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Optical Scanner Compensation for Bar Codes

IP.com Disclosure Number: IPCOM000081791D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Pujdowski, R: AUTHOR [+2]

Abstract

In the Universal Product Code (UPC) adopted by the grocery industry, uniform printing variations and systematic video-thresholding errors must be compensated to reduce the possibility of incorrect conflict resolution between certain digit pairs, such as 1-7 and 2-8.

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Optical Scanner Compensation for Bar Codes

In the Universal Product Code (UPC) adopted by the grocery industry, uniform printing variations and systematic video-thresholding errors must be compensated to reduce the possibility of incorrect conflict resolution between certain digit pairs, such as 1-7 and 2-8.

In Fig. 1, the video pulse-train intervals named T1, T2 and T3 are distances between white-to-white and black-to-black transitions, and are decoded to identify each digit on a UPC label half. In some cases, however, this process can produce two different identifications of the same digit. Such conflicts may be resolved by the use of a Delta B interval, which represents the width of one of the black bars in the digit. The nature of the T1, T2 and T3 measurements tends to cancel errors, but the Delta B measurement does not. This fact reduces the accuracy of the conflict-resolution process. Fig. 1 also shows guard-bar (GB) and center-bar (CNTR) intervals B0 and T0; by definition of the UPC code, these intervals are, respectively, 1/7 and 2/7 of the length TR=T1+T3 of a complete digit.

Fig. 2 shows apparatus for accomplishing the required compensation. A data store receives counts representing various intervals from a label. A compensation adder determines the value of (T0/2) - B0, and stores the result in a compensation register. Then, when a Delta B cycle is encountered, an AND gate allows this value to be added to every delta B value transmitted to an arithmet...