<s>
Transform	B-Algorithm
coding	I-Algorithm
is	O
a	O
type	O
of	O
data	B-General_Concept
compression	I-General_Concept
for	O
"	O
natural	O
"	O
data	O
like	O
audio	O
signals	O
or	O
photographic	O
images	O
.	O
</s>
<s>
The	O
transformation	O
is	O
typically	O
lossless	O
(	O
perfectly	O
reversible	O
)	O
on	O
its	O
own	O
but	O
is	O
used	O
to	O
enable	O
better	O
(	O
more	O
targeted	O
)	O
quantization	B-Algorithm
,	O
which	O
then	O
results	O
in	O
a	O
lower	O
quality	O
copy	O
of	O
the	O
original	O
input	O
(	O
lossy	B-Algorithm
compression	I-Algorithm
)	O
.	O
</s>
<s>
In	O
transform	B-Algorithm
coding	I-Algorithm
,	O
knowledge	O
of	O
the	O
application	O
is	O
used	O
to	O
choose	O
information	O
to	O
discard	O
,	O
thereby	O
lowering	O
its	O
bandwidth	O
.	O
</s>
<s>
Using	O
this	O
knowledge	O
allowed	O
RCA	O
to	O
develop	O
a	O
system	O
in	O
which	O
they	O
discarded	O
most	O
of	O
the	O
blue	O
signal	O
after	O
it	O
comes	O
from	O
the	O
camera	O
,	O
keeping	O
most	O
of	O
the	O
green	O
and	O
only	O
some	O
of	O
the	O
red	O
;	O
this	O
is	O
chroma	O
subsampling	O
in	O
the	O
YIQ	O
color	B-Algorithm
space	I-Algorithm
.	O
</s>
<s>
The	O
term	O
is	O
much	O
more	O
commonly	O
used	O
in	O
digital	O
media	O
and	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
.	O
</s>
<s>
The	O
most	O
widely	O
used	O
transform	B-Algorithm
coding	I-Algorithm
technique	O
in	O
this	O
regard	O
is	O
the	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
,	O
proposed	O
by	O
Nasir	O
Ahmed	O
in	O
1972	O
,	O
and	O
presented	O
by	O
Ahmed	O
with	O
T	O
.	O
Natarajan	O
and	O
K	O
.	O
R	O
.	O
Rao	O
in	O
1974	O
.	O
</s>
<s>
This	O
DCT	B-General_Concept
,	O
in	O
the	O
context	O
of	O
the	O
family	O
of	O
discrete	B-General_Concept
cosine	I-General_Concept
transforms	I-General_Concept
,	O
is	O
the	O
DCT-II	O
.	O
</s>
<s>
It	O
is	O
the	O
basis	O
for	O
the	O
common	O
JPEG	O
image	B-General_Concept
compression	I-General_Concept
standard	O
,	O
which	O
examines	O
small	O
blocks	O
of	O
the	O
image	O
and	O
transforms	O
them	O
to	O
the	O
frequency	O
domain	O
for	O
more	O
efficient	O
quantization	B-Algorithm
(	O
lossy	B-Algorithm
)	O
and	O
data	B-General_Concept
compression	I-General_Concept
.	O
</s>
<s>
In	O
video	B-Algorithm
coding	I-Algorithm
,	O
the	O
H.26x	B-Application
and	O
MPEG	O
standards	O
modify	O
this	O
DCT	B-General_Concept
image	B-General_Concept
compression	I-General_Concept
technique	O
across	O
frames	O
in	O
a	O
motion	O
image	O
using	O
motion	B-Algorithm
compensation	I-Algorithm
,	O
further	O
reducing	O
the	O
size	O
compared	O
to	O
a	O
series	O
of	O
JPEGs	O
.	O
</s>
<s>
MP3	B-Application
uses	O
a	O
hybrid	O
coding	O
algorithm	O
,	O
combining	O
the	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
MDCT	O
)	O
and	O
fast	O
Fourier	O
transform	O
(	O
FFT	O
)	O
.	O
</s>
<s>
It	O
was	O
succeeded	O
by	O
Advanced	B-Application
Audio	I-Application
Coding	I-Application
(	O
AAC	O
)	O
,	O
which	O
uses	O
a	O
pure	O
MDCT	O
algorithm	O
to	O
significantly	O
improve	O
compression	O
efficiency	O
.	O
</s>
<s>
The	O
basic	O
process	O
of	O
digitizing	O
an	O
analog	O
signal	O
is	O
a	O
kind	O
of	O
transform	B-Algorithm
coding	I-Algorithm
that	O
uses	O
sampling	B-Algorithm
in	O
one	O
or	O
more	O
domains	O
as	O
its	O
transform	O
.	O
</s>
