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.NET TWAIN image scanner

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12 May 2002Public Domain
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: SupportedSizes doesnt work Pin
Ninos Denkha17-Mar-11 12:56
memberNinos Denkha17-Mar-11 12:56 
GeneralNo response after acquire(); Pin
kengct6-Nov-08 18:29
memberkengct6-Nov-08 18:29 
RantRe: No response after acquire(); Pin
kengct12-Nov-08 23:46
memberkengct12-Nov-08 23:46 
GeneralRe: No response after acquire(); Pin
hom.rcp25-Dec-08 4:45
memberhom.rcp25-Dec-08 4:45 
GeneralRe: No response after acquire(); Pin
kengct12-Jan-09 21:10
memberkengct12-Jan-09 21:10 
GeneralRe: No response after acquire(); Pin
Joey Burgett17-Mar-09 16:20
memberJoey Burgett17-Mar-09 16:20 
Questionhow to scan image directly into picturebox instead of painting onto form? Pin
VirtualVoid.NET16-Oct-08 11:13
memberVirtualVoid.NET16-Oct-08 11:13 
AnswerRe: how to scan image directly into picturebox instead of painting onto form? Pin
MacSpudster9-Dec-08 11:16
professionalMacSpudster9-Dec-08 11:16 
GeneralRe: how to scan image directly into picturebox instead of painting onto form? Pin
Burhan ERSOY28-Jul-09 22:52
memberBurhan ERSOY28-Jul-09 22:52 
GeneralRe: how to scan image directly into picturebox instead of painting onto form? Pin
MacSpudster29-Jul-09 7:02
professionalMacSpudster29-Jul-09 7:02 
GeneralSet duplex capability Pin
Deiany15-Oct-08 0:50
memberDeiany15-Oct-08 0:50 
GeneralRe: Set duplex capability Pin
Deiany20-Oct-08 4:01
memberDeiany20-Oct-08 4:01 
GeneralRe: Set duplex capability Pin
RecycleYourLife10-Nov-08 10:27
memberRecycleYourLife10-Nov-08 10:27 
GeneralRe: Set duplex capability Pin
RecycleYourLife11-Nov-08 4:05
memberRecycleYourLife11-Nov-08 4:05 
QuestionHow do I get TWON_RANGE values (TWAIN) ? Pin
MuhtarQong10-Oct-08 10:15
memberMuhtarQong10-Oct-08 10:15 
QuestionHow to get TWON_RANGE values? Pin
MuhtarQong10-Oct-08 10:05
memberMuhtarQong10-Oct-08 10:05 
AnswerRe: How to get TWON_RANGE values? [modified] Pin
Linh Phan IS19-Jan-11 17:20
memberLinh Phan IS19-Jan-11 17:20 
QuestionTwo Face Pin
DCE_Erick3-Oct-08 8:08
memberDCE_Erick3-Oct-08 8:08 
QuestionHow setting DAT_GRAYRESPONSE Pin
Angelo Ciavarella30-Sep-08 2:16
memberAngelo Ciavarella30-Sep-08 2:16 
GeneralBlack-Boxify the code please Pin
qjay11-Sep-08 10:17
memberqjay11-Sep-08 10:17 
AnswerRe: Black-Boxify the code please Pin
NETMaster11-Sep-08 12:00
memberNETMaster11-Sep-08 12:00 
GeneralRe: Black-Boxify the code please Pin
qjay11-Sep-08 18:32
memberqjay11-Sep-08 18:32 
QuestionHow can I check if I scan a blank document? Pin
jhonny24727-Aug-08 7:11
memberjhonny24727-Aug-08 7:11 
AnswerRe: How can I check if I scan a blank document? Pin
MacSpudster9-Dec-08 11:50
professionalMacSpudster9-Dec-08 11:50 
QuestionRe: How can I check if I scan a blank document? Pin
NitinMakwana27-May-10 23:27
memberNitinMakwana27-May-10 23:27 

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Posted 16 Sep 2001


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