using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;

namespace TestZoom2
{
    public partial class Form1 : Form
    {        
        Image image; //Исходное изображение
        Image imageZoom; //Изображение после Zoom
        double zoom = 1.0; //Последний zoom
        double Stride = 0.005;

        public Form1()
        {
            InitializeComponent();            
            this.MaximizeBox = false;
            this.MinimizeBox = false;
        }

        private void Form1_Load(object sender, EventArgs e)
        {            
            this.FormBorderStyle = FormBorderStyle.FixedDialog;

            image = Image.FromFile("C:\\Users\\Acer\\Desktop\\image1.jpg");            

            pictureBox1 = new PictureBox();
            pictureBox1.Name = "pictureBox1";
            pictureBox1.SizeMode = PictureBoxSizeMode.AutoSize;            
            pictureBox1.Image = image;

            panel1.AutoScroll = true;
            panel1.Controls.Add(pictureBox1);            
            pictureBox1.MouseWheel += new MouseEventHandler(pictureBox1_MouseWheel);
            //pictureBox1.MouseHover += new System.EventHandler(pictureBox1_MouseHover);
            pictureBox1.Image = image;
            imageZoom = image;

            pictureBox1.Focus();
        }

        private void pictureBox1_MouseWheel(object sender, MouseEventArgs e)
        {
            if (pictureBox1.Image != null)
            {
                if (e.Delta < 0)
                {
                    zoom = zoom * (1 + Stride);
                }
                else if (e.Delta > 0)
                {
                    zoom = zoom * (1 - Stride);                    
                }

                Bitmap bmp = new Bitmap(imageZoom,
                                        Convert.ToInt32(pictureBox1.Width * zoom),
                                        Convert.ToInt32(pictureBox1.Height * zoom));
                Graphics g = Graphics.FromImage(bmp);
                g.InterpolationMode = InterpolationMode.Default;
                imageZoom = bmp;

                pictureBox1.Width = (int)Math.Round(pictureBox1.Image.Width * zoom);
                pictureBox1.Height = (int)Math.Round(pictureBox1.Image.Height * zoom);

                pictureBox1.Image = bmp;                
            }
        }

        /*private void pictureBox1_MouseHover(object sender, EventArgs e)
        {
            pictureBox1.Focus();
        }*/

        //Восстановление изображения
        private void panel1_MouseDown(object sender, MouseEventArgs e)
        {
            pictureBox1.Image = image;
            imageZoom = image;
            zoom = 1.0;
            //pictureBox1.Focus();
        }
    }
}