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.NET TWAIN image scanner

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12 May 2002Public Domain
Using TWAIN API to scan images

Sample Screenshot


In Windows imaging applications, the most used API for scanning is TWAIN Unfortunately, the new .NET Framework has no built-in support for TWAIN. So we have to work with the interop methods of .NET to access this API. This article doesn't explain this interop techniques, and good knowledge of the TWAIN 1.9 specifications is assumed! The sample code included doesn't present a finished library, only some essential steps for a minimal TWAIN adaption to .NET applications.


First step was to port the most important parts of TWAIN.H, these are found in TwainDefs.cs. The real logic for calling TWAIN is coded in the class Twain, in file TwainLib.cs.. As the TWAIN API is exposed by the Windows DLL, twain_32.dll, we have to use the .NET DllImport mechanism for interop with legacy code. This DLL has the central DSM_Entry(), ordinal #1 function exported as the entry point to TWAIN. This call has numerous parameters, and the last one is of variable type! It was found to be best if we declare multiple variants of the call like:

[DllImport("twain_32.dll", EntryPoint="#1")]
private static extern TwRC DSMparent(
    [In, Out] TwIdentity origin,
    IntPtr zeroptr,
    TwDG dg, TwDAT dat, TwMSG msg,
    ref IntPtr refptr );

The Twain class has a simple 5-step interface:

class Twain

For some sort of 'callbacks', TWAIN uses special Windows messages, and these must be caught from the application-message-loop. In .NET, the only way found was IMessageFilter.PreFilterMessage(), and this filter has to be activated with a call like Application.AddMessageFilter(). Within the filter method, we have to forward each message to Twain.PassMessage(), and we get a hint (enum TwainCommand) back for how we have to react.

Sample App

The sample is a Windows Forms MDI-style application. It has the two TWAIN-related menu items Select Source... and Acquire... Once an image is scanned in, we can save it to a file in any of the GDI+ supported file formats (BMP, GIF, TIFF, JPEG...)


All code was only tested on Windows 2000SP2, with an Epson Perfection USB scanner and an Olympus digital photo camera. The scanned picture is (by TWAIN spec) a Windows DIB, and the sample code has VERY little checking against error return codes and bitmap formats. Unfortunately, no direct method is available in .NET to convert a DIB to the managed Bitmap class... Some known problems may show up with color palettes and menus.

Note, TWAIN has it's root in 16-Bit Windows! For a more modern API supported on Windows ME/XP, have a look at Windows Image Acquisition (WIA).


This article, along with any associated source code and files, is licensed under A Public Domain dedication


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Comments and Discussions

AnswerRe: scanning software does not work with certain drivers Pin
HackRow22-Jan-09 11:38
memberHackRow22-Jan-09 11:38 
Questionhow to copy the image to clipboard ? Pin
linwei2480423-Jun-07 6:27
memberlinwei2480423-Jun-07 6:27 
AnswerRe: how to copy the image to clipboard ? Pin
hcihlen28-Sep-07 4:40
memberhcihlen28-Sep-07 4:40 
GeneralCannot Delete file afert view Pin
Hugo G31-May-07 14:13
memberHugo G31-May-07 14:13 
GeneralRe: Cannot Delete file afert view Pin
Hugo G19-Jun-07 7:10
memberHugo G19-Jun-07 7:10 
GeneralRe: Cannot Delete file afert view Pin
supxiaoxin18-May-09 0:41
membersupxiaoxin18-May-09 0:41 
General[Document Scanning] Pin
samshah51222-May-07 2:50
membersamshah51222-May-07 2:50 
GeneralVery nice job Pin
WillSmithWorld10-Apr-07 18:57
memberWillSmithWorld10-Apr-07 18:57 
GeneralHelp me...!!! Pin
GC9N26-Mar-07 23:27
memberGC9N26-Mar-07 23:27 
GeneralRe: Help me...!!! Pin
gabegabe2-May-07 9:12
membergabegabe2-May-07 9:12 
GeneralWindow with progressbar Pin
yo ncv23-Mar-07 3:59
memberyo ncv23-Mar-07 3:59 
GeneralSource Code for VB.NET 2005 Pin
phalcom21-Mar-07 13:20
memberphalcom21-Mar-07 13:20 
GeneralRe: Source Code for VB.NET 2005 Pin
gabegabe25-Apr-07 11:24
membergabegabe25-Apr-07 11:24 
QuestionInit() method hangs up Pin
DiMann1-Mar-07 11:54
memberDiMann1-Mar-07 11:54 
AnswerRe: Init() method hangs up Pin
Ronsch4-Dec-08 23:06
memberRonsch4-Dec-08 23:06 
GeneralSource Code para VB Pin
phalcom228-Feb-07 8:37
memberphalcom228-Feb-07 8:37 
GeneralRe: Source Code para VB Pin
rgf2128-Mar-07 1:45
memberrgf2128-Mar-07 1:45 
GeneralRe: Source Code para VB Pin
yalenap31-May-07 8:14
memberyalenap31-May-07 8:14 
AnswerRe: Source Code para VB Pin
cmchuan8-Jul-07 23:11
membercmchuan8-Jul-07 23:11 
AnswerRe: Source Code para VB Pin
cmchuan8-Jul-07 23:12
membercmchuan8-Jul-07 23:12 
AnswerRe: Source Code para VB Pin
cmchuan8-Jul-07 23:14
membercmchuan8-Jul-07 23:14 
GeneralRe: Source Code para VB Pin
svincetic13-Nov-09 1:46
membersvincetic13-Nov-09 1:46 
GeneralRe: Source Code para VB Pin
djdrew17-Dec-09 7:39
memberdjdrew17-Dec-09 7:39 
QuestionRe: Source Code para VB Pin
VBdotnetSara19-Oct-10 19:38
memberVBdotnetSara19-Oct-10 19:38 
QuestionHow to put this in a HTML page Pin
memovera26-Feb-07 10:40
membermemovera26-Feb-07 10:40 

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Posted 16 Sep 2001


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