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Posted 16 Sep 2001
Licenced Public Domain

.NET TWAIN image scanner

, 12 May 2002
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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:

[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

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About the Author

NETMaster
Web Developer
Switzerland Switzerland
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Comments and Discussions

 
Generalits Urgent and Matter of JOB Pin
farrukhahmedqureshi26-Jul-10 2:37
memberfarrukhahmedqureshi26-Jul-10 2:37 
QuestionHow can i read the image directly into a picture box using vb.net Pin
AmitSood198521-Jul-10 0:20
memberAmitSood198521-Jul-10 0:20 
QuestionHow to take Snapshots automatically by time ? Pin
circass3-Jul-10 9:19
membercircass3-Jul-10 9:19 
GeneralGetting Capability PinPopular
obrien.james1-Jul-10 13:59
memberobrien.james1-Jul-10 13:59 
GeneralICAP_AUTODISCARDBLANKPAGES Pin
strzata28-Jun-10 20:50
memberstrzata28-Jun-10 20:50 
GeneralRe: ICAP_AUTODISCARDBLANKPAGES Pin
Member 421407311-Oct-10 7:58
memberMember 421407311-Oct-10 7:58 
GeneralBadImageFormat Exception Pin
Shishir Shukla28-Jun-10 20:35
groupShishir Shukla28-Jun-10 20:35 
GeneralRe: BadImageFormat Exception Pin
strzata28-Jun-10 21:00
memberstrzata28-Jun-10 21:00 
GeneralRe: BadImageFormat Exception Pin
m_cozza27-Apr-11 5:46
memberm_cozza27-Apr-11 5:46 
QuestionHow to conver this project to asp.net c# Pin
Supachai Prasertsit27-Jun-10 0:47
memberSupachai Prasertsit27-Jun-10 0:47 
Questionare we obliged to open form to make acquisition and other steps? Pin
richardeau25-Jun-10 2:56
memberrichardeau25-Jun-10 2:56 
GeneralThanks a lot! Pin
Jan Kurbanaliev21-Jun-10 7:45
memberJan Kurbanaliev21-Jun-10 7:45 
GeneralDetect if there is a paper in feed ?! Pin
bgabel16-Jun-10 4:58
memberbgabel16-Jun-10 4:58 
GeneralRe: Detect if there is a paper in feed ?! Pin
strzata28-Jun-10 21:02
memberstrzata28-Jun-10 21:02 
GeneralNice Pin
Florian Reischl8-Jun-10 2:09
memberFlorian Reischl8-Jun-10 2:09 
GeneralDoesn't scan on EPSON 3490 - HELP Pin
verce0012-Jun-10 2:29
memberverce0012-Jun-10 2:29 
GeneralRe: Doesn't scan on EPSON 3490 - HELP Pin
redspiderke13-Jun-10 21:42
memberredspiderke13-Jun-10 21:42 
QuestionHelp needed getting list of available scanners displayed in my own listbox and NOT via the Twain's GUI... Pin Pin
NitinMakwana27-May-10 22:55
memberNitinMakwana27-May-10 22:55 
GeneralTwain Activex Pin
Mlinux14-May-10 7:59
memberMlinux14-May-10 7:59 
QuestionRe: Twain Activex Pin
LupinTheThird23-Oct-11 1:04
memberLupinTheThird23-Oct-11 1:04 
GeneralTWAIN ActiveX error at "evtmsg.EventPtr = Marshal.AllocHGlobal(Marshal.SizeOf(winmsg))" in" TwainLib.cs" Pin
Big Duck7-May-10 17:45
memberBig Duck7-May-10 17:45 
GeneralRe: TWAIN ActiveX error at "evtmsg.EventPtr = Marshal.AllocHGlobal(Marshal.SizeOf(winmsg))" in" TwainLib.cs" Pin
Mlinux14-May-10 7:49
memberMlinux14-May-10 7:49 
GeneralTransferring to Picturebox Pin
mazza19865-May-10 3:00
membermazza19865-May-10 3:00 
GeneralRe: Transferring to Picturebox Pin
Mlinux14-May-10 7:39
memberMlinux14-May-10 7:39 
GeneralRe: Transferring to Picturebox Pin
prcow17-Aug-10 6:43
memberprcow17-Aug-10 6:43 

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