c# bmp图片转 jpg格式

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Linq;
using System.Windows.Forms;
using System.IO;
using System.Drawing.Imaging;

namespace BMPChangeJPG
{
    public partial class Frm_Main : Form
    {
        Bitmap bitmap;//定义Bitmap类
        public Frm_Main（）
        {
            InitializeComponent（）;
        }

        private void buttonOpen_Click（object sender EventArgs e）
        {
            OpenFileDialog openFileDialog = new OpenFileDialog（）;		//实例化OpenFileDialog类
            openFileDialog.Filter = “*.bmp|*.bmp“;						//设置文件类型
            openFileDialog.title = “打开图像文件“;						//设置“打开文件”对话框的标题
            openFileDialog.Multiselect = false;							//只能

 属性            大小     日期    时间   名称
----------- ---------  ---------- -----  ----
     目录           0  2013-05-20 07:02  BMPChangeJPG\
     文件         926  2013-05-20 07:02  BMPChangeJPG.sln
     文件       18944  2010-11-04 01:45  BMPChangeJPG.suo
     目录           0  2011-12-22 23:11  BMPChangeJPG\bin\
     目录           0  2011-12-22 23:13  BMPChangeJPG\bin\Debug\
     文件        3839  2010-11-04 01:44  BMPChangeJPG\BMPChangeJPG.csproj
     文件         452  2013-05-20 07:02  BMPChangeJPG\BMPChangeJPG.csproj.user
     文件        4619  2010-07-13 00:13  BMPChangeJPG\Frm_Main.cs
     文件        7112  2010-07-08 21:48  BMPChangeJPG\Frm_Main.designer.cs
     文件        5814  2010-07-08 21:48  BMPChangeJPG\Frm_Main.resx
     目录           0  2011-12-22 23:11  BMPChangeJPG\obj\
     目录           0  2011-12-22 23:14  BMPChangeJPG\obj\Debug\
     文件        2236  2010-11-04 01:44  BMPChangeJPG\obj\Debug\BMPChangeJPG.csproj.FileListAbsolute.txt
     目录           0  2011-12-22 23:11  BMPChangeJPG\obj\Debug\Refactor\
     目录           0  2011-12-22 23:11  BMPChangeJPG\obj\Debug\TempPE\
     文件         496  2010-07-08 21:48  BMPChangeJPG\Program.cs
     目录           0  2011-12-22 23:11  BMPChangeJPG\Properties\
     文件        1356  2010-07-08 21:48  BMPChangeJPG\Properties\AssemblyInfo.cs
     文件        2874  2010-07-08 21:48  BMPChangeJPG\Properties\Resources.Designer.cs
     文件        5612  2010-07-08 21:48  BMPChangeJPG\Properties\Resources.resx
     文件        1097  2010-07-08 21:48  BMPChangeJPG\Properties\Settings.Designer.cs
     文件         249  2010-07-08 21:48  BMPChangeJPG\Properties\Settings.settings