<s>
CIF	O
(	O
Common	B-Application
Intermediate	I-Application
Format	I-Application
or	O
Common	O
Interchange	O
Format	O
)	O
,	O
also	O
known	O
as	O
FCIF	O
(	O
Full	O
Common	B-Application
Intermediate	I-Application
Format	I-Application
)	O
,	O
is	O
a	O
standardized	O
format	O
for	O
the	O
picture	B-Algorithm
resolution	I-Algorithm
,	O
frame	O
rate	O
,	O
color	B-Algorithm
space	I-Algorithm
,	O
and	O
color	O
subsampling	O
of	O
digital	O
video	O
sequences	O
used	O
in	O
video	B-Application
teleconferencing	I-Application
systems	O
.	O
</s>
<s>
It	O
was	O
first	O
defined	O
in	O
the	O
H.261	B-Algorithm
standard	I-Algorithm
in	O
1988	O
.	O
</s>
<s>
As	O
the	O
word	O
"	O
common	O
"	O
in	O
its	O
name	O
implies	O
,	O
CIF	O
was	O
designed	O
as	O
a	O
common	O
compromise	O
format	O
to	O
be	O
relatively	O
easy	O
to	O
convert	O
for	O
use	O
either	O
with	O
PAL	B-Language
or	O
NTSC	O
standard	O
displays	O
and	O
cameras	O
.	O
</s>
<s>
CIF	O
defines	O
a	O
video	O
sequence	O
with	O
a	O
resolution	O
of	O
352	O
×	O
288	O
,	O
which	O
has	O
a	O
simple	O
relationship	O
to	O
the	O
PAL	B-Language
picture	O
size	O
,	O
but	O
with	O
a	O
frame	O
rate	O
of	O
30000/1001	O
(	O
roughly	O
29.97	O
)	O
frames	O
per	O
second	O
like	O
NTSC	O
,	O
with	O
color	O
encoded	O
using	O
a	O
YCbCr	O
representation	O
with	O
4:2:0	O
color	O
sampling	O
.	O
</s>
<s>
It	O
was	O
designed	O
as	O
a	O
compromise	O
between	O
PAL	B-Language
and	O
NTSC	O
schemes	O
,	O
since	O
it	O
uses	O
a	O
picture	O
size	O
that	O
corresponds	O
most	O
easily	O
to	O
PAL	B-Language
,	O
but	O
uses	O
the	O
frame	O
rate	O
of	O
NTSC	O
.	O
</s>
<s>
The	O
compromise	O
was	O
established	O
as	O
a	O
way	O
to	O
reach	O
international	O
agreement	O
so	O
that	O
video	B-Application
conferencing	I-Application
systems	O
in	O
different	O
countries	O
could	O
communicate	O
with	O
each	O
other	O
without	O
needing	O
two	O
separate	O
modes	O
for	O
displaying	O
the	O
received	O
video	O
.	O
</s>
<s>
The	O
simple	O
way	O
to	O
convert	O
PAL	B-Language
video	O
to	O
CIF	O
is	O
to	O
similarly	O
capture	O
every	O
other	O
field	O
,	O
downsample	O
it	O
horizontally	O
by	O
2:1	O
,	O
and	O
introduce	O
some	O
jitter	O
in	O
the	O
frame	O
rate	O
by	O
skipping	O
or	O
repeating	O
frames	O
as	O
necessary	O
.	O
</s>
<s>
Since	O
H.261	B-Algorithm
systems	O
typically	O
operated	O
at	O
low	O
bit	O
rates	O
,	O
they	O
also	O
typically	O
operated	O
at	O
low	O
frame	O
rates	O
by	O
skipping	O
many	O
of	O
the	O
camera	O
source	O
frames	O
,	O
so	O
introducing	O
some	O
jitter	O
in	O
the	O
frame	O
rate	O
tended	O
not	O
to	O
be	O
noticeable	O
.	O
</s>
<s>
In	O
contrast	O
to	O
the	O
CIF	O
compromise	O
that	O
originated	O
with	O
the	O
