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.NET TWAIN image scanner

, 12 May 2002 Public Domain
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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

GeneralMy vote of 5 Pinmembershiva_194-Jul-13 20:30 
Questiontwain scanning in PinmemberDina_Du27-Jun-13 19:26 
Questionc# n vb PinmemberImam Azinuddin19-Jun-13 20:14 
QuestionError in the Code PinmemberHerman M. Reyes7-Jun-13 1:44 
AnswerRe: Error in the Code PinmemberMember 1015869416-Jul-13 11:14 
GeneralRe: Error in the Code PinmemberHerman M. Reyes26-Jul-13 2:06 
GeneralRe: Error in the Code PinmemberMember 1020463311-Sep-13 10:19 
Questionthanks PinmemberMember 786391322-May-13 13:15 
QuestionHow can i scan multi pages PinmemberMember 397326719-May-13 18:33 
QuestionNeed help to fix Issue in Twain .net Library Pinmembervinaykn.rao22-Apr-13 4:07 
QuestionException throws when I use in Win7 64 bit Pinmemberanisfathima18-Apr-13 23:11 
AnswerRe: Exception throws when I use in Win7 64 bit PinmemberJnnxp5-Aug-13 17:11 
Questionhow set Image info PinmemberMohamed Nabawy15-Apr-13 7:59 
QuestionScanner Error Pinmemberasheykh14-Apr-13 23:05 
i open twaingui_src project with visual studio 2012
and when i build it dot give me any error but when i run it gave this error
error is in this line :
<pre lang="c#">TwRC rc = DSMparent( appid, IntPtr.Zero, TwDG.Control, TwDAT.Parent, TwMSG.OpenDSM, ref hwndp );</pre>
<a href=""><a href=""></a>[<a href="" target="_blank" title="New Window">^</a>]</a>
Please help me.
QuestionTwainCommand.TransferReady: hbitmap to gdi+ bitmap Pinmemberliuxu093826-Mar-13 22:21 
QuestionThe "" is damaged? Pinmemberliuxu093826-Mar-13 1:16 
QuestionScanning on Win7 64Bit Pinmemberkhalilsa27-Feb-13 5:19 
AnswerRe: Scanning on Win7 64Bit Pinmemberricardofrias20-Mar-13 8:48 
AnswerRe: Scanning on Win7 64Bit PinmemberJnnxp5-Aug-13 17:12 
Questionuse in PinmemberKalpana Volety11-Jan-13 10:59 
AnswerRe: use in PinmemberJnnxp5-Aug-13 17:17 
QuestionWIA driver is not working with multiple pages Pinmemberanisfathima9-Jan-13 23:59 
AnswerRe: WIA driver is not working with multiple pages Pinmembersmile869114-Feb-13 9:51 
Bughow set boolean value CAP_PAPERDETECTABLE,ICAP_AUTOMATICDESKEW ecc..? Pinmembernturri13065-Jan-13 6:07 
QuestionNeed help PinmemberMember 806548423-Nov-12 18:54 
AnswerRe: Need help PinmemberAbdullah Çetinkaya23-Jan-13 0:11 
Questionget error in multipage scanning Pinmemberyuee17-Nov-12 3:08 
AnswerRe: get error in multipage scanning Pinmembersmile86917-Nov-12 3:09 
Questionhelp Pinmemberbijarcity24-Oct-12 7:09 
AnswerRe: help Pinmembersmile86911-Nov-12 6:34 
Questionhelp me Pinmemberbijarcity24-Oct-12 6:24 
Questionvery helpful and tested with some scanners PinmemberMember 667621-Oct-12 10:09 
QuestionNeed support, Pinmembermastermindinfo25-Sep-12 5:25 
AnswerNeed support, till pending Pinmembermastermindinfo3-Oct-12 0:47 
GeneralRe: Need support, till pending Pinmemberingbabic25-Oct-12 5:56 
GeneralRe: Need support, till pending PinmemberAbdullah Çetinkaya23-Jan-13 0:26 
GeneralMy vote of 4 PinmemberBurak Tunçbilek7-Sep-12 5:09 
QuestionImage Resolution Problem. Pinmemberrush2rajiv29-Jun-12 1:06 
AnswerRe: Image Resolution Problem. PinmemberMember 1018928526-Aug-13 18:53 
QuestionOut of Memory Exception PinmemberJaydeep Jadav15-Jun-12 21:56 
QuestionRe: Out of Memory Exception Pinmembernileshkakade26-Feb-13 20:17 
AnswerRe: Out of Memory Exception PinmemberJaydeep Jadav2-Mar-13 0:18 
QuestionLoader Lock Error Problem Pinmemberleenak8-Jun-12 3:11 
GeneralRe: Loader Lock Error Problem [modified] Pinmembersmile869110-Jul-12 12:59 
QuestionDuplex Scanning PinmemberIsuru Alahakoon8-Jun-12 2:14 
Questionhide progress bar window. PinmemberMember 46759534-Jun-12 22:32 
QuestionError on 64 bits machine Pinmemberdavid bong1-Jun-12 7:09 
AnswerRe: Error on 64 bits machine Pinmemberboblogan13-Jun-12 7:00 
GeneralRe: Error on 64 bits machine PinmemberAbdullah Çetinkaya23-Jan-13 0:33 
Questionset Flatbed or Feader PinmemberAndrew8231-May-12 22:22 

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