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.NET TWAIN image scanner

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4.91 (224 votes)
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: WIA driver is not working with multiple pages Pin
smile869114-Feb-13 8:51
Membersmile869114-Feb-13 8:51 
nturri13065-Jan-13 5:07
Membernturri13065-Jan-13 5:07 
QuestionNeed help Pin
Member 806548423-Nov-12 17:54
MemberMember 806548423-Nov-12 17:54 
AnswerRe: Need help Pin
Abdullah Çetinkaya22-Jan-13 23:11
MemberAbdullah Çetinkaya22-Jan-13 23:11 
Questionget error in multipage scanning Pin
yuee17-Nov-12 2:08
Memberyuee17-Nov-12 2:08 
AnswerRe: get error in multipage scanning Pin
smile86917-Nov-12 2:09
Membersmile86917-Nov-12 2:09 
Questionhelp Pin
bijarcity24-Oct-12 6:09
Memberbijarcity24-Oct-12 6:09 
AnswerRe: help Pin
smile86911-Nov-12 5:34
Membersmile86911-Nov-12 5:34 
Questionhelp me Pin
bijarcity24-Oct-12 5:24
Memberbijarcity24-Oct-12 5:24 
Questionvery helpful and tested with some scanners Pin
_Nizar21-Oct-12 9:09
Member_Nizar21-Oct-12 9:09 
QuestionNeed support, Pin
mastermindinfo25-Sep-12 4:25
Membermastermindinfo25-Sep-12 4:25 
AnswerNeed support, till pending Pin
mastermindinfo2-Oct-12 23:47
Membermastermindinfo2-Oct-12 23:47 
GeneralRe: Need support, till pending Pin
ingbabic25-Oct-12 4:56
Memberingbabic25-Oct-12 4:56 
GeneralRe: Need support, till pending Pin
Abdullah Çetinkaya22-Jan-13 23:26
MemberAbdullah Çetinkaya22-Jan-13 23:26 
GeneralMy vote of 4 Pin
Burak Tunçbilek7-Sep-12 4:09
MemberBurak Tunçbilek7-Sep-12 4:09 
QuestionImage Resolution Problem. Pin
rush2rajiv29-Jun-12 0:06
Memberrush2rajiv29-Jun-12 0:06 
AnswerRe: Image Resolution Problem. Pin
Member 1018928526-Aug-13 17:53
MemberMember 1018928526-Aug-13 17:53 
QuestionOut of Memory Exception Pin
Jaydeep Jadav15-Jun-12 20:56
MemberJaydeep Jadav15-Jun-12 20:56 
QuestionRe: Out of Memory Exception Pin
nilesh kakade26-Feb-13 19:17
Membernilesh kakade26-Feb-13 19:17 
AnswerRe: Out of Memory Exception Pin
Jaydeep Jadav1-Mar-13 23:18
MemberJaydeep Jadav1-Mar-13 23:18 
QuestionLoader Lock Error Problem Pin
leenak8-Jun-12 2:11
Memberleenak8-Jun-12 2:11 
GeneralRe: Loader Lock Error Problem Pin
smile869110-Jul-12 11:59
Membersmile869110-Jul-12 11:59 
QuestionDuplex Scanning Pin
Isuru Alahakoon8-Jun-12 1:14
MemberIsuru Alahakoon8-Jun-12 1:14 
Questionhide progress bar window. Pin
Member 46759534-Jun-12 21:32
MemberMember 46759534-Jun-12 21:32 
QuestionError on 64 bits machine Pin
david bong1-Jun-12 6:09
Memberdavid bong1-Jun-12 6:09 

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Posted 16 Sep 2001


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