Outdated Content Notice

This article has been flagged by support for review/rewrite. The general concepts are likely sound but there may be better ways to approach the subject in more recent DotImage. Please contact support if you have questions

Article Content

A common task in the document imaging world is to scan many pages into a single file. DotTwain, along with DotImage can easily be used to accomplish this task. The two most popular multi page image formats are TIFF and PDF, so this article will concentrate on those.

To start off, lets first look at what it takes to scan a single page. It is important to know that the entire acquisition process ('acquisition' refers to the process of scanning a page and transferring it into your application) is event driven. This means that anything which happens during this time, must be dealt with in an event handler, including saving the image. In DotTwain, the acquisition is controlled by an instance of the Acquisition class. For any one application, there should be exactly one Acquisition object. This is because the Acquisition object connects to the TWAIN interface, and TWAIN does not allow more than one connection. The following acquisition events are of interest to us:

AcquireCanceled: Raised if the user cancels the acquisition process.
AcquireFinished: Raised when the scanner has finished scanning the last page.
ImageAcquired: Raised each time the scanner finishes scanning a page.

C#

Acquisition myAcquisition = new Acquisition(this);

VB.NET

Dim WithEvents myAcquisition As New Acquisition(Me)

The reason we must pass the constructor a reference to the current window is that TWAIN uses it's parent window's message loop for interacting with our program. At this point, we can choose a device to use. Since we don't know what type or how many scanners the user will have, lets let them choose. The ShowSelectSource method will display a list of detected scanners and let the user pick one.

C#

Device activeDevice = myAcquisition.ShowSelectSource();

VB.NET

Dim activeDevice As Device = myAcquisition.ShowSelectSource()

The Device object holds a reference to the scanner that was selected, which is controlled through our acquisition object. In this way, we can use the activeDevice object to control the scan. Before we start off the actual scan, we need to set the event handlers. This is done with delegates in C# and declared as 'Handles' in VB:

C#

myAcquisition.AcquireCanceled += new EventHandler(OnAcquireCanceled);
myAcquisition.AcquireFinished += new EventHandler(OnAcquireFinished);
myAcquisition.ImageAcquired += new ImageAcquiredEventHandler(OnImageAcquired);
...
private void OnImageAcquired(object sender, AcquireEventArgs e)
{}

private void OnAcquireCanceled(object sender, EventArgs e)
{}

private void OnAcquireFinished(object sender, EventArgs e)
{}

VB.NET

Private  Sub OnImageAcquired(ByVal sender As Object, ByVal e As AcquireEventArgs) Handles myAcquisition.ImageAcquired
End Sub

Private  Sub OnAcquireCanceled(ByVal sender As Object, ByVal e As EventArgs) Handles myAcquisition.AcquireCanceled
End Sub

Private  Sub OnAcquireFinished(ByVal sender As Object, ByVal e As EventArgs) Handles myAcquisition.AcquireFinished
End Sub

Now that all the events are set up, we can start the scan. We do this using the Device object that we created earlier:

C#

activeDevice.Acquire();

VB.NET

activeDevice.Acquire()

We can now turn our attention the meat of the process: actually saving the images. There are two main ways to save a multi page image file using DotImage. The first way is to have all of the images loaded into memory, and pass them all to the image encoder. The second way is to save the images one by one (append, in the case of TIFF) or to supply a reference to a file on disk rather than an image in memory (as in the PDF encoder). For more information on this topic, please see the article describing conversion between TIFF and PDF. In this article we will use the second method.

The PdfEncoder class does not have the ability to append to an existing file, which means that we must supply the encoder with handles to each of the images. To do this, we will first need to save the aquired images as a TIFF image. Because the TiffEncoder has the ability to append, this is easy:

C#

private void OnImageAcquired(object sender, AcquireEventArgs e)
{
    if (e.Image != null)
    {
        TiffEncoder enc = new TiffEncoder(TiffCompression.Default, true);
        FileStream fs = new FileStream("outputTiff.tif", FileMode.OpenOrCreate, FileAccess.ReadWrite);
        enc.Save(fs, AtalaImage.FromBitmap(e.Image), null);
        fs.Close();
    }
}

VB.NET

Private Sub OnImageAcquired(ByVal sender As Object, ByVal e As AcquireEventArgs) Handles myAcquisition.ImageAcquired
 If Not e.Image Is Nothing Then
  Dim enc As TiffEncoder = New TiffEncoder(TiffCompression.Default, True)
  Dim fs As FileStream = New FileStream("outputTiff.tif", FileMode.OpenOrCreate, FileAccess.ReadWrite)
  enc.Save("outputTiff.tif", AtalaImage.FromBitmap(e.Image), Nothing)
  fs.Close()
 End If
End Sub

This will append each new image to "outputTiff.tif". The next step is to convert this file to PDF. We can do this inside the AcquireFinished event handler because we know that all of the images have been saved into the temporary tiff file.

