<s>
Block-matching	B-Algorithm
and	I-Algorithm
3D	I-Algorithm
filtering	I-Algorithm
(	O
BM3D	O
)	O
is	O
a	O
3-D	O
block-matching	B-General_Concept
algorithm	I-General_Concept
used	O
primarily	O
for	O
noise	O
reduction	O
in	O
images	O
.	O
</s>
<s>
There	O
are	O
two	O
cascades	O
in	O
BM3D	O
:	O
a	O
hard-thresholding	O
and	O
a	O
Wiener	O
filter	O
stage	O
,	O
both	O
involving	O
the	O
following	O
parts	O
:	O
grouping	O
,	O
collaborative	B-Algorithm
filtering	I-Algorithm
,	O
and	O
aggregation	O
.	O
</s>
<s>
Image	O
fragments	O
are	O
grouped	O
together	O
based	O
on	O
similarity	O
,	O
but	O
unlike	O
standard	O
k-means	B-Algorithm
clustering	I-Algorithm
and	O
such	O
cluster	B-Algorithm
analysis	I-Algorithm
methods	O
,	O
the	O
image	O
fragments	O
are	O
not	O
necessarily	O
disjoint	B-Algorithm
.	O
</s>
<s>
This	O
block-matching	B-General_Concept
algorithm	I-General_Concept
is	O
less	O
computationally	O
demanding	O
and	O
is	O
useful	O
later	O
on	O
in	O
the	O
aggregation	O
step	O
.	O
</s>
<s>
This	O
grouping	O
technique	O
is	O
called	O
block-matching	O
,	O
it	O
is	O
typically	O
used	O
to	O
group	O
similar	O
groups	O
across	O
different	O
frames	O
of	O
a	O
digital	O
video	O
,	O
BM3D	O
on	O
the	O
other	O
hand	O
may	O
group	O
macroblocks	B-General_Concept
within	O
a	O
single	O
frame	O
.	O
</s>
<s>
An	O
approach	O
that	O
integrates	O
a	O
convolutional	B-Architecture
neural	I-Architecture
network	I-Architecture
has	O
been	O
proposed	O
and	O
shows	O
better	O
results	O
(	O
albeit	O
with	O
a	O
slower	O
runtime	O
)	O
.	O
</s>
<s>
MATLAB	B-Language
code	O
has	O
been	O
released	O
for	O
research	O
purpose	O
.	O
</s>
<s>
Reference	O
implementation	O
in	O
MATLAB	B-Language
and	O
Python	B-Language
released	O
under	O
an	O
open-source	O
proprietary	B-Application
license	I-Application
:	O
</s>
<s>
Well	O
documented	O
C-based	O
implementation	O
released	O
under	O
the	O
GPLv3	O
:	O
</s>
<s>
CUDA	B-Architecture
and	O
C++	B-Language
based	O
implementation	O
released	O
under	O
the	O
GPLv3	O
:	O
</s>
