<s>
In	O
information	B-General_Concept
technology	I-General_Concept
,	O
lossy	B-Algorithm
compression	I-Algorithm
or	O
irreversible	B-Algorithm
compression	I-Algorithm
is	O
the	O
class	O
of	O
data	B-General_Concept
compression	I-General_Concept
methods	O
that	O
uses	O
inexact	O
approximations	O
and	O
partial	O
data	O
discarding	O
to	O
represent	O
the	O
content	O
.	O
</s>
<s>
This	O
is	O
opposed	O
to	O
lossless	B-Algorithm
data	I-Algorithm
compression	I-Algorithm
(	O
reversible	O
data	B-General_Concept
compression	I-General_Concept
)	O
which	O
does	O
not	O
degrade	O
the	O
data	O
.	O
</s>
<s>
The	O
amount	O
of	O
data	O
reduction	O
possible	O
using	O
lossy	B-Algorithm
compression	I-Algorithm
is	O
much	O
higher	O
than	O
using	O
lossless	B-Algorithm
techniques	O
.	O
</s>
<s>
Well-designed	O
lossy	B-Algorithm
compression	I-Algorithm
technology	O
often	O
reduces	O
file	O
sizes	O
significantly	O
before	O
degradation	O
is	O
noticed	O
by	O
the	O
end-user	O
.	O
</s>
<s>
The	O
most	O
widely	O
used	O
lossy	B-Algorithm
compression	I-Algorithm
algorithm	O
is	O
the	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
,	O
first	O
published	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>
Lossy	B-Algorithm
compression	I-Algorithm
is	O
most	O
commonly	O
used	O
to	O
compress	O
multimedia	O
data	O
(	O
audio	O
,	O
video	O
,	O
and	O
images	O
)	O
,	O
especially	O
in	O
applications	O
such	O
as	O
streaming	O
media	O
and	O
internet	B-Application
telephony	I-Application
.	O
</s>
<s>
By	O
contrast	O
,	O
lossless	B-Algorithm
compression	I-Algorithm
is	O
typically	O
required	O
for	O
text	O
and	O
data	O
files	O
,	O
such	O
as	O
bank	O
records	O
and	O
text	O
articles	O
.	O
</s>
<s>
It	O
can	O
be	O
advantageous	O
to	O
make	O
a	O
master	O
lossless	B-Algorithm
file	O
which	O
can	O
then	O
be	O
used	O
to	O
produce	O
additional	O
copies	O
from	O
.	O
</s>
<s>
This	O
allows	O
one	O
to	O
avoid	O
basing	O
new	O
compressed	O
copies	O
off	O
of	O
a	O
lossy	B-Algorithm
source	O
file	O
,	O
which	O
would	O
yield	O
additional	O
artifacts	B-Algorithm
and	O
further	O
unnecessary	O
information	O
loss	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
compress	O
many	O
types	O
of	O
digital	O
data	O
in	O
a	O
way	O
that	O
reduces	O
the	O
size	O
of	O
a	O
computer	B-Operating_System
file	I-Operating_System
needed	O
to	O
store	O
it	O
,	O
or	O
the	O
bandwidth	O
needed	O
to	O
transmit	O
it	O
,	O
with	O
no	O
loss	O
of	O
the	O
full	O
information	O
contained	O
in	O
the	O
original	O
file	O
.	O
</s>
<s>
A	O
picture	O
,	O
for	O
example	O
,	O
is	O
converted	O
to	O
a	O
digital	B-Operating_System
file	I-Operating_System
by	O
considering	O
it	O
to	O
be	O
an	O
array	O
of	O
dots	O
and	O
specifying	O
the	O
color	O
and	O
brightness	O
of	O
each	O
dot	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
