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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

QuestionHow to show only Scanners which are Twain related? This code shows all WIA as well as Twain related scanners in the list Pinmembersnprani2-Mar-15 21:27 
QuestionCustomization of Twain Application PinmemberKB.Rajesh24-Feb-15 21:02 
QuestionHow to Implement ICAP_AUTODISCARDBLANKPAGES Pinmemberallan-arg20-Jan-15 20:40 
QuestionHow to scan a multipage document [modified] PinprofessionalMember 1124361330-Dec-14 2:46 
QuestionExe not compatible PinmemberMember 1114919523-Nov-14 23:07 
Questionhow calculate the number image of paper? Pinmembernturri13063-Nov-14 6:27 
QuestionDLL TO SCAN FILE AND PROCESS THE DATA PinmemberMember 1119101629-Oct-14 13:01 
QuestionTwainLib PassMessage only returns TwainCommand.Not or TwainCommand.Null Pinmembermy_gino20-Oct-14 12:12 
QuestionHow can I set a source in source code? PinmemberMember 104012259-Oct-14 1:34 
AnswerRe: How can I set a source in source code? PinmemberKB.Rajesh24-Feb-15 21:32 
Questionquick and easy TWAIN scanning realization PinmemberMember 109392318-Sep-14 22:49 
QuestionGreat application Pinmembermuharremunlu8-Sep-14 22:43 
QuestionError at line 59 PinmemberMember 21496282-Sep-14 17:33 
AnswerRe: Error at line 59 PinmemberMAGSI13-Nov-14 1:44 
QuestionGreat! But id like to Change the filname of Picture PinmemberMember 1067838911-Aug-14 23:38 
AnswerRe: Great! But id like to Change the filname of Picture PinmemberKB.Rajesh24-Feb-15 22:17 
QuestionGreat PinmemberChirantha Jayasinghe16-Jul-14 22:31 
Questiongreat thanks! PinmemberDmitryDrosd9-Jun-14 3:36 
GeneralMy vote of 5 Pinmembersuperduck20-May-14 21:38 
GeneralFix for windows 8.0 Pinmemberprcow12-May-14 12:24 
GeneralRe: Fix for windows 8.0 Pinmembersmile869115-Dec-14 6:53 
GeneralRe: Fix for windows 8.0 Pinmemberbidyut1234519-Jan-15 0:55 
QuestionTwain Driver Interface Dialog Pinmemberdanajp_595-May-14 12:07 
AnswerRe: Twain Driver Interface Dialog PinmemberRavishankar chinnur8-May-14 1:06 
GeneralRe: Twain Driver Interface Dialog PinmemberImanol Pinto Lopez28-May-14 3:58 
GeneralRe: Twain Driver Interface Dialog PinmemberImanol Pinto Lopez29-May-14 0:18 
GeneralRe: Twain Driver Interface Dialog PinmemberKB.Rajesh24-Feb-15 22:31 
GeneralRe: Twain Driver Interface Dialog PinmemberKB.Rajesh24-Feb-15 22:29 
QuestionAbout disabling Scan Property form PinmemberMember 107179417-Apr-14 3:22 
AnswerRe: About disabling Scan Property form Pinmemberdanajp_595-May-14 12:23 
QuestionGreat Pinmembermagicyangjay18-Mar-14 22:50 
QuestionGet supported capabilities PinmemberM.Azadi9-Mar-14 23:15 
QuestionWindows 8 errors with TwainLib.Twain.DSMident Pinmemberpserrao5-Mar-14 4:57 
AnswerRe: Windows 8 errors with TwainLib.Twain.DSMident PinmemberRavishankar chinnur5-Mar-14 19:12 
GeneralRe: Windows 8 errors with TwainLib.Twain.DSMident Pinmemberpserrao6-Mar-14 10:37 
GeneralRe: Windows 8 errors with TwainLib.Twain.DSMident PinmemberRavishankar chinnur6-Mar-14 19:13 
GeneralRe: Windows 8 errors with TwainLib.Twain.DSMident Pinmembersmile869115-Dec-14 6:54 
Questionscanning one after another is not posiible PinmemberRavishankar chinnur5-Mar-14 3:08 
AnswerRe: scanning one after another is not posiible Pinmembermalcolmxu21-Mar-14 6:54 
AnswerRe: scanning one after another is not posiible PinmemberAntriksh Patel27-Jul-14 19:12 
BugInsufficient Memory Pinmemberkeencoder20-Jan-14 23:42 
GeneralRe: Insufficient Memory PinmemberMember 1035479622-Sep-14 23:13 
QuestionHow to scan on both sides of the document Pinmembersandeep7587-Jan-14 22:58 
Questionsave images Pinmemberezelden.sahi12-Nov-13 22:30 
QuestionHow can i change the transfer mode to File PinmemberMurugan Kolanji11-Nov-13 3:43 
GeneralThank you so much~! PinmemberCheon sang10-Nov-13 23:03 
Question.NET TWAIN image scanner Convert to for VB 2010 PinmemberDibakar Mishra30-Oct-13 4:55 
QuestionGdipSaveImageToStream brings back a empty stream PinmemberMember 391328323-Oct-13 9:49 
GeneralMy vote of 5 PinmemberLucas Lima Araujo27-Sep-13 7:37 
QuestionWindows 8 Fails PinmemberLucas Lima Araujo27-Sep-13 5:39 

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