//下面给出三个简单的方法，后面两个方法是扩展，估计有时用得着
//************************************************************//
/// <summary>
/// 缩小图片
/// </summary>
/// <param name="strOldPic">源图文件名(包括路径)</param>
/// <param name="strNewPic">缩小后保存为文件名(包括路径)</param>
/// <param name="intWidth">缩小至宽度</param>
/// <param name="intHeight">缩小至高度</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>
/// 按比例缩小图片，自动计算高度
/// </summary>
/// <param name="strOldPic">源图文件名(包括路径)</param>
/// <param name="strNewPic">缩小后保存为文件名(包括路径)</param>
/// <param name="intWidth">缩小至宽度</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>
/// 按比例缩小图片，自动计算宽度
/// </summary>
/// <param name="strOldPic">源图文件名(包括路径)</param>
/// <param name="strNewPic">缩小后保存为文件名(包括路径)</param>
/// <param name="intHeight">缩小至高度</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;
}
}
摘自：http://www.alixixi.com/program/a/2008020624216.shtml