文件流，内存流操作，偏移量

内存流例子：

       private void pictureBox1_Click(object sender, EventArgs e)
        {
            OpenFileDialog op = new OpenFileDialog();
            //op.Filter = "JPG图片|*.jpg|PNG图片|*.png";
            op.Filter = "(JPG图片,PNG图片,BMP文件)|*.jpg|*.png|*.bmp";

            if (op.ShowDialog() == DialogResult.OK)
            {
                label1.Text = op.FileName;
                FileStream fs = new FileStream(op.FileName,FileMode.Open);

                byte[] data = new byte[fs.Length];
                fs.Read(data,0,data.Length);
                fs.Close();

                MemoryStream ms = new MemoryStream(data);
                pictureBox1.Image = Image.FromStream(ms);
            }
        }