.NET TWAIN image scanner

NETMaster

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12 May 2002Public Domain2 min read

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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

Written By

NETMaster

Web Developer

Switzerland

This member has not yet provided a Biography. Assume it's interesting and varied, and probably something to do with programming.

Comments and Discussions

Re: Usage of Twain without a Form

bgunes11-Mar-07 22:04

bgunes

11-Mar-07 22:04

Dear m@u,

Is there any way todo this topic without NativeWindow interface? Only by events?

Thanks.

bg

Re: Usage of Twain without a Form

m@u12-Mar-07 12:46

m@u

12-Mar-07 12:46

Hi bgunes

you could implement the whole stuff in a control, override the wncproc according to the code i posted and handle the events in the parent-window

greets

m@u

Re: Usage of Twain without a Form

gabegabe25-Apr-07 10:31

gabegabe

25-Apr-07 10:31

take a closer look at openTwain, I wrapped up all of the messageloop handling in the library so you can scan without a form and without modifying your messageloop. it's event driven and works from console and windows service project. the sample code in the library includes a console and winforms project.

Re: Usage of Twain without a Form

shaggy847520-Mar-07 4:18

shaggy8475

20-Mar-07 4:18

hi M@U could you put this into VB Format?

Re: Usage of Twain without a Form

josepaulino22-Mar-07 18:26

josepaulino

22-Mar-07 18:26

I really appreciate what you did to wrap the twainlib class. I have a question, I would like to know how to call TransferPictures asynchronously so that the class that contains TwainMan doesn't have to wait on the scanner to acquire picture, we would just wait for the ImageScanned event. I've been playing around with it and can't figure out how to do it. The TransferPictures fails on:

rc = DSiinf( appid, srcds, TwDG.Image, TwDAT.ImageInfo, TwMSG.Get, iinf );

Any help would be appreciated,

Jose

Re: Usage of Twain without a Form

m@u23-Mar-07 3:32

m@u

23-Mar-07 3:32

Hi
Well Actually that's the way this class should work...
you call Scan(), the scanner scans, and when it's done you get the event...

how do you use the class?

greets
m@u

Re: Usage of Twain without a Form

josepaulino25-Mar-07 19:18

josepaulino

25-Mar-07 19:18

I call Scan(), but if the TransferPictures function(that is called in WndProc) is not on another thread the UI is not updated during transfer process so the form "locks up" during image scanning, which is something I would like to avoid aesthetically. I tried some type of Multi-threading but I couldn't get it to work. I think it has to do with the windows handle of the calling application(or thread).

Any ideas would help.

Re: Usage of Twain without a Form

m@u25-Mar-07 22:13

m@u

25-Mar-07 22:13

ok..

i think you could get it to work with something like this:

