Method and apparatus for decoding bar code symbols using gradient signals
First Claim
1. A method for reading a bar code symbol in a pixel image, comprising the steps of:
- (a) selecting a first scan line crossing at least a first portion of said symbol;
(b) generating a first gradient signal representative of the dark-to-bright transitions in said first portion of said symbol;
(c) generating a second gradient signal representative of the bright-to-dark transitions in said first portion of said symbol, wherein the first gradient signal is distinct from the second gradient signal;
(d) selecting a second scan line crossing at least a second portion of said symbol;
(e) generating an updated first gradient signal in accordance with the dark-to-bright transitions in said second portion and the first gradient signal;
(f) generating an updated second gradient signal in accordance with the bright-to-dark transitions in said second portion and the second gradient signal; and
(g) decoding said symbol in accordance with said updated first and second .gradient signals.
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Abstract
A bar code reader decodes a bar code symbol in a pixel image by transforming the data corresponding to the symbol along a first scan line, where the transformation comprises rotation and stretching. The reader generates a whitening gradient vector, a blackening gradient vector, and a count vector from the transformed data. The reader then transforms (by rotating and stretching) another set of data corresponding to the symbol along a second scan line. The reader updates the whitening and blackening gradient vectors and the count vector using the second set of transformed data. The reader then generates whitening and blackening gradient signals from the whitening and blackening gradient vectors and the count vector. The reader segments the whitening and blackening gradient signals and generates a single one-dimensional reconstructed signal based on the weighted centroids of the two segmented gradient signals. The reader then decodes the symbol by decoding the reconstructed signal.
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Citations
36 Claims
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1. A method for reading a bar code symbol in a pixel image, comprising the steps of:
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(a) selecting a first scan line crossing at least a first portion of said symbol; (b) generating a first gradient signal representative of the dark-to-bright transitions in said first portion of said symbol; (c) generating a second gradient signal representative of the bright-to-dark transitions in said first portion of said symbol, wherein the first gradient signal is distinct from the second gradient signal; (d) selecting a second scan line crossing at least a second portion of said symbol; (e) generating an updated first gradient signal in accordance with the dark-to-bright transitions in said second portion and the first gradient signal; (f) generating an updated second gradient signal in accordance with the bright-to-dark transitions in said second portion and the second gradient signal; and (g) decoding said symbol in accordance with said updated first and second .gradient signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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10. An apparatus for reading a bar code symbol in a pixel image, comprising:
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(a) means for selecting a first scan line crossing at least a first portion of said symbol; (b) means for generating a first gradient signal representative of the dark-to-bright transitions in said first portion of said symbol; (c) means for generating a second gradient signal representative of the bright-to-dark transitions in said first portion of said symbol, wherein the first gradient signal is distinct from the second gradient signal; (d) means for selecting a second scan line crossing at least a second portion of said symbol; (e) means for generating an updated first gradient signal in accordance with the dark-to-bright transitions in said second portion and the first gradient signal; (f) means for generating an updated second gradient signal in accordance with the bright-to-dark transitions in said second portion and the second gradient signal; and (g) means for decoding said symbol in accordance with said updated first and second gradient signals. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 28, 29, 30, 31, 32, 33, 34, 35, 36)
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Specification