Use of correlation histograms for improved glyph decoding

• US 6,714,677 B1
• Filed: 12/17/1999
• Issued: 03/30/2004
• Est. Priority Date: 12/17/1999
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Stearns, Richard G., Petrie, W. Glen, Jared, David A., Hecht, David L., Flores, L. Noah
• Primary Examiner(s): Patel, Jayanti K.
• Assistant Examiner(s): AZARIAN, SEYED H
• Application Number:
  US09/466,015
• Time in Patent Office: 1,565 Days
• Field of Search: 382/181, 382/100, 382/159, 382/310, 382/187, 382/161, 382/112, 382/155, 382/157, 382/228, 382/203, 382/204, 382/205, 382/206, 382/207, 382/182, 382/183, 235/495, 235/494, 235/456, 235/487
• US Class Current: 382/181
• 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 7/143 Glyph-codes

Abstract

A method of decoding a plurality of glyphs comprising the steps of scanning a group of glyphs to form image data for expected glyph locations, assigning for each location a first value indicative of the likelihood that location contains a glyph in a first state, assigning for each location a second value indicative of the likelihood that location contains a glyph in a second state, determining the difference between the first and second values for each potential glyph location, establishing a distribution analysis of the determined differences and using that distribution analysis at least in part to control decoding of the plurality of glyphs.

Claims

1. A method of decoding a plurality of glyphs comprising the steps of:

capturing an image of a group of said glyphs to form image data for expected glyph locations;

for at least a portion of the image data indicating a subset of expected glyph locations;

assigning, for each location in the subset, a first value indicative of the likelihood that location contains a glyph in a first state;

assigning, for each location in the subset, a second value indicative of the likelihood that location contains a glyph in a second state;

determining a difference value indicating a difference between said first and second values for each expected glyph location;

producing a distribution analysis of counts of expected glyph locations for each difference value; and

setting a decoding threshold based on said distribution analysis, and decoding the plurality of glyphs using the decoding threshold.

2. A method of claim 1 wherein said steps of assigning each include performing cross-correlations of said image data for each location, with first and second correlation kernels representing said first and second states, respectively.

3. A method of claim 1 wherein the decoding threshold is set to indicate a threshold value for the minimum determined difference indicative of unambiguous encoding of a glyph state.

4. A method of claim 1 wherein said distribution analysis includes:

developing a histogram of said counts of expected glyph locations for each difference value.

5. A method of claim 1, further including:

providing information to a printer system based on said distribution analysis for controlling print quality.

6. A method of claim 1, wherein the decoding threshold is set to indicate an optimal correlation threshold based on an amount of erasures.

7. A method of claim 1, further including:

providing information to a printer system based on said distribution analysis for controlling glyph image print quality.

8. A method of claim 1, further including:

providing information to a camera system based on said distribution analysis for controlling glyph image quality.

9. A method of claim 1, further including:

providing information to a system based on said distribution analysis for providing an alert that the glyph image has degraded in quality and adjustments to the system need to be made.

10. A method of claim 1 wherein the decoding threshold is set to indicate an optimal correlation threshold based on an amount of erasures and an erasure/error correction capacity of a glyph error correction code.

11. A method of claim 1, further including:

providing information based on said distribution analysis to an image capture device to adjust image capture quality.

12. A method of claim 1, further including:

providing information based on said distribution analysis to an image capture device to adjust glyph image capture quality.

13. A method of claim 1 wherein said decoding threshold is set based on said distribution analysis prior to beginning the step of decoding the plurality of glyphs.

14. A method of claim 1 wherein the decoding threshold is set to an initial threshold when the step of decoding the plurality of glyphs begins;

and wherein the decoding threshold is set based on said distribution analysis during the decoding step.

15. In a method for decoding a bitmap image space representation of a self-clocking glyph shape code composed of glyphs having shapes that encode digital values, the glyphs being spatially distributed in locations in the bitmap image space in substantial accordance with a spatial formatting rule, the decoding method including a filtering step for filtering the bitmap image space representation of glyphs using a plurality of correlation filters, each correlation filter being relatively strongly matched to one of the shapes, a digital value being assigned to a glyph shape based on glyph-by-glyph evaluation of correlation values produced by the filtering step when a correlation value exceeds a correlation threshold, the improvement comprising:

determining a correlation difference value indicating a difference between first and second correlation values for each glyph location during the glyph-by-glyph evaluation of correlation values produced by the filtering step;

producing a distribution analysis of counts of expected glyph locations for each correlation difference value; and

setting the correlation threshold based on said distribution analysis.