<s>
A	O
deblocking	B-General_Concept
filter	I-General_Concept
is	O
a	O
video	O
filter	O
applied	O
to	O
decoded	O
compressed	O
video	O
to	O
improve	O
visual	O
quality	O
and	O
prediction	O
performance	O
by	O
smoothing	O
the	O
sharp	O
edges	O
which	O
can	O
form	O
between	O
macroblocks	B-General_Concept
when	O
block	B-General_Concept
coding	I-General_Concept
techniques	O
are	O
used	O
.	O
</s>
<s>
It	O
is	O
a	O
part	O
of	O
the	O
specification	O
for	O
both	O
the	O
SMPTE	O
VC-1	B-Operating_System
codec	O
and	O
the	O
ITU	O
H.264	B-Application
(	O
ISO	O
MPEG-4	B-Application
AVC	I-Application
)	O
codec	O
.	O
</s>
<s>
In	O
contrast	O
with	O
older	O
MPEG-1/2/4	O
standards	O
,	O
the	O
H.264	B-Application
deblocking	B-General_Concept
filter	I-General_Concept
is	O
not	O
an	O
optional	O
additional	O
feature	O
in	O
the	O
decoder	O
.	O
</s>
<s>
It	O
is	O
a	O
feature	O
on	O
both	O
the	O
decoding	O
path	O
and	O
on	O
the	O
encoding	O
path	O
,	O
so	O
that	O
the	O
in-loop	O
effects	O
of	O
the	O
filter	O
are	O
taken	O
into	O
account	O
in	O
reference	O
macroblocks	B-General_Concept
used	O
for	O
prediction	O
.	O
</s>
<s>
The	O
filter	O
operates	O
on	O
the	O
edges	O
of	O
each	O
4×4	O
or	O
8×8	O
transform	O
block	O
in	O
the	O
luma	O
and	O
chroma	O
planes	O
of	O
each	O
picture	O
.	O
</s>
<s>
Each	O
small	O
block	O
's	O
edge	O
is	O
assigned	O
a	O
boundary	O
strength	O
based	O
on	O
whether	O
it	O
is	O
also	O
a	O
macroblock	B-General_Concept
boundary	O
,	O
the	O
coding	O
(	O
intra/inter	O
)	O
of	O
the	O
blocks	O
,	O
whether	O
references	O
(	O
in	O
motion	O
prediction	O
and	O
reference	B-General_Concept
frame	I-General_Concept
choice	O
)	O
differ	O
,	O
and	O
whether	O
it	O
is	O
a	O
luma	O
or	O
chroma	O
edge	O
.	O
</s>
<s>
The	O
filter	O
can	O
modify	O
as	O
many	O
as	O
three	O
samples	O
on	O
either	O
side	O
of	O
a	O
given	O
block	O
edge	O
(	O
in	O
the	O
case	O
where	O
an	O
edge	O
is	O
a	O
luma	O
edge	O
that	O
lies	O
between	O
different	O
macroblocks	B-General_Concept
and	O
at	O
least	O
one	O
of	O
them	O
is	O
intra	O
coded	O
)	O
.	O
</s>
<s>
Although	O
the	O
concept	O
of	O
an	O
"	O
in	O
loop	O
"	O
deblocking	B-General_Concept
filter	I-General_Concept
is	O
best	O
known	O
in	O
relation	O
to	O
H.264	B-Application
,	O
it	O
was	O
actually	O
also	O
standardized	O
earlier	O
(	O
in	O
a	O
somewhat	O
different	O
form	O
)	O
in	O
the	O
H.263v2	B-Algorithm
Annex	O
J	O
.	O
</s>
<s>
Prior	O
to	O
H.263	B-Algorithm
Annex	O
J	O
and	O
H.264	B-Application
,	O
the	O
use	O
of	O
a	O
deblocking	B-General_Concept
filter	I-General_Concept
as	O
a	O
post-processing	O
technique	O
to	O
improve	O
the	O
visual	O
quality	O
of	O
decoded	O
pictures	O
was	O
already	O
a	O
well-known	O
technology	O
.	O
</s>