<br />
using System;<br />
using System.Threading;<br />
using System.Collections<br />
public class MTScan<br />
{<br />
    private Thread scanThread;<br />
    TwainMan scanner;<br />
    public MTScan()<br />
    {<br />
        scanThread = new Thread(startScanApp);<br />
    }<br />
    private void startScanApp()<br />
    {<br />
        Application.Idle = new EventHandler(Application_Idle);<br />
        Application.Start();<br />
    }<br />
    private void Application_Idle(object sender, EventArgs e)<br />
    {<br />
        scanner = new TwainMan();<br />
        scanner.ImageScanned += new ImageScannedEventHandler(scanner_ImageScanned);<br />
    }<br />
    private void scanner_ImageScanned(object sender, ImageScannedEventArgs e)<br />
    {<br />
        onImageScanned(e);<br />
    }<br />
    protected virtual void onImageScanned(ImageScannedEventArgs e)<br />
    {<br />
        if (ImageScanned != null)<br />
        {<br />
            ImageScanned(this, e);<br />
        }<br />
    }<br />
    public void Select()<br />
    {<br />
        scanner.Invoke(new ThreadStart(scanner.Select));<br />
    }<br />
    public void Scan()<br />
    {<br />
        scanner.Invoke(new ThreadStart(scanner.Scan));<br />
    }<br />
    public void Dispose()<br />
    {<br />
        scanner.Invoke(new ThreadStart(dispose));<br />
    }<br />
    private void dispose()<br />
    {<br />
        scanner.Dispose();<br />
        Application.ExitThread();<br />
    }<br />
}<br />
public class ImageScannedEventArgs:EventArgs<br />
{<br />
    private Bitmap image;<br />
    public Bitmap Image<br />
    {<br />
        get<br />
        {<br />
            return image;<br />
        }<br />
    }<br />
    public ImageScannedEventArgs(Bitmap Image)<br />
    {<br />
        image = Image;<br />
    }<br />
}<br />
public delegate void ImageScannedEventHandler(object sender, ImageScannedEventArgs e);<br />
[StructLayout(LayoutKind.Sequential, Pack=2)]<br />
internal class BITMAPINFOHEADER<br />
{<br />
    public int biSize;<br />
    public int biWidth;<br />
    public int biHeight;<br />
    public short biPlanes;<br />
    public short biBitCount;<br />
    public int biCompression;<br />
    public int biSizeImage;<br />
    public int biXPelsPerMeter;<br />
    public int biYPelsPerMeter;<br />
    public int biClrUsed;<br />
    public int biClrImportant;<br />
}<br />
/// <br />
/// Zusammenfassung für TwainMan.<br />
/// <br />
public class TwainMan:NativeWindow,IDisposable<br />
{<br />
    private class InvokeHolder<br />
    {<br />
        private Delegate target;<br />
        private object[] args;<br />
        public InvokeHolder(Delegate Target, object[] Args)<br />
        {<br />
            target = Target;<br />
            args = Args;<br />
        }<br />
        public void Run()<br />
        {<br />
            target.DynamicInvoke(args);<br />
        }<br />
    }<br />
    [DllImport("kernel32.dll", ExactSpelling=true)]<br />
    internal static extern IntPtr GlobalLock( IntPtr handle );<br />
    [DllImport("kernel32.dll", ExactSpelling=true)]<br />
    internal static extern IntPtr GlobalFree( IntPtr handle );<br />
    private const int WM_USER = 0x400;<br />
    private const int WM_Invoke = WM_USER+5;<br />
    [DllImport("user32.dll", EntryPoint="PostThreadMessageA")]<br />
    public static extern int PostThreadMessage ( <br />
        int idThread,<br />
        int msg,<br />
        int wParam,<br />
        int lParam);<br />
    private Twain tw;<br />
    private BITMAPINFOHEADER bmi;<br />
    private Rectangle bmprect;<br />
    private bool ready = false;<br />
    public event ImageScannedEventHandler ImageScanned;<br />
    private int threadID;<br />
    private Queue delegateQueue;<br />
    public bool Ready<br />
    {<br />
        get<br />
        {<br />
            return ready;<br />
        }<br />
    }<br />
    public TwainMan()<br />
    {<br />
        CreateParams cp = new CreateParams();<br />
        cp.Parent = new IntPtr(-3);<br />
        //cp.ClassName = "Window";<br />
        cp.Caption = "";<br />
        this.CreateHandle(cp);<br />
        tw = new Twain();<br />
        tw.Init(Handle);<br />
        threadID = AppDomain.GetCurrentThreadId();<br />
        delegateQueue = new Queue();<br />
    }<br />
