

Claims

1. A method of imaging a coding pattern disposed on a surface of a substrate, said method comprising the steps of:

(a) capturing an image of a portion of said coding pattern, said coding pattern comprising;

a plurality of target elements defining a target grid, said target grid comprising a plurality of cells, wherein neighboring cells share target elements;

a plurality of data elements contained in each cell; and

a plurality of tags, each tag being defined by a plurality of contiguous cells, each tag comprising respective local tag data encoded by a respective set of said data elements,

wherein said data elements encode data values by pulse position modulation;

(b) low-pass filtering said captured image so as to obscure said data elements and preserve said target elements;

(c) observing a perspective distortion of said preserved target elements due to a 3D orientation of said reader relative to said surface; and

(d) calculating a 2D perspective transform using said target elements.

2. The method of claim 1, wherein said data elements are macrodots.

3. The method of claim 2, wherein a portion of data is represented by a macrodot occupying one of a plurality of possible positions within a cell, each position representing one of a plurality of possible data values.

4. The method of claim 2, wherein a n-bit portion of data is represented by a macrodot occupying one of 2ⁿ possible positions within a cell, each position representing one of 2ⁿ possible data values, wherein n is an integer.

5. The method of claim 1, wherein each cell defines a symbol group, each symbol group comprising a plurality of Reed-Solomon symbols encoded by a plurality of said data elements.

6. The method of claim 5, wherein each symbol comprises two halves, each half comprising 2 bits of data represented by a macrodot occupying one of 4 possible positions within said half.

7. The method of claim 5, wherein said local tag data is encoded as a local codeword comprised of a set of said Reed-Solomon symbols.

8. The method of claim 7, wherein each local codeword identifies a location of a respective tag.

9. The method of claim 1, wherein each tag comprises a plurality of replications of said local codeword, such that any tag-sized portion of said coding pattern is guaranteed to contain said local codeword irrespective of whether a whole tag is contained in said portion.

10. A system for imaging a coding pattern disposed on a surface of a substrate, said system comprising the steps of:

(A) said substrate, wherein said coding pattern comprises;

a plurality of target elements defining a target grid, said target grid comprising a plurality of cells, wherein neighboring cells share target elements;

a plurality of data elements contained in each cell; and

a plurality of tags, each tag being defined by a plurality of contiguous cells,

each tag comprising respective local tag data encoded by a respective set of said data elements,

wherein said data elements encode data values by pulse position modulation, and

(B) an optical reader comprising;

an image sensor for capturing an image of a portion of said coding pattern; and

a processor configured for;

low-pass filtering said captured image so as to obscure said data elements and preserve said target elements;

observing a perspective distortion of said preserved target elements due to a 3D orientation of said reader relative to said surface; and

calculating a 2D perspective transform using said target elements.

11. The system of claim 10, wherein said data elements are macrodots.

12. The system of claim 11, wherein a portion of data is represented by a macrodot occupying one of a plurality of possible positions within a cell, each position representing one of a plurality of possible data values.

13. The system of claim 11, wherein a n-bit portion of data is represented by a macrodot occupying one of 2ⁿ possible positions within a cell, each position representing one of 2ⁿ possible data values, wherein n is an integer.

14. The system of claim 10, wherein each cell defines a symbol group, each symbol group comprising a plurality of Reed-Solomon symbols encoded by a plurality of said data elements.

15. The system of claim 14, wherein each symbol comprises two halves, each half comprising 2 bits of data represented by a macrodot occupying one of 4 possible positions within said half.

16. The system of claim 14, wherein said local tag data is encoded as a local codeword comprised of a set of said Reed-Solomon symbols.

17. The system of claim 10, wherein each tag comprises a plurality of replications of said local codeword, such that any tag-sized portion of said coding pattern is guaranteed to contain said local codeword irrespective of whether a whole tag is contained in said portion.

18. The system of claim 10, wherein said reader is an optically imaging pen having a nib.