<s>
In	O
information	O
theory	O
,	O
data	B-General_Concept
compression	I-General_Concept
,	O
source	B-General_Concept
coding	I-General_Concept
,	O
or	O
bit-rate	B-General_Concept
reduction	I-General_Concept
is	O
the	O
process	O
of	O
encoding	O
information	O
using	O
fewer	O
bits	O
than	O
the	O
original	O
representation	O
.	O
</s>
<s>
Any	O
particular	O
compression	O
is	O
either	O
lossy	B-Algorithm
or	O
lossless	B-Algorithm
.	O
</s>
<s>
Lossless	B-Algorithm
compression	I-Algorithm
reduces	O
bits	O
by	O
identifying	O
and	O
eliminating	O
statistical	B-General_Concept
redundancy	I-General_Concept
.	O
</s>
<s>
No	O
information	O
is	O
lost	O
in	O
lossless	B-Algorithm
compression	I-Algorithm
.	O
</s>
<s>
Lossy	B-Algorithm
compression	I-Algorithm
reduces	O
bits	O
by	O
removing	O
unnecessary	O
or	O
less	O
important	O
information	O
.	O
</s>
<s>
Typically	O
,	O
a	O
device	O
that	O
performs	O
data	B-General_Concept
compression	I-General_Concept
is	O
referred	O
to	O
as	O
an	O
encoder	O
,	O
and	O
one	O
that	O
performs	O
the	O
reversal	O
of	O
the	O
process	O
(	O
decompression	O
)	O
as	O
a	O
decoder	O
.	O
</s>
<s>
The	O
process	O
of	O
reducing	O
the	O
size	O
of	O
a	O
data	B-General_Concept
file	I-General_Concept
is	O
often	O
referred	O
to	O
as	O
data	B-General_Concept
compression	I-General_Concept
.	O
</s>
<s>
In	O
the	O
context	O
of	O
data	O
transmission	O
,	O
it	O
is	O
called	O
source	B-General_Concept
coding	I-General_Concept
:	O
encoding	O
done	O
at	O
the	O
source	O
of	O
the	O
data	O
before	O
it	O
is	O
stored	O
or	O
transmitted	O
.	O
</s>
<s>
Source	B-General_Concept
coding	I-General_Concept
should	O
not	O
be	O
confused	O
with	O
channel	O
coding	B-Error_Name
,	O
for	O
error	O
detection	O
and	O
correction	O
or	O
line	B-Protocol
coding	I-Protocol
,	O
the	O
means	O
for	O
mapping	O
data	O
onto	O
a	O
signal	O
.	O
</s>
<s>
Data	B-General_Concept
compression	I-General_Concept
is	O
subject	O
to	O
a	O
space	O
–	O
time	O
complexity	O
trade-off	O
.	O
</s>
<s>
The	O
design	O
of	O
data	B-General_Concept
compression	I-General_Concept
schemes	O
involves	O
trade-offs	O
among	O
various	O
factors	O
,	O
including	O
the	O
degree	O
of	O
compression	O
,	O
the	O
amount	O
of	O
distortion	O
introduced	O
(	O
when	O
using	O
lossy	B-Algorithm
data	I-Algorithm
compression	I-Algorithm
)	O
,	O
and	O
the	O
computational	O
resources	O
required	O
to	O
compress	O
and	O
decompress	O
the	O
data	O
.	O
</s>
<s>
Lossless	B-Algorithm
data	I-Algorithm
compression	I-Algorithm
algorithms	O
usually	O
exploit	O
statistical	B-General_Concept
redundancy	I-General_Concept
to	O
represent	O
data	O
without	O
losing	O
any	O
information	O
,	O
so	O
that	O
the	O
process	O
is	O
reversible	O
.	O
</s>
<s>
Lossless	B-Algorithm
compression	I-Algorithm
is	O
possible	O
because	O
most	O
real-world	O
data	O
exhibits	O
statistical	B-General_Concept
redundancy	I-General_Concept
.	O
</s>
<s>
For	O
example	O
,	O
an	O
image	O
may	O
have	O
areas	O
of	O
color	O
that	O
do	O
not	O
change	O
over	O
several	O
pixels	B-Algorithm
;	O
instead	O
of	O
coding	B-Error_Name
"	O
red	O
pixel	B-Algorithm
,	O
red	O
pixel	B-Algorithm
,	O
...	O
"	O
the	O
data	O
may	O
be	O
encoded	O
as	O
"	O
279	O
red	O
pixels	B-Algorithm
"	O
.	O
</s>
<s>
This	O
is	O
a	O
basic	O
example	O
of	O
run-length	B-Algorithm
encoding	I-Algorithm
;	O
there	O
are	O
many	O
schemes	O
to	O
reduce	O
file	O
size	O
by	O
eliminating	O
redundancy	B-General_Concept
.	O
</s>
<s>
The	O
Lempel	B-Algorithm
–	I-Algorithm
Ziv	I-Algorithm
(	O
LZ	O
)	O
compression	O
methods	O
are	O
among	O
the	O
most	O
popular	O
algorithms	O
for	O
lossless	B-Algorithm
storage	O
.	O
</s>
<s>
DEFLATE	B-Algorithm
is	O
a	O
variation	O
on	O
LZ	O
optimized	O
for	O
decompression	O
speed	O
and	O
compression	O
ratio	O
,	O
but	O
compression	O
can	O
be	O
slow	O
.	O
</s>
<s>
In	O
the	O
mid-1980s	O
,	O
following	O
work	O
by	O
Terry	O
Welch	O
,	O
the	O
Lempel	B-Algorithm
–	I-Algorithm
Ziv	I-Algorithm
–	I-Algorithm
Welch	I-Algorithm
(	O
LZW	B-Algorithm
)	O
algorithm	O
rapidly	O
became	O
the	O
method	O
of	O
choice	O
for	O
most	O
general-purpose	O
compression	O
systems	O
.	O
</s>
<s>
LZW	B-Algorithm
is	O
used	O
in	O
GIF	O
images	O
,	O
programs	O
such	O
as	O
PKZIP	O
,	O
and	O
hardware	O
devices	O
such	O
as	O
modems	O
.	O
</s>
<s>
The	O
table	O
itself	O
is	O
often	O
Huffman	B-General_Concept
encoded	I-General_Concept
.	O
</s>
<s>
Other	O
practical	O
grammar	O
compression	B-General_Concept
algorithms	I-General_Concept
include	O
Sequitur	B-Algorithm
and	O
Re-Pair	B-Algorithm
.	O
</s>
<s>
The	O
strongest	O
modern	O
lossless	B-Algorithm
compressors	O
use	O
probabilistic	B-General_Concept
models	O
,	O
such	O
as	O
prediction	B-Algorithm
by	I-Algorithm
partial	I-Algorithm
matching	I-Algorithm
.	O
</s>
<s>
The	O
Burrows	B-Algorithm
–	I-Algorithm
Wheeler	I-Algorithm
transform	I-Algorithm
can	O
also	O
be	O
viewed	O
as	O
an	O
indirect	O
form	O
of	O
statistical	O
modelling	O
.	O
</s>
<s>
In	O
a	O
