using System; 
using System.Collections.Generic; 
using System.ComponentModel; 
using System.Data; 
using System.Drawing; 
using System.Linq; 
using System.Text; 
using System.Windows.Forms; 
using System.Drawing.Imaging; 
using System.IO; 
namespace WindowsFormsApplication51 
{ 
  public partial class Form1 : Form 
  { 
    public Form1() 
    { 
      InitializeComponent(); 
    } 
    string filename = "";//文件名 
    //文件菜单下的“打开”按钮 
    private void menuOpen_Click(object sender, EventArgs e) 
    { 
      OpenFileDialog of = new OpenFileDialog(); 
      of.Title = "打开文件"; 
      of.Filter = "图像文件|*.bmp;*.gif;*.jpg;*.png"; 
      if (of.ShowDialog() == DialogResult.OK) 
      { 
        filename = of.FileName; 
        pictureBox1.Image = Image.FromFile(filename); 
        pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage; 
      } 
    } 
    //“转换格式”按钮 
    private void menuConvert_Click(object sender, EventArgs e) 
    {   
      ImageFormat[] format = { ImageFormat.Bmp, ImageFormat.Gif, ImageFormat.Jpeg, ImageFormat.Png }; 
      //ImageFormat是using System.Drawing.Imaging;下的方法，用来指定文件的格式 
      Image image = Image.FromFile(filename); 
      SaveFileDialog sf = new SaveFileDialog(); 
      sf.InitialDirectory = Path.GetDirectoryName(filename);//system.io下的path里的GetDirectoryName()方法可以返回指定路径字符串的目录信息 
      sf.FileName = Path.GetFileNameWithoutExtension(filename);//返回不具有扩展名的指定路径字符串的文件名 
      sf.Filter = "位图(*.bmp)|*.bmp|交换图像格式(*.gif)|*.gif|联合图像专家组(*.jpg)|*.jpg;*.jpeg|可移植网络图形(*.png)|*.png"; 
      if (sf.ShowDialog() == DialogResult.OK) 
      { 
        image.Save(sf.FileName, format[sf.FilterIndex - 1]);//选择下拉表的第一个，则对应数组format[0] 
        MessageBox.Show("格式转换成功", "消息"); 
      } 
      else 
      { 
        MessageBox.Show("格式转换不成功", "消息"); 
      } 
    } 
  } 
}