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 using Clipper transformation.

The following image shows the clipping feature.

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

1. Add the following import statement.
   • Visual Basic
   • C#

   • Visual Basic

   Imports System.Drawing.Drawing2D
   

   • C#

   using System.Drawing.Drawing2D;
   

2. Initialize a rectangle and a point as global variables in Form1 class.
   • Visual Basic
   • C#

   • Visual Basic

   'Initialize a rectangle and a point
   Dim selection As New RectF(1.0F, 1.0F)
   Dim start As Point2L
   

   • C#

   //Initialize a rectangle and a point
   RectF selection = new RectF(1f, 1f);
   Point2L start;
   

3. Add the following code to apply clipper transformation.
   • Visual Basic
   • C#

   • Visual Basic

   'Transform method to apply transformation
   Private Sub ApplyTransform(t As BaseTransform)
       Dim newBitmap = bitmap.Transform(t)
       bitmap.Dispose()
       bitmap = newBitmap
       selection = New RectF(1.0F, 1.0F)
       UpdateImage()
   End Sub
   
   'Event to apply clipper transformation on button click
   Private Sub Btn_Clip_Click(sender As Object, e As EventArgs) _
       Handles Btn_Clip.Click
       Dim rect = New RectF(selection.X * bitmap.PixelWidth,
                            selection.Y * bitmap.PixelHeight,
                            selection.Width * bitmap.PixelWidth,
                            selection.Height * bitmap.PixelHeight)
       ApplyTransform(New Clipper(New ImageRect(rect.Round())))
   End Sub
   

   • C#

   //Transform method to apply transformation
   void ApplyTransform(BaseTransform t)
   {
       var newBitmap = bitmap.Transform(t);
       bitmap.Dispose();
   
       bitmap = newBitmap;
       selection = new RectF(1f, 1f);
   
       UpdateImage();
   }
   
   //Event to apply clipper tranformation on button click
   private void button2_Click(object sender, EventArgs e)
   {
       var rect = new RectF(selection.X * bitmap.PixelWidth,
          selection.Y * bitmap.PixelHeight,
          selection.Width * bitmap.PixelWidth,
          selection.Height * bitmap.PixelHeight);
   
       ApplyTransform(new Clipper(new ImageRect(rect.Round())));
   }
   

4. Add the following code to select a a portion of the image to be clipped.
   • Visual Basic
   • C#

   • Visual Basic

   'Events to select a portion of image using mouse 
   Private Sub pictureBox1_MouseClick(sender As Object, e As MouseEventArgs) _
       Handles pictureBox1.MouseClick
       If (e.Button And MouseButtons.Left) <> 0 Then
           Dim dcs = SystemInformation.DoubleClickSize
           If Math.Abs(e.X - start.X) _
               < dcs.Width AndAlso Math.Abs(e.Y - start.Y) < dcs.Height Then
               selection = New RectF(1.0F, 1.0F)
               pictureBox1.Invalidate()
           End If
       End If
   End Sub
   
   Private Sub pictureBox1_MouseDown(sender As Object, e As MouseEventArgs) _
       Handles pictureBox1.MouseDown
       If (e.Button And MouseButtons.Left) <> 0 Then
           start = New Point2L(e.X, e.Y)
       End If
   End Sub
   
   Private Sub pictureBox1_MouseMove(sender As Object, e As MouseEventArgs) _
       Handles pictureBox1.MouseMove
       If (e.Button And MouseButtons.Left) <> 0 Then
           Dim w As Integer = pictureBox1.Width
           Dim h As Integer = pictureBox1.Height
           Dim x As Integer = Math.Max(0, Math.Min(e.X, w))
           Dim y As Integer = Math.Max(0, Math.Min(e.Y, h))
   
           selection = New RectF(CSng(Math.Min(start.X, x)) / w,
                                 CSng(Math.Min(start.Y, y)) / h,
                                 CSng(Math.Abs(x - start.X)) / w,
                                 CSng(Math.Abs(y - start.Y)) / h)
   
           pictureBox1.Invalidate()
       End If
   End Sub
   
   Private Sub pictureBox1_Paint(sender As Object, e As PaintEventArgs) _
       Handles pictureBox1.Paint
       Dim w As Integer = pictureBox1.Width
       Dim h As Integer = pictureBox1.Height
       Dim path = New GraphicsPath(FillMode.Alternate)
       path.AddRectangle(New RectangleF(0, 0, w, h))
       path.AddRectangle(New RectangleF(selection.X * w,
                                        selection.Y * h,
                                        selection.Width * w,
                                        selection.Height * h))
   
       Dim brush = New SolidBrush(Color.FromArgb(&H66FFFFFF))
       e.Graphics.FillPath(brush, path)
       brush.Dispose()
   
       path.Dispose()
   End Sub
   

   • C#

   //Events to select a portion of image from the picture box using mouse
   private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
   {
       if ((e.Button & MouseButtons.Left) != 0)
       {
           start = new Point2L(e.X, e.Y);
       }
   }
   
   private void pictureBox1_MouseClick(object sender, MouseEventArgs e)
   {
       if ((e.Button & MouseButtons.Left) != 0)
       {
           var dcs = SystemInformation.DoubleClickSize;
           if (Math.Abs(e.X - start.X) 
               < dcs.Width && Math.Abs(e.Y - start.Y) < dcs.Height)
           {
               selection = new RectF(1f, 1f);
               pictureBox1.Invalidate();
           }
       }
   }
   
   private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
   {
       if ((e.Button & MouseButtons.Left) != 0)
       {
           int w = pictureBox1.Width;
           int h = pictureBox1.Height;
           int x = Math.Max(0, Math.Min(e.X, w));
           int y = Math.Max(0, Math.Min(e.Y, h));
   
           selection = new RectF(
               (float)Math.Min(start.X, x) / w,
               (float)Math.Min(start.Y, y) / h,
               (float)Math.Abs(x - start.X) / w,
               (float)Math.Abs(y - start.Y) / h);
   
           pictureBox1.Invalidate();
       }
   }
   
   private void pictureBox1_Paint(object sender, PaintEventArgs e)
   {
       int w = pictureBox1.Width;
       int h = pictureBox1.Height;
       var path = new GraphicsPath(FillMode.Alternate);
       path.AddRectangle(new RectangleF(0, 0, w, h));
       path.AddRectangle(new RectangleF(selection.X * w, selection.Y * h, 
           selection.Width * w, selection.Height * h));
   
       var brush = new SolidBrush(Color.FromArgb(0x66FFFFFF));
       e.Graphics.FillPath(brush, path);
       brush.Dispose();
   
       path.Dispose();
   }
   

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