如何在C#中实现图片缩放

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//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
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/// <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=Convert.ToInt32(((intWidth*1.0) / (objPic.Width*1.0)) * objPic.Height);
objNewPic=new System.Drawing.Bitmap(objPic,intWidth,intHeight);
objNewPic.Save(strNewPic,objPic.RawFormat);

}
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=Convert.ToInt32(((intHeight*1.0) / objPic.Height) * objPic.Width);
objNewPic=new System.Drawing.Bitmap(objPic,intWidth,intHeight);
objNewPic.Save(strNewPic,objPic.RawFormat);

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

*/

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//盛天 2004-11-5
//QQ：37878073(希望和大家一起来交流)