compressed	O
ZIP	B-General_Concept
file	I-General_Concept
is	O
smaller	O
than	O
its	O
original	O
,	O
but	O
repeatedly	O
compressing	O
the	O
same	O
file	O
will	O
not	O
reduce	O
the	O
size	O
to	O
nothing	O
.	O
</s>
<s>
Most	O
compression	B-General_Concept
algorithms	I-General_Concept
can	O
recognize	O
when	O
further	O
compression	O
would	O
be	O
pointless	O
and	O
would	O
in	O
fact	O
increase	O
the	O
size	O
of	O
the	O
data	O
.	O
</s>
<s>
Developing	O
lossy	B-Algorithm
compression	I-Algorithm
techniques	O
as	O
closely	O
matched	O
to	O
human	O
perception	O
as	O
possible	O
is	O
a	O
complex	O
task	O
.	O
</s>
<s>
The	O
terms	O
"	O
irreversible	O
"	O
and	O
"	O
reversible	O
"	O
are	O
preferred	O
over	O
"	O
lossy	B-Algorithm
"	O
and	O
"	O
lossless	B-Algorithm
"	O
respectively	O
for	O
some	O
applications	O
,	O
such	O
as	O
medical	O
image	B-General_Concept
compression	I-General_Concept
,	O
to	O
circumvent	O
the	O
negative	O
implications	O
of	O
"	O
loss	O
"	O
.	O
</s>
<s>
Artifacts	B-Algorithm
or	O
undesirable	O
effects	O
of	O
compression	O
may	O
be	O
clearly	O
discernible	O
yet	O
the	O
result	O
still	O
useful	O
for	O
the	O
intended	O
purpose	O
.	O
</s>
<s>
Or	O
lossy	B-Algorithm
compressed	B-General_Concept
images	I-General_Concept
may	O
be	O
'	O
visually	B-Algorithm
lossless	I-Algorithm
 '	O
,	O
or	O
in	O
the	O
case	O
of	O
medical	O
images	O
,	O
so-called	O
Diagnostically	B-Algorithm
Acceptable	I-Algorithm
Irreversible	I-Algorithm
Compression	I-Algorithm
(	O
DAIC	B-Algorithm
)	O
may	O
have	O
been	O
applied	O
.	O
</s>
<s>
Some	O
forms	O
of	O
lossy	B-Algorithm
compression	I-Algorithm
can	O
be	O
thought	O
of	O
as	O
an	O
application	O
of	O
transform	B-Algorithm
coding	I-Algorithm
,	O
which	O
is	O
a	O
type	O
of	O
data	B-General_Concept
compression	I-General_Concept
used	O
for	O
digital	B-Algorithm
images	I-Algorithm
,	O
digital	O
audio	O
signals	O
,	O
and	O
digital	O
video	O
.	O
</s>
<s>
The	O
transformation	O
is	O
typically	O
used	O
to	O
enable	O
better	O
(	O
more	O
targeted	O
)	O
quantization	B-Algorithm
.	O
</s>
<s>
The	O
most	O
common	O
form	O
of	O
lossy	B-Algorithm
compression	I-Algorithm
is	O
a	O
transform	B-Algorithm
coding	I-Algorithm
method	O
,	O
the	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
,	O
which	O
was	O
first	O
published	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>
DCT	B-General_Concept
is	O
the	O
most	O
widely	O
used	O
form	O
of	O
lossy	B-Algorithm
compression	I-Algorithm
,	O
for	O
popular	O
image	B-General_Concept
compression	I-General_Concept
formats	O
(	O
such	O
as	O
JPEG	O
)	O
,	O
video	B-Algorithm
coding	I-Algorithm
standards	I-Algorithm
(	O
such	O
as	O
MPEG	O
and	O
H.264/AVC	B-Application
)	O
and	O
audio	O
compression	O
formats	O
(	O
such	O
as	O
MP3	B-Application
and	O
AAC	B-Application
)	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
