Barcode Symbologies

A "symbology" is the mapping between data and the barcode format used to represent it. Just as human languages have different alphabets and grammar rules, different barcode symbologies have different rules for how bars and spaces are arranged to represent characters.

Continuous vs. Discrete Symbologies

1D symbologies generally fall into two categories:

• Discrete: Each character is encoded independently and separated by a small gap (intercharacter gap). Code 39 is a discrete symbology.
• Continuous: Characters abut one another without intercharacter gaps. Every space is part of a character's encoding. Code 128 is a continuous symbology.

Technical Details of Common Symbologies

Code 128

Code 128 is a high-density, continuous symbology capable of encoding all 128 ASCII characters. It uses three different character sets (A, B, and C) to maximize data density. Set C, for example, encodes pairs of numbers (00-99) into single characters, making it extremely compact for numeric data.

Code 39 (Code 3 of 9)

Code 39 is an older, discrete symbology. Its name comes from its structure: out of 9 elements (bars and spaces) representing a character, exactly 3 must be wide. It only supports 43 characters (uppercase letters, numbers, and some symbols). It is less dense but very easy to decode, making it popular in older industrial applications.

ITF (Interleaved 2 of 5)

ITF is a continuous, high-density numeric-only symbology. The "interleaved" part means characters are encoded in pairs: the first digit is encoded in the dark bars, and the second digit is encoded in the white spaces interleaved between those bars. It requires an even number of digits.

Data Matrix

A 2D symbology composed of black and white "cells" arranged in a square or rectangular pattern. It is recognized by an "L-shaped" finder pattern on its borders. It includes strong Reed-Solomon error correction and is heavily used to mark small items.