Method of programmable digitization and bar code scanning apparatus employing same
First Claim
1. A method of accurately reconstructing from a sampled analog signal bar-to-space and space-to-bar transition points in a symbol comprising the steps of:
- accepting as input successive samples from an analog signal, said samples being representative of levels of reflectivity of a symbol being scanned;
determining a white value associated with a space and a black value associated with a bar on said symbol;
determining a threshold between said black value and said white value;
determining from said input a preceding sample and a succeeding sample having values that bracket said threshold; and
determining a transition point and an offset of said transition point from said preceding sample to define a first time interval therebetween by performing an interpolation that is limited to an interval between said preceding sample and said succeeding sample in the absence of upsampling.
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Accused Products
Abstract
A method and apparatus are provided for detecting bar-space and space-bar transitions in a bar code symbol. A sequence of sparsely sampled analog signals from a photodetector in a bar code scanner is representative of the reflectance pattern of a symbol.
Following initialization, a threshold, representing the value of the analog signal at a transition point, is derived from observed samples of the bars and spaces in the bar code symbol. Sampled reflectance information is accumulated as the symbol is scanned, and a program driven microprocessor calculates and repeatedly updates this threshold, using observed maxima and minima in the analog samples, and also referencing a binary output to determine whether a bar or space is currently being viewed.
When the values of two successive analog samples bracket this threshold, then a bar-space or space-bar transition has occurred. Linear interpolation is performed on the two samples to determine the transition point and an offset from the first of the two samples. After a delay corresponding to this offset, the level of a binary output is changed. A bit serial binary output is thus produced, representative of the relative widths of bars and spaces.
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Citations
29 Claims
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1. A method of accurately reconstructing from a sampled analog signal bar-to-space and space-to-bar transition points in a symbol comprising the steps of:
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accepting as input successive samples from an analog signal, said samples being representative of levels of reflectivity of a symbol being scanned; determining a white value associated with a space and a black value associated with a bar on said symbol; determining a threshold between said black value and said white value; determining from said input a preceding sample and a succeeding sample having values that bracket said threshold; and determining a transition point and an offset of said transition point from said preceding sample to define a first time interval therebetween by performing an interpolation that is limited to an interval between said preceding sample and said succeeding sample in the absence of upsampling. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A bar code scanner, comprising:
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light receiving means for detecting light reflected from said symbol, and for generating a sampled analog signal in response thereto that is indicative of the bar-space pattern of said bar code symbol; analog to digital converting means for converting said analog signal to a digital signal; microprocessor means, accepting said digital signal as an input, for determining transition points that correspond to bar-to-space and space-to-bar transitions in said bar code symbol, said microprocessor means having a program resident in a memory thereof for determining a threshold, said program executing the steps of; determining a white value associated with a space and a black value associated with a bar on said bar code symbol; determining a threshold between said black value and said white value; determining from said digital signal a preceding sample and a succeeding sample having values that bracket said threshold; determining a transition point and an offset of said transition point from said preceding sample to define a first time interval therebetween by performing an interpolation that is limited to an interval between said preceding sample and said succeeding sample in the absence of upsampling; and generating an output that undergoes a transition between a first value representative of one of a high and low reflectivity levels to a second value representative of another of said high and low reflectivity levels after elapse of said first time interval following said determination of said transition point. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29)
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Specification