C#生成缩略图 (通用模式)

 转自：

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

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);
   //在指定位置而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();
   }
  }