audio	O
data	O
,	O
a	O
popular	O
form	O
of	O
transform	B-Algorithm
coding	I-Algorithm
is	O
perceptual	O
coding	O
,	O
which	O
transforms	O
the	O
raw	O
data	O
to	O
a	O
domain	O
that	O
more	O
accurately	O
reflects	O
the	O
information	O
content	O
.	O
</s>
<s>
While	O
data	O
reduction	O
(	O
compression	O
,	O
be	O
it	O
lossy	B-Algorithm
or	O
lossless	B-Algorithm
)	O
is	O
a	O
main	O
goal	O
of	O
transform	B-Algorithm
coding	I-Algorithm
,	O
it	O
also	O
allows	O
other	O
goals	O
:	O
one	O
may	O
represent	O
data	O
more	O
accurately	O
for	O
the	O
original	O
amount	O
of	O
space	O
–	O
for	O
example	O
,	O
in	O
principle	O
,	O
if	O
one	O
starts	O
with	O
an	O
analog	O
or	O
high-resolution	O
digital	B-Algorithm
master	I-Algorithm
,	O
an	O
MP3	B-Application
file	I-Application
of	O
a	O
given	O
size	O
should	O
provide	O
a	O
better	O
representation	O
than	O
a	O
raw	O
uncompressed	B-General_Concept
audio	O
in	O
WAV	O
or	O
AIFF	O
file	O
of	O
the	O
same	O
size	O
.	O
</s>
<s>
This	O
is	O
because	O
uncompressed	B-General_Concept
audio	O
can	O
only	O
reduce	O
file	O
size	O
by	O
lowering	O
bit	O
rate	O
or	O
depth	O
,	O
whereas	O
compressing	O
audio	O
can	O
reduce	O
size	O
while	O
maintaining	O
bit	O
rate	O
and	O
depth	O
.	O
</s>
<s>
Further	O
,	O
a	O
transform	B-Algorithm
coding	I-Algorithm
may	O
provide	O
a	O
better	O
domain	O
for	O
manipulating	O
or	O
otherwise	O
editing	O
the	O
data	O
–	O
for	O
example	O
,	O
equalization	O
of	O
audio	O
is	O
most	O
naturally	O
expressed	O
in	O
the	O
frequency	O
domain	O
(	O
boost	O
the	O
bass	O
,	O
for	O
instance	O
)	O
rather	O
than	O
in	O
the	O
raw	O
time	O
domain	O
.	O
</s>
<s>
Another	O
use	O
is	O
for	O
backward	B-General_Concept
compatibility	I-General_Concept
and	O
graceful	B-General_Concept
degradation	I-General_Concept
:	O
in	O
color	O
television	O
,	O
encoding	O
color	O
via	O
a	O
luminance-chrominance	O
transform	O
domain	O
(	O
such	O
as	O
YUV	O
)	O
means	O
that	O
black-and-white	O
sets	O
display	O
the	O
luminance	O
,	O
while	O
ignoring	O
the	O
color	O
information	O
.	O
</s>
<s>
Another	O
example	O
is	O
chroma	O
subsampling	O
:	O
the	O
use	O
of	O
color	B-Algorithm
spaces	I-Algorithm
such	O
as	O
YIQ	O
,	O
used	O
in	O
NTSC	O
,	O
allow	O
one	O
to	O
reduce	O
the	O
resolution	O
on	O
the	O
components	O
to	O
accord	O
with	O
human	O
perception	O
–	O
humans	O
have	O
highest	O
resolution	O
for	O
black-and-white	O
(	O
luma	O
)	O
,	O
lower	O
resolution	O
for	O
mid-spectrum	O
colors	O
like	O
yellow	O
and	O
green	O
,	O
and	O
lowest	O
for	O
red	O
and	O
blues	O
–	O
thus	O
NTSC	O
displays	O
approximately	O
350	O
pixels	O
of	O
luma	O
per	O
scanline	B-Algorithm
,	O
150	O
pixels	O
of	O
yellow	O
vs.	O
green	O
,	O
and	O
50	O
pixels	O
of	O
blue	O
vs.	O
red	O
,	O
which	O
are	O
proportional	O
to	O
human	O
sensitivity	O
to	O
each	O
