Codabar Explanation
From SoftwarePractice.org
Described below is a detailed visual description of the method used to decode a 'Codabar' standard barcode image.
This standard makes use of 20 characters which are represented by a unique set of binary code or bars and spaces. The code can only contain a single or a double bar or a space. A double zero is depicted by a wide space and a double one by a wide bar. The code used to decrypt the barcode in Matlab makes use of this detail.
There are two ways of encoding codabar – width encoding and barcode encoding. This project uses barcode encoding to decode the codabar given. The table displayed below gives information about what each character stands for in binary numbers( 0 and 1).
A single '0' is represented by a narrow space and a single '1' is represented by a narrow bar. Similarly, '00' is represented as a wide space and '11' is represented by a wide bar. The width of a wide space or bar is equal to the width of two narrow spaces or bars.
From the table listed below , note that 3 is represented as '110010101'. Therefore, in the barcode image, 3 is represented as - ‘wide bar, wide space, narrow bar, narrow space, narrow bar, narrow space, narrow bar’.
The characters in Codabar are represented as the following:
From the Codabar Rules outlined in the previous section and the explaination given above the barcode image can be decoded as follows -
Consider the image displayed below.
1. Every Codabar Image starts and ends with one of the following characters - A,B,C, or D.Using the information from the table displayed above,notice that this Barcode image starts with an 'A' and ends with a 'B'.
2. An important characteristic of the codabar standard is that,between every character there is a narrow inter character space.This is represented by a '0'.
3.In between the start and stop characters we have sets of bars and spaces that represent numerical digits such as 1,2,3 etc.Using the information listed in the table displayed above, we can decode the numbers as follows :
All this information has been used in our strategy to decode a codabar image in Matlab.
Reference
Vault Information LLC, ‘Codabar Symbology’, http://www.barcodeisland.com/codabar.phtml, last visited 7th October 2006.
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