| 摘要 |
A system for use in a bar code processing system using a combination of a first derivative signal (312) and a second derivative signal (322) to determine the bar edge. The predominant signal in determining the edge is the second derivative signal. A zero-cross (350) of the second derivative signal occurs at the bar edge. The first derivative signal is used to qualify the point in time (360) in the second derivative signal for which a zero-cross is examinated. The system is particularly suited for near field operations where a Fresnel diffraction pattern exists.
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