component	O
.	O
</s>
<s>
Lossy	B-Algorithm
compression	I-Algorithm
formats	O
suffer	O
from	O
generation	B-General_Concept
loss	I-General_Concept
:	O
repeatedly	O
compressing	O
and	O
decompressing	O
the	O
file	O
will	O
cause	O
it	O
to	O
progressively	O
lose	O
quality	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
with	O
lossless	B-Algorithm
data	I-Algorithm
compression	I-Algorithm
,	O
where	O
data	O
will	O
not	O
be	O
lost	O
via	O
the	O
use	O
of	O
such	O
a	O
procedure	O
.	O
</s>
<s>
Information-theoretical	O
foundations	O
for	O
lossy	B-Algorithm
data	I-Algorithm
compression	I-Algorithm
are	O
provided	O
by	O
rate-distortion	B-General_Concept
theory	I-General_Concept
.	O
</s>
<s>
Much	O
like	O
the	O
use	O
of	O
probability	O
in	O
optimal	O
coding	O
theory	O
,	O
rate-distortion	B-General_Concept
theory	I-General_Concept
heavily	O
draws	O
on	O
Bayesian	O
estimation	O
and	O
decision	O
theory	O
in	O
order	O
to	O
model	O
perceptual	O
distortion	O
and	O
even	O
aesthetic	O
judgment	O
.	O
</s>
<s>
There	O
are	O
two	O
basic	O
lossy	B-Algorithm
compression	I-Algorithm
schemes	O
:	O
</s>
<s>
In	O
lossy	B-Algorithm
transform	O
codecs	B-General_Concept
,	O
samples	O
of	O
picture	O
or	O
sound	O
are	O
taken	O
,	O
chopped	O
into	O
small	O
segments	O
,	O
transformed	O
into	O
a	O
new	O
basis	O
space	O
,	O
and	O
quantized	B-Algorithm
.	O
</s>
<s>
The	O
resulting	O
quantized	B-Algorithm
values	O
are	O
then	O
entropy	B-Algorithm
coded	I-Algorithm
.	O
</s>
<s>
In	O
lossy	B-Algorithm
predictive	O
codecs	B-General_Concept
,	O
previous	O
and/or	O
subsequent	O
decoded	O
data	O
is	O
used	O
to	O
predict	O
the	O
current	O
sound	O
sample	O
or	O
image	O
frame	O
.	O
</s>
<s>
The	O
error	O
between	O
the	O
predicted	O
data	O
and	O
the	O
real	O
data	O
,	O
together	O
with	O
any	O
extra	O
information	O
needed	O
to	O
reproduce	O
the	O
prediction	O
,	O
is	O
then	O
quantized	B-Algorithm
and	O
coded	O
.	O
</s>
<s>
In	O
some	O
systems	O
the	O
two	O
techniques	O
are	O
combined	O
,	O
with	O
transform	O
codecs	B-General_Concept
being	O
used	O
to	O
compress	O
the	O
error	O
signals	O
generated	O
by	O
the	O
predictive	O
stage	O
.	O
</s>
<s>
The	O
advantage	O
of	O
lossy	B-Algorithm
methods	O
over	O
lossless	B-Algorithm
methods	O
is	O
that	O
in	O
some	O
cases	O
a	O
lossy	B-Algorithm
method	O
can	O
produce	O
a	O
much	O
smaller	O
compressed	O
file	O
than	O
any	O
lossless	B-Algorithm
method	O
,	O
while	O
still	O
meeting	O
the	O
requirements	O
of	O
the	O
application	O
.	O
</s>
<s>
Lossy	B-Algorithm
methods	O
are	O
most	O
often	O
used	O
for	O
compressing	O
sound	O
,	O
images	O
or	O
videos	O
.	O
</s>
<s>
This	O
is	O
because	O
these	O
types	O
of	O
data	O
are	O
intended	O
for	O
human	O
interpretation	O
where	O
the	O
mind	O
can	O
easily	O
"	O
fill	O
in	O
the	O
blanks	O
"	O
or	O
see	O
past	O
very	O
