.NET TWAIN image scanner

NETMaster

Rate me:

4.91/5 (227 votes)

12 May 2002Public Domain2 min read

7.2M

132.2K

421

996

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

newbie question: mdi child form problem.

dude25175418-Oct-09 18:49

dude251754

18-Oct-09 18:49

Program works great without any modification. Big Grin | :-D

When I try to add a new mdi child form and try to call the tw.select using a button control, nothing happens. tw.acquire scans the document but hangs up at the end of the scan. I think it has something to do with the imessagefilter but I just can't figure it out. I went through all the postings on this page. There were 2 similar problems posted but no solid replies. I have spent countless hours googling it. Confused | :confused:

Please HELP.

I want to declare and call everything from the child form.

Great code. Thanx.

Connect to network scanner

ihsan4u28-Sep-09 0:17

ihsan4u

28-Sep-09 0:17

is it possible perform scanning using network scanner? how can i connect to network shared scanner?

Re: Connect to network scanner

James West1-Nov-09 12:08

James West

1-Nov-09 12:08

Hi,

We have entered into the network scanning arena in a big way recently and here's why:
We have 18 branches all over the UK, and have a good policy of using thin client devices for all purposes we can possibly get away with; indeed more than 98% of all end users use a thin client terminal plugged into a Citrix cloud.

PC's are incumbersome, break, are prone to viruses, you can fill in the rest...

One area where PC's have been required is for scanning paper documents such as proof of deliveries, invoices etc.

To remove that requirement we have replaced the PC's with Axis 70U network scanning boxes. One end is an ethernet port, the other is a USB port. They cost approximately £400 and can work with just about any scanner. One big green button on top does it all!

I would recommend to give simplicity and cut out confusion, adopt these boxes or something equivalent. Super easy.

Epson Supported Twain Commands

JohnSims19421-Sep-09 1:07

JohnSims194

21-Sep-09 1:07

It took me about 3 hours to find out how to get a list of Epson scanner supported Twain commands so thought I'd add a reference here for all of you building on this project and using Epson scanners.

Register at www.epsondevelopers.com/sections[^] and download both the EPSON TWAIN Capabilities Reference Check List and Programming Guide for EPSON TWAIN. These documents are listed within the Programming Guide Download section.

Scanner with Document Feeder

JohnSims19421-Sep-09 1:05

JohnSims194

21-Sep-09 1:05

I noticed when using the document feeder that it scanned and then aquired each document image at a time where as using the scanners own software it scanned through all the pages and then transferred from the buffer which was much better in performance.

To set it scan all the pages then read from the buffer use:

//// Set the autoscan pre catch
        TwCapability capAutoScan = new TwCapability(TwCap.CAP_AUTOSCAN, 1, TwType.Bool);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capAutoScan);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

(you'll notice this is using an overload that takes the TwType)

and add the enum

CAP_AUTOSCAN = 0x1010

Re: Scanner with Document Feeder

Member 39132834-Nov-09 23:23

Member 3913283

4-Nov-09 23:23

Hi sorry to bother i have added your code just above the "Dim guif As TwUserInterface = New TwUserInterface()" and i cant get it to work, and sorry just another question when you got yours to work does it do a continous scan or does it stop for a second on each page before it scans the new page thanks

Re: Scanner with Document Feeder

Member 39132834-Nov-09 23:35

Member 3913283

4-Nov-09 23:35

Hi sorry me again i figured out what you meant the setting is for the actual scanner software to be continuous thanks

Re: Scanner with Document Feeder

JohnSims1944-Nov-09 23:50

JohnSims194

4-Nov-09 23:50

Hmm - the code you've placed this above is in VB where as the code I gave is in C#. The code needs to be placed in TwainLib.cs under the "public void Aquire". To make it easy I've added the whole of my copy of the void below:

public void Acquire()
		{
		TwRC rc;
		CloseSrc();
		if( appid.Id == IntPtr.Zero )
			{
			Init( hwnd );
			if( appid.Id == IntPtr.Zero )
				return;
			}
		rc = DSMident( appid, IntPtr.Zero, TwDG.Control, TwDAT.Identity, TwMSG.OpenDS, srcds );
		if( rc != TwRC.Success )
			return;

        // 1 = only 1 image if we're not using the user interface
        // -1 = scan all images if we're not using the user interface
		TwCapability cap = new TwCapability( TwCap.XferCount, -1 );
		rc = DScap( appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, cap );
		if( rc != TwRC.Success )
			{
			CloseSrc();
			return;
			}

        // This bit sets it to use duplex scanning
        // Had to overload the TwCapability method for this and add the enum of CAP_DUPLEXENABLED
        // The enums can be found at http://guides.gdpicture.com/v6/html/content/frames.html?frmname=topic&frmfile=TwainCapabilities.html
        TwCapability capDuplex = new TwCapability(TwCap.CAP_DUPLEXENABLED, 0, TwType.Bool);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capDuplex);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

