C#实现图象放缩

/// <summary>
  /// 房缩图片
  /// </summary>
  /// <param name="bm">原Bitmap对象</param>  
  /// <param name="xStart">要放缩的起点x坐标</param>
  /// <param name="yStart">要放缩的起点y坐标</param>
  /// <param name="xEnd">要放缩的终点x坐标</param>
  /// <param name="yEnd">要放缩的终点y坐标</param>
  /// <returns>放缩的Bitmap对象</returns>
  public Bitmap drawImage(Bitmap bm,int xStart,int yStart,int xEnd,int yEnd)
  {
   try
   {
    Bitmap newBitmap=new Bitmap(800,80);
    System.Drawing.Graphics g=Graphics.FromImage(newBitmap);
    GraphicsUnit units = GraphicsUnit.Pixel;
    //放缩后的大小
    Rectangle rect=new Rectangle(0,0,800,800);
    g.DrawImage(bm,rect,xStart,yStart,xEnd,yEnd,units);
    return newBitmap;
   }
   catch(Exception e)
   {
    MessageBox.Show(e.Message.ToString());
    return null;
   }
  }