ASP.NET 按规定尺寸缩放图片

public string ImgFileUp(HttpPostedFile HPF, string saveDir)
{
string returnStr1 = "";
string Extension = new FileInfo(HPF.FileName).Extension;

#region  保存原始文件
//清除多余字符串
saveDir = saveDir.TrimEnd('/').TrimStart('/');
//获取上传日期
string time = string.Concat("/", DateTime.Now.ToString("yyyyMMdd"));
//判读上传文件夹是否存在
bool existDir = Directory.Exists(Server.MapPath(string.Concat("~/", saveDir, time)));
//不存在文件夹,自动创建
if (!existDir)
{
//创建文件夹
Directory.CreateDirectory(Server.MapPath(string.Concat("~/", saveDir, time)));
}
//上传的最初文件名+后缀
string dbImageName = "";
if (n == false)
{

dbImageName = System.IO.Path.GetFileName(HPF.FileName);
}
else
{
dbImageName = Guid.NewGuid() + DateTime.Now.ToString("yyyyMMddHHmmssfff") + Extension;
}

//上传的图像保存的物理路径
string originalImagePath = Server.MapPath(string.Concat("~/", saveDir, time, "/", dbImageName));
//保存图片
//HPF.SaveAs(originalImagePath);
//string originalImagePath = Server.MapPath("/" + saveDir + "/" + time + "/" + dbImageName);
//生成压缩文件
System.Drawing.Image originalImage = System.Drawing.Image.FromStream(HPF.InputStream);
int maxWidth =900;   //图片宽度最大限制
int maxHeight = 900;  //图片高度最大限制
int imgWidth = originalImage.Width;
int imgHeight = originalImage.Height;
if (imgHeight > maxHeight || imgWidth>maxWidth)  //如果宽度超或者高度超过进行压缩
{
if (imgWidth > imgHeight)
{
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
//新建一个bmp图片
System.Drawing.Image img = new System.Drawing.Bitmap(Convert.ToInt32(toImgWidth), Convert.ToInt32(toImgHeight));

Graphics g = System.Drawing.Graphics.FromImage(img);//新建画板
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;//设置高质量插值法
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;//设置高质量,低速度呈现平滑程度
g.Clear(Color.Transparent);//清空画布
g.DrawImage(originalImage, new Rectangle(0, 0, Convert.ToInt32(toImgWidth), Convert.ToInt32(toImgHeight)), new System.Drawing.Rectangle(0, 0, imgWidth, imgHeight), GraphicsUnit.Pixel);//绘制原图片
img.Save(originalImagePath, System.Drawing.Imaging.ImageFormat.Jpeg);

originalImage.Dispose();
img.Dispose();
g.Dispose();
}
}
else
{
if (imgHeight > maxHeight)
{
float toImgHeight = maxHeight;  //图片压缩后的高度
float toImgWidth = imgWidth / (float)(imgHeight / toImgHeight); //图片压缩后的宽度
//新建一个bmp图片
System.Drawing.Image img = new System.Drawing.Bitmap(Convert.ToInt32(toImgWidth), Convert.ToInt32(toImgHeight));

Graphics g = System.Drawing.Graphics.FromImage(img);//新建画板
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;//设置高质量插值法
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;//设置高质量,低速度呈现平滑程度
g.Clear(Color.Transparent);//清空画布
g.DrawImage(originalImage, new Rectangle(0, 0, Convert.ToInt32(toImgWidth), Convert.ToInt32(toImgHeight)), new System.Drawing.Rectangle(0, 0, imgWidth, imgHeight), GraphicsUnit.Pixel);//绘制原图片
img.Save(originalImagePath, System.Drawing.Imaging.ImageFormat.Jpeg);

originalImage.Dispose();
img.Dispose();
g.Dispose();

}
}
}
else
{
HPF.SaveAs(originalImagePath);
}

returnStr1 = time + "/" + dbImageName;
#endregion

return returnStr1;
}