Maxicode data extraction using spatial domain features exclusive of fourier type domain transfer processing

• US 5,814,801 A
• Filed: 11/01/1996
• Issued: 09/29/1998
• Est. Priority Date: 05/31/1995
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Metanetics Corporation
• Inventors: Wang, Ynjiun P., Ye, Angi
• Primary Examiner(s): Hajec, Donald T.
• Assistant Examiner(s): Eisenberg, Jacob
• Application Number:
  US08/742,367
• Time in Patent Office: 697 Days
• Field of Search: 235/454, 235/462, 235/464, 235/494
• US Class Current: 235/454
• CPC Class Codes: G06K 19/06037 multi-dimensional coding
• CPC Class Codes: G06K 19/06168 the marking being a concentric barcode
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence
• CPC Class Codes: G06K 7/1421 Circular bar codes
• CPC Class Codes: G06K 7/1456 determining the orientation of the optical code with respect to the reader and correcting therefore
• CPC Class Codes: G06K 7/1486 Setting the threshold-width for bar codes to be decoded
• CPC Class Codes: G06K 7/1491 the method including a reconstruction step, e.g. stitching two pieces of bar code together to derive the full bar code

Abstract

Prior methods of reading MaxiCode dataforms have been subject to reduced resolution image scaling and processing and speed constraints of Fourier transform computations. Described spatial domain data extraction methods provide bull'"'"'s eye center location by T-sequence pixel pattern analysis, axis identification by moment analysis of data cell pairs, and integral width square wave analysis of illumination transitions to avoid reading-line cell fragmentation. The center and top of a MaxiCode are identified in high-resolution pixel data, without scaling reduction or Fourier type frequency domain processing. Data is extracted serially from rows of data cells by sampling along lines of pixels aligned by fragmentation analysis so as to traverse complete rows of data cells. Dynamic thresholding accurately defines illumination value transitions between adjacent linear groups of data cells, each group consisting of one or more data cells of the same reflectivity. Application of disclosed methods to other types of dataforms is described.

Claims

1. A method of extracting data by processing a MaxiCode type of dataform entirely in the spatial domain exclusive of Fourier type domain transfer processing, said dataform including a pattern of similarly aligned hexagonal data cells, comprising the steps of:

(a) providing pixel data for an image area, said pixel data representative of illumination reflected from said hexagonal data cells;

(b) determining the orientation of a plurality of said hexagonal data cells positioned in a row in side-to-side straight line alignment;

(c) extracting data from said plurality of hexagonal data cells by sampling said pixel data along a line traversing each data cell of said plurality; and

(d) processing said extracted data to recover information encoded in said dataform, independently of use of Fourier type processing in any step of said method.

2. A method as in claim 1, wherein in step (b) said orientation is determined by moment analysis of a portion of said pixel data, said orientation corresponding to the derived moment of two hexagonal data cells of said plurality which are contiguous and of the same reflectivity.

3. A method as in claim 1, wherein in step (b) said row of hexagonal data cells is aligned with a reference line defined by sampling said pixel data to identify a traversal line of pixel data characterized by illumination value transitions spaced along said traversal line at integral multiples of data cell width.

4. A method of extracting data from a MaxiCode type of dataform, having a pattern of similarly aligned hexagonal data cells of differing reflectivity values, comprising the steps of:

(a) providing pixel data for an image area, said pixel data representative of illumination reflected from said hexagonal data cells;

(b) determining the orientation of a plurality of said hexagonal data cells positioned in a row in side-to-side straight line alignment;

(c) sampling image data from said plurality of hexagonal data cells along a line traversing each data cell of said plurality; and

(d) extracting data from said image data sampled in step (c) by determining spacings of illumination value transitions between data cell groups along said line, each said data cell group consisting of one or more contiguous data cells of similar reflectivity value.

5. A method as in claim 4, wherein in step (b) said orientation is determined by moment analysis of a portion of said pixel data, said orientation corresponding to the derived moment of two hexagonal data cells of said plurality which are contiguous and of the same reflectivity.

6. A method as in claim 4, wherein in step (b) said row of hexagonal data cells is aligned with a reference line defined by sampling said pixel data to identify a traversal line of pixel data characterized by illumination value transitions spaced along said traversal line at integral multiples of data cell width.

7. A method of extracting data from a dataform having a pattern of rows of similarly aligned lighter and darker data cells of a regular polygon shape, comprising the steps of:

(a) providing pixel data for an image area, said pixel data representative of reflected images of said data cells;

(b) determining, by moment analysis of a portion of said pixel data, the orientation of a normal traversal line having an alignment normal to sides of a series of said data cells positioned in a row in side-to-side straight line alignment;

(c) sampling image data from a plurality of said data cells along a sampling line traversing each data cell of said plurality; and

(d) extracting data from said sampled image data.

8. A method as in claim 7, wherein said dataform is a MaxiCode type of dataform.

9. A method as in claim 7, wherein step (b) comprises determining said orientation as the derived moment of two data cells which are contiguous and of similar reflectivity.

10. A method as in claim 7, wherein step (b) comprises determining said orientation as the derived moment of a group of data cells in side-to-side straight line alignment.

11. A method as in claim 7, wherein step (c) comprises sampling image data along a sampling line having one of the following orientations:

aligned with and parallel to said normal traversal line;

aligned with said normal traversal line at an angular separation of an integral multiple of 60 degrees.

12. A method as in claim 7, wherein step (d) comprises extracting data by determining spacings of illumination value transitions between data cell groups along said sampling line, each said data cell group consisting of one or more contiguous data cells of similar reflectivity value.

13. A method of extracting data from a dataform having a pattern of rows of similarly aligned lighter and darker data cells of a regular polygon shape, comprising the steps of:

(a) providing pixel data for an image area, said pixel data representative of reflected images of said data cells;

(b) determining, by the presence of illumination value transitions spaced at integral multiples of data cell width, the orientation of a normal traversal line having an alignment normal to sides of a series of said data cells positioned in a row in side-to-side straight line alignment;

(c) sampling image data from a plurality of said data cells along a sampling line traversing each data cell of said plurality; and

(d) extracting data from said sampled image data.

14. A method as in claim 13, wherein said dataform is a MaxiCode type of dataform.

15. A method as in claim 13, wherein step (c) comprises sampling image data along a sampling line having one of the following orientations:

aligned with and parallel to said normal traversal line;

aligned with said normal traversal line at an angular separation of an integral multiple of 60 degrees.

16. A method as in claim 13, wherein step (d) comprises extracting data by determining spacings of illumination value transitions between data cell groups along said sampling line, each said data cell group consisting of one or more contiguous data cells of similar reflectivity value.