Click here to Skip to main content
12,997,190 members (73,857 online)
Click here to Skip to main content
Add your own
alternative version


122 bookmarked
Posted 24 Jan 2006

Read Barcodes from an Image

, 31 Jan 2006
Rate this:
Please Sign up or sign in to vote.
How to read two-width barcodes from an image in VB.NET.


The following article describes an algorithm in VB.NET to detect 2 of 5 interleaved barcodes, which are widely used in industrial applications like document management (DMS). The algorithm can easily be extended to detect every other two-width barcode like 2 of 5 standard and Code 39.


If you want to read barcodes from an image in professional applications, for example in document processing, you mainly face two problems:

  1. You have to use an expensive barcode tool, mainly because of runtime licenses.
  2. Your customer wants you to read barcode from documents which are of bad quality (fax, copies, photos, …).

The solution: Develop an algorithm on your own and tune it to the needs of your customer. This article explains how to develop a generic algorithm for two-width barcodes and a working example to read 2 of 5 interleaved.

Using the code

Scanning the barcodes is as simple as this:

Dim bmp As New Bitmap("d:\sample2of5.bmp") 
Dim scanner As New gmseNWScanner(_
        New gmseBarcodeDef2of5interleaved)
Dim result As gmseNWResult

For Each result In scanner.Result

The main class is gmseNWScanner. It contains the generic scanning algorithm for two-width barcodes. The parameters are defined in the abstract class gmseNWBarcodeDef. The class gmseBarcodeDef2of5interleaved implements gmseNWBarcodeDef to decode 2 of 5 interleaved. The detected barcodes are saved in the following classes: gmseNWResult and gmseNWResultCollection.

Points of interest

Two-Width barcodes are represented with only two bar types: a narrow bar (n) and a wide bar (w). The tricky part is to get this representation from an image. Translating to text is straightforward. Scanning is done row by row (see chart). The array cBarWidth is computed. It contains the width of each bar in the current row. cBarWidth is scanned from left to right. The algorithm takes a subset of cBarWidth to find a candidate for a valid barcode. The subset is considered to be a candidate if the bars can be classified as narrow and wide bars. If a candidate is found, the algorithm extends the subset until a bar is found, this cannot be classified as a narrow or wide bar. The subset is then translated to the nw representation. The nw representation is then translated to the text with a Hashtable.

If you play with the algorithm you will see that sometimes regions in the image are identified as a barcode by accident. This is a common problem with barcode detection. Being restrictive in filtering out the unwanted regions will lead to an algorithm that does not detect barcodes on low quality images. So the best solution is to add a checksum. If possible, do some additional tests like using a fixed length of the coded text.



  • 01-24-06: Original article.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Germany Germany
No Biography provided

You may also be interested in...


Comments and Discussions

QuestionDetails of the code ... ? Pin
Member 1103734328-Aug-14 20:24
memberMember 1103734328-Aug-14 20:24 
AnswerRe: Details of the code ... ? Pin
Member 1103734328-Aug-14 23:36
memberMember 1103734328-Aug-14 23:36 
QuestionReading Barcode from an image Pin
ZeenY25-Feb-08 23:25
memberZeenY25-Feb-08 23:25 
AnswerRe: Reading Barcode from an image Pin
steve7g10-Jan-12 16:31
membersteve7g10-Jan-12 16:31 
GeneralReading barcode type 39 Pin
ciapal18-Feb-08 23:52
memberciapal18-Feb-08 23:52 
GeneralRe: Reading barcode type 39 Pin
cyos25-Apr-11 20:30
membercyos25-Apr-11 20:30 
GeneralRe: Reading barcode type 39 Pin
cyos25-Apr-11 20:44
membercyos25-Apr-11 20:44 
' Original Author: Georg Mackenbrock (c) 2006
' Barcode Reader for code 39
' Edited by 39412
Imports System.Text
Imports System.Drawing
Imports System.Drawing.Imaging

#Region "Barcode Structures"
Public Class gmseNWResult
Public Text As String
Public Count As Integer
End Class
Public Class gmseNWResultCollection
Implements IEnumerable

Dim hash As New Hashtable(CaseInsensitiveHashCodeProvider.Default, CaseInsensitiveComparer.Default)