H.261	B-Algorithm
standard	I-Algorithm
,	O
there	O
are	O
two	O
variants	O
of	O
the	O
SIF	O
(	O
Source	O
Input	O
Format	O
)	O
that	O
was	O
first	O
defined	O
in	O
the	O
MPEG-1	B-Algorithm
standard	O
.	O
</s>
<s>
SIF	O
on	O
525-line	O
(	O
"	O
NTSC	O
"	O
)	O
based	O
systems	O
is	O
352	O
×	O
240	O
with	O
a	O
frame	O
rate	O
of	O
30000/1001	O
frames	O
per	O
second	O
,	O
and	O
on	O
625-line	O
(	O
"	O
PAL	B-Language
"	O
)	O
based	O
systems	O
,	O
it	O
has	O
the	O
same	O
picture	O
size	O
as	O
CIF	O
(	O
352	O
×	O
288	O
)	O
but	O
with	O
a	O
frame	O
rate	O
of	O
25	O
frames	O
per	O
second	O
.	O
</s>
<s>
H.261	B-Algorithm
additionally	O
used	O
vertical	O
color	O
subsampling	O
,	O
resulting	O
in	O
what	O
is	O
known	O
as	O
4:2:0	O
.	O
</s>
<s>
QCIF	B-Application
means	O
"	O
Quarter	O
CIF	O
"	O
.	O
</s>
<s>
Terms	O
also	O
used	O
are	O
SQCIF	B-Application
(	O
Sub	O
Quarter	O
CIF	O
,	O
sometimes	O
Sub-QCIF	O
)	O
,	O
4CIF	B-Application
(	O
4	O
×	O
CIF	O
)	O
,	O
9CIF	O
(	O
9	O
×	O
CIF	O
)	O
and	O
16CIF	B-Application
(	O
16	O
×	O
CIF	O
)	O
.	O
</s>
<s>
xCIF	O
pixels	B-Algorithm
are	O
not	O
square	O
,	O
instead	O
having	O
a	O
native	O
aspect	O
ratio	O
of	O
12:11	O
,	O
as	O
with	O
the	O
standard	O
for	O
625-line	O
systems	O
(	O
see	O
CCIR	O
601	O
)	O
.	O
</s>
<s>
On	O
square-pixel	O
displays	O
(	O
e.g.	O
,	O
computer	O
screens	O
and	O
many	O
modern	O
televisions	O
)	O
xCIF	O
rasters	O
should	O
be	O
rescaled	O
so	O
that	O
the	O
picture	O
covers	O
a	O
4:3	O
area	O
,	O
in	O
order	O
to	O
avoid	O
a	O
"	O
stretched	O
"	O
look	O
:	O
CIF	O
content	O
expanded	O
horizontally	O
by	O
12:11	O
results	O
in	O
a	O
4:3	O
raster	O
of	O
384	O
×	O
288	O
square	O
pixels	B-Algorithm
.	O
</s>
<s>
The	O
CIF	O
and	O
QCIF	B-Application
picture	O
dimensions	O
were	O
specifically	O
chosen	O
to	O
be	O
multiples	O
of	O
16	O
because	O
of	O
the	O
way	O
that	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
based	O
video	O
compression/decompression	O
was	O
handled	O
in	O
H.261	B-Algorithm
,	O
using	O
16	O
×	O
16	O
macroblocks	B-General_Concept
and	O
8	O
×	O
8	O
transform	O
blocks	O
.	O
</s>
<s>
So	O
a	O
CIF-size	O
image	O
(	O
352	O
×	O
288	O
)	O
contains	O
22	O
×	O
18	O
macroblocks	B-General_Concept
and	O
a	O
QCIF	B-Application
image	O
(	O
176	O
×	O
144	O
)	O
contains	O
11	O
×	O
9	O
macroblocks	B-General_Concept
.	O
</s>
<s>
The	O
16	O
×	O
16	O
macroblock	B-General_Concept
concept	O
was	O
later	O
also	O
used	O
in	O
other	O
compression	O
standards	O
such	O
as	O
MPEG-1	B-Algorithm
,	O
MPEG-2	B-Algorithm
,	O
MPEG-4	B-Application
Part	I-Application
2	I-Application
,	O
H.263	B-Algorithm
,	O
and	O
H.264/MPEG	B-Application
-4	I-Application
AVC	I-Application
.	O
</s>
