Barcode

A barcode (also bar code) is a machine readable representation of information in the widths and spacings of printed parallel lines (or concentric circles, in at least one symbology). They can be read by optical scanners called barcode readers or scanned from an image by special software.

Table of contents

1 Applications 2 Symbologies 3 Types of barcodes 3.1 Linear barcodes 3.2 2-D barcodes 4 External links

Applications

Barcodes (and other machine readable tags like RFID) are used wherever physical objects need to be tagged with information that is to be processed by computers. Instead of painstakingly typing long strings of data into a terminal, the operator only has to display the code to a barcode reader. It also allows for processing without the help of human operators in fully automated environments.

The amount of data contained in a barcode varies with the application. In the simplest case only an identification number is provided which is used to index into a central database where the complete information is kept. The EAN-13 and UPC codes commonly found on retail articles work this way.

In many cases it is more desirable to include the complete information in the barcode itself without the requirement for an external database. This led to the development of barcode symbologies that can express more than decimal digits, ranging from additionally encoding just the upper case alphabet to the complete ASCII character set and beyond. The drive to encode ever more information in combination with the space requirements of simple barcodes led to the development of matrix codes which are often also named 2D barcodes, although most do not consist of bars but rather a grid of square cells.

Symbologies

The mapping between messages and barcodes is called a symbology. The specification of a symbology includes the encoding of the single digits/characters of the message as well as the start and stop markers into bars and space, the size of the quiet zone required to be before and after the barcode as well as the computation of a checksum.

Symbologies can be classified mainly by two properties:

• Continuous vs. discrete: Characters in continuous symbologies abut, with one character ending with a space and the next beginning with a bar, or vice versa. Characters in discrete symbologies begin and end with bars; the intercharacter space is ignored, as long as it is not wide enough to look like the code ends.
• Two-width vs. many-width: Bars and spaces in two-width symbologies are wide or narrow; how wide a wide bar is exactly has no significance as long as the symbology requirements for wide bars are adhered to (usually two to three times as wide than a narrow bar). Bars and spaces in many-width symbologies are all multiples of a basic width called the module; most such codes use four widths of 1, 2, 3 and 4 modules.

2-D barcodes

Symbology	Notes
3-DI	Developed by Lynn Ltd.
ArrayTag	From ArrayTech Systems.
Aztec Code	Public domain.
Small Aztec Code
Bullseye	This was the barcode tested in a Kroger store in Cincinnati. It used concentric bars.
Codablock	Stacked 1D barcodes.
Code 1	Public domain.
Code 16K	Based on 1D Code 128.
Code 49	Stacked 1D barcodes from Intermec Corp.
CP Code	From CP Tron, Inc.
Data Glyphs	From Xerox PARC.
Data Matrix	From RVSI Acuity CiMatrix.
Datastrip Code	From Datastrip, Inc.
Dot Code A
HueCode	From Robot Design Associates. Uses greyscale or colour.
INTACTA.CODE	From INTACTA Technologies, Inc.
MaxiCode	Used by United Parcel Service.
MiniCode	From Omniplanar, Inc.
PDF417	The most common 2D barcode. Public domain.
Micro PDF417
QR Code	From Nippondenso ID Systems. Public domain.
SmartCode	From InfoImaging Technologies.
Snowflake Code	From Marconi Data Systems, Inc.
SuperCode	Public domain.
UltraCode	Black-and-white & colour versions. Public domain.

See also : Global Trade Item Numbering, RFID

External links

• Online Barcode generator
• Barcode Island - description of many symbologies