    public void Invoke(Delegate Target, params object[] args)<br />
    {<br />
        delegateQueue.Enqueue(new InvokeHolder(Target, args);<br />
        PostThreadMessage(threadID, WM_Invoke,0,0);<br />
    }<br />
    public void Select()<br />
    {<br />
        ready = tw.Select();<br />
    }<br />
    public void Scan()<br />
    {<br />
        if (ready)<br />
        {<br />
            tw.Acquire();<br />
        }<br />
    }<br />
    protected IntPtr GetPixelInfo( IntPtr bmpptr )<br />
    {<br />
        bmi = new BITMAPINFOHEADER();<br />
        Marshal.PtrToStructure( bmpptr, bmi );<br />
        bmprect = Rectangle.Empty;<br />
        bmprect.X = bmprect.Y = 0;<br />
        bmprect.Width = bmi.biWidth;<br />
        bmprect.Height = bmi.biHeight;<br />
<br />
        if( bmi.biSizeImage == 0 )<br />
            bmi.biSizeImage = ((((bmi.biWidth * bmi.biBitCount) + 31) & ~31) >> 3) * bmi.biHeight;<br />
<br />
        int p = bmi.biClrUsed;<br />
        if( (p == 0) && (bmi.biBitCount <= 8) )<br />
            p = 1 << bmi.biBitCount;<br />
        p = (p * 4) + bmi.biSize + (int) bmpptr;<br />
        return (IntPtr) p;<br />
    }<br />
    protected virtual void onImageScanned(ImageScannedEventArgs e)<br />
    {<br />
        if (ImageScanned != null)<br />
        {<br />
            ImageScanned(this,e);<br />
        }<br />
    }<br />
    protected override void WndProc(ref Message m)<br />
    {<br />
        if (tw != null)<br />
        {<br />
            TwainCommand cmd = tw.PassMessage( ref m );<br />
            if( cmd != TwainCommand.Not )<br />
            {<br />
                switch( cmd )<br />
                {<br />
                    case TwainCommand.CloseRequest:<br />
                    {<br />
                        tw.CloseSrc();<br />
                        ready = false;<br />
                        break;<br />
                    }<br />
                    case TwainCommand.CloseOk:<br />
                    {<br />
                        tw.CloseSrc();<br />
                        ready = false;<br />
                        break;<br />
                    }<br />
                    case TwainCommand.DeviceEvent:<br />
                    {<br />
                        break;<br />
                    }<br />
                    case TwainCommand.TransferReady:<br />
                    {<br />
                        ArrayList pics = tw.TransferPictures();<br />
                        tw.CloseSrc();<br />
                        for( int i = 0; i < pics.Count; i++ )<br />
                        {<br />
                            IntPtr img = (IntPtr) pics[ i ];<br />
                            IntPtr bmpt = GlobalLock(img);<br />
                            IntPtr pi = GetPixelInfo(bmpt);<br />
                            IntPtr imgH = IntPtr.Zero;<br />
                            int Ret = GdiPlusLib.Gdip.GdipCreateBitmapFromGdiDib(bmpt,pi,ref imgH);<br />
                            if (img != IntPtr.Zero)<br />
                            {<br />
                                Bitmap bmp = (Bitmap)typeof(Bitmap).InvokeMember("FromGDIplus", BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.InvokeMethod, null, null, new object[] { imgH });<br />
                                onImageScanned(new ImageScannedEventArgs(bmp.Clone() as Bitmap));<br />
                            }<br />
                        }<br />
                        break;<br />
                    }<br />
                    case WM_Invoke:<br />
                    {<br />
                        if (invokeQueue.Count != 0)<br />
                        {<br />
                            do<br />
                            {<br />
                                InvokeHolder h = invokeQueue.Dequeue() as InvokeHolder;<br />
                                h.Run();<br />
                            }while(invokeQueue.Count != 0);<br />
                        }<br />
                        break;<br />
                    }<br />
                }<br />
            }<br />
        }<br />
    base.WndProc(ref m);<br />
}<br />
#region IDisposable Member<br />
<br />
public void Dispose()<br />
{<br />
    try<br />
    {<br />
        tw.CloseSrc();<br />
    }<br />
    catch{}<br />
    tw = null;<br />
}<br />
<br />
#endregion<br />
}<br />