minor	O
errors	O
or	O
inconsistencies	O
–	O
ideally	O
lossy	B-Algorithm
compression	I-Algorithm
is	O
transparent	B-Algorithm
(	O
imperceptible	O
)	O
,	O
which	O
can	O
be	O
verified	O
via	O
an	O
ABX	O
test	O
.	O
</s>
<s>
Data	O
files	O
using	O
lossy	B-Algorithm
compression	I-Algorithm
are	O
smaller	O
in	O
size	O
and	O
thus	O
cost	O
less	O
to	O
store	O
and	O
to	O
transmit	O
over	O
the	O
Internet	O
,	O
a	O
crucial	O
consideration	O
for	O
streaming	B-Application
video	I-Application
services	O
such	O
as	O
Netflix	O
and	O
streaming	O
audio	O
services	O
such	O
as	O
Spotify	B-Application
.	O
</s>
<s>
A	O
study	O
conducted	O
by	O
the	O
Audio	O
Engineering	O
Library	O
concluded	O
that	O
lower	O
bit	O
rate	O
(	O
112	O
kbps	O
)	O
lossy	B-Algorithm
compression	I-Algorithm
formats	O
such	O
as	O
MP3s	B-Application
have	O
distinct	O
effects	O
on	O
timbral	O
and	O
emotional	O
characteristics	O
,	O
tending	O
to	O
strengthen	O
negative	O
emotional	O
qualities	O
and	O
weaken	O
positive	O
ones	O
.	O
</s>
<s>
Flaws	O
caused	O
by	O
lossy	B-Algorithm
compression	I-Algorithm
that	O
are	O
noticeable	O
to	O
the	O
human	O
eye	O
or	O
ear	O
are	O
known	O
as	O
compression	B-Algorithm
artifacts	I-Algorithm
.	O
</s>
<s>
The	O
compression	B-General_Concept
ratio	I-General_Concept
(	O
that	O
is	O
,	O
the	O
size	O
of	O
the	O
compressed	O
file	O
compared	O
to	O
that	O
of	O
the	O
uncompressed	B-General_Concept
file	O
)	O
of	O
lossy	B-Algorithm
video	O
codecs	B-General_Concept
is	O
nearly	O
always	O
far	O
superior	O
to	O
that	O
of	O
the	O
audio	O
and	O
still-image	O
equivalents	O
.	O
</s>
<s>
An	O
important	O
caveat	O
about	O
lossy	B-Algorithm
compression	I-Algorithm
(	O
formally	O
transcoding	B-Algorithm
)	O
,	O
is	O
that	O
editing	O
lossily	O
compressed	O
files	O
causes	O
digital	O
generation	B-General_Concept
loss	I-General_Concept
from	O
the	O
re-encoding	O
.	O
</s>
<s>
This	O
can	O
be	O
avoided	O
by	O
only	O
producing	O
lossy	B-Algorithm
files	O
from	O
(	O
lossless	B-Algorithm
)	O
originals	O
and	O
only	O
editing	O
(	O
copies	O
of	O
)	O
original	O
files	O
,	O
such	O
as	O
images	O
in	O
raw	B-Application
image	I-Application
format	I-Application
instead	O
of	O
JPEG	O
.	O
</s>
<s>
If	O
data	O
which	O
has	O
been	O
compressed	O
lossily	O
is	O
decoded	O
and	O
compressed	O
losslessly	B-Algorithm
,	O
the	O
size	O
of	O
the	O
result	O
can	O
be	O
comparable	O
with	O
the	O
size	O
of	O
the	O
data	O
before	O
lossy	B-Algorithm
compression	I-Algorithm
,	O
but	O
the	O
data	O
already	O
lost	O
cannot	O
be	O
recovered	O
.	O
</s>
<s>
When	O
deciding	O
to	O
use	O
lossy	B-Algorithm
conversion	O
without	O
keeping	O
the	O
original	O
,	O
format	O
conversion	O
may	O
be	O
needed	O
in	O
the	O
future	O
to	O
achieve	O
compatibility	O
with	O
software	O
or	O
devices	O
(	O
format	B-Device
shifting	I-Device
)	O