ReadOnly Property Count() As Integer
Return hash.Count
End Get
End Property
ReadOnly Property Item(ByVal Index As Integer) As gmseNWResult
Return hash(Index)
End Get
End Property
Public Sub Add(ByVal Text As String)
Dim r As gmseNWResult

r = hash(Text)
If r Is Nothing Then
r = New gmseNWResult
r.Text = Text
hash.Add(r.Text, r)
End If
r.Count += 1
End Sub
Public Sub Remove(ByVal MinHeight As Integer)
Dim r As gmseNWResult
Dim tmp As New Hashtable(CaseInsensitiveHashCodeProvider.Default, CaseInsensitiveComparer.Default)

For Each r In hash.Values
If r.Count >= MinHeight Then
tmp.Add(r.Text, r)
End If
hash = tmp
End Sub

Public Function GetEnumerator() As System.Collections.IEnumerator Implements System.Collections.IEnumerable.GetEnumerator
Return hash.Values.GetEnumerator
End Function
End Class
#End Region

' Definition of one Symbol
Public Class gmseNWBarcodeSymbol
Public Value As Integer
Public Text As String
' Encoding of Symbol in NW notation
Public Encoding As String

Public Sub New(ByVal Value As Integer, ByVal Text As String, ByVal Encoding As String)
Me.Value = Value
Me.Text = Text
Me.Encoding = Encoding
End Sub
End Class

' Abstract parameters für barcode decoding for further extensions (2 of 5 standard,...)
Public MustInherit Class gmseNWBarcodeDef
' Minimum count of bars for a valid barcode.
MustOverride ReadOnly Property MinBarCount() As Integer
' Decode nw representation to text.
Public MustOverride Function Decode(ByVal symbol As String) As String
' NWidth * Fkt <WWidth (relation between narrow width and wide width.
Overridable ReadOnly Property MaxFktNW() As Integer
Return 10
End Get
End Property
' upped the tolerance to 67% due to bad scans 39412
Overridable ReadOnly Property PctNWTolerance() As Double
Return 0.67
End Get
End Property
' Min length of white space before first bar and after last bar in percent of wide bar (Quiet zone).
Overridable ReadOnly Property PctMinWhiteSpace() As Double
Return 0
End Get
End Property
' Barcode must be at least MinHeight height.
Overridable ReadOnly Property MinHeight() As Integer
Return 2
End Get
End Property
End Class

' Definition 2 of 5 interleaved
Public Class gmseBarcodeDef2of5interleaved
Inherits gmseNWBarcodeDef

Dim StartSymbol As gmseNWBarcodeSymbol
Dim StopSymbol As gmseNWBarcodeSymbol
Dim hash As New Hashtable(CaseInsensitiveHashCodeProvider.Default, CaseInsensitiveComparer.Default)

' We only accept barcodes with at least 23 bars.
Public Overrides ReadOnly Property MinBarCount() As Integer
Return 23
End Get
End Property

Private Sub CreateSymbolTable()
'in code 39 there are 43 chars
Dim BaseSymbol(43) As gmseNWBarcodeSymbol
Dim sym As gmseNWBarcodeSymbol
Dim x As Integer
Dim Text As String
Dim i As Integer

