<s>
Volumetric	B-Algorithm
path	I-Algorithm
tracing	I-Algorithm
is	O
a	O
method	O
for	O
rendering	O
images	O
in	O
computer	O
graphics	O
which	O
was	O
first	O
introduced	O
by	O
Lafortune	O
and	O
Willems	O
.	O
</s>
<s>
This	O
method	O
enhances	O
the	O
rendering	O
of	O
the	O
lighting	O
in	O
a	O
scene	O
by	O
extending	O
the	O
path	B-Algorithm
tracing	I-Algorithm
method	O
with	O
the	O
effect	O
of	O
light	O
scattering	O
.	O
</s>
<s>
Like	O
in	O
the	O
path	B-Algorithm
tracing	I-Algorithm
method	O
,	O
a	O
ray	O
gets	O
followed	O
backwards	O
,	O
beginning	O
from	O
the	O
eye	O
,	O
until	O
reaching	O
the	O
light	O
source	O
.	O
</s>
<s>
In	O
volumetric	B-Algorithm
path	I-Algorithm
tracing	I-Algorithm
,	O
scattering	O
events	O
can	O
occur	O
along	O
with	O
ray	B-Algorithm
tracing	I-Algorithm
.	O
</s>
<s>
The	O
in-scattering	O
is	O
the	O
most	O
expensive	O
part	O
to	O
calculate	O
because	O
it	O
needs	O
an	O
integration	O
over	O
all	O
paths	O
in	O
the	O
scene	O
that	O
consist	O
of	O
radiance	B-Application
.	O
</s>
<s>
In	O
volumetric	B-Algorithm
path	I-Algorithm
tracing	I-Algorithm
,	O
a	O
distance	O
between	O
the	O
ray	O
and	O
the	O
surface	O
gets	O
sampled	B-Algorithm
and	O
compared	O
with	O
the	O
distance	O
of	O
the	O
nearest	O
intersection	O
of	O
the	O
ray	O
with	O
the	O
surface	O
.	O
</s>
<s>
If	O
the	O
sampled	B-Algorithm
distance	O
is	O
smaller	O
,	O
a	O
scatter	O
event	O
occurs	O
.	O
</s>
<s>
It	O
works	O
similar	O
to	O
ray	B-Algorithm
tracing	I-Algorithm
but	O
operates	O
on	O
a	O
distance	B-Algorithm
field	I-Algorithm
of	O
the	O
scene	O
,	O
and	O
acts	O
in	O
discrete	O
steps	O
.	O
</s>
<s>
The	O
scattering	O
inside	O
the	O
media	O
can	O
be	O
determined	O
by	O
a	O
phase	O
function	O
using	O
importance	B-Algorithm
sampling	I-Algorithm
.	O
</s>
