C#生成縮略圖 (通用模式)

 轉自：

http://www.cnblogs.com/bokeren/archive/2006/04/10/371313.html

用數據庫保存圖片的路徑和文件名稱，把文件保存在文件夾中.
//保存在數據庫中的文件路徑
ArrayList arrFilePath=new ArrayList();
arrFilePath=myCommonMethod.UploadPic(Files,"/UpLoads/UpPicture/");
//獲取文件名稱
string fileName=arrFilePath[0].SubString(arrFilePath[0].LastIndexOf("/")+1);
//源圖路徑（物理路徑）
originalImagePath=Request.PhysicalApplicationPath+"/UpLoads/UpPicture/"+fileName;
//縮略圖路徑（物理路徑）
thumbnailPath     =Request.PhysicalApplicationPath+"/UpLoads/UpPicture/"+"thumb_"+fileName;
//調用生成縮略圖方法
this.MakeThumbnail(originalImagePath,thumbnailPath,120,150, strMode out outthumbnailPath);

#region  生成縮略圖
  ///<summary>
  /// 生成縮略圖
  /// </summary>
  /// <param name="originalImagePath">源圖路徑（物理路徑）</param>
  /// <param name="thumbnailPath">縮略圖路徑（物理路徑）</param>
  /// <param name="width">縮略圖寬度</param>
  /// <param name="height">縮略圖高度</param>
  /// <param name="mode">生成縮略圖的方式</param>
  public  void MakeThumbnail(string originalImagePath,  string thumbnailPath, int width, int height, string mode out string outthumbnailPath)
  {
   System.Drawing.Image originalImage =System.Drawing.Image.FromFile(originalImagePath);

   int towidth = width;
   int toheight = height;

   int x = 0;
   int y = 0;
   int ow = originalImage.Width;
   int oh = originalImage.Height;
   switch (mode)
   {
    case "HW"://指定高寬縮放（可能變形）
     break;
    case "W"://指定寬，高按比例
     toheight = originalImage.Height * width/originalImage.Width;
     break;
    case "H"://指定高，寬按比例
     towidth = originalImage.Width * height/originalImage.Height;
     break;
    case "Cut"://指定高寬裁減（不變形）
     if((double)originalImage.Width/(double)originalImage.Height > (double)towidth/(double)toheight)
     {
      oh = originalImage.Height;
      ow = originalImage.Height*towidth/toheight;
      y = 0;
      x = (originalImage.Width - ow)/2;
     }
     else
     {
      ow = originalImage.Width;
      oh = originalImage.Width*height/towidth;
      x = 0;
      y = (originalImage.Height - oh)/2;
     }
     break;
    default :
     break;
   }

   //新建一個bmp圖片
   System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth,toheight);
   //新建一個畫板
   Graphics g = System.Drawing.Graphics.FromImage(bitmap);
   //設置高質量插值法
   g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
   //設置高質量,低速度呈現平滑程度
   g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
   //清空畫布並以透明背景色填充
   g.Clear(Color.Transparent);
   //在指定位置並且按指定大小繪製原圖片的指定部分
   g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
    new Rectangle(x, y, ow,oh),
    GraphicsUnit.Pixel);
   try
   {
    //以jpg格式保存縮略圖
    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
    outthumbnailPath=thumbnailPath;
   }
   catch(System.Exception e)
   {
    throw e;
   }
   finally
   {
    originalImage.Dispose();
    bitmap.Dispose();
    g.Dispose();
   }
  }