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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>How does linear barcodes work?</title><link rel="stylesheet" type="text/css" href="manual.css"><meta name="generator" content="DocBook XSL Stylesheets V1.76.0"><link rel="home" href="index.html" title="JpGraph Manual"><link rel="up" href="ch24.html" title="Chapter 24. Linear Barcodes (One Dimensional Barcodes)"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">How does linear barcodes work?</th></tr><tr><td width="20%" align="left"> </td><th width="60%" align="center">Chapter 24. Linear Barcodes (One Dimensional Barcodes)</th><td width="20%" align="right"> </td></tr></table><hr></div><div class="sect1" title="How does linear barcodes work?"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2595788"></a>How does linear barcodes work?</h2></div></div></div>
<p>Linear barcodes are created by translating the supported characters that should be
displayed into combination of narrow and wide bars which are combined into a
barcode. To identify the start and end of a barcode special "guard" patterns are
used to indicate to the scanner that the barcode starts and also identify what type
of symbology is used.</p>
<p>To illustrate this <a class="xref" href="ch24s02.html#fig.explaining-barcode" title="Figure 24.1. Understanding linear barcodes. Example with Code 25 symbology">Figure 24.1. Understanding linear barcodes. Example with Code 25 symbology</a> shows an enlarged
and amended barcode thats uses the Code 25 symbology and encodes the numeric string
"123". In order to illustrate the different parts we have colored the start and stop
pattern and the three digits to make it clear how it is encoded.</p>
<p>
</p><div class="figure"><a name="fig.explaining-barcode"></a><p class="title"><b>Figure 24.1. Understanding linear barcodes. Example with Code 25 symbology</b></p><div class="figure-contents">
<div class="mediaobject"><img src="images/barcode-explained-1.png" alt="Understanding linear barcodes. Example with Code 25 symbology"></div>
</div></div><p><br class="figure-break">
</p>
<p>We have chosen to illustrate the principle with the code 25 symbology since it is
easy to understand. Each character is encoded with 5 black elements with spaces in
between, 2 wide and three narrow elements, hence the name 2 of 5 (or 25). The width
of the thinnest element is also known as the module width. Other symbologies have
more complicated patterns to achieve higher density (more encoded characters in a
given width) but the principle still stands.</p>
<p>The typical scanner sends out light which is reflected and is them measured as the
scanner swipes from left to right. The relative size of the black and white areas
are measured and translated back to a the encoded data.</p>
<p>The human readable string, usually at the bottom of the barcode is strictly
speaking not a part of the barcode. It is only there to help a human reader
interpret the barcode.</p>
<p>Some barcode symbologies also add a check digit at the end of the data. This check
digit (or digits) is used to verify that the interpretated data has been read
correctly.</p>
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