Browse Prior Art Database

Facet Dependent Digital Filter

IP.com Disclosure Number: IPCOM000052958D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Broockman, EC: AUTHOR

Abstract

This article describes a technique for implementing a variable digital filter in an optical bar code scanner. The filter threshold is changed for different scan lines in a scan pattern as a function of actual beam scan speed.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 69% of the total text.

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Facet Dependent Digital Filter

This article describes a technique for implementing a variable digital filter in an optical bar code scanner. The filter threshold is changed for different scan lines in a scan pattern as a function of actual beam scan speed.

In one type of supermarket checkout scanner, a rotating, faceted beam deflector (e.g., a holographic disc or a mirror wheel) is used to generate a multi- line scan pattern. For a given scan pattern, the speeds at which the beam actually sweeps across the label may vary over a range of 5 to 1.

Conventionally, the width of each dark area or light area on a surface being scanned is initially represented as a number of counts required for a beam to traverse the area at a fixed counting frequency. The bars and spaces in a valid UPC (Universal Product Code) label must be greater than a predetermined minimum width. This means that the number of counts for a valid bar or space must be equal to or greater than a predetermined minimum. If the actual number of counts for a given area is less than the predetermined minimum, it is assumed that the area was not a valid bar or space.

However, since the actual scan speed for different scan lines within a pattern may vary over a 5 to 1 range, the actual minimum acceptable width also varies over a 5 to 1 range for a fixed counting frequency. A given bar (or space) may appear to be acceptable when scanned at a slow speed but unacceptable when scanned at a high speed since relativ...