C#生成缩略图 (通用模式)

用数据库保存图片的路径和文件名称，把文件保存在文件夹中.
//保存在数据库中的文件路径
ArrayList arrFilePath=new ArrayList();
arrFilePath=myCommonMethod.UploadPic(Files,"/UpLoads/UpPicture/");
//获取文件名称
string fileName=arrFilePath[0].SubString(arrFilePath[0].LastIndexOf("/")+1);
//源图路径（物理路径）
originalImagePath=Request.PhysicalApplicationPath+"/UpLoads/UpPicture/"+fileName;
//缩略图路径（物理路径）
thumbnailPath     =Request.PhysicalApplicationPath+"/UpLoads/UpPicture/"+"thumb_"+fileName;
//调用生成缩略图方法
this.MakeThumbnail(originalImagePath,thumbnailPath,120,150, strMode out outthumbnailPath);

#region  生成缩略图 
  ///<summary> 
  /// 生成缩略图 
  /// </summary> 
  /// <param name="originalImagePath">源图路径（物理路径）</param> 
  /// <param name="thumbnailPath">缩略图路径（物理路径）</param> 
  /// <param name="width">缩略图宽度</param> 
  /// <param name="height">缩略图高度</param> 
  /// <param name="mode">生成缩略图的方式</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"://指定高宽缩放（可能变形）                 
     break; 
    case "W"://指定宽，高按比例                     
     toheight = originalImage.Height * width/originalImage.Width; 
     break; 
    case "H"://指定高，宽按比例 
     towidth = originalImage.Width * height/originalImage.Height;                     
     break;         
    case "Cut"://指定高宽裁减（不变形）                 
     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; 
   }     
            
   //新建一个bmp图片 
   System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth,toheight);

   //新建一个画板 
   Graphics g = System.Drawing.Graphics.FromImage(bitmap);

   //设置高质量插值法 
   g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

   //设置高质量,低速度呈现平滑程度 
   g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

   //清空画布并以透明背景色填充 
   g.Clear(Color.Transparent);        

   //在指定位置并且按指定大小绘制原图片的指定部分 
   g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight), 
    new Rectangle(x, y, ow,oh), 
    GraphicsUnit.Pixel);

   try 
   {             
    //以jpg格式保存缩略图 
    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg); 
    outthumbnailPath=thumbnailPath;
   } 
   catch(System.Exception e) 
   { 
    throw e; 
   } 
   finally 
   { 
    originalImage.Dispose(); 
    bitmap.Dispose();                         
    g.Dispose(); 
   } 
  }