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.NET TWAIN image scanner

, 12 May 2002
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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

About the Author

NETMaster
Web Developer
Switzerland Switzerland
No Biography provided

Comments and Discussions

 
GeneralRe: Windows 8 errors with TwainLib.Twain.DSMident PinmemberRavishankar chinnur6-Mar-14 18:13 
Questionscanning one after another is not posiible PinmemberRavishankar chinnur5-Mar-14 2:08 
AnswerRe: scanning one after another is not posiible Pinmembermalcolmxu21-Mar-14 5:54 
AnswerRe: scanning one after another is not posiible PinmemberAntriksh Patel27-Jul-14 18:12 
BugInsufficient Memory Pinmemberkeencoder20-Jan-14 22:42 
QuestionHow to scan on both sides of the document Pinmembersandeep7587-Jan-14 21:58 
Questionsave images Pinmemberezelden.sahi12-Nov-13 21:30 
QuestionHow can i change the transfer mode to File PinmemberMurugan Kolanji11-Nov-13 2:43 
GeneralThank you so much~! PinmemberCheon sang10-Nov-13 22:03 
Question.NET TWAIN image scanner Convert to for VB 2010 PinmemberDibakar Mishra30-Oct-13 3:55 
QuestionGdipSaveImageToStream brings back a empty stream PinmemberMember 391328323-Oct-13 8:49 
GeneralMy vote of 5 PinmemberLucas Lima Araujo27-Sep-13 6:37 
QuestionWindows 8 Fails PinmemberLucas Lima Araujo27-Sep-13 4:39 
AnswerRe: Windows 8 Fails Pinmemberblastnsmash10-Dec-13 6:59 
GeneralRe: Windows 8 Fails Pinmembersmile869128-Jan-14 7:37 
AnswerRe: Windows 8 Fails Pinmemberblastnsmash10-Dec-13 9:10 
Questionsave in Db Pinmemberpartia3-Sep-13 3:16 
AnswerRe: save in Db PinmemberWindy Liu13-Sep-13 0:05 
GeneralRe: save in Db Pinmemberpartia20-Sep-13 3:31 
GeneralRe: save in Db PinmemberWindy Liu21-Sep-13 21:23 
QuestionPage rotation PinmemberRicardo Valero29-Aug-13 2:11 
QuestionTWAIN PinmemberMember 1018928525-Aug-13 16:33 
AnswerRe: TWAIN Pinmemberp312ry3-Dec-13 15:41 
Questionusing TWAIN Kyocera FS-1035 [modified] PinmemberMember 998823614-Aug-13 0:48 
QuestionPass parameters to without using ui Pinmembersaijagadeesh30-Jul-13 3:13 

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