Clipping an Image

In two-dimensional images, clipping is an essential requirement as it provides selective rendering of pixels within the boundaries of the selected frame area. Bitmap lets you clip the source image and load a part of the whole image through Clipper transformation.

The following image shows the clipping feature.

Complete the following steps to clip an image using Bitmap in code.

Add the following import statement.
```
Imports System.IO
```
```
using System.IO;
```

Initialize a rectangle and a point as global variables in Form1 class.

'Initialize variables
Dim start As Point
Dim selection As Rect
Dim dragHelper As C1DragHelper

//Initialize variables
Point start;
Rect selection;
C1DragHelper dragHelper;

Initialize a variable to control drag gestures and subscribe a drag event in the MainWindow constructor.

'Initialize drag helper for drag gestures
dragHelper = New C1DragHelper(image)
'Subscribe a drag event
dragHelper.DragDelta += dragHelper_DragDelta()

//Initialize drag helper for drag gestures
dragHelper = new C1DragHelper(image);     
//Subscribe a drag event
dragHelper.DragDelta += dragHelper_DragDelta;

Add the following code to apply clipper transformation.

'Transform method to apply transformation
Private Sub ApplyTransform(t As BaseTransform)
    Dim newBitmap = bitmap.Transform(t)
    bitmap.Dispose()
    bitmap = newBitmap
    UpdateImage()
End Sub
'Event to apply clipper transformation on button click
Private Sub Button_Click(sender As Object, e As RoutedEventArgs)
    Dim cropRect = DirectCast(selection, RectD).Round()
    ApplyTransform(New Clipper(New ImageRect(cropRect)))
End Sub

//Transform method to apply transformation
void ApplyTransform(BaseTransform t)
{
    var newBitmap = bitmap.Transform(t);
    bitmap.Dispose();
    bitmap = newBitmap;
    UpdateImage();
}
//Event to apply clipper transformation on button click
private void Button_Click_1(object sender, RoutedEventArgs e)
{
    var cropRect = ((RectD)selection).Round();
    ApplyTransform(new Clipper(new ImageRect(cropRect)));
}

Add the following code to select a portion of the image to be clipped.

'Events to selection a portion of image
Private Sub dragHelper_DragDelta(sender As Object, e As C1DragDeltaEventArgs)
    Dim pos = e.GetPosition(image)
    pos = New Point(Math.Max(0, Math.Min(pos.X, bitmap.PixelWidth)),
                    Math.Max(0, Math.Min(pos.Y, bitmap.PixelHeight)))
    selection = New Rect(Math.Round(Math.Min(start.X, pos.X)),
                         Math.Round(Math.Min(start.Y, pos.Y)),
                         Math.Round(Math.Abs(start.X - pos.X)),
                         Math.Round(Math.Abs(start.Y - pos.Y)))
End Sub
Private Sub image_MouseLeftButtonDown(sender As Object, e As MouseButtonEventArgs) _
    Handles image.MouseLeftButtonDown
    MyBase.OnMouseLeftButtonDown(e)
    Dim pos = e.GetPosition(image)
    start = New Point(Math.Max(0, Math.Min(pos.X, bitmap.PixelWidth)),
                      Math.Max(0, Math.Min(pos.Y, bitmap.PixelHeight)))
End Sub
Private Sub image_MouseLeftButtonUp(sender As Object, e As MouseButtonEventArgs) _
    Handles image.MouseLeftButtonUp
    MyBase.OnMouseLeftButtonUp(e)
    Dim pt = e.GetPosition(image)
    If Math.Abs(pt.X - start.X) < 4 AndAlso Math.Abs(pt.Y - start.Y) < 4 Then
        selection = New Rect(0, 0, bitmap.PixelWidth, bitmap.PixelHeight)
    End If
End Sub

//Events to select a portion of image from the image
private void image_MouseLeftButtonDown(object sender, 
    System.Windows.Input.MouseButtonEventArgs e)
{
   base.OnMouseLeftButtonDown(e);
    var pos = e.GetPosition(image);
    start = new Point(
    Math.Max(0, Math.Min(pos.X, bitmap.PixelWidth)),
    Math.Max(0, Math.Min(pos.Y, bitmap.PixelHeight)));
}
private void image_MouseLeftButtonUp(object sender, 
    System.Windows.Input.MouseButtonEventArgs e)
{
    base.OnMouseLeftButtonUp(e);
    var pt = e.GetPosition(image);
    if (Math.Abs(pt.X - start.X) < 4 && Math.Abs(pt.Y - start.Y) < 4)
    {
        selection = new Rect(0, 0, bitmap.PixelWidth, bitmap.PixelHeight);
    }
}
void dragHelper_DragDelta(object sender, C1DragDeltaEventArgs e)
{
    var pos = e.GetPosition(image);
    pos = new Point(Math.Max(0, Math.Min(pos.X, bitmap.PixelWidth)),
        Math.Max(0, Math.Min(pos.Y, bitmap.PixelHeight)));
    selection = new Rect(
        Math.Round(Math.Min(start.X, pos.X)),
        Math.Round(Math.Min(start.Y, pos.Y)),
        Math.Round(Math.Abs(start.X - pos.X)),
        Math.Round(Math.Abs(start.Y - pos.Y)));
}

Press F5 to run the application and click 'Load Image' button to load an image.
Select a portion of the image through mouse and click 'Clip Image' button to crop the selected portion.

Clipping an Image

See Also