VintaSoft Twain .NET SDK 15.4: Documentation for .NET developer
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How to acquire black-white images from SANE image scanner?
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If you want to acquire black-white images from SANE image scanner, you should set the scan mode that allows to get black-white images. SDK allows to set the scan mode of SANE device using SaneLocalDevice.ScanMode property.

SANE API does not provide standard names for scan mode, which allow to acquire black-white images from SANE image scanner, and scanner vendors use different names for scan modes. For example, Canon, HP, Kodak and Samsung use "Lineart" name, Brother uses "Black & White" name, Kyocera uses "Mono" name.

Names of supported scan modes can be obtained using SaneLocalDevice.GetSupportedScanModes method.

Here is an example that demonstrates how to acquire black-white images from SANE device:
/// <summary>
/// Acquires black-white images from SANE device.
/// </summary>
public void AcquireBlackWhiteImageFromSaneDevice()
{
    // create SANE device manager
    using (Vintasoft.Sane.SaneLocalDeviceManager deviceManager = new Vintasoft.Sane.SaneLocalDeviceManager())
    {
        // open SANE device manager
        deviceManager.Open();

        // get count of SANE devices
        int deviceCount = deviceManager.Devices.Count;
        if (deviceCount == 0)
        {
            System.Console.WriteLine("Devices are not found.");
            return;
        }

        // select the first SANE device
        Vintasoft.Sane.SaneLocalDevice device = deviceManager.Devices[0];

        // open SANE device
        device.Open();


        string blackWhiteScanMode = "Lineart";
        // get names of supported scan modes
        string[] supportedScanModes = device.GetSupportedScanModes();
        foreach (string supportedScanMode in supportedScanModes)
        {
            if (supportedScanMode == "Black & White" || supportedScanMode == "Mono")
            {
                blackWhiteScanMode = supportedScanMode;
                break;
            }
        }

        // specify that black-white images must be acquired from SANE device
        device.ScanMode = blackWhiteScanMode;


        Vintasoft.Sane.SaneAcquiredImage acquiredImage;
        do
        {
            try
            {
                // acquire image from SANE device
                acquiredImage = device.AcquireImageSync();
                // if image is received
                if (acquiredImage != null)
                {
                    System.Console.WriteLine("Image is acquired.");
                }
                // if image is not received
                else
                {
                    System.Console.WriteLine("Scan is completed.");
                    break;
                }
            }
            catch (System.Exception ex)
            {
                System.Console.WriteLine(string.Format("Scan is failed: {0}", ex.Message));
                break;
            }
        }
        // while device has more images to scan
        while (device.HasMoreImagesToScan);

        // close SANE device
        device.Close();

        // close SANE device manager
        deviceManager.Close();
    }

    System.Console.ReadLine();
}
''' <summary>
''' Acquires black-white images from SANE device.
''' </summary>
Public Sub AcquireBlackWhiteImageFromSaneDevice()
    ' create SANE device manager
    Using deviceManager As New Vintasoft.Sane.SaneLocalDeviceManager()
        ' open SANE device manager
        deviceManager.Open()

        ' get count of SANE devices
        Dim deviceCount As Integer = deviceManager.Devices.Count
        If deviceCount = 0 Then
            System.Console.WriteLine("Devices are not found.")
            Return
        End If

        ' select the first SANE device
        Dim device As Vintasoft.Sane.SaneLocalDevice = deviceManager.Devices(0)

        ' open SANE device
        device.Open()


        Dim blackWhiteScanMode As String = "Lineart"
        ' get names of supported scan modes
        Dim supportedScanModes As String() = device.GetSupportedScanModes()
        For Each supportedScanMode As String In supportedScanModes
            If supportedScanMode = "Black & White" OrElse supportedScanMode = "Mono" Then
                blackWhiteScanMode = supportedScanMode
                Exit For
            End If
        Next

        ' specify that black-white images must be acquired from SANE device
        device.ScanMode = blackWhiteScanMode


        Dim acquiredImage As Vintasoft.Sane.SaneAcquiredImage
        Do
            Try
                ' acquire image from SANE device
                acquiredImage = device.AcquireImageSync()
                ' if image is received
                If acquiredImage IsNot Nothing Then
                    System.Console.WriteLine("Image is acquired.")
                Else
                    ' if image is not received
                    System.Console.WriteLine("Scan is completed.")
                    Exit Try
                End If
            Catch ex As System.Exception
                System.Console.WriteLine(String.Format("Scan is failed: {0}", ex.Message))
                Exit Try
            End Try
            ' while device has more images to scan
        Loop While device.HasMoreImagesToScan

        ' close SANE device
        device.Close()

        ' close SANE device manager
        deviceManager.Close()
    End Using

    System.Console.ReadLine()
End Sub