Upload image, rename it, make thumbnail and replace the original. (optimization)

I have created these functions which I described in the question. However I think the way I did it is not the optimal way of doing it.

        [HttpPost]
        public ActionResult Create(FormCollection collection, string schooljaarparam, FlatONASAanbieder foa) {

        if (ModelState.IsValid) {

            // var r = new List<ViewDataUploadFilesResult>();

            foreach (string file in Request.Files) {
                HttpPostedFileBase hpf = Request.Files[file] as HttpPostedFileBase;
                if (hpf.ContentLength == 0)
                    continue;

                //extensie nakijken. jpg, png, jpeg, of GIF. 
                if (MvcApplication.isImage(hpf.FileName)) {
                    //Image img = new Image();


                    string savedFileName = Path.Combine(
                       AppDomain.CurrentDomain.BaseDirectory + "uploads\\ONAS\\",
                       Path.GetFileName(hpf.FileName));
                    FileInfo fi = new FileInfo(savedFileName);

                    int i = 1;
                    while (fi.Exists) {
                        fi = new FileInfo(savedFileName.Substring(0, savedFileName.Length - Path.GetFileName(savedFileName).Length) + Path.GetFileNameWithoutExtension(savedFileName) + " (" + i++ + ") " + Path.GetExtension(savedFileName));
                    }
                    savedFileName = fi.DirectoryName + "\\" + fi.Name;
                    hpf.SaveAs(savedFileName);

                    using (Image Img = Image.FromFile(savedFileName)) {
                        //Size ThumbNailSize = NewImageSize(Img.Height, Img.Width, 79);
                        Size NewSize = VerkleinMaxHoogte(Img.Size, 79);

                        using (Image ImgThnail = new Bitmap(Img, NewSize.Width, NewSize.Height)) {
                            //string ss = savedFileName.Substring(0, savedFileName.Length - Path.GetFileName(savedFileName).Length) + Path.GetFileNameWithoutExtension(savedFileName) + "-thumb" + Path.GetExtension(savedFileName);
                            ImgThnail.Save(savedFileName + ".tmp", Img.RawFormat);
                            ImgThnail.Dispose();
                        }
                        Img.Dispose();
                    }
                    System.IO.File.Delete(savedFileName);
                    FileInfo f = new FileInfo(savedFileName + ".tmp");
                    f.MoveTo(savedFileName);


                } else {
                    ModelState.AddModelError("ONAS_Logo", "Het geuploadde bestand is geen afbeelding. ");

                }

                //r.Add(new ViewDataUploadFilesResult() {
                //    Name = savedFileName,
                //    Length = hpf.ContentLength
                //});
            }
        }

        // return View("UploadedFiles", r);

        return View();
    }


    [NonAction]
    public Size VerkleinMaxHoogte(Size orig, double height) {
        double tempval = height / orig.Height;

        return new Size(Convert.ToInt32(tempval * orig.Width), Convert.ToInt32(height));
    }

in global.asax

    public static bool isImage(string s) {
        if (s.EndsWith(".jpg", true, null) || s.EndsWith(".jpeg", true, null) || s.EndsWith(".gif", true, null) || s开发者_StackOverflow中文版.EndsWith(".png", true, null)) {
            return true;
        }
        return false;
    }

so the way I do it:

1. I get the file from the browser
2. I check if it is an Image
3. I check if the file exists, and if so, change the filename accordingly
4. I save the file on disk (IO, slow)
5. I open the file as an image
6. I calculate the width and height with the VerkleinMaxHoogte method
7. I create the thumbnail and save it with a tmp extension
8. I delete the original file
9. I rename the thumbnail to the original file name (this is what I want)

How do I do it faster?

You can always use HttpPostedFile.InputStream and Image.FromStream method to combine #4 & #5. This will also eliminate #8 & #9.