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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


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


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Comments and Discussions

AnswerRe: How Can I change scaning variables with c# code? Pin
Member 10025991 at 5-May-13 17:36
memberMember 100259915-May-13 17:36 
QuestionHow to check scanner is connected befor Acquire Pin
swapnil74345 at 13-Apr-12 22:02
memberswapnil7434513-Apr-12 22:02 
Questionconverting? Pin
darkalastair at 19-Mar-12 23:15
memberdarkalastair19-Mar-12 23:15 
AnswerRe: converting? Pin
Member 6676 at 21-Oct-12 9:58
memberMember 667621-Oct-12 9:58 
QuestionTwainLib Visual Studio 2010 Windows 7 64 bit Pin
sanvi61 at 5-Mar-12 4:10
membersanvi615-Mar-12 4:10 
AnswerRe: TwainLib Visual Studio 2010 Windows 7 64 bit Pin
UstesGreenridge at 26-Mar-12 4:55
memberUstesGreenridge26-Mar-12 4:55 
AnswerRe: TwainLib Visual Studio 2010 Windows 7 64 bit Pin
DanielMarzan at 14-May-12 9:19
memberDanielMarzan14-May-12 9:19 
GeneralRe: TwainLib Visual Studio 2010 Windows 7 64 bit Pin
smile8691 at 10-Jul-12 13:02
membersmile869110-Jul-12 13:02 
GeneralMy vote of 5 Pin
manoj kumar choubey at 26-Feb-12 19:23
membermanoj kumar choubey26-Feb-12 19:23 
Questionproblem ..!!!!!!!!!! Pin
A7mad_ at 22-Feb-12 8:43
memberA7mad_22-Feb-12 8:43 
QuestionEpson V30 scan problem with 16 bit grayscale tiff Pin
smarino60 at 21-Feb-12 8:52
membersmarino6021-Feb-12 8:52 
QuestionTransferPictures() method returns pics count 1 always Pin
appalanaidu Aug2011 at 7-Feb-12 23:29
memberappalanaidu Aug20117-Feb-12 23:29 
Question+1 Pin
miwalter at 4-Feb-12 23:06
membermiwalter4-Feb-12 23:06 
GeneralMy vote of 1 Pin
navidsoft at 10-Jan-12 23:39
membernavidsoft10-Jan-12 23:39 
it doen't work
QuestionThis get freezed the whole application Pin
Member 3337622 at 21-Dec-11 3:24
memberMember 333762221-Dec-11 3:24 
AnswerRe: This get freezed the whole application Pin
A7mad_ at 21-Feb-12 10:26
memberA7mad_21-Feb-12 10:26 
QuestionScanning area parameter through application Pin
Rajendrarajsri at 28-Nov-11 16:42
memberRajendrarajsri28-Nov-11 16:42 
QuestionTWAIN A3 Papersize change i.e. TwCapability capPaperSize = new TwCapability(TwCap.ICAP_SUPPORTEDSIZES, 1) Pin
WaynePorter at 18-Nov-11 3:55
memberWaynePorter18-Nov-11 3:55 
Questioncan any one give this whole project in Pin
nsk_saravana at 15-Nov-11 22:13
membernsk_saravana15-Nov-11 22:13 
AnswerRe: can any one give this whole project in Pin
wellhi at 18-Nov-11 17:43
memberwellhi18-Nov-11 17:43 
QuestionAutocrop Pin
nsk_saravana at 13-Nov-11 23:21
membernsk_saravana13-Nov-11 23:21 
QuestionRemoving Scanner UI Pin
nsk_saravana at 13-Nov-11 18:40
membernsk_saravana13-Nov-11 18:40 
Questionremoving the UI Pin
mist999 at 11-Nov-11 5:45
membermist99911-Nov-11 5:45 
