A C# method that resizes pictures and maintains their aspect ratio, optionally only if a maximum width is exceeded. The method works with both images that have a higher height than width and viceversa.

1.  public void ResizeImage(string OrigFile, string NewFile, int NewWidth, int MaxHeight, bool ResizeIfWider)
2.  {
3.          System.Drawing.Image FullSizeImage = System.Drawing.Image.FromFile(OrigFile);
4.          // Ensure the generated thumbnail is not being used by rotating it 360 degrees
5.          FullSizeImage.RotateFlip(System.Drawing.RotateFlipType.Rotate180FlipNone);
6.          FullSizeImage.RotateFlip(System.Drawing.RotateFlipType.Rotate180FlipNone);
7.   
8.          if (ResizeIfWider)
9.          {
10.                 if (FullSizeImage.Width <= NewWidth)
11.                 {
12.                         NewWidth = FullSizeImage.Width;
13.                 }
14.         }
15.  
16.         int NewHeight = FullSizeImage.Height * NewWidth / FullSizeImage.Width;
17.         if (NewHeight > MaxHeight) // Height resize if necessary
18.         {
19.                 NewWidth = FullSizeImage.Width * MaxHeight / FullSizeImage.Height;
20.                 NewHeight = MaxHeight;
21.         }
22.  
23.         // Create the new image with the sizes we've calculated
24.         System.Drawing.Image NewImage = FullSizeImage.GetThumbnailImage(NewWidth, NewHeight, null, IntPtr.Zero);
25.         FullSizeImage.Dispose();
26.         NewImage.Save(NewFile);
27. }