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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

 
QuestionRe: Urgent! Support for ADF Pin
Jwalant Natvarlal Soneji29-Jun-07 6:36
MemberJwalant Natvarlal Soneji29-Jun-07 6:36 
Questionhow disables the scanner user interface? Pin
matanyacode28-Mar-05 12:20
Membermatanyacode28-Mar-05 12:20 
AnswerRe: how disables the scanner user interface? Pin
Echooff318-Jul-05 8:18
MemberEchooff318-Jul-05 8:18 
GeneralUsing TwainLib.TwStatus Pin
Ramsey @ Edge28-Mar-05 5:31
MemberRamsey @ Edge28-Mar-05 5:31 
GeneralSetting/getting float from device Pin
ivaiva15-Mar-05 0:55
Memberivaiva15-Mar-05 0:55 
QuestionHow to TWAIN.Net in Asp.net Pin
jwalin khatri14-Mar-05 21:53
Memberjwalin khatri14-Mar-05 21:53 
AnswerRe: How to TWAIN.Net in Asp.net Pin
terryrey14-Mar-05 23:33
Memberterryrey14-Mar-05 23:33 
GeneralPaper Size Pin
terryrey10-Mar-05 21:22
Memberterryrey10-Mar-05 21:22 
Hi All,
I want to be able to change the paper size from the default 'Letter' to any of the other available sizes. I have created the TwSS constants in the TwainDefs.vb file e.g.

Friend Enum TwSS As Short
TwSS_None = &H0
TwSS_A4 = &H1
TwSS_B5Letter = &H2
TwSS_USLetter = &H3
..........
End Enum

and have created a var to hold the required paper size

Dim PSize As TwSS = TwSS.TwSS_A4


but am unsure of how to pass this to the scanner.

Can anyone please advise me on how to do this.
Thanks
Terry.
GeneralRe: Paper Size Pin
terryrey10-Mar-05 22:36
Memberterryrey10-Mar-05 22:36 
GeneralResolution of saved image Pin
ETollenaar8-Mar-05 1:14
MemberETollenaar8-Mar-05 1:14 
GeneralSave to Stream Pin
rruben3-Mar-05 3:03
Memberrruben3-Mar-05 3:03 
GeneralChanging Scanner Properties before Scanning Pin
appsoft2-Mar-05 3:15
Memberappsoft2-Mar-05 3:15 
GeneralVB.net IntPtr, Image HELP! Pin
Tonkutsche.de24-Feb-05 2:21
MemberTonkutsche.de24-Feb-05 2:21 
AnswerRe: VB.net IntPtr, Image HELP! Pin
surferxyzgmail28-Aug-08 1:12
Membersurferxyzgmail28-Aug-08 1:12 
Generalplease help me fast please!! Pin
sujith_murukan17-Feb-05 15:34
Membersujith_murukan17-Feb-05 15:34 
GeneralRe: please help me fast please!! Pin
Christian Graus17-Feb-05 16:10
mveChristian Graus17-Feb-05 16:10 
GeneralRe: please help me fast please!! Pin
sujith_murukan20-Feb-05 15:51
Membersujith_murukan20-Feb-05 15:51 
Generalmissing scanner Pin
jctools27-Jan-05 16:15
professionaljctools27-Jan-05 16:15 
GeneralSave to file after scanning Pin
SAN Peter6-Jan-05 23:51
MemberSAN Peter6-Jan-05 23:51 
GeneralRe: Save to file after scanning Pin
16-Jan-05 16:45
suss16-Jan-05 16:45 
GeneralRe: Save to file after scanning Pin
sheperd_011021-Dec-09 2:44
Membersheperd_011021-Dec-09 2:44 
GeneralRe: Save to file after scanning Pin
ArielR24-Jun-13 5:45
MemberArielR24-Jun-13 5:45 
GeneralRe: Save to file after scanning Pin
Raja Chandrasekaran20-Feb-06 4:51
MemberRaja Chandrasekaran20-Feb-06 4:51 
GeneralError in printing the image Pin
JoaoPauloDotNet3-Jan-05 3:50
MemberJoaoPauloDotNet3-Jan-05 3:50 
GeneralRe: Error in printing the image Pin
JoaoPauloDotNet7-Jan-05 4:14
MemberJoaoPauloDotNet7-Jan-05 4:14 

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