如何在C#中實現圖片縮放

//************************************************************//
//下面給出三個簡單的方法，後面兩個方法是擴充，估計有時用得著
//************************************************************//
  /// <summary>
  /// 縮小圖片
  /// </summary>
  /// <param name="strOldPic">源圖檔案名稱(包括路徑)</param>
  /// <param name="strNewPic">縮小後儲存為檔案名稱(包括路徑)</param>
  /// <param name="intWidth">縮小至寬度</param>
  /// <param name="intHeight">縮小至高度</param>
  public void SmallPic(string strOldPic, string strNewPic, int intWidth, int intHeight)
  {

   System.Drawing.Bitmap objPic,objNewPic;
   try
   {
    objPic = new System.Drawing.Bitmap(strOldPic);
    objNewPic=new System.Drawing.Bitmap(objPic,intWidth,intHeight);
    objNewPic.Save(strNewPic);

   }
   catch(Exception exp){throw exp;}
   finally
   {
    objPic=null;
    objNewPic=null;
   }
  }

  /// <summary>
  /// 按比例縮小圖片，自動計算高度
  /// </summary>
  /// <param name="strOldPic">源圖檔案名稱(包括路徑)</param>
  /// <param name="strNewPic">縮小後儲存為檔案名稱(包括路徑)</param>
  /// <param name="intWidth">縮小至寬度</param>
  public void SmallPic(string strOldPic, string strNewPic, int intWidth)
  {

   System.Drawing.Bitmap objPic,objNewPic;
   try
   {
    objPic = new System.Drawing.Bitmap(strOldPic);
    int intHeight=(intWidth / objPic.Width) * objPic.Height;
    objNewPic=new System.Drawing.Bitmap(objPic,intWidth,intHeight);
    objNewPic.Save(strNewPic);

   }
   catch(Exception exp){throw exp;}
   finally
   {
    objPic=null;
    objNewPic=null;
   }
  }

  /// <summary>
  /// 按比例縮小圖片，自動計算寬度
  /// </summary>
  /// <param name="strOldPic">源圖檔案名稱(包括路徑)</param>
  /// <param name="strNewPic">縮小後儲存為檔案名稱(包括路徑)</param>
  /// <param name="intHeight">縮小至高度</param>
  public void SmallPic(string strOldPic, string strNewPic, int intHeight)
  {

   System.Drawing.Bitmap objPic,objNewPic;
   try
   {
    objPic = new System.Drawing.Bitmap(strOldPic);
    int intWidth=(intHeight / objPic.Height) * objPic.Width;
    objNewPic=new System.Drawing.Bitmap(objPic,intWidth,intHeight);
    objNewPic.Save(strNewPic);

   }
   catch(Exception exp){throw exp;}
   finally
   {
    objPic=null;
    objNewPic=null;
   }
  }