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.NET TWAIN image scanner

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12 May 2002Public Domain2 min read 7.1M   132K   421   996
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:

C#
[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:

C#
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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Comments and Discussions

 
QuestionGreat Scanning code, but how do I scan multiple pages? Pin
Daniel Kaminski 202130-May-23 10:57
Daniel Kaminski 202130-May-23 10:57 
GeneralMy vote of 5 Pin
FREEWING-JP18-Oct-22 2:54
FREEWING-JP18-Oct-22 2:54 
Question.net Framework 4 windows form hits this line and stops debugger with no error message Pin
Member 1011884610-Jul-20 13:22
Member 1011884610-Jul-20 13:22 
QuestionHandling System.AccessViolationException potential solution? Pin
James McCullough5-Sep-19 6:57
professionalJames McCullough5-Sep-19 6:57 
AnswerRe: Handling System.AccessViolationException potential solution? PinPopular
Brent Lamborn9-Sep-19 9:31
Brent Lamborn9-Sep-19 9:31 
Questionis ther any way to get this for VB.Net? Pin
friedmad6-Jun-19 9:53
friedmad6-Jun-19 9:53 
QuestionPRESCAN Pin
Member 1026264219-Jan-19 0:16
Member 1026264219-Jan-19 0:16 
QuestionGetting Error can't locate devicel check cable and power.(-4536) Pin
Member 137494456-Dec-18 16:14
Member 137494456-Dec-18 16:14 
QuestionGreat starter program Pin
webster.ut25-Jul-18 11:08
webster.ut25-Jul-18 11:08 
QuestionIs it possible to scan all the pages of the document at once and then retrieve the data from the scanner in one call ? Pin
Member 138058987-May-18 20:30
Member 138058987-May-18 20:30 
QuestionSetting custom capabilities Pin
Member 137340832-Apr-18 3:04
Member 137340832-Apr-18 3:04 
QuestionHow i can convert IntPtr to Image? Pin
GHM_Master22-Jan-18 9:35
GHM_Master22-Jan-18 9:35 
QuestionError in windows 10 Pin
Member 45042266-Dec-17 5:41
Member 45042266-Dec-17 5:41 
Questionset setting inside the code Pin
Member 1282210518-Sep-17 3:07
Member 1282210518-Sep-17 3:07 
QuestionChoose the profile Pin
Danilo Bicas14-Aug-17 3:36
Danilo Bicas14-Aug-17 3:36 
Questionsave images directly to disc Pin
Member 1335223713-Aug-17 21:23
Member 1335223713-Aug-17 21:23 
QuestionUpdated continuation of this code on Github Pin
David Jeske2-Jun-17 17:38
David Jeske2-Jun-17 17:38 
QuestionScan again after error Feed Pin
Julian Rodriguez19-Apr-17 4:36
Julian Rodriguez19-Apr-17 4:36 
AnswerRe: Scan again after error Feed Pin
David Jeske2-Jun-17 17:37
David Jeske2-Jun-17 17:37 
Questionacquire more than one paper Pin
Member 1147033824-Dec-16 4:51
Member 1147033824-Dec-16 4:51 
QuestionBadImageFormatException Pin
Les Mok25-Oct-16 9:05
Les Mok25-Oct-16 9:05 
AnswerRe: BadImageFormatException Pin
HengFly10926-Oct-16 22:56
HengFly10926-Oct-16 22:56 
QuestionError System.AccessViolationException Windows 10 64bit Pin
Imran Abbas Khawaja28-Jul-16 21:05
Imran Abbas Khawaja28-Jul-16 21:05 
QuestionHow to set duplex scanning option as true Pin
MuzzyB19-Jul-16 22:58
MuzzyB19-Jul-16 22:58 
AnswerRe: How to set duplex scanning option as true Pin
MuzzyB21-Jul-16 1:11
MuzzyB21-Jul-16 1:11 

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