further	O
refinement	O
of	O
the	O
direct	O
use	O
of	O
probabilistic	B-General_Concept
modelling	O
,	O
statistical	O
estimates	O
can	O
be	O
coupled	O
to	O
an	O
algorithm	O
called	O
arithmetic	B-Algorithm
coding	I-Algorithm
.	O
</s>
<s>
Arithmetic	B-Algorithm
coding	I-Algorithm
is	O
a	O
more	O
modern	O
coding	B-Error_Name
technique	O
that	O
uses	O
the	O
mathematical	O
calculations	O
of	O
a	O
finite-state	B-Architecture
machine	I-Architecture
to	O
produce	O
a	O
string	O
of	O
encoded	O
bits	O
from	O
a	O
series	O
of	O
input	O
data	O
symbols	O
.	O
</s>
<s>
It	O
can	O
achieve	O
superior	O
compression	O
compared	O
to	O
other	O
techniques	O
such	O
as	O
the	O
better-known	O
Huffman	B-General_Concept
algorithm	I-General_Concept
.	O
</s>
<s>
Arithmetic	B-Algorithm
coding	I-Algorithm
applies	O
especially	O
well	O
to	O
adaptive	O
data	B-General_Concept
compression	I-General_Concept
tasks	O
where	O
the	O
statistics	O
vary	O
and	O
are	O
context-dependent	O
,	O
as	O
it	O
can	O
be	O
easily	O
coupled	O
with	O
an	O
adaptive	O
model	O
of	O
the	O
probability	O
distribution	O
of	O
the	O
input	O
data	O
.	O
</s>
<s>
An	O
early	O
example	O
of	O
the	O
use	O
of	O
arithmetic	B-Algorithm
coding	I-Algorithm
was	O
in	O
an	O
optional	O
(	O
but	O
not	O
widely	O
used	O
)	O
feature	O
of	O
the	O
JPEG	O
image	O
coding	B-Error_Name
standard	O
.	O
</s>
<s>
It	O
has	O
since	O
been	O
applied	O
in	O
various	O
other	O
designs	O
including	O
H.263	B-Algorithm
,	O
H.264/MPEG	B-Application
-4	I-Application
AVC	I-Application
and	O
HEVC	B-Algorithm
for	O
video	B-Algorithm
coding	I-Algorithm
.	O
</s>
<s>
Archive	O
software	O
typically	O
has	O
the	O
ability	O
to	O
adjust	O
the	O
"	O
dictionary	O
size	O
"	O
,	O
where	O
a	O
larger	O
size	O
demands	O
more	O
random	B-Architecture
access	I-Architecture
memory	I-Architecture
during	O
compression	O
and	O
decompression	O
,	O
but	O
compresses	O
stronger	O
,	O
especially	O
on	O
repeating	O
patterns	O
in	O
files	O
 '	O
content	O
.	O
</s>
<s>
In	O
the	O
late	O
1980s	O
,	O
digital	B-Algorithm
images	I-Algorithm
became	O
more	O
common	O
,	O
and	O
standards	O
for	O
lossless	B-Algorithm
image	B-General_Concept
compression	I-General_Concept
emerged	O
.	O
</s>
<s>
In	O
the	O
early	O
1990s	O
,	O
lossy	B-Algorithm
compression	I-Algorithm
methods	O
began	O
to	O
be	O
widely	O
used	O
.	O
</s>
<s>
Lossy	B-Algorithm
data	I-Algorithm
compression	I-Algorithm
schemes	O
are	O
designed	O
by	O
research	O
on	O
how	O
people	O
perceive	O
the	O
data	O
in	O
question	O
.	O
</s>
<s>
JPEG	O
image	B-General_Concept
compression	I-General_Concept
works	O
in	O
part	O
by	O
rounding	O
off	O
nonessential	O
bits	O
of	O
information	O
.	O
</s>
<s>
A	O
number	O
of	O
popular	O
compression	O
formats	O
exploit	O
these	O
perceptual	O
differences	B-General_Concept
,	O
including	O
psychoacoustics	O
for	O
sound	O
,	O
and	O
psychovisuals	B-Algorithm
for	O
images	O
and	O
video	O
.	O
</s>
<s>
Most	O
forms	O
of	O
lossy	B-Algorithm
compression	I-Algorithm
are	O
based	O
on	O
transform	B-Algorithm
coding	I-Algorithm
,	O
especially	O
the	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
.	O
</s>
<s>
DCT	B-General_Concept
is	O
the	O
most	O
widely	O
used	O
lossy	B-Algorithm
compression	I-Algorithm
method	O
,	O
and	O
is	O
used	O
in	O
multimedia	O
formats	O
for	O
images	O
(	O
such	O
as	O
JPEG	O
and	O
HEIF	O
)	O
,	O
video	O
(	O
such	O
as	O
MPEG	O
,	O
AVC	B-Application
and	O
HEVC	B-Algorithm
)	O
and	O
audio	O
(	O
such	O
as	O
MP3	B-Application
,	O
AAC	B-Application
and	O
Vorbis	B-Algorithm
)	O
.	O
</s>
<s>
Lossy	B-Algorithm
image	B-General_Concept
compression	I-General_Concept
is	O
used	O
in	O
digital	B-Device
cameras	I-Device
,	O
to	O
increase	O
storage	O
capacities	O
.	O
</s>
<s>
Similarly	O
,	O
DVDs	O
,	O
Blu-ray	O
and	O
streaming	B-Application
video	I-Application
use	O
lossy	B-Algorithm
video	B-Algorithm
coding	I-Algorithm
formats	I-Algorithm
.	O
</s>
<s>
Lossy	B-Algorithm
compression	I-Algorithm
is	O
extensively	O
used	O
in	O
video	O
.	O
</s>
<s>
In	O
lossy	B-Algorithm
audio	O
compression	O
,	O
methods	O
of	O
psychoacoustics	O
are	O
used	O
to	O
remove	O
non-audible	O
(	O
or	O
less	O
audible	O
)	O
components	O
of	O
the	O
audio	O
signal	O
.	O
</s>
<s>
Compression	O
of	O
human	O
speech	O
is	O
often	O
performed	O
with	O
even	O
more	O
specialized	O
techniques	O
;	O
speech	B-Application
coding	I-Application
is	O
distinguished	O
as	O
a	O
separate	O
discipline	O
from	O
general-purpose	O
audio	O
compression	O
.	O
</s>
<s>
Speech	B-Application
coding	I-Application
is	O
used	O
in	O
internet	B-Application
telephony	I-Application
,	O
for	O
example	O
,	O
audio	O
compression	O
is	O
used	O
for	O
CD	O
ripping	O
and	O
is	O
decoded	O
by	O
the	O
audio	O
players	O
.	O
</s>
<s>
Lossy	B-Algorithm
compression	I-Algorithm
can	O
cause	O
generation	B-General_Concept
loss	I-General_Concept
.	O
</s>
<s>
The	O
theoretical	O
basis	O
for	O
compression	O
is	O
provided	O
by	O
information	O
theory	O
and	O
