VintaSoft Twain ActiveX v6.0
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    Acquire images asynchronously
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    VintaSoft Twain ActiveX allows to acquire images from the scanner asynchronously.

    Here is to do list for acquiring images asynchronously:

    1. Open TWAIN device manager.
    2. Select TWAIN device.
    3. Subscribe to the events of TWAIN device: Device_ImageAcquiredDevice_ScanCompleted, etc.
    4. Open TWAIN device.
    5. Set the scanning settings.
    6. Start the asynchronous acquisition process.
    7. Retrieve acquired image one by one while the Device_ImageAcquired event fires.
    8. Stop image acquisition process when the Device_ScanCompleted event fires.

    Example: Here is an example that shows how to acquire images asynchronously using scanner driver user interface and save acquired images into multipage TIFF file:
    Private VSTwain1 As New VintaSoftTwain()
    ''' <summary>
    ''' Scans images asynchronously.
    ''' </summary>
    Private Sub ScanImages()
        ' specify name of scanning application
        VSTwain1.DeviceManager_ApplicationProductName = "MyTwainApplication"
        ' open the device manager
        If Not VSTwain1.DeviceManager_Open() Then
            Exit Sub
        End If
        ' select device using standard device selection dialog
        ' open the device
        If Not VSTwain1.Device_Open Then
            Exit Sub
        End If
        ' specify that device UI must be shown
        VSTwain1.Device_ShowUI = True
        ' specify that acquired image must be added to an existing TIFF file
        VSTwain1.TiffEncoder_MultiPage = True
        ' subscribe to the device events
        AddHandler VSTwain1.DeviceImageAcquired, AddressOf VSTwain1_ImageAcquired
        AddHandler VSTwain1.DeviceScanCompleted, AddressOf VSTwain1_ScanCompleted
        AddHandler VSTwain1.DeviceScanFailed, AddressOf VSTwain1_ScanFailed
        AddHandler VSTwain1.DeviceScanCanceled, AddressOf VSTwain1_ScanCanceled
        ' acquire images asynchronously
    End Sub
    Private Sub VSTwain1_ImageAcquired()
        ' get index of acquired image
        Dim imageIndex As Integer = VSTwain1.AcquiredImages_Count - 1
        ' save acquired image to TIFF file
        If Not VSTwain1.AcquiredImages_Save(imageIndex, "test.tif") Then
        End If
    End Sub
    Private Sub VSTwain1_ScanCompleted()
        Console.WriteLine("Scan is completed.")
    End Sub
    Private Sub VSTwain1_ScanFailed(errorString As String)
        Console.WriteLine(String.Format("Scan is failed: {0}.", errorString))
    End Sub
    Private Sub VSTwain1_ScanCanceled()
        Console.WriteLine("Scan is canceled.")
    End Sub