deflate stream result is disappointing , is it normal?

Question

I'm trying to compress image files to send it via network , here is my test compress method

public void compress(MemoryStream inStream)
    {
        using (MemoryStream outStream = new MemoryStream())
        {
            using (DeflateStream deflate = new DeflateStream(outStream, CompressionMode.Compress, true))
            {
                Console.WriteLine(inStream.Length);
                deflate.Write(inStream.GetBuffer(), 0, (int)inStream.Length);
                deflate.Close();
                Console.WriteLine(outStream.Length);

            }
        }

    }

the result was

375531

354450

I thought when compressing at least I should get 5 digits instead of 6 , is this normal ? am I doing it right ?

Thanks in advance

What format are your images in? A _lot_ of current image formats are already compressed... — Mat, Dec 23 '11 at 07:57
it is a JPG for now , but what I'm compressing is a 'MemoryStream' , I think it should first get compressed well , regardless losing the jpg data after that — Musaab, Dec 23 '11 at 08:06
JPG is already a compressed format. Compressing it again will, statistically, not gain you anything major. The compressed stream could come out _larger_ than the image in corner cases. — Mat, Dec 23 '11 at 08:10

score 3 · Accepted Answer · answered Dec 23 '11 at 08:03

You are probably attempting to compress a stream that cannot be compressed any further.

For instance, lossy image formats like JPEG typically have very little redundant data, so the ability to compress with DeflateStream is minimal.

Note that DeflateStream is intended to compress files on-the-fly while a stream is being read or written, and doesn't assume the whole stream is available during the compression process. Your example has the entire stream in memory, so you can use other "static" styles of compression.

For instance, you may find that you get better results with Zip compression: http://dotnetzip.codeplex.com is a well-regarded library for this.

Even so, for images that are already compressed, expect no better than ~15% compression.

deflate stream result is disappointing , is it normal?

1 Answers1