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Digital Filter for Bar Code Scanners

IP.com Disclosure Number: IPCOM000082162D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Heim, LS: AUTHOR [+3]

Abstract

Some optical bar codes are decoded by distance measurements made from an edge of one bar to an edge of another bar. In such applications it is important to eliminate false edge detections caused by small white voids in black bars and black spots in white bars.

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Digital Filter for Bar Code Scanners

Some optical bar codes are decoded by distance measurements made from an edge of one bar to an edge of another bar. In such applications it is important to eliminate false edge detections caused by small white voids in black bars and black spots in white bars.

Digital filter 10 suppresses voids and spots of less than a predetermined size. As long as input line 11 indicates black video, it holds a preset on white counter 12, which maintains a predetermined value 1-15 from storage 13. When line 11 changes to white video, the preset is removed, so that a clock signal on line 14 causes counter 12 to increment at a fixed rate. When it reaches zero, OR gate 15 is no longer made, and inverter 16 sets latch 17.

Output line 18 then switches to indicate the presence of valid white data.

But, if the input video reverts to a black level before counter 12 reaches zero, line 11 reapplies the preset value to inhibit the setting of latch 17, so that output 18 continues to indicate the presence of black data. Therefore, these components filter out small white voids.

To filter out small black spots, inverter 19 holds a preset on counter 20 as long as line 11 carries white video. When line 11 changes to a black level, counter 20 advances at the clock rate from the value in storage 21. Storage 21 need not contain the same value as storage 13, so that the void and spot thresholds may differ from each other. OR 22 and inverter 23 reset latch 17 whe...