Reducing speckle noise in electro-optical readers
AssigneeSymbol Technologies, Inc.
InventorDariusz J. Madej
Life of this patent
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Abstract
The influence of speckle noise in degrading performance of a reader for electro-optically reading a multiple element symbol is reduced by constructing wavelets for each element width, correlating each wavelet with a differentiated signal derived from light scattered from the symbol to obtain a correlated signal having peaks, each peak corresponding to a middle of a respective element, and processing the peaks to decode the symbol. Edge detection of the elements, which is susceptible to speckle noise degradation, is not used for decoding.
Claims8
A method of decoding electro-optically readable symbols having elements of different light reflectivities and widths, comprising the steps of:
- a) reflecting laser light off the elements to obtain an analog signal;
- b) constructing a wavelet for each element width by convoluting two spaced-apart Dirac delta functions by a Gaussian function to obtain the wavelet for each element width;
- c) correlating each wavelet with the analog signal to obtain a correlated signal having peaks, each peak corresponding to a middle of a respective element;
- and
- d) processing the peaks to decode a symbol with reduced influence from speckle noise.
A method of decoding electro-optically readable bar code symbols having bar elements and space elements of different light reflectivities and of different element widths, comprising the steps of:
- a) sweeping the symbol with a light beam in a scan across the symbol to scatter light therefrom, and detecting the light scattered from the symbol to generate an analog signal;
- b) differentiating the analog electrical signal derived from a symbol being read to obtain a differentiated signal;
- c) determining the number of different element widths present in the symbol to determine a symbology type to which the symbol belongs;
- d) determining the average element widths of the symbol;
- e) constructing a wavelet for each average element width by convoluting two spaced-apart Dirac delta functions of opposite polarity by a Gaussian function to obtain the wavelet for each average element width;
- f) correlating each wavelet with the differentiated signal to obtain a correlated signal having peaks, each peak corresponding to a middle of a respective element;
- g) detecting the peaks in the correlated signal for each average element width;
- and
- h) processing the peaks detected in the correlated signal to decode the symbol with reduced influence from speckle noise.
Dependencies are inferred from the claim text.