asp.net生成高质量缩略图通用函数(c#代码)

/**////   <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   static   void   MakeThumbnail(string   originalImagePath,   string   thumbnailPath,   int   width,   int   height,   string   mode)   
                  {   
                          Image   originalImage   =   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   
                          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);   
                          }   
                          catch(System.Exception   e)   
                          {   
                                  throw   e;   
                          }   
                          finally   
                          {   
                                  originalImage.Dispose();   
                                  bitmap.Dispose();                                                   
                                  g.Dispose();   
                          }   
                  }   
    
  关键方法Graphics.DrawImage见ms-help://MS.NETFrameworkSDKv1.1.CHS/cpref/html/frlrfsystemdrawinggraphicsclassdrawimagetopic11.htm