,	O
more	O
specifically	O
,	O
Shannon	B-Protocol
's	I-Protocol
source	I-Protocol
coding	I-Protocol
theorem	I-Protocol
;	O
domain-specific	O
theories	O
include	O
algorithmic	O
information	O
theory	O
for	O
lossless	B-Algorithm
compression	I-Algorithm
and	O
rate	B-General_Concept
–	I-General_Concept
distortion	I-General_Concept
theory	I-General_Concept
for	O
lossy	B-Algorithm
compression	I-Algorithm
.	O
</s>
<s>
Other	O
topics	O
associated	O
with	O
compression	O
include	O
coding	B-Error_Name
theory	I-Error_Name
and	O
statistical	O
inference	O
.	O
</s>
<s>
A	O
system	O
that	O
predicts	O
the	O
posterior	O
probabilities	O
of	O
a	O
sequence	O
given	O
its	O
entire	O
history	O
can	O
be	O
used	O
for	O
optimal	O
data	B-General_Concept
compression	I-General_Concept
(	O
by	O
using	O
arithmetic	B-Algorithm
coding	I-Algorithm
on	O
the	O
output	O
distribution	O
)	O
.	O
</s>
<s>
This	O
equivalence	O
has	O
been	O
used	O
as	O
a	O
justification	O
for	O
using	O
data	B-General_Concept
compression	I-General_Concept
as	O
a	O
benchmark	O
for	O
"	O
general	O
intelligence	O
"	O
.	O
</s>
<s>
An	O
alternative	O
view	O
can	O
show	O
compression	B-General_Concept
algorithms	I-General_Concept
implicitly	O
map	O
strings	O
into	O
implicit	O
feature	B-Algorithm
space	I-Algorithm
vectors	I-Algorithm
,	O
and	O
compression-based	O
similarity	O
measures	O
compute	O
similarity	O
within	O
these	O
feature	O
spaces	O
.	O
</s>
<s>
An	O
exhaustive	O
examination	O
of	O
the	O
feature	O
spaces	O
underlying	O
all	O
compression	B-General_Concept
algorithms	I-General_Concept
is	O
precluded	O
by	O
space	O
;	O
instead	O
,	O
feature	B-Algorithm
vectors	I-Algorithm
chooses	O
to	O
examine	O
three	O
representative	O
lossless	B-Algorithm
compression	I-Algorithm
methods	O
,	O
LZW	B-Algorithm
,	O
LZ77	O
,	O
and	O
PPM	O
.	O
</s>
<s>
Examples	O
of	O
AI-powered	O
audio/video	O
compression	B-General_Concept
software	I-General_Concept
include	O
VP9	B-Algorithm
,	O
NVIDIA	O
Maxine	O
,	O
AIVC	O
,	O
AccMPEG	O
.	O
</s>
<s>
Examples	O
of	O
software	O
that	O
can	O
perform	O
AI-powered	O
image	B-General_Concept
compression	I-General_Concept
include	O
OpenCV	B-Language
,	O
TensorFlow	B-Language
,	O
MATLAB	B-Language
's	O
Image	O
Processing	O
Toolbox	O
(	O
IPT	O
)	O
and	O
High-Fidelity	O
Generative	O
Image	B-General_Concept
Compression	I-General_Concept
.	O
</s>
<s>
Data	B-General_Concept
compression	I-General_Concept
can	O
be	O
viewed	O
as	O
a	O
special	O
case	O
of	O
data	B-Application
differencing	I-Application
.	O
</s>
<s>
Data	B-Application
differencing	I-Application
consists	O
of	O
producing	O
a	O
difference	O
given	O
a	O
source	O
and	O
a	O
target	O
,	O
with	O
patching	O
reproducing	O
the	O
target	O
given	O
a	O
source	O
and	O
a	O
difference	O
.	O
</s>
<s>
Since	O
there	O
is	O
no	O
separate	O
source	O
and	O
target	O
in	O
data	B-General_Concept
compression	I-General_Concept
,	O
one	O
can	O
consider	O
data	B-General_Concept
compression	I-General_Concept
as	O
data	B-Application
differencing	I-Application
with	O
empty	O
source	O
data	O
,	O
the	O
compressed	O
file	O
corresponding	O
to	O
a	O
difference	O
from	O
nothing	O
.	O
</s>
<s>
This	O
is	O
the	O
same	O
as	O
considering	O
absolute	O
entropy	O
(	O
corresponding	O
to	O
data	B-General_Concept
compression	I-General_Concept
)	O
as	O
a	O
special	O
case	O
of	O
relative	O
entropy	O
(	O
corresponding	O
to	O
data	B-Application
differencing	I-Application
)	O
with	O
no	O
initial	O
data	O
.	O
</s>
<s>
The	O
term	O
differential	B-Application
compression	I-Application
is	O
used	O
to	O
emphasize	O
the	O
data	B-Application
differencing	I-Application
connection	O
.	O
</s>
<s>
Entropy	B-Algorithm
coding	I-Algorithm
originated	O
in	O
the	O
1940s	O
with	O
the	O
introduction	O
of	O
Shannon	B-Algorithm
–	I-Algorithm
Fano	I-Algorithm
coding	I-Algorithm
,	O
the	O
basis	O
for	O
Huffman	B-General_Concept
coding	I-General_Concept
which	O
was	O
developed	O
in	O
1950	O
.	O
</s>
<s>
Transform	B-Algorithm
coding	I-Algorithm
dates	O
back	O
to	O
the	O
late	O
1960s	O
,	O
with	O
the	O
introduction	O
of	O
fast	O
Fourier	O
transform	O
(	O
FFT	O
)	O
coding	B-Error_Name
in	O
1968	O
and	O
the	O
Hadamard	B-Algorithm
transform	I-Algorithm
in	O
1969	O
.	O
</s>
<s>
An	O
important	O
image	B-General_Concept
compression	I-General_Concept
technique	O
is	O
the	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
,	O
a	O
technique	O
developed	O
in	O
the	O
early	O
1970s	O
.	O
</s>
<s>
DCT	B-General_Concept
is	O
the	O
basis	O
for	O
JPEG	O
,	O
a	O
lossy	B-Algorithm
compression	I-Algorithm
format	O
which	O
was	O
introduced	O
by	O
the	O
Joint	O
Photographic	O
Experts	O
Group	O
(	O
JPEG	O
)	O
in	O
1992	O
.	O
</s>
<s>
Its	O
highly	O
efficient	O
DCT-based	O
compression	B-General_Concept
algorithm	I-General_Concept
was	O
largely	O
responsible	O
for	O
the	O
wide	O
proliferation	O
of	O
digital	B-Algorithm
images	I-Algorithm
and	O
digital	B-Application
photos	I-Application
.	O
</s>
<s>