'code 39 symbols
BaseSymbol(0) = New gmseNWBarcodeSymbol(0, "0", "NNNWWNWNN")
BaseSymbol(1) = New gmseNWBarcodeSymbol(1, "1", "WNNWNNNNW")
BaseSymbol(2) = New gmseNWBarcodeSymbol(2, "2", "NNWWNNNNW")
BaseSymbol(3) = New gmseNWBarcodeSymbol(3, "3", "WNWWNNNNN")
BaseSymbol(4) = New gmseNWBarcodeSymbol(4, "4", "NNNWWNNNW")
BaseSymbol(5) = New gmseNWBarcodeSymbol(5, "5", "WNNWWNNNN")
BaseSymbol(6) = New gmseNWBarcodeSymbol(6, "6", "NNWWWNNNN")
BaseSymbol(7) = New gmseNWBarcodeSymbol(7, "7", "NNNWNNWNW")
BaseSymbol(8) = New gmseNWBarcodeSymbol(8, "8", "WNNWNNWNN")
BaseSymbol(9) = New gmseNWBarcodeSymbol(9, "9", "NNWWNNWNN")
BaseSymbol(10) = New gmseNWBarcodeSymbol(10, "A", "WNNNNWNNW")
BaseSymbol(11) = New gmseNWBarcodeSymbol(11, "B", "NNWNNWNNW")
BaseSymbol(12) = New gmseNWBarcodeSymbol(12, "C", "WNWNNWNNN")
BaseSymbol(13) = New gmseNWBarcodeSymbol(13, "D", "NNNNWWNNW")
BaseSymbol(14) = New gmseNWBarcodeSymbol(14, "E", "WNNNWWNNN")
BaseSymbol(15) = New gmseNWBarcodeSymbol(15, "F", "NNWNWWNNN")
BaseSymbol(16) = New gmseNWBarcodeSymbol(16, "G", "NNNNNWWNW")
BaseSymbol(17) = New gmseNWBarcodeSymbol(17, "H", "WNNNNWWNN")
BaseSymbol(18) = New gmseNWBarcodeSymbol(18, "I", "NNWNNWWNN")
BaseSymbol(19) = New gmseNWBarcodeSymbol(19, "J", "NNNNWWWNN")
BaseSymbol(20) = New gmseNWBarcodeSymbol(20, "K", "WNNNNNNWW")
BaseSymbol(21) = New gmseNWBarcodeSymbol(21, "L", "NNWNNNNWW")
BaseSymbol(22) = New gmseNWBarcodeSymbol(22, "M", "WNWNNNNWN")
BaseSymbol(23) = New gmseNWBarcodeSymbol(23, "N", "NNNNWNNWW")
BaseSymbol(24) = New gmseNWBarcodeSymbol(24, "O", "WNNNWNNWN")
BaseSymbol(25) = New gmseNWBarcodeSymbol(25, "P", "NNWNWNNWN")
BaseSymbol(26) = New gmseNWBarcodeSymbol(26, "Q", "NNNNNNWWW")
BaseSymbol(27) = New gmseNWBarcodeSymbol(27, "R", "WNNNNNWWN")
BaseSymbol(28) = New gmseNWBarcodeSymbol(28, "S", "NNWNNNWWN")
BaseSymbol(29) = New gmseNWBarcodeSymbol(29, "T", "NNNNWNWWN")
BaseSymbol(30) = New gmseNWBarcodeSymbol(30, "U", "WWNNNNNNW")
BaseSymbol(31) = New gmseNWBarcodeSymbol(31, "V", "NWWNNNNNW")
BaseSymbol(32) = New gmseNWBarcodeSymbol(32, "W", "WWWNNNNNN")
BaseSymbol(33) = New gmseNWBarcodeSymbol(33, "X", "NWNNWNNNW")
BaseSymbol(34) = New gmseNWBarcodeSymbol(34, "Y", "WWNNWNNNN")
BaseSymbol(35) = New gmseNWBarcodeSymbol(35, "Z", "NWWNWNNNN")
BaseSymbol(36) = New gmseNWBarcodeSymbol(36, "-", "NWNNNNWNW")
BaseSymbol(37) = New gmseNWBarcodeSymbol(37, ".", "WWNNNNWNN")
BaseSymbol(38) = New gmseNWBarcodeSymbol(38, " ", "NWWNNNWNN")
BaseSymbol(39) = New gmseNWBarcodeSymbol(39, "$", "NWNWNWNNN")
BaseSymbol(40) = New gmseNWBarcodeSymbol(40, "/", "NWNWNNNWN")
BaseSymbol(41) = New gmseNWBarcodeSymbol(41, "+", "NWNNNWNWN")
BaseSymbol(42) = New gmseNWBarcodeSymbol(42, "%", "NNNWNWNWN")

' Buildung the hash for decoding:
For x = 0 To 42
Text = ""
For i = 0 To 8
Text &= BaseSymbol(x).Encoding.Chars(i)
sym = New gmseNWBarcodeSymbol(x, BaseSymbol(x).Text, Text)
hash.Add(sym.Encoding, sym)

StartSymbol = New gmseNWBarcodeSymbol(-1, "Start", "NWNNWNWNN")
'in code 39 the start and stop symbols are the same
End Sub

Public Sub New()
End Sub

Public Overrides Function Decode(ByVal symbol As String) As String
Return Decode1(symbol, 0)
End Function

' Get human readable text from the barcode.
Public Function Decode1(ByVal symbol As String, ByVal offset As Integer) As String
Dim sym As String
Dim sb As New StringBuilder
Dim Pos As Integer = offset
Dim bi As gmseNWBarcodeSymbol

sym = symbol.Substring(Pos, StartSymbol.Encoding.Length)
' Make sure that the first symbol is the start symbol
If String.Compare(sym, StartSymbol.Encoding, True) <> 0 Then
Return ""
End If
' Get past the start symbol so we can start decoding.
Pos += StartSymbol.Encoding.Length + 1

