<s>
Lumi	B-Application
masking	I-Application
(	O
derived	O
from	O
luminance	O
)	O
,	O
also	O
known	O
as	O
psychovisual	B-Application
enhancements	I-Application
or	O
adaptive	O
quantization	O
,	O
is	O
a	O
technique	O
used	O
by	O
video	O
compression	O
software	O
,	O
which	O
reduces	O
quality	O
in	O
very	O
bright	O
or	O
very	O
dark	O
areas	O
of	O
the	O
picture	O
,	O
as	O
quality	O
loss	O
in	O
these	O
areas	O
is	O
less	O
likely	O
to	O
be	O
visible	O
.	O
</s>
<s>
The	O
reduction	O
in	O
quality	O
(	O
and	O
therefore	O
bit	O
rate	O
)	O
in	O
certain	O
areas	O
of	O
the	O
picture	O
caused	O
by	O
using	O
lumi	B-Application
masking	I-Application
allows	O
more	O
bits	O
to	O
be	O
allocated	O
to	O
the	O
rest	O
of	O
the	O
video	O
,	O
thus	O
improving	O
overall	O
quality	O
.	O
</s>
<s>
Lumi	B-Application
masking	I-Application
is	O
not	O
perfect	O
,	O
however	O
,	O
and	O
in	O
some	O
cases	O
the	O
degradation	O
in	O
quality	O
it	O
causes	O
is	O
visible	O
.	O
</s>