Lempel	B-Algorithm
–	I-Algorithm
Ziv	I-Algorithm
–	I-Algorithm
Welch	I-Algorithm
(	O
LZW	B-Algorithm
)	O
is	O
a	O
lossless	B-Algorithm
compression	I-Algorithm
algorithm	O
developed	O
in	O
1984	O
.	O
</s>
<s>
DEFLATE	B-Algorithm
,	O
a	O
lossless	B-Algorithm
compression	I-Algorithm
algorithm	O
specified	O
in	O
1996	O
,	O
is	O
used	O
in	O
the	O
Portable	O
Network	O
Graphics	O
(	O
PNG	O
)	O
format	O
.	O
</s>
<s>
Wavelet	O
compression	O
,	O
the	O
use	O
of	O
wavelets	O
in	O
image	B-General_Concept
compression	I-General_Concept
,	O
began	O
after	O
the	O
development	O
of	O
DCT	B-General_Concept
coding	B-Error_Name
.	O
</s>
<s>
In	O
contrast	O
to	O
the	O
DCT	B-General_Concept
algorithm	O
used	O
by	O
the	O
original	O
JPEG	O
format	O
,	O
JPEG	O
2000	O
instead	O
uses	O
discrete	O
wavelet	O
transform	O
(	O
DWT	O
)	O
algorithms	O
.	O
</s>
<s>
JPEG	O
2000	O
technology	O
,	O
which	O
includes	O
the	O
Motion	O
JPEG	O
2000	O
extension	O
,	O
was	O
selected	O
as	O
the	O
video	B-Algorithm
coding	I-Algorithm
standard	I-Algorithm
for	O
digital	O
cinema	O
in	O
2004	O
.	O
</s>
<s>
Audio	O
data	B-General_Concept
compression	I-General_Concept
,	O
not	O
to	O
be	O
confused	O
with	O
dynamic	O
range	O
compression	O
,	O
has	O
the	O
potential	O
to	O
reduce	O
the	O
transmission	O
bandwidth	O
and	O
storage	O
requirements	O
of	O
audio	O
data	O
.	O
</s>
<s>
Audio	O
compression	B-General_Concept
algorithms	I-General_Concept
are	O
implemented	O
in	O
software	O
as	O
audio	O
codecs	B-Application
.	O
</s>
<s>
In	O
both	O
lossy	B-Algorithm
and	O
lossless	B-Algorithm
compression	I-Algorithm
,	O
information	B-General_Concept
redundancy	I-General_Concept
is	O
reduced	O
,	O
using	O
methods	O
such	O
as	O
coding	B-Error_Name
,	O
quantization	B-Algorithm
,	O
DCT	B-General_Concept
and	O
linear	O
prediction	O
to	O
reduce	O
the	O
amount	O
of	O
information	O
used	O
to	O
represent	O
the	O
uncompressed	B-General_Concept
data	O
.	O
</s>
<s>
Lossy	B-Algorithm
audio	O
compression	B-General_Concept
algorithms	I-General_Concept
provide	O
higher	O
compression	O
and	O
are	O
used	O
in	O
numerous	O
audio	O
applications	O
including	O
Vorbis	B-Algorithm
and	O
MP3	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
one	O
640	O
MB	O
compact	O
disc	O
(	O
CD	O
)	O
holds	O
approximately	O
one	O
hour	O
of	O
uncompressed	B-General_Concept
high	O
fidelity	O
music	O
,	O
less	O
than	O
2	O
hours	O
of	O
music	O
compressed	O
losslessly	B-Algorithm
,	O
or	O
7	O
hours	O
of	O
music	O
compressed	O
in	O
the	O
MP3	B-Application
format	O
at	O
a	O
medium	O
bit	O
rate	O
.	O
</s>
<s>
Lossless	B-Algorithm
audio	O
compression	O
produces	O
a	O
representation	O
of	O
digital	O
data	O
that	O
can	O
be	O
decoded	O
to	O
an	O
exact	O
digital	O
duplicate	O
of	O
the	O
original	O
.	O
</s>
<s>
Compression	O
ratios	O
are	O
around	O
50	O
–	O
60%	O
of	O
the	O
original	O
size	O
,	O
which	O
is	O
similar	O
to	O
those	O
for	O
generic	O
lossless	B-Algorithm
data	I-Algorithm
compression	I-Algorithm
.	O
</s>
<s>
Lossless	B-Algorithm
codecs	I-Algorithm
use	O
curve	B-Algorithm
fitting	I-Algorithm
or	O
linear	O
prediction	O
as	O
a	O
basis	O
for	O
estimating	O
the	O
signal	O
.	O
</s>
<s>
A	O
number	O
of	O
lossless	B-Algorithm
audio	O
compression	O
formats	O
exist	O
.	O
</s>
<s>
See	O
list	O
of	O
lossless	B-Algorithm
codecs	I-Algorithm
for	O
a	O
listing	O
.	O
</s>
<s>
Some	O
formats	O
are	O
associated	O
with	O
a	O
distinct	O
system	O
,	O
such	O
as	O
Direct	O
Stream	O
Transfer	O
,	O
used	O
in	O
Super	O
Audio	O
CD	O
and	O
Meridian	B-Algorithm
Lossless	I-Algorithm
Packing	I-Algorithm
,	O
used	O
in	O
DVD-Audio	O
,	O
Dolby	O
TrueHD	O
,	O
Blu-ray	O
and	O
HD	B-Operating_System
DVD	I-Operating_System
.	O
</s>
<s>
Some	O
audio	O
file	O
formats	O
feature	O
a	O
combination	O
of	O
a	O
lossy	B-Algorithm
format	O
and	O
a	O
lossless	B-Algorithm
correction	O
;	O
this	O
allows	O
stripping	O
the	O
correction	O
to	O
easily	O
obtain	O
a	O
lossy	B-Algorithm
file	O
.	O
</s>
<s>
Such	O
formats	O
include	O
MPEG-4	B-Application
SLS	O
(	O
Scalable	O
to	O
Lossless	B-Algorithm
)	O
,	O
WavPack	B-Application
,	O
and	O
OptimFROG	O
DualStream	O
.	O
</s>
<s>
When	O
audio	O
files	O
are	O
to	O
be	O
processed	O
,	O
either	O
by	O
further	O
compression	O
or	O
for	O
editing	B-Application
,	O
it	O
is	O
desirable	O
to	O
work	O
from	O
an	O
unchanged	O
original	O
(	O
uncompressed	B-General_Concept
or	O
losslessly	B-Algorithm
compressed	O
)	O
.	O
</s>
<s>
Processing	O
of	O
a	O
lossily	O
compressed	O
file	O
for	O
some	O
purpose	O
usually	O
produces	O
a	O
final	O
result	O
inferior	O
to	O
the	O
creation	O
of	O
the	O
same	O
compressed	O
file	O
from	O
an	O
uncompressed	B-General_Concept
original	O
.	O
</s>
<s>
In	O
addition	O
to	O
sound	O
editing	B-Application
or	O
mixing	O
,	O
lossless	B-Algorithm
audio	O
compression	O
is	O
often	O
used	O
for	O
archival	O
storage	O
,	O
or	O
as	O
master	O
copies	O
.	O
</s>
<s>
Lossy	B-Algorithm
audio	O
compression	O
is	O
used	O
in	O
a	O
