34 lines
4.2 KiB
HTML
34 lines
4.2 KiB
HTML
<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>
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<p>Linear barcodes are created by translating the supported characters that should be
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displayed into combination of narrow and wide bars which are combined into a
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barcode. To identify the start and end of a barcode special "guard" patterns are
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used to indicate to the scanner that the barcode starts and also identify what type
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of symbology is used.</p>
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<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
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and amended barcode thats uses the Code 25 symbology and encodes the numeric string
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"123". In order to illustrate the different parts we have colored the start and stop
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pattern and the three digits to make it clear how it is encoded.</p>
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<p>
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</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">
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<div class="mediaobject"><img src="images/barcode-explained-1.png" alt="Understanding linear barcodes. Example with Code 25 symbology"></div>
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</div></div><p><br class="figure-break">
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</p>
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<p>We have chosen to illustrate the principle with the code 25 symbology since it is
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easy to understand. Each character is encoded with 5 black elements with spaces in
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between, 2 wide and three narrow elements, hence the name 2 of 5 (or 25). The width
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of the thinnest element is also known as the module width. Other symbologies have
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more complicated patterns to achieve higher density (more encoded characters in a
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given width) but the principle still stands.</p>
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<p>The typical scanner sends out light which is reflected and is them measured as the
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scanner swipes from left to right. The relative size of the black and white areas
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are measured and translated back to a the encoded data.</p>
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<p>The human readable string, usually at the bottom of the barcode is strictly
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speaking not a part of the barcode. It is only there to help a human reader
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interpret the barcode.</p>
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<p>Some barcode symbologies also add a check digit at the end of the data. This check
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digit (or digits) is used to verify that the interpretated data has been read
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correctly.</p>
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