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Posted 16 Sep 2001

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.NET TWAIN image scanner

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12 May 2002Public Domain2 min read
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

 
GeneralRe: about multiple images scan Pin
JoaoPauloDotNet3-Jan-05 3:03
JoaoPauloDotNet3-Jan-05 3:03 
Questionhow to get snapshot from webcam without using ui Pin
Zac K11-Jul-04 12:36
Zac K11-Jul-04 12:36 
GeneralGetting image in c#.net application Pin
Ranjani A.V.9-Jul-04 23:26
Ranjani A.V.9-Jul-04 23:26 
GeneralRe: Getting image in c#.net application Pin
gnomcho11-Jul-04 22:24
gnomcho11-Jul-04 22:24 
GeneralProblem on 'set DPI resolution' Pin
rallets16-Jun-04 1:08
rallets16-Jun-04 1:08 
GeneralRe: Problem on 'set DPI resolution' Pin
rallets4-May-05 8:14
rallets4-May-05 8:14 
GeneralRe: Problem on 'set DPI resolution' Pin
rallets17-May-05 9:00
rallets17-May-05 9:00 
GeneralCrashes on my scanner Pin
Sean Botha1-Jun-04 21:45
Sean Botha1-Jun-04 21:45 
Hi
The test program starts out fine and selectmy scanner but as soon as I start scanning it crashes in "public ArrayList.TransferPictures()" on the following line

"rc = dsixfer(appid,srcds,twdg.image.twdat.imagenativexfer,twmsg.get, ref hbitmap );" - line142 in twainLib.cs

Has anyone come across this what can I do to sove it?
GeneralRe: Crashes on my scanner Pin
Raja Chandrasekaran20-Feb-06 5:11
Raja Chandrasekaran20-Feb-06 5:11 
GeneralRe: Crashes on my scanner Pin
Sean Botha20-Feb-06 18:45
Sean Botha20-Feb-06 18:45 
GeneralScanning without source window from Scannersoftware Pin
_viper12-May-04 3:44
_viper12-May-04 3:44 
GeneralRe: Scanning without source window from Scannersoftware Pin
siemed17-Jun-04 8:45
siemed17-Jun-04 8:45 
GeneralRe: Scanning without source window from Scannersoftware Pin
_viper17-Jun-04 23:01
_viper17-Jun-04 23:01 
GeneralRe: Scanning without source window from Scannersoftware Pin
siemed18-Jun-04 8:03
siemed18-Jun-04 8:03 
GeneralRe: Scanning without source window from Scannersoftware Pin
ltrankhanh16-Jan-05 21:50
ltrankhanh16-Jan-05 21:50 
GeneralConverting this to a dll Pin
gthompson20052-May-04 18:39
gthompson20052-May-04 18:39 
GeneralRe: Converting this to a dll Pin
Anonymous7-May-04 13:59
Anonymous7-May-04 13:59 
GeneralRe: Converting this to a dll Pin
80x8623-May-04 10:02
80x8623-May-04 10:02 
Questionhow to get the scanned image into a picturebox? Pin
HansHunger26-Apr-04 5:24
HansHunger26-Apr-04 5:24 
AnswerRe: how to get the scanned image into a picturebox? Pin
William Ten Broek8-May-04 14:06
William Ten Broek8-May-04 14:06 
GeneralRe: how to get the scanned image into a picturebox? Pin
System.ZaX11-Jun-04 7:23
System.ZaX11-Jun-04 7:23 
GeneralRe: how to get the scanned image into a picturebox? Pin
12-Jun-04 0:56
suss12-Jun-04 0:56 
GeneralRe: how to get the scanned image into a picturebox? Pin
28-Jun-04 0:26
suss28-Jun-04 0:26 
AnswerRe: how to get the scanned image into a picturebox? Pin
RBRChicho22-Nov-04 10:46
RBRChicho22-Nov-04 10:46 
Generaldistinguish any kind of scanners Pin
Member 102589321-Apr-04 20:39
Member 102589321-Apr-04 20:39 

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