一个.net缩放图片保存的例子

//原始图片名称
string originalFilename = Server.MapPath("images/original.jpg");
//生成的高质量图片名称
string strGoodFile = Server.MapPath("images/small-good.jpg");
//生成的低质量图片名称
string strBadFile = Server.MapPath("images/small-bad.jpg");
//缩小的倍数
int iScale = 3;
//从文件取得图片对象
System.Drawing.Image image = System.Drawing.Image.FromFile(originalFilename);
//取得图片大小
System.Drawing.Size size = new Size(image.Width / iScale, image.Height / iScale);

//新建一个bmp图片
System.Drawing.Image bitmap = new System.Drawing.Bitmap(size.Width, size.Height);
//新建一个画板
System.Drawing.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;
//清空一下画布
g.Clear(Color.Blue);
//在指定位置画图
g.DrawImage(image, new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height),
            new System.Drawing.Rectangle(0, 0, image.Width, image.Height),
            System.Drawing.GraphicsUnit.Pixel);
//保存高清晰度的缩略图
bitmap.Save(strGoodFile, System.Drawing.Imaging.ImageFormat.Jpeg);
//取得原图像的普通缩略图
System.Drawing.Image img = image.GetThumbnailImage(image.Width / iScale, image.Height / iScale, null, IntPtr.Zero);
//保存普通缩略图
img.Save(strBadFile, System.Drawing.Imaging.ImageFormat.Jpeg);
g.Dispose();
//MessageBox.Show("生成完毕");