<s>
Image	B-Algorithm
quality	I-Algorithm
can	O
refer	O
to	O
the	O
level	O
of	O
accuracy	O
with	O
which	O
different	O
imaging	O
systems	O
capture	O
,	O
process	O
,	O
store	O
,	O
compress	O
,	O
transmit	O
and	O
display	O
the	O
signals	O
that	O
form	O
an	O
image	O
.	O
</s>
<s>
Another	O
definition	O
refers	O
to	O
image	B-Algorithm
quality	I-Algorithm
as	O
"	O
the	O
weighted	O
combination	O
of	O
all	O
of	O
the	O
visually	O
significant	O
attributes	O
of	O
an	O
image	O
"	O
.	O
</s>
<s>
The	O
difference	O
between	O
the	O
two	O
definitions	O
is	O
that	O
one	O
focuses	O
on	O
the	O
characteristics	O
of	O
signal	B-General_Concept
processing	I-General_Concept
in	O
different	O
imaging	O
systems	O
and	O
the	O
latter	O
on	O
the	O
perceptual	O
assessments	O
that	O
make	O
an	O
image	O
pleasant	O
for	O
human	O
viewers	O
.	O
</s>
<s>
Image	B-Algorithm
quality	I-Algorithm
should	O
not	O
be	O
mistaken	O
with	O
image	O
fidelity	O
.	O
</s>
<s>
Image	O
fidelity	O
refers	O
to	O
the	O
ability	O
of	O
a	O
process	O
to	O
render	O
a	O
given	O
copy	O
in	O
a	O
perceptually	O
similar	O
way	O
to	O
the	O
original	O
(	O
without	O
distortion	O
or	O
information	O
loss	O
)	O
,	O
i.e.	O
,	O
through	O
a	O
digitization	O
or	O
conversion	O
process	O
from	O
analog	O
media	O
to	O
digital	B-Algorithm
image	I-Algorithm
.	O
</s>
<s>
The	O
process	O
of	O
determining	O
the	O
level	O
of	O
accuracy	O
is	O
called	O
Image	B-Algorithm
Quality	I-Algorithm
Assessment	O
(	O
IQA	O
)	O
.	O
</s>
<s>
Image	B-Algorithm
quality	I-Algorithm
assessment	O
is	O
part	O
of	O
the	O
quality	O
of	O
experience	O
measures	O
.	O
</s>
<s>
Image	B-Algorithm
quality	I-Algorithm
can	O
be	O
assessed	O
using	O
two	O
methods	O
:	O
subjective	O
and	O
objective	O
.	O
</s>
<s>
Subjective	O
methods	O
are	O
based	O
on	O
the	O
perceptual	O
assessment	O
of	O
a	O
human	O
viewer	O
about	O
the	O
attributes	O
of	O
an	O
image	O
or	O
set	O
of	O
images	O
,	O
while	O
objective	O
methods	O
are	O
based	O
on	O
computational	O
models	O
that	O
can	O
predict	O
perceptual	O
image	B-Algorithm
quality	I-Algorithm
.	O
</s>
<s>
Therefore	O
,	O
the	O
goal	O
of	O
image	B-Algorithm
quality	I-Algorithm
assessment	O
research	O
is	O
to	O
design	O
algorithms	O
for	O
objective	O
assessment	O
that	O
are	O
also	O
consistent	O
with	O
subjective	O
assessments	O
.	O
</s>
<s>
They	O
can	O
be	O
used	O
to	O
monitor	O
image	B-Algorithm
quality	I-Algorithm
in	O
control	O
quality	O
systems	O
,	O
to	O
benchmark	O
image	O
processing	O
systems	O
and	O
algorithms	O
and	O
to	O
optimize	O
imaging	O
systems	O
.	O
</s>
<s>
The	O
image	B-Algorithm
formation	I-Algorithm
process	O
is	O
affected	O
by	O
several	O
distortions	O
between	O
the	O
moment	O
in	O
which	O
the	O
signals	O
travel	O
through	O
to	O
and	O
reach	O
the	O
capture	O
surface	O
,	O
and	O
the	O
device	O
or	O
mean	O
in	O
which	O
signals	O
are	O
displayed	O
.	O
</s>
<s>
Although	O
optical	O
aberrations	O
can	O
cause	O
great	O
distortions	O
in	O
image	B-Algorithm
quality	I-Algorithm
,	O
they	O
are	O
not	O
part	O
of	O
the	O
field	O
of	O
Image	B-Algorithm
Quality	I-Algorithm
Assessment	O
.	O
</s>
<s>
Optical	O
aberrations	O
caused	O
by	O
lenses	O
belong	O
to	O
the	O
optics	O
area	O
and	O
not	O
to	O
the	O
signal	B-General_Concept
processing	I-General_Concept
areas	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
digital	B-Algorithm
image	I-Algorithm
is	O
formed	O
by	O
electromagnetic	O
radiation	O
or	O
other	O
waves	O
as	O
they	O
pass	O
through	O
or	O
reflect	O
off	O
objects	O
.	O
</s>
<s>
That	O
information	O
is	O
then	O
captured	O
and	O
converted	O
into	O
digital	O
signals	O
by	O
an	O
image	B-Algorithm
sensor	I-Algorithm
.	O
</s>
<s>
Image	B-Algorithm
quality	I-Algorithm
can	O
be	O
assessed	O
using	O
objective	O
or	O
subjective	O
methods	O
.	O
</s>
<s>
In	O
the	O
objective	O
method	O
,	O
image	B-Algorithm
quality	I-Algorithm
assessments	O
are	O
performed	O
by	O
different	O
