Image Processing: Contrast Enhancement - Part 2

The window of the resulting application looks as follows:

The "Contrast Enhancement" frame filter's VC++ .NET project can also be downloaded from the top of this page. Please note that the frame filter's source code is not required in order to run and understand the following programming example.

The filter applies a function to the image that stretches its histogram. This means that the pixel brightness values between an upper and lower bound are mapped to the entire brightness value range. The pixels that are darker than the lower bound are set to 0. Those that are brighter than the upper bound are set to 255.

First of all, a variable filter of type TIS.Imaging.FrameFilter must be declared in the class Form1. This variable will contain the frame filter and is used to communicate with the frame filter.

[C#]
private TIS.Imaging.FrameFilter filter;

[VB.NET]
Dim filter As TIS.Imaging.FrameFilter

The upper and lower bounds of the frame filter can be manipulated with two scrollbars (sldLowerBound and sldUpperBound). The beginning of the program is extended by two function calls that initialize the controls on the main form.

[C#]
    private void Form1_Load(object sender, System.EventArgs e)
    {
        icImagingControl1.ShowDeviceSettingsDialog();
        if (!icImagingControl1.DeviceValid)
            return;

        filter = icImagingControl1.FrameFilterCreate("ContrastEnhancement", "");
        // Insert the frame filter in the device path of IC.
        icImagingControl1.DeviceFrameFilters.Add(filter);
        // Enable the filter.
        cbEnable.Checked = true;
        // Initialize the Enable check box.
        filter.SetBoolParameter("Enable", cbEnable.Checked);
        InitControls();
        UpdateControls();
        icImagingControl1.LiveStart();
    }

[VB.NET]
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    IcImagingControl1.ShowDeviceSettingsDialog()
    If Not IcImagingControl1.DeviceValid Then
        'Unload(Me)
        Exit Sub
    End If
    filter = IcImagingControl1.FrameFilterCreate("ContrastEnhancement", "")
    ' Insert the frame filter in the device path of IC.
    IcImagingControl1.DeviceFrameFilters.Add(Filter)
    ' Enable the filter
    filter.SetBoolParameter("Enable", True)
    InitControls()
    UpdateControls()
    IcImagingControl1.LiveStart()
End Sub

The function InitControls initializes the minimum and maximum values of the scrollbars sldLowerBound and sldUpperBound.

[C#]
private void InitControls()
{
    sldLowerBound.Minimum = 0;
    sldLowerBound.Maximum = 255;
    sldUpperBound.Minimum = 0;
    sldUpperBound.Maximum = 255;
}

[VB.NET]
Private Sub InitControls()
    sldLowerBound.Minimum = 0
    sldLowerBound.Maximum = 255
    sldUpperBound.Minimum = 0
    sldUpperBound.Maximum = 255
End Sub

The function UpdateControls assigns the filter's parameters "Enable", "Lower Bound" and "Upper Bound" to the checkbox cbEnable and the scrollbars sldLowerBound und sldUpperBound.

[C#]
  private void UpdateControls()
  {
      if (filter.GetBoolParameter("Enable"))
          cbEnable.Checked = true;
      else
          cbEnable.Checked = false;

      sldLowerBound.Value = filter.GetIntParameter("Lower Bound");
      txLowerBound.Text = sldLowerBound.Value.ToString();
      sldUpperBound.Value = filter.GetIntParameter("Upper Bound");
      txUpperBound.Text = sldUpperBound.Value.ToString();
  }

[VB.NET]
Private Sub UpdateControls()
    If filter.GetBoolParameter("Enable") Then
        cbEnable.Checked = True
    Else
        cbEnable.Checked = False
    End If
    sldLowerBound.Value = filter.GetIntParameter("Lower Bound")
    txLowerBound.Text = sldLowerBound.Value
    sldUpperBound.Value = filter.GetIntParameter("Upper Bound")
    txUpperBound.Text = sldUpperBound.Value
End Sub

The event handler for the scrollbar sldLowerBound ensures that its value is equal to or less than the value of the scrollbar sldUpperBound. After this check, the scrollbar value is assigned to the filter's parameter "Lower Bound" and the text field to the right of the scrollbar is updated. The event handler for the scrollbar sldUpperBound works similarly.

[C#]
private void sldLowerBound_Scroll(object sender, System.EventArgs e)
{
    if (sldLowerBound.Value >= sldUpperBound.Value)
        sldLowerBound.Value = sldUpperBound.Value - 1;

    filter.SetIntParameter("Lower Bound", sldLowerBound.Value);
    txLowerBound.Text = sldLowerBound.Value.ToString();
}

private void sldUpperBound_Scroll(object sender, System.EventArgs e)
{
    if (sldUpperBound.Value <= sldLowerBound.Value)
        sldUpperBound.Value = sldLowerBound.Value + 1;

    filter.SetIntParameter("Upper Bound", sldUpperBound.Value);
    txUpperBound.Text = sldUpperBound.Value.ToString();
}

[VB.NET]
Private Overloads Sub sldLowerBound_Scroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles sldLowerBound.Scroll
    If sldLowerBound.Value >= sldUpperBound.Value Then
        sldLowerBound.Value = sldUpperBound.Value - 1
    End If
    filter.SetIntParameter("Lower Bound", sldLowerBound.Value)
    txLowerBound.Text = sldLowerBound.Value
End Sub

Private Overloads Sub sldUpperBound_Scroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles sldUpperBound.Scroll
    If sldUpperBound.Value <= sldLowerBound.Value Then
        sldUpperBound.Value = sldLowerBound.Value + 1
    End If
    filter.SetIntParameter("Upper Bound", sldUpperBound.Value)
    txUpperBound.Text = sldUpperBound.Value
End Sub