Two dimensional (2D) Bar Code Symbologies

The need to encode more information in a smaller space has driven the development, standardization, and growing use of 2D bar codes. Where traditional 1D bar codes act as a license plate to reference information stored in a database, 2D codes can fulfill the same function while taking up significantly less space. Or 2D codes can function as the database itself, and therefore assure complete portability for 2D labeled items.

There are two types of 2D bar codes in current use: stacked codes and matrix codes.

· Stacked symbologies evolved as 1D codes - Code 39 and Code 128 - stacked in horizontal layers to create the multirow symbologies, Code 49 and Code 16K, respectively. PDF417 followed in 1990 with added features that increased data capacity, improved data density, and strengthened reading reliability by a scanner. These features enabled decoding from scan paths that span multiple adjacent rows while incorporating error detection and correcting techniques. PDF417 encodes the full ASCII character set at a maximum of about 2000 characters to four square inches. Uniform Symbol Specifications for Code 49, Code16K, and PDF417 are available from AIM. SuperCode, a stacked code that can break data into small packets and create various shaped symbols, is in the public domain, but a standards specification has not yet been created for it.

· Matrix symbologies offer higher data densities than stacked codes in most cases, as well as orientation-independent scanning. A matrix code is made up of a pattern of cells that can be square, hexagonal, or circular in shape. Data is encoded via the relative positions of these light and dark areas, and encoding schemes use error detection and correction techniques to improve reading reliability and enable reading of partially damaged symbols. Matrix codes are scaleable and well-suited both as small ID marks on products and as conveyor-scannable symbols on shipped packages.

Matrix codes currently in the public domain with symbology specifications available from AIM include Code One, Data Matrix, MaxiCode, Aztec Code, and QR Code. All matrix symbols require charge-coupled device (CCD) vision-based scanners.

Reprinted with permission from AIM, Inc.
www.aimglobal.org

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