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 using Clipper transformation.

The following image shows the clipping feature.

Apply clipping using ComponentOne Bitmap for WinForms

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

Add the following import statement. vbnet

Imports System.Drawing.Drawing2D

csharp

using System.Drawing.Drawing2D;

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

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

csharp

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

Add the following code to apply clipper transformation. vbnet

'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

csharp

//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())));
}

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

'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

csharp

//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();
}

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