        // Set the X resolution
        TwCapability capResX = new TwCapability(TwCap.CAP_RESX, 150, TwType.Fix32);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capResX);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

        // Set the Y resolution
        TwCapability capResY = new TwCapability(TwCap.CAP_RESY, 150, TwType.Fix32);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capResY);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

        // Set the scan type
        // 0 = BW | 1 = Gray | 4 = Colour
        TwCapability capPixelType = new TwCapability(TwCap.IPixelType, 0);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capPixelType);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

        // Set the scan size to A4
        TwCapability capPaperSize = new TwCapability(TwCap.ICAP_SUPPORTEDSIZES, 1);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capPaperSize);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

        //// Set the automatic deskew
        TwCapability capAutoDeskew = new TwCapability(TwCap.ICAP_AUTOMATICDESKEW, 1, TwType.Bool);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capAutoDeskew);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

        //// Set the autoscan pre catch
        TwCapability capAutoScan = new TwCapability(TwCap.CAP_AUTOSCAN, 1, TwType.Bool);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capAutoScan);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

        //// Set the threshold (bw only)
        TwCapability capThreshold = new TwCapability(TwCap.ICAP_THRESHOLD, 100, TwType.Fix32 );
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capThreshold);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

        //// Set the brightness (doesn't work for BW)
        TwCapability capBrightness = new TwCapability(TwCap.ICAP_BRIGHTNESS, 400, TwType.Fix32);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capBrightness);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

        //// Set the gamma (doesn't work for BW)
        TwCapability capGamma = new TwCapability(TwCap.ICAP_GAMMA, 2, TwType.Fix32);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capGamma);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

        //// Set the halftones !need to look at the capability overload
        TwCapability capHalfTones = new TwCapability(TwCap.ICAP_HALFTONES, "TextEnhancement Technology");
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capHalfTones);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }


        TwUserInterface	guif = new TwUserInterface();
        // ShowUI = 0 hide the user interface | 1 shows the user interface
		guif.ShowUI = 0;
		guif.ModalUI = 1;
		guif.ParentHand = hwnd;
		rc = DSuserif( appid, srcds, TwDG.Control, TwDAT.UserInterface, TwMSG.EnableDS, guif );
		if( rc != TwRC.Success )
			{
			CloseSrc();
			return;
			}
		}

You then need to update the TwainDef.cs file and replace the "internal enum TwCap : short" with the following (the bits commented // DOESN'T WORK are just commands that my particular scanner wouldn't support):

internal enum TwCap : short
	{
	XferCount		= 0x0001,			// CAP_XFERCOUNT
	ICompression	= 0x0100,			// ICAP_...
	IPixelType		= 0x0101,
	IUnits			= 0x0102,
	IXferMech		= 0x0103,
    CAP_DUPLEXENABLED = 0x1013,
    CAP_RESX = 0x1118,
    CAP_RESY = 0x1119,
    ICAP_SUPPORTEDSIZES = 0x1122,
    ICAP_AUTOMATICDESKEW = 0x1151,
    ICAP_AUTOMATICROTATE = 0x1152,      // DOESN'T WORK
    ICAP_AUTODISCARDBLANKPAGES = 0x1134,// DOESN'T WORK
    ICAP_NOISEFILTER = 0x1148, //DOESN'T WORK
    ICAP_AUTOBRIGHT = 0x1100, //DOESN'T WORK
    CAP_AUTOSCAN = 0x1010,
    ICAP_THRESHOLD = 0x1123,
    ICAP_BRIGHTNESS = 0x1101,
    ICAP_GAMMA = 0x1108,
    ICAP_HALFTONES = 0x1109,
    ICAP_PIXELFLAVOR = 0x111F //DOESN'T WORK
	}

Then also in the TwainDef.cs near the bottom you'll find this:

public TwCapability(TwCap cap, string sval)
    {
        Cap = (short)cap;
        ConType = (short)TwOn.One;
        Handle = Twain.GlobalAlloc(0x42, 6);
        IntPtr pv = Twain.GlobalLock(Handle);
        Marshal.WriteInt16(pv, 0, (short)TwType.Str32);
        Marshal.StringToHGlobalUni(sval);
        Twain.GlobalUnlock(Handle);
    }

Underneath this stick the following code in:

public TwCapability(TwCap cap, short sval, TwType TheType)
    {
        Cap = (short)cap;
        ConType = (short)TwOn.One;
        Handle = Twain.GlobalAlloc(0x42, 6);
        IntPtr pv = Twain.GlobalLock(Handle);
        if (TheType == TwType.Bool)
        {
            Marshal.WriteInt16(pv, 0, (short)TwType.Bool);
        }
        if (TheType == TwType.Fix32)
        {
            Marshal.WriteInt16(pv, 0, (short)TwType.Fix32);
        }
        
        Marshal.WriteInt32(pv, 2, (int)sval);
        Twain.GlobalUnlock(Handle);
    }

It should all work then

Re: Scanner with Document Feeder

zlov29-Sep-10 0:17

zlov

29-Sep-10 0:17

Have done all of this.
Autoscan didn't work - getting failure on line

rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capAutoScan);

If autoscan capability code commented, all works good, except pauses for about a second between each list of paper.