' Data
While Pos < symbol.Length
'symbols are 9 bars long plus the narrow whitespace
If symbol.Length - Pos > 10 Then
sym = symbol.Substring(Pos, 9)
bi = hash(sym)
If bi Is Nothing Then
Return ""
End If
Pos += 10
ElseIf String.Compare(sym, StartSymbol.Encoding, True) <> 0 Then ' StopSymbol and start symbol are the same
sym = symbol.Substring(Pos, 9)
bi = hash(sym)
If bi Is Nothing Then
Return ""
Return sb.ToString
End If
Return ""
End If
End While
Return ""
End Function
End Class

' Scanning algorithm:
Public Class gmseNWScanner
Dim cBitMask(7) As Byte
Dim cScanRow() As Byte
Dim nBar As Integer
Dim cBarWidth() As Integer
Dim cBarBlack() As Boolean
Dim cOffset As Integer
Dim cLength As Integer
Dim cNWidth As Integer
Dim cWWidth As Integer
Dim cBCDef As gmseNWBarcodeDef
Dim cResult As gmseNWResultCollection

ReadOnly Property Result() As gmseNWResultCollection
Return cResult
End Get
End Property
' Find all Code 39 barcodes in Bitmap
Public Sub Scan(ByVal bmp As Bitmap)
Dim data As BitmapData
Dim ScanRow() As Byte
Dim y As Integer
Dim x As Integer

data = bmp.LockBits(New Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadOnly, PixelFormat.Format1bppIndexed)
cResult = New gmseNWResultCollection
ReDim ScanRow(data.Stride - 1)
' Scan all rows of bitmap.
For y = 0 To bmp.Height - 1
For x = 0 To data.Stride - 1
ScanRow(x) = System.Runtime.InteropServices.Marshal.ReadByte(data.Scan0, data.Stride * y + x)
Scan(ScanRow, 0, bmp.Width)
End Try
End Sub

' ScanRow must be 1bppp format.
Private Sub Scan(ByVal ScanRow() As Byte, ByVal offset As Integer, ByVal Length As Integer)
cScanRow = ScanRow
cLength = Length
cOffset = offset
End Sub

' Calculate bars
Private Sub CalcBars()
Dim x As Integer
Dim bl As Boolean

nBar = 0
ReDim cBarWidth(10)
ReDim cBarBlack(10)

cBarBlack(0) = IsBlack(cOffset)
For x = 0 To cLength - 1
If nBar >= cBarWidth.Length - 1 Then
ReDim Preserve cBarWidth(nBar * 2)
ReDim Preserve cBarBlack(nBar * 2)
End If
bl = IsBlack(cOffset + x)
If cBarBlack(nBar) = bl Then
cBarWidth(nBar) += 1
nBar += 1
cBarBlack(nBar) = bl
cBarWidth(nBar) = 1
End If
nBar += 1
End Sub

' The scan
Private Sub Scan()
Dim Pos As Integer
Dim ValidNW As Boolean
Dim BCStart As Integer
Dim BCEnde As Integer
Dim Text As String
Dim sb As StringBuilder
Dim nwt As Integer

' We want a leading white space, so we start at position 1
Pos = 1
While Pos < nBar - cBCDef.MinBarCount
' Start with a black bar
If cBarBlack(Pos) Then
' Try to validate with a sample set, if we can classify the bars in N and W bars within a tolerance of 25%.
ValidNW = CalcNWWidth(Pos, cBCDef.MinBarCount)
If ValidNW Then ' n und w are OK.
sb = New StringBuilder
BCStart = Pos
BCEnde = Pos
' Start to decode, until no more valid bars are found.
While Pos < nBar

nwt = NWBarType(cBarWidth(Pos))
If nwt = -1 Then
Exit While
ElseIf nwt = 0 Then
End If
BCEnde += 1
Pos += 1
End While
BCEnde -= 1
Text = cBCDef.Decode(sb.ToString)
If Text <> "" Then
End If
Pos += 1
End If
Pos += 1
End If
End While
End Sub

' Classify width of a bar in -1: invalid, 0 N(arrow), 1 W(ide).
Private Function NWBarType(ByVal Width As Integer) As Integer
Dim MaxAbweichung As Double
Dim Abweichung As Integer

