How to skip blank pages while scanning

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Blank pages can be skipped while scanning by 2 ways:

using the scanner capabilities
using the library (ActiveX) features

1. Skipping of blank pages using the scanner capabilities

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

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

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

Here is an example showing how to skip blank pages if the scanner supports this ability:

VB.NET

Private VSTwain1 As New VintaSoftTwain()
Private imageCount As Integer


''' <summary>
''' Scans images asynchronously.
''' </summary>
Private Sub StartScan()
    ' open the device manager
    If Not VSTwain1.DeviceManager_Open() Then
        Console.WriteLine(VSTwain1.errorString)
        Exit Sub
    End If
    ' select device using standard device selection dialog
    VSTwain1.DeviceManager_ShowDefaultDeviceSelectionDialog()

    ' open the device
    If Not VSTwain1.Device_Open() Then
        Console.WriteLine(VSTwain1.errorString)
        Exit Sub
    End If

    ' specify that device UI must be shown
    VSTwain1.Device_ShowUI = True

    ' set settings of TIFF encoder
    VSTwain1.TiffEncoder_MultiPage = True

    ' set value of ICAP_AUTODISCARDBLANKPAGES to True
    VSTwain1.Device_Cap_Id = 4404  ' ICAP_AUTODISCARDBLANKPAGES
    VSTwain1.Device_Cap_ValueContainerType = DEVICECAPABILITYVALUECONTAINERTYPE.DEVICECAPABILITYVALUECONTAINERTYPE_OneValue
    VSTwain1.Device_Cap_Value = 1
    VSTwain1.Device_Cap_Set()

    ' 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
    VSTwain1.Device_AcquireImage()
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, Str(imageCount) + ".tif") Then
        Console.WriteLine(VSTwain1.errorString)
    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

Advantages of this technique:

When 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, scanners support skipping of blank pages.

2. Skipping of blank pages using the ActiveX features

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

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

VB.NET

Private VSTwain1 As New VintaSoftTwain()


''' <summary>
''' Scans images asynchronously.
''' </summary>
Private Sub StartScan()
    ' open the device manager
    If Not VSTwain1.DeviceManager_Open() Then
        Console.WriteLine(VSTwain1.errorString)
        Exit Sub
    End If

    ' select device using standard device selection dialog
    VSTwain1.DeviceManager_ShowDefaultDeviceSelectionDialog()

    ' specify that device UI must be shown
    VSTwain1.Device_ShowUI = 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
    VSTwain1.Device_AcquireImage()
End Sub

Private Sub VSTwain1_ImageAcquired()
    ' get index of acquired image
    Dim imageIndex As Integer = VSTwain1.AcquiredImages_Count - 1

    Dim currentNoiseLevel As Single
    ' if image is blank
    If VSTwain1.AcquiredImages_IsBlank(imageIndex, 0.01, currentNoiseLevel) Then
        Console.WriteLine("Image is blank.")
    Else
        If currentNoiseLevel = 100 Then
            Console.WriteLine("Image is not blank. " + VSTwain1.errorString)
        Else
            Console.WriteLine("Image is not blank. Noise level is " + Str(currentNoiseLevel) + "%")
        End If
    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

Advantages of this technique:

This works with every scanner.

Disadvantages of this technique:

Memory usage is greater than in first technique.

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