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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


About the Author

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Comments and Discussions

GeneralHow obtain where image has been saved? Pin
mehdimax30-Apr-11 21:52
Membermehdimax30-Apr-11 21:52 
QuestionHow to take picture from Digital Camera in C# application using TWAIN Pin
Member 77483387-Apr-11 20:08
MemberMember 77483387-Apr-11 20:08 
QuestionFailed to save 600dpi color to BMP Pin
worship66829-Mar-11 7:45
Memberworship66829-Mar-11 7:45 
GeneralHandling with the TW_ENTRYPOINT Pin
Tonkpils24-Mar-11 23:22
MemberTonkpils24-Mar-11 23:22 
GeneralRe: Handling with the TW_ENTRYPOINT Pin
Easy_Rider999915-Jun-11 22:56
MemberEasy_Rider999915-Jun-11 22:56 
GeneralRe: Handling with the TW_ENTRYPOINT Pin
Easy_Rider999915-Jun-11 22:58
MemberEasy_Rider999915-Jun-11 22:58 
GeneralRe: Handling with the TW_ENTRYPOINT Pin
Tonkpils16-Jun-11 11:27
MemberTonkpils16-Jun-11 11:27 
GeneralRe: Handling with the TW_ENTRYPOINT Pin
Easy_Rider999918-Jun-11 4:40
MemberEasy_Rider999918-Jun-11 4:40 
QuestionHow to scan and show on picturebox vc# ?? Pin
abdojawad24-Mar-11 13:21
Memberabdojawad24-Mar-11 13:21 
AnswerRe: How to scan and show on picturebox vc# ?? Pin
Easy_Rider999915-Jun-11 22:54
MemberEasy_Rider999915-Jun-11 22:54 
GeneralScanner F2-6130 does not respond....:zzz: Pin
kosxxx9s16-Mar-11 10:07
Memberkosxxx9s16-Mar-11 10:07 
AnswerRe: Scanner F2-6130 does not respond....:zzz: Pin
Member 14968626-Jun-11 22:32
MemberMember 14968626-Jun-11 22:32 
Generalscanner window closes quickly Pin
Member 473569127-Feb-11 1:42
MemberMember 473569127-Feb-11 1:42 
QuestionPDF format for image Pin
Member 770345524-Feb-11 18:29
MemberMember 770345524-Feb-11 18:29 
AnswerRe: PDF format for image Pin
Gagan_198428-Feb-11 6:33
MemberGagan_198428-Feb-11 6:33 
GeneralRe: PDF format for image Pin
Mike Chernoff18-Mar-11 4:35
MemberMike Chernoff18-Mar-11 4:35 
QuestionRe: PDF format for image Pin
VBdotnetSara3-Aug-11 19:50
MemberVBdotnetSara3-Aug-11 19:50 
QuestionHow to get Enum-Capability like ICAP_XRESOLUTION Pin
Jörg Boekhoff16-Feb-11 23:26
MemberJörg Boekhoff16-Feb-11 23:26 
QuestionHow to make it scan multiple files with name? Pin
zimfer16-Feb-11 22:49
Memberzimfer16-Feb-11 22:49 
GeneralGet Capabilities Pin
Chris Shaw14-Feb-11 0:25
MemberChris Shaw14-Feb-11 0:25 
GeneralRe: Get Capabilities [modified] Pin
Chris Shaw14-Feb-11 3:29
MemberChris Shaw14-Feb-11 3:29 
GeneralRe: Get Capabilities [modified] Pin
Christopher Walsalam15-Dec-13 23:57
MemberChristopher Walsalam15-Dec-13 23:57 
GeneralDetect scanner problem Pin
jymitra9-Feb-11 0:41
Memberjymitra9-Feb-11 0:41 
GeneralUse Driver default interface Pin
Member 473569115-Jan-11 2:00
MemberMember 473569115-Jan-11 2:00 
GeneralNetwork access for Twain Pin
satiss7pwr26-Dec-10 19:50
Membersatiss7pwr26-Dec-10 19:50 

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Posted 16 Sep 2001


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