public partial class Form1 : Form
    {
        Rectangle rubberBand,zoom_Rect;
        Bitmap bmp,bmp_cut;
        float m_Scalef = 1.0f;
        Image image,myImage;

        public Form1()
        {
            InitializeComponent();
            bmp = (Bitmap)pictureBox1.Image;

        }

        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            Point pt = pictureBox1.PointToScreen(new Point(e.X, e.Y));
            rubberBand = new Rectangle(pt.X, pt.Y, 1, 1);
            ControlPaint.DrawReversibleFrame(rubberBand, pictureBox1.BackColor, FrameStyle.Dashed);
            this.Invalidate();
        }

        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button != MouseButtons.Left)
                return;

            ControlPaint.DrawReversibleFrame(rubberBand, pictureBox1.BackColor, FrameStyle.Dashed);

            Point pt = pictureBox1.PointToScreen(new Point(e.X, e.Y));
            rubberBand = new Rectangle(rubberBand.X, rubberBand.Y, pt.X - rubberBand.X, pt.Y - rubberBand.Y);

            ControlPaint.DrawReversibleFrame(rubberBand, pictureBox1.BackColor, FrameStyle.Dashed);

            pictureBox1.Invalidate();

        }

        private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
              ControlPaint.DrawReversibleFrame(rubberBand, Color.Black, FrameStyle.Thick);
            }

        }


        private void button2_Click(object sender, EventArgs e)
        {
            zoom_Rect = pictureBox1.RectangleToClient(rubberBand);
            bmp_cut = new Bitmap(zoom_Rect.Width, zoom_Rect.Height);

            Graphics g = Graphics.FromImage(bmp_cut);
            image = pictureBox1.Image;
            g.DrawImage(image, 0, 0, zoom_Rect, GraphicsUnit.Pixel);
            pictureBox1.Image = bmp_cut;
            g.Dispose();


        }

        private void button3_Click(object sender, EventArgs e)
        {

            panel1.Refresh();
            if (comboBox1.SelectedIndex == 0)
                m_Scalef = .25f;
            if (comboBox1.SelectedIndex == 1)
                m_Scalef = .5f;
            if (comboBox1.SelectedIndex == 2)
                m_Scalef = .75f;
            if (comboBox1.SelectedIndex == 3)
                m_Scalef = 1.0f;
            if (comboBox1.SelectedIndex == 4)
                m_Scalef = 2.0f;

            m_Scalef = m_Scalef * 2.0f;
            
            int a_Width, b_Height;
            a_Width = (int)(rubberBand.Width * m_Scalef);
            b_Height = (int)(rubberBand.Height * m_Scalef);
            panel1.Size = new Size(a_Width, b_Height); 


                myImage = pictureBox1.Image;
                Graphics g = panel1.CreateGraphics();
                
                
                g.DrawImage(myImage, 0, 0, rubberBand.Width * m_Scalef, rubberBand.Height * m_Scalef);
                            
               


            Invalidate();
        }
   }