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.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

GeneralRe: how to scan image directly into picturebox instead of painting onto form? PinmemberBurhan ERSOY28-Jul-09 22:52 
GeneralRe: how to scan image directly into picturebox instead of painting onto form? PinmemberGary Noter29-Jul-09 7:02 
GeneralSet duplex capability PinmemberSerenaFab15-Oct-08 0:50 
GeneralRe: Set duplex capability PinmemberDeiany20-Oct-08 4:01 
GeneralRe: Set duplex capability PinmemberRecycleYourLife10-Nov-08 10:27 
GeneralRe: Set duplex capability PinmemberRecycleYourLife11-Nov-08 4:05 
QuestionHow do I get TWON_RANGE values (TWAIN) ? Pinmembermuhtarqong10-Oct-08 10:15 
QuestionHow to get TWON_RANGE values? Pinmembermuhtarqong10-Oct-08 10:05 
AnswerRe: How to get TWON_RANGE values? [modified] PinmemberMember 216026519-Jan-11 17:20 
QuestionTwo Face PinmemberDCE_Erick3-Oct-08 8:08 
QuestionHow setting DAT_GRAYRESPONSE PinmemberMember 64259930-Sep-08 2:16 
GeneralBlack-Boxify the code please Pinmemberqjay11-Sep-08 10:17 
AnswerRe: Black-Boxify the code please PinmemberNETMaster11-Sep-08 12:00 
GeneralRe: Black-Boxify the code please Pinmemberqjay11-Sep-08 18:32 
QuestionHow can I check if I scan a blank document? Pinmemberjhonny24727-Aug-08 7:11 
AnswerRe: How can I check if I scan a blank document? PinmemberGary Noter9-Dec-08 11:50 
QuestionRe: How can I check if I scan a blank document? PinmemberNitinMakwana27-May-10 23:27 
AnswerChanging brightness PinmemberMember 463781224-Aug-08 10:41 
GeneralRe: Changing brightness PinmemberMember 260553418-Jan-10 0:36 
Questioncould you please give me an simple example for Pinmemberbkkss20-Jul-08 16:29 
GeneralVS2008 x64 Vista Problem outside debugger... PinmemberTopper Price11-Jul-08 8:49 
GeneralRe: VS2008 x64 Vista Problem outside debugger... PinmemberTopper Price11-Jul-08 10:46 
Questionhow Pinmemberibulut2-Jul-08 23:12 
AnswerRe: how PinmemberGary Noter9-Dec-08 11:17 
Generalreturn TwainCommand.Not PinmemberMember 462883222-Jun-08 1:36 
GeneralRe: return TwainCommand.Not Pinmemberzedascoves9-Feb-11 3:10 
GeneralRe: return TwainCommand.Not PinmemberMember 833147720-Oct-11 3:08 
GeneralBad value by PixelType PinmemberMember 46378126-Jun-08 2:31 
QuestionVS2008 and Vista 64 bit Pinmembernxtwothou5-May-08 7:41 
AnswerRe: VS2008 and Vista 64 bit Pinmembernxtwothou5-May-08 9:51 
Questionhow to configure this lib(setting color,size,resolution???) PinmemberMember 447396622-Apr-08 1:02 
QuestionHow to set output size using twain capabilities? Pinmemberkantaiah13-Apr-08 19:14 
QuestionThis example doesn't work on VS2008 PinmemberMing_Z26-Feb-08 17:16 
AnswerRe: This example doesn't work on VS2008 PinmemberTopper Price11-Jul-08 8:57 
GeneralRe: This example doesn't work on VS2008 PinmemberMing_Z11-Jul-08 9:48 
GeneralScanner problem Pinmemberpiras10-Feb-08 7:35 
QuestionHow do I check if the scanner is plugged in Pinmemberpeter.goessweiner23-Jan-08 10:22 
AnswerRe: How do I check if the scanner is plugged in Pinmemberzahil5-Jun-08 18:57 
AnswerRe: How do I check if the scanner is plugged in Pinmembersptyangzhou16-Jul-08 3:58 
QuestionHow to set 100*100 Dpi without showing User Interface PinmemberMember 159761323-Jan-08 2:11 
AnswerRe: How to set 100*100 Dpi without showing User Interface Pinmemberzahil5-Jun-08 19:00 
GeneralResolution of saved image PinmemberZiggy Short17-Jan-08 5:33 
GeneralRe: Resolution of saved image [modified] PinmemberNeal175922-Jul-11 9:38 
QuestionLoading saved files PinmemberZiggy Short17-Jan-08 3:06 
Questionhelp on duplex PinmemberMember 376198314-Jan-08 9:37 
GeneralMaking renameable folders PinmemberRolly13-Jan-08 18:52 
GeneralAnother implementation available PinmemberPKultimPK28-Dec-07 2:07 
Questionhow to change the resolution in code.. Pinmemberaparichitudu10-Dec-07 18:38 
Questionhow to change the resolution within code.? Pinmembervissu10-Dec-07 17:48 
GeneralAttempted to read or write protected memory. This is often an indication that other memory is corrupt. [modified] PinmemberViRiX8-Dec-07 16:42 

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