上传并生成小图

            string simgUrl,bimgUrl;
            try
            {
                string strGuid = DateTime.Now.ToShortDateString() + System.Guid.NewGuid().ToString().ToLower();
                string strFileExt = GiftImgSrc.PostedFile.FileName.Substring(GiftImgSrc.PostedFile.FileName.LastIndexOf("."));
                string savebimgUrl = Server.MapPath(@"../GiftsImg") + @"\bimg\" + strGuid + strFileExt.ToLower();
                GiftImgSrc.PostedFile.SaveAs(savebimgUrl);
                bimgUrl = strGuid + strFileExt ;
                //注意这里要用: savebimgUrl 
                simgUrl = GetThumbNail(savebimgUrl, 150, 170, "white", GiftImgSrc.PostedFile.ContentType.ToString(), GiftImgSrc.PostedFile.InputStream);
            }
            catch(Exception)
            {
                Page.RegisterStartupScript("", @"<script>alert('上传图片与生成图形的过程出错!!\n请重试或查看是否有读写权限!!');</script>");
                return;
            }

        private System.Drawing.Imaging.ImageFormat GetImageType(object strContentType)
        {
            switch(strContentType.ToString().ToLower())
            {
                case "image/pjpeg":
                    return System.Drawing.Imaging.ImageFormat.Jpeg;
                case "image/gif":
                    return System.Drawing.Imaging.ImageFormat.Gif;
                case "image/bmp":
                    return System.Drawing.Imaging.ImageFormat.Bmp;
                case "image/tiff":
                    return System.Drawing.Imaging.ImageFormat.Tiff;
                case "image/x-icon":
                    return System.Drawing.Imaging.ImageFormat.Icon;
                case "image/x-png":
                    return System.Drawing.Imaging.ImageFormat.Png;
                case "image/x-emf":
                    return  System.Drawing.Imaging.ImageFormat.Emf;
                case "image/x-exif":
                     return System.Drawing.Imaging.ImageFormat.Exif;
                case "image/x-wmf":
                    return System.Drawing.Imaging.ImageFormat.Wmf;
                default:
                    return System.Drawing.Imaging.ImageFormat.MemoryBmp;
            }
        }

        private string GetThumbNail(string strFileName,int iWidth,int iHeight,string BgColor,string strContentType,System.IO.Stream ImgStream)
        {
            System.Drawing.Image oImg = System.Drawing.Image.FromFile(strFileName);
            //如果图直接小于生成的上图就直接上传不重生成
            if(oImg.Width < iWidth && oImg.Height < iHeight)
            {
                string strGuid = DateTime.Now.ToShortDateString() + System.Guid.NewGuid().ToString().ToLower();
                string strFileExt = strFileName.Substring(strFileName.LastIndexOf("."));
                //保存图片
                string strSaveUrl = Server.MapPath(@"../GiftsImg") + @"\simg\" +  strGuid + strFileExt.ToLower();
                GiftImgSrc.PostedFile.SaveAs(strSaveUrl);

                return strGuid + strFileExt;
            }
            else
            {
                //小图
                int intwidth, intheight;
                if(oImg.Width > oImg.Height)
                {
                    if(oImg.Width>iWidth)
                    {
                        intwidth = iWidth;
                        intheight = (oImg.Height * iWidth) / oImg.Width;
                    }
                    else
                    {
                        intwidth = oImg.Width;
                        intheight = oImg.Height;
                    }
                }
                else
                {
                    if(oImg.Height > iHeight)
                    {
                        intwidth = (oImg.Width * iHeight) / oImg.Height;
                        intheight = iHeight;
                    }
                    else
                    {
                        intwidth = oImg.Width;
                        intheight = oImg.Height;
                    }
                }

                //oImg = oImg.GetThumbnailImage(iWidth, iheight, Nothing, (New IntPtr).Zero);
                Bitmap b = new Bitmap(intwidth, intheight, PixelFormat.Format24bppRgb);
                Graphics g = Graphics.FromImage(b);
                Color myColor;
                if(BgColor ==null)
                    myColor = Color.FromName("white");
                else
                    myColor = Color.FromName(BgColor);
                g.Clear(myColor);

                //g.DrawImage(oImg, new Rectangle((iWidth - intwidth) / 2, (iHeight - intheight) / 2, intwidth, intheight), new Rectangle(0, 0, oImg.Width, oImg.Height), GraphicsUnit.Pixel);
                g.DrawImage(oImg, new Rectangle(0, 0, intwidth, intheight), new Rectangle(0, 0, oImg.Width, oImg.Height), GraphicsUnit.Pixel);

                string strGuid = DateTime.Now.ToShortDateString() + System.Guid.NewGuid().ToString().ToLower();
                string strFileExt = strFileName.Substring(strFileName.LastIndexOf("."));
                //保存图片
                string strSaveUrl = Server.MapPath(@"../GiftsImg") + @"\simg\" +  strGuid + strFileExt.ToLower();
                b.Save(strSaveUrl,GetImageType(strContentType));
                b.Dispose();
                g.Dispose();

                return strGuid + strFileExt;
            }

        }