<s>
Trellis	B-General_Concept
quantization	I-General_Concept
is	O
an	O
algorithm	O
that	O
can	O
improve	O
data	B-General_Concept
compression	I-General_Concept
in	O
DCT-based	O
encoding	O
methods	O
.	O
</s>
<s>
It	O
is	O
used	O
to	O
optimize	O
residual	O
DCT	B-General_Concept
coefficients	O
after	O
motion	O
estimation	O
in	O
lossy	B-Algorithm
video	O
compression	O
encoders	O
such	O
as	O
Xvid	B-Algorithm
and	O
x264	B-Language
.	O
</s>
<s>
Trellis	B-General_Concept
quantization	I-General_Concept
reduces	O
the	O
size	O
of	O
some	O
DCT	B-General_Concept
coefficients	O
while	O
recovering	O
others	O
to	O
take	O
their	O
place	O
.	O
</s>
<s>
This	O
process	O
can	O
increase	O
quality	O
because	O
coefficients	O
chosen	O
by	O
Trellis	O
have	O
the	O
lowest	O
rate-distortion	B-General_Concept
ratio	O
.	O
</s>
<s>
Trellis	B-General_Concept
quantization	I-General_Concept
effectively	O
finds	O
the	O
optimal	O
quantization	O
for	O
each	O
block	O
to	O
maximize	O
the	O
PSNR	O
relative	O
to	O
bitrate	O
.	O
</s>
