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Platforms, Frameworks & Libraries » .NET Framework » General     Advanced License: A Public Domain dedication

.NET TWAIN image scanner

By NETMaster

Using TWAIN API to scan images
C#.NET 1.0, Win2K, Dev
Posted:16 Sep 2001
Updated:12 May 2002
Views:656,238
Bookmarked:238 times
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Popularity: 9.96 Rating: 4.63 out of 5
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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:

[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
{
    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

About the Author

NETMaster


Member

Occupation: Web Developer
Location: Switzerland Switzerland

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 Msgs 1 to 25 of 561 (Total in Forum: 561) (Refresh)FirstPrevNext
Generalrunning to dead when cancel Pinmemberpclion19:04 17 Jun '09  
AnswerRe: running to dead when cancel PinmemberWolexie3:01 21 Jun '09  
Generalchange the source of the image to be acquire PinmemberPRProgrmmerAlexG12:09 9 Jun '09  
General1bpp b/w DIB problem Pinmembernasharu9:27 17 Apr '09  
GeneralYou are a living legend! Pinmembermartincook9:31 6 Apr '09  
QuestionUsing Twain driver : dsuerif does not wait user response from userinterface and returns directly a SUCCESS call PinmemberMember 39059881:42 1 Apr '09  
Question[Ask] 2 Image in one Click PinmemberReivina23:49 15 Mar '09  
AnswerRe: [Ask] 2 Image in one Click Pinmemberppmax4:57 17 Mar '09  
JokeRe: [Ask] 2 Image in one Click PinmemberWolexie2:44 10 Jun '09  
GeneralPb with Threading Pinmemberppmax23:49 9 Mar '09  
Generalscanner & application is gettig hanged Pinmemberamitnashtekar20:13 4 Mar '09  
General[HELP]No "Select Source..." window appears! PinmemberPalermo4ever5:32 16 Feb '09  
GeneralRe: [HELP]No "Select Source..." window appears! PinmemberFiorebat3:12 17 Apr '09  
QuestionPrinting Profile Pinmemberkengct19:45 5 Feb '09  
GeneralTransferring ONE image a time [modified] Pinmemberarkiduck2:54 28 Jan '09  
GeneralGdipSaveImageToFile function lock file [modified] Pinmemberlex-luthor7:34 27 Jan '09  
GeneralUnable to load DLL 'twain_32.dll': A dynamic link library (DLL) initialization routine failed. (Exception from HRESULT: 0x8007045A) PinmemberMember 41803740:57 22 Jan '09  
GeneralSupportedSizes doesnt work PinmemberMember 37116404:37 7 Nov '08  
GeneralRe: SupportedSizes doesnt work PinmemberMember 37116404:44 7 Nov '08  
GeneralNo response after acquire(); Pinmemberkengct19:29 6 Nov '08  
RantRe: No response after acquire(); Pinmemberkengct0:46 13 Nov '08  
GeneralRe: No response after acquire(); Pinmemberhom_rcp5:45 25 Dec '08  
GeneralRe: No response after acquire(); Pinmemberkengct22:10 12 Jan '09  
GeneralRe: No response after acquire(); PinmemberJoey Burgett17:20 17 Mar '09  
Questionhow to scan image directly into picturebox instead of painting onto form? PinmemberJuraj Suchan12:13 16 Oct '08  

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Last Updated: 12 May 2002
Editor: James T. Johnson
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