C# 将前端传来的图片文件分别以大图和缩略图保存

　　　 HttpPostedFile pic_upload = Request.Files["file"];
      Bitmap bitmap = (Bitmap)System.Drawing.Image.FromStream(pic_upload.InputStream);
      Size s = new Size();
      s.Height = 50;
      s.Width = 50;
      System.Drawing.Image minImage =  clsPublic.GetImageThumb(bitmap, s);　　　　

　　//下面这部分不重要,主要内容是在上面,有缩略图和原图后,直接按照常规的方法进行保存即可

string fileExtension = Path.GetExtension(pic_upload.FileName).ToLower();
string filepath = "~/upload/" + kis_web.DBHelper.sAcctNumber + "/files/";//图片存储路径:uppad+账套编号+images
string activitecode = Guid.NewGuid().ToString().Replace("-", "");
if (Directory.Exists(Server.MapPath(filepath)) == false)//如果不存在就创建file文件夹
{
Directory.CreateDirectory(Server.MapPath(filepath));
}
string virpath = filepath + activitecode + fileExtension;//这是存到服务器上的虚拟路径
string virMinpath = filepath + activitecode+"_min" + fileExtension;

 转缩略图方法

  public static Bitmap GetImageThumb(Bitmap mg, Size newSize)
  {
    double ratio = 0d;
    double myThumbWidth = 0d;
    double myThumbHeight = 0d;
    int x = 0;
    int y = 0;

    Bitmap bp;
    if (newSize.Width == 0)
    {
      newSize.Width = 1;
    }
    if (newSize.Height == 0)
    {
      newSize.Height = 1;
    }
    if ((mg.Width / Convert.ToDouble(newSize.Width)) > (mg.Height /
    Convert.ToDouble(newSize.Height)))
      ratio = Convert.ToDouble(mg.Width) / Convert.ToDouble(newSize.Width);
    else
      ratio = Convert.ToDouble(mg.Height) / Convert.ToDouble(newSize.Height);
    myThumbHeight = Math.Ceiling(mg.Height / ratio);
    myThumbWidth = Math.Ceiling(mg.Width / ratio);

    Size thumbSize = new Size((int)newSize.Width, (int)newSize.Height);
    bp = new Bitmap(newSize.Width, newSize.Height);
    x = (newSize.Width - thumbSize.Width) / 2;
    y = (newSize.Height - thumbSize.Height);
    System.Drawing.Graphics g = Graphics.FromImage(bp);
    g.SmoothingMode = SmoothingMode.HighQuality;
    g.InterpolationMode = InterpolationMode.HighQualityBicubic;
    g.PixelOffsetMode = PixelOffsetMode.HighQuality;
    Rectangle rect = new Rectangle(x, y, thumbSize.Width, thumbSize.Height);
    g.DrawImage(mg, rect, 0, 0, mg.Width, mg.Height, GraphicsUnit.Pixel);
    return bp;

  }

技术参考：https://www.cnblogs.com/zhangchaoran/p/7693166.html