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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

Abstract

In Windows imaging applications, the most used API for scanning is TWAIN www.twain.org. 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.

Details

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
{
    Init();
    Select();
    Acquire();
    PassMessage();
    TransferPictures();
}

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...)

Limitations

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).

License

This article, along with any associated source code and files, is licensed under A Public Domain dedication

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About the Author

NETMaster
Web Developer
Switzerland Switzerland
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Comments and Discussions

 
QuestionTWAIN PinmemberMember 1018928525-Aug-13 17:33 
AnswerRe: TWAIN Pinmemberp312ry3-Dec-13 16:41 
Questionusing TWAIN Kyocera FS-1035 [modified] PinmemberMember 998823614-Aug-13 1:48 
QuestionPass parameters to without using ui Pinmembersaijagadeesh30-Jul-13 4:13 
GeneralMy vote of 5 Pinmembershiva_194-Jul-13 20:30 
Questiontwain scanning in vb.net PinmemberDina_Du27-Jun-13 19:26 
Questionc# n vb PinmemberImam Azinuddin19-Jun-13 20:14 
QuestionError in the Code PinmemberHerman M. Reyes7-Jun-13 1:44 
I tried the demo and no problem on scanning via Twain or WIA.
 
But when I use the source code and run it, below is the error I get;
 
An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)
 
The error is show in this part of code
 
TwRC rc = DSMparent( appid, IntPtr.Zero, TwDG.Control, TwDAT.Parent, TwMSG.OpenDSM, ref hwndp );
 
Can anyone tell me what has to be don to correct this error? I am running VS2008 on Windows 7 ultimate 64Bit.
 
Thank you very much and I am hoping to get response to anyone soon.
AnswerRe: Error in the Code PinmemberMember 1015869416-Jul-13 11:14 
GeneralRe: Error in the Code PinmemberHerman M. Reyes26-Jul-13 2:06 
GeneralRe: Error in the Code PinmemberMember 1020463311-Sep-13 10:19 
Questionthanks PinmemberMember 786391322-May-13 13:15 
QuestionHow can i scan multi pages PinmemberMember 397326719-May-13 18:33 
QuestionNeed help to fix Issue in Twain .net Library Pinmembervinaykn.rao22-Apr-13 4:07 
QuestionException throws when I use in Win7 64 bit Pinmemberanisfathima18-Apr-13 23:11 
AnswerRe: Exception throws when I use in Win7 64 bit PinmemberJnnxp5-Aug-13 17:11 
Questionhow set Image info PinmemberMohamed Nabawy15-Apr-13 7:59 
QuestionScanner Error Pinmemberasheykh14-Apr-13 23:05 
QuestionTwainCommand.TransferReady: hbitmap to gdi+ bitmap Pinmemberliuxu093826-Mar-13 22:21 
QuestionThe "twaingui_demo.zip" is damaged? Pinmemberliuxu093826-Mar-13 1:16 
QuestionScanning on Win7 64Bit Pinmemberkhalilsa27-Feb-13 5:19 
AnswerRe: Scanning on Win7 64Bit Pinmemberricardofrias20-Mar-13 8:48 
AnswerRe: Scanning on Win7 64Bit PinmemberJnnxp5-Aug-13 17:12 
Questionuse in asp.net? PinmemberKalpana Volety11-Jan-13 10:59 
AnswerRe: use in asp.net? PinmemberJnnxp5-Aug-13 17:17 

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