Browse Prior Art Database

Three Level or Black Gray White Optical Bar Code

IP.com Disclosure Number: IPCOM000080844D
Original Publication Date: 1974-Feb-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

McMurtry, DH: AUTHOR

Abstract

This optical bar-code configuration is self-clocking and requires only standard black ink for high density and high reliability, even in typewriter applications. It is configured to minimize the effect of printing and scanning tolerances.

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Three Level or Black Gray White Optical Bar Code

This optical bar-code configuration is self-clocking and requires only standard black ink for high density and high reliability, even in typewriter applications. It is configured to minimize the effect of printing and scanning tolerances.

The code manifestation comprises short-black (or the like) bars 12, long black bars 14, and white spaces 16, as shown in Fig. 1, for an optical aperture stop represented by the rectangle 20. The long bars 14 are three times the length of the short bars 12, and the length of the stop 20 is twice the length of the short bar 12. The width w of the aperture is less than the width W of the bars and spaces, for insuring that the 0, 1, 2 transitions occur independent of bar width printing tolerances.

The binary values at the transitions are determined according to the conventional three-level algorithm diagrammed in Fig. 2 from the changes in levels 30, as shown in Fig. 1.

The vertical tolerance in positioning the aperture of the probe is equal to the length of the short bar 12. This position tolerance can be increased by extending the field vertically in multiples of long bar lengths, with the long bars continuous in extent.

The short bars 12 affect the photoresponsive device at the aperture 20, to produce voltages substantially midway between those produced by white spaces 16 and those produced by long bars 14. This is due to geometrical averaging. Bleeding of the ink along the vertica...