<s>
Zopfli	B-Application
is	O
a	O
data	B-General_Concept
compression	I-General_Concept
library	B-Library
that	O
performs	O
Deflate	B-Algorithm
,	O
gzip	B-Application
and	O
zlib	B-Language
data	O
encoding	O
.	O
</s>
<s>
It	O
achieves	O
higher	O
compression	O
ratios	O
than	O
mainstream	O
Deflate	B-Algorithm
and	O
zlib	B-Language
implementations	O
at	O
the	O
cost	O
of	O
being	O
slower	O
.	O
</s>
<s>
Google	B-Application
first	O
released	O
Zopfli	B-Application
in	O
February	O
2013	O
under	O
the	O
terms	O
of	O
Apache	B-Application
License	I-Application
2.0	I-Application
.	O
</s>
<s>
Zopfli	B-Application
can	O
either	O
generate	O
a	O
raw	O
Deflate	B-Algorithm
data	O
stream	O
or	O
encapsulate	O
it	O
into	O
gzip	B-Application
or	O
zlib	B-Language
formats	O
.	O
</s>
<s>
Zopfli	B-Application
achieves	O
higher	O
data	O
density	O
through	O
more	O
exhaustive	O
compression	B-General_Concept
techniques	I-General_Concept
.	O
</s>
<s>
The	O
method	O
is	O
based	O
on	O
iterating	O
entropy	O
modeling	O
and	O
a	O
shortest	O
path	O
search	O
algorithm	O
to	O
find	O
a	O
low	O
bit	O
cost	O
path	O
through	O
the	O
graph	O
of	O
all	O
possible	O
Deflate	B-Algorithm
representations	O
of	O
the	O
uncompressed	B-General_Concept
data	O
.	O
</s>
<s>
By	O
default	O
,	O
Zopfli	B-Application
performs	O
15	O
iterations	O
but	O
could	O
be	O
configured	O
to	O
performed	O
more	O
or	O
fewer	O
.	O
</s>
<s>
Under	O
default	O
settings	O
,	O
the	O
output	O
of	O
Zopfli	B-Application
is	O
typically	O
3	O
–	O
8%	O
smaller	O
than	O
zlib	B-Language
's	O
maximum	O
compression	O
,	O
but	O
takes	O
around	O
80	O
times	O
longer	O
.	O
</s>
<s>
Because	O
of	O
its	O
significantly	O
slower	O
compression	O
speed	O
,	O
Zopfli	B-Application
is	O
not	O
suited	O
for	O
on-the-fly	O
compression	O
.	O
</s>
<s>
This	O
is	O
typically	O
true	O
for	O
web	O
content	O
that	O
is	O
served	O
with	O
Deflate-based	O
HTTP	B-Protocol
compression	I-Protocol
or	O
web	O
content	O
in	O
a	O
Deflate-based	O
file	O
format	O
such	O
as	O
PNG	O
or	O
WOFF	O
font	O
files	O
.	O
</s>
<s>
Another	O
use	O
case	O
is	O
software	O
updates	O
or	O
downloads	O
with	O
software	O
package	O
files	O
that	O
have	O
a	O
zip-based	O
format	O
such	O
as	O
Android	B-Application
application	I-Application
packages	I-Application
(	O
APK	B-Application
)	O
or	O
Java	B-Language
Archives	I-Language
(	O
JAR	B-Language
)	O
,	O
especially	O
over	O
mobile	O
connections	O
.	O
</s>
<s>
Zopfli	B-Application
is	O
based	O
on	O
an	O
algorithm	O
from	O
Jyrki	O
Alakuijala	O
.	O
</s>
<s>
The	O
first	O
reference	O
implementation	O
of	O
Zopfli	B-Application
,	O
by	O
Jyrki	O
Alakuijala	O
and	O
Lode	O
Vandevenne	O
,	O
appeared	O
in	O
February	O
2013	O
.	O
</s>
<s>
The	O
reference	O
implementation	O
is	O
a	O
software	B-Library
library	I-Library
under	O
the	O
terms	O
of	O
Apache	B-Application
License	I-Application
2.0	I-Application
,	O
written	O
in	O
C	B-Language
.	O
</s>
<s>
Since	O
then	O
,	O
the	O
open-source	O
community	O
made	O
attempts	O
to	O
modify	O
Zopfli	B-Application
for	O
optimizing	O
Portable	O
Network	O
Graphics	O
(	O
PNG	O
)	O
files	O
because	O
PNG	O
uses	O
a	O
Deflate	B-Algorithm
compression	O
layer	O
.	O
</s>
<s>
The	O
fruit	O
of	O
these	O
modifications	O
was	O
ZopfliPNG	O
,	O
which	O
was	O
admitted	O
into	O
Google	B-Application
's	I-Application
Zopfli	B-Application
repository	B-General_Concept
in	O
May	O
2013	O
.	O
</s>
<s>
The	O
Zopfli	B-Application
algorithm	O
has	O
also	O
been	O
integrated	O
into	O
other	O
PNG	O
compression	O
optimization	O
tools	O
like	O
advpng	O
(	O
from	O
the	O
AdvanceCOMP	O
utility	O
suite	O
)	O
and	O
OxiPNG	O
.	O
</s>