Abweichung = Math.Min(Math.Abs(Width - cNWidth), Math.Abs(Width - cWWidth))
MaxAbweichung = (cWWidth - cNWidth) * cBCDef.PctNWTolerance
If Abweichung > MaxAbweichung Then
Return -1
ElseIf Math.Abs(Width - cNWidth) < Math.Abs(Width - cWWidth) Then
Return 0
Return 1
End If

End Function

' Calculate Narrow and Wide bar width.
Private Function CalcNWWidth(ByVal Pos As Integer, ByVal Length As Integer) As Boolean
Dim NWidth As Integer
Dim WWidth As Integer
Dim tmp As Integer
Dim Abweichung As Double
Dim MaxAbweichung As Double
Dim i As Integer

' Calc Min and Max.
NWidth = cBarWidth(Pos)
WWidth = cBarWidth(Pos)
For i = 0 To Length - 1
tmp = cBarWidth(Pos + i)
If tmp > WWidth Then
WWidth = tmp
End If
If tmp < NWidth Then
NWidth = tmp
End If

' As wide we accept as maximum NWidth * cBCDef.MaxFktNW
If NWidth * cBCDef.MaxFktNW < WWidth Then
cWWidth = 0
cNWidth = 0
Return False
End If

Abweichung = 0
' Calculate Tolerance
For i = 0 To Length - 1
tmp = Math.Min(Math.Abs(cBarWidth(Pos + i) - NWidth), Math.Abs(cBarWidth(Pos + i) - WWidth))
If tmp > Abweichung Then
Abweichung = tmp
End If

MaxAbweichung = (WWidth - NWidth) * cBCDef.PctNWTolerance
If Abweichung > MaxAbweichung Then
cWWidth = 0
cNWidth = 0
Return False
cWWidth = WWidth
cNWidth = NWidth
Return True
End If
End Function

' Is the pixel black?
Private ReadOnly Property IsBlack(ByVal x As Integer) As Boolean
Return (cScanRow(x \ 8) And cBitMask(x Mod 8)) = 0
End Get
End Property

' Hepler for calculating pixel color.
Private Sub CreateBitMask()
Dim b As Byte = 1
Dim i As Integer

For i = 0 To 7
cBitMask(7 - i) = b
If i < 7 Then
b = b * 2
End If
End Sub

Public Sub New(ByVal bcd As gmseNWBarcodeDef)
cBCDef = bcd
End Sub
End Class
GeneralRe: Reading barcode type 39 Pin
cyos25-Apr-11 20:46
membercyos25-Apr-11 20:46 
QuestionThe Speed for barcode decoder Pin
jackjack8916-Apr-07 23:30
memberjackjack8916-Apr-07 23:30 
QuestionChange BMP File Error! Pin
zfq30820-Nov-06 16:57
memberzfq30820-Nov-06 16:57 
AnswerRe: Change BMP File Error! Pin
mackenb25-Nov-06 4:52
membermackenb25-Nov-06 4:52 
AnswerRe: Change BMP File Error! [modified] Pin
Robert_Zenz23-Mar-09 4:57
memberRobert_Zenz23-Mar-09 4:57 
AnswerRe: Change BMP File Error! Pin
tqhang9998-Oct-09 6:01
membertqhang9998-Oct-09 6:01 
QuestionSome question? Pin
Pham Tuan21-Sep-06 21:58
memberPham Tuan21-Sep-06 21:58 
GeneralBarcode font Code 128 Pin
angelagke31-Jul-06 18:31
memberangelagke31-Jul-06 18:31 
GeneralRe: Barcode font Code 128 Pin
mackenb2-Aug-06 1:07
membermackenb2-Aug-06 1:07 
GeneralRe: Barcode font Code 128 Pin
angelagke2-Aug-06 5:24
memberangelagke2-Aug-06 5:24 
Questionmailto: Pin
KatliwaMax30-May-06 20:29
memberKatliwaMax30-May-06 20:29 
Generalhelp me, please! Pin
4aaaa9-Mar-06 16:43
member4aaaa9-Mar-06 16:43 
GeneralRe: help me, please! [modified] Pin
Pandele Florin31-May-06 1:46
memberPandele Florin31-May-06 1:46 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Praise Praise    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

Permalink | Advertise | Privacy | Terms of Use | Mobile
Web02 | 2.8.170622.1 | Last Updated 31 Jan 2006
Article Copyright 2006 by mackenb
Everything else Copyright © CodeProject, 1999-2017
Layout: fixed | fluid