,	O
or	O
to	O
avoid	O
paying	O
patent	O
royalties	O
for	O
decoding	O
or	O
distribution	O
of	O
compressed	O
files	O
.	O
</s>
<s>
By	O
modifying	O
the	O
compressed	B-General_Concept
data	I-General_Concept
directly	O
without	O
decoding	O
and	O
re-encoding	O
,	O
some	O
editing	O
of	O
lossily	O
compressed	O
files	O
without	O
degradation	O
of	O
quality	O
is	O
possible	O
.	O
</s>
<s>
The	O
primary	O
programs	O
for	O
lossless	B-Algorithm
editing	O
of	O
JPEGs	O
are	O
jpegtran	B-Language
,	O
and	O
the	O
derived	O
exiftran	O
(	O
which	O
also	O
preserves	O
Exif	O
information	O
)	O
,	O
and	O
(	O
which	O
provides	O
a	O
Windows	O
interface	O
)	O
.	O
</s>
<s>
The	O
freeware	O
Windows-only	O
IrfanView	B-Protocol
has	O
some	O
lossless	B-Algorithm
JPEG	O
operations	O
in	O
its	O
JPG_TRANSFORM	O
plugin	B-Application
.	O
</s>
<s>
Metadata	O
,	O
such	O
as	O
ID3	O
tags	O
,	O
Vorbis	B-Algorithm
comments	O
,	O
or	O
Exif	O
information	O
,	O
can	O
usually	O
be	O
modified	O
or	O
removed	O
without	O
modifying	O
the	O
underlying	O
data	O
.	O
</s>
<s>
One	O
may	O
wish	O
to	O
downsample	B-Algorithm
or	O
otherwise	O
decrease	O
the	O
resolution	O
of	O
the	O
represented	O
source	O
signal	O
and	O
the	O
quantity	O
of	O
data	O
used	O
for	O
its	O
compressed	O
representation	O
without	O
re-encoding	O
,	O
as	O
in	O
bitrate	B-General_Concept
peeling	I-General_Concept
,	O
but	O
this	O
functionality	O
is	O
not	O
supported	O
in	O
all	O
designs	O
,	O
as	O
not	O
all	O
codecs	B-General_Concept
encode	O
data	O
in	O
a	O
form	O
that	O
allows	O
less	O
important	O
detail	O
to	O
simply	O
be	O
dropped	O
.	O
</s>
<s>
Some	O
well-known	O
designs	O
that	O
have	O
this	O
capability	O
include	O
JPEG	O
2000	O
for	O
still	O
images	O
and	O
H.264/MPEG	B-Application
-4	I-Application
AVC	I-Application
based	O
Scalable	B-Application
Video	I-Application
Coding	I-Application
for	O
video	O
.	O
</s>
<s>
Such	O
schemes	O
have	O
also	O
been	O
standardized	O
for	O
older	O
designs	O
as	O
well	O
,	O
such	O
as	O
JPEG	O
images	O
with	O
progressive	O
encoding	O
,	O
and	O
MPEG-2	B-Algorithm
and	O
MPEG-4	B-Application
Part	I-Application
2	I-Application
video	O
,	O
although	O
those	O
prior	O
schemes	O
had	O
limited	O
success	O
in	O
terms	O
of	O
adoption	O
into	O
real-world	O
common	O
usage	O
.	O
</s>
<s>
Without	O
this	O
capacity	O
,	O
which	O
is	O
often	O
the	O
case	O
in	O
practice	O
,	O
to	O
produce	O
a	O
representation	O
with	O
lower	O
resolution	O
or	O
lower	O
fidelity	O
than	O
a	O
given	O
one	O
,	O
one	O
needs	O
to	O
start	O
with	O
the	O
original	O
source	O
signal	O
and	O
encode	O
,	O
or	O
start	O
with	O
a	O
compressed	O
representation	O
and	O
then	O
decompress	O
and	O
re-encode	O
it	O
(	O
transcoding	B-Algorithm
)	O
,	O
though	O
the	O
latter	O
tends	O
to	O
cause	O
digital	O
generation	B-General_Concept
loss	I-General_Concept
