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Posted 16 Sep 2001


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.NET TWAIN image scanner

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12 May 2002Public Domain2 min read
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

AnswerRe: How do I check if the scanner is plugged in Pin
zahil5-Jun-08 18:57
Memberzahil5-Jun-08 18:57 
AnswerRe: How do I check if the scanner is plugged in Pin
sptyangzhou16-Jul-08 3:58
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QuestionHow to set 100*100 Dpi without showing User Interface Pin
Member 159761323-Jan-08 2:11
MemberMember 159761323-Jan-08 2:11 
AnswerRe: How to set 100*100 Dpi without showing User Interface Pin
zahil5-Jun-08 19:00
Memberzahil5-Jun-08 19:00 
GeneralResolution of saved image Pin
Ziggy Short17-Jan-08 5:33
MemberZiggy Short17-Jan-08 5:33 
GeneralRe: Resolution of saved image [modified] Pin
Neal175922-Jul-11 9:38
MemberNeal175922-Jul-11 9:38 
QuestionLoading saved files Pin
Ziggy Short17-Jan-08 3:06
MemberZiggy Short17-Jan-08 3:06 
Questionhelp on duplex Pin
Member 376198314-Jan-08 9:37
MemberMember 376198314-Jan-08 9:37 
I have a MFP Xerox M20i with duplex facility. I was made all specification about to duplex scanning without positive results. There is not error when send the message.

Please help me urgently.

Thanks a lot.

GeneralMaking renameable folders Pin
Rolly 13-Jan-08 18:52
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GeneralAnother implementation available Pin
PKultimPK28-Dec-07 2:07
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Questionhow to change the resolution in code.. Pin
sreenivas keerthi10-Dec-07 18:38
Membersreenivas keerthi10-Dec-07 18:38 
Questionhow to change the resolution within code.? Pin
vissu10-Dec-07 17:48
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GeneralAttempted to read or write protected memory. This is often an indication that other memory is corrupt. [modified] Pin
ViRiX8-Dec-07 16:42
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GeneralRe: Attempted to read or write protected memory. This is often an indication that other memory is corrupt. Pin
ViRiX8-Dec-07 17:47
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GeneralRe: Attempted to read or write protected memory. This is often an indication that other memory is corrupt. Pin
flaviozoc27-Aug-10 5:08
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GeneralProblem w HP C4180, "HP Scanning" Pin
GuntiNDDS27-Dec-07 11:27
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GeneralRe: Problem w HP C4180, "HP Scanning" Pin
Member 641068622-Feb-10 0:55
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GeneralDSuserif exception Pin
slow_worker4-Dec-07 4:36
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GeneralRe: DSuserif exception (solved) Pin
slow_worker5-Dec-07 5:32
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GeneralRe: DSuserif exception (solved) Pin
carlshe19-Sep-09 19:48
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QuestionHow to obtain an image Group 4?? URGENT :S Pin
12047828-Nov-07 12:24
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GeneralRe: How to obtain an image Group 4?? URGENT :S Pin
Medet ÖZELLİ13-Dec-07 11:24
sussMedet ÖZELLİ13-Dec-07 11:24 
GeneralRe: How to obtain an image Group 4?? URGENT :S Pin
Salman10824-Jan-08 20:46
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Generalwants to scan and save batch images Pin
adnanmn19-Nov-07 21:21
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AnswerRe: wants to scan and save batch images Pin
12047828-Nov-07 9:24
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