1.Ajax无刷新上传图片,详情请阅我的这篇文章。（jquery + c# ashx）

2.C#位图处理  System.Drawing。

3.最新demo支持IE7,IE8,FireFox。

生成微缩图的核心方法：

CreateThumbnailPicture/// <summary>/// 图片微缩图处理/// </summary>/// <param name="srcPath">源图片</param>/// <param name="destPath">目标图片</param>/// <param name="width">宽度</param>/// <param name="height">高度</param>public static void CreateThumbnailPicture(string srcPath, string destPath, int width, int height){//根据图片的磁盘绝对路径获取 源图片 的Image对象System.Drawing.Image img = System.Drawing.Image.FromFile(srcPath);//bmp： 最终要建立的 微缩图 位图对象。Bitmap bmp = new Bitmap(width, height);//g: 绘制 bmp Graphics 对象Graphics g = Graphics.FromImage(bmp);g.Clear(Color.Transparent);//为Graphics g 对象 初始化必要参数，很容易理解。g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;//源图片宽和高int imgWidth = img.Width;int imgHeight = img.Height;//绘制微缩图g.DrawImage(img, new System.Drawing.Rectangle(0, 0, width, height), new System.Drawing.Rectangle(0, 0, imgWidth, imgHeight), GraphicsUnit.Pixel);ImageFormat format = img.RawFormat;ImageCodecInfo info = ImageCodecInfo.GetImageEncoders().SingleOrDefault(i => i.FormatID == format.Guid);EncoderParameter param = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L);EncoderParameters parameters = new EncoderParameters(1);parameters.Param[0] = param;img.Dispose();//保存已生成微缩图，这里将GIF格式转化成png格式。if (format == ImageFormat.Gif){destPath = destPath.ToLower().Replace(".gif", ".png");bmp.Save(destPath, ImageFormat.Png);}else{if (info != null){bmp.Save(destPath, info, parameters);}else{bmp.Save(destPath, format);}}img.Dispose();g.Dispose();bmp.Dispose();}

下面介绍ashx中AJAX调用方法,我们在AJAX异步上传图片成功后对源图片进行"PS"。关键代码片段如下：

//上传成功后网站内源图片相对路径string relativePath = System.Web.HttpContext.Current.Request.ApplicationPath + string.Format(@"Content/Upload/Images/{0}", fileName);/*比例处理微缩图高度（DefaultHeight属性值为 400）*/System.Drawing.Image img = System.Drawing.Image.FromFile(toFile);int width = img.Width;int height = img.Height;float ratio = (float)width / height;//微缩图高度和宽度int newHeight = height <= DefaultHeight ? height : DefaultHeight;int newWidth = height <= DefaultHeight ? width : Convert.ToInt32(DefaultHeight * ratio);FileInfo generatedfile = new FileInfo(toFile);string newFileName = "Thumb_" + generatedfile.Name;string newFilePath = Path.Combine(generatedfile.DirectoryName, newFileName);PictureHandler.CreateThumbnailPicture(toFile, newFilePath, newWidth, newHeight);string thumbRelativePath = System.Web.HttpContext.Current.Request.ApplicationPath + string.Format(@"/Content/Upload/Images/{0}", newFileName);//返回原图和微缩图的网站相对路径relativePath = string.Format("{0},{1}", relativePath, thumbRelativePath);return relativePath;

demo 见附件http://dl2.iteye.com/upload/attachment/0109/2590/06f8f52b-f228-35c3-9391-6b43bd18e3d6.rar