barcode

A barcode (also bar code) is a machine-readable representation of information in a visual format on a surface. Originally barcodes stored data in the widths and spacings of printed parallel lines, but today they also come in patterns of dots, concentric circles, and hidden in images. Barcodes can be read by optical scanners called barcode readers or scanned from an image by special software. Barcodes are widely used to implement Automated identification and data captureAuto ID Data Capture (AIDC) systems that improve the speed and accuracy of computer data entry. While traditionally, barcodes encoding schemes represented just numbers, newer symbologies add new characters such as from 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 (a type of 2D barcode), which do not consist of bars but rather a grid of square cells. Stacked barcodes are a compromise between true 2D barcodes and linear codes, and are formed by taking a traditional linear symbology and placing it in an envelope that allows multiple rows.

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.Linear 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.Stacked symbologies consist of a given linear symbology repeated vertically in multiple.There are a large variety of 2-D symbologies. The most common are matrix codes, which feature square or dot-shaped modules arranged on a grid pattern. 2-D symbologies also come in a variety of other visual formats. Aside from circular patterns, there are several 2-D symbologies which employ steganography by hiding an array of different-sized or -shaped modules within a user-specified image (for example, DataGlyph).

Scanner/symbology interaction - Linear symbologies are optimized to be read by a laser scanner, which sweeps a beam of light across the barcode in a straight line, reading a slice of the barcode light-dark patterns.Stacked symbologies are also optimized for laser scanning, with the laser making multiple passes across the barcode.2-D symbologies cannot be read by a laser as there is typically no sweep pattern that can encompass the entire symbol. They must be scanned by a camera capture device.

Types of barcodes -

Linear barcodes - & lt;tr>&l t;tr>&l t;tr>& lt;td>Libraries,? blood banks, !airbillsCode? !93&l t;td>Code? !128& lt;td>Code? !11&l t;td>Pharmacode& lt;td>Neither< ;td>Two&l t;tr>&l t;tr>&l t;tr>< /table>

Stacked barcodes -

Symbology	Cont/Disc	Two/Many
Plessey< /td>	Continuous< ;/td>	TwoCatalogs,? store shelves, !inventory	Universal ? Product Code!UPC	Contin uous	Many& lt;/td>	North? America !retail
European? Article Numbering-Uniform Code Council!EAN-UCC	Co ntinuous	M any	Worldw ide? !retail
Codabar	Discrete	Two
Interleave d? 2 of !5	Continuo us	Two< /td>	Wholesale,? Libraries (Norway!NO)
Code? !39	Discret e	Two	Various
Continu ous	Many&l t;/td>	Various< /td>
Contin uous	Many& lt;/td>	Various< ;/td>
Discret e	Two	Telephones< /td>
POSTNET&l t;/td>	Continuous& lt;/td>	Tall/short	Post? !office
PostBar	Discrete	Many	Post? !office
CPC? Binary BarcodeCPC !Binary	Dis crete	Two& lt;/td>	Post? !office
Telepen	Continuous< /td>	TwoLibraries,? etc !(UK)

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2D barcodes - A matrix code, also known as a 2D barcode, is a two-dimensional way of representing information. It is similar to a linear (1-dimensional) barcode, but has more data representation capability. Descriptions of most of these codes can be found at adams1.com - BarCode 1

See also -

Universal Product Code (UPC)

Automated identification and data capture (AIDC)

Semacode

ISBN

Inventory control system

Supply Chain Management

Barcode printer

Barcode scanner

Global Trade Item Numbering

RFID

Symbology	Notes	Codablock	Stacked? 1D !barcodes.	Code? 16K	Based on 1D Code !128.
Code? 49	Stacked 1D barcodes from Intermec !Corp.
PDF417	The? most common 2D barcode. Public !domain.
Micro? !PDF417	&nb sp;