string outFileName = FileSystem.ConvertPathFrom + "temp.jpg";

            System.Drawing.Image img = System.Drawing.Image.FromFile(filename);

            int w, h;
            if (img.Width > 5000 || img.Height > 5000)
            {
                w = img.Width / 10;
                h = img.Height / 10;
            }
            else
            {
                w = img.Width;
                h = img.Height;
            }

            System.Drawing.Bitmap bmSave = new System.Drawing.Bitmap(w, h);     //用于保存图片的位图对象

            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bmSave);
            g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighSpeed;
            System.Drawing.Rectangle rDes = new System.Drawing.Rectangle(0, 0, w, h);
            System.Drawing.Rectangle rScr = new System.Drawing.Rectangle(0, 0, img.Width, img.Height);
            g.DrawImage(img, r, r, System.Drawing.GraphicsUnit.Pixel);

            bmSave.Save(outFileName, System.Drawing.Imaging.ImageFormat.Jpeg);

            filename = outFileName;

            g.Dispose();
            bmSave.Dispose();
            img.Dispose();