2-D codes contain information both horizontally and vertically, allowing them to store much more data. For example, a single 2-D code can hold up to 3,116 numeric characters or 2,335 alphanumeric characters, compared to the 39 characters that Code 39 can hold.
Unlike 1-D barcodes, all 2-D codes have built-in error correction, similar to the check digits in some 1-D codes, which effectively eliminates misreads. Within a single DataMatrix code, the data is typically encoded three times, which significantly increases the chances the code will be read correctly. Vision-enabled barcode readers would have to scan 10.5 million codes to misread a single 2-D barcode; laser scanners, which cannot read 2-D codes, cannot claim this level of accuracy.
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While 1-D codes have quiet zones and guard patterns to identify where the code starts and stops, a 2-D code has a quiet zone, a finder pattern, and a clocking pattern. The finder pattern is the L-shaped pattern located around the outside edge of two sides of the 2-D code. This is used to ensure proper orientation during decoding. Opposite the finder pattern is the clocking pattern, a series of alternating black and white modules (or cells) that defines how big a single cell is and the size of the code (number of rows and columns) for decoding. The quiet zone is similar to that of 1-D barcodes; for 2-D codes, however, it must surround the entire code.
Common 2-D codes include: DataMatrix, utilized by aerospace, defense, printed media and the U.S. Postal Service; MaxiCode, a dot-based code that is used in logistics applications; QR codes, used in automotive and commercial marketing applications; and Aztec codes, used by ticket agencies and rental car companies.
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