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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

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

 
QuestionHow to scan a multipage document Pin
WHAK.com30-Dec-14 1:46
professionalWHAK.com30-Dec-14 1:46 
AnswerRe: How to scan a multipage document Pin
8-Jun-15 0:34
member8-Jun-15 0:34 
QuestionExe not compatible Pin
23-Nov-14 22:07
member23-Nov-14 22:07 
Questionhow calculate the number image of paper? Pin
nturri13063-Nov-14 5:27
membernturri13063-Nov-14 5:27 
QuestionDLL TO SCAN FILE AND PROCESS THE DATA Pin
29-Oct-14 12:01
member29-Oct-14 12:01 
QuestionTwainLib PassMessage only returns TwainCommand.Not or TwainCommand.Null Pin
my_gino20-Oct-14 11:12
membermy_gino20-Oct-14 11:12 
QuestionHow can I set a source in source code? Pin
9-Oct-14 0:34
member9-Oct-14 0:34 
AnswerRe: How can I set a source in source code? Pin
KB.Rajesh24-Feb-15 20:32
memberKB.Rajesh24-Feb-15 20:32 
GeneralRe: How can I set a source in source code? Pin
eqiz17-Jun-15 12:13
membereqiz17-Jun-15 12:13 
Questionquick and easy TWAIN scanning realization Pin
8-Sep-14 21:49
member8-Sep-14 21:49 
QuestionGreat application Pin
muharremunlu8-Sep-14 21:43
membermuharremunlu8-Sep-14 21:43 
QuestionError at line 59 Pin
2-Sep-14 16:33
member2-Sep-14 16:33 
AnswerRe: Error at line 59 Pin
MAGSI13-Nov-14 0:44
memberMAGSI13-Nov-14 0:44 
AnswerRe: Error at line 59 Pin
10-Jul-15 23:11
member10-Jul-15 23:11 
QuestionGreat! But id like to Change the filname of Picture Pin
Wolleschorge11-Aug-14 22:38
memberWolleschorge11-Aug-14 22:38 
AnswerRe: Great! But id like to Change the filname of Picture Pin
KB.Rajesh24-Feb-15 21:17
memberKB.Rajesh24-Feb-15 21:17 
QuestionGreat Pin
Chirantha Jayasinghe16-Jul-14 21:31
memberChirantha Jayasinghe16-Jul-14 21:31 
Questiongreat thanks! Pin
DmitryDrosd9-Jun-14 2:36
memberDmitryDrosd9-Jun-14 2:36 
GeneralMy vote of 5 Pin
superduck20-May-14 20:38
membersuperduck20-May-14 20:38 
GeneralFix for windows 8.0 Pin
prcow12-May-14 11:24
memberprcow12-May-14 11:24 
GeneralRe: Fix for windows 8.0 Pin
smile869115-Dec-14 5:53
membersmile869115-Dec-14 5:53 
GeneralRe: Fix for windows 8.0 Pin
bidyut1234518-Jan-15 23:55
memberbidyut1234518-Jan-15 23:55 
GeneralRe: Fix for windows 8.0 Pin
smile869118-Nov-15 6:14
membersmile869118-Nov-15 6:14 
GeneralRe: Fix for windows 8.0 Pin
15-Mar-16 11:04
member15-Mar-16 11:04 
QuestionTwain Driver Interface Dialog Pin
danajp_595-May-14 11:07
memberdanajp_595-May-14 11:07 

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