How to skip blank pages while TWAIN scanning?

In This Topic

Blank pages can be skipped while scanning by 2 ways:

using TWAIN scanner capabilities
using the library (SDK) features

1. Skipping of blank pages using TWAIN scanner capabilities

For the beginning, it is necessary to check if TWAIN scanner supports the ability to skip blank pages - check if TWAIN scanner supports ICAP_AUTODISCARDBLANKPAGES capability.

If TWAIN scanner supports that capability, then you need to set the value of the capability in a way to let TWAIN scanner skip blank pages or not.
Valid values of the capability:

-2 - TWAIN scanner must NOT skip blank pages while scanning
-1 - TWAIN scanner must skip blank pages while scanning

Here is an example that demonstrates how to skip blank pages if TWAIN scanner supports this ability:

VB.NET

' The project, which uses this code, must have references to the following assemblies:
' - Vintasoft.Twain

Partial Public Class How_to_skip_blank_pages_using_ICAP_AUTODISCARDBLANKPAGES
    Inherits Form

    ''' <summary>
    ''' TWAIN device manager.
    ''' </summary>
    Private _deviceManager As Vintasoft.Twain.DeviceManager



    Public Sub New()
        InitializeComponent()

        ' create and open device manager
        _deviceManager = New Vintasoft.Twain.DeviceManager(Me)
        _deviceManager.Open()
    End Sub



    ''' <summary>
    ''' Acquire images asynchronously.
    ''' </summary>
    Public Sub AcquireImagesAsynchronously()
        Try
            ' get reference to the default device
            Dim device1 As Vintasoft.Twain.Device = _deviceManager.DefaultDevice

            ' subscribe to the device events
            AddHandler device1.ImageAcquired, New EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
            AddHandler device1.ScanCanceled, New EventHandler(AddressOf device_ScanCanceled)
            AddHandler device1.ScanFailed, New EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
            AddHandler device1.ScanFinished, New EventHandler(AddressOf device_ScanFinished)

            ' set scanning settings
            device1.TransferMode = Vintasoft.Twain.TransferMode.Memory
            device1.ShowUI = False

            ' open the device
            device1.Open()

            ' get a reference to the IAutoDiscardBlankPages capability
            Dim autoDiscardBlankPagesCap As Vintasoft.Twain.DeviceCapability = device1.Capabilities.Find(Vintasoft.Twain.DeviceCapabilityId.IAutoDiscardBlankPages)
            ' if discarding of blank pages is not supported
            If autoDiscardBlankPagesCap Is Nothing Then
                MessageBox.Show("Device cannot automatically discard blank pages.")
            Else
                ' enable discarding of blank pages
                autoDiscardBlankPagesCap.SetValue(True)
            End If

            ' acquire images asynchronously
            device1.Acquire()
        Catch ex As Vintasoft.Twain.TwainException
            MessageBox.Show(ex.Message)
        End Try
    End Sub

    ''' <summary>
    ''' Image is acquired.
    ''' </summary>
    Private Sub device_ImageAcquired(ByVal sender As Object, ByVal e As Vintasoft.Twain.ImageAcquiredEventArgs)
        ' add the acquired image to a TIFF file
        e.Image.Save("d:\test.tif")

        ' dispose the acquired image
        e.Image.Dispose()
    End Sub

    ''' <summary>
    ''' Scan is canceled.
    ''' </summary>
    Private Sub device_ScanCanceled(ByVal sender As Object, ByVal e As EventArgs)
        MessageBox.Show("Scan is canceled.")
    End Sub

    ''' <summary>
    ''' Scan is failed.
    ''' </summary>
    Private Sub device_ScanFailed(ByVal sender As Object, ByVal e As Vintasoft.Twain.ScanFailedEventArgs)
        MessageBox.Show("Scan is failed: " + Convert.ToString(e.ErrorString))
    End Sub

    ''' <summary>
    ''' Scan is finished.
    ''' </summary>
    Private Sub device_ScanFinished(ByVal sender As Object, ByVal e As EventArgs)
        Dim device1 As Vintasoft.Twain.Device = DirectCast(sender, Vintasoft.Twain.Device)

