Как пропустить пустые страницы при TWAIN-сканировании?

В этом разделе

Пустые страницы можно пропускать при сканировании двумя способами:

используя возможности сканера TWAIN
используя возможности библиотеки (SDK)

1. Пропуск пустых страниц при использовании возможностей сканера TWAIN

Для начала необходимо проверить, поддерживает ли TWAIN-сканер возможность пропуска пустых страниц - проверьте, поддерживает ли TWAIN-сканер функцию ICAP_AUTODISCARDBLANKPAGES.

Если TWAIN-сканер поддерживает эту возможность, то вам нужно установить значение этой функции таким образом, чтобы TWAIN-сканер пропускал пустые страницы или нет.
Допустимые значения данной функции:

-2 - TWAIN-сканер НЕ должен пропускать пустые страницы при сканировании
-1 - TWAIN-сканер должен пропускать пустые страницы при сканировании

Вот пример, который демонстрирует, как пропускать пустые страницы, если TWAIN-сканер поддерживает эту опцию:

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.");
        }

    }
}

VB.NET

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

Преимущества этой техники:

Когда TWAIN-сканер пропускает пустую страницу при сканировании - он не отправляет страницу в приложение и тем самым экономит память.

Недостатки этой техники:

Только профессиональные, довольно дорогие сканеры TWAIN поддерживают пропуск пустых страниц.

2. Пропуск пустых страниц с использованием возможностей библиотеки (SDK)

Алгоритм этой техники довольно прост. TWAIN-сканер отправляет в библиотеку все изображения полученных страниц, а библиотека проверяет, является ли изображение пустым, используя метод Vintasoft.Twain.AcquiredImage.IsBlank.

Вот пример, который демонстрирует, как пропускать пустые страницы с помощью метода IsBlank:

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.");
        }

    }
}

VB.NET

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

Преимущества этой техники:

Она подходит для любого TWAIN-сканера.

Недостатки этой техники:

Расход памяти больше, чем в первой технике.

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