Scanner: Fujitsu fi-5110c.

Passing a string to TwCapability

JohnSims19421-Sep-09 0:46

JohnSims194

21-Sep-09 0:46

My scanner supports the TwCapability (ICAP_HALFTONES = 0x1109) = "TextEnhancement Technology".

So i've added into TwainLib.cs the following code:

TwCapability capHalfTones = new TwCapability(TwCap.ICAP_HALFTONES, "TextEnhancement Technology");
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capHalfTones);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

and created an overload in TwainDefs.cs:

public TwCapability(TwCap cap, string sval)
    {
        Cap = (short)cap;
        ConType = (short)TwOn.One;
        Handle = Twain.GlobalAlloc(0x42, 6);
        IntPtr pv = Twain.GlobalLock(Handle);
        Marshal.WriteInt16(pv, 0, (short)TwType.Str32);
        //HOW DO I WRITE THE STRING HERE?
        Twain.GlobalUnlock(Handle);
    }

My question is how to I use the Marshal object to write the string?

Many Thanks in advance

modified on Monday, September 21, 2009 7:07 AM

DSuserif will cause exception AccessViolationException:

carlshe19-Sep-09 20:17

carlshe

19-Sep-09 20:17

DSuserif will cause exception AccessViolationException: "Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

IS this project not compatiable with .Net framework 2.0?

Thank you!

Re: DSuserif will cause exception AccessViolationException:

LupinTheThird30-Oct-11 10:50

LupinTheThird

30-Oct-11 10:50

Having the same problem and just want to shoot myself! Smile | :)

Did you manage to solve it?

How to implement it to the User Control

chandresh.softobiz16-Sep-09 17:50

chandresh.softobiz

16-Sep-09 17:50

Hello,

I am trying to implement it to a user control but it in scan but doesn't works. Do I have to make specific changes or I am missing something can you please tell me.

Thank you

Is it possible to scan just one document from feeder

zodiacseven11-Aug-09 3:20

zodiacseven

11-Aug-09 3:20

I am having a problem because twain returns control only after all documents in feeder are scanned. This leads to high memory usage as reported by an earlier poster.

I am setting cap_xfercount to 1 but this does not seem to help:

TwCapability cap = new TwCapability(TwCap.XferCount, 1);
rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, cap);

What do I need to do to scan just one document from the feeder?
Any suggestions appreciated.

Use Duplex with Driver Twain - Help URGENT

IvesBertoli30-Jul-09 2:44

IvesBertoli

30-Jul-09 2:44

Please i study this program and not found a solution for this problem.
My Scanner support duplex mode, but i not think to get the images from scanner.
I need update the TransferPictures function? Confused | :confused:

Re: Use Duplex with Driver Twain - Help URGENT

JohnSims19418-Sep-09 0:47

JohnSims194

18-Sep-09 0:47

In TwainLib.cs before "TwUserInterface guif = new TwUserInterface();" at around line 108 add the following:

// This bit sets it to use duplex scanning (bit slow)
        // Had to overload the TwCapability method for this and add the enum of CAP_DUPLEXENABLED
        // The enums can be found at http://guides.gdpicture.com/v6/html/content/frames.html?frmname=topic&frmfile=TwainCapabilities.html
        TwCapability capDuplex = new TwCapability(TwCap.CAP_DUPLEXENABLED, 1, true);
        rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, capDuplex);
        if (rc != TwRC.Success)
        {
            CloseSrc();
            return;
        }

Then in TwainDef.cs add the following overloaded method at line 311:

public TwCapability(TwCap cap, short sval, bool blnType)
    {
        Cap = (short)cap;
        ConType = (short)TwOn.One;
        Handle = Twain.GlobalAlloc(0x42, 6);
        IntPtr pv = Twain.GlobalLock(Handle);
        Marshal.WriteInt16(pv, 0, (short)TwType.Bool);
        Marshal.WriteInt32(pv, 2, (int)sval);
        Twain.GlobalUnlock(Handle);
    }

Then in the enum TwCap add

CAP_DUPLEXENABLED = 0x1013

Re: Use Duplex with Driver Twain - Help URGENT

bennyshani19-Oct-09 11:38

bennyshani

19-Oct-09 11:38

I think you should set it up as a short so change
Marshal.WriteInt32(pv, 2, (int)sval);
into
Marshal.WriteInt16(pv, 2, (int)sval);

Re: Use Duplex with Driver Twain -Going Insane

morke4-Jan-10 1:23

morke

4-Jan-10 1:23

Hi,
I have spent about two days trying to get the duplex to work with a fijitsu f1-5110C scanner. Have any of you got this working?

