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Posted 16 Sep 2001
Licenced Public Domain

.NET TWAIN image scanner

, 12 May 2002
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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

QuestionTwain Driver Interface Dialog Pin
danajp_595-May-14 12:07
memberdanajp_595-May-14 12:07 
AnswerRe: Twain Driver Interface Dialog Pin
Ravishankar chinnur8-May-14 1:06
memberRavishankar chinnur8-May-14 1:06 
GeneralRe: Twain Driver Interface Dialog Pin
Imanol Pinto Lopez28-May-14 3:58
memberImanol Pinto Lopez28-May-14 3:58 
GeneralRe: Twain Driver Interface Dialog Pin
Imanol Pinto Lopez29-May-14 0:18
memberImanol Pinto Lopez29-May-14 0:18 
GeneralRe: Twain Driver Interface Dialog Pin
KB.Rajesh24-Feb-15 22:31
memberKB.Rajesh24-Feb-15 22:31 
GeneralRe: Twain Driver Interface Dialog Pin
KB.Rajesh24-Feb-15 22:29
memberKB.Rajesh24-Feb-15 22:29 
QuestionAbout disabling Scan Property form Pin
Member 107179417-Apr-14 3:22
memberMember 107179417-Apr-14 3:22 
AnswerRe: About disabling Scan Property form Pin
danajp_595-May-14 12:23
memberdanajp_595-May-14 12:23 
QuestionGreat Pin
magicyangjay18-Mar-14 22:50
membermagicyangjay18-Mar-14 22:50 
QuestionGet supported capabilities Pin
M.Azadi9-Mar-14 23:15
memberM.Azadi9-Mar-14 23:15 
QuestionWindows 8 errors with TwainLib.Twain.DSMident Pin
pserrao5-Mar-14 4:57
memberpserrao5-Mar-14 4:57 
AnswerRe: Windows 8 errors with TwainLib.Twain.DSMident Pin
Ravishankar chinnur5-Mar-14 19:12
memberRavishankar chinnur5-Mar-14 19:12 
GeneralRe: Windows 8 errors with TwainLib.Twain.DSMident Pin
pserrao6-Mar-14 10:37
memberpserrao6-Mar-14 10:37 
GeneralRe: Windows 8 errors with TwainLib.Twain.DSMident Pin
Ravishankar chinnur6-Mar-14 19:13
memberRavishankar chinnur6-Mar-14 19:13 
GeneralRe: Windows 8 errors with TwainLib.Twain.DSMident Pin
smile869115-Dec-14 6:54
membersmile869115-Dec-14 6:54 
Questionscanning one after another is not posiible Pin
Ravishankar chinnur5-Mar-14 3:08
memberRavishankar chinnur5-Mar-14 3:08 
AnswerRe: scanning one after another is not posiible Pin
malcolmxu21-Mar-14 6:54
membermalcolmxu21-Mar-14 6:54 
AnswerRe: scanning one after another is not posiible Pin
Antriksh Patel27-Jul-14 19:12
memberAntriksh Patel27-Jul-14 19:12 
BugInsufficient Memory Pin
keencoder20-Jan-14 23:42
memberkeencoder20-Jan-14 23:42 
GeneralRe: Insufficient Memory Pin
Member 1035479622-Sep-14 23:13
memberMember 1035479622-Sep-14 23:13 
GeneralRe: Insufficient Memory Pin
王文鹏19-Aug-15 0:48
member王文鹏19-Aug-15 0:48 
QuestionHow to scan on both sides of the document Pin
sandeep7587-Jan-14 22:58
membersandeep7587-Jan-14 22:58 
Questionsave images Pin
ezelden.sahi12-Nov-13 22:30
memberezelden.sahi12-Nov-13 22:30 
QuestionHow can i change the transfer mode to File Pin
Murugan Kolanji11-Nov-13 3:43
memberMurugan Kolanji11-Nov-13 3:43 
GeneralThank you so much~! Pin
Cheon sang10-Nov-13 23:03
memberCheon sang10-Nov-13 23:03 

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