<s>
Guetzli	B-Language
is	O
a	O
freely	O
licensed	O
JPEG	O
encoder	O
that	O
Jyrki	O
Alakujala	O
,	O
Robert	O
Obryk	O
,	O
and	O
Zoltán	B-Application
Szabadka	I-Application
have	O
developed	O
in	O
Google	B-Application
's	I-Application
Zürich	O
research	O
branch	O
.	O
</s>
<s>
It	O
is	O
named	O
after	O
the	O
Swiss	O
German	O
diminutive	O
expression	O
for	O
biscuits	O
,	O
in	O
line	O
with	O
the	O
names	O
of	O
other	O
compression	O
technology	O
from	O
Google	B-Application
.	I-Application
</s>
<s>
Guetzli	B-Language
optimizes	O
the	O
quantization	B-Algorithm
step	O
of	O
encoding	O
to	O
achieve	O
compression	O
efficiency	O
.	O
</s>
<s>
It	O
constructs	O
custom	O
quantization	B-Algorithm
tables	O
for	O
each	O
file	O
,	O
decides	O
on	O
color	O
subsampling	O
,	O
and	O
quantizes	O
adjacent	O
DCT	B-General_Concept
coefficients	O
to	O
zero	O
,	O
balancing	O
benefits	O
in	O
the	O
run-length	B-Algorithm
encoding	I-Algorithm
of	O
coefficients	O
and	O
preservation	O
of	O
perceived	O
image	O
fidelity	O
.	O
</s>
<s>
Zeroing	O
the	O
right	O
coefficients	O
is	O
the	O
most	O
effective	O
tool	O
in	O
Guetzli	B-Language
,	O
which	O
is	O
used	O
as	O
a	O
makeshift	O
means	O
of	O
spatially	O
adaptive	O
quantization	B-Algorithm
.	O
</s>
<s>
Guetzli	B-Language
uses	O
Butteraugli	O
(	O
another	O
open-source	O
Google	B-Application
project	O
)	O
to	O
guide	O
compression	O
.	O
</s>
<s>
Guetzli	B-Language
is	O
resource-intensive	O
,	O
requiring	O
orders	O
of	O
magnitude	O
more	O
processing	O
time	O
and	O
random-access	B-Architecture
memory	I-Architecture
than	O
other	O
JPEG	O
encoders	O
.	O
</s>
<s>
Guetzli	B-Language
supports	O
only	O
the	O
top	O
of	O
JPEG	O
's	O
quality	O
range	O
(	O
quantizer	O
settings	O
84	O
–	O
100	O
)	O
and	O
supports	O
only	O
sequential	O
(	O
non-	O
"	O
progressive	O
"	O
)	O
encoding	O
.	O
</s>
<s>
Guetzli	B-Language
is	O
more	O
effective	O
with	O
bigger	O
files	O
.	O
</s>
<s>
Google	B-Application
says	O
it	O
is	O
a	O
demonstration	O
of	O
the	O
potential	O
of	O
psychovisual	O
optimizations	O
,	O
intended	O
to	O
motivate	O
further	O
research	O
into	O
future	O
JPEG	O
encoders	O
.	O
</s>
<s>
Two	O
tests	O
found	O
that	O
Guetzli	B-Language
is	O
very	O
slow	O
(	O
about	O
4	O
magnitudes	O
slower	O
than	O
normal	O
JPEG	O
encoder	O
)	O
and	O
not	O
necessarily	O
better	O
than	O
mozjpeg	O
.	O
</s>
<s>
It	O
is	O
significantly	O
more	O
complex	O
than	O
traditional	O
metrics	O
like	O
PSNR	O
and	O
SSIM	B-Algorithm
,	O
but	O
claimed	O
to	O
perform	O
better	O
with	O
high-end	O
quality	O
,	O
where	O
degradations	O
are	O
not	O
or	O
barely	O
noticeable	O
.	O
</s>
<s>
It	O
uses	O
a	O
heat	B-Application
map	I-Application
of	O
changes	O
.	O
</s>
<s>
An	O
in-house	O
performance	O
evaluation	O
with	O
614	O
ratings	O
from	O
23	O
people	O
on	O
their	O
own	O
test	O
set	O
of	O
31	O
images	O
yielded	O
75%	O
of	O
ratings	O
favouring	O
of	O
JPEGs	O
encoded	O
for	O
Butteraugli	O
scores	O
over	O
libjpeg-turbo	O
encodes	O
,	O
which	O
usually	O
score	O
higher	O
on	O
SSIM	B-Algorithm
and	O
PSNR-HVS-M	O
.	O
</s>
<s>
Guetzli	B-Language
is	O
a	O
command-line	B-Application
app	O
.	O
</s>
<s>
Written	O
in	O
C++	B-Language
,	O
it	O
is	O
free	B-License
and	I-License
open-source	I-License
under	O
the	O
terms	O
of	O
Apache	B-Application
License	I-Application
2.0	I-Application
.	O
</s>
<s>
Windows	O
,	O
macOS	B-Application
,	O
and	O
Linux	B-Application
versions	O
of	O
Guetzli	B-Language
are	O
directly	O
available	O
from	O
Google	B-Application
's	I-Application
repository	O
on	O
GitHub	B-Application
.	O
</s>
<s>
In	O
addition	O
to	O
official	O
release	O
channel	O
,	O
openSUSE	B-Operating_System
and	O
Debian	O
distribute	O
it	O
via	O
their	O
official	O
software	B-Application
repositories	I-Application
.	O
</s>
<s>
(	O
For	O
Arch	O
Linux	B-Application
,	O
there	O
are	O
user	O
repositories	O
available	O
.	O
)	O
</s>
<s>
The	O
Homebrew	B-Application
repository	O
distributes	O
a	O
macOS	B-Application
version	O
.	O
</s>
<s>
Software	O
developers	O
that	O
use	O
Node.js	B-Language
can	O
integrate	O
Guetzli	B-Language
in	O
their	O
apps	O
via	O
a	O
package	O
available	O
on	O
the	O
npm	B-Language
repository	O
.	O
</s>