C#

private void OnAcquireFinished(object sender, EventArgs e)
{
    PdfImageCollection col = new PdfImageCollection();
    TifDecoder dec = new TiffDecoder();
    FileStream fs = new FileStream("outputTiff.tif", FileMode.Open, FileAccess.Read);
    int frameCount = dec.GetFrameCount(fs);
    fs.Close();
    for(int i=0; i< frameCount; i++)
        col.Add(new PdfImage("outputTiff.tif", i, PdfCompressionType.Auto));

    FileStream outStream = new FileStream("outputPdf.pdf", FileMode.OpenOrCreate, FileAccess.ReadWrite);
    PdfEncoder enc = new PdfEncoder();
    enc.Save(outStream, col, null);
}

VB.NET

Private Sub OnAcquireFinished(ByVal sender As Object, ByVal e As EventArgs) Handles myAcquisition.AcquireFinished
 Dim col As PdfImageCollection = New PdfImageCollection()
 Dim dec As TifDecoder = New TifDecoder()
 Dim fs As FileStream = New FileStream("outputTiff.tif", FileMode.Open, FileAccess.Read)
 Dim frameCount As Integer = dec.GetFrameCount(fs)
 fs.Close()
 Dim i As Integer=0
    Dim i As Integer
    For i = 0 To (frameCount - 1)
        col.Add(New PdfImage("outputTiff.tif", i, PdfCompressionType.Auto))
    Next i

 Dim outStream As FileStream = New FileStream("outputPdf.pdf", FileMode.OpenOrCreate, FileAccess.ReadWrite)
 Dim enc As PdfEncoder = New PdfEncoder()
 enc.Save(outStream, col, Nothing)
End Sub

The end result is a pdf file that contains all of the scanned images. The source code is attached in a zip file. The full code listing is shown below:

C#

public class AcquisitionClass
{
    private bool _acquireCanceled;
    private Acquisition myAcquisition = new Acquisition(this);

    public void ScanImages()
    {
        _acquireCanceled = false;
        myAcquisition.AcquireCanceled += new EventHandler(OnAcquireCanceled);
        myAcquisition.AcquireFinished += new EventHandler(OnAcquireFinished);
        myAcquisition.ImageAcquired += new ImageAcquiredEventHandler(OnImageAcquired);

        Device activeDevice = myAcquisition.ShowSelectSource();

        activeDevice.Acquire();
    }

    private void OnImageAcquired(object sender, AcquireEventArgs e)
    {
        if (e.Image != null)
        {
            TiffEncoder enc = new TiffEncoder(TiffCompression.Default, true);
            FileStream fs = new FileStream("outputTiff.tif",FileMode.OpenOrCreate, FileAccess.ReadWrite);
            enc.Save(fs, AtalaImage.FromBitmap(e.Image), null);
            fs.Close();
        }
    }

    private void OnAcquireCanceled(object sender, EventArgs e)
    {
        _acquireCanceled = true;
    }

    private void OnAcquireFinished(object sender, EventArgs e)
    {
        if (_acquireCanceled)
        {
            return;
        }

        PdfImageCollection col = new PdfImageCollection();
        TiffDecoder dec = new TiffDecoder();
        FileStream fs = new FileStream("outputTiff.tif", FileMode.Open, FileAccess.Read);
        int frameCount = dec.GetFrameCount(fs);
        fs.Close();
        for(int i=0; i< frameCount; i++)
        {
            col.Add(new PdfImage("outputTiff.tif", i, PdfCompressionType.Auto));
        }

        FileStream outStream = new FileStream("outputPdf.pdf", FileMode.OpenOrCreate, FileAccess.ReadWrite);
        PdfEncoder enc = new PdfEncoder();
        enc.Save(outStream, col, null);
    }
}

VB.NET

Public Class AcquisitionClass
    Private _acquireCanceled As Boolean
    Private myAcquisition As Acquisition = New Acquisition(Me)

    Public Sub ScanImages()
        _acquireCanceled = False

        Dim activeDevice As Device = myAcquisition.ShowSelectSource()

        activeDevice.Acquire()
    End Sub

    Private Sub OnImageAcquired(ByVal sender As Object, ByVal e As AcquireEventArgs) Handles myAcquisition.ImageAcquired
        If Not e.Image Is Nothing Then
            Dim enc As TiffEncoder = New TiffEncoder(TiffCompression.Default, True)
            Dim fs As New FileStream("outputTiff.tif", FileMode.OpenOrCreate, FileAccess.ReadWrite)
            enc.Save("outputTiff.tif", AtalaImage.FromBitmap(e.Image), Nothing)
            fs.Close()
        End If
    End Sub

    Private Sub OnAcquireCanceled(ByVal sender As Object, ByVal e As EventArgs) Handles myAcquisition.AcquireCanceled
        _acquireCanceled = True
    End Sub

    Private Sub OnAcquireFinished(ByVal sender As Object, ByVal e As EventArgs) Handles myAcquisition.AcquireFinished
        If _acquireCanceled Then
            Return
        End If

        Dim col As PdfImageCollection = New PdfImageCollection()
        Dim dec As TiffDecoder = New TiffDecoder()
        Dim fs As FileStream = New FileStream("outputTiff.tif", FileMode.Open, FileAccess.Read)
        Dim frameCount As Integer = dec.GetFrameCount(fs)
        fs.Close()
            Dim i As Integer
            For i = 0 To (frameCount - 1)
                col.Add(New PdfImage("outputTiff.tif", i, PdfCompressionType.Auto))
            Next i

        Dim outStream As FileStream = New FileStream("outputPdf.pdf", FileMode.OpenOrCreate, FileAccess.ReadWrite)
        Dim enc As PdfEncoder = New PdfEncoder()
        enc.Save(outStream, col, Nothing)
    End Sub
End Class

Original Article:
Q10129 - HOWTO: Scan a Multi-Page Document Into a PDF or TIFF