图片超过指定大小后等比例压缩图片

/// <summary>
/// 压缩图片
/// </summary>
/// <returns></returns>
public string ResizePic()
{
#region 压缩图片开始
bool IsImgFile = true;  //判断是否为图片文件
string filePathName = "123";   //文件存储的路径（文件夹名称）
string fileName = "a.jpg";   //上传文件的原始名称
string fileSysName = DateTime.Now.ToString("yyyyMMddHHmmssfff") + "_" + fileName;  //修改后的文件名称
string filePath = "";   //文件路径
string strImgPath = "/fileupload/";   //上传路径
if (IsImgFile)
{
int maxWidth = 600;   //图片宽度最大限制
int maxHeight = 400;  //图片高度最大限制
System.Drawing.Image imgPhoto =
System.Drawing.Image.FromFile(Server.MapPath(strImgPath) + filePathName + "/" + fileSysName);
int imgWidth = imgPhoto.Width;
int imgHeight = imgPhoto.Height;
if (imgWidth > imgHeight)  //如果宽度超过高度以宽度为准来压缩
{
if (imgWidth > maxWidth)  //如果图片宽度超过限制
{
float toImgWidth = maxWidth;   //图片压缩后的宽度
float toImgHeight = imgHeight / (float)(imgWidth / toImgWidth); //图片压缩后的高度

System.Drawing.Bitmap img = new System.Drawing.Bitmap(imgPhoto,
(int)toImgWidth,
(int)toImgHeight);
string strResizePicName = Server.MapPath(strImgPath) + filePathName + "/_small_" + fileSysName;
img.Save(strResizePicName);  //保存压缩后的图片
filePath = strImgPath + filePathName + "/_small_" + fileSysName;  //返回压缩后的图片路径
}
}
else
{
if (imgHeight > maxHeight)
{
float toImgHeight1 = maxHeight;
float toImgWidth1 = imgWidth / (float)(imgHeight / toImgHeight1);

System.Drawing.Bitmap img = new System.Drawing.Bitmap(imgPhoto,
(int)toImgWidth1,
(int)toImgHeight1);
string strResizePicName = Server.MapPath(strImgPath) + filePathName + "/_small_" + fileSysName;
img.Save(strResizePicName);
filePath = strImgPath + filePathName + "/_small_" + fileSysName;
}
}
}
return filePath;
#endregion
}