        ' unsubscribe from device events
        RemoveHandler device1.ImageAcquired, New EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
        RemoveHandler device1.ScanCanceled, New EventHandler(AddressOf device_ScanCanceled)
        RemoveHandler device1.ScanFailed, New EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
        RemoveHandler device1.ScanFinished, New EventHandler(AddressOf device_ScanFinished)

        ' if device is not closed
        If device1.State <> Vintasoft.Twain.DeviceState.Closed Then
            ' close the device
            device1.Close()
        End If

        MessageBox.Show("Scan is finished.")
    End Sub

End Class

// The project, which uses this code, must have references to the following assemblies:
// - Vintasoft.Twain

namespace TwainExamples_CSharp
{
    public partial class How_to_skip_blank_pages_using_ICAP_AUTODISCARDBLANKPAGES : System.Windows.Forms.Form
    {

        /// <summary>
        /// TWAIN device manager.
        /// </summary>
        Vintasoft.Twain.DeviceManager _deviceManager;



        public How_to_skip_blank_pages_using_ICAP_AUTODISCARDBLANKPAGES()
        {
            InitializeComponent();

            // create and open device manager
            _deviceManager = new Vintasoft.Twain.DeviceManager(this);
            _deviceManager.Open();
        }



        /// <summary>
        /// Acquire images asynchronously.
        /// </summary>
        public void AcquireImagesAsynchronously()
        {
            try
            {
                // get reference to the default device
                Vintasoft.Twain.Device device = _deviceManager.DefaultDevice;

                // subscribe to the device events
                device.ImageAcquired += new System.EventHandler<Vintasoft.Twain.ImageAcquiredEventArgs>(device_ImageAcquired);
                device.ScanCanceled += new System.EventHandler(device_ScanCanceled);
                device.ScanFailed += new System.EventHandler<Vintasoft.Twain.ScanFailedEventArgs>(device_ScanFailed);
                device.ScanFinished += new System.EventHandler(device_ScanFinished);

                // set scanning settings
                device.TransferMode = Vintasoft.Twain.TransferMode.Memory;
                device.ShowUI = false;

                // open the device
                device.Open();

                // get a reference to the IAutoDiscardBlankPages capability
                Vintasoft.Twain.DeviceCapability autoDiscardBlankPagesCap = device.Capabilities.Find(Vintasoft.Twain.DeviceCapabilityId.IAutoDiscardBlankPages);
                // if discarding of blank pages is not supported
                if (autoDiscardBlankPagesCap == null)
                    System.Windows.Forms.MessageBox.Show("Device cannot automatically discard blank pages.");
                else
                    // enable discarding of blank pages
                    autoDiscardBlankPagesCap.SetValue(true);

                // acquire images asynchronously
                device.Acquire();
            }
            catch (Vintasoft.Twain.TwainException ex)
            {
                System.Windows.Forms.MessageBox.Show(ex.Message);
            }
        }

        /// <summary>
        /// Image is acquired.
        /// </summary>
        private void device_ImageAcquired(object sender, Vintasoft.Twain.ImageAcquiredEventArgs e)
        {
            // add the acquired image to a TIFF file
            e.Image.Save(@"d:\test.tif");

            // dispose the acquired image
            e.Image.Dispose();
        }

        /// <summary>
        /// Scan is canceled.
        /// </summary>
        private void device_ScanCanceled(object sender, System.EventArgs e)
        {
            System.Windows.Forms.MessageBox.Show("Scan is canceled.");
        }

        /// <summary>
        /// Scan is failed.
        /// </summary>
        private void device_ScanFailed(object sender, Vintasoft.Twain.ScanFailedEventArgs e)
        {
            System.Windows.Forms.MessageBox.Show("Scan is failed: " + e.ErrorString);
        }

        /// <summary>
        /// Scan is finished.
        /// </summary>
        void device_ScanFinished(object sender, System.EventArgs e)
        {
            Vintasoft.Twain.Device device = (Vintasoft.Twain.Device)sender;