wide	O
range	O
of	O
applications	O
.	O
</s>
<s>
In	O
addition	O
to	O
standalone	O
audio-only	O
applications	O
of	O
file	O
playback	O
in	O
MP3	B-Application
players	O
or	O
computers	O
,	O
digitally	O
compressed	O
audio	O
streams	O
are	O
used	O
in	O
most	O
video	O
DVDs	O
,	O
digital	O
television	O
,	O
streaming	O
media	O
on	O
the	O
Internet	O
,	O
satellite	O
and	O
cable	O
radio	O
,	O
and	O
increasingly	O
in	O
terrestrial	O
radio	O
broadcasts	O
.	O
</s>
<s>
Lossy	B-Algorithm
compression	I-Algorithm
typically	O
achieves	O
far	O
greater	O
compression	O
than	O
lossless	B-Algorithm
compression	I-Algorithm
,	O
by	O
discarding	O
less-critical	O
data	O
based	O
on	O
psychoacoustic	O
optimizations	O
.	O
</s>
<s>
Most	O
lossy	B-Algorithm
compression	I-Algorithm
reduces	O
redundancy	B-General_Concept
by	O
first	O
identifying	O
perceptually	O
irrelevant	O
sounds	O
,	O
that	O
is	O
,	O
sounds	O
that	O
are	O
very	O
hard	O
to	O
hear	O
.	O
</s>
<s>
Due	O
to	O
the	O
nature	O
of	O
lossy	B-Algorithm
algorithms	O
,	O
audio	O
quality	O
suffers	O
a	O
digital	O
generation	B-General_Concept
loss	I-General_Concept
when	O
a	O
file	O
is	O
decompressed	O
and	O
recompressed	O
.	O
</s>
<s>
This	O
makes	O
lossy	B-Algorithm
compression	I-Algorithm
unsuitable	O
for	O
storing	O
the	O
intermediate	O
results	O
in	O
professional	O
audio	O
engineering	O
applications	O
,	O
such	O
as	O
sound	O
editing	B-Application
and	O
multitrack	O
recording	O
.	O
</s>
<s>
However	O
,	O
lossy	B-Algorithm
formats	O
such	O
as	O
MP3	B-Application
are	O
very	O
popular	O
with	O
end-users	O
as	O
the	O
file	O
size	O
is	O
reduced	O
to	O
5-20	O
%	O
of	O
the	O
original	O
size	O
and	O
a	O
megabyte	O
can	O
store	O
about	O
a	O
minute	O
's	O
worth	O
of	O
music	O
at	O
adequate	O
quality	O
.	O
</s>
<s>
To	O
determine	O
what	O
information	O
in	O
an	O
audio	O
signal	O
is	O
perceptually	O
irrelevant	O
,	O
most	O
lossy	B-Algorithm
compression	I-Algorithm
algorithms	O
use	O
transforms	O
such	O
as	O
the	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
MDCT	O
)	O
to	O
convert	O
time	O
domain	O
sampled	O
waveforms	O
into	O
a	O
transform	O
domain	O
,	O
typically	O
the	O
frequency	O
domain	O
.	O
</s>
<s>
Other	O
types	O
of	O
lossy	B-Algorithm
compressors	O
,	O
such	O
as	O
the	O
linear	B-Algorithm
predictive	I-Algorithm
coding	I-Algorithm
(	O
LPC	O
)	O
used	O
with	O
speech	O
,	O
are	O
source-based	O
coders	O
.	O
</s>
<s>
Lossy	B-Algorithm
formats	O
are	O
often	O
used	O
for	O
the	O
distribution	O
of	O
streaming	O
audio	O
or	O
interactive	O
communication	O
(	O
such	O
as	O
in	O
cell	O
phone	O
networks	O
)	O
.	O
</s>
<s>
Not	O
all	O
audio	O
codecs	B-Application
can	O
be	O
used	O
for	O
streaming	O
applications	O
.	O
</s>
<s>
Some	O
codecs	B-Application
will	O
analyze	O
a	O
longer	O
segment	O
,	O
called	O
a	O
frame	O
,	O
of	O
the	O
data	O
to	O
optimize	O
efficiency	O
,	O
and	O
then	O
code	O
it	O
in	O
a	O
manner	O
that	O
requires	O
a	O
larger	O
segment	O
of	O
data	O
at	O
one	O
time	O
to	O
decode	O
.	O
</s>
<s>
The	O
inherent	O
latency	O
of	O
the	O
coding	B-Error_Name
algorithm	O
can	O
be	O
critical	O
;	O
for	O
example	O
,	O
when	O
there	O
is	O
a	O
two-way	O
transmission	O
of	O
data	O
,	O
such	O
as	O
with	O
a	O
telephone	O
conversation	O
,	O
significant	O
delays	O
may	O
seriously	O
degrade	O
the	O
perceived	O
quality	O
.	O
</s>
<s>
In	O
the	O
minimum	O
case	O
,	O
latency	O
is	O
zero	O
samples	O
(	O
e.g.	O
,	O
if	O
the	O
coder/decoder	B-General_Concept
simply	O
reduces	O
the	O
number	O
of	O
bits	O
used	O
to	O
quantize	O
the	O
signal	O
)	O
.	O
</s>
<s>
Time	O
domain	O
algorithms	O
such	O
as	O
LPC	O
also	O
often	O
have	O
low	O
latencies	O
,	O
hence	O
their	O
popularity	O
in	O
speech	B-Application
coding	I-Application
for	O
telephony	O
.	O
</s>
<s>
In	O
algorithms	O
such	O
as	O
MP3	B-Application
,	O
however	O
,	O
a	O
large	O
number	O
of	O
samples	O
have	O
to	O
be	O
analyzed	O
to	O
implement	O
a	O
psychoacoustic	O
model	O
in	O
the	O
frequency	O
domain	O
,	O
and	O
latency	O
is	O
on	O
the	O
order	O
of	O
23ms	O
.	O
</s>
<s>
Speech	B-Application
encoding	I-Application
is	O
an	O
important	O
category	O
of	O
audio	O
data	B-General_Concept
compression	I-General_Concept
.	O
</s>
<s>
The	O
earliest	O
algorithms	O
used	O
in	O
speech	B-Application
encoding	I-Application
(	O
and	O
audio	O
data	B-General_Concept
compression	I-General_Concept
in	O
general	O
)	O
were	O
the	O
A-law	B-Algorithm
algorithm	I-Algorithm
and	O
the	O
μ-law	B-Algorithm
algorithm	I-Algorithm
.	O
</s>
<s>
There	O
,	O
in	O
1950	O
,	O
C	O
.	O
Chapin	O
Cutler	O
filed	O
the	O
patent	O
on	O
differential	B-General_Concept
pulse-code	I-General_Concept
modulation	I-General_Concept
(	O
DPCM	B-General_Concept
)	O
.	O
</s>
<s>
In	O
1973	O
,	O
Adaptive	B-Algorithm
DPCM	I-Algorithm
(	O
ADPCM	B-Algorithm
)	O
was	O
introduced	O
by	O
P	O
.	O
Cummiskey	O
,	O
Nikil	O
S	O
.	O
Jayant	O
and	O
James	O
L	O
.	O
Flanagan	O
.	O
</s>
<s>
Perceptual	O
coding	B-Error_Name