this code should theoretically start a different thread where the whole scanning should be handled.
it's not testet, so maybe it contains some syntax / logical errors. but i think the solution for scanning in a different thread is something like that..

greets
m@u

Re: Usage of Twain without a Form

chandresh.softobiz17-Sep-09 23:50

chandresh.softobiz

17-Sep-09 23:50

Hello,

I have used this class this is a very good class it works as you said. then I have tried to create a user control out of it that also works on windows applications. but I was trying to put on web application using object tag there i get security error. I think native window call back message loop dose not works here. Do you have any solution for this.

The Error I got is as follows:
<b>
Stack Trace:</b>

System.Security.SecurityException: Request for the permission of type 'System.Security.Permissions.SecurityPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.
at UserControlScan.UserControlScan.button2_Click(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
The action that failed was:
InheritanceDemand
The type of the first permission that failed was:
System.Security.Permissions.SecurityPermission
The Zone of the assembly that failed was:
Intranet

Error text

Application attempted to perform an operation not allowed by the security policy. To grant this application the required permission, contact your system administrator or use the Microsoft .NET Framework Configuration tool

Please give some alternative for this

Re: Usage of Twain without a Form [modified]

dahalbibek26-Dec-11 22:54

dahalbibek

26-Dec-11 22:54

Dear Sir,
I used above code to scan documents
however i can't select the device(which is printer+scanner) after tw.select().
what should i do to select the device to scan..

thank you,
Bibek

Software Spalsh Screen

MauSav3121-Dec-06 8:38

MauSav312

1-Dec-06 8:38

Hi. First of all I want to apologyze for my English in advance. I'm from Argentina, and I'm working with a HP scanner. The problem is that the driver displays a splash screen with the HP logo every time I need to make a scan and i want to remove it. Do you know if that's possible programatically?. Thanks!!! Smile | :)

Frame using TWFix32 instead of Int32 (capture 8.5x11)

pelstone30-Nov-06 5:16

pelstone

30-Nov-06 5:16

I've been asked to create a custom scanning app that will capture a US-Letter (8.5"x11") that saves to server w/ a specific filename format.

I've been successful with 8" width, and the scanner bed is almost 9" wide.

Attempts to set PaperSize fail (not supported for Canon CanoScan 4200F?)
capPS As TwCapability = _
New TwCapability(TwCap.SupportedSizes, TwSS.TwSS_USLetter, TwType.Int16)

Setting the Frame to 8" (or imageWidth) succeeds:
Dim myLayout As New TwImageLayout
With myLayout.Frame
.Right = 8
'other properties here..
End With
rc = Me.DSilayout(appid, srcds, TwDG.Image, TwDAT.ImageLayout, TwMSG.Set, myLayout) 'returns checkStatus
rc = Me.DSstatus(appid, srcds, TwDG.Image, TwDAT.ImageLayout, TwMSG.Get, s) 'returns success

<structlayout(layoutkind.sequential, pack:="2)"> Friend Structure TwFrame
Public Left As Int32
Public Top As Int32
Public Right As Int32
Public Bottom As Int32
End Structure

I need a frame structure that will accept decimal values?

Using the structure below (from other posts), I'm running into problems:
<structlayout(layoutkind.sequential, pack:="2)"> Friend Structure TwFrame
Public Left As TwFix32
Public Top As TwFix32
Public Right As TwFix32
Public Bottom As TwFix32
End Structure

Setting the frame using:
Frame.Bottom.FromFloat(11.0)
Frame.Right.FromFloat(8.5)
'*don't set top & left as they are 0*

returns (after settings have successfully been sent to scanner)
Frame.Bottom.Whole=11
Frame.Bottom.Frac=786431
Frame.Left.Whole=0
Frame.Left.Frac=0
Frame.Right.Whole=8
Frame.Right.Frac=589823
Frame.Top.Whole=0
Frame.Top.Frac=3579117570 *why isn't this 0? perhaps structure isn't what scanner is eexpeting?*

The scanned area is not even close to what is desired.
length starts ~2" from edge and is ~9"
width starts at edge but is ~2.8"

I'd appreciate any help as I (foolishly) promised this app for the users by mid-December.

Thanks!

Paul Elstone, Queensway-Carleton Hospital, Ottawa, Canada [pElstone@qch.on.ca]

Close after scanning / saving

qjay23-Nov-06 22:05

qjay

23-Nov-06 22:05

How would I get the program to close (using Close(); ) after you have saved the images... I'm trying to automate the thing so it runs, scans, saves and exits... very difficult without throwing loaderlock exceptions!

Please make sure you have a solution (i.e. you tried it and it worked) before posting back to me.