algorithms	O
that	O
analyze	O
the	O
distortions	O
and	O
degradations	O
introduced	O
in	O
an	O
image	O
.	O
</s>
<s>
Subjective	O
image	B-Algorithm
quality	I-Algorithm
assessments	O
are	O
a	O
method	O
based	O
on	O
the	O
way	O
in	O
which	O
humans	O
experience	O
or	O
perceive	O
image	B-Algorithm
quality	I-Algorithm
.	O
</s>
<s>
Subjective	O
methods	O
for	O
image	B-Algorithm
quality	I-Algorithm
assessment	O
belong	O
to	O
the	O
larger	O
area	O
of	O
psychophysics	O
research	O
,	O
a	O
field	O
that	O
studies	O
the	O
relationship	O
between	O
physical	O
stimulus	O
and	O
human	O
perceptions	O
.	O
</s>
<s>
A	O
subjective	O
IQA	O
method	O
will	O
typically	O
consist	O
on	O
applying	O
mean	O
opinion	O
score	O
techniques	O
,	O
where	O
a	O
number	O
of	O
viewers	O
rate	O
their	O
opinions	O
based	O
on	O
their	O
perceptions	O
of	O
image	B-Algorithm
quality	I-Algorithm
.	O
</s>
<s>
Since	O
visual	O
perception	O
can	O
be	O
affected	O
by	O
environmental	O
and	O
viewing	O
conditions	O
,	O
the	O
International	O
Telecommunication	O
Union	O
produced	O
a	O
set	O
of	O
recommendations	O
for	O
standardized	O
testing	O
methods	O
for	O
subjective	O
image	B-Algorithm
quality	I-Algorithm
assessment	O
.	O
</s>
<s>
Wang	O
&	O
Bovik	O
(	O
2006	O
)	O
classify	O
the	O
objective	O
methods	O
with	O
the	O
following	O
criteria	O
:	O
(	O
a	O
)	O
the	O
availability	O
of	O
an	O
original	O
image	O
;	O
(	O
b	O
)	O
on	O
the	O
basis	O
of	O
their	O
application	O
scopes	O
and	O
(	O
c	O
)	O
on	O
the	O
model	O
of	O
a	O
Human	B-Algorithm
Visual	I-Algorithm
System	I-Algorithm
simulation	O
to	O
assess	O
quality	O
.	O
</s>
<s>
Image	B-Algorithm
quality	I-Algorithm
metrics	O
can	O
also	O
be	O
classified	O
in	O
terms	O
of	O
measuring	O
only	O
one	O
specific	O
type	O
of	O
degradation	O
(	O
e.g.	O
,	O
blurring	B-Error_Name
,	O
blocking	O
,	O
or	O
ringing	O
)	O
,	O
or	O
taking	O
into	O
account	O
all	O
possible	O
signal	O
distortions	O
,	O
that	O
is	O
,	O
multiple	O
kinds	O
of	O
artifacts	B-Algorithm
.	O
</s>
<s>
Oversharpening	O
,	O
can	O
degrade	O
image	B-Algorithm
quality	I-Algorithm
by	O
causing	O
"	O
halos	O
"	O
to	O
appear	O
near	O
contrast	O
boundaries	O
.	O
</s>
<s>
Images	O
from	O
many	O
compact	O
digital	O
cameras	O
are	O
sometimes	O
oversharpened	O
to	O
compensate	O
for	O
lower	O
image	B-Algorithm
quality	I-Algorithm
.	O
</s>
<s>
Noise	B-Algorithm
is	O
a	O
random	O
variation	O
of	O
image	O
density	O
,	O
visible	O
as	O
grain	O
in	O
film	O
and	O
pixel	O
level	O
variations	O
in	O
digital	O
images	O
.	O
</s>
<s>
It	O
arises	O
from	O
the	O
effects	O
of	O
basic	O
physics	O
—	O
the	O
photon	O
nature	O
of	O
light	O
and	O
the	O
thermal	O
energy	O
of	O
heat	O
—	O
inside	O
image	B-Algorithm
sensors	I-Algorithm
.	O
</s>
<s>
Typical	O
noise	B-Algorithm
reduction	O
(	O
NR	O
)	O
software	O
reduces	O
the	O
visibility	O
of	O
noise	B-Algorithm
by	O
smoothing	O
the	O
image	O
,	O
excluding	O
areas	O
near	O
contrast	O
boundaries	O
.	O
</s>
<s>
It	O
is	O
closely	O
related	O
to	O
noise	B-Algorithm
:	O
high	O
noise	B-Algorithm
implies	O
low	O
dynamic	O
range	O
.	O
</s>
<s>
Color	O
accuracy	O
is	O
an	O
important	O
but	O
ambiguous	O
image	B-Algorithm
quality	I-Algorithm
factor	O
.	O
</s>
<s>
Distortion	O
tends	O
to	O
be	O
noticeable	O
in	O
low	O
cost	O
cameras	O
,	O
including	O
cell	O
phones	O
,	O
and	O
low	O
cost	O
DSLR	B-Algorithm
lenses	I-Algorithm
.	O
</s>
<s>
It	O
is	O
strongly	O
affected	O
by	O
demosaicing	B-Algorithm
.	O
</s>
<s>
It	O
is	O
affected	O
by	O
lens	O
sharpness	O
,	O
the	O
anti-aliasing	O
(	O
lowpass	O
)	O
filter	O
(	O
which	O
softens	O
the	O
image	O
)	O
,	O
and	O
demosaicing	B-Algorithm
software	O
.	O
</s>
<s>
Artifacts	B-Algorithm
–	O
software	O
(	O
especially	O
operations	O
performed	O
during	O
RAW	O
conversion	O
)	O
can	O
cause	O
significant	O
visual	O
artifacts	B-Algorithm
,	O
including	O
data	O
compression	O
and	O
transmission	O
losses	O
(	O
e.g.	O
</s>
