public static void CreateSmallImage(string minImageFullPath, System.Drawing.Image originalImage, int x, int y, int size)

    {

        System.Drawing.Image img = null;

        System.Drawing.Graphics graphic = null;

        int ow = originalImage.Width;

        int oh = originalImage.Height;

        int width;

        int height;
　　　　 //最小边宽度为size,按比例生成

        if (ow > oh)

        {

            height = size;

            width = size * ow / oh;

        }

        else

        {

            width = size;

            height = size * oh / ow;

        }

        img = new System.Drawing.Bitmap(width, height);

        graphic = System.Drawing.Graphics.FromImage(img);

        graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

        //设置高质量,低速度呈现平滑程度

        graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

        //清空画布并以透明背景色填充

        graphic.Clear(Color.Transparent);

        //在指定位置并且按指定大小绘制原图片的指定部分ImageFormat.Jpeg

        graphic.DrawImage(originalImage, new Rectangle(, , width, height), new Rectangle(x, y, ow, oh), GraphicsUnit.Pixel);

　　　　 //默认保存格式为ImageFormat.Png图片还是比较大，所以存为ImageFormat.Jpeg格式

        img.Save(minImageFullPath,ImageFormat.Jpeg);

        if (img != null)

        {

            img.Dispose();

        }

        if (graphic != null)

        {

            graphic.Dispose();

        }

    }

System.Drawing.Image image = System.Drawing.Image.FromFile(originalImagePath);

//或 HttpPostedFile file= Request.Files["Filedata"];

//System.Drawing.Image image = System.Drawing.Image.FromStream(file.InputStream);

CreateSmallImage(minFilePath, image, , , );