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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 1 Pinmembernavidsoft10-Jan-12 23:39 
QuestionThis get freezed the whole application PinmemberMember 333762221-Dec-11 3:24 
AnswerRe: This get freezed the whole application PinmemberA7mad_21-Feb-12 10:26 
QuestionScanning area parameter through application PinmemberRajendrarajsri28-Nov-11 16:42 
QuestionTWAIN A3 Papersize change i.e. TwCapability capPaperSize = new TwCapability(TwCap.ICAP_SUPPORTEDSIZES, 1) PinmemberWaynePorter18-Nov-11 3:55 
Questioncan any one give this whole project in Pinmembernsk_saravana15-Nov-11 22:13 
AnswerRe: can any one give this whole project in Pinmemberwellhi18-Nov-11 17:43 
QuestionAutocrop Pinmembernsk_saravana13-Nov-11 23:21 
QuestionRemoving Scanner UI Pinmembernsk_saravana13-Nov-11 18:40 
Questionremoving the UI Pinmembermist99911-Nov-11 5:45 
QuestionADF Question.....Help Me Pinmemberbeyond111717-Oct-11 17:59 
QuestionCapture color image using twain Pinmemberakul12321-Sep-11 1:43 
QuestionCould not compile Pinmemberditoroin21-Sep-11 1:33 
SuggestionRe: Could not compile PinmemberMrPetan21-Sep-11 6:29 
"BadImageFormatException" is thrown when the application loads a DLL having incompatible bitness
(a 64 bit exe tried to load a 32bit DLL or a 32 bit exe tried to load a 64 bit DLL).

Make sure you compile your exe file as 32 bit (x86) !!!!.

GeneralRe: Could not compile PinmemberMember 831300223-Apr-12 23:59 
QuestionCAP_DEVICEONLINE always returns false Pinmemberbennett cummins13-Sep-11 7:26 
Questionconverting this sample in Pinmemberakul12323-Aug-11 23:33 
AnswerRe: converting this sample in Pinmembermahamahmaha22-Jan-12 22:22 
QuestionImage size PinmemberVBCoder6818-Aug-11 6:14 
QuestionDont want dialog boxes PinmemberNeha Ameen16-Aug-11 2:22 
GeneralMy vote of 5 PinmemberShahin Khorshidnia12-Aug-11 20:50 
QuestionADF is not working Pinmembertelme2-Aug-11 23:32 
AnswerRe: ADF is not working Pinmemberbeyond111718-Oct-11 7:01 
GeneralRe: ADF is not working Pinmembertelme18-Oct-11 20:29 
QuestionIs it possible to do ADF and Flatbed Scanner in TWAIN Pinmembertelme31-Jul-11 0:27 
AnswerRe: Is it possible to do ADF and Flatbed Scanner in TWAIN Pinmemberbeyond111718-Oct-11 7:03 
AnswerRe: Is it possible to do ADF and Flatbed Scanner in TWAIN Pinmemberbalasofttouch11-Jan-12 1:01 
QuestionTwainLib.cs with full specification Pinmembertelme27-Jul-11 22:55 
QuestionRe: TwainLib.cs with full specification Pinmemberben06068327-Jul-11 23:23 
QuestionSelecting ADF and Flatbed scanning option Pinmembertelme26-Jul-11 2:33 
QuestionDemo works but not the source PinmemberSteven Szelei19-Jul-11 12:08 
AnswerRe: Demo works but not the source Pinmembergolanw20-Dec-11 17:32 
QuestionRetrive a List of Paper Sizes Pinmemberbennett cummins15-Jul-11 11:19 
GeneralAccess Violation with Nikon Coolscan IV PinmemberEasy_Rider999915-Jun-11 23:51 
Generalmessagefilter Pinmemberacep221-Jun-11 21:11 
GeneralSave each image PinmemberGabriel Perdigão1-Jun-11 8:42 
GeneralRange value of capability ICAP_GAMMA PinmemberWillzith Pham13-May-11 0:31 
SuggestionRe: Range value of capability ICAP_GAMMA PinmemberSpike0xFF14-Jul-11 13:05 
GeneralHow to save all pages in 1 file [modified] PinmemberLQUICK12-May-11 7:24 
GeneralRe: How to save all pages in 1 file Pinmembertrpugh17-May-11 9:35 
GeneralCapability ICAP_GAMMA PinmemberWillzith Pham12-May-11 0:45 
General[TWAIN][CAPABILITES] Set float value for ICAP_GAMMA PinmemberWillzith Pham11-May-11 17:58 
GeneralHow obtain where image has been saved? Pinmembermehdimax30-Apr-11 22:52 
QuestionHow to take picture from Digital Camera in C# application using TWAIN PinmemberMember 77483387-Apr-11 21:08 
QuestionFailed to save 600dpi color to BMP Pinmemberworship66829-Mar-11 8:45 
GeneralHandling with the TW_ENTRYPOINT PinmemberTonkpils25-Mar-11 0:22 
GeneralRe: Handling with the TW_ENTRYPOINT PinmemberEasy_Rider999915-Jun-11 23:56 
GeneralRe: Handling with the TW_ENTRYPOINT PinmemberEasy_Rider999915-Jun-11 23:58 
GeneralRe: Handling with the TW_ENTRYPOINT PinmemberTonkpils16-Jun-11 12:27 
GeneralRe: Handling with the TW_ENTRYPOINT PinmemberEasy_Rider999918-Jun-11 5:40 

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