關於圖片縮放的c#方法

  在網站建設中，關於圖片是必不可少的，後臺管理中往往需要上傳圖片，大的圖片在網絡中傳輸速率很慢，很不理想，因此解決辦法是，用戶上傳圖片時候，保存一個圖片的縮略圖，在網頁顯示用縮略圖，用戶下載，使用原圖，下面是通過搜索資料，整理的c#關於保存圖片縮略圖的方法，用戶只需要傳入適當參數，調用此方法就可以生成縮略圖。

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Web;
    using System.Web.UI;
    using System.Web.UI.WebControls;
    using System.IO;   
    public partial class upload : System.Web.UI.Page 
    {     
        protected void Page_Load(object sender, EventArgs e)     
        {         
                 
        }     
    }  
    /// <summary>     
    /// 圖片等比縮放     
    /// </summary>     
    /// <param name="postedfile">原圖地址加名稱</param>     
    /// <param name="savepath">縮略圖存放地址</param>     
    /// <param name="smallname">縮略圖名稱</param>     
    /// <param name="targetwidth">指定的最大寬度</param>     
    /// <param name="targetheight">指定的最大高度</param>     
    public static void zoomauto(string initpath, string savepath,string smallname, double targetwidth, double targetheight)     
    {         
        //虛擬路徑轉絕對路徑         
        initpath = System.Web.HttpContext.Current.Server.MapPath(initpath);         
        savepath = System.Web.HttpContext.Current.Server.MapPath(savepath);         
        //創建目錄         
        string dir = Path.GetDirectoryName(savepath);         
        if (!Directory.Exists(dir))             
            Directory.CreateDirectory(dir);  
        
        //原始圖片（獲取原始圖片創建對象，並使用流中嵌入的顏色管理信息）         
        System.Drawing.Image initimage = System.Drawing.Image.FromFile(initpath);  
        //原圖寬高均小於模版，不作處理，直接保存         
        if (initimage.Width <= targetwidth && initimage.Height <= targetheight)         
        {             
            //保存             
            initimage.Save(savepath + smallname, System.Drawing.Imaging.ImageFormat.Jpeg);         
        }         
        else         
        {             
            //縮略圖寬、高計算             
            double newwidth = initimage.Width;             
            double newheight = initimage.Height;  
            //寬大於高或寬等於高（橫圖或正方）             
            if (initimage.Width > initimage.Height || initimage.Width == initimage.Height)             
            {                 
                //如果寬大於模版                 
                if (initimage.Width > targetwidth) 
                {                     
                    //寬按模版，高按比例縮放                     
                    newwidth = targetwidth;                     
                    newheight = initimage.Height * (targetwidth / initimage.Width);                 
                }             
            }             
            //高大於寬（豎圖）             
            else             
            {                 
                //如果高大於模版                 
                if (initimage.Height > targetheight)                 
                {                     
                    //高按模版，寬按比例縮放                     
                    newheight = targetheight;                     
                    newwidth = initimage.Width * (targetheight / initimage.Height);                 
                }             
            }  
            
            //生成新圖             
            //新建一個bmp圖片             
            System.Drawing.Image newimage = new System.Drawing.Bitmap((int)newwidth, (int)newheight);             
            //新建一個畫板             
            System.Drawing.Graphics newg = System.Drawing.Graphics.FromImage(newimage);  
            //設置質量             
            newg.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;             
            newg.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;  
            //置背景色             
            newg.Clear(System.Drawing.Color.White);             
            //畫圖             
            newg.DrawImage(initimage, new System.Drawing.Rectangle(0, 0, newimage.Width, newimage.Height), new System.Drawing.Rectangle(0, 0, initimage.Width, initimage.Height), System.Drawing.GraphicsUnit.Pixel);  
            //保存縮略圖             
            newimage.Save(savepath + smallname, System.Drawing.Imaging.ImageFormat.Jpeg);  
            //釋放資源             
            newg.Dispose();             
            newimage.Dispose();             
            initimage.Dispose(); 
        
        }     
    }  
}