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Browse Prior Art Database

Bidirectional Robust Bar Code

IP.com Disclosure Number: IPCOM000115064D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Blahut, RE: AUTHOR

Abstract

Any simple tag on a bar code to distinguish frontwards from backwards reading is subject to error. This problem is solved by this invention. The damage resistant bar code uses massive error correction to recover data in the presence of many errors and missing data. If a bar code may be read either forward or backward (as a piece of mail passing backwards through a scanner) then a tag must be somehow built into the bar code so that the data can be oriented. However, if this tag cannot tolerate errors, then the ECC on the body of the message becomes somewhat pointless.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 80% of the total text.

Bidirectional Robust Bar Code

      Any simple tag on a bar code to distinguish frontwards from
backwards reading is subject to error.  This problem is solved by
this invention.  The damage resistant bar code uses massive error
correction to recover data in the presence of many errors and missing
data.  If a bar code may be read either forward or backward (as a
piece of mail passing backwards through a scanner) then a tag must be
somehow built into the bar code so that the data can be oriented.
However, if this tag cannot tolerate errors, then the ECC on the body
of the message becomes somewhat pointless.

      This invention is a bar code in which the direction indicator
is embedded deeply into the structure and is below the ECC.  Message
direction is need not and cannot be determined until after all errors
are corrected and all missing symbols are restored.

      The full codeword of (up to) 68 bars consists of two half
codewords; the left half codeword and the right half codeword.  The
bars of the right half codeword are indexed from right to left and
are turned upside down.  The bars of the left half codeword are
indexed from left to right and are not turned upside down.  If the
object containing the bar code is rotated 180 degrees the structure
is preserved.  Hence the same decoding algorithm is used whether or
not the bar code is rotated 180 degrees.  Thus all errors can be
corrected and missing data restored for an inverted bar code just as
for...