C#（winform）实现图片的无损放大缩小【点击鼠标滚动键放大缩小】

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Text;
using System.Windows.Forms;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;

namespace ImageLoader
{
    public partial class Form1 : Form
    {

        private Rectangle selectedArea;
        private Image loadedImage;
        private Color selectionColor;
        private int count = 10;

        public Form1()
        {
            InitializeComponent();
            this.MouseWheel +=new MouseEventHandler(picBox1_MouseWheel);
            picBox1.SizeMode = PictureBoxSizeMode.Zoom;
        }

        private void openToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                if (loadedImage != null)
                {
                    loadedImage.Dispose();
                }
                try
                {

                    loadedImage = Image.FromFile(openFileDialog1.FileName);

                    //Get a contrasting color for the image selection marker
                    using (Bitmap bmp = new Bitmap(loadedImage))
                    {
                        selectionColor = GetDominantColor(bmp, false);
                        selectionColor = CalculateOppositeColor(selectionColor);
                    }

                    ///tZoom.Value = 1;

                    //resizePictureArea();



                    //Map the area selected in the thumbail to the actual image size
                    Rectangle zoomArea = new Rectangle();
                    Rectangle localArea = new Rectangle();

                    zoomArea.Width = loadedImage.Width;
                    zoomArea.Height = loadedImage.Height;
                    
                    

                    int aScale;
                    aScale = loadedImage.Width / picBox1.Width;

                    localArea.Width = picBox1.Width;
                    localArea.Height = loadedImage.Height/aScale;
                    picBox1.Image = ZoomImage(loadedImage, zoomArea, localArea);
                    picBox1.Refresh();

                }
                catch (Exception)
                {
                    MessageBox.Show("图片太大，请缩小图片尺寸！");
                }
            }
        }

        private Image ZoomImage(Image input, Rectangle zoomArea, Rectangle sourceArea)
        {
            Bitmap newBmp = new Bitmap(sourceArea.Width, sourceArea.Height);

            using (Graphics g = Graphics.FromImage(newBmp))
            {
                //high interpolation
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;

                g.DrawImage(input, sourceArea, zoomArea, GraphicsUnit.Pixel);
            }

            return newBmp;
        }

        private Color GetDominantColor(Bitmap bmp, bool includeAlpha)
        {
            // GDI+ still lies to us - the return format is BGRA, NOT ARGB.
            BitmapData bmData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height),
                                           ImageLockMode.ReadWrite,
                                           PixelFormat.Format32bppArgb);

            int stride = bmData.Stride;
            IntPtr Scan0 = bmData.Scan0;

            int r = 0;
            int g = 0;
            int b = 0;
            int a = 0;
            int total = 0;

            unsafe
            {
                byte* p = (byte*)(void*)Scan0;

                int nOffset = stride - bmp.Width * 4;
                int nWidth = bmp.Width;

                for (int y = 0; y < bmp.Height; y++)
                {
                    for (int x = 0; x < nWidth; x++)
                    {
                        r += p[0];
                        g += p[1];
                        b += p[2];
                        a += p[3];

                        total++;

                        p += 4;
                    }
                    p += nOffset;
                }
            }

            bmp.UnlockBits(bmData);

            r /= total;
            g /= total;
            b /= total;
            a /= total;

            if (includeAlpha)
                return Color.FromArgb(a, r, g, b);
            else
                return Color.FromArgb(r, g, b);
        }

        /// <summary>
        /// Calculates the opposite color of a given color. 
        /// Source: http://dotnetpulse.blogspot.com/2007/01/function-to-calculate-opposite-color.html
        /// </summary>
        /// <param name="clr"></param>
        /// <returns></returns>
        private Color CalculateOppositeColor(Color clr)
        {
            return Color.FromArgb(255 - clr.R, 255 - clr.G, 255 - clr.B);
        }

        /// <summary>
        /// Constricts a set of given dimensions while keeping aspect ratio.
        /// </summary>
        private Size ShrinkToDimensions(int originalWidth, int originalHeight, int maxWidth, int maxHeight)
        {
            int newWidth = 0;
            int newHeight = 0;

            if (originalWidth >= originalHeight)
            {
                //Match area width to max width
                if (originalWidth <= maxWidth)
                {
                    newWidth = originalWidth;
                    newHeight = originalHeight;
                }
                else
                {
                    newWidth = maxWidth;
                    newHeight = originalHeight * maxWidth / originalWidth;
                }
            }
            else
            {
                //Match area height to max height
                if (originalHeight <= maxHeight)
                {
                    newWidth = originalWidth;
                    newHeight = originalHeight;
                }
                else
                {
                    newWidth = originalWidth * maxHeight / originalHeight;
                    newHeight = maxHeight;
                }
            }

            return new Size(newWidth, newHeight);

        }

        //private void Form1_Load(object sender, EventArgs e)
        //{
        //    picBox1.SizeMode = PictureBoxSizeMode.StretchImage;
        //}

        private void Form1_Resize(object sender, EventArgs e)
        {
            //StretchImage;

            //picBox1.SizeMode = PictureBoxSizeMode.AutoSize;
            int x = this.Width - 20;
            int y = this.Height - 70;
            //label1.Location = new Point(x, y); 
            picBox1.Width = this.Width - 10;
            picBox1.Height = this.Height - 27;

            Rectangle zoomArea = new Rectangle();
            Rectangle localArea = new Rectangle();

            zoomArea.Width = loadedImage.Width;
            zoomArea.Height = loadedImage.Height;


            int aScale; //这样简单处理可能会有问题
            aScale = loadedImage.Width / picBox1.Width;

            localArea.Width = picBox1.Width;
            localArea.Height = loadedImage.Height / aScale;
            picBox1.Image = ZoomImage(loadedImage, zoomArea, localArea);
            picBox1.Refresh();
        }

        private void picBox1_MouseWheel(object sender, MouseEventArgs e)
        {
            //MessageBox.Show("收到");
            zoom(e.Delta);
        }

        private void zoom(int delta)
        {
            if (delta >= 1)
            {
                resize(++count);
            }
            else if(delta <=-1)
            {
                resize(--count);
            }
        }

        private void resize(int c)
        {
            //窗体宽高作为参照，所以窗体宽高不能变，可以考虑用其他作参照物，窗体和图片一起放大缩小
            int w = this.Width;
            int h = this.Height;
            decimal percent = (decimal)(c + 100)/(decimal)100;
            decimal width = percent*w;
            decimal height = percent * h;
            picBox1.Width = Convert.ToInt32(width);
            picBox1.Height = Convert.ToInt32(height);
            panel1.Width = this.Width-10;
            panel1.Height = this.Height-60;
            if (panel1.Height < picBox1.Height || panel1.Width < picBox1.Width)
            {
                panel1.AutoScroll = true;
            }
           
        }
    }
}