What is a Barcode?

Introduction
During a shopping excursion to a shopping mall, you would have noticed the cashier scanning your products using some Laser device to produce a bill. What actually he is doing that he is reading the product barcodes using a Laser/Barcode scanner. Barcode scanner reads the code, data is sent to the computer, and computer looks up into the database for the price and description of the item.

Barcodes are structured to contain specific product related information. It basicallyencodes alphanumeric characters and symbols using black and white stripes, also called bars.  Bar-coding is one of the AIDC (Automatic Identification and Data Collection)technologies which reduce human involvement in data entry and collection and thereby also reducing error and time.
Structure of Barcode
A typical barcode consists of the following:
Quiet Zone –The minimum required space for bar code scan-ability, preceding the Start Character of a bar code symbol. The quiet zone should be free from any printing and be the same colour and reflectance as the background of bar code symbol. The Quiet Zone should be ten times the width of the narrowest element in the bar code, or 0.25 inch minimum. Also known as Clear Area.
Start Code –Indicates the start of the barcode. These are sspecial bar code characters & they signify the start of data to the scanner/reader. Start characters are usually stripped-off and not transmitted to the host. 
  Data –The actual data the barcode stores.
Check Digit –Check digit (not always present) is a mathematical sum that is used to verify the accuracy of the other elements of the barcode. It is the eextra digit added at the end of a bar code to allow the scanner to confirm that it read the bar code correctly. It is typically stripped from the data and not transmitted to the host.
Stop Code – Indicates the stopping point of the barcode. These characters signify the end of data to the scanner/reader. They are also stripped-off and not transmitted to the host.
Trailing Quiet Zone – Another clear space with no printing following the Stop Character.

Standards

Number of bar code standards have evolved over the years and are represented in different symbologies. A symbology specification defines the details necessary for the barcode to be printed and also provides details to read and decode barcode by a scanner/reader.

 

Symbology specification documents typically range from 8 pages to 120 pages. However, in a simplified way, the standard must contain:

·         A definition of the width of the bars and the spaces.

·         A method to define each character that is encodable (whether numeric only or full ASCII).

·         The start and stop characters.

·         Any check character support built in.

·         Any free space needed around the symbology to allow for a clean decode.

 Barcode symbologies can be either linear or two-dimensional.

Linear Barcode Standards

Linear barcodes use single row of black and white bars. Examples of linear barcodes are:

·             ISO/IEC 15420 Bar code symbology specification - EAN/UPC

UPC (Universal Product Code) uses 12-digit numeric containing a unique manufacturer ID number, and product number. EAN (European Article Numbering) is similar to UPC except the fact that it uses 13-digit numeric.

 ISO/IEC 16388 Bar code symbology specifications - Code 39

It is a discrete barcode. It implies that a single character is represented by a fixed pattern of bars. Each character is made up of 9 (5 black & 4 white) bars. Code 39 barcode symbology supports 43 characters set plus an additional character used as a delimiter or start/stop character. The start/stop character always occurs as the first and last character in a complete barcode and is represented in the human readable text by the *character.

 

The 43 character set includes the following: 1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ -   . $ / + % SPACE.

A check digit is generally not used with Code 39. The check digit is the modulus 43 sum of all the character values in the message and it is printed as the last data character.

 

ISO/IEC 15417 Bar code symbology specification - Code 128

CODE 128 allows the full ASCII 128 character set to be encoded. Each bar or space can be one of four different unit widths. The narrowest possible bar or space will thus be one quarter the width of the widest. It permits bidirectional scanning and theoretically, there is no restriction on the number of characters allowed in each symbol.

Code 128 has three different character sets as Code Set A, Code Set B and Code Set C. Any of these codes may be selected by appropriate selection of start character. The Code 128 Specification requires the inclusion of a check digit. The check digit is a Modulus 103 checksum.

Each character in the barcode symbol is composed of three bars and three spaces. The stop character has four bars and three spaces.  

 

· ISO/IEC 16390 Bar code symbology specifications - Interleaved 2-of-5 (ITF25)

Primarily used in the warehouse industry, Interleaved 2 of 5 encodes any even number of numeric characters in the width of both bars and spaces. It is called “Interleaved” because 2 characters are encoded in a unit of 5 bars and spaces. It uses both bar and space width to encode information so the density of ITF25 is much higher. Interleaved 2 of 5 is a numeric symbology and it character set only include 10 digital characters.