Morke

Re: Use Duplex with Driver Twain -Going Insane

bennyshani4-Jan-10 3:19

bennyshani

4-Jan-10 3:19

The following code worked for me (I did not check it with a Fujitsu scanner)
irc = SetCapability(TwCap.CAP_DUPLEXENABLED, (int)TwType.Bool, Value);
1st Note:
For setting TwType.Bool I used 2 bytes:

<br />
          case TwType.Bool:<br />
          case TwType.Int16:<br />
          case TwType.UInt16:<br />
                Int16 i16 = (Int16)Value;<br />
                cap = new TwCapability(CapType, i16, 2, (short)ItemType);<br />
                break;<br />

2nd Note
When you transfer the images, you need to loop

do<br />
    {<br />
        .<br />
        .<br />
        rc = DSpxfer( appid, srcds, TwDG.Control, TwDAT.PendingXfers, TwMSG.EndXfer, pxfr );<br />
        .<br />
        .<br />
}<br />
while( pxfr.Count != 0 );<br />

Good Luck

Re: Use Duplex with Driver Twain -Going Insane

morke4-Jan-10 23:02

morke

4-Jan-10 23:02

First Thanks for the code. After a long day +1 of attempting to get the duplex mode running using the instructions in the below message thread
" Use Duplex with Driver Twain - Help URGENT " I finally got the duplex mode by incorporating the code from that message thread along with setting TwCapability cap from 1 to 2 in TwainLib.cs (line 102 +-)
TwCapability cap= newTwCapability( TwCap.XferCount, 2 );

Again Thanks for the assist!
Morke

running to dead when cancel

pclion17-Jun-09 18:04

pclion

17-Jun-09 18:04

when i scanning multi-page documents, then cancel it to pause the operation, the program run into dead.

pclion

Re: running to dead when cancel

Wolexie21-Jun-09 2:01

Wolexie

21-Jun-09 2:01

You need to handle cancel event/return message.
VB.Net Sample:
In TwainLib
Declarations:
Public Event TransferReady()
Public Event AbortTranfer()
PassMessage:
RaiseEvent TransferReady()...
Or other events declared...

Heavy givers are light complainers

change the source of the image to be acquire

AlexG Solutions9-Jun-09 11:09

AlexG Solutions

9-Jun-09 11:09

when you not have a scanner device you use a file image to process . But when use this the twain dsm took the image from the default folder on the machine. I need to make a form to change the source of the image to be acquire. How can I do this. Plese help me !!!!!!

Re: change the source of the image to be acquire

Vankir24-Nov-09 7:07

Vankir

24-Nov-09 7:07

Hi, I use TWAIN Importer from http://www.scanworkssoftware.com/twnimporter.html[^] . Good news that there is FREE version which is good enough for testing TWAIN applications. All other drivers I found are not FREE unfortunately.

1bpp b/w DIB problem

nasharu17-Apr-09 8:27

nasharu

17-Apr-09 8:27

Hi!

I have a problem scanning from minolta microfilm scanner.
Pixel type returned is 1bpp, i get pointer to dib, but then when trying to aquire BITMAPINFOHEADER it sets all fields to -1, and image cannot be converted from DIB to Bitmap.

Anyone has any idea how to fix that?
Thanks

public static IntPtr GetPixelInfo(IntPtr bmpptr, ref Rectangle bmprect)
        {
            BITMAPINFOHEADER bmi = new BITMAPINFOHEADER();
            Marshal.PtrToStructure(bmpptr, bmi);    <<------ bmi fields set to -1
            
            bmprect.X = bmprect.Y = 0;
            bmprect.Width = bmi.biWidth;
            bmprect.Height = bmi.biHeight;
                       

            if (bmi.biSizeImage == 0)
                bmi.biSizeImage = ((((bmi.biWidth * bmi.biBitCount) + 31) & ~31) >> 3) * bmi.biHeight;

            int p = bmi.biClrUsed;
            if ((p == 0) && (bmi.biBitCount <= 8))
                p = 1 << bmi.biBitCount;
            p = (p * 4) + bmi.biSize + (int)bmpptr;
            return (IntPtr)p;
        }

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.