Zopfli Library Improves Zlib Compression by 3 to 8%

Google developers have released a new compression library called Zopfli. This library, written in C, is compatible with zlib, yet provide a better compression, more exactly 3 to 8% according to Google.

This library can be used on servers for better compression in order to save bandwidth, as well as delivering web pages faster. Since it’s fully compatible with zlib, the web browsers do not need to be changed. The only drawback is that it’s several magnitude slower than zlib, so it’s better used for static content that is compressed once, and sent over the Internet many times, and it may not be a good choice for dynamic content.

The source code is available at https://code.google.com/p/zopfli/, so let’s try it.

Get the code and build zopfli:

git clone https://code.google.com/p/zopfli/
cd zopfli
make

git clone https://code.google.com/p/zopfli/

cd zopfli

make

Different levels of compression are available:

./zopfli -h
Usage: zopfli [OPTION]... FILE
  -h    gives this help
  -c    write the result on standard output, instead of disk filename + '.gz'
  -v    verbose mode
  --gzip  output to gzip format (default)
  --deflate  output to deflate format instead of gzip
  --zlib  output to zlib format instead of gzip
  --i5  less compression, but faster
  --i10  less compression, but faster
  --i15  default compression, 15 iterations
  --i25  more compression, but slower
  --i50  more compression, but slower
  --i100  more compression, but slower
  --i250  more compression, but slower
  --i500  more compression, but slower
  --i1000  more compression, but slower

./zopfli -h

Usage: zopfli [OPTION]... FILE

-h gives this help

-c write the result on standard output, instead of disk filename + '.gz'

-v verbose mode

--gzip output to gzip format (default)

--deflate output to deflate format instead of gzip

--zlib output to zlib format instead of gzip

--i5 less compression, but faster

--i10 less compression, but faster

--i15 default compression, 15 iterations

--i25 more compression, but slower

--i50 more compression, but slower

--i100 more compression, but slower

--i250 more compression, but slower

--i500 more compression, but slower

--i1000 more compression, but slower

For testing purpose, I’ve just saved this blog as one html file (test.html – 67275 bytes) with different options to see the compression improvements and time it takes with zopfli.

Command line used for the test:

time ./zopfli --i15 test.html &amp;&amp;  ls-l test.html.gz

1	time ./zopfli --i15 test.html && ls-l test.html.gz

Here are the results (The first line is the compression with gzip (gzip -9 test.html):

Option	File Size (Bytes)	Improvement	Time (s)
Gzip -9	15337		0.011
i5	14942	2.58%	0.186
i10	14942	2.58%	0.287
i15	14942	2.58%	0.394
i25	14939	2.60%	0.619
i50	14937	2.61%	1.131
i100	14937	2.61%	2.199
i250	14934	2.63%	5.335
i500	14934	2.63%	11.679
i1000	14934	2.63%	21.412

If you run zopfli without options it will output to gzip format with 15 iterations (i15). With this particular html file, zopfli can achieve around 2.6% better compression than gzip -9, but it’s way slower on my machine, with the fastest option being about 17x slower.

Running gzip -d test.html.gz on a file compressed with zopfli, just works as advertised.

Jean-Luc Aufranc (CNXSoft)

Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.