was	O
first	O
used	O
for	O
speech	B-Application
coding	I-Application
compression	O
,	O
with	O
linear	B-Algorithm
predictive	I-Algorithm
coding	I-Algorithm
(	O
LPC	O
)	O
.	O
</s>
<s>
During	O
the	O
1970s	O
,	O
Bishnu	O
S	O
.	O
Atal	O
and	O
Manfred	O
R	O
.	O
Schroeder	O
at	O
Bell	O
Labs	O
developed	O
a	O
form	O
of	O
LPC	O
called	O
adaptive	O
predictive	O
coding	B-Error_Name
(	O
APC	O
)	O
,	O
a	O
perceptual	O
coding	B-Error_Name
algorithm	O
that	O
exploited	O
the	O
masking	O
properties	O
of	O
the	O
human	O
ear	O
,	O
followed	O
in	O
the	O
early	O
1980s	O
with	O
the	O
code-excited	B-Algorithm
linear	I-Algorithm
prediction	I-Algorithm
(	O
CELP	B-Algorithm
)	O
algorithm	O
which	O
achieved	O
a	O
significant	O
compression	O
ratio	O
for	O
its	O
time	O
.	O
</s>
<s>
Perceptual	O
coding	B-Error_Name
is	O
used	O
by	O
modern	O
audio	O
compression	O
formats	O
such	O
as	O
MP3	B-Application
and	O
AAC	B-Application
.	O
</s>
<s>
Discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
,	O
developed	O
by	O
Nasir	O
Ahmed	O
,	O
T	O
.	O
Natarajan	O
and	O
K	O
.	O
R	O
.	O
Rao	O
in	O
1974	O
,	O
provided	O
the	O
basis	O
for	O
the	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
MDCT	O
)	O
used	O
by	O
modern	O
audio	O
compression	O
formats	O
such	O
as	O
MP3	B-Application
,	O
Dolby	O
Digital	O
,	O
and	O
AAC	B-Application
.	O
</s>
<s>
In	O
1983	O
,	O
using	O
the	O
psychoacoustic	O
principle	O
of	O
the	O
masking	O
of	O
critical	O
bands	O
first	O
published	O
in	O
1967	O
,	O
he	O
started	O
developing	O
a	O
practical	O
application	O
based	O
on	O
the	O
recently	O
developed	O
IBM	B-Device
PC	I-Device
computer	O
,	O
and	O
the	O
broadcast	O
automation	O
system	O
was	O
launched	O
in	O
1987	O
under	O
the	O
name	O
Audicom	B-Application
.	O
</s>
<s>
A	O
literature	O
compendium	O
for	O
a	O
large	O
variety	O
of	O
audio	O
coding	B-Error_Name
systems	O
was	O
published	O
in	O
the	O
IEEE	O
's	O
Journal	O
on	O
Selected	O
Areas	O
in	O
Communications	O
(	O
JSAC	O
)	O
,	O
in	O
February	O
1988	O
.	O
</s>
<s>
While	O
there	O
were	O
some	O
papers	O
from	O
before	O
that	O
time	O
,	O
this	O
collection	O
documented	O
an	O
entire	O
variety	O
of	O
finished	O
,	O
working	O
audio	O
coders	O
,	O
nearly	O
all	O
of	O
them	O
using	O
perceptual	O
techniques	O
and	O
some	O
kind	O
of	O
frequency	O
analysis	O
and	O
back-end	O
noiseless	O
coding	B-Error_Name
.	O
</s>
<s>
Uncompressed	B-Device
video	I-Device
requires	O
a	O
very	O
high	O
data	O
rate	O
.	O
</s>
<s>
Although	O
lossless	B-Algorithm
video	O
compression	O
codecs	B-Application
perform	O
at	O
a	O
compression	O
factor	O
of	O
5	O
to	O
12	O
,	O
a	O
typical	O
H.264	B-Application
lossy	B-Algorithm
compression	I-Algorithm
video	O
has	O
a	O
compression	O
factor	O
between	O
20	O
and	O
200	O
.	O
</s>
<s>
The	O
two	O
key	O
video	O
compression	B-General_Concept
techniques	I-General_Concept
used	O
in	O
video	B-Algorithm
coding	I-Algorithm
standards	I-Algorithm
are	O
the	O
DCT	B-General_Concept
and	O
motion	B-Algorithm
compensation	I-Algorithm
(	O
MC	O
)	O
.	O
</s>
<s>
Most	O
video	B-Algorithm
coding	I-Algorithm
standards	I-Algorithm
,	O
such	O
as	O
the	O
H.26x	B-Application
and	O
MPEG	O
formats	O
,	O
typically	O
use	O
motion-compensated	O
DCT	B-General_Concept
video	B-Algorithm
coding	I-Algorithm
(	O
block	O
motion	B-Algorithm
compensation	I-Algorithm
)	O
.	O
</s>
<s>
Most	O
video	B-Application
codecs	I-Application
are	O
used	O
alongside	O
audio	O
compression	B-General_Concept
techniques	I-General_Concept
to	O
store	O
the	O
separate	O
but	O
complementary	O
data	O
streams	O
as	O
one	O
combined	O
package	O
using	O
so-called	O
container	O
formats	O
.	O
</s>
<s>
Such	O
data	O
usually	O
contains	O
abundant	O
amounts	O
of	O
spatial	O
and	O
temporal	O
redundancy	B-General_Concept
.	O
</s>
<s>
Video	O
compression	B-General_Concept
algorithms	I-General_Concept
attempt	O
to	O
reduce	O
redundancy	B-General_Concept
and	O
store	O
information	O
more	O
compactly	O
.	O
</s>
<s>
Most	O
video	B-Algorithm
compression	I-Algorithm
formats	I-Algorithm
and	O
codecs	B-Application
exploit	O
both	O
spatial	O
and	O
temporal	O
redundancy	B-General_Concept
(	O
e.g.	O
</s>
<s>
through	O
difference	O
coding	B-Error_Name
with	O
motion	B-Algorithm
compensation	I-Algorithm
)	O
.	O
</s>
<s>
Similarities	O
can	O
be	O
encoded	O
by	O
only	O
storing	O
differences	B-General_Concept
between	O
e.g.	O
</s>
<s>
temporally	O
adjacent	O
frames	O
(	O
inter-frame	B-Algorithm
coding	B-Error_Name
)	O
or	O
spatially	O
adjacent	O
pixels	B-Algorithm
(	O
intra-frame	B-General_Concept
coding	I-General_Concept
)	O
.	O
</s>
<s>
Inter-frame	B-Algorithm
compression	O
(	O
a	O
temporal	O
delta	B-Algorithm
encoding	I-Algorithm
)	O
(	O
re	O
)	O
uses	O
data	O
from	O
one	O
or	O
more	O
earlier	O
or	O
later	O
frames	O
in	O
a	O
sequence	O
to	O
describe	O
the	O
current	O
frame	O
.	O
</s>
<s>
Intra-frame	B-General_Concept
coding	I-General_Concept
,	O
on	O
the	O
other	O
hand	O
,	O
uses	O
only	O
