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Bar Code Basics
What Are Bar Codes?
We have all seen and probably worked with bar
codes. We most likely know what bar codes are used for and all of the benefits
and advantages that they provide in automated data collection systems. We have
heard the names of many different kinds of bar codes, such as UPC, Code 39 or I
2 of 5. But, just what are bar codes and how do they work? This article will
attempt to answer your basic questions on what bar codes are and how they work.
While an in-depth treatment of bar codes is not possible in a brief article, we
should be able to answer some of your basic questions.
Representing Information With Bars and Spaces
Bar codes were developed as a method of
representing information in a simple, reliable, efficient machine readable,
optical format. What does that mean? Simply speaking--bar codes are the
representation of information as patterns of marks on surfaces that can be
detected by machines using light and optical devices, and that can be
efficiently and reliably interpreted by machines. The printed text you are now
reading qualifies as a method of optically representing information, and
although special OCR machines are available to "read" printed text, they are not
very efficient or accurate. Bar codes were designed to be "machine readable", to
be easily and reliably detected and interpreted by machines.
A bar code is analogous to a printed
(optical) version of Morse Code. Morse Code represents letters and numbers as a
series of electrical pulses of two basic durations, short and long. If Morse
Code were to be printed, it would be depicted as a series of short (dots) and
long (dashes) printed rectangles.
Bar Code Symbologies
A bar code is analogous to a printed
(optical) version of Morse Code. Morse Code represents letters and numbers as a
series of electrical pulses of two basic durations, short and long. If Morse
Code were to be printed, it would be depicted as a series of short (dots) and
long (dashes) printed rectangles. Various combinations of printed dots and
dashes represent individual characters and numbers. By comparison, a bar code is
simply a series of parallel bars and spaces, each of various widths, that are
assembled as alternating patterns that can represent characters, numbers, or
both.
 Bar
codes come in many different formats or "languages", commonly referred to as "Symbologies".
Each symbology utilizes a specific pattern of bars and spaces to represent its
information characters. The information characters that a symbology can
represent are collectively termed the symbologies "Character Set" or "Alphabet".
Different symbologies usually support
different "Character Sets". Some symbologies such as UPC-A represent only
numbers. Others such as Code 39 can support both numbers and letters but not all
of the special characters.
Others can represent the full character set
and even binary numbers. The process of representing a series of characters,
from a symbologies "Character Set", in the symbologies specific e bar and
space patterns is called "encoding". The process of examining and interpreting
specific patterns of bars and spaces in order to determine the series of
information characters they represent is termed "decoding".
The two basic categories of bar code
symbologies are "Linear" or "1-Dimensional" symbologies and "2-Dimensional"
symbologies. The bar codes you are most familiar with fall in the category of
the Linear or 1-Dimensional. These bar codes encode their information
characters in one direction only and that is where the names Linear (straight
line) and 1-Dimensional are derived from. The 2-Dimensional bar codes are a
relatively recent development and are designed to increase the symbologies'
information "encode density". With a 2-Dimensional bar code more information
can be encoded per square inch. 2-Dimensional symbologies increase the encode
density by encoding information in two directions.
Many of these symbologies still employ a
pattern of bars and spaces to encode the information, but they encode the
information in both right to left and top to bottom directions and are termed
"Stacked Symbologies". Other symbologies, such as Data Matrix, forgo the
traditional use of bars and spaces and, instead, utilize various different
shapes or size objects such as squares, rectangles, or hexagons, all arranged in
specific patterns. These 2-dimensional symbologies are called "Matrix
Symbologies", since their information is encoded using a matrix of different
objects.
Also see Bar Code Printing
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