QuestionADF Question.....Help Me Pin
beyond1117 at 17-Oct-11 17:59
memberbeyond111717-Oct-11 17:59 
QuestionCapture color image using twain Pin
akul123 at 21-Sep-11 1:43
memberakul12321-Sep-11 1:43 
QuestionCould not compile Pin
ditoroin at 21-Sep-11 1:33
memberditoroin21-Sep-11 1:33 
SuggestionRe: Could not compile Pin
MrPetan at 21-Sep-11 6:29
memberMrPetan21-Sep-11 6:29 
GeneralRe: Could not compile Pin
Member 8313002 at 23-Apr-12 23:59
memberMember 831300223-Apr-12 23:59 
QuestionCAP_DEVICEONLINE always returns false Pin
bennett cummins at 13-Sep-11 7:26
memberbennett cummins13-Sep-11 7:26 
Questionconverting this sample in Pin
akul123 at 23-Aug-11 23:33
memberakul12323-Aug-11 23:33 
AnswerRe: converting this sample in Pin
mahamahmaha at 22-Jan-12 22:22
membermahamahmaha22-Jan-12 22:22 
QuestionImage size Pin
VBCoder68 at 18-Aug-11 6:14
memberVBCoder6818-Aug-11 6:14 
QuestionDont want dialog boxes Pin
Neha Ameen at 16-Aug-11 2:22
memberNeha Ameen16-Aug-11 2:22 
GeneralMy vote of 5 Pin
Shahin Khorshidnia at 12-Aug-11 20:50
memberShahin Khorshidnia12-Aug-11 20:50 
QuestionADF is not working Pin
telme at 2-Aug-11 23:32
membertelme2-Aug-11 23:32 
AnswerRe: ADF is not working Pin
beyond1117 at 18-Oct-11 7:01
memberbeyond111718-Oct-11 7:01 
GeneralRe: ADF is not working Pin
telme at 18-Oct-11 20:29
membertelme18-Oct-11 20:29 
QuestionIs it possible to do ADF and Flatbed Scanner in TWAIN Pin
telme at 31-Jul-11 0:27
membertelme31-Jul-11 0:27 
AnswerRe: Is it possible to do ADF and Flatbed Scanner in TWAIN Pin
beyond1117 at 18-Oct-11 7:03
memberbeyond111718-Oct-11 7:03 
AnswerRe: Is it possible to do ADF and Flatbed Scanner in TWAIN Pin
balasofttouch at 11-Jan-12 1:01
memberbalasofttouch11-Jan-12 1:01 
QuestionTwainLib.cs with full specification Pin
telme at 27-Jul-11 22:55
membertelme27-Jul-11 22:55 
QuestionRe: TwainLib.cs with full specification Pin
ben060683 at 27-Jul-11 23:23
memberben06068327-Jul-11 23:23 
QuestionSelecting ADF and Flatbed scanning option Pin
telme at 26-Jul-11 2:33
membertelme26-Jul-11 2:33 
QuestionDemo works but not the source Pin
Steven Szelei at 19-Jul-11 12:08
memberSteven Szelei19-Jul-11 12:08 
AnswerRe: Demo works but not the source Pin
golanw at 20-Dec-11 17:32
membergolanw20-Dec-11 17:32 
QuestionRetrive a List of Paper Sizes Pin
bennett cummins at 15-Jul-11 11:19
memberbennett cummins15-Jul-11 11:19 
GeneralAccess Violation with Nikon Coolscan IV Pin
Easy_Rider9999 at 15-Jun-11 23:51
memberEasy_Rider999915-Jun-11 23:51 
Generalmessagefilter Pin
acep22 at 1-Jun-11 21:11
memberacep221-Jun-11 21:11 
GeneralSave each image Pin
Gabriel Perdigão at 1-Jun-11 8:42
memberGabriel Perdigão1-Jun-11 8:42 
GeneralRange value of capability ICAP_GAMMA Pin
Willzith Pham at 13-May-11 0:31
memberWillzith Pham13-May-11 0:31 

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