Как обрезать изображение с помощью выделения мышью в picturebox в форме windows

        int cropX;
        int cropY;
        int cropWidth;
        int cropHeight;
        public Pen cropPen;

        public DashStyle cropDashStyle = DashStyle.DashDot;
        public bool Makeselection = false;

<pre>private void button4_Click(object sender, EventArgs e)
        {
            Makeselection = true;
            button4.Enabled = true;

            Cursor = Cursors.Default;

            try
            {
                if (cropWidth < 1)
                {
                    return;
                }
                Rectangle rect = new Rectangle(cropX, cropY, cropWidth, cropHeight);
                Bitmap OriginalImage = new Bitmap(pictureBox1.Image, pictureBox1.Width, pictureBox1.Height);
                Bitmap _img = new Bitmap(cropWidth, cropHeight);
                Graphics g = Graphics.FromImage(_img);

                g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
                g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
                g.DrawImage(OriginalImage, 0, 0, rect, GraphicsUnit.Pixel);

                pictureBox1.Image = _img;
                pictureBox1.Width = _img.Width;
                pictureBox1.Height = _img.Height;
            }
            catch (Exception ex)
            {

            }
        }

        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
         
                Cursor = Cursors.Default;
                if (Makeselection)
                {

                    try
                    {
                        if (e.Button == System.Windows.Forms.MouseButtons.Left)
                        {
                            Cursor = Cursors.Cross;
                            cropX = e.X;
                            cropY = e.Y;

                            cropPen = new Pen(Color.Red, 1);
                            cropPen.DashStyle = DashStyle.DashDotDot;


                        }                       
                        pictureBox1.Refresh();
                    }
                    catch (Exception ex)
                    {

                    }
                }
            
        }

        private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
        {
            if (Makeselection)
            {
                Cursor = Cursors.Default;
            }
        }

        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
                Cursor = Cursors.Default;
                if (Makeselection)
                {

                    try
                    {
                        if (pictureBox1.Image == null)
                            return;


                        if (e.Button == System.Windows.Forms.MouseButtons.Left)
                        {
                            pictureBox1.Refresh();
                            cropWidth = e.X - cropX;
                            cropHeight = e.Y - cropY;
                            pictureBox1.CreateGraphics().DrawRectangle(cropPen, cropX, cropY, cropWidth, cropHeight);
                        }



                    }
                    catch (Exception ex)
                    {
                        //if (ex.Number == 5)
                        //    return;
                    }
                }
            
        }

Cropping image is wrong. Where I'm wrong?