            // unsubscribe from device events
            device.ImageAcquired -= new System.EventHandler<Vintasoft.Twain.ImageAcquiredEventArgs>(device_ImageAcquired);
            device.ScanCanceled -= new System.EventHandler(device_ScanCanceled);
            device.ScanFailed -= new System.EventHandler<Vintasoft.Twain.ScanFailedEventArgs>(device_ScanFailed);
            device.ScanFinished -= new System.EventHandler(device_ScanFinished);

            // if device is not closed
            if (device.State != Vintasoft.Twain.DeviceState.Closed)
                // close the device
                device.Close();

            System.Windows.Forms.MessageBox.Show("Scan is finished.");
        }

    }
}

Advantages of this technique:

When TWAIN scanner skips blank page while scanning - it doesn't send the page to the application and thus saves the memory usage.

Disadvantages of this technique:

Only the professional, rather expensive, TWAIN scanners support skipping of blank pages.

2. Skipping of blank pages using the library (SDK) features

The algorithm of this technique is quite simple. TWAIN scanner sends to the library all images of acquired pages and the library checks if the image is blank using AcquiredImage.IsBlank method.

Here is an example that demonstrates how to skip blank pages using IsBlank method:

VB.NET

' The project, which uses this code, must have references to the following assemblies:
' - Vintasoft.Twain

Partial Public Class How_to_skip_blank_pages_using_IsBlank
    Inherits Form

    ''' <summary>
    ''' TWAIN device manager.
    ''' </summary>
    Private _deviceManager As Vintasoft.Twain.DeviceManager



    Public Sub New()
        InitializeComponent()

        ' create and open device manager
        _deviceManager = New Vintasoft.Twain.DeviceManager(Me)
        _deviceManager.Open()
    End Sub



    ''' <summary>
    ''' Acquire images asynchronously.
    ''' </summary>
    Public Sub AcquireImagesAsynchronously()
        Try
            ' get reference to the default device
            Dim device1 As Vintasoft.Twain.Device = _deviceManager.DefaultDevice

            ' subscribe to the device events
            AddHandler device1.ImageAcquired, New EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
            AddHandler device1.ScanCanceled, New EventHandler(AddressOf device_ScanCanceled)
            AddHandler device1.ScanFailed, New EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
            AddHandler device1.ScanFinished, New EventHandler(AddressOf device_ScanFinished)

            ' set scanning settings
            device1.TransferMode = Vintasoft.Twain.TransferMode.Memory
            device1.ShowUI = False

            ' acquire images asynchronously
            device1.Acquire()
        Catch ex As Vintasoft.Twain.TwainException
            MessageBox.Show(ex.Message)
        End Try
    End Sub

    ''' <summary>
    ''' Image is acquired.
    ''' </summary>
    Private Sub device_ImageAcquired(ByVal sender As Object, ByVal e As Vintasoft.Twain.ImageAcquiredEventArgs)
        ' if acquired image is not blank
        If Not e.Image.IsBlank(0.01F) Then
            ' add the acquired image to a TIFF file
            e.Image.Save("d:\test.tif")
        End If

        ' dispose the acquired image
        e.Image.Dispose()
    End Sub

    ''' <summary>
    ''' Scan is canceled.
    ''' </summary>
    Private Sub device_ScanCanceled(ByVal sender As Object, ByVal e As EventArgs)
        MessageBox.Show("Scan is canceled.")
    End Sub

    ''' <summary>
    ''' Scan is failed.
    ''' </summary>
    Private Sub device_ScanFailed(ByVal sender As Object, ByVal e As Vintasoft.Twain.ScanFailedEventArgs)
        MessageBox.Show("Scan is failed: " + Convert.ToString(e.ErrorString))
    End Sub

    ''' <summary>
    ''' Scan is finished.
    ''' </summary>
    Private Sub device_ScanFinished(ByVal sender As Object, ByVal e As EventArgs)
        Dim device1 As Vintasoft.Twain.Device = DirectCast(sender, Vintasoft.Twain.Device)

