jquery.imgareaselect实现图片的本地预览和选择截取实现代码

 protected void Page_Load(object sender, EventArgs e)
        {
            if (IsPostBack)
            {
                int x1 = Convert.ToInt32(Request["x1"]);
                int y1 = Convert.ToInt32(Request["y1"]);
                int x2 = Convert.ToInt32(Request["x2"]);
                int y2 = Convert.ToInt32(Request["y2"]);

                HttpFileCollection files = Request.Files;
                for (int i = 0; i < files.Count; i++)
                {
                    HttpPostedFile file = files[i];
                    file.SaveAs(Server.MapPath("Upload/" + file.FileName));

                    //设置缩略图
                    int Thumbnailwidth = 400;
                    int Thumbnailheight = 300;
                    //新建一个bmp图片 
                    Bitmap bitmap = new Bitmap(Thumbnailwidth, Thumbnailheight);

                    //新建一个画板 
                    Graphics graphic = Graphics.FromImage(bitmap);

                    //设置高质量插值法 
                    graphic.InterpolationMode = InterpolationMode.High;

                    //设置高质量,低速度呈现平滑程度 
                    graphic.SmoothingMode = SmoothingMode.HighQuality;

                    //清空画布并以透明背景色填充 
                    graphic.Clear(System.Drawing.Color.Transparent);

                    //原图片
                    Bitmap originalImage = new Bitmap(file.InputStream);

                    //在指定位置并且按指定大小绘制原图片的指定部分 
                    graphic.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, Thumbnailwidth, Thumbnailheight),
                        new System.Drawing.Rectangle(0, 0, originalImage.Width, originalImage.Height),
                        System.Drawing.GraphicsUnit.Pixel);

                    //得到缩略图
                    System.Drawing.Image ThumbnailImage = System.Drawing.Image.FromHbitmap(bitmap.GetHbitmap());

                    //创建选择图片
                    Bitmap selectbitmap = new Bitmap(x2-x1, y2-y1);

                    //新建一个画板 
                    Graphics selectgraphic = Graphics.FromImage(selectbitmap);
                  

                    //裁切
                    selectgraphic.DrawImage(ThumbnailImage, 0, 0, new Rectangle(x1, y1, x2 - x1, y2 - y1), GraphicsUnit.Pixel);

                    //保存
                    selectbitmap.Save(Server.MapPath("Upload/"+Guid.NewGuid() + file.FileName), ImageFormat.Jpeg);

                   //todo:将上述资源释放

                }
            }
        }