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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

GeneralMy vote of 5 Pin
Shahin Khorshidnia12-Aug-11 20:50
professionalShahin Khorshidnia12-Aug-11 20:50 
QuestionADF is not working Pin
telme2-Aug-11 23:32
membertelme2-Aug-11 23:32 
AnswerRe: ADF is not working Pin
beyond111718-Oct-11 7:01
memberbeyond111718-Oct-11 7:01 
GeneralRe: ADF is not working Pin
telme18-Oct-11 20:29
membertelme18-Oct-11 20:29 
QuestionIs it possible to do ADF and Flatbed Scanner in TWAIN Pin
telme31-Jul-11 0:27
membertelme31-Jul-11 0:27 
AnswerRe: Is it possible to do ADF and Flatbed Scanner in TWAIN Pin
beyond111718-Oct-11 7:03
memberbeyond111718-Oct-11 7:03 
AnswerRe: Is it possible to do ADF and Flatbed Scanner in TWAIN Pin
Bala_Subramaniam11-Jan-12 1:01
memberBala_Subramaniam11-Jan-12 1:01 
QuestionTwainLib.cs with full specification Pin
telme27-Jul-11 22:55
membertelme27-Jul-11 22:55 
QuestionRe: TwainLib.cs with full specification Pin
ben06068327-Jul-11 23:23
memberben06068327-Jul-11 23:23 
QuestionSelecting ADF and Flatbed scanning option Pin
telme26-Jul-11 2:33
membertelme26-Jul-11 2:33 
QuestionDemo works but not the source Pin
Steven Szelei19-Jul-11 12:08
memberSteven Szelei19-Jul-11 12:08 
AnswerRe: Demo works but not the source Pin
golanw20-Dec-11 17:32
membergolanw20-Dec-11 17:32 
QuestionRetrive a List of Paper Sizes Pin
bennett cummins15-Jul-11 11:19
memberbennett cummins15-Jul-11 11:19 
GeneralAccess Violation with Nikon Coolscan IV Pin
Easy_Rider999915-Jun-11 23:51
memberEasy_Rider999915-Jun-11 23:51 
Generalmessagefilter Pin
acep221-Jun-11 21:11
memberacep221-Jun-11 21:11 
GeneralSave each image Pin
Gabriel Perdigão1-Jun-11 8:42
memberGabriel Perdigão1-Jun-11 8:42 
GeneralRange value of capability ICAP_GAMMA Pin
Willzith Pham13-May-11 0:31
memberWillzith Pham13-May-11 0:31 
SuggestionRe: Range value of capability ICAP_GAMMA Pin
Spike0xFF14-Jul-11 13:05
memberSpike0xFF14-Jul-11 13:05 
GeneralHow to save all pages in 1 file [modified] Pin
LQUICK12-May-11 7:24
memberLQUICK12-May-11 7:24 
GeneralRe: How to save all pages in 1 file Pin
trpugh17-May-11 9:35
membertrpugh17-May-11 9:35 
GeneralCapability ICAP_GAMMA Pin
Willzith Pham12-May-11 0:45
memberWillzith Pham12-May-11 0:45 
General[TWAIN][CAPABILITES] Set float value for ICAP_GAMMA Pin
Willzith Pham11-May-11 17:58
memberWillzith Pham11-May-11 17:58 
GeneralHow obtain where image has been saved? Pin
mehdimax30-Apr-11 22:52
membermehdimax30-Apr-11 22:52 
QuestionHow to take picture from Digital Camera in C# application using TWAIN Pin
Member 77483387-Apr-11 21:08
memberMember 77483387-Apr-11 21:08 
QuestionFailed to save 600dpi color to BMP Pin
worship66829-Mar-11 8:45
memberworship66829-Mar-11 8:45 

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