        ' unsubscribe from device events
        RemoveHandler device1.ImageAcquired, New EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
        RemoveHandler device1.ScanCanceled, New EventHandler(AddressOf device_ScanCanceled)
        RemoveHandler device1.ScanFailed, New EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
        RemoveHandler device1.ScanFinished, New EventHandler(AddressOf device_ScanFinished)

        ' if device is not closed
        If device1.State <> Vintasoft.Twain.DeviceState.Closed Then
            ' close the device
            device1.Close()
        End If

        MessageBox.Show("Scan is finished.")
    End Sub

End Class

// The project, which uses this code, must have references to the following assemblies:
// - Vintasoft.Twain

namespace TwainExamples_CSharp
{
    public partial class How_to_skip_blank_pages_using_IsBlank : System.Windows.Forms.Form
    {

        /// <summary>
        /// TWAIN device manager.
        /// </summary>
        Vintasoft.Twain.DeviceManager _deviceManager;



        public How_to_skip_blank_pages_using_IsBlank()
        {
            InitializeComponent();

            // create and open device manager
            _deviceManager = new Vintasoft.Twain.DeviceManager(this);
            _deviceManager.Open();
        }



        /// <summary>
        /// Acquire images asynchronously.
        /// </summary>
        public void AcquireImagesAsynchronously()
        {
            try
            {
                // get reference to the default device
                Vintasoft.Twain.Device device = _deviceManager.DefaultDevice;

                // subscribe to the device events
                device.ImageAcquired += new System.EventHandler<Vintasoft.Twain.ImageAcquiredEventArgs>(device_ImageAcquired);
                device.ScanCanceled += new System.EventHandler(device_ScanCanceled);
                device.ScanFailed += new System.EventHandler<Vintasoft.Twain.ScanFailedEventArgs>(device_ScanFailed);
                device.ScanFinished += new System.EventHandler(device_ScanFinished);

                // set scanning settings
                device.TransferMode = Vintasoft.Twain.TransferMode.Memory;
                device.ShowUI = false;

                // acquire images asynchronously
                device.Acquire();
            }
            catch (Vintasoft.Twain.TwainException ex)
            {
                System.Windows.Forms.MessageBox.Show(ex.Message);
            }
        }

        /// <summary>
        /// Image is acquired.
        /// </summary>
        private void device_ImageAcquired(object sender, Vintasoft.Twain.ImageAcquiredEventArgs e)
        {
            // if acquired image is not blank
            if (!e.Image.IsBlank(0.01f))
                // add the acquired image to a TIFF file
                e.Image.Save(@"d:\test.tif");

            // dispose the acquired image
            e.Image.Dispose();
        }

        /// <summary>
        /// Scan is canceled.
        /// </summary>
        private void device_ScanCanceled(object sender, System.EventArgs e)
        {
            System.Windows.Forms.MessageBox.Show("Scan canceled.");
        }

        /// <summary>
        /// Scan is failed.
        /// </summary>
        private void device_ScanFailed(object sender, Vintasoft.Twain.ScanFailedEventArgs e)
        {
            System.Windows.Forms.MessageBox.Show("Scan failed: " + e.ErrorString);
        }

        /// <summary>
        /// Scan is finished.
        /// </summary>
        void device_ScanFinished(object sender, System.EventArgs e)
        {
            Vintasoft.Twain.Device device = (Vintasoft.Twain.Device)sender;

            // unsubscribe from device events
            device.ImageAcquired -= new System.EventHandler<Vintasoft.Twain.ImageAcquiredEventArgs>(device_ImageAcquired);
            device.ScanCanceled -= new System.EventHandler(device_ScanCanceled);
            device.ScanFailed -= new System.EventHandler<Vintasoft.Twain.ScanFailedEventArgs>(device_ScanFailed);
            device.ScanFinished -= new System.EventHandler(device_ScanFinished);

            // if device is not closed
            if (device.State != Vintasoft.Twain.DeviceState.Closed)
                // close the device
                device.Close();

            System.Windows.Forms.MessageBox.Show("Scan is finished.");
        }

    }
}

Advantages of this technique:

This works with every TWAIN scanner.

Disadvantages of this technique:

Memory usage is greater than in first technique.

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