data	O
from	O
within	O
the	O
current	O
frame	O
,	O
effectively	O
being	O
still-image	O
compression	O
.	O
</s>
<s>
The	O
intra-frame	B-General_Concept
video	B-Algorithm
coding	I-Algorithm
formats	I-Algorithm
used	O
in	O
camcorders	O
and	O
video	O
editing	B-Application
employ	O
simpler	O
compression	O
that	O
uses	O
only	O
intra-frame	B-General_Concept
prediction	I-General_Concept
.	O
</s>
<s>
This	O
simplifies	O
video	O
editing	B-Application
software	O
,	O
as	O
it	O
prevents	O
a	O
situation	O
in	O
which	O
a	O
compressed	O
frame	O
refers	O
to	O
data	O
that	O
the	O
editor	O
has	O
deleted	O
.	O
</s>
<s>
Usually	O
,	O
video	O
compression	O
additionally	O
employs	O
lossy	B-Algorithm
compression	I-Algorithm
techniques	O
like	O
quantization	B-Algorithm
that	O
reduce	O
aspects	O
of	O
the	O
source	O
data	O
that	O
are	O
(	O
more	O
or	O
less	O
)	O
irrelevant	O
to	O
the	O
human	O
visual	O
perception	O
by	O
exploiting	O
perceptual	O
features	O
of	O
human	O
vision	O
.	O
</s>
<s>
For	O
example	O
,	O
small	O
differences	B-General_Concept
in	O
color	O
are	O
more	O
difficult	O
to	O
perceive	O
than	O
are	O
changes	O
in	O
brightness	O
.	O
</s>
<s>
Compression	B-General_Concept
algorithms	I-General_Concept
can	O
average	O
a	O
color	O
across	O
these	O
similar	O
areas	O
in	O
a	O
manner	O
similar	O
to	O
those	O
used	O
in	O
JPEG	O
image	B-General_Concept
compression	I-General_Concept
.	O
</s>
<s>
As	O
in	O
all	O
lossy	B-Algorithm
compression	I-Algorithm
,	O
there	O
is	O
a	O
trade-off	O
between	O
video	B-Device
quality	I-Device
and	O
bit	O
rate	O
,	O
cost	O
of	O
processing	O
the	O
compression	O
and	O
decompression	O
,	O
and	O
system	O
requirements	O
.	O
</s>
<s>
Highly	O
compressed	O
video	O
may	O
present	O
visible	O
or	O
distracting	O
artifacts	B-Algorithm
.	O
</s>
<s>
Other	O
methods	O
other	O
than	O
the	O
prevalent	O
DCT-based	O
transform	O
formats	O
,	O
such	O
as	O
fractal	B-Algorithm
compression	I-Algorithm
,	O
matching	B-General_Concept
pursuit	I-General_Concept
and	O
the	O
use	O
of	O
a	O
discrete	O
wavelet	O
transform	O
(	O
DWT	O
)	O
,	O
have	O
been	O
the	O
subject	O
of	O
some	O
research	O
,	O
but	O
are	O
typically	O
not	O
used	O
in	O
practical	O
products	O
.	O
</s>
<s>
Wavelet	O
compression	O
is	O
used	O
in	O
still-image	O
coders	O
and	O
video	O
coders	O
without	O
motion	B-Algorithm
compensation	I-Algorithm
.	O
</s>
<s>
Interest	O
in	O
fractal	B-Algorithm
compression	I-Algorithm
seems	O
to	O
be	O
waning	O
,	O
due	O
to	O
recent	O
theoretical	O
analysis	O
showing	O
a	O
comparative	O
lack	O
of	O
effectiveness	O
of	O
such	O
methods	O
.	O
</s>
<s>
In	O
inter-frame	B-Algorithm
coding	B-Error_Name
,	O
individual	O
frames	O
of	O
a	O
video	O
sequence	O
are	O
compared	O
from	O
one	O
frame	O
to	O
the	O
next	O
,	O
and	O
the	O
video	B-Application
compression	I-Application
codec	I-Application
records	O
the	O
differences	B-General_Concept
to	O
the	O
reference	O
frame	O
.	O
</s>
<s>
This	O
longer	O
command	O
still	O
remains	O
much	O
shorter	O
than	O
data	O
generated	O
by	O
intra-frame	B-General_Concept
compression	O
.	O
</s>
<s>
Usually	O
,	O
the	O
encoder	O
will	O
also	O
transmit	O
a	O
residue	O
signal	O
which	O
describes	O
the	O
remaining	O
more	O
subtle	O
differences	B-General_Concept
to	O
the	O
reference	O
imagery	O
.	O
</s>
<s>
Using	O
entropy	B-Algorithm
coding	I-Algorithm
,	O
these	O
residue	O
signals	O
have	O
a	O
more	O
compact	O
representation	O
than	O
the	O
full	O
signal	O
.	O
</s>
<s>
In	O
areas	O
of	O
video	O
with	O
more	O
motion	O
,	O
the	O
compression	O
must	O
encode	O
more	O
data	O
to	O
keep	O
up	O
with	O
the	O
larger	O
number	O
of	O
pixels	B-Algorithm
that	O
are	O
changing	O
.	O
</s>
<s>
Commonly	O
during	O
explosions	O
,	O
flames	O
,	O
flocks	O
of	O
animals	O
,	O
and	O
in	O
some	O
panning	O
shots	O
,	O
the	O
high-frequency	O
detail	O
leads	O
to	O
quality	O
decreases	O
or	O
to	O
increases	O
in	O
the	O
variable	B-General_Concept
bitrate	I-General_Concept
.	O
</s>
<s>
Today	O
,	O
nearly	O
all	O
commonly	O
used	O
video	O
compression	O
methods	O
(	O
e.g.	O
,	O
those	O
in	O
standards	O
approved	O
by	O
the	O
ITU-T	O
or	O
ISO	O
)	O
share	O
the	O
same	O
basic	O
architecture	O
that	O
dates	O
back	O
to	O
H.261	B-Algorithm
which	O
was	O
standardized	O
in	O
1988	O
by	O
the	O
ITU-T	O
.	O
</s>
<s>
They	O
mostly	O
rely	O
on	O
the	O
DCT	B-General_Concept
,	O
applied	O
to	O
rectangular	O
blocks	O
of	O
neighboring	O
pixels	B-Algorithm
,	O
and	O
temporal	O
prediction	O
using	O
motion	O
vectors	O
,	O
as	O
well	O
as	O
nowadays	O
also	O
an	O
in-loop	O
filtering	O
step	O
.	O
</s>
<s>
In	O
the	O
prediction	O
stage	O
,	O
various	O
deduplication	B-General_Concept
and	O
difference-coding	O
techniques	O
are	O
applied	O
that	O
help	O
decorrelate	O
data	O
and	O
describe	O
new	O
data	O
based	O
on	O
already	O
transmitted	O
data	O
.	O
</s>
<s>
Then	O
rectangular	O
blocks	O
of	O
remaining	O
pixel	B-Algorithm
data	O
are	O
transformed	O
to	O
the	O
frequency	O
