GZipStream and DeflateStream produce bigger files

Question

I'm trying to use deflate/gzip streams in C# but it appears that the files after compression are bigger than before.

For example, I compress a docx file of 900ko, but it produce a 1.4Mo one !

And it does it for every file I tried.

May be I am wrong in the way I'm doing it? Here is my code :

  FileStream input = File.OpenRead(Environment.CurrentDirectory + "/file.docx");
  FileStream output = File.OpenWrite(Environment.CurrentDirectory + "/compressedfile.dat");

  GZipStream comp = new GZipStream(output, CompressionMode.Compress);

  while (input.Position != input.Length)
      comp.WriteByte((byte)input.ReadByte());

  input.Close();

  comp.Close(); // automatically call flush at closing
  output.Close();

Answer 1

Such a big difference seems strange to me, but you should keep in mind that docx is itself compressed in ZIP, so there is no reason to compress it again, results usually are bigger.

Answer 2

Firstly, deflate/gzip streams are remarkably bad at compression when compared to zip, 7z, etc.

Secondly, docx (and all of the MS document formats with an 'x' at the end) are just .zip files anyway. Rename a .docx to .zip to reveal the smoke and mirrors.

So when you run deflate/gzip over a docx, it will actually make the file bigger. (Its like doing a zip with a low level of compression over a zipped file with a high level of compression.)

However if you run deflate/gzip over HTML or a text file or something that is not compressed then it will actually do a pretty good job.