Qjay

Creating an ActiveX and calling it from Web Browser

IndoDev8-Nov-06 21:42

IndoDev

8-Nov-06 21:42

Hi,

First of all congratulations on writing this article. Recently I have been working on creating an ActiveX DLL which could be invoked using a Javascript call from an HTML page and the scanned image could be displayed within the page. I got most of the things but when I invoke the TWAIN driver, it displays the scanning control, I can perform New Scan multiple times within it but when I click at Accept nothing happens, the same code works perfectly when I invoke it from a Windows Form.

I trapped Windows Messages, it seems that when I do a call to the ActiveX from HTML it does not send any message back when I click Accept in the Scanning control.

Help would be highly appreciated.

Regards,

Re: Creating an ActiveX and calling it from Web Browser

SikeMullivan28-Dec-06 3:51

SikeMullivan

28-Dec-06 3:51

Use the code m@u created in thread "Usage of Twain without a Form [modified]". Your problem is that IE is not a .NET Application, so System.Windows.Forms.Application.AddMessageFilter(...) doesn't work. I haven't tried m@u's code but using the NativeWindow to handle the message sounds like it will work just fine.

Breaking your theories
Sully

Re: Creating an ActiveX and calling it from Web Browser

IndoDev5-Feb-07 2:28

IndoDev

5-Feb-07 2:28

Thanks a lot finally I have successfully addressed the issue.

Re: Creating an ActiveX and calling it from Web Browser

Scott G26-Feb-07 16:33

Scott G

26-Feb-07 16:33

How exactly did you solve it? I have the same problem, but am having trouble getting the code to be recognized as ActiveX

Re: Creating an ActiveX and calling it from Web Browser

bharathkashyap4-Oct-07 21:10

bharathkashyap

4-Oct-07 21:10

Hi,

Can you please let me know whether this works as web application. If so can u please instruct me on the same..

I'm struggling a lot sir from many days of night outs.. Please do help me.

Thanks Smile | :)

Regards.....
Bharath.

Re: Creating an ActiveX and calling it from Web Browser

LupinTheThird23-Oct-11 1:50

LupinTheThird

23-Oct-11 1:50

Yep, having a very similar issue here and would be VERY gratefull if anyone could help.

In fact my problem is that it works well until I call the code from an ActiveX wrapper class, i.e., when Internet Explorer instantiates the ActiveXObject which calls the MainFrame Form. I do get to the scanner's Twain GUI, but when I click the "Scan" button, no message is ever caught in the PreFilterMessage method.

Thank you in advance for helping.

Re: Creating an ActiveX and calling it from Web Browser

LupinTheThird23-Oct-11 2:12

LupinTheThird

23-Oct-11 2:12

Oh, I missed your hints. Will try the examples mentioned and will get back with the solution if I succeed.

Preview image stream without standart window [modified]

Victor VP6-Nov-06 0:32

Victor VP

6-Nov-06 0:32

Hi to all!

I work with digital photocamera. I want to get preview image stream without using standart window. How can I do this? Or, if it is imposible, how can I disable setting buttons on standart window?

Thanks for any answer.

-- modified at 9:42 Monday 6th November, 2006

Programmatically capturing the image

lifesabirch.org31-Oct-06 3:31

lifesabirch.org

31-Oct-06 3:31

This is an amazing example, thank you for posting it!

Would it be possible to programmatically capture the image coming in from the twain device? Your code demonstrates that you can set the guif.ShowUI to be set to 0.

Gratefully yours,
Alex

http://www.lifesabirch.org

How can I display the scanner settings dialog without starting the scan process?

DJM16-Oct-06 0:36

DJM

16-Oct-06 0:36

Thank you, this is all very helpful!

One quiestion: How can I display the scanner settings dialog without starting the scan process?

Re: How can I display the scanner settings dialog without starting the scan process?

gabegabe25-Apr-07 10:32

gabegabe

25-Apr-07 10:32

look into EnableDsUiOnly

Autocrop

MrPieGuy12-Oct-06 7:59

MrPieGuy

12-Oct-06 7:59

Hey love the code, but I have to crop the images I'm uploading. I'm definetly a newbie to TWAIN, and am using the VB.Net version. Right now Im just saving it and doing it in another program, is there anyway to crop it rogramatically... right now I just need any black space to be cropped out. Thanks for any suggestions.

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