ASP.NET生成缩略图代码

public void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
{
WebRequest wr=WebRequest.Create(originalImagePath);
WebResponse res=wr.GetResponse();
System.Drawing.Image originalImage = System.Drawing.Image.FromStream(res.GetResponseStream());
//System.Drawing.Image.FromFile(originalImagePath);
//originalImagePath 来源路径
//thumbnailPath 目的路径
//width 源图片宽
//height 源图片高
//mode 缩放模式

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;
case "D":
if((double)originalImage.Width>(double)originalImage.Height)
{
toheight = originalImage.Height * width/originalImage.Width;
}
else
{
towidth = originalImage.Width * height/originalImage.Height;
}
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( Server.MapPath(".")+"\\"+thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
}
catch(System.Exception e)
{
throw e;
}
finally
{
originalImage.Dispose();
bitmap.Dispose();
g.Dispose();
}
}