.	O
</s>
<s>
Another	O
approach	O
is	O
to	O
encode	O
the	O
original	O
signal	O
at	O
several	O
different	O
bitrates	O
,	O
and	O
then	O
either	O
choose	O
which	O
to	O
use	O
(	O
as	O
when	O
streaming	O
over	O
the	O
internet	O
–	O
as	O
in	O
RealNetworks	O
 '	O
"	O
SureStream	O
"	O
–	O
or	O
offering	O
varying	O
downloads	O
,	O
as	O
at	O
Apple	O
's	O
iTunes	O
Store	O
)	O
,	O
or	O
broadcast	O
several	O
,	O
where	O
the	O
best	O
that	O
is	O
successfully	O
received	O
is	O
used	O
,	O
as	O
in	O
various	O
implementations	O
of	O
hierarchical	B-Protocol
modulation	I-Protocol
.	O
</s>
<s>
Similar	O
techniques	O
are	O
used	O
in	O
mipmaps	B-Data_Structure
,	O
pyramid	B-Algorithm
representations	O
,	O
and	O
more	O
sophisticated	O
scale	B-Algorithm
space	I-Algorithm
methods	O
.	O
</s>
<s>
Some	O
audio	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
which	O
when	O
combined	O
reproduce	O
the	O
original	O
signal	O
;	O
the	O
correction	O
can	O
be	O
stripped	O
,	O
leaving	O
a	O
smaller	O
,	O
lossily	O
compressed	O
,	O
file	O
.	O
</s>
<s>
Such	O
formats	O
include	O
MPEG-4	B-Algorithm
SLS	O
(	O
Scalable	O
to	O
Lossless	B-Algorithm
)	O
,	O
WavPack	B-Application
,	O
OptimFROG	O
DualStream	O
,	O
and	O
DTS-HD	O
Master	O
Audio	O
in	O
lossless	B-Algorithm
(	O
XLL	O
)	O
mode	O
)	O
.	O
</s>
<s>
Windows	B-Application
Media	I-Application
Audio	I-Application
(	O
WMA	B-Application
)	O
(	O
Standard	O
and	O
Pro	O
profiles	O
are	O
lossy	B-Algorithm
.	O
</s>
<s>
WMA	B-Application
Lossless	B-Algorithm
is	O
also	O
available	O
.	O
)	O
</s>
<s>
Opus	B-Algorithm
(	O
Notable	O
for	O
lack	O
of	O
patent	O
restrictions	O
,	O
low	O
delay	O
,	O
and	O
high	O
quality	O
speech	O
and	O
general	O
audio	O
.	O
)	O
</s>
<s>
Researchers	O
have	O
performed	O
lossy	B-Algorithm
compression	I-Algorithm
on	O
text	O
by	O
either	O
using	O
a	O
thesaurus	O
to	O
substitute	O
short	O
words	O
for	O
long	O
ones	O
,	O
or	O
generative	B-General_Concept
text	I-General_Concept
techniques	O
,	O
although	O
these	O
sometimes	O
fall	O
into	O
the	O
related	O
category	O
of	O
lossy	B-General_Concept
data	I-General_Concept
conversion	I-General_Concept
.	O
</s>
<s>
A	O
general	O
kind	O
of	O
lossy	B-Algorithm
compression	I-Algorithm
is	O
to	O
lower	O
the	O
resolution	O
of	O
an	O
image	O
,	O
as	O
in	O
image	B-Algorithm
scaling	I-Algorithm
,	O
particularly	O
decimation	B-Algorithm
.	O
</s>
<s>
One	O
may	O
also	O
remove	O
less	O
"	O
lower	O
information	O
"	O
parts	O
of	O
an	O
image	O
,	O
such	O
as	O
by	O
seam	B-Algorithm
carving	I-Algorithm
.	O
</s>
<s>
Many	O
media	O
transforms	O
,	O
such	O
as	O
Gaussian	B-Error_Name
blur	I-Error_Name
,	O
are	O
,	O
like	O
lossy	B-Algorithm
compression	I-Algorithm
,	O
irreversible	O
:	O
the	O
original	O
signal	O
cannot	O
be	O
reconstructed	O
from	O
the	O
transformed	O
signal	O
.	O
</s>