domain	O
.	O
</s>
<s>
In	O
the	O
main	O
lossy	B-Algorithm
processing	O
stage	O
,	O
frequency	O
domain	O
data	O
gets	O
quantized	O
in	O
order	O
to	O
reduce	O
information	O
that	O
is	O
irrelevant	O
to	O
human	O
visual	O
perception	O
.	O
</s>
<s>
In	O
the	O
last	O
stage	O
statistical	B-General_Concept
redundancy	I-General_Concept
gets	O
largely	O
eliminated	O
by	O
an	O
entropy	B-Algorithm
coder	I-Algorithm
which	O
often	O
applies	O
some	O
form	O
of	O
arithmetic	B-Algorithm
coding	I-Algorithm
.	O
</s>
<s>
The	O
most	O
popular	O
example	O
are	O
deblocking	B-General_Concept
filters	I-General_Concept
that	O
blur	O
out	O
blocking	O
artifacts	B-Algorithm
from	O
quantization	B-Algorithm
discontinuities	O
at	O
transform	O
block	O
boundaries	O
.	O
</s>
<s>
In	O
1967	O
,	O
A.H.	O
Robinson	O
and	O
C	O
.	O
Cherry	O
proposed	O
a	O
run-length	B-Algorithm
encoding	I-Algorithm
bandwidth	O
compression	O
scheme	O
for	O
the	O
transmission	O
of	O
analog	O
television	O
signals	O
.	O
</s>
<s>
The	O
DCT	B-General_Concept
,	O
which	O
is	O
fundamental	O
to	O
modern	O
video	O
compression	O
,	O
was	O
introduced	O
by	O
Nasir	O
Ahmed	O
,	O
T	O
.	O
Natarajan	O
and	O
K	O
.	O
R	O
.	O
Rao	O
in	O
1974	O
.	O
</s>
<s>
H.261	B-Algorithm
,	O
which	O
debuted	O
in	O
1988	O
,	O
commercially	O
introduced	O
the	O
prevalent	O
basic	O
architecture	O
of	O
video	O
compression	O
technology	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
video	B-Algorithm
coding	I-Algorithm
format	I-Algorithm
based	O
on	O
DCT	B-General_Concept
compression	O
.	O
</s>
<s>
H.261	B-Algorithm
was	O
developed	O
by	O
a	O
number	O
of	O
companies	O
,	O
including	O
Hitachi	O
,	O
PictureTel	B-Application
,	O
NTT	O
,	O
BT	O
and	O
Toshiba	O
.	O
</s>
<s>
The	O
most	O
popular	O
video	B-Algorithm
coding	I-Algorithm
standards	I-Algorithm
used	O
for	O
codecs	B-Application
have	O
been	O
the	O
MPEG	O
standards	O
.	O
</s>
<s>
MPEG-1	B-Algorithm
was	O
developed	O
by	O
the	O
Motion	O
Picture	O
Experts	O
Group	O
(	O
MPEG	O
)	O
in	O
1991	O
,	O
and	O
it	O
was	O
designed	O
to	O
compress	O
VHS-quality	O
video	O
.	O
</s>
<s>
It	O
was	O
succeeded	O
in	O
1994	O
by	O
MPEG-2/H.262	O
,	O
which	O
was	O
developed	O
by	O
a	O
number	O
of	O
companies	O
,	O
primarily	O
Sony	O
,	O
Thomson	O
and	O
Mitsubishi	O
Electric	O
.	O
</s>
<s>
MPEG-2	B-Algorithm
became	O
the	O
standard	O
video	O
format	O
for	O
DVD	O
and	O
SD	B-Device
digital	I-Device
television	I-Device
.	O
</s>
<s>
In	O
1999	O
,	O
it	O
was	O
followed	O
by	O
MPEG-4/H.263	O
.	O
</s>
<s>
H.264/MPEG	B-Application
-4	I-Application
AVC	I-Application
was	O
developed	O
in	O
2003	O
by	O
a	O
number	O
of	O
organizations	O
,	O
primarily	O
Panasonic	O
,	O
Godo	O
Kaisha	O
IP	O
Bridge	O
and	O
LG	O
Electronics	O
.	O
</s>
<s>
AVC	B-Application
commercially	O
introduced	O
the	O
modern	O
context-adaptive	B-Algorithm
binary	I-Algorithm
arithmetic	I-Algorithm
coding	I-Algorithm
(	O
CABAC	B-Algorithm
)	O
and	O
context-adaptive	B-Algorithm
variable-length	I-Algorithm
coding	I-Algorithm
(	O
CAVLC	B-Algorithm
)	O
algorithms	O
.	O
</s>
<s>
AVC	B-Application
is	O
the	O
main	O
video	O
encoding	O
standard	O
for	O
Blu-ray	O
Discs	O
,	O
and	O
is	O
widely	O
used	O
by	O
video	O
sharing	O
websites	O
and	O
streaming	O
internet	O
services	O
such	O
as	O
YouTube	B-General_Concept
,	O
Netflix	O
,	O
Vimeo	O
,	O
and	O
iTunes	O
Store	O
,	O
web	O
software	O
such	O
as	O
Adobe	B-Operating_System
Flash	I-Operating_System
Player	I-Operating_System
and	O
Microsoft	B-Application
Silverlight	I-Application
,	O
and	O
various	O
HDTV	B-Device
broadcasts	O
over	O
terrestrial	O
and	O
satellite	O
television	O
.	O
</s>
<s>
Genetics	O
compression	B-General_Concept
algorithms	I-General_Concept
are	O
the	O
latest	O
generation	O
of	O
lossless	B-Algorithm
algorithms	O
that	O
compress	O
data	O
(	O
typically	O
sequences	O
of	O
nucleotides	O
)	O
using	O
both	O
conventional	O
compression	B-General_Concept
algorithms	I-General_Concept
and	O
genetic	O
algorithms	O
adapted	O
to	O
the	O
specific	O
datatype	O
.	O
</s>
<s>
In	O
2012	O
,	O
a	O
team	O
of	O
scientists	O
from	O
Johns	O
Hopkins	O
University	O
published	O
a	O
genetic	O
compression	B-General_Concept
algorithm	I-General_Concept
that	O
does	O
not	O
use	O
a	O
reference	O
genome	O
for	O
compression	O
.	O
</s>
<s>
HAPZIPPER	O
was	O
tailored	O
for	O
HapMap	O
data	O
and	O
achieves	O
over	O
20-fold	O
compression	O
(	O
95%	O
reduction	O
in	O
file	O
size	O
)	O
,	O
providing	O
2	O
-	O
to	O
4-fold	O
better	O
compression	O
and	O
is	O
less	O
computationally	O
intensive	O
than	O
the	O
leading	O
general-purpose	O
compression	B-General_Concept
utilities	I-General_Concept
.	O
</s>
<s>
It	O
is	O
estimated	O
that	O
the	O
total	O
amount	O
of	O
data	O
that	O
is	O
stored	O
on	O
the	O
world	O
's	O
storage	O
devices	O
could	O
be	O
further	O
compressed	O
with	O
existing	O
compression	B-General_Concept
algorithms	I-General_Concept
by	O
a	O
remaining	O
average	O
factor	O
of	O
4.5:1	O
.	O
</s>
